Mechanism of silver-promoted ligand metathesis in square-planar complexes of d(8) Ions. Kinetics of formation and molecular structures of a trinuclear intermediate [(Me)(N-N)Pt(mu-Cl)Ag(mu-Cl)Pt(N-N)(Me)](+) and its dinuclear evolution product [(Me)(N-N)Pt(mu-Cl)Pt(N-N)(Me)](+) (N-N = ArN=C(Me)C(Me)=NAr,Ar = 2,6-(i-Pr)(2)C(6)H(3))

The silver-assisted ligand metathesis reaction involving a platinum(II) complex of formula [PtClMe(N,N-chelate)] with acetonitrile has been investigated. By using a suitably hindered N,N-chelate, an otherwise hardly detectable trinuclear species has been isolated and characterized through X-ray diffractometry. The trinuclear cation consists of two nearly orthogonal [PtCl(Me)(N,N-chelate)] square-planar units entrapping an Ag(+) cation through the chloride ligands that, acting as bidentate, form a linear AgCl(2) unit with two nonequivalent Ag-Cl bonds. The residual acidity of the silver cation is satisfied by one secondary Ag-Pt interaction [Ag-Pt(1) = 2.82 A] in which the platinum atom acts as a donor. Kinetic studies have demonstrated that the silver assistance operates both through a simple associative step and through a pathway in which the above trinuclear complex is an active intermediate. In a noncoordinating solvent the latter species evolves with AgCl loss and formation of a dinuclear Pt,Pt complex showing a rare single chloride bridge.     

New phosphite-oxazoline ligands for efficient Pd-catalyzed substitution reactions

We have designed and synthesized a new family of readily available highly modular phosphite-oxazoline ligands for the Pd-catalyzed asymmetric allylic substitution reactions. The introduction of a pi-acceptor flexible bulky biphenyl phosphite moiety in the ligand design is highly adventitious in the product outcome. Thus, this ligand series affords excellent reaction rates (TOF's up to >2400 mol.(mol.h)-1) and enantioselectivities (ee's up to >99%) and, at the same time, shows a broad scope for different substrate types.     

Asymmetric Synthesis of α-Substituted-γ-butyrolactone Empolying Prolinol Type of Auxiliaries

Eleven (S)-(-)-bishydrocarbyl-(l-alkanoylpyrrolidin-2_yl)_methanol derivatives of three types were synthesized from L-proline.asymmtncally selective alkylation products were obtained oy LDA treatment and alkylation using methyl 2-bromoethyl ether, and three types of chiral α-Substituted-γ-butyrolactones were obtained by hydrolyzing the alkylation products, with %e.e. beijing up to 89 percent.     

2,4,6-三硝基苯酚改性锆铝复合氧化物固定相分离富勒烯的色谱性能研究

制备了用于分离C60和C70的2，4，6－三硝基苯酚改性锆铝复合氧化物高效液相色谱固定相，考察了流动相中甲苯的含量、柱温及流速对C60和C70分离的影响，同时比较了酸腐蚀前后锆铝复合氧化物基质对分离的影响，结果表明，2，4，6－三硝基苯酚改性酸腐蚀后锆铝复合氧化物填料对富勒烯表现出较强的分离能力，具有作为富勒烯制备分离的潜力。     

Heavy metal biosorption by bacterial cells

Microbial biomass provides available ligand groups on which metal ions bind by different mechanisms. Biosorption of these elements from aqueous solutions represents a remediation technology suitable for the treatment of metal-contaminated effluents. The purpose of the present investigation was the assessment of the capability of Brevibacterium sp. cells to remove bivalent ions, when present alone or in pairs, from aqueous solutions, using immobilized polyacrylamide cells of the microorganism in a flow-through system. The biosorption capacity of Brevibacterium cells was studied for lead, cadmium and copper. The metal cell binding capacity followed the order Cu > Pb > Cd, based on estimated q_max. These values, expressed as mmol metal/g dry weight cells, were 0.54 for Cu, 0.36 for Pb and 0.14 for Cd. Polyacrylamide-gel immobilized cells were effective in Pb, Cu and Cd removal. Lead removal was not affected by the presence of Cd and Cu; lead instead inhibited Cd and Cu removal. The desorption of the metal, by fluxing a chelating solution, restored the metal binding capacity of the cells, thus affording the multiple use of the same biomass in the remediation treatment. Received: 31 July 1997 / Revised: 22 December 1997 / Accepted: 30 December 1997     

