Formation Of Cross-links Research Articles

Sample size dependence of high-temperature thermal stability of Ti2AlN MAX phase

The thermal stability of Titanium Aluminum Nitride (Ti2AlN) microcrystalline powder in vacuum has been studied by in-situ high-temperature X-ray diffraction. The limit of thermal stability for Ti2AlN phase is T < 850 °C. The process of thermal decomposition consists of the Al atoms sublimation and the formation of a new TiNx phase on the sample surface. An increase in sample size leads to an increase in thermal stability limit (850 °C for microcrystals and 1550 °C for dense bulk sample). Based on crystal chemical analysis and quantum chemical calculations, a mechanism of thermal dissociation was proposed. Kinetics of thermal dissociation of the Ti2AlN phase was modeled using the Avrami equation. Avrami exponent parameters (n = 1.09; 1.28) indicate that the process of germs formation occurs at a subgrain boundaries of the sample. The observed temperature dependence of the parameter n can be associated with a probability change of crosslinking formation during the growth of a new phase. The size dependence of Ti2AlN thermal stability was explained by the ratios of Al diffusion coefficients in the crystallite bulk and along the subgrain boundaries.

THERMAL PROPERTIES OF CROSS-LINKED POLYMERS BASED ON CHITOSAN AND POLYACRYLAMIDE

The thermal properties of cross-linked polymers based on chitosan and polyacrylamide were studied. Samples of the resulting network polymers, which included chains of polyacrylamide and chitosan, were obtained as hydrogel materials by radical polymerization of acrylamide in the presence of chitosan using the redox system of cerium (IV) ammonium nitrate as an initiator and N,N’-methylene-bis-acrylamide as a crosslinker. The structure of the obtained polymers was confirmed by comparing their IR spectra with the spectra of chitosan and polyacrylamide. It was shown that in the IR spectrum of the chitosan-containing sample, the peak at 2932 cm -1 indicates the presence of CH2 groups in the polymer chains and the formation of cross-links. Deformation and valence vibrations of the amide group in polyacrylamide are observed at 1600–1660 cm -1, and the band at 1633 and 1411 cm -1, which appears when the amide bond of polyacrylamide is formed, corresponds to C-N vibrations in the graft copolymer. These characteristic bands confirm the possibility of graft copolymerization of acrylamide on chitosan. The influence of the mass ratio of chitosan and polyacrylamide on the thermal properties of polymer systems was investigated by the method of thermogravimetric and differential thermogravimetric analysis. Atmospheric gas (1 bar, 40 % relative humidity) was used in all thermoanalytical measurements. The samples were examined after vacuum drying at 4 × 10-7 bar and 60 °C using Concentrator Plus. TGA and DTG curves were obtained in the temperature range from 30 to 500 °C with a scanning speed of 5 °C/min using 40 μl aluminum oxide crucibles. It was established that increasing the concentration of chitosan during synthesis reduces the amount of bound water in the obtained samples. Analysis of thermal destruction at the final stages of heating indicates that the presence of chitosan in samples of cross-linked polymers increases their heat resistance by 10–15 °C. The obtained regularities can be used in the creation of composite materials for hydrogel wound dressings and covering medical agents for external use.

Building Porous Ni(Salen)-Based Catalysts from Waste Styrofoam via Autocatalytic Coupling Chemistry for Heterogeneous Oxidation with Molecular Oxygen.

The development of robust and industrially viable catalysts from plastic waste is of great significance, and the facile construction of high performance heterogeneous catalyst systems for phenol-quinone conversions remains a grand challenge. Herein, a feasible strategy is demonstrated to reclaim Styrofoam into hierarchically porous nickel-salen-loaded hypercrosslinked polystyrene (PS@Ni-salen) catalysts with high activities through an unusual autocatalytic coupling route. The salen is immobilized onto PS chain by Friedel-Crafts alkylation of benzyl chloride derivatives, and the generated hydrogen chloride coordinately promotes the simultaneous crosslinking and bridge formation between aromatic rings via a Scholl coupling route, leading to hierarchically porous networks. After the metallization with Ni, the resultant networks exhibit high catalytic activity for the oxidation of 2,3,6-trimethylphenol to 2,3,5-trimethyl-1,4-benzoquinone under mild conditions (303 K, 1bar of O2 ). This catalyst also demonstrates attractive recycling performance without an obvious loss of catalytic efficiency over five consecutive cycles. This methodology might provide a potential sustainable alternative to construct environmentally benign and cost-effective catalysts for specific organic transformation.

