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P B Armentrout - One of the best experts on this subject based on the ideXlab platform.

  • Alkali Metal Cation interactions with 15 crown 5 in the gas phase revisited
    Journal of Physical Chemistry A, 2014
    Co-Authors: P B Armentrout, C.a. Austin, M T Rodgers
    Abstract:

    Quantitative interactions of the Alkali Metal Cations with the cyclic 15-crown-5 polyether ligand (15C5) are studied. In this work, Rb+(15C5) and Cs+(15C5) complexes are formed using electrospray ionization and studied using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted to yield bond dissociation energies (BDEs) using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion–neutral collisions. 0 K BDEs of 175.0 ± 9.7 and 159.4 ± 9.6 kJ/mol, respectively, are determined and exceed those previously measured [J. Am. Chem. Soc. 1999, 121, 417−423] by 68 and 57 kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. Because the analysis techniques have advanced since this early study, we also reanalyze the published data for the Na+(15C5) and K+(15C5) systems to ensure a sel...

  • Alkali Metal Cation interactions with 12 crown 4 in the gas phase revisited
    International Journal of Mass Spectrometry, 2012
    Co-Authors: P B Armentrout, C.a. Austin, M T Rodgers
    Abstract:

    Abstract Quantitative interactions of Alkali Metal Cations with the cyclic 12-crown-4 polyether ligand (12C4) are studied. Experimentally, Rb + (12C4) and Cs + (12C4) complexes are formed using electrospray ionization and their bond dissociation energies (BDEs) determined using threshold collision-induced dissociation of these complexes with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion-neutral collisions. 0 K BDEs of 151.5 ± 9.7 and 137.0 ± 8.7 kJ/mol, respectively, are determined and exceed those previously measured by 60 and 54 kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. In order to provide comparable thermochemical results for the Na + (12C4) and K + (12C4) systems, the published data for these systems are reinterpreted using the same analysis techniques, which have advanced since the original data were acquired. Revised BDEs for these systems are obtained as 243.9 ± 12.6 and 182.0 ± 17.3 kJ/mol, respectively, which are within experimental uncertainty of the previously reported values. In addition, quantum chemical calculations are conducted at the B3LYP and MP2(full) levels of theory with geometries and zero point energies calculated at the B3LYP level using both HW*/6-311+G(2d,2p) and def2-TZVPPD basis sets. The theoretical results are in reasonable agreement with experiment, with B3LYP/def2-TZVPPD values being in particularly good agreement. Computations also allow the potential energy surfaces for dissociation of the M + (12C4) complexes to be elucidated. These are used to help explain why the previous studies formed excited conformers of Rb + (12C4) and Cs + (12C4) but apparently not of Na + (12C4) and K + (12C4).

  • thermochemistry of Alkali Metal Cation interactions with histidine influence of the side chain
    Journal of Physical Chemistry A, 2012
    Co-Authors: P B Armentrout, Y. Chen, Murat Citir, M T Rodgers
    Abstract:

    The interactions of Alkali Metal Cations (M+ = Na+, K+, Rb+, Cs+) with the amino acid histidine (His) are examined in detail. Experimentally, bond energies are determined using threshold collision-induced dissociation of the M+(His) complexes with xenon in a guided ion beam tandem mass spectrometer. Analyses of the energy dependent cross sections provide 0 K bond energies of 2.31 ± 0.11, 1.70 ± 0.08, 1.42 ± 0.06, and 1.22 ± 0.06 eV for complexes of His with Na+, K+, Rb+, and Cs+, respectively. All bond dissociation energy (BDE) determinations include consideration of unimolecular decay rates, internal energy of reactant ions, and multiple ion-neutral collisions. These experimental results are compared to values obtained from quantum chemical calculations conducted previously at the MP2(full)/6-311+G(2d,2p), B3LYP/6-311+G(2d,2p), and B3P86/6-311+G(2d,2p) levels with geometries and zero point energies calculated at the B3LYP/6-311+G(d,p) level where Rb and Cs use the Hay–Wadt effective core potential and ba...

