Intermolecular Crosslinking Reactions Research Articles

Influence of polyethylene glycol-based deep eutectic solvent on vulcanization and mechanical properties of natural rubber gum vulcanizates

Rubber vulcanization generates volatile organic compounds emissions associated with the intermolecular crosslinking reactions at rather higher temperatures mediated by many kinds of indispensable additive. To achieve the carbon peaking and neutrality targets in China, rubber processing industries call for ecofriendly, green additives to satisfy demands of high-efficiency vulcanization at low temperatures. Herein an oligomer deep eutectic solvent (DES) based on polyethylene glycol is used for the first time for regulating vulcanization kinetics of natural rubber (NR) gums. It is found that DES at 0.2–1.0 phr (parts per hundred parts of rubber) dosages could accelerate the vulcanization at 120–140 °C without marked influences on crosslinking density and storage modulus at vulcanization equilibrium. The vulcanization of DES-containing gums at 120 °C is faster than that of the DES-free one at 140 °C while the DES-containing vulcanizates cured at 120 °C exhibit nonlinear rheological responses being similar to the DES-free one cured at 140 °C. The low-temperature vulcanization in general generates vulcanizates exhibiting higher tensile strength in comparison with those cured at 140 °C. Furthermore, DES could not influence the Mullins effect of the vulcanizates undergoing cyclic tension deformation. The results show that the non-volatile DES could be used to adjust the vulcanization kinetics without impact on the crosslinking density and Mullins effect, paving the way for developing energy-saving green vulcanization technologies.

Enhanced Penetration and Retention of CuS‐Based Nanosystem Through NIR Light and In Situ Enzyme Response for Improved Tumor Therapy

AbstractThe efficient way to increase the therapeutic efficacy of nanomedicines is by encouraging the penetration and enhancing the retention of nanoparticles at the tumor site. However, it is a serious dilemma that small nanoparticles can penetrate deep into the tumor tissue but easily be cleared into the surrounding tissues. In order to solve this dilemma, a smart nanosystem is created to address this problem, ensuring both the effective penetration of tiny nanoparticles (NPs) and their appropriate retention at the tumor site. CuS NPs that is modified with peptides are prepared facilely, and can aggregate in situ through the intermolecular crosslinking reaction catalyzed by the transglutaminase (TGase) abundantly expressed at the tumor site, resulting in an outstanding photothermal effect for tumor therapy. Upon NIR irradiation, the photothermal effect of CuS‐K and CuS‐Q induced the disintegration of liposomes and prompted the release of CuS‐K, CuS‐Q, and indocyanine green (ICG). Simultaneously, CuS‐K and CuS‐Q aggregated under the catalysis of TGase after being internalized by tumor cells to enhance photothermal therapy. The current study provides valuable inspiration to design nanomedicines with prolonged circulation time in the blood system, better penetration, and retention at the tumor site, and multimodal tumor therapy to achieve the desired therapeutic efficacy.

Physicochemical properties of zein films cross-linked with glutaraldehyde

To improve the mechanical properties of zein films, glycerol (GLY) and glutaraldehyde (GDA) were, respectively, selected as plasticizer and cross-linking agent to fabricate modified zein films by casting method. It was generally believed that the tensile strength (TS) of the modified film was improved with more GDA content. However, there was an interesting phenomenon that above 1 wt% GDA would reduce the TS value. Optimum films were obtained by using 25 wt% GLY and 1 wt% GDA, given dry state properties of tensile strength (TS), elongation at break (EAB %), oxygen transmission rate as 15.22 MPa, 4.25%, 15.5061 cm3/(m2·24 h·0.1 MPa). Circular dichroism (CD) spectroscopy and rheological properties of the film-forming solutions were evaluated. The films were further characterized through using Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), oxygen-permeability coefficient (OTR), transmittance (T%) and water contact angle (CA). The cross-linking mechanism of zein films was demonstrated that GLY was effective to fully “lubricate” between the zein molecular chains, GDA was beneficial to obtain the network structure through intra- and intermolecular cross-linking reactions of zein protein. Improving the understanding of this cross-linking mechanism can be useful to develop an environment-friendly, biodegradable polymer which has a strong potential in the packaging industrial applications.

