Ultraviolet spectroscopy solvent shifts

Ultraviolet (UV) spectroscopy does not tend to be the method of choice for structure determination, but a list of UV absorptions was given in the review by Knowles <1996CHEC-II(7)489>. Fluorescence properties and triplet yields of [l,2,3]triazolo[4,5-r/ pyridazines in various solvents have been reported <2002JPH83>. These heterocyclic systems were found to be photochemically very stable. In a recent paper, Wierzchowski et al. studied the fluorescence emission properties of 8-azaxanthine ([l,2,3]triazolo[4,5-r/ pyrimidine-5,7-dione) and its A -alkyl derivatives at various pH s <2006JPH276>. For the 8-azaxanthines, an important characteristic of emission spectra in aqueous solutions was the unusually large Stokes shift. Since 8-azaxanthine is a substrate for purine nucleoside phosphorylase II from Escherichia coli, the reaction is now monitored fluorimetrically. The fluorescence properties of [l,2,3]triazolo[4,5-r/ -pyrimidine ribonucleosides were earlier described by Seela et al. <2005HCA751>. 

Ultraviolet-visible (UV-Vis) spectroscopy (281, 337) is one of the oldest spectroscopic techniques and hence one of the first to be applied to structure determination. The substitution pattern of many aromatic natural products - flavonoids being an excellent example (241) - are still determined by UV-Vis spectroscopy including acid-based-, and aluminum trichloride-induced shifts of absorbance bands (227, 288, 343, 389). Adduct formation of the purine and pyrimidine bases are also investigated by UV-Vis spectroscopy (352), and solvent-induced shifts are often useful tools of structure determination for many other classes of compounds. There remains, however, a wealth of uncovered information in the UV-Vis spectra of natural products masked by broad, overlapping bands with little or no fine structure. 

The results obtained from viscosity to characterize the unfolded state are presented in Chapter 5. In the present section, the data obtained by optical methods currently used in the study of the transition between native and denatured proteins are briefly discussed. Various reviews describe spectrophotometric methods and their use in the conformational studies of proteins (Wetlaufer, 1962 Hermans, 1965 Herskovits, 1967 Donovan, 1969b, 1973 Yon, 1969 Chen, 1967 Weber and Teale, 1965 Chen et ai, 1969 Lehrer and Fasman, 1967). Ultraviolet difference spectroscopy is the most current method used to study conformational transitions of proteins. When a protein undergoes a conformational transition from the native to the unfolded state, several chromophoric groups are transferred from the interior of the protein to the solvent. The alteration of their environment is accompanied by a small variation of the absorption spectrum, which is shifted in wavelength (A>1) and in intensity (As). The variation of intensity is in first approximation given by the first derivative of the absorption spectrum... 

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