The site of initial metal-carbonyl bond-breaking during ligand-exchange reactions in a series of octahedral metal carbonyls of the type (L2)M(CO)4 (M = Cr, Mo, W; L2 = diphos, phen, dipy) has been determined employing infrared spectroscopy and Fourier transform nuclear magnetic resonance spectroscopy. The results of this study reveal, for all metal carbonyl complexes of the type mentioned above, that loss of CO occurs exclusively at an axial position (cis to the bidentate ligand, I^)• The dynamic nature of the five-coordinate intermediates, such as (diphos)Mo(CO)3, (phen)M(CO)3 (M = Cr, Mo, W), and (dipy)Cr(CO)3, which are generated in solution upon CO dissociation, is reported and discussed. The results of this investigation confirm that these intermediates are fluxional on the time scale of CO-exchange process. A mechanism which describes the site of initial metal-carbonyl bond-breaking and the fluxionality of the five-coordinate intermediate during ligand-exchange reactions in the complexes (L2)M(CO)4 is proposed. A kinetic study of reactions of W(CO)6 with pseudo-halide anions (NCS-, NCO-, CN-) has been initiated. The results indicate that these reactions proceed via a bimolecular path, which involves initial attack of the pseudo-halide anion at a carbonyl carbon of W(CO)6,

This study is concerned with the regulation of Lasparaginase (LA) in the cell-free crude extracts from Lactobacillus plantarum (ATCC8014). A previously reported finding that adenosine triphosphate (ATP) inhibits the action of LA in crude extracts was confirmed. The study was extended to include the mono-, di-, and triphosphates of adenosine, guanosine, cytidine, and uridine. These compounds were also shown to inhibit LA activity. These andother studies revealed that LA appears to be an allosteric type enzyme exhibiting positive homotropism with respect to substrate and heterotropism with respect to the nucleotides tested. The regulation of LA activity by high energy compounds, when coupled with asparagine synthetaseL suggests a relationship between amide synthesis-amide degradation and the energy levels of the cell.