  • an experimental and theoretical study of Alkali Metal Cation interactions with cysteine
    Journal of Physical Chemistry B, 2010
    Co-Authors: P B Armentrout, Theresa E Cooper, Erin I Armentrout, Amy Clark, Elana M S Stennett, Damon R Carl
    Abstract:

    The interactions of Alkali Metal Cations (M+ = Li+, Na+, K+, Rb+) with the amino acid cysteine (Cys) are examined in detail. Experimentally, bond energies are determined using threshold collision-i...

  • infrared multiple photon dissociation spectroscopy of Cationized methionine effects of Alkali Metal Cation size on gas phase conformation
    Physical Chemistry Chemical Physics, 2010
    Co-Authors: Damon R Carl, Jos Oomens, Theresa E Cooper, Jeffrey D Steill, P B Armentrout
    Abstract:

    The gas-phase structures of Alkali-Metal Cation complexes of the amino acid methionine (Met) as well as protonated methionine are investigated using infrared multiple photon dissociation (IRMPD) spectroscopy utilizing light generated by a free electron laser. Spectra of Li+(Met) and Na+(Met) are similar and relatively simple, whereas the spectra of K+(Met), Rb+(Met), and Cs+(Met) include distinctive new bands. Measured IRMPD spectra are compared to spectra calculated at the B3LYP/6-311+G(d,p) level of theory to identify the conformations present in the experimental studies. For Li+ and Na+ complexes, the only conformation present is a charge-solvated, tridentate structure that binds the Metal Cation to the amine and carbonyl groups of the amino acid backbone and the sulfur atom of the side chain, [N,CO,S]. In addition to the [N,CO,S] conformer, bands corresponding to Alkali-Metal Cation binding to a bidentate zwitterionic structure, [CO2−], are clearly present for the K+, Rb+, and Cs+ complexes. Theoretical calculations of the lowest energy conformations of Rb+ and Cs+ complexes suggest that the experimental spectra could also include contributions from two additional charge-solvated structures, tridentate [COOH,S] and bidentate [COOH]. For H+(Met), the IRMPD action spectrum is reproduced by multiple low-energy [N,CO,S] conformers, in which the protonated amine group hydrogen bonds to the carbonyl oxygen atom and the sulfur atom of the amino acid side chain. These [N,CO,S] conformers only differ in their side-chain orientations.

Richard A Bartsch - One of the best experts on this subject based on the ideXlab platform.

  • side arm participation in lariat ether carboxylate Alkali Metal Cation complexes in solution
    Tetrahedron, 2005
    Co-Authors: Lokman Torun, Thomas W Robison, Jan Krzykawski, David W Purkiss, Richard A Bartsch
    Abstract:

    Abstract Lariat ether carboxylic acids of structure CECH2OCH2C6H4–2-CO2H with crown ether (CE) ring sizes of 12-crown-4, 15-crown-5 and 18-crown-6 are prepared and converted into Alkali Metal–lariat ether carboxylate complexes. Absorptions for the diastereotopic benzylic protons in the 1H NMR spectra of the complexes in CDCl3 are utilized to probe the extent of side arm interaction with the crown ether-complexed Metal ion as a function of the crown ether ring size and identity of the Alkali Metal Cation.

  • Evaluation of Alkali and Alkaline earth Metal Cation selectivities of lariat ether amides by electrospray ionization mass spectrometry
    Journal of the American Society for Mass Spectrometry, 2003
    Co-Authors: Sheldon M. Williams, Jennifer S Brodbelt, Richard A Bartsch
    Abstract:

    Lariat ethers with pendant amide groups have shown promise as new ion sensors because of their selectivity towards particular Metal ions. In this study we report Alkali and Alkaline earth Metal binding selectivities of dibenzo-16-crown-5 and fifteen dibenzo-16-crown-5 lariat ether amides (LEAs) as determined by electrospray ionization mass spectrometry (ESI-MS). Additionally, the influence of the acid/base nature of the solution on Metal Cation selectivity is investigated. The validity of using ESI-MS for determination of selectivities is established by analogous experiments using hosts with known binding constants for the same Metal Cations and solvent systems. Collisionally activated dissociation (CAD) is used to evaluate the influence of the Alkali Metal Cation binding on the fragmentation of the LEAs.

