Borate Anion (borate + anion)

Distribution by Scientific Domains

Selected Abstracts

Anionic Gold(I) Complexes,Twelve- and Ten-Vertex Monocarba- closo -borate Anions with Carbon,Gold , Bonds

Maik Finze Dr.
Abstract The anionic gold(I) complexes [1-(Ph3PAu)- closo -1-CB11H11], (1), [1-(Ph3PAu)- closo -1-CB9H9], (2), and [2-(Ph3PAu)- closo -2-CB9H9], (3) with gold,carbon 2c,2e , bonds have been prepared from [AuCl(PPh3)] and the respective carba- closo -borate dianion. The anions have been isolated as their Cs+ salts and the corresponding [Et4N]+ salts were obtained by salt metathesis reactions. The salt Cs- 3 isomerizes in the solid state and in solution at elevated temperatures to Cs- 2 with ,Hiso=(,755),kJ,mol,1 (solid state) and ,H,=(11810),kJ,mol,1 (solution). The compounds were characterized by vibrational and multi-NMR spectroscopies, mass spectrometry, elemental analysis, and differential scanning calorimetry. The crystal structures of [Et4N]- 1, [Et4N]- 2, and [Et4N]- 3 were determined. The bonding parameters, NMR chemical shifts, and the isomerization enthalpy of Cs- 3 to Cs- 2 are compared to theoretical data. [source]

Designing Ionic Liquids: 1-Butyl-3-Methylimidazolium Cations with Substituted Tetraphenylborate Counterions

Joep van den Broeke
Abstract The hydrophobic, low melting, 1-butyl-3-methylimidazolium (BMIm) salts [BMIm][BPh4] (1), [BMIm][B(C6H4Me-4)4] (2), [BMIm][B{C6H4(CF3)-4}4] (3), [BMIm][B{C6H3(CF3)2 -3,5}4] (4), [BMIm][B{C6H4(C6F13)-4}4] (5), [BMIm][B{C6H4(SiMe3)-4}4] (6), [BMIm][B(C6H4{SiMe2(CH2CH2CF3)}-4)4] (7), [BMIm][B{C6H4(SiMe2C8H17}-4}4] (8) and [BMIm][B(C6H4{SiMe2(CH2CH2C6F13)}-4)4] (9) have been prepared. Systematic variation of the substituents on the tetraphenylborate anion allowed an assessment of their influence on the physical properties of the imidazolium salts. Structural investigations using NMR and IR spectroscopy, combined with single crystal X-ray structure determinations for 2, 3, 5 and 6, revealed hydrogen-bonding interactions between the imidazolium ring protons and the borate anion, both in the solid state and in solution. These interactions are weakened upon the introduction of electron-withdrawing substituents in the anion and follow the order 3,5-(CF3)2 < ,C6F13 < ,CF3 < ,SiMe2CH2CH2C6F13 < ,SiMe2CH2CH2CF3 < ,H < ,Me < ,SiMe3. The melting points of the salts depend primarily on the bulk of the lipophilic substituents, and decrease with increasing size. Bulky lipophilic substituents dramatically enhance the solubility of the imidazolium borates 8 and 9 in hexane and reduce their relative polarity. These unique properties make imidazolium borates 8 and 9 interesting as amphiphilic ionic liquids with low polarity. Attempts to crystallise 7 resulted in decomposition. A single-crystal X-ray structure determination of the product, isolated in 6% yield, showed that a carbene,tris[4-{dimethyl(3,3,3-trifluoropropyl)silyl}phenyl]borane adduct was formed. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

Styrylpyridinium borate salts as dye photoinitiators of free-radical polymerization

Beata J, drzejewska
Abstract Styrylpyridinium borate salts photoinitiate free-radical polymerization. The rate of photopolymerization depends on the ,Go of electron transfer between a borate anion and a styrypyridinium cation. This latter value was estimated for a series of styrylpyridinium borate salts, and the relationship between the rate of polymerization and the free energy of activation gives the dependence predicted by the classical theory of electron transfer. This relation was independently observed for the two series of styrylpyridinium borate salts tested,one for the photoredox pair with an iodine atom and the second without. Styrylpyridinium borate salts were stable at ambient temperature in the formulations prepared for the photopolymerization experiments. Photopolymerization initiated by the photoredox pairs tested proceeded by the conventional mechanism in which bimolecular termination occurs by a reaction between two macroradicals. 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1433,1440, 2002 [source]

