Rate Of Crosslinking Research Articles

Detecting the Formation Kinetics of Doxorubicin-DNA Interstrand Cross-link at the Single-Molecule Level and Clinically Relevant Concentrations of Doxorubicin.

Doxorubicin (DOX) ranks among the most effective anticancer agents. Increasing the formation of covalent DOX-DNA interstrand cross-links can improve the anticancer activity of DOX. However, due to the low stability of the DOX-DNA cross-links to heat and alkali, DOX can be extensively lost during isolation procedures of biochemical methods, thus reducing the apparent clinical relevance of this mechanism. Here, we developed a drug label-free, single-molecule magnetic tweezers assay that can detect a single DOX-DNA cross-link on the basis of the significant increase of the unzipping forces of DNA hairpins upon drug binding. Using this assay, we measured the DOX concentration-dependent cross-linking rates at clinically relevant concentrations of DOX. We report an ∼26-fold higher formaldehyde concentration dependence of cross-linking rates than previously reported and 0.9 ± 0.8 cross-links/103 bp at the clinically relevant concentrations of 70 nM DOX and 50 μM formaldehyde. Our results suggest a much higher cross-link formation ability than previous bulk measurements have reported and suggest that the cross-linking mechanism has promising therapeutic potential. This general method can be used to detect the formation kinetics of other DNA lesions or DNA adducts that affect DNA duplex stability.

Vanillin Acrylate-Based Resins for Optical 3D Printing.

The investigation of biobased systems as photocurable resins for optical 3D printing has attracted great attention in recent years; therefore, novel vanillin acrylate-based resins were designed and investigated. Cross-linked polymers were prepared by radical photopolymerization of vanillin derivatives (vanillin dimethacrylate and vanillin diacrylate) using ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate as photoinitiator. The changes of rheological properties were examined during the curing with ultraviolet/visible irradiation to detect the influences of solvent, photoinitiator, and vanillin derivative on cross-linking rate and network formation. Vanillin diacrylate-based polymers had higher values of yield of insoluble fraction, thermal stability, and better mechanical properties in comparison to vanillin dimethacrylate-based polymers. Moreover, the vanillin diacrylate polymer film showed a significant antimicrobial effect, only a bit weaker than that of chitosan film. Thermal and mechanical properties of vanillin acrylate-based polymers were comparable with those of commercial petroleum-derived materials used in optical 3D printing. Also, vanillin diacrylate proved to be well-suited for optical printing as was demonstrated by employing direct laser writing 3D lithography and microtransfer molding techniques.

Genetic Control of Radical Cross-linking in a Semisynthetic Hydrogel.

Enhancing materials with the qualities of living systems, including sensing, computation, and adaptation, is an important challenge in designing next-generation technologies. Living materials address this challenge by incorporating live cells as actuating components that control material function. For abiotic materials, this requires new methods that couple genetic and metabolic processes to material properties. Toward this goal, we demonstrate that extracellular electron transfer (EET) from Shewanella oneidensis can be leveraged to control radical cross-linking of a methacrylate-functionalized hyaluronic acid hydrogel. Cross-linking rates and hydrogel mechanics, specifically storage modulus, were dependent on various chemical and biological factors, including S. oneidensis genotype. Bacteria remained viable and metabolically active in the networks for a least 1 week, while cell tracking revealed that EET genes also encode control over hydrogel microstructure. Moreover, construction of an inducible gene circuit allowed transcriptional control of storage modulus and cross-linking rate via the tailored expression of a key electron transfer protein, MtrC. Finally, we quantitatively modeled hydrogel stiffness as a function of steady-state mtrC expression and generalized this result by demonstrating the strong relationship between relative gene expression and material properties. This general mechanism for radical cross-linking provides a foundation for programming the form and function of synthetic materials through genetic control over extracellular electron transfer.

