Carbon-13 Nuclear Magnetic Resonance Spectroscopy Research Articles

Synthesis and Antifungal Activity of Novel Tetrahydrogeranyl Quaternary Ammonium Salts

Due to the excessive use of antifungal agents, drug resistance and ecological problems are increasing. Some antifungal agents are difficult to degrade and have high toxicity and several side effects. In this study, 15 novel tetrahydrogeranyl quaternary ammonium salts (8a–8o) were synthesized from the natural compound citral. The structures of the quaternary ammonium salts were characterized by Fourier transform infrared, proton nuclear magnetic resonance, carbon-13 nuclear magnetic resonance spectroscopy, and mass spectrometry, and the antifungal activities of these compounds at a concentration of 0.25 mg/mL against 10 plant pathogenic fungi were tested. The results showed that compound 8i had the best antifungal activity, and its inhibition rates against Rhizoctonia solani, Phytophthora parasitica var. nicotianae, Sphaeropsis sapinea, Fusarium oxysporum f. sp. niveum, and Poria vaporaria reached 100%. For Fusarium verticillioides, the inhibition rate of compound 8i was 93.28%, which was higher than that of chlorothalonil. In addition, it was found that the inhibition rates of compounds with N,N-di- n-propyl group (8l, 8m) against R solani, F oxysporum f. sp. niveum, S sapinea, P parasitica var. nicotianae, F verticillioides, Colletotrichum acutatum, and Coriolus versicolor were higher than compounds with N,N-diethyl and N,N-dimethyl groups (8a, 8b, 8j, 8k). The inhibition rates of compounds with morpholine groups (8n, 8o) were generally low.

Retanning Performance of Carboxymethyl Starch and Its Effects on Dyeing

The tanning characteristics of starch samples modified by different methods were investigated in our previous studies. In this study, utilization of modified starch in leather making as a retanning agent and its effect on dyeing process have been investigated. For this purpose, the molecular size of native corn starch was reduced by H2O2 oxidation and then carboxymethylated. A series of analyses (water solubility, degree of substitution, Fourier Transform Infrared Spectroscopy, Proton and Carbon Nuclear Magnetic Resonance Spectroscopy) were carried out for characterization. Then, carboxymethyl starches were used in retanning processes to be 3, 5 and 10% based on leather weight and the shrinkage temperatures and filling coefficients of the leathers were determined. Acid and metal complex dyestuffs were used in dyeing processes and the effect of carboxymethyl starch on dyeing was also investigated by examining dye consumption, dry and wet rubbing fastness and color of the leathers. From the results it was concluded that carboxymethyl starch showed a noticeable solo performance in terms of filling property and shrinking temperature without any considerable adverse effect on dyeing.

Coumarin based polymeric material: Synthesis, characterization, thermal properties, and antibacterial activity of Copoly (7-Methacryloxy-4-methylcoumarin-co-N-Vinyl pyrrolidone)

Methacrylic monomer of 7-Methacryloxy-4-methylcoumarin (MAOMC) was synthesized by reacting 7-hydroxy-4-methyl coumarin with Methacryloyl chloride. Copolymers of 7-Methacryloxy-4-methylcoumarin with N-vinyl pyrrolidone (NVP) at different feed composition was prepared by free radical solution polymerization at 70 ± 1 °C using Benzoyl peroxide (BPO) as an initiator and Ethylmethylketone (EMK) as a solvent. The synthesized monomer and copolymers were analysized by Fourier transform infrared spectroscopy (FT-IR), Proton and Carbon nuclear magnetic resonance (1H &13C NMR) spectroscopy. The polydispersity indices of the copolymers determined using gel permeation chromatography, which suggest that the chain termination is predominantly by disproportion. Thermal analysis(TGA) of the copolymers was done in N2 atmosphere, the polymers are thermally stable upto 475 °C. The result shows, the polymer stability increases with the increase of MAOMC unit in the copolymer. Antibacterial activity of the polymers was also investigated against the pathogenic bacteria Bacillus subtilis, Klebshella planticola and Escherichia coli in a standard disk diffusion assay against microbes using Ampicillin as a standard. The antibacterial activity of the copolymer increases with MAOMC content increases in the copolymer; this indicates that coumarin constituent placed essential role in antimicrobial agent.

