Glass-forming solvent

There are substantial difficulties in the interpretation of temperature-dependent shifts of protein spectra because of the thermal lability of proteins and the possibility of temperature-dependent conformational transitions. Low-temperature studies in aqueous solutions revealed that for many of the proteins investigated the observed shifts of the fluorescence spectra within narrow temperature ranges were probably the result of cooperative conformational transitions, and not of relaxational shifts/100 1 Spectral shifts have also been observed for proteins in glass-forming solvents, 01) but here there arise difficulties associated with the possible effects of viscous solvents on the protein dynamics. 

Greenspan, H., and E. Fischer Viscosity of Glass-forming Solvent Mixtures at Low Temperatures. J. phys. Chem. 69, 2466 (1965). 

Table 1 Table of some useful low temperature glass-forming solvents and solvent mixrnres. Mixtures are specified by voliune ratios... 

The planarity of PF2/6 can be controlled by the local environment via its bulky side groups. In Fig. 3 the absorption and emission spectra of dilute PF2/6 in MCH is shown at room temperature and at 77 K (MCH being an excellent glass forming solvent). It is clearly seen that in the low temperature glass, steric distribution and reorganization is hindered and so the absorption band becomes structured and the emission band features sharpen [4],... 

E.s.r. data for 7-irradiated carbaboranes in organic glass-forming solvents at 77 K suggest the formation of cage-centred o-carbaborane anions." ... 

The solutions are always clear.They are then poured together in varying ratios. A few ml of the initially clear solutions are concentrated by evaporating the solvent in small glass dishes with flat bottoms in a drying oven until a film of the polymer blend forms (solvent not to be removed by distillation ). 

Ultraviolet sources are chiefly mercury-discharge lamps in various forms. These lamps are fragile and quite inefficient. The design of reactors using these lamps is hampered by these considerations, and by the limited ultraviolet transmission, of common glasses and solvents. The transmission is further decreased by coatings of opaque materials which form... 

Glasses. The solvents used to form the glass with polymers should be clear in the UV region to allow maximum absorption of radiation by the polymer. The ESR of irradiated solvents should not interfere with that of the polymer. Three solvents were found to be close to ideal tetrahydrofuran (THF) p-dioxane (DX) and tetrahydropyran (TP). All three were purified by repeated distillation and column chromatography. Poly(vinyl chloride) and the copolymer solutions (5-15%, w/v) were prepared from these solvents, degassed, sealed under vacuum (10-6 torr), and irradiated. 

Differences in low temperature emission spectra of benzil in methylcyclohexane and in isopentane have been ascribed to inhibition of the conformational changes involved in the skewed to planar relaxation in isopentane 33). Emission spectra were identical in both solvents at temperatures above the glass-forming temperature. Preference for an s-cis conformation in ethylene glycol solution has been suggested 33b) to account for anomalous emission spectra of benzil in that medium. Other aspects of benzil emission have been examined 33c). 

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