Electronic and hydrophobic

N-Alkylhydroxamic acid hydrolysis Methyl Violet + OH" Cl C12H25S03Na + H30+, CTABr + OH". An attempt made to separate electronic and hydrophobic effects on the micellar reaction Anionic and cationic micelles. Effect of surfactant structure examined Berndt el at., 1984 Malaviya and Katiyar, 1984... 

In the Balaban MTD approach the additional influence of electronic and hydrophobic effects is accounting for by adding e.g. and a... 

Equations 18-20 give about the same results and the standard obtained in the procedure that led to Equation 20 is shown in Figure 7. Since these equations contain only steric parameters, the picture obtained from the MTD method can directly be used to compare the biological activity of the compounds. MTD and MTD are in principle the same in this example because no electronic and hydrophobic parameters are involved. However, extrapolation outside the hypermolecule is not permissible. 

Description Calculation of steric, electronic, and hydrophobic descriptors. 

Mracec, M., Kurunczi, L., Nusser, T, Simon, Z. and Naray-Szabo, G. (1996). QSAR Study with Steric (MTD), Electronic and Hydrophobicity Parameters on Psychotomimetic Phenylalkyl-amines. J.Mol.Struct.(Theochem), 367,139-149. 

From the Hammett equation [Hammett, 1935, 1937], the seminal vork of Hammett gave rise to the a—p culture in the delineation of substituent effects on organic reactions, whose aim was to search for linear free energy relationships (LFER) [Hammett, 1938] steric, electronic, and hydrophobic constants were derived for several substituents and used in an additive model to estimate the biological activity of congeneric series of compounds. 

In general models that describe/calculate key properties of chemical compounds are composed of three types of inherent characteristics of the molecule, i.e. structural, electronic and hydrophobic characteristics. Depending on the actual model few or many of these descriptors may be taken into account. Thus, eqn. 1 can be rewritten as... 

In actual practice, however, there are two distinct Topliss Schemes, namely (a) For aromatic substituents and (Z>) For aliphatic side-chain substituents. It is pertinent to mention here that the said two schemes were so meticulously designed by taking into consideration both electronic and hydrophobicity features (i.e., substituents) with acommon objective to arrive at the optimum biological active substituents . 

In eqn (8.4), k is the rate constant for the hydrolysis of an R substituted ester, and is corresponding constant for the methyl substituted parent, thus all comparisons are made between the substituent and a methyl group. These substituent constant values are used in the same way as the electronic and hydrophobic substituent constants discussed earlier, that is to say they are found in tabulations of substituent constant values, and of course the same problems of missing values apply. In fact, the situation can be even worse for Es as a number of substituents are themselves unstable under the conditions of acid hydrolysis. It has also been argued that this descriptor is not just a measure of steric effects, but that it also includes some electronic information. A number of more or less ingenious fixes were proposed to solve such problems, but a much more popular and generally useful measure of steric effects for both substituents and whole molecules was adopted in the form of molar refraction (MR), as defined by the Lorentz-Lorenz equation [eqn (8.5)]. 

Oxidation of different substituted benzaldehydes catalyzed by xanthine oxidase in different reverse micellar media was reported by Bommarius and collaborators [149]. The main aim of this study was to compare and quantify the enzymatic activity in water and microemulsions formulated with surfactants of different polarities. Kinetic constants were calculated in each of the reverse micellar media for substituted benzaldehydes with varying electronic and hydrophobic properties and were found similar to those calculated in aqueous solution. 

Enzyme Studies - Log P, along with the Hammett a constant, has found use in the correlation of enzymic reactions. The study of Blomquist on the electronic effects of substituents in alcohol dehydrogenase reactions illustrates the point. Blomquist noted that both electronic and hydrophobic effects appear to be involved in the enzymic reduction of benzaldehydes. 

Electronic and hydrophobic-intermolecular force parameters may be accounted within the a-term of eq.C2), or by considering intermole-cular force parameters present or absent at certain vertices j of H. 

NTD s are calculated for the R2 side chains. Some of the molecules of Table 29 extend beyond the hypermolecule of Figure 10, especially the D-aminoacid derivatives, in which R2 sticks out from vertex j = 14 towards j = 9,8, etc. All new vertices are assigned Sy +1, i.e., they are considered as part of cavity walls. Electronic and hydrophobic effects are taken into account by introducing a-Hammett and 7r-Hansch constants in a(i.e., a=a + a a + 012 in Eq.2 for A ). 

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