Search results for "Proton"
showing 10 items of 5886 documents
Coordination Chemistry of Cu2+ Complexes of Small N-Alkylated Tetra-azacyclophanes with SOD Activity
2018
A new tetraaza-pyridinophane macrocycle (L1) N-alkylated with two isopropyl and one methyl groups symmetrically disposed has been prepared and its behavior compared with those of the unsubstituted pyridinophane (L3) and the related compound with three methyl groups (L2). The protonation studies show that, first, a proton binds to the central methylated amine group of L1, while, second protonation leads to a reorganization of the protons that are at this stage attached to the lateral isopropylated amines. The X-ray structure of [HL1]+ agrees with the UV–vis and NMR studies as well as with the results of DFT calculations. The stability of the Cu2+ complexes decreases on increasing the bulkine…
111 Bioluminescence analysis and numerical evaluation of ATP-synthesis by native and reconstituted membranes containing bacterial ATP-synthase
1992
ATP-synthase is a large membrane protein complex, which plays a key role in the energy metabolism of most organisms. It consists of at least eight types of subunits and can be isolated and purified from several organisms, e.g. bacteria. The enzyme couples two reversible reactions: vectorial proton transport through a membrane and synthesis of the energy rich molecule ATP. Both can be investigated with vesicles from native membranes or with reconstituted liposomes from purified ATPsynthase. The analysis is complicated because ATP-synthase catalyzes ATP-synthesis as well as ATP-hydrolysis. Furthermore the ATP level of membrane samples is influenced by adenylate kinase activities of other enzy…
Strukturaufklärung der bei der Addition von 2-Cyano-2-propylradikalen an p-Tolyl- und 4-Cyclohexylphenyl-methacrylat entstehenden Produkte mittels 1H…
1978
The chromatographically pure products, gained on the suppression of polymerisation of p-tolyl or 4-cyclohexylphenyl methacrylates (1, 2) by a great excess of 2-cyano-2-propyl radicals, could be isolated in a total yield of 95 to 100%. The structure of these products was established by 1H NMR and mass spectroscopy. There are p-tolyl or 4-cyclohexylphenyl 4-cyano-2-(2-cyano-2-propyl)-2,4-dimethylvalerate (1a, 2a), p-tolyl or 4-cyclohexylphenyl 2-(2-cyano-2-methylpropyl)acrylate (1b, 2b), p-tolyl or 4-cyclohexylphenyl 4-cyano-4-methyl-2-(2-cyano-2-methylpropyl)valerate (1c, 2c), p-tolyl or 4-cyclohexylphenyl 4-cyano-2,4-dimethylvalerate (1d, 2d), and p-tolyl or 4-cyclohexylphenyl 4-cyano-2,4-d…
ChemInform Abstract: Dihydrooxazine Oxides as Key Intermediates in Organocatalytic Michael Additions of Aldehydes to Nitroalkenes.
2013
Pause and play: dihydrooxazine oxides are stable intermediates that are protonated directly, without the intermediacy of the zwitterions, in organocatalytic Michael additions of aldehydes and nitroalkenes (see scheme, R=alkyl). Protonation of these species explains both the role of the acid co-catalyst in these reactions, and the observed stereochemistry when the reaction is conducted with α-alkylnitroalkenes.
Trienediolates of hexadienoic acids in synthesis. synthesis of retinoic and nor-retinoic acids.
1993
Abstract Double deprotonation of either (E,E)-3-methyl-2,4-hexadienoic acid 2, or 4,6-dimethyldihydro-2-pyrone 3 generates apparently the same lithium trienediolate, which affords ω-hydroxy acids 9 on reaction with ketones 7. Hydroxy acids 9 are easily dehydrated to octatrienoic acids 5, which are structurally related to retinoic acid. Similarly, sorbic acid 1 leads to nor-retinoic acid analogs 6.
ChemInform Abstract: Conjugate Addition of Organolithium Reagents to α,β-Unsaturated Carboxylic Acids.
2010
Abstract Conjugate addition of primary, secondary, tertiary alkyl and phenyl lithium reagents to 2-alkenoic acids affords good yields of branched saturated carboxylic acids. Methyl groups at the α- and β-carbon of the 2-alkenoic acid decrease reactivity as acceptors, and foster deprotonation, respectively. The lithium enediolate resulting from the conjugate addition can react with electrophiles. PM3 calculations are in agreement with the substituent effects.
Acid—base properties of azo dyes in the presence of surfactants
1991
Abstract The changes in the acid—base properties of an azo dye produced by the presence of surfactants, at surfactant concentrations below and above the CMC, are quantitatively described using a simple model and spectrophotometric and potentiometric measurements. The azo dye formed by aniline and N -(1-naphthyl)-ethylenediamine, and the surfactants sodium dodecyl sulphate, Triton X-100 and N -cetylpyridinium chloride (NCPC) are used. The protonation constants of the free and surfactant-bound dye species, the binding constant of the protonated and unprotonated forms of the dye, and the average aggregation number of the dye—NCPC aggregates are evaluated.
Synthesis of Highly Substituted Unsymmetrical 1,2-Diamines, 1,2-Diimines, Imidazolium Salts and Imidazolylidenes by Aldimine Cross-Coupling
2007
α-Aminonitriles derived from aromatic aldehydes and primary amines can be deprotonated quantitatively without the use of protecting groups. The 1,2-addition of the resulting stabilized α-aminocarbanions to imines yields α-aminoimines and the tautomeric enediamines. These unstable compounds can directly be oxidized to 1,2-diimines or reduced to 1,2-diamines in a one-pot reaction. 1,2-Diamines can be obtained in high diastereoselectivity by reduction of the 1,2-diimines. In this case, the relative configuration of the products can be chosen depending on the reduction conditions. Cyclization of the unsymmetrical diimines with halomethyl ethers or esters leads to 1,3,4,5-tetrasubstituted imidaz…
Enantioselective Synthesis of α-Quaternary Amino Acids by Alkylation of Deprotonated α-Aminonitriles.
2015
A series of α-quaternary arylglycines were prepared in high optical purity (up to 98% ee) by α-alkylation of deprotonated α-aminonitriles derived by the Strecker reaction from (4S,5S)-5-amino-2,2-dimethyl-4-phenyl-1,3-dioxane. The procedure includes only chromatographic purification of the final products and is devoid of chromatography or crystallization operations on intermediates to raise the optical purity.
A novel synthesis of polymers with anthracene and dihydroanthracene subunits in the main chain
1993
A new polycondensation method to connect redox-active and chromophoric subunits by forming a C-C bond and leading to a polyhydrocarbon is described. 1,ω-bis(9,10-Dihydro-9-anthry)alkanes with various alkylene spacers can be deprotonated by butyllithium to afford a monoanion in each dihydroanthracene moiety. Alkylation with dielectrophiles such as dibromoalkanes yields soluble polymers with dihydroanthracene units in the main chain. The reaction proceeds regioselectively in the 9,10-position. Aromatization generates a polymer with anthracene units. The molecular weights are determined by GPC up to Mn = 10 000. To prove the structure and to calibrate the GPC, suitable model compounds were syn…