Chain Degradation Research Articles

Molecular Dynamics Study of the Photodegradation of Polymeric Chains

The development of reusable polymeric materials inspires an attempt to combine renewable biomass with upcycling to form a biorenewable closed system. It has been reported that 2,5-furandicarboxylic acid (FDCA) can be recovered for recycling when incorporated as monomers into photodegradable polymeric systems. Here, we conduct density functional theory (DFT) studies with periodic boundary conditions on microscopic structures involved in the photodegradation of polymeric chains incorporating FDCA and 2-nitro-1,3-benzenedimethanol. The photodegradation process of polymeric chains is studied using time-dependent excited-state molecular dynamics (TDESMD) in vacuum and aqueous environments. Changes in the photophysical properties for reaction intermediates are characterized by ground-state observables. The distribution of reaction intermediates and products is obtained from TDESMD trajectories using cheminformatics techniques. Results show that a higher degree of polymeric chain degradation is achieved in the vacuum environment. Additionally, one finds that the FDCA molecule is recoverable in the aqueous environment, in qualitative agreement with experimental findings.

Texture and rehydration properties of texturised soy protein: analysis based on soybean 7S and 11S proteins

SummarySoy protein, one of the most commonly used raw materials for texturised vegetable protein, has an important influence on texturised soy protein (TSP) with its 7S and 11S fractions. In this study, soy 7S and 11S proteins were extracted from soybean isolate and added back to the raw material to prepare TSP and analyse the effect of both on the physical properties of TSP. The results showed that the addition of 5% soy 7s or 11s protein increased the water‐holding capacity (up to 9.04%) and rehydration rate (up to 25.71%) of TSP. Compared with adding soy 11s protein, adding soy 7s protein has a faster rehydration rate at a lower temperature (30 and 45 °C). After extrusion, the content of free sulphhydryl groups, total sulphhydryl groups, and disulphide bonds was significantly reduced (P < 0.05). The extrusion treatment caused degradation of the protein chains, and the proteins mainly formed insoluble polymers. Electrophoretic analysis revealed that the sodium dodecyl‐sulphate (SDS) reducing the extractable rate of the precipitate after SDS non‐reduction extraction of the TSP added with 5% soy 7S and 11S proteins were lower than that of the control. The proportion of different soybean protein components in TSP could change its texture, water‐holding, and rehydration characteristics of it, which provides a new method for the characteristics design of TSP.

The Effects of Zinc-Containing Mouthwashes on the Force Degradation of Orthodontic Elastomeric Chains: An In Vitro Study.

Objective This study aimed to evaluate and compare the force degradation of two types of elastomeric chains following different periods of immersion in zinc-containing mouthwashes. Materials and Methods Four hundred and forty pieces of Elasto-Force and Super Elasto-Force elastomeric chains were divided into two control and eight experimental groups. The pieces were stretched to 25 mm on pins mounted on an acrylic block and stored in distilled water at 37°C. The experimental groups were immersed in four different types of mouthwash for one minute twice a day throughout the test period. Ten continuous thermocycles per day between cold and hot water baths (5–55°C) were carried out. Forces were measured at six-time intervals (initial, 24 hours, 1, 3, 6, and 8 weeks). The mean force was calculated and compared among different elastomeric chains, mouthwashes, and times using the t-test and one-way ANOVA test followed by Tukey's HSD test. The level of significance was set at 0.05. Results Both types of elastomeric chains had significant force degradation over time (74–79% at 8 weeks). The Super Elasto-Force generated a higher force level than the Elasto-Force elastomeric chain at all time points. SmartMouth Clinical DDS mouthwash had a significantly lower effect on force degradation than other mouthwashes with no significant difference compared to control groups. Conclusions Depending on these results: there is no clinically significant difference between both types of elastomeric chains, although Super Elasto-Force delivered a higher force level. The pH of the mouthwashes could play a role in force degradation over time, rather than other ingredients including zinc. The SmartMouth mouthwash had the minimum effect on force degradation of elastomeric chains, followed by Halita, Listerine Total Care Zero, and Breath Rx, respectively.

