Monday, August 18, 2008

Marcel's Update

REDOR recoupling in polymer-stabilized liquid crystals undergoing MAS — Two-dimensional NMR applications with strongly aligned proteins

Jean-François Trempe, Ekaterina Pomerantseva, and Kalle Gehring

Can. J. Chem. 86(6): 608–615 (2008)

Abstract: We recently introduced a technique, termed SAD-REDOR, for recoupling residual dipolar couplings in a single-domain polymer-stabilized liquid crystal (PSLC) undergoing magic-angle spinning (MAS). The experiment was demonstrated with 1H–15N dipolar couplings in a small molecule. Here, we show the applicability of the technique to a strongly aligned protein and we describe a novel two-dimensional experiment to generate in-phase and anti-phase (IPAP) doublets in the 1H dimension of an HSQC NMR spectrum. This pulse sequence, SAD-IPAP, was tested on a sample of 15N-labeled ubiquitin (5 mmol/L) in a polyacrylamide-stabilized Pf1 phage liquid crystal (20 mg/mL). 15N–1H residual dipolar couplings (RDCs) were measured with the SAD-IPAP pulse sequence at spinning speeds of 1000 and 1250 Hz. RDSs were also measured using the conventional HSQC-IPAP method in a sample of 15N-ubiquitin dissolved in a solution of Pf1 phage (1 mg/mL). The resulting RDCs were fitted to the solution structure of ubiquitin to estimate the alignment tensor and to determine the accuracy of the measured couplings. The results highlight the benefits of SAD-REDOR for the measurement of RDCs in strongly aligned macromolecules.

Carbon and silicon substitution in (4, 4) aluminum nitride nanotube — Density functional study of 27Al and 14N electric field gradient tensors

Ahmad Seif, Mehran Aghaie, and Hossein Aghaie

Can. J. Chem. 86(8): 745–750 (2008)

Abstract: A computational study at the level of density functional theory (DFT) was performed to investigate the influence of Si and C substitution on the 14N and 27Al quadrupole coupling constants (CQ) in the armchairsingle-walled aluminum nitride nanotube (SWAlNNT). To this aim, a 1 nm AlNNT consisting of 28 Al and 28 N atoms was considered in which both mouths of the nanotube are capped by hydrogen atoms. Additionally, two other forms of this model of AlNNT were considered in which five Si and five C atoms were substituted in place of the five Al and five N atoms, with two rings in the length of nanotube, like a wire, in the first form; and three Si and three C atoms were substituted in place of three Al and three N atoms as a central ring on the surface of the AlNNT in the second form. The calculated CQ values for three optimized AlNNT systems (raw and Si- and C-substituted) reveal diverse electronic environments in the above-mentioned systems. All the calculations were carried out using the Gaussian 98 software pac

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