Preparation of a sustainable bio-copolymer based on Luffa cylindrica cellulose and poly(ɛ-caprolactone) for bioplastic applications

In this research, a bio-based graft copolymer (LCC-g-PCL) based on the cellulose of Luffa cylindrica (LCC) main chain possessing poly(ɛ-caprolactone) (PCL) pendant groups is synthesized through a grafting from approach via ring-opening polymerization (ROP). For this purpose, LCC, extracted from luffa sponges by combined method, is utilized for ROP of ɛ-caprolactone (ɛ-CL) as a macro-initiator in the presence of stannous octoate as a catalyst. Fourier transform infrared (FT-IR), proton and carbon nuclear magnetic resonance (1H NMR and 13C NMR) spectroscopies are utilized to structurally indicate the success of ROP, while the achieved graft copolymer is analyzed in detail by comparing with LCC and neat PCL in terms of wettability, thermal and degradation behaviors by conducting water contact angle (WCA) measurements, thermogravimetric and differential scanning calorimetry analyses (TGA and DSC) and in vitro both hydrolytic and enzymatic biodegradation tests, respectively. The results of conducted tests show that the incorporation of PCL groups on LCC provide the increasing hydrophobicity. In addition, the degradation behavior of the LCC-g-PCL copolymer is found to be more pronounced under enzymatic medium rather than hydrolytic conditions. It is anticipated from the results that LCC-g-PCL can be a potential eco-friendly material particularly in bioplastic industry.

Effect of pH on the formation of benzyl ester bonds between glucuronic acid and dehydrogenation polymer

The effect of pH on the addition reaction of glucuronic acid to quinone methides generated in the synthesis of dehydrogenation polymer (DHP or artificial lignin) was investigated. The DHP-glucuronic acid complexes were formed during DHP polymerization catalyzed by a mixture of laccase, β-glucosidase, and O2 within the pH range 7 to 4 in the presence of coniferin as a precursor. The structure of the product and the content of benzyl ester bonds were characterized by Fourier transform infrared spectroscopy, solid-state cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance spectroscopy, ion chromatography, high performance liquid chromatography, and elemental analysis. The results showed that the pH of the reaction system had an important role in the formation of the benzyl ester bonds. Acidic conditions favored the reaction of quinone methide intermediates with carboxyl groups of glucuronic acid in the biosynthesis of DHP. However, weakly acidic conditions (pH 6) enhanced the reaction of quinone methide intermediates with glucose. In neutral conditions, the DHP-protein complex can be efficiently synthesized by the addition reaction of quinone methide intermediates with amino acids in protein.

Novel Poly(Methylenelactide-g-L-Lactide) Graft Copolymers Synthesized by a Combination of Vinyl Addition and Ring-Opening Polymerizations.

In this work, a novel poly (methylenelactide-g-L-lactide), P(MLA-g-LLA) graft copolymer was synthesized from poly(methylenelactide) (PMLA) and L-lactide (LLA) using 0.03 mol% liquid tin(II) n-butoxide (Sn(OnBu)2) as an initiator by a combination of vinyl addition and ring-opening polymerization (ROP) at 120 °C for 72 h. Proton and carbon-13 nuclear magnetic resonance spectroscopy (1H- and 13C-NMR) and Fourier-transform infrared spectroscopy (FT-IR) confirmed the grafted structure of P(MLA-g-LLA). The P(MLA-g-LLA) melting temperatures (Tm) range of 144–164 °C, which was lower than that of PLA (170–180 °C), while the thermal decomposition temperature (Td) of around 314–335 °C was higher than that of PLA (approx. 300 °C). These results indicated that the grafting reaction could widen the melt processing range of PLA and in doing so increase PLA’s thermal stability during melt processing. The graft copolymers were obtained with weight-average molecular weights () = 4200–11,000 g mol−1 and a narrow dispersity (Đ = 1.1–1.4).

Simple Esterification of [1-13C]-Alpha-Ketoglutarate Enhances Membrane Permeability and Allows for Noninvasive Tracing of Glutamate and Glutamine Production.

