Effect of Amino Acid Types on the Mechanical and Antimicrobial Properties of Amino Acid-Based Polyionic Liquid Hydrogels

Polyionic liquid hydrogels attract increasing attention due to their unique properties and potential applications. However, research on amino acid-based polyionic liquid hydrogels is still in its infancy stage. Moreover, the effect of amino acid types on the properties of hydrogels is rarely studied to date. In this work, amino acid-based polyionic liquid hydrogels (D/L-PCAA hydrogels) are synthesized by copolymerizing vinyl choline–amino acid ionic liquids and acrylic acids using Al³⁺ as a crosslinking agent and bacterial cellulose (BC) as a reinforcing agent. The effects of amino acid types on mechanical and antimicrobial properties are systematically investigated. D-arginine-based hydrogel (D-PCArg) shows the highest tensile strength (220.7 KPa), D-phenylalanine-based hydrogel (D-PCPhe) exhibits the highest elongation at break (1346%), and L-aspartic acid-based hydrogel (L-PCAsp) has the highest elastic modulus (206.9 KPa) and toughness (1.74 MJ m⁻³). D/L-PCAsp hydrogels demonstrate stronger antibacterial capacity against Escherichia coli and Staphylococcus aureus, and D/L-PCPhe hydrogels possess higher antifungal activity against Cryptococcus neoformans. Moreover, the resultant hydrogels exhibit prominent hemocompatibility and low toxicity, as well as excellent self-healing capabilities (86%) and conductivity (2.8 S m⁻¹). These results indicate that D/L-PCAA hydrogel provides a promise for applications in wound dressings.     

Copper and Nickel Removal from Aqueous Solutions Using New Chelating Poly[Acrylamide/N‐vinyl pyrrolidone/3‐(2‐hydroxyethyl carbamoyl)acrylic acid] Hydrogels

New poly[Acrylamide/N‐vinyl pyrrolidone/3‐(2‐hydroxyethyl carbamoyl)acrylic acid], poly [AAm/NVP/HECA], chelating hydrogels with different composition of HECA monomer have been prepared via free radical solution polymerization using N,N‐methylene bisacrylamide as a crosslinker. The hydrogels obtained were loaded with metal ions and characterized by FT‐IR spectroscopy, Scanning Electron Microscope (SEM) and Thermogravimatric analysis (TGA). The removal of Cu²⁺ and Ni²⁺ from aqueous solutions by the hydrogel was examined by a batch equilibrium method. The influence of treatment time, pH, initial concentration of the metal ions and HECA content in the feed compositions on the amount of adsorbed metal ions was studied. Swelling of the hydrogel was also carried out in distilled water and metal ion solutions. The removal of the metal ions followed the following order: Ni²⁺>Cu²⁺. The amount of metal ions removed increased with increasing HECA content in the feed composition, treatment time, pH of the medium and initial concentration of metal ions. The desorption of metal ions were carried out using 1 N HCl and 0.5 N H₂SO₄. The poly[AAm/NVP/HECA] hydrogels could be used many times without significantly decreasing their adsorption capacity.     

一步法制备PNIPAAm-g-PAN/PSt载银复合微球及其抗菌性能研究

以AgNO3为金属源,通过乙醇将与聚N-异丙基丙烯酰胺接枝聚丙烯腈/聚苯乙烯（PNIPAAm-g-PAN/PSt）聚合物微球表面酰胺基团配位的银离子（Ag+）还原,一步法制备了PNIPAAm-g-PAN/PSt载银复合微球。通过傅立叶变换红外（FTIR）和紫外-可见光光谱表征发现,由Ag+还原所得的Ag纳米颗粒被成功地固载在PNIPAAm-g-PAN/PSt 微球上;用透射电子显微镜（TEM）对载银微球的大小和形态进行了表征;热重分析（TGA）结果表明,固载在微球表面的银纳米颗粒的含量（质量分数）为12%;抗菌实验结果表明,所制备的载银微球具有抗革兰氏阴性菌的活性。     

