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Using Fourier Transform Infrared (FTIR) spectroscopy, we investigate the temperature dependence of the bending vibrations of water confined in the pores of a silica hydrogel in the temperature interval of 270–180 K. We also investigate the presence of thermal hysteresis by cooling and reheating temperature scans. The results clearly show the presence, at about 230 K, of a crossover in the temperature dependence of the IR spectra; moreover, the presence of hysteresis is clearly demonstrated. By comparing FTIR data with neutron diffraction data and previous calorimetric data on the same samples, we conclude that the crossover and the hysteretical behavior do not involve a water glass transition or crystallization but are related to a first-order-like liquid-liquid transition. [ABSTRACT FROM AUTHOR]

Functionally relevant electric-field induced perturbations of the prosthetic group of yeast ferrocytochrome c mutants Saccharomyces cerevisiae obtained from a vibronic analysis of low-temperature absorption spectra were studied. It was found that all investigated mutations substantially increase the electronic perturbation so that the spectral properties become similar to those of horse heart cytochrome c and this electronic perturbation was also found to correlate nonlinearly with the enthalpy changes associated with the reduction of the heme iron.

Research has been conducted on the heme pocket of a recombinant sperm whale myoglobin. The structure and dynamics of the heme pocket have been examined via different spectroscopic approaches and the results indicate that the affinity of the globin for the heme is decreased by the low pH exposure.

A study was conducted to analyze the temperature dependence of the Soret band of different metal-octaethylporphyrins dissolved in the glass-forming mixture isopentane/ethyl ether. Resonance Raman and low-temperature optical absorption spectroscopies were utilized in the study. Experimental results indicated that the metal-octaethylporphyrins supported several types of motions. These include high and low-frequency harmonic vibrations and anharmonic motions.

The binding of azide to the active site of oxidized and reduced form of bovine copper, zinc superoxide dismutase and to the copper-free derivative was investigated using Fourier transform infrared spectroscopy. In addition, the perturbation of the antisymmetric stretching vibration of the azide anion in a copper model complex, in the presence of free amino acids and in three different derivatives of copper, zinc superoxide was examined. Results show that azide does not directly interact with copper in the reduced form of copper, zinc superoxide dismutase.

The zinc site of the Cu,Zn bovine superoxide dismutase is more rigid than the copper site. The dynamics of the cobalt site is harmonic, indicating that the enzyme exhibits different dynamic properties at different sites. An analysis of the electronic spectra of the enzyme in which the zinc site is substituted by Cu(I) and Co(II) indicate that His61 imidazole bridge is released when the copper ion is reduced. The low energy visible bands of the cobalt chromophore is split into two components at low temperatures.

Low-temperature optical absorption spectroscopic studies of the structural dynamics of native and azide-reacted Cu,Zn superoxide dismutase (SOD) reveals that a lowering of temperature is associated with changes in the metal ligand positions in the native and anion-bound enzymes. Such structural repositioning involves all the Cu ligands except His61 in the native enzyme, while it involves only the copper-bound anion in the azide derivative. His61-Cu(II) ligand to metal charge transfer transition in the native enzyme is shown by the band at 23,720 per cm.

The Boson peak of deeply cooled water confined in the pores of a silica xerogel is studied by inelastic neutron scattering at different hydration levels to separate the contributions from matrix, water on the pore surfaces and "internal" water. Our results reveal that at high hydration level, where the contribution from internal water is dominant, the temperature dependence of the Boson peak intensity shows an inflection point at about 225 K. The complementary use of differential scanning calorimetry to describe the thermodynamics of the system allows identifying the inflection point as the signature of a water liquid-liquid crossover. [ABSTRACT FROM AUTHOR]

We have measured and analyzed the low-temperature (T=10 K) absorption spectrum of reduced horse heart and yeast cytochrome c. Both spectra show split and asymmetric Q0 and Qv bands. The spectra were first decomposed into the individual split vibronic sidebands assignable to B1g (ν15) and A2g (ν19, ν21, and ν22) Herzberg-Teller active modes due to their strong intensity in resonance Raman spectra acquired with Q0 and Qv excitations. The measured band splittings and asymmetries cannot be rationalized solely in terms of electronic perturbations of the heme macrocycle. On the contrary, they clearly point to the importance of considering not only electronic perturbations but vibronic perturbations as well. The former are most likely due to the heterogeneity of the electric field produced by charged side chains in the protein environment, whereas the latter reflect a perturbation potential due to multiple heme-protein interactions, which deform the heme structure in the ground and excited states. Additional information about vibronic perturbations and the associated ground-state deformations are inferred from the depolarization ratios of resonance Raman bands. The results of our analysis indicate that the heme group in yeast cytochrome c is more nonplanar and more distorted along a B2g coordinate than in horse heart cytochrome c. This conclusion is supported by normal structural decomposition calculations performed on the heme extracted from molecular-dynamic simulations of the two investigated proteins. Interestingly, the latter are somewhat different from the respective deformations obtained from the x-ray structures. [ABSTRACT FROM AUTHOR]

The dynamic behavior of different amino acid residues is measured separately and has assessed the contribution of each type of side chain to the anharmonic dynamic of proteins. The studies have shown that the dynamical transition occurring at 230 K is attributed to motions involving backbone fluctuations.