1-Germavinylidene (Ge═CH2), germyne (HGeCH), and 2-germavinylidene (H2Ge═C) molecules and isomerization reactions among them: anharmonic rovibrational analyses

Theoretical investigations of three equilibrium structures and two associated isomerization reactions of the GeCH(2) - HGeCH - H(2)GeC system have been systematically carried out. This research employed ab initio self-consistent-field (SCF), coupled cluster (CC) with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] wave functions and a wide variety of correlation-consistent polarized valence cc-pVXZ and cc-pVXZ-DK (where X = D, T, Q) basis sets. For each structure, the total energy, geometry, dipole moment, harmonic vibrational frequencies, and infrared intensities are predicted. Complete active space SCF (CASSCF) wave functions are used to analyze the effects of correlation on physical properties and energetics. For each of the equilibrium structures, vibrational second-order perturbation theory (VPT2) has been utilized to obtain the zero-point vibration corrected rotational constants, centrifugal distortion constants, and fundamental vibrational frequencies. The predicted rotational constants and anharmonic vibrational frequencies for 1-germavinylidene are in good agreement with available experimental observations. Extensive focal point analyses, including CCSDT and CCSDT(Q) energies and basis sets up to quintuple zeta, are used to obtain complete basis set (CBS) limit energies. At all levels of theory employed in this study, the global minimum of the GeCH(2) potential energy surface (PES) is confirmed to be 1-germavinylidene (GeCH(2), 1). The second isomer, germyne (HGeCH, 2) is predicted to lie 40.4(41.1) ± 0.3 kcal mol(-1) above the global minimum, while the third isomer, 2-germavinylidene (H(2)GeC, 3) is located 92.3(92.7) ± 0.3 kcal mol(-1) above the global minimum; the values in parentheses indicate core-valence and zero-point vibration energy (ZPVE) corrected energy differences. The barriers for the forward (1→2) and reverse (2→1) isomerization reactions between isomers 1 and 2 are 48.3(47.7) ± 0.3 kcal mol(-1) and 7.9(6.6) ± 0.3 kcal mol(-1), respectively. On the other hand, the barriers of the forward (2→3) and reverse (3→2) isomerization reactions between isomers 2 and 3 are predicted to be 55.2(53.2) ± 0.3 kcal mol(-1) and 3.3(1.6) ± 0.3 kcal mol(-1), respectively.     

A new and convenient approach for the preparation of β-cyanoethyl protected trinucleotide phosphoramidites

Herein we report a convenient approach for the preparation of fully protected trinucleotide synthons to be used for the synthesis of gene libraries. The trinucleotide synthons bear β-cyanoethyl groups at the phosphate residues, and thus can be used in standard oligonucleotide synthesis without additional steps for deprotection and work-up.     

α-N-Linked glycopeptides: conformational analysis and bioactivity as lectin ligands

Natural N-glycosylation involves a β-anomeric linkage connecting the sugar to one asparagine residue of the protein. We herein report NMR- and modelling-based data on glycomimetics containing α-glycosidic linkages. The bioactivity of α-Gal-containing glycopeptides has been documented by revealing binding to two plant lectins, i.e. a potent β-trefoil toxin (Viscum album agglutinin) and β-sandwich lectin (Erythrina corallodendron agglutinin), by NMR protocols. Docking provided insights into the 3D structures of the resulting complexes. These results provide the basis to introduce α-substituted neoglycopeptides to the toolbox of scaffold for the design of potent lectin inhibitors.     

Investigations into the Formation and Stability of Cationic Rhodium Diphosphane η(6) -Arene Complexes

Rhodium-η(6) -arene complexes can be generated in the presence of arenes following the hydrogenation of the diolefin in rhodium catalyst precursors of the type [Rh(PP*)(diolefin)]X (PP*=chelating diphosphane, X=noncoordinating anion). In this paper we report the characterization of such arene complexes with the ligands DuPhos, dipamp, dppe, Tangphos, dppf, and diop by means of NMR spectroscopy ((31) P, (103) Rh) and X-ray analysis. A procedure that follows the approach to equilibrium as a function of time monitored by using an UV/Vis diode array was used to determine 20 stability constants. Analyses were accomplished directly from the spectra by either a numeric and/or a new analytic solution of the underlying system of differential equations. Additionally thermodynamic parameters were determined in the temperature range between 278 and 318?K.     

