Microbial fuel cell (MFC) technology is a renewable energy source that employs microorganisms as biocatalysts to degrade substrates into electrons and protons, and then transfer the electrons to the anode electrode. Electron transfer rates by microorganisms depend on many factors as well as on their diverse electron transfer mechanisms. The present study compared cytochromes, flavoproteins, electron transfer complexes, redoxins and other extracellular membrane proteins that have direct involvement in electron transfer mechanisms in Escherichia coli str. K-12 MG1655, Rhodopseudomonas pulastris DX-1 and Shewanella oneidensis MR-1. Escherichia coli str. The results showed that K-12 MG1655 had a more diverse range of extracellular proteins for electron transfer mechanisms compared to Rhodopseudomonas pulastris DX-1 and Shewanella oneidensis MR-1. Escherichia coli str. K-12 MG1655 expressed more flavoproteins, redoxin and electron transfer complex related proteins that had direct involvement in electron transfer mechanisms compared to two other bacterial species indicating that it may be able to transfer more electrons when employed in MFC technique. Escherichia coli str. K-12 MG1655 expressed 16 cytochromes, 9 flavoproteins, 6 redoxins, 6 electron transport complexes, 1 hypothetical and 1 oxidoreductase proteins. On the other hand, Rhodopseudomonas pulastris DX-1 and Shewanella oneidensis MR-1 expressed 26 and 35 cytochromes proteins. But these two bacterial species expressed less flavoproteins and redoxin related proteins and they didn’t express any electron transport complexes or hypothetical and oxidoreductase related proteins for electron transfer. STRING and SMART results suggested that the identified proteins transferred electrons either by connecting with other types of identified proteins in the constructed gene network or independently by taking part in oxidation-reduction reaction, metal ion reduction reaction or by their FMN binding activities.

<div>The first chapter reports a study of aryl nitrene intermediates. Although extensively studied over the past 30 years, phenyl nitrenes have a propensity to undergo rearrangement reactions and form polymeric tars. This is in stark contrast to the phenyl carbenes which are known to undergo several important reactions to produce a library of useful organic compounds. One such reaction is the insertion of phenyl carbenes into a double bond to produce a cyclopropane moiety. If aryl nitrenes can be exploited to conjure a similar reactivity, they would be an excellent synthetic route to produce aziridine rings which are a crucial component of many natural products. This review chapter is a collection of all the efforts that have been made in this regard.</div><div><br></div><div>In the next chapter, the electronic effect of the azide functional group on an aromatic system has been investigated by using Hammett-Taft parameters obtained from the effect of azide-substitution on the gas-phase acidity of phenol. Gas-phase acidities of 3- and 4-azidophenol have been measured by using mass spectrometry and the kinetic method and found to be 340.8 ± 2.2 and 340.3 ± 2.0 kcal/mol respectively. The relative electronic effects of the azide substituent on an aromatic system have been measured by using Hammett-Taft parameters. The σF and σR values are determined to be 0.38 and 0.02 respectively, consistent with predictions based on electronic structure calculations. The values of σF and σR demonstrate that azide acts an inductively withdrawing group but has negligible resonance contribution on the phenol. In contrast, acidity values calculated for substituted benzoic acids gives values of σF = 0.69 and σR = -0.39, indicating that the azide is a strong  donor, comparable to that of a hydroxyl group. The difference is explained as being the result of “chimeric” electronic behavior of the azide, similar to that observed previously for the n-oxide moiety, which can be more or less resonance donating depending on the electronic effects of other groups in the system.</div><div><br></div><div>Phenyl nitrenes undergo bimolecular chemistry under very specific circumstances. For example, having an oxide substituent at the para position of the phenyl ring enables the formation of an indophenol product from a photocatalyzed reaction of the nitrene. Although, this reaction has been reported before, the mechanism involved in this reaction has not been fully understood. A two-electron mechanism involving electrophilic aromatic substitution reaction has been proposed in the literature, however we found evidence that did not support this theory. Instead, we find this reaction analogous to the popular Gibbs’ reaction whose single electron transfer mechanism has been extensively studied. The following chapter encompasses a study of the mechanism of the photolysis reaction to look for evidence of a single electron transfer similar to the Gibbs’ reaction.</div><div><br></div><div>As mentioned earlier, phenyl nitrenes have a proclivity to undergo rearrangement reactions instead of exhibiting bimolecular reactivity that can lead to useful products. One of the strategies to overcome this challenge is to spatially separate the two electrons of an open-shell singlet nitrene so as to minimize electron-electron repulsion. This separation can be achieved by delocalizing the individual electrons over multiple aromatic rings and heteroatoms which can act as radical stabilizers. In this chapter, a short review of literature that sets precedence for developing a unique heteroatom containing aromatic backbone to achieve the necessary stabilization is presented. Our efforts in synthesizing the model azide precursor compound have also been discussed.</div>

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