Photochemical synthesis and crystal structure of two potentially useful metal carbonyl complexes: pentacarbonyl(η2-cis-cyclooctene)-tungsten(0) and tetracarbonylbis(η2-cis-cyclooctene)tungsten(0)

W(CO)₅(C₈H₁₄) and W(CO)₄(C₈H₁₄)₂ were synthesized photochemically from W(CO)₆ andcis-cyclooctene with a respective yield of 71% and 18%. The compounds were characterized by NMR, IR and single X-ray crystallography. The IR spectra of the two compounds exhibited characteristic bands for the mono- and bis-substituted metal carbonyl complexes. In W(CO)₄(C₈H₁₄)₂, thecis-cyclooctene ligands are in atrans configuration with the double bonds perpendicular to each other. The two crystal structures were refined toR=0.040 for W(CO)₅(C₈H₁₄) and 0.025 for W(CO)₄(C₈H₁₄)₂. Although the tungsten-carbon (of the carbonyl groups) distances are very similar in both structures, the distances between the tungsten atom and the olefinic carbons are shorter in W(CO)₄(C₈H₁₄)₂, 2.36 Å, than in W(CO)₅(C₈H₁₄), 2.51 Å.     

The potential of achiral sponge-derived and synthetic bromoindoles as selective cytotoxins against PANC-1 tumor cells

Our quest to isolate and characterize natural products with in vitro solid tumor selectivity is driven by access to repositories of Indo-Pacific sponge extracts. In this project an extract of a species of Haplosclerida sponge obtained from the US NCI Natural Products Repository displayed, by in vitro disk diffusion assay (DDA) and IC₅₀ determinations, selective cytotoxicity with modest potency to a human pancreatic cancer cell line (PANC-1) relative to the human lymphoblast leukemia cell line (CCRF-CEM). Two brominated indoles, the known 6-bromo conicamin (1) and the new derivative, 6-Br-8-keto-conicamin A (2), were identified and 2 (IC₅₀ 1.5 μM for the natural product vs 4.1 μM for the synthetic material) was determined to be responsible for the cytotoxic activity of the extract against the PANC-1 tumor cell line. The new natural product and ten additional analogs were prepared for further SAR testing.     

An efficient transition path sampling algorithm for nanoparticles under pressure

We apply transition path sampling to the simulation of nanoparticles under pressure. As a barostat we use a bath of ideal gas particles that form a stochastically updated atmosphere around the nanoparticle. We justify this algorithm by showing that it preserves the distribution of an ideal gas at constant temperature and pressure by satisfying detailed balance. Based on this result, we present a simple and efficient transition path sampling scheme for the study of activated processes in nanoparticles under pressure. As a first application, we investigate the h-MgO to rocksalt transformation in faceted CdSe nanocrystals. Starting from an artificial mechanism involving a uniform motion of all atoms, trajectories quickly converge towards the dominant mechanism of nucleation and growth along parallel (100) planes.     

Detecting naphthenic acids in waters by gas chromatography-mass spectrometry

Naphthenic acids (general formula C(n)H(2n+Z)O(2)) are water-soluble, toxic compounds found in petroleum and bitumen. Some of the current methods for detecting these acids in waters depend on measuring the presence of the carboxylic acid functional group, and therefore many of these methods also detect naturally occurring carboxylic acids that are not naphthenic acids. We report a procedure that includes liquid-liquid extraction, cleanup, and derivatization to form t-butyldimethylsilyl esters prior to gas chromatography-mass spectrometry (GC-MS) analysis. Using low- and high-resolution MS to detect the ion C(15)H(27)O(2)Si(+) (nominal m/z=267) is an excellent indicator of the presence of naphthenic acids at concentrations > or =10microgL(-1).