Measurements by adiabatic calorimetry of heat capacities and enthalpy relaxation rates of a 20% (w/w) aqueous solution of bovine serum albumin (BSA) by Kawai, Suzuki, and Oguni [Biophys. J. 2006, 90, 3732] have found several enthalpy relaxations at long times indicating different processes undergoing glass transitions. In a quenched sample, one enthalpy relaxation at around 110 K and another over a wide temperature range (120-190 K) were observed. In a sample annealed at 200-240 K after quenching, three separated enthalpy relaxations at 110, 135, and above 180 K were observed. Dynamics of processes probed by adiabatic calorimetric data are limited to long times on the order of 10(3) s. A fuller understanding of the processes can be gained by probing the dynamics over a wider time/frequency range. Toward this goal, we performed broadband dielectric measurements of BSA-water mixtures at various BSA concentrations over a wide frequency range of thirteen decades from 2 mHz to 1.8 GHz at temperatures from 80 to 270 K. Three relevant relaxation processes were detected. For relaxation times equal to 100 s, the three processes are centered approximately at 110, 135, and 200 K, in good agreement with those observed by adiabatic calorimetry. We have made the following interpretation of the molecular origins of the three processes. The fastest relaxation process having relaxation time of 100 or 1000 s at ca. 110 K is due to the secondary relaxation of uncrystallized water (UCW) in the hydration shell. The intermediate relaxation process with 100 s relaxation time at ca. 135 K is due to ice. The slowest relaxation process having relaxation time of 100 s at ca. 200 K is interpreted to originate from local chain conformation fluctuations of protein slaved by water. Experimental evidence supporting these interpretations include the change of temperature dependence of the relaxation time of the UCW at approximately T(gBSA) approximately = 200 K, the glass transition temperature of protein in the hydration shell, similar to that found for the secondary relaxation of water in a mixture of myoglobin in glycerol and water [Swenson et al. J. Phys.: Condens. Matter 2007, 19, 205109; Ngai et al. J. Phys. Chem. B 2008, 112, 3826]. The data all indicate in hydrated BSA or other proteins that the secondary relaxation of water and the conformation fluctuations of the protein in the hydration shell are inseparable or symbiotic processes.

The relaxation processes of water mixtures of glycerol, ethylene glycol, ethylene glycol oligomers with two to six repeat units, poly(ethylene glycol) 400 and 600, fructose, and propanol have been studied by broadband dielectric spectroscopy at different water contents in the frequency range 10 μHz-20 GHz and in the temperature range 300-80 K without water crystallization. The results show that, in the vicinity of the glass transition temperature of the mixtures, two kinds of water exist. Part of the water behaves as excess water retaining its inherent mobility and appearing as a separate relaxation process (named here the ν-process) at frequencies higher than the structural α-process at subzero temperatures. Another part of the water moves cooperatively with solute molecules and contributes to the α-process.

The dielectric behavior of living tissues and a number of biological materials was examined by new equipment of the time domain reflectometry method in a wide frequency range of 107-1010 Hz. We found two peaks of Debye absorption around 100 MHz and 20 GHz fpr all the materials. The low-frequency absorption is probably due to bound water while the high-frequency absorption to free water. From the observed relaxation times of bound water a hypothesis is ventured on the structure of bound water and its relaxation mechanism.

Dielectric measurements on water mixtures of polymers such as poly(vinylpyrrolidone) (PVP), poly(ethylene glycol) (PEG), poly(vinyl methyl ether) (PVME), poly(vinyl alcohol) (PVA), poly(acrylic acid) (PAA), poly(ethylenimine) (PEI), and poly(allylamine) (PAlA) were performed over a frequency range from 300 MHz to 15 GHz at 25 °C. Dielectric dispersion and absorption curves related to the orientational motion of water can be described well by the Cole−Cole equation. The distribution of the relaxation time is interpreted by the variation of the water structure. The logarithmic plot of the relaxation time against the parameter for the distribution of the relaxation time suggests two groups of polymers. One group contains nonelectrolyte polymers and another contains electrolyte polymers and PVA. This result implies that water structures in the mixtures of the former group are more uniform and stable than that in the mixtures of the latter group.