Optical sensor for sulfur dioxide based on fluorescence quenching

A series of potential indicator dyes is evaluated for use in the development of optical sensors for measuring sulfur dioxide in gaseous samples. Rhodamine B isothiocyanate is selected on the basis of relative sensitivity to dynamic quenching by sulfur dioxide and oxygen. A solid-state fluorometer is described for monitoring the sulfur dioxide induced fluorescence quenching of sensing membranes composed of silicone and rhodamine B isothiocyanate. A modulated blue LED is coupled with the lock-in detection of a photodiode detector to provide high signal-to-noise ratios. The limit of detection is 0.114+/-0.009% for sulfur dioxide in a carrier stream of nitrogen gas. Selectivity measurements indicate no interference from several common gases (HCl, NH(3), NO, and CO(2)). Oxygen alters the sensor response when comparing signals for sulfur dioxide in 0, 20 and 100% oxygen environments.     

Capto-dative Substituent Effects in Syntheses with Radicals and Radicophiles [New synthetic methods (32)]

The 100 yers old Wurster's salts have long been recognized as compounds with redical cations. Their unusual stabilization derives partly form capto-dative (cd) substitution. This principle is now discussed as one factor of radical stabilization and it is applied to simple methine derivatives. cd-Substitution has synthetically useful applications: cd-substituents on a carbon atom allow its selective dehydrodimerization. Olefines with geminal and thus cross-conjugated cd-substituents are “radicophilic” and permit twofold carbon radical addition. cd-Substituted olefines are useful antioxidants, polymerization inhibitors and are promising agents in the control of biological radical reactions. Generally, many reactions of cd-substituted molecules appear to involve radicals.     

Electrophoretically mediated microanalysis with partial filling technique and indirect or direct detection as a tool for inhibition studies of enzymatic reaction

The inhibition of the model enzyme, haloalkane dehalogenase from Sphingomonas paucimobilis, was investigated by a combination of electrophoretically mediated microanalysis with a partial filling technique, followed by indirect or direct detection. In this setup, part of the capillary is filled with a buffer suitable for the enzymatic reaction (20 mM glycine buffer, pH 8.6) whereas the rest of the capillary is filled with the background electrolyte optimal for separation of substrates and products. Two different background electrolytes and corresponding detection approaches were used to show the versatility of the developed method. The inhibition effect of 1,2-dichloroethane on the dehalogenation of brominated substrate 1-bromobutane was studied by means of 10 mM chromate - 0.1 mM cetyltrimethylammonium bromide (pH 9.2) in combination with indirect detection or 20 mM beta-alanine - hydrochloric acid (pH 3.5) in combination with direct detection. The method was used to estimate the inhibition constant K(I) (0.44 mM by indirect detection and 0.63 mM by of direct detection) and to determine the inhibition type. Compared to spectrophotometric and other discontinuous assays, the method is rapid, can be automated, and requires only small amount of reagents that is especially important in the case of enzymes and inhibitors.     

Study of the fragmentation of small sulphur clusters

The fragmentation of sulphur clusters caused by electron impact ionization was studied. For this purpose, a beam ofS _n -clusters withn≦8 was generated in a gas aggregation source and ionized by electrons of variable energy. Special care was taken to maintain constant nucleation conditions so that the neutral cluster composition remained unchanged. It was found that the cluster ion mass spectra drastically depend on the electron energy. Even near threshold fragmentation processes contribute significantly to the dependence of the ion intensities on the electron energy.     

Study of perrhenate reduction by capillary electrophoresis

The influence of perrhenate concentration, the concentration of the reducing agent and pH of the reaction mixture on the yield of perrhenate reduction were studied to find a possibility to decrease the stannous chloride concentration in the reaction mixture without negative changes on the yield of perrhenate reduction. Britton-Robinson buffer solutions were selected as the background electrolytes because of their buffering capacity in a wide pH interval. The highest degree of perrhenate reduction was obtained at pH 2 at perrhenate concentrations ranging from 10(-4) to 10(-3) mol/L. The stability of reduced rhenium against pH change from 2 to 5.5 and against dilution of rhenium in the reaction mixture to the concentration suitable for the application in radiotherapy were studied as well. The results obtained by capillary electrophoresis and by thin-layer chromatography with radiometric detection were compared.     

