Polymers from Plant Oils Linked by Siloxane Bonds for Programmed Depolymerization.

The increased production of plastics is leading to the accumulation of plastic waste and depletion of limited fossil fuel resources. In this context, we report a strategy to create polymers that can undergo controlled depolymerization by linking renewable feedstocks with siloxane bonds. α,ω-Diesters and α,ω-diols containing siloxane bonds were synthesized from an alkenoic ester derived from castor oil and then polymerized with varied monomers, including related biobased monomers. In addition, cyclic monomers derived from this alkenoic ester and hydrosiloxanes were prepared and cyclized to form a 26-membered macrolactone containing a siloxane unit. Sequential ring-opening polymerization of this macrolactone and lactide afforded an ABA triblock copolymer. This set of polymers containing siloxanes underwent programmed depolymerization into monomers in protic solvents or with hexamethyldisiloxane and an acid catalyst. Monomers afforded by the depolymerization of polyesters containing siloxane linkages were repolymerized to demonstrate circularity in select polymers. Evaluation of the environmental stability of these polymers toward enzymatic degradation showed that they undergo enzymatic hydrolysis by a fungal cutinase from Fusarium solani. Evaluation of soil microbial metabolism of monomers selectively labeled with 13C revealed differential metabolism of the main chain and side chain organic groups by soil microbes.

Environmental Biodegradation of Water-Soluble Polymers: Key Considerations and Ways Forward.

Water-soluble polymers (WSPs) have unique properties that are valuable in diverse applications ranging from home and personal care products to agricultural formulations. For applications that result in the release of WSPs into natural environments or engineered systems, such as agricultural soils and wastewater streams, biodegradable as opposed to nonbiodegradable WSPs have the advantage of breaking down and, thereby, eliminating the risk of persistence and accumulation. In this Commentary, we emphasize central steps in WSP biodegradation, discuss how these steps depend on both WSP properties and characteristics of the receiving environment, and highlight critical requirements for testing WSP biodegradability.

Quantification of Synthetic Polyesters from Biodegradable Mulch Films in Soils.

Soil biodegradable mulch films composed of the polyester polybutylene adipate-co-terephthalate (PBAT) are being increasingly used in agriculture. Analytical methods to quantify PBAT in field soils are needed to assess its soil occurrence and fate. Here, we report an analytical method for PBAT in soils that couples Soxhlet extraction or accelerated solvent extraction (ASE) with quantitative protonnuclear magnetic resonance (q-1H NMR) spectroscopy detection. The 1H NMR peak areas of aromatic PBAT protons increased linearly with PBAT concentrations dissolved in deuterated chloroform (CDCl3), demonstrating accurate quantitation of PBAT by q-1H NMR. Spike-recovery experiments involving PBAT addition to model sorbents and soils showed increased PBAT extraction efficiencies into chloroform (CHCl3) with methanol (MeOH) as cosolvent, consistent with MeOH competitively displacing PBAT from H-bond donating sites on mineral surfaces. Systematic variations in solvent composition and temperatures in ASE revealed quantitative PBAT extraction from soil with 90/10 volume % CHCl3/MeOH at 110-120 °C. Both Soxhlet extraction and ASE resulted in the complete recovery of PBAT added to a total of seven agricultural soils covering a range of physicochemical properties, independent of whether PBAT was added to soils dissolved in CHCl3, as film, or as particles. Recovery was also complete for PBAT added to soil in the form of a commercial soil biodegradable mulch film with coextractable polylactic acid (PLA). The presented analytical method enables accurate quantification and biodegradation monitoring of PBAT in agricultural field soils.

Biodegradation of Polymeric Mulch Films in Agricultural Soils: Concepts, Knowledge Gaps, and Future Research Directions.

