Biomedical subjects

George D Cody

Publications and source records attributed to George D Cody.

4 recordsLinked to original sources

PubMed2005

Hydrogen bonding and dynamics of methanol by high-pressure diamond-anvil cell NMR.

Liquid methanol at densities up to rhorho(0) = 1.7 was studied by NMR in a specially designed diamond-anvil cell. Methyl and hydroxyl resonances have been separately observed at pressures to 43 kbars which exceeds equilibrium freezing pressure of methanol. The chemical shift difference between methyl and hydroxyl protons increases nonlinearly with increasing density, indicating a noticeable decrease in hydrogen bond length. The analyses of spin-lattice relaxation rates of both hydroxyl and methyl protons indicate that compression enhances intermolecular proton exchange and selectively reduces motion of the hydroxyl protons. Collectively these observations reveal that hydrogen bonding interaction in liquid methanol noticeably increases with compression, inhibiting the liquid-solid transition even above the freezing pressure.

Journal Article↗

PubMed2005

Structure of B2O3 Glass at High Pressure: A 11B Solid-State NMR Study.

We report spectroscopic evidence for the pressure-induced structural changes in B2O3 glass quenched from melts at pressures up to 6 GPa using solid-state NMR. While all borons are tri-coordinated at 1 atm, the fraction of tetra-coordinated boron increases with pressure, being about 5% and 27% in the B2O3 glass quenched from melts at 2 and 6 GPa, respectively. The fraction of boroxol ring species increases with pressure up to 2 GPa and apparently decreases with further compression up to 6 GPa. Two densification mechanisms are proposed to explain the variation of boron species with pressure.

Journal Article↗

PubMed2004

Evolution of xylem lignification and hydrogel transport regulation.

In vascular plants, the polysaccharide-based walls of water-conducting cells are strengthened by impregnation with the polyphenolic polymer lignin. The fine-scale patterning of lignin deposition in water-conducting cells is shown here to vary phylogenetically across vascular plants. The extent to which water transport in xylem cells can be modified in response to changes in the ionic content of xylem sap also is shown to vary in correlation with variation in lignification patterns, consistent with the proposed mechanism for hydraulic response through size change of middle-lamella pectins. This covariation suggests that the fine-scale distribution of hydrophilic polysaccharides and hydrophobic lignin can affect hydraulic as well as mechanical properties, and that the evolutionary diversification of vascular cells thus reflects biochemical as well as morphological innovations evolved to fulfill opposing cell functions of transport and structural support.

Biological Evolution↗

PubMed2002

Microbial activity at gigapascal pressures.

We observed physiological and metabolic activity of Shewanella oneidensis strain MR1 and Escherichia coli strain MG1655 at pressures of 68 to 1680 megapascals (MPa) in diamond anvil cells. We measured biological formate oxidation at high pressures (68 to 1060 MPa). At pressures of 1200 to 1600 MPa, living bacteria resided in fluid inclusions in ice-VI crystals and continued to be viable upon subsequent release to ambient pressures (0.1 MPa). Evidence of microbial viability and activity at these extreme pressures expands by an order of magnitude the range of conditions representing the habitable zone in the solar system.

Adaptation, Physiological↗