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Tuesday, 25 March 2014 20:45

Acid Rain Lab Report

WRITTEN_BY Administrator

Acid Rain Lab Report


Data

Gas

Maximum  pH

Minimum pH

DpH

CO2

7.13

5.83

1.30

NO2

7.08

2.62

4.46

SO2

7.04

2.41

4.63

#1

            The gas that caused the smallest drop in pH is carbon dioxide, CO2 whose ∆pH = 1.30

#2

            The gas which caused the largest drop in pH is sulfur dioxide, SO2 for it had the largest drop ∆pH = 4.63. Nitrogen dioxide, NO2 had the second largest drop in pH because it had ∆pH = 4.46.

#3

            In a situation where low sulfur coal is burned, it produces less sulfur dioxide. Having lower concentrations level of sulfur dioxide in the atmosphere, less sulfurous acid is being produced by the reaction;

SO2 (g) + H2O (g) ⎯→ H2SO3 (aq)

#4

            The two acids in acid rain that results from the nitrogen oxides in automobile exhaust are nitrous acid, HNO2, and nitric acid HNO3. They are being produced by the reaction.

2 NO2 (g) + H2O (g) ⎯→ HNO2 (aq) + HNO3 (aq)

#5

            The gas and resulting acid that would cause the rainfall in unpolluted air to have a pH value which is less than 7 and at times as low as 5.6 is carbon dioxide gas (CO2). This is a natural component of the atmosphere, which dissolves in rainwater then forms carbonic acid, H2 CO3.


 Work Cited:

Morgan, S. Acid Rain: Sea-To-Sea Publications, 2009


Properties Of Metals And Alloys And Their Applications


Introduction

Metals are essential elements that have extensive applications. The application of any metallic element is dependent upon its properties. Alloys encompass a combination of metals and other elements. This provides metals with distinct properties which are not necessarily similar to the properties exhibited by constituent elements. Although different metals have distinctive properties, some characteristics are predominant among most metals. Conductivity is among the most predominant characteristic among most metals (Oxlade, 2007). In essence, this is evidenced by the capacity of metallic elements to transfer electricity. However, it is essential to pinpoint that some metallic elements do not have the capacity to conduct or transfer electricity.


 In addition to conductivity, metals are characterized by high melting points. This attribute is due to the extensive metallic bonds within the structure of metallic elements. High boiling point is another notable attribute in most metallic elements (Baldwin, 2005). This property is also attributed to the complex bonds in metallic structures. Based on these properties, metallic elements have different applications. The property to conduct electricity makes metallic elements like copper suitable for the production of electric wiring. This property also forms the basis of manufacturing numerous electric appliances and gadgets. The production of jewels is dependent on the lustrous properties of metals. This strongly applies to metals like gold. The production of electrodes hinges on the high boiling and melting points of metals.  


 In all metallic elements, the outer shell comprises of loose electrons. This property is immensely useful in terms of enhancing the capacity of metals to conduct electricity. For most alloys, the properties are strongly dependent on the individual properties of constituent elements. In essence, the properties of most alloys are superior compared to metals. For instance, alloys are characterized by extensive strength compared to metallic elements. This property is evident in the use of alloys in the construction of essential structures such as bridges. Hardness serves as another property evident in most alloys. This is largely because of the combination of different elements during the process of alloy formation. Resistance to wear is another conspicuous property evident in most alloys. This property is evident in most compounds where chromium has been used as an alloying agent.


 The property of resistivity to wear is used in the manufacture of stainless steel (Holloway, 2009). Additionally, this property is essential in terms of streamlining the production of medical equipment. In contrast to metals, alloys are characterized by excellent resistance to corrosion (Wang, 2005). This property forms the basis of producing turbines. The hardness evident in most alloys is occasioned by the large size of atoms. In contrast, the atoms in metals are considerably smaller and this makes it easier for them to slide over each other (Ashraf, 2009). The tensile strength of alloys is considerably higher compared to metals. This exemplifies why alloys have numerous applications as compared to individual metallic elements.


 Concept Statement

This project narrows down on the different properties of alloys and metals. Through this analysis, the different applications of alloys and metals will be identified. The standards of industrialization across the globe have risen tremendously in recent decades. In view of such developments, it is pertinent to demystify the various applications of metals and alloys. Both are extremely influential in numerous aspects of life. The project will help in identifying these uses and also specifying the inherent differences between metals and alloys.


 References

Ashraf, S. M. (2009). A laboratory manual of metals and alloys, New Delhi: I. K. International

Baldwin, C. (2005). Metals, Heinemann Raintree

Holloway, P. H. (2009). Characterization of metals and alloys, New York, NY:Momentum Press

Oxlade, C. (2007). Metals, Heinemann Library

Wang, F. E. (2005). Bonding theory for metals and alloys, San Diego, CA: Elsevier 


 

Thursday, 12 September 2013 22:06

Synthetic Receptors for Biologically Relevant Anions

WRITTEN_BY Administrator

Synthetic Receptors for Biologically Relevant Anions


The receptor-substrate is a concept in organic chemistry that has been studied for a considerable period of time (Rosser, 1993). Perhaps, it is as old as the 'lock and key' concept proposed by Emil Fischer in 1894. However, knowledge of the interactions leading to the recognition of a given substrate by a particular receptor has only been gained in fairly the recent past. Vital to gaining an understanding of the concept has been the development of synthetic "macrocyclic" receptors, an area of science which has grown. Several synthetic "macrocyclic" receptors have now been developed and their varying abilities to bind various substrates well analyzed.


The result has been the development of good knowledge of the interactions involved in synthetic receptor-substrate chemistry and, by extension, the interactions in biochemical receptor-substrate systems such as proteins, antibodies, DNA and RNA.The prime goal is to build the capacity and prepare substrates that will specifically bind to a specific receptor (Steed & Atwood, 2009). Conversely, receptors that recognize a particular substrate can be tailored. Chemists and biochemists are on the brink of an agreement which will promote rational, targeted drug design (tailoring of a substrate) and the preparation of fully synthetic enzymes and sensors (tailoring of a receptor). Synthetic receptors are the principal focal points. It is with the latter - synthetic receptors - that this work shall be concerned.


 Role of Anions in the Modern World

Perhaps, it is important to discuss the application of anions, in order to justify the significance of synthetic receptors (Diederich & Tykwinski, 2008). Anions are omnipresent in the natural world. Chloride anions are present in high quantities in the oceans while sulfate and nitrate anions are present in acid rain. Carbonates are principal constituents in bio-mineralized materials. Anthropogenic anions, including pertechnetate, a radioactive product of nuclear fuel reprocessing, and nitrates and phosphates from agriculture and other human activities, are the major pollution hazards.


 Anions are fundamental to maintenance of life-support processes (Sessler, Gale & Cho, 2006). In fact, anion recognition, transportation, or transformation is involved at specific levels in almost every biochemical operation. Anions are vital for the formation of enzyme-substrate and enzyme-cofactor complexes, as well as the interaction between proteins and RNA or DNA. High-energy anionic derivatives such as ATP and phosphocreatine are the main functional components in diverse power processes such as biosynthesis, muscle contraction, and molecular transport. In addition, these compounds serve as energy currency for many several enzymatic transformations. Anion carriers and channels transport small anions such as phosphate, sulfate, and chloride. In this case, they serve to regulate movement of metabolites across cell membranes while maintaining osmotic balance.


