Using neutron spin echo spectroscopy, we have studied the melt dynamics of polyisoprene (PI), saturated polybutadiene (PEB-2), and poly(ethylene-propylene) alternating copolymer (PEP). The experiments on all three polymers show that beyond a characteristic length d and after a crossover time re the relaxational density fluctuations within a given chain are strongly impeded. The presence of an intermediate dynamic length scale in the chain dynamics establishes the microscopic existence of a well-defined entanglement distance confirming thereby one of the essential assumptions of the reptation concept. The microscopically determined lengths agree well with those obtained from the plateau moduli if interpreted in terms of the reptation theory. The detailed line shape of the dynamic structure factor supports the concept of local reptation.

Lipase catalyzed copolymerization of the monomers lactide and glycolide by Pseudomonas cepacia employing a molar ratio of 80L/20G has been studied. The copolymers were characterized by MALDI-ToF-MS, DSC, SEC and NMR. MALDI-ToF-MS has successfully been used not only to determine end groups and chemical composition but even the microstructure of the copolymers. We demonstrated that for this lipase catalyzed copolymerization, the main product of the reaction at 100 degrees C was linear homopolymer of lactide while at 130 degrees C the main product was cyclic random copolymer.

SignificanceUnderstanding the thermodynamic factors responsible for enhanced stability of thermophilic cytochrome P450 enzymes is significant in their development as efficient catalysts for high-temperature monooxygenation reactions. These factors are usually inferred from structural comparison with mesophilic P450s and invoke rigidifying enthalpic interactions as primary thermodynamic determinants for thermostability. Using the thermophilic P450 CYP119 as an example, the present work, however, questions this enthalpy-driven notion of P450 thermostability and provides strong experimental evidence that their thermostability may actually be entropy-driven due to increased flexibility in the folded state relative to mesophilic P450s and that this flexibility is partitioned effectively between functional activity and thermal stability. This represents a major paradigm shift in understanding the basis of thermostability in thermophilic P450s.

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Software developed in house in combination with a recently developed method of MALDI‐TOF MS enable not only the elucidation of individual chain structures of poly(lactide‐co‐glycolide), a polymer used extensively in the medical sector, but a full characterization of this copolymer including even its chemical composition and topology (random, gradient, block (see figure), or alternating).