Adaptation of bulk constitutive equations to insoluble monolayer collapse at the air-water interface.

A constitutive equation based on stress-strain models of bulk solids was adapted to relate the surface pressure, compression rate, and temperature of an insoluble monolayer of monodendrons during collapse at the air-water interface. A power law relation between compression rate and surface pressure and an Arrhenius temperature dependence of the steady-state creep rate were observed in data from compression rate and creep experiments in the collapse region. These relations were combined into a single constitutive equation to calculate the temperature dependence of the collapse pressure with a maximum error of 5 percent for temperatures ranging from 10 degrees to 25 degrees C.

Repeated 1 hour electrocardiographic monitoring of survivors of myocardial infarction at 6 month intervals: arrhythmia detection and relation to prognosis.

In a study of the relation between ventricular premature beats and sudden death among 1,739 male of myocardial infarction enrolled in the Health Insurance Plan of Greater New York (HIP), patients underwent 1 hour of electrocardiographic monitoring at a baseline examination. During follow-up periods of up to 5 1/2 years, survivors underwent repeated monitoring at 6 month intervals for a maximum of four monitorings. At each monitoring a constant proportion of the men--25 percent--showed complex ventricular premature beats (runs of two or more, R on T phenomenon, bigeminal or multiform beats) during the hour. In comparison with men free of such arrhythmia, those demonstrating these complex forms in a given hour were three times as likely to show such beats in a subsequent monitoring hour. The mortality risk over 3 1/2 years after each of the four monitoring observations was in all cases elevated among men with complex ventricular premature beats. The risk of sudden death over this period was 6 percent for men without and 13 to 17 percent for men with such complexes. A study of the 1,445 men who underwent monitoring both at baseline examination and 6 months later identified the presence of runs of ventricular premature betas in either observation as a particularly important harbinger of sudden death.

Functional tethered lipid bilayers.

Our strategy to provide the structural basis for the build-up of functional tethered membranes focuses on three approaches: the first one is based on the pre-organization of a monomolecular layer of a lipopolymer at the water/air interface which is then transferred to a solid support. Prior to deposition, the substrate is coated with a layer of benzophenone-derivatized silane molecules that allow for a stable covalent attachment by photo-cross-linking of some of the monomer units of the lipopolymer to the support. An alternative concept realizes a layer-by-layer deposition of the various structural elements: (1) the attachment layer with the reactive sites for the chemical stabilization; (2) a polymer 'cushion' prepared by adsorption and simultaneous or subsequent partial covalent binding to the reactive sites; and (3) a lipid monolayer transferred from the water/air interface, that contains a certain amount of lipids with reactive headgroups which, upon binding to the polymer tether, act as anchor lipids stabilizing the whole monolayer/cushion-composite. And finally, we build peptide-supported monolayers by first (self-) assembling amino acid sequences of various lengths via a SH-group near their N-terminus onto Au substances and use then their COO(-)-terminus to chemically attach phosphatidyl-ethanolamine lipids to form a stable monolayer of lipid-peptide conjugates. All the individual preparation steps and the various resulting (multi-) layers are characterized by surface plasmon spectroscopy, X-ray and neutron-reflectometry, contact angle measurements, IR spectroscopy, fluorescence microscopy, scanning probe microscopies, as well as, electrochemical techniques. For all tethering systems, the final membranes' architecture is obtained by fusing lipid vesicles onto the lipid monolayer. Proteins can be incorporated by either fusing vesicles that are loaded with the respective receptors, pores, or ion pumps via a reconstitution procedure, or via a transfer directly from a micellar solution to the pre-formed lipid bilayer at the solid support by a dialysis step. Two structural/dynamical features of tethered membranes which are considered to be of particular functional relevance, i.e. the degree of water uptake and, hence, the degree of swelling of the polymer support, as well as the lateral mobility of the lipid molecules in the membrane, are tested by surface plasmon optics and by measurements of the fluorescence recovery after photobleaching (FRAP), respectively. The results confirm that the presented preparation protocols yield fluid bilayers that mimic certain relevant properties of biological membranes. The functional characterization of tethered membranes, which is briefly summarized, is based on various electrochemical techniques, in particular, impedance spectroscopy, cyclic voltammetry, and chronoamperometric studies. The results obtained for reconstituted H(+)-ATPase from chloroplasts and E. coli and for cytochrome oxidase (with and without cytochrome c) confirm the incorporation of the proteins in an active form, thus, opening opportunities for novel sensor formats or offering a completely new model membrane system.