 In an unpleasant level, misregulation of the various mechanisms for anion transport may have serious consequences (Piletsky & Whitcombe, 2013).  For example, the failure of CFTR chloride transport channel is implicated in cystic fibrosis, a most common heritable disease among the Caucasians. In the same way, the ATP cassette transport systems (multi specific organic anion transporters) can confer resistance to several modern pharmaceutical agents and are very fundamental causes of the most pressing problems in medicine, such as multidrug resistance. On a different level, the inability to process or metabolize xenobiotic anions including chemically simple anions such as oxalates, cyanides, nitrites, and arsenates can cause acute toxicity. Inability to process naturally occurring sulfates and phosphates is a serious problem for patients suffering from kidney failure. In the same way, lack of capacity to excrete excess peroxynitrite and superoxide is associated with diverse symptoms related to reperfusion injury resulting from stroke and heart attacks.


On the other hand, anionic species are beneficial. For instance, anionic species administered directly as in the case of fluorides are useful in preventing dental caries. The anionic species produced in vitro are very vital for the manufacture of drugs such as aspirin and AZT, which are the key features in modern medicine. This exploration underscores the significance and complexity of anion recognition in biology. It underscores the need for knowledge of synthetic anion receptor chemistry and the potential utility of anions.In this paper, biologically relevant paradigms involving synthetic anion receptors are discussed. Chemists achieve anion recognition through natural processes such electrostatics, hydrogen bonding, size/shape complementarily, hydrophobicity, and metal-anion complex formation. The paper discusses the design and synthesis of state-of-the-art synthetic receptor systems. To begin with, it is fundamental to recognize the challenges that anion complexation poses to the supramolecular chemist.


 Anion Receptors in Nature

In nature, phosphate- and sulfate-binding proteins are essential for the active transport of sulfate and phosphate anions in the cell and organelles (Scheerder, Engbersen, & Reinboudt, 1996). Anion receptors belong to a class of proteins that weigh between 25000 and 45000 g/mol and serve as high-affinity receptors for the active transport of a variety of amino acids, carbohydrates, oxyanions, and oligopeptides. Synthetic receptors play a significant role in biology and chemistry through processes such as anion recognition and molecular recognition and anion complexation. For instance, nucleotide polyphosphatases are the prime components in the energy metabolic processes, in all living organisms. Anions play several metabolic functions. Nitrate, sulfate, chloride, and carbonate anions are present in significant amounts, in biological systems. Several anions act as bases, redox agents, phase-transfer catalyses and nucleophiles. Complexation of anions can create changes in chemical reactivity as does the complexation of cations.


Anions are equally essential to the various biological mechanisms. Artificial host systems (synthetic receptors) are highly relevant because of their analogies, which can be drawn with natural receptor systems.In the construction of anion receptor molecules, it is fundamental to gain knowledge of selective recognition processes (Sessler, Gale & Cho, 2006). In order to be able to study and mimic significant biological mechanisms involving the action of anionic species, it is necessary to have receptors that complex anions. This is a challenging process because it implies a design of receptors that are highly selective of biologically relevant anions such as sulfate, phosphate, carbonate, and chloride anions. This is particularly challenging because, unlike cations, anions have a variety of geometrics. They can be trigonal planer, spherical, tetrahedral or octahedral.


 The Challenges of Anion Complexation

In comparison to the design of receptors for cations, the design for anion receptors is challenging (Rosser, 1993). There are many reasons that explain this phenomenon.  Anions are bigger the equivalent isoelectronic cations. Therefore, they have a lower charge to radius ratio compared to cation. The diffuse nature of anions implies that electrostatic binding interactions are less effective than they would be for the corresponding isoelectronic cation. Anions are pH sensitive; they became protonated at low pH, and so lose their negative charge. Therefore, the receptors must function within the pH window of the target anion (example is ammonium containing receptor) as the protonation window of the receptor (and the anion) must be considered. For neutral receptors or receptors containing permanent built-in charges deigned to operate in aprotic media, it is less of a problem.  Anionic species have a wide range of geometries; a higher degree of design and complementarity is required to make the receptors that are selective for a specific anionic guest than for most cations.


 Table 1.0 shows the difference in radii for typical isoelectronic anions and cations (in octahedral environments) and exhibits the relatively diffuse nature anionic species.

Group 1

Group 17

∆r

Cation

Radius

Anion

Radius

 

Na+

1.16

F-

1.19 Å

0.03

K+

1.52

Cl-

1.67 Å

0.15

Rb+

1.66

Br-

1.82 Å

0.16

Cs+

1.81

I-

2.06 Å

0.25

 


 The type of solvent in which the anion-binding event occurs plays a significant role in controlling the anion-binding strength and selectivity (Piletsky & Whitcombe, 2013). In general, electrostatic interactions dominate over other recognition forces and vital in stabilizing anions in solution. However, hydroxylic solvents also have the ability to form hydrogen bonds with anions. In relation to this, a potential anion receptor must compete, effectively, with the solvent environment where the anion recognition event is taking place. For instance, neutral receptors that bind anions, solely, through hydrogen bonding interactions are less likely to be capable


 Non-Covalent Bonds

A receptor ('host’) has been defined to have convergent binding sites (Diederich & Tykwinski, 2008). In macrocyclic receptors, the sites are aligned to a cavity where a substrate ('guest'), having divergent binding sites, is captured, creating a receptor-substrate (host-guest) complex. The interaction results from forces different from those in conventional covalent bond or an ionic lattice. It has been defined as a "noncovalent bond". It is implicit that an additive integration of relatively weak interactions such as hydrogen bonding, π-stacking, electrostatic attraction, and other dispersive forces. The steadiness of the complex produced depends on how the interactions integrate. From the survey of the many receptor-substrate complexes that have been formed, some universal guidelines have been elucidated, which can assist to predict or give an explanation of the relative stability of the complexes. These are described in the section that follows with examples of the kinds of macrocycles that have been developed and complexes that have been studied.


 Number of Binding Sites and Contact Area

The non-covalent bond results from the integration of weak interactions and its strength bond is obviously associated with the number of the interactions between the substrate and the receptor, with multiple interactions leading to stronger bonds (Rosser, 1993). Van Der Waals' forces should be maximized by having a large area of contact between receptor and substrate as possible. This is achieved by shaping the receptor to create a concave cavity. This is done to complement the convex surface of the substrate's electron density. The number of binding sites, such as hydrogen bonding or electron donor-acceptor ("EDA") should also be maximized. The receptor cavity and substrate should have corresponding sizes, with a tighter 'fit' between the two resulting in the formation of highly stable complexes.


 The Principle of Pre-organization and the Macrocyclic Effect

It is a recognized feature that macrocycles have a cyclic nature that has great significance, in terms of their ability to form stable complexes (Scheerder, Engbersen, & Reinboudt, 1996). The reasons for the “macrocyclic” effect are both entropic and enthalpic. The open-chain analogue, having more degrees of freedom than its macrocyclic counterpart, requires more re-organization in order to contain a guest species, and more energy to free it from the solvent so that binding can take place. This reasoning was fostered by Cram, who developed the principle of pre-organization which results from the observation that receptor molecules, which are flexible, and need a change in conformation on complexation have lower stability constants than those which are rigid and have an 'open' structure, and are consequently predisposed to the binding of a guest and require less energy to desolvate the receptor.


 For instance, the Crown Ethers and Cryptands in a liquid state do not have a cavity; it is filled by inwardly aligned methylene groups. In the formation of a complex, the methylene groups re-align outwards and oxygen or nitrogen donor atoms are conformed inwards in the correct orientation for binding. This reorganization relates not only to a detrimental entropy requirement in the formation of the complex but also limits the favorable enthalpy variation on complexation. In macrocycles which are rigid and which possess a preformed cavity, this detrimental entropy requirement is accounted for in the creation of the macrocycle. For instance, Cram's spherands are very inflexible and have a cavity surrounded by oxygen donor atoms which are ideally arranged for binding spherical metal cations, leading to stability constants, which are very high. The other consequence of very inflexible receptors is that they show enhanced size selectivity for similar potential substrates. There is a contrast with the crown ethers and cryptands which are flexible and can undergo some distortion from their most stable conformations in order to accommodate guests of different sizes.