The agricultural use of conventional, polyethylene-based mulch films leads to the accumulation of remnant film pieces in agricultural soils with negative impacts for soil productivity and ecology. A viable strategy to overcome this accumulation is to replace conventional with biodegradable mulch films composed of polymers designed to be degraded by soil microorganisms. However, understanding polymer biodegradation in soils remains a significant challenge due to its dependence on polymer properties, soil characteristics, and prevailing environmental conditions. This perspective aims to advance our understanding of the three fundamental steps underlying biodegradation of mulch films in agricultural soils: colonization of the polymer film surfaces by soil microorganisms, depolymerization of the polymer films by extracellular microbial hydrolases, and subsequent microbial assimilation and utilization of the hydrolysis products for energy production and biomass formation. The perspective synthesizes the current conceptual understanding of these steps and highlights existing knowledge gaps. The discussion addresses future research and analytical advancements required to overcome the knowledge gaps and to identify the key polymer properties and soil characteristics governing mulch film biodegradation in agricultural soils.

Photochemical Transformation of Poly(butylene adipate- co-terephthalate) and Its Effects on Enzymatic Hydrolyzability.

Biodegradable polyesters are being increasingly used to replace conventional, nondegradable polymers in agricultural applications such as plastic film for mulching. For many of these applications, poly(butylene adipate- co-terephthalate) (PBAT) is a promising biodegradable material. However, PBAT is also susceptible to photochemical transformations. To better understand how photochemistry affects the biodegradability of PBAT, we irradiated blown, nonstabilized, transparent PBAT films and studied their enzymatic hydrolysis, which is considered the rate-limiting step in polyester biodegradation. In parallel, we characterized the irradiated PBAT films by dynamic mechanical thermal analysis. The rate of enzymatic PBAT hydrolysis decreased when the density of light-induced cross-links within PBAT exceeded a certain threshold. Mass-spectrometric analysis of the enzymatic hydrolysis products of irradiated PBAT films provided evidence for radical-based cross-linking of two terephthalate units that resulted in the formation of benzophenone-like molecules. In a proof-of-principle experiment, we demonstrated that the addition of photostabilizers to PBAT films mitigated the negative effect of UV irradiation on the enzymatic hydrolyzability of PBAT. This work advances the understanding of light-induced changes on the enzyme-mediated hydrolysis of aliphatic-aromatic polyesters and will therefore have important implications for the development of biodegradable plastics.

High-Throughput Analysis of Enzymatic Hydrolysis of Biodegradable Polyesters by Monitoring Cohydrolysis of a Polyester-Embedded Fluorogenic Probe.

Biodegradable polyesters have the potential to replace nondegradable, persistent polymers in numerous applications and thereby alleviate plastic accumulation in the environment. Herein, we present an analytical approach to study enzymatic hydrolysis of polyesters, the key step in their overall biodegradation process. The approach is based on embedding fluorescein dilaurate (FDL), a fluorogenic ester substrate, into the polyester matrix and on monitoring the enzymatic cohydrolysis of FDL to fluorescein during enzymatic hydrolysis of the polyester. We validated the approach against established techniques using FDL-containing poly(butylene adipate) films and Fusarium solani cutinase (FsC). Implemented on a microplate reader platform, the FDL-based approach enabled sensitive and high-throughput analysis of the enzymatic hydrolysis of eight aliphatic polyesters by two fungal esterases (FsC and Rhizopus oryzae lipase) at different temperatures. While hydrolysis rates for both enzymes increased with decreasing differences between the polyester melting temperatures and the experimental temperatures, this trend was more pronounced for the lipase than the cutinase. These trends in rates could be ascribed to a combination of temperature-dependent polyester chain flexibility and accessibility of the enzyme active site. The work highlights the capability of the FDL-based approach to be utilized in both screening and mechanistic studies of enzymatic polyester hydrolysis.

Enzymatic Hydrolysis of Polyester Thin Films at the Nanoscale: Effects of Polyester Structure and Enzyme Active-Site Accessibility.