Recent advances in the development of the physically crosslinked hydrogels and their biomedical applications

Hydrogels are three-dimensional networks formulated from natural or synthetic polymers with a high capacity to absorb and transport water in their structure. Hydrogels are prepared from the crosslinking of their polymeric chains, which involves two basic mechanisms: chemical crosslinking and physical crosslinking. In chemical crosslinking, hydrogels are held together by covalent bonds; while physically cross-linked hydrogels are produced by non-covalent interactions, such as hydrogen bonds, electrostatic interactions, and hydrophobic forces, among others. Physically cross-linked hydrogels are more similar to biological systems due to their assembly dynamics, so they have wide biomedical applications. The most used approaches in the preparation of hydrogels by physical crosslinking include freeze-thaw, formation of stereocomplexes, ionic interaction, hydrogen bonding, crystallization, and crosslinking by hydrophobic interactions. These approaches are briefly discussed in this review. Some biomedical applications of these hydrogels will also be discussed.

Preparation of UV Debonding Acrylate Adhesives by a Postgrafting Reaction.

UV debonding acrylate adhesive (UDAA) plays a crucial role in the semiconductor industry, where its excellent adhesion is required to ensure the stability of silicon wafers and leave no residue on the surface after UV irradiation. The necessary UV debonding is achieved through the formation of rigid networks by the reactions of all the vinyl groups in the system. Acrylate copolymers with vinyl groups are typically obtained by the grafting reaction of isocyanate with a side-chain hydroxyl comonomer. However, these grafting reactions easily fail due to early cross-link formation. In this study, we illustrate a straightforward method for preparing UDAA by conducting a postgrafting reaction after one-step mixing of isocyanate functional monomer (IPDI-H) and hydroxyl acrylate copolymers (BA-H), thereby skipping the abovementioned vinyl grafting process. The chemical structures of the synthesized IPDI-H and BA-H were confirmed using Fourier transform infrared spectroscopy (FTIR) and proton nuclear magnetic resonance (1H-NMR) analysis. Gel permeation chromatography (GPC) was employed to determine their molecular weights, while differential scanning calorimetry (DSC) was used to determine their glass transition temperatures. The postgrafting reactions successfully introduced vinyl groups onto the polyacrylate copolymer chains, resulting in high bonding strength during use and a significant decrease in peeling strength after UV irradiation. Rheological methods, including the three-interval thixotropy test (3ITT) and tack test modes, were employed to characterize a series of acrylate UV debonding adhesives. The recovery percentage of the storage modulus in the 3ITT mode indicated that a 0.6 wt% isocyanate curing agent made the UV debonding adhesives resistant to deformation. From the maximum normal force in the tack test mode, it was found that UDAA with 10 wt% PETA monomer and 30 wt% C5 tackifying resin exhibited excellent combined adhesion and debonding properties, which were further confirmed by peel strength tests. Microscope images of the wafer surfaces after removing the adhesive tapes demonstrated the excellent UV debonding properties achieved after 40 s of UV irradiation through the postgrafting reaction. The prepared UDAA has excellent properties; the peel strength can reach 15 N/25 mm before UV irradiation and can be reduced to 0.5 N/25 mm after ultraviolet irradiation. This research establishes a comprehensive method for understanding and applying UDAA in various applications.

Thermomechanical Stress Analysis of Hydrated Vital Gluten with Large Amplitude Oscillatory Shear Rheology.