 However, it should be recognized that whilst receptors that have a high degree of reorganization form very steady complexes, they have dynamic properties, which, for many reasons, are not close to being ideal. They decomplex slowly, although acid catalyzed dissociation may be fast, and so have poor transport properties. Also, where macrocycles are to be used as models for enzymes or other biologically active substances they may be required to catalyze a reaction on a bound substrate. This inevitably leads to a conformational change of the substrate which a very rigid host may be unable to accommodate. Finally, if a complex is to form, then the receptor must have a cavity which is accessible.In the case of inflexible receptors, this implies that if the cavity is fully encapsulated then there are large, static barriers which inhibit the uptake of the substrate, and complexation or decomplexation cannot occur without breaking covalent bonds. Unless the substrate is included during the cyclisation step in the synthesis of the macrocycles (in which case it could be a template for the reaction), complexes will not form.


 Solvent Effects

In most complexation studies that take place in solution, the solvent used plays a critical role (Rosser, 1993). Its influence on the interaction between the receptor and substrate depends upon how well it solvates both receptor and substrate differently, the complex when formed and also upon the cohesive forces between the solvent molecules themselves.

In the solution state, the following demonstration can be used to express the development of a complex from solvated host and guest.

R (solvated) =R, S (solvated) =S, R+S =R.S; where R=receptor, S=substrate and R.S=complex

The various steps are discussed in the coming sections, briefly.


 $1(i)                 Desolvation of Receptor.

In the simplest case, salvation of the external of the receptor remains unchanged, i.e. we consider only the elimination of solvent molecules from the receptor cavity. A close approximation of inflexible receptors for more flexible receptors an enthalpy/entropy requirement for the rearrangement of the receptor must also be considered. The system’s enthalpy is heightened by the loss of any attractive interactions between solvent and the cavity and the cohesive attractions of the solvent molecules within the cavity. The system’s enthalpy is reduced by the association of the liberated solvent molecules with the bulk liquid. The entropy of the system is increased by the loss of the ordered solvation of the cavity.


 $1(ii)               Desolvation of Substrate

When the substrate is removed from its solvation sphere, the system’s enthalpy is increased by the loss of guest-solvent interactions and solvent-solvent interactions within the solvation sphere. It is decreased by the cohesive interactions of the solvent removed to the bulk liquid. Entropy is amplified by the loss of the oriented solvation shell.


 $1(iii)             Complex Formation

Receptor and substrate associate to form a complex. The enthalpy of the system is decreased by attractive receptor-substrate interactions, but the entropy change is detrimental because of the formation of an arranged complex. In general, there are several factors that contribute energy to the process. The size and sign of ∆Gcomplexation depends on the net gain or loss of entropy and enthalpy at each step.In both solvents, “entropy” is unfavorable term and so the complexation is driven by enthalpy. However, the enthalpy term for the association of receptor and substrate must be just about equal in the two solvents and so a great part of the variation in AH must arise from the desolvation terms. In fact, water is very cohesive i.e. strong solvent-solvent interactions and the large variation in AH are, perhaps, because the cohesive solvent exchanges in methanol are to a great extent weaker. In the desolvation of the receptor and substrate, there is a superior net enthalpy increase in water than in methanol. This is due to the favorable enthalpy term gained from the interaction of the liberated solvent molecules with the bulk.  In fact, the above expresses what is normally called the "hydrophobic effect", observed in aqueous solutions with a substrate that is lipophilic and a receptor that has a hydrophilic exterior, but a lipophilic cavity.


 In the excessively unique case, there is a negative enthalpy term for the solvation of the substrate and the receptor cavity, and both are abandoned by the solvating water molecules. The substrate is 'moved' into the cavity formed by the receptor. The hydrophobic effect is again observed for the other kinds of receptors, including enzymes, antibodies and cyclodextrins. This is in contrast to, for instance, the complexation of cations by cryptands or crown ethers in water, where the substrate is hydrophilic, and the aqueous solvent competes effectively for the substrate. This causes a low stability constant for the complex. However, when the complexation is analyzed in less polar solvents, the charged substrate is not so robustly solvated, and stability constants of the complexes are superior e.g. the Na+ complex (Cl^ counter ion).


 Synthetic Macrocyclic Receptors

A macrocycle can be perceived as a cyclic oligomer i.e. the smallest macrocycles comprising at least four monomer units (Rosser, 1993). The monomer units should not necessarily be identical. Whilst the smallest macrocycles are able to form complexes, the cavities are small, and the macrocycle exist just as a multidentate ligand. A "sandwich" complex is formed. For instance, Benzo-15-crown-5 is based on the cyclic tetramer of -CH2CH2O-. It forms complexes with KI, but the K+ cation is not encapsulated. Larger macrocycles can form a cavity capable of encapsulating small organic molecules, or inorganic or organic ions. The macrocycle is the host or receptor; the included species is the guest or substrate. Naturally occurring receptors (enzymes, antibodies, etc.) and macrocycles (cyclodextrins, porphyrins, etc.) have been known for some time but fully synthetic macrocycles have been studied only fairly recently. However, these studies have been intense, and progress has been rapid. The subject can be divided into a few broad areas, each of which is


 Crowns and Cryptands

Crown ethers were the first synthetic macrocycles to be properly analyzed. It is with these receptors that the field of synthetic, macrocyclic chemistry is widely recognized to have begun. Crowns form complexes with cations by interactions and with principal ammonium cations by hydrogen bonds between the ammonium N-H and the crown/cryptand ether oxygen. They have been extensively derivatised and utilized as phase transfer catalysts, in cation enrichment and detection, as anion receptors for chiral recognition of amines and reaction catalysis.


 Cyclodextrins

Cyclodextrins, as stated above, occur naturally. They have been recognized since 1891 and, as a result, have been the focus of much study. They have been widely manipulated and have a broad range of uses. They are cyclic oligomers of saccharides, made up of 6-12 monomer units. The 6, 7, and 8 member macrocycles are the most common and thus the most analyzed, and are in that order referred to as a, p, and y cyclodextrins.Cyclodextrins create complexes with a broad variety of substrates as the inflexible, hydrophobic cavity is well-matched to the binding of aromatic and aliphatic substrates, (Van Der Waals' interactions) and the primary and secondary hydroxyl groups give hydrogen bonding capacity and are capable of forming EDA bonds. They also cause aqueous solubility, so the hydrophobic effect is frequently a major cause of the formation of stable complexes.


 Cyclophanes

Cyclophanes were the earliest wholly synthetic macrocycles to be prepared, but their analysis as receptors did not start until the 1970's, when methods such as NMR became broadly available (Rosser, 1993). They are macrocycles that have aromatic residues (typically 5 or 6-membered rings) making up part of the framework of the 13 macrocyclic ring. Orthocyclophanes have their 6-membered rings connected at the C1 and C2 positions. In the same way, metacyclophanes are connected via the C1 and C3 and paracyclophanes at the C1 and C4 positions.


