Biomedical subjects

Diego Benitez

Publications and source records attributed to Diego Benitez.

3 recordsLinked to original sources

PubMed2005

The isomerization equilibrium between cis and trans chloride ruthenium olefin metathesis catalysts from quantum mechanics calculations.

The cis-trans chloride isomerization of a ruthenium olefin metathesis catalyst is studied using quantum mechanics (B3LYP DFT), including the Poisson-Boltzmann (PBF) continuum approximation. The predicted geometries agree with experiment. The energies in methylene chloride, lead to DeltaG = -0.70 kcal/mol and a cis:trans ratio of 76:24, quite close to the experimental value of DeltaG = -0.78 kcal/mol or c:t 78:22. In contrast, we predict that in benzene c:t = 4:96 in agreement with the experimental observation of only the trans isomer. Our calculated relative activation energies explain the observed difference in initiation rates and suggest that each isomer should be isolable in high ratio by simply changing solvent.

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PubMed2003

Synthesis of cyclic polybutadiene via ring-opening metathesis polymerization: the importance of removing trace linear contaminants.

The synthesis of cyclic polybutadienes using ring-opening metathesis polymerization (ROMP) was accomplished. A cyclic Ru alkylidene catalyst, where a terminal ligand was covalently linked to the Ru alkylidene, was used to polymerize either 1,5-cyclooctadiene (COD) or 1,5,9-trans-cis-trans-cyclododecatriene (CDT). Trace amounts of an acyclic impurity, 4-vinylcyclohexene, found in the COD led to samples which were contaminated with linear polymer. In contrast, CDT, which was free of the impurity, afforded pure cyclic polymer. These results provide a convenient method for discerning samples of pure cyclic polymer from those which contain trace to large amounts of linear polymer. Furthermore, they emphasize the need to use monomers that are free of acyclic impurities when preparing cyclic polymers using ROMP.

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PubMed2002

An "endless" route to cyclic polymers.

A new synthetic route to cyclic polymers has been developed in which the ends of growing polymer chains remain attached to a metal complex throughout the entire polymerization process. The approach eliminates the need for linear polymeric precursors and high dilution, drawbacks of traditional macrocyclization strategies, and it effectively removes the barrier to producing large quantities of pure cyclic material. Ultimately, the strategy offers facile access to a unique macromolecular scaffold that may be used to meet the increasing demand of new applications for commercial polymers. As a demonstration of its potential utility, cyclic polyethylenes were prepared and found to exhibit a variety of physical properties that were distinguishable from their linear analogs.

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