Determination of the self-diffusion coefficient of intracellular water using PGSE NMR with variable gradient pulse length.

A new pulsed-gradient spin-echo NMR protocol for assessing the local self-diffusion coefficient D(0) of water confined within living cells is proposed. Equations for the apparent mean-square displacement as a function of the effective diffusion time t(d) and the duration of the displacement-encoding gradient pulses delta are derived. The standard method of estimating D(0)—reducing t(d) until the influence of collisions between the water molecules and the plasma membrane can be neglected—often fails because of the small size of typical cells. As demonstrated here, the decrease of the apparent with increasing delta at constant t(d) can be utilized to measure D(0).