Dta/TG study of the formation of the (Bi,Pb)2Sr2Ca2Cu3O10+δ superconductor

In order to get insight in some of the yet unanswered questions about the formation process of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀₊ superconducting compound, coupled DTA-TG measurements have been performed in parallel with other techniques such as X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Microanalysis. The path leading to the formation of the (Bi,Pb)₂Sr₂Ca₂Cu₃O₁₀₊ compound, starting from coprecipitated oxalates powders was studied. The activation energy of some of the involved transformation processes were determined. Relationships between the differences induced in the DTA traces by various sample nominal compositions and the intergranular magnetic properties of the superconductor will be discussed.     

Molecular structure of [(tBu)2Al(μ-OPh)]2

The molecular structure of [(^tBu)₂Al(-OPh)]₂ has been determined. The intramolecular steric interaction between the phenyl groups and thetert-butyl ligands results in the geometry about aluminum being significantly distorted from tetrahedral, with the AlC₂ planes are pitched 62° with respect to the Al₂O₂ plane. The greater distortion from tetrahedral about aluminum, and the orientation of the phenoxide ring more nearly perpendicular to the M₂O₂ core as compared to that in [(^tBu)₂Ga(-OPh)]₂ are all consistent with increased^tBu...Ph steric interaction as a consequence of the smaller M₂O₂ core for [(^tBu)₂Al(-OPh)]₂. Crystal data: tetragonal, I4₁/acd,a=16.44(1),c=21.41(1) Å,V=5788(7) ų,Z=8,R=0.047,R _w=0.045.     

Forensic comparative glass analysis by laser-induced breakdown spectroscopy

Glass samples of four types commonly encountered in forensic examinations have been analyzed by laser-induced breakdown spectroscopy (LIBS) for the purpose of discriminating between samples originating from different sources. Some of the glass sets were also examined by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). Refractive index (RI) measurements were also made on all glass samples and the refractive index data was combined with the LIBS and with the LA-ICP-MS data to enhance discrimination. The glass types examined included float glass taken from front and side automobile windows (examined on the non-float side), automobile headlamp glass, automobile side-mirror glass and brown beverage container glass. The largest overall discrimination was obtained by employing RI data in combination with LA-ICP-MS (98.8% discrimination of 666 pairwise comparisons at 95% confidence), while LIBS in combination with RI provided a somewhat lower discrimination (87.2% discrimination of 1122 pairwise comparisons at 95% confidence). Samples of side-mirror glass were less discriminated by LIBS due to a larger variance in emission intensities, while discrimination of side-mirror glass by LA-ICP-MS remained high.     

Cyclization of Zincated α‐N‐Homoallylamino Nitriles: A New Entry to Enantiopure 2,3‐Methanopyrrolidines

Stereoselective cyclization of zincated α‐N‐homoallylamino nitriles has been developed. Following treatment with lithium diisopropylamide (LDA) and transmetalation with zinc bromide, α‐N‐(1‐phenylethyl)‐N‐homoallylamino nitriles lead to 2,3‐methanopyrrolidines in moderate to good yields (up to 66 %) and excellent selectivities (up to >98:2). With substrates derived from α‐branched homoallylic amines, a stereospecific inversion of the homoallylic stereogenic center was observed. To account for this, a mechanistic rationale involving the formation of zincioiminium ions from zincated α‐amino nitriles is put forward. 2,3‐Methanopyrrolidines should then arise from a sequence involving an aza‐Cope rearrangement providing a configurationally stable (2‐azoniaallyl)zinc species that then undergoes a [3+2] cycloaddition reaction.     

Application of a chiral scaffolding ligand in catalytic enantioselective hydroformylation

The synthesis of β-amino-aldehydes has been achieved through enantioselective hydroformylation of PMP-protected allylic amines. The reaction is accomplished by using a scalemic scaffolding ligand that covalently and reversibly binds to the substrate. These ligands behave like chiral auxiliaries because they are covalently attached to the substrate during hydroformylation; however, similar to traditional asymmetric ligands, they can be used in catalytic quantities. The directed hydroformylation of disubstituted olefins occurs under mild conditions (35 °C and 50 psi CO/H(2)), and Z-olefins afford excellent enantioselectivities (up to 93% ee).     

