Four Dimensional Graphene

Mimicking pristine 2D graphene, we revisit the BBTW model for 4D lattice QCD given in ref.[5] by using the hidden SU(5) symmetry of the 4D hyperdiamond lattice H_4. We first study the link between the H_4 and SU(5); then we refine the BBTW 4D lattice action by using the weight vectors \lambda_1, \lambda_2, \lambda_3, \lambda_4, \lambda_5 of the 5-dimensional representation of SU(5) satisfying {\Sigma}_i\lambda_i=0. After that we study explicitly the solutions of the zeros of the Dirac operator D in terms of the SU(5) simple roots \alpha_1, \alpha_2, \alpha_3, \alpha_4 generating H_4; and its fundamental weights \omega_1, \omega_2, \omega_3, \omega_4 which generate the reciprocal lattice H_4^\ast. It is shown, amongst others, that these zeros live at the sites of H_4^\ast; and the continuous limit D is given by ((id\surd5)/2) \gamma^\muk_\mu with d, \gamma^\mu and k_\mu standing respectively for the lattice parameter of H_4, the usual 4 Dirac matrices and the 4D wave vector. Other features such as differences with BBTW model as well as the link between the Dirac operator following from our construction and the one suggested by Creutz using quaternions, are also given. Keywords: Graphene, Lattice QCD, 4D hyperdiamond, BBTW model, SU(5) Symmetry.Comment: LaTex, 26 pages, 1 figure, To appear in Phys Rev

Graphene and Cousin Systems

Graphene is a new material that exhibits remarkable properties from both fundamental and applied issues. This is a 2D matter system whose physical and mechanical features have been approached by using tight binding model, first principle calculations based on DFT and membrane theory. Graphene as a carbon molecule has also hidden symmetries that motivated extensions in various dimensions such as chain-type configurations, that are frequently observed as the graphene bridge narrowed down to a few- or single-atom width, graphene multi-layers thought of as electric capacitors, doped graphene to gain more physical properties as well as cousin systems such as diamond and hyperdiamond. In this work, we use tight binding model ideas and field theory method as well as the hidden symmetries of the underlying crystals to study physical aspects of 2D graphene and its homologues. We also study the relation between 2D graphene with the Bori\c{c}i-Creutz fermions considered recently in literature as an adequate model to perform numerical simulations in 4D lattice QCD where the two Dirac zeros are interpreted in terms of the light quarks up and down.Comment: 34 pages, 14 figure

Pd embedded in chitosan microspheres as tunable soft-materials for Sonogashira cross-coupling in water-ethanol mixture

