Schiff Base Formation Research Articles

Polysaccharide-Based Self-Healing Hydrogel for pH-Induced Smart Release of Lauric Acid to Accelerate Wound Healing.

It is highly desirable yet significantly challenging to fabricate an injectable, self-healing, controlled-release wound dressing that is responsive to the alkaline pH of the wounds. Herein, we propose a facile approach to prepare pH-responsive chitosan-oxidized carboxymethyl cellulose (CS-o-CMC) hydrogel constructs in which gelation was achieved via electrostatic and Schiff base formation. Importantly, the Schiff base was formed in acidic medium and the final pH of pregel solution was intrinsically raised to 7.0-7.4 due to the cross-linking by β-glycerol phosphate. The self-healing behavior of the hydrogel was an enthalpy-driven process and efficient in alkaline compared to acidic pH. The pH responsiveness offered a controlled release of lauric acid (LA) from CS-o-CMC/LA hydrogel and regulated the M2 polarization. Overall, reduction in inflammation led to rapid vascularization, reepithelialization, and significantly accelerated wound healing in rats. Our findings demonstrate a promising strategy for developing injectable, immunomodulatory wound dressings tailored to the challenging environment of wounds.

Recent advances in modifications, biotechnology, and biomedical applications of chitosan-based materials: A review.

Chitosan, a natural polysaccharide with recognized biocompatibility, non-toxicity, and cost-effectiveness, is primarily sourced from crustacean exoskeletons. Its inherent limitations such as poor water solubility, low thermal stability, and inadequate mechanical strength have hindered its widespread application. However, through modifications, chitosan can exhibit enhanced properties such as water solubility, antibacterial and antioxidant activities, adsorption capacity, and film-forming ability, opening up avenues for diverse applications. Despite these advancements, realizing the full potential of modified chitosan remains a challenge across various fields. The purpose of this review article is to conduct a comprehensive evaluation of the chemical modification techniques of chitosan and their applications in biotechnology and biomedical fields. It aims to overcome the inherent limitations of chitosan, such as low water solubility, poor thermal stability, and inadequate mechanical strength, thereby expanding its application potential across various domains. This review is structured into two main sections. The first part delves into the latest chemical modification techniques for chitosan derivatives, encompassing quaternization, Schiff base formation, acylation, carboxylation, and alkylation reactions. The second part provides an overview of the applications of chitosan and its derivatives in biotechnology and biomedicine, spanning areas such as wastewater treatment, the textile and food industries, agriculture, antibacterial and antiviral activities, drug delivery systems, wound dressings, dental materials, and tissue engineering. Additionally, the review discusses the challenges associated with these modifications and offers insights into potential future developments in chitosan-based materials. This review is anticipated to offer theoretical insights and practical guidance to scientists engaged in biotechnology and biomedical research.

Conformational versatility among crystalline solids of L-phenylalanine derivatives.

