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Biomedical subjects

F A Schultz

Publications and source records attributed to F A Schultz.

10 recordsLinked to original sources
PubMed1999

In vivo degradation of bleaching gel used in whitening teeth.

BACKGROUND: The purpose of the study described here was to determine the in vivo degradation rate of 10 percent carbamide peroxide, or CP, gel in bleaching trays. The degradation rate indicates the remaining concentration of the active agent on the facial surfaces at various intervals. METHODS: The researchers fabricated bleaching trays with 0.5-millimeter reservoirs and loaded them with a 10 percent CP whitening gel. The tray was seated in place in 15 patients for six different intervals that ranged from 15 seconds to 10 hours. When the tray was removed, three samples were collected from each patient: the gel remaining in the tray; the adherent gel scraped from the teeth; and a "grab" sample from the reservoir of tooth no. 8. The researchers analyzed these samples for CP according to the method specified by the U.S. Pharmacopeial Convention. RESULTS: The percentage of CP recovered decreased as the intervals increased: 87 percent at 15 seconds, 10 percent at 10 hours. Log of tray, teeth and grab samples, respectively, at 15 seconds were 0.94, 0.98 and 0.96 and at 10 hours were -0.13, -0.38 and 0.11. The first-hour degradation rate for tray, teeth and grab samples, respectively, was 2.0 times, 3.6 times and one time the rate during the next nine hours. The within-subject repeatability of the samples was excellent. CONCLUSIONS: The degradation rate of CP during the bleaching process is biexponential. In the tray and teeth samples, the degradation rate was accelerated during the first hour. Further research is needed to determine the cause of this acceleration. CLINICAL IMPLICATIONS: The active agent in CP bleaching gel is available in bleaching trays for more than 10 hours. After two hours, more than 50 percent of the active agent is available, and 10 percent is available after 10 hours.

Adult↗
PubMed1990

Electrochemical cells for voltammetry, coulometry, and protein activity assays of small-volume biological samples.

Cell designs, experimental protocols, and results for electrochemical investigation of small quantitites of biological materials under anaerobic conditions are reported. Three types of electrochemical experiments are considered: (i) cyclic voltammetry of 20- to 100-microliters samples; (ii) direct coulometry of 0.5- to 1.5-ml samples; and (iii) an electrochemically initiated protein activity assay which includes provision for analysis of gaseous reaction products and correlation with electron flux. The first two procedures are illustrated by measurement of the formal electrode potential (E0') and number of electrons transferred (n) in redox reactions of small quantities of biological and inorganic materials. The third procedure is illustrated by assaying the activity of the MoFe protein plus Fe protein complex from Azotobacter vinelandii nitrogenase for reduction of C2H2 to C2H4.

Acetylene↗
PubMed1989

Isolated iron-molybdenum cofactor of nitrogenase exists in multiple forms in its oxidized and semi-reduced states.

Electrochemical and EPR spectroscopic experiments demonstrate that the isolated iron-molybdenum cofactor from the molybdenum-iron protein of nitrogenase from Azotobacter vinelandii exists in multiple forms in both its oxidized and semi-reduced states. The particular forms found in either oxidation state appear to be a function of the acid/base status of the solvent, N-methylformamide. In "alkaline" N-methylformamide, a single, detectable form of iron-molybdenum cofactor is observed for both oxidized and semi-reduced states. The semi-reduced form, termed R(s-r), is the one previously recognized with an S = 3/2 EPR spectrum with apparent g values of 4.6, 3.4, 2.0. Its oxidized counterpart, termed B(ox), is characterized electrochemically by a differential pulse voltammetric reduction peak at -0.37 V versus the normal hydrogen electrode. In "acidic" solvent, two distinct, previously unrecognized redox pairs of iron-molybdenum cofactor forms exist. The two semi-reduced forms, N(s-r) and W(s-r), are characterized by EPR spectra with g = 4.5, 3.6, 2.0 and g = 4.9, 3.1, 1.9, respectively. Their oxidized counterparts, A(ox) and C(ox), have differential pulse voltammetric reduction peaks at -0.32 and -0.43 V versus the normal hydrogen electrode, respectively. Manipulations of either the isolation protocol or the sample conditions affects both the type and distribution of forms present. Each form likely corresponds to a biologically significant state of the cofactor cluster within the protein.

Azotobacter↗
PubMed1988

Iron-molybdenum cofactor of nitrogenase: electrochemical determination of the electron stoichiometry of the oxidized/semi-reduced couple.

The number of electrons involved in the more positive of the two redox couples of the iron-molybdenum cofactor of Azotobacter vinelandii nitrogenase has been investigated by controlled potential coulometry in both the oxidizing and reducing directions. A n value of 1 was determined for interconversion of the oxidized and semi-reduced states of the cofactor. This electron count was confirmed by double integration of the S = 3/2 electron paramagnetic resonance signal exhibited by the semi-reduced state.

Azotobacter↗
PubMed1976

Drinking during pregnancy.

Pregnant women reported a decrease in the use of alcoholic beverages during pregnancy, often citing adverse physiological effects as a reason for the decline.

Alcohol Drinking↗
PubMed1968

Solid ion-exchange electrode selective for calcium ion.

A calcium-selective electrode with solid ion exchanger was prepared from a solution of the calcium salt of a dialkylphosphoric acid in collodion. The electrode responds rapidly and reproducibly to activity of calcium ion and demonstrates a selective response for calcium ion in the presence of alkaline earth and alkali metal cations.

Calcium↗