Base Hydrolysis of Pentaaminecobalt (III) Complexes: The [CoX(dien) (dapo)]n+ system. Part 3. The internal conjugate base mechanism

Azide anation and racemization of optically pure mer-exo(H)- and mer-endo(H)-[Co(OH)(dien)(dapo)]²⁺ ( A and B (X = OH), resp.; dien = N-(2-aminoethyl)ethane-1,2-diamine; dapo = 1,3-diaminopropan-2-ol) involve the same symmetrical pentacoordinate intermediate as the base hydrolyses of the corresponding mer-exo(H)- and mer-endo(H)-[CoX(dien)(dapo)]²⁺ species A and B , respectively, where X = Cl, Br, or N₃. The kinetic parameters of the anation process are fully compatible with the independently measured competition ratio. The rate data reveal that substitution of OH^? is unexpectedly fast, viz. it is not consistent with the usual sequence Br^? > Cl^? > H₂O > N > OH^?. This behavior is interpreted on the basis of an internal conjugate base mechanism which involves an amino-hydroxo/aminato-aqua tautomerism, viz. the reaction is actually an OH^? -catalyzed substitution of [CoH₂O(dien)(dapo)]³⁺ where deprotonation occurs effectively at the secondary-amine site NH of dien.     

Complexes of 3,3′-Oxybis[(diphenylphosphino)methylbenzene] with Ni(II), Pd(II), Pt(II), Rh(I), and Ag(I). How Important is Backbone Rigidity in the Formation of trans-Spanning Bidenatate Chelates??

The bidentate diphosphine ligand, 3,3′-oxybis[(dipenylphosphino)methylbenzene] ( 1 ) forms monomeric, trans-square-planar complexes MX₂( 1 ) (M = Ni, Pd, Pt; X = Cl^?, Br^? I^?, and, in part, N, NCS^?, CN^?, NO) as well as Pt(H)Cl( 1 ), Pt(H)Br( 1 ), and RhCl(CO)( 1 ). Polymeric species have been observed with substitutionally inert metal centres: trans-[PtCl₂( 1 )]₂ and cis-[PtCl₂( 1 )]_n (mean value of n ≈ 4–5) ³¹P-NMR, and selected IR and UV/VIS parameters are reported. Ligand 1 shows a marked preference for trans-spanning and monomeric chelate formation, despite its various degrees of freedom of internal rotation in the lignad backbone. The readily available ligand 1 as well as analogues with other donor atoms, therefore, appear useful in most potential applications of trans-spanning chelate ligands. The crystal structure of AgCl( 1 )·0.5 (CH₃)₂C?O·0.39 C₆H₁₂ (space group C2/c,a = 21.02 Å, b = 14.57 Å, c = 24.79 Å, β = 99.77°, V = 7531.4 ų, Z = 8) confirms the presence of three-coordinate Ag( I ), with a coordination intermediate between a trigonal-planar and a T-shaped geometry (P-Ag-P = 145.61(8)°).     

Multiparameter regularization for Volterra kernel identification via multiscale collocation methods

Identification of the Volterra system is an ill-posed problem. We propose a regularization method for solving this ill-posed problem via a multiscale collocation method with multiple regularization parameters corresponding to the multiple scales. Many highly nonlinear problems such as flight data analysis demand identifying the system of a high order. This task requires huge computational costs due to processing a dense matrix of a large order. To overcome this difficulty a compression strategy is introduced to approximate the full matrix resulted in collocation of the Volterra kernel by an appropriate sparse matrix. A numerical quadrature strategy is designed to efficiently compute the entries of the compressed matrix. Finally, numerical results of three simulation experiments are presented to demonstrate the accuracy and efficiency of the proposed method.     

Model independent bounds on reaction cross-sections in heavy-ion scattering

The coupled cluster equations first proposed by Coester and Kümmel and developed by Kümmel, Lührmann, and Zabolitsky are derived explicitly from the variational principle for the ground state energy (the “true” energy) using a new set of simple formulas relating density matrices (equal time limits of Green functions) to the coupled cluster functions. In this respect a simplification appears to be achieved by working with a normalized ground state wave function. The further transformation of the variational equations into the standard forms given by the previous authors differs mainly in its pedagogical aspects from ideas found in the existing literature.     

Rare earth doped α-alumina thin films prepared by pulsed laser deposition: structural and optical properties

-Al₂O₃ films doped with about 1% Eu³⁺ were grown on sapphire (012) substrates by pulsed laser deposition using an ArF excimer laser under 10^-4 mbar oxygen pressure and at temperatures higher than 1050 °C. The Eu doping rate was measured by Rutherford backscattering spectroscopy. The crystalline structure was determined by X-ray diffraction and transmission electron microscopy. The films are grown epitaxially on the sapphire substrate. The Eu³⁺ fluorescence spectra are constituted of narrow lines. By means of pulsed laser deposition, Eu³⁺ ions may be introduced into a single site of the -phase lattice, with a concentration that cannot be reached using conventional crystal-growth methods. PACS 81.15.Fg; 68.37.Lp; 78.55.Hx     

Addition of arenes to ethylene and propene catalyzed by ruthenium

TpRuII(CO)(Me)(NCMe) (Tp = hydridotris(pyrazolyl)borate) serves as a catalyst precursor for the conversion of benzene and ethylene or propene to alkylaromatic products. The reaction proceeds via the formation of the active catalyst TpRu(CO)(Ph)(NCMe) and is mildly selective for linear propylbenzene over isopropylbenzene.     

Lipase from Carica papaya latex presents high enantioselectivity toward the resolution of prodrug (R,S)-2-bromophenylacetic acid octyl ester

Besides the well-known papain, lipolytic activity is another interesting enzymatic activity present in latex from Carica papaya. This lipolytic activity is strongly attached to the latex solid phase, resulting in a naturally immobilized biocatalyst. In this work we describe the kinetic resolution of (R,S)-2-bromophenylacetic acid octyl ester by Carica papaya crude latex and two partially purified latex fractions. Several parameters, such as substrate concentration and solvent effects were studied. The best results were obtained using decane as solvent with 50 mM of substrate and 50 mg/mL enzyme/reaction medium; under these conditions, a high enantioselectivity (E >200) was obtained with crude latex. A twofold increase of the initial rate maintaining E >200 was obtained using purified fractions without protease and without esterase. Lipase from Carica papaya latex is the most enantioselective wild-type enzyme ever described for the studied reaction.     

Synthesis of linear and hyperbranched sugar‐grafted polysiloxanes using N‐hydroxysuccinimide‐activated esters

A straightforward method for the preparation of polysiloxanes grafted with carbohydrate side groups is described. Two kinds of backbones have been functionalized, namely one‐dimensional, linear polysiloxanes, and hyperbranched poly(siloxysilane)s based on cyclotetrasiloxanes. The method enables us to keep a good integrity of the polysiloxane backbone. The introduction of intermediate activated esters as side groups on the polysiloxane backbone ensures a complete homogeneity of the reaction medium during sugar grafting in dimethyl sulfoxide, and consequently an easy grafting with the unprotected amino sugar. Solubility of the resulting polysiloxanes has been tested in various solvents. The sugar‐grafted polysiloxanes are good candidates for applications such as silicone formulations, hydrophilic silicone elastomers, interactions with metallic nanoparticles, and suspension stabilization, or as starting point for the design of more complex polysiloxanes for molecular recognition. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3607–3618