Poincaré Duality and <Emphasis Type="Italic">G</Emphasis><Superscript>+++</Superscript> Algebras

Theories with General Relativity as a sub-sector exhibit enhanced symmetries upon dimensional reduction, which is suggestive of “exotic dualities”. Upon inclusion of time-like directions in the reductions one can dualize to theories in different space-time signatures. We clarify the nature of these dualities and show that they are well captured by the properties of infinite-dimensional symmetry algebras (G ⁺⁺⁺- algebras), but only after taking into account that the realization of Poincaré duality leads to restrictions on the denominator subalgebra appearing in the non-linear realization. The correct realization of Poincaré duality can be encoded in a simple algebraic constraint, that is invariant under the Weyl-group of the G ⁺⁺⁺-algebra, and therefore independent of the detailed realization of the theory under consideration. We also construct other Weyl-invariant quantities that can be used to extract information from the G ⁺⁺⁺-algebra without fixing a level decomposition. Post-doctoraal onderzoeker van het Fonds voor Wetenschappelijk Onderzoek, Vlaanderen.     

Ruthenium-catalyzed cycloisomerization of cis-3-en-1-ynes to cyclopentadiene and related derivatives through a 1,5-sigmatropic hydrogen shift of ruthenium-vinylidene intermediates

We report a new ruthenium-catalyzed cycloisomerization of unactivated cis-3-en-1-ynes, which produces substituted cyclopentadiene and related derivatives. The mechanism of this cyclization is proposed to involve a [1,5]-sigmatropic hydrogen shift of ruthenium-vinylidene intermediates on the basis of deuterium-labeling experiments.     

Comprehensive two‐dimensional GC for the analysis of low‐molecular‐weight oxygenates in three different matrices from a petrochemical pilot plant using a single calibration

A method using comprehensive ²DGC with flame ionisation detection was developed to quantify 17 low‐molecular‐weight oxygenates in three different matrices, namely water, oil and gas, using a single calibration. The method was required for the pilot‐plant experiments of a chemical process unit. From an analytical perspective, the first task was to find a suitable analytical method with sufficient selectivity and sensitivity to analyse the selected oxygenates at low levels in the presence of high levels of hydrocarbons. The second was the accurate quantitation of oxygenates in the water, oil and gas fractions, using the same instrument and calibration. Both these requirements were met by using comprehensive ²DGC in the inverse configuration and calibrating the detector with the number of moles injected versus response. The method was successfully applied for the characterisation of the reactor product stream of the chemical process unit and made it possible to determine the fate of the selected oxygenates after passing through the reactor. The development of the method and some of the results are described in this paper.     

A homogeneous quenching resonance energy transfer assay for the kinetic analysis of the GTPase nucleotide exchange reaction

A quenching resonance energy transfer (QRET) assay for small GTPase nucleotide exchange kinetic monitoring is demonstrated using nanomolar protein concentrations. Small GTPases are central signaling proteins in all eukaryotic cells acting as a “molecular switches” that are active in the GTP-state and inactive in the GDP-state. GTP-loading is highly regulated by guanine nucleotide exchange factors (GEFs). In several diseases, most prominently cancer, this process in misregulated. The kinetics of the nucleotide exchange reaction reports on the enzymatic activity of the GEF reaction system and is, therefore, of special interest. We determined the nucleotide exchange kinetics using europium-labeled GTP (Eu-GTP) in the QRET assay for small GTPases. After GEF catalyzed GTP-loading of a GTPase, a high time-resolved luminescence signal was found to be associated with GTPase bound Eu-GTP, whereas the non-bound Eu-GTP fraction was quenched by soluble quencher. The association kinetics of the Eu-GTP was measured after GEF addition, whereas the dissociation kinetics could be determined after addition of unlabeled GTP. The resulting association and dissociation rates were in agreement with previously published values for H-Ras^Wt, H-Ras^Q61G, and K-Ras^Wt, respectively. The broader applicability of the QRET assay for small GTPases was demonstrated by determining the kinetics of the Ect2 catalyzed RhoA^Wt GTP-loading. The QRET assay allows the use of nanomolar protein concentrations, as more than 3-fold signal-to-background ratio was achieved with 50 nM GTPase and GEF proteins. Thus, small GTPase exchange kinetics can be efficiently determined in a HTS compatible 384-well plate format.

Skin Cancer Risks Avoided by the Montreal Protocol—Worldwide Modeling Integrating Coupled Climate‐Chemistry Models with a Risk Model for UV

The assessment model for ultraviolet radiation and risk “AMOUR” is applied to output from two chemistry‐climate models (CCMs). Results from the UK Chemistry and Aerosols CCM are used to quantify the worldwide skin cancer risk avoided by the Montreal Protocol and its amendments: by the year 2030, two million cases of skin cancer have been prevented yearly, which is 14% fewer skin cancer cases per year. In the “World Avoided,” excess skin cancer incidence will continue to grow dramatically after 2030. Results from the CCM E39C‐A are used to estimate skin cancer risk that had already been inevitably committed once ozone depletion was recognized: excess incidence will peak mid 21st century and then recover or even super‐recover at the end of the century. When compared with a “No Depletion” scenario, with ozone undepleted and cloud characteristics as in the 1960s throughout, excess incidence (extra yearly cases skin cancer per million people) of the “Full Compliance with Montreal Protocol” scenario is in the ranges: New Zealand: 100–150, Congo: ?10–0, Patagonia: 20–50, Western Europe: 30–40, China: 90–120, South‐West USA: 80–110, Mediterranean: 90–100 and North‐East Australia: 170–200. This is up to 4% of total local incidence in the Full Compliance scenario in the peak year.     

