Perturbing group

There follows in Sect. Ill a detailed discussion of substituent effects and their dependence on different geometric relationships of carbon atoms with respect to the perturbing group. This, however, is strictly confined to sp3 carbon atoms, though allowing for all conceivable kinds of substituents, including unsaturated ones (phenyl, cyano, etc.). 

Methyl alkyl sulfoxides that do not contain other strongly perturbing groups have negative Cotton effects centered at the strong absorption band near 200 nm and have the (i > configuration. 

For the discussion of the relationship between the sign of the (n, tc ) Cotton effect and molecular structure of spiran-type cyclopropyl ketones, such as 3a,5-cyclo-5a-cholestan-6 one (142), one must consider that the perturbing group comes into the near lower left (nil) octant. Then, the reversed octant rule predicts a negative sign for the (n, tc ) CE which is... 

The examination of additive contributions (1, 3, 5, 6, ) such as configurational, conformational, and vicinal effects of optically active ligands has been useful in the correlation of stereochemical effects and CD spectra. The ligand-polarization model (20, 21, 22, 24) of optical activity depends upon the polarizability of the perturbing groups which constitute the dissymmetric environment around the symmetric chromophore. Phenyl subsitutents which have large anisotropic polarizability can make contributions with signs reversed from those expected (20). 

Interaction of small molecules and ions with lipid bilayers is of importance from the point of view of membrane transport and other processes such as aaion of drugs and anesthetics on membranes. This includes a number of antibiotics and fatty acids also. The effect of these perturbations on the lipid bilayer in terms of differences in the structure and dynamics of the lipids close to the perturbative group versus the bulk lipids is also interesting and may... 

It is amazing that quinones have sustained interest of radiation chemists for over three decades. The basic radiation chemistry of simple quinones and their simple derivatives is now well-understood. Therefore, efforts have to be diverted to complex derivatives of quinones, as the characteristics of the parent as well as the semiquinones will depend heavily on the perturbing groups/rings present. The accumulated data will give a clear insight into the perturbation effect of the overall substitution. 

The As atom has been found to induce a HAE on a Trp residue of Eco RI methyltransferase (Table II). The perturbing group is (CH3)2 As (III) that is produced, for example, by reduction of cacodylic acid with mercaptides. Like CH3Hg+, it binds to accessible Cys residues. The use of mutant enzymes has shown that the perturbed residue is Trp-225, and that the perturbing As binds with high affinity to Cys-223, thus revealing the proximity of the side chains of these residues in the methylase structure. In addition to the HAE, which is T -specific, reducing its lifetime to around 25 msec, a phosphorescence red shift of 9.8 nm also is induced. This may reflect an increase in local polarizability from introduction of the As atom. 

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