Sublimation properties of CoF(3): mass spectrometric and quantum chemical studies

The sublimation of cobalt trifluoride was studied using the Knudsen effusion method combined with mass spectrometry. The pressure of F was directly measured for decomposition of CoF(3)(s) into CoF(2)(s). The average kinetic energy of CoF(2)(+), CoF(+) and Co(+) fragment ions was determined and the relative ionisation cross section curves measured from 6 eV to 100 eV. Thermodynamic functions of gaseous CoF(3) and Co(2)F(6), were evaluated from geometrical and vibrational parameters provided from theoretical calculations. Heats of formation of CoF(3)(s), CoF(3)(g), Co(2)F(6)(g) were established as (-784 +/- 6) kJ/mol, (-565 +/- 11) kJ/mol and (-1289 +/- 22) kJ/mol, respectively.     

1-硅萘和2-硅萘二聚反应的比较理论研究

采用密度泛函理论(DFT)方法在B3LYP/6-311G**水平研究了1-硅萘和2-硅萘[2+2]及[4+2]二聚反应的微观机理、势能剖面,考察了苯溶剂对反应势能剖面的影响.计算结果表明,[2+2]二聚反应为同步的协同反应,而[4+2]二聚反应以协同但非同步的方式进行.1-硅萘的[2+2]反应与2-硅萘的[2+2]反应在热力学和动力学上很接近,但它们的[4+2]反应则有较大不同.在1-硅萘的二聚反应中,[4+2]反应在热力学和动力学上都比[2+2]反应容易进行;但在2-硅萘的二聚反应中,反而是[2+2]反应容易进行.苯溶剂对所研究反应的势能剖面影响不大.     

The diphosphate monoanion in the gas phase: a joint mass spectrometric and theoretical study

H(3)P(2)O(7) (-) ions were obtained in an electrospray ion source of a Fourier transform ion cyclotron resonance (ESI/FTICR) mass spectrometer from a CH(3)CN/H(2)O (1:1) pyrophosphoric acid solution and in the ionic source of a triple quadrupole (TQ) mass spectrometer from the chemical ionisation (CI) of pyrophosphoric acid introduced by a thermostatically controlled direct insertion probe. The ions were structurally characterised by mass spectrometric techniques and theoretical calculations. Consistent with collisionally activated dissociation (CAD) mass spectrometric results, theoretical calculations identified the linear diphosphate anion (I) as the most stable isomer on the H(3)P(2)O(7) (-) potential energy surface. The joint application of mass spectrometric techniques and theoretical methods provided information on the dissociative processes of diphosphate anions in the gas phase. Finally, this study provides an insight into the structures and stabilities of the [H(3)PO(4).PO(3)](-), [HP(2)O(6).H(2)O](-) and [H(2)PO(4).HPO(3)](-) clusters and allows the stability and structure of the dimetaphosphate anion, HP(2)O(6) (-), to be investigated at the B3LYP6-31+G* and CCSD(T) levels of theory.     

The importance of dihydrogen complexes HnGe(H2)+ (n=0,1) to the chemistry of cationic germanium hydrides: advanced theoretical and mass spectrometric analysis

Investigations of [Ge,Hn]-/0/- (n = 2,3) have been performed using a four-sector mass spectrometer. The results reveal that the complexes HnGe(H2)+ (n = 0,1) play an important role in the unimolecular dissociation of the metastable cations. Theoretical calculations support the experimental observations in most instances, and the established view that the global minimum of [Ge,H2]+ is an inserted structure may need reexamination; CCSD(T,full)/cc-pVTZ//CCSD(T)/6-311 ++ G(d,p) and B3LYP/cc-pVTZ studies of three low-lying cation states (2A1 HGeH+, 2B2 Ge(H2)+ and 2B1 Ge(H2)+) indicate a very small energy difference (ca. 4 kcal mol(-1)) between 2A1 HGeH+ and 2B2 Ge(H2)+; B3LYP favours the ion-molecule complex, whereas coupled-cluster calculations favour the inserted structure for the global minimum. Single-point multireference (MR) averaged coupled-pair functional and MR-configuration interaction calculations give conflicting results regarding the global minimum. We also present theoretical evidence indicating that the orbital-crossing point implicated in the spin-allowed metastable dissociation HGeH+* --> Ge(H2)+* --> Ge+ + H2 lies above the H-loss asymptote. Thus, a quantum-mechanical tunneling mechanism is invoked to explain the preponderance of the H2-loss signal for the metastable ion.     