Biodegradable polyesters have a large potential to replace persistent polymers in numerous applications and to thereby reduce the accumulation of plastics in the environment. Ester hydrolysis by extracellular carboxylesterases is considered the rate-limiting step in polyester biodegradation. In this work, we systematically investigated the effects of polyester and carboxylesterase structure on the hydrolysis of nanometer-thin polyester films using a quartz-crystal microbalance with dissipation monitoring. Hydrolyzability increased with increasing polyester-chain flexibility as evidenced from differences in the hydrolysis rates and extents of aliphatic polyesters varying in the length of their dicarboxylic acid unit and of poly(butylene adipate-co-terephthalate) (PBAT) polyesters varying in their terephthalate-to-adipate ratio by Rhizopus oryzae lipase and Fusarium solani cutinase. Nanoscale nonuniformities in the PBAT films affected enzymatic hydrolysis and were likely caused by domains with elevated terephthalate contents that impaired enzymatic hydrolysis. Yet, the cutinase completely hydrolyzed all PBAT films, including films with a terephthalate-to-adipate molar ratio of one, under environmentally relevant conditions (pH 6, 20 °C). A comparative analysis of the hydrolysis of two model polyesters by eight different carboxylesterases revealed increasing hydrolysis with increasing accessibility of the enzyme active site. Therefore, this work highlights the importance of both polyester and carboxylesterase structure to enzymatic polyester hydrolysis.

Competitive Coadsorption Dynamics of Viruses and Dissolved Organic Matter to Positively Charged Sorbent Surfaces.

Adsorption onto solid-water interfaces is a key process governing the fate and transport of waterborne viruses. Although negatively charged viruses are known to extensively adsorb onto positively charged adsorbent surfaces, virus adsorption in such systems in the presence of negatively charged dissolved organic matter (DOM) as coadsorbate remains poorly studied and understood. This work provides a systematic assessment of the adsorption dynamics of negatively charged viruses (i.e., bacteriophages MS2, fr, GA, and Qß) and polystyrene nanospheres onto a positively charged model sorbent surface in the presence of varying DOM concentrations. In all systems studied, DOM competitively suppressed the adsorption of the viruses and nanospheres onto the model surface. Electrostatic repulsion of the highly negatively charged MS2, fr, and the nanospheres impaired their adsorption onto DOM adlayers that formed during the coadsorption process. In contrast, the effect of competition on overall adsorption was attenuated for less-negatively charged GA and Qß because these viruses also adsorbed onto DOM adlayer surfaces. Competition in MS2-DOM coadsorbate systems were accurately described by a random sequential adsorption model that explicitly accounts for the unfolding of adsorbed DOM. Consistent findings for viruses and nanospheres suggest that the coadsorbate effects described herein generally apply to systems containing negatively charged nanoparticles and DOM.

Enzymatic Hydrolysis of Polyester Thin Films: Real-Time Analysis of Film Mass Changes and Dissipation Dynamics.

Cleavage of ester bonds by extracellular microbial hydrolases is considered a key step during the breakdown of biodegradable polyester materials in natural and engineered systems. Here we present a novel analytical approach for simultaneous detection of changes in the masses and rigidities of polyester thin films during enzymatic hydrolysis using a Quartz Crystal Microbalance with Dissipation monitoring (QCM-D). In experiments with poly(butylene succinate) (PBS) and the lipase of Rhizopus oryzae (RoL), we detected complete hydrolysis of PBS thin films at pH 5 and 40 °C that proceeded through soft and water-rich film intermediates. Increasing the temperature from 20 to 40 °C resulted in a larger increase of the enzymatic hydrolysis rate of PBS than of nonpolymeric dibutyl adipate. This finding was ascribed to elevated accessibility of ester bonds to the catalytic site of RoL due to increasing polyester chain mobility. When the pH of the solution was changed from 5 to 7, initial hydrolysis rates were little affected, while a softer film intermediate that lead to incomplete film hydrolysis was formed. Hydrolysis dynamics of PBS, poly(butylene adipate), poly(lactic acid), and poly(ethylene terephthalate) in assays with RoL showed distinct differences that we attribute to differences in the polyester structure.

Biomimetic Approach to Enhance Enzymatic Hydrolysis of the Synthetic Polyester Poly(1,4-butylene adipate): Fusing Binding Modules to Esterases.

