Search results for "Reagent"
showing 10 items of 699 documents
Home-based HIV testing: Using different strategies among transgender women in Argentina.
2019
Background In Argentina, HIV prevalence among transgender women (TGW) has been reported at 34%. The stigma is one of the most important factors limiting their access to healthcare services. The aims of this study were to compare different HIV testing methodologies, to determine the factors associated with HIV diagnosis and to determine the feasibility of a home-based HIV testing service for TGW. Methods A multidisciplinary team performed home-based HIV testing interventions in four cities of Argentina. Participants self-identified as TGW, older than 14 years and with a negative or unknown HIV status. Blood samples were screened by two rapid tests (RT), one based on antibodies (Determine™ HI…
The Source of the Carbon Monoxide in the Classical Belousov-Zhabotinsky Reaction
2007
CO and CO2 evolution was measured in a cerium and in a ferroin-catalyzed Belousov−Zhabotinsky (BZ) reaction. These gases were stripped from the reaction mixture by a N2 carrier gas, mixed with H2, converted to methane on a Ni catalyst, and then measured by a flame ionization detector (FID). CO could be detected separately by absorbing CO2 on a soda lime column. In separate experiments it was proven that CO is produced in a reaction of BrO2• radicals with bromomalonic acid (BrMA). To this end BrO2• radicals were generated in two different ways: (i) in the reaction HBrO2 + HBrO3 ↔ 2 BrO2• + H2O and (ii) by reducing HBrO3 to BrO2• by Fe2+. It was found that •OH radicals produced by Fenton's r…
On the mechanism of the addition of organolithium reagents to cinnamic acids
2001
Abstract The regioselectivity of the addition of tert-butyllithium to cinnamic acid is subject to reaction conditions and to substituent electronic effects. Significant effects are observed in the presence of several additives including a radical trap such as α-methylstyrene. Competition experiments by addition of the organolithium reagent to mixtures of substituted cinnamic acids show that the relative rates of both conversion of the starting acids and formation of the 1,3-adducts are subject to electronic effects, whereas rates for 1,4-addition are independent of the substituents. These features are in agreement with a polar addition mechanism, but a fast SET equilibrium followed by slow …
Efficient flow injection and sequential injection methods for spectrophotometric determination of oxybenzone in sunscreens based on reaction with Ni(…
2001
Spectrophotometric determination of a widely used UV-filter, such as oxybenzone, is proposed. The method is based on the complexation reaction between oxybenzone and Ni(II) in ammoniacal medium. The stoichiometry of the reaction, established by the Job method, was 1:1. Reaction conditions were studied and the experimental parameters were optimized, for both flow injection (FI) and sequential injection (SI) determinations, with comparative purposes. Sunscreen formulations containing oxybenzone were analyzed by the proposed methods and results compared with those obtained by HPLC. Data show that both FI and SI procedures provide accurate and precise results. The ruggedness, sensitivity and LO…
Three-Component Synthesis of α-Aminoperoxides Using Primary and Secondary Dialkylzinc Reagents with O2 and α-Amido Sulfones
2020
A straightforward strategy for the synthesis of unprecedented α-aminoperoxides bearing primary and secondary alkylperoxide substituents is described. Commercially available dialkylzinc reagents are oxidized with molecular oxygen and the consequent peroxide species react with stable (hetero)aromatic and aliphatic α-amido sulfones in excellent yields (>90%). The now available α-aminoperoxides are of potential interest in medicinal chemistry, specifically for the synthesis of antimalarial compounds. Moreover, modification of the reaction conditions selectively leads to N,O-acetals in good yields.
Reactivity difference between diphosgene and phosgene in reaction with (2,3-anti)-3-amino-1,2-diols
2006
In reactions of (2,3-anti)-3-amino-1,2-diols with diphosgene and phosgene and their conversion into 1,3-oxazolidin-2-ones, some differences in the stereochemistry of the reactions have been found with these two reagents. The reactions with phosgene afforded the expected cis-oxazolidinones, and in the reaction with diphosgene under the same reaction conditions, the trans-oxazolidinones were also obtained.
Über eine neue Methode zum Nachweis des als Primärprodukt der Autoxydation der Metalle Eisen, Nickel und Kobalt in Säure- und Salzlösungen gebildeten…
1971
H2O2 als Zwischenprodukt der Autoxydation (bzw. · OOH oder · OH) kann mit Hilfe der Phosphin-, Phosphinoxid- Methode bei Fe, Ni und Co wirksamer als mit Hilfe der Jodometrie erfast werden. In saurem Medium sind Tris-(m-aminophenyl)-phosphin (1), im alkalischen Bereich Tris-(p-carboxyphenyl)- phosphin (2) wirksame auch fur quantitative Bestimmungen geeignete Reagentien auf H2O2 · 1 und 2 reagieren bei hoheren Konzentrationen bis zu 20 ma1 schneller mit H2O2 als dieses mit der Eisengrenzflache. Ni und Co erzeugen mehr H2O2 als Fe. Bei Eisen entsteht im neutralen Medium mehr H2O2 als im sauren Bereich. Die unterschiedlichen Anfangsgeschwindigkeiten des Sauerstoffverbrauchs in sauerstoffhaltige…
Efficient Synthesis of 5-Chalcogenyl-1,3-oxazin-2-ones by Chalcogen-Mediated Yne-Carbamate Cyclisation: An Experimental and Theoretical Study
2014
A very efficient synthesis of 5-chalcogenyl-1,3-oxazin-2-ones has been accomplished by the chalcogen-mediated yne–carbamate cyclisation of chiral, non-racemic N-Cbz-protected propargylic amines using PhXY (X = Se, S, Te; Y = Br or Cl) as electrophile sources. The reactions gave good-to-excellent yields for a wide range of substrates. In all cases the reaction was totally regioselective, occurring by a 6-endo-dig process regardless of the nature of the reagent and of the substituents in the starting material. This methodology permits the formation of the 1,3-oxazin-2-one moiety as well as the simultaneous installation of a chalcogen functionality onto the heterocyclic ring. The experimental …
Propan-2-ol dehydration on H-ZSM-5 and H-Y zeolite: a DFT study
2012
The catalytic dehydration of propan-2-ol over H-Y and H-ZMS-5 aluminated zeolite models, mimicking both internal cavities and external surfaces, was studied by DFT calculations to investigate the reaction mechanism. After the adsorption of propan-2-ol on the zeolite, the dehydration mechanism starts with alcohol protonation, occurring by one acidic –OH group of the zeolite fragment, followed by a concerted β-elimination to give propene. The catalytic activity is affected by the size of the zeolite cavity, which is larger in the H-Y than in the H-ZMS-5 zeolite. The adsorption energy of the reagent, as an example, decreases in the order: H-Y cavity ≃ H-ZMS-5 surface > H-ZMS-5 cavity, pointing…
A DFT study of the polar Diels–Alder reaction between 4-aza-6-nitrobenzofuroxan and cyclopentadiene
2005
Abstract The polar Diels–Alder reaction between 4-aza-6-nitrobenzofuroxan (ANBF) and cyclopentadiene has been studied using DFT procedures at the B3LYP/6-31G* level. Only one highly asynchronous transition state structure associated to the formation of the [4+2] adduct 13 is found. A further [3,3] sigmatropic shift on the [4+2] cycloadduct 13 allows its conversion into the thermodynamically more stable [2+4] cycloadduct 14 . The analysis of the global and local electrophilicities of the reagents correctly explain the behaviour of ANBF as a strong electrophile in polar cycloadditions.