Degradation Of Backbone Research Articles

Carbohydrate composition of compost during composting and mycelium growth of Agaricus bisporus

Changes of plant cell wall carbohydrate structures occurring during the process to make suitable compost for growth of Agaricus bisporus are unknown. In this paper, composition and carbohydrate structures in compost samples collected during composting and mycelium growth were analyzed. Furthermore, different extracts of compost samples were prepared with water, 1M and 4M alkali and analyzed. At the beginning of composting, 34% and after 16 days of mycelium growth 27% of dry matter was carbohydrates. Carbohydrate composition analysis showed that mainly cellulose and poorly substituted xylan chains with similar amounts and ratios of xylan building blocks were present in all phases studied. Nevertheless, xylan solubility increased 20% over the period of mycelium growth indicating partial degradation of xylan backbone. Apparently, degradation of carbohydrates occurred over the process studied by both bacteria and fungi, mainly having an effect on xylan-chain length and solubility.

Modification of cell wall polysaccharide during ripening of Chinese bayberry fruit

Experiments were conducted to investigate the modification of cell wall polysaccharide in Chinese bayberry during ripening. Cellular wall materials were isolated from Chinese bayberry fruit at four ripening stages. Three pectin fractions and two hemicellulose fractions were obtained and their compositional changes were analyzed. The process of ripening and softening of the fruit corresponded to an increase in the water soluble pectin (WSP) and 1mol/L KOH-soluble hemicellulose (HC1) fractions, and a decrease in Na2CO3-soluble pectin (SSP) and 4mol/L KOH-soluble hemicellulose (HC2) fractions which suggested the solubilization and conversion of cellular wall components. However, the content of CDTA-soluble pectin (CSP) changed slightly. Furthermore, arabinose, as the major branch monosaccharide, decreased in three pectin fractions during the whole ripening period, whereas the relative content of rhamnose, the backbone monosaccaride, tend to decrease in CSP and SSP pectin fractions, but increased gradually in WSP pectin during ripening. Analysis of (Ara+Gal)/Rha ratio showed that the degradation of WSP pectin mainly occurred in branch chains, conversely, the degradation of backbone played a more important role in degradation of CSP and SSP. In HC1, the breakdown of the branch chain of matrix xyloglucan, arabinoxylan and arabinogalactan are predominant while more backbones of xyloglucan, arabinoxylan and arabinogalactan were depolymerized in HC2. Moreover, it was found that the molecular weight of WSP decreased gradually throughout ripening while the depolymerization of ionic CSP and covalent SSP mainly occurred at late and early ripening stages, respectively. Loosely bound (HC1) and tightly bound (HC2) hemicellulose fractions exhibited distinct molecular mass downshift throughout ripening stages, especially at late ripening stage. Overall, fruit softening of Chinese bayberry during ripening involved in differential modification of pectin and hemicellulose.

The influence of the primary and secondary xanthan structure on the enzymatic hydrolysis of the xanthan backbone

Differently modified xanthans, varying in degree of acetylation and/or pyruvylation were incubated with the experimental cellulase mixture C1-G1 from Myceliophthora thermophila C1. The ionic strength and/or temperature of the xanthan solutions were varied, to obtain different xanthan conformations. The exact conformation at the selected incubation conditions was determined by circular dichroism. The xanthan degradation was analyzed by size exclusion chromatography. It was shown that at a fixed xanthan conformation, the backbone degradation by cellulases is equal for each type of xanthan. Complete backbone degradation is only obtained at a fully disordered conformation, indicating that only the secondary xanthan structure influences the final degree of hydrolysis by cellulases. It is thereby shown that, independently on the degree of substitution, xanthan can be completely hydrolyzed to oligosaccharides. These oligosaccharides can be used to further investigate the primary structure of different xanthans and to correlate the molecular structure to the xanthan functionalities.

