Showing papers on "Reagent published in 1998"

Laser Control of Chemical Reactions

Abstract: Experiments show how product pathways can be controlled by irradiation with one or more laser beams during individual bimolecular collisions or during unimolecular decompositions. For bimolecular collisions, control has been achieved by selective excitation of reagent vibrational modes, by control of reagent approach geometry, and by control of orbital alignment. For unimolecular reactions, control has been achieved by quantum interference between different reaction pathways connecting the same initial and final states and by adjusting the temporal shape and spectral content of ultrashort, chirped pulses of radiation. These collision-control experiments deeply enrich the understanding of how chemical reactions occur.

Integrated fluid manipulation cartridge

Abstract: A cartridge (101) for separating a desired analyte from a fluid sample includes a sample port (103) and a sample flow path extending from the port through the body of the cartridge. The sample flow path includes at least one flow-through component (122), e.g., filter paper or a microfabricated chip, for capturing the desired analyte from the sample as the sample flows through the cartridge. The cartridge also includes an elution flow path for carrying elution fluid through the component (122) to release captured analyte from the component into the elution fluid. The elution flow path diverges from the sample flow path after passing through the component (122). Flow controllers (41A and 41B) direct the remaining fluid sample into a waste chamber (139) after the sample flows through the component (122) and direct the elution fluid and eluted analyte into a reagent chamber (141) and reaction chamber (143). The continuous-flow design of the cartridge permits the rapid processing of a fluid sample that is larger in volume than any interactive region within the cartridge, allowing increased sensitivity in the detection of low copy concentrations of analytes, such as nucleic acid.

Use of Onium Salt-Based Coupling Reagents in Peptide Synthesis1

Abstract: Peptide coupling methods derived from onium salts based on 1-hydroxybenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt) are becoming incorporated in synthetic strategies more frequently than the classical carbodiimide methods. We have correlated the reactivity of various onium salts derived from HOXt (X = A, B), with the structure of the reagents in question. Thus, we confirmed that the aza derivatives are more reactive than the parent benzotriazole derivatives in both activation and coupling. In addition, the activation step is determined by the structure of the carbon skeleton. Thus, pyrrolidino derivatives appear to be reagents of choice relative to the piperidino analogues or those derived from trialkylamines. Furthermore although phosphonium salts are slightly less reactive than the corresponding aminium/uronium salts, the former should be used for the activation of hindered species, since the latter may lead to the formation of guanidino derivatives.

Oxidative Biaryl Coupling Reaction of Phenol Ether Derivatives Using a Hypervalent Iodine(III) Reagent

Abstract: The hypervalent iodine(III)-induced intramolecular biaryl coupling reaction of phenol ether derivatives (nonphenolic derivatives) was investigated with the aim of preparing various dibenzo heterocyclic compounds. 1,3-Diarylpropanes (1a−e), N-benzyl-N-phenethylamines (2a−c) and N,N-dibenzylamines (3a−e) react with a hypervalent iodine reagent, phenyliodine(III) bis(trifluoroacetate) (PIFA), containing BF3·Et2O in CH2Cl2 to give the biaryl coupling products (4−6) in good yield. As an application of the reaction, we examined the synthesis of oxygen- and sulfur-containing dibenzoheterocyclic compounds (12−15), whose side chain moiety could be easily cleaved by the known method to give 2,2‘-substituted biphenyl compounds (16−18).

Template Recognition in Inorganic−Organic Hybrid Films Prepared by the Sol−Gel Process

Abstract: Inorganic−organic hybrid sol−gel processing has been utilized to fabricate thin, porous, chemically selective silicate films. These materials have been fabricated using a template-based approach that involves the formation of a cross-linked matrix around a specific reagent followed by removal of that reagent. The silica sol consisted of a hybrid mixture of functionalized organosilicon precursors (phenyltrimethoxysilane and methyltrimethoxysilane), a network former (tetramethoxysilane), and the template molecule, dopamine (DA). Silicate thin films were prepared by spin casting an aliquot of the composite sol on the surface of a glassy carbon electrode. Dopamine was extracted from the dried film via soaking in phosphate buffer, and the affinity and selectivity of the DA-templated films were characterized using cyclic voltammetry. The results show that the DA-templated films have an increased affinity for dopamine over that of structurally related molecules including serotonin, epinephrine, and dihydroxynaph...

Oxoammonium Salts. 6.1 4-Acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium Perchlorate: A Stable and Convenient Reagent for the Oxidation of Alcohols. Silica Gel Catalysis

Abstract: 4-Acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium perchlorate, 1, is a stable, nonhygroscopic oxoammonium salt that is easily prepared and can be used for the oxidation of alcohols to keton...

Reagent and method for attaching target molecules to a surface

Abstract: Method and reagent composition for covalent attachement of target molecules, such as nucleic acids, onto the surface of a substrate. The reagent composition includes groups capable of attracting the target molecule as well as groups capable of covalently binding to the target molecule, once attracted. Optionally, the composition can contain photoreactive groups for use in attaching the reagent composition to the surface.