Easy shaping of chitosan (CS) as porous self-standing nanofibrillar microspheres allows their use as a palladium carrier. Amino-groups on CS enable the modulation of Pd coordination, giving rise to three different support-catalyst interactions: weakly-coordinated Pd-CS in native CS, incarcerated Pd-CS-Glu in cross-linked CS and strongly-ligated Pd-CS-SH, obtained by the introduction of thiol arms in CS. These catalysts efficiently promote Sonogashira cross-coupling of a large library of functional substrates under mild and sustainable conditions (water-ethanol as solvent at 65 degrees C) and stand as recyclable, metal-scavenging catalytic systems.Frindy, S.; Primo Arnau, AM.; Lahcini, M.; Bousmina, M.; García Gómez, H.; El Kadib, A. (2015). Pd embedded in chitosan microspheres as tunable soft-materials for Sonogashira cross-coupling in water-ethanol mixture. Green Chemistry. 17(3):1893-1898. doi:10.1039/c4gc02175dS18931898173Johansson Seechurn, C. C. C., Kitching, M. O., Colacot, T. J., & Snieckus, V. (2012). Palladium-Catalyzed Cross-Coupling: A Historical Contextual Perspective to the 2010 Nobel Prize. Angewandte Chemie International Edition, 51(21), 5062-5085. doi:10.1002/anie.201107017Sehnal, P., Taylor, R. J. K., & Fairlamb, I. J. S. (2010). Emergence of Palladium(IV) Chemistry in Synthesis and Catalysis. Chemical Reviews, 110(2), 824-889. doi:10.1021/cr9003242Torborg, C., & Beller, M. (2009). Recent Applications of Palladium-Catalyzed Coupling Reactions in the Pharmaceutical, Agrochemical, and Fine Chemical Industries. Advanced Synthesis & Catalysis, 351(18), 3027-3043. doi:10.1002/adsc.200900587Hartwig, J. F. (2008). Carbon–heteroatom bond formation catalysed by organometallic complexes. Nature, 455(7211), 314-322. doi:10.1038/nature07369Loska, R., Volla, C. M. R., & Vogel, P. (2008). Iron-Catalyzed Mizoroki-Heck Cross-Coupling Reaction with Styrenes. Advanced Synthesis & Catalysis, 350(18), 2859-2864. doi:10.1002/adsc.200800662Sun, C.-L., Li, B.-J., & Shi, Z.-J. (2011). Direct C−H Transformation via Iron Catalysis. Chemical Reviews, 111(3), 1293-1314. doi:10.1021/cr100198wCzaplik, W. M., Mayer, M., Cvengroš, J., & von Wangelin, A. J. (2009). Coming of Age: Sustainable Iron-Catalyzed Cross-Coupling Reactions. ChemSusChem, 2(5), 396-417. doi:10.1002/cssc.200900055Fürstner, A., Leitner, A., Méndez, M., & Krause, H. (2002). Iron-Catalyzed Cross-Coupling Reactions. Journal of the American Chemical Society, 124(46), 13856-13863. doi:10.1021/ja027190tBarluenga, J., & Valdés, C. (2011). Tosylhydrazones: New Uses for Classic Reagents in Palladium-Catalyzed Cross-Coupling and Metal-Free Reactions. Angewandte Chemie International Edition, 50(33), 7486-7500. doi:10.1002/anie.201007961Yin, & Liebscher, J. (2007). Carbon−Carbon Coupling Reactions Catalyzed by Heterogeneous Palladium Catalysts. Chemical Reviews, 107(1), 133-173. doi:10.1021/cr0505674Phan, N. T. S., Van Der Sluys, M., & Jones, C. W. (2006). On the Nature of the Active Species in Palladium Catalyzed Mizoroki–Heck and Suzuki–Miyaura Couplings – Homogeneous or Heterogeneous Catalysis, A Critical Review. Advanced Synthesis & Catalysis, 348(6), 609-679. doi:10.1002/adsc.200505473Weck, M., & Jones, C. W. (2007). Mizoroki−Heck Coupling Using Immobilized Molecular Precatalysts:  Leaching Active Species from Pd Pincers, Entrapped Pd Salts, and Pd NHC Complexes. Inorganic Chemistry, 46(6), 1865-1875. doi:10.1021/ic061898hWEBB, J., MACQUARRIE, S., MCELENEY, K., & CRUDDEN, C. (2007). Mesoporous silica-supported Pd catalysts: An investigation into structure, activity, leaching and heterogeneity. Journal of Catalysis, 252(1), 97-109. doi:10.1016/j.jcat.2007.09.007Garrett, C. E., & Prasad, K. (2004). The Art of Meeting Palladium Specifications in Active Pharmaceutical Ingredients Produced by Pd-Catalyzed Reactions. Advanced Synthesis & Catalysis, 346(8), 889-900. doi:10.1002/adsc.200404071Glasspoole, B. W., Webb, J. D., & Crudden, C. M. (2009). Catalysis with chemically modified mesoporous silicas: Stability of the mesostructure under Suzuki–Miyaura reaction conditions. Journal of Catalysis, 265(2), 148-154. doi:10.1016/j.jcat.2009.04.020Modak, A., Mondal, J., & Bhaumik, A. (2012). Pd-grafted periodic mesoporous