Stoichiometric and catalytic reactivity of tris(oxazolinyl)phenylborato zinc and magnesium compounds

Recently, our research group has synthesized a new class of monoanionic tridentate ligands, ToR (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate and ToP = tris(4-S-isopropyl-2-oxazolinyl)phenylborate), and developed the corresponding stoichiometric and catalytic chemistry of zirconium, yttrium, rhodium, iridium, and magnesium complexes. This thesis begins with the comparison of this new class of scorpionate-type ligands (ToM and ToP) with more classical Tp (tris(pyrazolyl)borates) and Cp (cyclopentadienyl) analogues, both in terms of relative electron donating ability as well as steric bulk. Group 7 metal tricarbonyl complexes of ToM and ToP (ToMM(CO)3 and ToPMC(O)3; M = Re, Mn) were synthesized in this purpose and the corresponding νCO IR stretching frequency data were used for the electron donating ability comparison. Solid angles of these ancillary ligands were calculated using coordinates from crystal structures or molecular models with the program Solid-G to obtain a quantitative assessment of the relative steric properties. The thesis then mainly focuses on the chemistry of four-coordiante zinc complexes using ToM as the supportive ancillary ligand. The main interest lies on the synthesis of molecular terminal zinc hydride and its catalytic activity in Si−O bond formation reactions, as well as the isolation and reactivity study of alkylperoxy zinc compounds (ToMZnOOR) obtained from the reactions of the corresponding zinc alkyls (ToMZnR) with molecular O2. The later part of this thesis also discusses the chemistry of ToM-supported magnesium complexes and the comparison with analogous zinc complexes. It starts with the synthesis of ToM-supported zinc and magnesium bulky silyl complexes, both comprising with and without β-SiH moieties (ToMM−SiR3; M = Zn, Mg; R = SiHMe2, SiMe3). The study further extends to divergent reaction pathways of ToMMSi(SiHMe2)3 (M = Zn, Mg) towards CO2. Finally, the thesis discusses the catalytic activity of ToMZnH and ToMMgMe in carbonyl reduction. ToMMgMe mediated catalytic Tischenko coupling of aldehydes, reversible trans-esterification, and reductive ester cleavage are also discussed in details

Determinants of the Hypergeometric Period Matrices of an Arrangement and its Dual

We fix three natural numbers k, n,N, such that n + k + 1 = N, and introduce the notion of two dual arrangements of hyperplanes. One of the arrangements is an arrangement of N hyperplanes in a k-dimensional affine space, the other is an arrangement of N hyperplanes in an n-dimensional affine space. We assign weights α1, . . . , αN to the hyperplanes of the arrangements and for each of the arrangements consider the associated period matrices. The first is a matrix of k-dimensional hypergeometric integrals and the second is a matrix of n-dimensional hypergeometric integrals. The size of each matrix is equal to the number of bounded domains of the corresponding arrangement. We show that the dual arrangements have the same number of bounded domains and the product of the determinants of the period matrices is equal to an alternating product of certain values of Euler’s gamma function multiplied by a product of exponentials of the weights

Current clinical perspectives on myocardial angiogenesis

Currently accepted modalities of treatment for atherosclerotic coronary artery disease (CAD) include pharmacological therapy, and revascularization with either bypass surgery or percutaneous coronary intervention (PCI). Similarly, conventional treatment of congestive heart failure (HF) is limited to medical therapy, temporary assist devices and in a select few, cardiac transplantation. A significant subset of patients with severe symptomatic CAD and end stage HF is not eligible for these traditional methods of treatment. In spite of maximal medical and revascularization therapy, these patients may not get adequate symptomatic relief. After a decade of investigations, gene therapy is emerging as a promising therapeutic option for this group of patients. This review discusses myocardial angiogenesis as a therapeutic modality in these patients including therapeutic angiogenesis with growth factors and cell transplantation. (Mol Cell Biochem 264: 157–167, 2004)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/45341/1/11010_2004_Article_5275122.pd

Carotid artery stenting vs. endarterectomy

Randomized clinical trials have demonstrated that carotid endarterectomy (CEA) is superior to medical management for stroke prevention in patients with symptomatic and, to a lesser degree, asymptomatic internal carotid artery stenosis. However, large-scale registries have shown that the adverse event rates following CEA are commonly higher than observed in the trials. In the last decade, carotid artery stenting (CAS) has emerged as a less invasive alternative to surgery. In order to address the efficacy of CAS, we performed a meta-analysis of 10 randomized trials comparing CAS with CEA in 4648 mainly symptomatic patients. The analysis showed that CAS was associated with a statistically significant increased death or stroke rate at 30 days compared with CEA (odds ratio 1.60, 95% confidence interval 1.26-2.02). However, most of the trials had inadequate requirements in terms of endovascular expertise and did not mandate the use of emboli protection devices. Beyond 30 days, long-term follow-up of the trials previously reported suggest that both revascularization techniques are equivalent in terms of stroke prevention. Conversely, large-scale high-quality CAS registries—mostly with independent neurological assessment and clinical event committee adjudication—have reported results in the range of current recommendation for CEA in over 20 000 patients, despite the fact that the majority of patients were at high risk for surgery. Until further data become available, the performance of CAS should be limited to protocols or centres of excellence and targeted especially to patients at high risk for surger

Conversion of a Zinc Disilazide to a Zinc Hydride Mediated by LiCl

An unusual β-elimination reaction involving zinc(II) and LiCl is reported. LiCl and a coordinatively saturated disilazido zinc compound form an adduct that contains activated SiH moieties. In THF/toluene mixtures, this adduct is transformed into a zinc hydride and 0.5 equiv. cyclodisilazane. The Li+ and Cl− ions apparently affect the reaction pathway of the disilazido zinc in a synergistic fashion. Thus, the zinc hydride and cyclodisilazane products of formal β-elimination are not observed upon treatment of the zinc disilazide with Cl− or Li+separately