Managing of hydrogen bonding in aqueous poly(vinyl alcohol) solutions: new perspectives towards preparation of more homogeneous poly(vinyl butyral)

This paper follows up investigations in the field of solution properties of poly(vinyl alcohol). Here we present a combined investigation based on both theoretical and various experimental methods focused on peculiarities in hydrogen bond reorganization in aqueous poly(vinyl alcohol) solutions discussed as a function of temperature. It was demonstrated that the specific polymeric effect takes place in binary poly(vinyl alcohol)/water systems. The effect is characterized by the delay in response of the polymer system on heating until the critical temperature is reached. It was demonstrated in this paper that hydrogen bond reorganization in binary aqueous systems may lead to an increase in the degree of undesirable intermolecular cross-linking reaction. This finding was in contrast to previously made proposition based on hydrogen bond reorganization in ternary poly(vinyl alcohol) solutions. This assumption based on the theoretical studies was confirmed experimentally. Thus, a series of poly(vinyl butyral) samples were synthesized in various solvents using traditional catalysts (HCl) as well as the modern thermosensitive polymeric catalyst. It was demonstrated by using GPC and viscometry experiments that poly(vinyl butyral) samples with a low degree of acetalization (<10%) prepared in water in the absence of co-solvent additives are characterized by large molecular weights and bimodal molecular weight distribution. On the contrary, polymers prepared in mixed (ternary) systems and in the presence of a thermosensitive polymeric catalyst demonstrate relatively narrow molecular weight distribution. This indicates the preparation of more homogeneous products which also facilitates mechanisms of hydrogen bond reorganizations observed in binary and ternary poly(vinyl alcohol) solutions.

A highly stable PBI solvent resistant nanofiltration membrane prepared via versatile and simple crosslinking process

A polybenzimidazole (PBI) solvent resistant nanofiltration (SRNF) membrane with super high stability is designed and fabricated by a simple and effective intermolecular cross-linking reaction. There is a dramatic improvement in the solvent stability of the PBI membranes after crosslinking. The membrane keeps stable in even strong apolar solvent like N,N-dimethyl formamide (DMF), N,N-dimethylacetamide (DMAc) after crosslinking. The morphology together with performance can be easily tuned by the polymer concentration. The results indicate that with increasing polymer concentration in cast solution, an increased rejection and a decreased flux are realized. The prepared cross-linked membranes show a rejection of 99% on Rose Bengal (RB) in Ethanol, isopropanol (IPA) and DMF, exhibiting very good prospects in SRNF application. This paper provides a simple and versatile way to create PBI SRNF membranes.

Unraveling Polymer Structures with RAFT Polymerization and Diels–Alder Chemistry

Using Diels–Alders (DA) chemistry as a dynamic-covalent linkage, we explored the kinetic growth mechanism of polymer structures including starlike materials and nanogels. The use of reversible addition–fragmentation chain transfer (RAFT) polymerization allows for precise control of DA linkages within the polymer backbone. Controlling the competition between intra- and intermolecular cross-linking reactions allows for the preparation of polymer structures that can expand their volume after cleavage of the DA linkages as determined by dynamic light scattering (DLS). Macroscopically, this would be analogous to untying a rope ball knot, commonly termed a “monkey’s fist”.

Investigation of degradation pathways of poly(semiperfluoroalkyl methacrylate) thin films induced by electron‐beam irradiation

ABSTRACTIn this article, we report the results of high‐energy electron beam (e‐beam) irradiation of polymer thin films made of poly(semiperfluoroalkyl methacrylate)s (PRFMAs) and propose plausible chemical reactions that may cause their solubility to change in fluorous liquids. It was observed that the polymer films were converted to a more soluble state under low exposure doses of e‐beam, possibly due to main‐chain scission. However, the films became insoluble with higher doses of e‐beam. Three hypotheses were proposed to explain the reduction in solubility, and we used data from Fourier transform infrared spectroscopy, X‐ray photoelectron spectroscopy, mass spectrometry (MS), and nanoindentation to eliminate the less probable hypotheses. The results derived from e‐beam‐irradiated thin films of three PRFMAs showed that the radical‐related Norrish Type I and II pathways may not be the main decomposition routes. The data also suggested that sufficient scission reactions of the perfluorooctyl moieties of PRFMAs do not occur by e‐beam. We therefore assumed that the decrease in solubility of the fluorinated polymers results from intermolecular crosslinking reactions between the free radicals and reactive moieties generated on the perfluorooctyl groups by the e‐beam. The unique imaging mechanism of PRFMAs may be developed further to synthesize radiation‐sensitive materials working under e‐beam and extreme ultraviolet (λ = 13.5 nm) lithography conditions for advanced patterning applications. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 2672–2680

