Progress in Synthetic Polymers Based on Natural Amino Acids

ROS-Responsive and Self-Tumor Curing Methionine Polymer Library Based Nanoparticles with Self-Accelerated Drug Release and Hydrophobicity/Hydrophilicity Switching Capability for Enhanced Cancer Therapy

The applications of amino acid-based polymers are impeded by their limited structure and functions. Herein, a small library of methionine-based polymers (Met-P) with programmed structure and reactive oxygen species (ROS)-responsive properties is developed for tumor therapy. The Met-P can self-assemble into sub-100 nm nanoparticles (NPs) and effectively load anticancer drugs (such as paclitaxel (PTX) (P@Met-P NPs)) via the nanoprecipitation method. The screened NPs with superior stability and high drug loading are further evaluated in vitro and in vivo. When encountering with ROS, the Met-P polymers will be oxidized and then switch from a hydrophobic to a hydrophilic state, triggering the rapid and self-accelerated release of PTX. The in vivo results indicated that the screened P@2Met10 NPs possessed significant anticancer performance and effectively alleviated the side effects of PTX. More interestingly, the blank 2Met10 NPs displayed an obvious self-tumor inhibiting efficacy. Furthermore, the other Met-P NPs (such as 2Met8, 4Met8, and 4Met10) are also found to exhibit varied self-anti-cancer capabilities. Overall, this ROS-responsive Met-P library is a rare anticancer platform with hydrophobic/hydrophilic switching, controlled drug release, and self-anticancer therapy capability.

Synthesis and characterization of novel poly cysteine methacrylate nanoparticles and their morphology and size studies

Polymer nanoparticles (PNPs) have significantly advanced the field of biomedicine, showcasing the remarkable potential for precise drug delivery, administration of nutraceuticals, diagnostics/imaging applications, and the fabrication of biocompatible materials, among other uses. Despite these promising developments, the invention faces notable challenges related to biodegradability, bioactivity, target-site specificity, particle size, carrier efficiency, and controlled release. Addressing these concerns is essential for optimizing the functionality and impact of PNPs in biomedical applications. Here, new poly cysteine methacrylate nanoparticles (PCMANPs), ca. (200 nm) in size have been synthesized from the cysteine methacrylate (CysMA) monomer using different strategies, including emulsion and inverse emulsion polymerization techniques. The monomer was synthesized using the Michael addition reaction, involving the addition of 3-(acryloyloxy)-2-hydroxypropyl methacrylate to the sulfhydryl group (-SH) of the cysteine (Cys) active site, with the aid of dimethyl phenyl phosphine (DMPP) as a nucleophilic agent as previously reported. To enhance nano-polymerization, a thorough exploration of various initiators, including ammonium persulfate (APS) and 4,4'-azobis (4-cyanovaleric acid) (ACVA), alongside surfactants, such as polyvinyl alcohol (PVA), polyvinyl pyrrolidone (PVP), and sodium dodecyl sulfate (SDS), was conducted. Additionally, critical parameters, such as reaction time, temperature, and solvents, were systematically investigated due to their substantial influence on the shape, size, stability, and morphology of the synthesized polymer nanoparticles. This comprehensive approach aims to optimize the synthesis process, ensuring precise control over the key characteristics of the resulting nanoparticles for enhanced performance in diverse applications. Various characterization techniques, including field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), zeta potential, and zeta sizer dynamic light scattering (DLS) analysis, were utilized to investigate purity, morphology, and particle size of the PNPs. As a result, a spherical, monodispersed (homogenized), and stable PCMANP with defined size and morphology was achieved. This may exhibit a remarkable achievement in the future of drug delivery systems and therapeutic index.

Ascertaining the Influence of Lacto-Fermentation on Changes in Bovine Colostrum Amino and Fatty Acid Profiles

The aim of this study was to collect samples of bovine colostrum (BCOL) from different sources (agricultural companies A, B, C, D and E) in Lithuania and to ascertain the influence of lacto-fermentation with Lactiplantibacillus plantarum strain 135 and Lacticaseibacillus paracasei strain 244 on the changes in bovine colostrum amino (AA), biogenic amine (BA), and fatty acid (FA) profiles. It was established that the source of the bovine colostrum, the used LAB, and their interaction had significant effects (p < 0.05) on AA contents; lactic acid bacteria (LAB) used for fermentation was a significant factor for aspartic acid, threonine, glycine, alanine, methionine, phenylalanine, lysine, histidine, and tyrosine; and these factor's interaction is significant on most of the detected AA concentrations. Total BA content showed significant correlations with glutamic acid, serine, aspartic acid, valine, methionine, phenylalanine, histidine, and gamma amino-butyric acid content in bovine colostrum. Despite the differences in individual FA contents in bovine colostrum, significant differences were not found in total saturated (SFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fatty acids. Finally, the utilization of bovine colostrum proved to be challenging because of the variability on its composition. These results suggest that processing bovine colostrum into value-added formulations for human consumption requires the adjustment of its composition since the primary production stage. Consequently, animal rearing should be considered in the employed bovine colostrum processing technologies.