In this study, we present a new N-derivative of L-phenylalanine with 2-naphthaldehyde (PN), obtained by the Schiff base formation procedure and its subsequent reduction. This compound was crystallized as a zwitterion {2-[(naphthalen-2-ylmethyl)azaniumyl]-3-phenylpropanoate, C20H19NO2}, as an anion in a sodium salt (catena-poly[[diaquasodium(I)-di-μ-aqua] 2-[(naphthalen-2-ylmethyl)amino]-3-phenylpropanoate monohydrate], {[Na(H2O)4](C20H18NO2)·H2O}n), as a cation in a chloride salt [(1-carboxy-2-phenylethyl)(naphthalen-2-<!?tlsb=-0.2pt>ylmethyl)azanium chloride acetic acid monosolvate, C20H20NO2+·Cl-·CH3COOH], and additionally acting as a ligand in the pentacoordinated zinc compound aquabis{2-[(naphthalen-2-ylmethyl)amino]-3-phenylpropanoato-κO}zinc(II), [Zn(C20H18NO2)2(H2O)] or [Zn(PN)2(H2O)], denoted (PN-Zn), with the amino acid derivative in its carboxylate form. Interestingly, both enantiomers of the zinc complex co-exist within the crystalline structure, one constructed by the ligands with the L (or S) configuration and the other with the ligands having the D (or R) configuration, represented as L,L-PN-Zn and D,D-PN-Zn, respectively. Also, in the structure of the zwitterion, the racemate L,D is observed. These results imply that chirality inversion of the amino acid derivative synthesized from enantiomerically pure L-phenylalanine is taking place, a phenomenon known as oscillatory transenantiomerization. The analysis of these crystal structures reveals that they are primarily stabilized through electrostatic interactions assisted by hydrogen bonds. An interesting finding is that the conformation of PN varies along this family: it is unfolded in the zwitterionic and cationic forms, and folded in the anionic form. To evaluate such conformational differences, we propose the use of a dimensionless Shape Factor quantity defined as the Structural Aspect Ratio (SAR), computed from the geometrical features of the parallelepiped that tightly encloses a conformer constructed by rigid spheres. This parameter provides a simple but useful tool to distinguish conformational differences, providing insights that complement traditional structural analyses. The study of the structural features, conformational diversity, chirality and supramolecular properties of these compounds is also supported by density functional theory (DFT) calculations.

Synthetic Strategies for the Development of Ibuprofen Derivatives: A Classified Study.

Ibuprofen, a widely used NSAID from the aryl propionic acid class, effectively relieves pain, fever, and inflammation. On prolonged use, it leads to gastrointestinal, hepatic, and renal toxicities, particularly gastrointestinal ulcers. These side effects are largely attributed to the carboxylic acid functional group common to NSAIDs. The present review highlights the different modifications done to the carboxylic group in Ibuprofen, by various researchers such as estersgramma, amides, hydroxamic acids, and N-substituted hydrazides, along with the integration of heterocyclic moieties like triazoles, tetrazoles, and oxadiazoles. Additionally, Ibuprofen has been hybridized with other drugs and complexed with metals to enhance therapeutic effects. The different synthetic strategies that were employed were esterification, amidation, condensation, Schiff's base formation, etc. These modifications have resulted in derivatives with antimicrobial, antifungal, anticancer, and other biological activities, aiming to reduce side effects while retaining or enhancing antiinflammatory, analgesic, and antipyretic properties.

Cooking‐Induced Lipid–Protein Oxidation in Kavurma (a Cooked Meat Product)

Optimizing the nutritional quality of cooked meat requires a better understanding of the mechanisms responsible for lipid–protein changes caused by cooking. In this study, the aim was to determine the levels of protein–lipid oxidation that could occur during the kavurma production process. For this purpose, cooking was performed at 100°C for 30, 60, 90, and 120 min, and protein oxidation was determined by measuring carbonyl content, sulfhydryl (S‐H) group levels, and Schiff base formation, while lipid oxidation was assessed by measuring thiobarbituric acid reactive substances (TBARS), peroxide, p‐anisidine, and free fatty acid (FFA) values. Also, the changes in protein structure were identified by Fourier‐transform infrared spectroscopy (FT‐IR). Carbonyl, formation of Schiff bases, peroxide, p‐anisidine, and FFA values significantly increased throughout the cooking time (p &lt; 0.05). TBARS values showed a significant increase within the first 30 min, followed by a decrease. The level of S‐H groups significantly decreased with increasing cooking time (p &lt; 0.05). FT‐IR analysis of the myofibrillar extract revealed 13 major peaks, with peak areas decreasing depending on the cooking time. Analysis of the secondary structure indicated higher relative intensities of α‐helix and random coil up to 90 min of cooking time. Results indicate that protein–lipid oxidation is dependent on the cooking time, which point out to an effect on the nutritional quality of proteins and lipids in kavurma. Also, these results not only enhance our comprehension of the complex relationship between cooking time and product quality but also present encouraging prospects for fostering healthier and safer cooking methods.