  • Structure–Alkali Metal Cation complexation relationships for macrocyclic PNP-lariat ether ligands
    Journal of The Chemical Society-perkin Transactions 1, 2002
    Co-Authors: Richard A Bartsch, Sangki Chun, Nazar S. A. Elkarim, Krystyna Brandt, Iwona Porwolik-czomperlik, Mariola Siwy, Dariusz Lach, Jerzy Silberring
    Abstract:

    Water-insoluble, mono- and diarmed PNP-lariat ethers containing various aryloxy and regioisomerically-positioned binaphthylylenedioxy substituents linked to the phosphorus atoms of the cyclophosphazene ring via oxygen atoms are synthesized by regioselective, sodium ion-assisted arylolysis of tetrachloro-16-PNP-6 crown ether 1. Heterogeneously-substituted, mixed aryloxy-amino PNP-lariat ethers and bis-lariat ethers with two different substituents linked to the PNP-macrocycle via an oxygen and a nitrogen atom are prepared by stepwise arylolysis and aminolysis reactions of 1. The Alkali-Metal Cation complexation behavior of the PNP-lariat ethers is evaluated in solvent polymeric membrane electrodes. The PNP-lariat and bis-lariat ethers exhibit pronounced selectivity for large Alkali Metal Cations (Rb+ and Cs+) over small ones (Li+ and Na+). The selectivity is influenced by the configuration of the crown ether ring and the number of oxygen donor atoms in the ligand. For some PNP-lariat ethers, evidence for formation of 2 : 1 (ligand–Metal ion) complexes with Rb+ and Cs+ is provided by ESI-MS.

  • Chromogenic lariat ethers for selective Alkali Metal Cation recognition.
    Analytical Chemistry, 2001
    Co-Authors: Galina G. Talanova, Hong-sik Hwang, Vladimir S. Talanov, Richard A Bartsch
    Abstract:

    : Twelve new proton-ionizable, picrylamino-type chromogenic lariat ethers derived from dibenzo-14-crown-4, dibenzo-16-crown-5 and dibenzo-19-crown-6 demonstrate good selectivity and remarkable color response upon extraction of Alkali Metal Cations from basic aqueous solutions into chloroform.

  • new lipophilic crown ethers with intraannular carboxylic acid groups synthesis and Alkali Metal Cation extraction
    Journal of Heterocyclic Chemistry, 2000
    Co-Authors: Larry D Bratton, Richard A Bartsch
    Abstract:

    A six-step synthetic route to four lipophilic crown ethers with intraannular carboxylic acid groups and ring sizes of 15-crown-4, 18-crown-5, 21-crown-6 and 24-crown-7 is described. Eight new polyether compounds that bear inward-facing bromo and formate ester substituents are prepared as synthetic intermediates. Selectivities and efficiencies of the four new lipophilic crown ether carboxylic acids in competitive Alkali Metal Cation extraction from aqueous solutions into chloroform are evaluated.

Hana Sychrová - One of the best experts on this subject based on the ideXlab platform.

  • fluconazole affects the Alkali Metal Cation homeostasis and susceptibility to Cationic toxic compounds of candida glabrata
    Microbiology, 2014
    Co-Authors: Hana Elicharova, Hana Sychrová
    Abstract:

