Key mechanistic features of enantioselective C-H bond activation reactions catalyzed by [(chiral mono-N-protected amino acid)-Pd(II)] complexes

Monoprotected chiral amino acids have recently been established as a class of ligand scaffolds for effecting Pd-catalyzed enantioselective C-H bond activation reactions. However, to elucidate the mechanistic details and controlling factors of these reactions, more comprehensive studies are needed. In this work we report computational investigations into the key mechanistic features of enantioselective C-H bond activation reactions catalyzed by a [chiral (mono-N-protected amino acid)-Pd(II)] complex. Structural analysis points to a C-H insertion intermediate in which the nitrogen atom of the ligand is bound as a neutral σ-donor. The formation of this C-H insertion intermediate could, in principle, proceed via a "direct C-H cleavage" or via "initial N-H bond cleavage followed by C-H cleavage". The computational studies presented herein show that the pathway initiated by N-H bond cleavage is more kinetically favorable. It is shown that the first step of the reaction is the N-H bond cleavage by the coordinated acetate group (OAc). In the next stage, the weakly coordinated OAc(-) (the second acetate group) activates the ortho-C-H bond of the substrate and transfers the H-atom from the C-atom to the bound N-atom of the ligand. As a result, a new Pd-C bond is formed and the carbamate is converted from X-type to L-type ligand. The absolute configuration of the products that are predicted on the basis of the calculated energies of the transition states matches the experimental data. The calculated enantioselectivity is also comparable with the experimental result. On the basis of these data, the origin of the enantioselectivity can be largely attributed to steric repulsions in the transition states.     

Hints on integrability in the Wilsonian/holographic renormalization group

The Polchinski equations for the Wilsonian renormalization group in the D-dimensional matrix scalar field theory can be written at large N in a Hamiltonian form. The Hamiltonian defines evolution along one extra holographic dimension (energy scale) and can be found exactly for the subsector of Trϕ ⁿ (for all n) operators. We show that at low energies independently of the dimensionality D the Hamiltonian system in question reduces to the integrable effective theory. The obtained Hamiltonian system describes large wavelength KdV type (Burger-Hopf) equation with an external potential and is related to the effective theory obtained by Das and Jevicki for the matrix quantum mechanics.     

Broad‐Spectrum Liquid‐ and Gas‐Phase Decontamination of Chemical Warfare Agents by One‐Dimensional Heteropolyniobates

A wide range of chemical warfare agents and their simulants are catalytically decontaminated by a new one‐dimensional polymeric polyniobate (P‐PONb), K₁₂[Ti₂O₂][GeNb₁₂O₄₀]?19 H₂O ( KGeNb ) under mild conditions and in the dark. Uniquely, KGeNb facilitates hydrolysis of nerve agents Sarin (GB) and Soman (GD) (and their less reactive simulants, dimethyl methylphosphonate (DMMP)) as well as mustard (HD) in both liquid and gas phases at ambient temperature and in the absence of neutralizing bases or illumination. Three lines of evidence establish that KGeNb removes DMMP, and thus likely GB/GD, by general base catalysis: a) the k(H₂O)/k(D₂O) solvent isotope effect is 1.4; b) the rate law (hydrolysis at the same pH depends on the amount of P‐PONb present); and c) hydroxide is far less active against the above simulants at the same pH than the P‐PONbs themselves, a critical control experiment.     

Hybrid nanocomposites based on guanidine methacrylate monomer and polymer and layered aluminosilicates: Synthesis, structure, and properties

Hybrid nanostructures (organomodified montmorillonite) have been synthesized on the basis of activated Na⁺-montmorillonite and new water-soluble ionogenic Na⁺-montmorillonite monomers containing quaternary ammonium guanidine cations. The structure and properties of poly(guanidine methacrylate) nanocomposites have been studied. It has been shown that these compounds efficiently adsorb heavy metals and exhibit a prolonged biocide effect due to the presence of quaternary ammonium guanidine cations.     

Gel based on microcrystalline cellulose and azidin

The structure of a gel based on microcrystalline cellulose (MCC) and the antiprotozoic preparation azidin is studied. Intense ultrasonic irradiation produces a physicochemical reaction in the MCC:azidin system that lengthens the effective lifetime of the drug. Institute of Chemistry and Physics of Polymers, Academy of Sciences of the Republic of Uzbekistan, Mirzo Ulugbek Tashkent State University, Tashkent, fax (3712) 44 26 61; 46 08 97. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 577–580, September–October, 1999.