Tandem β‐Boration/Arylation of α,β‐Unsaturated Carbonyl Compounds by Using a Single Palladium Complex To Catalyse Both Steps

Diphenyl(3‐methyl‐2‐indolyl)phosphine (C₉H₈NPPh₂, 1 ) gives stable dimeric palladium(II) complexes that contain the phosphine in P,N‐bridging coordination mode. On treating 1 with [Pd(O₂CCH₃)₂], the new complexes [Pd(μ‐C₉H₇NPPh₂)(NCCH₃)]₂ ( 2 ) or [Pd(μ‐C₉H₇NPPh₂)(μ‐O₂CCH₃)]₂ ( 3 ) were isolated, depending on the solvent used, acetonitrile or toluene, respectively. Further reaction of 3 with the ammonium salt of 1 led to the substitution of one carboxylate ligand to afford [Pd(μ‐C₉H₇NPPh₂)₃(μ‐O₂CCH₃)] ( 4 ), in which the bimetallic unit is bonded by three C₉H₇NPPh₂^? moieties and one carboxylate group. Using this methodology, [Pd₂(μ‐C₆H₄PPh₂)₂(μ‐C₉H₇NPPh₂)(μ‐O₂CCX₃)] (X=H ( 7 ); X=F ( 8 )) were synthesised from the ortho‐metalated compounds [Pd(C₆H₄PPh₂)(μ‐O₂CCX₃)]₂ (X=H ( 5 ); X=F ( 6 )). Complexes 3 , 4 , 7 , and 8 have been found to be active in the catalytic β‐boration of α,β‐unsaturated esters and ketones under mild reaction conditions. Hindrance of the carbonyl moiety has an influence on the reaction rate, but quantitative conversion was achieved in many cases. More remarkably, when aryl bromides were added to the reaction media, complex 7 induced a highly successful consecutive β‐boration/cross‐coupling reaction with dimethyl acrylamide as the substrate (99 % conversion, 89 % isolated yield).     

Nitridorhenium(V) Complexes with 1,3‐Dialkyl‐4,5‐dimethylimidazole‐2‐ylidenes

The nitridorhenium(V) complexes [ReNCl₂(PR₂Ph)₃] (R = Me, Et) react with the N‐heterocyclic carbenes (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐5‐ylidene (L^Et) or 1,3,4,5‐tetramethylimidazole‐2‐ylidene (L^Me) in absolutely dry THF under complete replacement of the equatorial coordination sphere. The resulting [ReNCl(L^R)₄]⁺ complexes (L^R = L^Me, L^Et) are moderately stable as solids and in solution, but decompose in hot methanol under formation of [ReO₂(L^R)₄]⁺ complexes. With 1,3‐diisopropyl‐4,5‐dimethylimidazole‐5‐ylidene (L^i‐Pr), the loss of the nitrido ligand and the formation of a dioxo species is more rapid and no nitridorhenium intermediate could be isolated. The Re‐C bond lengths in [ReNCl(L^Et)₄]Cl of approximately 2.195Å are relatively long and indicate mainly σ‐bonding in the electron‐deficient d² system under study. The hydrolysis of the nitrido complexes proceeds via the formation of [ReO₃N]^2? anions as could be verified by the isolation and structural characterization of the intermediates [{ReN(PMe₂Ph)₃}{ReO₃N}]₂ and [{ReN(OH₂)(L^Et)₂}₂O][ReO₃N].     

Na2Ge3P3 and Na5Ge7P5 Comprising Heteroatomic Polyanions Mimicking the Structure of Fibrous Red Phosphorus

Recently lithium phosphidogermanates were discovered as fast lithium ion conductors for potential usage as solid electrolytes in all solid-state batteries. In this context we also studied sodium phosphidogermanates since sodium ion conductors are of equal interest. Na₂Ge₃P₃ and Na₅Ge₇P₅ both crystallize in the monoclinic space group C2/m with unit cell parameters of a = 17.639(4) Å, b = 3.6176(7) Å, c = 11.354(2) Å, β = 92.74(3)° and a = 16.168(5) Å, b = 3.6776(7) Å, c = 12.924(4) Å, β = 91.30(3)°, respectively. Both show linearly condensed 9-atom cages of four Ge / five P and five Ge / four P atoms, respectively. These cages contain Ge–Ge bonds and form one-dimensional tubes by sharing three atoms. The parallel tubes are paired through further Ge–Ge bonds. Both structures are closely related to the one of the fibrous type of crystalline red phosphorus. A comparison with other compounds such as NaGe₃P₃ and GeP reveals recurring structural motifs with a broad variety of connection patterns. According to the general formula Na_4+xGe_6+xP_6–x with x = 0 and 1, the two novel structures hint for the possibility of a variable Na content which might allow Na ion mobility.     

Identification and expression analysis of genes encoding putative cellulose synthases (CesA) in the hybrid aspen, Populus tremula (L.) × P. tremuloides (Michx.)

Cellulose is synthesized in plant cell walls by large membrane-bound protein complexes proposed to contain several copies of the catalytic subunit of the cellulose synthase, CesA. Here we report identification of 10 distinct CesA genes within a database of 100,000 ESTs of the hybrid aspen, Populus tremula (L.) × P. tremuloides (Michx.). Expression analyses in normal wood undergoing xylogenesis and in tension wood indicate xylem specific expression of four putative CesA isoenzymes, PttCesA1, PttCesA3-1, PttCesA3-2 and PttCesA9. Both the protein sequences and the expression profiles of PttCesA3-1 and PttCesA3-2 are very similar, and they may thus represent redundant copies of an enzyme with essentially the same function. Further, one of the generally more constitutively expressed CesA genes, PttCesA2, seems to be activated on the opposite side of a tension wood induced stem, while PttCesA6 appears to be more specific for leaf tissues. The rest of the hybrid aspen CesA genes were found to be relatively evenly expressed over the poplar tissues hereby studied.     

