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Biomedical subjects

S G Schulman

Publications and source records attributed to S G Schulman.

At least 19 recordsLinked to original sources
PubMed1998

Chemiluminescence-based detection: principles and analytical applications in flowing streams and in immunoassays.

The present paper provides the principles of chemiluminescence (CL) and its powerful applications in analytical chemistry, mainly in the area of flow injection analysis, column liquid chromatographic and capillary electrophoretic separating systems, and its potential in immunoassays. CL is light produced by a chemical reaction. The most common advantages of chemiluminescent reactions are the relatively simple instrumentation required, the very low detection limits and wide dynamic ranges, which have contributed to the interest of CL detection in flow injection analysis, high performance liquid chromatography, including miniaturized systems, and, most recently, the exploding area of capillary electrophoresis. The latter powerful microanalytical separation technique offers high numbers of theoretical plates and relatively short analysis times requiring only small sample volumes, the migrating system comprising aqueous buffer solutions. In non-isotopic immunoassays, covering a great variety of applications in human and veterinary medicine, forensic medicine, agriculture and food industry, the radioisotope is replaced by a fluorescence or chemiluminescent label. The use of CL as a detection principle permits quantitative determination of various compounds at low concentrations. Disadvantages of the CL-based technique may include lack of sufficient selectivity and sensitivity to various physicochemical factors.

Chemistry Techniques, Analytical↗
PubMed1993

Determination of accurate and thermodynamically significant pH in alcohol/water solutions.

2-Hydroxybiphenyl demonstrates proton transfer in the lowest excited singlet state in alcohol/water mixtures as well as in pure water. The dissociation reaction of the directly excited neutral molecule is strongly solvent dependent and independent of solution acidity. The reprotonation of the conjugate base, however, depends predominantly on the acidity of the solution and only on the bulk dielectric constant of the solvent. The linear relationship between the ratio of the relative fluorescence efficiencies of 2-hydroxybiphenyl and its conjugate base and the hydrogen ion concentration is obtained only if proper Bronsted activity factors are included in the relationship. These factors can be calculated from classical electrostatics and are simple powers of the activity coefficients that would be derived from Debye-Hückel theory and which are necessary to convert the formal hydrogen ion concentration to hydrogen ion activity. With this approach it is possible to calculate pH from hydrogen ion concentration in alcohol/water solutions containing mole fractions of methanol, ethanol, isopropyl alcohol, and t-butyl alcohol up to 0.5, 0.3, 0.1, and 0.05, respectively.

Alcohols↗
PubMed1991

Penicillin-enhanced chemiluminescence of the luminol-H2O2-Co2+ system.

The luminol-H2O2-Co2+ system has been widely used in chemical and biological analysis. We report here an investigation of the observation that penicillins have the ability to prolong and enhance the intensity of chemiluminescence from luminol. The basis of this phenomenon appears, as revealed by difference spectroscopy, to be the formation of a complex between the beta-lactam and the superoxide ion. The latter is the oxidizing species responsible for the oxidation of luminol in alkaline solution and has a mean lifetime, in solution, of milliseconds. The stabilization of the superoxide ion by penicillin complexation extends the effective lifetime of the superoxide ion by a few orders of magnitude and thereby allows for more efficient oxidation of the beta-lactam. Several penicillins were determined by their enhancement of luminol chemiluminescence. A detection limit of 100 ng mL was obtained for penicillin G with a less-than-ideal detection system.

Catalysis↗
PubMed1985

Analysis of N-benzoyl-L-tyrosyl-p-aminobenzoic acid (bentiromide) metabolites in urine by ion-pair high-performance liquid chromatography.

A high-performance liquid chromatographic method is described for the analysis of bentiromide metabolites in urine. The procedure involves no more than direct injection of the diluted urine sample, obviating the need for an extraction step or an internal standard. A mu Bondapak C18 column is used with a mobile phase of 0.01 M tetrabutylammonium chloride (pH 7.4)--methanol (9:1). A flow-rate of 1.4 ml/min, detection at 254 nm and column temperature of 40 degrees C are employed. These conditions were achieved by investigating the effects of mobile phase pH, and concentrations and types of organic modifiers, buffers and ion-pairing agents on the resolution of the metabolites. The analysis time is 18 min per sample and the coefficient of variation on replicate assays is less than 10% for most concentrations studied. Analytical recoveries were between 95 and 100% throughout the appropriate concentration ranges and no interferences were obtained with the exception of p-acetamidobenzoyl glucuronide which could be eliminated by treatment of the samples with beta-glucuronidase. Concentration profiles of the metabolites were studied in normal subjects, and the method was found to be potentially useful for clinical situations in which the existing bentiromide test leads to ambiguous results because of small bowel and hepatic dysfunctions.

4-Aminobenzoic Acid↗
PubMed1985

Measurement of flurbiprofen-human serum albumin interaction by fluorimetry.

