Synthesis, Conformational Studies and Enantioselective Homogeneous Catalytic Hydrogenation with CRC-PHOS, and Some Congeners

The lactone of (1S,3R)-1-hydroxy-1-diphenylphosphino metyl- 2,2,3-trimethylcyclopentan-3-carboxylic acid (8, CRC-PHOS), and (1R,3R)-bis(diphenylphosphinoxymethyl)-2,2,3-trimethylcyclopentane (16), were prepared starting from ( + )-camphanic and (-)- isocamphoric acid, respectively. Their complex salts [Rh(norbornadiene) lactone of (1S,3R)-1-hydroxy-1-diphenylphosphinomethyl- 2,2,3-trimethylcyclopentan-3-carboxylic acid] perchlorate (27), and [Rh(norbornadiene (1R,3R)-1,2,2-trimethyl-1,3-bis ( diphenylphosphinoxymethyl) cyclopentane)] perchlorate (28) were isolated and their catalytic and enantioselective ability tested on some model prochiral carboxylic acids. The asymetric bias did not exceed 35°/o e. e. in either case. Attepmts at preparation of the diphosphine congener of 16, i.e. 21, as well as isolation of the phosphinite congener of 8, i. e. 22, failed. NMR LIS study of the conformation in solution of 8, and model compounds 6 and 9 revealed that 6 and 8 possess in their most stable conformations a dihedral angle 1P of 165°, (Figure 4.) while for 9 two stable conformations with 1P 200° and 350° are found. These results indicate that bidentate binding of metal to heteroatom X (0, P) in the side chain, and to the tetrahedral oxygen within lactone group is scarcely possible

A Chiral Phosphine (CRC-PHOS) Derived from ( + )-Champhanic Acid. A New Ligand for Homogeneous Asymmetric Hydrogenation

The lactone of 1S,3S-1-hydroxy-1-diphenylphosphinomethyl- 2,2,3-tri-methyl-cyclopentan-3-carboxylic acid (4, CRC-PHOS) was prepared from ( + )-camphanic acid methylester 1, and its complex salt [Rh(CRC-PHOS)2NBD] · CI04 • THF (5) was isolated. The latter exhibited rather a high rate, but low enantioselectivity in the first attempt at asymmetric hydrogenation

Synthesis, Conformational Studies and Enantioselective Homogeneous Catalytic Hydrogenation with CRC-PHOS, and Some Congeners

The lactone of (1S,3R)-1-hydroxy-1-diphenylphosphino metyl- 2,2,3-trimethylcyclopentan-3-carboxylic acid (8, CRC-PHOS), and (1R,3R)-bis(diphenylphosphinoxymethyl)-2,2,3-trimethylcyclopentane (16), were prepared starting from ( + )-camphanic and (-)- isocamphoric acid, respectively. Their complex salts [Rh(norbornadiene) lactone of (1S,3R)-1-hydroxy-1-diphenylphosphinomethyl- 2,2,3-trimethylcyclopentan-3-carboxylic acid] perchlorate (27), and [Rh(norbornadiene (1R,3R)-1,2,2-trimethyl-1,3-bis ( diphenylphosphinoxymethyl) cyclopentane)] perchlorate (28) were isolated and their catalytic and enantioselective ability tested on some model prochiral carboxylic acids. The asymetric bias did not exceed 35°/o e. e. in either case. Attepmts at preparation of the diphosphine congener of 16, i.e. 21, as well as isolation of the phosphinite congener of 8, i. e. 22, failed. NMR LIS study of the conformation in solution of 8, and model compounds 6 and 9 revealed that 6 and 8 possess in their most stable conformations a dihedral angle 1P of 165°, (Figure 4.) while for 9 two stable conformations with 1P 200° and 350° are found. These results indicate that bidentate binding of metal to heteroatom X (0, P) in the side chain, and to the tetrahedral oxygen within lactone group is scarcely possible

Optical conductivity of the Hubbard model at finite temperature

The optical conductivity, $\sigma(\omega)$, of the two dimensional one-band Hubbard model is calculated at finite temperature using exact diagonalization techniques on finite clusters. The in-plane d.c. resistivity, $\rho_{ab}$, is also evaluated. We find that at large U/t and temperature T, $\rho_{ab}$ is approximately linear with temperature, in reasonable agreement with experiments on high-T$_c$ superconductors. Moreover, we note that $\sigma(\omega)$ displays charge excitations, a mid-infrared (MIR) band and a Drude peak, also as observed experimentally. The combination of the Drude peak and the MIR oscillator strengths leads to a conductivity that decays slower than $1/\omega^2$ at energies smaller than the insulator gap near half-filling.Comment: 12 pages, 3 figures appended, Revtex version 2.0, preprin