Modeling the electrophoresis of oligoglycines

Stuart A. Allison
Abstract The electrophoretic mobility of low molecular mass oligoglycines is examined in this study using a "coarse-grained" bead modeling methodology [Pei, H., Allison, S. A., J. Chromatogr. A 2009, 1216, 1908,1916]. The advantage of focusing on these peptides is that their charge state is well known [Plasson, R., Cottet, H., Anal. Chem. 2006, 78, 5394,5402] and extensive electrophoretic mobility data are also available in different buffers [Survay, M. A., Goodall, D. M., Wren, S. A. C., Rowe, R. C., J. Chromatogr. A 1996, 741, 99,113] and over a broad range of temperatures [Plasson, R., Cottet, H., Anal Chem. 2005, 77, 6047,6054]. Except for assumptions about peptide secondary structure, the B model has no adjustable parameters. It is concluded that the oligoglycines adopt a random configuration at high temperature (50C and higher), but more compact conformations at lower temperature. It is proposed that triglycine through pentaglycine adopt compact cyclic structures at low temperature (up to about 25C) in aqueous solution. At 25C, buffer interactions are also examined and may or may not influence peptide conformation depending on the buffer species. In a borate buffer at high pH, the mobility data are consistent with complex formation between the oligoglycine and borate anion. [source]

Analysis of glycopeptide antibiotics using micellar electrokinetic chromatography and borate complexation

Carmelle Lucas
Abstract Micellar electrokinetic chromatography (MEKC) was investigated as a technique for the separation and analysis of the following related glycopeptide antibiotics: ,-avoparcin, ,-avoparcin, ristocetin A, ristocetin B and vancomycin. Sodium dodecyl sulfate (SDS) micelles were employed as the pseudostationary phase in conjunction with borate or CHES buffers at pH 9.2. A complete separation of the glycopeptides was achieved only when two separation mechanisms were employed simultaneously: (i) differential partitioning of the glycopeptides into SDS micelles; and (ii) differential complexation of the glycopeptides with the borate anion from the borate buffer. Quantitatively, linearity was confirmed for each antibiotic from 0.5 to 40,ppm, with correlation coefficients (r2) ranging from 0.9996 (vancomycin and ,-avoparcin) to 0.9986 (,-avoparcin). Detection limits ranging from 0.01,ppm (vancomycin) to 0.2,ppm (avoparcin) were achieved, and the mean recovery of avoparcin at the 10,ppm level was 99.2%. Copyright 2003 John Wiley & Sons, Ltd. [source]

Capillary electrophoresis analysis of glucooligosaccharide regioisomers

Gilles Joucla
Abstract Complex gluco-oligosaccharide mixtures of two regioisomer series were successfully separated by CE. The gluco-oligosaccharide series were synthesized, employing a dextransucrase from Leuconostoc mesenteroides NRRL B-512F, by successive glucopyranosyl transfers from sucrose to the acceptor glucose or maltose. The glucosyl transfer to both acceptors, occurring through the formation of ,1,6 linkages, differed for the two series only in the glucosidic bond to the reducing end namely ,1,6 or ,1,4 bond for glucose or maltose acceptor, respectively. Thus, the combination of the two series results in mixed pairs of gluco-oligosaccharide regioisomers with different degrees of polymerization (DP). These regioisomer series were first derivatized by reductive amination with 9-aminopyrene-1,4,6-trisulfonate (APTS). Under acidic conditions using triethyl ammonium acetate as electrolyte, the APTS-gluco-oligosaccharides of each series were separated enabling unambiguous size determination by coupling CE to electrospray-mass spectrometry. However, neither these acidic conditions nor alkaline buffer systems could be adapted for the separation of the gluco-oligosaccharide regioisomers arising from the two combined series. By contrast, increased resolution was observed in an alkaline borate buffer, using differential complexation of the regioisomers with the borate anions. Such conditions were also successfully applied to the separation of glucodisaccharide regioisomers composed of ,1,2, ,1,3, ,1,4, and ,1,6 linkages commonly synthesized by glucansucrase enzymes. [source]