Vital gluten is increasingly researched as a non-food product for biodegradable materials. During processing, the protein network is confronted with increased thermal and mechanical stress, altering the network characteristics. With the prospect of using the protein for materials beyond food, it is important to understand the mechanical properties at various processing temperatures. To achieve this, the study investigates hydrated vital gluten under thermomechanical stress based on large amplitude oscillatory shear (LAOS) rheology. LAOS rheology was conducted at increasing shear strains (0.01-100%), various frequencies (5-20 rad/s) and temperatures of 25, 45, 55, 65, 70 and 85 °C. With elevating temperatures up to 55 °C, the linear viscoelastic moduli decrease, indicating material softening. Then, protein polymerization and the formation of new cross-links due to thermal denaturation cause more network connectivity, resulting in significantly higher elastic moduli. Beyond the linear viscoelastic regime, the strain-stiffening ratio rises disproportionately. This effect becomes even more evident at higher temperatures. Lacking a viscous contribution, the highly elastic but also stiff network shows less mechanical resilience. Additionally, at these elevated temperatures, structural changes during the protein's denaturation and network shrinkage due to water evaporation could be visualized with confocal laser scanning microscopy (CLSM).

Thermal decomposition behaviors and degradation kinetics of biobased polyesters with partial crosslinking to eliminate cyclic compounds

A series of poly(butylene adipate-co-butylene itaconate) (PBAPI) copolyesters with and without a small amount of ethylenediaminetetraacetic acid (EDTA) were synthesized via melt polymerization. Thermogravimetric analysis -gas chromatography/mass spectroscopy (TGA-GC/MS) techniques were used to identify the thermal degradation behaviors. By introducing 0.1 mol % EDTA into BA/BI = 10/0, the dominant degradation product was converted from furan and cyclopentanone derivatives to CO2 and formation of cyclic compounds was notably inhibited. Moreover, similar tendencies were observed when the BI content increased, demonstrating that the existence ratio of CO2 and furan derivatives increased while the concentrations of cyclopentanone and cyclic compounds reduced during decomposition. Finally, no cyclic compound product was detected in the BA/BI = 7/3 copolyester. These results indicate that the introduction of both EDTA and BI inhibits generation of cyclic compounds, which are attributed to the formation of partial crosslinking for chemical structures. The nonisothermal degradation kinetic was also carried out to investigate the decomposition behaviors. The activation energy requirements at each degradation stage varied with the composition of BA/BI ratios and the introduction of EDTA, demonstrating further evidence of degradation behavior transformation.

Development of 4,4′-dibromobinaphthalene analogues with potent photo-inducible DNA cross-linking capability and cytotoxicity towards breast MDA-MB 468 cancer cells

Photoinduced DNA cross-linking process showed advantages of high spatio-temporal resolution and control. We have designed, synthesized, and characterized several 4,4′-dibromo binaphthalene analogues (1a-f) that can be activated by 350 nm irradiation to induce various DNA damage, including DNA interstrand cross-links (ICL) formation, strand cleavages, and alkaline labile DNA lesions. The degree and types of DNA damage induced by these compounds depend on the leaving groups of the substrates, pH value of the buffer solution, and DNA sequences. The DNA ICL products were produced from the carbocations formed via the oxidation of free radicals photo-generated from 1a-f. Most of these compounds alone exhibited minimum cytotoxicity towards cancer cells while 350 nm irradiation greatly improved their anticancer effects (up to 40-fold enhancement) because of photo-induced cellular DNA damage. This work provides guidance for further design of photo-inducible DNA cross-linking agents as potent photo-activated anticancer prodrugs with good control over toxicity and selectivity.