Poly(1,2-glycerol carbonate): A Fundamental Polymer Structure Synthesized from CO2 and Glycidyl Ethers

The functional, aliphatic poly(1,2-glycerol carbonate) as a fundamental, simple polymer structure based on glycerol and CO2 was prepared by combination of glycidyl ether monomers with carbon dioxide via two different approaches. The material was obtained by two-step procedures either via copolymerization of (i) ethoxy ethyl glycidyl ether (EEGE) or (ii) benzyl glycidyl ether (BGE) with CO2, followed by removal of the respective protecting groups via acidic cleavage for (i) and hydrogenation for (ii). The resulting protected polycarbonate structures and the targeted poly(1,2-glycerol carbonate) were investigated with 1H NMR and 13C NMR spectroscopy as well as 2D-NMR methods. Removal of both protecting groups was possible without significant backbone degradation; however, the hydrogenation route for (ii) turned out to be advantageous. All new poly(carbonate)s have been characterized with respect to their thermal behavior. Protected and deprotected poly(1,2-glycerol carbonate)s were obtained with molecular weights in the range of 5000–25 200 g/mol and a PDI from 1.24 to 2.33. The degradation kinetics of poly(1,2-glycerol carbonate) in DMF has also been studied, demonstrating rather rapid degradation within several days to oligomers and cyclic carbonates.

Two-dimensional NMR spectroscopy reveals cation-triggered backbone degradation in polysulfone-based anion exchange membranes

Anion exchange membranes (AEMs) find widespread applications as an electrolyte and/or electrode binder in fuel cells, electrodialysis stacks, flow and metal-air batteries, and electrolyzers. AEMs exhibit poor stability in alkaline media; their degradation is induced by the hydroxide ion, a potent nucleophile. We have used 2D NMR techniques to investigate polymer backbone stability (as opposed to cation stability) of the AEM in alkaline media. We report the mechanism behind a peculiar, often-observed phenomenon, wherein a demonstrably stable polysulfone backbone degrades rapidly in alkaline solutions upon derivatization with alkaline stable fixed cation groups. Using COSY and heteronuclear multiple quantum correlation spectroscopy (2D NMR), we unequivocally demonstrate that the added cation group triggers degradation of the polymer backbone in alkaline via quaternary carbon hydrolysis and ether hydrolysis, leading to rapid failure. This finding challenges the existing perception that having a stable cation moiety is sufficient to yield a stable AEM and emphasizes the importance of the often ignored issue of backbone stability.

Acid-Degradable Cationic Poly(ketal amidoamine) for Enhanced RNA Interference In Vitro and In Vivo

Efficient delivery of small interfering RNA (siRNA) is one of major challenges in the successful applications of siRNA in clinic. In the present study, we report a new acid-degradable poly(ketal amidoamine) (PKAA) as a siRNA carrier, which has high delivery efficiency and low cytotoxicity. PKAA was designed to have acid-cleavable ketal linkages in the backbone of cationic biodegradable poly(amidoamine). PKAA efficiently self-assembled with siRNA to form nanocomplexes with a diameter of ~200 nm and slightly positive charges, which are stable under physiological conditions, but rapidly release siRNA at acidic pH. PKAA exhibited sufficient buffering capability and endosomolytic activity due mainly to the presence of secondary amine groups in its backbone and rapid degradation in acidic endosomes, leading to the enhanced release of siRNA to cytoplasm. Cell culture studies demonstrated that PKAA is capable of delivering anti-TNF (tumor necrosis factor)-α siRNA to lipopolysaccharide (LPS)-stimulated macrophages and significantly inhibits the expression of TNF-α. A mouse model of acetaminophen (APAP)-induced acute liver failure was used to evaluate in vivo siRNA delivery efficacy of PKAA. PKAA/anti-TNF-α siRNA nanocomplexes significantly reduced the ALT (alanine transaminase) and the hepatic cellular damages in APAP-intoxicated mice. We anticipate that acid-degradable PKAA has great potential as siRNA carriers based on its excellent biocompatibility, pH sensitivity, potential endosomolytic activity, and high delivery efficiency.

Preparation and properties of cyclic acetal based biodegradable gel by thiol-ene photopolymerization

Synthetic, hydrolytically degradable biomaterials have been widely developed for biomedical use; however, most of them will form acidic products upon degradation of polymer backbone. In order to address this concern, we proposed to fabricate a biodegradable gel based on the crosslinking of a cyclic acetal monomer with reactable diallyl group and multifunctional thiols by thiol-ene photopolymerization. This gel produces diols and carbonyl end groups upon hydrolytic degradation and could be entirely devoid of acidic by-products. Real time infrared spectroscopy was employed to investigate the effect of different light intensities and concentrations of photoinitiator on the polymerization kinetics. With the increase of the concentration of photoinitiator and light intensity, both the rate of polymerization and final double bond conversion increased. Degradation of cyclic acetal based networks was investigated in PBS medium so as to simulate physiological conditions. The remaining mass of the materials after 25days incubation was 84%. TGA analysis showed that the gels exhibited a typical weight loss (97.2%) at around 378°C. In vitro cytotoxicity showed that the cyclic acetal based gels had non-toxicity to cell L-929 and had good biocompatibility.

