Showing papers on "Reagent published in 1984"

Determination ofD-amino acids. II. Use of a bifunctional reagent, 1,5-difluoro-2,4-dinitrobenzene

Abstract: 1-fluoro-2,4-dinitrophenyl-5-l-alanine amide has been synthesized in high yield (76%) from 1,5-difluoro-2,4-dinitrobenzene andl-Ala-NH2. This compound contains a reactive fluorine atom which can be used for the reaction with a mixture ofl- andd-amino acids. The resulting diastereomers which are obtained in quantitative yield can be separated and estimated by HPLC. With the five amino acids studied (Ala, Asp, Glu, Met and Phe),l-diastereomers were eluted from the reverse-phase column befored-diastereomers. This behavior can be explained by a stronger intramolecular hydrogen bonding in the latter diastereomer. When artificial mixtures of the five amino acids containing known proportions ofl- andd-isomers were derivatized with the reagent and the reaction products analyzed by HPLC, it was possible to determine the relative content of each isomer in nanomole range.

Reagent for the enzymatic determination of serum total triglycerides with improved lipolytic efficiency

Abstract: A fully enzymatic assay is described for the determination of triglycerides. The coupled activities of triacylglycerol acylhydrolase and glycerol kinase result in the formation of glycerol-3-phosphate. The system also contains L-alpha-glycerol-phosphate oxidase, which produces hydrogen peroxide from glycerol-3-phosphate, and a sensitive chromogenic indicator system, consisting of peroxidase, 4-chlorophenol and 4-aminophenazone. We evaluated this method with respect to kinetics, linearity, blank rates, precision, accuracy, reagent stability and interfering substances. The accuracy of the triglyceride assay demands that each enzymatic reaction step be complete and homogeneous. We therefore developed HPTLC-1) and HPLC-2) methods to monitor the course and completeness of each step.

Analytical Uses of Immobilized Enzymes

Abstract: Although soluble enzymes can be used as excellent reagents for the analysis of inorganic and organic compounds, they face a serious challenge when attempts are made to utilize them in complex matrices, like blood or crude water. Problems center about the effect of activators, inhibitors, other substrates, pH, and temperature on the soluble enzyme. However, upon immobilization most of these effects can be eliminated or minimized. For example, an enzyme with a narrow pH range of 4–6 can be transformed upon insolubilization to a more viable reagent with a broad pH range of 4–10. Also, following immobilization the enzymes are much more stable; they can be heated to 37, 40 or 50°C, with little loss of activity; and the activity persists after several thousand analysis are performed. However, the biggest advantage, analytically speaking, of immobilization, is that the insolubilized reagent becomes a much more selective reagent. No longer do many activators and inhibitors have an effect; only the most powerful can actually attack the enzyme.

Multiple reactor system and method for polynucleotide synthesis

Abstract: A reactor system and method for synthesizing or degrading polynucleotides and other linear polymers includes a tubular reactor connected to a reagent manifold. The polynucleotide is immobilized on a loosely packed solid-phase support material in the tubular reactor, and reagents are sequentially introduced into the tubular reactor. After each reagent is introduced, the tubular reactor is isolated from the reagent manifold and the reagent agitated by alternately pressurizing the opposite ends of the tubular reactor. The method provides rapid and efficient synthesis of polynucleotides. By connecting two or more tubular reactors to the reagent manifold, a plurality of polynucleotides having different sequences may be synthesized simultaneously.

Ferene — a new spectrophotometric reagent for iron

Abstract: Ferene iron reagent, 3-(2-pyridyl)-5,6-bis(2-(5-furyl sulfonic acid)-1,2,4-triazine, disodium salt, monohydrate, has been synthesized and characterized. Results of a study of its complex formation ...

2'-Nitro-2'-propen-1'-yl 2,2-dimethylpropanoate (NPP), a multiple coupling reagent

Abstract: The title compound 1 (NPP) is prepared from formaldehyde, nitromethane, an pivaloyl chloride. It is shown to be a versatile nitroallylating reagent combining with nucleophiles as different as anilines, indoles, enolates, and organolithium compounds. This is documented by ca. 40 examples (2–30). The mechanism of the reaction is discussed. Some examples of addition of two different nucleophiles to the C3-moiety of NPP are described (35-46). This demonstrates the usefulness of NPP as a multiple coupling reagent for convergent syntheses, also of products not containing nitro groups ((Scheme 4)).

Cobalt-nickel separation by solvent extraction with bis(2,4,4 trimethylpentyl)phosphinic acid

Abstract: The use of an organophosphinic acid to separate cobalt from nickel by solvent extraction is described. Comparative data indicate that the phosphinic acid is superior to analagous phosphoric and phosphonic acids in terms of cobalt-nickel selectivity and the ability to reject calcium. Important reagent properties, such as low aqueous solubility and hydrolytic stability, are discussed. The results of continuous, counter-current, mini-plant tests demonstrate the recovery of high purity cobalt from concentrated nickel sulphate solutions.

Syntheses of stationary phases for reversed-phase LC using silanization and polymer coating

Abstract: Various methods and reagents for silanization of silicas originating from different manufacturers were investigated in comparison to the method published by the authors which makes use of an enolate of acetylacetone. This reagent proved to be highly reactive.