 Porphyrins

Porphyrins are cyclophanes that occur naturally and occur based on cyclic tetramers of disubstituted pyrroles. They are of enormous biological significance, being concerned in oxygen transport in the blood (hemoglobin) and storage in muscle (myoglobin). It also participates in photosynthesis. Expanded porphyrins have a range of applications. Porphyrins are the basic units that form complexes with di- and tri-valent cations such as copper, iron, magnesium, cobalt, and zinc, by EDA interactions between the bound cation and the porphyrin ring nitrogens. Porphyrins are widely delocalised, and the positive charge is spread over the entire ring.


In chlorophyll, magnesium (II) complexes of Porphyrins are concerned in a compound series of redox reactions that are responsible for oxidation of water to di-oxygen followed by the decrease in carbon dioxide to glucose i.e. during photosynthesis.In the muscles and blood, iron (II) complexes of porphyrins are the cause of reversible binding of di-oxygen. In natural systems, the porphyrin ring exists in the hydrophobic cleave of a protein. In the hemoglobin binding of iron (II), the porphyrin ring takes up four equatorial ligand sites. A histidine residue of the protein acts as a fifth axial ligand, and dioxygen is reversibly bound as a sixth ligand, also axial, at the opposite face of the porphyrin. Medical research, in this area, concerns the synthesis of derivatives analogues of the biological porphyrins and analysis of their capacity to reversibly bind di-oxygen, in the aim that this will enhance a better appreciation of the biochemical mechanisms.


In the initial analogues synthesized, it was established that cobalt (II) complexes can be prepared to mimic the biological iron (II) complexes. The synthetic iron (II) complexes, however, were quickly and permanently oxidised to iron (III) complexes. Later, it was established that oxidation to iron (III) occurred via an intermediate mechanism, which is followed by the development of an oxygen bridged dimer. This permanent oxidation can be prevented by blocking the production of the dimer demonstrated by the bridged porphyrins, most successfully. One side of the porphyrin has a hydrophobic bridge attached at the edges of the ring. A cavity is created above the side of the porphyrin that is too small to allow the approach of large molecules, but large enough to allow the coordination of dioxygen to the bound iron (II).


 Calixarenes

Calixarenes are cyclic oligomers of p-substituted phenols. It is a cyclic oligomer with n monomer units. A prefix represents the p-substituent. They form complexes with a broad variety of substrates, including metal ions by  EDA interactions with the phenolic oxygen molecules; amines by means of hydrogen bonds to the hydroxyl groups; and small organic molecules (acetone and chloroform, for instance, are bound by Van Der Waals forces; benzene and other arenes are bound by TC-stacking attractions).  Calixarenes have conformations that are mobile; the hydroxyl groups are tiny enough to pass through the annulus of the macrocyclic ring. The calixarene is 'locked' in a particular conformation. Almost always, only a sole isomer is secluded, usually the cone or partial cone. However, it is impossible to forecast which isomer a specific substituent will produce, although the cone is definitely the most likely, in terms of receptor characteristics as it has a complete cavity.


 Synthetic Receptors for Acetylcholine (AcCh)

Studies of synthetic receptors for AcCh might significantly contribute to the discussion of the various receptors and provides by providing models for the biological receptors (Scheerder, Engbersen, & Reinboudt, 1996). The structure of the complex was not established, but experiments show that AcCh is found in the cavity of the macrocycle and bound to the carboxylate groups by an electrostatic attraction at the end of the cavity. The aliphatic chain then lies in the cavity where a hydrophobic interaction with the aromatic residues occurs. The binding of AcCh is, thus, the type proposed in the early theories. Despite this fairly strong binding, it was revealed that the negatively charged carboxylate groups are insignificantly involved in the process of binding AcCh; the chief interaction is the ammonium cation (aromatic K attraction).


 Hybrids and Polytopic Co-receptors

In case the structural units from different types of macrocycles are integrated, a receptor is created, which may have exciting properties (Kubik, Reyheller & Stuwe, 2005). For example, spherands have been integrated with cryptands and crowns to produce the monotopic, hybrid receptors. In resemblance to their parent compounds, they bind cations but have some degree of rigidity.


 Conclusion

Receptors recognize substrates through a combination of interactions (Vilar, 2008). An exploration of these interactions has been conducted utilizing illustrations by means of examples from the various areas of macrocyclic chemistry. Chemists have demonstrated that the forces leading to complex formation can be adequately understood. Receptors can be designed for particular biological tasks, with respect to specific substrates.


 References

Diederich, F. & Tykwinski, R. (2008). “Modern Supramolecular Chemistry”. Weinheim: Wiley-VCH

Kubik, S., Reyheller, C. & Stuwe, S. (2005). “Recognition of Anions by Synthetic Receptors in Aqueous Solution”. Journal of Inclusion Phenomena and Macrocyclic Chemistry, 52 (3-4): 137-187

Piletsky, S. & Whitcombe, M. (2013). “Designing Receptors for the Next Generation of Biosensors”, New York, NY: Springer

Rosser, M.J. (1993). “Synthetic Receptors”. PhD Thesis, Durham University. Www.etheses.dur.ac.uk/5761/

Sessler, J., Gale, P. & Cho, V-S. (2006). “Anion Receptor Chemistry”. Cambridge, UK: The Royal Society of Chemistry

Steed, J. & Atwood, J. (2009). “Supramolecular Chemistry”. Hoboken, NJ: John Wiley & Sons.

Vilar, R. (2008). “Recognition of Anions”. New York, NY: Springer

Scheerder, J. & Engbersen, J. & Reinboudt, D. (1996). “Synthetic receptors for anion complexation”. Recueil Review, 115(6): 307-320


 

Tuesday, 13 August 2013 18:02

Reactive Oxygen Species

WRITTEN_BY Administrator

Reactive Oxygen Species


Introduction : Definition, function, purposes,  and source

$1a.)    Definition of reactive oxygen species

$11.      Reactive oxygen species (ROS) are free radicals and ions that are highly reactive. In their outer orbit, they contain chemicals with unpaired electrons and atoms. ROS are the free radicals that contain molecules of oxygen while   free radicals no not have oxygen.

$12.      Characteristics;

$1·         Unstable,

$1·         Short-lived

$1·         Highly reactive with molecules for them to attain stability.

 B. Sources of ROS

2. Exposure to radiation with ionization.

4. Herbicides smoking, fried foods, pesticides etc.

5. Production:

            a.) normal cellular respiration within the electron transport system. This normally happens in the terminal electron of the acceptor in mitochondria cell.

b.) chain reaction seen in   steals of free radical of an electron from a   compound nearby. This leads to the formation of free radical. These radicals can steal electrons from molecules and cellular structures.  

C. production on free radical species.

C, Purpose and Function

$11.      Cell signaling and normal functioning of cells

$12.       Are produced to engulf pathogens or kill some bacteria types.

$13.       Meant for the production of some types of hormones such as thyroxine.

$14.       There work is to balance: 

         a.) Excessive presence of free radicals may cause damage when there is lack of defense mechanism.

        b.)  Free radicals are produced by the commonly known processes, but become harmful when there are no adequate defense mechanisms. Therefore, there is need to balance    the inactivation/ removal and production.

c.)  anti-oxidants: Vitamin C, glutathione peroxides, SOD, coenzyme Q, beta-carotene and catalase.

d.) Anti-oxidants; theses re compounds that provide electrons to the free radicals for neutralization purposes.  These compounds can accommodate the electron loss without having to become inactive.  

D. Free radicals and diseases: the production of   free radicals in excesses causes various   disease processes. These diseases are:

$11.      Fibrosis

$12.      Aging

$13.      Inflammation

$14.      Drug toxicities

$15.      Carcinogenesis

$16.      Oxygen toxicity

$17.      Species diseases:

$1a.       Injury of reperfusion

$1b.      degenerative neurologic

$1c.       atherosclerosis

$18.      Cellular membranes lipid peroxidation.


