Development of an RNA-protein crosslinker to capture protein interactions with diverse RNA structures in cells

Characterization of RNA-protein interaction is fundamental for understanding the metabolism and function of RNA. UV crosslinking has been widely used to map the targets of RNA-binding proteins, but is limited by low efficiency, requirement for zero-distance contact, and biases for single-stranded RNA structure and certain residues of RNA and protein. Here, we report the development of an RNA-protein crosslinker (AMT-NHS) composed of a psoralen derivative and an N-hydroxysuccinimide ester group, which react with RNA bases and primary amines of protein, respectively. We show that AMT-NHS can penetrate into living yeast cells and crosslink Cbf5 to H/ACA snoRNAs with high specificity. The crosslinker induced different crosslinking patterns than UV and targeted both single- and double-stranded regions of RNA. The crosslinker provides a new tool to capture diverse RNA-protein interactions in cells.

Anti-Inflammatory and Prochondrogenic In Situ-Formed Injectable Hydrogel Crosslinked by Strontium-Doped Bioglass for Cartilage Regeneration

Directed differentiation of bone marrow mesenchymal stem cells (BMSCs) toward chondrogenesis plays a predominant role in cartilage repair. However, the uncontrolled inflammatory response to implants is found to impair the stability of scaffolds and the cartilage regeneration outcome. Herein, we fabricated an injectable hydrogel crosslinked by strontium-doped bioglass (SrBG) to modulate both human BMSC (hBMSC) differentiation and the inflammatory response. The results revealed that the introduction of Sr ions could simultaneously enhance the proliferation of hBMSCs, upregulate cartilage-specific gene expression, and improve the secretion of glycosaminoglycan. Moreover, after cultured with SA/SrBG extracts in vitro, a majority of macrophages were polarized toward the M2 phenotype and subsequently facilitated the chondrogenic differentiation of hBMSCs. Furthermore, after the composite hydrogel was injected into a cartilage defect model, neonatal cartilage-like tissues with a smooth surface and tight integration with original tissues could be found. This study suggests that the synergistic strategy based on an enhanced differentiation ability and a regulated inflammatory response is promising and may lead the way to new anti-inflammatory biomaterials.

Quaternary Ammonium Salts Anchored on Cross-Linked (R)-(+)-Lipoic Acid Nanoparticles for Drug-Resistant Tumor Therapy

A membrane-lytic mechanism-based nanodrug is developed for drug-resistant tumor therapy by anchoring the small-molecule quaternary ammonium salt (QAS) on cross-linked (R)-(+)-lipoic acid nanoparticles (cLANs). The anchoring of QAS on the nanoparticle avoids the direct attack of long alkyl chains to the cell membrane under physiological conditions, while after entering tumor cells, the QAS is released from the dissociated cLANs, migrates to the phospholipid bilayer via electrostatic interaction, and destroys the cell membrane by the puncture of long alkyl chains. Since the QAS is designed to finally be hydrolyzed to amino acid betaine and food additive cetanol and the cLANs degrade to dihydrolipoic acid (DHLA, reduced form of dietary antioxidant lipoic acid in cells), the QAS@cLANs hold superior biosafety. In addition to the drug-resistant tumors, the QAS@cLANs demonstrate significant inhibition of metastatic tumors. This work provides not only a general and clinic-promising treatment for the refractory tumors but also opens a door for the medicinal use of QAS.

Constructing High-Recognition Protein-Imprinted Materials Using "Specially Designed" Block Macromolecular Chains as Functional Monomers and Crosslinkers

The use of a macromolecularly functional monomer and crosslinker (MFM) to stabilize and imprint a template protein is a new method to construct high-recognition protein-imprinted materials. In this study, for the first time, a "specially designed" block MFM with both "functional capability" and "crosslinking capability" segments was synthesized via reversible addition-fragmentation chain-transfer polymerization and used to fabricate bovine serum albumin (BSA)-imprinted microspheres (SiO₂@MPS@MIPs-MFM) by the surface imprinting strategy. Results from circular dichroic spectrum experiments reflected that the block MFM could maintain the natural form of BSA, whereas its corresponding and equivalent micromolecularly functional monomer (MIM) seriously destroyed the secondary structure of proteins. Batch rebinding experiments showed that the maximum adsorption capacity and imprinting factor of SiO₂@MPS@MIPs-MFM reached 314.9 mg g^-1 and 4.02, which were significantly superior to that of MIM-based imprinted materials. In addition, since the crosslinking capability segments in block MFM involved zwitterionic functional groups with a protein-repelling effect, SiO₂@MPS@MIPs-MFM showed better specific rebinding ability than the imprinted material prepared by MFM without this component. Besides, scanning electron microscopy and transmission electron microscopy images showed that the shell thickness of SiO₂@MPS@MIPs-MFM was approximately 15 nm, and such a thin imprinted layer ensured its rapid adsorption equilibrium (120 min). As a result, SiO₂@MPS@MIPs-MFM revealed fantastic selectivity and recognition ability in a mixed protein solution and could efficiently extract BSA from biological samples of bovine calf serum. The proposal of block MFM enriched the options and designability of monomers in protein imprinting technology, thereby laying a foundation for developing high-performance protein-imprinted materials.

1,3-Diketone-Modified Nucleotides and DNA for Cross-Linking with Arginine-Containing Peptides and Proteins

Linear or branched 1,3-diketone-linked thymidine 5'-O-mono- and triphosphate were synthesized through CuAAC click reaction of diketone-alkynes with 5-azidomethyl-dUMP or -dUTP. The triphosphates were good substrates for KOD XL DNA polymerase in primer extension synthesis of modified DNA. The nucleotide bearing linear 3,5-dioxohexyl group (HDO) efficiently reacted with arginine-containing peptides to form stable pyrimidine-linked conjugates, whereas the branched 2-acetyl-3-oxo-butyl (PDO) group was not reactive. Reaction with Lys or a terminal amino group formed enamine adducts that were prone to hydrolysis. This reactive HDO modification in DNA was used for bioconjugations and cross-linking with Arg-containing peptides or proteins (e.g. histones).

Interstrand Cross-Link Formation Involving Reaction of a Mispaired Cytosine Residue with an Abasic Site in Duplex DNA

The formation of interstrand cross-links in duplex DNA is important in biology, medicine, and biotechnology. Interstrand cross-links arising from the reaction of the aldehyde residue of an abasic (apurinic or AP) site with the exocyclic amino groups of guanine or adenine residues on the opposing strand of duplex DNA have previously been characterized. The canonical nucleobase cytosine has an exocyclic amino group but its ability to form interstrand cross-links by reaction with an AP site has not been characterized before now. Here it is shown that substantial yields of interstrand cross-links are generated in sequences having a mispaired cytosine residue located one nucleotide to the 3'-side of the AP site on the opposing strand (e.g., 5'XA/5'CA, where X = AP). Formation of the dC-AP cross-link is pH-dependent, with significantly higher yields at pH 5 than pH 7. Once formed, the dC-AP cross-link is quite stable, showing less than 5% dissociation over the course of 96 h at pH 7 and 37 °C. No significant yields of cross-link are observed when the cytosine residue is paired with its Watson-Crick partner guanine. It was also shown that a single AP site can engage with multiple nucleobase cross-linking partners in some sequences. Specifically, the dG-AP and dC-AP cross-links coexist in dynamic equilibrium in the sequence 5'CXA/5'CAG (X = AP). In this sequence, the dC-AP cross-link dominates. However, in the presence of NaBH3CN, irreversible reduction of small amounts of the dG-AP cross-link present in the mixture shifts the equilibria away from the dC-AP cross-link toward good yields of the dG-APred cross-link.

