NMR investigations of interactions between anesthetics and lipid bilayers

Interactions between anesthetics (lidocaine and short chain alcohols) and lipid membranes formed by dimyristoylphosphatidylcholine (DMPC) were studied using NMR spectroscopy. The orientational order of lidocaine was investigated using deuterium NMR on a selectively labelled compound whereas segmental ordering in the lipids was probed by two-dimensional 1H-13C separated local field experiments under magic-angle spinning conditions. In addition, trajectories generated in molecular dynamics (MD) computer simulations were used for interpretation of the experimental results. Separate simulations were carried out with charged and uncharged lidocaine molecules. Reasonable agreement between experimental dipolar interactions and the calculated counterparts was observed. Our results clearly show that charged lidocaine affects significantly the lipid headgroup. In particular the ordering of the lipids is increased accompanied by drastic changes in the orientation of the P-N vector in the choline group

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ISSN:1439-230

Nonfatal Injuries 1 Week After Hurricane Sandy — New York City Metropolitan Area, October 2012

On October 29, 2012, Hurricane Sandy (Sandy) made landfall in densely populated areas of New York, New Jersey, and Connecticut. Flooding affected 51 square miles (132 square kilometers) of New York City (NYC) and resulted in 43 deaths, many caused by drowning in the home, along with numerous storm-related injuries. Thousands of those affected were survivors of the World Trade Center (WTC) disaster of September 11, 2001 (9/11) who had previously enrolled in the WTC Health Registry (Registry) cohort study. To assess Sandy-related injuries and associated risk factors among those who lived in Hurricane Sandy-flooded areas and elsewhere, the NYC Department of Health and Mental Hygiene surveyed 8,870 WTC survivors, who had provided physical and mental health updates 8 to 16 months before Sandy. Approximately 10% of the respondents in flooded areas reported injuries in the first week after Sandy; nearly 75% of those had more than one injury. Injuries occurred during evacuation and clean-up/repair of damaged or destroyed homes. Hurricane preparation and precautionary messages emphasizing potential for injury hazards during both evacuation and clean-up or repair of damaged residences might help mitigate the occurrence and severity of injury after a hurricane

Structure and elastic properties of a nematic liquid crystal: A theoretical treatment and molecular dynamics simulation

The Frank elasticity constants which describe splay $(K_1)$, twist $(K_2)$, and bend $(K_3)$ distortion modes are investigated for 4-n-pentyl-$4'$-cyanobiphenyl (5CB) in the nematic liquid crystal. The calculations rest on statistical-mechanical approaches where the absolute values of $K_i (i=1,2,3)$ are dependent on the direct correlation function (DCF) of the corresponding nematic state. The DCF was determined using the pair correlation function by solving the Ornstein-Zernike equation. The pair correlation function, in turn, was obtained from molecular dynamics (MD) trajectory. Three different approaches for calculations of the elasticity constants were employed based on different level of approximation about the orientational order and molecular correlations. The best agreement with experimental values of elasticity constants was obtained in a model where the full orientational distribution function was used. In addition we have investigated the approximation about spherical distribution of the intermolecular vectors in the nematic phase, often used in derivation of various mean-field theories and employed here for the construction of the DCF. We found that this assumption is not strictly valid, in particular a strong deviation from the isotropic distribution is observed for short intermolecular distances

Theoretical investigations of rotational phenomena and dielectric properties in a nematic liquid crystal

The molecular dynamics (MD) simulation, based on a realistic atom-atom interaction potential, was performed on 4-$n$-pentyl-$4'$-cyanobiphenyl (5CB) in the nematic phase. The rotational viscosity coefficients (RVCs) $\gamma_i$, ($i = 1,2$) and the ratio of the RVCs $\lambda = - \gamma_2/\gamma_1$ were investigated. Furthermore, static and frequency-dependent dielectric constants $\epsilon_{\parallel}$ and $\epsilon_{\perp}$ were calculated using parameters obtained from the MD simulation. Time correlation functions were computed and used to determine the rotational diffusion coefficient, $D_{\perp}$. The RVCs and $\lambda$ were evaluated using the existing statistical-mechanical approach (SMA), based on a rotational diffusion model. The SMA rests on a model in which it is assumed that the reorientation of an individual molecule is a stochastic Brownian motion in a certain potential of mean torque. According to the SMA, $\gamma_i$ are dependent on the orientational order and rotational diffusion coefficients. The former was characterized using: i) orientational distribution function (ODF), and ii) a set of order parameters, both derived from analyses of the MD trajectory. A reasonable agreement between the calculated and experimental values of $\gamma_i$ and $\lambda$ was obtained

Nuclear spin relaxation and translational diffusion study of Benzene-Hexa-n-alkanoat

The molecular dynamics of benzene-hexa-n-heptanoate (BHA7) have been studied in the isotropic liquid phase by multified carbon-13 nuclear spin relaxation of a carboxyl carbon labeled compound. The experimental data are analyzed with a dynamical model based on the assumption of three trypes of motion: a fast internal motion in the aliphatic chains, a slow overall reorientation of the molecule, and an intermediate process connected with the flexibility of the carboxyl group. The first two motions occur clearly on different time scales, whereas the last process is not time scale separated from the global molecular tumbling. Preciously reported carbon-13 line shapes in the mesophase and in the solid state of BHA7 were used for vertification of the results. Measurements of translational diffusion coefficients in isotropic and ordered phases of BHA6 and BHA7 were performed using 1H pulsed field gradient NMR spin-echo techniques

Carbon-13 NMR chemical shifts in columnar liquid crystals

In this article, we present quantum chemical density functional theory (DFT) calculations of the NMR 13C chemical shift (CS) tensors in 2,3,6,7,10,11−hexahexylthiotriphenylene (HHTT). The DFT calculations are performed on a smaller model molecule where the hexyl chains were reduced to methyl groups (HMTT). These tensors are compared with our previously reported experimental results carried out under magic−angle spinning (MAS) conditions. The phase diagram of HHTT is K T H T Dhd T I, where H is a helical phase and Dhd is a columnar liquid crystal. The motivation for the present study was to explain experimentally observed and puzzling thermal history effects, which resulted in different behavior in the helical phase upon cooling and heating. In particular, the CS tensors for the aromatic carbons measured in the helical phase upon heating from the solid phase were essentially unaffected, while the cooling from the columnar liquid crystal resulted in a significant averaging. We investigate the effect on the CS tensors of (i) conformational transitions, and (ii) relative molecular orientations within the columns for dimer and trimer configurations. Finally a motional wobbling (PIZZA) model for the dynamic averaging of the CS tensor in the helical phase is suggeste