The isomolecular exchange reaction Ga2S(g) + In2S(g) = 2 InGaS(g)

Equilibria involving the molecules Ga₂S(g), In₂S(g), and InGaS(g), by the reaction Ga₂S(g) + In₂S(g) = 12InGaS(g) were investigated between 1060–1350 K by the Knudsen-effusion, mass-spectrometric method. The reaction enthalpy at 298 K was calculated to be 0±1 kJ mol⁻¹. The enthalpy of formation of InGaS at 298 K and the enthalpy of atomization of InGaS at 298 K were calculated to be 80±18 kJ mol⁻¹ and 710±18 kJ mol⁻¹, respectively. The equilibrium constant and the enthalpy of reaction indicated that the three gaseous molecules have a bent triatomic structure in which S is a center atom and no bond between metals.     

Septin 2 phosphorylation: theoretical and mass spectrometric evidence for the existence of a single phosphorylation site in vivo

Septins constitute a family of conserved proteins that are required for cytokinesis in a wide range of organisms. Most cells express a set of septin proteins and these are found to assemble into hetero-oligomeric septin complexes that appear filamentous. However, the mechanisms controlling the function and polymerization of septins are not known. We therefore examined the possibility that septins could be post-translationally modified by phosphorylation. We present herein a combined theoretical and experimental approach for the analysis of Septin 2 (Sept2) monophosphorylation in vivo. We purified and characterized the human recombinant Sept2, a 45-kDa protein, expressed from Sf21 insect cells. Analysis by matrix-assisted laser desorption/ionization quadrupole time-of-flight mass spectrometry on the full-length protein sequence of wild-type Sept2 revealed a unique phosphorylation site at residue Ser248 in vivo, which is consistent with one of the twelve phosphorylation sites in the protein sequence theoretically predicted by the Netphos program. Additional predictions with the motif scan programs Scansite and Prosite suggest that the phosphorylation of wild-type Sept2 might be a potential substrate for casein kinase 2. Site-directed mutagenesis of residue 248 from serine to alanine abrogated this phosphorylation. The location of phosphorylation in Sept2 differs from the sites predicted for cGMP-dependent protein kinase (PKG) phosphorylation in Septin 3, raising the possibility that different septins may undergo distinct phosphorylation events that could control their functions in important cellular processes such as neurotransmission or cytokinesis.     

The K2 2(3)Pi(g) state: new observations and analysis

Totally 3045 transitions into the 2(3)Pi(g) v = 0-42, J = 0-103, Omega = 0, 1, 2 rovibrational levels have been observed by infrared-infrared double resonance fluorescence excitation and two-photon spectroscopy. Molecular constants including the spin-orbit interaction parameters are obtained. Although the K2 2(3)Pi(g) state dissociates to the 4s + 3d atomic limit, it is strongly mixed with the 3P ionic states in the range of the potential well. This mixing results in a relatively large equilibrium internuclear distance Re = 5.254 A and a larger spin-orbit constant A0 approximately 14.17 cm(-1) than that of the atomic limit -2.33 cm(-1). Strong perturbations of the 2(3)Pi(g) levels observed are attributed to the spin-orbit coupling with the 4(1)Sigma(g)+ state.     

The role of mass spectrometric methods in ionic reaction mechanistic studies

The role of various mass spectrometric methods, including electron ionization, collisional activation, metastable peak shapes, analysis of neutrals from ionic unimolecular dissociations, field ionization kinetics, drift cell, and Fourier transform ion cyclotron resonance spectrometry, in ionic reaction mechanistic studies is described. This is illustrated by selected examples of research performed in the author’s group over the last three decades. They comprise inter alia intramolecular acid–base, anchimeric assistance, nucleophilic attack, isomerization, cycloaddition, S_N2, and hydride ion transfer reactions.     

Derivatization of synthetic polymers in mass spectrometric studies

The review describes various derivatization approaches employed for the investigation of synthetic polymers by mild ionization mass spectrometry (fast atom and ion bombardment, matrix-assisted laser desorption/ionization, electrospray/ionization). The potentials of chemical methods for modification of end- and side-chain functional groups without the decomposition of molecules are demonstrated. Methods of the preliminary chemical degradation of polymer molecules for the investigation of their microstructure are considered. The possibilities of the chemical modification of polymer surfaces for the identification and quantitative determination of functionalized fragments are shown.     

