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Complex Stability (complex + stability)
Selected AbstractsMacrocyclic Receptor Showing Improved PbII/ZnII and PbII/CaII SelectivitiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2010Raquel Ferreirós-Martínez Abstract Herein we report on the macrocyclic receptor N,N,-bis[(6-carboxy-2-pyridyl)methyl]-1,10-diaza-15-crown-5 (H2bp15c5) and its coordination properties towards ZnII, CdII, PbII, and CaII. The stability constants of these complexes determined by pH-potentiometric titration at 25 °C in 0.1 M KNO3 vary in the following order: PbII > CdII >> ZnII > CaII. As a result, bp15c5 presents very important PbII/ZnII and PbII/CaII selectivities. These results are in contrast to those reported for the related receptor derived from 1,7-diaza-12-crown-4, which provides very similar complex stabilities for ZnII and PbII. The X-ray crystal structure of [Cd(Hbp15c5)]+ shows heptadentate binding of the ligand to the metal ion, with two oxygen atoms of the macrocyclic unit remaining uncoordinated. The 1H NMR spectra of the complexes formed with PbII, ZnII, and CaII (D2O) show very broad peaks in the region 2,5 ppm, indicating an important degree of flexibility of the crownmoiety in these complexes. On the contrary, the 1H and 13C NMR spectra recorded for the CdII complex are well resolved and could be fully assigned. A detailed conformational investigation using theoretical calculations performed at the DFT (B3LYP) level predict a minimum energy conformation for [Cd(bp15c5)] that is very similar to that observed in the solid state. Analogous calculations performed on the [M(bp15c5)] (M = Zn or Pb) systems predict hexadentate binding of the ligand to these metal ions. In the case of the PbII complex our calculations indicate that the 6s lone pair is stereochemically active, which results in a hemidirected coordination geometry around the metal ion. The minimum energy conformations calculated for the ZnII, CdII, and PbII complexes are compatible with the experimental NMR spectra obtained in D2O solution. [source] Structural Trends in Divalent Benzil Bis(thiosemicarbazone) ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2005David G. Calatayud Abstract Redox-related changes in the biological properties of copper bis(thiosemicarbazones) are induced by the backbone of the ligand. To get information about how these changes depend on the structural parameters, three X-ray structures of complexes with different behaviour of the benzil bis(thiosemicarbazone) ligand have been determined. These include two almost planar copper(II) complexes with different grades of deprotonation in the ligand and a ZnII complex in which the ligand acts as a monoanion and a nitrate group is bonded to the metal ion in a square-based pyramid. The changes in the backbone bond lengths agree with the variation in the ionic radius and with the grade of electronic charge delocalisation in the chelate rings; these have consequences for the coordination sphere, allowing the metal to fit slightly better into the ligand cavity, which in turn may affect the complex stability and the redox potential. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Effect of the disease-causing mutations identified in human ribonuclease (RNase) H2 on the activities and stabilities of yeast RNase H2 and archaeal RNase HIIFEBS JOURNAL, Issue 19 2008Muhammad S. Rohman Eukaryotic ribonuclease (RNase) H2 consists of one catalytic and two accessory subunits. Several single mutations in any one of these subunits of human RNase H2 cause Aicardi,Goutičres syndrome. To examine whether these mutations affect the complex stability and activity of RNase H2, three mutant proteins of His-tagged Saccharomyces cerevisiae RNase H2 (Sc-RNase H2*) were constructed. Sc-G42S*, Sc-L52R*, and Sc-K46W* contain single mutations in Sc-Rnh2Ap*, Sc-Rnh2Bp*, and Sc-Rnh2Cp*, respectively. The genes encoding the three subunits were coexpressed in Escherichia coli, and Sc-RNase H2* and its derivatives were purified in a heterotrimeric form. All of these mutant proteins exhibited enzymatic activity. However, only the enzymatic activity of Sc-G42S* was greatly reduced compared to that of the wild-type protein. Gly42 is conserved as Gly10 in Thermococcus kodakareansis RNase HII. To analyze the role of this residue, four mutant proteins, Tk-G10S, Tk-G10A, Tk-G10L, and Tk-G10P, were constructed. All mutant proteins were less stable than the wild-type protein by 2.9,7.6 °C in Tm. A comparison of their enzymatic activities, substrate binding affinities, and CD spectra suggests that the introduction of a bulky side chain into this position induces a local conformational change, which is unfavorable for both activity and substrate binding. These results indicate that Gly10 is required to make the protein fully active and stable. [source] Evaluation of the silanol-suppressing potency of ionic liquidsJOURNAL OF SEPARATION SCIENCE, JSS, Issue 8 2006Micha, Piotr Marsza Abstract Recently, increasing attention has been paid to the use of ionic liquids for high-performance liquid chromatography (HPLC) and capillary electrophoresis. In the present study, the silanol-suppressing potency of ionic liquids was evaluated by HPLC using the two-retention site model proposed previously by Nahum and Horváth (J. Chromatogr. 