The activity of an yttrium alkoxide complex supported by a ferrocene-based ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The oxidized complex was characterized by X-ray crystallography and (1)H NMR, XANES, and Mössbauer spectroscopy. Switching in situ between the oxidized and reduced yttrium complexes resulted in a change in the rate of polymerization of L-lactide. Synthesized polymers were analyzed by gel permeation chromatography. Polymerization of trimethylene carbonate was also performed with the reduced and oxidized forms of an indium alkoxide complex. The indium system showed the opposite behavior to that of yttrium, revealing a metal-based dependency on the rate of polymerization.

High-resolution analysis of protein, and DNA conformational changes during DNA polymerization, established relationships between the enzymatic function and conformational dynamics of individual domains for a DNA polymerase.

The activity of cerium alkoxide complexes supported by a Schiff base ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The rate of L-lactide polymerization was modified by switching in situ between the cerium(III) and cerium(IV) species.

Numerous kinetic, structural, and theoretical studies have established that DNA polymerases adjust their domain structures to enclose nucleotides in their active sites and then rearrange critical active site residues and substrates for catalysis, with the latter conformational change acting to kinetically limit the correct nucleotide incorporation rate. Additionally, structural studies have revealed a large conformational change between the apoprotein and the DNA–protein binary state for Y-family DNA polymerases. In previous studies [Xu, C., Maxwell, B. A., Brown, J. A., Zhang, L., and Suo, Z. (2009) PLoS Biol.7, e1000225], a real-time Förster resonance energy transfer (FRET) method was developed to monitor the global conformational transitions of DNA polymerase IV from Sulfolobus solfataricus (Dpo4), a prototype Y-family enzyme, during nucleotide binding and incorporation by measuring changes in distance between locations on the enzyme and the DNA substrate. To elucidate further details of the conformational transitions of Dpo4 during substrate binding and catalysis, in this study, the real-time FRET technique was used to monitor changes in distance between various pairs of locations in the protein itself. In addition to providing new insight into the conformational changes as revealed in previous studies, the results here show that the previously described conformational change between the apo and DNA-bound states of Dpo4 occurs in a mechanistic step distinct from initial formation or dissociation of the binary complex of Dpo4 and DNA.

The dinuclear indium catalyst [(NNO)InCl] 2 (μ-OEt)(μ-Cl), previously reported to be highly active for the living ring-opening polymerization of cyclic esters lactide (LA) and β-butyrolactone (BBL), was used to generate a series of triblock copolymers of poly(lactic acid) (PLA) and poly(hydroxybutyrate) (PHB). Copolymers PLLA−PDLLA−PLLA and PLLA−PDLLA−PDLA, synthesized via sequential monomer addition, showed low molecular weight distributions and excellent correlation between the calculated and experiment molecular weights. Significantly, triblock copolymers of the type PLA−PHB−PLA were also synthesized for the first time through a sequential addition technique. Analysis of polymers after each addition of monomer showed that although only 85% conversion was achieved after addition of BBL, the remaining chain ends were active and addition of more lactide yielded a triblock. Rheological studies of PLLA−PHB−PDLA indicated solid like behavior even well above the temperature at which stereocomplex formation was observed. These elastomeric triblocks exhibited elongations at break 5−10 times greater than those of corresponding PLLA−PDLLA−PLDA triblocks.