Search results for "HYDROGEN"

Complexation of the potassium ion by diaza crown compounds in aqueous solutions

1988

The conductance behavior of potassium nitrate in water with and without 1,7,10,16-tetraoxa-4,13-diazacyclooctandecane[2.2] and 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-8.8.8-exacosane[2.2.2] macrocyclic ligands have been studied in order to analyze the complexation behavior of potassium cations in water. The absence of the complexation found in the [2.2] system is discussed in terms of the ligand structural features (presence of hydrogen bond donor and acceptor sites). The ion pair association constant of potassium cryptate as obtained from conductance measurements is also reported and discussed.

Calculation of the pH and the titratable acidity in clinically used infusion solutions.

2006

Clinically used infusion solutions are complex aqueous mixtures composed of a variety of different salts, acids, and non-electrolytes, and are characterized by composition, initial pH, and titratable acidity (TA). By rigorous treatment as a multi-composed acid-base system, pH and TA were calculated from proton dissociation equilibria, mass balance equations and electroneutrality condition. Nine were arbitrarily chosen as model solutions in which pH and TA were experimentally determined. From composition, and based on a set of apparent acidity constants (pK values) at 37 degrees C and total ionic strength 0.155 mol/l, pH was calculated by iteration. In the model solutions, measured pH was in…

Hole Localization and Thermochemistry of Oxidative Dehydrogenation of Aqueous Rutile TiO2(110)

2012

Measurement of interactions between polysaccharides and flavour compounds by exclusion size chromatography: Advantages and limits

1998

Interactions between flavour compounds and polysaccharides have been studied by exclusion size chromatography, the Hummel and Dreyer method. Hydrogen bonding was found between 2-acetyl thiazole and dextrines of different degrees of polymerisation. The number of binding sites and the affinity constant increase by increasing the degree of polymerisation. Hydrogen bonding was also responsible for the interactions between xanthane and 1-octen-3-ol or 2-acetyl pyrazine, with 1 mole of 1-octen-3-ol bound per pentasaccharide repeating unit. Unfortunately, the number of flavour compounds, which can be studied with this method, is limited due to their low water solubility and their low UV absorption.

Hydrogen-bond tuning of ferromagnetic interactions: synthesis, structure and magnetic properties of polynuclear copper(ii) complexes incorporating p-…

2006

The reaction of copper(II) hydroxide with 2,2'-bipyridine (bipy) (1 : 1) in alkaline aqueous solution (pH 14) at room temperature affords the alternating carbonate/hydroxo-bridged copper(II) polymeric chain compound {[Cu3(bipy)3(mu-OH)2(mu-CO3)2].11H2O}n, 1, as determined by single-crystal X-ray diffraction. The structure of 1 is built up from two similar centro-symmetric dinuclear [(bipy)Cu(mu-OH)]2 cores which link together via bridging carbonate groups to mononuclear [(bipy)Cu] fragments to form the chain. Interdigitation of adjacent chains through pi-pi interactions, which involve each bipy ligand, forms sheets that are separated by the water molecules of crystallisation. Variable-tempe…

Viscous Synergy of Pure Monoalcohol Mixtures in Water and Its Relation to Concentration

2004

Pure or aqueous alcohols are the solvents most widely used in industry, including in the manufacture of pharmaceuticals and cosmetic products. However, water–alcohol mixtures generate hydrogen-bonded molecular associations that lead to volume contraction and an increase in viscosity greater than that expected in the absence of any interaction between the components of the mixture. This phenomenon is referred to as viscous synergy. The present study investigates viscous synergy in monoalcohol systems containing up to five carbon atoms, since beyond hexanol all alcohols are practically insoluble in water. In all cases, determinations were made of the proportions of water and alcohol for which…

Self-Assembly of Water-Mediated Supramolecular Cationic Archimedean Solids

2013

Understanding the self-assembly of small structural units into large supramolecular assemblies remains one of the great challenges in structural chemistry. We have discovered that tetrahedral supramolecular cages, exhibiting the shapes of Archimedean solids, can be self-assembled by hydrogen bonding interactions using tricationic N-donors (1 or 2) in cooperation with water (W). Single crystal X-ray analysis shows that cage (2)4(W)6, assembled in an aqueous solution of cation 2 and KPF6, consists of four tripodal trications linked by six water monomers and resembles the shape of a truncated tetrahedron. Similarly, cage (1)4(W6)4 spontaneously self-assembles in an aqueous solution of cation 1…

2D and 3D coordination polymers based on 2,2′-bipyrimidine and cyanide bridging ligands incorporating coordinated and guest ammonia molecules. Synthe…

2005

The coordination polymers {[Ni(CN)4]2[(Ni(NH3)2)2(bpym)]·2H2O}n1 and {[Cu2(CN)2(bpym)]·NH3}n2 have been prepared from the reactions of M(NO3)2·nH2O [Cu(II), n = 3 and M = Ni(II), n = 6] with NaCN and bpym (2,2′-bipyrimidine) in concentrated aqueous ammonia, respectively. The structure of 1 is made of bipyrimidine bridged centrosymmetric dinuclear [Ni(NH3)2(μ-bpym)Ni(NH3)2] fragments connected by four [Ni(CN)4]2− anions giving rise to a 2D framework. Layers, which adopt a stair-like conformation, are stacked with an ABAB… repeat pattern. Water molecules are located in the interlayer space and are involved in hydrogen bond interactions with the non-bridging cyanide groups of the [Ni(CN)4]2− a…

The Silica-Water Interface: How the Silanols Determine the Surface Acidity and Modulate the Water Properties.

2015

Silica is the most abundant metal oxide and the main component of the Earth's crust. Its behavior in contact with water plays a critical role in a variety of geochemical and environmental processes. Despite its key role, the details of the aqueous silica interface at the microscopic molecular level are still elusive. Here we provide such a detailed understanding of the molecular behavior of the silica-water interface, using density functional theory based molecular dynamics (DFTMD) simulations, where a consistent treatment of the electronic structure of solvent and surface is provided. We have calculated the acidity of the silanol groups at the interface directly from the DFTMD simulations,…

Synthesis, Characterization, and X-ray Crystal Structures of Cyclam Derivatives. 8. Thermodynamic and Kinetic Appraisal of Lead(II) Chelation by Octa…

2005

En route toward the development of hybrid organic−inorganic extracting materials incorporating lead-selective chelators and their implementation in water purification processes, the lead(II) binding properties of three N-carbamoylmethyl-substituted 1,4,8,11-tetraazacyclotetradecanes (cyclams) have been fully investigated by spectroscopic (IR, UV−vis, MALDI-TOF MS, 1H and 13C NMR), X-ray crystallographic, potentiometric, and kinetic methods. Solution NMR studies revealed that the Pb2+ ion is entrapped in a molecular cage constituted by the four macrocyclic nitrogen and four amidic oxygen atoms. Protonation and lead binding constants determined in aqueous solution were shown to be linearly de…