Biomedical subjects

A Novoselsky

Publications and source records attributed to A Novoselsky.

13 recordsLinked to original sources

PubMed2001

Effect of albumin on the kinetics of ascorbate oxidation.

The fluorescence intensity of the fluorophore in dansyl piperidine-nitroxide is intramolecularly quenched by the nitroxyl fragment. Therefore, the oxidation of ascorbic acid by the fluorophore-nitroxide (FN) probe can be monitored by two independent methods: steady-state fluorescence and electron paramagnetic resonance. Bovine serum albumin (BSA) affects the rate of this reaction. The influence of BSA on the rate is attributed to the adsorption of both ascorbate and the probe to BSA. Adsorption of ascorbate to BSA is confirmed by NMR relaxation experiments. The spatial distribution of the molecules on the BSA surface changes the availability of ascorbate and FN to each other. The results also point out that, in the presence of BSA, the autoxidation of ascorbate is significantly slowed down. The effect is studied at different pH values and explained in terms of the electrostatic interaction between the ascorbate anion and the BSA molecule.

Adsorption↗

PubMed2000

Eight-membered-ring solid-state conformational interconversion via the atom-flip mechanism, a CPMAS 13C NMR and crystallographic stereochemical study.

Nefopam methohalide (chloride, bromide, and iodide) medium-ring quaternary ammonium salts of the non-narcotic analgesic tertiary amine drug give crystals belonging to the identical monoclinic P2(1)/c space group, and all of these pseudopolymorphs exhibit the same packing motif. A singular boat-boat (BB) more compact conformation is observed in the nefopam methochloride crystal. Larger halide anions (bromide and iodide) increase the void distance between the 2(1)-screw axis related adjacent ammonium cations to accommodate void-size dependent equilibrium quantities of the twist-chair-chair (TCC) more extended conformation. The BB:TCC occupancy factors are 0.961(5):0.039(5) [193 K], 0.780(5):0.220(5) [293 K], and 0.755(6):0.245(6) [343 K] for the methobromide crystal, while values of 0.657(5):0.343(5) [193 K] and 0.592(7):0.408(7) [293 K] were measured for the methiodide. Above a minimum of ca. 2.53 A, the occupancy factors were found to be linearly correlated to the intermolecular (TCC)Me(eq)-H...H-Me(ax)(TCC) distance between abutting methyl group protons in 2(1)-screw axis related neighbors. Temperature-dependent occupancy factors for the two conformers are interpreted in terms of a medium ring atom-flip facile interconversion between the two low energy conformations in crystals containing the appropriate size intercation void. A BB/TCC atom-flip interconversion in the methochloride unit cell would result in van der Waals interactions due to an estimated 2.31 A close intermolecular (TCC)Me(eq)-H...H-Me(ax)(TCC) distance between adjacent 2(1)-screw symmetry ammonium cations. The 203 K low-temperature CPMAS 13C NMR spectrum of the methiodide salt showed two slow exchange limit (SEL) delta 57.91 [BB] and delta 63.10 [TCC] OCH2CH2N peaks. A variable low-temperature CPMAS NMR investigation of the solid methiodide showed complex dynamic behavior that cannot be interpreted solely on the basis of an atom-flip conformational interconversion. Local magnetic fields from the gem-dimethyl rapidly rotating proton magnetic dipoles provide a distance-dependent T1 relaxation mechanism for neighboring carbons in the solid-state.

Analgesics, Non-Narcotic↗

PubMed1999

NMR studies of electrostatic potential distribution around biologically important molecules.

A new experimental approach has been developed to study the distribution of local electrostatic potential around specific protons in biologically important molecules. The approach is the development of a method denoted as "spin label/spin probe," which was proposed by one of us (. Mol. Biol. 6:498-507). The proposed method is based upon the quantitative measurement of the contribution of differently charged nitroxide probes to the spin lattice relaxation rate (1/T1) of protons in the molecule of interest, followed by calculation of local electrostatic potential using the classical Debye equation. In parallel, the theoretical calculation of potential distribution with the use of the MacSpartan Plus 1.0 program has been performed. Application of the method to solutions of simple organic molecules (aliphatic and aromatic alcohols, aliphatic carboxylates (propionate anion), and protonated ethyl amine and imidazole) allowed us to estimate the effective potential around the molecules under investigation. These were found to be in good agreement with theoretically expected values. This technique was then applied to zwitterionic amino acids bearing neutral and charged side chains (glycine, lysine, histidine, and aspartic acid). The reliability of the general approach is proved by the data presented in this paper. Application of this new methodology can afford insight into the biochemical significance of electrostatic effects in biological systems.

Alcohols↗

PubMed1998

An alternative technique for mandibular advancement prosthesis fabrication.

One of the conservative and successful modalities of treatment for obstructive sleep apnea is the mandibular advancement prosthesis. This prosthesis engages teeth on both dental arches for retention and stability. This article describes a technique that allows the fabrication of such a prosthesis in one piece and in a single laboratory step. This may be beneficial in reducing the laboratory time required for fabrication of such a prosthesis.

Dental Prosthesis Design↗

PubMed1996

Maxillary definitive obturators: rationale of design.

Maxillary definitive obturators are usually fabricated for patients who have an acquired defect. The obturators help patients with speech, swallowing, mastication, esthetics and psychological well-being. The main goals in restoring a maxillary defect with a completely edentulous or partially dentate obturator are to provide adequate retention, increased stability and strong vertical support. This article addresses the step-by-step fabrication of a maxillary obturator that meets these goals.

Dental Implantation, Endosseous↗

PubMed1995