Effect of Binding Site Mutations in Fibrinogen αC (233-425) On FXIII Substrate Specificity

In blood coagulation, the transglutaminase Factor XIII (FXIII) catalyzes the crosslinking of specific glutamine and lysine residues between fibrin and other coagulation proteins to generate fibrin clots resistant to fibrinolysis. The αC region (233-425) of the fibrinogen alpha chain contains three reactive glutamines (Q237, Q328, Q366) and a putative FXIII binding region (αC 389-403), where E396 is reported to be the key binding residue. FXIII can be activated proteolytically by thrombin with low calcium concentration (∼4 mM Ca2+, FXIIIA°) or non-proteolytically with high calcium concentration (>25 mM Ca2+, FXIII A°), both leading to FXIIIA conformational sets that vary in transglutaminase activity. These features were explored further by assaying glutamine reactivities (Fbg αC WT, E396A, and αC 389Stop) with the lysine mimic glycine ethyl ester (GEE) by MALDI-ToF mass spectrometry. Across all αC variants, the reactivity ranking from FXIII A° and FXIII A° was Q237 >> Q366 ∼ Q328. Neither the αC E396A (233-425) nor the αC 389Stop (233-388) mutant prevented transglutaminase activity from FXIII A° or FXIII A°. However, the Q237-GEE crosslinking rate for either mutant was hindered compared to WT for both FXIIIA forms. Removal of the putative FXIII binding region in αC 389Stop had less of an adverse effect on FXIII A°-catalyzed GEE crosslinking to Q237 than αC E396A. Additionally, the Q237-GEE crosslinking in αC 389Stop was slightly faster with FXIII A° than with A°, in contrast to WT and E396A where FXIII A' crosslinking was faster. Overall for the FXIII A° studies, the Q-reactivities were WT > E396A > 389Stop whereas with FXIII A°, they were relatively similar. Differences in transglutaminase function between FXIII A° and FXIII A° involve more than activity and include how they interface with substrates like Fbg αC.

Возможность применения пластометра Брабендера для изучения пероксидной сшивки полиэтилена. Часть 2. Применение смеси 1,3- и 1,4-бис(трет-бутилпероксиизопропил)бензола для сшивки полиэтилена

The paper shows the possibility of using the mixture 1,3- and 1,4-bis(tert-butylperoxyisopropyl)-benzene as a cross-linking agent in the production of polyethylene foam. Most often, cross-linked polyethylene foam, which has high performance properties, is obtained by pressing, using azoicarbonamide as a foaming agent and dicumyl peroxide as a cross-linking agent. Dicumyl peroxide has a significant drawback: high toxicity of decomposition products. Using the soxlet extratctor, the optimal degree of crosslinking (57-62%) required to obtain foam with optimal performance properties was determined. Using the brabender plastograph, which allows you to study, in a wide range of values, the crosslinking kinetics. It was found that the degree of crosslinking 57-62% corresponds to the torque in the range of 1700-2500 g∙m. a comparative characteristic of two crosslinking agents is given: traditional (dicumyl peroxide) and the studied peroxide. It was found that the crosslinking rate in the presence of the mixture 1,3- and 1,4-bis(tert-butylperoxyisopropyl)-benzene is significantly lower, but the final degree of crosslinking is at the same level as when using dicumyl peroxide. The dependence of the maximum torque on temperature is studied. There are restrictions on the Use of the brabender plastometer for studying the crosslinking kinetics. When the degree of crosslinking is more than 70%, the composition goes into a non-melting state, and the device's performance drops sharply. For practical use of the mixture 1,3- and 1,4-bis(tert-butylperoxyisopropyl)-benzene, the degree of crosslinking in the presence of the foaming agent azodicarbonamide was studied. It is shown that the introduction of a gas-forming agent (azodicarbonamide) into the composition significantly reduces the degree of crosslinking of polyethylene foam only in the case of the mixture 1,3- and 1,4-bis(tert-butylperoxyisopropyl)benzene. The optimal concentration of new crosslinking peroxides, allowing to foam, density 80-100 kg/m3, not inferior to original compositions by main technical-economic indicators have been determined.

Chemically triggered crosslinking with bioorthogonal cyclopropenones.

We report a proximity-driven crosslinking strategy featuring bioorthogonal cyclopropenones. These motifs react with phosphines to form electrophilic ketene-ylides. Such intermediates can be trapped by neighboring proteins to form covalent adducts. Successful crosslinking was achieved using a model split reporter, and the rate of crosslinking could be tuned using different phosphine triggers. We further demonstrated that the reaction can be performed in cell lysate. Based on these features, we anticipate that cyclopropenones will enable unique studies of protein-protein and other biomolecule interactions.