Controlled Cationic Polymerization of 1‐Methoxy‐1,3‐Butadiene: Long‐Lived Species‐Mediated Reaction and Control over Microstructure with Weak Lewis Bases

ABSTRACTControlled cationic polymerization of trans‐1‐methoxy‐1,3‐butadiene was achieved through the design of appropriate initiating systems, yielding soluble polymers with controllable molecular weights. The combined use of SnCl4 or GaCl3 as a Lewis acid catalyst and a weak Lewis base in conjunction with HCl as a protonogen resulted in efficient and controlled polymerization. The Mn values of the product polymers increased linearly along the theoretical line, which indicates that intermolecular crosslinking reactions negligibly occurred. In addition, the polymer microstructure was critically dependent on the weak Lewis base employed. In particular, the use of tetrahydrofuran as an additive resulted in the highest 4,1/4,3‐structure ratio (96/4). Weak Lewis bases also affected the polymerization rates but exhibited unique trends that differed from their effects on the cationic polymerization of alkyl vinyl ethers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 288–296

Thermoresponsive phenolic formaldehyde amines with strong intrinsic photoluminescence: Preparation, characterization and application as hardeners in waterborne epoxy resin formulations

Thermoresponsive phenolic formaldehyde amine (PFA) derivatives with intrinsic photoluminescence were prepared through the modification of PFA with hydrophilic polyethylene glycol diglycidyl ether (PEG) and hydrophobic E20 epoxide resin and benzyl glycidyl ether (BGE). Turbidimetry measurements showed that the cloud point temperature (Tcp) of the obtained PFA derivatives in water could be effectively modulated through adjusting the ratio of E20 and PEG. The thermoresponsive PFA derivatives prepared under the first addition of E20 exhibited a sharper phase transition than those prepared under the first addition of PEG. Air-oxidation of thermoresponsive PFA derivatives led to the depression of Tcp, which was ascribed to the occurrence of slight intermolecular crosslinking reaction verified by the gradual increase of hydrodynamic size. Although no traditional fluorophores existed, thermoresponsive PFA derivatives could emit blue fluorescence centered at ca. 488 nm. Air-oxidation resulted in not only the red-shift of maximum emission wavelength, but also marked enhancement of fluorescence intensity. The QY of thermoresponsive PFA derivative in water was ca. 3.4% before oxidation, while 57-h oxidation led to the QY boost to 6.9%. Such thermoresponsive PFA derivatives were used as polyamine hardener in the waterborne epoxy resin formulations to form coating films onto the surface of mild steel. Corrosion evaluation around the scribe and adhesion tests demonstrated that the coating film cured by oxidized thermoresponsive PFA derivative with a lower Tcp value exhibited a better comprehensive anticorrosion performance. Moreover, this coating film could emit bright blue fluorescence under UV-light irradiation.

Multistep pyrolysis behavior of core-shell type hyperbranched azide copolymer: Kinetics and reaction mechanism via experiment and simulation

As an attractive new energetic fuel, core–shell type hyperbranched azide copolymer (POG) have been investigated with regard to its pyrolysis kinetics and mechanism. Through Asymmetric Double Sigmoidal (Asym2sig) function deconvolution, POG pyrolysis profiles could be separated into two reactions well (the first and second step). Based on reasonable kinetics analysis methods, mechanism functions of the first and second step reactions were constructed to n-th order reaction model of f1(α1) = (1 − α1)1.05 and 3D diffusion model of f2(α2) = 1.95(1 − α2)2/3[1 − (1 − α2)1/3]−0.54. The gaseous products and residual morphology in different pyrolytic steps are identified by TG-FTIR-MS and SEM. Through molecular simulation, the intermediate reactions between the first and second step were successfully captured, and then the detailed pyrolysis mechanism of POG was established. In the initial stage of POG pyrolysis, thermal cracking of N3 generates nitrenes and releases N2 (fitting n-th order model). Next, the intermolecular crosslinking and intramolecular cyclization reactions of nitrenes form a new cross-linked layer on the outside of hyperbranched polyether core of POG (PEHO-c), delaying the decomposition of inner PEHO-c. Furthermore, pyrolysis of cross-linked layer and PEHO-c is gradually performed by 3D diffusion model from outside to inside, which is very suitable for 3D core-shell structure of POG.

