Reaction Partners (reaction + partner)

Distribution by Scientific Domains

Selected Abstracts

Synthesis and use of a pseudo-cysteine for native chemical ligation

David A. Alves
Abstract The process of native chemical ligation (NCL) is well described in the literature. An N -terminal cysteine-containing peptide reacts with a C -terminal thioester-containing peptide to yield a native amide bond after transesterification and acyl transfer. An N -terminal cysteine is required as both the N -terminal amino function and the sidechain thiol participate in the ligation reaction. In certain circumstances it is desirable, or even imperative, that the N -terminal region of a peptidic reaction partner remain unmodified, for instance for the retention of biological activity after ligation. This work discusses the synthesis of a pseudo- N -terminal cysteine building block for incorporation into peptides using standard methods of solid phase synthesis. Upon deprotection, this building block affords a de factoN -terminal cysteine positioned on an amino acid sidechain, which is capable of undergoing native chemical ligation with a thioester. The syntheses of several peptides and structures containing this motif are detailed, their reactions discussed, and further applications of this technology proposed. Copyright 2003 European Peptide Society and John Wiley & Sons, Ltd. [source]

Percolation model of hyperbranched polymerization

Henryk Galina
Abstract Computer simulations of the step-growth homopolymerization of an AB2 monomer have been carried out on a square lattice. No rearrangements of units were made between reaction events. Instead, the capture radius, i.e., the maximum distance between the randomly selected unit and its reaction partner was changed. The reaction was considered as controlled either by diffusion and local concentration fluctuations or by the law of mass action (classical limit). The size distribution of polymer species and the extent of cyclization reactions in the polymerization are discussed. [source]

Role of electrostatics in the interaction between plastocyanin and photosystem I of the cyanobacterium Phormidium laminosum

FEBS JOURNAL, Issue 23 2002
Beatrix G. Schlarb-Ridley
The interactions between photosystem I and five charge mutants of plastocyanin from the cyanobacterium Phormidium laminosum were investigated in vitro. The dependence of the overall rate constant of reaction, k2, on ionic strength was investigated using laser flash photolysis. The rate constant of the wild-type reaction increased with ionic strength, indicating repulsion between the reaction partners. Removing a negative charge on plastocyanin (D44A) accelerated the reaction and made it independent of ionic strength; removing a positive charge adjacent to D44 (K53A) had little effect. Neutralizing and inverting the charge on R93 slowed the reaction down and increased the repulsion. Specific effects of MgCl2 were observed for mutants K53A, R93Q and R93E. Thermodynamic analysis of the transition state revealed positive activation entropies, suggesting partial desolvation of the interface in the transition state. In comparison with plants, plastocyanin and photosystem I of Phormidium laminosum react slowly at low ionic strength, whereas the two systems have similar rates in the range of physiological salt concentrations. We conclude that in P. laminosum, in contrast with plants in vitro, hydrophobic interactions are more important than electrostatics for the reactions of plastocyanin, both with photosystem I (this paper) and with cytochrome f[Schlarb-Ridley, B.G., Bendall, D.S. & Howe, C.J. (2002) Biochemistry41, 3279,3285]. We discuss the implications of this conclusion for the divergent evolution of cyanobacterial and plant plastocyanins. [source]

Treatment of Carbon Tetrafluoride with Gas Discharges

Gerhard J. Pietsch
Abstract Waste gases from semiconductor industry contain perfluorocarbons, which cause global warming and therefore should be removed. There are several possibilities to do this, for example the treatment of the gas by thermal and non-thermal plasmas, as well as by heating. In model gases containing up to 10,000 ppm CF4, destruction removal efficiencies of nearly 100% have been reached at atmospheric pressure using dielectric barrier and arc discharges. In order to reach high values, the dissociation products of CF4 must be bonded by reaction partners such as SiO2, CaO or H2O. [source]

New Templating Strategies with Salen Scaffolds (Salen=N,N,-Bis(salicylidene)ethylenediamine Dianion)

Abstract Templated approaches towards selective organic synthesis is a common feature in nature in which nucleic acid templated synthesis plays a crucial role in various fundamental biological processes. The key feature that allows control over the amazing selectivity found in natural processes is evidently the effective molarity of the reaction partners that is mediated by the macromolecular templation event. An ongoing challenge within many chemical sciences is to exploit similar templating principles and make use of synthetic systems that are designed for specific chemical conversions. Here, we describe the recent developments that involve (metallo)salen scaffolds that are used for diverse templating events (salen=N,N,-bis(salicylidene)ethylenediamine dianion). [source]