Investigation of parameters affecting the on-line combination of supercritical fluid extraction with capillary gas chromatography

Two different injectors, a split/splitless injector and a programmed temperature vaporizer (PTV) injector were investigated as the interface in on-line supercritical fluid extraction (SFE)-capillary gas chromatography (cGC). The parameters affecting the chromatographic peak shapes as well as the quantitative performance of the interfaces in on-line SFE-cGC were identified and studied. Particular attention was paid to the case where modified extraction fluids were used. Experiments were performed on two different samples. The first sample consisted of PAHs spiked on sand at different concentration levels. The other sample was a polymeric material.     

Reactivity of pseudobases from pyridinium salts competition between hydrogen transfer and ring-opening reactions

The reactions of 3-cyano-1-methylpyridinium iodide (1a) and l-benzyl-3-cyanopyridinium chloride (1b) in aqueous NaOH have been studied over a range of concentrations from N 0.5 to N 2.5 with respect to the hydroxide ion, and with the concentrations of the reactants at different ratios. It has been found that the intermediate, not isolable pseudobases can undergo, depending on the experimental conditions, two competitive reaction channels, namely, a redox process leading to the dihydropyridines 3–5 and pyridones 2,6, and a ring-opening reaction leading to the pentadienenitrile 7, 2-imino-3-pyridinecarbaldehyde 8, and 2-(aryl)alkylamino-3-pyridinecarbaldehyde 9.     

丝氨酸织组膜电极的研究

利用猪肝组织膜配合氨气敏电极,研制了丝氨酸生物催化传感电极。丝氨酸浓度的测定范围为5.1×10~(-5)～3.2×10~(-3)mol/L,检出限为3.1×10~(-5)mol/L。研究和讨论了电极的最佳工作条件,并测定了实验条件下酶催化反应的米氏常数Km。该电极用于合成样品分析,效果满意。     

Investigation on the Interaction of Bendazac with β-, Hydroxypropyl-β-, and γ-, yclodextrins

The interactions of Bendazac, a topical non-steroidal anti-inflammatory drug, with-cyclodextrin, hydroxypropyl--cyclodextrin and -cyclodextrinwere investigated to evaluate possibilities to improve the drug's poor water solubilityand eventually to enhance the topical delivery of Bendazac. Phase solubility studiesdemonstrated the ability of the selected cyclodextrins to complex with Bendazac andincrease drug solubility. The amount of solubilized Bendazac increased linearly withthe addition of each cyclodextrin according toA_L type plots. ¹³C-NMR studiesshowed that the Bendazac A-ring was included in the cavity of the three cyclodextrins.The -cyclodextrin was also able to include the B-ring of Bendazac, forminga complex where one drug molecule fitted into two cyclodextrin molecules. Equimolarsolid systems of the drug with each cyclodextrin carrier were prepared using varioustechniques (physical mixing, spray-drying and freeze-drying). The results of differential scanning calorimetry and Fourier transform infrared analysis, performed on the solid systems, demonstrated that freeze-dried and spray-dried products had a high degree of amorphization and agreed with the hypothesis of the existence of drug–cyclodextrin interaction in the solid state. The cyclodextrins tested were able to improve the dissolution of Bendazac. The dissolution profile of the drug was also affected by the physico-chemical properties of each solid system, the freeze-dried products being the most rapidly dissolving forms.     

2020 Roadmap on two-dimensional nanomaterials for environmental catalysis

This roadmap demonstrates a series of two-dimensional nanomaterials, such as graphene, black phosphorus, oxides, layered double hydroxides, chalcogenides, bismuth-based layered compounds, MXenes, metal organic frameworks, covalent organic frameworks, and others, for environmental catalysis.