Properties and reactivity of chlorovinylcobalamin and vinylcobalamin and their implications for vitamin B12-catalyzed reductive dechlorination of chlorinated alkenes.

Vitamin B12-catalyzed reductive dechlorination of perchloroethylene (PCE) and trichloroethylene (TCE) is a potential strategy for cleanup of polluted environments. Presented are crystal structures of vinylcobalamin 2 and cis-chlorovinylcobalamin 1. They show a strong resistance toward photolysis.

Characterization of chlorovinylcobalamin, a putative intermediate in reductive degradation of chlorinated ethylenes.

The first X-ray structure of a vinylcobalamin is reported. Chlorovinylcobalamin is formed in the reaction of cob(I)alamin with chloroacetylene. Subsequently, cob(I)alamin catalyzes the reduction of chlorovinylcobalamin to vinylcobalamin in the presence of excess titanium(III)citrate.

Analysis of federal support for postgraduate general dentistry.

We compared the funding granted by the federal government between 1985 and 1997 to stimulate the growth of AEGD and GPR programs across HRSA regions, states, and populations. Information regarding the number, size, and location of programs available during the time period of 1985 to 1997 was collected. During this period, although the number of programs remained constant, the composition of the programs changed, with AEGD programs increasing by 113 percent and GPR programs decreasing by 13 percent.

Views of practicing dentists regarding a mandatory fifth year of training.

As part of a U.S. Health Resources and Services Administration-funded evaluation of the impact of federal funding on postgraduate general dentistry programs, a random sample of 6,725 dentists graduating in 1989, 1993, and 1997 were surveyed regarding practice patterns, advanced training, populations served, services provided, and their position on a mandatory fifth year of training.

Dichloroacetylene is not the precursor to dichlorinated vinylcobaloxime and vinylcobalamin in cobalt catalyzed dechlorination of perchloro- and trichloroethylene.

Vitamin B(12) catalyzes the reductive dechlorination of perchloroethylene (PCE), a process for which vinylcobalamins have been proposed as intermediates. Previous model studies have shown that PCE and trichloroethlylene (TCE) react with cob(I)aloxime to form cis-1,2-dichlorovinylcobaloxime (1). This compound could be formed by nucleophilic vinylic substitution of cob(I)aloxime on TCE or its syn-addition to dichloroacetylene.

Mechanistic investigation of a novel vitamin B(12)-catalyzed carbon [bond] carbon bond forming reaction, the reductive dimerization of arylalkenes.

In the presence of catalytic vitamin B(12) and a reducing agent such as Ti(III)citrate or Zn, arylalkenes are dimerized with unusual regioselectivity forming a carbon [bond] carbon bond between the benzylic carbons of each coupling partner. Dimerization products were obtained in good to excellent yields for mono- and 1,1-disubstituted alkenes. Dienes containing one aryl alkene underwent intramolecular cyclization in good yields.

Synthesis and characterization of chlorinated alkenylcobaloximes to probe the mechanism of vitamin B(12)-catalyzed dechlorination of priority pollutants.

Vitamin B(12) catalyzes the reductive dechlorination of several ubiquitous pollutants such as perchloroethylene (PCE) and trichloroethylene (TCE). Several mechanisms have been proposed for these transformations, some of which involve the intermediacy of chlorinated vinylcobalamins. To evaluate the currently unknown chemical and physical properties of such species, various chlorinated vinylcobaloxime complexes [cobaloxime = bis(dimethylglyoximato)(pyridine)cobalt(III)] were prepared and characterized.