Calendar
Calendar
Seminar Series: Fall 2007
All seminars are Fridays, 3-4pm Druckenmiller room 20 and a student reception in Druckenmiller 26 prior to the seminar, unless otherwise noted.
Friday, November 16, 2007
Sylvia Ceyer MIT
J. C. Sheehan Professor of Chemistry
Massachusetts Institute of Technology
Bulk H: A new kind of surface species with a chemistry of it's own
Abstract:
Experiments that document the distinctive reactivity of H embedded in the bulk of a Ni metal catalyst are described. Specifically, a transient H atom emerging from the bulk onto the surface is observed to be the reactive species in hydrogenation of ethylene and acetylene adsorbed on Ni to form ethane and ethylene, respectively. A H atom adsorbed on the Ni surface does not hydrogenate ethylene or acetylene. However, a surface bound H atom will react with adsorbed acetylene to form ethylidyne, a precursor to coke that poisons the catalyst. The different reactivities of bulk and surface bound H arise from the very different energetics of the two kinds of H atoms. A bulk H atom reacts with an adsorbate while it is a transiently energetic species emerging from the bulk onto the surface with as much as 24 kcal/mol more energy than a reacting surface bound H atom. These results demonstrate that bulk H is not solely a source of surface bound H in catalytic hydrogenation as proposed 50 years ago, but rather, a reactant with a chemistry of its own.
The Unique Chemistry of Hydrogen Beneath the Surface: Catalytic Hydrogenation of Hydrocarbons, Accts. Chem. Res. 34, 737 (2001)
Friday, November 30, 2007
Ross Widenhoefer
Department of Chemistry
Duke University
Platinum and Gold-Catalyzed Hydroamination of C=C Bonds
Abstract:
We have developed a family of Pt- and Au-catalyzed protocols for the intramolecular addition of the H–X (X = C, N, and O) bond of a carbon, nitrogen, or oxygen nucleophile across the C=C bond of an unactivated alkene or allene (hydrofunctionalization). These transformations possess considerable potential as methods for the synthesis of naturally occurring and biologically active heterocycles in both industrial and academic settings. Recent milestones from our efforts include development of the first transition metal-catalyzed protocols for the 1) hydroarylation of unactivated alkenes with indoles (JACS 2004, 126, 3700), 2) hydroalkoxylation of unactivated alkenes with alcohols (JACS 2004, 126, 9536), 3) intermolecular hydroamination of ethylene with carboxamides (Organometallics 2004, 23, 1649), 4) hydroamination of unactivated alkenes with alkyl amines (JACS 2005, 127, 1070), 5) hydroamination of unactivated alkenes with carbamates (Angew. Chem. Int. Ed. 2006, 45, 1747), and 6) enantioselective hydroalkoxylation of allenes with alcohols (Angew. Chem. Int. Ed. 2007, 46, 283).
Previously:
Friday, October 26, 2007
(Please note that this seminar will begin at 2:30)
Das Thamattoor
Associate Professor of Chemistry
Colby College
Short Stories from an Undergraduate Research Laboratory
Abstract:
The talk will describe undergraduate research projects on the mechanisms of carbene reactions, atomic carbon chemistry, and crystal polymorphism.
