Huining Xiao

Antimicrobial Polymeric Materials with Quaternary Ammonium and Phosphonium Salts

Polymeric materials containing quaternary ammonium and/or phosphonium salts have been extensively studied and applied to a variety of antimicrobial-relevant areas. With various architectures, polymeric quaternary ammonium/phosphonium salts were prepared using different approaches, exhibiting different antimicrobial activities and potential applications. This review focuses on the state of the art of antimicrobial polymers with quaternary ammonium/phosphonium salts. In particular, it discusses the structure and synthesis method, mechanisms of antimicrobial action, and the comparison of antimicrobial performance between these two kinds of polymers.

Synthesis and characterization of cationically modified nanocrystalline cellulose

In this study, nanocrystalline cellulose (NCC) resulting from sulfuric acid hydrolysis of wood cellulose fiber, was rendered cationic by grafting with glycidyltrimethylammonium chloride (GTMAC). An optimization of the reaction parameters, such as water content, reactant mole ratio, and reaction media was performed. The presence of cationic GTMAC on the surface of NCC was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). The cationically modified NCC was characterized by surface charge density, degree of substitution, ζ potential, and particle size. It was found that the cationic surface charge density of NCC can be increased by controlling the water content of the reaction system. Surface cationization of NCC led to an increase in the surface charge density over the un-modified NCC. The cationically modified NCC was well dispersed and stable in aqueous media due to enhanced cationic surface charge density. Transmission electron microscopy (TEM) images showed the improvement in state of dispersion of cationically modified NCC over the un-modified NCC. The optimum water content was found to be 36 wt% for aqueous based media and 0.5 water to DMSO volume ratio for aqueous-organic solvent reaction media. The increased surface charge density of NCC also delayed the onset of gelation in aqueous system.

Quaternary Ammonium β-Cyclodextrin Nanoparticles for Enhancing Doxorubicin Permeability across the In Vitro Blood−Brain Barrier

This study describes novel quaternary ammonium beta-cyclodextrin (QAbetaCD) nanoparticles as drug delivery carriers for doxorubicin (DOX), a hydrophobic anticancer drug, across the blood-brain barrier (BBB). QAbetaCD nanoparticles show 65-88 nm hydrodynamic radii with controllable cationic properties by adjusting the incorporated amount of quaternary ammonium group in their structure. ATR-FTIR studies confirm the complexation between the QAbetaCD nanoparticles and DOX. QAbetaCD nanoparticles are not toxic to bovine brain microvessel endothelial cells (BBMVECs) at concentrations up to 500 microg x mL(-1). They also do not change the integrity of BBMVEC monolayers, an in vitro BBB model, including transendothelial electrical resistance value, Lucifer yellow permeability, tight junction protein occludin and ZO-1 expression and morphology, cholesterol extraction, and P-glycoprotein (P-gp) expression and efflux activity, at a concentration of 100 microg x mL(-1). Some QAbetaCD nanoparticles not only are twice as permeable as dextran (M(w) = 4000 g x mol(-1)) control, but also enhance DOX permeability across BBMVEC monolayers by 2.2 times. Confocal microscopy and flow cytometry measurements imply that the permeability of QAbetaCD nanoparticles across the in vitro BBB is probably due to endocytosis. DOX/QAbetaCD complexes kill U87 cells as effectively as DOX alone. However, QAbetaCD nanoparticles completely protect BBMVECs from cytotoxicity of DOX at 5 and 10 microM after 4 h incubation. The developed QAbetaCD nanoparticles have great potential in safely and effectively delivering DOX and other therapeutic agents across the BBB.

A combined acidification/PEO flocculation process to improve the lignin removal from the pre-hydrolysis liquor of kraft-based dissolving pulp production process

The presence of lignin impairs the utilization of the hemicelluloses dissolved in the pre-hydrolysis liquor (PHL) of the kraft-based dissolving pulp production process. In this paper, a novel process was developed by combining the acidification and poly ethylene oxide (PEO) flocculation concepts to improve the lignin removal. The results showed that the lignin removal was improved by the addition of PEO to the acidified PHL, particularly at a low pH of 1.5. The main mechanisms involved are the lignin/PEO complex formation and the bridging of the formed complexes. This hypothesis was supported by the turbidity, FTIR and particle size measurements. Interestingly, the hemicelluloses removal from the acidification/PEO flocculation was marginal, which would be beneficial for the down-stream ethanol production from the PHL. Additionally, a process flow diagram was proposed that incorporates this new concept into the existing configuration of kraft-based dissolving pulp production process.

Hydrophobic-modified nano-cellulose fiber/PLA biodegradable composites for lowering water vapor transmission rate (WVTR) of paper.

New biodegradable nanocomposites have been successfully prepared by incorporating modified nano-cellulose fibers (NCF) in a biodegradable polylactic acid (PLA) matrix in this work. The hydrophobic-modified NCF was obtained by grafting hydrophobic monomers on NCF to improve the compatibility between NCF and PLA during blending. The resulting NCF/PLA composites were then applied on paper surface via a cast-coating process in an attempt to reduce the water vapor transmission rate (WVTR) of paper. The WVTR tests, conducted under various testing conditions and with different coating weights, demonstrated that the modified NCF/PLA composites coating played a critical role in lowering WVTR of paper. The lowest WVTR value was 34 g/m(2)/d, which was obtained with an addition of 1% of modified NCF to PLA and the composites coating weight at 40 g/m(2) and substantially lower than the control value at 1315 g/m(2)/d. The paper coated with the modified biodegradable composite is promising as green-based packaging materials.