Reduction-Responsive Chemo-Capsule-Based Prodrug Nanogel for Synergistic Treatment of Tumor Chemotherapy

Chemotherapy is currently the most universal therapeutics to tumor treatment; however, limited curative effect and undesirable drug resistance effect are the two major clinical bottlenecks. Herein, we develop a two-in-one cross-linking strategy to prepare a stimuli-responsive prodrug nanogel by virtue of delivering a combination of chemotherapeutic drugs of 10-hydroxy camptothecin and doxorubicin for ameliorating the deficiencies of chemotherapy and amplifying the cancer therapeutic efficiency. The obtained prodrug nanogel has both high drug loading capacity and suitable nanoscale size, which are beneficial to the cell uptake and tumor penetration. Moreover, the chemotherapeutic drugs are released from the prodrug nanogel in response to the reductive tumor microenvironment, enhancing tumor growth inhibition in vitro and in vivo by the synergistic DNA damage. Based on these results, the unique prodrug nanogel would be a promising candidate for satisfactory tumor treatment-based chemotherapy by a simple but efficient strategy.

Collagen-Based Thiol-Norbornene Photoclick Bio-Ink with Excellent Bioactivity and Printability

As the essential foundation of bioprinting technology, cell-laden bio-ink is confronted with the inevitable contradiction between printability and bioactivity. For example, type I collagen has been widely applied for its excellent biocompatibility; however, its relatively low self-assembly speed restricts the performance in high-precision bioprinting of cell-laden structures. In this study, we synthesize norbornene-functionalized neutral soluble collagen (NorCol) by the reaction of acid-soluble collagen (Col) and carbic anhydride in the aqueous phase. NorCol retains collagen triple-helical conformation and can be quickly orthogonally cross-linked to build a cell-laden hydrogel via a cell-friendly thiol-ene photoclick reaction. Moreover, the additional carboxyl groups produced in the reaction of carbic anhydride and collagen obviously improve the solubility of NorCol in neutral buffer and miscibility of NorCol with other polymers such as alginate and gelatin. It enables hybrid bio-ink to respond to multiple stimuli, resulting in continuous cross-linked NorCol networks in hybrid hydrogels. For the first time, the collagen with a triple helix structure and gelatin can be mixed and printed, keeping the integrity of the printed construct after gelatin's dissolution. The molecular interaction among giant collagen molecules allows NorCol hydrogel formation at a low concentration, which leads to excellent cell spreading, migration, and proliferation. These properties give NorCol flexible formability and excellent biocompatibility in temperature-, ion-, and photo-based bioprinting. We speculate that NorCol is a promising bio-ink for emerging demands in tissue engineering, regenerative medicine, and personalized therapeutics.

Bifunctional Reagents for Formylglycine Conjugation: Pitfalls and Breakthroughs

Formylglycine-generating enzymes specifically oxidize cysteine within the consensus sequence CxPxR to Cα -formylglycine (FGly). This noncanonical electrophilic amino acid can subsequently be addressed selectively by bioorthogonal hydrazino-iso-Pictet-Spengler (HIPS) or Knoevenagel ligation to attach payloads like fluorophores or drugs to proteins to obtain a defined payload-to-protein ratio. However, the disadvantages of these conjugation techniques include the need for a large excess of conjugation building block, comparably low reaction rates and limited stability of FGly-containing proteins. Therefore, functionalized clickable HIPS and tandem Knoevenagel building blocks were synthesized, conjugated to small proteins (DARPins) and subsequently linked to strained alkyne-containing payloads for protein labeling. This procedure allowed the selective bioconjugation of one or two DBCO-carrying payloads with nearly stoichiometric amounts at low concentrations. Furthermore, an azide-modified tandem Knoevenagel building block enabled the synthesis of branched PEG linkers and the conjugation of two fluorophores, resulting in an improved signal-to-noise ratio in live-cell fluorescence-imaging experiments targeting the EGF receptor.

Boronate ester cross-linked PVA hydrogels for the capture and H2O2-mediated release of active fluorophores

A new set of PVA hydrogels were formed using the boronate ester fluorescent probe PF1 and the novel boronate fluorescent probe PT1 as the covalent crosslinkers. Treatment with aqueous H2O2 allowed triggered release of the fluorescent dye accompanied by complete dissolution of the hydrogel.

Exploring Spacer Arm Structures for Designs of Asymmetric Sulfoxide-Containing MS-Cleavable Cross-Linkers

Cross-linking mass spectrometry (XL-MS) has become a powerful structural tool for defining protein-protein interactions (PPIs) and elucidating architectures of large protein assemblies. To advance XL-MS studies, we have previously developed a series of sulfoxide-containing MS-cleavable cross-linkers to facilitate the detection and identification of cross-linked peptides using multistage mass spectrometry (MSn). While current sulfoxide-based cross-linkers are effective for in vivo and in vitro XL-MS studies at the systems-level, new reagents are still needed to help expand PPI coverage. To this end, we have designed and synthesized six variable-length derivatives of disuccinimidyl sulfoxide (DSSO) to better understand the effects of spacer arm modulation on MS-cleavability, fragmentation characteristics, and MS identification of cross-linked peptides. In addition, the impact on cross-linking reactivity was evaluated. Moreover, alternative MS2-based workflows were explored to determine their feasibility for analyzing new sulfoxide-containing cross-linked products. Based on the results of synthetic peptides and a model protein, we have further demonstrated the robustness and predictability of sulfoxide chemistry in designing MS-cleavable cross-linkers. Importantly, we have identified a unique asymmetric design that exhibits preferential fragmentation of cross-links over peptide backbones, a desired feature for MSn analysis. This work has established a solid foundation for further development of sulfoxide-containing MS-cleavable cross-linkers with new functionalities.