Me3P complexes of p-block Lewis acids SnCl4, SnCl3+ and SnCl2(2+)

Reactions of Me(3)P with SnCl(4) in the presence of nAlCl(3) (n = 0, 1, 2) yields a series of P-Sn complexes illustrating new bonding environments for tin.     

New designer drug 4-iodo-2,5-dimethoxy-beta-phenethylamine (2C-I): studies on its metabolism and toxicological detection in rat urine using gas chromatographic/mass spectrometric and capillary electrophoretic/mass spectrometric techniques

Studies are described on the metabolism and the toxicological analysis of the phenethylamine-derived designer drug 4-iodo-2,5-dimethoxy-beta-phenethylamine (2C-I) in rat urine using gas chromatographic/mass spectrometric (GC/MS) techniques, and for a particular question, using capillary electrophoretic/mass spectrometric (CE/MS) techniques. The identified metabolites indicated that 2C-I was metabolized on the one hand by O-demethylation in position 2 and 5, respectively, followed either by N-acetylation or by deamination with subsequent oxidation to the corresponding acid or reduction to the corresponding alcohol, respectively. The latter metabolite was hydroxylated in beta-position and further oxidized to the corresponding oxo metabolite. On the other hand, 2C-I was metabolized by deamination with subsequent oxidation to the corresponding acid or reduction to the corresponding alcohol, respectively. 2C-I and most of its metabolites were partially excreted in conjugated form. The authors' systematic toxicological analysis (STA) procedure using full-scan GC/MS after acid hydrolysis, liquid-liquid extraction and microwave-assisted acetylation allowed the detection of an intake of a dose of 2C-I in rat urine that corresponds to a common drug users' dose. Assuming similar metabolism, the described STA procedure should be suitable for proof of an intake of 2C-I in human urine.     

A mass spectrometric study of Al(2)O(3)-SiO(2) melts using a Knudsen cell

The thermodynamic activities of SiO(2) in Al(2)O(3)-SiO(2) liquid slags were measured by the high-temperature Knudsen cell mass spectromeric method in the present work. The measurements were carried out in the temperature range 1863-2169 K. Tungsten crucibles were used to hold the slags. The system was calibrated using a CaF(2) standard. The mass spectra obtained for pure SiO(2) were in agreement with earlier data. The activities of silica, measured in the present work at 2150 K, show a slight negative deviation at very low alumina mole fractions which changed to a positive deviation at higher alumina contents. The activity values are in reasonable agreement with the assessment carried out by Hillert et al. The results were analysed on the basis of a slag model developed earlier at KTH, Stockholm. The present results are found to be compatible with the phase diagram proposed by Klug et al.     

The 39K(2) 2(3)Sigma(g)+ state: observation and analysis

The (39)K(2) 2 (3)Sigma(g) (+) state has been observed by perturbation-facilitated infrared-infrared double resonance spectroscopy and two-photon excitation. Resolved fluorescence spectra into the a (3)Sigma(u) (+) state have been recorded. The observed vibrational levels have been assigned as the v=23-25, 27, 28, 31-33, 38-45, 47, and 53 levels by comparing the observed and calculated spectra of the 2 (3)Sigma(g) (+)-->a (3)Sigma(u) (+) transitions. Molecular constants have been obtained using a global fitting procedure with a comprehensive set of experimental data. Fine and hyperfine splittings have been resolved in the excitation spectra. Perturbations between the 2 (3)Sigma(g) (+) and 2 (3)Pi(g) states were observed. The hyperfine patterns of the 2 (3)Sigma(g) (+) levels are strongly affected by the perturbation. The perturbation-free and weakly perturbed levels follow the case b(betaS) coupling scheme, while the perturbed levels follow case b(beta J) coupling. A Fermi contact constant, b(F)=65+/-10 MHz, has been obtained. Intensity anomalies of rotational lines appeared both in the 2 (3)Sigma(g) (+) approximately 2 (3)Pi(g)<--b (3)Pi(u) excitation spectra and in the 2 (3)Sigma(g) (+) approximately 2 (3)Pi(g)-->a (3)Sigma(u) (+) resolved fluorescence spectra. These intensity anomalies can be explained in terms of a quantum-mechanical interference effect.     

Towards a fully conjugated, double-stranded cycle: a mass spectrometric and theoretical study.

