Percentage Of Crosslinker Research Articles

Optimization of application of natural rubber based API adhesive for the production of laminated wood

The use of natural rubber latex (NRL) for wood adhesive has been identified since a long time ago, even though its adhesion quality is fair. Some modifications of the NRL, as well as the blending of NRL with other commercial wood adhesives, have already been reported. Another potential use of NRL in the wood adhesive formulation is a base polymer of isocyanate type adhesive, which is called aqueous polymer isocyanate (API) adhesive. This study aimed to optimize the aqueous polymer isocyanate (API) type adhesive made from natural rubber latex (NRL) using response surface methodology (RSM). Central composite design (CCD) was used for the RSM. Three factors have been optimized, namely the percentage of crosslinker (7.3-20.7% of the weight of base polymer), glue spread rate (112-298 g/m2), and pressing time (2-22 hours). Results of the study showed that the model generated from the optimization was fit and could be used to predict the relationship between the three factors and the bonding strength. Optimum conditions for the adhesive application for the production of laminated wood used 16.4% crosslinker, glue spread rate of 298 g/m2 with a pressing time of 6 hours. Using these conditions, the shear strength of the laminated wood obtained was 8.8 MPa.

Influence of ultraviolet radiation on polymethylmethacrylate (PMMA)

Polymethylmethacrylate (PMMA) was irradiated (360–811 h) in a UV-B accelerated aging chamber at room temperature and oxidizing atmosphere. The macromolecular changes attributed to the radiation were investigated by means of tests such as: traction test, percent cross-linking, thermogravimetric analysis (TGA), Fourier transform spectroscopy (FTIR) and ultraviolet visible spectroscopy (UV–Vis). Scanning electron microscopy (SEM) analysis was used to evaluate the influence of radiation on PMMA fracture behavior. The results indicate that changes occurred due to UV-B radiation, such as chain scission and color change, which may lead to a decrease in resistance. The mechanical properties curves showed a similar pattern for the irradiated samples, which are confirmed by the fragile fracture surface identified.

Cross-linked polystyrene/titanium tetrachloride as a tightly bound complex catalyzed the modified Mannich reaction for the synthesis of piperidin-4-ones

Cross-linked polystyrene beads were prepared, characterized and the resulting polymer carrier was functionalized with titanium tetrachloride (TiCl4) via complexation of polystyrene with TiCl4 to afford the corresponding cross-linked polystyrene-TiCl4 stable complex (PSt/TiCl4) in an one step reaction and characterized by FT-IR, UV, TGA, DSC, XRD, SEM, BET. This tightly bound coordination complex was used as a water tolerant, heterogeneous, recoverable and reusable Lewis acid catalyst for the synthesis of substituted piperidin-4-ones via the modified Mannich multi-component condensation of ketones, aromatic aldehydes, and ammonium acetate in 1:2:1 M ratio under mild conditions. The rate of reactions was found to decrease with an increasing percentage of crosslinking and the mesh size of the copolymer beads. The catalyst is water tolerant, stable and can be easily recovered and reused at least four times without any loss of activity.

Chemical Characterization of Hydrogels Crosslinked with Polyethylene Glycol for Soft Tissue Augmentation.

