Synthesis of Chiral Silanes

The lack of a simple, single step synthesis of chiral silanes is an obstacle to the use of chiral silanes in the synthesis of chiral drugs or materials because there are no naturally occurring chiral, nonracemic silicon compounds. Therefore, it would be useful to find a method that provides high yields of chiral, nonracemic, silicon compounds that can be used in synthesizing chiral drugs. Initial studies done in Sommer’s et al. (1964) laboratory required a multistep synthesis for preparing chiral silicon compounds. This method had poor yields and required much time and hence hindered the use of chiral silicon compounds. Therefore, finding the development of a single-step synthesis for making chiral silanes is important and can lead to several advantages over a multistep synthesis such as it is more efficient, it is less expensive, and it would take less time to make. A previous GVSU student has shown that reaction of a pro-chiral dimenthoxyphenylmethylsilane with nucleophiles can produce a chiral silane with good selectivity for phenyl and methyl groups. In our current study, the overall goal of this project was to find a single-step synthesis that can yield a single enantiomer when the substituents are a phenyl and a vinyl group. The starting material, dimenthoxyphenylvinylsilane was prepared from dichlorophenylvinylsilane. Dicholorophenylvinylsilane reacted with 2 equivalents of menthoxyllithium in THF solvent to produce dimenthoxyphenylvinylsilane, which was then purified by column chromatography and the product was isolated in a 72.6 % yield. The dimenthoxyphenylvinylsilane was used for the reactions in preparing chiral silicon compounds. Napthyllithium, butyllithium, methyllithium, and tert-butyllithium reacted with the dimenthoxyphenylvinylsilane to form the chiral silicon compounds. These reactions were performed under N2, in hexane solvent at -78o C except the reaction of dimenthoxyphenylvinylsilane with tert-butyllithium which was done in diethyl ether solvent. After the products were made, these compounds were purified by column chromatography, then they were analyzed with the use of NMR, GC- Mass Spectrum, and HPLC. The yields of these reactions varied from 18.4% to 72.05% and in the case of the methyllithium substitution initial results were consistent with a high selectivity for one enantiomer. Our hypothesis for the selectivity observed in these reactions is that nucleophiles are more likely to attack the silicon at the more open-side that would lead into a higher selectivity. The crowded side of the dimenthoxyphenylvinylsilane is less likely to undergo nucleophilic substitution because steric-effect would occur and would prevent the nucleophile from attacking the electrophilic silicon atom. We have investigated the reactions of dimenthoxyphenylvinylsilane with different organolithiums to produce a series of chiral silanes which have been isolated in moderate to good yield. Future studies of these compounds will involve further characterization of the new compounds made and substitution of the menthoxy group with hydride and bromide to form a silicon compound that can be readily used in the synthesis of chiral organic molecules. *This scholar and faculty mentor have requested that only an abstract be published

Two-dimensional monadicity

The behaviour of limits of weak morphisms in 2-dimensional universal algebra is not 2-categorical in that, to fully express the behaviour that occurs, one needs to be able to quantify over strict morphisms amongst the weaker kinds. F-categories were introduced to express this interplay between strict and weak morphisms. We express doctrinal adjunction as an F-categorical lifting property and use this to give monadicity theorems, expressed using the language of F-categories, that cover each weaker kind of morphism

Well-defined protein-polymer conjugates—synthesis and potential applications

During the last decades, numerous studies have focused on combining the unique catalytic/functional properties and structural characteristics of proteins and enzymes with those of synthetic molecules and macromolecules. The aim of such multidisciplinary studies is to improve the properties of the natural component, combine them with those of the synthetic, and create novel biomaterials in the nanometer scale. The specific coupling of polymers onto the protein structures has proved to be one of the most straightforward and applicable approaches in that sense. In this article, we focus on the synthetic pathways that have or can be utilized to specifically couple proteins to polymers. The different categories of well-defined protein-polymer conjugates and the effect of the polymer on the protein function are discussed. Studies have shown that the specific conjugation of a synthetic polymer to a protein conveys its physico-chemical properties and, therefore, modifies the biodistribution and solubility of the protein, making it in certain cases soluble and active in organic solvents. An overview of the applications derived from such bioconjugates in the pharmaceutical industry, biocatalysis, and supramolecular nanobiotechnology is presented at the final part of the articl

xArx2: An Aristaless Homolog That Regulates Brain Regionalization During Development in Xenopus laevis

The aristaless-related gene, Arx, plays a fundamental role in patterning the brain in humans and mice. Arx mutants exhibit lissencephaly among other anomalies. We have cloned a Xenopus aristaless homolog that appears to define specific regions of the developing forebrain. xArx2 is transcribed in blastula through neurula stages, and comes to be restricted to the ventra and lateral telencephalon, lateral diencephalon, neural floor plate of the anterior spinal cord, and somites. In this respect, Arx2 expresses in regions similar to Arx with the exception of the somites. Overexpression enlarges the telencephalon, and interference by means of antisense morpholino-mediated translation knockdown reduces growth of this area. Overexpression and inhibition studies demonstrate that misregulation of xArx2 imposes dire consequences upon patterns of differentiation not only in the forebrain where the gene normally expresses, but also in more caudal brain territories and derivatives as well. This suggests that evolutionary changes that expanded Arx-expression from ventral to dorsal prosencephalon might be one of the determinants that marked development and expansion of the telencephalon. genesis 47:19-31, 2009. (C) 2008 Wiley-Liss, Inc

Physical Volcanology of Tseax Volcano, British Columbia, Canada

Tseax volcano erupted ∼ 250 years ago in NW British Columbia, Canada producing tephra deposits and lava flows. Field mapping has defined the stratigraphy of Tseax and the lava flow morphologies. Aerial photogrammetry and bathymetry surveys were used to create a high resolution digital elevation model of the volcano to facilitate mapping and estimates of erupted material volumes. Tseax volcano (∼ 10.4 ± 0.7 × 106 m3) comprises an outer breached spatter rampart and an inner conical tephra cone. Tseax is associated with a 32 km long and 0.49 ± 0.08 km3 basanite-to-tephrite lava flow field covering ∼ 36 km2 and divided into 4 distinct lava flows with heterogeneous surface morphologies. We present a volcanological map of Tseax volcano at a scale of 1:22,500. This will serve as supporting information for further research on the eruptive history of Tseax volcano and the lava flow field emplacement

Évaluation de la participation des Cris dans la procédure d'évaluation environnementale de la Convention de la Baie James et du Nord Québécois (CBJNQ) /

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

A General Formula for Black Hole Gravitational Wave Kicks

Although the gravitational wave kick velocity in the orbital plane of coalescing black holes has been understood for some time, apparently conflicting formulae have been proposed for the dominant out-of-plane kick, each a good fit to different data sets. This is important to resolve because it is only the out-of-plane kicks that can reach more than 500 km/s and can thus eject merged remnants from galaxies. Using a different ansatz for the out-of-plane kick, we show that we can fit almost all existing data to better than 5 %. This is good enough for any astrophysical calculation, and shows that the previous apparent conflict was only because the two data sets explored different aspects of the kick parameter space.Comment: 14 pages

Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports

Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate