No abstract

A new solid-state NMR-based strategy is established for the precise and efficient analysis of orientation and dynamics of transmembrane peptides in fluid bilayers. For this purpose, several dynamically averaged anisotropic constraints, including (13)C and (15)N chemical shift anisotropies and (13)C-(15)N dipolar couplings, were determined from two different triple-isotope-labeled WALP23 peptides ((2)H, (13)C, and (15)N) and combined with previously published quadrupolar splittings of the same peptide. Chemical shift anisotropy tensor orientations were determined with quantum chemistry. The complete set of experimental constraints was analyzed using a generalized, four-parameter dynamic model of the peptide motion, including tilt and rotation angle and two associated order parameters. A tilt angle of 21 degrees was determined for WALP23 in dimyristoylphosphatidylcholine, which is much larger than the tilt angle of 5.5 degrees previously determined from (2)H NMR experiments. This approach provided a realistic value for the tilt angle of WALP23 peptide in the presence of hydrophobic mismatch, and can be applied to any transmembrane helical peptide. The influence of the experimental data set on the solution space is discussed, as are potential sources of error.

This paper addresses the linear and second-order nonlinear optical properties of two anil derivatives and in particular their variations upon switching between the enol-imine and keto-amine forms. Quantum chemical evaluations of the first hyperpolarizabilities, accounting for both solvent and electron correlation effects, are compared with hyper-Rayleigh scattering and electric field-induced second harmonic generation measurements. For both compounds, the E/K first hyperpolarizability ratios are larger than 2, demonstrating that the enol forms present the largest responses but also that the switching is associated with a substantial β contrast.