Characterization of the alkali-induced protein cross-linking in buckwheat sourdough steamed bread

This study elucidated the alkali-induced protein cross-linking behaviors of buckwheat sourdough steamed bread (BSSB). When the alkali concentration increased to 1.5% (on a total flour weight basis), the protein extractability in sodium dodecyl sulfate (SDS) decreased by 2.29% while the disulfide (SS) bond content increased by 5.97 μmol/g protein, indicating that the alkali promoted the SS cross-linking of the proteins. The formation of dehydroalanine (DHA) and lanthionine (LAN) at alkali concentrations of 2.0% and 2.5% demonstrated the occurrence of DHA-derived cross-linking. To explore the role of SS cross-linking in the quality of BSSB, the thiol-blocking agent N-ethylmaleimide (NEM) was also employed. It was determined that the BSSB with NEM had almost no gas cells and that the specific volume was 48.41% lower than the control. The alkali increased the specific volume by up to 26.75% at 2.0% concentration and ameliorated the crumb structure of the BSSB. Dynamic thermo-mechanical analysis revealed that the alkali also delayed the starch gelatinization and gas cell opening, which may have contributed to the gas holding capacity of the BSSB. The amino acid residues involved in the DHA-derived cross-linking and the potential cross-linking sites were identified via liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. It was found that both the Cys197 from wheat peroxidase and the Cys105 from the wheat alpha-amylase/trypsin inhibitor CM16 were crucial to the formation of the DHA-derived cross-links and that the LAN between two cysteines was inter-chain.

Adsorptive recovery of rare earth elements from aqueous solution by citric acid crosslinked carboxymethylated cellulose nanofibril aerogel

Rare earth elements (REEs) have become crucial resources in the electric vehicle industry; however, their recycling remains challenging. In this study, we developed a carboxymethylated cellulose nanofibril aerogel crosslinked with citric acid (CMCNF-CA aerogel) through thermal treatment and employed it as an adsorbent for REE recovery. The CMCNF-CA aerogel possesses a substantial amount of free –COOH groups, resulting in a strong negative charge. This unique characteristic enables the aerogel to exhibit excellent adsorption capacities of 200 mg/g for lanthanum(La3+) and 170 mg/g for cerium(Ce3+). The findings from FTIR and XPS analyses provide insights into the adsorption mechanism. It is revealed that hydroxo-complexes, such as La-(OH)x and Ce-(OH)x, are adsorbed onto the CMCNF-CA aerogel through strong electrostatic interactions with the –COOH groups. This leads to the formation of metal ionic crosslinking. Remarkably, the CMCNF-CA aerogel maintains its high adsorption performance even after undergoing five consecutive adsorption-desorption cycles. Based on these results, we demonstrate that the CMCNF-CA aerogel is an efficient and reusable adsorbent for the sustainable recovery of La3+ and Ce3+ from aqueous solutions. This study offers promising prospects for addressing the challenges in the recycling of REEs, highlighting the potential of the CMCNF-CA aerogel as a practical solution in the field of REE recovery.

Intermolecular electron transfer in radical SAM enzymes as a new paradigm for reductive activation

Radical S-adenosyl-L-methionine (rSAM) enzymes bind one or more Fe-S clusters and catalyze transformations that produce complex and structurally diverse natural products. One of the clusters, a 4Fe-4S cluster, binds and reductively cleaves SAM to generate the 5'-deoxyadenosyl radical, which initiates the catalytic cycle by H-atom transfer from the substrate. The role(s) of the additional auxiliary Fe-S clusters (ACs) remains largely enigmatic. The rSAM enzyme PapB catalyzes the formation of thioether cross-links between the β-carbon of an Asp and a Cys thiolate found in the PapA peptide. One of the twoACs in the protein binds to the substrate thiol where, upon formation of a thioether bond, one reducing equivalent is returned to the protein. However, for the next catalytic cycle to occur, the protein must undergo an electronic state isomerization, returning the electron to the SAM-binding cluster. Using a series of iron-sulfur cluster deletion mutants, our data support a model whereby the isomerization is an obligatorily intermolecular electron transfer event that can be mediated by redox active proteins or small molecules, likely via the second AC in PapB. Surprisingly, a mixture of FMN and NADPH is sufficient to support both the reductive and the isomerization steps. These findings lead to a new paradigm involving intermolecular electron transfer steps in the activation of rSAM enzymes that require multiple iron-sulfur clusters for turnover. The implications of these results for the biological activation of rSAM enzymes are discussed.

Robust Chemoenzymatic Synthesis of Keratinimicin Aglycone Analogues Facilitated by the Structure and Selectivity of OxyB.

The emergence of multidrug-resistant pathogens poses a threat to public health and requires new antimicrobial agents. As the archetypal glycopeptide antibiotic (GPA) used against drug-resistant Gram-positive pathogens, vancomycin provides a promising starting point. Peripheral alterations to the vancomycin scaffold have enabled the development of new GPAs. However, modifying the core remains challenging due to the size and complexity of this compound family. The recent successful chemoenzymatic synthesis of vancomycin suggests that such an approach can be broadly applied. Herein, we describe the expansion of chemoenzymatic strategies to encompass type II GPAs bearing all aromatic amino acids through the production of the aglycone analogue of keratinimicin A, a GPA that is 5-fold more potent than vancomycin against Clostridioides difficile. In the course of these studies, we found that the cytochrome P450 enzyme OxyBker boasts both broad substrate tolerance and remarkable selectivity in the formation of the first aryl ether cross-link on the linear peptide precursors. The X-ray crystal structure of OxyBker, determined to 2.8 Å, points to structural features that may contribute to these properties. Our results set the stage for using OxyBker broadly as a biocatalyst toward the chemoenzymatic synthesis of diverse GPA analogues.

Effect of addition of triallyl isocyanurate and post‐ultraviolet irradiation on the selected properties of composites of poly(lactic acid), poly(butylene succinate) and nano‐sized calcium carbonate

AbstractComposites of poly(lactic acid) (PLA), poly(butylene succinate) (PBS), and nano‐sized calcium carbonate (CaCO3) with triallyl isocyanurate (TAIC), glycidyl methacrylate and benzophenone (BP) were prepared by using a double screw extruder and blown into films by extrusion blow molding. After exposure to ultraviolet (UV) light at 10, 20, and 40 J/cm2 of irradiation doses, the selected performances of the irradiated films were investigated. UV irradiation increased the tensile performances but had little effect on the thermal behaviors. Scanning electron microscope revealed that UV irradiation enhanced the connection between the two phases of PLA and PBS. The improvement in tensile properties was attributed to the formation of crosslinking during UV irradiation in the presence of TAIC and BP and the enhancement of the interface bonding between the two. However, excessive exposure reduced the elongation at break and fracture energy, attributed to the molecular chain breakage at high doses. On the other hand, the tensile performances improved and the light transmission decreased with increasing the TAIC content up to 2.5 phr after UV exposure at the same irradiation dose. UV irradiation was revealed to be a simple and effective technique to improve the tensile performances of LA/PBS/CaCO3 films with bicontinuous phases.

Exploring the Interplay between Polyphenols and Lysyl Oxidase Enzymes for Maintaining Extracellular Matrix Homeostasis.

Collagen, the most abundant structural protein found in mammals, plays a vital role as a constituent of the extracellular matrix (ECM) that surrounds cells. Collagen fibrils are strengthened through the formation of covalent cross-links, which involve complex enzymatic and non-enzymatic reactions. Lysyl oxidase (LOX) is responsible for catalyzing the oxidative deamination of lysine and hydroxylysine residues, resulting in the production of aldehydes, allysine, and hydroxyallysine. These intermediates undergo spontaneous condensation reactions, leading to the formation of immature cross-links, which are the initial step in the development of mature covalent cross-links. Additionally, non-enzymatic glycation contributes to the formation of abnormal cross-linking in collagen fibrils. During glycation, specific lysine and arginine residues in collagen are modified by reducing sugars, leading to the creation of Advanced Glycation End-products (AGEs). These AGEs have been associated with changes in the mechanical properties of collagen fibers. Interestingly, various studies have reported that plant polyphenols possess amine oxidase-like activity and can act as potent inhibitors of protein glycation. This review article focuses on compiling the literature describing polyphenols with amine oxidase-like activity and antiglycation properties. Specifically, we explore the molecular mechanisms by which specific flavonoids impact or protect the normal collagen cross-linking process. Furthermore, we discuss how these dual activities can be harnessed to generate properly cross-linked collagen molecules, thereby promoting the stabilization of highly organized collagen fibrils.

