Anna Zheng

Damage of Escherichia coli membrane by bactericidal agent polyhexamethylene guanidine hydrochloride: micrographic evidences

Aims:  The purpose of this study was to provide micrographic evidences for the damaged membrane structure and intracellular structure change of Escherichia coli strain 8099, induced by polyhexamethylene guanidine hydrochloride (PHMG).

Morphology and mechanical properties of poly(butylene adipate-co-terephthalate)/potato starch blends in the presence of synthesized reactive compatibilizer or modified poly(butylene adipate-co-terephthalate)

The biodegradable poly(butylene adipate-co-terephthalate)(PBAT)/thermoplastic starch (TPS) composite has received considerable attention because of the environmental concerns raised by solid waste disposal. However, the application of PBAT/TPS blends was limited due to the poor mechanical properties originating from the incompatibility between PBAT and TPS. In this work, two approaches were developed to improve the mechanical properties of PBAT/TPS blends. One approach is to use compatibilizers, including the synthesized reactive compatibilizer - a styrene-maleic anhydride-glycidyl methacrylate (SMG) terpolymer, and the commercial compatibilizer (Joncryl-ADR-4368). The chemical structures of SMG were analyzed with (1)H NMR and FT-IR. The other approach is to use the modified PBAT (M-PBAT) to replace part of PBAT in the PBAT/TPS blends. M-PBATs with higher molecular weight were obtained via reactive extrusion of PBAT in the presence of a chain extender. The better dispersion of TPS in PBAT was observed in SEM images when using M-PBAT, leading to the higher tensile strength and elongation at break of PBAT/TPS blends. However, the elongation at break decreased in the presence of compatibilizer (SMG or 4368), though the tensile strength remained in a similar level or slightly higher. Overall, the tensile strength and the elongation at break of the resulting biodegradable PBAT/M-PBAT/TPS blends (TPS=40wt%) were above 27.0MPa and 500%, respectively, which is promising for various applications, including packaging and agricultural mulching films.

Investigation of extensional rheological behaviors of polypropylene for foaming

This study investigated the relationship between the extensional rheological behaviors and the foamability of polypropylenes (PPs). Both the shear and extensional rheological properties of four types of PPs with different molecular structures (linear PP, linear PP with high-molecular component, long-chain-branched PP, and cross-linked PP) were tested by rheometers and the PPs were foamed by batch process with supercritical carbon dioxide as foam agent. It was found that when the PP showed strain-hardening behavior at certain strain rates (on the order of 1 s−1), the obtained foams had high expansion ratio and fine cell structures. Otherwise, the strain-hardening behavior of PP had limited effects on the foamability. In addition, a theoretical analysis suggested that the strain-hardening behavior provided higher melt strength and simultaneously changed the rupture behavior of the melt, thus the gas bubble could be stable during expansion step and the cellular structure was generated. The foamability of PPs can be predicted from the extensional properties without considering their molecular structures.

Amphoteric calix[8]arene-based complex for pH-triggered drug delivery

Amphoteric calix[8]arene with negatively charged upper rim and positively charged lower rim was synthesized based on water-soluble p-sulfonato-calix[8]arene. The pH-sensitive amphoteric calix[8]arenes exhibit not only a good hydrophobic drug loading capacity but also a pH-triggered drug releasing behavior. The in vitro release studies demonstrated that release of ciprofloxacin from amphoteric calix[8]arene complexes was highly pH-sensitive. More efficient drug release was observed at mildly acidic pH 5.0 and basic pH 8.5 compared to physiological pH. The amphoteric calix[8]arene complexes hold out great promise of being pH-sensitive drug carrier.

Synthesis and Characterization of Ciprofloxacin Pendant Antibacterial Cationic Polymers.

A methacrylate monomer containing ciprofloxacin (CPF) was synthesized, followed by the free-radical co-polymerization of the methacrylate monomer, acrylamide and diallyl dimethyl ammonium chloride (DADMAC). The resulting antimicrobial cationic tripolymers were characterized by 1H-NMR, gel-permeation chromatography, thermogravimetric analysis and differential scanning calorimetry. The in vitro antibacterial activity of the monomer, as well as of the polymers, was investigated against E. coli. The CPF pendant tripolymer exhibited excellent antibacterial activities, thus permitting the cationic tripolymers to be used as antibacterial intensifier, retention or filtration aid for various hygiene products, including those based on cellulose fibres.

Interactions of biocidal guanidine hydrochloride polymer analogs with model membranes: a comparative biophysical study.