The two compounds, 1 and 5, are investigated by means of collision-induced dissociation experiments by using ion cyclotron resonance mass spectrometry and other mass spectrometric techniques as to their ability to act as precursors for the fully unsaturated double-stranded target compound 2. These experiments are complemented by flask-type pyrolyses of 5, the products of which are analyzed by mass spectrometry. For 1, no conditions were found under which the expected molecular ion of 2 at m/z 932 appeared, however, for its derivative 5 this was possible. This interesting finding is not in contradiction with the chemical structure of the long sought for compound 2 but calculations suggest that this compound may have isomerized into one where the conjugation is interrupted by hydrogen shift from the solubilizing alkyl chains into the cycle's perimeter. The key driving force for such an isomerization would be the considerable relief of strain energy.     

Electrospray tandem mass spectrometric studies of phosphopeptides and phosphopeptide analogues

A set of synthetic phosphopeptides and phosphopeptide analogues was studied by tandem nano-electrospray mass spectrometry. The influence of the collision offset and of the charge state of the molecular ion on phosphate-specific fragmentation processes was investigated in detail. H--D exchange experiments and structural considerations support a six-centered transition being present in the neutral loss of H3PO4 from serine, threonine and homoserine phosphopeptides, where the C-alpha hydrogen of serine or threonine or the C-beta hydrogen of homoserine is transferred to the protonated phosphate group. Neutral loss of H3PO4 at moderate collision offset potential represents a very abundant fragmentation process for serine, threonine and homoserine phosphopeptides. The most specific feature for discrimination of these phosphopeptides from tyrosine phosphopeptides is the m/z 79:97 ratio in the negative ion product spectra, which is consistently elevated in tyrosine phosphopeptides as compared with serine, threonine and homoserine phosphopeptides. The fragment ions of methylphosphono- and H-phosphonopeptides can be explained by the same mechanisms as are applicable to phosphopeptides.     

Bromodifluoroacetyl fluoride,CF2BrC(O)F: Experimental and theoretical studies

Bromodifluoroacetyl fluoride, CF₂BrC(O)F, was prepared through the gas-phase reaction of bromotrifluoroethene, CF₂CFBr, with molecular oxygen initiated either by NO₂ or CF₃OF. The compound was experimentally studied by FTIR spectroscopy of the gas phase and also isolated in Ar and N₂ matrices at low temperature. The energy differences between the possible conformers were theoretically studied, as well as the vibrational spectra of the conformers.     

Ion chemistry in germane/fluorocompounds gaseous mixtures: a mass spectrometric and theoretical study

The ion-molecule reactions occurring in GeH(4)/NF(3), GeH(4)/SF(6), and GeH(4)/SiF(4) gaseous mixtures have been investigated by ion trap mass spectrometry and ab initio calculations. While the NF(x)(+) (x=1-3) react with GeH(4) mainly by the exothermic charge transfer, the open-shell Ge(+) and GeH(2)(+) undergo the efficient F-atom abstraction from NF(3) and form GeF(+) and F-GeH(2)(+) as the only ionic products. The mechanisms of these two processes are quite similar and involve the formation of the fluorine-coordinated complexes Ge-F-NF(2)(+) and H(2)Ge-F-NF(2)(+), their subsequent crossing to the significantly more stable isomers FGe-NF(2)(+) and F-GeH(2)-NF(2)(+), and the eventual dissociation of these ions into GeF(+) (or F-GeH(2)(+)) and NF(2). The closed-shell GeH(+) and GeH(3)(+) are instead much less reactive towards NF(3), and the only observed process is the less efficient formation of GeF(+) from GeH(+). The theoretical investigation of this unusual H/F exchange reaction suggests the involvement of vibrationally-hot GeH(+). Passing from NF(3) to SF(6) and SiF(4), the average strength of the M-F bond increases from 70 to 79 and 142 kcal mol(-1), and in fact the only process observed by reacting GeH(n)(+) (n=0-3) with SF(6) and SiF(4) is the little efficient F-atom abstraction from SF(6) by Ge(+). Irrespective of the experimental conditions, we did not observe any ionic product of Ge-N, Ge-S, or Ge-Si connectivity. This is in line with the previously observed exclusive formation of GeF(+) from the reaction between Ge(+) and C-F compounds such as CH(3)F. Additionally observed processes include in particular the conceivable formation of the elusive thiohypofluorous acid FSH from the reaction between SF(+) and GeH(4).     

In situ generation of HCN for mass spectrometric studies

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me(3)SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F(-)(HCN), Cl(-)(HCN), CN(-)(HCN), PhNO(2)(.-)(HCN), Me(3)SiO(-)(HCN),and PhSiF(4)(-)(HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN(-)(HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0.87 +/- 0.07 eV.