Dopamine@Nanodiamond as novel reinforcing nanofillers for polyimide with enhanced thermal, mechanical and wear resistance performance.

In this study, to achieve a homogeneous dispersion of nanodiamond (ND) in a polyimide (PI) matrix and a strong interfacial adhesion between ND and the PI matrix, a biomimetic nondestructive dopamine chemistry was employed for surface modification of ND. FTIR and Raman spectroscopy studies revealed that self-polymerization of dopamine could produce thinner polydopamine (PDA) layers on the ND surface via spontaneous oxidation and the intermolecular cross-linking reaction of PDA molecules. The structure and morphology of PDA–ND were studied by FTIR, SEM, and Raman spectroscopy, which verified the π–π interactions between PDA and ND. The facile dispersion of PDA–ND in a polyamic acid prepolymer made it possible to obtain PI/ND composites with no obvious ND aggregation. The effect of PDA–ND nanoparticles on the thermal, mechanical and tribological properties of the resulting PI/PDA–ND composites were evaluated, and the results showed that the incorporation of PDA–ND could increase the hardness, tensile strength, storage modulus, as well as the wear resistance properties. PI/PDA–ND composites prepared in this study showed that PDA–ND is a promising nanoreinforcing filler for PI composites.

Preparation of lipid nanoparticles with high loading capacity and exceptional gastrointestinal stability for potential oral delivery applications

Exploitation of lipid nanoparticles for oral delivery of nutrients and drugs is limited by their poor stability under gastrointestinal tract and low loading capacity, unless a high concentration of synthetic surfactants is formulated. The main objective of present study is to design a series of new formulations for solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) that are suitable for potential oral delivery applications, using natural biopolymers, i.e. sodium caseinate (NaCas) as emulsifier and pectin as coating, with minimal addition of a synthetic surfactant, Tween 80. Effects of pectin coating, concentration of Tween 80, thermal treatment (80°C for 30min), as well as two chemical cross-linkers on the particulate characteristics, stability, encapsulation efficiency, controlled release and drying feasibility were comprehensively investigated. The intermolecular interactions and cross-linking reactions were studied using Fourier transform infrared spectroscopy. Tween 80 at 0.15% (w/v) together with 0.15% (w/v) NaCas was proved effective to obtain stable cross-linked pectin-coated SLN (PSLN) under 200nm with high loading capacity for curcumin, while NLC prepared under the same condition failed to pass storage stability test. The 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide (EDC/NHS) cross-linked PSLN exhibited superior characteristics than glutaradehyde (GA) cross-linked PSLN, especially for the stability and controlled release under simulated gastrointestinal conditions, with curcumin studied as a model compound. The feasibility of both nano spray drying and freeze-drying technologies were both investigated to transform of colloidal lipid nanoparticles into dry powders. Our results demonstrated a novel strategy to prepare small and homogenous SLN with exceptional GI stability and high loading capacity as a potential oral delivery system.

Elucidating the role of ammonia-based salts on the preparation of cellulose-derived carbon aerogels

The effects of using (NH4)2SO4 as a carbonization promoter for producing cellulose-derived carbon aerogels (CAG) was studied. The effects of pretreatment on the textural, morphological, and chemical properties of pristine cellulose nanofibers (CNF) were analyzed through N2 adsorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), elemental analysis, inductively coupled plasma optical emission spectrometry (ICP-OES), and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the thermal behaviors of raw CNF and those impregnated with (NH4)2SO4 were investigated by coupling thermogravimetric analysis with mass spectrometry (TGA-MS). The results suggested that the pretreatment did not cause any morphological/structural changes in the nanofibers. However, the presence of (NH4)2SO4 affected their pyrolysis by favoring intermolecular dehydration, thereby reducing the formation of levoglucosan and increasing the carbon yield during pyrolysis. Interestingly, above certain impregnation level, the concentration of sulfate-derived species in the gas phase increased. This phenomenon was attributed to an excess of salt within the fiber structure and on their surfaces. Consequently, the levoglucosan-to-carbon route was inhibited, and the mechanisms of intra- and inter-molecular dehydration, chain scission, and crosslinking reactions were affected, leading to a reduced char yield. The chemical effects of ammonia-based salts is elucidated supported on the interpretation of MS signals and kinetic modeling results.

