Measurement of (1)J(NC') and (2)J(H(N))(C') couplings from spin-state-selective two-dimensional correlation spectrum.

A method for the measurement of (1)J(NC') and (2)J(H(N))(C') coupling constants from a simplified two-dimensional [(15)N, (1)H] correlation spectrum is presented. The multiplet components of the (1)J(NC') doublet in the indirect dimension and (2)J(H(N))(C') in the direct dimension are separated into two subspectra by spin-state-selective filters. Thus each subspectrum contains no more peaks than the conventional [(15)N, (1)H]-HSQC spectrum. Furthermore, the method for the measurement of (1)J(NC') and (2)J(H(N))(C') is designed to exploit destructive relaxation interference (TROSY). The results are verified against the measurements of (1)J(NC') from spin-state-selective [(13)C', (1)H] correlation spectra recorded with additional sequence described here.     

Calculations of nuclear quadrupole coupling in noble gas-noble metal fluorides: interplay of relativistic and electron correlation effects

The nuclear quadrupole coupling constants (NQCCs) of noble gas and noble metal nuclei in the recently found noble gas-noble metal fluorides (NgMF, where Ng=Ar,Kr,Xe and M=Cu,Ag,Au) are obtained theoretically by high-level ab initio calculations, where both relativistic and electron correlation effects are included, and compared to experimental results. Fully relativistic four-component Dirac-Hartree-Fock (DHF) calculations are carried out at the basis set limit for electric field gradient that couples with the electric quadrupole moment of the nucleus, and uncorrelated relativistic effects are extracted by comparing DHF results to nonrelativistic (NR) HF calculations. Electron correlation effects are investigated both at fully relativistic second-order Moller-Plesset (DMP2) and at NR MP2 levels of theory, as well as at the NR coupled-cluster singles and doubles with perturbational triples [CCSD(T)] level. The validity of the approximation where relativistic effects, on the one hand, and nonrelativistically obtained correlation effects, on the other hand, are evaluated separately and assumed to be additive, is investigated by comparison with the DMP2 results. Inclusion of relativistic effects is shown to be necessary for obtaining the correct NQCC trends as the nucleus of interest and/or its neighbors become heavier. Electron correlation treatment is needed for approaching quantitative agreement with the experimental NQCCs. The assumption of additive electron correlation and relativistic effects, corresponding to the NR correlation treatment added on top of relativistic DHF data, gives qualitatively correct noble gas NQCCs. For noble metal NQCCs, correlation treatment at the relativistic level of theory is mandatory for reaching agreement with experimental results. Current work also confirms the experimental trends of NQCCs, which have been taken as an indication of nearly covalent interaction between noble gas and noble metal in the heaviest present systems, especially in XeAuF.     

Efficient calculation of accurate masses of isotopic peaks

This paper presents a new method for calculating accurate masses of isotopic peaks. It is based on breaking the calculation into a binary series of calculations. The molecule is built up by a series of such calculations. At each step the accurate masses are calculated as a probability weighted sum of the masses of the contributing peaks. The method is computationally efficient and accurate for both mass and relative abundance.     

Tilt: major factor in sterols' ordering capability in membranes

Using extensive atomistic simulations, we show that there is a single experimentally accessible parameter--the sterol tilt--that can be used to determine a sterol's capability to induce order, and thus to promote, e.g., formation of lipid rafts. The observations also facilitate designing new effective sterols.     

The synthesis and characterization of phenylacetylene tripodal compounds containing boroxine cores

A convergent synthesis of phenylacetylene tripodal compounds containing boroxine cores has been accomplished. The boroxine cores are assembled in high yield either by chemical dehydration or ligand-facilitated trimerization of the corresponding monomeric boronic acids.     

Hyperdimensional NMR spectroscopy with nonlinear sampling

An approach is described for joint interleaved recording, real-time processing, and analysis of NMR data sets. The method employs multidimensional decomposition to find common information in a set of conventional triple-resonance spectra recorded in the nonlinear sampling mode, and builds a model of hyperdimensional (HD) spectrum. While preserving sensitivity per unit of measurement time and allowing for maximal spectral resolution, the approach reduces data collection time on average by 2 orders of magnitude compared to the conventional method. The 7-10 dimensional HD spectrum, which is represented as a set of deconvoluted 1D vectors, is easy to handle and amenable for automated analysis. The method is exemplified by automated assignment for two protein systems of low and high spectral complexity: ubiquitin (globular, 8 kDa) and zetacyt (naturally disordered, 13 kDa). The collection and backbone assignment of the data sets are achieved in real time after approximately 1 and 10 h, respectively. The approach removes the most critical time bottlenecks in data acquisition and analysis. Thus, it can significantly increase the value of NMR spectroscopy in structural biology, for example, in high-throughput structural genomics applications.     

Hetero-arylboroxines: the first rational synthesis, X-ray crystallographic and computational analysis

A novel series of hetero-arylboroxines were synthesized and structurally characterized by X-ray diffraction, NMR and computational analysis. The solid-state structures of the hetero-arylboroxines represent the first report of AB(2)-type hetero-arylboroxines.     

Inverse-phosphocholine lipids: a remix of a common phospholipid

Zwitterionic inverse-phosphocholine (iPC) lipids contain headgroups with an inverted charge orientation relative to phosphocholine (PC) lipids. The iPC lipid headgroup has a quaternary amine adjacent to the bilayer interface and a phosphate that extends into the aqueous phase. Neutral iPC lipids with ethylated phosphate groups (CPe) and anionic iPC lipids nonethylated phosphate groups (CP) were synthesized. The surface potential of CPe liposomes remains negative across a broad pH range and in the presence of up to 10 mM Ca(2+). CP liposomes aggregate in the presence of Ca(2+), but at a slower rate than other anionic lipids. Hydrolysis of CP lipids by alkaline phosphatases generates a cationic lipid. CPe liposomes release encapsulated anionic carboxyfluorescein (CF) 20 times faster than PC liposomes and release uncharged glucose twice as fast as PC liposomes. As such, iPC lipids afford a unique opportunity to investigate the biophysical and bioactivity-related ramifications of a charge inversion at the bilayer surface.     

Relativistic spin-orbit coupling effects on secondary isotope shifts of (13)C nuclear shielding in CX(2) (X = O, S, Se, Te)

Rovibrational corrections, temperature dependence, and secondary isotope shifts of the (13)C nuclear shielding in CX(2) (X = O, S, Se, Te) are calculated taking into account the relativistic spin-orbit (SO) interaction. The SO effect is considered for the first time for the secondary isotope shifts. The nuclear shielding hypersurface in terms of nuclear displacements is calculated by using a density-functional theory method. Ab initio multiconfiguration self-consistent field calculations are done at the equilibrium geometry for comparison. (13)C NMR measurements are carried out for CS(2). The calculated results are compared with both present and earlier experimental data on CO(2), CS(2), and CSe(2). The heavy-atom SO effects on the rovibrational corrections of (13)C shielding are shown to be significant. For CSe(2) and CTe(2), reliable prediction of secondary isotope effects and their temperature dependence requires the inclusion of the SO corrections. In particular, earlier discrepancies of theory and experiment for CSe(2) are fully resolved by taking the SO interactions into account.