Biocompatible Polymeric Nanoparticles Degrade and Release Cargo in Response to Biologically Relevant Levels of Hydrogen Peroxide

Oxidative stress is caused predominantly by accumulation of hydrogen peroxide and distinguishes inflamed tissue from healthy tissue. Hydrogen peroxide could potentially be useful as a stimulus for targeted drug delivery to diseased tissue. However, current polymeric systems are not sensitive to biologically relevant concentrations of H(2)O(2) (50-100 μM). Here we report a new biocompatible polymeric capsule capable of undergoing backbone degradation and thus release upon exposure to such concentrations of hydrogen peroxide. Two polymeric structures were developed differing with respect to the linkage between the boronic ester group and the polymeric backbone: either direct (1) or via an ether linkage (2). Both polymers are stable in aqueous solution at normal pH, and exposure to peroxide induces the removal of the boronic ester protecting groups at physiological pH and temperature, revealing phenols along the backbone, which undergo quinone methide rearrangement to lead to polymer degradation. Considerably faster backbone degradation was observed for polymer 2 over polymer 1 by NMR and GPC. Nanoparticles were formulated from these novel materials to analyze their oxidation triggered release properties. While nanoparticles formulated from polymer 1 only released 50% of the reporter dye after exposure to 1 mM H(2)O(2) for 26 h, nanoparticles formulated from polymer 2 did so within 10 h and were able to release their cargo selectively in biologically relevant concentrations of H(2)O(2). Nanoparticles formulated from polymer 2 showed a 2-fold enhancement of release upon incubation with activated neutrophils, while controls showed a nonspecific response to ROS producing cells. These polymers represent a novel, biologically relevant, and biocompatible approach to biodegradable H(2)O(2)-triggered release systems that can degrade into small molecules, release their cargo, and should be easily cleared by the body.

Structural analysis of immunostimulating sulfated polysaccharides from Ulva pertusa

Sulfated polysaccharides were extracted from Ulva pertusa and fractionated to obtain the most immunostimulating fraction (F2). The glycosidic linkages of the polysaccharides in the fraction F2 were determined using GC–MS and 2D-NMR spectroscopy after chemical modifications, including reduction and desulfation under various conditions. Methanol was used as a sulfate acceptor for the removal of sulfates from the polysaccharides. When desulfation was carried out at 120°C, the sulfates were removed upto 90.1% from the F2 fraction without considerable backbone degradation. The GC–MS analysis as well as NMR spectra revealed that the backbone of the polysaccharides was mainly composed of α-(1→4)-l-rhamnopyranosyl, β-(1→4)-d-glucuronosyl, β-(1→2)-l-rhamnopyranosyl, and β-(1→4)-d-xylopyranosyl residues with branches at O-2 position of rhamnose. The sulfate groups were mostly found on glucuronic acid at O-3 position.

Backbone stability of quaternized polyaromatics for alkaline membrane fuel cells

The backbone stability of benzyl-trimethyl ammonium (BTMA) functionalized polyaromatics was investigated in two structurally differing polymer architectures; quaternized poly(arylene ether) (PAE) and poly(phenylene) (PP). FTIR analysis indicated the cleavage of aryl-ether linkages in quaternized PAEs under high pH environments, while no backbone degradation in quaternized PP was observed. The backbone degradation of PAEs not only significantly reduced the mechanical properties of the membranes, but also negatively impacted hydroxide conductivity. Membrane electrode assemblies (MEAs) using both PAE and PP membranes showed good initial alkaline membrane fuel cell performance. However, the PAE MEA displayed larger performance losses and failure after only 55h, due to a mechanical breach. No catastrophic failure of the PP MEA occurred after 300h, which further confirmed the stability of the polymer backbone.