Facile Synthesis of Hybrid Nanoflowers Using Glycine and Phenylalanine and Investigation of Their Catalytic Activity

In the context of the proposed work, two different amino acids (Glycine, Phenylalanine) have interacted with copper ions in a phosphate buffer (PBS) in place of enzymes. This interaction resulted in the nucleation of copper phosphate crystals and the formation of flower-shaped amino acid-copper hybrid nanostructures (AA-hNFs), which grew through self-assembly. While Cu (II) ions in the structure of AA-hNFs were used as Fenton's agent for the catalytic activity. SEM, energy dispersive X-ray spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy measurements were used to define the AA-hNFs' characterisation. The peroxidase-like activities of AA-hNFs were investigated by UV/VIS spectrophotometer. Metal nanoparticles have peroxidase-like activity. A class of enzymes known as peroxidases is able to catalyze the conversion of hydrogen peroxide into hydroxyl radicals. These radicals also take part in electron transfers with substrates, which results in color during oxidation. When cupric oxide nanoparticles are added to the peroxidase substrate while H2 O2 is present, a blue color product with a maximum absorbance at=652 nm can result, demonstrating the catalytic activity of a peroxidase. The morphology and composition of AA-hNFs were carefully characterized and the synthesized parameters were optimized systematically. Results showed that the nanoparticles were dispersed with an average diameter of 7-9 μm and indicated a uniform flower shape. The results of the investigation are anticipated to significantly advance a number of technical and scientific sectors.

Qualitative characterisation and identification of microplastics in a freshwater dam at Gauteng Province, South Africa, using pyrolysis-gas chromatography-time of flight-mass spectrometry (Py-GC-ToF-MS)

Pyrolysis GC-ToF-MS-based analytical study was employed in the identification of microplastics (MPs) in the freshwater of a dam Rietvlei (RTV) located at Gauteng Province, South Africa. These MPs extracted in five locations of the dam were found to contain five different plastic polymeric constituents including PE, PS, PA, PVC and PET along with phthalate esters and fatty acid (amides and esters) derivatives as additives. Based on the fragmented pyrolyzate products, the contribution of plastic polymers and additives was 74% and 26% respectively. Among polymers, PA was dominant with 52% followed by PVC (16%) and others (13%) such as PE, PET and PS in MPs. Scanning electron micrographs of MPs in this aquatic body displayed the rough and fibrous typed patterns. The residual mass of 8-14% was left after the thermal degradation of MPs in RTV samples in the temperature range of 500-550 °C. The results of thermogravimetry (TGA) and energy-dispersive (EDS) analyses are mutually dependent and coherent to each other by way of demonstrating the presence of various inorganic compounds in the form of additives and/or sorbates. The lessened intensities of carbonyl stretching in PA (1625 cm-1) and PET (1725 cm-1) type of MPs attributed the occurrence of degradation and weathering in this aquatic system. The possible causes to the contamination of MPs in this freshwater are the located industries and poor waste management strategies being practised in this densely populated city. Based on the industry, waste management and population perspectives, the increased contamination of MPs is very likely in this freshwater which will drastically affect the ecosystem in the near future. Based on the characterisation results, the presence of various polymers, additives and the metals in MPs is envisaged to deteriorate the aquatic life along with successive risks for the people as a consequence of bio-magnification.

Evaluation of Structural and Optical Properties of Graphene Oxide-Polyvinyl Alcohol Thin Film and Its Potential for Pesticide Detection Using an Optical Method

In the present work, graphene oxide (GO)–polyvinyl alcohol (PVA) composites thin film has been successfully synthesized and prepared by spin coating techniques. Then, the properties and morphology of the samples were characterized using Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), and atomic force microscopy (AFM). Experimental FTIR results for GO–PVA thin film demonstrated the existence of important functional groups such as -CH2 stretching, C=O stretching, and O–H stretching. Furthermore, UV-Vis analysis indicated that the GO–PVA thin film had the highest absorbance that can be observed at wavelengths ranging from 200 to 500 nm with a band gap of 4.082 eV. The surface morphology of the GO–PVA thin film indicated the thickness increased when in contact with carbaryl. The incorporation of the GO–PVA thin film with an optical method based on the surface plasmon resonance (SPR) phenomenon demonstrated a positive response for the detection of carbaryl pesticide as low as 0.02 ppb. This study has successfully proposed that the GO–PVA thin film has high potential as a polymer nanomaterial-based SPR sensor for pesticide detection.

