Biological fuel

We now assess the factors that optimize the enthalpy of combustion of carbon-based fuels, with an eye toward understanding such biological fuels as carbohydrates, fats, and proteins. The combustion of 1 mol CH4(g) releases 890 kj of energy as heat per mole of C atoms  

Another factor that determines the enthalpy of combustion is the number of carbon atoms in hydrocarbon compounds. For example, whereas the enthalpy of combustion of methane is -890 kJ mol , that of iso-octane (CgHig, 2,2,4-trimethyl-pentane (1), a typical component of gasoline) is —5461 kJ mol (Table 1.6). The much larger value for iso-octane is a consequence of each molecule having eight C atoms to contribute to the formation of carbon dioxide, whereas methane has only one. 

The concept of oxidation numbers, familiar from introductory chemistry, clarifies the point made in this paragraph. The formation of CO2 from CH4 involves an increase in the oxidation number—that is, an oxidation —of carbon from -4 in CH4 to +4 in CO2. By contrast, the carbon atom in CH3OH has an oxidation number of—2 and is in a higher oxidation state than the carbon in methane. 

As we have seen, the presence of partially oxidized carbons lowers the energy output of a fuel. Fats are commonly used as an energy store, to be used only when the more readily accessible carbohydrates have fallen into short supply. In Arctic species, the stored fat also acts as a layer of insulation in desert species (such as the camel), the fat is also a source of water, one of its oxidation products. 

Proteins are also used as a source of energy, but their components, the amino acids, are also used to construct other proteins. When proteins are oxidized (to urea, CO(NH2)2), the equivalent specific enthalpy is comparable to that of carbohydrates (about 17 kj = 4 Cal g )- 

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Can biofuel be used to replace petroleum-based fuels Biofuel can be made from biological materials, snch as plants and animal fats. Biodiesel and ethanol are the two most common biological fuels. As part of your research, find ont what biofnel is nsed for. Think about factors that may be holding back the sale of biofuel on the Canadian market. 

Biological fuel cells have a long history in the literature,but in recent years, they have come to prominence as more conventional fuel cell technologies have approached mass-market acceptance. Driving the recent ascendance of biofuel cells are the aspects of biocatalysis that are unmatched by conventional low-temperature oxidation—reduction catalysts, namely, activity at near-room temperatures and neutral pH and, more importantly, selective catalytic activity. 

Extensive review literature exists in the area of biological fuel cells. Notably, Palmore and Whitesides summarized biological fuel cell concepts and performance up to 1992." More recently, Katz and Willner discussed recent progress in novel electrode chemistries for both microbial and enzymatic fuel cells,and Heller reviewed advances in miniature cells.This article does not duplicate these valuable contributions. Instead, we focus on the strengths and weak-... 

Fig. 14.41. Schematic representation of the biological fuel cell concept. (Reprinted from J. O M. Bockris and S.

Moore then explained how mitochondria are biological fuel cells. The oxygen reduction taking place in a mitochondrion is exactly the same as in a standard fuel cell. Using several enzymes and only earth-abundant elements, the mitochondrion converts electrochemical potential to biochemical work with efficiency greater than 90 percent. This is a steady-state process in which protons are pumped across the membrane to maintain its electrical potential. If... 

Fig.1. 13. Schematic representation of the principle of the biological fuel cell concept. R and RH representtheoxidizedand reduc form of a bio-molecule. ADR is adenosine diphosphate ATP is adenosine triphospate. (Reprinted from J. O M. Bockrisand S. U. M. Khan, Surface Electrochemistry, p. 699. Plenum Press, New York, 1993.)...

What is missing from both these books, however, is an answer to the question how do the biological fuels (most commonly ATP and proton gradients) ultimately produce coordinated motion Even more conspicuously absent from those - and virtually [14] all other - depictions of biological motors is any atomic detail. That absence is due to lack of knowledge, not imprecise graphics. 

Besides a source of energy, organisms require a source of materials for biosynthesis of cellular matter and products in cell operation, maintenance and reproduction. These materials must supply all the elements necessary to accomplish this. Some microorganisms utilize elements in the form of simple compounds, others require more complex compounds, usually related to the form in which they ultimately will be incorporated in the cellular material. The four predominant types of polymeric cell compounds are the lipids (fats), the polysaccharides (starch, cellulose, etc.), the information-encoded polydeoxyribonucleic acid and polyribonucleic acids (DNA and RNA), and proteins. Lipids are essentially insoluble in water and can thus be found in the nonaqueous biological phases, especially the plasma and organelle membranes. Lipids also constitute portions ofmore complex molecules, such as lipoproteins and liposaccharides. Lipids also serve as the polymeric biological fuel storage. 

Mitochondria are the sites in cells where raw, biological fuels... 

Most redox reactions involving organic molecules occur in the range OmV> " > —400mV. The oxidation of a biological fuel (e.g. carbohydrate) involves reactions in which... 

See also Ketogenesis, Thiolase, Acetoacetate, Acetone, / -Hydroxybutyrate, Biological Fuel, Brain Metabolism, Liver Metabolism... 

See also Biological Fuel, Liver Metabolism, Ketogenesis (from Chapter 18), Biochemistry of Neurotransmission, (from Chapter 21) Neurotransmitters and Receptors (from Chapter 21), Figure... 

See also Biological Fuel, Hormonal Regulation of Fuel Metabolism, Figure 23.4... 

Biological fuel cells are those in which at least one of the following two conditions is met ... 

At present, biological fuel cells are a subject of great interest for the following two reasons ... 

However, in their mechanism and in their action nature bacterial and enzymatic fuel cells have much in common. In bacterial fuel cells intermediate redox systems are often used, as well, to facilitate electron transfer to (or from) the substrate. As the effect of microorganisms is much less specific than that of enzymes, a much wider selection of redox systems can be used, in particular, the simplest iron(III)/iron(II) system. The working conditions of these two kinds of biological fuel cells are similar as well a solution with pH around 7.0 and a moderate temperature, close to room temperature. 

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