Novel Small Molecule Derived from Hydroxy Naphthaldhyde as Potential Anti-Leukemia Agents: Spectroscopic, DFT, Docking Molecular and ADME/T Investigations

New ligand derived from hydroxy naphthaldhyde (LCAT1) was synthetized and the structure of the formed Schiff base was confirmed by various analytical and spectroscopic methods. Elemental analysis, mass spectrometry and NMR studies confirmed the structure of the ligand. Theoretical calculations (DFT) were performed to study the molecular structure, chemical reactivity and electronic properties of this ligand. This study shows good agreement with the experimental results obtained using infrared spectrometry and UV-visible spectrophotometry. The optimized structure has been used to perform the molecular docking studies. The homology modeling and molecular docking were investigated in order to check their anti-leukemia activities toward several leukemia cells. In addition, in silico ADME/T modeling was employed to evaluate absorption, distribution, metabolism, and excretion pharmacological parameters of the ligand. The DFT study indicates that the evaluated parameters, such as Mulliken charges and molecular orbitals, as well as the MEP results, are consistent with the localization of electrophilic and nucleophilic attack sites. Furthermore, the data indicate significant chemical reactivity associated with low kinetic stability of the ligand. In accordance with the principle of a 90% critical assessment, the homological modeling model used is considered to be the most appropriate. The molecular docking results indicated that our molecule has a strong affinity for DNA by forming hydrogen bonds with the donor’s groups and exhibits a good leukemia activity against cell lines through the formation of strong interaction with their receptors. The results showed high binding energy and remarkable inhibition constants toward receptors 5VOM (−8.03 Kcal/mol, 1. 31 µM), 1NJS (−7.68 Kcal/mol, 2.35 µM), 7JXU. In silico ADME/T modeling showed that the properties of the synthesized ligand are similar to those of the drugs. The predicted toxicity of the ligand reveals that LCAT1 is nontoxic, with no hepatotoxicity, no mutagenicity and no carcinogenicity.

Characterization of the polysaccharide schizophyllan and schizophyllan-chitosan hydrogel formation by diffusing-wave spectroscopy.

Schizophyllan (SPG) is a semi-flexible, triple-helical polysaccharide with attractive properties as an efficient viscosifying compound and biological response modifier. We report microrheological characterization of schizophyllan as dispersed in solution and the changes associated when crosslinked with chitosan over an extended frequency range using diffusing wave spectroscopy (DWS). A SPG with high molecular weight (Mw=1.1×106Da) was selectively oxidized in the side chains (20% or 40%) to promote Schiff base formation with chitosan (CHI) amine groups, thus inducing crosslinking. The microrheological characterization of the dispersed SPG revealed characteristic features of the semiflexible structure, where also coupling between flexure and longitudinal modes was indicated based on scaling coefficient close to 7/8 of the loss modulus G"(ω) vs ω for ω in the range 3×103-105rad/s. The in-situ characterization of the gelation process by DWS revealed changes in the scattered intensity-correlation function caused by the embedded colloidal probe-particles, from which the mean-square displacement of the probes and the shear moduli of the SPG-chitosan hydrogel samples were determined for various SPG concentrations and degrees of oxidation. It is found that SPG - chitosan hydrogels can be prepared with a polymer content in the range of 0.5-2.0mg/mL and that tuning the molecular parameters allowed control of mechanical moduli in soft hydrogels in the range of 0.3Pa up to 1000Pa.

