Selective Nuclear Overhauser Effect Research Articles

The calculation of nuclear overhauser effects in coupled spin systems

A theory and computational method are described for the calculation of selective nuclear Overhauser effects for scalar coupled nuclear spins. Sample calculations are included for three spins (two protons and one heteronucleus). The effect of rf power levels is described. Conclusions regarding the utility of selective nuclear Overhauser effects in structural chemistry are drawn.

Individual assignments of amide proton resonances in the proton NMR spectrum of the basic pancreatic trypsin inhibitor

Studies of proton-proton nuclear Overhauser effects were used to obtain individual assignments of 17 amide proton resonances in the 360 MHz proton nuclear magnetic resonance spectrum of the basic pancreatic trypsin inhibitor. First, optimizing the conditions for obtaining selective nuclear Overhauser effects in the presence of spin diffusion in macromolecules is discussed. Truncated driven nuclear Overhauser experiments were used to assing the amide proton resonances of the β-sheet in the inhibitor. It is suggested that these techniques could serve quite generally to obtain individual resonance assignments in β-sheet secondary structures of proteins. Combination of nuclear Overhauser studies with spin decoupling further resulted in individual assignments of the γ-methyl resonances of the two isoleucines and numerous C α and C β protons.

Pyridopyrimidines. 9. An unusual rearrangement in the 8-substituted pyrido[2,3-d]pyrimidine series. Application of the selective nuclear Overhauser effect to unambiguous proton chemical shift assignment

Pyridopyrimidines. 9. An unusual rearrangement in the 8-substituted pyrido[2,3-d]pyrimidine series. Application of the selective nuclear Overhauser effect to unambiguous proton chemical shift assignment

Pulsed FT-NMR double resonance studies of yeast tRNAPhe: specific nuclear Overhauser effects and reinterpretation of low temperature relaxation data

Cross-relaxation effects are demonstrated between the imino protons and other protons in yeast tRNAPhe and H2O. A detailed examination has been made of the observed relaxation rate of the proton resonance at 11.8 ppm from DSS as a function of the D2O content in the solvent. This result, as well as the size and number of observed nuclear Overhauser effects, suggests that dipolar magnetization transfer between solvent H2O, amino, imino, and other tRNA protons may dominate the relaxation processes of the imino protons at low temperature. At higher temperatures the observed relaxation rate is dominated by chemical exchange. The selective nuclear Overhauser effects are shown to be an important aid in resonance assignments. By these means we were able to identify tow protons from the wobble base pair GU4 at 11.8 ppm and 10.4 ppm.

NMR relaxation parameters in a two-spin system by selective nuclear overhauser effects

Relaxation rate parameters in coupled spin systems can be obtained by steady-state selective saturation experiments. The overdetermined relaxation matrix is calculated from experimental intensity changes by utilizing the concept of a generalized inverse of a singular matrix. The theory is applied to the two-spin AX system of C-13-enriched sodium formate in D 2O. The simplicity of the method and its independence of specific relaxation models and motional assumptions make this type of experiment a feasible alternative to transient methods.

Selective nuclear Overhauser effect experiments on coupled spin systems

A formalism describing selective nuclear Overhauser effect (NOE) experiments on coupled spin systems is developed for the study of relaxation processes. The formalism is completely general, and is developed in terms of the fractional intensity changes Gab,cd of various transitions ab γ relative to the irradiated line cd. The general properties of the Gab,cd are discussed. The symmetry properties of coupled spin systems can be investigated conveniently using group theoretical considerations by setting up a geometrical figure to correspond to the relaxation problem. This procedure was illustrated for weakly coupled three-spin systems, where the systematics of selective NOE experiments can be described in terms of the transformation properties of a cube. Analytical expressions for the Gab,cd were obtained for the intramolecular dipole-dipole and external random field relaxation mechanisms. These expressions provide a good approximate description even for strongly coupled systems. Relaxation analyses were performed on the ABX proton system vinyl bromide and the A2X proton system 1,1,2-trichloroethane. It was shown that the particular experiment where an outer line of the X multiplet is saturated is quite sensitive to the detailed relaxation mechanism. The remaining lines of the X multiplet directly reflect the fractional contribution of the intramolecular dipole-dipole mechanism. The results for vinyl bromide were interpreted in terms of anisotropic reorientation using an inertial model. It is suggested that the selective NOE technique can be useful when information regarding molecular conformations is required, and the conventional NOE experiments (where an entire multiplet is saturated) are difficult to perform.