Influence of Hydrolyzed Polyacrylamide (HPAM) Molecular Weight on the Cross-Linking Reaction of the HPAM/Cr3+ System and Transportation of the HPAM/Cr3+ System in Microfractures

The influence of the molecular weight (Mw) of hydrolyzed polyacrylamide (HPAM) on the cross-linking reaction of HPAM/Cr3+ and the transportation of HPAM/Cr3+ in microfractures is systematically studied using viscometry, ultraviolet–visible absorption spectrophotometry, and displacement experiment with a visual microfractured model. The results show that a high-Mw HPAM is advantageous to the intramolecular cross-linking reaction of the HPAM/Cr3+ system but disadvantageous to the transportation of the HPAM/Cr3+ system in microfractures. At the intramolecular cross-linking stage, the injection pressure of the HPAM/Cr3+ system in microfractures is almost equal to that of the HPAM solution, which undergoes no change with the degree of the cross-linking reaction. The higher the HPAM Mw, the earlier the intramolecular cross-linking ends (thus, the intermolecular cross-linking reaction of HPAM/Cr3+ occurs earlier, which leads to an earlier increase in the injection pressure of the HPAM/Cr3+ system). Moreover, there is a matching relationship between the fracture aperture and the HPAM/Cr3+ system to minimize the chromatographic separation when the HPAM/Cr3+ system transports in the microfracture. For the conformance control of a fractured tight oil reservoir, we conclude that an HPAM/Cr3+ system with a low-Mw HPAM can more easily enter the deep reservoir to expand the swept volume on a larger scale. However, the system with a high-Mw HPAM can form a gel with a higher viscosity to produce a higher plugging strength.

Re‐entrant transition of aluminum‐crosslinked partially hydrolyzed polyacrylamide in a high salinity solvent by rheology and NMR

ABSTRACTLinked polymer solution (LPS) is a nanoparticle polymer and designed by crosslinking a high molecular weight partially hydrolyzed polyacrylamide (HPAM) with aluminum (III). It has been applied in the oil industry to enhance oil recovery by improving sweep efficiency and by microscopic diversion in porous media. To achieve good propagation properties, aggregates formed by intermolecular crosslinking and gel formation should be avoided. To our knowledge, there is no established method to distinguish between intra‐ and intermolecular crosslinking for high molecular weight (&gt;10 × 106 Da), low concentration (&lt;1000 ppm), polydisperse solutions of partially hydrolyzed polyacrylamides in high salinity solvents (5 wt % NaCl). The high salinity solvent is relevant to represent for formation water in many oil reservoirs. The main objective of the present study is to establish an experimental method for determining phase transition of LPS from monomeric coiled state to aggregated state in a high salinity solvent. No single experimental methods are conclusive and we have therefore applied a combinatorics approach including two‐dimensional NMR, dynamic rheology, and UV spectroscopy. The different techniques show similar trends, which allow overall interpretations of phase transitions to be made. The experimental results indicated that the LPS solution at high salinity solvent underwent a phase transition by chain re‐expansion, called reentrant transition. The transition point was observed at addition of 100 ppm of Al3+. Higher concentrations of Al3+ suppressed the rate of reentrant transition, most likely because of intramolecular crosslinking of HPAM chains by Al3+. Intermolecular crosslinking reaction was not observed at these conditions. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43825.

