Alkali metal mediated resorcarene capsules: an ESI-FTICRMS study on gas-phase structure and cation binding of tetraethyl resorcarene and its per-methylated derivative

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS) with additional ab initio calculations were used to examine the alkali metal cation binding selectivity (i.e., molecular recognition) and host properties of tetraethyl resorcarene (1) and its per-methylated derivative (2). The significance of intramolecular hydrogen bonding for the crown conformation was demonstrated. The presence of intramolecular flip-flop hydrogen bonding in 1 was confirmed both with calculations and in ND3-exchange experiments. All the alkali metal cations formed host-guest complexes by docking inside the cavity of the host. Complexation with the larger cations, especially Cs+, was favored. All the alkali metal cations also formed dimeric resorcarene capsules with 1. The capsules were directly H-bonded species, with no linking solvent molecules. ND3-exchange experiments and molecular modeling revealed the significance of direct intermolecular H-bonding for the crown conformation of 1 and stability of the capsule structure.     

芬太尼及其哌啶季铵离子的电子结构研究

改进了CNDO/2计算机程序,可减少对高速内存的要求,从而实现在65K内存的计算机上对价轨道在150个以内的大药物分子的半经验自洽场计算。对芬太尼分子及其哌啶季铵离子进行了CNDO/2半经验分子轨道计算,讨论了它们的电子结构特征,指出了它们与受体作用时可能的活性中心及其作用性质。     

Negative gas-phase ion chemistry of silane: A quadrupole ion trap study

Silicon clusters are of considerable interest for their importance in astrophysics and chemical vapour deposition processes, as well as from a fundamental point of view. Here, we present a quadrupole ion trap study of the self-condensation ion/molecule reactions of anions of silane. In the high-pressure regime, several ion clusters are formed with increasing size: the largest ions detected are Si5Hn- (n = 0-3). Selective ion isolation and storage allowed detection of the main reaction sequences occurring in the reacting system. The most frequent condensation step is followed by single or multiple dehydrogenation, this latter being particularly observed for the high-mass reactant ions. As a consequence, the most abundant ions in the mass spectra are those with a low content of hydrogen, namely Si2H-, Si3H-, and Si4H-. These results are discussed with reference to literature data on silicon cluster anions and related systems.     

The gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene--energetics,structure and interconversion of dihydrotropylium ions

The hitherto unknown gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene (CHT) have been determined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Several independent techniques were used in order to exclude ambiguities due to proton-induced isomerisation of the conjugate cyclic C(7)H(9)(+) ions, [CHT + H](+). The gas-phase basicity obtained by the thermokinetic method, GB(CHT) = 799 +/- 4 kJ mol(-1), was found to be identical, within the limits of experimental error, with the values measured by the equilibrium method starting with protonated reference bases, and with the values resulting from the measurements of the individual forward and reverse rate constants, when corrections were made for the isomerised fraction of the C(7)H(9)(+) population. The experimentally determined gas-phase basicity leads to the proton affinity of cycloheptatriene, PA(CHT) = 833 +/- 4 kJ mol(-1), and the heat of formation of the cyclo-C(7)H(9)(+) ion, deltaH(f)(0)([CHT + H](+)) = 884 +/- 4 kJ mol(-1). Ab initio calculations are in agreement with these experimental values if the 1,2-dihydrotropylium tautomer, [CHT + H((1))](+), generated by protonation of CHT at C-1, is assumed to be the conjugate acid, resulting in PA(CHT) = 825 +/- 2 kJ mol(-1) and deltaH(f)(0)(300)([CHT + H((1))](+)) = 892 +/- 2 kJ mol(-1). However, the calculations indicate that protonation of cycloheptatriene at C-2 gives rise to transannular C-C bond formation, generating protonated norcaradiene [NCD + H](+), a valence tautomer being 19 kJ mol(-1) more stable than [CHT + H((1))](+). The 1,4-dihydrotropylium ion, [CHT + H((3))](+), generated by protonation of CHT at C-3, is 17 kJ mol(-1) less stable than [CHT + H((1))](+). The bicyclic isomer [NCD + H](+) is separated by relatively high barriers, 70 and 66 kJ mol(-1) from the monocyclic isomers, [CHT + H((1))](+) and [CHT + H((3))](+), respectively. Therefore, the initially formed 1,2-dihydrotropylium ion [CHT + H((1))](+) does not rearrange to the bicyclic isomer [NCD + H](+) under mild protonation conditions.     

