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Tetramer Formation (tetramer + formation)
Selected AbstractsTheoretical study of the oxidative polymerization of aniline with peroxydisulfate: Tetramer formationINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 2 2008-Marjanovi, Gordana Abstract Semi-empirical quantum chemical study of the oxidative polymerization of aniline with ammonium peroxydisulfate, in aqueous solutions without added acid, has been based on the MNDO-PM3 computations of thermodynamic, redox, and acid,base properties of reactive species and the intermediates, combined with the MM2 molecular mechanics force-field method and conductor-like screening model of solvation. The main reaction routes of aniline tetramerization are proposed. The regioselectivity of the formation of aniline tetramers by redox and electrophilic aromatic substitution reactions is analyzed. It was proved that the linear NC4 coupled tetra-aniline is formed as a dominant product by three different pathways: comproportionation redox reaction between N -phenyl-1,4-benzoquinonediimine and 4-aminodiphenylamine, the one-electron oxidation of aniline with its half-oxidized NC4 coupled trimer, and the electrophilic aromatic substitution reaction of aniline with fully oxidized NC4 coupled trianiline nitrenium cation. The electrophilic aromatic substitution reaction of the NC4 coupled aniline trimer with aniline nitrenium cation, as well as the oxidation of aniline with half-oxidized branched trimer, lead to the branched aniline tetramers. The competing character of different tetramerization routes is highlighted. The oxidative intramolecular cyclization of branched oligoanilines and polyaniline, leading to the generation of substituted phenazine units, has been predicted to accompany the classical routes of the polymerization of aniline. Various molecular (branched vs. linear) oligomeric structures produced at different level of acidity during the course of polymerization and their impact on the formation of supramolecular structures of conducting polyaniline (nanorods and nanotubes vs. granular morphology), are discussed. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Important region in the ,-spectrin C -terminus for spectrin tetramer formationEUROPEAN JOURNAL OF HAEMATOLOGY, Issue 2 2002Bing-Hao Luo Abstract: Many hereditary hemolytic anemias are due to spectrin mutations at the C -terminal region of ,-spectrin (the ,C region) that destabilize spectrin tetramer formation. However, little is known about the ,C region of spectrin. We have prepared four recombinant ,-peptides of different lengths from human erythrocyte spectrin, all starting at position 1898 of the C -terminal region, but terminating at position 2070, 2071, 2072 or 2073. Native polyacrylamide gel electrophoresis showed that the two peptides terminating at positions 2070 and 2071 did not associate with an N -terminal region ,-peptide (Sp,1,156) in the micromolar range. However, the peptides that terminated at positions 2072 and 2073 associated with the ,-peptide. Circular dichroism results showed that the unassociated helices in both ,- and ,-peptides became associated, presumably to form a helical bundle, for those ,-peptides that formed an ,, complex, but not for those ,-peptides that did not form an ,, complex. In addition, upon association, an increase in the ,-helical content was observed. These results showed that the ,-peptides ending prior to residue 2072 (Thr) would not associate with ,-peptide, and that no helical bundling of the partial domains was observed. Thus, we suggest that the C -terminal segment of ,-spectrin, starting from residue 2073 (Thr), is not critical to spectrin tetramer formation. However, the C -terminal region ending with residue 2072 is important for its association with ,-spectrin in forming tetramers. [source] Energetic aspects of locked nucleic acids quadruplex association and dissociationBIOPOLYMERS, Issue 6 2006Luigi Petraccone Abstract The design of modified nucleic acid aptamers is improved by considering thermodynamics and kinetics of their association/dissociation processes. Locked Nucleic Acids (LNA) is a promising class of nucleic acid analogs. In this work the thermodynamic and kinetic properties of a LNA quadruplex formed by the TGGGT sequence, containing only conformationally restricted LNA residues, are reported and compared to those of 2,-OMe-RNA (O-RNA) and DNA quadruplexes. The thermodynamic analysis indicates that the sugar-modified quadruplexes (LNA and O-RNA) are stabilized by entropic effects. The kinetic analysis shows that LNA and O-RNA quadruplexes are characterized by a slower dissociation and a faster association with respect to DNA quadruplex. Interestingly, the LNA quadruplex formation process shows a second-order kinetics with respect to single strand concentration and has a negative activation energy. To explain these data, a mechanism for tetramer formation with two intermediate states was proposed. © 2006 Wiley Periodicals, Inc. Biopolymers 83: 584,594, 2006 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Crystallization and X-ray structure of full-length recombinant human butyrylcholinesteraseACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 9 2007Michelle N. Ngamelue Human butyrylcholinesterase (BChE) has been shown to function as an endogenous scavenger of diverse poisons. BChE is a 340,kDa tetrameric glycoprotein that is present in human serum at a concentration of 5,mg,l,1. The well documented therapeutic effects of BChE on cocaine toxicity and organophosphorus agent poisoning has increased the need for effective methods of producing recombinant therapeutic BChE. In order to be therapeutically useful, BChE must have a long circulatory residence time or associate as tetramers. Full-length recombinant BChE produced in Chinese hamster ovary (CHO) cells or human embryonic kidney cells has been shown to associate as monomers, with a shorter circulatory residence time than the naturally occurring tetrameric serum protein. Based on the preceding observation as well as the need to develop novel methodologies to facilitate the mass production of therapeutic recombinant BChE, studies have been initiated to determine the structural basis of tetramer formation. Towards these ends, full-length monomeric recombinant BChE has been crystallized for the first time. A 2.8,Å X-ray structure was solved in space group P4212, with unit-cell parameters a = b = 156, c = 146,Å. [source] Elucidation of the mechanism and end products of glutaraldehyde crosslinking reaction by X-ray structure analysisBIOTECHNOLOGY & BIOENGINEERING, Issue 3 2007Yariv Wine Abstract Glutaraldehyde has been used for several decades as an effective crosslinking agent for many applications including sample fixation for microscopy, enzyme and cell immobilization, and stabilization of protein crystals. Despite of its common use as a crosslinking agent, the mechanism and chemistry involved in glutaraldehyde crosslinking reaction is not yet fully understood. Here we describe feasibility study and results obtained from a new approach to investigate the process of protein crystals stabilization by glutaraldehyde crosslinking. It involves exposure of a model protein crystal (Lysozyme) to glutaraldehyde in alkaline or acidic pH for different incubation periods and reaction arrest by medium exchange with crystallization medium to remove unbound glutaraldehyde. The crystals were subsequently incubated in diluted buffer affecting dissolution of un-crosslinked crystals. Samples from the resulting solution were subjected to protein composition analysis by gel electrophoresis and mass spectroscopy while crosslinked, dissolution resistant crystals were subjected to high resolution X-ray structural analysis. Data from gel electrophoresis indicated that the crosslinking process starts at specific preferable crosslinking site by lysozyme dimer formation, for both acidic and alkaline pH values. These dimer formations were followed by trimer and tetramer formations leading eventually to dissolution resistant crystals. The crosslinking initiation site and the end products obtained from glutaraldehyde crosslinking in both pH ranges resulted from reactions between lysine residues of neighboring protein molecules and the polymeric form of glutaraldehyde. Reaction rate was much faster at alkaline pH. Different reaction end products, indicating different reaction mechanisms, were identified for crosslinking taking place under alkaline or acidic conditions. Biotechnol. Bioeng. 2007;98:711,718. © 2007 Wiley Periodicals, Inc. [source] | ||||||||||