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Using NMR, we measure the proton chemical shift [delta], of super-cooled nanoconfined water in the temperature range 195 K < T < 350 K. Because [delta] is directly connected to the magnetic shielding tensor, we discuss the data in terms of the local hydrogen bond geometry and order. We argue that the derivative -[([partial derivative] ln [delta]/[partial derivative]T).sub.P] should behave roughly as the constant pressure specific heat [C.sub.P](T), and we confirm this argument by detailed comparisons with literature values of [C.sub.P](T) in the range 290-370 K. We find that -[([partial derivative] ln [delta]/[partial derivative]T).sub.P] displays a pronounced maximum upon crossing the locus of maximum correlation length at [approximately equal to] 240 K, consistent with the liquid-liquid critical point hypothesis for water, which predicts that [C.sub.P](T) displays a maximum on crossing the Widom line. configurational specific heat | nuclear magnetic resonance | proteins | proton chemical shift

We use (1)H NMR to probe the energy landscape in the protein folding and unfolding process. Using the scheme ⇄ reversible unfolded (intermediate) → irreversible unfolded (denatured) state, we study the thermal denaturation of hydrated lysozyme that occurs when the temperature is increased. Using thermal cycles in the range 295 < T < 365 K and following different trajectories along the protein energy surface, we observe that the hydrophilic (the amide NH) and hydrophobic (methyl CH3 and methine CH) peptide groups evolve and exhibit different behaviors. We also discuss the role of water and hydrogen bonding in the protein configurational stability.

The anomalous behavior of thermodynamic response functions is an unsolved problem in the physics of water. The mechanism that gives rise to the dramatic indefinite increase at low temperature in the heat capacity, the compressibility, and the coefficient of thermal expansion, is unknown. We explore this problem by analyzing both new and existing experimental data on the power spectrum S(Q, ω) of bulk and confined water at ambient pressure. When decreasing the temperature, we find that the liquid undergoes a structural transformation coinciding with the onset of an extended hydrogen bond network. This network onset seems to give rise to the marked viscoelastic behavior, consistent with the interesting possibility that the sound velocity and response functions of water depend upon both the frequency and wave vector.

It is becoming common practice to partition glass-forming liquids into two classes based on the dependence of the shear viscosity η on temperature T. In an Arrhenius plot, ln η vs 1/T, a strong liquid shows linear behavior whereas a fragile liquid exhibits an upward curvature [super-Arrhenius (SA) behavior], a situation customarily described by using the Vogel-Fulcher-Tammann law. Here we analyze existing data of the transport coefficients of 84 glass-forming liquids. We show the data are consistent, on decreasing temperature, with the onset of a well-defined dynamical crossover η(×), where η(×) has the same value, η(×) ≈ 10(3) Poise, for all 84 liquids. The crossover temperature, T(×), located well above the calorimetric glass transition temperature T(g), marks significant variations in the system thermodynamics, evidenced by the change of the SA-like T dependence above T(×) to Arrhenius behavior below T(×). We also show that below T(×) the familiar Stokes-Einstein relation D/T ∼ η(-1) breaks down and is replaced by a fractional form D/T ∼ η(-ζ), with ζ ≈ 0.85.

The temperature dependence of the density of water, rho(T), is obtained by means of optical scattering data, Raman and Fourier transform infrared, in a very wide temperature range, 30 < T < 373 K. This interval covers three regions: the thermodynamically stable liquid phase, the metastable supercooled phase, and the low-density amorphous solid phase, at very low T. From analyses of the profile of the OH stretching spectra, we determine the fractional weight of the two main spectral components characterized by two different local hydrogen bond structures. They are, as predicted by the liquid-liquid phase transition hypothesis of liquid water, the low- and the high-density liquid phases. We evaluate contributions to the density of these two phases and thus are able to calculate the absolute density of water as a function of T. We observe in rho(T) a complex thermal behavior characterized not only by the well known maximum in the stable liquid phase at T = 277 K, but also by a well defined minimum in the deeply supercooled region at 203 +/- 5 K, in agreement with suggestions from molecular dynamics simulations.