MR1 presents vitamin B6–related compounds for recognition by MR1-reactive T cells

The major histocompatibility complex class I related protein (MR1) presents microbially derived vitamin B2 precursors to mucosal-associated invariant T (MAIT) cells. MR1 can also present other metabolites to activate MR1-restricted T cells expressing more diverse T cell receptors (TCRs), some with anti-tumor reactivity. However, knowledge of the range of the antigen(s) that can activate diverse MR1-reactive T cells remains incomplete. Here, we identify pyridoxal (vitamin B6) as a naturally presented MR1 ligand using unbiased mass spectrometry analyses of MR1-bound metabolites. Pyridoxal, and the related compound, pyridoxal 5-phosphate bound to MR1 and enabled cell surface upregulation of wild type MR1*01 and MR1 expressing the Arg9His polymorphism associated with the MR1*04 allotype in a manner dependent on Lys43-mediated Schiff-base formation. Crystal structures of MR1*01 in complex with pyridoxal and pyridoxal 5-phosphate showed how these ligands were accommodated within the A-pocket of MR1. T cell lines transduced with the 7.G5 TCR, which has reported "pan-cancer" specificity, were specifically activated by pyridoxal presented by antigen-presenting cells expressing MR1*01 and MR1 allotypes bearing the less common Arg9His polymorphism. 7.G5 T cells also recognized, to a lesser extent, pyridoxal 5-phosphate and, importantly, recognition of both vitamers was blocked by an anti-MR1 antibody. 7.G5 TCR reactivity toward pyridoxal was enhanced when presented by the Arg9His polymorphism-bearing MR1 allotypes. Vitamin B6, and vitamers thereof, have been associated with various cancers, and here we describe a link between this ligand, MR1, and its allomorphs, and the pan-cancer 7.G5 TCR. This work identifies an MR1 ligand that can activate a diverse MR1-restricted TCR.

Fibrillar Hydrogel Inducing Cell Mechanotransduction for Tissue Engineering.

One of the key strategies for tissue engineering is to design multifunctional bioinks that balance printability with cytocompatibility. Here, we describe fibrillar hydrogels produced by Schiff base formation between B-type gelatin and oxidized sodium alginate, followed by the incorporation of type I collagen, yielding a new gel (MyoColl). The resulting hydrogel exhibits a temperature- and mass-ratio-dependent sol-gel transition, showing variability of hydrogel properties depending on the component ratio. MyoColl composition provides a convenient platform for biofabrication in terms of shear thinning, yielding, Young's modulus, and shape accuracy. Metabolic activity tests and fluorescent microscopy of 2D hydrogel-based mouse C2C12 myoblast cell culture show significant cytocompatibility of the developed carriers. In addition, primary signs of cell mechanotransduction and myofilament formation of 3D printed MyoColl-based cell cultures were detected and described. Due to these promising results, the described hydrogel composition has shown itself as a convenient platform for muscle tissue engineering.

Schiff-Base Cross-Linked Hydrogels Based on Properly Synthesized Poly(ether urethane)s as Potential Drug Delivery Vehicles in the Biomedical Field: Design and Characterization.

In situ-forming hydrogels based on the Schiff-base chemistry are promising for drug delivery applications, thanks to their stability under physiological conditions, injectability, self-healing properties, and pH-responsiveness. In this work, two water-soluble poly(ethylene glycol)-based poly(ether urethane)s (PEUs) were engineered. A high-molecular-weight PEU (SHE3350, M̅ n 24 kDa, D 1.7), bearing primary amino groups along each polymeric chain, was synthesized using N-Boc serinol and subjected to an acidic treatment to expose primary amines (ca. 1020 units/gSHE3350). In parallel, a low-molecular-weight PEU (AHE1500, M̅ n 4 kDa, D 1.5) with aldehyde end groups was synthesized by end-capping an isocyanate-terminated prepolymer with 4-hydroxybenzaldehyde, and the aldehyde groups were quantified to be around 1020 units/gAHE1500. Hydrogels were prepared by simply mixing SHE3350 and AHE1500 aqueous solutions and characterized to assess their physico-chemical and rheological properties. Schiff-base bond formation was proved through carbon-13 and proton solid-state NMR spectroscopies. Rheological characterization confirmed the formation of gels with high resistance to applied strain (ca. 1000%). Hydrogels exhibited high absorption ability (ca. 270% increase in wet weight) in physiological-like conditions (i.e., 37 °C and pH 7.4) up to 27 days. In contact with buffer at pH 5, enhanced fluid absorption was observed until dissolution occurred starting from 13 days due to Schiff-base hydrolysis in acidic conditions. Conversely, gels showed a reduced absorption ability at pH 9 due to shrinkage phenomena. Furthermore, they exhibited high permeability and controlled, sustained, and pH-triggered release of a model molecule (i.e., fluorescein isothiocyanate dextran) for up to 17 days. Lastly, the hydrogels showed easy injectability and self-healing ability.

