A new role for organometallic reactions in organic synthesis in industry

Abstract -Organometallic compounds are coming to play a significant role as catalysts and reagents for the synthesis of organic compounds in high technology industry. Some examples involving C-C bond formation include alkylation of chloronaphthoquinones and halobenzenes, a titanium-mediated cyclization of diynes, and a simultaneous alkylation and ring closure of hexenedioates to give cyclopentanone derivatives. Transition metal imides provide convenient reagents for C-N bond formation in a new synthesis of allylic amines

Automated prediction of catalytic mechanism and rate law using graph-based reaction-path sampling

In a recent article [J. Chem. Phys., 143, 094106 (2015)], we have introduced a novel graph-based sampling scheme which can be used to generate chemical reaction paths in many-atom systems in an efficient and highly-automated manner. The main goal of this work is to demonstrate how this approach, when combined with direct kinetic modelling, can be used to determine the mechanism and phenomenological rate law of a complex catalytic cycle, namely cobalt-catalyzed hydroformylation of ethene. Our graph-based sampling scheme generates 31 unique chemical products and 32 unique chemical reaction pathways; these sampled structures and reaction paths en- able automated construction of a kinetic network model of the catalytic system when combined with density functional theory (DFT) calculations of free energies and resul- tant transition-state theory rate constants. Direct simulations of this kinetic network across a range of initial reactant concentrations enables determination of both the re- action mechanism and the associated rate law in an automated fashion, without the need for either pre-supposing a mechanism or making steady-state approximations in kinetic analysis. Most importantly, we find that the reaction mechanism which emerges from these simulations is exactly that originally proposed by Heck and Breslow; fur- thermore, the simulated rate law is also consistent with previous experimental and computational studies, exhibiting a complex dependence on carbon monoxide pres- sure. While the inherent errors of using DFT simulations to model chemical reactivity limit the quantitative accuracy of our calculated rates, this work confirms that our automated simulation strategy enables direct analysis of catalytic mechanisms from first principles

Quantum spin coverings and statistics

SL_q(2) at odd roots of unity q^l =1 is studied as a quantum cover of the complex rotation group SO(3,C), in terms of the associated Hopf algebras of (quantum) polynomial functions. We work out the irreducible corepresentations, the decomposition of their tensor products and a coquasitriangular structure, with the associated braiding (or statistics). As an example, the case l=3 is discussed in detail.Comment: 15 page

Mechanical land clearing to promote establishment of coastal sandplain grassland and shrubland communities

Author Posting. © The Author(s), 2005. This is the author's version of the work. It is posted here by permission of Blackwell Publishing for personal use, not for redistribution. The definitive version was published in Restoration Ecology 14 (2006): 220-232, doi:10.1111/j.1526-100X.2006.00124.x.The decline in grasslands and other species-rich early-successional habitats on the coastal sandplains of the northeastern U.S. has spurred management to increase the area of these declining plant communities. We mechanically removed overstory oak and applied seed from a nearby sandplain grassland on the island of Martha’s Vineyard, Massachusetts to evaluate this technique for creating an open oak community able to support sandplain herbaceous species. We compared vegetation structure and composition before and after clearing in an area of total tree removal (clearcutting), an area where 85% of tree basal area was removed (savanna cutting) and in adjacent coastal oak forest. Plant responses to clearcutting and savanna cutting were similar. Sandplain herbs colonized at high frequencies after seeding and increasing herbaceous cover from <7% before clearing to 22-38% three growing seasons later. Carex pensylvanica (Pennsylvania sedge) increased in cover ~ 6-fold, accounting for 84-90% of the increased herbaceous cover. Other native ruderals, and exotic herbs reached 6%, 2%, and 1%, cover respectively, after three years. Species richness across cleared treatments increased from 30 to 79 species. All forest species were retained. Forest shrubs and trees initially declined from their dominant cover, but rebounded after three years. Tree clearing plus seeding appeared to be a viable management practice for increasing cover of herbaceous sandplain species while causing minimal increases in exotic herbaceous cover. The long-term persistence of sandplain herbs may require periodic disturbances that limit woody regrowth.This work was funded by grants from the A. W. Mellon Foundation and the Massachusetts Environmental Trust to MBL and from the Kohlberg Foundation to TNC

The genetic basis and evolution of red blood cell sickling in deer

Crescent-shaped red blood cells, the hallmark of sickle-cell disease, present a striking departure from the biconcave disc shape normally found in mammals. Characterized by increased mechanical fragility, sickled cells promote haemolytic anaemia and vaso-occlusions and contribute directly to disease in humans. Remarkably, a similar sickle-shaped morphology has been observed in erythrocytes from several deer species, without obvious pathological consequences. The genetic basis of erythrocyte sickling in deer, however, remains unknown. Here, we determine the sequences of human β-globin orthologues in 15 deer species and use protein structural modelling to identify a sickling mechanism distinct from the human disease, coordinated by a derived valine (E22V) that is unique to sickling deer. Evidence for long-term maintenance of a trans-species sickling/non-sickling polymorphism suggests that sickling in deer is adaptive. Our results have implications for understanding the ecological regimes and molecular architectures that have promoted convergent evolution of sickling erythrocytes across vertebrates