The structure of simple aluminosilicate anions formed by the reaction of silicate and aluminate anions was investigated by {sup 29}Si and {sup 27}Al NMR spectroscopy. The extent of aluminosilicate formation was found to increase with increasing silicate ratio and increasing cation size. The first of these trends is attributed to the redistribution of Si ...

In the present study we investigate free electron attachment to the amino acid valine. Mass spectra and anion efficiency curves are measured in the electron energy range from about zero eV to about 15 eV and the anionic fragments are analyzed with a double focusing mass spectrometer. The high sensitivity of the present setup allows the ...

Protein structures are stabilized using noncovalent interactions. In addition to the traditional noncovalent interactions, newer types of interactions are thought to be present in proteins. One such interaction, an anion-? pair, in which the positively charged edge of an aromatic ring interacts with an anion, forming a favorable ...

The last three years of this project have focused on the basic chemical aspects of anion receptor design of functional pH independent systems, with the ultimate goal of targeting the selective binding of sulfate, as well as design of separations strategies for selective and efficient removal of targeted anions. Key findings during these years include: (1) ...

Pairing of halide anions with ammonium, as well as with trialkylated and tetraalkylated ammonium cations in water, is investigated by molecular dynamics simulations, which are verified by ab initio calculations and experimental excess chemical potentials. We find that ammonium prefers to pair with smaller halides over the larger ones, ...

The N-H stretching frequencies of tri-n-octylammonium salts are reported for a series of weakly basic anions (A(-)), many of which are the conjugate bases of known strong acids and superacids. Data have been collected primarily in carbon tetrachloride, where Oct(3)N(+)-H...A(-) contact ion pairs are formed. In the more polar solvent ...

This project have focuses on the basic chemical aspects of anion receptor design of functional pH independent systems, with the ultimate goal of targeting the selective binding of sulfate, as well as design of separations strategies for selective and efficient removal of targeted anions. Key findings include: (1) the first synthetic sulfate-selective ...

... in the formation of fewer ion pairs in ... nitrogen, oxygen, and sulfur atoms (ions) in CF3SO3Li ... imide, (CF3SO2)2N'Li+, and lithium methide, (CF3SO2 ...

The search for receptors that can selectively capture small and potentially toxic anions in protic media has sparked a renewed interest in the synthesis and anion-binding properties of polydentate Lewis acids. Seeking new paradigms to enhance the anion affinities of such systems, we synthesized a bidentate Lewis ...

The concentration, major fractions, and contribution of dissolved organic carbon (DOC) to stream chemistry were examined in two paired streams draining upland catchments in eastern Maine. Although SO(-2) was the dominant stream anion, followed by Cl(-), organic anions were also determined to be an important component of these stream ...

The molecular recognition of fluoride and cyanide anions has become an increasingly pertinent objective in research due to the toxicity associated with these anions, as well as their widespread use. Fluoride is commonly added to drinking water and toothpastes to promote dental health, and often used in the treatment of osteoporosis, however, high doses can ...

... ammonium and phosphonium cations paired with a wide array of anions. ... such as ethyl and propyl with anions such as halides, acetates, nitrates, ...

Evidence has been gathering from several laboratories that protons in proton-pumping membranes move along or within the bilayer rather than exchange with the bulk phase. These experiments are typically conducted on the natural membrane in vivo or in vitro or on fragments of natural membrane. Anionic lipids are present in all proton-pumping membranes. Model studies on the ...

In biomedical studies, dyes are divided into "acid" and "basic" dyes. This classification cannot be reconciled with current chemical definitions of acids and bases. Br�nsted-Lowry acids are compounds that can donate protons; bases are proton acceptors. The definition of acids and bases is independent of the ...

Experimental and molecular modeling studies are conducted to investigate the underlying mechanisms for the high solubility of CO2 in imidazolium-based ionic liquids. CO2 absorption isotherms at 10, 25, and 50 degrees C are reported for six different ionic liquids formed by pairing three different anions with two cations that differ only in the nature of ...

Extraction mechanism strongly depends on the acid-base properties of the extractant as well as on those of the extracted acid. For amines of basicity similar to that of the anion of the extracted acid, or higher, extraction is governed by ion-pair formation. H-bonding of undissociated ...

