Gy. Batta

The role of mixing time in 2D heteronuclear NOE experiments

Heteronuclear NOE experiments are promising for the determination of carbonproton distances in organic molecules in solution. A heteronuclear 2D NOE experiment (I, 2) has recently been described for the study of heteronuclear dipole-dipole interactions. In those preliminary reports it is generally accepted that the optimal value of the mixing time (T,,,~) in the pulse sequence depends only on the average proton relaxation time r,. In this note we show that to obtain cross peaks of significant intensities choice of mixing time needs more care. We have verified that the optimum of mixing time depends as well on the pertinent relaxation times Ti of carbon nuclei. To calculate the optimum mixing time (TV. m) we used the two-spin approximation AX, A = ‘H and X = 13C. The time dependence of the peaks in a two-dimensional heteronuclear NOE spectrum can be expressed in a matrix format, similar to the homonuclear case (3-5) add btiR~m)lid ill

Easy implementation of homonuclear 1d correlation nmr techniques. Application to oligosaccharioes.

Abstract A combination of selective excitation by DANTE pulse train and chemical shift selective filtering (CSSF) allows one to record clean 1D COSY, RELAY and NOE spectra.

Strong coupling effects and their suppression in two-dimensional heteronuclear NOE experiments

Abstract Strong coupling effects in two-dimensional heteronuclear NOE spectroscopy are analyzed experimentally. A simple method is proposed for suppression of spurious “ghost” peaks resulting from second-order effects. The disadvantage of this method is that it decreases the sensitivity.

One-dimensional heteronuclear chemical-shift correlation using chemical-shift-selective filters

Abstract The technique of a chemical-shift-selective filter has been applied to the heteronuclear correlation experiment, resulting in effective selective one-dimensional correlations. The proposed method has several distinct advantages over the more common selective population-transfer techniques: a chemical-shift resolution of only a few hertz in the 1H spectrum is needed to achieve an unambiguous correlation, practically no knowledge of 1J(C, H) is required, and finally only nonselective proton pulses are used during the course of the experiment. When applied to CH, CH3 or equivalent CH2 protons this technique gives a level of sensitivity similar to that achieved in ordinary INEPT experiments. Application to nonequivalent CH2 protons is discussed in detail and a special experiment is proposed for this case. The concept of a chemical-shift-selective filter has also been applied to proton-proton-carbon relay experiments.

Indirect, Negative Heteronuclear Overhauser Effect Detected in a Steady-State, Selective 13C-{1H} NOE Experiment at Natural Abundance

It has recently been shown that both selective 13C-{1H} NOE measurements (1–10) and non-selective two-dimensional (2D) NOE (11–13) (cross-relaxation) spectroscopy are promising techniques for the determination of carbon-proton distances in organic molecules in solution.

Simple difference experiments for detection of cross-correlation

Cross-correlation of dipole-dipole interactions in methyl and methylene groups is measured using simple 1D difference experiments designed to monitor the appearance of longitudinal three-spin order during a recovery period. The advantage of the approach is that it is not sensitive to the spread of one-bond proton-carbon couplings. Furthermore, both methyl and methylene groups can be studied simultaneously.

Backbone dynamics and amide proton exchange at the two sides of the eremomycin dimer by 15N NMR

15 N-labelling of the glycopeptide antibiotic eremomycin has made possible the dynamic characterization of the two sides of the dimer; in the presence of acetate anion the backbone amides are dynamically equivalent and the fastest amide proton exchange rate was found at the heart of the binding pocket.

A Comparative Study on Liquid State CSA Methods

There is a gaining interest in obtaining chemical shift anisotropy data of molecules in solution. Relaxation interferences between two different second rank tensorial relaxation mechanisms are manifested in differential multiplet relaxation [1] or line broadening [2], and this effect can be put to good use in structural and dynamics studies. We propose enhanced CSA/DD cross-correlated relaxation experiments for the measurement of chemical shift anisotropy in solution and demonstrate that their performance can be improved by spin-lock (SL) and/or field gradient pulses. Though the measured effects may be as small as 0.002 s−1, the methods are often suitable at natural isotopic abundance. 1H and heteronucleus CSA data were measured for triphenyl-silane (TPSi) (29Si), cyclosporin A (15N) and α-D-Trehalose, a symmetric disaccharide of glucose, (13C). 1D data are evaluated both with the initial rate and the Redfield relaxation matrix approach providing cross-correlated relaxation rates and CSA values. 1D experiments and the 2D unbiased method (2D in the sense of magnetization modes too) were compared for our model compounds. The comparison gives experimental evidence on the equivalence of the 1 and 2D methods within the limits of two-spin approach. For the easy application of the 2D method double G-BIRD, X-filtered 1H-1H NOESY is suggested. It is shown that transversal and rotating frame (ortho-ROESY) experiments provide comparable 13C-CSA effects, and both methods are suitable for macromolecules. Recent studies suggest that simultaneous use of longitudinal/transversal methods may yield additional dynamics/exchange information for proteins [3].