Search results for " solution"
showing 10 items of 3084 documents
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…
Equilibrium solution coordination chemistry
2018
Welcome to this themed issue of New Journal of Chemistry entitled “Equilibrium Solution Coordination Chemistry”.
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 …
Die polymerisation und pfropf-mischpolymerisation des acroleins unter dem einfluß von Co - 60 - gamma - strahlen. Polymere acroleine. 14. Mitteilung
1959
Die Polymerisation des Acroleins im reinen Zustand und in Losung unter dem Einflus von γ-Strahlen wird beschrieden und mit anderen Polymerisations-Methoden verglichen. Bei der Block-Polymerisation entsteht ein stark vernetztes, glasartiges Polymerisat, das in wasriger schwefliger Saure unloslich ist. In Losung polymerisiert das Acrolein viel rascher; die relative Geschwindigkeit der Polymerisation ist am grosten in wasriger Losung. Das hier erhaltene Polymere enthalt reaktionsfahige Aldehyd-Gruppen und ist loslich in schwefliger Saure. Acrolein last sich auf Polymethacrylester aufpfropfen. Sowohl oberflachliche als auch durchgehende Pfropfung vorgeformter Proben des Polymethacrylesters ist …
Structural characterization in solution of multifunctional nucleotide coordination systems
2000
The interaction in aqueous solution of the cyclophane receptors 2,6,10,13,17,21-hexaaza[22]orthocyclophane (L11) and 2,6,10,13,17,21-hexaaza[22]paracyclophane (L22) with the nucleotides ATP, ADP and AMP has been studied by pH titration and NMR. The obtained results are compared with those previously reported for the analogous meta-substituted receptor 2,6,10,13,17,21-hexaaza[22]metacyclophane (L). All the experimental data support the actuation of these cyclophane molecules as multi-point binders of nucleotides through electrostatic, hydrogen bonding and π-stacking interactions. The combined use of NMR and molecular dynamics permits us to get a rather reliable picture of the way in which th…