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Dimerization Reaction (dimerization + reaction)

Distribution by Scientific Domains

Chemistry	100%

Selected Abstracts

ChemInform Abstract: Novel Formaldehyde-Mediated Dimerization Reaction of N-Alkyl-1-naphthylamine Derivatives under Mild/Neutral Conditions; Application to Synthesis of Naphthylamine-Derived Macrocycles.

CHEMINFORM, Issue 15 2002
Hiroyasu Takahashi
Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]

Electrochemical Approach to the Radical Anion Formation from 2,-Hydroxy Chalcone Derivatives

ELECTROANALYSIS, Issue 5 2006
P. Quintana-Espinoza
Abstract Three 2,-hydroxy chalcone derivatives were electrochemically reduced to the radical anion by a reversible one-electron transfer followed by a chemical dimerization reaction. Under suitable conditions of the medium, the one-electron reduction produces very well resolved cyclic voltammograms due to the formation of the radical anion. By using appropriately the wide versatility of the cyclic voltammetric technique, was possible to study the generation of the radical anion and its stability. [source]

Voltammetric Study of Nitro Radical Anion Generated from Some Nitrofuran Compounds of Pharmacological Significance

ELECTROANALYSIS, Issue 1 2003
S. Bollo
Abstract The electrochemical behavior of 2-(5-amino- 1,3,4-oxadiazolyl)-5-nitrofuran (NF359) and its comparison with well-known drugs such as nifurtimox (NFX) and nitrofurazone (NFZ) in protic, mixed and aprotic media by cyclic voltammetry, tast and differential pulse polarography was studied. All the compounds were electrochemically reducible in all media being the reduction of the nitrofuran group the main voltammetric signal. The one-electron reduction couple due to the nitro radical anion formation was visualized in mixed (for NF359 and NFZ) and aprotic media (for all compounds). By applying a cyclic voltammetric methodology we have calculated the decay constants (k2) of the corresponding nitro radical anions in mixed and aprotic media. In mixed medium data fit well with a disproportionation reaction of the nitro radical anion but in aprotic medium fit better with a dimerization reaction. Also, considering cyclic voltammetric measurements in aprotic media we have estimated the reduction potential of the RNO2/RNO2., couple in aqueous medium, pH 7 (E17 values) finding very good correlation with E17 values obtained by pulse radiolysis. Furthermore we have calculated the equilibrium constants from the electron transfer from nitro radical anion to oxygen (kO2) finding that nitro radical anion from NF359 is thermodynamically favored to react with oxygen in respect to both NFZ and NFX. [source]

Thermal dimerization kinetics of 3-(p -bromo-phenyl)-pyridazinium benzoyl methylid in solutions

INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2008
V. Melnig
3-(p -Bromo-phenyl)-pyridazinium-benzoyl methylid (BPPBM) participates in solution at 3 + 3 dipolar thermal dimerization that can be spectrally monitored by the extinction in its visible intramolecular charge transfer (ICT) band. The attenuation of ICT band intensity shows the decrease of the BPPBM concentration with the increasing of dimer concentration. The complex kinetics of light-assisted dimerization process was studied taking into account that the thermodynamic equilibrium is reached after more than 24 h. On the basis of general order of reaction theory, we found that the dimerization reaction must be described as a multistep mechanism. The rate constants of the dimerization reactions in ethanol (k = 0.00897 s,1) and benzene (k = 0.00774 s,1) solutions were correlated with the BPPBM and dimer structural features established by using the HyperChem 5.02 simulation program package. A kinetic mechanism of 3 + 3 dipolar thermal dimerization for the studied ylid is proposed. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 230,239, 2008 [source]

An enigmatic peptide ligation reaction: Protease-catalyzed oligomerization of a native protein segment in neat aqueous solution