Biometals as conformational modulators of α-synuclein photochemical crosslinking

Metal dyshomeostasis has long been linked to Parkinson's disease (PD), and the amyloidogenic protein α-synuclein (αS) is universally recognized as a key player in PD pathology. Structural consequences upon coordination of copper and iron to αS have gained attention due to significant dyshomeostasis of both metals in the PD brain. Protein-metal association can navigate protein folding in distinctive pathways based on the identity of the bio-metal in question. In this work, we employed photo-chemical crosslinking of unmodified proteins (PICUP) to evaluate these potential metal ion-induced structural alterations in the folding dynamics of N-terminally acetylated αS (NAcαS) following metal coordination. Through fluorescence analysis and immunoblotting analyses following photoirradiation, we discovered that coordination of iron obstructs copper-promoted crosslinking. The absence of intra-molecular crosslinking upon iron association further supports its C-terminal coordination site and suggests a potential role for iron in mitigating nearby post-translational modification of tyrosine residues. Decreased fluorescence emission upon synergistic coordination of both copper and iron highlighted that although copper acts as a conformational promotor of NAcαS crosslinking, iron inhibits analogous conformational changes within the protein. The metal coordination preferences of NAcαS suggest that both competitive binding sites as well as dual metal coordination contribute to the changes in folding dynamics, unveiling unique structural orientations for NAcαS that have a direct and measureable influence on photoinitiated dityrosine crosslinks. Moreover, our findings have physiological implications in that iron overload, as is associated with PD-insulted brain tissue, may serve as a conformational block of copper-promoted protein oxidation.

One-pot synthesis of multi-functional and environmental friendly tannic acid polymer with Fe3+ and formaldehyde as double crosslinking agents for selective removal of cation pollutants

A novel multi-functional and environmental friendly tannic acid polymer (Fe³⁺-TA-HCHO) with Fe³⁺ and formaldehyde as double crosslinking agents together with cysteine as heteroatom source was prepared by a one-pot hydrothermal method. Characterization with transmission electron microscope (TEM), scanning electron microscopy (SEM), Fourier transform infrared spectrometer (FT-IR), and elemental analysis demonstrated that the Fe³⁺-TA-HCHO possessed uniform structure and particle size as well as plentiful functional groups. The resulted Fe³⁺-TA-HCHO material as a adsorbent to remove methylene blue, sunset yellow, Pb²⁺, Hg²⁺, and AsO₃^3- from water. The results suggested that Fe³⁺-TA-HCHO polymer (pHpzc is 2.33) showed different adsorption properties for anionic pollutants (sunset yellow and AsO₃^3-) and cationic pollutants (methylene blue, Pb²⁺, and Hg²⁺). The material exhibited remarkable selectivity for adsorption and separation of pollutants. The maximum adsorption capacities calculated from Langmuir model for methylene blue, Pb²⁺, and Hg²⁺ were 154.32, 819.67, and 699.30 mg g^-1, respectively. This is the first time that tannic acid polymer is synthesized by double crosslinking method, which not only developed a promising adsorbent for selective removal of cation pollutants, but also opened up a new avenue for synthesis and application of tannic acid polymer.

Identification of Cross-linked Peptides Using Isotopomeric Cross-linkers

Chemical cross-linking combined with mass spectrometry (CL-MS) is a powerful method for characterizing the architecture of protein assemblies and for mapping protein-protein interactions. Despite its proven utility, confident identification of cross-linked peptides remains a formidable challenge, especially when the peptides are derived from complex mixtures. MS cleavable cross-linkers are gaining importance for CL-MS as they permit reliable identification of cross-linked peptides by whole proteome database searching using MS/MS information. Here we introduce a novel class of MS cleavable cross-linkers called isotopomeric cross-linkers (ICLs), which allow for confident and efficient identification of cross-linked peptides by whole proteome database searching. ICLs are simple, symmetrical molecules that asymmetrically incorporate heavy and light stable isotopes into the two arms of the cross-linker. As a result of this property, ICLs automatically generate pairs of isotopomeric cross-linked peptides, which differ only by the positions of the heavy and light isotopes. Upon fragmentation during MS analysis, these isotopomeric cross-linked peptides generate unique isotopic doublet ions that correspond to the individual peptides in the cross-link. The doublet ion information is used to determine the masses of the two cross-linked peptides from the same MS2 spectrum that is also used for peptide spectrum matching (PSM) by sequence database searching. Here we present the rationale for and mechanism of cross-linked peptide identification by ICL-MS. We describe the synthesis of the ICL-1 reagent, the ICL-MS workflow, and the performance characteristics of ICL-MS for identifying cross-linked peptides derived from increasingly complex mixtures by whole proteome database searching.

Coaxial PCL/PEG-thiol-ene microfiber with tunable physico-chemical properties for regenerative scaffolds

Tissue regeneration requires scaffolds that exhibit mechanical properties similar to the tissues to be replaced while allowing cell infiltration and extracellular matrix production. Ideally, the scaffolds' porous architecture and physico-chemical properties can be precisely defined to address regenerative needs. We thus developed techniques to produce hybrid fibers coaxially structured with a polycaprolactone core and a 4-arm, polyethylene glycol thiol-norbornene sheath. We assessed the respective effects of crosslink density and sheath polymer size on the scaffold architecture, physical and mechanical properties, as well as cell-scaffold interactions in vitro and in vivo. All scaffolds displayed high elasticity, swelling and strength, mimicking soft tissue properties. Importantly, the thiol-ene hydrogel sheath enabled tunable softness and peptide tethering for cellular activities. With increased photopolymerization, stiffening and reduced swelling of scaffolds were found due to intra- and inter-fiber crosslinking. More polymerized scaffolds also enhanced the cell-scaffold interaction in vitro and induced spontaneous, deep cell infiltration to produce collagen and elastin for tissue regeneration in vivo. The molecular weight of sheath polymer provides an additional mechanism to alter the physical properties and biological activities of scaffolds. Overall, these robust scaffolds with tunable elasticity and regenerative cues offered a versatile and effective platform for tissue regeneration.

Engineering Irrigation Drippers with Rechargeable N-Halamine Nanoparticles for Antifouling Applications

The increased demand for water highlights the need to utilize reclaimed water of various types. In agriculture, for example, which is considered the largest consumer of freshwater, irrigation with treated wastewater can replace much of the need for freshwater. Wastewater is generally used for irrigation through drippers, releasing small amounts of water to the crops. The contaminants found in treated wastewater increase the accumulation of fouling on the drippers, ultimately culminating in blocking of water exit. Thus, there is a crucial need to develop novel approaches to limit biofilm formation on the dripper. Here, we describe the synthesis of N-halamine-derivatized cross-linked polymethacrylamide nanoparticles (NPs) by copolymerization of the monomer methacrylamide and the cross-linker monomer N, N-methylenebisacrylamide and their subsequent embedding in the polyethylene that is used to fabricate the drippers. The newly designed drip system was activated by chlorinating the incorporated NPs and then was fully characterized. The nanofunctionalized drippers were tested in the field, showing excellent antifouling activity for at least 5 months compared to the control. In addition, the inherent recharging capacity of the antifouling NPs constitutes yet another valuable advantage of the currently reported technology.