BACKGROUND:Hyaluronic acid (HA) based hydrogels for esthetic applications found widespread use. HA should be crosslinked for this application to achieve the correct viscoelastic properties and avoid fast degradation by the hyaluronidase enzyme naturally present in the skin: these properties are controlled by the amount of crosslinker and the fraction that is effectively crosslinked (i.e. that binds two HA chains).AIM:Crosslinking by polyethylene glycol diglycidyl ether (PEGDE) has been more recently introduced and showed attractive features in terms of viscoelastic properties and reduced biodegradation. Aim of this paper is to define a method for the determination of the crosslinking properties of these recently introduced fillers, method that is lacking at the moment.MATERIAL AND METHOD:The percentage of crosslinker and the fraction that is effectively crosslinked were determined by proton Nuclear Magnetic Resonance (1H NMR) and by 13C NMR, respectively. The filler were preliminarily washed with acetonitrile to remove residual PEG and then digested by hyaluronidase to obtain a sample that can be analysed by NMR.RESULTS:The crosslinking parameters were determined in four samples of NEAUVIA PEG-crosslinked dermal fillers (produced by MatexLab S.p.A., Italy). The percentage of crosslinker was between 2.8% and 6.2% of HA, whereas the effective crosslinker ratios were between 0.07 and 0.16 (ratio between the moles of effectively crosslinked PEG and total moles of PEG). Moreover, a digestion procedure alternative to enzymatic digestion, based on acidic hydrolysis, was successfully tested for the determination of crosslinker percentage.CONCLUSIONS:The proposed method successfully determined the two crosslinking parameters in PEG-crosslinked dermal fillers. The estimated percentage of crosslinker is similar to previously reported data for other crosslinkers, whereas the effective crosslinker ratio is lower for PEG crosslinked hydrogels.

Biodegradable water hyacinth cellulose-graft-poly(ammonium acrylate-co-acrylic acid) polymer hydrogel for potential agricultural application

Swollen cellulose fibres isolated from water hyacinth were utilized in the synthesis of water hyacinth cellulose-graft-poly(ammonium acrylate-co-acrylic acid) polymer hydrogel (PHG). Acrylic acid (AA) partially neutralized with NH3 was heterogeneously grafted onto swollen cellulose by radical polymerization reaction using N,N-methylene-bis-acrylamide (MBA) as the cross-linker and ammonium persulphate (APS) as the initiator. The reaction conditions were optimized through assessment of grafting parameters such as grafting cross-linking percentage (GCP), percentage grafting cross-linking efficiency (%GCE) and water absorption tests. Characterization of the copolymer by Fourier Transform Infra-red (FTIR) spectroscopy revealed successful grafting of the monomer onto cellulose. Transmission electron microscopy (TEM) image of acetone-extracted PHG displayed micro-porous structure. The optimized product swelled in distilled water up to 165 times its own dry weight. The swelling was influenced by the pH and presence, nature and concentration of ions. The hydrogel had the capacity to retain moisture in soil, and degradation testing revealed a higher mass loss in cellulose grafted copolymer compared to the copolymer without cellulose. Degradation by soil microbial isolates showed significantly higher (P ≤ 0.05) accumulation of NH4+ in the cellulose grafted copolymer up to 0.05% (w/v) from 40 to 100 h, relative to similar amounts of copolymer without cellulose. The use of water hyacinth, a notorious weed in Kenyan waters, to produce cellulose-based polymer hydrogels has not been explored and yet, it could form an effective and beneficial way of utilizing this plant. A mechanism of graft polymerization reaction has also been proposed. The synthesized product can be applied in agriculture and other fields where biodegradability and effective utilization of water is essential.

Viscoelastic Behavior, Curing and Reinforcement Mechanism of Various Silica and POSS Filled Methyl-Vinyl Polysiloxane MVQ Rubber

The role of Aerosil silicas, A90, R812, R812s on the complex dynamic viscosity η* of methyl-vinyl polysiloxane MVQ at processing temperature 80°C was analyzed based on experiments with a torsional rheometer Rubber Process Analyzer RPA. The influence of surface area and surface activity on the Payne’s effect was determined by oscillating rheometer Ares G2. The decrease in complex modulus G* by increasing strain for silicas R812, R812s was mostly due to the breaking down of filler-filler networking, the modification of surface led to better processability resulting in the increase of tensile strength TS, from 0.42 MPa unfilled silicone to 9.31 MPa MVQ containing R812. Higher surface activity of silica A90 caused a decrease in filler networking due to a better filler-polymer interactions, which resulted in the increase of the percentage of non-covalent crosslinks determined for samples treated with ammonia. The decrease of static water contact angle θ of silicone rubber after incorporation of A90 was observed. Influence of allylisobutylPOSS on curing, crosslink density, static and dynamic behavior of silicone rubber was considered.