II Reactive Oxygen Species

           A. Single Species

$1a.)    Hydroxyl radical

$1b.)    Nitric oxide

$1c.)    Ozone

$1d.)   Superoxide anion

$1e.)    Carbon centered radicals

$1f.)     Thiyl radicals

$1g.)     Hypochlorite ion

 


III ROS’s and HBOT

              The effects of ROS depend on:

$11.      Anti-oxidant production balance.

$12.      The patient’s physical condition.

$13.      Frequency, duration, and concentration to exposure of hyperbaric oxygen.

        B. Limits to exposure

$11.       Less than 2. 5 ATA

$12.      Duration and frequency of treatment decrease the production of ROS. This helps in limiting acute and accumulative exposure. 

$13.      Benefits  of the production of ROS

$1a.       ) Enhance the effects of antimicrobial on cellular immunity.


IV facts on ROS

 Important role in killing micro-organism. 


Reference

Raskin P, Lipman L, Oloff C (2007) Effects of hyperbaric oxygen on lipid peroxidation in the lung.  42: 28-30.

Thom S (1990) Molecular mechanism for antagonism of lipid peroxidation in the rat.17; 53-54.


 

The Role of Biochemical Components of Bacteria in Pathogenesis.


      The fundamental unit of life on the planet earth gets composed of organic matter. The organic material is made up of a relatively small handful of elements. A cell contains over 97% of Oxygen, Carbon, Hydrogen, Sulfur and Nitrogen. Todar Kenneth (2008) projects the key elements of bacteria as follows; Hydrogen 8%, Oxygen 20%, Nitrogen 15%, Phosphorus 3%, Sulfur1% and Carbon 50%. Carbon has the highest percentage component in bacteria which causes the advance increase the role in the pathogenesis.  


       A chemical compound is formed when two of more elements get into contact with each other and achieve stability. The Molecule is the negligible part of the amalgam that retains the chemical properties of the compound. Furthermore, the atom in a molecule gets joined to one another by some sort of chemical bond.  Hence, two atoms of nitrogen (N) joined together form nitrogen gas (the predominant gases in earth’s atmosphere) while two atoms of Oxygen (O) joined together form molecular Oxygen gas. Carbon (C) joined or bonded with two atoms of Oxygen form carbon dioxide; while carbon bonded with 4atoms of hydrogen (methane) - the two most predominant greenhouse gases.


      On the other hand, two atoms of hydrogen (H) bonded to an atom of Oxygen form a molecule of (H2O) or water, which gets to be the most predominant liquid on the planet earth. All microbes have various structural and functional components of macromolecules that explain for almost every facet of their survival and behavior as cells. Some of these cells are the same cells which contain bacterial microorganisms that play a role in pathogenesis (Todar Kenneth, 2008).


       The bacteria cell structure are unrelated to human beings as living things can be, but bacterial are fundamental to human life and life on the planet earth. However, bacteria get notorious since they cause several types of diseases humans and animals experience. Some of the diseases include; tooth decay to the black plague, there are beneficial bacterial species that get fundamental to better health. For example, the species that live symbiotically in the large intestine generates vitamin K, vital for blood clotting. Other bacteria species get beneficial indirectly. For example, bacterial make it possible for ruminant animals like sheep, cows and goats to digest plant cellulose and for some plants (alfalfa, soybean, peas) to convert nitrogen to a more utilizable form.


     Comprehensive studies indicate that bacteria were in existence as long as 3.5 billion years ago; hence making them the oldest living organisms on earth. Surprisingly, there are even older organisms known as archeans (also known as archaebacteria) tiny prokaryotic organisms that exist in some of the most severe environments; supper salty pools, boiling water, acidic water, deep in the Antarctic ice and sulfur-spewing volcanic vents.

Many scholars believe that the archaea and bacteria organisms originated from the same ancestor, but they later became different in characteristics depending on the environmental changes they got exposed during their cellular metamorphosis. As mentioned earlier, there are bacteria components, which generate energies that break down other components such as the bacteria used in decaying of fermenting other organisms. These procedures play a key role in the pathogenesis since they create pathogens-causes of diseases. Some of these organisms form toxic elements, which generate pathogens, enabling the pathogenesis process.


           Motility or the spontaneous movement of microorganisms enables the bacteria organism to move spontaneously in the humans white blood cells; hence eating up the cells used in securing the body from disease causing pathogens. The bacterium moves from the host and makes a motile behavior towards the security cells and antibodies eating them up; thus causing the infections or conditions in the human body. Quorum sensing in bacteria causes fluctuation in cell-population density.


       This means that the quorum sensing bacteria produce and release chemical signal molecules (autoinducers) that raise the concentration as a function of the cell density. This process leads to an increased concentration of bacteria cells in the antibodies; thus causing or playing the role of pathogenesis. Furthermore, the release of the molecules causes the movement of the bacterial from low concentrated areas to high autoinducers concentrated areas. Secretion systems such as anus sweat pore and urethras can be strategic hideouts for disease causing bacteria. These areas of the human body provide better channels for bacterial organisms, which facilitate the role of causing the pathogen organisms in the body.


      The pathogens move to the cellular organisms of the body (antibodies, blood cells) weakening then and therefore, causing diseases in the human body. The immune-system consists of the white blood cells, which produce antibodies responsible for killing and eliminating pathogens. When the immune system fails to protect the body from the disease causing organisms, they play a role in pathogenesis process.  Toxics and adhesion factors also contribute in creating freeway for pathogenesis. Thus, the toxic elements such as poison produce elements which help in stimulating the disease causing organisms. This process place a comprehensive role in effecting the pathogenesis process within the body.


                                                           Reference:

Davidson W. Michael (1995) Bacteria cell structure retrieved on 11/12/2012 from http://micro.magnet.fsu.edu/cells/bacteriacell.html

Todar Kenneth (2008) Chemical and Molecular composition and microbes retrieved on 11/12/2012 from http://textbookofbacteriology.net/themicrobialworld/chemoc.html


 

Friday, 26 July 2013 06:12

Metals and Metallic Alloys

WRITTEN_BY Administrator

Metals and Metallic Alloys


Properties

The terminology “Metals” is a general term that refers to metals and metallic alloys (Tisza, 2001, p.15). Metals have an abundant natural occurrence comprising more than half of natural elements. Pure metals contain only one metallic material component, for example, aluminum, iron, and copper. Alloys of metals are combinations of more than one component (Dennis, 2010). The base component (basic material) of metallic alloys is a metal, but the complimentary component or material may not necessarily be a metallic. Metals have a crystalline structure in which atoms align themselves in a regular manner (Ibid). Materials of metallic nature have high thermal and electrical conductivity, lustrous appearance, relatively high rigidity, and relative flexibility. The atomic and crystal structure of metallic alloys determines the direct properties of metallic alloys.


 Classification

Metals are of two prime groups. The first group comprises ferrous metals and iron-based alloys (Fesquet, 2002). This group of materials has iron as the main material. It contains steel and cast iron which are the most essential materials in engineering. The second main group comprises the non-ferrous metals and alloys. These include aluminum, titanium, copper, and many other metals including their alloys. Non-ferrous metals are many and are the main components used in alloys.

Metals

Ferrous metals

Non-Ferrous metals

Examples

Cast Iron and Steel.

Copper, Aluminum, Titanium, and Brass.


