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Biomedical subjects

R G Bryant

Publications and source records attributed to R G Bryant.

100 records · Page 6Linked to original sources
PubMed1969

Study of carbonic anhydrase using perturbed angular correlations of gamma radiation.

The angular correlation of the 150-247 kev gamma-ray cascade of (111m)Cd is strongly perturbed when this nucleus is bound to the enzyme carbonic anhydrase. A comparison of the perturbed angular correlation for the apoenzyme with that for native carbonic anhydrase confirms that the (111m)Cd binds at the active region of the enzyme. These results provide good evidence that the perturbed angular correlation reflects the effective molecular rotational correlation time at the metal binding site, and that this radioactive nucleus can be used as a rotational tracer to label biological macromolecules. The qualitative dependence of the perturbed angular correlation of the (111m)Cd cascade on the molecular rotational correlation time at the metal binding site is illustrated using a cadmium-complex solution at various temperatures.

Binding Sites↗
PubMedDate not supplied

New ways of probing surface nuclear relaxation and microdynamics of water and oil in porous media.

The microdynamics of water and oil in macroporous media with SiO2 or CaCO3 surfaces has been probed at various temperatures by magnetic field-cycling measurements of spin-lattice relaxation rates. These measurements and an original theory of surface diffusion allow us to obtain surface dynamical parameters such as surface correlation times, residence times and diffusion coefficients. A coefficient of affinity of the liquids for the pore surface is deduced.

Calcium Carbonate↗
PubMedDate not supplied

Proton magnetic relaxation of manganese (II) tetrakis(4-sulfophenyl)porphine ion in water.

Water proton nuclear magnetic spin-lattice relaxation rates are reported as a function of magnetic field strength for aqueous solutions of manganese tetrakis(4-sulfophenyl)porphine complexes. The manganese(III) complex displays relaxation that is remarkably independent of temperature at low magnetic field and a magnetic field dependence that is characteristic of the electron spin relaxation rates, making a contribution to the correlation time that dominates the electron-nuclear coupling. The manganese(II) complex is much more effective in relaxing water protons, but the usual models of first coordination sphere and outer-sphere relaxation fail to account for the magnitude and the magnetic field dependence of the relaxation rates. The data suggest that the delocalization of the electron density into the ligand system provides an increase in the effectiveness of what may be called the outer-sphere paths for water proton relaxation.

Chemical Phenomena↗
PubMedDate not supplied

Nuclear magnetic spin-lattice relaxation of water protons caused by metal cage compounds.

The nuclear magnetic spin-lattice relaxation rates of water protons are reported for solutions of manganese(II), copper(II), and chromium(III) cage complexes of the sarcophagine type. As simple aqueous solutions, the complexes are only modest magnetic relaxation agents, presumably because they lack protons on atoms in the first-coordination-sphere protons that are sufficiently labile to mix the large relaxation rate at the metal complex with that of the bulk solvent. The relaxation is approximately modeled using spectral density functions derived for translational diffusion of the interacting dipole moments with the modification that the electron spin relaxation rate is directly included as a contribution to the correlation time. In all cases studied, the electron spin relaxation rate is sufficiently large that it contributes directly to the water-proton spin relaxation process. The poor relaxation efficiency of the cage compound may, however, be improved dramatically by binding the complex to a protein. The efficiency is improved even further if the rotational motion of the protein is reduced drastically by an intermolecular cross-linking reaction. The relaxation efficiency of the cross-linked protein-cage complexes rivals that of the best first-coordination-sphere relaxation agents like [Gd(DTPA)(H2O)]2- and [Gd(DOTA)(H2O)]-.

Aza Compounds↗
PubMedDate not supplied

The magnetic field dependence of water proton T1 in aqueous solutions: implications for magnetic imaging contrast media.

The magnetic field dependence of the water proton nuclear magnetic relaxation induced by a nitroxide radical both free and covalently bound to serum albumin has been measured from 0.23 mT to 0.7 T. The field dependence of the water proton 1/T1 shows only a minor dependence on the degree of radical immobilization, though the electron spin resonance (ESR) spectrum is very sensitive to the correlation time of the radical. The results and theory are described in more detail elsewhere (Journal of Chemical Physics, in press). The observed relaxation behavior arises because the long electron relaxation time of the nitroxide forces the correlation time for the magnetic interaction driving the water proton relaxation to become the correlation time for the relative translational motion of the water and the nitroxide. The relative insensitivity of the water proton relaxation to nitroxide immobilization should not change if the nitroxide is used as a contrast reagent for magnetic imaging in vivo.

Cyclic N-Oxides↗
PubMedDate not supplied

Monitoring of therapy for deep vein thrombosis using magnetic resonance imaging.

Magnetic resonance imaging using limited-flip-angle, gradient refocused pulse sequences has been used to monitor the course of anticoagulant or fibrinolytic therapy for deep vein thrombosis in two patients. The findings demonstrate the capacity of this technique to delineate the extent of thrombosis and characterize changes in size in response to treatment. Advantages of this approach include high anatomic resolution, speed of examination and non-invasiveness, properties that make it well-suited to following the progress of therapy with potentially significant implications for improving treatment.

Adult↗
PubMedDate not supplied

Staphylococcal food poisoning associated with an Easter egg hunt.

Staphylococcal contamination of intact, hard-boiled eggs resulted in the food poisoning of an estimated 300 children out of 850 who had participated in an Easter egg hunt. Enterotoxigenic staphylococci that were isolated from the Easter eggs matched that obtained from an infected cook who prepared the eggs three to five days before the hunt and which he left unrefrigerated. Experimental studies demonstrated that heated eggs can absorb 2 mL of contaminated cool water through intact eggshells. When water was inoculated with pathogenic staphylococci at even low contamination levels, rapid growth and enterotoxin production within cooked eggs could be easily duplicated. This is the first large outbreak of its type; safeguards can and should be employed to prevent future ones.

Adolescent↗