Effect of metal ion and water coordination on the structure of a gas-phase amino acid.

The mode of metal ion and water binding to the amino acid valine is investigated using both theory and experiment. Computations indicate that without water, the structure of valine is nonzwitterionic. Both Li(+) and Na(+) are coordinated to the nitrogen and carbonyl oxygen (NO coordination), whereas K(+) coordinates to both oxygens (OO coordination) of nonzwitterionic valine. The addition of a single water molecule does not significantly affect the relative energies calculated for the cationized valine clusters. Experimentally, the rates of water evaporation from clusters of Val.M(+)(H(2)O)(1), M = Li, Na, and K, are measured using blackbody infrared radiative dissociation. The dissociation rate from the valine complex is compared to water evaporation rates from model complexes of known structure. These results indicate that the metal ion in the lithiated and the sodiated clusters is NO-coordinated to nonzwitterionic valine, while that in the potassiated cluster has OO coordination, in full agreement with theory. The zwitterionic vs nonzwitterionic character of valine in the potassiated cluster cannot be distinguished experimentally. Extensive modeling provides strong support for the validity of inferring structural information from the kinetic data.     

Formation of gas-phase clusters monitored during electrospray mass spectrometry: a study of quaternary ammonium pesticides

Gas-phase cluster formation between the quaternary ammonium pesticides paraquat, diquat, difenzoquat, chlormequat and mepiquat, and chloride and acetate anions present in a liquid chromatography (LC) mobile phase, has been studied using electrospray mass spectrometry. The clusters of paraquat, mepiquat and chlormequat were revealed over the entire m/z range of the mass spectrometer, and their formation is dependent on the concentrations of both the cationic and the anionic species. Mepiquat and chlormequat form clusters of the type [2M(q)(+) + A(-)](+), where M(q)(+) is the quaternary ammonium cation and A(-) is the anion. Paraquat forms a cluster species with ammonia and also an ion-pair complex with chloride anions. Diquat and difenzoquat did not form observable ion-pair complexes or clusters with any of the anions studied. Competitive binding of acetate and chloride anions reflects the higher charge density of chloride, which forms the dominant clusters with mepiquat and chlormequat. The formation of cluster species has implications for the quantification of quaternary ammonium pesticides and may have an influence on the linearity of calibrations.     

Noncovalent complex formation of tetratosylated resorcarene with aromatic,aliphatic, and cyclic alkyl ammonium ions: a mass spectrometric study of complex properties

The ability of tetratosylated resorcarene to form complexes with aromatic ammonium ions was investigated by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The formation of noncovalent complexes, [1+guest]⁺ and [1 · 1+guest]⁺, as observed with singly charged aromatic anilinium and phenylene aminoammonium guests. Comparison of the complexation efficiencies of the aromatic and aliphatic ammonium ions showed the importance of proton affinity of conjugate amines in complex formation. In collision‐induced dissociation experiments, gas‐phase stability was found to be lower for complexes formed with aromatic ions and this behavior was not found to depend on the proton affinity of conjugate amines. Fast oxidation of the para and ortho aminoammonium ions and complexation of these ions with tetratosylated resorcarene was observed. Copyright © 2005 John Wiley & Sons, Ltd.     

Isolation and purification of cat albumin from cat serum by copper ion affinity chromatography: further analysis of its primary structure

Proteins, regardless of their origin, have to be highly purified, particularly from the immunochemical point of view, if they are to be used to study their allergenicity. It is shown that cat albumin, a highly potent allergen for cat-sensitive humans, can be isolated and purified from cat serum using immobilized metal ion affinity chromatography (copper ions) instead of a salting-out process or precipitation with alcohol, techniques generally used for the preparation of serum proteins. During the process described, immunoglobulins are concomitantly isolated in a relatively pure form. Cat albumin amino acid composition and sequence were analysed after an ultimate purification by ion-exchange chromatography. The highest homology (greater than 80%) was found with the rat serum albumin.     

