Comparison of two diphenyl polyenes as acid‐sensitive additives during the biodegradation of a thermoset polyester polyurethane coating

Abstract

Aims: Biochemical hydrolysis and chemical catalysis are involved in the successful biodegradation of polymers. In order to evaluate the potential separation between biochemical and chemical catalysis during the biodegradation process, we report the use of two diphenylpolyenes (DPPs), all trans-1,4-diphenylbutadiene (DPB) and all trans-1,6-diphenylhexatriene (DPH), as potential acid-sensitive indicators in polymers. Methods and Results: 1,4-Diphenylbutadiene and DPH (0.1% w/w) were melt-cast successfully with poly(ethylene succinate) hexamethylene (PES-HM) polyurethane (thermoset polyester polyurethane) coatings above 80℃. When these two DPP/ PES-HM coatings were exposed to a concentrated supernatant with significant esterase activity resulting from the growth of a recently isolated and identified strain of Tremellomycetes yeast (Naganishia albida 5307AI), the DPB coatings exhibited a measurable and reproducible localized decrease in the blue fluorescence emission in regions below where hydrolytic biodegradation was initiated in contrast with DPH blended coatings. The fluorescence changes observed in the biodegraded DPB coating were similar to exposing them to concentrated acids and not bases. Conclusions:Our experiments resulted in (1) a method to blend DPP additives into thermoset coatings, (2) the first report of the biodegradation of polyester polyurethane coating by N. albida, and (3) demonstration that hydrolytic supernatants from this strain generate acidic region within degrading polyester coatings using DPB as the indicator.Significance and Impact of the Study: Our experiments confirm that N. albida is an active polyester degrader and that DPB is a promising acid sensitive polymer coating additive.

Calculation of the relative basicity of three α,ω‐diphenylpolyenes with trifluoroacetic acid

“…To date, the basicity of DPB and DPH have only been reported in the gas phase using semi‐empirical ZINDO level calculations with published thermodynamic values for the gas phase proton. [ 7 ] In direct contradiction to the calculated basicities in the current work, these previous gas phase‐only calculations suggested that DPB is a stronger base than DPH. There are two potential reasons why our earlier ZINDO results were flawed.…”

“…DPPs are polarizable over the length of the conjugated system (like numerous other pure polyenes) and the polarizability results in large non‐linear optical properties with potential applications in optical sensors or photorefractive crystals [ 5 ] or as imaging agents in the case of α,ω‐di(4‐pyridyl)polyenes. [ 6 ] In our recent study, to characterize the effectiveness of DPPs as acid sensitive probes in biodegrading polymer coatings, [ 7 ] trans ‐1,4‐diphenyl‐1,3‐butadiene (DPB) and all trans 1,6‐diphenyl‐1,3,5‐hexatriene (DPH) were chosen because of their commercial availability, their ease of use in molten polymers (DPB and DPH are low melting solids), and because DPPs are significantly more stable against oxidative degradation than retinoids and carotenoids. This makes DPPs interesting polymer additives for biodegradation research since they can be blended into non‐polar polymer formulations, but the DPPs are not bioavailable to the microorganism degrading the polymers because when released they are not soluble in water.…”

Current advances in polyurethane biodegradation

“…In 2021, Biffinger and co‐workers first used a Tremellomycetes yeast, Naganishia albida 5307AI, to degrade thermoset PS‐PU supplemented with diphenylpolyenes. The crude protein supernatants exhibited esterase activities of 420 ± 14 and 380 ± 21 U mL −1 toward acetate and butyrate p ‐nitrophenyl ester, respectively 43 …”

“…The crude protein supernatants exhibited esterase activities of 420 ± 14 and 380 ± 21 U mL −1 toward acetate and butyrate p-nitrophenyl ester, respectively. 43 There are also many PS-PU-degrading bacteria, of which Pseudomonas species are the most promising resources. 44 In 2016, Shah et al investigated the degradation efficiency of bacterial co-culture against PS-PU and found that Bacillus subtilis MZA-75 and Pseudomonas aeruginosa MZA-85 strains could promote PS-PU degradation, probably by producing large amounts of esterase.…”

Draft Genome Sequence of the Nonmotile Tremellomycetes Yeast Naganishia albida, Isolated from Aircraft

“…Here, we describe the draft genome sequence of the yeast Naganishia albida strain 5307AI, which was isolated from the polymer-coated surface of an aircraft. This microorganism was sequenced to understand the taxonomy and enzymatic functions underlying biodegradation and bioremediation on polymer coatings ( 1 ).…”