The polyaminosaccharide-based buffers as a new type of zwitterionic buffering macromolecules for biochemical applications

A new type of biocompatible buffers based on zwitterionic polyaminosaccharides is reported. The carboxy- and amino-groups containing carboxymethyl chitosan (CM-CS) was synthesized and reacted with hydrochloric/acetic acid resulting in CM-CS-HCl and CM-CS-HAc buffers with buffering capacity of 20.6 and 15.2 mM/pH. The new buffers were comprehensively characterized for their physicochemical properties and checked on enzymatic reactions of acetylcholinesterase (AChE) and alkaline phosphatase (ALP). Their performance was compared to the phosphate and Tris buffers. The chloride-free, CM-CS-HAc demonstrated excellent buffering activity with Michaelis constants of 0.50 and 1.00 mM and maximum reaction rates of 5.62 and 2.26 μmol/min/mL for AChE and ALP reactions, respectively. Toxicity studies on stress-sensitive bioreporter bacteria verified nontoxicity of CM-CS-HAc. Zwitterionic polyaminosaccharides overcome drawbacks of monomeric buffers, such as interference with enzyme active sites, cell membrane injury and purification difficulties. Therefore, they may become the next generation of effective buffers for biological and biochemical applications.

Bio-inspired zwitterionic polymeric chelating assembly for treatment of copper-induced cytotoxicity and hemolysis

We developed a hemocompatible, bio-inspired, multivalent, polymeric-chelating assembly based on the poly(2-methacryloyloxyethyl phosphorylcholine)-b-poly(serinyl acrylate) (PMPC-b-PserA) zwitterionic diblock copolymer. Functional PMPC-b-PserA was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization to catch and encapsulate free copper ions (Cu²⁺) in a solution. PMPC with an identical polar group to phospholipids exhibits high hydrophilicity and fouling resistance against non-specific adsorption, and inertness to the metal ions. On the other hand, PserA with pendant groups of amino acids possesses a strong capability to react with Cu²⁺ by coordination interaction. Therefore, when PMPC-b-PserA was brought into contact with Cu²⁺, a hydrophobic core with multiple coordination "bridges" between polymers and Cu²⁺ was formed, leading to self-assembly of core-shell polymer-metal nanoparticles. As a result, free Cu²⁺ ions can be removed from the solution to prevent damage to cells and tissues. The synthesis and chemical structure of PMPC-b-PserA were characterized, and the formation of self-assembled polymer-Cu²⁺ nanoparticles and colloidal stability were analyzed. More importantly, the detoxification of PMPC-b-PserA in presence of Cu²⁺ with fibroblast cells was demonstrated by increased cell viability >80%. In addition, the hemolysis, which occurred due to disruption of RBC membranes by free Cu²⁺, was effectively suppressed by adding PMPC-b-PserA. The bio-inspired and biocompatible chelating agent of PMPC-b-PserA provides a new treatment approach to encapsulate and detoxify heavy metals in complex media for chelation therapy.

l-Histidine-Derived Smart Antifouling Biohybrid with Multistimuli Responsivity

A novel dual pH/thermoresponsive amphiphilic poly(histidine methacrylamide)-block-hydroxyl-terminated polybutadiene-block-poly(histidine methacrylamide) (PHisMAM-b-PB-b-PHisMAM) triblock copolymer biohybrid, composed of hydrophobic PB and ampholytic PHisMAM segments, is developed via direct switching from living anionic polymerization to recyclable nanoparticle catalyst-mediated reversible-deactivation radical polymerization (RDRP). The transformation involved in situ postpolymerization modification of living polybutadiene-based carbanionic species, end-capped with ethylene oxide, into dihydroxyl-terminated polybutadiene and a subsequent reaction with 2-bromo-2-methylpropionyl bromide resulting in a telechelic ATRP macroinitiator (Br-PB-Br). Br-PB-Br was used to mediate RDRP of an l-histidine-derived monomer, HisMAM, yielding a series of PHisMAM-b-PB-b-PHisMAM triblock copolymers. The copolymer's stimuli response was assessed against pH and temperature changes. The copolymer is capable of switching among its zwitterionic, anionic, and cationic forms and exhibited unique antifouling properties in its zwitterionic form. These novel triblock copolymers are expected to be show promising potential in biomedical applications.

Bio-Inspired Amphoteric Polymer for Triggered-Release Drug Delivery on Breast Cancer Cells Based on Metal Coordination

