Structurally Tunable pH-responsive Phosphine Oxide Based Gels by Facile Synthesis Strategy

Trivinylphosphine Oxide: Synthesis, Characterization, and Polymerization Reactivity Investigated Using Single-Crystal Analysis and Density Functional Theory

Organophosphorus chemicals are versatile and important in industry. Trivinylphosphine oxide (TVPO), for example, exhibited a promising precursor as a flame-retardant additive for industrial applications. Density functional theory (DFT) simulations were used to explore the kinetic and thermodynamic chemical processes underlying the nucleophilic addition reactions of TVPO in order to better understand their polymerization mechanisms. An experimental X-ray single-crystal study of TVPO supported this work's theory based on its computed findings. TVPO was prepared using POCl3 and VMB in a temperature-dependent reaction. TVPO, the thermodynamically favourable product, is preferentially produced at low temperatures. The endothermic anionic addition polymerization reaction between TVPO and VMB begins when the reaction temperature rises. An implicit solvation model simulated TVPO and piperazine reactions in water, whereas a hybrid model modelled VMB interactions in tetrahydrofuran. The simulations showed a pseudo-Michael addition reaction mechanism with a four-membered ring transition state. The Michael addition reaction is analogous to this process.

Rational design of a supramolecular hydrogel with customizable pH-responsiveness on the basis of pH-induced ionization/protonation transition of BSA

Developing customizable pH-responsiveness for supramolecular hydrogels is of great significance and has drawn tremendous attention. Through systematic simulation analysis, we formulated a simple supramolecular hydrogel (i.e., poly(AAm-co-NaSS)/BSA on the basis of electrostatic interaction between the sulfonate groups of poly(AAm-co-NaSS) and the protonated side groups of BSA, and proposed a novel pH-responsive mode for it: changing the internal electric charge composition of the hydrogel through pH-induced ionization/protonation transition of BSA, thereby regulating the structural stability/shrinkage/extension of the supramolecular network. On basis of this theory, the pH-responsiveness of the poly(AAm-co-NaSS)/BSA hydrogel, in principle, could be pre-designed by adjusting the initial BSA/NaSS ratio. In this regard, we fabricated a poly(AAm-co-NaSS)/BSA hydrogel prototype with a BSA/NaSS ratio of 1/57 and investigated its rheological/swelling/disassembling behavior under different pH conditions (1.7, 4.7, 7.7, 10.7, and 13.7). In addition, we also prepared two capecitabine-loaded poly(AAm-co-NaSS)/BSA hydrogel prototypes with BSA/NaSS ratios of 1/57 and 1/102 respectively at pH 4.0, and compared their drug release behavior in SGF and SIF. Finally, the experimental results fitted well with our theoretical expectations, which testified the rationality of our assumption. Thus, we believed that the poly(AAm-co-NaSS)/BSA supramolecular hydrogel could find diverse applications in the future.

Smartphone-Based Pure DNAzyme Hydrogel Platform for Visible and Portable Colorimetric Detection of Cell-Free DNA

Cell-free DNA (cfDNA), as a tumor marker, is of great importance for the diagnosis of cancer and targeted therapy. However, the need for huge analytical instruments for cfDNA analysis has restricted its practical applications, especially in rural areas and third-world countries. Herein, a portable and visual smartphone-based DNAzyme hydrogel platform is developed for cfDNA detection. The target cfDNA triggers rolling circle amplification to produce a G-quadruplex-comprised DNA hydrogel with an horseradish peroxidase (HRP)-like catalytic function, which further catalyzes the chromogenic substrate to generate a visible output signal. Notably, the naked-eye detection of cfDNA can be realized by the macroscale visibility and catalytic ability of the DNA hydrogel. The linear range of the DNAzyme hydrogel platform for cfDNA detection is 0.1 pM-1500 nM with a detection limit of 0.042 pM. Moreover, this platform is exploited for the detection of cfDNA in spiked human serum with favorable sensitivity and recovery. Therefore, the DNAzyme hydrogel platform provides highly promising potential for testing other nucleic acid biomarkers.