Using a photodriven radical-mediated [3 + 2] cyclization reaction to prepare embolic microspheres from sucrose allyl ether without degradative chain transfer

Preparing polymers from allyl monomers without being hindered by degradative chain transfer (DCT) remains a challenge. Herein, we report the synthesis and characterization of embolic microspheres based on allyl monomers for transcatheter arterial embolization using a photodriven radical-mediated [3 + 2] cyclization reaction (PRMC) without metal catalysis. The mechanism of PRMC was validated by thermal and spectral experiments, indicating that PRMC overcomes the restrictions of DCT and makes it possible to synthesize a variety of well-defined polymers from inert allyl monomers. The embolization microspheres based on poly(sucrose allyl ether) were characterized by morphological determination, degradation and swelling tests. Cell experiments show that the microspheres have good biocompatibility. The complete arterial occlusion of the embolized kidneys was observed, indicating that microspheres have broad application prospects in embolization interventional therapy.

Switchable Copolymerization of Maleic Anhydride/Epoxides/Lactide Mixtures: A Straightforward Approach to Block Copolymers with Unsaturated Polyester Sequences

AbstractSwitchable copolymerization of oxygenated heterocycle mixtures by a single catalytic system has been proved to be a promising approach to sequence‐controlled block copolymers. However, there are still big challenges in one‐step synthesis of multiblock copolymers containing unsaturated polyester blocks from maleic anhydride, epoxides, and lactone mixtures. Herein, a switchable pathway for polylactide‐b‐poly(MAH‐alt‐epoxide)‐b‐polylactide block copolymers is established. The excellent chemoselectivity in multicomponent copolymerization is achieved by bipyridine bisphenolate aluminum complexes that can induce an obvious kinetic differentiation between ring‐opening copolymerization of maleic anhydride/epoxides and ring‐opening polymerization of lactide. The scope of the epoxide for switchable copolymerization is explored and it is found that the steric hindrance of the substituents on epoxide significantly influences the formation of block copolymers. Block copolymers with various sequential and topological structures can be easily prepared by exquisite selection of different initiators. Furthermore, it is demonstrated that the conversion of cis‐maleate units in the block copolyester could be completely converted to trans‐fumarate units by isomerization without chain degradation, cross‐linking, and chain scrambling.

Pattern of Specific Oxidation of Konjac Glucomannan with TEMPO/NaBr/NaClO system

The TEMPO/NaBr/NaClO system was used to modify konjac glucomannan and prepare β-1,4-linked D-mannuronic/glucuronic acid oligosaccharides. The impact of oxidant amount on the degree of oxidation, molecular weight, terminal structure and the ratio of sugar units were systematically investigated. Mannoses were transformed to mannuronic acids quantitatively, while some glucose were transformed to glucuronic acids, some degraded. The unspecific oxidation causes strong degradation of konjac glucomannan sugar chains. Multiple terminal structures were observed in the oxidized KGM products. According to those observations, the oxidation pattern of konjac glucomannan with the TEMPO/NaBr/NaClO system was speculated. It is suggested that the axial hydroxyl group at position 2 in mannose might form a hydrogen bond with the oxygen on the sugar ring. It would against the unspecific oxidation. While, both specific and unspecific oxidations were observed at glucose units with an equatorial hydroxyl group at position 2, and the degradation occurs mostly on glucose during the oxidation.

Biotransformation of Ferulic acid to Vanillin by the fungus, Schizophyllum commune Fr.

The abundant and readily available precursor Ferulic acid (4-hydroxy-3-methoxycinnamic acid) was utilized to evaluate the biotransformation potential of S. commune in catabolizing the precursor Ferulic acid, Ferulic acid metabolism is expected to occur via. propanoic chain degradation to form Vanillic acid which was further metabolized to Protocatechuic aldehyde (3,4-dihydroxybenzaldehyde) via. Protocatechuic acid (3, 4-dihydroxybenzoic acid) or by reductive pathway forming Vanillin (4-hydroxy-3- methoxybenzaldehyde) The percentage of biotransformation was found to be 93 in production of Vanillic acid (4-hydroxy-3- methoxybenzoic acid) from Ferulic acid for biomass of 0.025gms (fresh weight) at a concentration of 02.5mM Ferulic acid in 50ml. Minimal media, at 370 C, pH (6.0) and an incubation period of 10 days. The presence of Vanillin is detected. along with Protocatechuic acid. Vanillin accumulation was found to be in remarkable amounts when Vanillic acid was fed as sole carbon source. Vanillic acid is an intermediate metabolite of Ferulic acid and immediate precursor of Vanillin. The potential of the fungus to convert Vanillic acid (10.0mM) concentration was explored and an yield of 4.5gl-1 was found on 12th day of incubation. Formation of Protocatechuic acid alone from Ferulic acid was noticed at pH (8.0) under static experimental conditions. This indicates that S. commune follows an entirely novel path of catabolism in alkaline conditions in comparison to acidic environment.