Preparation and properties of antibacterial ABS plastics based on polymeric quaternary phosphonium salts antibacterial agents

Antibacterial acrylonitrile‐butadiene‐styrene (ABS) plastics were prepared by adding polymeric quaternary phosphonium salts as antibacterial agents through a double screw extruder. The novel polymeric quaternary phosphonium salts (PBrMAP‐n) with alkyl chain length ranging from 3 to 11 were synthesized, and their chemical structures were confirmed by Nuclear magnetic resonance hydrogen spectroscopy (¹H‐NMR) and Fourier transform infrared spectroscopy (FT‐IR) spectra. The thermogravimetric analysis (TGA) results showed that all of the antibacterial agents had good thermal stability. The influence of addition amount as well as the alkyl chain length on mechanical properties and antibacterial properties was investigated. Compared with the pure ABS, all of PBrMAP‐n containing specimens had comparable tensile strength and flexural properties but reduced impact strength. Only samples with 10 wt% of PBrMAP‐11 exhibited more than 90% antibacterial efficiency against Escherichia coli and Staphylococcus aureus.     

Purification assay to prepared ultrapure carboxymethyl-chitosan

Carboxymethyl Chitosan (CMCh) is a semi-synthetic derivative of chitosan (a natural biopolymer) with increasing biomedical applications as a matrix or scaffold material for tissue engineering applications. Since, the presence of impurities can cause immunological reactions in vivo where ultimately pure materials are needed. To this end, purity of commercial-grade CMCh samples was investigated here along with their purification by a solvent/nonsolvent technique. The resulting polymer was characterized by differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR) and energy dispersive X-ray spectroscopy (EDX) to confirm the validity of the purification process.     

Preparation and Characterization of the Antibacterial Zn2+ or/and Ce3+ Loaded Montmorillonites

A series of modified montmorillonites including Zn²⁺ loaded montmorillonite (Zn/MMT), Ce³⁺ loaded montmorillonite (Ce/MMT) and Zn²⁺‐Ce³⁺ loaded montmorillonites (Zn‐Ce/MMT) were prepared by an ion‐exchange reaction, and characterized using X‐ray photoelectron spectroscopy (XPS), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The specific surface areas, zeta potentials and antibacterial activity of the modified montmorillonites were also investigated. Zinc and cerium were proved to be present as bivalent zinc state and trivalent cerium state in the modified montmorillonites. For the modified montmorillonites, the d₀₀₁ basal spacings increased and the particles were formed of irregular shapes. The antibacterial activity of the modified montmorillonites was enhanced with the increase of specific surface areas and zeta potentials, and Zn²⁺‐Ce³⁺ loaded montmorillonites displayed obvious synergistic antibacterial effect. When Zn/Ce atomic ratio was 1.24, the Zn‐Ce/MMT showed high antibacterial efficiency and broad‐spectrum antibacterial activity, possessing the MIC against Escherichia coli, Staphylococcus aureus, Candida albicans and Mucor of 1500, 1000, 2000 and 3000 mg·L^?1, respectively.     

Tensile,thermal, and antibacterial characterization of composites of cellulose/modified Pennisetum purpureum natural fibers with in situ generated copper nanoparticles

Eco-friendly all cellulose composites were developed using cellulose as matrix and nanocomposite (in situ generated copper nanoparticles modified Napier Grass Fibers (NGFs)) as fillers for the antibacterial applications. The content of the nanocomposite filler was increased from 1?wt.% to 5?wt.% in the cellulose matrix. All these composites were characterized by Scanning Electron Microscopy (SEM), Tensile, Thermo Gravimetric Analysis (TGA), and antibacterial tests. SEM-EDX analysis revealed the in situ generation of copper nanoparticles on the surface of the films. Further, all cellulose composites showed good thermal stability. A minimum of 30% increase in char residue was observed in all cellulose nanocomposites compared to matrix. Antibacterial analysis indicated an excellent clear zone formation against both Gram Negative (Escherichia coli) and Gram Positive (Staphylococcus) bacteria. Hence, all these cellulose nanocomposite films can be considered as antibacterial packaging and dressing materials in medical field.     