Some aspects of regio-, stereo-, and chemoselective reactions in carbohydrate chemistry

Abstract: Selective transformations in carbohydrate chemistry will be illustrated with examples chosen from three distinct areas: 1 Phase transfer reactions are useful in obtaining partially substituted carbohydrate intermediates The substitution patterns frequently are quite different to those obtained in homogeneous phase 2 Various reagent systems have been developed for the conversion of hyd roxy compounds to chlorodeoxy b romodeoxy and deoxyiod o compounds as well as to olefinic derivatives A number of partial substitutions have been achieved starting from unsubstituted hexopyranosides providing easy access to some compounds of biological significance 3 Benzylidene acetals, phenyl substituted derivatives of these and also 2—propenylidene acetals may be reductively cleaved in the presence of proton or Lewis acids to give partially substituted derivatives useful as intermediates in various synthetic work The regioselectivity may be manipulated by change in reagent or solvent

Solid phase peptide synthesizer.

Abstract: An apparatus for peptide synthesis in which a plurality of supply valves are arranged in series to define a line for supplying successive reagents to a reaction vessel in which a peptide is to be synthesized. A corresponding plurality of containers contain respective reagents and each, by actuation of its corresponding valve, is connectable through downstream ones of the series of valves to supply its respective reagent to the reaction vessel. For cleaning or reacting with peptide starting material therein further valving permits draining of the reaction vessel to waste and, between applications of successive reagents to the reaction vessel, cleaning of the line of valves by flushing with a cleaning reagent sent from the upstream end of the series of valves through the line to waste. In modified embodiments, the plurality of reagent containers and series line of valves supplies reagents to multiple reaction vessel chambers in such a way that the multiple chamber may simultaneously be occupied by the same reagent in one peptide synthesis step and by several differing reagents, delivered thereto in sequence, in a differing peptide synthesis step, to enable simultaneous production of similar but different peptide analogs.

Capillary tube immunoassay

Abstract: A component of a sample may be detected or quantitatively measured by an immunoreaction, namely causing a target substance-immunoreactive reagent labelled with a marker-reaction product and/or any remaining, unreacted, immunoreactive reagent to move while making use of capillarity, causing the reaction product or any remaining, unreacted, immunoreactive reagent to combine with a substance packed in a capillary tube, and is immobilized on a carrier and adapted to uptake labelled substance so as to immobilize the reaction product or any remaining, unreacted, immunoreactive reagent, and measuring the amount of the thus-immobilized labelled substance. Since reagents are all filled in the capillary tube, there is no such troublesome that the reagents have to be prepared and/or any extra reagents have to be discarded upon conducting the measurement. The immunoassay may be carried out at bed side in hospitals. An extremely small amount of the sample may be sufficient for its measurement. After the measurement, the capillary tube may be stored as is or may be thrown away with ease.

Liquid chromatographic-fluorescence determination of ammonia from nitrogenase reactions: a 2-min assay.

Abstract: The analytical potential of the reaction of ammonia with o-phthalaldehyde mercaptoethanol reagent at pH 7 (an atypical fluorescence) has already been demonstrated. This, coupled with additional findings reported here, has led to an ammonia determination well suited to nitrogenase studies. As a result, large numbers of samples can be rapidly analyzed by high-pressure liquid chromatrography methods under mild conditions and without prior microdiffusion. Neither sodium dithionite (or other components of the usual nitrogenase assay), nor alternative substrates (cyanide, azide, methyl isonitrile), nor their products (methylamine, dimethylamine, hydrazine) interfere. High-pressure liquid chromatography showed that the fluorescent “product” of the o-phthalaldehyde mercaptoethanol reagent-ammonia reaction was, in fact, more than just a single compound. Despite this, once the proper solvent composition was found, high-pressure liquid chromatography with a small inexpensive C18 “guard” column proved quite fast and reproducible for this measurement. Fluorescence response to ammonia was linear to at least 40 nmol/ml. A previous problem, long-term stability of the fluorescence, was solved by running the reactions in the dark. Background ammonia in the buffer could be substantially reduced by an analogous o-phthalaldehyde mercaptoethanol reagent reaction, using t-butyl mercaptan, and solvent extraction.

Terbium chelate for use as a label in fluorescent immunoassays

Abstract: Human serum albumin has been labelled with a terbium complex by means of a reagent prepared from the bis-cyclic anhydride of diethylenetriamine pentaacetic acid and p-aminosalicylic acid. This reagent combines high fluorescent intensity with stability at high dilution (10–9M). The fluorescent conjugate so produced has been used in a simple fluoroimmunoassay, using human serum albumin as a model analyte.

New Aspects in Thiourea Leaching of Precious Metals

Abstract: High reagent consumption and low efficiencies are the main obstacles against common use of thiourea for the leaching of precious metals. A new technique of universal application has been developed by which reagent consumption is depressed to about 0.5 kg/t while high metal yields are achieved and passivation of feed material is avoided. The basic principle is the selective reduction of formamidine disulfide to thiourea during leaching, maintaining the oxidized part of the initial thiourea to about 50%. This prevents the generation of passivating sulfur and enables high redox potentials of above 400 mV for rapid metal dissolution at low thiourea concentration. Pulp processes with activated carbon or resins as adsorbents can be applied. Stripping of precious metals is achieved with hot thiourea or acid solutions.

Determination of HDL-Cholesterol Using 2,4,6-Tribromo-3-Hydroxybenzoic Acid with a Commercial CHOD—PAP Reagent

Abstract: The Boehringer one-component high-performance cholesterol oxidase reagent has been modified by the inclusion of 2,4,6-tribromo-3-hydroxybenzoic acid (TBHBA) to give a fourfold increase in sensitivity to a molar absorbance of approximately equal to 29,000 with respect to cholesterol. The resulting reagent system is particularly suitable for the determination of plasma HDL-cholesterol for which a reagent of high sensitivity is required. A simple method of bromination avoiding the use of elemental bromine is used to prepare TBHBA. The modified reagent system has been found to have good within- and between-batch precision and has shown itself to be reliable and trouble-free.