Thursday, October 18, 2007, 4 PM
Jason Sello
Assistant Professor of Chemistry
Department of Molecular Pharmacology, Physiology and Biotechnology
Brown University
Antibiotic Production and Antibiotic Resistance in Streptomyces Bacteria
Abstract:
Streptomyces is a large genus of soil-dwelling bacteria that are best known for producing antibiotics. In fact, streptomycetes produce half of the 10,000 known naturally-occurring antibiotics and two-thirds of the antibiotics used in clinical and veterinary medicine (e.g.,Streptomyces bacteria to produce antibiotics and to resist the antibiotics that they produce. tacrolimus, neomycin, doxorubicin, and the tetracyclines). As antibiotic producers, these bacteria are also considered a reservoir of antibiotic resistance genes that pose a serious threat to human health. Research on these bacteria has implications for chemistry, biology, and medicine. Prof. Sello will discuss his studies of molecular mechanisms that enable
Friday, October 19, 2007
Norm Laurendeau
School of Mechanical Engineering, School of Mechanical Engineering
Purdue University
A Career in Combustion Diagnostics: Fruitful Insights and Lessons Learned
Abstract:
The author reviews his career in combustion diagnostics, with a focus on relevant contributions, salient issues, painful episodes and future research problems. Four aspects of various basic and applied programs on laser-induced fluorescence (LIF) encompassing some 25 years are surveyed, including scientific and technical contributions to (1) laser-saturated fluorescence (LSF) measurements of OH and NO in laminar premixed flames at atmospheric pressure; (2) LSF investigations of OH in laminar premixed flames at pressures up to 10 atm; (3) LIF studies of NO in laminar counterflow flames, both nonpremixed and partially premixed, at pressures up to 15 atm; and (4) picosecond time-resolved laser-induced fluorescence (PITLIF) measurements of OH in turbulent nonpremixed and partially premixed flames at atmospheric pressure. In each case, I develop the basic LIF theory, provide experimental verification, share pertinent results, offer important lessons, and suggest avenues for further research. My primary intention is to acquaint young investigators with the realities of the research enterprise, including surely the fun and breakthroughs, but also the pitfalls and setbacks. Beyond publications and grants, I seek to spotlight the joys of academic research, from participating in the intellectual maturity of motivated individuals to developing lifelong friendships with graduate students, colleagues and even sponsors.
Friday, September 14, 2007
Tom Tullius
Department of Chemistry
Boston University
Structure-based identification of functional regions in the human genome
Abstract:
Do some parts of the human genome function by virtue of their structure, and not directly by their nucleotide sequence? To address this question we have used hydroxyl radical cleavage patterns to produce a structural map of 30 megabases of human genomic DNA, at single-nucleotide resolution. To accomplish this, we constructed a freely available database, ORChID (OH Radical Cleavage Intensity Database), to house experimental hydroxyl radical cleavage data (1). We then used the ORChID data to develop an algorithm to predict the hydroxyl radical cleavage pattern of any DNA sequence to high accuracy, and applied this algorithm to the human genome. This dataset of DNA structural data can be searched for structural patterns in genomic DNA that may be associated with biological function (2), including DNase hypersensitive sites (2,3), nucleosome positioning sequences, enhancers, and other functional genomic regions for which consensus nucleotide sequences are not apparent. In recent work we have developed a novel algorithm to assess evolutionary constraint based on DNA structure rather than primary sequence. Our results suggest that structural constraint is widespread in the human genome, and that these regions are informative of functional sites. That natural selection not only acts to preserve information encoded in the primary sequence of DNA, but also in its local structure, is likely to be of critical importance to understanding genome function. This new concept challenges what is meant by ‘evolutionary constraint’ to also include more complex grammars, like the one we are developing in this work.
This work was funded by an ENCODE Technology Development grant from the National Human Genome Research Institute of the National Institutes of Health (R01 HG003541).
(1) J. A. Greenbaum, B. Pang & T. D. Tullius. 2007. Construction of a genome-scale structural map at single-nucleotide resolution. Genome Research 17, 947-953.
(2) The ENCODE Consortium. 2007. Identification and analysis of functional elements in 1% of the human genome by the ENCODE pilot project. Nature 447, 799-816.
(3) J. A. Greenbaum, S. C. J. Parker & T. D. Tullius. 2007. Detection of DNA structural motifs in functional genomic elements. Genome Research 17, 940-946.
Friday, September 28, 2007
Tom Pochapsky
Professor of Chemistry Protein Structure
Brandeis University
A tale of two (or three) enzymes: Protein conformational changes as servants of enzyme function
Abstract:
Enzyme catalysis requires enzyme motion. The apparently mutually exclusive requirements for selective binding of substrates, stabilization of transition states and product release by an enzyme can be reconciled by assuming that each step in the catalytic cycle takes place from a different enzyme conformation, and that these different conformations are discrete on the time scale of catalysis.
We are investigating the role of conformational change in determining both the efficiency and direction of enzyme catalysis in two metalloenzymes, cytochrome P450cam and acireductone dioxygenase (ARD). P450cam catalyzes some of the most difficult chemistry to be found in nature, the selective oxidation of an unactivated C-H bond, while ARD is capable of changing the chemistry it performs depending upon the metal ion bound in the active site. NMR, molecular biology, computations and organic synthesis all play a role in our research.