Involvement of Parkin-mediated mitophagy in the pathogenesis of chronic obstructive pulmonary disease-related sarcopenia.

BackgroundSarcopenia is characterized by the loss of skeletal muscle mass and strength and is associated with poor prognosis in patients with chronic obstructive pulmonary disease (COPD). Cigarette smoke (CS) exposure, a major cause for COPD, induces mitochondrial damage, which has been implicated in sarcopenia pathogenesis. The current study sought to examine the involvement of insufficient Parkin‐mediated mitophagy, a mitochondrion‐selective autophagy, in the mechanisms by which dysfunctional mitochondria accumulate with excessive reactive oxygen species (ROS) production in the development of COPD‐related sarcopenia.MethodsThe involvement of Parkin‐mediated mitophagy was examined using in vitro models of myotube formation, in vivo CS‐exposure model using Parkin−/− mice, and human muscle samples from patients with COPD‐related sarcopenia.ResultsCigarette smoke extract (CSE) induced myotube atrophy with concomitant 30% reduction in Parkin expression levels (P < 0.05). Parkin‐mediated mitophagy regulated myotube atrophy by modulating mitochondrial damage and mitochondrial ROS production. Increased mitochondrial ROS was responsible for myotube atrophy by activating Muscle Ring Finger 1 (MuRF‐1)‐mediated myosin heavy chain (MHC) degradation. Parkin−/− mice with prolonged CS exposure showed enhanced limb muscle atrophy with a 31.7% reduction in limb muscle weights (P < 0.01) and 2.3 times greater MuRF‐1 expression (P < 0.01) compared with wild‐type mice with concomitant accumulation of damaged mitochondria and oxidative modifications in 4HNE expression. Patients with COPD‐related sarcopenia exhibited significantly reduced Parkin but increased MuRF‐1 protein levels (35% lower and 2.5 times greater protein levels compared with control patients, P < 0.01 and P < 0.05, respectively) and damaged mitochondria accumulation demonstrated in muscles. Electric pulse stimulation‐induced muscle contraction prevented CSE‐induced MHC reduction by maintaining Parkin levels in myotubes.ConclusionsTaken together, COPD‐related sarcopenia can be attributed to insufficient Parkin‐mediated mitophagy and increased mitochondrial ROS causing enhanced muscle atrophy through MuRF‐1 activation, which may be at least partly preventable through optimal physical exercise.

Thermal and Mechanical Properties of the Recycled and Virgin PET-Part I.

In various countries, polyethylene terephthalate (PET) represents one of the plastics with a very high recycling rate. Since currently there is no analytical method enabling direct distinction between recycled PET (rPET) and virgin PET (vPET), there are various attempts to differentiate these materials indirectly. One of these approaches claims that the recycling of PET leads to polymer chain degradation, which is reflected in changed thermal, mechanical and crystalline properties, and testing of these properties can therefore be used to distinguish rPET and vPET. However, there are many sources leading to changes in the molecular structure and consequently to the changes of the above-mentioned properties of the PET. The purpose of this study is to analyze the glass transition and melting temperature, degree of crystallinity as well as bending and impact properties of 20 different commercially available PET recyclates from 14 suppliers and evaluate the results with respect to the literature values for vPET. The main results of this study show that the range of vPET properties is so broad that all of the corresponding properties of the tested rPET lie within this range.