Aromatic aldehyde functionalized polycaprolactone and polystyrene macromonomers: Synthesis, characterization and aldehyde–aminooxy click reaction

New bis-aldehyde functionalized initiators, viz, 4,4′-(4,4′-(5-hydroxypentane-2,2-diyl)bis(4,1-phenylene))bis(oxy)dibenzaldehyde (1) and 4,4′-bis(4-(4-(formylphenoxy) phenyl) pentyl 2-bromopropanoate (2) were synthesized starting from commercially available 4,4′-bis(4-hydroxyphenyl) pentanoic acid. These initiators were utilized, respectively, for ring opening polymerization of ε-caprolactone and atom transfer radical polymerization of styrene. Well-defined polycaprolactone macromonomers (MnGPC: 2600–19400, PDI: 1.37–1.47) and polystyrene macromonomers (MnGPC: 2800–28200, PDI: 1.11–1.16) with bis-aldehyde functionality were synthesized. The kinetic study of styrene polymerization showed controlled polymerization behaviour. The presence of aldehyde functionality in macromonomers was confirmed by 1H NMR spectroscopy. The reactivity of aldehyde functionality was demonstrated by carrying out aldehyde–aminooxy click reaction of polycaprolactone macromonomer with O-(2-azidoethyl) hydroxylamine which proceeded in a quantitative manner without backbone degradation.

Modification of polysaccharides via thiol‐ene chemistry: A versatile route to functional biomaterials

AbstractWe present herein a mild and rapid method for the modular functionalization of polysaccharides. Several ene‐functional charged and neutral polysaccharides, that is, hyaluronic acid and dextran, were prepared by esterification of the hydroxyl groups with pentenoic anhydride. The modified polysaccharides were then reacted with six model mercaptans under UV light, leading to linear polymers modified with hydrophobic groups, peptides, or oligosaccharides as well as chemical hydrogels. The thiol‐ene coupling reactions were found to proceed with high efficiency in short reaction times and with nearly no degradation of the polysaccharide backbone. Moreover, they were carried out in aqueous media, without the use of any metal catalysts, enhancing the attractive nature of this process. Notably, we investigated whether it is feasible to prepare cell‐responsive hydrogels by sequential bioconjugation and cross‐linking of the polysaccharide backbone with a bioactive peptide and poly(ethylene glycol)‐dithiol, respectively. All together, these results highlight the potential of this coupling strategy for the modular functionalization of polysaccharides under click chemistry‐like conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012

Nafion Polymer Backbone Degradation Mechanism in PEM Fuel Cell from Quantum Mechanics Calculations

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Reactive mono- and di-epoxy-functionalized poly(3-hydroxybutyrate)s. Synthesis and characterization

This work describes universal transformation method of low molar mass crotonate-terminated poly(3-hydroxybutyrate)s (PHB), obtained by anionic ROP of β-butyrolactone and controlled degradation of high-molar mass bacterial PHB, into mono- and di-epoxy-functionalized reactive poly(3-hydroxybutyrate)s via oxidation of crotonate end groups to α-3-methyloxirane-2-carboxylates, while carboxylate terminal groups were functionalized by simple alkylation with epibromohydrin. Combining these two methods resulted in telechelic structures: α-3-methyloxirane-2-carboxylate-ω-glicydyl PHB. Moreover, the reactivity of 3-methyloxirane groups of a functional aPHB, was confirmed in experiment with primary amine and primary alcohol, revealing very high yield in reaction with alcohol, while degradation of polymer backbone was noticed during reaction with amine.

Direct Insertion Mass Spectrometric Analysis of Thermal Degradation of Poly(2‐alkyl‐2‐oxazoline)

AbstractDirect pyrolysis mass spectrometry is applied to investigate the thermal behavior of poly(2‐isopropyl‐2‐oxazoline) (PIPOX, a thermoresponsive polymer) and poly[2‐(3‐butenyl)‐2‐oxazoline] (PBOX, a “clickable” polymer). It is found that the thermal degradation of PIPOX is started by a loss of side chains. At slightly higher temperatures the degradation of the polymer backbone occurs by random chain scission processes. In the case of PBOX, vinyl polymerization of the side chains produces chains with variable thermal stabilities. The number of repeating units of the polymer has almost no effect on the thermal behavior of PIPOX, but significantly affects both thermal stability and degradation product distribution of PBOX.

Grafting polymerization of acrylonitrile and methyl acrylate on chitosan in the presence of cobalt(III) complexes

The kinetic features of the grafting polymerization of acrylonitrile and methyl acrylate on chitosan with the use of hexaamminecobalt(III) chloride as an initiator are studied in the temperature range 294–333 K. It is shown that hexaamminecobalt(III) chloride as an initiator provides a high grafting efficiency of vinyl polymers without degradation of the polysaccharide backbone. The activation energy of the process is ∼17 kJ/mol. The mechanical properties of the films of graft copolymers are better than those of the initial chitosan.