    Candida glabrata is a salt-tolerant and fluconazole (FLC)-resistant yeast species. Here, we analyse the contribution of plasma-membrane Alkali-Metal-Cation exporters, a Cation/proton antiporter and a Cation ATPase to Cation homeostasis and the maintenance of membrane potential (ΔΨ). Using a series of single and double mutants lacking CNH1 and/or ENA1 genes we show that the inability to export potassium and toxic Alkali-Metal Cations leads to a slight hyperpolarization of the plasma membrane of C. glabrata cells; this hyperpolarization drives more Cations into the cells and affects Cation homeostasis. Surprisingly, a much higher hyperpolarization of C. glabrata plasma membrane was produced by incubating cells with subinhibitory concentrations of FLC. FLC treatment resulted in a substantially increased sensitivity of cells to various Cationic drugs and toxic Cations that are driven into the cell by negative-inside plasma-membrane potential. The effect of the combination of FLC plus Cationic drug treatment was enhanced by the malfunction of Alkali-Metal-Cation transporters that contribute to the regulation of membrane potential and Cation homeostasis. In summary, we show that the combination of subinhibitory concentrations of FLC and Cationic drugs strongly affects the growth of C. glabrata cells.

  • yeast 14 3 3 proteins participate in the regulation of cell Cation homeostasis via interaction with nha1 Alkali Metal Cation proton antiporter
    Biochimica et Biophysica Acta, 2012
    Co-Authors: Jaromir Zahradka, Paul G H Van Heusden, Hana Sychrová
    Abstract:

    Abstract Background In yeast, 14-3-3 proteins bind to hundreds of phosphorylated proteins and play a role in the regulation of many processes including tolerance to NaCl. However, the mechanism of 14-3-3 involvement in the cell answer to salt or osmotic stresses is weakly understood. Methods We studied the role of the Saccharomyces cerevisiae 14-3-3 homologs Bmh1 and Bmh2 in the regulation of Alkali-Metal-Cation homeostasis using the genetic-interaction approach. Obtained results were confirmed with the Bimolecular-Fluorescence-Complementation method. Results Deletion of BMH1, encoding the major 14-3-3 isoform, resulted in an increased sensitivity to Na+, Li+ and K+ and to Cationic drugs but did not affect membrane potential. This bmh1Δ phenotype was complemented by overexpression of BMH2. Testing the genetic interaction between BMH genes and genes encoding plasma-membrane Cation transporters revealed, that 14-3-3 proteins neither interact with the potassium uptake systems, nor with the potassium-specific channel nor with the Na+(K+)-ATPases. Instead, a genetic interaction was identified between BMH1 and NHA1 which encodes an Na+(K+)/H+ antiporter. In addition, a physical interaction between 14-3-3 proteins and the Nha1 antiporter was shown. This interaction does not depend on the phosphorylation of the Nha1 antiporter by Hog1 kinase. Our results uncovered a previously unknown interaction partner of yeast 14-3-3 proteins and provided evidence for the previously hypothesized involvement of Bmh proteins in yeast salt tolerance. General significance Our results showed for the first time that the yeast 14-3-3 proteins and an Alkali-Metal-Cation efflux system interact and that this interaction enhances the cell survival upon salt stress.

  • Alkali Metal Cation influx and efflux systems in nonconventional yeast species
    Fems Microbiology Letters, 2011
    Co-Authors: Jose Ramos, Joaquin Arino, Hana Sychrová
    Abstract:

    To maintain optimal intracellular concentrations of Alkali–Metal–Cations, yeast cells use a series of influx and efflux systems. Nonconventional yeast species have at least three different types of efficient transporters that ensure potassium uptake and accumulation in cells. Most of them have Trk uniporters and Hak K+–H+ symporters and a few yeast species also have the rare K+ (Na+)-uptake ATPase Acu. To eliminate surplus potassium or toxic sodium Cations, various yeast species use highly conserved Nha Na+ (K+)/H+ antiporters and Na+ (K+)-efflux Ena ATPases. The potassium-specific yeast Tok1 channel is also highly conserved among various yeast species and its activity is important for the regulation of plasma membrane potential.