Alpha-ketoglutarate (α-KG) is a key metabolite and signaling molecule in cancer cells, but the low permeability of α-KG limits the study of α-KG mediated effects in vivo. Recently, cell-permeable monoester and diester α-KG derivatives have been synthesized for use in vivo, but many of these derivatives are not compatible for use in hyperpolarized carbon-13 nuclear magnetic resonance spectroscopy (HP-13C-MRS). HP-13C-MRS is a powerful technique that has been used to noninvasively trace labeled metabolites in real time. Here, we show that using diethyl-[1-13C]-α-KG as a probe in HP-13C-MRS allows for noninvasive tracing of α-KG metabolism in vivo.

Probing changes in humus chemical characteristics in response to biochar addition and varying bulking agents during composting: A holistic multi-evidence-based approach

Despite the various benefits of humus, the changes in its chemical characteristics during composting in response to biochar addition and varying bulking agents remain to be further explored. In this study, three treatments were conducted, in which swine manure, bulking agent, and biochar were mixed at ratios of 4:1:0, 8:1:0, and 8:1:1. Fourier transform infrared spectroscopy (FTIR), carbon nuclear magnetic resonance spectroscopy (13C-NMR), three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM), and near-edge X-ray absorption fine structure (NEXAFS) were employed to characterize the chemical and structural properties of humus from multiple perspectives. The 3D-EEM spectra in this study showed a larger increase in humic acids (HAs) content (56%) and HAs to fulvic acids ratio (128%) during composting, indicating stronger humification in biochar-amended treatment. FTIR, 13C-NMR, and NEXAFS all confirmed the essential properties of HA as the core agronomic functional substance with rich aromatic and carboxyl groups, and that its aromaticity increased gradually during composting. In addition, 13C-NMR demonstrated that biochar addition and a relatively higher bulking agent ratio aided an increase in the carboxyl C proportion in HA after composting. In particular, NEXAFS revealed that biochar addition promoted the diversification of C, N, and O species in HA, with the emergence of quinone C and O-alkyl C as the main representatives. This work suggests that biochar addition and a relatively high bulking agent ratio could enhance humification and improve the agronomic function of humus.

Secondary metabolites from a marine sponge-derived actinomycete <italic>Streptomyces parvulus</italic> MA1076

In recent years, researchers have discovered a large number of secondary metabolites with novel chemical structures and diverse activities from sponge-derived actinomycetes. Sponge-derived actinomycetes have become important sources of new drug lead compounds. The actinomycete <italic>Streptomyces parvulus</italic> MA1076 is derived from the sponge( <italic>Pseudoceratina</italic> sp.) on Yongxing Island in the South China Sea. In order to obtain the structural type and potential medicinal value of the secondary metabolites, strain identification and chemical composition analysis were carried out on the sponge-associated actinomycete <italic>Streptomyces parvulus</italic> MA1076. Bacterial genomic DNA rapid extraction kit was used to extract streptomyces genomic DNA. Streptomyces universal primers 27F and 1492R were used for PCR amplification, and the amplified products was sent for sequence testing. The sequencing result was used for strain identification through 16S rDNA sequence analysis and phylogenetic tree construction. Silica gel column chromatography, Sephadex LH-20 gel column chromatography, semi-preparative high performance liquid chromatography and other techniques were applied to separate and purify the ethyl acetate extract of the sponge-derived actinomycetes <italic>Streptomyces parvulus</italic> MA1076. The structure of the compound was identified by spectral data such as proton nuclear magnetic resonance spectroscopy (¹H-NMR), carbon nuclear magnetic resonance spectroscopy (¹³C-NMR), high-resolution mass spectrometry (HR-MS),and combined with the comparison with literature data. Six compounds were isolated and identified from the actinomycetes <italic>Streptomyces parvulus</italic> MA1076, which were actinomycin D (compound 1), daucosterol (compound 2), cyclo-((<italic>S</italic>)-Pro-(<italic>R</italic>)-Leu) (compound 3), thymidine (compound 4), 3′-<italic>O</italic>-acetylthymidine (compound 5), and indole-3-carboxyli acid (compound 6). Compounds 2-6 were isolated for the first time from <italic>Streptomyces parvulus</italic> MA1076. The six compounds were tested for their cell proliferation inhibitory activity on two pancreatic cancer cell lines (pc-12 and bc-16). Results showed that compound 1 had obvious proliferation inhibitory activity on both pancreatic cancer cell lines. Compounds 2-6 showed no obvious anti-tumor cell proliferation activity. The results of the study make full use of the abundant Chinese sponge resources and their associated microbial resources, exploring the structural diversity of sponge secondary metabolites to discover new chemical substances that may be contained in natural products, and to develop new antibacterial , antitumor drugs is of great theoretical significance and potential application value.

