Search results for "aqueous solution"

Salt effects on the protonation of l-histidine and l-aspartic acid: a complex formation model

1991

Abstract Protonation constants of l -histidine (histidinate: his − ) and l -aspartic acid (aspartate: asp 2− ) were determined potentiometrically, using the (H + ) glass electrode, in aqueous tetraethylammonium iodide (Et 4 NI), calcium chloride and sodium chloride solutions, at 0 −3 and 10 ⩽, T ⩽, 45 ° C. Differences in protonation constants determined in different salt media were explained by a complex formation model and, according to this model, the presence of the following species was hypothesized: Ca(his) + , CaH(his) 2+ , CaH 2 (his) 3+ Na(his) 0 , H 3 (his)X + , H 2 (his)X 0 , Et 4 N(his) 0 , Et 4 NH(his) + , Ca(asp) 0 , CaH(asp) + , CaH 2 (asp) 2+ , Na(asp) − , NaH(asp) 0 , H 3 (a…

Photocatalytic Selective Oxidation of 4-Methoxybenzyl Alcohol to Aldehyde in Aqueous Suspension of Home-Prepared Titanium Dioxide Catalyst

2007

WOS: 000246040000026

Recognition, Transformation, Detection of Nucleotides and Aqueous Nucleotide-Based Materials

2019

Extraction of amino acids with emulsion liquid membranes using industrial surfactants and lecithin as stabilisers

2000

Abstract Industrial surfactants (being the mixtures of several individual compounds) were used as stabilisers of emulsion liquid membranes (ELMs). Although, some impurities present in technical formulations of these compounds were extracted to aqueous solutions of amino acids, most of the used surfactants well served to this purpose. In the case of amino acid transport, they do not act as carriers and application of additional carrier (such as D2EHP) was required in order to facilitate the transport. Interestingly, the same properties were found for lecithin, industrially important natural surfactant. Lecithin applied as a chiral discriminator, used either as an emulsion stabiliser or carri…

Concentration of amino acids using supported liquid membranes with di-2-ethylhexyl phosphoric acid as a carrier

1997

Abstract Basic studies of a procedure for extraction of amino acids using a supported liquid membrane containing di-2-ethylhexyl phosphoric acid are presented. The extractions are made from an aqueous donor phase with pH 3 to a more acidic acceptor phase and the mass transfer is driven by the proton gradient between these phases. For 0.01 mM tryptophan and with 1 M HCl as acceptor phase, an extraction efficiency of 60% is obtained, constant up to at least 12 h. This permits concentration enrichment factors linearly increasing with time up to values of at least 150. For higher amino acid concentrations, the extraction efficiency is constant only over shorter time intervals.

Interaction of Dimethyltin(IV)2+ Cation with Gly-Gly, Gly-His, and Some Related Ligands. A New Case of a Metal Ion Able To Promote Peptide Nitrogen D…

1999

Equilibrium (pH-metric) and spectroscopic (1H,13C, and 119Sn NMR and 119Sn Mossbauer) studies were performed to characterize the interaction of the dimethyltin(IV) cation with glycine, glycyl-glycine (Gly-Gly), imidazole-4-acetic acid, histamine, histidine, glycyl-histamine, glycyl-histidine (Gly-His), and β-alanyl-histidine (carnosine). For histamine and glycyl-histamine (having only nitrogen donor atoms) no complex formation was detected. The hydrolyzed species of the dimethyltin(IV) cation are always dominant over the complexes formed with the other ligands, except with Gly-Gly and Gly-His. For these two ligands, {COO-,N-,NH2} coordinated complexes are dominant in the neutral pH range wi…

A comparative study of the multicomponent Ugi reactions of an oxabicycloheptene-based β-amino acid in water and in methanol

2006

Di-exo-3-amino-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylic acid 1, five aldehydes and two isocyanides were reacted both in methanol and in water to prepare a 10-membered β-lactam library via a Ugi-4-centre-3-component reaction. The yields were found to be similar in water and methanol. The diastereoselectivities of the aqueous reactions were similar, though in a few cases higher than those in methanol. The benefits of water are the facile isolation of the precipitated product and the shorter reaction time.

A Photoredox-Catalyzed Four Component Reaction for the Atom-Efficient Synthesis of Complex Secondary Amines

2020

The one-pot sulfonylation/aminoalkylation of styrene derivatives furnishing highly substituted gamma-sulfonylamines was accomplished through a photoredox-catalyzed four-component reaction. Apart from one molecule of water and the sodium counterion of the sulfinate, all atoms of the starting materials are transferred to the final product, rendering this process highly atom-efficient. The operationally simple protocol allows for the simultaneous formation of three new single bonds (C–S, C–N, and C–C) and therefore grants rapid access to structurally diverse products. The reaction proceeds under mild conditions in aqueous acetonitrile and shows a broad scope, including natural products and dru…

Microwave synthesis of core-shell structured biocompatible magnetic nanohybrids in aqueous medium

2011

In the past decade, biocompatible magnetic nanohybrids, i.e. materials consisting of an inorganic core encapsulated by a biocompatible polymeric corona, went throw various developments in biomedical applications especially in the fields of diagnosis and therapy. Numerous descriptions of their syntheses can be found in the literature (Zhang et al., 2002; Flesch et al., 2004; Fan et al., 2007; etc). These two-steps protocols often describe the use of organic or aqueous solvents, classical thermal heating, long time reaction as well as fastidious exchange and drying steps. In recent years, microwave heating has been proven to be a very original technology for nanoparticles synthesis due to its…

Umwandlung von 2-Bromäthoxycarbonyl-Schutzgruppen in 2-Phosphonioäthoxycarbonyl-Schutzgruppen für Aminosäuren1)

1976

Die Bromide 2 von 2-Phosphonioathoxycarbonylaminosauren (Peoc-Aminosauren) werden durch Umsetzung von 2-Bromathoxycarbonylaminosauren (Beoc-Aminosauren) mit tertiaren Phosphinen erhalten. Hierbei entstehen durch Reaktion mit Methyl(diphenyl)phosphin die mit der modifizierten Peoc-Gruppe geschutzten Verbindungen 2e - h in besonders guten Ausbeuten. Diese eignen sich zur Peptidsynthese nach dem Carbodiimid-Verfahren und sind besser in Wasser loslich als die entsprechenden Triphenylphosphonium-Derivate. Die Abspaltung der Me(Ph2)Peoc-Gruppe gelingt mit 0.01 N NaOH in Methanol/Wasser. Modification of 2-Brornoethoxycarbonyl Protective Groups to 2-Phosphonioethoxycarbonyl Protective Functions of …