Electric field effects on one-bond indirect spin-spin coupling constants and possible biomolecular perspectives

Revisiting the influence of pH on 1JCαH and chemical shifts of glycine and alanine short oligopeptides

The pH dependence of several NMR parameters of glycine and alanine short oligopeptides has been reported previously in different studies. Here we have thoroughly examined, summarized and demonstrated the dependences of 1H, 13C and 15N chemical shifts and protonation states of amino acids using two-dimensional NMR experiments. Nevertheless, 1JCαH one bond spin-spin coupling constants are more informative and convenient for determination of the position and protonation state of glycine and alanine residue in the oligopeptide chain. In particular, for various oligopeptides (up to six residues), it was shown that the pH dependence of 1JCαH of N-terminal glycine and alanine residues is larger than that of C-terminal groups, and in backbone residues, it is not influenced by pH and only slightly depends on the position of the amino acid residue in the chain.

Pressure response of amide one-bond J-couplings in model peptides and proteins

The pressure dependence of the one-bond indirect spin-spin coupling constants (1)J(N-H) was studied in the protected tetrapeptides Ac-Gly-Gly-Xxx-Ala-NH2 (with Xxx being one of the 20 proteinogenic amino acids). The response of the (1)J(N-H) coupling constants is amino acid type specific, with an average increase of its magnitude by 0.6 Hz at 200 MPa. The variance of the pressure response is rather large, the largest pressure effect is observed for asparagine where the coupling constant becomes more negative by -2.9 Hz at 200 MPa. The size of the J-coupling constant at high pressure is positively correlated with its low pressure value and the β-propensity, and negatively correlated with the amide proton shift and the first order nitrogen pressure coefficient and the electrostatic solvation free energy.

15N NMR of 1,4-dihydropyridine derivatives

In this article, we describe the characteristic (15)N and (1)HN NMR chemical shifts and (1)J((15)N-(1)H) coupling constants of various symmetrically and unsymmetrically substituted 1,4-dihydropyridine derivatives. The NMR chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as character and position of the substituent in heterocycle, N-alkyl substitution, nitrogen lone pair delocalization within the conjugated system, and steric effects.

The coupling constant polarizability and hyperpolarizabilty of 1J(NH) in N-methylacetamide, and its application for the multipole spin-spin coupling constant polarizability/reaction field approach to solvation

We present a benchmark study of a combined multipole spin-spin coupling constant (SSCC) polarizability/reaction field (MJP/RF) approach to the calculation of both specific and bulk solvation effects on SSCCs of solvated molecules. The MJP/RF scheme is defined by an expansion of the SSCCs of the solvated molecule in terms of coupling constant dipole and quadrupole polarizabilities and hyperpolarizabilities derived from single molecule ab initio calculations. The solvent electric field and electric field gradient are calculated based on data derived from molecular dynamics (MD) simulations thereby accounting for solute-solvent dynamical effects. The MJP/RF method is benchmarked against polarizable QM/MM calculations for the one-bond N-H coupling constant in N-methylacetamide. The best agreement between the MJP/RF and QM/MM approaches is found by truncating the electric field expansion in the MJP/RF approach at the linear electric field level. In addition, we investigate the sensitivity of the results due to the choice of one-electron basis set in the ab initio calculations of the coupling constant (hyper-)polarizabilities and find that they are affected by the basis set in a way similar to the coupling constants themselves.

Radiofrequency quadrupolar NMR stark spectroscopy: steady state response calibration and tensorial mapping

Radiofrequency electric (E) fields oscillating at twice the usual NMR frequency (2ω(0)) can induce double-quantum transitions in quadrupolar nuclei, an NMR Stark effect. Characterization of such is of interest to aid understanding of electrostatic effects in NMR spectra. Calibration of Stark responses to an applied electric field may also be used to assess native fields within molecules and materials. We present high-field (14.1 T), room-temperature NMR experiments to calibrate the 2ω(0) Stark response in crystalline GaAs. This system presents an important test of current techniques and conditions, as historical studies at low field (500-900 mT) and low temperature (77 K) provide a basis for comparison. Our measurements of steady state response reveal the quadrupolar Stark tuning rate for (69)Ga in this material. The value, β(Q) = (11.5 ± 0.1) × 10(12) m(-1), is 3.6 times larger than the most-reliable prior result. In the process, we also uncovered a previously unobserved double-quantum steady state coherence. It appears as a completely separable dispersive signal component in quadrature-detected presaturation spectra versus offset from 2ω(0). The new component may eventually afford an independent route to calibrating β(Q). Finally, we demonstrated exceptional agreement with theory of the orientation-dependent Stark response for rotation of the sample relative to B(0) over a range of 90° and for E-field amplitudes from 30-180 V/cm.

15N-1H scalar coupling perturbation: an additional probe for measuring structural changes due to ligand binding

Chemical shift perturbation mapping of backbone amides is one of the most widely employed techniques in biomolecular NMR, providing residue-by-residue information on interaction interfaces, ligand binding, and chemical modification sites, even for samples where poor solubility, short lifetime, or large size precludes more sophisticated experimental approaches. Significant changes can also occur in the amide one-bond (15)N-(1)H scalar coupling constants for glutamine binding protein (GlnBP) due to ligand binding. Like chemical shift perturbations, large changes (>1 Hz) are seen near the site of glutamine binding, though perturbations also occur distant to the site. The coupling constant perturbations correlate with significant structural changes, especially changes in backbone hydrogen bonding. Thus, amide scalar coupling perturbation can serve as an adjunct to chemical shift perturbation, providing additional information on both short-range and longer-range, allosteric structural changes.