Characterization and Mechanism of Gel Deterioration of Egg Yolk Powder during Storage.

Egg yolk forms have several health and industrial applications, but their storage characteristics and gel mechanisms have not been thoroughly studied. In order to investigate the relationship between the changes in structure and properties of egg yolk gel and egg yolk powder during storage, in this paper, egg yolk powder was stored at 37 °C for 0, 1, 3, and 6 months in an accelerated storage experiment, and the influence of storage time on the gel properties of egg yolk powder was analyzed. The results showed that the contents of protein carbonylation and sulfhydryl in the yolk decreased gradually with the extension of storage time. Circular dichroism and fluorescence spectra showed that the ordered structure and structural stability of egg yolk proteins decreased gradually. Oxidation led to the formation of intermolecular crosslinking in the egg yolk proteins and oxidized aggregates, resulting in a decrease in surface hydrophobicity, which affected the gel properties of the egg yolk powder after rehydration, resulting in the phenomenon of lipid migration and gel degradation. The results provide a theoretical basis for improving egg yolk powder's overall quality and storage stability.

Characterisation, slow-release, and antibacterial properties of carboxymethyl chitosan/inulin hydrogel film loaded with novel antilisterial durancin GL

This paper reports the development of a hydrogel film with antibacterial activity and controlled release characteristics. Carboxymethyl chitosan (CMCS) is grafted onto durancin GL and inulin via a mediated reaction between N-hydroxysuccinimide and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Rheology tests, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy, and lap shear tests confirmed the formation of a stable chemical cross-linking and excellent adhesion hydrogel with 4 % CMCS and 8 % inulin. The CMCS/inulin hydrogel film loaded with durancin GL appears transparent and uniform. FTIR spectroscopy results reveal the interaction mode among CMCS, inulin, durancin GL, and the hydrogel film structure. Cross-linking improved thermal stability and water-vapour barrier performance. The hydrophobicity of CMCS/inulin @Durancin GL increased under a durancin GL concentration of 0.036 g/30 mL, and the release of active substances is prolonged. In-vitro antibacterial capacity and salmon preservation experiments show that the addition of durancin GL enhanced the antibacterial activity of the hydrogel film. Therefore, CMCS/inulin@Durancin GL hydrogel films can be used as fresh-keeping packaging materials in practical applications.

Synthesis of diamond nanoparticles/urethane-based bio-adhesive and investigation of its morphology and thermal, physicomechanical, and biological properties

Diamond nanoparticles/urethane-based bio-adhesives (ND-U-BA) were synthesized via in-situ polymerization. Chemical structure and curing kinetics of the samples were studied by Fourier-transform infrared spectroscopy. Results showed NDs controlled the curing profile of samples. Thermal and crystalline properties were studied using differential scanning calorimetry and X-ray diffraction analyses. Results indicated hard segments had higher ordering levels in the presence of NDs which is due to the lower hydrogen bonding among polyurethane chains. Mechanical results showed ND-U-BA had higher adhesion strength due to the formation of chemical crosslinks and a controlled curing mechanism. MTT and biodegradation studies showed ND-U-BA had acceptable cell viability and degradation content. • Urethane and diamond nanoparticles/urethane-based bio-adhesives were synthesized. • Results showed ND nanoparticles had controlling effect on curing kinetic of samples. • Cell viability of bio-adhesives was improved with the ND nanoparticles’ addition. • Incorporation of ND nanoparticles increased the adhesion strength of bio-adhesive.

