20 research outputs found
A Natural Love of Natural Products
Recent research on the chemistry of natural products from the author’s group that led to the receipt of the ACS Ernest Guenther Award in the Chemistry of Natural Products is reviewed. REDOR NMR and synthetic studies established the T-taxol conformation as the bioactive tubulin-binding conformation, and these results were confirmed by the synthesis of compounds which clearly owed their activity or lack of activity to whether or not they could adopt the T-taxol conformation. Similar studies with the epothilones suggest that the current tubulin-binding model needs to be modified. Examples of natural products discovery and biodiversity conservation in Suriname and Madagascar are also presented, and it is concluded that natural products chemistry will continue to make significant contributions to drug discovery. My first real exposure to natural products chemistry came in my third and final year as an undergraduate at Cambridge University, when I attended a course of lectures on the chemistry of natural products by the Nobel Prize-winning chemist Sir Alexander Todd (later to become Lord Todd). The lectures included many references to his own work in the field, with stories of his early work on the structure of cholesterol, th
Polycrystalline indium phosphide on silicon by indium assisted growth in hydride vapor phase epitaxy
Polycrystalline InP was grown on Si(001) and Si(111) substrates by using indium (In) metal as a
starting material in hydride vapor phase epitaxy (HVPE) reactor. In metal was deposited on silicon
substrates by thermal evaporation technique. The deposited In resulted in islands of different size
and was found to be polycrystalline in nature. Different growth experiments of growing InP were
performed, and the growth mechanism was investigated. Atomic force microscopy and scanning
electron microscopy for morphological investigation, Scanning Auger microscopy for surface and
compositional analyses, powder X-ray diffraction for crystallinity, and micro photoluminescence
for optical quality assessment were conducted. It is shown that the growth starts first by phosphidisation
of the In islands to InP followed by subsequent selective deposition of InP in HVPE regardless
of the Si substrate orientation. Polycrystalline InP of large grain size is achieved and the
growth rate as high as 21 lm/h is obtained on both substrates. Sulfur doping of the polycrystalline
InP was investigated by growing alternating layers of sulfur doped and unintentionally doped InP
for equal interval of time. These layers could be delineated by stain etching showing that enough
amount of sulfur can be incorporated. Grains of large lateral dimension up to 3 lm polycrystalline
InP on Si with good morphological and optical quality is obtained. The process is generic and it
can also be applied for the growth of other polycrystalline III–V semiconductor layers on low cost
and flexible substrates for solar cell applications