Studies on the tosylation of cellulose in mixtures of ionic liquids and a co-solvent

The tosylation of cellulose in ionic liquids (ILs) was studied. Due to the beneficial effect of different co-solvents, the reaction could be performed at 25°C without the need of heating (in order to reduce viscosity) or cooling (in order to prevent side reactions). The effects of reaction parameters, such as time, molar ratio, and type of base, on the degree of substitution (DS) with tosyl- and chloro-deoxy groups as well as on the molecular weight were evaluated. Products with a DStosyl≤1.14 and DSCl≤0.16 were obtained and characterized by means of NMR- and FT-IR spectroscopy in order to evaluate their purity and distribution of functional groups within the modified anhydroglucose unit (AGU). Tosylation of cellulose in mixtures of IL and a co-solvent was found to result in predominant substitution at the primary hydroxyl group. Size exclusion chromatography (SEC) revealed only a moderate degradation of the polymer backbone at a reaction time of 4–8h. Finally, the nucleophilic displacement (SN) of tosyl- and chloro-deoxy groups by azide as well as recycling of the ILs was studied.

Rapid and Tunable Reductive Degradation of Disulfide‐Labeled Polyesters

AbstractA new approach for rapid and tunable degradation of reductively degradable polyesters (ssPESs) with multiple disulfides on the polymer backbones is reported. The approach centers on the control of the amount of disulfides in the synthesis of ssPESs by polycondensation of a disulfide‐containing diacid with various single and mixed diols having different molecular weights and disulfides. The disulfide concentration in ssPESs is tuned by incorporation of diols labeled with disulfides or diols with different MWs. The degradation rate is enhanced with increasing ssPES molecular weight. With ssPESs bearing disulfides positioned repeatedly along the backbone, the rapid and controlled degradation is compared with the slow degradation of polyesters with only a single disulfide in the center.

D -Xylose Concentration-Dependent Hydrolase Expression Profiles and the Function of CreA and XlnR in Aspergillus niger

Aspergillus niger is an important organism for the production of industrial enzymes such as hemicellulases and pectinases. The xylan-backbone monomer, d-xylose, is an inducing substance for the coordinate expression of a large number of polysaccharide-degrading enzymes. In this study, the responses of 22 genes to low (1 mM) and high (50 mM) d-xylose concentrations were investigated. These 22 genes encode enzymes that function as xylan backbone-degrading enzymes, accessory enzymes, cellulose-degrading enzymes, or enzymes involved in the pentose catabolic pathway in A. niger. Notably, genes encoding enzymes that have a similar function (e.g., xylan backbone degradation) respond in a similar manner to different concentrations of d-xylose. Although low d-xylose concentrations provoke the greatest change in transcript levels, in particular, for hemicellulase-encoding genes, transcript formation in the presence of high concentrations of d-xylose was also observed. Interestingly, a high d-xylose concentration is favorable for certain groups of genes. Furthermore, the repressing influence of CreA on the transcription and transcript levels of a subset of these genes was observed regardless of whether a low or high concentration of d-xylose was used. Interestingly, the decrease in transcript levels of certain genes on high d-xylose concentrations is not reflected by the transcript level of their activator, XlnR. Regardless of the d-xylose concentration applied and whether CreA was functional, xlnR was constitutively expressed at a low level.

Ketalized poly(amino ester) for stimuli-responsive and biocompatible gene delivery

Stimuli-triggered degradation and facilitated intracellular release of nucleic acids are key design factors in developing efficient and biocompatible nonviral gene carriers. In this study, a cationic polymer was developed with aims to achieve enhanced gene transfection and low cytotoxicity via rapid biodegradation and subsequent intracellular de-complexation in response to dual stimuli in a cell. Diaminoethane was polymerized to synthesize cationic and hydrolytically degradable poly(amino ester), and then it was further conjugated with acid-degradable amino ketal branches. The resulting polymer, ketalized poly(amino ester) (K-PAE), differentially degrades via rapid hydrolysis of the ketal branches in the mildly acidic endosome and subsequent gradual degradation of the polyester backbone in the cytoplasm. DNA/K-PAE polyplexes underwent acid-triggered de-complexation at an endosomal pH, leading to efficient intracellular release of DNA and significantly enhanced transfection efficiency. In addition, DNA/K-PAE polyplexes demonstrated low cytotoxicity and serum-resistant gene transfection, in comparison with commercial counterpart polymers, promising for efficient and safe gene delivery in vivo. This study presents insightful design clues for developing efficient, versatile, stimuli-responsive, and biocompatible polymers for nonviral gene delivery.