"Twisted'' scorpionates: synthesis of a tris(2-pyridonyl)borate (Thp) ligand; lessons in the requirements for successful B(L2D)(3) type ligands

The synthesis of a new charge-neutral zwitterionic tripodal borate ligand based on 2-hydroxypyridine is reported. (Dimethylaminopyridinium)tris(2-pyridonyl)borate, (DMAP)Thp, has been complexed to copper(I) chloride to give a pseudo-C3 symmetric complex. The propensity for this ligand and other flexible scorpionates to exhibit such helical chirality upon complexation is discussed

Reductive dehalogenation of polychlorinated biphenyls by anaerobic microorganisms enriched from Dutch sediments

The dehalogenation of PCBs by anaerobic microbial cultures enriched from Dutch sediments was investigated. One mixed culture originating from estuarine sediments of the River Rhine (the Chemie Harbour), dehalogenated 2,2',3,3',4,4'- and 2,2,',3,3',6,6'-hexachlorobiphenyls (HCB) to yield penta- and tetrachlorobiphenyls, whereas no lower chlorinated biphenyls could be detected. Mainly ortho dehalogenated products were found, but meta and para dehalogenated products were also present. Another anaerobic culture which had been enriched from River Rhine sediments with 2,3,6-trichlorobenzoate as selective substrate reductively dehalogenated hexachlorobiphenyls without a lag-phase to give penta- tetra- and trichlorobiphenyls. No dimono- or non-chlorinated biphenyls could be detected. Sulphidogenic conditions appeared to reduce the dehalogenation rate. A mixture of the two enrichments described above dehalogenated decachlorobiphenyl to give traces of nona-, hepta-, hexa-, penta-, tetra- and trichlorobiphenyls; with a hexachlorobiphenyl, tentively identified as either 2,3,3',4,5,5'- or 2,3,3',4',5,5'-hexachlorobiphenyl, as major product. In contrast to other reports of anaerobic PCB dehalogenation, the presence of sediment was not necessary for dehalogenation and low initial concentrations (+/- 1.5 mu M or 0.7 ppm) were dehalogenated. Copyright (C) 1996 Elsevier Science Lt