Dynamics of Zeeman and dipolar states in the spin locking in a liquid entrapped in nano-cavities: Application to study of biological systems

Determining the internal orientation, degree of ordering, and volume of elongated nanocavities by NMR: Application to studies of plant stem

This study investigates the fibril nanostructure of fresh celery samples by modeling the anisotropic behavior of the transverse relaxation time (T₂) in nuclear magnetic resonance (NMR). Experimental results are interpreted within the framework of a previously developed theory, which was successfully used to model the nanostructures of several biological tissues as a set of water filled nanocavities, hence explaining the anisotropy the T₂ relaxation time in vivo. An important feature of this theory is to determine the degree of orientational ordering of the nanocavities, their characteristic volume, and their average direction with respect to the macroscopic sample. Results exhibit good agreement between theory and experimental data, which are, moreover, supported by optical microscopic resolution. The quantitative NMR approach presented herein can be potentially used to determine the internal ordering of biological tissues noninvasively.

Anisotropy of Transverse Spin Relaxation in H2O-D2O Liquid Entrapped in Nanocavities: Application to Studies of Connective Tissues

The spin-spin relaxation in connective tissues is simulated using a model in which a connective tissue is represented by a set of nanocavities containing H₂O-D₂O liquid. Collagen fibrils in connective tissues form ordered hierarchical long structures of hydrated nano-cavities with characteristic diameter from 1 nm to several tens of nanometers and length of about 100 nm. We consider influence of the restricted Brownian motion of molecules inside a nano-cavity on spin-spin relaxation. The analytical expression for the transverse time T ₂ for H₂O-D₂O liquid in contained a nanocavity was obtained. We show that the angular dependence of the transverse relaxation rate does not depend on the concentration of D₂O. The theoretical results could explain the experimentally observed dependence of the degree of deuteration on the relaxation time T ₂. Accounting the orientation distribution of the nanocavities well agreement with the experimental dependence of the relaxation for articular cartilage on the deuteration degree was obtained.

Anisotropy of transverse and longitudinal relaxations in liquids entrapped in nano- and micro-cavities of a plant stem

We studied the anisotropy of ¹H NMR spin-lattice and spin-spin relaxations in a fresh celery stem experimentally and modeled the sample theoretically as the water-containing nano- and micro-cavities. The angular dependence of the spin-lattice and the spin-spin relaxation times was obtained, which clearly shows the presence of water-filled nano- and micro-cavities in the celery stem, which have elongated shapes and are related to non-spherical vascular cells in the stem. To explain the experimental data, we applied the relaxation theory developed by us and used previously to interpret similar effects in liquids in nanocavities located in biological tissues such as cartilages and tendons. Good agreement between the experimental data and theoretical results was obtained by adjusting the fitting parameters. The obtained values of standard deviations (0.33 for the mean polar angle and 0.1 for the mean azimuthal angle) indicate a noticeable ordering of the water-filled nano- and micro-cavities in the celery stem. Our approach allows the use of the NMR technique to experimentally determine the order parameters of the microscopic vascular structures in plants.