Generation of mass tags by the inherent electrochemistry of electrospray for protein mass spectrometry

We present herein a review of our work on the on-line electrochemical generation of mass tags toward cysteine residues in peptides and proteins. Taking advantage of the inherent electrochemical nature of electrospray generated from a microfabricated microspray emitter, selective probes for cysteine were developed and tested for on-line nonquantitative mass tagging of peptides and proteins. The nonquantitative aspect of the covalent tagging thus allows direct counting of free cysteines in the mass spectrum of a biomolecule through additional adduct peaks. Several substituted hydroquinones were investigated in terms of electrochemical properties, and their usefulness for on-line mass tagging during microspray experiments were assessed with L-cysteine, peptides, and intact proteins. Complementarily, numerical simulations were performed to properly understand the respective roles of mass transport, kinetics of electrochemical-chemical reactions, and design of the microspray emitter in the mass tagging overall efficiency. Finally, the on-line electrochemical tagging of cysteine residues was applied to the analysis of tryptic peptides of purified model proteins for protein identification through peptide mass fingerprinting.     

Polarizability and optical rotation calculated from the approximate coupled cluster singles and doubles CC2 linear response theory using Cholesky decompositions

A new implementation of the approximate coupled cluster singles and doubles CC2 linear response model using Cholesky decomposition of the two-electron integrals is presented. Significantly reducing storage demands and computational effort without sacrificing accuracy compared to the conventional model, the algorithm is well suited for large-scale applications. Extensive basis set convergence studies are presented for the static and frequency-dependent electric dipole polarizability of benzene and C60, and for the optical rotation of CNOFH2 and (-)-trans-cyclooctene (TCO). The origin-dependence of the optical rotation is calculated and shown to persist for CC2 even at basis set convergence.     

Intermediate temperature ionic conductivity of Sm1.92Ca0.08Ti2O7–δ pyrochlore

The results of concentration cell electromotive force methods (EMF) and electrochemical impedance spectroscopy measurements on the pyrochlore system Sm_1.92Ca_0.08Ti₂O_7–δ are presented. The data have been used to estimate total and partial conductivities and determine transport numbers for protons and oxide ions under various conditions. The EMF techniques employed include corrections for electrode polarisation resistance. The measurements were performed using wet and dry atmospheres in a wide \( {p_{{{{\rm{O}}_{{2}}}}}} \) range using mixtures of H₂, N₂, O₂, and H₂O in the temperature region where proton conductivity was expected (500–300 °C). The impedance measurements revealed the conductivity to be mainly ionic under all conditions, with the highest total conductivity measured being 0.045 S/m under wet oxygen at 500 °C. Both bulk and grain boundary conductivity was predominantly ionic, but electronic conductivity appeared to play a slightly larger part in the grain boundaries. EMF data confirmed the conductivity to be mainly ionic, with oxide ions being the major conducting species at 500 °C and protons becoming increasingly important below this temperature.

     

Methodology for determination of 89Sr and 90Sr in radiological emergency: I. Scenario dependent evaluation of potentially interfering radionuclides

Early determination of ⁸⁹Sr and ⁹⁰Sr in radiological emergency is hampered by the presence of interfering short-lived fission products. In this study, three commonly used radioanalytical strategies for ⁸⁹Sr and ⁹⁰Sr were evaluated theoretically considering their suitability in a nuclear explosion scenario. The methods were evaluated with respect to the need for decay time of interfering short-lived strontium and yttrium isotopes, and reduction of other known interfering nuclides prior to measurement. The strategy shown to be most successful included initial separation of strontium and determination of ⁸⁹Sr, followed by an yttrium separation and counting of ⁹⁰Y. ⁸⁹Sr and ⁹⁰Sr could be determined about 5 and 9 days after a nuclear explosion, respectively.     

Molecular dynamics study of tryptophylglycine: a dipeptide nanotube with confined water

To investigate the mechanism of structural changes of a peptide nanotube and water confined inside the channel, the helical peptide tryptophylglycine monohydrate (WG.H2O) was studied by molecular dynamics (MD) simulations using the three-dimension parallel MD program ddgmq (software package) and a consistent force field. Simulations were performed on both the water-containing system and a model system without water molecules. The details of the structural behavior with temperature are investigated for the entire simulated temperature range. Phase transitions were obtained at 115, 245, 270, 310, and 385 K, due to the contributions of both the peptide and the confined water subsystems. The crystalline, amorphous, liquidlike, liquid, and superheated phases of water were observed in the temperature ranges 40-115, 115-245, 245-310, 310-385, and >385 K, respectively. At 300 K, the diffusion constant of the confined water is 0.46 x 10-5 cm2 s-1, a value comparable to that of other peptide nanotubes. The empty peptide system melts at 440 K. Mechanisms of the negative thermal expansion (NTE) along the tube axis were investigated for different temperature ranges. The contraction of the crystalline water (or amorphous water) draws also the tube walls in and leads to NTE below 245 K. The other NTEs appear to be connected to the collapse of the ice network or the solid peptide network between 245 K and room temperature or from 310 to 440 K, respectively.