Ab initio analytical potential energy surface and quasiclassical trajectory study of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+))-->OH(+)(X (3)Sigma(-))+H((2)S) reaction and isotopic variants

An analytical potential energy surface (PES) representation of the O(+)((4)S)+H(2)(X (1)Sigma(g) (+)) system was developed by fitting around 600 CCSD(T)/cc-pVQZ ab initio points. Rate constant calculations for this reaction and its isotopic variants (D(2) and HD) were performed using the quasiclassical trajectory (QCT) method, obtaining a good agreement with experimental data. Calculations conducted to determine the cross section of the title reaction, considering collision energies (E(T)) below 0.3 eV, also led to good accord with experiments. This PES appears to be suitable for kinetics and dynamics studies. Moreover, the QCT results show that, although the hypotheses of a widely used capture model are not satisfied, the resulting expression for the cross section can be applied within a suitable E(T) interval, due to errors cancellation. This could be a general situation regarding the application of this simple model to ion-molecule processes.     

Ab initio potential energy surface, variational transition state theory, and quasiclassical trajectory studies of the F+CH4-->HF+CH3 reaction

In this work we present a study of the F+CH(4)-->HF+CH(3) reaction (DeltaHdegrees(298 K)=-32.0 kcal mol(-1)) using different methods of the chemical reaction theory. The ground potential energy surface (PES) is characterized using several ab initio methods. Full-dimensional rate constants have been calculated employing the variational transition state theory and using directly ab initio data. A triatomic analytical representation of the ground PES was derived from ab initio points calculated at the second- and fourth-order M?ller-Plesset levels with the 6-311+G(2df,2pd) basis set, assuming the CH(3) fragment to be a 15 a.m.u. pseudoatom in the fitting process. This is suggested from experiments that indicate that the methyl group is uncoupled to the reaction coordinate. A dynamics study by means of the quasiclassical trajectory (QCT) method and employing this analytical surface was also carried out. The experimental data available on the HF internal states distributions are reproduced by the QCT results. Very recent experimental information about the reaction stereodynamics is also borne out by our QCT calculations. Comparisons with the benchmark F+H(2) and analogous Cl+CH(4) reactions are established throughout.     

Characterization of a new qQq-FTICR mass spectrometer for post-translational modification analysis and top-down tandem mass spectrometry of whole proteins

The use of a new electrospray qQq Fourier transform ion cyclotron mass spectrometer (qQq-FTICR MS) instrument for biologic applications is described. This qQq-FTICR mass spectrometer was designed for the study of post-translationally modified proteins and for top-down analysis of biologically relevant protein samples. The utility of the instrument for the analysis of phosphorylation, a common and important post-translational modification, was investigated. Phosphorylation was chosen as an example because it is ubiquitous and challenging to analyze. In addition, the use of the instrument for top-down sequencing of proteins was explored since this instrument offers particular advantages to this approach. Top-down sequencing was performed on different proteins, including commercially available proteins and biologically derived samples such as the human E2 ubiquitin conjugating enzyme, UbCH10. A good sequence tag was obtained for the human UbCH10, allowing the unambiguous identification of the protein. The instrument was built with a commercially produced front end: a focusing rf-only quadrupole (Q0), followed by a resolving quadrupole (Q1), and a LINAC quadrupole collision cell (Q2), in combination with an FTICR mass analyzer. It has utility in the analysis of samples found in substoichiometric concentrations, as ions can be isolated in the mass resolving Q1 and accumulated in Q2 before analysis in the ICR cell. The speed and efficacy of the Q2 cooling and fragmentation was demonstrated on an LCMS-compatible time scale, and detection limits for phosphopeptides in the 10 amol/muL range (pM) were demonstrated. The instrument was designed to make several fragmentation methods available, including nozzle-skimmer fragmentation, Q2 collisionally activated dissociation (Q2 CAD), multipole storage assisted dissociation (MSAD), electron capture dissociation (ECD), infrared multiphoton induced dissociation (IRMPD), and sustained off resonance irradiation (SORI) CAD, thus allowing a variety of MS(n) experiments. A particularly useful aspect of the system was the use of Q1 to isolate ions from complex mixtures with narrow windows of isolation less than 1 m/z. These features enable top-down protein analysis experiments as well structural characterization of minor components of complex mixtures.     

Synthesis and characterisation of the platinum complexes [PtCl(CClPAr)(PPh3)2] and [PtCl(CClPAr′)(PPh3)2] as potential intermediates in the preparation of phosphaalkynes

Oxidative addition reactions of Cl₂CPR (R = 2,4,6-tris(trifluoromethyl)phenyl (Ar) or 2,6-bis(trifluoromethyl)phenyl (Ar′) with Pt(PPh₃)₄ yield the cis and trans (at platinum) complexes [PtCl(ClCPAr)(PPh₃)₂] and [PtCl(ClCPAr′)(PPh₃)₂]. All starting materials and intermediates have been characterised by NMR spectroscopy. The crystal and molecular structures of the trans-platinum complexes have been determined by single-crystal X-ray diffraction at low temperature.     

