Optical rotation reversible change

Mutarotation (Section 25.5) The change in optical rotation observed when a pure anomer of a sugar is dissolved in water. Mutarotation is caused by the reversible opening and closing of the acetal linkage, which yields an equilibrium mixture of anomcrs. 

With heating from 5 to 45°C, thermal changes in conformation in the major /3-casein are observed by spectral methods (Garnier 1966). From measurements of the optical density at 286 nm and of the specific optical rotation at 436 nm, a rapidly reversible endothermic transition (AH 30 kcal/mole) with a half-transition temperature of 23-24°C is observed. The optical rotatory dispersion data suggest a decrease in the poly-L-proline II structure (12 to 5%) and a slight increase in a-helix (11 to 16%) with increasing temperature. This transition probably occurs prior to association, since it is rapid, and the carboxyacyl derivative of the monomer, which does not polymerize with increasing temperature, also demonstrates the optical rotatory disperson thermal transition. 

When the most common spiropyran SP-4 was mixed in poly(y-benzylglutamate) to prepare a film, a reversible change in optical rotation was observed upon 365 nm light irradiation and visible light irradiation [49], The largest Aa before and after UV irradiation at sodium D-line (589 nm) was 1.225° for 4 mol% concentration. It was supposed that the change might have arisen from the chiral interaction between the chiral polypeptide environment and the colored merocyanine. Indeed, an induced CD was observed. 

For some carbonyl compounds, a reverse in optical rotation sign has been observed when the ORD spectra were measured in solvents of different polarity. For example, (5)-5-hydroxy-l,7-diphenyl-3-heptanone is dextrorotatory in trichloromethane (molar optical rotation [interaction between the y9-ketol moiety and the solvent is responsible for the change and reversal in optical rotation with increasing solvent polarity. 

The reversion of gelatins to collagen has also been discussed with refer ence to cross-links. The denaturation of collagen results in marked changes of viscosity, optical rotation, molecular weight, volume, kinetics of proteolysis, and other properties. Under certain conditions a partial reversal of these changes can be achieved (Flory and Garrett, 1958 von Hippel... 

The dynamics for the ring opening of the diarylethene derivative (29) has been shown to be a one-step process with a reaction rate of 1.7 x 10 s Reversible changes in the optical rotation have been observed on irradiation of... 

A change of one of the gronps on an asymmetric atom should at least invoke a change in magnitude of optical rotation, even if not sufficient to cause a reversal ... 

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