Palladium(II)-allyl complexes containing chiral N-donor ferrocenyl ligands

A study of the reactivity of enantiopure ferrocenylimine (S_C)-[FcCHN-CH(Me)(Ph)] {Fc =  (η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-} (1a) with palladium(II)-allyl complexes [Pd(η³-1R¹,3R²-C₃H₃)(μ-Cl)]₂ {R¹ = H and R² = H (2), Ph (3) or R¹ = R² = Ph (4)} is reported. Treatment of 1a with 2 or 3 {in a molar ratio Pd(II):1a = 1} in CH₂Cl₂ at 298 K produced [Pd(η³-3R²-C₃H₄){FcCHN-CH(Me)(Ph)}Cl] {R² = H (5a) or Ph (6a)}. When the reaction was carried out under identical experimental conditions using complex 4 as starting material no evidence for the formation of [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(Ph)}Cl] (7a) was found. Additional studies on the reactivity of (S_C)-[FcCHN-CH(R³)(CH₂OH)] {R³ = Me (1b) or CHMe₂ (1c)} with complex 4 showed the importance of the bulk of the substituents on the palladium(II) allyl-complex (2-4) or on the ferrocenylimines (1) in this type of reaction. The crystal structure of 5a showed that: (a) the ferrocenylimine adopts an anti-(E) conformation and behaves as an N-donor ligand, (b) the chloride is in acis-arrangement to the nitrogen and (c) the allyl group binds to the palladium(II) in a η³-fashion. Solution NMR studies of 5a and 6a and [Pd(η³-1,3-Ph₂-C₃H₃){FcCHN-CH(Me)(CH₂OH)}Cl] (7b) revealed the coexistence of several isomers in solution. The stoichiometric reaction between 6a and sodium diethyl 2-methylmalonate reveals that the formation of the achiral linear trans-(E) isomer of Ph-CHCH-CH₂Nu (8) was preferred over the branched derivative (9). A comparative study of the potential utility of ligand 1a, complex 5a and the amine (S_C)-H₂N-CH(Me)(Ph) (11) as catalysts in the allylic alkylation of (E)-3-phenyl-2-propenyl (cinnamyl) acetate with the nucleophile diethyl 2-methylmalonate (Nu⁻) is reported.     

Characterization of equatorial and axial six-membered-ring peroxyl radicals

Spectroscopic data are consistent with computations that show that, in their most stable conformations, the peroxyl moiety is equatorial in cyclohexylperoxyl radicals and axial in oxa- and most polyoxacyclohexyl-2-peroxyl radicals.     

Raman scattering investigation of selenomethionine replacement in protein SOUL crystals

The vibrational properties of both wild‐type and selenomethionine (SeMet)‐substituted protein SOUL crystals have been investigated here by Raman spectroscopy. Several Raman peaks observed in the spectra of methionine and SeMet were identified as specific markers. The unambiguous assignment of these peaks has been inferred by comparing the experimental Raman spectra of the pure amino acids, recorded in solid state and in aqueous solution, and the Raman intensities computed using quantum chemical calculations. Moreover, a quantitative evaluation of the relative amount of SeMet replacement in the crystals of protein SOUL labelled with SeMet has been estimated through the ratio between the Raman intensities of marker peaks. These results offer evidence of the potential of Raman microscopy as a reliable and non‐invasive tool for novel in‐depth structural investigations in biocrystallography. Copyright © 2009 John Wiley & Sons, Ltd.     

Detection of glutamate and glutamine (Glx) by turbo spectroscopic imaging

Turbo spectroscopic imaging (TSI) is a spin echo spectroscopic imaging technique in which two or more echoes are acquired per excitation to reduce the acquisition time. The application of TSI has primarily been limited to the detection of uncoupled spins because the signal from coupled spins is modulated as a function of echo time. In this work we demonstrate how the TSI sequence can be modified to observe spins like the C₂ protons of Glx (≈3.75 ppm) which are involved solely in weak-coupling interactions. The technique exploits the chemical shift displacement effect by employing TSI refocusing pulses that have bandwidths which are less than the chemical shift difference between the target spins and the spins to which they are weakly coupled. The modified TSI sequence rewinds the J-evolution of the target protons in the slice of interest independently of the echo time or echo spacing, thereby removing any signal variation between successive echoes (apart from T₂ relaxation effects). In this study we tailored the narrow-bandwidth TSI sequence for observation of the C₂ Glx protons. The echo time was experimentally optimized to minimize signal contamination from myo-inositol, and the efficacy of the method was verified on phantom solutions of Glx and on brain in vivo.     