Mimicking a concept of nature for the hydrolysis of biopolymers, the Thermobifida cellulosilytica cutinase 1 (Thc_Cut1) was fused to a polymer binding module (PBM) to enhance the hydrolysis of the polyester poly(1,4-butylene adipate) (PBA). Namely, the binding module of a polyhydroxyalkanoate depolymerase from Alcaligenes faecalis (Thc_Cut1_PBM) was attached to the cutinase via two different linker sequences varying in length. In order to investigate the adsorption behavior, catalytically inactive mutants both of Thc_Cut1 and Thc_Cut1_PBM were successfully constructed by site-directed mutagenesis of serine 131 to alanine. Quartz crystal microbalance with dissipation monitoring (QCM-D) analysis revealed that the initial mass increase during enzyme adsorption was larger for the inactive enzymes linked with the PBM as compared to the enzyme without the PBM. The hydrolysis rates of PBA were significantly enhanced when incubated with the active, engineered Thc_Cut1_PBM as compared to the native Thc_Cut1. Thc_Cut1_PBM completely hydrolyzed PBA thin films on QCM-D sensors within approximately 40 min, whereas twice as much time was required for the complete hydrolysis by the native Thc_Cut1.

Biodegradation of poly(butylene succinate) in soil laboratory incubations assessed by stable carbon isotope labelling.

Using biodegradable instead of conventional plastics in agricultural applications promises to help overcome plastic pollution of agricultural soils. However, analytical limitations impede our understanding of plastic biodegradation in soils. Utilizing stable carbon isotope (13C-)labelled poly(butylene succinate) (PBS), a synthetic polyester, we herein present an analytical approach to continuously quantify PBS mineralization to 13CO2 during soil incubations and, thereafter, to determine non-mineralized PBS-derived 13C remaining in the soil. We demonstrate extensive PBS mineralization (65 % of added 13C) and a closed mass balance on PBS-13C over 425 days of incubation. Extraction of residual PBS from soils combined with kinetic modeling of the biodegradation data and results from monomer (i.e., butanediol and succinate) mineralization experiments suggest that PBS hydrolytic breakdown controlled the overall PBS biodegradation rate. Beyond PBS biodegradation in soil, the presented methodology is broadly applicable to investigate biodegradation of other biodegradable polymers in various receiving environments.

Biodegradation of synthetic polymers in soils: Tracking carbon into CO2 and microbial biomass.

Plastic materials are widely used in agricultural applications to achieve food security for the growing world population. The use of biodegradable instead of nonbiodegradable polymers in single-use agricultural applications, including plastic mulching, promises to reduce plastic accumulation in the environment. We present a novel approach that allows tracking of carbon from biodegradable polymers into CO2 and microbial biomass. The approach is based on 13C-labeled polymers and on isotope-specific analytical methods, including nanoscale secondary ion mass spectrometry (NanoSIMS). Our results unequivocally demonstrate the biodegradability of poly(butylene adipate-co-terephthalate) (PBAT), an important polyester used in agriculture, in soil. Carbon from each monomer unit of PBAT was used by soil microorganisms, including filamentous fungi, to gain energy and to form biomass. This work advances both our conceptual understanding of polymer biodegradation and the methodological capabilities to assess this process in natural and engineered environments.

Polyol Structure Influences Enzymatic Hydrolysis of Bio-Based 2,5-Furandicarboxylic Acid (FDCA) Polyesters.

Polyesters of 2,5-furandicarboxylic acid (FDCA) have gained attention as they can be regarded as the bio-based alternatives to the petroleum-based polyesters of terephthalic acid. However, only little is known about the biodegradation and enzymatic hydrolysis of FDCA-based polyesters. This work aims to investigate the influence of different polyols on enzymatic hydrolysis of FDCA-based polyesters. A series of polyesters containing various polyols are synthesized and analyzed regarding susceptibility to enzymatic hydrolysis by cutinase 1 from Thermobifida cellulosilytica (Thc_Cut1). FDCA-based polyesters' number average molecular weight (Mn ) ranged from 9360-35 800 g mol-1 according to gel permeation chromatography (GPC) analysis. Differential scanning calorimetry (DSC) analyses show decreasing glass transition temperature (Tg ) with increasing diol chain length. Crystallinity of all polyesters is below 1% except for polyesters containing 1,6-hexanediol, 1,8-octanediol, and 1,12-dodecanediol for which calculated crystallinities are 27, 37, and 30%, respectively. Thc_Cut1 hydrolyzes all tested polyesters with preference for polyesters containing 1,5-pentanediol and 1,9-nonanediol (57.7 ± 7.5 and 52.8 ± 4.0% released FDCA). Enzyme activity increases when the linear diol 1,3-propanediol is replaced by the branched analog 1,2-propanediol or ethoxy units are introduced into the polyester chain. The results will contribute to expand the knowledge of microbial biodegradation of FDCA-based polyesters.