Radiation synthesis and characterization of nanosilver/gelatin/carboxymethyl chitosan hydrogel

A series of antibacterial hydrogels were fabricated from an aqueous solution of AgNO₃, gelatin and carboxymethyl chitosan (CM-chitosan) by radiation-induced reduction and crosslinking at ambient temperature. The nanosilver particles were in situ synthesized accompanying with the formation of gelatin/CM-chitosan hydrogel. Transmission Electron Microscope and UV–vis analysis have verified the formation and homogeneous distribution of nanosilver particles in the hydrogel matrix. The nanosilver/gelatin/CM-chitosan hydrogels possessed interconnected porous structure, had a compressive modulus of 44 to 56 kPa, and could absorb 62 to 108 times of deionized water to its dry weight. Furthermore, the hydrogels were found to have sound antibacterial effect on Escherichia coli (E. coli), and their antibacterial ability could be significantly enhanced by the increasing of AgNO₃ content. The comprehensive results of this study suggest that nanosilver/gelatin/CM-chitosan hydrogels have potential as an antibacterial wound dressing.     

An efficient one pot I2/DMSO mediated synthesis and molecular modeling of novel fused pyrimidine-chromone hybrids bearing potential antibacterial and antifungal pharmacophores sites

A series of novel ethyl-l, 1, 2, 3, 6-tetrahydro-4-methyl-1-(6-methyl-4-oxo-4H-chromene-2-yl)-2-oxo/thioxo-6-phenyl pyrimidine-5-carboxylate compounds ( 2a–2k ) were synthesized using I₂/DMSO as a competent and cost-effective catalyst in one pot green solvent system from corresponding chalcones ( 1a–1k ) in better yields. IR, ¹H-NMR, ¹³C-NMR, Mass, and X-ray diffraction spectroscopic techniques were used for the characterization of newly synthesized compounds. All the compounds were tested for in-vitro antibacterial activities against gram-positive and gram-negative bacteria like Staphylococcus aureus, Salmonella abony, Staphylococcus epidermidis, and Escherichia coli. Antifungal activities were also performed against Candida albicans and Aspergilus niger. It was found that the presence of electron withdrawing group on the aromatic ring attached to chromone ring increases the antibacterial activities ( 2g , 2h , and 2k ); while the presence of electron releasing groups decreases activities. The presence of electron donating groups (─OCH₃, ─Cl), on the phenyl ring attached to pyrimidine skeleton influenced negatively for the antibacterial activities.     

Synthesis,characterization and antimicrobial activity of a new macrocycle and its transition metal complexes

The semicarbazone (L¹) has been prepared by reaction of semicarbazide and glutaraldehyde (2 : 1) in distilled water and methanol (1 : 1). The reaction of semicarbazide, glutaraldehyde and diethyl oxalate in distilled water and methanol gave Schiff-base L², 1,2,4,7,9,10-hexaazacyclo-pentadeca-10,15-dien-3,5,6,8-tetraone. Complexes of first row transition metal ions Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) have also been synthesized. The ligand and its complexes were characterized by elemental analysis, molar conductance, magnetic moment measurements, IR, ¹H NMR, UV–Visible spectra and thermogravimetric analysis (TGA). Molar conductance values show that the complexes of Ni(II), Cu(II), Zn(II), Mn(II) and Co(II) are 1 : 2 electrolytes. On the basis of electronic spectral studies and molar conductance measurements an octahedral structure has been proposed for Mn(II) and Co(II) complexes, tetrahedral for Zn(II) complex and square planar for Ni(II) and Cu(II). The thermal behavior of the compounds, studied by TGA in a nitrogen atmosphere up to 800°C, reveal that the complexes have higher thermal stability than the macrocycle. All the synthesized compounds and standard drugs kanamycin (antibacterial) and miconazole (antifungal) have been screened against bacterial strains Staphylococcus areus, Escherichia coli and fungal strains Candida albicans, Aspergillus niger. The metal complexes inhibit growth of bacteria to a greater extent than the ligand.     