Bifidobacterium-mediated high-intensity focused ultrasound for solid tumor therapy: comparison of two nanoparticle delivery methods

Purpose This study was conducted to prepare a novel tumor-biotargeting high-intensity focused ultrasound (HIFU) synergist for indirectly delivering lipid nanoparticles based on the targeting ability of Bifidobacterium longum to the hypoxic region of solid tumors. The effects of two different delivery methods on the imaging and treatment of solid tumors enhanced by lipid nanoparticles were compared. Methods Biotinylated lipid nanoparticles coated with PFH were prepared, cross-linked with B. longum in vitro using a streptavidin-conjugated B. longum antibody (SBA), and observed and detected by laser confocal microscopy and flow cytometry. Solid tumors were treated with HIFU and PFH/BL-NPs. The effects of different delivery methods on the tumor targeting and efficiency of retention of PFH/BL-NPs were observed using Small animal live imaging and frozen sections from small animals. Results The PFH/BL-NPs prepared in this study showed good biocompatibility and safety. PFH/BL-NPs and B. longum were cross-linked in a cluster-like manner (confocal laser scanning microscope) in vitro, with a cross-linking rate of 84 ± 6.23% (flow cytometry). The delivery of B. longum followed by that of PFH/BL-NPs not only enhanced the ability of PFH/BL-NPs to target solid tumors (small animal live imaging), but also increased the retention time of PFH/BL-NPs in the tumor (frozen slices), enhancing the effect of the HIFU synergist. Conclusion Delivery of B. longum followed by that of PFH/BL-NPs can enhance the imaging of solid tumors and effectively improve the efficiency of HIFU treatment of solid tumors, providing a basis for further clinical work.

Waterborne Methacrylate-Based Vitrimers.

We demonstrate waterborne, unimolecularly dissolved vitrimer prepolymer systems that can be transferred into a vitrimer material using catalytic transesterification. The one-component prepolymer system can be processed via film casting and subsequent heat-induced cross-linking. A variation of the density of side chain hydroxy groups over ester and amide groups in the methacrylate/methacrylamide backbone, as well as of the Lewis acid catalyst loading, allow control of the extent of cross-linking and exchange rates. The increase of the amount of both catalyst and hydroxy groups leads to an acceleration of the relaxation times and a decrease of the activation energy of the transesterification reactions. The system features elastomeric properties, and the tensile properties are maintained after two recycling steps. Thus far, vitrimers have been limited largely to hydrophobic polymers; this system is a step forward toward waterborne, one-component materials, and we demonstrate its use in waterborne bioinspired nanocomposites.

Effects of modified silica on the co‐vulcanization kinetics and mechanical performances of natural rubber/styrene–butadiene rubber blends

ABSTRACTRubber blends are widely used for combining the advantages of each rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co‐vulcanization process is still a challenge. Herein, high‐resolution pyrolysis gas chromatography–mass spectrometry (HR PyGC‐MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene–butadiene rubber (SBR) in NR/SBR blends filled with modified silica (SiO2). The reaction rates of crosslinking of each rubber phase in NR/SBR were calculated, which showed that the crosslinking rates of NR were much lower than those of SBR phase in the unfilled blends and blends filled with unmodified and silane modified silica. Interestingly, the vulcanization rates of NR and SBR phase were approximately same in the vulcanization accelerator modified silica filled blends, showing better co‐vulcanization. In addition, the vulcanization accelerator modified silica was uniformly dispersed and endowed rubber blends with higher mechanical strength compared to the untreated silica. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2020,137, 48838.