organosilica: an efficient heterogeneous catalyst for Hiyama and Sonogashira couplings, and cyanation reactions. Green Chemistry, 14(10), 2840. doi:10.1039/c2gc35820dMacquarrie, D. J., & Hardy, J. J. E. (2005). Applications of Functionalized Chitosan in Catalysis†. Industrial & Engineering Chemistry Research, 44(23), 8499-8520. doi:10.1021/ie050007vA. El Kadib , ChemSusChem20158217244El Kadib, A., Primo, A., Molvinger, K., Bousmina, M., & Brunel, D. (2011). Nanosized Vanadium, Tungsten and Molybdenum Oxide Clusters Grown in Porous Chitosan Microspheres as Promising Hybrid Materials for Selective Alcohol Oxidation. Chemistry – A European Journal, 17(28), 7940-7946. doi:10.1002/chem.201003740El Kadib, A., & Bousmina, M. (2012). Chitosan Bio-Based Organic-Inorganic Hybrid Aerogel Microspheres. Chemistry - A European Journal, 18(27), 8264-8277. doi:10.1002/chem.201104006Kadib, A. E., Bousmina, M., & Brunel, D. (2014). Recent Progress in Chitosan Bio-Based Soft Nanomaterials. Journal of Nanoscience and Nanotechnology, 14(1), 308-331. doi:10.1166/jnn.2014.9012Primo, A., & Quignard, F. (2010). Chitosan as efficient porous support for dispersion of highly active gold nanoparticles: design of hybrid catalyst for carbon–carbon bond formation. Chemical Communications, 46(30), 5593. doi:10.1039/c0cc01137aValentin, R., Molvinger, K., Quignard, F., & Brunel, D. (2003). Supercritical CO2 dried chitosan: an efficient intrinsic heterogeneous catalyst in fine chemistry. New Journal of Chemistry, 27(12), 1690. doi:10.1039/b310109fPrimo, A., Atienzar, P., Sanchez, E., Delgado, J. M., & García, H. (2012). From biomass wastes to large-area, high-quality, N-doped graphene: catalyst-free carbonization of chitosan coatings on arbitrary substrates. Chemical Communications, 48(74), 9254. doi:10.1039/c2cc34978gNgah, W. S. W., Ab Ghani, S., & Kamari, A. (2005). Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads. Bioresource Technology, 96(4), 443-450. doi:10.1016/j.biortech.2004.05.022El Hankari, S., El Kadib, A., Finiels, A., Bouhaouss, A., Moreau, J. J. E., Crudden, C. M., … Hesemann, P. (2011). SBA-15-Type Organosilica with 4-Mercapto-N,N-bis-(3-Si-propyl)butanamide for Palladium Scavenging and Cross-Coupling Catalysis. Chemistry - A European Journal, 17(32), 8984-8994. doi:10.1002/chem.201002190Crudden, C. M., Sateesh, M., & Lewis, R. (2005). Mercaptopropyl-Modified Mesoporous Silica:  A Remarkable Support for the Preparation of a Reusable, Heterogeneous Palladium Catalyst for Coupling Reactions. Journal of the American Chemical Society, 127(28), 10045-10050. doi:10.1021/ja0430954McEleney, K., Crudden, C. M., & Horton, J. H. (2009). X-ray Photoelectron Spectroscopy and the Auger Parameter As Tools for Characterization of Silica-Supported Pd Catalysts for the Suzuki−Miyaura Reaction. The Journal of Physical Chemistry C, 113(5), 1901-1907. doi:10.1021/jp808837kRoy, A. S., Mondal, J., Banerjee, B., Mondal, P., Bhaumik, A., & Islam, S. M. (2014). Pd-grafted porous metal–organic framework material as an efficient and reusable heterogeneous catalyst for C–C coupling reactions in water. Applied Catalysis A: General, 469, 320-327. doi:10.1016/j.apcata.2013.10.017Kadib, A. E., Molvinger, K., Cacciaguerra, T., Bousmina, M., & Brunel, D. (2011). Chitosan templated synthesis of porous metal oxide microspheres with filamentary nanostructures. Microporous and Mesoporous Materials, 142(1), 301-307. doi:10.1016/j.micromeso.2010.12.012Kühbeck, D., Saidulu, G., Reddy, K. R., & Díaz, D. D. (2012). Critical assessment of the efficiency of chitosan biohydrogel beads as recyclable and heterogeneous organocatalyst for C–C bond formation. Green Chem., 14(2), 378-392. doi:10.1039/c1gc15925aKhalafi-Nezhad, A., & Mohammadi, S. (2014). Chitosan supported ionic liquid: a recyclable wet and dry catalyst for the direct conversion of aldehydes into nitriles and amides under mild conditions. RSC Advances, 4(27), 13782. doi:10.1039/c3ra43440kEl Kadib, A., McEleney, K., Seki, T., Wood, T. K., & Crudden, C. M. (2011). Cross-Coupling in the Preparation of Pharmaceutically Relevant Substrates using Palladium Supported on Functionalized Mesoporous Silicas. ChemCatChem, 3(8), 1281-1285. doi:10.1002/cctc.20110002