Magnesium monocationic complexes: a theoretical study of metal ion binding energies and gas-phase association kinetics

Bond dissociation energies (BDEs) for complexes of ground state Mg+ (2S) with several small oxygen- and nitrogen-containing ligands (H2O, CO, CO2, H2CO, CH3OH, HCOOH, H2CCO, CH3CHO, c-C2H4O, H2CCHOH, CH3CH2OH, CH3OCH3, NH3, HCN, H2CNH, CH3NH2, CH3CN, CH3CH2NH2, (CH3)2NH, H2NCN, and HCONH2) have been calculated at the CP-dG2thaw level of theory. These BDE values, as well as counterpoise-corrected MP2(thaw)/6-311+G(2df,p) calculations on the Mg+ complexes of several larger ligands, augment and complement existing experimental or theoretical determinations of gas-phase Mg+/ligand bond strengths. The reaction kinetics of complex formation are also investigated via variational transition state theory (VTST) calculations using the computed ligand and molecular ion parameters. Radiative association rate coefficients for most of these systems increase by approximately 1 order of magnitude with every 3-fold reduction in temperature from 300 to 10 K. Several of the largest molecules surveyed-notably, CH3COOH, (CH3)2CO, and CH3CH2CN-exhibit comparatively efficient radiative association with Mg+ (k(RA) > or = 1.0 x 10(-10) cm3 molecule(-1) s(-1)) at temperatures as high as 100 K, implying that these processes may have a considerable influence on the metal ion chemistry of warm molecular astrophysical environments known to contain these potential ligands. Our calculations also identify the infrared chromophoric brightness of various functional groups as a significant factor influencing the efficiency of the radiative association process.     

Ammonium adduct ion in ammonia chemical ionization mass spectrometry: 2—Mechanism of elimination of neutrals from the ammonium adduct ion

The mechanism of elimination of ROH (R = H or CH₃) from the ammonium adduct ion, [M+NH₄]⁺, of 1-adamantanol and its methyl ether is examined by using linked-scan metastable ion spectra and by measuring the dependence of the peak intensity ratio [M+NH₄]⁺/[M+NH₄? ROH]⁺ on ammonia pressure. For 1-adamantanol both S_Ni and S_N1 reactions are suggested in metastable ion decomposition, while only the S_N1 mechanism is operative in the ion source. For 1-adamantanol methyl ether the S_N1 reaction predominates both in metastable ion decomposition and in the ion source reaction.     

樟脑酮亚胺衍生物的合成及立体结构研究

从d-樟脑出发, 经六步反应合成了一种新的樟脑酮亚胺衍生物──7,7-二甲基-双环[2,2,1]=2-(苄)亚胺-10-(N-邻羟基苯基酰胺(2)。化合物的晶体的晶胞参数a=8.6904(9), b=10.9400(16), c=20.8583(33)埃; Z=4; V=1983.06(0.45)埃^3; 属P212121空间群, 用反常散射法测定分子的绝对构型为1S, 4R, 并讨论了该化合物作为不对称反应合成子的立体选择的影响因素。     

Comparison of the orders of gas-phase basicities and ammonium ion affinities of polyethers by the kinetic method and ligand exchange technique

The orders of relative gas-phase basicities and ammonium ion affinities of a series of polyethers obtained by application of the kinetic method and ligand exchange technique are compared to evaluate the discrepancies of results between the two techniques. The order of gas-phase basicities determined by the ligand exchange technique in a quadrupole ion trap agrees with the order established previously by Kebarle using equilibrium methods in a high-pressure mass spectrometer. The order obtained by the kinetic method in a triple quadrupole mass spectrometer varies for the ranking of one polyether (12-crown-4), and this discrepancy is attributed to a difference in the rates of the competing dissociation pathways from the triethylene glycol dimethyl ether/12-crown4 proton-bound adduct, owing to a substantial variation in the flexibilities of these two ethers. For the order of gas-phase ammonium ion affinities, the kinetic method results agree overall with the ligand exchange results; however, the order of ammonium ion affinities for tetraethylene glycol dimethyl ether and 15-crown-5 could not be differentiated by the ligand exchange method because of the rapidity of ammonium ion transfer between the two polyethers in both directions.     

A theoretical study on the structure and hygroscopicity of ammonium dinitramide

Density functional theory (DFT) and the dispersion corrected DFT have been used to investigate the hygroscopicity of ammonium dinitramide (ADN). Calculation results show that the gaseous ADN has a strong hydrogen bond. But the ionic pair structure NH₄ ⁺ · N(NO₂)^? is stabilized upon the addition of water molecules. Natural bond orbital calculations suggest that the intra- and intermolecular orbital interactions LP(O) → σ*(N–H) or LP(O) → σ*(O–H) make the system stabilized as a whole. En energy decomposition analysis reveals that the interactions between ADN and H₂O are dominated by the electrostatic and orbital interactions. The formation reactions become more spontaneous with the increasing number of water molecules but can be weakened by the growing temperature from 200 to 400 K. Moreover, the molecular dynamic method is applied to explore a more realistic cluster model to study the interactions between ADN and H₂O.     

