Hydrophobes, isomer effect

The conversion rates of individual components in a commercial LAS mixture are dependent on the molecular structure. For example, the length of the alkyl chain is positively correlated with the primary degradation rate, and as such, isomers with the phenyl substituted at central positions are degraded more slowly than other isomers [79,80]. Both effects are a direct consequence of the enzymatic attack on the hydrophobic moiety. The relation between surfactant structure and the biodegradation has been termed as Swisher s distance principle which, in summary, describes that an increased distance between... 

These flavopapains (Fig. 19) were shown to be effective redox catalysts for the oxidation of hT-alkyl-l,4-dihydronicotinamides. The localization of the flavin moiety adjacent to the hydrophobic binding groove of the active site further allowed the constructs to exhibit substrate selectivity and, in some cases, saturation kinetics. The most effective flavopapain was the 8-isomer (FP-8) which reacted rapidly with a variety of M-alkyl-1,4-dihydronicotinamides. The best substrate was N-hexyl-l,4-dihydronicotinamide for which the of its... 

The high mineralization activity of the PVDF-W10 membrane in comparison to the homogeneous catalyst can be ascribed to the selective absorption of the organic substrate from water on the hydrophobic PVDF polymer membrane that increases the effective phenol concentration around the catalytic sites. Moreover, the polymeric hydrophobic environment protects the decatungstate from the conversion over longer time to a less-reactive isomer that has a maximum absorption at a wavelength of 280 nm. 

Murakami et al. have utilized Mayer vesides to study aldolase-type reactions [48]. Formation of [i-phenylserinc from glydne and benzaldehyde proceeded effectively by cooperative catalysis of a hydrophobic pyridoxal derivative (47) and Zn(n) ions in the bilayer vesicle formed with 32. The threo isomer was dominantly produced over the erythro form. A marked enantioselectivity was observed in the co-veside of 32 and 35 in combination with 47 and Cu(ii) the ee for formation of (2S,3R)-P-phcnylscrinc over its enantiomeric (2R,3S)-isomer was 58%. Enantioselectivity also arose with another bilayer assembly, formed with 32, 35, and 37 in the presence of Cu(ii), where the (2R,3S) isomer was dominant over the (2S,3R) species in 13% ee. The opposite enantioselectivity performed by the second system, as compared with that for 47, might reflect a different stereochemical environment around the quinoid intermediate that allows the attack of benzaldehyde. 

Since the ir value is constitutive, the stereospecific nature of hydro-phobic bonding for drug-receptor interactions can be delineated by regression analyses with the tt values of substituents separately for each position of the congeners. Thus, the substituent effect on the emulsin hydrolysis of substituted phenylglucosides has been nicely delineated by analyzing kinetic constants separately for meta and para isomers. The meta substituents play no hydrophobic role in the enzyme-substrate complex formation 24). 

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