PROTEIN SCIENCE, Issue 4 2000
Sangaralingam Kumaran
Abstract We report an enigmatic peptide ligation reaction catalyzed by Glu-specific Staphylococcus aureus V8 protease that occurs in neat aqueous solution around neutral pH utilizing a totally unprotected peptide substrate containing free ,-carboxyl and ,-amino groups. V8 protease catalyzed a chain of ligation steps between pH 6 and 8 at 4 °C, producing a gamut of covalent oligomers (dimer through octamer or higher) of a native protein segment TAAAKFE (S39) derived from ribonuclease A (RNAse A). Size-exclusion chromatography suggested the absence of strong interaction between the reacting peptides. The circular dichroism spectra of monomer through pentamer showed length-dependent enhancement of secondary structure in the oligomers, suggesting that protease-catalyzed ligation of a monomer to an oligomer resulted in a product that was more structured than its precursor. The relative conformational stability of the oligomers was reflected in their ability to resist proteolysis, indicating that the oligomerization reaction was facilitated as a consequence of the "conformational trapping" of the product. The ligation reaction proceeded in two phases,slow formation and accumulation of the dimer followed by a fast phase of oligomerization, implying that the conformational trap encountered in the oligomerization reaction was a two-step process. The Gly substitution at any position of the TAAAKFE sequence was deleterious, suggesting that the first step of the conformational trap, namely the dimerization reaction, that proceeded very slowly even with the parent peptide, was quite sensitive to amino acid sequence. In contrast, the oligomerization reaction of an Ala analog, AAAAKFE, occurred in much the same way as S39, albeit with faster rate, suggesting that Ala substitution stabilized the overall conformational trapping process. The results suggest the viability of the product-directed "conformational trap" as a mechanism to achieve peptide ligation of totally unprotected peptide fragments in neat aqueous solution. Further, the study projects the presence of considerable innate synthetic potential in V8 protease, baring rich possibilities of protein engineering of this enzyme to generate a "V8 peptide ligase." [source]

Supramolecular Solids as a Medium for Single-Crystal-to-Single-Crystal E/Z Photoisomerization: Kinetic Study of the Photoreactions of Two Zn-Coordinated Tiglic Acid Molecules

CHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2008
Shao-Liang Zheng Dr.
Abstract [Zn(TA)2(H2O)2] (H-TA=tiglic acid) has been embedded in a framework composed of CECR (CECR=C -ethylcalix[4]resorcinarene) molecules to examine its E,Z photoisomerization in a periodic framework. The photoisomerization of tiglic acid in CECR-[Zn(TA)2(H2O)2],4,H2O proceeds without the [2+2]-dimerization reaction that often occurs in crystals of uncomplexed analogues, and without breakdown of the crystal lattice that frequently occurs in neat crystals. The two Zn-coordinated TA molecules are located in different size cavities. The rate constants of the isomerization reaction are strongly affected by the size of the reaction cavity. Analysis of the temperature dependence of the reaction rates and the occupancies in the final photostationary state shows that the activation energies and the standard enthalpies of activation are dependent on the difference between the reaction cavities. This is the first quantitative diffraction study of solid-state E/Z isomerization of a metal-coordinated ligand in a periodic host environment. [source]

Solid-State Photodimerization of Guest Molecules in Inclusion Compounds

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2006
Irena Zouev
Abstract Photochemical dimerization reactions of 1,3-diphenyl-1-propen-3-one (chalcone), 9-acetylanthracene, and 9-(methoxycarbonyl)anthracene as guest molecules in inclusion compounds with 1,1,6,6-tetraphenyl-2,4-hexadiyne-1,6-diol were studied. The irradiation of a single crystal containing chalcone was carried out in a single step and resulted in a single crystal containing the photodimer in full occupancy. In the case of the crystal containing 9-acetylanthracene, X-ray diffraction data were collected after irradiation for different periods of time. Only one of the two crystallographically independent pairs of 9-acetylanthracene underwent solid-state photodimerization at ca. 11,% conversion to the head-to-tail dimer. Photodimerization of the 9-(methoxycarbonyl)anthracene inclusion compound led, after irradiation for 2.5 h, to ca. 37,% conversion. It was found that the molecules that were arranged in stacks had undergone photodimerization in two different ways, so that on the average it looked as if all the guest molecules had polymerized. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]