James R. Cavanaugh

A piezoelectric crystal detector for determination of acetoin in air

Abstract A method is presented for the determination of acetoin (3-hydroxy-2-butanone) in air with a piezoelectric crystal detector coated with semicarbazide. The response time is about 5 min, is fully reversible, and is selective for acetoin in the presence of the interferences normally found in air. The detector has a sensitivity of 12.4 Hz 1 μl−1 for acetoin and the response varies linearly with concentration in the 50– μl l−1 range.

19F-NMR of fluorine labeled acyl chains in phospholipid bilayer vesicles

Abstract 19F-labeled phospholipids, L-α-bis-(ω-fluoro palmitoyl)phosphatidylcholine, L-α-bis-(12,12-difluoro stearoyl)phosphatidylcholine and L-α-bis-(6,6-difluoro palmitoyl)phosphatidylcholine, were incorporated in phospholipid vesicles by sonication of aqueous lipid emulsions. Vesicles were prepared both from the pure fluorine substituted phospholipids as well as from lipid mixtures obtained by combining the fluorine substituted lipids with the synthetic phospholipids, L-α-dilauroyl-, L-α-dimyristoyl-, L-α-dipalmitoyl- and L-α-distearoyl-phosphatidylcholine. Characterization by gel permeation chromatography showed that stable unilamellar vesicles with diameters of ≌200 A could be obtained with a minimum or absence of multilamellar material. The vesicles give rise to two 19F resonances in most cases as observed previously [K.J. Longmuir and F.W. Dahlquist, Proc. Natl. Acad. Sci. U.S.A., 73 (1976) 2716]. The chemical shift differences undergo systematic changes that confirm the interpretations that the dual 19F resonances arise from the inner and outer halves of the vesicle bilayer. The shift separation increases systematically as the fluorine label is positioned closer to the phospholipid headgroup and decreases systematically with increasing temperature. Both observations agree with what is currently known about phospholipid vesicle structure. Anomalous results are obtained with DSPC as host vesicle since only a single resonance of inbedded fluorinated phospholipids is found.

Interaction between gramicidin-A and bacteriorhodopsin in reconstituted purple membrane

Abstract The addition of gramicidin-A to reconstituted purple membrane, significantly inhibits light-induced proton movement. Kinetic analyses indicate that the treatment decreases the initial proton pumping rate (Ro), alters the interdependence (m) between the pumping process and its associated H+ leak path (kL-kD), but has no detectable effect on the proton permeability associated with phospholipid bilayers in the dark (kD). These results suggest that gramicidin-A, under the experimental conditions, interacts directly with bacteriorhodopsin in the membrane. This suggestion is supported by the findings that both the resonance Raman and circular dichroism spectra of bacteriorhodopsin are affected by the antibiotic.

19F-Nuclear magnetic resonance of fluorine-labeled fatty acids in phospholipid bilayer vesicles

Abstract 19 F-labeled fatty acids, labeled at the 4, 6, 9, 12 and terminal positions, and intercalated into dimyristoylphosphatidylcholine (DMPC) small unilamellar vesicles were studied using 19 F-NMR as a function of temperature and perturbant incorporation. The perturbants studied were cholesterol, gramicidin A and polylysine. It was found that the fluorines give rise to a single resonance whose line width decreases substantially with increasing temperature and increases as the fluorine is positioned from the chain terminus toward the polar head group, peaking at the 6 position. When cholesterol is incorporated into the phospholipid vesicles, the fluorine resonance line widths increase dramatically and uniformly along the chain at all temperatures. Gramicidin A incorporation leads to a similar though smaller increase in line widths which, in contrast, diminish with increasing temperatures. On the other hand polylysine interactions lead to little change in the line width of the fluorine-substituted fatty acids. Incorporation of cholesterol increases the size of the phospholipid vesicles but the other perturbants do not, as determined by gel-permeation chromatography. These results are consistent with what is known about the changes in phospholipid bilayer structure brought about by the incorporation of these substances and indicate that 19 F-NMR of fluorine-substituted fatty acids intercalated in lipid bilayers can extend our knowledge of model membrane systems.