Ester Oils Prepared from Fully Renewable Resources and Their Lubricant Base Oil Properties.

The work reports on the physicochemical and tribological properties of gallate ester oils prepared from fully renewable resources, such as gallic acid and fatty acids. The ester structures were identified by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectra (HRMS) data. The density at 20 °C (d20), kinematic viscosity (KV), viscosity index (VI), pour point (PP), flash point (FP), thermal and oxidative stabilities, friction-reducing and antiwear properties of gallate ester oils were evaluated. The tribological properties of gallate ester oils as lubricants for steel, copper, and aluminum tribo-pairs can be compared with those of the commercially available lubricating oil tris(2-ethylhexyl) trimellitate (Phe–3Ci8), but their viscosity-temperature characteristics, thermal and oxidative stabilities are better than those of Phe–3Ci8. More importantly, they have much higher biodegradabilities than Phe–3Ci8. The study of the lubrication mechanism shows that the physical and/or chemical adsorption film formed by gallate ester molecules between friction pairs is the key factor for them to obtain friction-reducing and antiwear properties.

Regulation of alkoxysilane on stereoregular polymerization of Butene-1 catalyzed by TiCl4/MgCl2 Ziegler-Natta catalysts

External electron donors (ED) as one of the components in traditional Ziegler-Natta (Z-N) catalysts play important roles in determining the activity, stereoregularity of the active species for ɑ-olefin polymerization. Alkoxysilanes with different size and different electron-donating alkyl substituents were investigated to study the stereoregular polymerization of butene-1 catalyzed by TiCl4/MgCl2 Z-N catalysts. The obtained polybutene-1 (PB) was fractionated into three components including high isotactic PB (HiPB), medium isotactic PB (MiPB) and atactic PB (aPB) and the number of active centers ([C*]/[Ti]) of each component were measured accordingly. The mmmm sequence concentration, weight-average molecular weight (Mw), molecular weight distribution (MWD), and crystallizability of PB were studied by carbon-13 nuclear magnetic resonance spectrometry (13C-NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The addition of dimethyldimethoxysilane (D1) with 120.1 Å3 volume and 0.6802 a.u. electron density had little influence on the stereoregular polymerization of butene-1. The incorporation of diphenyldimethoxysilane (D3) with higher steric hindrance (231.2 Å3 volume), stronger electro-donating ability (0.6969 a.u. electron density) produced PB with higher HiPB component, higher mmmm sequence concentration, accompanying by the reduced catalytic activity and [C*]/[Ti]. The probably active center models absorbing different ED were proposed to explain the catalytic behaviors for butene-1 polymerization and formation of PB with different components.

Functionalization effect on the corrosion inhibition of novel eco-friendly compounds based on 8-hydroxyquinoline derivatives: Experimental, theoretical and surface treatment