Palladium-catalyzed, stereoselective rearrangement of a tetracyclic allyl cyclopropane under arylation

The first example of a pi,sigma domino-Heck reaction under concomitant rearrangement of the tetracyclic allylcyclopropane endo,exo-bishomobarrelene (5) is reported; the stereoselective reaction proceeds via an intramolecular insertion of a primarily-formed carbopalladation intermediate into a strained cyclopropane C-C sigma-bond, giving 9.     

Simultaneous measurement of glucose and glutamine in aqueous solutions by near infrared spectroscopy

A method is described for measuring the concentrations of both glucose and glutamine in binary mixtures from near infrared (NIR) absorption spectra. Spectra are collected over the range from 5000–4000/cm (2.0–2.5μm) with a 1-mm optical path length. Glucose absorbance features at 4710, 4400, and 4300/cm and glutamine features at 4700, 4580, and 4390/cm provide the analytical information required for the measurement. Multivariate calibration models are generated by using partial least squares (PLS) regression alone and PLS regression combined with a preprocessing digital Fourier filtering step. The ideal number of PLS factors and spectral range are identified separately for each analyte. In addition, the optimum Fourier filter parameters are established for both compounds. The best overall analytical performance is obtained by combining Fourier filtering and PLS regression. Glucose measurements are established over the concentration range from 1.66–59.91 mM, with a standard error of prediction (SEP) of 0.32 mM and a mean percent error of 1.84%. Glutamine can be measured over the concentration range from 1.10–30.65 mM with a SEP of 0.75 mM and a mean percent error of 6.67%. These results demonstrate the analytical utility of NIR spectroscopy for monitoring glucose and glutamine levels in mammalian and insect cell cultures.     

Studies on the distribution and concentration of thiamine in blood and urine

Studies are reported resulting in a reliable procedure for estimating the thiamine content in human blood and urine. For the determination in blood, heparinized blood is hemolyzed with 0.3 N hydrochloric acid at 100 °C. Cocarboxylase is then converted to free thiamine by means of wheat germ acid phosphatase at pH 5.0 in an acetate buffer. The liberated thiamine is adsorbed to a CG-50 (Rohm & Haas) carboxylic acid ion exchange acrylic resin column and then eluted with 1 N H₂SO₄. The thiamine is then oxidized to thiochrome and extracted with n-butyl alcohol, at pH 9.8–10.0, in the presence of disodium phosphate. Readout is by fluorometry at an excitation wavelength of 371 nm and an emission wavelength of 425 nm. The range found for thiamine in whole blood by this procedure on 18 normal adults was 1.9–3.9 μg/100 ml, with a mean value of 2.77 μg/100 ml of whole blood. The mean recovery of 12 recovery experiments was 94.1%. The same procedure is applicable to the determination of thiamine in urine. Conversion of cocarboxylase to free thiamine is not necessary since it was determined that practically all of the thiamine found in urine is not phosphorylated. Urine values were variable, the range for 11 healthy adults being 5.6–77.9 μg/100 ml with a mean value of 19.2 μg/100 ml. This corresponds to a value of 346 μg of thiamine/24 hours.     

Comparison of standard capillary and chip separations of sodium dodecylsulfate-protein complexes

Conditions for converting a set of five standard proteins to electrochemically active sodium dodecylsulfate (SDS) complexes were worked out with the aim of using such complexes for conductivity detection with a a chip electrophoresis system. The results obtained were compared with standard capillary electrophoresis (37 cm (effective length 30 cm)×75 μm I.D. capillary, 10 kV, negative polarity at the inlet). The chip separations were run at 500 V per chip (100 V/cm) as compared to the standard capillary arrangement, which was run at 266.6 V/cm. For the capillary set-up the protein complexes were prepared in aqueous solution (Milli-Q water) made 10 mM with respect to SDS. If the SDS concentration was increased to 50 mM, the separation in the capillary was incomplete. On the other hand with the chip system both approaches yielded acceptable results. The chip separations were slightly (but not distinctly) shorter and offered better separations than the standard set-up. The concentration of the surfactant used for the preparation the complexes results in alternations of the elution sequence, which is preserved if the chip separation is used instead of the capillary set-up. Apparently the full capacity of protein–SDS binding is not exploited for the preparation of the adducts.     

Isolierung und Aminosäuresequenz von Substanz P aus Pferdedarm

The isolation and amino acid sequence of substance P from horse intestine is reported. The sequence, H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH₂ is identical with the sequence reported for substance P isolated from bovine hypothalami.