Vibrational spectroscopy of water in hydrated lipid multi-bilayers. II. Two-dimensional infrared and peak shift observables within different theoretical approximations

In a previous report, we calculated the infrared absorption spectrum and both the isotropic and anisotropic pump-probe signals for the OD stretch of isotopically dilute water in dilauroylphosphatidylcholine (DLPC) multi-bilayers as a function of the lipid hydration level. These results were then compared to recent experimental measurements and are in generally good agreement. In this paper, we will further investigate the structure and dynamics of hydration water using molecular dynamics simulations and calculations of the two-dimensional infrared and vibrational echo peak shift observables for hydration water in DLPC membranes. These observables have not yet been measured experimentally, but future comparisons may provide insight into spectral diffusion processes and hydration water heterogeneity. We find that at low hydration levels the motion of water molecules inside the lipid membrane is significantly arrested, resulting in very slow spectral diffusion. At higher hydration levels, spectral diffusion is more rapid, but still slower than in bulk water. We also investigate the effects of several common approximations on the calculation of spectroscopic observables by computing these observables within multiple levels of theory. The impact of these approximations on the resulting spectra affects our interpretation of these measurements and reveals that, for example, the cumulant approximation, which may be valid for certain systems, is not a good approximation for a highly heterogeneous environment such as hydration water in lipid multi-bilayers.     

Tailoring the optimal control cost function to a desired output: application to minimizing phase errors in short broadband excitation pulses

The de facto standard cost function has been used heretofore to characterize the performance of pulses designed using optimal control theory. The freedom to choose new, creative quality factors designed for specific purposes is demonstrated. While the methodology has more general applicability, its utility is illustrated by comparison to a consistently chosen example--broadband excitation. The resulting pulses are limited to the same maximum RF amplitude used previously and tolerate the same variation in RF homogeneity deemed relevant for standard high-resolution NMR probes. Design criteria are unchanged: transformation of I(z)--> I(x) over resonance offsets of +/-20 kHz and RF variability of +/-5%, with a peak RF amplitude equal to 17.5 kHz. However, the new cost effectively trades a small increase in residual z magnetization for improved phase in the transverse plane. Compared to previous broadband excitation by optimized pulses (BEBOP), significantly shorter pulses are achievable, with only marginally reduced performance. Simulations transform I(z) to greater than 0.98 I(x), with phase deviations of the final magnetization less than 2 degrees, over the targeted ranges of resonance offset and RF variability. Experimental performance is in excellent agreement with the simulations.     

Characterisation of the oxygen transfer in BIMEVOX membranes under applied current conditions

Oxygen isotopic exchange has been studied for a number of materials in the BIMEVOX family of compounds. The exchanges were undertaken at 620 °C with gold grid electrodes on the samples and with a constant current flowing through the samples during the exchange anneals. These conditions simulate those used when these materials are employed in oxygen separation devices where substantial oxygen fluxes can be sustained using such simple gold grid electrodes.The results showed that samples exchanged under current flow conditions exhibit substantial oxygen exchange at the cathode, in contrast to samples where no electrical bias is applied. This effect was sustained in regions remote from the sputtered gold electrode. Complementary studies of the samples using X-ray diffraction revealed subtle changes in the diffraction patterns following experiments with current flow. These changes are ascribed to a reduction of V⁵⁺ to V⁴⁺ at the cathode locally transforming the BIMEVOX material into a mixed conducting material, and hence enhancing the oxygen isotopic exchange process.     

Linear Polymers from Diene Monomers by the Cyclic Polymerization Mechanism. XI. Polyphosphonium Salts via Cyclopolymerization

A wide variety of diunsaturated phosphonium salts have been synthesized in order to determine whether or not such structures undergo cyclopolymerization. As intermediates for these monomers, a number of previously unreported unsaturated phosphines have been prepared and characterized. Polymerization studies using a wide variety of free radical initiating conditions led to polymers in those cases which were predicted to undergo cyclopolymerization leading to five-, six-, or seven-membered rings with one exception. The properties of the polymers are consistent with the cyclopolymerization mechanism. The conversion of poly(diallyldiphenylphosphonium bromide) to polfidiallyldiphenylphosphine oxide) offers additional evidence for cyclopolymerization. Di-3-butenyldiphenylphosphonium bromide, a monomer functionally capable of forming a polymer containing an eight-membered ring, did not polymerize. Divinylphenylphosphine was found to undergo copolymerization with acrylonitrile in accordance with the cyclo-copolymerization mechanism.     

A Two‐Armed Lanthanoid‐Chelating Paramagnetic NMR Probe Linked to Proteins via Thioether Linkages

Paramagnetic NMR probes provide valuable long‐range structural information on proteins and protein complexes. A new, stable, two‐armed lanthanoid probe is reported that can be attached to a protein site‐specifically via chemically inert thioether linkages.     

Next‐Generation Heteronuclear Decoupling for High‐Field Biomolecular NMR Spectroscopy

Ultra‐high‐field NMR spectroscopy requires an increased bandwidth for heteronuclear decoupling, especially in biomolecular NMR applications. Composite pulse decoupling cannot provide sufficient bandwidth at practical power levels, and adiabatic pulse decoupling with sufficient bandwidth is compromised by sideband artifacts. A novel low‐power, broadband heteronuclear decoupling pulse is presented that generates minimal, ultra‐low sidebands. The pulse was derived using optimal control theory and represents a new generation of decoupling pulses free from the constraints of periodic and cyclic sequences. In comparison to currently available state‐of‐the‐art methods this novel pulse provides greatly improved decoupling performance that satisfies the demands of high‐field biomolecular NMR spectroscopy.     

The blind bartender's problem

We present a two-player game with restricted information for one of the players. The game takes place on a transitive group action. The winning strategies depend on chains of structures in the group action. We also study a modification of the game with further restrictions on one of the players.