Fabrication of Cellulase Catalysts Immobilized on a Nanoscale Hybrid Polyaniline/Cationic Hydrogel Support for the Highly Efficient Catalytic Conversion of Cellulose

A novel conductive nanohydrogel hybrid support was prepared by in situ polymerization of polyaniline nanorods on an electrospun cationic hydrogel of poly(ε-caprolactone) and a cationic phosphine oxide macromolecule. Subsequently, the cellulase enzyme was immobilized on the hybrid support. Field-emission scanning electron microscopy and Brunauer-Emmett-Teller analyses confirmed a mesoporous, rod-like structure with a slit-like pore geometry for the immobilized support and exhibiting a high immobilization capacity and reduced diffusion resistance of the substrate. For comparison, the catalytic activity, storage stability, and reusability of the immobilized and free enzymes were evaluated. The results showed that the immobilized enzymes have higher thermal stability without changes in the optimal pH (5.5) and temperature (55 °C) for enzyme activity. A high immobilization efficiency (96%) was observed for the immobilized cellulose catalysts after optimization of parameters such as the pH, temperature, incubation time, and protein concentration. The immobilized enzyme retained almost 90% of its original activity after 4 weeks of storage and 73% of its original activity after the ninth reuse cycle. These results strongly suggest that the prepared hybrid support has the potential to be used as a support for protein immobilization.

Smart hydrogel-microsphere embedded silver nanoparticle catalyst with high activity and selectivity for the reduction of 4-nitrophenol and azo dyes

A simple method is reported for the preparation of silver nanoparticle (AgNP) embedded pH-responsive hydrogel microparticle catalyst via Michael addition gelation and in-situ silver nitrate (AgNO₃) reduction. The AgNP-hydrogel microsphere exhibited an efficient reduction of pollutants like 4-Nitrophenol (4-NP) and Congo red (CR) under acidic medium with turn over frequency (TOF) of ~170 h^-1 and ~124 h^-1 respectively. Interestingly, the activity of the catalysts was turned-OFF under a basic medium (≥ pH 12) due to the deswelling pH-responsive matrix surrounding the AgNPs. On the contrary, turning-OFF the hydrogenation of a cationic pollutant like methylene blue (MB) using high pH (≥ 12) was not possible, due to ionic interaction of MB molecules with the negatively charged catalyst at this pH. This feature was used to demonstrate selective hydrogenation of only MB from a mixture of 4-NP and MB. Finally, five recycling steps confirmed the reusability and practical application potential of the catalyst.

Improving physical and biological properties of nylon monofilament as suture by Chitosan/Hyaluronic acid

One way to give some properties such as antibacterial and good frictional properties to sutures is the application of natural antibacterial and hydrophilic components on their surfaces through layer by layer assembly (LBL) technique. In this regard, Chitosan as an antibacterial polycationic natural polymer along with Hyaluronic acid (HA) as a polyanionic polysaccharide could be used to form a polyelectrolyte complex. In this study, HA was extracted from rooster comb using different solvents. Characterization of the extracted HA by FTIR and GPC analysis showed extracted HA with M_w = 2.53 × 10⁵ Da had no cytotoxicity. Then, a nylon monofilament (NMy) was coated by the extracted HA and chitosan with different concentrations using bilayer coating technique. Two dyes also were loaded to coating layer to investigate the release behavior of these two drug models. The morphology of coated layer showed that coating NMy by chitosan (4% w/v) following by HA (8% w/v) with roughness of 164 ± 129 nm and friction coefficient of 0.26 had suitable interaction between two layers to prevent from exfoliation of coating layers. The antibacterial activity and controlled release of coated NMy indicated how a NMy coated by Chitosan and HA is a promising material for using as a suture.