Nanoscale coordination polymers are promising vehicles for anticancer drug delivery because their surface composition and particle size can be tuned to exploit the enhanced permeability and retention effect, and their reversible interaction with metal cations enables triggered drug release at the tumor site. Here, we develop a novel nanoscale coordination polymer using the diblock copolymer poly(2-methacryloyloxyethyl phosphorylcholine)-block-poly(serinyl acrylate) (PMPC-b-PserA) and demonstrate its use for encapsulation of a hydrophobic drug and triggered drug release to induce breast cancer cell apoptosis in vitro. The zwitterionic PMPC block was inspired by the antifouling structure of cell membranes, and the PserA block was inspired by the amphoteric amino acids of proteins. The polymer was synthesized by reversible addition-fragmentation chain transfer polymerization, and a mixture of the polymer and FeCl3 self-assembled into nanoparticles via complexation of Fe3+ with PserA, with the hydrophilic PMPC block at the particle surface. At a molar ratio of Fe3+ to serA of 3:1, the hydrodynamic diameter of the particles was 22.2 nm. Curcumin, a natural water-insoluble polyphenol used to enhance the effects of chemotherapeutics, was encapsulated in the particles as an oil-in-water emulsion, with an encapsulation efficiency of 99.6% and a particle loading capacity of 32%. Triggered release of curcumin was achieved by adding deferoxamine, an FDA-approved Fe3+ chelating agent; curcumin release efficiency increased at higher deferoxamine concentrations and lower pH. Triggered release of curcumin induced apoptosis in human triple-negative breast cancer cells; cell viability decreased to 34.3% after 24 h of treatment with the curcumin-loaded nanoparticles and deferoxamine, versus >80% viability without deferoxamine to trigger drug release. The biocompatibility, tunable composition and size, high hydrophobic drug loading, and triggered-release capability of this nanoscale coordination polymer make it well-suited for use in anticancer drug delivery.

Mixed Polyplex Micelles with Thermoresponsive and Lysine-Based Zwitterionic Shells Derived from Two Poly(vinyl amine)-Based Block Copolymers

Two series of poly(vinyl amine) (PVAm)-based block copolymers with zwitterionic and thermoresponsive segments were synthesized by the reversible addition-fragmentation chain transfer polymerization. A mixture of the two copolymers, poly(N-acryloyl-l-lysine) (PALysOH) and poly(N-isopropylacrylamide) (PNIPAM), which have the same cationic PVAm chain but different shell-forming segments, were used to prepare mixed polyplex micelles with DNA. Both PVAm-b-PALysOH and PVAm-b-PNIPAM showed low cytotoxicity, with characteristic assembled structures and stimuli-responsive properties. The cationic PVAm segment in both block copolymers showed site-specific interactions with DNA, which were evaluated by dynamic light scattering, zeta potential, circular dichroism, agarose gel electrophoresis, atomic force microscopy, and transmission electron microscopy measurements. The PVAm-b-PNIPAM/DNA polyplexes showed the characteristic temperature-induced formation of assembled structures in which the polyplex size, surface charge, chiroptical property of DNA, and polymer-DNA binding were governed by the nitrogen/phosphate (N/P) ratio. The DNA binding strength and colloidal stability of the PVAm-b-PALysOH/DNA polyplexes could be tuned by introducing an appropriate amount of zwitterionic PALysOH functionality, while maintaining the polyplex size, surface charge, and chiroptical property, regardless of the N/P ratio. The mixed polyplex micelles showed temperature-induced stability originating from the hydrophobic (dehydrated) PNIPAM chains upon heating, and remarkable stability under salty conditions owing to the presence of the zwitterionic PALysOH chain on the polyplex surface.

A zwitterionic serine modified chitosan derivative for improving protein stability and activity

A zwitterionic phosphoryldiserine (PDS)- chitosan conjugate was synthesized via Atherton-Todd reaction, and its degree of substitution of PDS and structure were characterized by ¹H and ³¹P NMR spectra, ICP, FTIR and XRD. Thermal analysis confirmed that there existed the freezing bound water surrounding PDS-chitosan due to the introduction of zwitterionic PDS groups onto chitosan backbone. In vitro cytotoxicity and hemolysis assay demonstrated that PDS-chitosan had excellent cell compatibility. UV adsorption and fluorescence spectra revealed that the model protein, bovine serum albumin (BSA) tended to keep its native conformation and showed better thermal stability in aqueous media in the presence of PDS-chitosan. We also found that the esterase-like activity of BSA could be enhanced by low concentration of PDS-chitosan (C_BSA = 0.33 mg/mL, C_PDS-chitosan = 0.0625 and 0.125 mg/mL, pH = 7.4, T = 25 °C). The results indicated that zwitterionic PDS-chitosan showed great potential for maintaining protein function in biomedical applications.

A zwitterionic polymer containing a hydrophobic group: enhanced rheological properties

A zwitterionic polymer containing a hydrophobic long chain, named MANPS, was independently developed by free radical solution polymerization.

Biomimetic strategies to produce catalytically reactive CuS nanodisks

Copper sulfide materials have diverse applications from cancer therapy to environmental remediation due to their narrow bandgap and easily tuned plasmon. The synthesis of these materials often involves toxic reagents and harsh conditions where biomimetic methods may provide opportunities to produce these structures under sustainable conditions. To explore this capability, simple amino acids were exploited as biological ligands for the ambient synthesis of CuS materials. Using an aqueous-based approach, CuS nanodisks were prepared using acid-containing amino acid molecules that stabilize the materials against bulk aggregation. These structures were fully characterized by UV-vis analysis, transmission electron microscopy, dynamic light scattering, atomic force microscopy, selected area electron diffraction, and X-ray diffraction, which confirmed the formation of CuS. The materials possessed a vibrant plasmon band in the near IR region and demonstrated enhanced photocatalytic reactivity for the advanced oxidation of organic dyes in water. These results demonstrate a room temperature synthetic route to optically important materials, which could have important application in catalysis, optics, nanomedicine, etc.