The present study has investigated the functional effect of modifying a simple function (NH2) that correspond to a heterocycle (Benzodiazepine), acquired through two similar reactions, on the inhibition of mild steel corrosion (m-steel) in hydrochloric medium (1.0 M HCl). [5-((2-aminobutoxy) methyl)-quinolin-8-ol (Q-2) and 7-chloro-2,2,4-trimethyl-2,3 dihydro-1H benzo[b][1,4]diazepin-1-yl)methyl)quinolin-8-ol (Q-1)] were synthesized by two environmentally friendly reactions and characterized using Proton nuclear magnetic resonance (1H NMR) and Carbon nuclear magnetic resonance (13C NMR) spectroscopy. The inhibitory action of both organic compounds was evaluated by numerous techniques that have been already described in the literature (electrochemical impedance spectroscopy (EIS) and Potentiodynamic Polarization (PDP)).The inhibition efficiency increased with the increasing inhibitor concentration to 92.8% and91.1 % for Q-1 and Q-2 respectively at 10−3 M. The submerged surface of steel has been identified by scanning electron microscopy coupled with Energy Dispersive X-Ray Spectroscopy (SEM/EDS), Infrared spectroscopy (FT-IR), atomic force microscopy (AFM) spectroscopy and Contact angle measurements (θ). The corrosive solutions after corrosion tests have been identified by UV–visible spectrometry (UV–vis) and Inductively Coupled Plasma Emission Spectroscopy analysis (ICP-OES). The experimental studies PDP and EIS were completed by the theoretical studies Density-functional theory (DFT) and Monte Carlo (MC) simulation). Experimental data have shown that the studied additives Q-1 and Q-2 are effective against the corrosion acid of m-steel. In addition, their adsorption onto steel surface follow Langmuir adsorption isotherm.

An eco‐friendly procedure for achieving high‐yield carrageenan from Hypnea cervicornis suitable for wet spinning

AbstractIn this study, an eco‐friendly method was proposed to prepare carrageenan suitable for spinning into fibers. The extract from Hypnea cervicornis without alkali pretreatment was directly converted into the spinning solution, and carrageenan fibers were obtained via wet spinning. The improved procedure had a higher yield (61.8% ± 1.1%) than the traditional method (36.0% ± 1.3%). The chemical structure of the carrageenan was analyzed via fourier transform infrared spectroscopy (FTIR) and carbon nuclear magnetic resonance spectroscopy (13C NMR). It was confirmed that carrageenan extracted from Hypnea cervicornis was mainly ι‐carrageenan and its structure was not changed by alkali pretreatment. The properties of the spinning solution and fibers were characterized using dynamic light scattering (DLS), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and tensile tests. The results showed that the spinning solution prepared by the improved procedure was homogeneous and suitable for spinning, and the mechanical strength of the novel prepared carrageenan fibers was equal to the fibers spanned from traditional carrageenan.

Dissertation Project for the Forensic Science Laboratory: Birch Reduction of Ephedrine and Analysis of Byproducts of Forensic Science Interest

This undergraduate dissertation project was designed to enhance organic and analytical chemistry skills of final year forensic science students. A modified Birch reaction method was employed to synthesize amphetamine from ephedrine and detect the most known byproduct of clandestine manufacture of amphetamines, e.g., 1-(1,4-cyclohexadienyl)-2-methylaminopropane (CMP). The use of this synthetic method led to simultaneous N-demethylation and dehydroxylation of the alkaloid. Harmful liquid ammonia and lithium metal, which are the typical reagents of the classic Birch reaction, were replaced by the safer sodium silica gel stage I (Na-SG-I) and an alcoholic proton source. Liquid chromatography–mass spectrometry (LC-MS) was used to monitor reaction progress and identify starting material, products, and byproducts, whereas proton and carbon nuclear magnetic resonance (1H and 13C NMR) and heteronuclear single-quantum correlation (HSQC) NMR spectroscopy experiments were employed to characterize amphetamine and the parent compound ephedrine. This multiweek project-based learning experience has been running for three years at De Montfort University (DMU), which offers a well-established Forensic Science BSc (Hons) undergraduate course. The students were guided with the help of an academic instructor through a research-like setting delving into synthesis, characterization, and analysis of a drug of abuse and its byproduct. As part of this learning experience, which culminated in a body of work that informed the content of final year dissertations, the students gained useful organic chemistry skills and consolidated previously acquired knowledge in trace analysis. A survey of the dissertations’ final grades and evaluation of end-of-project questionnaires revealed that students responded well to the challenges posed by the organic chemistry aspect of the lab and that the project topic and methods were engaging and very relevant to the forensic science course.

