Anthracene methyl affinity

Hemoglobin is another heme-containing protein, which has been shown to be active towards PAH, oxidation in presence of peroxide [420], This protein was also modified via PEG and methyl esterification to obtain a more hydrophobic protein with altered activity and substrate specificity. The modified protein had four times the catalytic efficiency than that of the unmodified protein for pyrene oxidation. Several PAHs were also oxidized including acenaphthene, anthracene, azulene, benzo(a)pyrene, fluoranthene, fluorene, and phenanthrene however, no reaction was observed with chrysene and biphenyl. Modification of hemoglobin with p-nitrophenol and p-aminophenol has also been reported [425], The modification was reported to enhance the substrate affinity up to 30 times. Additionally, the solvent concentration at which the enzyme showed maximum activity was also higher. Both the effects were attributed to the increase in hydrophobicity of the active site. 

The piTj5-values of the methyl derivatives of benz[a]anthracene, summarized in Table 23, are particularly interesting. In the case of the unsubstituted compound, two positions of approximately equal proton affinity have to be taken into account. Thus two isomeric proton addition complexes A and B are present in solution (cf. IID, page 229). 

The first reaction was found by Levy and Szwarc to be predominant when methyl radicals attacked isooctane. The second reaction is predominant, however, for aromatic hydrocarbons. The free radicals formed in the above two reactions will react with each other, with other free radicals, or with impurities. The affinity of the methyl radical to attack an aromatic increases in the following order benzene, diphenyl ether, pyridine, diphenyl, benzophenone, naphthalene, quinoline, phenanthrene, pyrene, and anthracene. The ability of free alkyl radicals to interact with isopropylbenzene and cyclohexene decreases in the following order methyl, ethyl, propyl, butyl, isopropyl, sec-butyl, and tertiary butyl. 

The sensing of potential pollutants has led to the development of 23, which can distinguish elegantly between Cd(ll) and Zn(n) but due to similar affinity of many receptors, it has been difficult to achive such selectivity to date." On the basis of the use of iminodiacetate receptors connected to an anthracene fluorophore by covalent methyl spacers, the sensor was found to be highly water soluble where the fluorescence was switched off between pH 3 and 11, owing to PET quenching of the anthracene excited state by the receptor. On Zn(ll) titration, a broad, red-shifted emission occurred, centered at 468 nm however, in the presence of Cd(II), a red-shifted emission was observed, centered at... 

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