Understanding the complex dissociation dynamics of energy selected dichloroethylene ions: neutral isomerization energies and heats of formation by imaging photoelectron-photoion coincidence

The dissociative photoionization of 1,1-C(2)H(2)Cl(2), (E)-1,2-C(2)H(2)Cl(2), and (Z)-1,2-C(2)H(2)Cl(2) has been investigated at high energy and mass resolution using the imaging photoelectron photoion coincidence instrument at the Swiss Light Source. The asymmetric Cl-atom loss ion time-of-flight distributions were fitted to obtain the dissociation rates in the 10(3) s(-1) < k < 10(7) s(-1) range as a function of the ion internal energy. The results, supported by ab initio calculations, show that all three ions dissociate to the same C(2v) symmetry ClC═CH(2)(+) product ion. The 0 K onset energies thus establish the relative heats of formation of the neutral isomers, that is, the isomerization energies. The experimental rate constants, k(E), as well as ab initio calculations indicate an early isomerization transition state and no overall reverse barrier to dissociation. The major high energy channels are the parallel HCl loss and the sequential ClC═CH(2)(+) → HCCH(+) + Cl process, the latter in competition with a ClC═CH(2)(+) → ClCCH(+) + H reaction. A parallel C(2)H(2)Cl(2)(+) → C(2)HCl(2)(+) + H channel also weakly asserts itself. The 0 K onset energy for the sequential Cl loss reaction suggests no barrier to the production of the most stable acetylene ion product; thus the sequential Cl-atom loss is preceded by a ClC═CH(2)(+) → HC(Cl)CH(+) reorganization step with a barrier lower than that of the second Cl-atom loss. The breakdown diagram corresponding to this sequential dissociation reveals the internal energy distribution of the first C(2)H(2)Cl(+) daughter ion, which is determined by the kinetic energy release in the first, Cl loss reaction at high excess energies. At low kinetic energy release, this distribution corresponds to the predicted two translational degrees of freedom, whereas at higher energies, the excess energy partitioning is characteristic of only one translational degree of freedom. New Δ(f)H(o)(298K) of 3.7, 2.5, and 0.2 ± 1.75 kJ mol(-1) are proposed for 1,1-C(2)H(2)Cl(2), (E)-1,2-C(2)H(2)Cl(2), and (Z)-1,2-C(2)H(2)Cl(2), respectively, and the proton affinity of ClCCH is found to be 708.6 ± 2.5 kJ mol(-1).     

First efficient uncharged reactivators for the dephosphylation of poisoned human acetylcholinesterase

Nerve agents are highly toxic organophosphorus compounds with strong inhibition potency against acetylcholinesterase (AChE). Herein, we describe two first extremely promising uncharged reactivators for poisoned human AChE with a superior or similar in vitro ability to reactivate the enzyme as compared to that of HI-6, obidoxime, TMB-4 and HL?-7.     

1,2-diphosphaacenaphthene 1,2-dications: synthetic, stereochemical and computational study of the stabilising role of naphthalene-1,8-diyl backbone

Syntheses and full characterisation data (including single crystal diffraction) of three 1,2‐diphosphonium dicationic species with the naphthalene‐1,8‐diyl (Nap) backbone are reported. The oxidation of Nap[P(NMe₂)₂]₂ with P₂I₄ to its 1,2‐dication was achieved. meso‐ and rac‐forms of “all carbon” 1,2‐diphosphonium dications were obtained in good yields and purity by double alkylation of the parent diphosphine (1,2‐diphenyl‐1,2‐diphosphaacenaphthene) with methyl triflate or trimethyloxonium tetrafluoroborate. Each methylating reagent produces one of the rac‐ or meso‐forms of the dication diastereospecifically. Structural parameters of the new dications are discussed with respect to other phosphorus 1,2‐dications. DFT (B3LYP) computations revealed the significant role of the naphthalene backbone in stabilisation of the dicationic motif and helped to assess the energy cost of the steric clash of a variety of groups attached to the peri‐positions of naphthalene. The synthesis and single crystal X‐ray data of the extremely crowded Nap[P(?Se)(OiPr)₂]₂ are discussed, and are contrasted with the unsuccessful synthesis of Nap(PtBu₂)₂ from NapLi₂ and ClPtBu₂.     

A type 2 Ferrier rearrangement-based synthesis of d-myo-inositol 1,4,5-trisphosphate

The synthesis of d-myo-inositol 1,4,5-trisphosphate (InsP₃) from methyl α-d-glucopyranose, via a type 2 Ferrier rearrangement is reported. A key intermediate in this synthesis possesses orthogonal protecting groups at the 1-, 4- and 5-position, making it a versatile starting point for the synthesis of unnatural InsP₃ derivatives. Biological evaluation of the synthetic InsP₃ demonstrates that this compound evokes selective Ca²⁺ release via activation of InsP₃ receptors.     

