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The emergence of biodegradable plastics has necessitated the development of standard methods to determine biodegradation rates in various environments. Standardized accelerated marine and soil laboratory biodegradation test systems were developed in which comparative polymer biodegradation rates could be determined by quantifying and plotting the weight loss/surface area of each sample over time and determining the maximum slopes of the curves generated. The results indicate that, in general and depending on the environment, biodegradation rates for unblended polymers were: polyhydroxybutyrate-co-valerate > cellophane > chitosan > polycaprolactone. Results from blends are more difficult to interpret since different biodegradation rates of the component polymers and leaching of plasticizers and additives can impact the data.The assessment of biodegradability of polymer films in natural environments is a difficult problem because of the inherent variations in environmental conditions from one site to another. This is further confounded by the need to balance material performance vs. rates of biodégradation (1,2). Therefore, many laboratory approaches have been developed to simulate natural biodégradation processes, but in a more controlled setting to try and predict natural environmental susceptibility of materials to biodégradation. These methods recently have been summarized and include enzyme assays, plate tests, clearing zones or changes in optical absorbance, biological oxygen demand, changes in carbon isotope ratios, release of radioactive products from radioactively labeled polymers, automated respirometry in biometer flasks, and acceleratated simulated laboratory systems or mesocosms (3-5). Many of these methods are coupled to assessments of changes in weight, molecular weight, mechanical properties, morphological appearance, or chemical functionalities of the This chapter not subject to U.S.

Abstract

A biomimetic approach to the formation of titania (TiO) nanostructures is desirable because of the mild conditions required in this form of production. We have identified a series of serine-lysine peptides as candidates for the biomimetic production of TiO nanostructures. We have assayed these peptides for TiO-precipitating activity upon exposure to titanium bis(ammonium lactato)dihydroxide and have characterized the resulting coprecipitates using scanning electron microscopy. A subset of these assayed peptides efficiently facilitates the production of TiO nanospheres. Here, we investigate the process of TiO nanosphere formation mediated by the S-K peptides KSSKK- and SKSKSKS using one-dimensional and two-dimensional solid-state NMR (ssNMR) on peptide samples with uniformly C-enriched residues. ssNMR is used to assignC chemical shifts (CSs) site-specifically in each free peptide and TiO-embedded peptide, which are used to derive secondary structures in the neat and TiO coprecipitated states. The backbone C CSs are used to assess secondary structural changes undergone during the coprecipitation process. Side-chainC CS changes are analyzed with density functional theory calculations and used to determine side-chain conformational changes that occur upon coprecipitation with TiO and to determine surface orientation of lysine side chains in TiO-peptide composites.

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