Design of Brønsted Acid-Assisted Chiral Lewis Acid (BLA) Catalysts for Highly Enantioselective Diels−Alder Reactions

Abstract: Bronsted acid-assisted chiral Lewis acid (BLA) was highly effective as a chiral catalyst for the enantioselective Diels−Alder reaction of both α-substituted and α-unsubstituted α,β-enals with various dienes. Hydroxy groups in optically active binaphthol derivatives and boron reagents with electron-withdrawing substituents were used as Bronsted acids and Lewis acids, respectively. Intramolecular Bronsted acids in a chiral BLA catalyst played an important role in accelerating the rate of Diels−Alder reactions and in producing a high level of enantioselectivity. In particular, excellent enantioselectivity was achieved due to intramolecular hydrogen bonding interaction and attractive π−π donor−acceptor interaction in the transition-state assembly by hydroxy aromatic groups in a chiral BLA catalyst.

Oxidative Intramolecular Phenolic Coupling Reaction Induced by a Hypervalent Iodine(III) Reagent: Leading to Galanthamine-Type Amaryllidaceae Alkaloids

Abstract: By extending our oxidative phenol-coupling reactions using a hypervalent iodine(III) reagent, a versatile synthetic procedure for the galanthamine-type Amaryllidaceae alkaloids was accomplished. The first total synthesis of (±)-sanguinine and the total syntheses of (±)-galanthamine, (±)-narwedine, (±)-lycoramine, and (±)-norgalanthamine were also successfully carried out.

Functionalization of Nanocrystalline Porous Silicon Surfaces with Aryllithium Reagents: Formation of Silicon−Carbon Bonds by Cleavage of Silicon−Silicon Bonds

Abstract: Reaction of nanocrystalline (“porous”) silicon with phenyllithium and lithium phenylacetylide results in functionalization of the silicon surface with phenyl and phenylacetylene moieties, respectively. The reaction proceeds by addition of the aryllithium reagent across a surface Si−Si bond, resulting in a Si−aryl bond and Si−Li species. The highly reactive Si−Li surface species is readily hydrolyzed by water, resulting in significant surface oxidation. The surface-bound Li can also be replaced with H or acyl species by addition of trifluoroacetic acid, acetyl chloride, heptanoyl chloride, or 4-butylbenzoyl chloride. These latter treatments significantly reduce the rate of air oxidation of the porous silicon surface. The nanocrystalline silicon samples used display visible photoluminescence arising from quantum confinement effects. Functionalization with phenyllithium preserves some of the photoluminescence, while the lithium phenylacetylide reaction results in almost complete loss of photoluminescence fro...

Simultaneous particle separation and chemical reaction

Abstract: This invention provides a method and apparatus for detecting the presence of analyte particles in a sample fluid also comprising larger particles, particularly blood. It exploits diffusion to provide simultaneous filtering of the larger particles and reaction of the analyte particles. A sample stream and a reagent stream join on the upstream end of a laminar flow reaction channel and flow in adjacent laminar streams. The reagents can be in solution or immobilized on a bead. The analyte particles diffuse from the sample stream into the reagent stream, leaving behind the larger particles in the residual sample stream. In the reagent stream the analyte particles react with reagent particles and form product particles, thereby creating a product stream. At the downstream end of the reaction channel, the residual sample stream and the product stream are divided. The product particles are then detected, preferably optically, in the product stream. Prior to detection, the product stream can undergo further filtering or separation, or can join a second reagent stream to form secondary product particles. This apparatus and method can be used to implement competitive immunoassays or sandwich immunoassays using enzymatically or fluoroscently labeled immunoreagents. The apparatus and method can also be used to synthesize products, in which case two reagent streams join in the laminar flow reaction channel.

Magnetically assisted binding assays utilizing a magnetically responsive reagent

Abstract: Assay methods utilizing the response of a magnetically responsive reagent to the influence of a magnetic field to qualitatively or quantitatively measure binding between specific binding pair members. According to the invention, the presence of an analyte mediates whether or not the magnetically responsive reagent binds to a mobile solid phase reagent. The extent of binding will modulate the response of the magnetically responsive reagent or that of the mobile solid phase reagent, or both, to the influence of a magnetic field. Hence, by measuring the response to the magnetic field of the magnetically responsive reagent, or that of the mobile solid phase reagent, the presence or amount of analyte contained in a test sample can accurately be determined. The invention utilizes various devices to carry out the assay methods described.