Theoretical study of the gas-phase interaction between a chloride ion and a solvent molecule

Ten different ion clusters, ⁻(RH), are investigated by means of SCF and Cl computations in a double-zeta plus polarization basis set. For RH = H₂O, CH₃OH and other compounds with a hydroxy group, Cl⁻ is located along the line somewhat deviated from the extension of the OH bond. This bridge-type structure comes from the electrostatic bonding force plus the minor covalent nature of the OH. Cl⁻ bond. The standard OH...Cl− distance is obtained to be 2.2–2.4 A. The calculated stabilization energies are found to be in reasonable agreement with the available gas-phase experimental values of ΔH⁰ except for Cl⁻(HCOOH).     

The structure of the ion: An ion kinetic energy spectrometry study

The kinetic energy release (T) values for the loss of CO from ions from five compounds have been obtained and are consistent with at least two different structures for the ion. This result is supported by the T value obtained for the decomposition of the molecular ions.     

Creatinine biosensor based on ammonium ion selective electrode and its application in flow-injection analysis

A new, highly sensitive, fast responding and stable potentiometric biosensor for creatinine determination is developed. The biosensor is based on an ammonium ion-selective electrode. Creatinine deiminase (EC 3.5.4.21) is chemically immobilized on the surface of the polymeric ion-sensitive membrane in the form of monomolecular layer using a simple, one-step carbodiimide covalent attachment method. The resulting enzyme electrodes are useful for measurement under flow injection analysis (FIA) conditions. The biosensors exhibit excellent operational and storage stability. The enzyme electrodes retain over 70% of initial sensitivity after ten weeks of work under FIA conditions. The storage stability at 4 °C is longer than half a year without loss of sensitivity. Under optimized conditions near 30 samples per hour can be analyzed and the determination range (0.02-20.0 mmol l⁻¹) fully covers creatinine concentrations important from clinical and biomedical point of view. The simple biosensor/FIA system has been successfully used for determination of creatinine in urine, serum and posthemodialysate samples.     

An ab initio study of the reaction of ammonium ion with hydride ion and lithium hydride

Both the abstraction and substitution mechanisms for the reaction of NH⁺₄ with H^? and the abstraction mechanisms for the reaction with LiH in the gas phase have been investigated by theoretical methods. LiH results to be a better reagent and reactions with and without scrambling are competitive in accordance with experimental findings.     

Electron affinity of Al13: a correlated electronic structure study

Neutral and anionic 13-atom aluminum clusters are studied with high-level, fully ab initio methods: second-order perturbation theory (MP2) and coupled cluster theory with singles, doubles, and perturbative triples (CCSD(T)). Energies and vibrational frequencies are reported for icosahedral and decahedral isomers, and are compared with density functional theory results. At the MP2 level of theory, with all of the basis sets employed, the icosahedral structure is energetically favored over the decahedral structure for both the neutral and anionic Al(13) clusters. Hessian calculations imply that only the icosahedral structures are potential energy minima. The CCSD(T)/aug-cc-pVTZ adiabatic electron affinity of Al(13) is found to be 3.57 eV, in excellent agreement with experiment.     

Theoretical study of structure and stability of fullerene derivative: C50O

A total of eight possible isomers of C₅₀O, an oxide of fullerene C₅₀ (D_5h), have been investigated by B3LYP/3‐21G calculations. The isomer, which has an annulene‐like structure with oxygen bridging across a [5,6] type C? C bond at the site between the pole and the equatorial belt, is found being the ground state of C₅₀O. Four isomers are relatively more stable and the energy differences between them are not large. This result indicates that more than one C₅₀O isomer will coexist once C₅₀O is synthesized. The relative stabilities of the C₅₀O isomers may be determined mainly by the strain release and by the formation of the cyclic phenylene substructure at the equatorial belt of the cage. The calculated nucleus independent chemical shifts (NICS) of the C₅₀O isomers will be useful because from them one can expect outstanding NMR properties that can lead to their identification and characterization. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005