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1. Dihydroxyterephthalate—A Trojan Horse PET Counit for Facile Chemical Recycling

   https://doi.org/10.1002/adma.202210154  

   Lee, Ting‐Han; Forrester, Michael; Wang, Tung‐ping; Shen, Liyang; Liu, Hengzhou; Dileep, Dhananjay; Kuehl, Baker; Li, Wenzhen; Kraus, George; Cochran, Eric (March 2023, Advanced Materials)

   Here, low-energy poly(ethylene terephthalate) (PET) chemical recycling in water: PET copolymers with diethyl 2,5-dihydroxyterephthalate (DHTE) undergo selective hydrolysis at DHTE sites, autocatalyzed by neighboring group participation, is demonstrated. Liberated oligomeric subchains further hydrolyze until only small molecules remain. Poly(ethylene terephthalate-stat-2,5-dihydroxyterephthalate) copolymers were synthesized via melt polycondensation and then hydrolyzed in 150–200 °C water with 0–1 wt% ZnCl2, or alternatively in simulated sea water. Degradation progress follows pseudo-first order kinetics. With increasing DHTE loading, the rate constant increases monotonically while the thermal activation barrier decreases. The depolymerization products are ethylene glycol, terephthalic acid, 2,5-dihydroxyterephthalic acid, and bis(2-hydroxyethyl) terephthalate dimer, which could be used to regenerate virgin polymer. Composition-optimized copolymers show a decrease of nearly 50% in the Arrhenius activation energy, suggesting a 6-order reduction in depolymerization time under ambient conditions compared to that of PET homopolymer. This study provides new insight to the design of polymers for end-of-life while maintaining key properties like service temperature and mechanical properties. Moreover, this chemical recycling procedure is more environmentally friendly compared to traditional approaches since water is the only needed material, which is green, sustainable, and cheap. 

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2. Neutral Hydrolysis of Post-Consumer Polyethylene Terephthalate Waste in Different Phases

   https://doi.org/10.1021/acssuschemeng.3c00946  

   Pereira, Patrícia; Savage, Phillip E.; Pester, Christian W. (May 2023, ACS Sustainable Chemistry & Engineering)

   Post-consumer polyethylene terephthalate (PET) was hydrolyzed in pure water over a wide range of temperatures (190−400 °C) and pressures (1−35 MPa) to produce terephthalic acid (TPA). Solid or molten PET was subjected to water as a saturated vapor, superheated vapor, saturated liquid, compressed liquid, and supercritical fluid. The highest TPA yields were observed for the hydrolysis of molten PET in saturated liquid water. Isothermal and non-isothermal hydrolysis of PET was also explored. Rapidly heating the reactor contents at about 5−10 °C/s (“fast” hydrolysis) led to high TPA yields, as did isothermal PET hydrolysis, but within 1 min instead of 30 min. Notably, these conditions resulted in the lowest environmental energy impact metric observed to date for uncatalyzed hydrolysis. 

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3. Environmental Consortium Containing Pseudomonas and Bacillus Species Synergistically Degrades Polyethylene Terephthalate Plastic

   https://doi.org/https://doi.org/10.1128/mSphere.01151-20.  

   Cameron Roberts; Sabrina Edwards; Morgan Vague; Rosa León-Zayas; Henry Scheffer; Gayle Chan; Natasja A. Swartz; Jay L. Mellies (September 2022, mSphere)

   Katherine McMahon, University of (Ed.)