Synergistic catecholamine and coordination chemistry for enhanced bioactivity and secondary grafting activity of zirconia dental implants

The inherent bioinertness of zirconia (ZrO2) hinders its early bone integration, presenting a significant obstacle to its widespread use in dental implant technologies. Addressing this, we developed a surface coating leveraging the synergistic effects of catecholamine and coordination chemistry inspired by the mussel byssus cuticle. This coating, named PDPA@Sr, is enriched with strontium ions and amine groups, resulting from a simple immersion of polydopamine (PD)-coated ZrO2 in an alkaline strontium chloride and poly(allylamine) (PA) solution. Compared to conventional mussel-inspired PD coatings, PDPA@Sr demonstrates enhanced aesthetic properties and mechanical stability. The continuous release of strontium ions from the coating significantly enhances osteogenesis, while the abundant surface amine groups offer notable antibacterial effects. More importantly, these amine groups also enable a variety of chemical modifications, including electrostatic adsorption, carbodiimide chemistry, Michael addition, Schiff base formation, and click chemistry, thus providing a multifaceted platform for the advanced surface modification of ZrO2 implants.

Cinnamaldehyde release behavior of Pickering emulsion synergistically stabilized by Sapindus mukorossi modified palygorskite and chitosan

Most of the studies are committed to explore the natural green stabilizer or bio-stabilizer to design biocompatible Pickering emulsion, while few works focus on developing a dynamic interfacial regulatory effect for the slow-release of active molecules from Pickering emulsion. Herein, Pickering emulsion was fabricated for the controlled release of cinnamaldehyde, which was synergistically stabilized by palygorskite modified with the active ingredients leached from Sapindus mukorossi and chitosan. The results showed that the interfacial cross-linking between chitosan and cinnamaldehyde took place at the oil-water interface based on the formation of Schiff base, while the modified palygorskite was adsorbed onto the oil-water interface to co-stabilize Pickering emulsion. The simulated gastrointestinal experiment indicated that the emulsion was stable in simulated gastric fluid (SGF) of pH 1.5, and then destroyed in simulated intestinal fluid (SIF) of pH 6.8 to realize the continuous release of cinnamaldehyde, where the amount of chitosan played a vital role. Furthermore, the antibacterial test showed that the growth of Escherichia coli and Staphylococcus aureus was almost completely suppressed when the concentration of Pickering emulsion was 25 µL/mL. Therefore, this study developed a facile strategy to regulate the controlled release of cinnamaldehyde based on green Pickering emulsion.

Development of Ribityllumazine Analogue as Mucosal-Associated Invariant T Cell Ligands.

Mucosal-associated invariant T (MAIT) cells are a subset of innate-like T cells abundant in human tissues that play a significant role in defense against bacterial and viral infections and in tissue repair. MAIT cells are activated by recognizing microbial-derived small-molecule ligands presented by the MHC class I related-1 protein. Although several MAIT cell modulators have been identified in the past decade, potent and chemically stable ligands remain limited. Herein, we carried out a structure-activity relationship study of ribityllumazine derivatives and found a chemically stable MAIT cell ligand with a pteridine core and a 2-oxopropyl group as the Lys-reactive group. The ligand showed high potency in a cocultivation assay using model cell lines of antigen-presenting cells and MAIT cells. The X-ray crystallographic analysis revealed the binding mode of the ligand to MR1 and the T cell receptor, indicating that it forms a covalent bond with MR1 via Schiff base formation. Furthermore, we found that the ligand stimulated proliferation of human MAIT cells in human peripheral blood mononuclear cells and showed an adjuvant effect in mice. Our developed ligand is one of the most potent among chemically stable MAIT cell ligands, contributing to accelerating therapeutic applications of MAIT cells.