Synthesis, Assembled Structures, and DNA Complexation of Thermoresponsive Lysine-Based Zwitterionic and Cationic Block Copolymers

A series of anionic, zwitterionic, and cationic lysine-based block copolymers with a thermoresponsive segment were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of N-acryloyl- N-carbobenzoxy-l-lysine [A-Lys(Cbz)-OH], which contains a carboxylic acid and a protected amine-functionality in the monomer unit. Carboxylic acid-containing homopolymers, poly(A-Lys(Cbz)-OH), with predetermined molecular weights with relatively low polydispersities were initially synthesized by RAFT polymerization of A-Lys(Cbz)-OH. The chain extension of the dithiocarbamate-terminated poly(A-Lys(Cbz)-OH) to N-isopropylacrylamide (NIPAM) via the RAFT process and subsequent deprotection afforded the zwitterionic block copolymer composed of thermoresponsive poly(NIPAM) and poly(A-Lys-OH), which exhibited switchability among the zwitterionic, anionic, and cationic states by pH change. The assembled structures and thermoresponsive and chiroptical properties of these block copolymers were evaluated by dynamic light scattering, circular dichroism, and turbidity measurements. Finally, the cationic block copolymer, poly(A-Lys-OMe)- b-poly(NIPAM), was obtained by the methylation of the carboxylic acid group in the zwitterionic poly(A-Lys-OH) segment. Selective interactions of DNA with the cationic poly(A-Lys-OMe) segment in the lysine-based block copolymer were further evaluated by agarose gel electrophoresis and atomic force microscopy measurements, which revealed characteristic assembled structures and temperature-responsive properties of the polyplexes.

Amino acid-derived alternating polyampholyte luminogens

A unique polyampholyte luminogen comprised of alternatively placed oppositely charged moieties onto the poly(styrene-alt-maleimide) skeleton was synthesized, and used for the specific detection of carbon disulfide (CS₂) in both solution and vapor phases.

A stimuli-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding antifouling polymer with tunable thermosensitivity

This report describes a dual pH- and thermo-responsive methionine-based zwitterionic methacryloyl sulfonium sulfonate monomer and the corresponding zwitterionic antifouling polymer with ion-induced tunable thermosensitivity.

Amino Acid Functional Polymers: Biomimetic Polymer Design Enabling Catalysis, Chiral Materials, and Drug Delivery

Amino acids are the natural building blocks for the world around us. Highly functional, these small molecules have unique catalytic properties, chirality, and biocompatibility. Imparting these properties to surfaces and other macromolecules is highly sought after and represents a fast-growing field. Polymers functionalized with amino acids in the side chains have tunable optical properties, pH responsiveness, biocompatibility, structure and self-assembly properties. Herein, we review the synthesis of amino acid functional polymers, discuss manipulation of available strategies to achieve the desired responsive materials, and summarize some exciting applications in catalysis, chiral particles, and drug delivery.

Thermoplasmonic effect of silver nanoparticles modulates peptide amphiphile fiber into nanowreath-like assembly

This study demonstrates the beneficial role of di-tryptophan containing short peptide amphiphiles (sPA), for the synthesis and stabilization of AgNPs in the presence of sunlight followed by garlanding of AgNPs along the fibrous network of sPA. Such hybrid structures were precisely and selectively moulded into a nanowreath-type morphology due to the thermoplasmonic effect of AgNPs, and can be used for several bio-nanotechnological applications.

Highly compact co-poly(amide-imide)s from polycondensation of an imide-modified derivative of l-aspartic acid

The direct polycondensation of a monomer derived from l-aspartic acid together with adipic acid as a modifier co-monomer with aromatic diamines was studied to synthesize co-poly(amide-imide)s (CPAIs). The relative reactivity of the co-monomers and the manner of their insertion into polymer chains were evaluated using a model reaction and 1H NMR spectroscopy, respectively. The synthesized polymers depicted optical rotations similar to those of the monomer precursor and inherent viscosities in the range of 0.13–0.95 dl/g. Thermal stability and behavior as well as the weight-loss pattern of the CPAIs were studied by thermo-analytical techniques (thermogravimetric analysis-differential thermal analysis, dynamic mechanical thermal analysis and differential scanning calorimetry). Onset decomposition temperatures >300°C and carbonization residues of more than 50% at 600°C were detected for the treated polymers. Almost all of the copolyamides were noncrystalline solids, as illustrated in the X-ray diffraction patterns, and had good levels of solubility in a variety of polar organic solvents. These polymers could afford transparent and flexible to brittle films in solution casting on glass plates. Scanning electron microscopy on the polymer films showed a uniform and continuous morphology, indicating good film forming ability.