Investigating the high-energy QCD approaches for prompt-photon production at the LHC

We investigate the rapidity and transverse-momentum distributions of the prompt photon production at the CERN LHC energies considering the current perturbative QCD approaches for this scattering process. Namely, we compare the predictions from the usual NLO pQCD calculations to the color-dipole formalism, using distinct dipole cross sections. Special attention is paid to parton-saturation models at high energies, which are expected to be important at the forward rapidities in pp collisions (  TeV) at the LHC.     

Combining direct & indirect kaon CP violation to constrain the warped KK scale

The Randall–Sundrum (RS) framework has a built in protection against flavour violation, but still generically suffers from little CP problems. The most stringent bound on flavour violation is due to ?K${\mathrm{?}}_K$, which is inversely proportional to the fundamental Yukawa scale. Hence the RS ?K${\mathrm{?}}_K$ problem can be ameliorated by effectively increasing the Yukawa scale with a bulk Higgs, as was recently observed in arXiv:0810.1016. We point out that incorporating the constraint from ?^′/?K${\mathrm{?}}^{\prime }/{\mathrm{?}}_K$, which is proportional to the Yukawa scale, raises the lower bound on the KK scale compared to previous analyses. The bound is conservatively estimated to be 5.5 TeV, choosing the most favorable Higgs profile, and 7.5 TeV for the profile which roughly reproduces the two site case. Relaxing this bound might require some form of RS flavour alignment. As a by-product of our analysis, we also provide the leading order flavour structure of the theory with a bulk Higgs.     

Optimal egress time calculation and path generation for large evacuation networks

Finding the optimal clearance time and deciding the path and schedule of evacuation for large networks have traditionally been computationally intensive. In this paper, we propose a new method for finding the solution for this dynamic network flow problem with considerably lower computation time. Using a three phase solution method, we provide solutions for required clearance time for complete evacuation, minimum number of evacuation paths required for evacuation in least possible time and the starting schedules on those paths. First, a lower bound on the clearance time is calculated using minimum cost dynamic network flow model on a modified network graph representing the transportation network. Next, a solution pool of feasible paths between all O-D pairs is generated. Using the input from the first two models, a flow assignment model is developed to select the best paths from the pool and assign flow and decide schedule for evacuation with lowest clearance time possible. All the proposed models are mixed integer linear programing models and formulation is done for System Optimum (SO) scenario where the emphasis is on complete network evacuation in minimum possible clearance time without any preset priority. We demonstrate that the model can handle large size networks with low computation time. A numerical example illustrates the applicability and effectiveness of the proposed approach for evacuation.     

Facile separation of chiral 1,3-dihydrobenzo[c]furan derivatives using a -xylose moiety as a protecting group

1,2-O-Isopropylidene-α- -xylofuranose has been used to protect one aldehyde group of o-phthalaldehyde. This chiral protecting group acts as a resolving agent and this leads to separable diastereoisomers when a new stereogenic centre is created by the conversion of the second aldehyde group to a benzyloxyhydroxyethyl chain. These separated diastereoisomers were cyclised to 1,3-dihydrobenzo[c]furans with retention of chiral integrity at the C3 site thus allowing further elaboration to enantiomerically pure nucleoside analogues.     

Cathodically deposited polypyridine films: A novel electroactive polyconjugated polymer

Poly-2,5- and poly-2,6-pyridine coatings have been produced on glassy-carbon electrodes by nickelcatalysed reduction of the corresponding dibromopyridine in acetonitrile. Poly-2,5-pyridine films display two reversible cathodic cycles, one of which is due to nickel ions coordinated to pyridine moieties and the other to the polymeric backbone. Both reductions lead to the polymer changing from the insulating to the conductive state. Conversely, Poly-2,6-pyridine films are not reversibly electroactive and the differences are discussed in terms of conjugation along the polymeric chain.