Chemical Capture and Sensing of Bovine Serum Albumin with Phenothiazinylcarbaldehyde-Labeled 2′-Deoxyuridine

AbstractChemical-capture-mediated sensing has had a great impact on proteomic research. Toward this end, we demonstrate the chemical trapping of BSA by the reactive formyl functionality of a newly developed fluorescent nucleoside probe, formylphenothiazine-labeled-2′-deoxyuridine. The probe is capable of trapping BSA via Schiff base formation leading to fluorescence ‘switch-on’ sensing with a large hypsochromic shift of ca. 100 nm. The α-amylase does not show any significant change in fluorescence response, demonstrating the efficiency of the probe in selective sensing of BSA. Docking studies suggest the preferential interaction of the phenothiazinylcarbaldehyde-labeled dU with the residual amino acids in site I of the BSA protein as compared to site II.

Acidic dimethyl sulfoxide: A solvent system for the fast dissolution of pectin derivatives suitable for subsequent modification

This study investigates the use of dimethyl sulfoxide (DMSO) as a solvent for the dissolution and subsequent chemical modification of various pectin derivatives. DMSO was found to effectively dissolve low-methoxy pectin, high-methoxy pectin, polygalacturonic acid hydrazide, pectin amide, and polygalacturonic hydroxamic acid when the negative charges on the polysaccharide backbone were neutralized with organic acids. The dissolution process was further enhanced by increasing the temperature, although higher temperatures also promoted chain cleavage. The dissolved pectin derivatives were successfully modified through transesterification and Schiff base formation, demonstrating the potential of acidic DMSO as a non-toxic and cost-effective solvent system for homogeneous pectin chemistry. The study opens new possibilities for the functionalization of pectin in various industrial and biomedical applications.

Comparison of protein immobilization methods with covalent bonding on paper for paper-based enzyme-linked immunosorbent assay

In this study, two methods were examined to optimize the immobilization of antibodies on paper when conducting a paper-based enzyme-linked immunosorbent assay (P-ELISA). Human IgG, as a test-capture protein, was immobilized on paper via the formation of Schiff bases. Aldehyde groups were introduced onto the surface of the paper via two methods: NaIO4 and 3-aminopropyltriethoxysilane (APTS) with glutaraldehyde (APTS-glutaraldehyde). In the assay, horseradish peroxidase-conjugated anti-human IgG (HRP-anti-IgG) binds to the immobilized human IgG, and the colorimetric reaction of 3,3′,5,5′-tetramethylbenzyzine (TMB) produces a blue color in the presence of H2O2 and HRP-anti-IgG as a model analyte. The immobilization of human IgG, the enzymatic reaction conditions, and the reduction of the chemical bond between the paper surface and immobilized human IgG all were optimized in order to improve both the analytical performance and the stability. In addition, the thickness of the paper was examined to stabilize the analytical signal. Consequently, the APTS-glutaraldehyde method was superior to the NaIO4 method in terms of sensitivity and reproducibility. Conversely, the reduction of imine to amine with NaBH4 proved to exert only minimal influence on sensitivity and stability, although it tended to degrade reproducibility. We also found that thick paper was preferential when using P-ELISA because a rigid paper substrate prevents distortion of the paper surface that is often caused by repeated washing processes.