Four synthesized biocidal guanidine hydrochloride polymers with different alkyl chain length, including polyhexamethylene guanidine hydrochloride and its three new analogs, were used to investigate their interactions with phospholipids vesicles mimicking bacterial membrane. Characterization was conducted by using fluorescence dye leakage, isothermal titration calorimetry, and differential scanning calorimetry. The results showed that the gradually lengthened alkyl chain of the polymer increased the biocidal activity, accompanied with the increased dye leakage rate and the increased binding constant and energy change value of polymer-membrane interaction. The polymer-membrane interaction induced the change of pretransition and main phase transition (decreased temperature and increased width) of phospholipids vesicles, suggesting the conformational change in the phospholipids headgroups and disordering in the hydrophobic regions of lipid membranes. The above information revealed that the membrane disruption actions of guanidine hydrochloride polymers are the results of the polymers strong binding to the phospholipids membrane and the subsequent perturbations of the polar headgroups and hydrophobic core region of the phospholipids membrane. The alkyl chain structure significantly affects the binding constant and energy change value of the polymer-membrane interactions and the perturbation extent of the phospholipids membrane, which lead to the different biocidal activity of the polymer analogs. This work provides important information about the membrane disruption action mechanism of biocidal guanidine hydrochloride polymers.

Synthesis and Characterization of Antimicrobial Polyvinyl Pyrrolidone Hydrogel as Wound Dressing

Novel antimicrobial PVP-GP hydrogels were prepared by polycondensation of hexamethylenediamine and guanidine hydrochloride, followed by cross-linking reaction using N-vinyl pyrrolidone (NVP) and N,N’-methylene bisacrylamide (MBAm). The products were characterized by 1H NMR, FTIR, SEM, and their performances for wound dressing applications were also evaluated. Swelling study showed that the water absorptivity of the hydrogels decreased as the cross-linking density increased either in water or in physiological saline solution. Both PVP and PVP-GP hydrogels possessed excellent mechanical strength which could address the requirements for wound dressing. The water vapor transmission rates (WVTR) of PVP and PVP-GP hydrogels were in the range of 1727–2320 g/m2/day, indicating that the prepared hydrogels were suitable for wound dressings without dehydrating the wound surface or accumulating exudates. Kirby-Bauer inhibition zone test and microbe penetration assay proved that the PVP-GP hydrogels had high antimicrobial activity.

Synthesis and characterization of a novel water-soluble cationic diblock copolymer with star conformation by ATRP

A water-soluble cationic diblock copolymer, CD-PAM-b-PMeDMA, was synthesized through atom transfer radical polymerization (ATRP) from a β-cyclodextrin (CD) macroinitiator with 10-active sites (10Br-β-CD). In order to reduce the cytotoxicity of the CD-PAM-b-PMeDMA, biocompatible polyacrylamide (PAM) was first introduced onto the surface of β-CD as a scaffold structure by ATRP using the 10Br-β-CD as a macroinitiator. The reaction conditions of AM were explored and optimized. The ATRP of [2-(methacryloyloxy)ethyl] trimethyl ammonium chloride (MeDMA) was also performed to synthesize the second cationic block using the resulting CD-PAM as a macroinitiator. The resulting diblock copolymer shows an increased hydrodynamic radius in aqueous solution with a pretty low concentration compared with β-CD. In addition, it appears a near-uniform coniform after being deposited on mica ascribed to the presence of an asymmetric 10-arm structure.

Condensation between guanidine hydrochloride and diamine/multi-amine and its influence on the structures and antibacterial activity of oligoguanidines

Abstract The polycondensation of guanidine hydrochloride and diamine leads to various types of oligoguanidines, including linear and branched/cyclic types, which constitutes the mixture of oligoguanidines exhibiting efficient biocidal activities. In the present work, a series of polyhexamethylene guanidine hydrochloride (PHMG) were prepared by varying the mole ratio of hexamethylenediamine to guanidine hydrochloride and the reaction conditions, and their antibacterial activities were investigated. The contents of linear and branched/cyclic types in the mixture varied with different reaction conditions, and more branched/cyclic types led to more efficient antibacterial activity. Other oligoguanidines PDMG and PMXMG were synthesized using guanidine hydrochloride and decamethylenediamine and 1,3- benzenedimethanamine, respectively. Their chemical structures were similar to PHMG’s while the antibacterial activities were slightly different from PHMG’s. Further when the polycondensation were conducted between guanidine hydrochloride and multi-amine, such as diethylenetriamine or trithylenetetramine, the chemical structures of products were completely different from the above oligoguanidines. A new five-membered ring structure was observed, and the fivemembered ring structure further decreased the antibacterial activities.

Permanent antimicrobial cotton fabrics obtained by surface treatment with modified guanidine

Antimicrobial cotton fabrics received much attention for the demand of health and hygiene fields. In this work, an antimicrobial copolymer was prepared via a reaction between polyhexamethylene guanidine hydrochloride and polypropylene glycol diglycidyl ether. The copolymer has amphiphilic characteristic and excellent antimicrobial properties. When the copolymer was adhered onto cotton fabrics through physical adsorption and chemical bonding using dipping-drying method, the resultant cotton fabrics had excellent and durable antimicrobial properties. The antimicrobial rates against Escherichia coli and Staphylococcus aureus were higher than 99.99% when the adsorption amount of the copolymer was above 35.5mg/g. The antimicrobial cotton fabrics remained the excellent antimicrobial properties even after laundered with detergent solution.