Computational Characterization of Nylon 4, a Biobased and Biodegradable Polyamide Superior to Nylon 6

Marine bacteria have multiple polyamide 4-degrading enzymes

Polyamide 4 (PA4) is expected to solve the issue of marine plastic pollution due to its excellent mechanical properties and biodegradability. In this study, to reveal the mechanism of PA4 biodegradation in the marine environment, we isolated 5 strains of PA4-degrading bacteria belonging to Aliiglaciecola, Dasania, and Pseudophaeobacter from a marine environment. The isolated 5 strains are novel PA4-degrading bacteria that are phylogenetically distinct from those isolated in previous studies. In addition, we compared the PA4-degrading activities and structures of the PA4-degrading enzymes secreted by the 5 strains and PA4-degrading strains isolated in our previous study. The PA4-degrading activity in the supernatant of the cultivation solutions differed among the strains. Native-PAGE and zymography using a polyacrylamide gel containing a PA4 emulsion demonstrated that PA4-degrading enzymes are classified into no less than three types of structures. These results suggested that marine PA4-degrading bacteria have multiple PA4-degrading enzymes. Our findings will contribute to a better understanding of the microbial degradation of PA4 in the marine environment.

Enhancing Polymer Sustainability: Eco-Conscious Strategies

Polymer sustainability is a pressing concern in today's world driven by the increasing demand for environmentally friendly materials. This review paper provides a comprehensive overview of eco-friendly approaches towards enhancing the sustainability of polymers. It synthesized recent research and developments in various areas such as green polymer synthesis methods, biodegradable polymers, recycling technologies, and emerging sustainable alternatives. The environmental impact of traditional polymer production processes and the importance of adopting greener alternatives were critically examined. The review delved into the advancements in polymer recycling technologies like mechanical, chemical, and biological processes aimed at minimizing plastic waste and promoting a circular economy. The innovative approaches such as upcycling, hybrid methods etc., which offer promising solutions for addressing plastic pollution and achieving long-term sustainability goals were also analyzed. Finally, the paper discussed the challenges and future prospects of eco-friendly approaches for polymer sustainability, emphasizing the need for researchers and concerted efforts from scientists across industries and academia to drive meaningful change towards a more sustainable future.

Photodegradation of biodegradable plastics in aquatic environments: Current understanding and challenges

Direct and indirect photolysis are important abiotic processes in aquatic environments through which plastics can be transformed physically and chemically. Transport of biodegradable plastics in water is influenced by vertical mixing and turbulent flow, which make biodegradable plastics remain susceptible to sunlight and photolysis despite their high density. In general, biodegradable plastics are composed of ester containing polymers (e.g., poly(butylene succinate), polyhydroxyalkanoate, and polylactic acid), whereas non-biodegradable plastics are composed of long chains of saturated aliphatic hydrocarbons in their backbones (e.g., polyethylene, polypropylene, and polystyrene). Based on the reviewed knowledge and discussion, we may hypothesize that 1) direct photolysis is more pronounced for non-biodegradation than for biodegradable plastics, 2) smaller plastics such as micro/nano-plastics are more prone to photodegradation and photo-transformation by direct and indirect photolysis, 3) the production rate of reactive oxygen species (ROS) on the surface of biodegradable plastics is higher than that of non-biodegradable plastics, 4) the photodegradation of biodegradable plastics may be promoted by ROS produced from biodegradable plastics themselves, and 5) the subsequent reactions of ROS are more active on biodegradable plastics than non-biodegradable plastics. Moreover, micro/nanoplastics derived from biodegradable plastics serve as more effective carriers of organic pollutants than those from non-biodegradable plastics and thus biodegradable plastics may not necessarily be more ecofriendly than non-biodegradable plastics. However, biodegradable plastics have been largely unexplored from the viewpoint of direct or indirect photolysis. Roles of reactive oxygen species originating from biodegradable plastics should be further explored for comprehensively understanding the photodegradation of biodegradable plastics.

Synergistic Niobium Doped Two-Dimensional Zirconium Diselenide: An Efficient Electrocatalyst for O2 Reduction Reaction

The development of high-activity and low-price cathodic catalysts to facilitate the electrochemically sluggish O2 reduction reaction (ORR) is very important to achieve the commercial application of fuel cells. Here, we have investigated the electrocatalytic activity of the two-dimensional single-layer Nb-doped zirconium diselenide (2D Nb-ZrSe2) toward ORR by employing the dispersion corrected density functional theory (DFT-D) method. Through our study, we computed structural properties, electronic properties, and energetics of the 2D Nb-ZrSe2 and ORR intermediates to analyze the electrocatalytic performance of 2D Nb-ZrSe2. The electronic property calculations depict that the 2D monolayer ZrSe2 has a large band gap of 1.48 eV, which is not favorable for the ORR mechanism. After the doping of Nb, the electronic band gap vanishes, and 2D Nb-ZrSe2 acts as a conductor. We studied both the dissociative and the associative pathways through which the ORR can proceed to reduce the oxygen molecule (O2). Our results show that the more favorable path for O2 reduction on the surface of the 2D Nb-ZrSe2 is the 4e- associative path. The detailed ORR mechanisms (both associated and dissociative) have been explored by computing the changes in Gibbs free energy (ΔG). All of the ORR reaction intermediate steps are thermodynamically stable and energetically favorable. The free energy profile for the associative path shows the downhill behavior of the free energy vs the reaction steps, suggesting that all ORR intermediate structures are catalytically active for the 4e- associative path and a high 4e- reduction pathway selectivity. Therefore, 2D Nb-ZrSe2 is a promising catalyst for the ORR, which can be used as an alternative ORR catalyst compared to expensive platinum (Pt).

