Enzyme selectivity, solvent control

G. Carrea, G. Ottolina, and S. Riva, Role of solvents in the control of enzyme selectivity in organic media, Trends Biotechnol. 1995, 13, 63-70. 

Also of great interest is the so-called FIA scanning as a method for investigating, for instance, the influence of pH on the solvent extraction of metal dithizonates95 by controlled-potential continuous alteration of the pH of the carrier stream. Many other investigations can thus be made, such as the catalytic activity of enzymes and the influence of pH on ion-selective electrodes. 

Zacharis, E., Omar, I.C., Partridge, J. and Robb, D.A. (1997) Selection of salt hydrate pairs for use in water control in enzyme catalysis in organic solvents. Biotechnol. 

Before 1940 optically active compounds could only be obtained in stereo-isomerically pure form by isolation from natural sources, by resolution of racemic mixtures, or by a few laboratory controlled enzymic reactions. Many of the chemical reactions described in this book lead to products which contain chiral centres, axes, or planes, but in which the isolated material is the optically inactive (racemic) form. This is a direct consequence of the fact that the reactants, reagents, or solvents are achiral or are themselves racemic. The following selection of reactions drawn from the text illustrate this statement they may be cross-referenced to the relevant discussion sections, namely (a) Section 5.4.1, p. 519, (b) Section 5.4.3, p.542, (c) Section 5.11.7, p.687, (d) Section 8.1.3, p. 1133, e) Section 5.2.4, p. 504 and (/) Section 5.4.2, p. 531. 

Inhibition of peroxidation of unsaturated lipid chains in biomembranes is of particular significance and interest, because uncontrolled oxidation disrupts the protective layer around cells provided by the membranes. Furthermore, radical chain transfer reactions can also initiate damage of associated proteins, enzymes and DNA. The volume of literature is immense and expanding in the field of antioxidants. We will select certain milestones of advances where micelles and lipid bilayers, as mimics of biomembranes, provided media for quantitative studies on the activities of phenolic antioxidants. One of us, L. R. C. Barclay, was fortunate to be able to spend a sabbatical in Dr. Keith Ingold s laboratory in 1979-1980 when we carried out the first controlled initiation of peroxidation in lipid bilayers of egg lecithin and its inhibition by the natural antioxidant a-Toc . A typical example of the early results is shown in Figure 4. The oxidizability of the bilayer membrane was determined in these studies, but we were not aware that phosphatidyl cholines aggregate into reverse micelles in non-protic solvents like chlorobenzene, so this determination was not correct in solution. This was later corrected by detailed kinetic and P NMR studies, which concluded that the oxidizability of a lipid chain in a bilayer is very similar to that in homogeneous solution . ... 

As discussed above, enzymes have been used to synthesize biodegradable polymers. Russell and co-workers demonstrated that the molecular weight and polydis-persity of polyesters synthesized by lipases in supercritical solvents can be controlled by selecting the fluid s density, which in turn is controlled by pressure and temperature.The fluid density dictates the solubility of polymer hence, upon reaching a critical size, polymers precipitate from solution. 

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