Metabolic engineering of microorganisms for L-alanine production

L-alanine is extensively used in chemical, food, and medicine industries. Industrial production of L-alanine has been mainly based on the enzymatic process using petroleum-based L-aspartic acid as the substrate. L-alanine production from renewable biomass using microbial fermentation process is an alternative route. Many microorganisms can naturally produce L-alanine using aminotransferase or L-alanine dehydrogenase. However, production of L-alanine using the native strains has been limited due to their low yields and productivities. In this review, metabolic engineering of microorganisms for L-alanine production was summarized. Among them, the Escherichia coli strains developed by Dr. Lonnie Ingram's group which can produce L-alanine with anaerobic fermentation process had several advantages, especially having high L-alanine yield, and it was the first one that realized commercialization. L-alanine is also the first amino acid that could be industrially produced by anaerobic fermentation.

Metabolic Engineering of Pediococcus acidilactici BD16 for Heterologous Expression of Synthetic alaD Gene Cassette and L-Alanine Production in the Recombinant Strain Using Fed-Batch Fermentation

Metabolic engineering substantially aims at the development of more efficient, robust and industrially competitive microbial strains for the potential applications in food, fermentation and pharmaceutical industries. An efficient lab scale bioprocess was developed for high level fermentative production of L-alanine using metabolically engineered Pediococcus acidilactici BD16 (alaD⁺). Computational biology tools assisted the designing of a synthetic alaD gene cassette, which was further cloned in shuttle vector pLES003 and expressed using an auto-inducible P289 promoter. Further, L-alanine production in the recombinant P. acidilactici BD16 (alaD⁺) strain was carried out using fed-batch fermentation under oxygen depression conditions, which significantly enhanced L-alanine levels. The recombinant strain expressing the synthetic alaD gene produced 229.12 g/L of L-alanine after 42 h of fed-batch fermentation, which is the second highest microbial L-alanine titer reported so far. After extraction and crystallization, 95% crystal L-alanine (217.54 g/L) was recovered from the culture broth with an enantiomeric purity of 97%. The developed bioprocess using recombinant P. acidilactici BD16 (alaD⁺) is suggested as the best alternative to chemical-based commercial synthesis of L-alanine for potential industrial applications.

Synthetic Formatotrophs for One-Carbon Biorefinery

The use of CO2 as a carbon source in biorefinery is of great interest, but the low solubility of CO2 in water and the lack of efficient CO2 assimilation pathways are challenges to overcome. Formic acid (FA), which can be easily produced from CO2 and more conveniently stored and transported than CO2, is an attractive CO2-equivalent carbon source as it can be assimilated more efficiently than CO2 by microorganisms and also provides reducing power. Although there are native formatotrophs, they grow slowly and are difficult to metabolically engineer due to the lack of genetic manipulation tools. Thus, much effort is exerted to develop efficient FA assimilation pathways and synthetic microorganisms capable of growing solely on FA (and CO2). Several innovative strategies are suggested to develop synthetic formatotrophs through rational metabolic engineering involving new enzymes and reconstructed FA assimilation pathways, and/or adaptive laboratory evolution (ALE). In this paper, recent advances in development of synthetic formatotrophs are reviewed, focusing on biological FA and CO2 utilization pathways, enzymes involved and newly developed, and metabolic engineering and ALE strategies employed. Also, future challenges in cultivating formatotrophs to higher cell densities and producing chemicals from FA and CO2 are discussed.

Synthesis and solvent-controlled self-assembly of diketopiperazine-based polyamides from aspartame

An aspartame-based AB-type diketopiperazine monomer, cyclo(l-aspartyl-4-amino-l-phenylalanyl) (ADKP), was synthesized and subsequently utilized in the polycondensation of homo-polyamides with high molecular weights. By using various amino acids, dicarboxylic acids, and diamines, random DKP-based copolymers were also synthesized. The self-assembly properties of ADKP and poly(cyclo(l-aspartyl-4-amino-l-phenylalanyl)) (PA1) were studied via the solvent displacement method. Notably, PA1 self-assembled into particles with various morphologies in different solvent systems, such as irregular networks, ellipsoids, and hollow particles. The morphological transformation was also confirmed by dropping acetone and toluene onto the PA1 particles. Furthermore, infrared spectra and Hansen solubility parameters of PA1 and different solvents revealed the particle formation mechanism, which provided more insights into the relationship between the morphology and strength of the hydrogen bonding of each solvent.