Chiral Dawson‐Type Hybrid Polyoxometalate Catalyzes Enantioselective Diels–Alder Reactions

Can achiral organocatalysts linked to chiral polyanionic metal oxide clusters provide good selectivity in enantioselective C?C bond formations? The answer to this question is investigated by developing a new active hybrid polyoxometalate‐based catalyst for asymmetric Diels–Alder reaction. Chirality transfer from the chiral anionic polyoxometalate to the covalently linked achiral imidazolidinone allows Diels–Alder cycloaddition products to be obtained with good yields and high enantioselectivities when using cyclopentadiene and acrylaldehydes as partners.     

Direct analysis of environmental and biological samples for total mercury with comparison of sequential atomic absorption and fluorescence measurements from a single combustion event

A Direct Mercury Analyzer (DMA) based on sample combustion, concentration of mercury by amalgamation with gold, and cold vapor atomic absorption spectrometry (CVAAS) was coupled to a mercury-specific cold vapor atomic fluorescence spectrometer (CVAFS). The purpose was to evaluate combustion-AFS, a technique which is not commercially available, for low-level analysis of mercury in environmental and biological samples. The experimental setup allowed for comparison of dual measurements of mercury (AAS followed by AFS) for a single combustion event. The AFS instrument control program was modified to properly time capture of mercury from the DMA, avoiding deleterious combustion products from reaching its gold traps. Calibration was carried out using both aqueous solutions and solid reference materials. The absolute detection limits for mercury were 0.002 ng for AFS and 0.016 ng for AAS. Recoveries for reference materials ranged from 89% to 111%, and the precision was generally found to be <10% relative standard deviation (RSD). The two methods produced similar results for samples of hair, finger nails, coal, soil, leaves and food stuffs. However, for samples with mercury near the AAS detection limit (e.g., filter paper spotted with whole blood and segments of tree rings) the signal was still quantifiable with AFS, demonstrating the lower detection limit and greater sensitivity of AFS. This study shows that combustion-AFS is feasible for the direct analysis of low levels of mercury in solid samples that would otherwise require time-consuming and contamination-prone digestion.     

Asymmetric Synthesis of Planar Chiral (Arene)tricarbonylchromium Complexes via Enantioselective Deprotonation by Conformationally Constrained Chiral Lithium‐Amide Bases

Enantioselective lithiation/electrophile addition reactions with eight chiral Li‐amide bases, 1 – 8 , and five [Cr(arene)(CO)₃] complexes, 9 – 13 , were investigated. Restriction of conformational freedom in the chiral Li‐amide base Li‐ 1 , in general, did not result in an increase in asymmetric induction. A new route to enantiomerically enriched (75 – 92%) planar chiral ortho‐substituted benzaldehyde complexes via enantioselective lithiation of benzaldimine complexes 16 and 17 is reported. Within the (1S)‐enantiomer series of o‐substituted benzaldehyde complexes 18a – d , the sign of the specific rotation, [α], is found to be positive, except for the trimethylstannyl derivative 18b . This is interpreted in terms of a reversed conformation of the aldehyde group.     

Good preclinical bioanalytical chemistry requires proper sampling from laboratory animals: automation of blood and microdialysis sampling improves the productivity of LC/MSMS.

The preclinical bioanalytical process with animal models begins with sampling biological fluids and tissue. The goal is to understand oral absorption kinetics, distribution, metabolism, excretion, blood brain barrier penetration, drug-drug interactions, and the influences on biomarkers, hematology, electrophysiology, cardiology, blood pressure and behavior. An overview is obtained by periodic blood sampling of 8-12 samples over a total time span of 10-24 h. Urine, feces, bile and microdialysates can augment the information available from whole blood. In today's preclinical environment, the majority of samples are processed by LC/MSMS augmented by robotic sample preparation tools. These tools save labor and improve precision for smaller volume/lower concentration samples. Our laboratories have been engaged in a project that is focused on improving both the quality and throughput for laboratory animal studies, while providing for reduced numbers of animals and enhanced animal comfort. We have implemented a robotic system that can accomplish most of the above goals for laboratory rats, dogs and primates. Studies with mice are at an earlier stage, but feasibility has been demonstrated. This presentation is a progress report on this evolving research program in cooperation with multiple pharmaceutical and drug development companies. We will illustrate results and discuss future directions.