Investigation of thermal energy storage properties of a microencapsulated phase change material using response surface experimental design methodology

The response surface experimental design methodology was used to investigate thermal energy storage properties of the microencapsulated phase change material (MicroPCM). The capric acid and oleic acid mixture in the presence of hexadecane were encapsulated with styrene-divinylbenzene copolymer shell by emulsion polymerization technique. Response surface design experiments were conducted to determine the effect of three factors, namely, the shell:core ratio, emulsification time and crosslinker percentage at three distinctly different levels. Main effects and interaction effects of the factors on the latent heat of melting (ΔHm), the amount of produced MicroPCM and the encapsulation ratio were examined using statistical methods. The regression models were derived fully fit the experimental data. According to the statistical analysis results, the most significant effect on the thermal energy storage capacity, the amount of MicroPCM and the encapsulation ratio was attributed to the shell:core ratio. The properties of optimal MicroPCM were investigated by Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR). The analysis results demonstrated that optimal MicroPCM with its latent heat of fusion value (123 J/g) and encapsulation ratio (85.85%) can be accepted as a good candidate for thermal energy storage applications.

Cross-linked polystyrene-TiCl4 complex as a reusable Lewis acid catalyst for solvent-free Knoevenagel condensations of 1,3-dicarbonyl compounds with aldehydes

Cross-linked polystyrene copolymer beads with the average particle size in the range of (50–80 mesh size) were prepared by a new method, characterized and functionalized with titanium tetrachloride to afford the corresponding polystyrene‑titanium tetrachloride complex in one step reaction and characterized by FT-IR, UV, TGA, DSC, XRD, SEM, BET. This polymer metal complex (PS/TiCl4) was used as a heterogeneous, recoverable, reusable Lewis acid for solvent-free Knoevenagel condensations of 1,3-diketones with aromatic aldehydes under green and mild conditions. The rate of reactions was found to decrease with an increasing percentage of crosslinking and the mesh size of the copolymer beads. This complex showed good stability and catalytic activity in the Knoevenagel reactions.

Diffusion and relaxation contributions in the release of vitamin B6 from a moving boundary of genipin crosslinked gelatin matrices

A fundamental study was carried out to evaluate patterns of vitamin B6 release from genipin crosslinked gelatin in aqueous media at ambient temperature. Up to ninety percent crosslinking was achieved, with FTIR and WAXD data arguing for partial replacement of the triple helix with a covalent pattern of bonding between protein and crosslinker. Formation of a “composite network” yielded increasing compressive stress-at-failure values followed by a decrease as a function of genipin addition, with the yield strain decreasing continuously. Electron microscopy images showed a reduction in the size of the hydrogel pores with a higher degree of crosslinking. Experimental evidence was supported by the Flory-Rehner theory that predicted a lower swelling ratio and reduced molecular weight between adjacent crosslinks with genipin addition. Furthermore, Peppas-Sahlin equation was used to rationalise the interplay between network morphology and diffusion of bioactive compound over prolonged timeframes of release testing.

Comparative study in physico-chemical properties of gelatin derivatives and their microspheres as carriers for controlled release of green tea's extract

Two types of gelatin derivatives were prepared from type A and type B gelatin, respectively. Cationized gelatin was produced by conjugation of ethylenediamine into type A gelatin using carbodiimide reaction. Anionized gelatin was produced by conjugation of succinic anhydride to type B gelatin. Characteristics of four gelatin types and their microspheres fabricated by water-in-oil emulsion and glutaraldehyde crosslinking were evaluated. Cationized gelatin showed the highest positive charge and free amino group concentration due to the ethylenediamine conjugation, resulting in the highest crosslinking percentage and slowest degradation rate of cationized gelatin microspheres. Type A, B and anionized gelatin which had lower concentration of free amino groups produced the low crosslinking and fast-degrading microspheres. These gelatin microspheres were introduced as carrier for controlled release of epigallocatechin 3-gallate (EGCG), a high antioxidant green tea's extract. The cationized gelatin microspheres showed prolonged release of EGCG due to the slow degradation and ionic attraction with the negative-charged EGCG. The release of EGCG from type A, B and anionized gelatin microspheres was accelerated as a result of diffusion and microsphere's swelling mechanisms. These EGCG-loaded gelatin microspheres can be further studied as injectable drug for localized treatment of inflammation-related diseases with minimal invasion.