Diketopiperazine-based polyamides have been synthesized from aspartame, and could self-assemble into particles with various morphologies in different solvents.

The Thermal Properties and Degradability of Chiral Polyester-Imides Based on Several l/d-Amino Acids

Eight kinds of chiral diacid monomers were prepared with amino acids with different side groups or configurations. Polyester-imides (PEIs) were synthesized from these diacid monomers and diphenol monomers through polycondensation reaction, and the performances and properties were compared with the chiral polyamide-imides (PAIs) previously synthesized by our work group. Their thermal properties were analyzed by thermo gravimetric analysis (TGA) and dynamic thermomechanical analysis (DMA), and it was found that the glass transition temperature (Tg) of PEI was mainly affected by the volume of side groups. Their degradability was studied through buffer degradation experiments, and the changes in their water contact angle, molecular weight, structure and appearance during the degradation process were characterized by contact angle tester, gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). With degradation, the hydrophilicity of PEI was improved, and when amino acids with larger side groups or D configuration were introduced into the backbone of PEI, the degradability decreased.

Optimization of a reduced enzymatic reaction cascade for the production of L-alanine

Cell-free enzymatic reaction cascades combine the advantages of well-established in vitro biocatalysis with the power of multi-step in vivo pathways. The absence of a regulatory cell environment enables direct process control including methods for facile bottleneck identification and process optimization. Within this work, we developed a reduced, enzymatic reaction cascade for the direct production of L-alanine from D-glucose and ammonium sulfate. An efficient, activity based enzyme selection is demonstrated for the two branches of the cascade. The resulting redox neutral cascade is composed of a glucose dehydrogenase, two dihydroxyacid dehydratases, a keto-deoxy-aldolase, an aldehyde dehydrogenase and an L-alanine dehydrogenase. This artificial combination of purified biocatalysts eliminates the need for phosphorylation and only requires NAD as cofactor. We provide insight into in detail optimization of the process parameters applying a fluorescamine based L-alanine quantification assay. An optimized enzyme ratio and the necessary enzyme load were identified and together with the optimal concentrations of cofactor (NAD), ammonium and buffer yields of >95% for the main branch and of 8% for the side branch were achieved.

Preparation of a new benzylureido-β-cyclodextrin-based column and its application for the determination of phenylmercapturic acid and benzylmercapturic acid enantiomers in human urine by LC/MS/MS

A benzylureido-β-cyclodextrin was synthesized by the reaction of 6-amino-β-cyclodextrin with an active benzyl isocyanate. Then, it was bonded to silica gel by a thiol-ene addition reaction, obtaining a new benzylureido-β-cyclodextrin-based chiral stationary phase (BzCDP). Its chemical structure was characterized by infrared spectroscopy, elemental analysis, and solid-state nuclear magnetic resonance spectroscopy. The BzCDP was successfully used to separate phenylmercapturic acid (PMA) and benzylmercapturic acid (BMA) enantiomers, which were confirmed as biomarkers of exposure to benzene and toluene in human urine. The enantiomeric separations were also optimized through the investigation of related factors. The resolutions of PMA and BMA enantiomers could be up to 2.25 and 2.14, respectively, within 30 min under reversed-phase chromatography. Based on the optimal chromatographic and mass spectrometry conditions, a new LC-MS/MS quantitative method for the PMA and BMA enantiomers was established by negative ion multiple reaction monitoring (MRM) and an isotope-labeled PMA (d²-PMA) as an internal standard. The limits of detection (LODs) of enantiomers were less than 0.17 μg/L for PMA and 0.14 μg/L for BMA, and the averaged recoveries of enantiomers were in the range of 86~100% for PMA and 86~113% for BMA. The method had good reproducibility levels with the RSDs (3.5~11.3% for intra-day and 3.9~13.1% for inter-day). The method was successfully applied to urine testing of 60 painting and printing workers. The results showed that only L-PMA was detected in the urine of the Printers, while a high content of L-PMA (27.5~106 μg/L) and D-PMA (19.9~82.8 μg/L) can be detected simultaneously in the urine of the Painters, indicating that benzene pollution was more serious in this group. The positive rate of BMA was rather higher, indicating that toluene pollution was more common than benzene. BMA also existed in the form of two enantiomers (L-BMA and D-BMA), but the difference between the two types of occupational groups was small. It is a meaningful work to deeply study the existence and content of chiral markers in human urine, which will help to better understand and evaluate the harmful effects of benzene series on human beings. Graphical abstract.