Mechanism of H2S Oxidation by Ferric Oxide and Hydroxide Surfaces

Abstract: The interaction of H2S with the surface of either α-Fe2O3 or amorphous ferric hydroxide at low temperatures has been characterized using FTIR and quantified using volumetric methods. The mechanism of the interaction of H2S with either reagent is ionic and involves heterolytic dissociation of H2S and exchange of S2- and SH- anions for O2- or OH-. Subsequently water is eliminated and, in coupled redox reactions, sulfide is oxidized to elemental sulfur and Fe3+ cations are reduced to Fe2+. Initially, almost all the surface sites can interact readily with H2S, to form a layer of iron sulfides. Over longer reaction times reaction occurs with deeper sites, to form bulk sulfides. Regeneration of ferric (hydr)oxide by oxidation with oxygen converts Fe2+ to Fe3+, and S2- anions are replaced by O2- with formation of elemental sulfur. The surface species involved in each reaction have been characterized using FTIR and, for the first time, direct evidence has been obtained for the presence of SH- anions as very react...

Method and device for measuring blood coagulation or lysis by viscosity changes

Abstract: The present invention provides a single-use electronic device and test card for use therein which performs a coagulation or lysis assay of a blood sample. The device includes a housing having an exterior surface and defining an interior area and means for receiving the sample through the housing into the interior space. A non-porous substrate is positioned within the interior space for receiving the sample thereon. A reagent accelerates the coagulation of the sample and is positioned on the substrate and in contact with the sample. Optionally, an electroactive species may also be reacted with the sample. The device also includes means for measuring the viscosity of the sample and generating an electrical signal which correlates to a curve of the coagulation/lysis assay. Processing means positioned within the interior space is connected to the measuring means for receiving and converting the electrical signal into a digital output corresponding to the coagulation/lysis assay using assay calibration information stored therein. Display means visually displays the digital output external to the housing and is connected to the processing means. A method of determining the coagulation or lysis of a sample provides for accelerating the coagulation of the sample by chemically reacting the sample with at least one reagent on the substrate to produce a detectable change in the viscosity of the sample which correlates with the state of coagulation or lysis of the sample and measuring the viscosity of the sample and generating an electrical signal which correlates to a curve of the coagulation/lysis assay.

Application of Chromogenic and Fluorogenic Reactands in the Optical Sensing of Dissolved Aliphatic Amines

Abstract: A new class of dyes has been investigated that reversibly interacts with aliphatic amines, resulting in changes in absorbance or fluorescence. These dyes, which combine the properties of both a chemical reagent and a ligand, are termed “reactands”. When embedded in plasticized PVC membranes, the reactand 4-(N,N-dioctylamino)-4‘-trifluoroacetylazobenzene (ETHT 4001) shows a significant signal change on exposure to aqueous amine solutions, with a decrease in absorbance around 490 nm and an increase in absorbance around 420 nm wavelength. This change in absorbance is caused by a conversion of the trifluoroacetyl group of the reactand into a hemiaminal or a zwitterion. Upon interaction with 1-butylamine, the sensor layer exhibits a dynamic range from 1 to 100 mM 1-butylamine, with maximum relative signal changes of 90%. The limit of detection with this approach is 0.3 mM.The forward response time (t95) for a decade change in activity is 10 min, and the reverse response time is 5 min. The selectivity of ETHT 4...

A rapid method for the measurement of Leucaena spp. proanthocyanidins by the proanthocyanidin (butanol/HCl) assay

Abstract: Proanthocyanidin (PA) extraction, sample preparation and proanthocyanidin assay (butanol/HCl) reaction conditions were evaluated for measuring PA in Leucaena spp leaf material. The optimal conditions for extracting PA from leaf tissue are described, with short sequential sonications in 70% aqueous acetone being as efficient as prolonged sequential mechanical agitation. In methanol–based extracts, after back extraction to remove pigments, increasing the water content of the reagent/sample matrix suppressed colour development. The addition of low concentrations of Fe3+ to the butanol/HCl reagent enhanced colour yield, but higher Fe3+ concentrations suppressed colour development. The presence of ascorbic acid in the sample extract was shown to increase colour development. Varying the reagent: sample extract ratio from 4:1 to 6:1 significantly decreased colour yield, but neither ratio was different from 5:1. Optimum conditions for the PA assay were as follows: a water content of 8%, the omission of Fe3+, a reagent: sample extract ratio of 5:1 and the addition of ascorbic acid to the stock PA standard solution to match that contributed by the extract in the final mixture. Sample preparation procedures, using back extraction to remove pigments and non-PA phenolics with diethyl ether and ethyl acetate, respectively, were time-consuming and subject to PA losses. The measurement of PA directly in the 70% aqueous acetone extract eliminated these PA losses, but the PA assay required additional optimisation for direct analysis of crude acetone extracts. In the final optimised procedure, PA was extracted by sequential sonication with 70% aqueous acetone containing 5·26 mM sodium metabisulphite as the antioxidant. These extracts were directly analysed by the butanol/HCl reaction using a reagent: sample extract ratio of 5:1, the omission of Fe3+ from the butanol/HCl reagent and the addition of sodium metabisulphite to match that contributed by the extract. This produced consistent linear calibration curves over the range 25–1000 μg PA with an average recovery of 101%. © 1998 Society of Chemical Industry.