The electron affinity and the propensity to electron-induced proton transfer (PT) of hydrogen-bonded complexes between the Watson-Crick adenine-thymine pair (AT) and simple organic acid (HX), attached to adenine in the Hoogsteen-type configuration, were studied at the B3LYP/6-31+G** level. Although the carboxyl group is deprotonated at physiological pH, ...

The electron affinity and the propensity to electron-induced proton transfer (PT) of hydrogen-bonded complexes between the Watson�Crick adenine�thymine pair (AT) and simple organic acid (HX), attached to adenine in the Hoogsteen-type configuration, were studied at the B3LYP/6-31+G** level. Although the carboxyl group is deprotonated at physiological ...

... considered. Kinetic data for the electroreduction of ferricyanide anion in both water and formamide are presented and analyzed. ...

The homologous series of volatile perfluorinated acids�trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA) and heptafluorobutyric acid (HFBA)�continue to be excellent anionic ion-pairing reagents for reversed-phase high-performance liquid chromatography ...

Despite the continuing dominance of trifluoroacetic acid (TFA) as the anionic ion-pairing reagent of choice for peptide separations by reversed-phase high-performance liquid chromatography (RP-HPLC), we believe that a step-by-step approach to re-examining the relative efficacy of TFA compared to other ion-pairing ...

A reversed phase ion pair chromatographic method for the simultaneous determination of Cr species and common anions on a C(18)-bonded stationary phase was developed by using acetonitrile-water (2:98 v/v) containing 1.0 mM tetrabutylammonium hydroxide and 0.5 mM trans-1,2-diaminecyclohexane-N,N,N',N'-tetraacetic acid (DCTA) at pH 6.5 as ...

Disclosed is a cost-effective method for purifying and acidifying carboxylic acids, including organic acids and amino acids. The method involves removing impurities by allowing the anionic form of the carboxylic acid to bind to an anion exchange column and washing the ...

The gas-phase acidities of the 20 protein amino acids (PAAs) have been determined using an electrospray ionization-quadrupole ion trap instrument. Three different methods were used to determine both the absolute acidities and the relative acidity ordering of the PAAs. The extended kinetic method was used to ...

Nonbonding valence electrons, better known as lone pairs, are found in all anions as well as in cations in their lower oxidation states. In this paper the properties of lone pairs are analyzed using a bond valence model defined in terms of a core-and-valence-shell picture, which can be reduced to the point charges of the ionic model. A ...

When DNA is damaged by ionizing radiation, the genes in a cell may acquire mutations or the cell could die. The smallest known DNA-damaging unit is an electron, often low-energy secondary electrons. Additional electrons and transfers involving hydrogen atoms, protons, and hydride anions can damage DNA subunits, including individual nucleobases and nucleoside ...

In nonprotogenic solvents boron trifluoride behaves as a Lewis acid that is close in strength to tin tetrachloride. The character of the ionic equilibria in ester solutions of boron trifluoride paired with other Lewis acids (halides of elements of Groups II-V) depends on the relative strengths of these acids. In ...

Metoprolol, a widely used adrenoreceptor blocking drug, is commonly administered as the succinate or tartrate salt. The structure of metoprolol succinate, C₁₅H₂₆NO₃ ⁺�0.5C₄H₄O₄ ^2?, is ...

Compared with simple ion receptors, which are able to bind either a cation or an anion, ion pair receptors bearing both a cation and an anion recognition site offer the promise of binding ion pairs or pairs of ions strongly as the result of direct or indirect cooperative interactions between ...

The structures, infrared spectra, and electronic properties of the N7,N9-dimethylguaninium chloride have been studied. The interaction of one cation with one to four Cl anions and one Cl anion with two cations were investigated. Fifteen stable conformers are obtained. It is found that there are four acidic regions in the vicinity of ...

We have isolated the stable form of the formic acid dimer anion (HCOOH)2-, a model for electron-induced proton transfer between nucleic acid base-pairs, in the gas phase. The vibrational signatures of this species and its various isotopomers were investigated using Ar predissociation and photodetachment ...

