15N NMR study of a mixture of uniformly labeled tRNAs

15N NMR spectra were taken of 15N-enriched tRNA extracted from bakers yeast; ammonium sulfate was used as a nitrogen source. The increase in the degree of denaturation of tRNA, which occurs with increase in temperature from 30 degrees C to 70 degrees C, resulted in no large changes in 15N chemical shifts at acidic and neutral pH but quite pronounced changes in proton-15N nuclear Overhauser effects

D<i>i</i>CE: Diastereomeric in Silico Chiral Elucidation, Expanded DP4 Probability Theory Method for Diastereomer and Structural Assignment

NMR chemical shift prediction at the B3LYP/cc-pVDZ level of theory was used to develop a highly accurate probability theory algorithm for the determination of the stereochemistry of diastereomers as well as the regiochemistry. DFT-GIAO calculations were performed for each conformer using geometry optimization and a CPCM solvent model. Boltzmann averaged shielding constants were converted to chemical shifts for ¹H and ¹³C, using the generalized linear scaling terms determined in four different solvents for ¹H and ¹³C and extended to ¹⁵N in DMSO. The probability theory algorithm, D<i>i</i>CE, was based on the DP4 method and developed for ¹H, ¹³C, and ¹⁵N NMR using individual and combined probability data. The chemical shift calculation errors were fitted to a Student’s <i>t</i>-distribution for ¹H and ¹³C and a normal distribution for ¹⁵N. The application yielded a high accuracy for structural assignment with a low computational cost

Studies of tautomers and protonation of adenine and its derivatives by nitrogen-15 nuclear magnetic resonance spectroscopy

High-resolution nitrogen-15 NMR spectra of adenine have been obtained both at the S-adenosylmethionine level and for a uniformly enriched sample prepared from S-adenosylmethionine isolated from yeast grown with ^(15)NH_4CI as the principal nitrogen source. Specific ^(15)N labeling at N1, N3, N6’, N7, and N9 provided unequivocal assignments of the chemical shifts as well as elucidation of the position of the tautomeric equilibrium. For comparison, the nitrogen resonances of several adenine derivatives were determined at the natural-abundance level. The protonation sites of many of these substances were determined from the effect of pH on the nitrogen chemical shifts. Both adenine and its conjugate acid clearly exist as the N9-H tautomers in aqueous solution. Conversion of adenine to its conjugate base (pK, ~ 10) results in a 56 ppm downfield shift of the N9 resonance

Development of a ¹³C NMR Chemical Shift Prediction Procedure Using B3LYP/cc-pVDZ and Empirically Derived Systematic Error Correction Terms: A Computational Small Molecule Structure Elucidation Method

An accurate and efficient procedure was developed for performing ¹³C NMR chemical shift calculations employing density functional theory with the gauge invariant atomic orbitals (DFT-GIAO). Benchmarking analysis was carried out, incorporating several density functionals and basis sets commonly used for prediction of ¹³C NMR chemical shifts, from which the B3LYP/cc-pVDZ level of theory was found to provide accurate results at low computational cost. Statistical analyses from a large data set of ¹³C NMR chemical shifts in DMSO are presented with TMS as the calculated reference and with empirical scaling parameters obtained from a linear regression analysis. Systematic errors were observed locally for key functional groups and carbon types, and correction factors were determined. The application of this process and associated correction factors enabled assignment of the correct structures of therapeutically relevant compounds in cases where experimental data yielded inconclusive or ambiguous results. Overall, the use of B3LYP/cc-pVDZ with linear scaling and correction terms affords a powerful and efficient tool for structure elucidation

Residues 21-30 within the extracellular N-terminal region of the C5a receptor represent a binding domain for the C5a anaphylatoxin

UI - 98221176NRC publication: Ye