Fragmental volume constants

C and above this temperature tends to be independent. A correlation between the rotational frequency of a nitroxide spin label (Oc) and the rate constant kiso of 4-dimethyl-aminostilbene trans-cis photoisomerization has been found [76]. The label volume is similar to the stilbene fragments volume in the twisted state. The calibration allowed using the correlation for the estimation of the rotational correlation time of the stilbene fragments in the excited state of PSS for the fixed angle 180° (Figure 4.2). 

C atomic fragmental volume, solvation param. IC grid map constant energy... 

Various methods by which the Kow of PAHs could be calculated are based on their molecular structures, i. e., a quantitative structure-property relationship (QSPR) approach [ 1,199,200]. One of the most famous techniques involves summation of hydrophobic fragmental constants (or f-values) for all groups in a molecule of a specific compound. On the other hand, Aboul-Kassim [1] and Aboul-Kassim et al. [202, 203] introduced a modeling technique based on the molecular connectivity indices of various PAHs, ranging from low- to high-molecular weight compounds. More details are given in Chap. 4 of this volume. 

The yield of the hydrolysis reaction depends on the competition between recombination and diffusion. The rate of diffusion (kD) depends sharply on the molar mass of the fragments, since the diffusivity of a given molecular species is a decreasing exponential function of its molar volume (Van Krevelen, 1990). Thus one can imagine a process in which all the groups A-B are equireactive (kH constant), but in which the yield of small molecules (high kD) is higher than predicted from the hypothesis of a random process. 

There are many ways in which hormone-receptor interactions may be studied, the classic method being the Scatchard technique, named in honor of George Scatchard. This technique is applicable to any protein-small molecule interaction, and it provides a means of determining the heterogeneity of binding sites, dissociation constants, and the number of binding sites per receptor unit. The last may be a protein molecule, a cell, a cell membrane fragment, or a unit volume of cytosol with a known protein content. 

There are several methods developed for the calculation of logP from molecular structure, based on -> substituent constants, - fragmental constants, - electronic descriptors, -> steric descriptors, - connectivity indices, surface areas, - volume descriptors, and -> chromatographic descriptors [Leo, 1990 Hansch et al., 1995b Carrupt et al., 1997 Reinhard and Drefahl, 1999]. 

Motoc, I. and Marshall, G.R. (1985). Van der Waals Volume Fragmental Constants. Chem.Phys. Lett., 116,415 19. 

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