The extraction behavior of technetium, thorium, uranium, neptunium, plutonium, americium and curium in the Aliquat-336 (diluted with 1,3-diisopropyl benzene)--nitric acid system have been studied. Aliquat-336 (tricapryl-methyl ammonium nitrate) is a quaternary ammonium salt extracting different species with an anion exchange mechanism. Distribution data ...

The anion exchange behavior of thorium in sulfuric acid solution and the separation of lanthanum from thorium by anion exchange were investigated. (C.H.)

The nature of the weak lipophilic acid used in synergistic combination with a model crown ether cation host was shown to have a strong effect on the strength and selectivity of sodium hydroxide separation from alkaline aqueous salt solutions. Sodium ion-pair extraction employing only cis-syn-cis-dicyclohexano-18-crown-6 (1) in nitrobenzene (NB) was ...

Optical spectroscopy was used to study the photolysis by 365-nm light of solutions of chlorine in a matrix of a vitreous aqueous HCl solution ({approx_equal}10 M) at 77 K. A scheme of the reactions occurring during the photolysis is presented. The scheme includes a photochemical reaction of formation of Cl{sub 2}{sup -} radical-anion pairs, a step of ...

In response to drought stress the phytohormone ABA (abscisic acid) induces stomatal closure and, therein, activates guard cell anion channels in a calcium-dependent as well as-independent manner. Two key components of the ABA signaling pathway are the protein kinase OST1 (open stomata 1) and the protein phosphatase ABI1 (ABA insensitive 1). The recently ...

The addition of salts, specifically sodium perchlorate (NaClO₄), to mobile phases at acidic pH as ion-pairing reagents for reversed-phase high-performance liquid chromatography (RP-HPLC) has been generally overlooked. To demonstrate the potential of NaClO₄ as an effective anionic ...

Both cationic and anionic polymeric additives were used for the capillary electrophoretic separation of proteins in food samples. The cationic polyelectrolyte polydiallyldimethylammonium chloride was more effective in minimizing protein-wall interactions at pH 3 than at pH 7, presumably due to greater repulsion between the adsorbed polymer and proteins. Improved resolution was ...

The extraction of Catechol Violet, Chrome Azurol S and Eriochrome Cyanine R with chloroform solutions of tri-n-octylamine (TOA), TOA hydrochloride and Aliquat 336 has been investigated. From the extraction isotherms, absorption spectra of the organic phases and dependence of the extraction coefficients on extractant concentration, it was found that the singly-charged anions ...

In the gas-phase reactions of halonitro- and dinitrophenide anions with X (X = F, Cl, Br, NO(2)) and NO(2) groups in ortho or para position to each other with selected C-H acids: CH(3)CN, CH(3)COCH(3), and CH(3)NO(2), products of the S(N)Ar-type reaction are formed. Nitrophenide anions are generated by decarboxylation of the respective ...

The photoreduction of benzophenone by N,N-diethylaniline and triethylamine has been examined in a number of solvents by both nano- and picosecond laser photolysis. With diethylaniline, electron transfer is the primary step and the spectrum of the ion pair has been detected even in nonpolar solvents such as benzene and cyclohexane. Rapid proton transfer then takes place to form ...

Biological organization depends on a sensitive balance of noncovalent interactions, in particular also those involving interactions between ions. Ion-pairing is qualitatively described by the law of "matching water affinities." This law predicts that cations and anions (with equal valence) form stable contact ion pairs if their sizes ...

Biological organization depends on a sensitive balance of noncovalent interactions, in particular also those involving interactions between ions. Ion-pairing is qualitatively described by the law of �matching water affinities.� This law predicts that cations and anions (with equal valence) form stable contact ion pairs if their ...

Cytosine-cytosinium base pairs are interconnected by triple hydrogen bonds thereby resembling a pseudo-Watson-Crick pattern and generates two characteristic R {2/2}(8)-motifs. Both molecules of the salicylic acids interconnect the base pair and lead to the formation of one dimensional supramolecular hexameric tape along b-axis. This ...

In the direct Mannich reaction and synthesis of ?,?-unsaturated ketones, the use of organobismuth complexes as catalysts leads to high diastereoselectivity and products of single trans conformation. In this paper, we illustrate the relationship between structure and catalytic activity as well as diastereoselectivity of organobismuth complexes having a 5,6,7,12-tetrahydrodibenz ...