Conditioning-annealing studies of natural organic matter solids linking irreversible sorption to irreversible structural expansion.

The assumption of reversibility underpins the sorption term in current models dealing with the fate and impact of organic compounds in the environment, yet experimentally sorption of organic compounds in soils and sediments often shows "irreversible" behaviors such as hysteresis and the conditioning effect (enhanced repeat sorption). The objective of this study was to test whether a glassy polymer irreversibility model applies to natural organic matter (NOM) solids. Irreversible sorption in polymers is believed to be caused by irreversible expansion and creation of internal micropores by penetrating molecules, leading to enhanced affinity during desorption or subsequent resorption. Using chlorobenzene as a conditioning agent and polychlorinated benzenes as test compounds in a second sorption step, we observed conditioning effects for a peat soil, a soil humic acid, and a model glassy polymer, poly- (vinyl chloride), but not for a model rubbery polymer, poly- (ethylene). The conditioning effect for the two natural solids, probed bythe enhancement in the sorption distribution coefficient of 1,2,4-trichlorobenzene, relaxed upon sample annealing between 45 and 91 degrees C in a manner similar to the relaxation of free volume and enthalpy of glassy polymers. Relaxation of the conditioning effect in the NOM solids depended on annealing temperature and, at a given temperature, followed a double additive exponential rate law with a nonzero constant term descriptive of the final state that depends inversely on temperature. At environmentally relevant temperatures, the conditioning effect may "never" completely relax. The results provide compelling evidence for the glassy, nonequilibrium nature of natural organic matter solids and for irreversible structural expansion as a cause of irreversible sorption.

The prevalence of hereditary neuropathy with liability to pressure palsies in patients with multiple surgically treated entrapment neuropathies.

PURPOSE: Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal-dominant peripheral neuropathy that results from deletion of a 1.5-Megabase pair (Mb) segment of the short arm (p) of chromosome 17. Hereditary neuropathy with liability to pressure palsies increases susceptibility of peripheral nerves to pressure and trauma and can be associated with symptoms at multiple anatomic entrapment sites. Many patients present with multiple upper-extremity entrapment neuropathies and the etiology is uncertain. We hypothesized that some of these patients have an underlying hereditary neuropathy. The purpose of this study was to determine the prevalence of HNPP in patients with multiple surgically treated upper-extremity entrapment neuropathies. METHODS: The inclusion criterion for the study was history of more than 1 carpal tunnel release and/or ulnar nerve transposition. The exclusion criteria were history of diabetes or history of Charcot-Marie-Tooth neuropathy. Fifty-nine patients were in the study group. Two patients known to have the 17p11.2 deletion were used as controls. Genomic DNA was extracted from peripheral blood. Each sample was genotyped using polymerase chain reaction (PCR) amplification with short tandem repeat polymorphism markers within the 1.5-Mb region of 17p deleted in HNPP. Markers were scored as homozygous or heterozygous after resolution by polyacrylamide gel electrophoresis and silver staining. RESULTS: The 2 control patients were homozygous for 11 markers. None of the 59 study patients were homozygous for all markers tested in the deleted region. No study patient had the 17p deletion diagnostic for HNPP. Based on the sample size of 59 patients the 95% confidence interval for the prevalence of the 17p11.2 deletion in this population is 0% to 5%. CONCLUSIONS: We found no evidence for an association between HNPP and patients who have multiple surgical releases for upper-extremity entrapment neuropathies.