Water spectra temperature dependence

Figure 15. Temperature dependence of absorption spectrum of the viologen bilayer membrane having biphenyl chromophore, CnBphCfV 2Br in water.

The contribution of the poly(Pro)II conformation to the ensemble of unordered peptides has been considered.1158 The temperature dependence of [0]222 for the peptide Ac-YEAAAKEAPAKEAAAKA-NH2 in 8 M guanidinium chloride and of poly(Lys) in water and in ethylene glycol/water (2 1) mixtures 156 was fitted to a two-state equation for a poly(Pro)II-unordered equilibrium with a temperature-independent AH and temperature-independent molar ellipticities for the two components. The peptide with a Pro at the central position is an unordered peptide, the spectrum of which has pronounced poly(Pro)II-like features at low temperatures. This fit yielded [0]222=- -9580 deg-cm2dmol 1 for the poly (Pro)II component and —5560 deg-cm2-dmol 1 for the unordered component. These values provide a method for roughly estimating the poly(Pro)II content, /Pn, of an unordered peptide from [0]222 ... 

However Morita and Nagakura104 concluded from similar studies that in aqueous solution cytosine exists as an equilibrium mixture of two forms, 2 and 6, only. According to these authors the first form predominates in trimethyl phosphate and water at room temperature, but the second prevails at high temperature. The imine form is considered to predominate also in acetonitrile. From the temperature dependence of the absorption spectrum of cytosine in aqueous solution, Morita and Nagakura estimated the tautomeric ratios Kf-e to be equal to 33, 14, and 8 at 30, 50, and 70°, respectively. The energy115 and entropy differences between the imine form 6 and the amine form 2 were evaluated as 5.5 kcal/mole and 12 cal/mole. deg., respectively. 

Figure 2. Temperature dependence of spin-probe EPR spectrum constant 2aN for frozen water and dispersions of silica and carbon nanoparticles of different concentrations (1) -frozen water (2) - silica dispersion, 1 mg/ml (3) - 0.1 mg/ml C60/C70 (4) - 0.1 mg/ml C60/C70 + 0.015 M NaCl (5) - 0.1 mg/ml ShC (6) - 1 mg/ml ShC (7) - 10 mg/ml ShC (unstable dispersion).

Figure 3. Temperature dependence of spin-probe EPR spectrum non-dimensional parameter for water and dispersions of silica, and carbon nanoparticles of different concentrations ...

Steinhoff et al. (1989) measured the temperature and hydration dependence of the ESR spectra of hemoglobin spin-labeled at cysteine )8-93. They observed the critical temperature near 200 K, as described above, and the sensitivity of the spectrum to hydration level. Spectrum simulations suggested that there were two types of motion in the dry protein, a fast vibration of the label within a limited motion cone upon the addition of water, a hydration-dependent motion assigned to the fluctuations of the protein, of correlation time 10 sec in samples of high hydration and at 300 K. The temperature dependence of the motional properties of a spin probe (TEMPONE), diffused into hydrated single crystals, closely paralleled the motional properties of the label. This was taken to be evidence for coupling between the dynamical properties of the protein and the adjacent solvent. 

The temperature dependence of the absorption spectrum of the solvated electron has been recorded not only in water but also in alcohols (Fig. 3). Measurements are performed using nanosecond pulse radiolysis with a specific cell for high temperature and high pressure in a temperature range up to around 600 K depending on the solvent. Indeed, by increasing the temperature, the decay of solvated electrons becomes faster for example, this decay is much faster in alcohols than in water, so, the data obtained with nanosecond set-up are limited at lower temperatures for alcohols compared with water. 

All IR measurements were performed by a transmission method. IR spectra through a Cap2 plate without any samples were first measured from 25 to -120°C to clarify how the IR spectra depend on measurement temperatures. The IR spectrum at 25 C was used as a background spectrum k to obtain absorption spectra Ahs = -log(///o)) for all IR measurements. The spectra for the methane hydrate and water-ice films were taken at every 20°C after keeping for 10 minutes at temperatures from -120 to -20 C. An IR spectrum for the liquid water film was performed at 25 C. 

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