GREEN CHEMISTRY
Heavy-metal analysis of shellfish
Structure of PHA films The poly(hydroxyalkanoic acids) are bacterial polymers with remarkable biodegradability characteristics. N. Koyama and Y. Doi reported on how the structure of polyhydroxyalkanoate films influenced their enzymatic degradation. Several homopolymers and copolymers were studied, and polymer films crystallized from the melt. Crystallinity ranged from 53% to 80% for the homopolymers and from 39% to 71% for the copolymers. The rates of enzymatic degradation decreased with increases in crystallinity. The copolymer films were degraded several times faster than homopolymer films with the same degree of crystallinitv The authors suggested that degradation rettft
is
affected by the degree of crvstallinity and the structure of the polvhydroxyalkanoate film (Macromolecules 1997 30 826-32)
Biodegradable polymers Amino acid linkages can be inserted into the backbone of synthetic polymers to provide sites for cleavage by enzymes widely distributed in the environment. Such polymers could have enhanced biodegradability. S. Jin and colleagues report synthesis of two monomers containing the leucine-tyrosine linkage and two different length spacers: hexamethylenediamine and Jeffamine®-D400. Three polyureas, a polyamide, and a polyesteramide were synthesized from combinations of the monomers The polyureas had higher molecular weights and greater polydispersities than the polyamides The authors conclude that their techniques can be used in synthesizing polymers containing amino acid linkages with a variety of properties and that they have the notential for biodeeradabilitv (J Polvm Sci : Part A:Polvm Chem 1997 95 499-507)
Analysis of the heavy-metal content of shellfish requires a suitable initial digestion procedure to release elements from the tissue matrix. Kostas Daskalakis and co-workers recommend a hot acid digestion mixture of HCI and HN03 in sealed vessels for determining silver concentrations in mussels and oysters. The results obtained using this method agreed well with those from neutron activation analysis. Original analysis of archived samples from the Mussel Watch project involved digestion with HN0 -HCI0 or HN0 alone Reanalysis of these samples usino, HCI-HN0 digestion indicated significantly greater Ag levels because this procedure i