One-Pot Synthesis of 7, 7-Dimethyl-4-Phenyl-2-Thioxo-2,3,4,6,7, 8-Hexahydro-1H-Quinazoline-5-OnesUsing Zinc Ferrite Nanocatalyst and Its Bio Evaluation

A simple and highly efficient protocol for the synthesis of derivatives 7, 7-dimethyl-4-phenyl-2-thioxo-2, 3, 4, 6, 7, 8-hexahydro-1H-quinazoline-5-one from 5, 5-dimethyl cyclohexane-1, 3-dione (4a–4h) (dimedone) has been described. The aryl aldehydes were substituted with thiourea in the presence of synthesized zinc ferrite nanocatalyst, which increased the yield under reflux through condensation, followed by cyclization to give desired products. The other advantages are that it is eco-friendly and economically affordable for large-scale production. Structural validation and characterization of all the newly synthesized compounds were evaluated by spectral analysis (mass spectrometry, proton nuclear magnetic resonance (1HNMR), and Carbon-13 nuclear magnetic resonance(13CNMR)spectroscopies. The structure of antibacterial and antifungal assays was performed with the newly synthesized compounds. The antimicrobial activity of title compounds possessing electron-withdrawing groups such as (4e–4h) (Cl, Br, and cyano group) exhibited more active potential than the electron-donating groups, C6H5,4-C6H4, 3-OC2H5-4OH-C6H3, etc., (4a–4d) containing moiety.

Yield and Selectivity Improvement in the Synthesis of Carbonated Linseed Oil by Catalytic Conversion of Carbon Dioxide.

Carbonation of epoxidized linseed oil (CELO) containing five-membered cyclic carbonate (CC5) groups has been optimized to 95% by reacting epoxidized linseed oil (ELO) with carbon dioxide (CO2) and tetrabutylammonium bromide (TBAB) as catalysts. The effect of reaction variables (temperature, CO2 pressure, and catalyst concentration) on the reaction parameters (conversion, carbonation and selectivity) in an autoclave system was investigated. The reactions were monitored, and the products were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), carbon-13 nuclear magnetic resonance (13C-NMR) and proton nuclear magnetic resonance (1H-NMR) spectroscopies. The results showed that when carrying out the reaction at high temperature (from 90 °C to 120 °C) and CO2 pressure (60–120 psi), the reaction’s conversion improves; however, the selectivity of the reaction decreases due to the promotion of side reactions. Regarding the catalyst, increasing the TBAB concentration from 2.0 to 5.0 w/w% favors selectivity. The presence of a secondary mechanism is based on the formation of a carboxylate ion, which was formed due to the interaction of CO2 with the catalyst and was demonstrated through 13C-NMR and FT-IR. The combination of these factors makes it possible to obtain the largest conversion (96%), carbonation (95%), and selectivity (99%) values reported until now, which are obtained at low temperature (90 °C), low pressure (60 psi) and high catalyst concentration (5.0% TBAB).

A Practical and Efficient Synthesis of Uniform Conjugated Rod-Like Oligomers.

Herein, a more practical and efficient synthesis protocol for the preparation of uniform rod-like oligo(1,4-phenylene ethynylene)s (OPE)s is presented. Applying an iterative reaction cycle consisting of a decarboxylative coupling reaction and a saponification of an alkynyl carboxylic ester, a uniform pentamer is obtained in ten steps with 14% overall yield. The copper-free conditions prevent homocoupling until the trimer stage, resulting in a significantly easier work-up of the products. Homocoupling is observed from the tetramer stage on, but a simple variation of the work-up procedure also yields the uniform tetramer and pentamer. A thorough comparison with the commonly used and described Sonogashira approach reveals that with the new presented strategy, OPEs can be built in similar overall yield, but easier purification and in a quarter of the time. All oligomers are fully characterized by proton and carbon nuclear magnetic resonance spectroscopy (NMR), mass spectrometry (MS), size-exclusion chromatography (SEC), and infrared spectroscopy (IR).