A novel method to prepare microporous and nanofibrous hydrogel scaffolds as neural tissue engineering

A new method to prepare poly (vinyl alcohol) hydrogels by nebulization method.is introduced. A blend of Poly (vinyl alcohol) (PVA), sodium gum malate (SGM) and cellulose nanofibers (CNFs) originated from Catha Edulis was prepared and tested as neural tissue substitutes. Glutaraldehyde (GLA) was used as a crosslinker. Presence of SGM and CNFs in the formulation improved the nebulization process of PVA solution as well as mechanical properties of the fabricated hydrogels. The tensile strength of neat PVA films attains 46.7 MPa, while the tensile strength was 94.23 MPa for crosslinked-PVA. The tensile strength was found to increase with the increase in the CNFs content in the PVA compared with PVA/SGM. These soft tissues were characterized by using FTIR, SEM, and DSC. Scanning electron microscopy (SEM) results showed that PVA/SGM/CNFs blends has a diameter about 50 ± 8µm. The hydrogels were tested also for antimicrobial activities against pathogenic bacteria like Candida albicans (fungus), Bacillus subtilis (G + Ve), Staphylococcus aureus (G + Ve), Proteus vulgaris (G ? Ve) and Erwinia carotovora (G ? Ve). Favorable mechanical, thermal properties and biodegradation nature of the hydrogels, as well as antimicrobial property indicate that prepared hydrogels are suitable for tissue engineering applications.     

Some features of hydrolysis of organic and inorganic substrates by Escherichia coli inorganic pyrophosphatase in the presence of various activator cations

The kinetics of hydrolysis of the inorganic (PP_i) and organic (ATP) substrates by Escherichia coli inorganic pyrophosphatase (PPase) and its mutant forms with Asp42 replaced by Ala, Asn, or Glu was studied. The Mn²⁺ or Zn²⁺ ions were used as activators of the enzymatic reaction. The kinetic parameters of hydrolysis were determined. The inhibitory effect of these cations on substrate hydrolysis was investigated. The dissociation constants were calculated for the Mn²⁺- and Zn²⁺-binding activator and inhibitor subsites of E. coli PPase. The observed hydrolysis rate of PP_i increases in the series Zn²⁺ < Mn²⁺ < Mg²⁺, whereas the potential efficiency of these cations decreases in this series. Hydrolysis of ATP by E. coli PPase occurs only in the presence of Mn²⁺. The reasons for the observed differences in the substrate specificity of the enzyme are discussed.     

Antibacterial Activities of Tellurium Nanomaterials

We prepared four differently shaped Te nanomaterials (NMs) as antibacterial reagents against Escherichia coli. By controlling the concentrations of hydrazine (N₂H₄) as reducing agent, NaCl, and temperature, we prepared Te nanowires, nanopencils, nanorices, and nanocubes. These four Te NMs resulted in a live/dead ratio of E. coli cells of less than 0.1, which is smaller than that of Ag nanoparticles. The order of antibacterial activity against E. coli is nanocubes ≈ nanorices > nanopencils ≈ nanowires. This is in good agreement with the concentration order of tellurite (TeO₃²⁻) ions released from Te NMs in E. coli cells, revealing that TeO₃²⁻ ions account for the antibacterial activity of the four Te NMs. We found that spherical Te nanoparticles (32 nm in diameter) with TeO₃²⁻ ions were formed in the E. coli cells. Compared to Ag nanoparticles that are commonly used as antibacterial reagents, Te NMs have higher antibacterial activity and lower toxicity. Thus, Te NMs hold great practical potential as a new and efficient antibacterial agent.     