Mechanism Study of the Cross-Linking Reaction of Hydrolyzed Polyacrylamide/Ac3Cr in Formation Water

The mechanism of the cross-linking reaction between hydrolyzed polyacrylamide (HPAM) and chromium acetate in formation water was systematically studied by viscometry, ultraviolet-visual absorption spectrometry, and core flow experiments. The results show that the process and outcome of the cross-linking reaction between HPAM and chromium acetate is significantly affected by salinity. In formation water, chromium acetate cannot cross-link HPAM when the salinity is too low. With an increase of salinity, the cross-linking reaction occurs, and the degree of the reaction increases to a balance point. When the cross-linking reaction occurs, two different types of the reaction appear under different salinity. The intramolecular cross-linking reaction is the first to happen, whether under high salinity or under low salinity. In this stage, the cross-linking reaction is a first-order reaction and plays a greater role in the whole process of the reaction due to its higher reaction rate and higher reaction degree. Next, the intramolecular cross-linking continues to occur if the formation water is in the low salinity range, but the intermolecular cross-linking reaction occurs if the formation water is in the high salinity range. In this stage, the cross-linking reaction is a multistage reaction. Meanwhile, the experiments quantify a matching relationship between cations in the formation water and the profile control and oil displacement agent. The experimental results in this paper can provide theoretical guidance for the practical application of profile control and oil displacement using HPAM/Ac3Cr.

Study on the stabilization of isotropic pitch based fibers

Evolution of chemical structure and out gases of isotropic pitch fibers were studied in terms of stabilization. As stabilization plays an important role in the mechanical properties of carbon fibers (CF), thermogravimetric analysis was performed to optimize the duration and temperature of stabilization in this study. Fourier transform-infrared spectroscopy was applied to investigate chemical structure and formation of O2 containing functional groups during the stabilization. In addition, mass spectrometry showed that O2 uptake started at around 150 ℃ along with formation of various gases such as CO, CO2, and H2O. The longer stabilization resulted in higher tensile strength of the pitch fiber with higher strain-to-failure due to intermolecular crosslinking reactions leading to a network formation of pitch molecules. The stabilized fibers were carbonized at 1500 ℃ in a furnace under nitrogen atmosphere. Maximum tensile strengths of ~900 MPa were obtained from CF stabilized for 60 min at 280 ℃. Open image in new window

Effect of thermal modification on rheological properties of polyethylene blends

We examined the effects of thermal modification under flow field on the rheological properties of linear low-density polyethylene (LLDPE) with high molecular weight, low-density polyethylene (LDPE), and their blends, without thermal stabilizer. Although structural changes during processing are not detected by size extrusion chromatography or nuclear magnetic resonance spectroscopy, linear viscoelastic properties changed greatly, especially for the LLDPE. A cross-linking reaction took place, leading to, presumably, star-shaped long-chain branches. Consequently, the modified LLDPE, having high zero-shear viscosity, became a thermorheologically complex melt. Moreover, it should be noted that the drawdown force, defined as the uniaxial elongational force at a constant draw ratio, was significantly enhanced for the blends. Enhancement of elongational viscosity was also detected. The drawdown force and elongational viscosity are marked for the thermally modified blend as compared with those for the blend of thermally modified pure components. Intermolecular cross-linking reactions between LDPE and LLDPE, yielding polymers with more than two branch points per chain, result in marked strain-hardening in the elongational viscosity behavior even at small strain. The recovery curve of the oscillatory modulus after the shear modification is further evidence of a branched structure.

Protein products obtained by site‐preferred partial crosslinking in protein crystals and “liberated” by redissolution

The use of protein crystals as a source of nanoscale biotemplates has attracted growing interest in recent years owing to their inherent internal order. As these crystals are vulnerable to environmental changes, potential applications require their stabilization by chemical crosslinking. We have previously shown that such intermolecular chemical crosslinking reactions occurring within protein crystals are not random events, but start at preferred crosslinking sites imposed by the alignment of protein molecules and their packing within the crystalline lattice. Here we propose a new working hypothesis and demonstrate its feasibility in enabling us to extricate homogeneous populations of single protein molecules that display chemical point mutations or of dimers that show homogeneous chemical crosslinking, and that have the potential for isolation of higher structures. Characterization of the crosslinking mechanism and its end products opens the way to the potential retrieval of such specific modified/intermolecular crosslinked products simply by effecting partial crosslinking at identified preferred sites, followed by time-controlled arrest of the crosslinking reaction and dissolution of the crystals by medium exchange complemented by chromatographic purification.

Sortase A catalyzed reaction pathways: a comparative study with six SrtA variants

Different enzyme variants of sortase A fromStaphylococcus aureuswere found to have distinct catalytic properties with regard to site-directed protein fusion and competing intermolecular crosslinking reactions.