Rotational diffusion measurements of suspended colloidal particles using two-dimensional exchange nuclear magnetic resonance

Abstract

Deuterium twodimensional exchange nuclear magnetic resonance by rotorsynchronized magic angle spinning J. Chem. Phys. 98, 7699 (1993); 10.1063/1.464578The determination of the reorientational angle distribution in twodimensional exchange nuclear magnetic resonance spectroscopy on powder samplesWe present here an experimental and theoretical study of the application of two-dimensional exchange nuclear magnetic resonance spectroscopy ͑NMR͒ to the investigation of the rotational diffusion of colloidal particles. The theoretical discussion includes the nature of the NMR frequency time-correlation function where the NMR interaction is represented by the chemical shift anisotropy ͑CSA͒. Time-correlation functions for the isotropic rotational diffusion of a suspension of colloidal particles containing single and multiple sites are derived in addition to time-correlation functions for the rotational diffusion of a suspension of symmetric top particles containing an isotropic distribution of a single CSA interaction. Simulations of two-dimensional exchange spectra for particles undergoing isotropic rotational diffusion are presented. We performed two-dimensional exchange NMR experiments on a colloidal suspension of spherical poly͑methyl methacrylate͒ ͑PMMA͒ particles which were synthesized with a 20% enrichment in 13 C at the carbonyl site. Rotational diffusion time-correlation functions determined from the experimental exchange spectra are consistent with the composition of the colloidal suspension. Detailed explanations of the syntheses of the enriched methyl 13 C-͑carbonyl͒-methacrylate monomer and the small quantities of 20% enriched 13 C-͑carbonyl͒-poly͑methyl methacrylate͒ microspheres used for this study are presented.

Direct Determination of Motional Correlation Times by 1D MAS and 2D Exchange NMR Techniques

“…The time scale can be quantified directly from the experimental spectra by computing the rise of the ratios of off-diagonal intensity to overall intensity R 2D (t m ) from each individual spectrum (in slices where diagonal and off-diagonal intensities are well separated), by calculating the time-dependent second-order orientational autocorrelation function C 2 (t m ) ϭ ͗(0)(t m )͘ ϭ ͗ 1 2 ͘(t m ) ϭ ͐d 1 ͐d 2 S( 1 , 2 ; t m ) 1 2 (1,16), or by following the loss of correlation from the decrease of the echo intensity of the 2D exchange time-domain signal for selected values of the evolution time t 1 as a function of the mixing time (17). The latter provides complementary information to the 2D exchange experiment, because the echo intensity is related to the diagonal fraction of the 2D exchange spectrum and can be used to probe the decrease of the spectral diagonal in favor of off-diagonal exchange intensity.…”

Measurement of the Lateral Diffusion of Dipalmitoylphosphatidylcholine Adsorbed on Silica Beads in the Absence and Presence of Melittin: A 31P Two-Dimensional Exchange Solid-State NMR Study

“…A method for determining the isotropic rotational diffusion from 2D NMR exchange spectra has been developed by Schmidt-Rohr and Spiess (1994) and used by Barrall et al (1995) on polymers. This method is close to the intuitive method elaborated by and is based on the calculation of the time-dependent orientational autocorrelation function of order 2, C 2 (t m ).…”

“…In the present study, we have used the above model to determine the lateral diffusion constant of dipalmitoylphosphatidylcholine (DPPC) deposited on silica beads by a 2D 31 P NMR approach similar to the one used by Barrall et al (1995) for the determination of rotational diffusion in polymers. One of the goals of our study is to determine whether the beads alter the diffusion of lipids and therefore to verify whether the SSV model is a good system for the study of lateral diffusion of lipids.…”

Self-diffusion in sheared suspensions by dynamic simulation

“…Short-time rotational diffusivities at equilibrium for all volume fractions were determined by Stokesian Dynamics simulations by Phillips, Brady & Bossis (1988). Many advances have been made recently in experimentally measuring rotational self-diffusion using techniques ranging from dynamic depolarized light scattering (Degiorgio et al 1995), forced Rayleigh scattering (Kanetakis & Sillescu 1996), and nuclear magnetic resonance spectroscopy (Barrall et al 1996;Kanetakis, Tölle & Sillescu 1997). To date, work has been performed at equilibrium with extensive focus on the behaviour of the short-time rotational self-diffusivity over a wide range of volume fraction, φ.…”