  • Alkali Metal Cation transport and homeostasis in yeasts
    Microbiology and Molecular Biology Reviews, 2010
    Co-Authors: Joaquin Arino, Jose Ramos, Hana Sychrová
    Abstract:

    Summary: The maintenance of appropriate intracellular concentrations of Alkali Metal Cations, principally K+ and Na+, is of utmost importance for living cells, since they determine cell volume, intracellular pH, and potential across the plasma membrane, among other important cellular parameters. Yeasts have developed a number of strategies to adapt to large variations in the concentrations of these Cations in the environment, basically by controlling transport processes. Plasma membrane high-affinity K+ transporters allow intracellular accumulation of this Cation even when it is scarce in the environment. Exposure to high concentrations of Na+ can be tolerated due to the existence of an Na+, K+-ATPase and an Na+, K+/H+-antiporter, which contribute to the potassium balance as well. Cations can also be sequestered through various antiporters into intracellular organelles, such as the vacuole. Although some uncertainties still persist, the nature of the major structural components responsible for Alkali Metal Cation fluxes across yeast membranes has been defined within the last 20 years. In contrast, the regulatory components and their interactions are, in many cases, still unclear. Conserved signaling pathways (e.g., calcineurin and HOG) are known to participate in the regulation of influx and efflux processes at the plasma membrane level, even though the molecular details are obscure. Similarly, very little is known about the regulation of organellar transport and homeostasis of Alkali Metal Cations. The aim of this review is to provide a comprehensive and up-to-date vision of the mechanisms responsible for Alkali Metal Cation transport and their regulation in the model yeast Saccharomyces cerevisiae and to establish, when possible, comparisons with other yeasts and higher plants.

  • Schizosaccharomyces pombe possesses two plasma membrane Alkali Metal Cation/H antiporters differing in their substrate specificity.
    Fems Yeast Research, 2007
    Co-Authors: Klara Papouskova, Hana Sychrová
    Abstract:

    : The Schizosaccharomyces pombe plasma membrane Na(+)/H(+) antiporter, SpSod2p, has been shown to belong to the subfamily of yeast Na(+)/H(+) antiporters that only recognize Na(+) and Li(+) as substrates. Nevertheless, most of the studied plasma membrane Alkali Metal Cation/H(+) antiporters from other yeasts have broader substrate specificities, exporting K(+) and Rb(+) as well. Such antiporters probably play two roles in the physiology of cells: the elimination of surplus toxic Cations, and the regulation of stable intracellular K(+) content, pH and cell volume. The systematic sequencing of the Sch. pombe genome revealed the presence of an as-yet uncharacterized homolog of the Spsod2 gene (designated Spsod22). Spsod22 and Spsod2 were expressed in Saccharomyces cerevisiae cells lacking their own Alkali Metal Cation efflux systems, and the transport properties of both Sch. pombe antiporters were compared to those of the Sac. cerevisiae Nha1 antiporter expressed under the same conditions. Here we show that SpSod22p has broad substrate specificity upon heterologous expression in Sac. cerevisiae cells and contributes to cell tolerance to high external levels of K(+). Thus, the Sch. pombe genome encodes two plasma membrane Alkali Metal Cation/H(+) antiporters that play different roles in the physiology of the yeast.

M T Rodgers - One of the best experts on this subject based on the ideXlab platform.

  • Infrared multiple photon dissociation action spectroscopy of Alkali Metal Cation–cyclen complexes: Effects of Alkali Metal Cation size on gas-phase conformation
    International Journal of Mass Spectrometry, 2020
    Co-Authors: C.a. Austin, Giel Berden, Jos Oomens, Y. Chen, C.m. Kaczan, M T Rodgers
    Abstract:

    The gas-phase structures of Alkali Metal Cationized complexes of cyclen (1,4,7,10-tetraazacyclododecane) are examined via infrared multiple photon dissociation (IRMPD) action spectroscopy and electronic structure theory calculations. The measured IRMPD action spectra of four M+(cyclen) complexes are compared to IR spectra predicted for the stable low-lying conformers of these complexes calculated at the B3LYP/def2-TZVPPD level of theory to identify the structures accessed in the experiments. The IRMPD yields of the M+(cyclen) complexes investigated increase as the size of the Alkali Metal Cation increases, in accordance with the decrease in the strength of Alkali Metal Cation binding. The IRMPD spectrum of the Na+(cyclen) complex is relatively simple, and the features observed are retained for all of the other Alkali Metal Cation-cyclen complexes. New spectral features begin to appear for K+(cyclen) and become very obvious for the Rb+(cyclen) and Cs+(cyclen) complexes. The IRMPD action spectra for the complexes of cyclen to K+, Rb+, and Cs+ are well reproduced by the calculated spectra predicted for the most stable conformations computed. Overall comparisons suggest that only the ground-state conformations of the M+(cyclen) complexes were accessed in the experiments for the complexes to Na+ and K+, whereas evidence for a very small population of the first excited conformers is observed for the complexes to Rb+ and Cs+