Simultaneous aging of DGEBA/MeHHPA epoxy resin under thermal heating and gamma irradiation up to 1000 kGy

Although epoxy resins in nuclear facilities may be exposed to elevated temperatures and gamma irradiation, changes in the chemical structures and mechanical properties of a diglycidyl ether of bisphenol-A (DGEBA)/methyl hexahydrophthalic anhydride (MeHHPA) epoxy resin under these conditions have not been reported yet. In this study, we aim to understand the accelerated aging of the DGEBA/MeHHPA epoxy resin under simultaneous thermal heating and gamma irradiation. Samples were irradiated at ambient temperature and 70 °C with a dose rate of 2 kGy/h and a total dose of up to 1000 kGy. Various characterizations were performed to investigate the changes in their chemical structures and mechanical properties. The results showed that the relative oxygen content of the resin increased near the surface owing to the degradation of the main macromolecular chains, which was accompanied by a decrease in the thermal stability and glass transition temperature (Tg). Under gamma irradiation at room temperature, the tensile strength increased with the absorbed dose up to 500 kGy and then decreased with higher doses. This trend indicated that thermal heating at 70 °C significantly enhanced the degradation of the DGEBA/MeHHPA epoxy resin upon gamma irradiation.

Analytical model and Monte Carlo simulations of polymer degradation with improved chain cut statistics

The degradation of polymers is described by mathematical models based on bond cleavage statistics including the decreasing probability of chain cuts with decreasing average chain length. We derive equations for the degradation of chains under a random chain cut and a chain end cut mechanism, which are compared to existing models. The results are used to predict the influence of internal molecular parameters. It is shown that both chain cut mechanisms lead to a similar shape of the mass or molecular mass loss curve. A characteristic time is derived, which can be used to extract the maximum length of soluble fragments l of the polymer. We show that the complete description is needed to extract the degradation rate constant k from the molecular mass loss curve and that l can be used to design polymers that lose less mechanical stability before entering the mass loss phase.Graphical abstract

Curcumin and Graphene Oxide Incorporated into Alginate Hydrogels as Versatile Devices for the Local Treatment of Squamous Cell Carcinoma.

With the aim of preparing hybrid hydrogels suitable for use as patches for the local treatment of squamous cell carcinoma (SCC)-affected areas, curcumin (CUR) was loaded onto graphene oxide (GO) nanosheets, which were then blended into an alginate hydrogel that was crosslinked by means of calcium ions. The homogeneous incorporation of GO within the polymer network, which was confirmed through morphological investigations, improved the stability of the hybrid system compared to blank hydrogels. The weight loss in the 100–170 °C temperature range was reduced from 30% to 20%, and the degradation of alginate chains shifted to higher temperatures. Moreover, GO enhanced the stability in water media by counteracting the de-crosslinking process of the polymer network. Cell viability assays showed that the loading of CUR (2.5% and 5% by weight) was able to reduce the intrinsic toxicity of GO towards healthy cells, while higher amounts were ineffective due to the antioxidant/prooxidant paradox. Interestingly, the CUR-loaded systems were found to possess a strong cytotoxic effect in SCC cancer cells, and the sustained CUR release (~50% after 96 h) allowed long-term anticancer efficiency to be hypothesized.

One‐Step Synthesis of Degradable Vinylic Polymer‐Based Latexes via Aqueous Radical Emulsion Polymerization

AbstractAqueous emulsion copolymerizations of dibenzo[c,e]oxepane‐5‐thione (DOT) were performed with n‐butyl acrylate (BA), styrene (S) and a combination of both. In all cases, stable latexes were obtained in less than two hours under conventional conditions; that is in the presence of sodium dodecyl sulfate (SDS) used as surfactant and potassium persulfate (KPS) as initiator. A limited solubility of DOT in BA was observed compared to S, yielding to a more homogeneous integration of DOT units in the PS latex. In both cases, the copolymer could be easily degraded under basic conditions. Emulsion terpolymerization between DOT, BA and S allowed us to produce stable latexes not only composed of degradable chains but also featuring a broad range of glass transition temperatures.

One-Step Synthesis of Degradable Vinylic Polymer-Based Latexes via Aqueous Radical Emulsion Polymerization.

