Biomedical subjects

ID Williams

Publications and source records attributed to ID Williams.

10 recordsLinked to original sources

PubMed2000

HMPA promotes retro-aldol reaction, resulting in syn-selective addition of lithiated 1-naphthylacetonitrile to aromatic aldehydes

In HMPA-THF solution, lithiated 1-naphthylacetonitrile undergoes highly syn-selective addition to aromatic aldehydes, providing the first access to such syn-aldols. Syn-selectivity is also observed with two other arylacetonitriles. Aldolate equilibration and crossover experiments demonstrate that HMPA promotes retro-aldol reaction and that aldol diastereoselectivity under these conditions is thermodynamically controlled.

Journal Article↗

PubMed2000

Dimerization of an Inactive Fragment of Huperzine A Produces a Drug with Twice the Potency of the Natural Product This work was supported by the Research Grants Council of Hong Kong (HKUST6156/97M), the Biotechnology Research Institute (HKUST), the Mayo Foundation, and the Istituto Pasteur Fondazione Cenci Bolognetti (E.P.). We thank Prof. X. C. Tang (Shanghai Institute of Materia Medica) for a gift of (-)-1.

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Journal Article↗

PubMed2000

Measurement of Charge Exchange and X-Ray Emission Cross Sections for Solar Wind-Comet Interactions.

X-ray emission from a comet was observed for the first time in 1996. One of the mechanisms believed to be contributing to this surprisingly strong emission is the interaction of highly charged solar wind ions with cometary gases. Reported herein are total absolute charge-exchange and normalized line-emission (X-ray) cross sections for collisions of high-charge state (+3 to +10) C, N, O, and Ne ions with the cometary species H2O and CO2. It is found that in several cases the double charge-exchange cross sections can be large, and in the case of C3+ they are equal to those for single charge exchange. Present results are compared to cross section values used in recent comet models. The importance of applying accurate cross sections, including double charge exchange, to obtain absolute line-emission intensities is emphasized.

Journal Article↗

PubMed1999

A chemically functionalizable nanoporous material

Although zeolites and related materials combine nanoporosity with high thermal stability, they are difficult to modify or derivatize in a systematic way. A highly porous metal coordination polymer [Cu3(TMA)2(H2O)3]n (where TMA is benzene-1,3,5-tricarboxylate) was formed in 80 percent yield. It has interconnected [Cu2(O2CR)4] units (where R is an aromatic ring), which create a three-dimensional system of channels with a pore size of 1 nanometer and an accessible porosity of about 40 percent in the solid. Unlike zeolites, the channel linings can be chemically functionalized; for example, the aqua ligands can be replaced by pyridines. Thermal gravimetric analysis and high-temperature single-crystal diffractometry indicate that the framework is stable up to 240 degreesC.

Journal Article↗

PubMed1999

Withanolides from hyoscyamus niger seeds

Three withanolide class steroids were isolated from the seeds of Hyoscyamus niger. Two of them were identified as daturalactone-4 (1) and Nic-3 (which is now named hyoscyamilactol) (2). The new compound was elucidated as 16alpha-acetoxyhyoscyamilactol (3) on the basis of spectroscopic properties and X-ray crystallographic analysis.

Journal Article↗

PubMed1996