Alginate/poly(amidoamine) injectable hybrid hydrogel for cell delivery.

A covalently cross-linked injectable hybrid hydrogel, namely, alginate/poly(amidoamine) (PAMAM), with the objective of cell delivery was innovatively designed and synthesized using tetra-amino-functional PAMAM dendrimer as the cross-linker. With the increase in percentage of PAMAM cross-linker, the pore size and swelling ratio of hydrogels were in the range of 57 ± 18 μm to 88 ± 25 μm and 110 ± 16 to 157 ± 20, respectively. The study of attachment and proliferation of MC3T3-E1 pre-osteoblasts using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay through indirect and direct contact methods indicated a continuous increase in metabolically active live cells with time, implying non-cytotoxicity of the synthesized hydrogel. The live-dead assay showed >95% of live cells for alginate/PAMAM hydrogels, suggesting viability of the encapsulated cells. When the percentage of PAMAM cross-linker in alginate/PAMAM hydrogel was increased from 5 to 25, the percentage degradation rate decreased from 1.1 to 0.29%/day. Given that the poly(ethylene glycol) is commonly used cross-linker for hydrogel syntheses, we compared the behavior with poly(ethylene glycol). The incorporation of poly(ethylene glycol) in alginate/PAMAM hydrogel reduced the activity of MC3T3-E1 cells and their viability compared to the alginate/PAMAM hydrogels. The protonation of amino groups in alginate/PAMAM injectables under physiological conditions led to the formation of cationic hydrogels. These cationic hydrogels showed enhanced cell encapsulation and attachment ability because of electrostatic interaction with negatively charged cell surface as determined by cell adhesion and extensions from scanning electron microscope and vinculin assay and ability of in situ calcium phosphate mineralization. These observations point toward the potential use as an injectable scaffold for cell delivery and tissue engineering applications.

Accelerated ReaxFF Simulations for Describing the Reactive Cross-Linking of Polymers.

Various methods have been developed to perform atomistic-scale simulations for the cross-linking of polymers. Most of these methods involve connecting the reactive sites of the monomers, but these typically do not capture the entire reaction process from the reactants to final products through transition states. Experimental time scales for cross-linking reactions in polymers range from minutes to hours, which are time scales that are inaccessible to atomistic-scale simulations. Because simulating reactions on realistic time scales is computationally expensive, in this investigation, an accelerated simulation method was developed within the ReaxFF reactive force field framework. In this method, the reactants are tracked until they reach a nonreactive configuration that provides a good starting point for a reactive event. Subsequently, the reactants are provided with a sufficient amount of energy-equivalent or slightly larger than their lowest-energy reaction barrier-to overcome the barrier for the cross-linking process and form desired products. This allows simulation of cross-linking at realistic, low temperatures, which helps to mimic chemical reactions and avoids unwanted high-temperature side reactions and still allows us to reject high-barrier events. It should be noted that not all accelerated events are successful as high local strain can lead to reaction rejections. The validity of the ReaxFF force field was tested for three different types of transition state, possibly for polymerization of epoxides, and good agreement with quantum mechanical methods was observed. The accelerated method was further implemented to study the cross-linking of diglycidyl ether of bisphenol F (bis F) and diethyltoluenediamine (DETDA), and a reasonably high percentage (82%) of cross-linking was obtained. The simulated cross-linked polymer was then tested for density, glass transition temperature, and modulus and found to be in good agreement with experiments. Results indicate that this newly developed accelerated simulation method in ReaxFF can be a useful tool to perform atomistic-scale simulations on polymerization processes that have a relatively high reaction barrier at a realistic, low temperature.