... Accession Number : ADA522181. Title : Pairing Heterocyclic Cations with closo-Icosahedral Borane and Carborane Anions. II. ...

... Accession Number : ADA506521. Title : Pairing Heterocyclic Cations with closo-Icosahedral Borane and Carborane Anions. ...

... Accession Number : ADA506257. Title : Pairing Heterocyclic Cations with closo-Icosahedral Borane and Carborane Anions. ...

Possible isomerisation of 1,2,3-trialkylimidazolium and 1-alkylpyridinium ion pairs by proton transfer and by the nucleophilic addition of the anion to the cation have been investigated at the B3LYP/6-31+G* and B3LYP/6-311+G** levels of density functional theory. The deprotonation energies of 1,2,3-trialkylimidazolium and 1-alkylpyridinium cations to ...

Singly charged dicarboxylic acid anions, studied in depth by Wang et al. offer insight into the role of ring strain and conformation on the formation of intramolecular hydrogen bonds. These shared proton bonds, common in proteins and polymer systems, can be crucial in secondary and tertiary structure formation. By tracking the infrared spectra of ...

... Structure of the Hydrogen Bonded Ion Pair ... X RAY DIFFRACTION, HYDROGEN, CHEMICAL BONDS, SPECTRA, MOLECULAR ...

The reactions of the azotetrazole anion with dilute nitric, sulfuric, hydrochloric, phosphoric, perchloric, acetic, carbonic acids, and acidic cerid ammonium nitrate were investigated. The degeneration of the azotetrazole anion by dilute hydrochloric and ...

Ion-pair interactions between pyridinium cations and various carboxylate anions are explored using noisy light based coherent anti-Stokes Raman scattering (I(2)CARS). Binary mixtures of pyridine and various carboxylic acids (including halo-acetic acids, straight-chain carboxylic acids, and ...

Stomatal pores formed by a pair of guard cells in the leaf epidermis control gas exchange and transpirational water loss. Stomatal closure is mediated by the release of potassium and anions from guard cells. Anion efflux from guard cells involves slow (S-type) and rapid (R-type) anion channels. Recently the SLAC1 ...

The addition of plasticizers into Li(+)-conductive solid polymer electrolytes (SPEs) is a commonly known technique to enhance the ionic conductivity. Among the used plasticizers, alkoxides of group-13 elements [such as poly(ethylene glycol) (PEG)-borate ester] are promising candidates due to the Lewis acidity of the elements of this group (i.e. B, Al, and so on), which ...

Different nonvolatile mobile phases have been tested for the combination of ion-exchange chromatography combined with mass spectrometric detection of anions and organic acids. Buffer systems based on carbonate, sulfate, oxalate and citrate as the eluting species have been used. Among these, citrate proved to be the most versatile eluent allowing the ...

Jun 16, 2011 � Description: The leaching of calcium and magnesium from forests by atmospherically-deposited strong acid anions (sulfate and nitrate) is ...

... acid. The final aromatization step in the formation of pyrans from 2-aryloxyacetic acids is effected by persulphate anions. ...

Recently, we have shown that dilute multivalent cationic reagents can be paired with analyte anions in ESI-MS, thereby allowing them to be detected in the positive mode at very low limits of detection. However, there can be differences in the efficiency of this technique depending on the nature of the cationic pairing agent and the ...

The endogenous potent vasodilators and inhibitors of platelet aggregation S-nitrosoglutathione (GSNO) and S-nitroglutathione (GSNO2) are frequently analyzed by high-performance liquid chromatography (HPLC) using mobile phases of acidic pH. These systems are associated with problems stemming from rapid and considerable artifactual formation of GSNO from glutathione (GSH) and ...

Two novel calix[6]cryptamides bearing a tren-based cap have been synthesized and their host-guest properties have been investigated by (1)H and (19)F NMR spectroscopy. One of them behaves as a remarkable heteroditopic receptor toward either polar neutral guests, anions or contact ion pairs. It has been shown that only F(-) can be encapsulated into the ...

Systematic molecular dynamics simulations are used to study the structure, dynamics and transport properties of the ionic liquids composed of the tetra-butylphosphonium ([TBP](+), or [P(C(4)H(9))(4)](+)) cation with six amino acid ([AA](-)) anions. The structural features of these ionic liquids were characterized by calculating the partial site-site radial ...

