THE VISUAL PIGMENT CYANIDE EFFECT

The visual pigment of the Tokay gecko (Gekko gekko) with its in situ absorption maximum at 521 nm has its spectral position at 500 to 505 nm when chloride-deficient digitonin is used for the extraction. In this case the addition of chloride or bromide to the extract restores the maximum to 521 nm. This property, characteristic of gecko pigments in general, does not occur with any of the rhodopsins that have been tested. Simple salts of cyanide, a pseudohalogenoid with an ionic radius close to those of chloride and bromide and/or its hydrolysis product attacks both this gecko pigment and rhodopsins in the dark. This is seen as a slow thermal loss of photopigment if (sodium) cyanide is present at concentrations above 40 mM for the gecko pigment and 150 mM for the rhodopsins of the midshipman (Porichthys notatus) and of the frog (Rana pipiens). In all cases the loss of the photopigment is accompanied by the appearance of a spectral product with maximum absorption at about 340 nm. Cyanide addition has no effect on the photosensitivity of the native pigments and neither does it alter, as do chloride, bromide and other anions, the spectral absorbance curve. The spectral product at 340 nm also appears when the visual pigments are photolyzed in the presence of cyanide salts below the threshold concentrations given above. Incubation of digitonin-solubilized all-trans-retinal with (sodium) cyanide leads to a reaction product with absorption spectrum similar to that obtained with visual pigments under comparable conditions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mass selective detection of amphetamine, methamphetamine, and related compounds in urine

A method is presented for the routine analysis of amphetamine, methamphetamine, and related compounds in urine with gas chromatography coupled with mass spectrometry operated in the selective ion monitoring mode. The analytes are isolated by liquid-liquid extraction and are derivatized with trifluoroacetic anhydride. 3,4-Methylenedioxy-methamphetamine-D(5) is employed as the internal standard. Standard solutions are prepared using spiked urine samples, which are subjected to all phases of sample preparation. Disposable deactivated glass containers are employed throughout the process.     

PHOTOCHEMICAL BEHAVIOR OF BACTERIORHODOPSIN IMMOBILIZED IN NaCl PELLETS

Abstract— Some photochemical reactions of bacteriorhodopsin (BR) embedded in NaCl pellets (BR-NaCI) in the visible region are described here. BR in these preparations is a mixture of two classes of species: a drastically blue-shifted form and the unchanged purple pigment. Depending on the illumination history of the BR before being immobilized, both kinds of BR could be demonstrated in light-adapted (LA) and dark-adapted (DA) forms, but light adaptation was not possible once the pellets were made. Analogously to BR suspensions, the light-adapted blue-shifted BRexhibited an a/l-trans type photocycle, but the thermal steps were greatly slowed down (time constants 1 to 5 min). The parent species absorb at 506 nm. The DA blue-shifted BR exhibited absorption changes resolved into two photoreactions, one all-(rans- like (as in LA-BR) and another, 13-cw like, whose decay rate is also greatly slowed down (recovery time several hours). The parent species of the 13-cis like cycle absorb at 480 nm. That pigment fraction in the pellets whose absorption was not blue-shifted, also exhibited similar photoreactions to BR in suspension, but with an overall turnover rate only one order of magnitude slower. From a previous report (Lazarev and Terpugov, Biochim. Biophys. Acta 590 ,324–338,1980) and this one, it appears that the very slow photocycles in NaCl-BR of low moisture content originate from blue-shifted chromophores rather than from unchanged BR.     

Quantitative analysis of the sulfur mustard hydrolysis product thiodiglycol (2,2'-sulfobisethanol) in in vivo microdialysates using gas chromatography coupled with pulsed flame photometric detection

An analytical method employing gas chromatography is presented for assessing the concentrations of the sulfur mustard hydrolysis product thiodiglycol (TDG) in cutaneous in vivo microdialysates. The use of a pulsed flame photometric detector allows for selective detection of the analyte following solvent exchange and derivatization with heptafluorobutyric anhydride. Quantitative assessment is performed using thiodipropanol (TDP) as a surrogate internal standard. A linear relationship and a very significant correlation (r2 = 0.9982) between the ratio of TDG and TDP concentrations and the ratio of the square root of peak heights is demonstrated. The suitability of the analytical method is verified by the evaluation of blank in vivo microdialysates spiked with known amounts of TDG. The limit of detection in microdialysates is 0.200 nmol/mL (24.4 ng/mL) and the limit of quantitation was 0.364 nmol/mL (44.4 ng/mL). The presented method provides selective, sensitive, rapid, and high-throughput analysis of microdialysates containing TDG, providing an efficient alternative for high-performance liquid chromatography and capillary electrophoresis techniques.     

Sensitive,High-Throughput Liquid Chromatography-Tandem Mass Spectrometry Analysis of Atorvastatin and Its Pharmacologically Active Metabolites in Serum for Supporting Precision Pharmacotherapy

The antihyerlipidemic drug atorvastatin (ATR) is used worldwide as part of the strategy to prevent cardiovascular events. The high prevalence of patient nonadherence remains an important challenge which could be addressed efficiently by precision pharmacotherapy based on therapeutic drug monitoring (TDM). ATR is metabolized to pharmacologically active metabolites, and evidence shows that the sums of ATR acid and lactone form concentrations (ATR + ATRL), or of ATR and hydroxylated metabolites (ATR + MET) should be assayed. A method is presented for the analysis of these substances in serum. Method validation included the estimation of the quantitative relationship between the concentrations and the standard deviations (SD), which supports the optimal incorporation of TDM results into nonparametric pharmacokinetic models. The concentrations of the analytes were evaluated in human subjects receiving ATR. The method’s performance improved by taking the sums of acid and lactone concentrations into account. The concentration–SD relationship was linear, and we recommend applying Theil’s regression for estimating the assay error. All analytes could be detected by 2 h post dose in the samples of human subjects. The changes in metabolite/parent drug concentration ratios in time depended on the dose. The method is suitable for the TDM of ATR with a focus on precision pharmacotherapy.