The effect of dental amalgam restorations on blood mercury levels.

Mercury levels in blood and in mouth air before and after chewing were measured in 47 persons with and 14 persons without dental amalgam restorations. Questionnaires relating to exogenous sources of mercury exposure were administered to both groups. Differences in the mouth air mercury levels before and after chewing were statistically significant in the group with amalgams, but not in the group without amalgams. Analysis of the data from the questionnaires indicated that little or no exogenous exposure to mercury occurred among the two groups. Blood mercury concentrations were positively correlated with the number and surface area of amalgam restorations and were significantly lower in the group without dental amalgams.

The effect of dental amalgams on mercury levels in expired air.

The expired air of a group of 48 persons, 40 with and eight without dental amalgam restorations, was analyzed for its mercury content before and after chewing. Expired air samples were collected in polyethylene bags, and a known quantity of each was pumped into the mercury detector for measurement. The results showed that examined subjects with dental amalgams had higher pre-chewing mercury levels in their expired air than those without amalgams. After chewing, these levels were increased an average of 15.6-fold in the former and remained unchanged in the latter group. It was concluded that in situ dental amalgams can increase the level of mercury in expired air.

Dehydration of tetracycline.

The dehydration of tetracycline at the C-5a-C-6 position as a function of acidity was investigated at various temperatures. The rate was first order with respect to tetracycline and with respect to [H+]. Rate constants and an activation energy are reported. Tetracycline was unstable in dilute acid.

Circular dichroism spectra of tetracycline complexes with Mg+2 and Ca+2.

The study of Ca+2 and Mg+2 complexes of tetracycline in buffered solution was undertaken to determine their stoichiometry and the chelation sites. Circular dichroism was used to follow complex formation. Modified tetracyclines, in which potential complexation sites were blocked, were used to determine the participation of particular sites in complexation. Calcium formed a 2:1 metal-ion to ligand complex, while the magnesium complex formed at a 1:1 ratio. Formation of the calcium complex involved addition of one metal ion to the C-10, C-11 site with subsequent addition of a second metal ion at the C-12, C-1 site. The magnesium chelate occurred at the C-11, C-12 beta-diketone site.

Preparation, isolation, and identification of 4-dedimethylamino-11-methoxyanhydrotetracycline.

The reaction of diazomethane with 4-dedimethylaminoanhydrotetracycline produced a number of mono-, di-, and tri- methylated products. The isolation of one monomethylated product (4-dedimethylamino-11-methoxyanhydrotetracycline) and its subsequent identification utilizing mass spectral and NMR data are described.

Potentiometric and spectral investigations of anhydrotetracycline and its metal-ion complexes.

The interaction of various metal ions with anhydrotetracycline was investigated. A comparison of the UV-visible and fluorescence spectral characteristics of anhydrotetracycline and its metal-ion complexes with a number of modified anhydrotetracyclines in the presence of metal ions suggested that the C-11 oxygen was involved in metal-ion binding. Secondary binding was observed in the A-ring by circular dichroism when the primary site was blocked.

Determination of nitrate and nitrite in blood and urine by chemiluminescence.

Methodology has been developed for the rapid determination of nitrate and nitrite in blood and urine. In solution, these species are selectively reduced to nitric oxide, which is outgassed and determined via its gas phase chemiluminescence reaction with ozone. Differentiation between nitrate and nitrite is obtained by careful selection of reducing agents and conditions.