Criteria to define the standard deviation for proficiency assessment for the determination of essential trace elements in serum: comparison of Z-scores based on the Horwitz function or on biological variability

A critical issue in the organisation of Proficiency Testing/External Quality Assessment Schemes is the definition of the criteria against which the performance of individual laboratories should be evaluated. Organisers of EQAS in Occupational and Environmental Laboratory Medicine (http://www.occupational-environmental-laboratory.com) collaborate to define common acceptable levels of performance. The aim of this study was to compare the Horwitz function to the Fraser’s approach. Sets of results obtained from the distribution of test materials in the Network schemes (for the measurands: copper, selenium or zinc in serum) were used to calculate Z-scores according to both approaches. Quality specifications derived from both approaches were also compared to the standard deviations obtained. Except for selenium, Horwitz criteria suggests a more stringent evaluation than Fraser criteria, the latter being very stringent as regard the participant analytical variability.     

Dioxo-2,5 pipérazines. 1. La synthèse des carboxythiazolo dioxo-2,5 pipérazines

A new and general synthesis of 2,5-dioxopiperazine condensed with the thiazolidine ring is described. The synthesis involves the use of N-ethoxy carbonyl-2-ethoxy-1-2-dihydroquinoleine (EEDQ) as activating agent to form the 2,5-diketopiperazine (EEDQ) as activating agent to form the 2,5-diketopiperazine ring. By this method 9-carbobutoxy-7,7-dimethyl-2,5-dioxo-8-this-1,4-diazabicyclo[4.3.0] nonane (6) and 9-carboxy-8,8 dimethyl-2,5-dioxo-7-thia-1,4-diazabicy clo [4.3.0] nonane (8) were obtained, with near quantitative yield, from 4-carboxy-2-carbobutoxy-5,5 dimethylthiazolidine (4). The former was transformed into acid 7 by hydrolysis with barium bydroxyde and the latter was esterified with diazornethane thus producing a methylester 9. The use of the ethy lester of N-(2-cabobutoxy-4-carboxy-5,5-dimethyl-thiazolidine)glycine (10) for synthesis of 6 was also successful. The spectromethric data were interpreted and confirm the proposed structure of the new compounds.     

Etude par spectrométrie de masse de la fragmentation du désoxy-3-di-O-isopropylidène-1,2: 5,6-méthylidène-3-α-D-hexofurannose et de quelques analogues substitués en C(3′)

Electron Impact Mass Spectrometry of the 3-Desoxy-1,2: 5,6-di-O-isopropylidene-3-methylidene-δ-D -hexofuranose and Some C(3′)-Substituted Analogues The mass spectra of the 3-desoxy-1,2:5, 6-di-O-isopropylidene-3-methylidene- α-D -ribo-hexofuranose and of some C(3′)-mono- and -disubstituted derivatives have been investigated. Deuterium labelled molecules allow fragmentation modes to be proposed.     

Etude des conditions d'accès au triazino-1,2,4-[4,5-b] indazole

1,2,4-Triazino[4,5-b]indazol-1(2H)one and its derivatives were prepared by transposition of 3-[2-(-1,3,4-oxadiazolyl)]indazole or by ring closure of indazole ethoxymethylidenehydrazides. The synthesis of 1,2,3,4-tetrahydro-l,2,4-triazino[4,5-b]indazole-1,4-dione was achieved by cyclising the N-carbethoxyhydrazide of indazole-3-carboxylic acid and the synthesis of 1,2,4-triazino-[4,5-b]indazol-4(3H)one was made by cyclising the N-carbethoxy-hydrazone of indazole-3-carboxaldehyde. The Oxydation of 1,2,4-triazino[4,5-b]indazole-l(2H)thione gave 1,2,4-triazino-[4,5-b]indazoles. Nmr spectral data are reported.     

Ferrocenyltrithiocarbonates : I. Direct access from α-ferrocenylcarbinols by a SNi mechanism. Absolute x-ray structure determination of (R)-ferrocenylmethylmethane S-methyl-trithiocarbonate

¹⁰³Rh Chemical shifts of a variety of mono- and di-nuclear rhodium carbonyl complexes are reported together with the modifications to the probe and decoupler unit of a JEOL PS-100 PFT spectrometer which enable these ¹⁰³Rh-decoupled ¹³C NMR measurements to be made. These data are discussed in conjunction with ¹³C NMR data on other rhodium carbonyls.     

Induction asymétrique et réaction des α-hydroxy-oximes avec le bromure de phenylmagnésium. Synthéses stéreoselectives d'alcools aziridiniques et d'aza-bicyclo[3.1.0]oxo-2 oxaisothiazolidines-1,2,3

A facile synthesis of aziridine is describe. It is the reaction between Grignard regents and α-hydroxoximes in toluene. The aziridine alchohols are cyclised into 2-oxo-oxathiazolidines. The use of the nuclear Overhauser effect allows the assignment of the relative configurations of these latter compounds and also the configuration of the aziridine alcohols. A proof of the Grignard reagent complex with the alcoolate id given by action of methylmagensium bromide with 2-phenyl 3-methanol azirine. The asymetrie insuction observed is discussed with a transition state involving this complex.