The binding of the anti-inflammatory drug, flurbiprofen, to human serum albumin is accompanied by a reduction of the fluorescence efficiency of the drug. The quenching effect has been used to evaluate the strength of binding at different pH values. Equations have also been developed for calculating binding constants for a 1:1 drug-protein complex, when fluorescence measurements are made at wavelengths where the emission spectra of the free drug, free protein and the complex overlap. Over the pH range 6.20-8.04, a binding constant of ca 1.0 x 10(7) was found for flurbiprofen.

Journal Article↗
PubMed1984

Microcalorimetric investigation of the binding of some chemotherapeutic agents and related molecules to calf thymus DNA.

Batch microcalorimetry was used to estimate directly the standard enthalpies of the binding of small molecules to DNA. These values were compared with those obtained from spectrophotometric binding constants and van't Hoff plots. The close agreement between the independently obtained enthalpies indicates that the appropriate (best) binding model has four phosphates per binding site. Thermodynamic binding constants were obtained from apparent binding constants measured at different ionic strengths. From these and the measured standard enthalpies, standard free energies and standard entropies of binding were calculated. The weak, presumably external, binding alleged to occur at high formal molar concentration ratios of ligand to DNA bases could not be detected by a measurable heat of binding.

Aminacrine↗
PubMed1983

The effect of ibuprofen on serum digoxin concentrations.

This study was undertaken to determine the effects of ibuprofen (Motrin), in daily doses of at least 1600 mg, on steady-state digoxin concentrations. A total of 12 ambulatory patients (10, female; 2, male), with a mean age of 66 years (38-81 yr), completed the study. An initial baseline serum digoxin level was obtained, with follow-up levels at 7 days and, whenever possible, 28 days after ibuprofen initiation. Serum creatinine concentrations were not significantly different from baseline to 7 or 28 days of ibuprofen therapy. Results show a statistically significant (p less than 0.05) increase in digoxin levels after seven days of ibuprofen. The mean increase was 59 percent (range, 10.7-325.4 percent), with 10 of the 12 patients displaying increased seven-day levels. Digoxin levels drawn 28 days after ibuprofen initiation were not statistically different from baseline or seven-day digoxin levels.

Aged↗
PubMed1978

Binding of 3-aminoacridinium and 7-aminoquinolinium monocations to double-stranded DNA: evidence for nonlinear binding isotherm in intercalative region.

The complexations of the singly charged cations of 3-aminoacridine and 7-aminoquinoline by double-stranded, calf thymus DNA were studied by electronic absorption spectrophotometry. At high ratios of total DNA phosphate concentration to total probe concentration (the region associated with intercalative binding), four DNA phosphate units are associated with each bound monocation. However, a binding isotherm based on four DNA phosphate groups in a single binding site does not yield a reproducible equilibrium constant for the binding process. Rather, the sequestration of the monocations by two binding sites, each containing two DNA phosphate units, yields a satisfactory equilibrium expression. This result suggests that the intercalative mode of binding by DNA is not a simple one-step process, which is in agreement with previous kinetic studies. In the region of low DNA phosphate concentration to monocation concentration (the external binding region), the binding is described adequately by a linear isotherm.

Acridines↗
PubMed1978

Spectroscopic approach to estimation of microequilibrium constants of prototropic reactions of aminobenzoic acids.

The microequilibrium constants of protolytic dissociation of diprotic acids, dihydric bases, or ampholytes such as the aminobenzoic acids, with dissimilar ionizing groups, can be estimated by spectrophotometric titration and measurement of the molar absorptivity at the long wavelength absorption maximum of simple alkylated derivatives. The method is applicable when the long wavelength absorption spectral bands of the tautomeric species are well resolved. Compared to the traditional method of estimating microequilibrium constants using the dissociation constants of alkylated derivatives, the proposed method is simpler, faster, and more accurate.

Aminobenzoates↗
PubMed1978

Tautomerism of singly protonated chloroquine and quinacrine.

Differential absorptiometric pH titrations of the antimalarials chloroquine and quinacrine, employing the respective uncharged species at pH 12.5 in the reference cell, show that protolytic dissociation from the heterocyclic ring nitrogen atoms occurs over pH 6--12. This finding indicates that the singly charged cations of the drugs exist measurably in two tautomeric forms. The tautomeric equilibrium constants were calculated from the titration data. The existence of these tautomeric equilibria may have significance in the pharmacodynamics of chloroquine and quinacrine.

Chloroquine↗
PubMed1977

Electronic absorption spectra and protolytic equilibria of doxorubicin: direct spectrophotometric determination of microconstants.

The ground- and excited-state dissociation constants and the electronic absorption and fluorescence spectra of doxorubicin were investigated by spectrophotometry. A general method for the direct calculation of individual microscopic dissociation constants was derived using the spectrophotometric data obtained. It was concluded that the protonated amino sugar group is slightly more acidic than the phenolic group. The spectrophotometric data were analyzed, and the macro- and microconstants for the various equilibria was reported.

Chemical Phenomena↗