Effect of organoclay content on mechanical and rheological properties of dynamically cross-linked acrylonitrile-butadiene rubber/poly(ethylene-co-vinyl acetate)/organoclay nanocomposites

Blends of poly(ethylene-co-vinyl acetate) (EVA) and acrylonitrile-butadiene rubber (NBR) with NBR content of 50 wt% and organoclay (OC) contents of 1, 3, 5 and 7 wt% have been prepared and cross-linked with 0.3 wt% dicumyl peroxide (DCP) in an internal mixer. The results obtained from x-ray diffraction and transmission electron microscopy for the uncross-linked nanocomposites containing 7 wt% OC show that although a part of the nanofiller layers are exfoliated, the rest of the particles remained almost intercalated. However, it is found that cross-linking with DCP markedly increased the amount of exfoliated platelets. The results also reveal that gel content and cross-linking rate slightly increased in the presence of the OC. The analysis of data obtained from the tensile experiments indicates that the tensile modulus and yield stress of the nanocomposites are superior to those of the unfilled blend and the values improve with the increase in the OC content. Apart from the value of strain at break, all other mechanical properties studied are found to be higher for the cross-linked nanocomposites than those of their uncross-linked counterparts. Moreover, the relaxation ratio and relaxation rate index are decreased with an increase in the OC content for the uncross-linked and cross-linked materials.

In Situ Cyclization of Proteins (INCYPRO): Cross-Link Derivatization Modulates Protein Stability.

Protein macrocyclization represents a very efficient strategy to increase the stability of protein tertiary structures. Here, we describe a panel of novel C3-symmetric tris-electrophilic agents and their use for the cyclization of proteins. These electrophiles are reacted with a protein domain harboring three solvent-exposed cysteine residues, resulting in the in situ cyclization of the protein (INCYPRO). We observe a clear dependency of cross-linking rates on the electrophilicity. All nine obtained cross-linked protein versions show considerably increased thermal stability (up to 29 °C increased melting temperature) when compared to that of the linear precursor. Most interestingly, the degree of stabilization correlates with the hydrophilicity of the cross-link. These results will support the development of novel cross-linked proteins and enable a more rational design process.

Tri-functional phthalonitrile monomer as stiffness increasing additive for easy processable high performance resins

A new tri-functional phthalonitrile monomer tris(3-(3,4-dicyanophenoxy)phenyl) phosphate (TPP) was first synthesized and characterized with the intent of increasing the cross-linking rate of phthalonitrile resins. By combining TTP and di-functional phthalonitrile with aromatic diamine easy-processable formulations (η < 200 mPa·s at 150 °C) were developed. Thermosets were derived from the formulations by curing at 330 and 375 °C. The polymers that were post-cured at 375 °C demonstrated Young's moduli up to 7.2 GPa — which is the highest value reported for phthalonitriles. Thermal stability of these materials was on the high level featured to phthalonitriles (Tg > 450 °C, T5% > 500 °C, TOS5% > 500 °C, Yc at 900 °C > 80%). TPP, the introduced monomer, can be used as a stiffness increasing additive with common di-functional phthalonitriles, and easy-processable formulations for cost-effective techniques of composites manufacturing.

Predicting degradation rate of genipin cross-linked gelatin scaffolds with machine learning.

Genipin can improve weak mechanical properties and control high degradation rate of gelatin, as a cross-linker of gelatin which is widely used in tissue engineering. In this study, genipin cross-linked gelatin biodegradable porous scaffolds with different weight percentages of gelatin and genipin were prepared for tissue regeneration and measurement of their various properties including morphological characteristics, mechanical properties, swelling, degree of crosslinking and degradation rate. Results indicated that the sample containing the highest amount of gelatin and genipin had the highest degree of crosslinking and increasing the percentage of genipin from 0.125% to 0.5% enhances ultimate tensile strength (UTS) up to 113% and 92%, for samples with 2.5% and 10% gelatin, respectively. For these samples, increasing the percentage of genipin, reduce their degradation rate significantly with an average value of 124%. Furthermore, experimental data are used to develop a machine learning model, which compares artificial neural networks (ANN) and kernel ridge regression (KRR) to predict degradation rate of genipin-cross-linked gelatin scaffolds as a property of interest. The predicted degradation rate demonstrates that the ANN, with mean squared error (MSE) of 2.68%, outperforms the KRR with MSE = 4.78% in terms of accuracy. These results suggest that machine learning models offer an excellent prediction accuracy to estimate the degradation rate which will significantly help reducing experimental costs needed to carry out scaffold design.

