Detailed dynamical features of the slow hydration water in the vicinity of poly(ethylene oxide) chains.

Poly(ethylene oxide) (PEO) is a well-known biocompatible polymer and has widely been used for medical applications. Recently, we have investigated the dynamic behavior of hydration water in the vicinity of PEO chains at physiological temperature and shown the presence of slow water with diffusion coefficient one order of magnitude less than that of bulk water. This could be evidence for the intermediate water that is critical for biocompatibility; however, its detailed dynamical features were not established. In this article, we analyze the quasi-elastic neutron scattering from hydration water through mode distribution analysis and present a microscopic picture of hydration water as well as its relation to cold crystallization.

Cyanotoxin Analysis and Amino Acid Profiles of Cyanobacterial Food Items from Chad.

In some parts of the world, cyanobacteria are used as a food in the human diet, due to their ready availability. Lake Chad, has long been a traditional site for the collection of Arthrospira fusiformis which is dried and processed at the lake into thin wafers called Dihé for later consumption or is transported to market for sale. However, Dihé purchased from markets in Chad has not been analyzed for known cyanobacterial toxins or assessed for total amino acid content. Since BMAA in traditional foodstuffs of the indigenous Chamorro people of Guam causes neurodegenerative illness, it is important that Dihé from Chad be analyzed for this neurotoxin. BMAA and its isomer AEG were not detected in our analyses, but a further isomer DAB was detected as both a free and bound amino acid, with an increase in the free concentration after acid hydrolysis of this fraction. Microcystins were present in 6 samples at up to 20 µg/g according to UPLC-PDA, although their presence could not be confirmed using PCR for known microcystin synthetic genes. Amino acid analysis of the cyanobacterial material from Chad showed the presence of large amounts of canonical amino acids, suggesting that this may supplement indigenous people on low protein diets, although regular monitoring of the foodstuffs for the presence of cyanotoxins should be performed.

Effects of a chair-yoga exercises on stress hormone levels, daily life activities, falls and physical fitness in institutionalized older adults.

UNLABELLED: The aim of this study was to assess the changes mediated by exercise on activities of daily life and falls, physical fitness, salivary cortisol and alpha amylase in older adults living in social and health care givers centers. METHODS: Sample consisted in 35 women (83.81 ± 6.6 years old) were divided into two groups: chair-yoga exercises group (CY, n = 20) and control group (CG, n = 15). All subjects were evaluated before and after 14-weeks. CY was involved in exercise classes two times per week, while the GC did not participate in any exercise. RESULTS: Fear of falling decreased in both groups, cortisol increased and alpha-amylase decreased in the CG. No significant changes occurred in physical fitness outcomes. CONCLUSION: CY practice was able to maintain the physical fitness scores and stress hormone levels, but was not able to improve the subject's perception on the ability to perform the instrumental activities of daily life.

The free-energy barrier to hydride transfer across a dipalladium complex.

We use density-functional theory molecular dynamics (DFT-MD) simulations to determine the hydride transfer coordinate between palladium centres of the crystallographically observed terminal hydride locations, Pd-Pd-H, originally postulated for the solution dynamics of the complex bis-NHC dipalladium hydride [{(MesIm)2CH2}2Pd2H][PF6], and then calculate the free-energy along this coordinate. We estimate the transfer barrier-height to be about 20 kcal mol(-1) with a hydride transfer rate in the order of seconds at room temperature. We validate our DFT-MD modelling using inelastic neutron scattering which reveals anharmonicity of the hydride environment that is so pronounced that there is complete failure of the harmonic model for the hydride ligand. The simulations are extended to high temperature to bring the H-transfer to a rate that is accessible to the simulation technique.

Dynamics of water confined in single- and double-wall carbon nanotubes.

Using high-resolution quasielastic neutron scattering, we investigated the temperature dependence of single-particle dynamics of water confined in single- and double-wall carbon nanotubes with the inner diameters of 14+/-1 and 16+/-3 A, respectively. The temperature dependence of the alpha relaxation time for water in the 14 A nanotubes measured on cooling down from 260 to 190 K exhibits a crossover at 218 K from a Vogel-Fulcher-Tammann law behavior to an Arrhenius law behavior, indicating a fragile-to-strong dynamic transition in the confined water. This transition may be associated with a structural transition from a high-temperature, low-density (<1.02 gcm(3)) liquid to a low-temperature, high-density (>1.14 gcm(3)) liquid found in molecular dynamics simulation at about 200 K. However, no such dynamic transition in the investigated temperature range of 240-195 K was detected for water in the 16 A nanotubes. In the latter case, the dynamics of water simply follows a Vogel-Fulcher-Tammann law. This suggests that the fragile-to-strong crossover for water in the 16 A nanotubes may be shifted to a lower temperature.

Molecular dynamics study of the n-hexane-water interface: towards a better understanding of the liquid-liquid interfacial broadening.

By molecular dynamics simulations, we have studied the hydrophilic-hydrophobic interface between water and n-hexane liquid phases. For all temperatures studied our computed interfacial tension agrees very well with the experimental value. However, the interfacial width calculated from capillary wave theory systematically overestimates the width obtained from fitting either the total density or composition profile. We rationalize the applicability of capillary wave theory for our system by reconsidering the usual value taken for the correlation length. This is motivated by the presence of order at the interface. Possible implications for recent experimental studies on the structure of model alkane-water interfaces are discussed, including the significance of the intrinsic width parameter.