Structure and swelling-release behaviour of poly(vinyl pyrrolidone) (PVP) and acrylic acid (AAc) copolymer hydrogels prepared by gamma irradiation

Copolymer network hydrogels were prepared by gamma irradiation of aqueous solutions of poly(vinyl pyrrolidone) (PVP) and acrylic acid monomer (AAc). The composition of the final hydrogels compared to the composition of the initial preparation solutions of hydrogels was determined. The chemical structure and nature of bonding was characterized by IR spectroscopy analysis, while the thermal durability of the prepared hydrogels was assessed by thermogravimetric analysis (TGA). The kinetic swelling in water and the pH-sensitivity of PVP/AAc copolymer hydrogels was studied. The drug release properties of PVP/AAc hydrogels taking methyl orange indicator as a drug model was investigated. The IR spectra indicate the formation of copolymer networks, whereas the TGA study showed that the PVP/AAc hydrogels possess higher thermal stability than pure PAAc and lower than PVP hydrogels. The kinetic swelling in water showed that all the hydrogels reached equilibrium after 24 h and that the degree of swelling increases with increasing the ratio of AAc in the initial feeding solutions. It was found that the degree of swelling of PVP/AAc hydrogels increases greatly within the pH range 4-7 depending on composition.     

A new nano‐sized mononuclear Cu (II) complex with N,N‐donor Schiff base ligands: sonochemical synthesis,characterization, molecular modeling and biological activity

A new, simple Cu²⁺ nano‐structure Schiff base complex in methanol medium has been synthesized by the ultrasonic method. Structure of the compound was confirmed by FT‐IR, GC‐Mass and other spectroscopic techniques. The copper oxide (CuO) was achieved from the copper nano‐structure Schiff base complex as the raw material after calcination for 3 hr at 600 °C. According to results Cu²⁺ gives a complex with mole ratio 1:2 of metal to ligand (ML₂) with Schiff base which a distorted square planer is the most probable geometry for it. The calculations results from XRD patterns propose the nano‐sized complexes. The SEM images show morphology of both the copper complex and the CuO powder were plate‐like. The metal chelates of Cu²⁺ in two states of bulk and nano have been screened for their in vitro antibacterial activity against four bacteria, gram‐positive (Staphylococcus aureus) and gram‐negative (Escherichia coli) and three strains of fungus (Aspergillus flavus). The nano metal chelates were shown to possess more antibacterial activity than the bulk chelate. Finally, the empirical parameters of Schiff base compounds showed a good agreement with theoretical ones.     

Durable antibacterial Ag/polyacrylonitrile (Ag/PAN) hybrid nanofibers prepared by atmospheric plasma treatment and electrospinning

Durable antibacterial Ag/polyacrylonitrile (Ag/PAN) hybrid nanofibers were prepared by atmospheric plasma treatment and electrospinning. Atmospheric helium plasma treatment was first used to reduce the AgNO₃ precursor in pre-electrospinning solutions into metallic silver nanoparticles, followed by electrospinning into continuous and smooth nanofibers with Ag nanoparticles embedded in the matrix. SEM, TEM, and EDX spectra were used to study the structure and surface elemental composition of the nanofibers. Silver nanoparticles, with diameters ranging between 3 and 6 nm, were found to be uniformly dispersed in the nanofiber matrix. The Ag/PAN nanofibers exhibited slow and long-lasting silver ion release, which provided robust antibacterial activity against both Gram-positive Bacillus cereus and Gram-negative Escherichia coli microorganisms.     

Characterization of Starch/Acrylic Acid Super‐Absorbent Hydrogels Prepared by Ionizing Radiation

Copolymerization of acrylic acid (AAc) and gelatinized maize starch in aqueous medium using γ‐irradiation, followed by neutralization with alkali solution was carried out. The preparation conditions, such as irradiation dose and starch/AAc compositions were investigated. The higher the irradiation dose, as well as the AAc content in the feed solution, the higher the gel content. The copolymers were characterized by FTIR spectroscopy, thermo‐gravimetric analysis (TGA) and scanning electron microscopy (SEM). SEM revealed that the higher the dose, the lower the copolymer pore size. Starch/AAc copolymers have thermal stability higher than that for starch and poly acrylic acid individually. The swelling of starch/AAc hydrogels reduced as the gel content increases. The maximum water absorption obtained for starch/AAc hydrogels in distilled water was 200 g/g, and for neutralized starch/AAc hydrogels was 350 g/g. The swelling ratio of starch/AAc hydrogels of different compositions in NaCl solution is lower than that obtained in distilled water. The results suggest that the neutralized starch/AAc hydrogels have a high swelling property, and can be used in a variety of commercial applications.     