Synergistic Pd(OAc)2/CuI-catalyzed alkynylation of β-lactam derivative via Sonogashira coupling

Herein, a novel approach of bimetallic Pd(OAc)2/CuI-catalyzed alkynylation of 3-chloroazetidin-2-one (β-lactam derivative) with terminal alkyne via tandem C–C bond activation/Sonogashira-type cross-coupling reaction is developed. This synthesis encompasses a sequence of inert Csp3–X/Csp–H functionalization processes involving the coupling of the C(sp3) adjacent to the 3-chloroazetidin-2-one with the C(sp) of a terminal alkyne. The final analogs are synthesized by means of the indole-benzothiazole Schiff base formation, cyclization of the Schiff base to generate the β-lactam derivative, and Sonogashira coupling to afford a C(sp3)–C(sp) bond. In addition, indole, benzothiazole, and azetidine-2-one have been identified to be highly efficient heterocyclic scaffolds with a range of pharmacological benefits. It encouraged us to discover a hybrid compound that had each of these moieties. Cooperation between two different metals is essential for the successful implementation of this approach. Specifically, the interaction between the Pd and Cu centers in the transmetallation step is depicted through a plausible mechanistic route. The reaction conditions have been optimized by varying catalyst and ligand loadings, bases, temperatures, and solvents. The reaction is highly efficient, yielding alkynylated products in up to 84 % yield with a wide range of substrates and functional group tolerance, thereby serving as a functional model for the Sonogashira coupling reaction.

Ambroxol Hydrochloride: A Comprehensive Review on Industrial‐Scale Synthesis, Pharmacological Aspects &amp; Therapeutic Applications

AbstractAmbroxol hydrochloride is a pharmaceutical compound that is primarily used to treat respiratory disorders characterized by excessive mucus production. It is a mucolytic agent used in treating various respiratory conditions, including bronchitis, asthma, COPD (Chronic Obstructive Pulmonary Disease), and cystic fibrosis. The standard industrial‐scale synthesis involves Schiff's base formation followed by reduction; this method is widely adopted due to its efficiency and cost‐effectiveness. Apart from this, various patented methodologies have emerged recently, along with novel therapeutic applications, where it is used for treating Parkinson's and Alzheimer's diseases, including anti‐inflammatory and antioxidant properties. These findings open new avenues for its use in various medical treatments. The current review aims to assess the industrial scale processes in the current market, examine its pharmacological action, and explore recently evaluated therapeutic applications, offering a comprehensive overview of its potential in modern medicine.

The Synthesis of Melamine Cored Schiff Bases and Investigation of Heteronuclear Metal Complexes

In this study, 2,4,6-triamino-s-triazine (melamine) is the starting material. The condensation reaction of melamine and 4-hydroxybenzaldehyde resulted in the formation of the monopodal Schiff base. An oxygen-bridged monopodal complex of [(Fe(III)Salophen)Cl] ligand complex with monopodal Schiff base ligand was then obtained. Tripodal Schiff base ligand was obtained by condensing 2-hydroxybenzaldehyde with a monopodal complex and this ligand in some transition metal complexes were synthesized. As a result, the ligand and complexes of this ligand were isolated, as well as elemental analyses, FT-IR, 1H-NMR, TGA and magnetic susceptibility measurements of the obtained compounds were taken to elucidate their structures.

Gelatin film cross-linked with laccase-catalyzed purple cauliflower extract and coated with Zn-carbon dots exhibits excellent physicochemical properties and functionality for intelligent and active packaging

Preparation of oxidized purple cauliflower extract (OPE) was conducted by laccase oxidation and served as a reinforcing agent for enhancing physicochemical properties of gelatin (Gel) films. Chitosan (CS) loaded with biowaste-derived Zn-carbon dots (Zn-CD) coating further enhanced the functionality and stability of Gel/OPE film. Structural characterization revealed that OPE and Gel form Schiff base bonds and hydrogen bonds. After the formation of CS/Zn-CD coating, hydrogen bonds formed between CS and Zn-CD, and CS and Gel were closely bonded through electrostatic interactions and hydrogen bonding. OPE crosslinking and CS/Zn-CD coating improve mechanical, barrier properties and water resistance of Gel films. CS/Zn-CD coating improved antibacterial and antioxidant ability and illumination stability of composite film, effectively reflected the freshness of salmon during storage. Hence, the functional Gel films developed in this study is hopeful candidate for intelligent and active food packaging application.