In Vitro Studies on the Degradation of Poly(cis-1,4-Isoprene)

Cleavage of the backbone of poly(cis-1,4-isoprene) (IR) in solid rubber material was accomplished by the addition of partially purified latex clearing protein (Lcp1(VH2)) using a 200-mL enzyme reactor. Two strategies for the addition of Lcp1(VH2) were studied revealing that the daily addition of 50 mu g mL(-1) of Lcp1(VH2) for 5 days was clearly a more efficient regime in comparison to a one-time addition of 250 mu g of Lcp1(VH2) at the beginning. Soluble oligo(cis-1,4-isoprene) molecules occurred as degradation products and were identified by ESI-MS and GPC. Oxygenase activity of Lcp1(VH2) with solid IR particles as substrate was shown for the first time by measuring the oxygen consumption in the reaction medium. A strong decrease of the dissolved oxygen concentration was detected at the end of the assay, which indicates an increase in the number of cleavage reactions. The oligo(cis-1,4-isoprene) molecules comprised 1 to 11 isoprene units and exhibited an average molecular weight (M-n) of 885 g mol(-1). Isolation of the oligo(cis-1,4-isoprene) molecules was achieved by using silica gel column chromatography. The relative quantification of the isolated products was performed by HPLC-MS after derivatization with 2,4-dinitrophenilhydrazyne yielding a concentration of total degradation products of 1.62 g L-1. Analysis of the polymer surface in samples incubated for 3 days with Lcp1(VH2) via ATR-FTIR indicated the presence of carbonyl groups, which occurred upon the cleavage reaction. This study presents a cell-free bioprocess as an alternative rubber treatment that can be applied for the partial degradation of the polymer. (C) 2018 American Institute of Chemical Engineers