Catalytic reduction of 4-nitrophenol by means of nanostructured polymeric Schiff base complexes

Polymeric Schiff base ligands were synthesized using 2-hydroxybenzaldehyde (L²), 4-hydroxy-3-methoxybenzaldehyde (L⁴), and 5-aminoisophthalic acid. The nanostructured complexes were then synthesized using Ni²⁺, Cu²⁺, and Mn³⁺. The ligands and complexes thus synthesized were characterized using Fourier-transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis (TGA), and field-emission scanning electron microscopy. The thermal stability of the complexes was confirmed using TGA. The synthesized complexes were used as catalysts in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol in an aqueous phase in the presence of sodium borohydride. In this work, the catalytic reactivity of nanostructured complexes was compared using the rate constant (k) of the reaction. The reaction time for the reduction of 4-NP was 5–14 min for different complexes. The catalytic system based on Ni²⁺/2-hydroxybenzaldehyde was the most active and displayed reusability in the reduction of 4-NP.     

Encapsulation of Pd(II) by N4 and N2O2 macrocyclic ligands: their use in catalysis and biology

New macrocyclic Schiff base Pd(II) compounds were synthesized by treating N₄ and N₂O₂ macrocycles with palladium chloride in a 1 : 1 ratio. The resulting macrocyclic compounds were characterized by elemental, IR, ¹H-NMR, ¹³C-NMR, mass, molar conductance, magnetic susceptibility, electronic spectra, and thermal analysis. These compounds were used as catalysts in the development of an efficient catalytic method for reduction of organic substrates having nitro, olefinic, acetylenic, and aldehyde groups under mild reaction conditions. The biological activities of all the macrocycles and macrocyclic Pd(II) compounds have been tested against gram positive (Bacillus subtilis and Staphylococcus aureus) and gram negative (Escherichia coli and Klebsiella pneumonia) bacteria and found to be more active than commercially available antibacterial drugs like Streptomycin and Ampicillin.     

Synthesis of n-alkylated quaternary ammonium chitosan and its long-term antibacterial finish for rabbit hair fabric

In this work, n-alkyl chitosan (N-CTS) was obtained by alkylation modification of chitosan with n-butylaldehyde using Schiff alkali method. The etherifying agent 3-chloro-2-hydroxypropyl triethylammonium chloride (CHPTAC-ethyl) was synthesized from triethylamine and epichlorohydrin. The N-CTS and CHPTAC-ethyl were etherized to finally synthesize n-alkyl quaternary ammonium chitosan (N-CCTS). Scanning electron microscope, X-ray diffractometer, Fourier transform infrared, X-ray photoelectron spectroscopy, and ¹³CNMR were used to characterize the surface morphology and chemical structure. Viscosity method and spectrophotometry were used to determine its physical and chemical properties. The etherification reaction mechanism was studied systematically and the influence of reaction conditions on the degree of substitution and solubility of N-CCTS was investigated. The minimum inhibitory concentration (MIC) of N-CCTS against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was both 0.15 g/L, which was superior to the MIC value of natural chitosan. N-CCTS was used to finish rabbit hair fabric with citric acid as cross-linking agent and sodium hypophosphite as catalyst. The antibacterial and washing resistance of the product were investigated. After 25 times of washing, the antibacterial rate of N-CCTS against E. coli and S. aureus remained stable at about 90%, and the antibacterial rate was higher than that of N-CTS and natural chitosan, and it was a kind of natural polymer long-acting antibacterial finishing agent for rabbit hair fabric.