Modification of regenerated cellulose membranes with cationic polymer and its Cr(VI) retention capacity

In this work, we report the modification of regenerated cellulose membranes through the “in situ” polymerization of [2-(acryloyloxy)ethyl] trimethylammonium chloride monomer and N,N'-methylenebis(acrylamide) crosslinker. The polymerization reaction was performed using 1% mol of ammonium persulfate as initiator, and varying both the monomer concentration (10–25 mmol/L) and the percentage of crosslinker (4 and 8 mol%). The degree of modification (DM) and water absorption capacity (WAC) at different pHs were calculated gravimetrically. These modified membranes were characterized by FTIR, SEM, TGA, electrokinetic potential and permeability. The Cr(VI) retention capacity of the modified membranes was evaluated at different pHs.The DM values were between 23.46% and 41.82%. The highest WAC was for the membrane prepared with 25 mmol/L of monomer and 4 mol% of crosslinker independent of the pH value. The FTIR characterization showed absorption bands confirming this membrane modification. The SEM analysis showed the morphological changes of the membranes by the presence of interpolymeric networks. TGA showed a typical thermogravimetric curve of the polymers that contain quaternary ammonium groups. Modified ultrafiltration membranes exhibited good thermal stability. Electrokinetic potential revealed that the modified membrane is cationic in a wide range of pH and permeability test showed that all the modified membranes decrease the volumetric flux.The results of Cr(VI) retention indicate that it is possible to remove this metal at different pHs (3, 6 and 9), highlighting the highest retention at pH 6, reaching a value of 94% when 20 mg/L of chromium (VI) was used in the feed.

Immobilization of microalgae on the surface of new cross-linked polyethylenimine-based sorbents

We report on the use of the polyethylenimine-based (PEI) sorbents for immobilization and harvesting of microalgae (MA) cells. Specific materials assessed were porous solid polymers from highly-branched PEI synthesized by cross-linking with epichlorohydrin (ECH) or diethylene glycol diglycidyl ether (DGDE). We estimated the effect of PEI/cross-linker ratio on the MA attachment and biocompatibility of the sorbents with the MA cells. A decrease in the cross-linker percentage resulted in the enhancement of the immobilization efficiency but impaired the cell viability as was manifested by inhibition of the photosynthetic activity of the MA cells. The rate of Chlorella vulgaris cell attachment to the sorbents with ECH was faster as compared to that of the PEI–DGDE-based polymers. The cells immobilized on the PEI–ECH sorbents showed a more profound decline in their viability (assessed via photosynthetic activity). The sorbents with 60% of DGDE were characterized by high immobilization efficiency. These sorbents supported a prolonged cultivation of the immobilized MA without impairing their viability and metabolic activity. We conclude that the sorbents with a lower percentage of DGDE (<30%) and sorbents with ECH are suitable for harvesting of the MA cells intended for immediate downstream processing, potentially without the cell desorption. To the best of our knowledge, this is the first report on successful application of PEI-based sorbents in microalgal biotechnology.

Physical Networks from Multifunctional Telechelic Star Polymers: A Rheological Study by Experiments and Simulations.

The equilibrium mechanical properties of a cross-linked gel of telechelic star polymers are studied by rheology and Brownian dynamics simulations. The Brownian dynamics model consists of cores to which Rouse arms are attached. Forces between the cores are obtained from a potential of mean force model developed by Likos and co-workers. Both experimentally and in the simulations, networks were created by attaching sticker groups to the ends of the arms of the polymers, which were next allowed to form bonds among them in a one to one fashion. Simulations were sped up by solving the Rouse dynamics exactly. Moreover, the Rouse model was extended to allow for different frictions on different beads. In order to describe the rheology of the non-cross-linked polymers, it had to be assumed that bead frictions increase with increasing bead number along the arms. This friction model could be transferred to describe the rheology of the network without any adjustments other than an overall increase of the frictions due to the formation of bonds. The slowing down at intermediate times of the network rheology compared to that of the non-cross-linked polymers is well described by the model. The percentage of stickers involved in forming inter-star bonds in the system was determined to be 25%, both from simulations and from an application of the Green–Tobolsky relation to the experimental plateau value of the shear relaxation modulus. Simulations with increasing cross-link percentages revealed that on approaching the gel transition the shear relaxation modulus develops an algebraic tail, which gets frozen at a percentage of maximum cross-linking of about 11%.

