Through-bond NMR Research Articles

ADAPT-NMR 3.0: utilization of BEST-type triple-resonance NMR experiments to accelerate the process of data collection and assignment.

ADAPT-NMR (Assignment-directed Data collection Algorithm utilizing a Probabilistic Toolkit in NMR) is a software package whose Bayesian core uses on-the-fly chemical shift assignments to guide data acquisition by non-uniform sampling from a panel of through-bond NMR experiments. The new version of ADAPT-NMR (ADAPT-NMR v3.0) has the option of utilizing 2D tilted-plane versions of 3D fast spectral acquisition with BEST-type pulse sequences, while also retaining the capability of acquiring and processing data from tilted-plane versions of conventional sensitivity-enhanced experiments. The use of BEST experiments significantly reduces data collection times and leads to enhanced performance by ADAPT-NMR.

Indirectly detected through-bond chemical shift correlation NMR spectroscopy in solids under fast MAS: Studies of organic–inorganic hybrid materials

Indirectly detected, through-bond NMR correlation spectra between 13C and 1H nuclei are reported for the first time in solid state. The capabilities of the new method are demonstrated using naturally abundant organic–inorganic mesoporous hybrid materials. The time performance is significantly better, almost by a factor of 10, than in the corresponding 13C detected experiment. The proposed scheme represents a new analytical tool for studying other solid-state systems and the basis for the development of more advanced 2D and 3D correlation methods.

Structure determination of β-Pb2ZnF6 by coupling multinuclear solid state NMR, powder XRD and ab initio calculations

The results from one-dimensional multinuclear (19F, 207Pb and 67Zn) magic-angle spinning nuclear magnetic resonance experiments combined with the use of the ISODISPLACE program allow for the space group determination of beta-Pb2ZnF6 (no. 138 P4(2)/ncm). The structure was refined from X-ray powder diffraction data (a = 5.633 (1) A and c = 16.247 (1) A, Z = 4). beta-Pb2ZnF6 has one six-fold coordinated Zn, one eleven-fold coordinated Pb and five F non-equivalent crystallographic sites and is built from alternated layers parallel to the (a, b) plane; tilted ZnF4(2-) layers of corner sharing ZnF6(4-) octahedra and FPb+ layers of edge sharing FPb4(7+) tetrahedra. The structure of beta-Pb2ZnF6 was then optimized using the ab initio code WIEN2k and the calculated 67Zn EFG is in agreement with the NMR results. 19F-19F proximities and 19F-207Pb connectivities were evidenced using through-space and through-bond NMR correlation experiments, respectively, and support the proposed structure. 19F-207Pb J-coupling was also used to select fluorine resonances depending on the number of neighbouring lead ions, leading to an unambiguous assignment of the different 19F resonances.

Characterization of the Room-Temperature Structure of SnP2O7 by 31P Through-Space and Through-Bond NMR Correlation Spectroscopy

The room-temperature structure of SnP2O7 has been investigated using various one- and two-dimensional (1- and 2D) magic-angle spinning (MAS) NMR experiments. We show that 31P homonuclear through-bond and through-space correlation NMR spectroscopies allow us to discriminate between the 12 possible space group symmetries of the structure. In particular, the 31P 2D refocused INADEQUATE experiment allows us to resolve an impressive number of distinct 31P resonances, showing that the asymmetric unit contains at least 49 different P2O7 groups with two inequivalent P sites. The results suggest that the symmetry of the SnP2O7 room-temperature structure is monoclinic with space group P21 or Pc.

Molecular Recognition in the FMN – RNA Aptamer Complex

We report on a combined NMR – molecular dynamics calculation approach that has solved the solution structure of the complex of flavin mononucleotide (FMN) bound to the conserved internal loop segment of a 35 nucleotide RNA aptamer identified through in vitro selection. The FMN – RNA aptamer complex exhibits exceptionally well-resolved NMR spectra that have been assigned following application of two, three and four-dimensional heteronuclear NMR techniques on samples containing uniformly 13C, 15N-labeled RNA aptamer in the complex. The assignments were aided by a new through-bond NMR technique for assignment of guanine imino and adenine amino protons in RNA loop segments. The conserved internal loop zippers up through the formation of base-pair mismatches and a base-triple on complex formation with the isoalloxazine ring of FMN intercalating into the helix between a G·G mismatch and a G·U·A base-triple. The recognition specificity is associated with hydrogen bonding of the uracil like edge of the isoalloxazine ring of FMN to the Hoogsteen edge of an adenine at the intercalation site. There is significant overlap between the intercalated isoalloxazine ring and its adjacent base-triple platform in the complex. The remaining conserved residues in the internal loop participate in two G·A mismatches in the complex. The zippered-up internal loop and flanking stem regions form a continuous helix with a regular sugar – phosphate backbone except at a non-conserved adenine, which loops out of the helix to facilitate base-triple formation. Our solution structure of the FMN – RNA aptamer complex is to our knowledge the first structure of an RNA aptamer complex and outlines folding principles that are common to other RNA internal and hairpin loops, and molecular recognition principles common to model self-replication systems in chemical biology.