Crystalline Lamellar Structure of Thermosetting Urea–Formaldehyde Resins at a Low Molar Ratio

Reducing formaldehyde emission from cured urea–formaldehyde (UF) resins forced us to synthesize UF resins at a low formaldehyde to urea (F/U) molar ratio (≤1.0), resulting in low emission and poor adhesion by forming crystalline domains instead of building a three-dimensional network in cured resins. For the first time, we report a crystalline lamellar structure of thermosetting UF resins at a low molar ratio and compare it with highly amorphous UF resins at a high F/U molar ratio (1.6). Films of crystalline and amorphous UF resins were prepared using a spin-coater and characterized using atomic force microscopy. In addition, transmission electron microscopy, gel permeation chromatography, and X-ray diffraction were also employed for their characterization. The results showed that 1.0 UF resins had a low molecular weight with a lamellar structure of the crystalline domain, whereas 1.6 UF resins exhibited a high molecular weight with an amorphous structure and had a lower surface roughness. Fourier transform infrared and carbon-13 nuclear magnetic resonance spectroscopy also proved that linear molecules and hydrogen bonding were responsible for the formation of crystalline lamellar structures in thermosetting UF resins at a low molar ratio.

Catechol-modified epoxy coatings with high adhesive strength on saturated concrete substrate

A series of catechol-modified epoxy resin biomimetic coatings (CE-X, X represents the weight fraction of catechol-modified epoxy resin, X = 0, 5%, 10%, 15%, 20%, 25%) with high adhesive strength on saturated concrete substrate were designed and synthesized. The chemical structures of the CE-X were confirmed by proton nuclear magnetic resonance (1H NMR), carbon-13 nuclear magnetic resonance spectroscopy (13C NMR), and Fourier transform infrared spectroscopy (FTIR). The thermal property of CE-X was characterized by thermogravimetric analysis (TGA). The adhesive properties were characterized by pull-off tests. Results showed that when the content of catechol–epoxy resin was under 20% by weight, the adhesive strength could be further increased by forming hydrogen bonds and coordination complexes in the interface of coating and saturated concrete of the substrate. When the content of catechol–epoxy resin was above 20% by weight, the pull-off tests showed cohesive failure, and the adhesive strength on saturated concrete substrate reached the maximum value of 4.61 ± 0.8 MPa, which was improved by ~ 3 MPa compared to that of the control sample. The adhesive properties of epoxy coatings on saturated concrete substrate could be improved by adding a proper amount of catechol groups. In addition, when it was immersed in water for 30 and 120 days, its adhesive strength was reduced by about 7.8% and 22%, respectively. This work provides a new method for designing and synthesizing protective coatings with high adhesive strength on the saturated concrete substrate.

Novel sulfonated polyimide-nafion nanocomposite membranes: Fabrication, morphology and physiochemical investigations for fuel cell applications

Herein, Nafion/sulfonated polyimide (SPI-x) composite membranes have been fabricated using different ratios of Nafion and SPI. The SPI was synthesized using 1, 4, 5, 8-Napthalenetetracarboxylic dianhydride (NTDA) via a one-step high-temperature imidization method in an inert atmosphere. The incorporation of SPI membrane with ion exchange capacity (IEC) of about 1.0 mmol−1 in Nafion showed improvement in physicochemical properties, such as IECs, hydrolytic/oxidative stability, water uptake, and dimensional changes (3.61). Nafion/SPI-x composite membranes showed good proton exchange nature i.e. proton conductivity and thermal stability. Scanning electron micrographs (SEM) reveals that the Nafion/SPI-x nanocomposites membranes display well defined micro-phase separation morphology based on SPI content in the composites. Fourier-transform infrared spectroscopy (FT-IR) confirmed the presence of important functional groups in synthesized membranes. The protons present in membranes were studied by nuclear magnetic resonance (1H NMR) spectroscopy, carbon-13 nuclear magnetic resonance (13C NMR) spectroscopy, and X-ray diffraction analysis (XRD) investigated the nature of polymer material. The thermal stability of the synthesized membranes was found up to be 500–550 °C by thermogravimetric analysis (TGA), a clear indication of good thermal stability of synthesized membranes. Among all Nafion/SPI composites with 60 and 80 wt.% of SPI show good morphology for membranes because of cross-linking between Nafion and SPI. In conclusion, the findings revealed that Nafion/SPI-x membrane could be used as a polymer electrolyte membrane (PEM) for direct methanol fuel cells (DMFCs) applications.