Synthesis of modified guanidine-based polymers and their antimicrobial activities revealed by AFM and CLSM.

Modified guanidine-based polymers with chain extension were synthesized by condensation and cross-linking polymerizations in an attempt to increase molecular weight and charge density of the antimicrobial polymers. The antimicrobial activity and the corresponding mechanisms were investigated by several approaches. The results indicated that the antimicrobial activities of the modified guanidine-based polymer, based on the minimum inhibition concentration (MIC) against E.coli, varied with alkyl monomer ratios. UV absorption at 260 nm further quantified the amount of intracellular components leaked into bacteria suspension. The UV absorption measurements were also used to monitor inhibition processes dynamically. It was found that the modified guanidine-based polymer inhibited the growth of bacteria by causing membrane compromised and intracellular leaked. Dual fluorescent dyes were used to stain all bacteria including the dead ones, which enabled us to utilize CLSM to visualize the viability of bacteria in the presence of various modified guanidine-based polymers without causing any damage. The morphologies of bacteria untreated and treated with modified guanidine-based polymer were observed using an atomic force microscope (AFM), which further demonstrated the damage of E.coli membrane and the leakage of intracellular component induced by the modified guanidine-based polymers.

Synergistic effects of chitosan-guanidine complexes on enhancing antimicrobial activity and wet-strength of paper.

Chitosan-guanidine complexes were prepared by reacting chitosan and polyhexamethylene guanidine hydrochloride or crosslinked polyhexamethylene guanidine hydrochloride in the presence of sodium tripolyphosphate as a crosslinking agent. The complexes, used as functional additives for paper, synergistically improved wet-strength and antimicrobial activities. In comparison with the control sample, the wet/dry strength ratio of hand-sheets treated with the complexes was increased from 2.65% up to 23.3%. The MIC values of the chitosan-PHGH and chitosan-PHGHE complexes against Escherichia coli were 15.6 and 31.2 microg mL(-1), respectively, thus demonstrating excellent antimicrobial activity. Hand-sheets treated with the complexes exhibited antibacterial activity against E. coli and Staphylococcus aureus. The release of the guanidine polymers included in the complexes was dynamically monitored using UV and the results showed the amount released exceeded 80%. Atomic force microscopy images indicated that the antimicrobial mechanism of the complexes was likely due to membrane damage.

Single and binary adsorption of heavy metal ions from aqueous solutions using sugarcane cellulose-based adsorbent

A high efficient and eco-friendly sugarcane cellulose-based adsorbent was prepared in an attempt to remove Pb2+, Cu2+ and Zn2+ from aqueous solutions. The effects of initial concentration of heavy metal ions and temperature on the adsorption capacity of the bioadsorbent were investigated. The adsorption isotherms showed that the adsorption of Pb2+, Cu2+ and Zn2+ followed the Langmuir model and the maximum adsorptions were as high as 558.9, 446.2 and 363.3mg·g-1, respectively, in single component system. The binary component system was better described with the competitive Langmuir isotherm model. The three dimensional sorption surface of binary component system demonstrated that the presence of Pb2+ decreased the sorption of Cu2+, but the adsorption amount of other metal ions was not affected. The result from SEM-EDAX revealed that the adsorption of metal ions on bioadsorbent was mainly driven by coordination, ion exchange and electrostatic association.

Enhanced water vapour barrier and grease resistance of paper bilayer-coated with chitosan and beeswax.

In order to overcome the deficiencies of single layer coating, bilayer coated papers were prepared by two separate coating procedures using various combinations of proteins or polysaccharides with beeswax. Among those combinations, chitosan-beeswax bilayer coated paper showed the best water vapour barrier property. It was observed that as the concentration of chitosan solution increased from 1.0 to 3.0 wt%, its water vapour transport rate (WVTR) decreased from 171.6 to 52.8 g/m(2)/d but using reduced beeswax coating weight (from 10.1 to 4.9 g/m(2)). It also displayed an enhanced performance of grease resistance. Scanning electron microscopy (SEM) showed that beeswax layer was fitted to chitosan layer so closely that these two layers are indistinguishable. Confocal laser scanning microscope (CLSM) further confirmed the existence of an integrated chitosan film between beeswax layer and paper base and a thin composite layer consisting of chitosan and beeswax.

Organo-modified cationic silica nanoparticles/anionic polymer as flocculants.

The synthesis of quaternized silica nanoparticles and its application to fine clay flocculation were investigated. N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride was used as a cationic reagent to introduce quaternary amine groups onto the surfaces of silica nanoparticles via the formation of covalent bonds between the methoxy groups of the cationic reagents and the silanol groups in the silica surface. The zeta potential, zeta, and charge density of the silica particles modified under various reaction conditions were determined. Dynamic clay flocculation experiments using a photometric dispersion analyzer (PDA) showed that the cationic silica alone contributed little to the flocculation. However, the cationic silica, in conjunction with an anionic polymer of high M(w) and low charge density, led to a significant improvement in the flocculation of fine clay particles. The mechanism of flocculation was explored by a systematic investigation of interaction between cationic silica and anionic polymers as well as of their adsorption behavior on clay surfaces. The influence of factors such as pH and electrolyte concentration on clay flocculation was also investigated.