Effects of vulcanization accelerator functionalized graphene on the co-vulcanization kinetics and mechanical strength of NR/SBR blends

Rubber blends are widely used for combining the advantages of individual rubber component. However, to date, how to determine and distinguish the vulcanization kinetics for each single rubber phase in rubber blends during the co-vulcanization process are still a challenge. Herein, high resolution pyrolysis gas chromatography-mass spectrometry (PyGC-MS) was employed for the first time to investigate the vulcanization kinetics of natural rubber (NR) and styrene-butadiene rubber (SBR) in their blends filled with graphene. It is shown that the crosslinking rate of NR chains (kNR) was much lower than that of SBR chains (kSBR) in the unfilled blends and blends with untreated graphene. Interestingly, the gap between kSBR and kNR was narrowed effectively in the blends with vulcanization accelerator grafted graphene, showing a better co-vulcanization of NR and SBR. In addition, the vulcanization accelerator grafted graphene was uniformly dispersed in rubber matrix and endowed rubber blends with higher mechanical strength and thermal conductivity did the untreated graphene.

The Ultrafast and Continuous Fabrication of a Polydimethylsiloxane Membrane by Ultraviolet-Induced Polymerization.

The polydimethylsiloxane (PDMS) membrane commonly used for separation of biobutanol from fermentation broth fails to meet demand owing to its discontinuous and polluting thermal fabrication. Now, an UV-induced polymerization strategy is proposed to realize the ultrafast and continuous fabrication of the PDMS membrane. UV-crosslinking of synthesized methacrylate-functionalized PDMS (MA-PDMS) is complete within 30 s. The crosslinking rate is three orders of magnitude larger than the conventional thermal crosslinking. The MA-PDMS membrane shows a versatile potential for liquid and gas separations, especially featuring an excellent pervaporation performance for n-butanol. Filler aggregation, the major bottleneck for the development of high-performance mixed matrix membranes (MMMs), is overcome, because the UV polymerization strategy demonstrates a freezing effect towards fillers in polymer, resulting in an extremely high-loading silicalite-1/MA-PDMS MMM with uniform particle distribution.

The Ultrafast and Continuous Fabrication of a Polydimethylsiloxane Membrane by Ultraviolet‐Induced Polymerization

AbstractThe polydimethylsiloxane (PDMS) membrane commonly used for separation of biobutanol from fermentation broth fails to meet demand owing to its discontinuous and polluting thermal fabrication. Now, an UV‐induced polymerization strategy is proposed to realize the ultrafast and continuous fabrication of the PDMS membrane. UV‐crosslinking of synthesized methacrylate‐functionalized PDMS (MA‐PDMS) is complete within 30 s. The crosslinking rate is three orders of magnitude larger than the conventional thermal crosslinking. The MA‐PDMS membrane shows a versatile potential for liquid and gas separations, especially featuring an excellent pervaporation performance for n‐butanol. Filler aggregation, the major bottleneck for the development of high‐performance mixed matrix membranes (MMMs), is overcome, because the UV polymerization strategy demonstrates a freezing effect towards fillers in polymer, resulting in an extremely high‐loading silicalite‐1/MA‐PDMS MMM with uniform particle distribution.

The role of Lys2-Cl- -Lys2 salt linkages in oligomeric intermediates of RbsD protein in Escherichia coli.

As a homo-oligomeric protein, the disassembly of Escherichia coli RbsD decamer produces a urea-unfolded oligomeric intermediate structure, asthe dissociation speed of the protein is lower than that of the unfolding process. There are five Lys2-Cl- -Lys2 salt linkages to connect these subunits. To explore the role of the salt linkages in these oligomeric intermediates, the Lys2Ala mutated in the N-terminal of E. coli RbsD protein subunit was designed. It was found that the RbsD mutation protein (RbsD:K2A) loses its minor larger oligomers, which exist in RbsD, and displays other several oligomeric states (less than decamers), meanwhile the state of the oligomers depends on the protein concentration. It was also found that compared with RbsD, the crosslinking capability of the subunits of RbsD:K2A is weaker, while the crosslinking rate ofdimers is higher, RbsD:K2A needs to substantially adjust its conformation to meet the space requirements when combined with d-ribose. On the basis of these results, we suggest that Lys2-Cl- -Lys2 salt linkages in E. coli RbsD protein play an important role in stabilizing the intermediate products of oligomers and maintaining interaction betweenthe intermediate products of oligomers, which may shedlight on the studyofthese oligomeric proteins.