   Plastics, such as polyethylene terephthalate (PET) from water bottles, are polluting our oceans, cities, and soils. While a number of Pseudomonas species have been described that degrade aliphatic polyesters, such as polyethylene (PE) and polyurethane (PUR), few from this genus that degrade the semiaromatic poly- mer PET have been reported. In this study, plastic-degrading bacteria were isolated from petroleum-polluted soils and screened for lipase activity that has been associ- ated with PET degradation. Strains and consortia of bacteria were grown in a liquid carbon-free basal medium (LCFBM) with PET as the sole carbon source. We moni- tored several key physical and chemical properties, including bacterial growth and modi!cation of the plastic surface, using scanning electron microscopy (SEM) and attenuated total re"ectance-Fourier transform infrared spectroscopy (ATR-FTIR) spec- troscopy. We detected by-products of hydrolysis of PET using 1H-nuclear magnetic resonance (1H NMR) analysis, consistent with the ATR-FTIR data. The full consortium of !ve strains containing Pseudomonas and Bacillus species grew synergistically in the presence of PET and the cleavage product bis(2-hydroxyethyl) terephthalic acid (BHET) as sole sources of carbon. Secreted enzymes extracted from the full consor- tium were capable of fully converting BHET to the metabolically usable monomers terephthalic acid (TPA) and ethylene glycol. Draft genomes provided evidence for mixed enzymatic capabilities between the strains for metabolic degradation of TPA and ethylene glycol, the building blocks of PET polymers, indicating cooperation and ability to cross-feed in a limited nutrient environment with PET as the sole carbon source. The use of bacterial consortia for the biodegradation of PET may provide a partial solution to widespread planetary plastic accumulation. 

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4. A near-tight lower bound on the density of forward sampling schemes

   https://doi.org/10.1093/bioinformatics/btae736  

   Kille, Bryce; Groot_Koerkamp, Ragnar; McAdams, Drake; Liu, Alan; Treangen, Todd_J; Ponty, ed., Yann (December 2024, Bioinformatics)

   Abstract MotivationSampling k-mers is a ubiquitous task in sequence analysis algorithms. Sampling schemes such as the often-used random minimizer scheme are particularly appealing as they guarantee at least one k-mer is selected out of every w consecutive k-mers. Sampling fewer k-mers often leads to an increase in efficiency of downstream methods. Thus, developing schemes that have low density, i.e. have a small proportion of sampled k-mers, is an active area of research. After over a decade of consistent efforts in both decreasing the density of practical schemes and increasing the lower bound on the best possible density, there is still a large gap between the two. ResultsWe prove a near-tight lower bound on the density of forward sampling schemes, a class of schemes that generalizes minimizer schemes. For small w and k, we observe that our bound is tight when k≡1(mod w). For large w and k, the bound can be approximated by 1w+k⌈w+kw⌉. Importantly, our lower bound implies that existing schemes are much closer to achieving optimal density than previously known. For example, with the current default minimap2 HiFi settings w = 19 and k = 19, we show that the best known scheme for these parameters, the double decycling-set-based minimizer of Pellow et al. is at most 3% denser than optimal, compared to the previous gap of at most 50%. Furthermore, when k≡1(mod w) and the alphabet size σ goes to ∞, we show that mod-minimizers introduced by Groot Koerkamp and Pibiri achieve optimal density matching our lower bound. Availability and implementationMinimizer implementations: github.com/RagnarGrootKoerkamp/minimizers ILP and analysis: github.com/treangenlab/sampling-scheme-analysis. 

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5. Gas flow through atomic-scale apertures

   https://doi.org/10.1126/sciadv.abc7927  

   Thiruraman, Jothi Priyanka; Dar, Sidra Abbas; Masih Das, Paul; Hassani, Nasim; Neek-Amal, Mehdi; Keerthi, Ashok; Drndić, Marija; Radha, Boya (December 2020, Science Advances)

   null (Ed.)

   Gas flows are often analyzed with the theoretical descriptions formulated over a century ago and constantly challenged by the emerging architectures of narrow channels, slits, and apertures. Here, we report atomic-scale defects in two-dimensional (2D) materials as apertures for gas flows at the ultimate quasi-0D atomic limit. We establish that pristine monolayer tungsten disulfide (WS 2 ) membranes act as atomically thin barriers to gas transport. Atomic vacancies from missing tungsten (W) sites are made in freestanding (WS 2 ) monolayers by focused ion beam irradiation and characterized using aberration-corrected transmission electron microscopy. WS 2 monolayers with atomic apertures are mechanically sturdy and showed fast helium flow. We propose a simple yet robust method for confirming the formation of atomic apertures over large areas using gas flows, an essential step for pursuing their prospective applications in various domains including molecular separation, single quantum emitters, sensing and monitoring of gases at ultralow concentrations. 

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