Preparation and in vitro characterization of cross-linked collagen-gelatin hydrogel using EDC/NHS for corneal tissue engineering applications

Corneal disease is considered as the second leading cause of vision loss and keratoplasty is known as an effective treatment for it. However, the tissue engineered corneal substitutes are promising tools in experimental in vivo repair of cornea. Selecting appropriate cell sources and scaffolds are two important concerns in corneal tissue engineering. The object of this study was to investigate biocompatibility and physical properties of the bio-engineered cornea, fabricated from type-I collagen (COL) and gelatin (Gel). Two gelatin based hydrogels cross-linked with EDC/NHS were fabricated, and their physicochemical properties such as equilibrium water content, enzymatic degradation, mechanical properties, rheological, contact angle and optical properties as well as their ability to support human bone-marrow mesenchymal stem cells (hBM-MSCs) survival were characterized. The equilibrium water content and enzymatic degradation of these hydrogels can be easily controlled by adding COL. Our findings suggest that incorporation of COL-I increases optical properties, hydrophilicity, stiffness and Young's modulus. The viability of hBM-MSCs cultured in Gel and Gel: COL was assessed via CCK-8 assay. Also, the morphology of the hBM-MSCs on the top of Gel and Gel: COL hydrogels were characterized by phase-contrast microscopy. This biocompatible hydrogel may promise to be used as artificial corneal substitutes.

Designing well-defined photopolymerized synthetic matrices for three-dimensional culture and differentiation of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs) are of interest for the study of disease, where these cells can be derived from patients and have the potential to be differentiated into any cell type; however, three-dimensional (3D) culture and differentiation of iPSCs within well-defined synthetic matrices for these applications remains limited. Here, we aimed to establish synthetic cell-degradable hydrogels that allow precise presentation of specific biochemical cues for 3D culture of iPSCs with relevance for hypothesis testing and lineage-specific differentiation. We synthesized poly(ethylene glycol)-(PEG)-peptide-based hydrogels by photoinitiated step growth polymerization and used them to test the hypothesis that the viability of iPSCs within these matrices could be rescued with appropriate biochemical cues inspired by proteins and integrins important for iPSC culture on Matrigel. Specifically, we selected a range of motifs inspired by iPSC binding to Matrigel, including laminin-derived IKVAV and YIGSR, α5β1-binding PHSRNG10RGDS, αvβ5-binding KKQRFRHRNRKG, and RGDS that is known to bind a variety of integrins for generally promoting cell adhesion. YIGSR and PHSRNG10RGDS resulted in the highest iPSC viability, where binding of β1 integrin was key, and these permissive compositions also allowed iPSC differentiation into neural progenitor cells (NPCs) (decreased oct4 expression and increased pax6 expression) in response to soluble factors. The resulting NPCs formed clusters of different sizes in response to each peptide, suggesting that matrix biochemical cues affect iPSC proliferation and clustering in 3D culture. In summary, we have established photopolymerizable synthetic matrices for the encapsulation, culture, and differentiation of iPSCs for studies of cell-matrix interactions and deployment in disease models.

Aryl sulfonate based anticancer alkylating agents

This research work revolves around synthesis of antineoplastic alkylating sulfonate esters with dual alkylating sites for crosslinking of the DNA strands. These molecules were evaluated as potential antineoplastic cross linking alkylating agents by reaction with the nucleoside of Guanine DNA nucleobase at both ends of the synthesized molecule. Synthesis of the alkylating molecules and the crosslinking with the guanosine nucleoside was monitored by MALDITOF mass spectroscopy. The synthesized molecule's crosslinking or adduct forming rate with the nucleoside was compared with that of 1,4 butane disulfonate (busulfan), in form of time taken for the appearance of [M+H]⁺. It was found that aryl sulfonate leaving group was causing higher rate of nucleophilic attack by the Lewis basic site of the nucleobase. Furthermore, the rate was also found to be a function of electron withdrawing or donating nature of the substituent on the aryl ring. Compound with strong electron withdrawing substituent on the para position of the ring reacted fastest. Hence, new alkylating agents were synthesized with optimized or desired reactivity.

Oxidation-induced generation of a mild electrophile for proximity-enhanced protein-protein crosslinking

We report a strategy to introduce a reactive electrophile into proteins through the conversion of a chemically inert group into a bioreactive group in response to an inducer molecule. This strategy was demonstrated by oxidation-induced and proximity-enhanced protein-protein crosslinking in the presence of a large excess of free nucleophile.

Palladium Oxidative Addition Complexes for Peptide and Protein Cross-linking

A new method for cysteine-lysine cross-linking in peptides and proteins using palladium oxidative addition complexes is presented. First, a biarylphosphine-supported palladium reagent is used to transfer an aryl group bearing an O-phenyl carbamate substituent to a cysteine residue. Next, this carbamate undergoes chemoselective acyl substitution by a proximal lysine to form a cross-link. The linkage so formed is stable toward acid, base, oxygen, and external thiol nucleophiles. This method was applied to cross-link cysteine with nearby lysines in sortase A*. Furthermore, we used this method for the intermolecular cross-linking between a peptide and a protein based on the p53-MDM2 interaction. These studies demonstrate the potential for palladium-mediated methods to serve as a platform for the development of future cross-linking techniques for peptides and proteins with natural amino acid residues.

Cross-Linked Polymer-Stabilized Nanocomposites for the Treatment of Bacterial Biofilms

Infections caused by bacterial biofilms are an emerging threat to human health. Conventional antibiotic therapies are ineffective against biofilms due to poor penetration of the extracellular polymeric substance secreted by colonized bacteria coupled with the rapidly growing number of antibiotic-resistant strains. Essential oils are promising natural antimicrobial agents; however, poor solubility in biological conditions limits their applications against bacteria in both dispersed (planktonic) and biofilm settings. We report here an oil-in-water cross-linked polymeric nanocomposite (∼250 nm) incorporating carvacrol oil that penetrates and eradicates multidrug-resistant (MDR) biofilms. The therapeutic potential of these materials against challenging wound biofilm infections was demonstrated through specific killing of bacteria in a mammalian cell-biofilm coculture wound model.

Development and characterization of crosslinked hyaluronic acid polymeric films for use in coating processes

The aim of this work was to develop and characterize new hyaluronic acid-based responsive materials for film coating of solid dosage forms. Crosslinking of hyaluronic acid with trisodium trimetaphosphate was performed under controlled alkaline aqueous environment. The films were produced through casting process by mixing crosslinked or bare biopolymer in aqueous dispersion of ethylcellulose, at different proportions. Films were further characterized regarding morphology by scanning electron microscopy, robustness by permeation to water vapor transmission, and ability to hydrate in simulated gastric and intestinal physiological fluids. The safety and biocompatibility of films were assessed against Caco-2 and HT29-MTX intestinal cells. The permeation to water vapor transmission was favored by increasing hyaluronic acid content in the final formulation. When in simulated gastric fluid, films exhibited lower hydration ability compared to more extensive hydration in simulated intestinal fluids. Simultaneously, in simulated intestinal fluids, films partially lost weight, revealing ability for preventing drug release at gastric pH, but tailoring the release at higher intestinal pH. The physiochemical characterization suggests thermal stability of films and physical interaction between compounds of formulation. Lastly, cytotoxicity tests demonstrated that films and individual components of the formulations, when incubated for 4h, were safe for intestinal cells Overall, these evidences suggest that hyaluronic acid-based responsive films, applied as coating material of oral solid dosage forms, can prevent the premature release of drugs in harsh stomach conditions, but control the release it in gastrointestinal tract distal portion, assuring safety to intestinal mucosa.