Gelation via cationic chelation/crosslinking of acrylic‐acid‐based polymers

AbstractThe gelation characteristics of acrylic‐acid‐based polymers in the presence of a range of cationic species, namely Ca2+, Mg2+ and Al3+, were investigated using in situ rheological measurements during photo‐polymerisation. Fourier transform mechanical spectroscopy was used to identify the gel point, using the Winter–Chambon criteria which allow the gel point to be pinpointed by establishing the sample spanning network and quantitatively determining stiffness, relaxation exponent, gel stiffness and fractal dimensions. The results showed that the gelation processes were greatly influenced by the type of cationic species that was used in the syntheses. At the gel point, more open network clusters were formed when Al3+ cations were used instead of Ca2+ cations or Mg2+ cations, all relating to chloride salts. Although the concentrations of the chelating/crosslinking aluminium species affected the kinetics of the gelation, the critical gel characteristics were hardly affected. Also the solubility of the chosen aluminium salt was shown to dictate the crosslinking rates and the properties of the critical gels. The extents of the reactions and the types of network formed at the gel point and beyond indicated that reactions between the Al3+ ions and COOH sites, from growing poly(acrylic acid) molecular chains, differ from those exhibited by Mg2+ and Ca2+ ions. All of the chelation/crosslinking reactions met the criteria of low mutation number (Nmu), such that in all cases Nmu ≪ 1. © 2019 Society of Chemical Industry

Mesoscale model of the assembly and cross-linking of HPV virus-like particles

We present a novel kinetic Monte Carlo model to simulate the real process time-scale of the assembly of Human Papillomavirus (HPV) virus-like particles (VLPs) incorporating the formation of intercapsomeric disulfide bonds. The objective was to develop insights into the underlying mechanisms of HPV VLP assembly and cross-linking during in vitro production of the HPV vaccine. The model integrates actual experimental data and detailed information of VLP geometrical structure in microscopic mechanistic steps. The principal novelty of this model is in the concurrent simulation of VLP assembly and cross-linking including a variable for spatial angular arrangement of capsomeres during their assembly that affects the overall rates of VLP assembly and cross-linking. The cross-linking modeled by using the mechanistic probability rules between involved cysteine residues. The model was utilized to better understand the actual process data and check on the hypothesis related to factors affecting the rates of HPV growth and maturation.

Enhanced capacitance characteristic of microporous carbon spheres through surface modification by oxygen-containing groups

The synthesis of porous carbon spheres with good dispersity and oxygen-rich content from phenolic resin remains challenging due to weak interactions between carbon precursors and soft templates, as well as fast cross-linking rate of precursors. Herein, we demonstrate a facile and efficient organic-organic self-assembly hydrothermal method to prepare microporous carbon spheres (MCSs) with perfect dispersity and rich oxygen-containing groups under highly acidic conditions. Both the precursors and templates are partly protonated by high concentration acid and thus provide an additional Coulombic interactions between resol and F108 via the I+X−S+ mechanism. Such enhanced interaction improve the self-assembly ability of resol and F108, lead to more matching the cross-linking rate of resol, which efficient avoid macroscopic phase separation and aggregate. Results indicate that the MCSs are modified with a considerable number of oxygen-containing functional groups (hydroxyl and carbonyl) under acidic conditions, and the oxygen content increases with the concentration of HCl. The optimal MCSs with a high specific surface area of 1449 m2 g−1, large pore volume of 0.77 cm3 g−1 and high oxygen content of 8.5 at%, exhibits an enhanced specific capacitance of 361 F g−1 and excellent long-term stability (93.8% retention after 10 000 cycles) when used as the electrode materials for supercapacitors. Furthermore, the MCSs based symmetrical supercapacitors delivers a maximum energy density of 18.5 W h kg−1 at power density of 750 W kg−1. This feasible hydrothermal method develops a new strategy for the fabrication of functionalized porous carbon spheres.