Steric conformations

This is actually observed, except when either potentially aromatic molecules such as thiepin dioxide (358) or when (relatively) sterically/conformationally rigid systems are involved. 

These data demonstrate that both GSH and GSSG have profound effects on Na/K ATPase activity and may act in concert to modify enzyme activity during oxidant stress. However, it should be recognized that the steric conformation of an isolated enzyme preparation in a chemically buffered solution may be considerably different to the native enzyme located in a dynamic lipid bilayer. For this reason, these investigations have been extended to include a variety of preparations in which the Na/K pump is in its native environment. 

Partial Least Squares (PLS) regression (Section 35.7) is one of the more recent advances in QSAR which has led to the now widely accepted method of Comparative Molecular Field Analysis (CoMFA). This method makes use of local physicochemical properties such as charge, potential and steric fields that can be determined on a three-dimensional grid that is laid over the chemical stmctures. The determination of steric conformation, by means of X-ray crystallography or NMR spectroscopy, and the quantum mechanical calculation of charge and potential fields are now performed routinely on medium-sized molecules [10]. Modem optimization and prediction techniques such as neural networks (Chapter 44) also have found their way into QSAR. 

Shape (geometric, steric, conformational, topological) properties... 

No generally applicable Q s can be given for methylene protons, for example of the propionates (Fig. 2), since the electron-proton coupling depends strongly on the sterical conformation of the molecule (16). 

The bond dissociation energy of cleavable bonds of telogens appears to be a key parameter to take into account regarding reactivity. This is followed by various factors controlling the reactivity (such as energetic, electronic, polar, steric, conformational effects and role of orbital interactions) of a radical and its orientation of addition. 

The ESR method combined with a flow system should be very powerful for studying short lived transient radicals during vinyl polymerization in solutions. As will be made clear later, however, the conditions for the reaction occurring in the flow cell are quite different from the conventional solution polymerization studied during a steady-state process. Nevertheless, the hyperfine structure of the ESR spectra observed by the flow technique, can provide straightforward information on the structure, concentration, reactivity, and even the steric conformation of the transient radicals involved, particularly at the initial stage of the polymerization. 

Modifying the Active Conformation of Biomolecules. Class B metals such as Hg have been shown to alter the steric conformation of proteins via interactions with sulfur atoms, particularly disulphide bonds. For example, Hg insertion between the two sulfurs involved in a disulfide bond can significantly alter the shape of the protein and reduce or abolish its activity. This has been demonstrated with ribonuclease, for example. 

An example for a very unusual and interesting steric conformation is given in figure 4. ... 

Fig. (5). Sterical conformation of the active site of pea amine oxidase [29].

Fig. 7.1 Steric conformation of end alkyl radicals (plane ABCD is perpendicular to direction of (Ca )—Cp bond) Broken hnes and primes indicate the projection of the corresponding items on the plane ABCD...

The cooperativity factor a is a dimensionless constant greater than 1 in the case of positive cooperativity, equal to 1 in the case of noncooperativity and smaller than 1 in the case of negative cooperativity. It can be viewed as the equihbrium constant for the conversion of the hypothetical complex with noninteracting sites (noncooperative) into the complex with interacting sites (cooperative), as illustrated in Fig. 13 for the simplest case with = 2. The cooperative interaction may be of any sort (electrostatic, steric, conformational, and so on). 

Mohamed, R. K., Peterson, P. W., Alabugin, I. V. (2013). Concerted Reactions That Produce Diradicals and Zwitterions Electronic, Steric, Conformational, and Kinetic Control of Cycloaromatization Processes. Chemical Reviews, http //pubs.acs.org/doi/pdf/10.1021/cr4000682... 

The results of experiments with electrons [64] were, as expected, different to those using y-rays because electrons are known to cause a temperature increase in PET, and to disrupt crystallinity by affecting the steric conformation of the chain. Cel formation was not observed at up to 175 °C for doses up to 2000 Mrad rapid crosslinking occurred even at low doses at >200 °C. 

Exposure-related parameters influence of steric conformations... 

Concerted reactions that produce diradicals and zwitterions Electronic, steric, conformational, and kinetic control of cycloaromatization processes 13CRV7089. 

A number of non-condensed dimers are formed and only some of these have the right steric conformation to undergo an addition dehydrogenation reaction to give fully condensed molecules with only six-membered rings involving the most reactive position 9 for this to... 

Although 8-azaguauiosine and 8-azaadenosine possess the normal C-N glycosyl bond, they are free of the steric conformational restraints produced by the C8H-sugar interactions. Due to extreme difficulties in... 

An antigen can provoke formation of antibodies against manj different determinants, each determinant being defined as that part of the molecule which reacts immunospecifically with the combining site of the antibody. These may consist of sequentiar determinants, which are due to stretches of amino acid sequences in a protein and conformationar determinants which result from the steric conformation of the macromolecule (Sela et al., 1967). 

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