Development of a Multifunctional Benzophenone Linker for Peptide Stapling and Photoaffinity Labelling

Photoaffinity labelling is a useful method for studying how proteins interact with ligands and biomolecules, and can help identify and characterise new targets for the development of new therapeutics. We present the design and synthesis of a novel multifunctional benzophenone linker that serves as both a photo-crosslinking motif and a peptide stapling reagent. Using double-click stapling, we attached the benzophenone to the peptide via the staple linker, rather than by modifying the peptide sequence with a photo-crosslinking amino acid. When applied to a p53-derived peptide, the resulting photoreactive stapled peptide was able to preferentially crosslink with MDM2 in the presence of competing protein. This multifunctional linker also features an extra alkyne handle for downstream applications such as pull-down assays, and can be used to investigate the target selectivity of stapled peptides.

1,3-diphenylethenylcarbazolyl-based monomer for cross-linked hole transporting layers

A new cross-linkable monomer containing 1,3-diphenylethenylcarbazolyl-based hole-transporting moieties and four reactive epoxy groups, was prepared by a multistep synthesis route from 1,3-bis(2,2-diphenylethenyl)-9H-carbazol-2-ol and its application for the in situ formation of cross-linked hole transporting layers was investigated. A high concentration of flexible aliphatic epoxy chains ensures good solubility and makes this compound an attractive cross-linking agent. The synthesized compounds were characterized by various techniques, including differential scanning calorimetry, xerographic time of flight, and electron photoemission in air methods.

Crosslinked Porous Starch Particles--a Promising Carrier

Background. Starch is one of the most potential natural polymers used for various bio applications. Literature reports a num- ber of modification strategies such as physical, chemical, enzymatic and genetic to enhance the positive attributes and iron out the undesired features of neat starch.

OBJECTIVES

To synthesize a crosslinked porous starch (CPS) as an efficient cargo for the delivery of calcium carbonate in an efficiently controlled manner for the treatment of hyperphosphatemia.

MATERIAL AND METHODS

The CPS carrier was synthesized using a natural crosslinker, malic acid. The drug delivery system was formulated, followed by the in situ loading of calcium carbonate during the preparation of the CPS. The developed system was characterized with respect to FTIR, DSC, SEM, moisture content, zeta potential, encapsulation efficiency, phosphate binding efficiency and dissolution studies.

RESULTS

The developed formulation was observed to deliver calcium carbonate in an enterically controlled manner. The binding of calcium to phosphate was established to be pH dependent and efficient at pH 7. The moisture content of CPS was in the range of 0.2-0.8%. The zeta potential of the colloidal system was noted to be sufficiently high, indicating the stability. The encapsulation efficiency of CPS particles for calcium was found to be 88-96%.

CONCLUSIONS

An efficient, cost-effective, facile and commercially-viable formulation was demonstrated to deliver calcium carbonate for the treatment of hyperphosphatemia.

Preparation and characterization of highly cross-linked polyimide aerogels based on polyimide containing trimethoxysilane side groups

In this study, highly cross-linked and completely imidized polyimide aerogels were prepared from polyimide containing trimethoxysilane side groups, which was obtained as the condensation product of polyimide containing acid chloride side groups and 3-aminopropyltrimethoxysilane. After adding water and acid catalyst, the trimethoxysilane side groups hydrolyzed and condensed one another, and a continuous increase in the complex viscosities of the polyimide solutions with time was observed. The formed polyimide gels were dried by freeze-drying from tert-butyl alcohol to obtain polyimide aerogels, which consisted of a three-dimensional network of polyimide fibers tangled together. By varying the solution concentration of the polyimide containing trimethoxysilane side groups, polyimide aerogels with different densities (ranging from 0.19 to 0.42 g/cm(3)) were obtained. The resulting polyimide aerogels had small pore diameter (ranging from 20.7 to 58.3 nm), high surface area (ranging from 310 to 344 m(2)/g), high 5% weight loss temperature in air (at about 440 °C), and an excellent mechanical property. In addition, the glass transition temperature (349 °C) of the polyimide aerogels was much higher than that (210 °C) of the corresponding linear polyimide. So, even after being heated at 300 °C for 30 min, the porous structure of the polyimide aerogels was not completely destroyed.

A study of physical and covalent hydrogels containing pH-responsive microgel particles and graphene oxide

In this study we mixed low concentrations of graphene oxide (GO) with microgel (MG) particles and formed composite doubly cross-linked microgels (DX MG/GO) gels. The MG particles comprised poly(ethyl acrylate-co-methacrylic acid-co-1,4-butanediol diacrylate) with pendant glycidyl methacrylate units. The MG/GO mixed dispersions formed physical gels of singly cross-linked MGs (termed SX MG/GO), which were subsequently heated to produce DX MG/GO gels by free-radical reaction. The influence of the GO concentration on the mechanical properties of the SX MG/GO and DX MG/GO gels was investigated using dynamic rheology and static compression measurements. The SX MG/GO physical gels were injectable and moldable. The moduli for the DX MG/GO gels increased by a factor of 4-6 when only ca. 1.0 wt % of GO was included. The isostrain model was used to describe the variation of modulus with DX MG/GO composition. Inclusion of GO dramatically altered the stress dissipation and yielding mechanisms for the gels. GO acted as a high surface area, high modulus filler and played an increasing role in load distribution as the GO concentration increased. It is proposed that MG domains were dispersed within a percolated GO network. Comparison of the modulus data with those published for GO-free DX MGs showed that inclusion of GO provided an unprecedented rate of modulus increase with network volume fraction for this family of colloid gels. Furthermore, the DX MG/GO gels were biocompatible and the results imply that there may be future applications of these new systems as injectable load supporting gels for soft tissue repair.

Bifunctionalized allenes. Part XIII. A convenient and efficient method for regioselective synthesis of phosphorylated α-hydroxyallenes with protected and unprotected hydroxy group

The paper describes a convenient and efficient method for regioselective synthesis of phosphorylated α-hydroxyallenes using an atom economical [2,3]-sigmatropic rearrangement of intermediate propargyl phosphites or phosphinites. These can be readily prepared via reaction of protected alkynols with dimethyl chlorophosphite or chlorodiphenyl phosphine respectively in the presence of a base.

