Dipolar Coupling

Residual dipolar couplings are useful global structural restraints. The dipolar couplings define the orientation of a vector with respect to the alignment tensor. Although the size of the alignment tensor can be derived from the distribution of the experimental dipolar couplings, its orientation with respect to the coordinate system of the molecule is unknown at the beginning of structure determination. This causes convergence problems in the simulated annealing process. We therefore propose a protocol that translates dipolar couplings into intervector projection angles, which are independent of the orientation of the alignment tensor with respect to the molecule. These restraints can be used during the whole simulated annealing protocol.

Calcium-43 (nuclear spin, S=7/2) is an NMR insensitive low-gamma quadrupolar nucleus and up until recently only one-dimensional solid-state (43)Ca NMR spectra have been reported. Through-space correlation experiments are challenging between spin-12 and low-gamma quadrupolar nuclei because of the intrinsically weak dipolar interaction and the often-low natural abundance of the quadrupolar nucleus. Rotary-resonance recoupling (R(3)) has recently been used to re-introduce hetero-nuclear dipolar interactions for sensitive high-gamma quadrupolar nuclei, but has not yet been applied in the case of low-gamma half-integer quadrupolar nuclei. Here an effective and robust 2D (1)H-(43)Ca NMR correlation experiment combining the R(3) dipole-recoupling scheme with 2D HMQC is presented. It is demonstrated that the weak (43)Ca-(1)H dipolar coupling in hydroxyapatite and oxy-hydroxyapatite can be readily re-introduced and that this recoupling scheme is more efficient than conventional cross-polariz...

Substitution of natural nucleobases in PNA oligomers with ligands is a strategy for directing metal ion incorporation to specific locations within a PNA duplex. In this study, we have synthesized PNA oligomers that contain up to three adjacent bipyridine ligands and examined the interaction with Ni{sup 2+} and Cu{sup 2+} of these oligomers and of duplexes formed from them. Variable-temperature

Muonium has been studied in single crystals of H2O and D2O. Two-frequency precession in low transverse fields and a single zero-field oscillation indicate a small anisotropy of axial symmetry in the muonium hyperfine interaction. The anisotropy is shown to be the cause of the hitherto unexplained temperature independent contribution to muonium spin relaxation in polycrystalline samples. Relaxation rates for 99 K–263 K are reported for muonium in a single crystal of H2O. Relaxation is attributed to electron-nuclear dipolar coupling of muonium to lattice protons, modulated by translational diffusion of muonium alongc-axis channels of the ice lattice. A simple model for H and Mu diffusion in ice is investigated.

It is shown that dissolving a paramagnetic protein in a lyotropic liquid crystal solvent results in measurable splittings of several hyperfine-shifted proton lines, without excessive broadening. These splittings are due to residual dipolar coupling of neighboring geminal protons and are interpreted in terms of an orientation tensor, whose magnitude corresponds to about 1% orientation. The reasonable agreement obtained between observed splittings and their calculated absolute values shows that the simplified analysis used is essentially ...

Homonuclear higher quantum NMR spectra of heteronuclear spin systems result in fewer transitions aiding the analyses. In such experiments the spin states of the heteronuclei do not get disturbed in both single and multiple quantum dimensions resulting in the separation of active homonuclear and passive heteronuclear couplings in two dimensions. The cross sections of the single-quantum dimension get displaced according

Several HNCO-based three-dimensional experiments are described for the measurement of 13C'(i - 1)-13Calpha(i - 1), 5N(i)-13C'(i - 1), 15N(i)-13Calpha(i), 15N(i)-13Calpha(i - 1), 1H(N)(i)-13Calpha(i), 1H(N)(i)-13Calpha(i - 1), and 13Calpha(i - 1)-13Cbeta(i - 1) scalar and dipolar couplings in 15N, 13C, (2H)-labelled protein samples. These pulse sequences produce spin-state edited spectra superficially resembling an HNCO correlation spectrum, allowing accurate and simple measurement of couplings without introducing additional spectral crowding. Scalar and dipolar couplings are measured with good sensitivity from relatively large proteins, as demonstrated with three proteins: cardiac Troponin C, calerythrin and ubiquitin. Measurement of several dipolar couplings between spin-1/2 nuclei using spin-state selective 3D HNCO spectra provides a wealth of structural information.

A perturbation method deals with dipolar coupling spins in solids is presented. As examples of the application the method, the multile-quantum coherence dynamics in clusters of a linear chain of four nuclear spins and a ring of six spins coupled by dipole-dipole interaction are considered. The calculated 0Q- and 2Q intensities in a linear chain of four nuclear spins and 6Q intensity in a ring of six spins vs the duration of the preparation period agree well with the exact solutions (for linear chain of four nuclear spins) and simulation data (for linear chain of four nuclear spins and a ring of six spin).