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Methods for measuring longitudinal relaxation times of protons in heavily overlapped [sup 1]H NMR spectra are introduced and exemplified using a solution of cholesteryl acetate. The methods are based on 1-dimensional and 2-dimensional maximum quantum NMR spectroscopy (MAXY), which makes possible the selective detection of CH, CH[sub 2] and CH[sub 3] [sup 1]H NMR resonances. A modification of the BIRD pulse sequence to achieve selective inversion of protons bonded to either [sup 12]C or [sup 13]C is given. The approach should find application in studies of molecular dynamics where isotopic enrichment is not possible and the level of available sample dictates the use of [sup 1]H NMR spectroscopy. [ABSTRACT FROM AUTHOR]

NMR spectroscopy can be used to measure molecular self-diffusion coefficients using a modified spin-echo pulse sequence known as the longitudinal eddy current delay (LED) method which incorporates pulsed magnetic field gradients. The effect of such gradients on multiple quantum coherences is investigated and shown to be of benefit for the measurement of diffusion coefficients using modest gradient strengths. The multiple quantum coherences involved in the spin operator 8Ix Iy Iy Sy of a weakly coupled SI spin system (13CH at natural abundance, in alanine in this case) were studied. The multiple quantum coherences included the quadruple-quantum (QQ) order of (3 I + S ), double-quantum (DQ) order of (3 I - S ) and (3 I + S ), and zero-quantum (ZQ) order of ( I - S ) with effective magnetogyric ratios of (3gammaH + gammaC), (3gammaH-gammaC), (gammaH + gammaC) and (gammaH-gammaC) respectively. The results show that the use of higher level quantum coherences for diffusion coefficient measurement can have the practical effect of significantly enhancing the gradient strength and this is important for slowly diffusing species. [ABSTRACT FROM AUTHOR]