Ni-Catalyzed Regio- and Enantioselective Homoallylic Coupling: Synthesis of Chiral Branched 1,5-Dienes Featuring a Quaternary Stereogenic Center and Mechanistic Analysis

Asymmetric synthesis of small molecules comprising quaternary stereogenic carbon centers represents a challenging objective. Here regio- and enantioselective synthesis of chiral 1,5-dienes featuring quaternary stereocenters is reported via nickel-promoted by reductive homoallylic coupling. The developed methodology features an atypical preference for the formation of unusual branched regioisomers (rr >20 : 1) in a sterically challenging allylic substitution event and furnishes the products with enantiomeric ratios of up to 98 : 2 and with high chemo- and E-selectivity. A range of experimental evidences suggest that zinc plays a dual role to generate electrophilic and nucleophilic Ni(II)-allyl intermediates empowering a unique formal bimetallic cross-electrophile manifold in two separate kinetic regimes.     

Supramolecular adsorption of alkaloids by metallosalphen complexes

Mono and bis-zinc(II)-centered salphen derivatives 1-5 are presented as efficient adsorption materials for pyridine-based alkaloid derivatives. The different alkaloid assemblies were studied by UV-vis and NMR spectroscopy, and high binding constants (Ks approximately 10(5)) were additionally determined for the supramolecular complexes based on nicotine. X-ray analyses furthermore revealed, together with spectroscopic solution data, a preferential positioning of the nicotine guest(s). Upon binding to bis-Zn(II)-bis-salphen complexes, the dinicotine assembly provokes a colorimetric change that may be useful for colorimetric analyses. The adsorption/desorption process of nicotine was studied using a polymeric bis-Zn(salphen) complex (5) and showed a recycling potential of this type of complexes in the binding of alkaloid compounds.     

Facile isolation of bisimines based on 3,3'-diaminobenzidine: direct access to unsymmetrical bimetallic salphen building blocks

Diimines obtained from 3,3'-diaminobenzidine and tert-butyl-substituted salicylaldehydes in MeOH can be readily isolated in 60-90% yield and were obtained as a mixture of geometrical isomers. Two distinct diimine intermediates (4 and 5) with a higher molecular symmetry as related to the other isomeric diimine products were both isolated by crystallization of which 5 was subsequently used to demonstrate that nonsymmetrical bis-salphen complexes with different functional groups and metal centers can be assembled via a three-component one-pot procedure.     

Measurements and quasi-quantum modeling of the steric asymmetry and parity propensities in state-to-state rotationally inelastic scattering of NO (2Pi1/2) with D2

Relative integrated cross sections are measured for spin-orbit-conserving, rotationally inelastic scattering of NO (2Pi1/2), hexapole-selected in the upper Lambda-doublet level of the ground rotational state (j = 0.5), in collisions with D2 at a nominal energy of 551 cm-1. The final state of the NO molecule is detected by laser-induced fluorescence (LIF). The state-selected NO molecule is oriented with either the N end or the O end toward the incoming D2 molecule by application of a static electric field E in the scattering region. This field is directed parallel or antiparallel to the relative velocity vector v. Comparison of signals taken for the different applied field directions gives the experimental steric asymmetry SA, defined by SA = (sigma v upward arrow downward arrow E - sigma v upward arrow upward arrow E)/(sigma v upward arrow downward arrow E + sigma v upward arrow upward arrow E), which is equal to within a factor of -1 to the molecular steric effect, Si-->f identical with (sigmaD2-->NO - sigmaD2-->ON)/(sigmaD2-->NO + sigmaD2-->ON). The dependence of the integral inelastic cross section on the incoming Lambda-doublet component is also measured as a function of the final rotational (jfinal) and Lambda-doublet (epsilonfinal) state. The measured steric asymmetries are similar to those previously observed for NO-He scattering. Spin-orbit manifold-conserving collisions exhibit a larger propensity for parity conservation than their NO-He counterparts. The results are interpreted in the context of the recently developed quasi-quantum treatment (QQT) of rotationally inelastic scattering [Gijsbertsen, A.; Linnartz, H.; Taatjes, C. A.; Stolte, S. J. Am. Chem. Soc. 2006, 128, 8777]. The QQT predictions can be inverted to obtain a fitted hard-shell potential that reproduces the experimental steric asymmetry; this fitted potential gives an empirical estimate of the anisotropy of the repulsive interaction between NO and D2. QQT computation of the differential cross section using this simple model potential shows reasonable agreement with the measured differential cross sections.