Metallic Alloys

An alloy of a metal is a combination of more than one material (Srinivasan, 2010). One of the elements in the combination must be a metal with a high proportion for it to qualify as a metallic alloy. The other components in the combination may be metals or non metals. Brass and steel are examples of metallic alloys. Brass is a combination of copper and zinc while steel combines iron and carbon. Metallic alloys have a wide variety of applications in the manufacturing industry. Pure metals are useful in situations that require specificity as regards properties such as high ductility, high electrical conductivity, or high corrosion resistance. These properties exist at maximum values in pure metals. However, alloys improve mechanical properties such as hardness, yield point, and tensile strength.


 Alloys can either exist in a single phase, or as a mixture (Chatterjee, 2007). Phases are states of materials that are physically distinct or homogeneous. An alloy in the metal state has three possible phases: pure metal, solid solution, and intermediate phase. If a material has a single phase, then it can either be a solid solution or intermediate phase. If the alloy is a mixture, then it could have a composition made combination of any of the three phases. A solid solution is a state of an alloy that has the solute atoms distributed in the solvent matrix and has the same structure of the solvent. A solvent is the component present in a higher proportion than the other component, the solvent (Habashi, 1998). Intermediate phases (chemical compounds) comprise two different elements with divergent electrochemical properties.


General Applications

Metals have a wide variety of functions ranging from structural to chemical functions. Metals are materials that are most common in engineering functions including the manufacture of various devices and equipments (Tisza, 2001, p.16). These include household appliances, equipments for aircraft and astronautics, car components, or machines and devices. These are devices and equipments that contain metals as the base materials. In most cases, the manufacture of these metals use metallic alloys. The manufacture of aircraft turbine engine uses super alloys to increase the power and efficiency. A nickel-based super alloy can withstand extreme temperatures of up to 1000C, and, so, is applicable in the manufacture of the engine.


 Uses of Metallic Alloys

Metallic alloys have several essential functions (Habashi, 1998).

a) Bearing alloys: These are alloys applied in the manufacture of metallic components that encounter sliding contact under pressure with another surface. The bearing alloys comprise hard inter metallic particles that have the capacity to resist wear. Bearing alloys have these particles embedded in the matrix of softer material.

b) Corrosion-resisting alloys: These are noble methods that resist corrosion and include precious metal alloys. Some alloys resist corrosion because they develop a protective oxide film. These include stainless steel and aluminum alloys. Other corrosion resisting alloys are Monel and Incol.

c) Dental alloys: These are alloys used for hardening purposes. Examples include silver based alloys and dental-based alloys. Silver based alloys, made of silver amalgam, contain small amounts of tin, zinc, and copper for the purpose of hardening.


d) Die-casting alloys: These are alloys that have low melting temperatures such that, in the liquid form, injection into steel dies can occur under pressure. The castings are useful for household and office appliances, and automobile parts. These appliances and vehicle parts are complex.

e) Fusible Alloys: These are alloys with extremely low melting points used for several purposes such as in fusible elements, in automatic spinners.

f) High temperature alloys: These alloys are strong at high temperatures such as in jet engines, power generating plants, and gas turbines. They also resist oxidation by steam and fuel-air mixtures.


g) Joining alloys: These are alloys used for bonding by soldering, brazing and welding. They provide filler material will lower melting point than that of the joined parts.

h) Light-metal alloys: These are alloys composed of low density elements such as magnesium, titanium, and aluminum. They are useful in the age hardening processes.

i) Low-expansion alloys: These are alloys that do not change their dimensions over the atmospheric temperature range. Their uses include the manufacture of temperature-sensitive devices such as watches and glass-to-metal seals.


j) Magnetic alloys: These are alloys applicable for magnetization purposes. Purposes include magnetic cores of transformers and motors. For instance, an alloy of silicon and ferrite applies to alternating current applications.

k) Precious-metal alloys: Precious metals are scarce and beautiful. Uses include application in electronic devices, temperature-measuring devices, and catalytic applications.

l) Metallic glasses: These are alloys that are strong, corrosion resistant, and tough. Rapid solidification technology is one of the applications of metallic glasses.

m) Prosthetic alloys: These are alloys used for surgical procedures such as implants. Corrosion property is essential for use in these alloys.


 References

Chatterjee, K. (2007). “Uses of metals and Metallic Minerals”. New Delhi: New Age International Publishers.
Dennis, W. (2010). “Metallurgy: 1863-1963”. Chicago, IL: Transaction Publishers.
Fesquet, A. (2002) “A Guide to the Manufacture of Metallic Alloys”. Palm Springs, CA: Wexford College Press.
Habashi, F. (1998). “Alloys: Preparation, Properties, and Applications”. Hoboken, NJ: John Wiley & Sons.
Srinivasan, R. (2010). “Engineering Materials and Metallurgy (2ed.)”. New York: McGraw Hill.
Tisza, M. (2001). “Physical Metallurgy for Engineers”. Materials Park, OH: ASM International.

Metals: Properties of Metals and Alloys and their Applications


Literature Review

Carbon steel, according to Seblin and colleagues (2003) is the most commonly used among all types of steel. The carbon steel properties mainly depend on the contained amount of carbon.  Carbon steel usually has carbon content below 1%.  Carbon steel is used in the making of kitchen appliances, car bodies, cans and structural beans (Seblin, et al, 2003).  The pure carbon steel appears in three types. These are the medium carbon steel, low carbon steel and high carbon steel.  They are named based on the content of carbon that forms those (Seblin et al, 2003).


There are the high strength and low strength alloy of steel. The high strength low alloy steels are also known as the micro alloyed steels that are designed to improve on the chemical properties. They are also designed for greater resistance from the atmospheric corrosion (ASM, international, 2001). The chemical composition of high-strength low alloy steel varies based on their composition. Iron can be alloyed with carbon steel so has to increase its hardness and strengthens its treatment with heat. Addition of carbon on steel provides it with additional strength and hardness (ASM, international, 2001).   


 Davis (1996) on cast irons indicates that just like steel, it comprises of a large family of alloys.  Cast irons are alloys of multi component ferrous types, which become solid with cutectic (Davis, 1996).  Cast iron is mainly made up of carbon, silicon and iron. The cast iron has a higher silicon and carbon contents compared to steel. This is because of the high level of carbon content. The cast iron structure portrays a high phase of carbon more than that in steel.  Cast iron solidifies with the thermodynamically meltable selection potential, of the cooling rate, chemical component and liquid.  The cast iron is classified into white iron and grey iron (Davis, 1996).  


 Cast irons and steel are the common light weight irons that are commonly used in various engineering applications. There hardness and exceptional strength and other properties make them be common used in the development of low density vessels. Other metals of low density are the beryllium, aluminum, titanium, and magnesium. The commonly used are titanium and aluminum, but, have the limitation of becoming mechanically troublesome. Beryllium, on the other hand, is highly expensive especially when used as a metal base.


 The low-density metals are mainly useful in the space, rocket and aviation technology. The light weight metals are also applicable in the building of ship, automobile engineering and in other industries.  The main reason for the use of light weight alloys of metal is because it results in the reduction of fuel consumption and the mass of the exceptional (Prentice hall India & Chandra, 2004, p 133).  


 Davis (2004), indicates that copper alloys and copper can be welded in different solid state and fusion processes. The process of fusion welding involves the solidification of base metal, localized melting and filter metal. The method of fusion melting is commonly used in welding copper and its alloys. Other processes include resistance welding process, ultrasonic welding, friction welding, and explosion welding. Copper alloys and copper in manufacturing are mainly joined by welding. Many metals are alloyed by use of copper in order to produce different forms of copper alloys.


