Search results for "Ion pairs"
showing 10 items of 19 documents
Ion-Pairing Effects in the Self-Assembly of a Fluorescent Pseudorotaxane
2006
Herein we report on the self-assembly, in a low polarity solvent, of a pseudorotaxane species comprising binaphthyl-26-crown-8 (BN26C8) as the macrocyclic host and anthracenyl-benzylammonium as the threadlike positively charged guest (ABH+). Absorption and luminescence data reveal a very efficient energy transfer process occurring from the binaphthyl to the anthracene singlet excited states. The self-assembly is highly dependent on the nature of the counteranion confirming the crucial role played by it in the competition between the self-assembly process and the formation of ion pairs (ABH+X-). This behavior can be readily evidenced in dilute solutions from the analysis of the luminescence …
Protonation of Carbonate in Aqueous Tetraalkylammonium Salts at 25°C.
2006
Protonation constants of carbonate were determined in tetramethylammonium chloride (Me4NClaq 0.1≤I/mol kg−1 ≤4) and tetraethylammonium iodide (Et4NIaq 0.1≤I/mol kg−1 ≤1) by potentiometric ([H+]-glass electrode) measurements. Dependence of protonation constants on ionic strength was taken into account by modified specific ion interaction theory (SIT) and by Pitzer models. Literature data on the protonation of carbonate in NaClaq (0.1≤I/mol kg−1 ≤6) were also critically analysed. Both protonation constants of carbonate follow the trend Et4NI>Me4NCl > NaCl. An ion pair formation model designed to take into account the different protonation behaviours of carbonate in different supporting electr…
Amine basicity: measurements of ion pair stability in ionic liquid media
2007
Abstract The stability constants relevant to the formation of amine/p-nitrophenol ion pairs have been determined in [bmim][BF4] solution, in the presence of butylamine, piperidine, and triethylamine, by using spectrophotometric measurements. In order to evaluate how the ion pair stability is affected by ionic liquid structure, piperidine has been chosen as model amine for studies in [bmim][PF6], [bmim][NTf2], [bm2im][NTf2] and in several [bmim][BF4]/1,4-dioxane binary mixtures. Data obtained in ionic liquid solutions have been compared with those previously reported in conventional organic solvents.
Über den einfluß der monomerkonzentration auf die geschwindigkeitskonstante kw der monomeraddition an das ionenpaar eines „lebenden” polymeren
1966
Fur den Zahlenwert der Geschwindigkeit skonstante kw(±) fanden die Arbeitsgruppen in Mainz und Syracuse voneinander abweichende Werte. Es wurde angenommen, das die Ursache dieser Diskrepanz die um Grosenordnungen verschiedenen Konzentrationsbereiche sind, in denen die Messungen ausgefuhrt wurden. Nachfolgend wird ein Reaktionsschema vorgeschlagen und kinetisch durchgerechnet, welches eine schneller polymerisierende Komplexverbindung zwischen dem Ionenpaar und dem Monomeren voraussetzt. The rate constant kw(±) for the addition of monomer to the ion pair of a „living” polymer was measured by workers in Mainz and in Syracuse. Their results lack agreement. It was assumed that this disparity is …
Extractive Spectrophotometric Determination of Ondansetron by Ion-Pair Formation with Bromocresol Green
1996
Abstract An empirical spectrophotometric procedure for the determination of the antiemetic ondansetron is carried out. The method is based on the formation of a 1:1 ion pair with bromocresol green in the pH range over 3.2 – 4.4, extraction into chloroform layer and spectrophotometric measurement at 420.8 nm. The calibration graph is linear over the range 0.1 – 20 μg ml−1 ondansetron, with a relative standard deviation of 2.7%; the influence of foreign substances is also studied. The method is applied to ondansetron determination in human urine.
Kinetic control in the chiral recognition of three-bladed propellers
2010
The ion pair of the stereolabile C(3)-symmetric, i(+)o proton complex [1H](+) of diaza-macropentacycle 1 and the configurationally stable Delta-TRISPHAT ([Delta-3](-)) anion exists in the form of two diastereomers, namely, [Delta-(1.H)][Delta-3] and [Lambda-(1.H)][Delta-3], the ratio of which, in terms of diastereomeric excess (de) decreases in the order [D(8)]THF (28%)CD(2)Cl(2) (22%)CDCl(3) (20%)[D(8)]toluene (16%)C(6)D(6) (7%)[D(6)]acetone (0%) at thermodynamic equilibrium. Except in the case of [D(6)]acetone, the latter is reached after a period of time that increases from 1 h ([D(8)]THF) to 24 h (CDCl(3)). Moreover, the initial value of the de of [1.H][Delta-3] in CDCl(3), before the t…
Low-Q peak in X-ray patterns of choline-phenylalanine and homophenylalanine: a combined effect of chain and stacking
2016
Abstract In this contribution we report for the first time the X-ray patterns of choline-phenylalanine and choline-homophenylalanine ionic liquids. The presence of a low Q peak in both systems is another evidence that a long alkyl chain is not always needed to establish a nanodomain segregation in the liquid sufficient to be revealed by the diffraction experiment. These new data are compared with the diffraction patterns and the theoretical calculations of other choline-aminoacid ionic liquids recently reported. A significant role might be played by the stacking interactions between aromatic rings.
Leitfahigkeitsmessungen an Polystyrylnatrium in Dimethoxiäthan (DME) und Tetrahydrofuran (THF)
1971
An Polystyrylnatrium werden in zwei polaren organischen Losungsmitteln Leitfahigkeitsmessungen uber einen groseren Temperaturbereich ausgefuhrt. Aus der Temperaturabhangigkeit der Dissoziationskonstante ergibt sich, das die undissoziierte Verbindung in zwei Formen, dem Kontaktionenpaar (I) und dem solvatgetrennten Ionenpaar (II), vorkommt. Enthalpie- und Entropiedifferenz beim ubergang von I nach II, sowie die entsprechenden thermodynamischen Parameter der Dissoziation von II werden ermittelt. Der effektive Ladungsabstand im solvatgetrennten Ionenpaar betragt etwa 7 A. Conductivity measurements were carried out with polystyryl sodium in two polar solvents within a large temperature range. T…
Development of an efficient system for the separation of indole alkaloids by high performance liquid chromatography and its applications
2001
An efficient system for the analysis of indole alkaloids by HPLC on a reversed-phase column using an ion pair technique is described. The optimised chromatographic conditions allowed the successful separation of 22 standard monoterpenoid indole alkaloids (including some isomers) and tryptamine. The described HPLC system was applied to the analysis of alkaloids in intergeneric somatic hybrid cell cultures of Rauvolfia serpentina x Rhazya stricta.
N-Heterocyclic Phosphenium, Arsenium, and Stibenium Ions as Ligands in Transition Metal Complexes: A Comparative Experimental and Computational Study
2005
Reaction of 2-chloro-1,3,2-diazaarsolenes and -diazaphospholenes with Tl[Co(CO)4] gives instable complexes of type [Co(ER2)(CO)4] which decarbonylated to yield [Co(ER2)(CO)3]. Spectroscopic and X-ray diffraction studies revealed that the tetracarbonyl complexes can be formulated as ion pair for E = P and as covalent metalla-arsine for E = As, and the tricarbonyl complexes as carbene-like species with a formal E=Co double bond. A similar reactivity towards Tl[Co(CO)4] was also inferred for 1,3,2-diazastibolenes although the products were not isolable and their constitution remained uncertain. Evaluation of structural and computational data suggests that the weak and polarized Co–As bond in […