  • Intrinsic affinities of Alkali Metal Cations for diaza-18-crown-6: Effects of Alkali Metal Cation size and donor atoms on the binding energies
    International Journal of Mass Spectrometry, 2015
    Co-Authors: C.a. Austin, M T Rodgers
    Abstract:

    Abstract Threshold collision-induced dissociation of Alkali Metal Cation-diaza-18-crown-6 complexes, M+(da18C6), with xenon is studied using guided ion beam tandem mass spectrometry techniques. The Alkali Metal Cations examined here include: Na+, K+, Rb+, and Cs+. In all cases, M+ is the only product observed, corresponding to endothermic loss of the intact da18C6 ligand. The cross section thresholds are analyzed to extract zero and 298 K M+ da18C6 bond dissociation energies (BDEs) after properly accounting for the effects of multiple ion-neutral collisions, the kinetic and internal energy distributions of the reactants, and the lifetimes for dissociation. Density functional theory calculations at the B3LYP/def2-TZVPPD and B3LYP/6-31+G* levels of theory are used to determine the structures of da18C6 and the M+(da18C6) complexes and provide molecular constants necessary for the thermodynamic analysis of the experimental data. Theoretical BDEs are determined from single point energy calculations at the B3LYP and MP2(full) levels of theory using the def2-TZVPPD and 6-311+G(2d,2p) basis sets using the B3LYP/def2-TZVPPD and B3LYP/6-31+G* optimized geometries. The agreement between B3LYP/def2-TZVPPD theory and experiment is excellent for all four M+(da18C6) complexes. The M+ da18C6 BDEs decrease as the size of the Alkali Metal Cation increases, consistent with the electrostatic nature of the binding in these complexes. The M+(da18C6) structures and BDEs are compared to those previously reported for the analogous complexes of 18-crown-6 and hexaaza-18-crown-6, to examine the effects of the donor atoms (N versus O) on the structure and strength of binding.

  • Alkali Metal Cation-Hexacyclen Complexes: Effects of Alkali Metal Cation Size on the Structure and Binding Energy
    Journal of Physical Chemistry A, 2014
    Co-Authors: C.a. Austin, M T Rodgers
    Abstract:

    Threshold collision-induced dissociation (CID) of Alkali Metal Cation–hexacyclen (ha18C6) complexes, M+(ha18C6), with xenon is studied using guided ion beam tandem mass spectrometry techniques. The Alkali Metal Cations examined here include: Na+, K+, Rb+, and Cs+. In all cases, M+ is the only product observed, corresponding to endothermic loss of the intact ha18C6 ligand. The cross-section thresholds are analyzed to extract zero and 298 K M+–ha18C6 bond dissociation energies (BDEs) after properly accounting for the effects of multiple M+(ha18C6)–Xe collisions, the kinetic and internal energy distributions of the M+(ha18C6) and Xe reactants, and the lifetimes for dissociation of the activated M+(ha18C6) complexes. Ab initio and density functional theory calculations are used to determine the structures of ha18C6 and the M+(ha18C6) complexes, provide molecular constants necessary for the thermodynamic analysis of the energy–resolved CID data, and theoretical estimates for the M+–ha18C6 BDEs. Calculations us...

