Biomedical subjects

Konstantin I Momot

Publications and source records attributed to Konstantin I Momot.

4 recordsLinked to original sources

PubMed2005

Convection-compensating diffusion experiments with phase-sensitive double-quantum filtering.

We present a design scheme for phase-sensitive, convection-compensating diffusion experiments with gradient-selected homonuclear double-quantum filtering. The scheme consists of three blocks: a 1/2J evolution period during which antiphase single-quantum coherences are created; a period of double-quantum evolution; and another 1/2J period, during which antiphase single-quantum coherences are converted back into an in-phase state. A single coherence transfer pathway is selected using an asymmetric set of gradient pulses, and both diffusion sensitization and convection compensation are built into the gradient coherence transfer pathway selection. Double-quantum filtering can be used either for solvent suppression or spectral editing, and we demonstrate examples of both applications. The new experiment performs well in the absence of a field-frequency lock and does not require magnitude Fourier transformation. The proposed scheme may offer advantages in diffusion measurements of spectrally crowded systems, particularly small molecules solubilized in colloidal solutions or bound to macromolecules.

Carbon Tetrachloride↗

PubMed2005

Acquisition of pure-phase diffusion spectra using oscillating-gradient spin echo.

Oscillating-gradient spin echo (OGSE) diffusion experiments have long been used to measure the short-time apparent diffusion coefficient, D(app)(t), in the presence of restricted diffusion, as well as the spectrum of the slow-motion velocity autocorrelation function. In this work, we focus on two previously unexplored aspects of OGSE experiments: convection compensation and acquisition of pure-phase diffusion spectra in the presence of homonuclear scalar couplings. We demonstrate that convection compensation afforded by single-echo OGSE compares well with that in double-echo convection-compensated PGSE experiments. We also show that, in the presence of homonuclear scalar couplings, setting the OGSE echo time to 1/2J enables acquisition of pure-phase diffusion spectra and yields more reliable D estimates than mixed-phase PGSE or OGSE spectra. Pure-phase OGSE acquisition is also compatible with measurements of the apparent diffusion coefficient at an arbitrary diffusion time. These features of OGSE can be valuable in diffusion measurements of scalar-coupled small-molecule probes in cellular and other heterogeneous systems.

Algorithms↗

PubMed2004

Enhancement of Na+ diffusion in a bicontinuous cubic phase by the ionophore monensin.

Pulsed field gradient spin-echo NMR diffusion and relaxation measurements were used to investigate how the Na+ ionophore monensin affected the dynamics of sodium ions in a Myverol 18-99/saline bicontinuous Ia3d cubic phase (BCP). The monensin Na+ binding number was estimated from 23Na line widths to be between 3 and 6. The dependence of the apparent Na+ diffusion coefficient on the concentration of monensin revealed monensin-induced Na+ transport. At high monensin concentrations, the enhancement of D(Na+) was offset by Na+-monensin binding. The greatest enhancement was measured at short diffusion times (delta < or = 5 ms), which we explain in terms of the bicontinuous topology of the cubic phase and a combination of tortuosity and bilayer permeability effects. We also propose numerical simulations which would enable the separation of the two effects. To our knowledge, this is the first study of ionophore-mediated cation diffusion in a bicontinuous cubic phase. The approach could be used to study the dynamics of hydrophilic species in the aqueous channels of BCPs and similar structures, as well as to measure the ion-transporting efficiency of ionophores.

Diffusion↗

PubMed2004

Convection-compensating PGSE experiment incorporating excitation-sculpting water suppression (CONVEX).

We present a new diffusion experiment which provides simultaneous suppression of an on-resonance solvent peak and compensation for convection. The experiment, which we name CONVEX, exploits similarities between two functionally different pulse sequences to enable the same sequence to be used simultaneously for two different purposes. The CONVEX pulse sequence combines a double-echo PGSE with double excitation-sculpting water suppression, using unequal gradient pulse-pair amplitudes (g1 and g2) and unequal diffusion intervals (Delta1 and Delta2). Convection compensation is achieved by setting g1:g2 = Delta2:Delta1. The new experiment provides the spectral quality, flat baseline, and water-suppression power characteristic of excitation-sculpting experiments, combined with excellent compensation for convection. The resulting Stejskal-Tanner plots are linear over a greater range of signal attenuation than in the absence of water suppression. Possible applications include protein NMR; NMR of cellular or colloidal systems; and the monitoring of technological processes.

Journal Article↗