Improved applicability of DOSY experiments by high resolution probes combined with gradient amplifiers of diffusion units

Abstract

Short relaxation times and small diffusion coefficients often impede reliable diffusion experiments due to insufficient signal to noise ratios, especially in low temperature studies, where in the case of small diffusion coefficients in combination with very short T2 times and substantial convection, double-stimulated-echo experiments are required as last resort of convection-compensating DOSY pulse sequences. Therefore, the combination of a strong gradient amplifier of a diffusion unit with Z-gradient high resolution probes is tested for low temperature applications to combine the advantages of high 1H resolution, flexible temperature, and multinuclear applications with short gradient durations and diffusion delay. The experimental spectra on phosphoramidite ligands and phosphoramidite-copper complexes show that signal to noise improvements up to 176% were achieved despite longer eddy current delays and increased noise levels. Calculational estimations of the enhancement factors predict special benefits for systems with short transversal relaxation times and small diffusion coefficients and promise even higher enhancement factors for noise level optimized combinations. In addition, an easy way is presented to find fast and effectively relaxation optimized DOSY parameters for the convection-compensated double-stimulated-echo pulse sequence of Jerschow and Müller.