Synthesis and characterization of optically active magnetic PAI/Fe3O4 nanocomposites

This work presents the preparation and characterization of hybrid organic-inorganic optically active poly(amide-imide)/nano-Fe₃O₄ composites with different amount of modified Fe₃O₄ nanoparticles as new nanocomposites by ultrasonic irradiation and characterized by Fourier transform infrared spectra, X-ray diffraction, scanning electron microscopy (SEM), thermogravimetric analysis and vibrating sample magnetometry. The surface of Fe₃O₄ nanoparticles was modified with 3-aminopropyltriethoxyl silane because of the homogeneous distribution of nano-Fe₃O₄ in polymer matrix, which the SEM results confirmed that the Fe₃O₄ nanoparticles were dispersed uniformly in polymer matrix. Furthermore, as compared with pure polymer, thermogravimetric analysis data indicated an improvement of thermal stability of nanocomposites.

A Highly Hydrophilic and Biodegradable Novel Poly(amide-imide) for Biomedical Applications

A novel biodegradable poly(amide-imide) (PAI) with good hydrophilicity was synthesized by incorporation of l-glycine into the polymer chain. For comparison purposes, a pure PAI containing no l-glycine was also synthesized with a three-step method. In this study, we evaluated the novel PAI's thermal stability, hydrophilicity, solubility, biodegradability and ability to support bone marrow mesenchymal stem cell (BMSC) adhesion and growth by comparing with the pure PAI. The hydrophilic tests demonstrated that the novel PAI has possible hydrophilicity at a 38° water contact angle on the molecule surface and is about two times more hydrophilic than the pure PAI. Due to an extra unit of l-glycine in the novel PAI, the average degradation rate was about 2.4 times greater than that of the pure PAI. The preliminary biocompatibility studies revealed that all the PAIs are cell compatible, but the pure PAI exhibited much lower cell adhesion than the l-glycine-incorporated novel PAI. The hydrophilic surface of the novel PAI was more suitable for cell adhesion, suggesting that the surface hydrophilicity plays an important role in enhancing cell adhesion and growth.

Amino acids-incorporated nanoflowers with an intrinsic peroxidase-like activity

Functional molecules synthesized by self-assembly between inorganic salts and amino acids have attracted much attention in recent years. A simple method is reported here for fabricating hybrid organic–inorganic nanoflowers using copper (II) ions as the inorganic component and natural amino acids as the organic component. The results indicate that the interactions between amino acid and copper ions cause the growth of the nanoflowers composed by C, N, Cu, P and O elements. The Cu ions and Cu(AA)_n complexes containing Cu-O bond are present in the nanoflowers. The nanoflowers have flower-like porous structure dominated by the R groups of amino acids with high surface-to-volume ratios, which is beneficial for exerting its peroxidase-like activity depending on Fenton-like reaction mechanism with ABTS and Rhodamine B as the substrates. It is expected that the nanoflowers hold great promise as enzyme mimics for application in the field of biosensor, bioanalysis and biocatalysis.

Efficient L-Alanine Production by a Thermo-Regulated Switch in Escherichia coli

L-Alanine has important applications in food, pharmaceutical and veterinary and is used as a substrate for production of engineered thermoplastics. Microbial fermentation could reduce the production cost and promote the application of L-alanine. However, the presence of L-alanine significantly inhibit cell growth rate and cause a decrease in the ultimate L-alanine productivity. For efficient L-alanine production, a thermo-regulated genetic switch was designed to dynamically control the expression of L-alanine dehydrogenase (alaD) from Geobacillus stearothermophilus on the Escherichia coli B0016-060BC chromosome. The optimal cultivation conditions for the genetically switched alanine production using B0016-060BC were the following: an aerobic growth phase at 33 °C with a 1-h thermo-induction at 42 °C followed by an oxygen-limited phase at 42 °C. In a bioreactor experiment using the scaled-up conditions optimized in a shake flask, B0016-060BC accumulated 50.3 g biomass/100 g glucose during the aerobic growth phase and 96 g alanine/100 g glucose during the oxygen-limited phase, respectively. The L-alanine titer reached 120.8 g/l with higher overall and oxygen-limited volumetric productivities of 3.09 and 4.18 g/l h, respectively, using glucose as the sole carbon source. Efficient cell growth and L-alanine production were reached separately, by switching cultivation temperature. The results revealed the application of a thermo-regulated strategy for heterologous metabolic production and pointed to strategies for improving L-alanine production.