Aqueous emulsion copolymerizations of dibenzo[c,e]oxepane-5-thione (DOT) were performed with n-butyl acrylate (BA), styrene (S) and a combination of both. In all cases, stable latexes were obtained in less than two hours under conventional conditions; that is in the presence of sodium dodecyl sulfate (SDS) used as surfactant and potassium persulfate (KPS) as initiator. A limited solubility of DOT in BA was observed compared to S, yielding to a more homogeneous integration of DOT units in the PS latex. In both cases, the copolymer could be easily degraded under basic conditions. Emulsion terpolymerization between DOT, BA and S allowed us to produce stable latexes not only composed of degradable chains but also featuring a broad range of glass transition temperatures.

Localized Corrosion of Mooring Chain Steel in Seawater

Corrosion of mooring chains is regarded as one of main threats to the offshore mooring systems. Localized corrosion is even more dangerous than uniform corrosion because it may not show significant mass loss but it can cause stress concentration and initiate cracks under force, leading to accelerated degradation of mooring chains. Localized corrosion of steel in seawater is influenced by many factors such as the local heterogeneities of the steel, and the local electrochemical and microbiological environments. It is difficult to predict and the mechanism is not fully understood. The aim of this work was to study the mechanism of localized corrosion on mooring chain steel in seawater which is helpful in the search for corresponding monitoring tools and mitigation methods. The corrosion behavior of chain steel grade R4 was studied in artificial seawater and artificial seawater containing microorganisms collected from a practice field. The corrosion behavior of the steel was studied using different techniques such as potentiodynamic polarization, linear polarization resistance measurements and electrochemical impedance spectroscopy. The microstructures such as inclusions and compositions of the chain steel were studied using SEM: Scanning Electron Microscope and EDS: Energy Dispersive Spectroscopy. The microbial cells were observed using epi-fluorescence microscopy. The corrosion morphology and pit geometry were investigated using photo-microscopy. The localized corrosion rate has been found to be much higher than the uniform corrosion rate of the steel in the seawater in the presence of bacteria. In the case of localized corrosion, applying uniform corrosion measurement techniques and formulas is not considered representative. The representative areas have to be introduced to match physical results with the measurements. Inclusions, such as MnS and TiVCr found in the steel have a critical influence on localized corrosion. The corrosion mechanism of the steel in seawater is discussed.

Preparation and characterization of a magnetic microsphere synthesized from sucrose allyl ether for transcatheter arterial embolization

The polymerization of allyl monomers has been reported as notoriously difficult because of degradative chain transfer induced by the allyl radical as a primary radical with resonance-stabilized structure. A favorable approach is to produce polymers from inert monomers by using photodriven radical–mediated cyclization reaction (PRMC). In this study, Fe3O4 at sucrose allyl ether (Fe3O4@SAE) magnetic microspheres with sucrose as the skeleton and encapsulated nanomagnetic particles was prepared by PRMC. Its morphology and performance were characterized by using microscope, infrared, thermogravimetric and differential scanning calorimetry, scanning electron microscope/energy-dispersive spectrometer, and vibrating sample magnetometer. The feasibility as an embolic agent was evaluated by catheter transportability and cell compatibility. The results show that Fe3O4@SAE (sucrose allyl ether) magnetic microspheres have an average particle size of 371 μm, regular spherical shape, good dispersion, basically non-toxicity, and good cell compatibility. It has a certain degree of magnetism and can use alternating magnetic fields to achieve targeted embolization.

Potential benefit of the cathepsin S inhibitor, ASP1617, as a treatment for systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by the dysregulation of various cell types and immunological pathways. Autoantibodies play an important role in its pathogenesis. The presence of autoantibodies suggests that self-antigen presentation through major histocompatibility complex (MHC) class II on antigen presenting cells is involved in the pathogenesis of autoimmune diseases, including SLE. Cathepsin S (CatS) is a key protease for antigen peptide loading onto lysosomal/endosomal MHC class II molecules through invariant chain degradation to promote antigen presentation. Inhibition of CatS is therefore expected to suppress antigen presentation via MHC class II, T and B cell activation, and antibody production from B cells. Here, we report the pharmacological profile of ASP1617, a novel CatS inhibitor. ASP1617 induced invariant chain accumulation and decreased the expression level of MHC class ΙΙ on the cell surface in both mouse and human B cells. Further, ASP1617 prevented DO11.10 mice T cell proliferation to ovalbumin antigen. We investigated the effects of ASP1617 and mycophenolate mofetil (MMF) on the development of lupus-like nephritis in NZB/W F1 mice, a widely used SLE mouse model. Oral administration of ASP1617 suppressed anti-dsDNA IgG, prevented progression of lupus-like glomerulonephritis, and significantly prevented proteinuria excretion. In contrast, MMF did not suppress anti-dsDNA IgG. Further, we found that plasma and/or urine CatS levels were increased in specimens from NZB/W F1 mice and several SLE patients. These results indicate that CatS may be an attractive therapeutic target for the treatment of SLE.