1981, 203, 53,63). The binding constant, KA, in that approach has been demonstrated to reliably reflect the ability of the ionic liquids to block the silanols of the silica support material of the stationary phase. The determinations were carried out for ionic liquids of the 1-alkyl-3-methylimidazolium group with the use of a series of basic drugs as the test analytes. Comparison of ionic liquids with standard mobile phase additives such as triethylamine showed the former to possess advantages as silanol suppressors in HPLC. The main advantage of the method is that it provides a simple and fast determination of the silanol complex stability, which allowed comparison of the suppressing efficiency of several ionic liquids. [source] Application of quantitative immunoprecipitation combined with knockdown and cross-linking to Chlamydomonas reveals the presence of vesicle-inducing protein in plastids 1 in a common complex with chloroplast HSP90CPROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 11 2009Heinrich Heide Abstract Knowledge of the interaction partners of a protein of interest may provide important information on its function. Common to currently available tools for the identification of protein,protein interactions, however, is their high rates of false positives. Only recently an assay was reported that allowed for the unequivocal identification of protein,protein interactions in mammalian cells in a single experiment. This assay, termed quantitative immunoprecipitation combined with knockdown (QUICK), combines RNAi, stable isotope labeling with amino acids in cell culture, immunoprecipitation, and quantitative MS. We are using the unicellular green alga Chlamydomonas reinhardtii to understand the roles of chaperones in chloroplast biogenesis. The goal of this work was to apply QUICK to Chlamydomonas for the identification of novel interaction partners of vesicle-inducing protein in plastids 1 (VIPP1), a protein required for the biosynthesis/maintenance of thylakoid membranes and known substrate of chloroplast HSP70B. We report here a robust QUICK protocol for Chlamydomonas that has been improved (i) by introducing a cross-linking step (-X) to improve protein complex stability and (ii) by including a control for the correction of unequal immunoprecipitation and/or labeling efficiencies. Using QUICK and cross-linking we could verify that HSP70B and CGE1 form a complex with VIPP1 and could also demonstrate that chloroplast HSP90C is part of this complex. Moreover, we could show that the chaperones interact with VIPP1 also in membrane fractions. [source] Gas-phase behavior of noncovalent transmembrane segment complexesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 24 2008Linda M. M. Weigang Specific helix oligomerization between transmembrane segments (TMSs) is often promoted by motifs like GxxxG. Disruption of this motif in the transmembrane segments of vesicular stomatitis virus G-protein and of glycophorin A results in a reduced dimerization level studied by in vivo systems like ToxR. This paper reports the influence of sequence motifs like GxxxG in solution and the gas phase. The transmembrane segments may behave differently in the gas and liquid phase, because of the absence of surrounding solvent molecules in the gas phase. Comparison of experiments depending on peptide properties performed in the gas and liquid phase discloses that the peptides retain ,some memory' of their liquid-phase structure in the gas phase. A direct correlation has been found between helicity in solution as determined by circular dichroism and dimerization in the gas phase monitored by electrospray mass spectrometry. These results show that a proper folding in solution is required for oligomerization. On the other hand, sequence-specific oligomerization depending on the GxxxG motif was not observed with the mass spectrometric detection. Further on, neither concentration-dependent complex studies nor studies regarding complex stability in the gas phase , via collision-induced dissociation (CID) , led to sequence-specific differences. Finally, the findings show that in mass spectrometric measurements noncovalent interactions of studied TMSs is rather more dependent on the secondary structure and proper folding than on their primary structure. Copyright © 2008 John Wiley & Sons, Ltd. [source] Minimum sequence requirements for the binding of paromomycin to the rRNA decoding site ABIOPOLYMERS, Issue 2 2007Peter C. Anderson Abstract We have recently introduced a computational methodology that combines molecular dynamics (MD) simulations, free-energy calculations, and in vitro binding assays to predict the minimum RNA structural requirements for selective, high-affinity RNA binding to small-molecule ligands. Here, we show that this methodology can be applied to the conformationally flexible aminoglycoside antibiotic paromomycin. A RNA consisting of an 11-mer:10-mer duplex that contains one 16S ribosome RNA decoding A-site bound to paromomycin was simulated for 4 ns. The methodology predicts that the 11-mer:10-mer duplex binds to paromomycin with high affinity, whereas smaller RNA duplexes lose complex stability and the ability to bind paromomycin. The predicted high-affinity binding to paromomycin of the 11-mer:10-mer duplex was confirmed experimentally (EC50 = 0.28 ,M), as well as the inability of smaller complexes to bind. Our simulations show good agreement with experiment for dynamic and structural properties of the isolated A-site, including hydrogen-bonding networks and RNA structural rearrangements upon ligand binding. The results suggest that MD simulations can supplement in vitro methods as a tool for predicting minimum RNA-binding motifs for both small, rigid ligands, and large, flexible ligands when structural information is available. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 95,111, 2007. 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] | ||||||||||