Imidazopyridine and pyrimidinopyridine systems from perfluorinated pyridine derivatives

Annelation of pentafluoropyridine via an intramolecular nucleophilic aromatic substitution process with benzamidine gave an imidazopyridine system in high yield in a two step process whilst alkyl amidines gave 4-aminotetrafluoropyridine by a competing elimination reaction. 4-Phenylsulfonyl tetrafluoropyridine reacts with amidines to give the corresponding imidazo[4,5-b]pyridine systems. In contrast, 4-cyanotetrafluoropyridine gave a [6,6]-fused pyrimidinopyridine system arising from initial nucleophilic substitution at the C-3 position of the pyridine ring followed by intramolecular cyclization onto the pendant cyano group. The systems prepared by this annelation methodology further demonstrate the utility of perfluorinated heterocyclic substrates for the synthesis of heterocyclic scaffolds that possess multiple functionality and have potential applications in the drug discovery arena.     

Synthesis and antimalarial effects of N,N-dialkyl-6-(substituted phenyl)-1,2,4,5-tetrazin-3-amines

The synthesis of a series of N,N-dialkyl-6-(substituted phenyl)-1,2,4,5-tetrazin-3-amines (IV) by two routes is described. The first route (Scheme I) involved the oxidative cyclization of formazans (II) to 3-bromo-6-(substituted phenyl)-1,2,4,5-tetrazines (III), followed by treatment with amines. The second (Scheme II) utilized the treatment of 3-(methylthio)-6-(substituted phenyl)-1,2,4,5-tetrazines (VII) with amines to provide the desired products. The intermediate 3-(methylthio)-6-(substituted phenyl)-1,2,4,5-tetrazines (VII) were obtained by thiobenzoylation of hydrazinecarbohydrazonothioic acid methyl ester with [[(substituted phenyl)thioxomethyl]thio]-acetic acids (V) to afford the 1,2-dihydro-3-(methylthio)-6-(substituted phenyl)-1,2,4,5-tetrazines (VI). Oxidation with bromine in acetic acid provided the desired intermediates. The target 6-(substituted phenyl)-1,2,4,5-tetrazin-3-amines (IV) displayed modest antimalarial activity.     

Probes for narcotic receptor mediated phenomena. Part 31: Synthesis of rac-(3R,6aS,11aS)-2-methyl-1,3,4,5,6,11a-hexahydro-2H-3,6a-methanobenzofuro[2,3-c]azocine-10-ol, and azocine-8-ol, the ortho-c and the para-c oxide-bridged phenylmorphan isomers

Two of the 12 possible oxide-bridged phenylmorphans, were synthesized, rac-(3R,6aS,11aS)-2-methyl-1,3,4,5,6,11a-hexahydro-2H-3,6a-methanobenzofuro[2,3-c]azocine-10-ol (7) (the ortho-c compound), and rac-(3R,6aS,11aS)-2-methyl-1,3,4,5,6,11a-hexahydro-2H-3,6a-methanobenzofuro[2,3-c]azocine-8-ol (8) (the para-c compound). Single-crystal X-ray diffraction studies indicated that the dihedral angle between the least squares planes through the phenyl ring and the atoms C₁, C_11a, C₁₂, and C₃ in the piperidine ring in both 7·CHCl₃ and 8·HBr was 6.9°. The C₁₂-C_6a-C_6b-C_10a torsion angle was found to be 139.3° for both compounds. The angular relationship between the phenolic ring and the piperidine ring in phenylmorphans that interact with specific opioid receptors as agonists or antagonists is of considerable theoretical interest.     

Uncountable autohomeomorphism groups of thin-tall locally compact scattered spaces

Under a hypothesis weaker thanCH, both the free group with ₁ generators and the free Abelian group with ₁ generators are non-trivial autohomeomorphism groups of locally compact thin-tall scattered spaces.Presented by V. Trnkova.     

Arylzinc alkoxides: [ArZnOCHPr(i)2]2 and Ar2Zn3(OCHPr(i)2)4 when Ar = C6H5, p-CF3C6H4, 2,4,6-Me3C6H2, and C6F5

From the reactions between diarylzinc compounds (Ar2Zn) and the alcohol (Pr(i)2CHOH) in toluene, the compounds [ArZn(OCHPr(i)2)]2 (Ar = C6H5, C6F5, p-CF3C6H4, and 2,4,6-Me3C6H2) have been isolated and shown to exist in equilibra with the trinuclear complexes Ar2Zn3(OCHPr(i)2)4 and Ar2Zn when Ar = C6H5, C6F5, and p-CF3C6H4. The trinuclear complexes have also been prepared from reactions of the Ar2Zn compounds with the alcohol, which reveals that the ease of Zn-C(aryl) bond cleavage is sensitive to the nature of the Ar group: C6H5 > 4-CF3C6H4 > C6F5. The molecular structures of Ar2Zn3(OCHPr(i)2)4 where Ar = p-CF3C6H4 and C6F5 and [ArZn(OCHPr(i)2)]2 where Ar = C6F5, p-CF3C6H4, and 2,4,6-Me3C6H2 are reported based on single-crystal X-ray diffraction studies. The X-ray structure of Zn(p-CF3C6H4)2 is also reported. The reactivity of these new compounds toward the polymerization of propylene oxide (PO) and the copolymerization of PO and CO2 have been investigated along with related reactions involving the partial hydrolysis of the Ar2Zn and R2Zn compounds, where R = t-Bu, n-Bu, and n-Oct. These results are compared with the previous studies employing Et2Zn as an organozinc precursor.