  • Alkali Metal Cation binding affinities of cytosine in the gas phase revisited
    Physical Chemistry Chemical Physics, 2014
    Co-Authors: Bo Yang, M T Rodgers
    Abstract:

    Binding of Metal Cations to the nucleobases can influence base pairing, base stacking and nucleobase tautomerism. Gas-phase condensation of dc discharge generated Alkali Metal Cations and thermally vaporized cytosine (DC/FT) has been found to produce kinetically trapped excited tautomeric conformations of the M+(cytosine) complexes, which influences the threshold collision-induced dissociation (TCID) behavior. In order to elucidate the effects of the size of Alkali Metal Cation on the strength of binding to the canonical form of cytosine, the binding affinities of Na+ and K+ to cytosine are re-examined here, and studies are extended to include Rb+ and Cs+ again using TCID techniques. The M+(cytosine) complexes are generated in an electrospray ionization source, which has been shown to produce ground-state tautomeric conformations of M+(cytosine). The energy-dependent cross sections are interpreted to yield bond dissociation energies (BDEs) using an analysis that includes consideration of unimolecular decay rates, the kinetic and internal energy distributions of the reactants, and multiple M+(cytosine)–Xe collisions. Revised BDEs for the Na+(cytosine) and K+(cytosine) complexes exceed those previously measured by 31.9 and 25.5 kJ mol−1, respectively, consistent with the hypothesis proposed by Yang and Rodgers that excited tautomeric conformations are accessed when the complexes are generated by DC/FT ionization. Experimentally measured BDEs are compared to theoretical values calculated at the B3LYP and MP2(full) levels of theory using the 6-311+G(2d,2p)_HW* and def2-TZVPPD basis sets. The B3LYP/def2-TZVPPD level of theory is found to provide the best agreement with the measured BDEs, suggesting that this level of theory can be employed to provide reliable energetics for similar Metal–ligand systems.

  • Alkali Metal Cation interactions with 15 crown 5 in the gas phase revisited
    Journal of Physical Chemistry A, 2014
    Co-Authors: P B Armentrout, C.a. Austin, M T Rodgers
    Abstract:

    Quantitative interactions of the Alkali Metal Cations with the cyclic 15-crown-5 polyether ligand (15C5) are studied. In this work, Rb+(15C5) and Cs+(15C5) complexes are formed using electrospray ionization and studied using threshold collision-induced dissociation with xenon in a guided ion beam tandem mass spectrometer. The energy-dependent cross sections thus obtained are interpreted to yield bond dissociation energies (BDEs) using an analysis that includes consideration of unimolecular decay rates, internal energy of the reactant ions, and multiple ion–neutral collisions. 0 K BDEs of 175.0 ± 9.7 and 159.4 ± 9.6 kJ/mol, respectively, are determined and exceed those previously measured [J. Am. Chem. Soc. 1999, 121, 417−423] by 68 and 57 kJ/mol, respectively, consistent with the hypothesis proposed there that excited conformers had been studied. Because the analysis techniques have advanced since this early study, we also reanalyze the published data for the Na+(15C5) and K+(15C5) systems to ensure a sel...

Hamilton Varela - One of the best experts on this subject based on the ideXlab platform.

  • the effect of the Alkali Metal Cation on the electrocatalytic oxidation of formate on platinum
    RSC Advances, 2014
    Co-Authors: B A F Previdello, Eduardo G Machado, Hamilton Varela
    Abstract:

    Non-covalent interactions between hydrated Alkali Metal Cations and adsorbed oxygenated species on platinum might considerably inhibit some electrocatalytic reactions. We report in this communiCation the effect exerted by electrolyte Alkali Metal Cations on the electro-oxidation of formate ions on platinum. The system was investigated by means of cyclic voltammetry and chronoamperometry in the presence of an electrolyte containing Li+, Na+, or K+. As already observed for other systems, the general activity towards the electro-oxidation of formate ions was found to increase in the sequence Li+ < Na+ < K+. In addition, we observed that the inhibition caused by smaller Cations has a peculiar potential dependence because of the multi-peaked current profile of the electro-oxidation of formate on platinum. In this respect, we have also identified a new effect caused by Cation inhibition at intermediate potentials, namely a peak splitting towards the use of smaller Cations. Results are discussed in connection with mechanistic aspects of this model system.