Water Jump Reorientation: From Theoretical Prediction to Experimental Observation.
Summary of "Water Jump Reorientation: From Theoretical Prediction to Experimental Observation."
Liquid water is remarkably labile in reorganizing its hydrogen-bond (HB) network through the breaking and forming of HBs. This rapid restructuring, which occurs on the picosecond time scale, is critical not only for many of the pure liquid's special features but also for a range of aqueous media phenomena, including chemical reactions and protein activity. An essential part of the HB network reorganization is water molecule reorientation, which has long been described as Debye rotational diffusion characterized by very small angular displacements. Recent theoretical work, however, has presented a starkly contrasting picture: a sudden, large-amplitude jump mechanism, in which the reorienting water molecule rapidly exchanges HB partners in what amounts to an activated chemical reaction. In this Account, we first briefly review the jump mechanism and then discuss how it is supported by a series of experiments. These studies range from indirect indications to direct characterization of the jumps through pioneering two-dimensional infrared spectroscopy (2D-IR), the power of which accords it a special focus here. The scenarios in which experimental signatures of the jump mechanism are sought increase in complexity throughout the Account, beginning with pure water. Here 2D-IR in combination with theory can give a glimpse of the jumps, but the tell-tale markers are not pronounced. A more fruitful arena is provided by aqueous ionic solutions. The difference between water-water and water-anion HB strengths provides the experimental handle of differing OH stretch frequencies; in favorable cases, the kinetic exchange of a water between these two sites can be monitored. Sole observation of this exchange, however, is insufficient to establish the jump mechanism. Fortunately, 2D-IR with polarized pulses has demonstrated that HB exchange is accompanied by significant angular displacement, with an estimated jump angle similar to theoretical estimates. The Janus-like character of amphiphilic solutes, with their hydrophobic and hydrophilic faces, presents a special challenge for theory and experiment. Here a consensus on the 2D-IR interpretation has not yet been achieved; this lack of accord impedes the understanding of, for example, biochemical solutes and interfaces. We argue that the influence of hydrophobic groups on water jumps is only modest and well accounted for by an excluded volume effect in the HB exchange process. Conversely, hydrophilic groups have an important influence when their HB strength with water differs significantly from that of the water-water HB. The power of 2D-IR is argued to be accompanied by subtleties that can lead to just the opposite and, in our view, erroneous conclusion. We close with a prediction that a hydrophobic surface offers an arena in which the dynamics of "dangling" water OHs, bereft of a HB, could provide a 2D-IR confirmation of water jumps.
Chemistry Department, Ecole Normale Supérieure , UMR ENS-CNRS-UPMC 8640, 24 rue Lhomond, 75005 Paris, France.
This article was published in the following journal.
Name: Accounts of chemical research
Medical and Biotech [MESH] Definitions
The act of regarding attentively and studying facts and occurrences, gathering data through analyzing, measuring, and drawing conclusions, with the purpose of applying the observed information to theoretical assumptions. Observation as a scientific method in the acquisition of knowledge began in classical antiquity; in modern science and medicine its greatest application is facilitated by modern technology. Observation is one of the components of the research process.
The withholding of water in a structured experimental situation.
Theoretical representations that simulate the behavior or activity of systems, processes, or phenomena. They include the use of mathematical equations, computers, and other electronic equipment.
Predicting the time of OVULATION can be achieved by measuring the preovulatory elevation of ESTRADIOL; LUTEINIZING HORMONE or other hormones in BLOOD or URINE. Accuracy of ovulation prediction depends on the completeness of the hormone profiles, and the ability to determine the preovulatory LH peak.
The study, based on direct observation, use of statistical records, interviews, or experimental methods, of actual practices or the actual impact of practices or policies.
Molecular dynamics and analytic theory results are presented for the reorientation dynamics of first hydration shell water molecules around fluoride and iodide anions. These ions represent the extreme...
The mechanism of the OH bond reorientation in liquid methanol and ethanol is examined. It is found that the extended jump model, recently developed for water, describes the OH reorientation in these l...
The dynamics of dimethyl sulfoxide (DMSO)/water solutions with a wide range of water concentrations are studied using polarization selective infrared pump-probe experiments, two-dimensional infrared (...
Reorientation correlation times in protein solutions are key determinants for feasibility and quality of NMR experiments. Yet, their accurate estimate is not easy, especially in the case of very large...
The reorientation dynamics of interfacial water molecules was recently shown to change non-monotonically next to surfaces of increasing hydrophilicity, with slower dynamics next to strongly hydrophobi...
Advice to increase water consumption as part of a weight-reducing diet - typically to 8 cups (64 fl oz, ~2 L) per day ("8x8" water recommendation) - is almost ubiquitously recommended by h...
The study will evaluate whether the blood concentrations of eletriptan administered using two test formulations of oral disintegrating tablets are comparable to those observed with the sta...
The principal objective of this research is the evaluation of the effect of mineralized water consumption upon evolution of LDL Cholesterol and triglycerides, compared to a low mineralized...
Drinking water is largely advocated for obesity prevention and management. Recent studies have suggested that water has a thermogenic effect, this has not been examined in children. In thi...
Background: It has been suspected in our clinic patients that when patients do not wash their hands after receiving NAET treatments, the effect of their treatments has been reduced or in...