Mechanical and Barrier Properties of Potato Protein Isolate-Based Films

Potato protein isolate (PPI) was studied as a source for bio-based polymer films. The objective of this study was the determination of the packaging-relevant properties, including the mechanical properties and barrier performance, of casted potato protein films. Furthermore, the films were analyzed for cross-linking properties depending on the plasticizer concentration, and compared with whey protein isolate (WPI)-based films. Swelling tests and water sorption isotherm measurements were performed to determine the degree of swelling, the degree of cross-linking, and the cross-linking density using the Flory–Rehner approach. The effects of different plasticizer types and contents on compatibility with potato protein were studied. Glycerol was the most compatible plasticizer, as it was the only plasticizer providing flexible standalone films in the investigated concentration range after three weeks of storage. Results indicated that increasing glycerol content led to decreasing cross-linking, which correlated in an inversely proportional manner to the swelling behavior. A correlation between cross-linking and functional properties was also reflected in mechanical and barrier characterization. An increasing number of cross-links resulted in higher tensile strength and Young’s modulus, whereas elongation was unexpectedly not affected. Similarly, barrier performance was significantly improved with increasing cross-linking. The overall superior functional properties of whey protein-based films were mainly ascribed to their higher percentage of cross-links. This was primarily attributed to a lower total cysteine content of PPI (1.6 g/16 g·N) compared to WPI (2.8 g/16 g·N), and the significant lower solubility of potato protein isolate in water at pH 7.0 (48.1%), which was half that of whey protein isolate (96%). Comparing on an identical glycerol level (66.7% (w/w protein)), the performance of potato protein isolate was about 80% that of whey protein isolate regarding cross-linking, as well as mechanical and barrier properties.

Effect of matrix metalloproteinase-mediated matrix degradation on glioblastoma cell behavior in 3D PEG-based hydrogels.

Glioblastoma (GBM) is the most common and aggressive form of primary brain tumor with median survival of 12 months. To improve clinical outcomes, it is critical to develop in vitro models that support GBM proliferation and invasion for deciphering tumor progression and screening drug candidates. A key hallmark of GBM cells is their extreme invasiveness, a process mediated by matrix metalloproteinase (MMP)-mediated degradation of the extracellular matrix. We recently reported the development of a MMP-degradable, poly(ethylene-glycol)-based hydrogel platform for culturing GBM cells. In the present study, we modulated the percentage of MMP-degradable crosslinks in 3D hydrogels to analyze the effects of MMP-degradability on GBM fates. Using an immortalized GBM cell line (U87) as a model cell type, our results showed that MMP-degradability was not required for supporting GBM proliferation. All hydrogel formulations supported robust GBM proliferation, up to 10 fold after 14 days. However, MMP-degradability was essential for facilitating tumor spreading, and 50% MMP-degradable hydrogels were sufficient to enable both robust tumor cell proliferation and spreading in 3D. The findings of this study highlight the importance of modulating MMP-degradability in engineering 3D in vitro brain cancer models and may be applied for engineering in vitro models for other cancer types. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 770-778, 2017.

Thickness-dependent glass transition temperature and charge mobility in cross-linked polyfluorene thin films.