          The common alloy elements are nickel, zinc, tin, silicon, and aluminum. Other metals and elements are alloyed in order to improve on their material characteristics. Copper and its alloys are divided into nine different categories. These are the copper-zinc alloys that contain 40% Zinc.  Second category is the high –copper allots with 5% of various alloying elements.  Third is the coppers category with 99% Cu.  The fourth category is the copper-tin alloys with 0.2% P and 10% SN. The others are the copper aluminum alloys, copper silicon alloys, copper nickel alloys, special alloys, and copper-zinc-nickel alloys (Davis, 2001).  


            Cobalt-base alloys were essentially used for surgical implants. The Ni-Co alloys deposits differ based on their chemical properties and their annealing behavior. Cobalt has an atomic weight of 58.93, and it is considered as a transition metal.  It has an atomic number of twenty seven. Its existence is between nickel and iron. Cobalt is less abundant compared to iron and comprises 0.0020 % in the crust of the earth.  Therefore, cobalt is a valuable and rare substance compared to other metals (Shedd, 2006). Cobalt is combined with other metals so as to produce alloys.


The cobalt content super alloys are used as parts in making gas turbine engines. Commonly used as military devices and other commercial products.  The demand of cobalt made elements has in the recent past become highly demanded due to the need for rechargeable batteries. Cobalt is used in the making of dyes, petroleum, electronics, and magnet for it has its ferromagnetic property.  The alloys of   cobalt have further been applied in the biomedical spheres, such as for dental use; neurological, cardiovascular, and orthopedic implants devices (Disegi, Kennedy, & Robert, 2001).     


 Nickel is also considered as a transition n metal with an atomic weight of twenty eight and a   weight of 58.69.  The appearance of nickel is golden and silver shine. It is among the abundant elements on this planet.  Nickel is mainly applied in various parts of the world especially in America and China. It is the key ingredient in the making of stainless steel, low alloys steels and cast irons. It has unique characteristics similar to those of cobalt such as heat resistance to magnetic alloys, resistant coatings ideal for corrosion resistance. Nickel is mainly used in making rechargeable batteries by combining it with cadmium (Petrucci, Harwood, Herring, & Madura, 2009).


             The high silicon irons are those irons with a high level of silicon. Its maim property is that it is resistant to corrosion. The high iron silicon is commonly used in the chemical industry in making highly corrosive substances and fluid. The component of this iron depended on the availability of 14.20-14.75% of the silicon. The iron is resistant to any effect from industrial acids, nitric acid, and sulfuric acids (Kohl, 2001).  


 Reference

 Davis J (1996) ASM Specialty Handbook: Cast Irons. p 45
 Davis, J (2001) ASM Specialty handbook on copper and copper alloys. Asm Internal, p 277
 Seblin, B, Jahazeah, Y, Sejeebun S and Wong, K (2003) material science. Carbon steel. Retrieved from http://www.uom.ac.mu/Faculties/foe/MPED/Students_Corner/notes/EnggMaterials/steelbklet.pdf
On November 20, 2012
ASM international (2001) High-strength low-alloy Steels. Retrieved from
On November 20th 2012
Prentice Hall India and Chandra P (2004) Engineering Materials: Properties and Applications of Metals and Alloys. PHL publisher’s p, 133
Disegi, A, Kennedy, K & Robert (2001) Pillar - Cobalt-Base Alloys for Biomedical: Nickel, Cobalt, and Their Alloys
Shedd, K (2006) the United States Geological Survey 2006 Minerals Yearbook
Petrucci, Harwood, Herring, and Madura (1001) General Chemistry 9th Edition
Walter H. Kohl - Handbook of Materials and Techniques for Vacuum Device

                          Properties of Metals and Alloys and their Applications


Introduction Chapter

Background

Metals materials have existed since time in memorial. In fact, civilization of mankind demonstrates a story of development of metals as materials considered to be the foundation of technological advances. Several centuries have passed since metal got discovered as a tool useful for mechanical tools.  In the past humans used smelted metal materials to create tools like agricultural tools and weapons among others Sharma (P. Chandra 2004).


Metal materials continuous advances provided the growth of heavy metal industries such as steel and diamond just to mention but few. There are several types of metals categorized as heavy and light metals. Heavy metals include Mercury lead and steel while light metals include aluminum, magnesium among others. The resourcefulness of metals attests to the extremely extensive range of properties of more than 70 metals on the periodic table.  The following therefore provides an introduction to some of the more outstanding metal properties.


 Materials:

First and foremost, are the mechanical properties, power and ductility enabling the extensive use of metals in structures and machinery.   Metals as well as allows demonstrate flexibility, manipulability and the ability to be deformed without breaking; hence making them easy to shape into steel beams of construction. As if not enough, the metal gets also used in extrusion of other metallic material like aluminum windows and door frames, as well as metal cans and variety of fasteners (paper clip and nails).  


The sear strength of metals under pressure and other forms of forces make them ideal for structural services such as construction of buildings, aircrafts, automobiles bridges, gas pipelines, road safety guards and cables.  Another type is the chemical properties.  In chemical properties metals blend with other non-metallic elements, to form an enormous number of alloys that result to enhancement of metals in applications. For example, the blending of iron, chromium and nickel offers a sequence of stainless steel alloys used by alloy reams automobile manufactures.


 Metals like molybdenum, nickel, rare earths, cobalt and the platinum group metals enhance the catalystic response for the synthesis of organic chemicals from petroleum. An enormous variety of metal compounds and salts inject profitable impacts to products, like plastics in terms of resistance to degradation, flames resistance, brightness and colour effects. Furthermore, effects on metal salts have made photography a reality in the modern technology appliances.  


 Another type of metal properties gets to be, magnetic properties. Iron and several other metals reveal ferromagnetism properties naturally inhabited in them.  Additionally, paramagnetism can be exhibited by electrically (in an electrical field) magnetizing alloys and other metals. Magnetic properties can be engaged in various systems such as speaker systems (for audio gadgets) electric motors used in cars and other machines. Eminent studies reveal that metals emanate/ emit electrons when exposed to a short wavelength, radiation or when heated to adequately high temperatures. 


In addition, when metals get exposed to sufficiently high temperatures they deform and result into smelting. When the metal is at this state, can be used to make various types of metallic gadgets such as; vehicles cover metals, construction beams and beautiful curios or ornaments.  The same phenomenon gets applied in Television screens, using rare oxides and a variety of electronic instruments and devices. Metals like lead have the ability to absorb radiation; hence it gets employed in protecting the patient like the apron the dentists provide in an X-ray assessment. 


 In conductivity, metals are superb conductors of electricity and heat. The conductivity of metals simultaneously increases in accordance with the rise of temperatures. This means than the higher the temperature the excellent the conductivity of the metal.  Electrical conductivity provides people with electricity supplies used for domestic purposes or industrial purposes.  For example,  electrical conductivity provides transmission of power over long distances providing  people with electricity in house hold appliances such as; cookers, TV, and Microwave.   On thermal conductivity, thermal transmission gets harnessed in cooking utensils, as well as in automobile radiators and water heaters appliances.


Furthermore, metals get used in applications sensitive to corrosion such as food preparation, chemical plants, lead in storage batteries, plumbing and medical applications.  On the other hand, the wear resistance and deformity issues get considered especially during transportation since some metals do not have much ability to resist breaking. However, there are others such as metals in gear levers and springs which do not break due to much of deformation (bending) hence they enable the automobiles to balance the masses effectively.  Most of the metals have lusting effects a part from some which includes copper and gold among others.    