Synthesis of pH-responsive chitosan nanocapsules for the controlled delivery of doxorubicin

Well-defined chitosan nanocapsules (CSNCs) with tunable sizes were synthesized through the interfacial cross-linking of N-maleoyl-functionalized chitosan (MCS) in miniemulsions, and their application in the delivery of doxorubicin (Dox) was investigated. MCS was prepared by the amidation reaction of CS with maleic anhydride in water/DMSO at 65 °C for 20 h. Subsequently, thiol-ene cross-linking was conducted in oil-in-water miniemulsions at room temperature under UV irradiation for 1 h, using MCS as both a surfactant and precursor polymer, 1,4-butanediol bis(3-mercapto-propionate) as a cross-linker, and D-α-tocopheryl poly(ethylene glycol) 1000 succinate as a cosurfactant. With the increase in cosurfactant concentration in the reaction systems, the sizes of the resulting CSNCs decreased steadily. Dox-loaded CSNCs were readily prepared by in situ encapsulation of Dox during miniemulsion cross-linking. With acid-labile β-thiopropionate cross-linkages, the Dox-loaded CSNCs demonstrated a faster release rate under acidic conditions. Relative to free Dox, Dox-loaded CSNCs exhibited enhanced cytotoxicity toward MCF-7 breast cancer cells without any noticeable cytotoxicity from empty CSNCs. The effective delivery of Dox to MCF-7 breast cancer cells via Dox-loaded CSNCs was also observed.

Photo-cross-linking approach to engineering small tyrosine-containing peptide hydrogels with enhanced mechanical stability

Peptide-based supramolecular hydrogels have been extensively explored in biomaterials owing to their unique bioactive, stimulus-responsive, and biocompatible features. However, peptide-based hydrogels often have low mechanical stability with storage moduli of 10-1000 Pa. They are susceptible to mechanical destruction and solvent erosion, greatly hindering their practical application. Here, we present a photo-cross-linking strategy to enhance the mechanical stability of a peptide-based hydrogel by 10(4)-fold with a storage modulus of ~100 kPa, which is one of the highest reported so far for hydrogels made of small peptide molecules. This method is based on the ruthenium-complex-catalyzed conversion of tyrosine to dityrosine upon light irradiation. The reinforcement of the hydrogel through photo-cross-linking can be achieved within 2 min thanks to the fast reaction kinetics. The enhancement of the mechanical stability was due to the formation of a densely entangled fibrous network of peptide dimers through a dityrosine linkage. We showed that in order to implement this method successfully, the peptide sequence should be rationally designed to avoid the cross talk between self-assembly and cross-linking. This method is convenient and versatile for the enhancement of the mechanical stability of tyrosine-containing peptide-based hydrogels. We anticipate that the photo-cross-linked supramolecular hydrogels with much improved mechanical stability will find broad applications in tissue engineering and drug controlled release.

Creation of cross-linked bilayer membranes that can incorporate membrane proteins from oligo-Asp-based peptide gemini surfactants

We designed novel bilayer-forming amphiphiles based on the cyclic oligo-Asp-based peptide gemini (PG) surfactants cr-D2C12 and cr-D3C12, which consist of -Cys(Asp)nCys- (n = 2 or 3) as a core peptide and two Cys residues containing a dodecylamidomethyl group. Dynamic light scattering and transmission electron microscopy measurements revealed the formation of spherical bilayer membranes that could incorporate the light-harvesting antenna complex 2 (LH2) from Rhodopseudomonas acidophila . Furthermore, this proteoliposome-like conjugate could be assembled onto cationized glass and mica to form planar bilayer membranes incorporating LH2. Using atomic force microscopy, we observed LH2 protruding (ca. 1.2-1.5 nm) from flat terraces of the planar bilayer membranes formed from cr-D2C12 or cr-D3C12. Thus, our designed PG surfactants are a new class of bilayer-forming amphiphiles that may be applied to the study of various membrane proteins.

Assembly of free-standing polypeptide films via the synergistic combination of hyperbranched macroinitiators, the grafting-from approach, and cross-chain termination

Cross-linked polypeptide-based films are fabricated via a novel and robust method employing surface-initiated ring opening polymerization of α-amino acid N-carboxyanhydrides (NCA-ROP). The judicious combination of amine-based hyperbranched macroinitiators and benzyl ester-protected NCA derivatives promotes network formation by cross-chain terminations, which allows the formation of stable cross-linked peptide-based capsules in a one-pot system.

Tuning the mechanical properties of nanoporous hydrogel particles via polymer cross-linking

Soft hydrogel particles with tunable mechanical properties are promising for next-generation therapeutic applications. This is due to the increasingly proven role that physicochemical properties play in particulate-based delivery vectors, both in vitro and in vivo. The ability to understand and quantify the mechanical properties of such systems is therefore essential to optimize function and performance. We report control over the mechanical properties of poly(methacrylic acid) (PMA) hydrogel particles based on a mesoporous silica templating method. The mechanical properties of the obtained particles can be finely tuned through variation of the cross-linker concentration, which is hereby quantified using a cross-linking polymer with a fluorescent tag. We demonstrate that the mechanical properties of the particles can be elucidated using an atomic force microscopy (AFM) force spectroscopy method, which additionally allows for the study of hydrogel material properties at the nanoscale through high-resolution force mapping. Young's modulus and stiffness of the particles were tuned between 0.04 and 2.53 MPa and between 1.6 and 28.4 mN m(-1), respectively, through control over the cross-linker concentration. The relationship between the concentration of the cross-linker added and the amount of adsorbed polymer was observed to follow a Langmuir isotherm, and this relationship was found to correlate linearly with the particle mechanical properties.

C-peptide inhibitors of Ebola virus glycoprotein-mediated cell entry: effects of conjugation to cholesterol and side chain-side chain crosslinking

We previously described potent inhibition of Ebola virus entry by a 'C-peptide' based on the GP2 C-heptad repeat region (CHR) targeted to endosomes ('Tat-Ebo'). Here, we report the synthesis and evaluation of C-peptides conjugated to cholesterol, and Tat-Ebo analogs containing covalent side chain-side chain crosslinks to promote α-helical conformation. We found that the cholesterol-conjugated C-peptides were potent inhibitors of Ebola virus glycoprotein (GP)-mediated cell entry (~10(3)-fold reduction in infection at 40 μM). However, this mechanism of inhibition is somewhat non-specific because the cholesterol-conjugated peptides also inhibited cell entry mediated by vesicular stomatitis virus glycoprotein G. One side chain-side chain crosslinked peptide had moderately higher activity than the parent compound Tat-Ebo. Circular dichroism revealed that the cholesterol-conjugated peptides unexpectedly formed a strong α-helical conformation that was independent of concentration. Side chain-side chain crosslinking enhanced α-helical stability of the Tat-Ebo variants, but only at neutral pH. These result provide insight into mechanisms of C-peptide inhibiton of Ebola virus GP-mediated cell entry.

Nanocomposite hydrogels for cartilage tissue engineering: mesoporous silica nanofibers interlinked with siloxane derived polysaccharide

Injectable materials for mini-invasive surgery of cartilage are synthesized and thoroughly studied. The concept of these hybrid materials is based on providing high enough mechanical performances along with a good medium for chondrocytes proliferation. The unusual nanocomposite hydrogels presented herein are based on siloxane derived hydroxypropylmethylcellulose (Si-HPMC) interlinked with mesoporous silica nanofibers. The mandatory homogeneity of the nanocomposites is checked by fluorescent methods, which show that the silica nanofibres dispersion is realized down to nanometric scale, suggesting an efficient immobilization of the silica nanofibres onto the Si-HPMC scaffold. Such dispersion and immobilization are reached thanks to the chemical affinity between the hydrophilic silica nanofibers and the pendant silanolate groups of the Si-HPMC chains. Tuning the amount of nanocharges allows tuning the resulting mechanical features of these injectable biocompatible hybrid hydrogels. hASC stem cells and SW1353 chondrocytic cells viability is checked within the nanocomposite hydrogels up to 3 wt% of silica nanofibers.

Exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymers for preparation of robust, multifunctional mesoporous hybrid microcapsules

A facile approach to preparing mesoporous hybrid microcapsules is developed by exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymer. The preparation process contains four steps: segregation of cationic hydrophilic polymer during template formation, cross-linking of the segregated polymer, biomimetic mineralization within cross-linked polymer network, and removal of template to simultaneously generate capsule lumen and mesopores on the capsule wall. Poly(allylamine hydrochloride) (PAH) is chosen as the model polymer, its hydrophilicity renders the segregating capacity and spontaneous enrichment in the near-surface region of CaCO3 microspheres; its biopolyamine-mimic structure renders the mineralization-inducing capacity to produce titania from the water-soluble titanium(IV) precursor. Meanwhile, CaCO3 microspheres serve the dual templating functions in the formation of hollow lumen and mesoporous wall. The thickness of capsule wall can be controlled by changing the polymer segregating and cross-linking conditions, while the pore size on the capsule wall can be tuned by changing the template synthesizing conditions. The robust hybrid microcapsules exhibit desirable efficiency in enzymatic catalysis, wastewater treatment and drug delivery. This approach may open facile, generic, and efficient pathway to designing and preparing a variety of hybrid microcapsules with high and tunable permeability, good stability and multiple functionalities for a broad range of applications.

Synthesis of a new conjugated polymer for DNA alkylation and gene regulation

A new polyfluorene derivative containing pendent alkylating chlorambucil (PFP-Cbl) was synthesized and characterized. Under direct incubation with DNA in vitro, PFP-Cbl could undergo an efficient DNA alkylating reaction and induce DNA cross-linking. In vitro transcription and translation experiment exhibited that the PFP-Cbl significantly down-regulated the gene expression of luciferase reporter plasmid. The down-regulation of gene expression was also verified through the transfection experiment of p-EGFP plasmid, which showed decreased green fluorescent protein (GFP) in cells. Meanwhile, the self-luminous property of PFP-Cbl could make it able to trace the internalized PFP-Cbl and plasmid complexes resulted from cross-linking in cells by fluorescent microscopy. Combining the features of alkylating function, multivalent binding sites, and fluorescent characteristics, PFP-Cbl provides a new insight in the area of gene regulation and extends the new applications of conjugated polymers (CPs).

Synthesis of a disulfide cross-linked polygalacturonic acid hydrogel for biomedical applications

Polygalacturonic acid (PGA) hydrogel cross-linked via disulfide bonds was synthesized using a thiol oxidation reaction. PGA was grafted with cysteine to yield thiolated PGA (denoted PGAcys). Per gram, PGA-conjugated cysteine was 725 ± 77 μmol, and the degree of modification was 16.24 %. A PGAcys hydrogel film was fabricated under physiological conditions, with gel content 91.6 % and water content 43.3 %. The PGAcys hydrogel was used as a drug carrier for rosmarinic acid (RA) (denoted PGAcys/RA) and to prevent postsurgical adhesion. The in vitro dynamic release behavior of RA from the PGAcys hydrogel was analyzed. The profiles showed that 80 % of the total RA was released from the hydrogel within 15 min, followed by zero-order kinetic release. Animal implant studies showed that PGAcys and PGAcys/RA hydrogel films reduced adhesion incidence by over 90 %, significantly higher than did Hyaluronate/Carboxymethylcellulose (analogous Seprafilm™) (42 %). The PGAcys/RA hydrogel film also reduced the early inflammatory reaction.

Effect of polymer-graft modification on the order formation in particle assembly structures

The propensity of particle brush materials to form long-ranged ordered assembly structures is shown to sensitively depend on the brush architecture (i.e., the particle radius as well as molecular weight and grafting density of surface-bound chains). In the limit of stretched chain conformations of surface-grafted chains the formation of regular particle array structures is observed and interpreted as a consequence of hard-sphere-type interactions between polymer-grafted particles. As the degree of polymerization of surface-grafted chains increases beyond a threshold value, a reduction of the structural regularity is observed that is rationalized with the increased volume occupied by relaxed polymer segments. The capacity of polymer grafts to increase or decrease order in particle brush assembly structures is interpreted on the basis of a mean-field scaling model, and "design criteria" are developed to help guide the future synthesis of colloidal systems that are capable of forming mechanically robust yet ordered assembly structures.

Simple, clean preparation method for cross-linked α-cyclodextrin nanoparticles via inclusion complexation

A simple, clean method was presented in this letter to prepare cross-linked α-cyclodextrin (α-CD) nanoparticles with a low dispersion. The nanoparticles were synthesized in water by cross-linking the inclusion complex of α-CDs and poly(ethylene glycol) (PEG). The structure of the nanoparticles was characterized by (1)H NMR, nuclear overhauser enhancement spectroscopy (NOESY), and wide-angle X-ray diffraction (XRD). Spherical morphology was observed by scanning electron microscopy (SEM) for these nanoparticles. Their average hydrodynamic radius was determined to be 67 nm by dynamic light scattering (DLS). Small guest molecules could be included in the cross-linked α-CD nanoparticles, and anticancer drug cisplatin was used to evaluate the drug release behavior.

Novel Pickering emulsifiers based on pH-responsive poly(2-(diethylamino)ethyl methacrylate) latexes

The emulsion copolymerization of 2-(diethylamino)ethyl methacrylate (DEA) with a divinylbenzene cross-linker in the presence of monomethoxy-capped poly(ethylene glycol) methacrylate (PEGMA) at 70 °C afforded near-monodisperse, sterically stabilized PEGMA-PDEA latexes at 10% solids. Dynamic light scattering studies indicated intensity-average diameters of 190 to 240 nm for these latexes at pH 9. A latex-to-microgel transition occurred on lowering the solution pH to below the latex pKa of 6.9. When dilute HCl/KOH was used to adjust the aqueous pH, a systematic reduction in the cationic microgel hydrodynamic diameter of 80 nm was observed over ten pH cycles as a result of the gradual buildup of background salt. However, no such size reduction was observed when using CO2/N2 gases to regulate the aqueous pH because this protocol does not generate background salt. Thus, the latter approach offers better reversibility, albeit at the cost of slower response times. PEGMA-PDEA microgel does not stabilize Pickering emulsions when homogenized at pH 3 with n-dodecane, sunflower oil, isononyl isononanoate, or isopropyl myristate. In contrast, PEGMA-PDEA latex proved to be a ubiquitous Pickering emulsifier at pH 10, forming stable oil-in-water emulsions with each of these four model oils. Lowering the solution pH from 10 to 3 resulted in demulsification within seconds. This is because these pH-responsive particles undergo a latex-to-microgel transition, which leads to their interfacial desorption. Six successive demulsification/emulsification cycles were performed on these Pickering emulsions using HCl/KOH to adjust the solution pH. Demulsification could also be achieved by purging the emulsion solution with CO2 gas to lower the aqueous pH to 4.8. However, complete phase separation required CO2 purging for 4 h at 20 °C. A subsequent N2 purge raised the aqueous pH sufficiently to induce a microgel-to-latex transition, but rehomogenization did not produce a stable Pickering emulsion. Presumably, a higher pH is required, which cannot be achieved by a N2 purge alone.