Designing poly(gamma-aminobutyric acid)-based nanoparticles for the treatment of major depressive disorders

Major depressive disorder (MDD) is a worldwide concern owing to its negative impact on the quality of life. Gamma-aminobutyric acid (GABA), an essential neurotransmitter in the brain, is important for regulating the enteric nervous system and gut-brain dual communication (gut-brain axis), thus providing gastrointestinal GABA and GABA-related pathways with possible targets for MDD treatment. However, the use of GABA for this disease remains limited due to its poor pharmacokinetic properties, including the low permeability through the blood-brain barrier, and the rapid clearance from the gastrointestinal tract. Since poly(amino acid)s are advantageous for improving the beneficial bioactivities of conventional amino acids, poly(gamma-aminobutyric acid) (poly(GABA)) is a potential candidate for MDD therapy. Nevertheless, the non-water-soluble and non-dispersible characteristics of poly(GABA) render difficulty in administering its conventional forms in vitro/in vivo, thereby hindering its therapeutic applications. Therefore, this study proposes a new design for poly(GABA) in nanoparticle form, which is composed of the amphiphilic diblock copolymers of poly(GABA) and poly(ethylene glycol), providing a suitable formulation for medication applications. Herein, we report on a new orally deliverable poly(GABA)-based nanoparticles (NanoGABA) in aqueous media and their efficacy on mouse depression models. NanoGABA treatment efficiently attenuated depression-like symptoms as evidenced by behavioral tests (forced swimming tests and tail suspension tests) and stress biomarkers (corticosterone). These findings suggest that the newly designed poly(GABA)-based nanoparticles are a promising candidate for the treatment of depression. STATEMENT OF SIGNIFICANCE: This research is the first to report the preparation of poly(GABA)-based nanoparticles in aqueous conditions with beneficial physical properties to open the gate for medical and pharmaceutical applications of poly (GABA). It is also a pioneer in using poly(GABA)-based materials for major depressive disorder therapeutics in vivo. Oral administration of NanoGABA attenuates depressive-like symptoms by targeting the enteric nervous system possibly through modulation of the gut-brain axis pathways with negligible toxicity, suggesting that NanoGABA is a promising therapeutic agent for major depressive disorders.

Efficient cell factories for the production of N-methylated amino acids and for methanol-based amino acid production

The growing world needs commodity amino acids such as L-glutamate and L-lysine for use as food and feed, and specialty amino acids for dedicated applications. To meet the supply a paradigm shift regarding their production is required. On the one hand, the use of sustainable and cheap raw materials is necessary to sustain low production cost and decrease detrimental effects of sugar-based feedstock on soil health and food security caused by competing uses of crops in the feed and food industries. On the other hand, the biotechnological methods to produce functionalized amino acids need to be developed further, and titres enhanced to become competitive with chemical synthesis methods. In the current review, we present successful strain mutagenesis and rational metabolic engineering examples leading to the construction of recombinant bacterial strains for the production of amino acids such as L-glutamate, L-lysine, L-threonine and their derivatives from methanol as sole carbon source. In addition, the fermentative routes for bioproduction of N-methylated amino acids are highlighted, with focus on three strategies: partial transfer of methylamine catabolism, S-adenosyl-L-methionine dependent alkylation and reductive methylamination of 2-oxoacids.

Water-Induced Crystal Transition and Accelerated Relaxation Process of Polyamide 4 Chains in Microfibers

Microplastics have recently been identified as one of the major contributors to environmental pollution. To design and control the biodegradability of polymer materials, it is crucial to obtain a better understanding of the aggregation states and thermal molecular motion of polymer chains in aqueous environments. Here, we focus on melt-spun microfibers of a promising biodegradable plastic, polyamide 4 (PA4), with a relatively greater number density of hydrolyzable amide groups, which is regarded as an alternative to polyamide 6. Aggregation states and thermal molecular motion of PA4 microfibers without/with a post-heating drawing treatment under dry and wet conditions were examined by attenuated total reflectance-Fourier transform infrared spectroscopy and wide-angle X-ray diffraction analysis in conjunction with dynamic mechanical analysis. Sorbed water molecules in the microfibers induced the crystal transition from a meta-stable γ-form to a thermodynamically stable α-form via activation of the molecular motion of PA4 chains. Also, the post-drawing treatment caused a partial structural change of PA4 chains, from an amorphous phase to a crystalline phase. These findings should be useful for designing PA4-based structural materials applicable for use in marine environments.