Novel poly(N-vinyl-2-pyrrolidone) nanocomposites containing poly(amide–imide)/aluminum oxide nanostructure hybrid as a filler

In this work, the physicochemical properties of poly( N-vinyl-2-pyrrolidone) (PVP) reinforced with the poly(amide–imide)/alumina nanocomposite (PAN) under sonochemical treatment were studied. In the process of manufacturing PAN, the surface of alumina nanoparticles was grafted with 15 wt% of the bioactive dicarboxylic acid based on amino acid, and an amount of 10 wt% of this modified nanoparticle was loaded into the poly(amide–imide) using some powerful ultrasound irradiation. Subsequently, in order to prepare the PVP-PAN, various contents (2, 4, and 6 wt%) of the PANs were incorporated into the PVP matrix. The structure morphology and the physical properties of the obtained PVP/PANs were analyzed by Fourier transform infrared spectroscopy, X-ray diffraction, thermal gravimetric analysis, field-emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. The data obtained from the thermal analysis of PVP/PANs indicated their noteworthy thermal stability, thereby implying the complete miscibility between PVP and the PAN hybrid.

Lignocellulosic biomass: a sustainable platform for the production of bio-based chemicals and polymers

The ongoing research activities in the field of lignocellulosic biomass for production of value-added chemicals and polymers that can be utilized to replace petroleum-based materials are reviewed.

Effect of organically modified Ni–Al layered double hydroxide loading on the thermal and morphological properties of l-methionine containing poly(amide-imide) nanocomposites

This work deals with the synthesis of an organically modified Ni–Al layered double hydroxide (LDH) and the effect of the LDH loading on the thermal and morphological behavior of poly(amide-imide)/Ni–Al LDH nanocomposites.

Functionalization of TiO2 nanoparticles with bio-safe poly(vinyl alcohol) to obtain new poly(amide-imide) nanocomposites containing N,N′-(pyromellitoyl)-bis-L-leucine linkages

Nanocomposites (NCs) based on the reinforcement of polymers with nanoparticles (NPs) have attracted increasing attention for researchers. The goal of this study was production of new NCs based on poly(amide-imide) (PAI) and modified titanium dioxide (TiO2) NPs. Due to the tendency of the NPs for agglomeration, the surface of the TiO2 NPs was modified with poly(vinyl alcohol). Then the PAI was prepared from the polymerization reaction of N, N′-(pyromellitoyl)-bis-L-leucine diacid with 4,4 ′-diaminodiphenylmethane under green conditions. Finally, NCs were synthesized by incorporating modified TiO2 NPs into the PAI matrix by ultrasonic irradiation. The resulting NCs were studied by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analyses (TGA), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). TGA results showed good thermal stability for the prepared NCs by addition of the modified TiO2 NPs into the PAI matrix. Results of TEM and FE-SEM showed that the modified TiO2 NPs homogenously dispersed in the PAI matrix.

High-performance polymer nanocomposites having a biosafe amino acid by incorporating modified nanozirconia with a flame-retardant coupling agent

A lot of polymeric materials are flammable, requiring modification to decrease their flammability. Nanoparticle (NP) fillers are very attractive for this purpose as they can improve both the physical and the flammable properties of the nanocomposites (NCs). Zirconium oxide (ZrO2) is one of the NPs having flame-retardant property. For the first time, ZrO2 NPs were modified using a fire-resistant modifier and then the chiral NCs were prepared via incorporating modified ZrO2-NPs into the poly(amide–imide) matrix. By decreasing the flammability of these NCs, severe aggregation of ZrO2-NPs could be reduced by surface modification. The surface modification of ZrO2 and the synthesis of NCs were performed through ultrasonic irradiations. The resulting modified ZrO2 and NPs-reinforced composites were characterized by different analyses. Field-emission scanning electron microscopy and transmission electron microscopy results proved that ZrO2-NPs were homogeneously distributed after the surface modification and successfully incorporated into the PAI matrix. The grafting of modifier on the surface of ZrO2 was confirmed by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy techniques. TGA also showed high thermally stable and flame-retardant properties of the obtained NCs.