Electron momentum distribution in underdoped cuprates

We investigate the electron momentum distribution function (EMD) in a weakly doped two-dimensional quantum antiferromagnet (AFM) as described by the t-J model. Our analytical results for a single hole in an AFM based on the self-consistent Born approximation (SCBA) indicate an anomalous momentum dependence of EMD showing 'hole pockets' coexisting with a signature of an emerging large Fermi surface. The position of the incipient Fermi surface and the structure of the EMD is determined by the momentum of the ground state. Our analysis shows that this result remains robust in the presence of next-nearest neighbor hopping terms in the model. Exact diagonalization results for small clusters are with the SCBA reproduced quantitatively.Comment: 5 pages, submitted to PR

Hall effect of charge carriers in a correlated system

The dynamical Hall response in a correlated electronic system is analysed within the linear response theory for tight binding models. At $T=0$ the d.c. Hall constant for a single quasiparticle is expressed explicitly via the charge stiffness, and a semiclassical result is recovered. As expected a hole-like response is found for the mobile hole introduced into a quantum antiferromagnet, as represented by the $t-J$ model.Comment: 4 pages, RevTeX, no figure

Novel analgesic/anti-inflammatory agents: 1,5-diarylpyrrole nitrooxyalkyl ethers and related compounds as cyclooxygenase-2 inhibiting nitric oxide donors

A series of 3-substituted 1,5-diarylpyrroles bearing a nitrooxyalkyl side chain linked to different spacers were designed. New classes of pyrrole-derived nitrooxyalkyl inverse esters, carbonates, and ethers (7-10) as COX-2 selective inhibitors and NO donors were synthesized and are herein reported. By taking into account the metabolic conversion of nitrooxyalkyl ethers (9, 10) into corresponding alcohols, derivatives 17 and 18 were also studied. Nitrooxy derivatives showed NO-dependent vasorelaxing properties, while most of the compounds proved to be very potent and selective COX-2 inhibitors in in vitro experimental models. Further in vivo studies on compounds 9a,c and 17a highlighted good anti-inflammatory and antinociceptive activities. Compound 9c was able to inhibit glycosaminoglycan (GAG) release induced by interleukin-1β (IL-1β), showing cartilage protective properties. Finally, molecular modeling and (1)H- and (13)C-NMR studies performed on compounds 6c,d, 9c, and 10b allowed the right conformation of nitrooxyalkyl ester and ether side chain of these molecules within the COX-2 active site to be assessed

Properties of the Liquid-Vapor Interface of Acetone-Water Mixtures. A Computer Simulation and ITIM Analysis Study

Molecular dynamics simulations of the liquid-vapor interface of acetone-water mixtures of different compositions, covering the entire composition range have been performed on the canonical (N, V, T) ensemble at 298 K, using a model combination that excellently describes the mixing properties of these compounds. The properties of the intrinsic liquid surfaces have been analyzed in terms of the Identification of the Truly Interfacial Molecules (ITIM) method. Thus, the composition, width, roughness, and separation of the subsurface molecular layers, as well as self-association, orientation, and dynamics of exchange with the bulk phase of the surface molecules have been analyzed in detail. Our results show that acetone molecules are strongly adsorbed at the liquid surface, and this adsorption extends to several molecular layers. Like molecules in the surface layer are found to form relatively large lateral self-associates. The effect of the vicinity of the vapor phase on a number of properties of the liquid phase vanishes beyond the first molecular layer, with the second subsurface layer already part of the bulk liquid phase in these respects. The orientational preferences of the surface molecules are governed primarily by the dipole-dipole interaction of the neighboring acetone molecules, and hydrogen bonding interaction of the neighboring acetone-water pairs. (Figure Presented). © 2015 American Chemical Society

The 3-Band Hubbard-Model versus the 1-Band Model for the high-Tc Cuprates: Pairing Dynamics, Superconductivity and the Ground-State Phase Diagram