1. The passive net transport of Li+ and Na+ across the human red cell membrane was accelerated by the divalent anions carbonate, sulphite, oxalate, phosphite and malonate. Phthalate, maleate, sulphate and succinate were found additionally to stimulate downhill transport of K+. Marked differences in anion efficacy and selectivity were observed. 2. The ...

Electrospray ionization mass spectrometry with variable collision induced dissociation of the isolated [(cation)(2)anion](+) and/or [(anion)(2)cation](-) ions of imidazolium-, pyridinium-, pyrrolidinium-, and piperidinium-based ionic liquids (ILs) combined with a large set of anions, such as chloride, tetrafluoroborate, ...

Quantitative analysis of the brightener component bis (sodium-sulfopropyl) disulfide (SPS) in acidic copper plating baths poses a real challenge due to the complex chemical matrix containing large amounts of Cu(II) ion and sulfuric acid together with other organic additives and additive decomposition products. We developed a new ...

Ring-opening metathesis polymerization- (ROMP) derived monoliths were prepared from 5-norborn-2-enemethyl bromide (NBE-CH(2)Br) and tris(5-norborn-2-enemethoxy)methylsilane ((NBE-CH(2)O)(3)SiCH(3)) within the confines of surface-silanized borosilicate columns (100�3 mm I.D.), applying Grubbs' first generation benzylidene-type catalyst [RuCl(2)(PCy(3))(2)(CHPh)]. Monoliths were converted into ...

The effect of anions contained in solutions on the energy transfer from Tb(III) and Dy(III) ions to different Ln(III) ions is investigated in aqueous and alcohol solutions. It is shown that the regularities revealed in the energy transfer are completely determined by the ratio between the dissociation rate of the binuclear complex and the rate of energy transfer in it. The ...

Anion exchange in nitric acid is a prominent aqueous process used to recover and purify plutonium from impure nuclear materials. This process is sensitive to fluoride ion, which complexes plutonium in competition with the anionic nitrato complex that is s...

This chapter covers advances in calixpyrrole chemistry and specifically in the application of these species as anion and ion-pair complexation agents over the last 5 years. Over this time, the chemistry of these easy-to-make macrocycles advanced with the discovery of the ion-pair complexation properties of calixpyrroles, in addition to ...

The photoelectron spectra of the adenine-formic acid (AFA)- and 9-methyladenine-formic acid (MAFA)- anionic complexes have been recorded with 2.540 eV photons. These spectra reveal broad features with maxima at 1.5-1.4 eV that indicate formation of stable valence anions in the gas phase. The neutral and ...

An empirical method is proposed to rank order Lewis acids and bases in terms of their local hardness, {tilde {eta}}, at their reaction sites. The method uses bond energy differences between two acids (or bases) of different chemical hardness. The assumption is made that in an exchange reaction, A:B' + A':B = A:B + A':B', ...

The oxidation of benzoin by lumiflavin-3-acetic acid (Fl/sub ox/) to provide benzil and 1,5-dihydrolumiflavin-3-acetic acid (FlH/sub 2/) is a readily reversible reaction. It has been established that the mechanism involves general base ionization of benzoin carbon acid (..cap alpha..-ketol) to yield endiolate ...

This study aimed to establish complementary high performance liquid chromatography (HPLC) methods including three modes of separation: ion pairing, cation exchange, and anion exchange chromatography, with detection by inductively coupled plasma mass spectrometry (ICPMS). The ion pairing mode enabled the separation of inorganic arsenate ...

The concentration, major fractions, and contribution of dissolved organic carbon (DOC) to stream chemistry were examined in two paired streams draining upland catchments in eastern Maine. Concentrations of DOC in East and West Bear Brooks were 183 {plus minus} 73 and 169 {plus minus} 70 {mu}mol CL {sup {minus}1}, respectively. Organic acids were the ...

... SINGLE CRYSTALS, CATALYSTS, ANIONS, MOLYBDENUM COMPOUNDS, ARSONIC ACID, ARSENATES, CHEMICAL DERIVATIVES. ...