Arthur G. Palmer

Sensitivity improvement in proton-detected two-dimensional heteronuclear correlation NMR spectroscopy

Abstract The sensitivity of proton-detected two-dimensional heteronuclear correlation NMR spectroscopy can be increased by as much as a factor of √2 relative to that of the conventional methods, for heteronuclei with a single attached proton. The enhanced sensitivity is obtained by refocusing and detecting two orthogonal in-phase proton magnetization components, rather than the single component recorded conventionally. The two magnetization components are deconvoluted to produce two pure-phase spectra that are added together to produce a spectrum with an enhanced signal-to-noise ratio. Methods for improving the sensitivity of the main classes of heteronuclear correlation experiments are presented and the effect of relaxation during the new experiments on the sensitivity enhancement is discussed. The new methods are demonstrated by comparing conventional and sensitivity-enhanced 1H-15N heteronuclear correlation spectra of bovine pancreatic trypsin inhibitor at 15N natural abundance.

Suppression of the effects of cross-correlation between dipolar and anisotropic chemical shift relaxation mechanisms in the measurement of spin-spin relaxation rates

Cross correlation between dipolar and anisotropic chemical shift relaxation mechanisms complicates measurements of heteronuclear spin-spin relaxation rate constants by the Carr-Purcell-Meiboom-Gill (CPMG) technique if the magnitudes of the chemical shift anisotropy and the dipolar interaction are comparable. Experimental schemes are described that attenuate the effects of cross correlation and permit accurate measurements of spin-spin relaxation rate constants for heteronuclei with significant chemical shift anisotropies. The theoretical analysis is confirmed by measurements of 15N and 13C spin-spin relaxation in a peptide. Application of 180° pulses to the protons directly attached to the heteronuclei in synchrony with the even echoes of the heteronuclear spins yields more accurate results than continuous irradiation of the protons with a composite pulse decoupling sequence or application of a single 180° pulse to the protons in the middle of the CPMG pulse train.

Measurement of relaxation time constants for methyl groups by proton-detected heteronuclear NMR spectroscopy

Abstract Experimental schemes are described that allow proton-detected NMR spectroscopy to measure accurately 13 C spin—lattice relaxation time constants of methyl groups. By using magic angle pulses in DEPT-base sequences, or analogously tuned delays in INEPT-based sequences, contributions to the observed NMR signal are eliminated that would otherwise complicate the measurement of the desired time constants. Experimental verification of the proposed techniques is provided by measurements on sodium acetate and on a peptide.

Improved resolution in three-dimensional constant-time triple resonance NMR spectroscopy of proteins.

SummaryTwo new protocols for the three-dimensional, triple resonance, constant-time HCA(CO)N NMR experiment are presented that significantly increase the experimental resolution attainable in the Cα frequency dimension. Experimental verification of the new experiments is provided by spectra of the IIA domain of glucose permease fromBacillus subtilis.