We report thickness-dependent glass transition temperature (T_{g}) and charge mobility in cross-linked thin films made of conjugated polymer poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)diphenylamine) (TFB). Monotonic T_{g} depressions with reducing film thickness in thermally and UV cross-linked TFB thin films supported on Si-SiOx substrates are observed through ellipsometry measurements, suggesting that a surface mobile layer with enhanced chain dynamics still exists in cross-linked TFB thin films, even with a high cross-linking percentage. Data fitting using a three-layer model shows that the T_{g} in the interface, bulk and surface layer both increases with increasing cross-linking, while the thickness of the interface and surface layer increases and reduces, respectively. Cross-linking of TFB thin film generates traps that hinder charge transport and consequently reduce charge mobility. The charge mobility converges in thick (>140 nm) and thin (<40 nm) TFB films but shows strong thickness dependence in between, reducing from 4.0×10^{-4}cm^{2}/Vs in a 180-nm film to 0.1×10^{-4}cm^{2}/Vs in a 20-nm thin film.

Developing Molecular Imprinted Layers As Electro-Analytical Probes for Dydrogesterone Determination

Dydrogesterone is a synthetic derivative of female sex hormone whose structure and pharmacological action is similar to progesterone. This drug is used in various conditions including lack of endogenous, hormone replacement therapy and others. The increasing use of dydrogesterone as synthetic hormone also demands its rapid and accurate analysis in biological as well as environmental bodies. In this perspective, we developed molecular imprinted polymer (MIPs) coatings as recognition element for electro-analytical determination of dydrogesterone. Imprinted polymers are synthesized by self-organization of monomer chains around template structure keeping high percentage of cross-linker. Dydrogesterone-imprinted polymer gel is synthesized by free radical polymerization taking methacrylic acid and methyl methacrylate (functional co-monomers), ethyleneglycol dimethacrylate (cross-linker) and dydrogesterone (template). The non-imprinted polymer layer was taken as control material i.e. synthesized using the same polymer composition without introducing template. Following spin coating method, the developed polymeric gel was integrated with interdigital electrodes (IDEs) i.e. patterned on printed circuit board. IDEs fabricated with imprinted as well as non-imprinted polymer layer, respectively were connected to impedance analyzer. The subsequent shift in capacitive values of imprinted and non-imprinted layers was determined respectively as function of dydrogesterone concentration. The shift in capacitive values for imprinted layer was higher than the non-imprinted one. As the imprinted layer offers geometrical as well as chemical adaptation sites and upon fitting in these cavities the charge transfer between two electrode fingers is reduced which results in higher capacitance shift. On the other hand, the non-imprinted layer lack such functionality and offer only non-specific binding thus, leads to lower capacitive shifts. These results suggest that imprinted layers integrated with IDEs can be suitably used for dydrogesterone determination in complex matrices.

The Importance of Non-accessible Crosslinks and Solvent Accessible Surface Distance in Modeling Proteins with Restraints From Crosslinking Mass Spectrometry

Crosslinking mass spectrometry (XL-MS) is becoming an increasingly popular technique for modeling protein monomers and complexes. The distance restraints garnered from these experiments can be used alone or as part of an integrative modeling approach, incorporating data from many sources. However, modeling practices are varied and the difference in their usefulness is not clear. Here, we develop a new scoring procedure for models based on crosslink data—Matched and Nonaccessible Crosslink score (MNXL). We compare its performance with that of other commonly-used scoring functions (Number of Violations and Sum of Violation Distances) on a benchmark of 14 protein domains, each with 300 corresponding models (at various levels of quality) and associated, previously published, experimental crosslinks (XLdb). The distances between crosslinked lysines are calculated either as Euclidean distances or Solvent Accessible Surface Distances (SASD) using a newly-developed method (Jwalk). MNXL takes into account whether a crosslink is nonaccessible, i.e. an experimentally observed crosslink has no corresponding SASD in a model due to buried lysines. This metric alone is shown to have a significant impact on modeling performance and is a concept that is not considered at present if only Euclidean distances are used. Additionally, a comparison between modeling with SASD or Euclidean distance shows that SASD is superior, even when factoring out the effect of the nonaccessible crosslinks. Our benchmarking also shows that MNXL outperforms the other tested scoring functions in terms of precision and correlation to Cα-RMSD from the crystal structure. We finally test the MNXL at different levels of crosslink recovery (i.e. the percentage of crosslinks experimentally observed out of all theoretical ones) and set a target recovery of ∼20% after which the performance plateaus.