One central challenge in high-$T_c$ superconductivity (SC) is to derive a detailed understanding for the specific role of the $Cu$-$d_{x^2-y^2}$ and $O$-$p_{x,y}$ orbital degrees of freedom. In most theoretical studies an effective one-band Hubbard (1BH) or t-J model has been used. Here, the physics is that of doping into a Mott-insulator, whereas the actual high-$T_c$ cuprates are doped charge-transfer insulators. To shed light on the related question, where the material-dependent physics enters, we compare the competing magnetic and superconducting phases in the ground state, the single- and two-particle excitations and, in particular, the pairing interaction and its dynamics in the three-band Hubbard (3BH) and 1BH-models. Using a cluster embedding scheme, i.e. the variational cluster approach (VCA), we find which frequencies are relevant for pairing in the two models as a function of interaction strength and doping: in the 3BH-models the interaction in the low- to optimal-doping regime is dominated by retarded pairing due to low-energy spin fluctuations with surprisingly little influence of inter-band (p-d charge) fluctuations. On the other hand, in the 1BH-model, in addition a part comes from "high-energy" excited states (Hubbard band), which may be identified with a non-retarded contribution. We find these differences between a charge-transfer and a Mott insulator to be renormalized away for the ground-state phase diagram of the 3BH- and 1BH-models, which are in close overall agreement, i.e. are "universal". On the other hand, we expect the differences - and thus, the material dependence to show up in the "non-universal" finite-T phase diagram ($T_c$-values).Comment: 17 pages, 9 figure

Intercomparison Exercise for Heavy Metals in PM10

The Joint Research Centre (JRC) has carried out an Intercomparison Exercise (IE) for the determination of heavy metals in particulate matter (PM10). The IE focussed on Lead (Pb), Arsenic (As), Nickel (Ni) and Cadmium (Cd), the heavy metals regulated by the 1st and 4th Daughter Directives for Air Pollution. Copper (Cu), Chromium (Cr) and Zinc (Zn), the elements included in the EMEP programme together with Aluminium (Al), Cobalt (Co), Iron (Fe), Manganese (Mn) and Vanadium (V) were also tested. Fourteen Laboratories, generally members of the Network of Air Quality Reference Laboratories (AQUILA), participated in the IE. The participants mainly used microwave digestion with nitric acid and hydrogen peroxide and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) or Graphite Furnace Atomic Absorption Spectrometry (GF-AAS) for analysis as recommended in the reference method (EN 14902). However, a few participants used other methods: Energy Dispersive X-ray Fluorescence (EDXRF), Atomic Emission Spectrometry (ICP-AES) and Voltammetry for analysis and vaporisation on hot plate before microwave digestion, Soxhlet extraction, high pressure or cold Hydrogen Fluoride methods for digestion. Each participant received 5 samples to be analysed: a liquid sample prepared by dilution of a Certified Reference Material (CRM), a solution of a dust CRM sample digested by the JRC13F, a sub-sample of a dust CRM that each participating laboratory had to digest and analyse, a solution prepared by JRC after digestion of an exposed filter and a pair of filters (one blank filter and one exposed filter) to be digested and analysed by each participant. For 89 % of all types of samples, the DQOs of the 1st and 4th European Directives (uncertainty of 25 % for Pb and 40 % for As, Cd and Ni) were met. All together, this is a very good score. The best results were obtained for the liquid CRM, dust CRM digested by JRC, dust CRM and filter digested by JRC with 92, 90, 96 and 93 % of DQOs being met, respectively. It was found that the DQOs were not met if the difference of acidity between test samples and participant calibration standards was high. Conversely, only 76 % of DQOs were met for the filter to be digested by each participant with (about 85 % for Cd and Ni, 73/64 % for Pb and As, the most difficult element to determine). The worst results were associated with special events: explosion in microwave oven during digestion for two participants, a wrong dilution factor used by one participant and a huge contamination in the blank filter for another participant. Among the two explosions, one of them was probably the effect of a lack of temperature control in the digestion vessel. For the other explosion, the microwave digestion and the digestion program advised by EN 14902 is to be questioned. Moreover, satisfactory results were obtained using Soxhlet extraction, high pressure method and cold Hydrogen Fluoride digestion methods which are not presented in EN 14902. The DQOs of As and Cd could not be met with EDXRF whose limit of detection was too high for these two elements and for Cd using Voltammetry which suffered a strong interference for this element. Regarding the methods of analysis, apart the points mentioned just before about EDXRF and Voltammetry, good results were observed using ICP-OES for Cd, Ni and Pb. A few discrepancies were also registered for GF-AAS and ICP-MS but they were created by the special events or acidity problem mentioned before. This shows that even though GF-AAS and ICP-MS are found suitable, the implementation by each participant may be responsible for important mistakes.JRC.H.4-Transport and air qualit