Asymmetric synthesis of densely functionalized medium-ring carbocycles and lactones through modular assembly and ring-closing metathesis of sulfoximine-substituted trienes and dienynes

An asymmetric synthesis of densely functionalized 7-11-membered carbocycles and 9-11-membered lactones has been developed. Its key steps are a modular assembly of sulfoximine-substituted C- and O-tethered trienes and C-tethered dienynes and their Ru-catalyzed ring-closing diene and enyne metathesis (RCDEM and RCEYM). The synthesis of the C-tethered trienes and dienynes includes the following steps: 1) hydroxyalkylation of enantiomerically pure titanated allylic sulfoximines with unsaturated aldehydes, 2) α-lithiation of alkenylsulfoximines, 3) alkylation, hydroxy-alkylation, formylation, and acylation of α-lithioalkenylsulfoximines, and 4) addition of Grignard reagents to α-formyl(acyl)alkenylsulfoximines. The sulfoximine group provided for high asymmetric induction in steps 1) and 4). RCDEM of the sulfoximine-substituted trienes with the second-generation Ru catalyst stereoselectively afforded the corresponding functionalized 7-11-membered carbocyles. RCDEM of diastereomeric silyloxy-substituted 1,6,12-trienes revealed an interesting difference in reactivity. While the (R)-diastereomer gave the 11-membered carbocyle, the (S)-diastereomer delivered in a cascade of cross metathesis and RCDEM 22-membered macrocycles. RCDEM of cyclic trienes furnished bicyclic carbocycles with a bicyclo[7.4.0]tridecane and bicyclo[9.4.0]pentadecane skeleton. Selective transformations of the sulfoximine- and bissilyloxy-substituted carbocycles were performed including deprotection, cross-coupling reaction and reduction of the sulfoximine moiety. Esterification of a sulfoximine-substituted homoallylic alcohol with unsaturated carboxylic acids gave the O-tethered trienes, RCDEM of which yielded the sulfoximine-substituted 9-11-membered lactones. RCEYM of a sulfoximine-substituted 1,7-dien-10-yne showed an unprecedented dichotomy in ring formation depending on the Ru catalyst. While the second-generation Ru catalyst gave the 9-membered exo 1,3-dienyl carbocycle, the first-generation Ru catalyst furnished a truncated 9-membered 1,3-dieny carbocycle having one CH(2) unit less than the dienyne.     

Micelle-assisted one-pot synthesis of water-soluble polyaniline-gold composite particles

A micelle-based method to synthesize dispersed polyaniline (PANI)-Au composite particles by direct oxidation of aniline using AuCl4- as the oxidant is presented. The obtained composite particles have a core-shell structure, where Au nanoparticles of 20 nm mean diameter are encapsulated by PANI of well-defined tetrahedron shape with 150 nm average edge length. The polaron band of the dispersed PANI-Au composite particles is centered at 745 nm and is rather narrow compared to the broad 835 nm absorption of PANI synthesized by the IUPAC procedure. The surface plasmon absorption of Au nanoparticles normally centered at around 520 nm is absent in the composite particles with oxidized PANI. Our results point to a strong electronic interaction between the encapsulated Au nanoparticles and the shell of oxidized PANI. Films and pellets produced from these composite particles show a twofold higher conductivity than IUPAC PANI.     

Binding of single gold atoms on thin MgO(001) films

In the present Letter the first electron paramagnetic resonance spectra of single metal atoms on a single crystalline oxide surface are presented. For Au atoms on a MgO(001) film investigated here an analysis of the angular dependent resonance positions and the hyperfine coupling to (17)O shows that the atoms are bound on top of oxygen ions on the terrace of the film. This result is in perfect agreement with scanning tunneling microscopy measurements at 5 K presented here. The measured hyperfine matrix components allow an experimental verification of the theoretically proposed binding mechanism of Au atoms on MgO. In particular, the large reduction of the isotropic hyperfine coupling constant of supported Au as compared to free atoms is not due to a charge transfer at the interface but a hybridization of orbitals and a resulting polarization of the unpaired electron.     

First enantioselective total synthesis of neocarazostatin B, determination of its absolute configuration and transformation into carquinostatin A

The first enantioselective total synthesis of neocarazostatin B, the determination of its absolute configuration and transformation into carquinostatin A are described.