Tableting-induced mechanochemical matrix crosslinking: Towards non-disintegrating chitosan-based sustained delivery tablets

BackgroundMechanochemistry involves the application of mechanical force to induce chemical changes in the material solid state. Mechanochemistry promises to overcome many drawbacks in pharmaceutical formulation. Chitosan (CS), a semisynthetic polymer obtained by N-deacetylation of chitin, has attracted attention in various biomedical and pharmaceutical applications. MethodsCS was grafted with 2,4-dichlorophenoxyacetic acid (2,4-D), a significantly hydrophobic and safe substituent, to promote facile adsorption of CO2. Physical mixtures and corresponding tablets comprised of model drugs and CS-2,4-D were prepared and characterized by DSC, XRD, and IR, and were compared with pure drugs and their mixtures with unmodified CS. Tensile strength and drug-release profiles of CS-2,4-D tablets were evaluated and compared with counterparts prepared from unmodified CS. ResultsAdsorbed CO2 promoted the formation of powerful and extensive carbamate crosslinks within CS-2,4-D upon mechanochemical stress induced by mixing the new polymer with model drugs followed by tableting. Corresponding tablets showed increased tensile strength, sustained drug release and resistance to disintegration over 72 h of exposure to dissolution media. MTT bioassay indicated CS-2,4-D to be less cytotoxic than unmodified CS. Conclusionsthe current study provided a proof-of-principle on tableting mediated mechanochemical matrix crosslinking.

Metal- and Peroxide-Free Silicone Rubbers with Antibacterial Properties Obtained at Room Temperature

Metal- and peroxide-free silicone rubbers were obtained via a reaction between amino-containing poly(dimethylsiloxanes) (amino-terminated (APDMS-1) or a copolymer with pendant amino groups (APDMS-2)) and iodine-containing polysiloxanes (PIMSs) (Menshutkin reaction). Simple mixing of functional polymers at room temperature resulted in forming silicone materials. The formation of ammonium cross-links was confirmed using solid-state 1H and 13C NMR spectroscopy. The equimolar ratio of NH2 groups to the I-containing moiety (1:1) was the most optimal among other ratios (2:1 and 1:2) to carry out cross-linking and led to the highest cross-linking density according to the swelling measurements. PIMS/APDMS-1 (1:1) rubbers had the lowest average molecular weight of segments between cross-links Mc = 250 compared to PIMSs/APDMS-1 (1:2) and (2:1) with Mc = 1110 and 390, respectively. The obtained silicone rubbers showed antibacterial activity against Escherichia coli and Staphylococcus aureus and thereby could be applied in biomedicine and the food industry as antibacterial coatings and materials.

A Single DNA Point Mutation Leads to the Formation of a Cysteine-Tyrosine Crosslink in the Cysteine Dioxygenase from Bacillus subtilis.

Cysteine dioxygenase (CDO) is a non-heme iron-containing enzyme that catalyzes the oxidation of cysteine (Cys) to cysteine sulfinic acid (CSA). Crystal structures of eukaryotic CDOs revealed the presence of an unusual crosslink between the sulfur of a cysteine residue (C93 in Mus musculus CDO, MmCDO) and a carbon atom adjacent to the phenyl group of a tyrosine residue (Y157). Formation of this crosslink occurs over time as a byproduct of catalysis and increases the catalytic efficiency of CDO by at least 10-fold. Interestingly, in bacterial CDOs, the residue corresponding to C93 is replaced by a highly conserved glycine (G82 in Bacillus subtilis CDO, BsCDO), which precludes the formation of a C-Y crosslink in these enzymes; yet bacterial CDOs achieve turnover rates paralleling those of fully crosslinked eukaryotic CDOs. In the present study, we prepared the G82C variant of BsCDO to determine if a single DNA point mutation could lead to C-Y crosslink formation in this enzyme. We used gel electrophoresis, peptide mass spectrometry, electron paramagnetic resonance spectroscopy, and kinetic assays to characterize this variant alongside the natively crosslinked wild-type (WT) MmCDO and the natively non-crosslinked WT BsCDO. Collectively, our results provide compelling evidence that the G82C BsCDO variant is indeed capable of C-Y crosslink formation. Our kinetic studies indicate that G82C BsCDO has a reduced catalytic efficiency compared to WT BsCDO and that activity increases as the ratio of crosslinked to non-crosslinked enzyme increases. Finally, by carrying out a bioinformatic analysis of the CDO family, we were able to identify a large number of putatively crosslinked bacterial CDOs, the majority of which are from Gram-negative pathogenic bacteria.