Design, synthesis and application of a new class of stimuli-responsive separation materials

Preparation of pH-responsive block copolymers for separation of cephalosporin antibiotics by open-tubular capillary electrochromatography

Stimuli-responsive block copolymers have exhibited their feasibility for drug delivery and analysis of biomolecules. However, study of the electrophoretic behavior of antibiotics by open tubular capillary electrochromatography (OT-CEC) based on smart block copolymers coatings is still a substantial challenge. Herein, we reported an OT-CEC protocol for analysis of cephalosporin antibiotics with pH-responsive block copolymers as coatings. By using the reversible addition-fragmentation chain-transfers radical polymerisation technique, the smart poly(styrene-maleic anhydride-acrylic acid) (P(St-MAn-AA)) was synthesized and subsequently chemical bonded onto the inner walls of amino-grafted capillaries. The pH induced changes in the stretch/curl states of P(St-MAn-AA) chains were used to generate an adjustable hydrophobic/hydrophilic interaction and hydrogen bonds between the polymer coatings and the analytes. The OT-CEC performance was evaluated by varying the monomer ratios, polymer coating amounts and layers, buffer concentrations and pH values. Baseline separation of the three-test antibiotics was achieved at pH 8.0. The proposed OT-CEC technique was further applied to the determination of rat serum antibiotics in the metabolic processes. The present work demonstrates an enhancement in antibiotics separation efficiency, and shows a great potential for the preparation of stimuli-responsive block copolymers coatings and in OT-CEC analysis of real samples in living bio-systems.

Synthesis and Characterization of Alkoxysilane-Bearing Photoreversible Cinnamic Side Groups: A Promising Building-Block for the Design of Multifunctional Silica Nanoparticles

The present study reports on the synthesis of a new alkoxysilane-bearing light-responsive cinnamyl group and its application as a surface functionalization agent for the development of SiO₂ nanoparticles (NPs) with photoreversible tails. In detail, cinnamic acid (CINN) was activated with N-hydroxysuccinimide (NHS) to obtain the corresponding NHS-ester (CINN-NHS). Subsequently, the amine group of 3-aminopropyltriethoxysilane (APTES) was acylated with CINN-NHS leading to the generation of a novel organosilane, CINN-APTES, which was then exploited for decorating SiO₂ NPs. The covalent bond to the silica surface was confirmed by solid state NMR, whereas thermogravimetric analysis unveiled a functionalization degree much higher compared to that achieved by a conventional double-step post-grafting procedure. In light of these intriguing results, the strategy was successfully extended to naturally occurring sepiolite fibers, widely employed as fillers in technological applications. Finally, a preliminary proof of concept of the photoreversibility of the obtained SiO₂@CINN-APTES system has been carried out through UV diffuse reflectance. The overall outcomes prove the consistency and the versatility of the methodological protocol adopted, which appears promising for the design of hybrid NPs to be employed as building blocks for photoresponsive materials with the ability to change their molecular structure and subsequent properties when exposed to different light stimuli.

Isothermal modelling of protein adsorption to thermo-responsive polymer grafted Sepharose Fast Flow sorbents

In this study, five adsorption isotherm models, that is, the Langmuir, Freundlich, Langmuir-Freundlich, Temkin and Brunauer-Emmett-Teller isotherms, were utilized for the analysis of the experimental adsorption data for six classes of poly(N-isopropylacrylamide)-based thermo-responsive copolymer-grafted Sepharose Fast Flow sorbents of different copolymer compositions with two structurally related proteins, namely bovine holo-lactoferrin and bovine holo-transferrin at 20 and 50°C. The experimental data for bovine holo-lactoferrin could be mathematically fitted to the Freundlich and Temkin isotherms when the protein feed concentrations were in the range of 1-40 mg/mL at both 20 and 50°C. Similar analysis of the binding of the homologous protein, bovine holo-transferrin, to the same thermo-responsive copolymer-grafted sorbents revealed that the experimental data could be fitted to the Langmuir, Freundlich and Temkin isotherms with coefficients of determination value over 0.90.

Adsorption of a Humanized Monoclonal Antibody onto Thermoresponsive Copolymer-Grafted Sepharose Fast Flow Sorbents

The batch adsorption behavior of a humanized monoclonal antibody (hIgG2 mAb) with thermoresponsive polymer (TRP)-modified Sepharose Fast Flow sorbents with different compositions of grafted copolymers is described. At high protein loadings, the adsorption with negatively charged copolymer-modified sorbents exhibited S-shaped isotherms in most cases, indicative of unrestricted multilayer adsorption. The adsorption capacity of the negatively charged copolymer-modified sorbents increased with an increase in the applied environmental temperature due to increased protein-sorbent surface hydrophobic and electrostatic interactions. The affinity of the hIgG2 mAb for a positively charged copolymer-grafted sorbent was much lower than that found for the negatively charged copolymer-grafted sorbents at both 20 and 50 °C due to electrostatic repulsive effects. This study has documented that the molecular functionalities of the grafted copolymer can significantly affect the adsorption behavior of this humanized mAb at both 20 and 50 °C with the isothermal dependencies revealing subtle effects due to copolymer composition.

In Vitro and in Vivo Studies of pH-Sensitive GHK-Cu-Incorporated Polyaspartic and Polyacrylic Acid Superabsorbent Polymer

The main aim of this study was to evaluate the in vitro and in vivo efficiency of the polyaspartic acid- and acrylic acid-based superabsorbent polymer. The synthesized polymer was first investigated to check the blood compatibility by protein adsorption and blood clotting tests. Further, the GHK-Cu peptide was incorporated within the polymer and release studies were performed to evaluate the drug-delivery efficiency of the superabsorbent polymer. The polymer with best peptide release results were further used for in vivo analysis for wound healing. The healing efficiency of polymer with and without peptide was analyzed using wound closure, biochemical assay, histopathological, and toxicity studies.

Investigations into the interaction thermodynamics of TRAP-related peptides with a temperature-responsive polymer-bonded porous silica stationary phase

The interaction thermodynamics of the thrombin receptor agonistic peptide (TRAP-1), H-Ser-Phe-Leu-Leu-Arg-Asn-Pro-OH, and a set of alanine scan substitution peptides, have been investigated with an n-octadecylacrylic polymer-bonded porous silica (Sil-ODA₁₈) and water-acetonitrile mobile phases at temperatures ranging from 5 to 80 °C in 5 °C increments. The retention of these peptides on the Sil-ODA₁₈ stationary phase decreased as the water content in the mobile phase was lowered from 80% (v/v) to ca. 45% (v/v) and reached a minimum value for each peptide at a specific water-acetonitrile composition. Further decreases in the water content of the mobile phase led to increased retention. The magnitude of the changes in enthalpy of interaction, Δ H a s s o c 0 , changes in entropy of interaction, Δ S a s s o c 0 , and changes in heat capacity, Δ C p 0 , were found to be dependent on the molecular properties of the mobile phase, the temperature, the structure/mobility of the stationary phase, and the conformation and solvation state of the peptides. With water-rich mobile phases, the retention behaviour of the TRAP analogues was dominated by enthalpic processes, consistent with the participation of strong hydrogen bonding effects, but became dominated by entropic effects with acetonitrile-rich mobile phases as the temperature was increased. These changes in the retention behaviour of these TRAP peptides are consistent with the generation of water or acetonitrile clusters in the mobile phase depending on the volume fractions of the organic solvent as the Sil-ODA₁₈ stationary phase transitions from its crystalline to its isotropic state.