Highly selective immobilization of Au nanoparticles onto isolated and dense nanopatterns of poly(2-vinyl pyridine) brushes down to single-particle resolution

Chemical patterns consisting of poly(2-vinyl pyridine) (P2VP) brushes in a background of a cross-linked polystyrene (PS) mat enabled the highly selective placement of citrate-stabilized Au nanoparticles (NPs) in arrays on surfaces. The cross-linked PS mat prevented the nonspecific binding of Au NPs, and the regions functionalized with P2VP brushes allowed the immobilization of the particles. Isolated chemical patterns of feature sizes from hundreds to tens of nanometers were prepared by standard lithographic techniques. The number of 13 nm Au NPs bound per feature increased linearly with increasing area of the patterns. This behavior is similar to previous reports using 40 nm particles or larger. Arrays of single NPs were obtained by reducing the dimensions of patterned P2VP brushes to below ~20 nm. To generate dense (center-to-center distance = 80 nm) linear chemical patterns for the placement of rows of single NPs, a block-copolymer (BCP)-assisted lithographic process was used. BCPs healed defects associated with the standard lithographic patterning of small dimensions at high densities and led to highly registered, linear, single NP arrays.

Covalent cross-linking of kinases with their corresponding peptide substrates

Protein phosphorylation represents the most dominant and evolutionary conserved posttranslational modification for information transfer in cells and organisms. The human genome encodes >500 protein kinases, and thousands of phosphorylation sites are present in mammalian proteome. To develop a global view of phosphorylation network, there is a need to map the connectivity between kinases and phosphoproteome. We developed a chemical kinase-substrate cross-linker 1 that converts transient kinase-substrate interactions into a covalently linked kinase-substrate complex in vitro and in the presence of cell lysates. The method can be applied to identify unknown upstream kinases responsible for phosphorylation events in cell lysates.

Separating and analyzing sulfur-containing RNAs with organomercury gels

Polyacrylamide gel electrophoresis is a widely used technique for RNA analysis and purification. The polyacrylamide matrix is highly versatile for chemical derivitization, enabling facile exploitation of thio-mercury chemistry without the need of tedious manipulations and/or expensive coupling reagents, which often give low yields and side products. Here, we describe the use of [(N-acryloylamino)phenyl]mercuric chloride in three-layered polyacrylamide gels to detect, separate, quantify, and analyze sulfur-containing RNAs.

pH-Sensitive micelles with cross-linked cores formed from polyaspartamide derivatives for drug delivery

A series of polyaspartamide derivatives were synthesized by grafting O-(2-aminoethyl)-O'-methylpoly(ethylene glycol) 5000 (MPEG), 1-(3-aminopropyl) imidazole (API), and cinnamate onto polysuccinimide (PSI) with the respective degrees of substitution adjusted by the feed molar ratio. The chemical structure of the prepared polymer was confirmed using FT-IR and (1)H NMR spectroscopy. A new pH-sensitive polymeric micelle based on the synthesized polymer was prepared and characterized, and its pH-sensitive properties were characterized by the measurement of light transmittance and particle sizes at varying pH values. pH-dependent aggregation and deaggregation behavior was clearly observed in the polymer aqueous dispersion system. Photo-cross-linking of the cinnamate branches cross-linked the core of the micelles. The core cross-linked micelles showed high stability over a wider pH range and displayed obvious pH-dependent swelling-shrinking behavior instead of micelle-unimer transition behavior. This micelle system overcame the drawback of the facile disintegration of normal polymeric micelles and showed obvious delayed paclitaxel release in in vitro drug delivery experiments.

Enzymatic triggered release of an HIV-1 entry inhibitor from prostate specific antigen degradable microparticles

This paper describes the design, construction and characterization of the first anti-HIV drug delivery system that is triggered to release its contents in the presence of human semen. Microgel particles were synthesized with a crosslinker containing a peptide substrate for the seminal serine protease prostate specific antigen (PSA) and were loaded with the HIV-1 entry inhibitor sodium poly(styrene-4-sulfonate) (pSS). The particles were composed of N-2-hydroxyproplymethacrylamide and bis-methacrylamide functionalized peptides based on the PSA substrates GISSFYSSK and GISSQYSSK. Exposure to human seminal plasma (HSP) degraded the microgel network and triggered the release of the entrapped antiviral polymer. Particles with the crosslinker composed of the substrate GISSFYSSK showed 17 times faster degradation in seminal plasma than that of the crosslinker composed of GISSQYSSK. The microgel particles containing 1 mol% GISSFYSSK peptide crosslinker showed complete degradation in 30 h in the presence of HSP at 37°C and pSS released from the microgels within 30 min reached a concentration of 10 μg/mL, equivalent to the published IC(90) for pSS. The released pSS inactivated HIV-1 in the presence of HSP. The solid phase synthesis of the crosslinkers, preparation of the particles by inverse microemulsion polymerization, HSP-triggered release of pSS and inactivation of HIV-1 studies are described.

[Application of BODIPY-trimethylmelamine conjugate for DNA cross-linking in vitro]

Conjugate the fluorescent dye 4,4-difluoro-1,3,5,7-tetramethyl-4-bora-3a,4a-diaza-s-indatsen-8-propionic acid (BODIPY) and N2,N4,N6-trimethylmelamine was obtained. It was shown that this compound in the presence of formaldehyde generates covalent cross-links of DNA strands in vitro.

Bifunctional avidin with covalently modifiable ligand binding site

The extensive use of avidin and streptavidin in life sciences originates from the extraordinary tight biotin-binding affinity of these tetrameric proteins. Numerous studies have been performed to modify the biotin-binding affinity of (strept)avidin to improve the existing applications. Even so, (strept)avidin greatly favours its natural ligand, biotin. Here we engineered the biotin-binding pocket of avidin with a single point mutation S16C and thus introduced a chemically active thiol group, which could be covalently coupled with thiol-reactive molecules. This approach was applied to the previously reported bivalent dual chain avidin by modifying one binding site while preserving the other one intact. Maleimide was then coupled to the modified binding site resulting in a decrease in biotin affinity. Furthermore, we showed that this thiol could be covalently coupled to other maleimide derivatives, for instance fluorescent labels, allowing intratetrameric FRET. The bifunctional avidins described here provide improved and novel tools for applications such as the biofunctionalization of surfaces.