High-field Solid-state NMR Research Articles

67Zn solid-state and single-crystal NMR spectroscopy and X-ray crystal structure of zinc formate dihydrate.

The crystal structure, quadrupole coupling parameters, and the orientation of the electric field gradient tensors for each site of zinc formate dihydrate have been determined. There are two distinct sites in the asymmetric unit: one containing four in-plane waters with two bridging formats, the other containing six bridging formates. The solid-state NMR lineshapes have been assigned to their respective sites by using isotopic labeling and cross-polarization methods. The hydrated site corresponds to the lineshape having a quadrupole coupling constant (Cq) of 9.6 MHz and the anhydrous site has a Cq of 6.2 MHz. The absence of chemical shielding contributions to the observed lineshapes has been verified with a high-field solid-state NMR experiment performed at 18.8 T.

Localization of 23Na+ in a DNA Quadruplex by High-Field Solid-State NMR

Monovalent cations such as Na+, K+, and NH4+ are known to stabilize DNA quadruplexes formed of guanine-quartets. Such structures readily form from the guanine-rich repeat sequences found in telomeres, the physical ends of eukaryotic chromosomes. We present a solid-state NMR approach for studying ions associated with G-quartets based on the direct NMR observation of 23Na+ ion resonances and report new methods for studying quadrupolar nuclei in biological solids. In the tetraplex forming oligonucleotide d(TG4T), high-field (17.6 T) NMR spectra cleanly resolve three distinct classes of sodium ions. A high-resolution 2D-MQMAS spectrum established the assignment of an amorphously broadened signal at −19 ppm (relative to 0.1 M NaCl) to surface-bound Na+ ions. Two-dimensional nutation spectroscopy was used to indicate the relative size of the quadrupole coupling for each line, while a standard exchange experiment established a correlation between surface (−19 ppm) and channel-bound (6.8 ppm) Na+ ions. Finally, f...

Detection of the ‘invisible aluminium’ and characterisation of the multiple aluminium environments in zeolite USY by high-field solid-state NMR

The detection of all of the aluminium present in steamed zeolite H-Y catalysts by 27Al MAS NMR at high field (18.8 T, 800 MHz for 1H) is reported; further, it is shown that it is possible by 27Al MAS and MQMAS measurements to clearly identify four separate aluminium environments characteristic of these materials and to unambiguously assign their coordinations.

Chemical shift and electric field gradient tensors for the amide and carboxyl hydrogens in the model peptide N-acetyl-D,L-valine. Single-crystal deuterium NMR study

Solid-state NMR spectroscopy is well established as a method for describing molecular structure with resolution on the atomic scale. Many of the NMR observables result from anisotropic interactions between the nuclear spin and its environment. These observables can be described by second-rank tensors. For example, the eigenvalues of the traceless symmetric part of the hydrogen chemical shift (CS) tensor provide information about the strength of inter- or intramolecular hydrogen bonding. On the other hand, the eigenvectors of the deuterium electric field gradient (EFG) tensor give deuteron/proton bond directions with an accuracy rivalled only by neutron diffraction. In this paper the authors report structural information of this type for the amide and carboxyl hydrogen sites in a single crystal of the model peptide N-acetyl-D,L-valine (NAV). They use deuterium NMR to infer both the EFG and CS tensors at the amide and carboxyl hydrogen sites in NAV. Advantages of this technique over multiple-pulse proton NMR are that it works in the presence of {sup 14}N spins which are very hard to decouple from protons and that additional information in form of the EFG tensors can be derived. The change in the CS and EFG tensors upon exchange of a deuteron for amore » proton (the isotope effect) is anticipated to be very small; the effect on the CS tensors is certainly smaller than the experimental errors. NAV has served as a model peptide before in a variety of NMR studies, including those concerned with developing solid-state NMR spectroscopy as a method for determining the structure of proteins. NMR experiments on peptide or protein samples which are oriented in at least one dimension can provide important information about the three-dimensional structure of the peptide or the protein. In order to interpret the NMR data in terms of the structure of the polypeptide, the relationship of the CS and EFG tensors to the local symmetry elements of an amino acide, e.g., the peptide plane, is essential. The main purpose of this work is to investigate this relationship for the amide hydrogen CS tensor. The amide hydrogen CS tensor will also provide orientational information for peptide bonds in proteins complementary to that from the nitrogen CS and EFG tensors and the nitrogen-hydrogen heteronuclear dipole-dipole coupling which have been used previously to determine protein structures by solid-state NMR spectroscopy. This information will be particularly valuable because the amide hydrogen CS tensor is not axially symmetric. In addition, the use of the amide hydrogen CS interaction in high-field solid-state NMR experiments will increase the available resolution among peptide sites.« less