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7 Jan 2012

Volume 136, Issue 1, Articles (01xxxx)

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J. Chem. Phys. 136, 014501 (2012); http://dx.doi.org/10.1063/1.3665140 (8 pages)

Minbiao Ji, Robert W. Hartsock, Zheng Sung, and Kelly J. Gaffney
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back to top Biological Molecules, Biopolymers, and Biological Systems

Solid effect dynamic nuclear polarization and polarization pathways

Albert A. Smith, Björn Corzilius, Alexander B. Barnes, Thorsten Maly, and Robert G. Griffin

J. Chem. Phys. 136, 015101 (2012); http://dx.doi.org/10.1063/1.3670019 (16 pages) | Cited 11 times

Online Publication Date: 4 January 2012

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Using dynamic nuclear polarization (DNP)/nuclear magnetic resonance instrumentation that utilizes a microwave cavity and a balanced rf circuit, we observe a solid effect DNP enhancement of 94 at 5 T and 80 K using trityl radical as the polarizing agent. Because the buildup rate of the solid effect increases with microwave field strength, we obtain a sensitivity gain of 128. The data suggest that higher microwave field strengths would lead to further improvements in sensitivity. In addition, the observation of microwave field dependent enhancements permits us to draw conclusions about the path that polarization takes during the DNP process. By measuring the time constant for the polarization buildup and enhancement as a function of the microwave field strength, we are able to compare models of polarization transfer, and show that the major contribution to the bulk polarization arises via direct transfer from electrons, rather than transferring first to nearby nuclei and then transferring to bulk nuclei in a slow diffusion step. In addition, the model predicts that nuclei near the electron receive polarization that can relax, decrease the electron polarization, and attenuate the DNP enhancement. The magnitude of this effect depends on the number of near nuclei participating in the polarization transfer, hence the size of the diffusion barrier, their T1, and the transfer rate. Approaches to optimizing the DNP enhancement are discussed.
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76.70.Fz Double nuclear magnetic resonance (DNMR), dynamical nuclear polarization
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

Effect of glycerol and dimethyl sulfoxide on the phase behavior of lysozyme: Theory and experiments

Christoph Gögelein, Dana Wagner, Frédéric Cardinaux, Gerhard Nägele, and Stefan U. Egelhaaf

J. Chem. Phys. 136, 015102 (2012); http://dx.doi.org/10.1063/1.3673442 (12 pages) | Cited 4 times

Online Publication Date: 4 January 2012

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Salt, glycerol, and dimethyl sulfoxide (DMSO) are used to modify the properties of protein solutions. We experimentally determined the effect of these additives on the phase behavior of lysozyme solutions. Upon the addition of glycerol and DMSO, the fluid–solid transition and the gas–liquid coexistence curve (binodal) shift to lower temperatures and the gap between them increases. The experimentally observed trends are consistent with our theoretical predictions based on the thermodynamic perturbation theory and the Derjaguin-Landau-Verwey-Overbeek model for the lysozyme-lysozyme pair interactions. The values of the parameters describing the interactions, namely the refractive indices, dielectric constants, Hamaker constant and cut-off length, are extracted from literature or are experimentally determined by independent experiments, including static light scattering, to determine the second virial coefficient. We observe that both, glycerol and DMSO, render the potential more repulsive, while sodium chloride reduces the repulsion.
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87.15.km Protein-protein interactions
87.15.R- Reactions and kinetics
87.15.Zg Phase transitions
05.70.Ce Thermodynamic functions and equations of state
87.14.ej Enzymes
87.15.B- Structure of biomolecules

Structure and dynamics of nano-sized raft-like domains on the plasma membrane

Fernando E. Herrera and Sergio Pantano

J. Chem. Phys. 136, 015103 (2012); http://dx.doi.org/10.1063/1.3672704 (11 pages) | Cited 3 times

Online Publication Date: 5 January 2012

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Cell membranes are constitutively composed of thousands of different lipidic species, whose specific organization leads to functional heterogeneities. In particular, sphingolipids, cholesterol and some proteins associate among them to form stable nanoscale domains involved in recognition, signaling, membrane trafficking, etc. Atomic-detail information in the nanometer/second scale is still elusive to experimental techniques. In this context, molecular simulations on membrane systems have provided useful insights contributing to bridge this gap. Here we present the results of a series of simulations of biomembranes representing non-raft and raft-like nano-sized domains in order to analyze the particular structural and dynamical properties of these domains. Our results indicate that the smallest (5 nm) raft domains are able to preserve their distinctive structural and dynamical features, such as an increased thickness, higher ordering, lower lateral diffusion, and specific lipid-ion interactions. The insertion of a transmembrane protein helix into non-raft, extended raft-like, and raft-like nanodomain environments result in markedly different protein orientations, highlighting the interplay between the lipid-lipid and lipid-protein interactions.
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87.16.dt Structure, static correlations, domains, and rafts
87.16.dj Dynamics and fluctuations
87.14.Cc Lipids
87.14.E- Proteins
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