 The objectives:

$1·         To explore on some properties of metals and alloys

$1·         To examine metals and alloys application in life

$1·         To assess the significance of metals and alloys in modern technology


 References

Cohn C. Sigmund (1991) Properties of metals and alloys retrieved on 11th/18th/12 from  https://docs.google.com/viewer?a=v&q=cache:RSnJHmuoMoIJ:www.sigmundcohn.com/pdf/EN/properties_metals_alloys.pdf+&hl=en&gl=ke&pid=bl&srcid=ADGEEShvezk72G7mE-Js5x8p8NciWtbHOnriNA76EZAe4guXeF5MlfLukRemO3EeWAs4D88eYBwPC3hTDLbSc-cv_DFJzCX8A8GbM9nDSomTQYSg-jZbG3kN2cmbasUKz1B2-_SIYpig&sig=AHIEtbTYQOXovdBJpIAgC6LGMrBa1FrJEg
Habashi F. and Wiley J. (2008) Alloys: preparation, properties application 321Pgs
Sharma P. Chandra (2004) Engineering materials: properties and applications of metal and alloys Prentice Hall India Pvt., Limited 258Pgs
Tuesday, 23 July 2013 09:42

First Post

WRITTEN_BY Administrator

First Post


Using GPower3, the sample size was 100. This sample size is viable as it meets the threshold of normality. The sample size is greater than 30 hence the justification that it is normally distributed.


 T-test is to be used for testing the difference in means of the two groups. The study should be designed in a manner whereby there is intrinsic pairing of the corresponding items in one sample with those of the other sample. This will test the mean of the two groups effectively. One of the samples would act as the control while the others act as the treatment.


The aim of the testing will be determining whether the populations from which the samples were drawn are significantly different. A descriptive design is to be used as two samples are drawn from a similar population.  


          In this test, the assumption was that the data was normally distributed. The type one error, alpha level was set at 0.05 levels. The statistical power level for calculating of the sample size is to be set at 0.8. The effect size in the test is set at 1. The sample size was equal for business unit one together with business unit 2. The sample size in the two samples was 200 with each sample having 100.


               Sampling comes with its costs; therefore, the research design should be designed in a manner that consumes the least cost. However, the data integrity and authenticity should not be compromised. Samples should be selected randomly from the business units without bias. The test is ethical as it has no bias; different potential subjects were accorded equal chances of being incorporated in the study (Liu, & Raudenbush, 2000).


 Second post

With a margin error of 5%, confidence interval of 95% and a population size of 200, the recommended sample size is 132. This sample size arrived after an online calculation and it is justifiable by being more than 30 hence it meets the threshold of normality.


 A random sample will be selected from the business units. The samples are selected concurrently from business unit one and business unit two. Selecting them alongside one another will ensure equal selection, as well as avoidance of bias. Simple random sample would be obtained by allocating random numbers to different units randomly. The units allotted with different numbers are then selected one after another and included in the sample survey. This design is efficient in including the units in the sample design.


 It is assumed that sample one and two have a bivariate independent variable. The samples are continuous dependent variables. Each observation of the dependent variable has independence of the other observations of the dependent variable. The dependent variable is also assumed to have a normal distribution with similar variance and standard deviation. The alpha is assumed to be 0.05, with the statistical power assumed to be 0.8. Taking the standard deviation to 14 the sample size was found to be 125.


 A controlled study will be reliable in this study. This is because the subjects are assigned randomly to a given treatment or another. This diminishes any inherent bias amongst the subjects. The calculations needed are on how many participants are required to determine any relations. The design is ethical in that it avoids any form of bias (Kirk, 1995).


 References

Karl Wuensch's Statistics Lessons: Estimating the Sample Size Necessary to Have Enough Power" from Power Tables for Effect Size dUnpaired t-test Retrieved from http://www.biomath.info/power/ttest.htm
Kirk, R. E. (1995). Procedures for the behavioral sciences: experimental design: (3rd Ed.) Pacific Grove, CA: Brooks/Cole Publishing.
Liu, X. & Raudenbush, S. W. (2000). Statistical power and optimal design for multisite randomized trails. Psychological Methods, 5, 199-213.
Monday, 22 July 2013 06:52

Hydrogen Fuel Versus Fossil Fuel

WRITTEN_BY Administrator

Hydrogen Fuel Versus Fossil Fuel


Hydrogen is a natural element which combines with oxygen to form water.

The hydrogen element is not a source of energy, but it is a carrier of energy because a great deal of extraction energy is required to make an extraction of hydrogen from water. However, it is used as an energy source in batteries and fuel cells. There is a lot of research that is underway to develop efficient technology that can allow exploitation of the hydrogen energy potential. This dream may solve many problems associated with fossil fuels. These problems include the high fuel costs, pollution from oil spills and combustion as well as probability of exhaustion of fossil fuel resources (Lau & Padro, 2000).


 Hydrogen fuel is preferred because it is a clean source of energy that does not emit greenhouse gases during combustion. It also burns to produce higher levels of energy than fossil fuels (Lau & Padro, 2000). Despite these advantages the design and use hydrogen fuel technology and systems has been very challenging. Firstly, the technology of production, storage, distribution and burning of hydrogen has not been put in place and may be very challenging to establish. Secondly, the design of internal (IC) combustion engines is very challenging due to the chemical properties of hydrogen. Hydrogen has very wide flammability range, this may be an advantage in some considerations, but it creates constraints on IC engine design. The ‘hot spots’ in an engine may cause pre-ignition, or “pinging” as known in hydrocarbon engines. This is bound to be a problem because hydrogen has a low ignition temperature. Hydrogen also has a high flame temperature during combustion. The high temperature is a benefit in principle, but because air is 80% Nitrogen the high heat may cause oxidation of nitrogen which will result to nitrogen oxides emissions (pollutants). The challenge about how sufficient H2 can be manufactured economically as well as the infrastructure to supply it nationally is unsolved. H2 may require greater amounts of storage space on automobiles because it cannot be highly compressed and thus there is a need for frequent refueling after short distances.


 A comparison of hydrogen (H2) to CH4 based on equal masses seemingly shows that there is a 16/2 merit (on molecular weights) in favor of H2; but, on basis of equal energy H2O=H2 +1/2 O2 in comparison with 2O2+CH4 =2H2O +CO2 with all components in the gas state the advantage is ~3.6 (Tim, 2004). This is because a great amount of energy is derived from the process of forming CO2. Another un-addressed issue with potential challenges is potency of water as a greenhouse gas. The combustion within hydrogen IC engines releases water vapor. The high release of water to the atmosphere may result in trading smog for fog, and this is another unaddressed potential challenge (Tim, 2004).

 Hydrogen also has a smaller quenching distance compared to gasoline. As a result, flames from combusting hydrogen travel close to walls of the IC engine’s cylinders before they extinguish. This makes it difficult to quench flames of H2 compared to gasoline. This small quenching distance may increase the backfiring tendency because the air-hydrogen mixture’s flame easily goes through intake valves that are nearly closed compared to air-hydrocarbon flames (College of the Desert, 2001).
Conclusively, hydrogen may be a cleaner fuel, but the challenges posed by its chemical properties and production necessitate further research for its use to be implemented.

  References
 
College of the Desert, (2001). Hydrogen Use in Internal Combustion Engines. Retrieved on 11

th

 August, 2010. Retrieved fromhttp://www1.eere.energy.gov/hydrogenandfuelcells/tech_validation/pdfs/fcm03r0.pdf.

Tim, D, (2004). Hydrogen versus Fossil Fuels. Retrieved on 11th August, 2010 from http://www.newton.dep.anl.gov/askasci/phy00/phy00886.htm.

Lau, F. and Padro, G.E.C, (2000). Advances in hydrogen energy. New York, NY: Springer Publishers.


 

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