Insightful understanding of the role of clay topology on the stability of biomimetic hybrid chitosan-clay thin films and CO2-dried porous aerogel microspheres

[EN] Three natural clay-based microstructures, namely layered montmorillonite (MMT), nanotubular halloysite (HNT) and micro-fibrillar sepiolite (SP) were used for the synthesis of hybrid chitosan-clay thin films and porous aerogel microspheres. At a first glance, a decrease in the viscosity of the three gel forming solutions was noticed as a result of breaking the mutual polymeric chains interaction by the clay microstructure. Upon casting, chitosan-clay films displayed enhanced hydrophilicity in the order CS < CS-MMT < CS-HNT < CS-SP. Irrespective to the clay microstructure, an improvement in the mechanical properties of the chitosan-clay films has been substantiated with CS-SP reaching the highest value at 5% clay loading. While clay addition provides a way to resist the shrinkage occurring for native chitosan, the enhanced hydrophilicity associated to the water content affects the efficacy of the CO2 super-critical drying as the most hydrophilic CS-SP microspheres face the highest shrinkage, resulting in a lowest specific surface area compared to CS-HNT and CS-MMT. Chitosan-clay exhibits enhanced thermal properties with the degradation delayed in the order CS < CS-MMT < CS-HNT < CS-SP. Under acidic environment, a longevity has been substantiated for chitosan-clay compared to native chitosan, evidencing the beneficial protective effect of the clay particulates for the biopolymer. However, under hydrothermal treatment, the presence of clay was found to be detrimental to the material stability as a significant shrinkage occurs in hybrid CS-clay microspheres, which is attributed again to their increased hydrophilicity compared to the native polymeric microspheres. In this framework, a peculiar behavior was observed for CS-MMT, with the microspheres standing both against contraction during CO2 gel drying and under hydrothermal conditions. The knowledge gained from this rational design will constitute a guideline toward the preparation of ultra-stable, practically-optimized food-packaging films and commercially scalable porous bio-based adsorbents.S. F thanks MAScIR foundation, CNRST and Erasmus Mundus-Maghreb & Egypt- EMMAG.Frindy, S.; Primo Arnau, AM.; Qaiss, AEK.; Bouhfid, R.; Lahcini, M.; García Gómez, H.; Bousmina, M.... (2016). Insightful understanding of the role of clay topology on the stability of biomimetic hybrid chitosan-clay thin films and CO2-dried porous aerogel microspheres. Carbohydrate Polymers. 146:353-361. doi:10.1016/j.cabpel.2016.03.022S35336114

Magnetic Skyrmions: Theory and Applications

Magnetic skyrmions have been subject of growing interest in recent years for their very promising applications in spintronics, quantum computation and future low power information technology devices. In this book chapter, we use the field theory method and coherent spin state ideas to investigate the properties of magnetic solitons in spacetime while focussing on 2D and 3D skyrmions. We also study the case of a rigid skyrmion dissolved in a magnetic background induced by the spin-tronics; and derive the effective rigid skyrmion equation of motion. We examine as well the interaction between electrons and skyrmions; and comment on the modified Landau-Lifshitz-Gilbert equation. Other issues, including emergent electrodynamics and hot applications for next-generation high-density efficient information encoding, are also discussed

Chemically specifi C multiscale modeling of clay-polymer nanocomposites reveals intercalation dynamics, tactoid self-assembly and emergent materials properties

A quantitative description is presented of the dynamical process of polymer intercalation into clay tactoids and the ensuing aggregation of polymerentangled tactoids into larger structures, obtaining various characteristics of these nanocomposites, including clay-layer spacings, out-of-plane clay-sheet bending energies, X-ray diffractograms, and materials properties. This model of clay-polymer interactions is based on a three-level approach, which uses quantum mechanical and atomistic descriptions to derive a coarse-grained yet chemically specifi c representation that can resolve processes on hitherto inaccessible length and time scales. The approach is applied to study collections of clay mineral tactoids interacting with two synthetic polymers, poly(ethylene glycol) and poly(vinyl alcohol). The controlled behavior of layered materials in a polymer matrix is centrally important for many engineering and manufacturing applications. This approach opens up a route to computing the properties of complex soft materials based on knowledge of their chemical composition, molecular structure, and processing conditions.This work was funded in part by the EU FP7 MAPPER project (grant number RI-261507) and the Qatar National Research Fund (grant number 09–260–1–048). Supercomputing time was provided by PRACE on JUGENE (project PRA044), the Hartree Centre (Daresbury Laboratory) on BlueJoule and BlueWonder via the CGCLAY project, and on HECToR and ARCHER, the UK national supercomputing facility at the University of Edinburgh, via EPSRC through grants EP/F00521/1, EP/E045111/1, EP/I017763/1 and the UK Consortium on Mesoscopic Engineering Sciences (EP/L00030X/1). The authors are grateful to Professor Julian Evans for stimulating discussions during the course of this project. Data-storage and management services were provided by EUDAT (grant number 283304)