By confining water in a nanoporous structure so narrow that the liquid could not freeze, it is possible to study properties of this previously undescribed system well below its homogeneous nucleation temperature TH = 231 K. Using this trick, we were able to study, by means of a Fourier transform infrared spectroscopy, vibrational spectra (HOH bending and OH-stretching modes) of deeply supercooled water in the temperature range 183 < T < 273 K. We observed, upon decreasing temperature, the building up of a new population of hydrogen-bonded oscillators centered around 3,120 cm(-1), the contribution of which progressively dominates the spectra as one enters into the deeply supercooled regime. We determined that the fractional weight of this spectral component reaches 50% just at the temperature, TL approximately 225 K, where the confined water shows a fragile-to-strong dynamic cross-over phenomenon [Ito, K., Moynihan, C. T., Angell, C. A. (1999) Nature 398:492-494]. Furthermore, the fact that the corresponding OH stretching spectral peak position of the low-density-amorphous solid water occurs exactly at 3,120 cm(-1) [Sivakumar, T. C., Rice, S. A., Sceats, M. G. (1978) J. Chem. Phys. 69:3468-3476.] strongly suggests that these oscillators originate from existence of the low-density-liquid phase derived from the occurrence of the first-order liquid-liquid (LL) phase transition and the associated LL critical point in supercooled water proposed earlier by a computer molecular dynamics simulation [Poole, P. H., Sciortino, F., Essmann, U., Stanley, H. E. (1992) Nature 360:324-328].

By confining water in nanopores, so narrow that the liquid cannot freeze, it is possible to explore its properties well below its homogeneous nucleation temperature T(H) approximately equals 235 K. In particular, the dynamical parameters of water can be measured down to 180 K, approaching the suggested glass transition temperature T(g) approximately equals 165 K. Here we present experimental evidence, obtained from Nuclear Magnetic Resonance and Quasi-Elastic Neutron Scattering spectroscopies, of a well defined decoupling of transport properties (the self-diffusion coefficient and the average translational relaxation time), which implies the breakdown of the Stokes-Einstein relation. We further show that such a non-monotonic decoupling reflects the characteristics of the recently observed dynamic crossover, at approximately 225 K, between the two dynamical behaviors known as fragile and strong, which is a consequence of a change in the hydrogen bond structure of liquid water.

With an assay that quantitates the transfer of 6-thioguanylic acid from hypoxanthine phosphoribosyltransferase (IMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.8)-positive donor cells to negative recipient cells through gap junctions, differences in contact-mediated communication between normal and transformed human cells in culture have been detected. We have compared cells cultured from human tumors and simian virus 40-transformed cells with the normal human fibroblasts from which they were derived as well as with gap junction-deficient L cells. The communication, which is extensive in normal cells, is significantly reduced when transformed cells are used as either donors or recipients in the contact-feeding assay. Furthermore, the reduction in the transfer of nucleotides is enhanced when transformed cells are used as both donors and recipients, indicating a dosage effect or synergism, independent of enzyme activity. Fetal cells have a contact-feeding phenotype intermediate between that of normal and that of transformed cells. We suggest that the decrease in communication of nucleotides in transformed cells reflects quantitative or qualitative changes in membrane components responsible for gap junction formation.

Lesch-Nyhan fibroblasts and normal human leukocytes with different glucose-6-phosphate dehydrogenase genotypes were fused by Sendai virus. Clones were isolated on the basis of their resistance to a medium containing hypoxanthine, amethopterin, and thymidine and ability to proliferate in monolayer culture. These mononuclear cells (1) incorporated [(3)H]hypoxanthine, (2) expressed the glucose-6-phosphate dehydrogenase heteropolymer, and (3) were polyploid. Therefore, hybrids can originate from the fusion of two diploid human cells. X chromosome inactivation did not occur in these hybrid cells of male origin. The hybrids expressed both parental genomes and exhibited the senescence and contact feeding characteristic of the human skin fibroblast.