Publications by authors named "Robert B Yelle"

4 Publications

  • Page 1 of 1

Investigation of the reactivity of Pt phosphinito and molybdocene nitrile hydration catalysts with cyanohydrins.

Inorg Chem 2009 Aug;48(16):7828-37

Department of Chemistry, University of Oregon, Eugene, Oregon 97403, USA.

Aldehyde- and ketone-derived cyanohydrins were reacted with the nitrile hydration catalysts [PtCl(PR(2)OH){(PR(2)O)(2)H}] (1) and Cp(2)Mo(OH)(OH(2))(+) (2) under a variety of hydration reaction conditions. In general, the cyanohydrins were hydrated to the amides rather slowly using these catalysts, but no subsequent hydrolysis of the amide products occurred. Catalyst 2 was much less reactive than catalyst 1, showing at best trace amounts of amide product. Product inhibition-, substrate inhibition-, and cyanide poisoning-tests demonstrated that coordination of cyanide, generated by dehydrocyanation of the cyanohydrins, is responsible for the generally low catalytic activity of 1 and 2 with cyanohydrin substrates. Addition of KCN to reaction mixtures of acetonitrile and 1 gave a linear plot of rate versus cyanide concentration, indicating that binding of cyanide to the catalysts is irreversible. Density functional theory (DFT) calculations showed that, for the hydration reaction catalyzed by 2, the formation of most intermediates and the overall reaction itself are energetically more favorable for lactonitrile (a cyanohydrin) than for 3-hydroxypropionitrile (not a cyanohydrin). From this result, it is concluded that, from an electronic standpoint, there is no intrinsic reason for the lack of reactivity observed for cyanohydrins, a result consistent with the finding that the slow hydration reactivity is caused by cyanide poisoning. In addition, DFT calculations showed that, for nitriles in general (not necessarily cyanohydrins), product inhibition occurs because coordination of the amide product to the metal center is stabilized by isomerization to the more strongly bonded iminol tautomer.
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http://dx.doi.org/10.1021/ic900734dDOI Listing
August 2009

Theoretical studies of N2 reduction to ammonia in Fe(dmpe)2N2.

Inorg Chem 2009 Feb;48(3):861-71

Computational Science Institute, 5294 University of Oregon, 1600 Millrace Drive Suite 105, Eugene, Oregon 97403, USA.

Electronic structure calculations using density functional theory were performed on potential intermediates in the reaction of Fe(dmpe)(2)N(2) (dmpe = 1,2-bis(dimethylphosphino)ethane) with protons. Three mechanisms were investigated and compared, and the possibility of a two-electron reduction by a sacrificial Fe(dmpe)(2)N(2) complex was considered in each mechanism. A Chatt-like mechanism, involving the stepwise addition of protons to the terminal nitrogen, was found to be the least favorable. A second pathway involving dimerization of the Fe(dmpe)(2)N(2) complex, followed by the stepwise addition of protons leading to hydrazine, was found to be energetically favorable; however many of the dimeric intermediates prefer to dissociate into monomers. A third mechanism proceeding through diazene and hydrazine intermediates, formed by alternating protonation of each nitrogen atom, was found to be the most energetically favorable.
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http://dx.doi.org/10.1021/ic800930tDOI Listing
February 2009

Structure-property investigations of conjugated thiophenes fused onto a dehydro[14]annulene scaffold.

J Org Chem 2008 Jun 29;73(12):4424-32. Epub 2008 May 29.

Department of Chemistry and Materials Science Institute, University of Oregon, Eugene, OR 97403, USA.

A series of 12 thieno-fused macrocycles based on the dehydro[14]annulene framework have been prepared. Studies have focused on the optical and electronic properties of the dehydrobenzothieno[14]annulenes (DBTAs) and dehydrothieno[14]annulenes (DTAs) utilizing NMR spectroscopy, UV-vis spectrophotometry, electrochemistry, and DFT computations. X-ray crystal structures were also obtained for two of the macrocycles. The structure-property relationships were found to vary significantly based on the relative orientation of the thiophenes. The stability, properties, and reactivity of these macrocycles were found to be more typical of dehydroannulenes rather than oligothiophenes.
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http://dx.doi.org/10.1021/jo800225uDOI Listing
June 2008

Protein control of electron transfer rates via polarization: molecular dynamics studies of rubredoxin.

Biophys J 2004 Apr;86(4):2030-6

School of Molecular Biosciences, Washington State University, Pullman, Washington 99164-4660, USA.

The protein matrix of an electron transfer protein creates an electrostatic environment for its redox site, which influences its electron transfer properties. Our studies of Fe-S proteins indicate that the protein is highly polarized around the redox site. Here, measures of deviations of the environmental electrostatic potential from a simple linear dielectric polarization response to the magnitude of the charge are proposed. In addition, a decomposition of the potential is proposed here to describe the apparent deviations from linearity, in which it is divided into a "permanent" component that is independent of the redox site charge and a dielectric component that linearly responds or polarizes to the charge. The nonlinearity measures and the decomposition were calculated for Clostridium pasteurianum rubredoxin from molecular dynamics simulations. The potential in rubredoxin is greater than expected from linear response theory, which implies it is a better electron acceptor than a redox site analog in a solvent with a dielectric constant equivalent to that of the protein. In addition, the potential in rubredoxin is described well by a permanent potential plus a linear response component. This permanent potential allows the protein matrix to create a favorable driving force with a low activation barrier for accepting electrons. The results here also suggest that the reduction potential of rubredoxin is determined mainly by the backbone and not the side chains, and that the redox site charge of rubredoxin may help to direct its folding.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1304056PMC
http://dx.doi.org/10.1016/S0006-3495(04)74264-2DOI Listing
April 2004