Research on the Morphology Reconstruction of Deep Cryogenic Treatment on PtRu/nitrogen-Doped Graphene Composite Carbon Nanofibers.

To improve the performance of PtRu/nitrogen-doped graphene composite carbon nanofibers, the composite carbon nanofibers were thermally compensated by deep cryogenic treatment (DCT), which realized the morphology reconstruction of composite carbon nanofibers. The effects of different DCT times were compared: 12 h, 18 h, and 24 h. The morphology reconstruction mechanism was explored by combining the change of inner chain structure and material group. The results showed that the fibers treated for 12 h had better physical and chemical properties, where the diameter is evenly distributed between 500 and 800 nm. Combined with Fourier infrared analysis, the longer the cryogenic time, the more easily the water vapor and nitrogen enter polymerization reaction, causing changes of chain structure and degradation performance. With great performance of carbonization and group transformation, the PtRu/nitrogen-doped graphene composite carbon nanofibers can be used as an efficient direct alcohol fuel cell catalyst and promote its commercialization.

Glass transition temperature of Risø B3 radiochromic film dosimeter and its importance on the post-irradiation heating procedure

Full-color development and stability of measured absorbance of the commercially used Risø B3 radiochromic film dosimeter can be achieved by applying a post-irradiation heat treatment procedure, typically at 60 °C for 10 min. However, the choice of post-irradiation heating duration and temperature has only been based on a trial and error method, and thus, the thermal stability of the material has not been fully studied before. We show that B3 film undergoes a rapid thermal decomposition of the PVB polymer base at 400 °C, with an initiation of the process at 70 °C. It means that higher irradiation temperatures, which can occur e.g. at high-dose electron beam irradiation, may cause polymer degradation. We also show that the post-irradiation heating temperature agrees with the polymer material's glass transition temperature as measured by differential scanning calorimetry (DSC). The post-irradiation heating procedure successfully removes the film's thermal history. This can be seen as an endothermic peak in the first heating cycle, which becomes smaller for higher irradiation doses. Glass transition temperatures of irradiated and post-irradiation heated B3 film are lower than those of the non-irradiated film, and decrease with increasing the dose. That implies a probable chain scission or degradation of the base polymer upon irradiation using high dose rates with no irradiation temperature control.

DFT Study on Side Chain Detachment of Perfluorosulfonic Acid Ionomers by Radical-Assisted Nucleophilic Attack of Water

Chemical degradation of perfluorosulfonic acid (PFSA) ionomer membranes is still an unresolved critical issue in the development of polymer electrolyte fuel cells (PEFCs). Its reaction mechanism has not been settled yet even after experimental and computational studies for decades. In this study, the role of hydroxyl radical to side chain degradation is revisited and a new reaction mechanism is proposed. Its nucleophilic attack on the carbon atom in the ether group induces detachment of the side chain. The reactions are supposed to be feasible as their reaction barrier heights are only slightly higher than those of tertiary fluorine atom abstraction reactions by hydrogen radical in absence of the solvation effect. When a single water molecule is present with hydroxyl or hydroperoxyl radical it is the oxygen in the water that undergoes the nucleophilic attack on the carbon in the ether groups and the calculated barrier heights are lowered to 70∼100 kJ mol−1 as the radical assists the reaction as a hydrogen acceptor. Possible reaction pathways of the products are also calculated to explain the occurrence of the experimentally observed degradation products of Nafion after chemical durability tests.