Environmental contamination by microplastics originating from textiles: Emission, transport, fate and toxicity

Microplastic (MP) pollution has become a global concern in terms of its environmental abundance and potential detrimental effects. Fibrous microplastics (FMPs) released from synthetic textiles are believed to contribute significantly to environmental MP pollution. This review provides an overview of current knowledge relating to the environmental impact of FMPs through a summary and discussion of (1) the concentrations in different environmental compartments including water, soil and air, (2) emission from wastewater treatment plants: via effluent discharges to waters and via sludge to land, (3) environmental transport and fate, and (4) toxicity and associated effects. How the properties of FMPs influence these aspects is discussed and their behaviour is compared to MPs of other shapes. We have summarised the Environmental Concentrations and derived Predicted No-Effect Concentrations for a preliminary risk assessment of FMPs by extrapolating the risk quotient for each respective environmental compartment. The uncertainties surrounding current assessment methods are discussed. In particular we address the need to improve determination of exposure levels and to better characterise the effects of FMPs. We conclude by presenting topics for future studies to address, which will improve our still limited understanding of the interactions between FMPs and the environment.

Conformational characteristics and conformation-dependent properties of poly(ε-caprolactone)

Structures and properties of isolated and crystalline poly(ε-caprolactone) (PCL) chains have been investigated. Ab initio molecular orbital (MO) calculations were conducted for methyl 6-acetoxyhexanoate (MAH), a model compound of PCL, to yield Gibbs free energies of all its existent conformers. Bond conformations of its seven bonds corresponding to the repeating unit of PCL were calculated therefrom; two C-C bonds close to the ester group show gauche preferences owing to intramolecular C-H⋯O attractions, and the other five prefer trans forms. ¹H and ¹³C NMR vicinal coupling constants of ¹³C-labeled MAH yielded bond conformations consistent with the MO calculations. The rotational isomeric state (RIS) calculations on PCL led to the characteristic ratios (4.1-4.5) that agree with those estimated experimentally from the Stockmayer-Fixman plots. Periodic density functional theory calculations on PCL crystals yielded the optimum structures and Young's moduli in the a-, b-, and c (fiber)-axis directions. The fiber-axis modulus (252 GPa) falls short of that (333 GPa) of polyethylene but exceeds that (182 GPa) of poly(ethylene terephthalate), whereas the three-dimensionally averaged Young's modulus (10.7 GPa) of PCL is the smallest of those of representative polymers investigated so far. The enzymatic selectivity of biodegradable polyesters is discussed herein in terms of their conformational characteristics and surface structures of enzymes.

An Integrated Cofactor/Co-Product Recycling Cascade for the Biosynthesis of Nylon Monomers from Cycloalkylamines

We report a highly atom-efficient integrated cofactor/co-product recycling cascade employing cycloalkylamines as multifaceted starting materials for the synthesis of nylon building blocks. Reactions using E. coli whole cells as well as purified enzymes produced excellent conversions ranging from >80 and 95 % into desired ω-amino acids, respectively with varying substrate concentrations. The applicability of this tandem biocatalytic cascade was demonstrated to produce the corresponding lactams by employing engineered biocatalysts. For instance, ϵ-caprolactam, a valuable polymer building block was synthesized with 75 % conversion from 10 mM cyclohexylamine by employing whole-cell biocatalysts. This cascade could be an alternative for bio-based production of ω-amino acids and corresponding lactam compounds.

Molecular Design of Aromatic Polythionoesters

As an example of molecular design of new polymers, structures and properties of poly(ethylene thionoterephthalate) (PET[S₂]) and the related polymers have been predicted from calculations of ab initio molecular orbital (MO) theory, rotational isomeric state (RIS) scheme, and periodic density functional theory (DFT). The MO calculations were confirmed by NMR experiments and introduced to the RIS scheme for PET[S₂] to yield its configurational properties, which are compared herein with those of analogous polyester, polythioester, and polydithioester. Configurational properties of randomly thiono-substituted poly(ethylene terephthalate) (PET), PET[S _z O_1-z ], were also evaluated as a function of sulfidity (z). On the assumption that the crystal of PET[S₂] can be expressed as an isomorphic replacement of the PET crystal, the crystal structure was optimized by a periodic DFT simulation and its Young's moduli in the a-, b-, and c-axis directions were, respectively, evaluated to be E_a = 0.94(7.20) GPa, E _b = 19.58(22.26) GPa, and E _c = 142.1(182.4) GPa, where the parenthetic values are those of the PET crystal. There is a possibility that properties of PET[S _z O_1-z ] will be controlled between those of PET and PET[S₂] by adjusting the sulfidity. The potential practical applications of the polythionoesters are also discussed herein. By purely theoretical computations, the structures and properties of the not-yet synthesized polymers were predicted quantitatively; that is, the theoretical molecular design of new polymers has been achieved.