University of Minnesota Duluth
University of Minnesota Department of Chemistry and Biochemistry
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Thursday , September 18, 2014; 4:00 p.m.; MWAH 195

 

Department of Chemistry & Biochemistry Welcomes:

Dr. Rik Tykwinski

SCSE Academy of Science & Engineering 2013 Inductee, Department of Chemistry and Pharmacy & Interdisciplinary Center of Molecular Materials (ICMM), University of Erlangen-Nuremberg, Germany

Presents:

 

“Carbyne: In Search of a Carbon Allotrope Built From sp-Hybridized Carbon”

Carbon allotropes from sp3-hybridized carbon (diamond) and sp2-hybridized carbon (graphite, graphene, fullerenes, nanotubes) have well-established properties, many of which are technologically important. The recent discovery of fullerenes and graphenes has captured the imagination of many chemists and materials scientists since these allotropes (or their derivatives) might serve as platforms for the next generation of electronic, optical, and energy capture devices. One needs to look no further than Nobel Prizes awarded in 1996 for buckminsterfullerene (C60) and in 2010 for graphene to appreciate the impact of these discoveries. A carbon allotrope derived from sp-hybridized carbon atoms (carbyne), has been discussed in the literature since the 1960s, when El Goresy and Donnay reported on a natural sample of carbyne supposedly isolated from the Ries meteor crater in Bavaria. This discovery, however, has been debated, and many researchers believe that an authentic sample of “natural” carbyne has not yet been identified. Thus, the search for carbyne continues.

Organic chemists have tackled carbyne through the synthesis of model compounds in order to potentially predict its properties. With this goal in mind we have developed a number of methods toward the synthesis of polyynes, and these efforts provide us with a unique opportunity to explore the physical characteristics of polyynes as a function of length, including, for example, electronic structure. Polyynes offer one possible view of an sp-carbon allotrope, and an alternative would be a structure composed of cumulated double bonds. It is interesting to note that significant progress has been made in the synthesis of polyynes over the past decade,[2] while little is known about cumulenes beyond the early studies of Bohlmann and Kuhn.[3] A major challenge in cumulene synthesis is the instability of the final products. Using many of the same techniques that have pushed forward our polyyne chemistry, we have recently achieved the formation of extended cumulenes that show reasonable stability and are persistent for some time under an inert environment.[3] This now allows for the study of the cumulene version of carbyne, through the analysis of model compounds as a function of molecular length.

This presentation will highlight and contrast general aspects of our work with both polyynes and cumulenes, through correlations drawn from spectroscopic analyses as well as X-ray crystallography. The chemical reactivity of selected derivatives will also be discussed. Finally, some predictions for the properties of the elusive carbon allotrope carbyne will be offered.


[1] A. El Goresy, G. Donnay, Science, 1969, 161, 363–364.   [2]    W. A. Chalifoux, R. R. Tykwinski, Nature Chem. 2010, 2, 967–971.   [3] J. A. Januszewski, D. Wendinger, C. D. Methfessel, F. Hampel, R. R. Tykwinski, Angew. Chem. 2013, 52, 1817–1821.

 

 

Friday , September 19, 2014; 3:00 p.m.; LSci 175

 

Department of Chemistry & Biochemistry Welcomes:

Dr. Richard Holz

SCSE Academy of Science & Engineering 2014 Inductee, Dean, Klingler College of Arts & Sciences, Professor of Chemistry, Marquette University

Presents:

 

“Biological Nitrile Hydration: Understanding the Catalytic Mechanism of Nitrile Hydratases”

Nitrile hydratases (NHases, EC 4.2.1.84) catalyze the hydration of nitriles to their corresponding amides under ambient conditions and physiological pH.  Since the currently employed industrial conditions used to hydrate nitriles to amides (either acid or base hydration), are often incompatible with the sensitive structures of many industrially and synthetically relevant compounds, NHases have attracted substantial interest as biocatalysts in preparative organic chemistry.  NHases are already used in several industrial applications such as the synthesis of specialty chemicals and pharmaceuticals including acrylamide and nicotinamide.  Because of their exquisite reaction specificity, the nitrile-hydrolyzing potential of NHase enzymes is becoming increasingly recognized as a truly new type of “Green” chemistry.  X-ray crystallographic studies on NHases revealed that they are α2β2 heterotetramers with an active site consisting of three cysteine residues, two amide nitrogen’s, a water molecule, and either a non-heme Fe(III) ion (Fe-type) or a non-corrin Co(III) ion (Co-type).  Two of the active site cysteine residues are post-translationally modified to cysteine-sulfinic acid (–SO2H) and cysteine-sulfenic acid (–SOH) yielding an unusual metal coordination geometry, termed a “claw-setting”.  As no catalytic intermediates have been identified for NHase enzymes, a combination of pre-steady state stopped-flow spectroscopy, electron paramagnetic resonance (EPR) spectroscopy and X-ray crystallography was used to identify NHase catalytic intermediates allowing a novel catalytic mechanism to be proposed.

Salette Martinez,1,2 Rui Wu,2 Natalie Gumataotao,1,2 Dali Liu,3 Brian Bennett,2 and Richard Holz1*

Contribution from the 1Department of Chemistry, Marquette University, Milwaukee, Wisconsin 53201, the2Department of Physics, Marquette University, Milwaukee, Wisconsin 53201, and the 3Department of Chemistry and Biochemistry, Loyola University Chicago, Chicago, Illinois 60660