Synthesis, characterization and applications of copper(II) complexes with Schiff bases derived from chitooligosaccharide and iodosubstituted salicylaldehyde

Advances in the preparation, characterization, and biological functions of chitosan oligosaccharide derivatives: A review

Chitosan oligosaccharide (COS), which represent the positively charged basic amino oligosaccharide in nature, is the deacetylated and degraded products of chitin. COS has become the focus of intensive scientific investigation, with a growing body of practical and clinical studies highlighting its remarkable health-enhancing benefits. These effects encompass a wide range of properties, including antibacterial, antioxidant, anti-inflammatory, and anti-tumor activities. With the rapid advancements in chemical modification technology for oligosaccharides, many COS derivatives have been synthesized and investigated. These newly developed derivatives possess more stable chemical structures, improved biological activities, and find applications across a broader spectrum of fields. Given the recent interest in the chemical modification of COS, this comprehensive review seeks to consolidate knowledge regarding the preparation methods for COS derivatives, alongside discussions on their structural characterization. Additionally, various biological activities of COS derivatives have been discussed in detail. Lastly, the potential applications of COS derivatives in biomedicine have been reviewed and presented.

Synthesis and Characterization of Slow-Release Chitosan Oligosaccharide Pyridine Schiff Base Copper Complexes with Antifungal Activity

Herein, a series of chitosan oligosaccharide copper complexes modified with pyridine groups (CPSx-Cu complexes) were successfully prepared via the Schiff base reaction and ion complexation reaction for slow-release fungicide. The structures of the synthesized derivatives were characterized via Fourier transform infrared spectroscopy and 1H and 13C nuclear magnetic resonance spectroscopy, and the unit configuration of the complexes was calculated using Gaussian software. The slow-release performance experiment demonstrated that the cumulative copper ion release rate of CPSx-Cu complexes was dependent on the type of substituents on the pyridine ring. Furthermore, the in vitro and in vivo antifungal activities of the CPSx-Cu complexes were investigated. At a concentration of 0.4 mg/mL, CPSx-Cu complexes completely inhibited the growth of Pythium vexans and Phytophthora capsici. Results indicated that CPSx-Cu complexes with slow-release ability exhibited better antifungal activity than thiodiazole-copper and copper sulfate basic. This study confirmed that combining chitosan oligosaccharide with bioactive pyridine groups and copper ions is an effective approach to further developing slow-release copper fungicides, providing new possibilities for the application of copper fungicides in green agriculture. This study lays the foundation for further studies on biogreen copper fungicides.

Chitosan-based Schiff bases: Promising materials for biomedical and industrial applications

There is plenty of scope for modifying chitosan, an only polycationic natural polysaccharide, owing to its reactive functional groups, namely hydroxyl and amino groups. Although innumerable numbers of chitosan derivatives have been synthesized by modifying these groups and reported elsewhere, in this review article, an attempt has been exclusively made to demonstrate the syntheses of various chitosan-based Schiff bases (CSBs) simply by allowing the reactions of reactive amino groups of chitosan with different aldehydes/ketones of interest. Due to their very peculiar and unique characteristics, such as biodegradability, biocompatibility, metal-binding capability, etc., they are found to be very useful for diversified applications. Thus, we have also attempted to showcase their very specific biomedical fields, including tissue engineering, drug delivery, and wound healing, to name a few. In addition, we have also discussed the utilization of CSBs for industrial applications such as wastewater treatment, catalysis, corrosion inhibition, sensors, etc.

Synthesis of acylated derivatives of chitosan oligosaccharide and evaluation of their potential antifungal agents on Fusarium oxysporum

Chitosan oligosaccharide (COS) is an important carbohydrate-based biomaterial for synthesizing candidate drugs and biological agents. This study synthesized COS derivatives by grafting acyl chlorides of different alkyl chain lengths (C8, C10, and C12) onto COS molecules and further investigated their physicochemical properties and antimicrobial activity. The COS acylated derivatives were characterized using Fourier transform infrared spectroscopy, ¹H nuclear magnetic resonance spectroscopy, X-ray diffraction, and thermogravimetric analysis. COS acylated derivatives were successfully synthesized and possessed high solubility and thermal stability. As for the evaluation of antibacterial activity, COS acylated derivatives did not significantly inhibit Escherichia coli and Staphylococcus aureus, but they significantly inhibited Fusarium oxysporum, which was superior to that of COS. Transcriptomic analysis revealed that COS acylated derivatives exerted antifungal activity mainly by downregulating the expression of efflux pumps, disrupting cell wall integrity, and impeding normal cell metabolism. Our findings provided a fundamental theory for the development of environmentally friendly antifungal agents.

Effects of Octenyl-Succinylated Chitosan-Whey Protein Isolated on Emulsion Properties, Astaxanthin Solubility, Stability, and Bioaccessibility

The synthesis of octenyl-succinylated chitosan with different degrees of substitution resulting from chemical modification of chitosan and controlled addition of octenyl succinic acid was investigated. The modified products were characterized using 1H NMR, FTIR, and XRD, and the degree of substitution was also determined. The properties of the modified chitosan oligosaccharide in solution were evaluated by surface tension and dye solubilization, finding that the molecules self-assembled when they are above the critical aggregation concentration. The two methods yielded consistent results, showing that the self-assembly was reduced with higher levels of substitution. The antimicrobial activity of the octanyl-succinylated chitosan oligosaccharide (OSA-COS) derivatives against Staphylococcus aureus, Escherichia coli, and Fusarium oxysporum f.sp cucumerinum was investigated by the Oxford cup method. While the acetylated COS derivatives were not significantly effective against either E coli or S. aureus, they showed significant antifungal activity toward F. oxysporum that was superior to that of COS. The modified product was found to form a stable emulsion when mixed with whey protein isolate. The emulsion formed by the highly substituted derivatives have a certain stability and loading efficiency, which can be used for the encapsulation and delivery of astaxanthin.

Preparation and antimicrobial mechanism of Maillard reaction products derived from ε-polylysine and chitooligosaccharides

Chitooligosaccharides can be combined with amino acids or polypeptide to form Maillard reaction products (MRPs) with the antibacterial characteristics through Maillard reaction. This research aims to clarify the structure, antimicrobial effect and mechanism against Shewanella putrefaciens (S. putrefaciens) of ε-polylysine and chitooligosaccharides Maillard reaction products (LC-MRPs). The results of intrinsic fluorescence (IF) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction, proton nuclear magnetic resonance (¹H NMR) spectra and scanning electron microscope (SEM) indicated Maillard reaction occurred between ε-polylysine and chitooligosaccharides. The observation of confocal laser scanning microscopy (CLSM), SEM and growth curves of S. putrefaciens evidenced that LC-MRPs have the strongest antibacterial effects. The leakage of alkaline phosphatase (AKP) and lactate dehydrogenase (LDH) implied that LC-MRPs sabotaged bacterial barrier (cell wall and cell membrane). The changes in content of nucleic acids, reactive oxygen species (ROS) level, lipid peroxidation content (LPO), succinate dehydrogenase (SDH) activity and adenosine triphosphate (ATP) content showed LC-MRPs will affect bacterial genetic gene transcription, material and energy metabolism. Therefore, the LC-MRPs were effective antibacterial agents to inhibit S. putrefaciens, which will help to preserve food with S. putrefaciens as the main spoilage bacteria.

Effects of ε-polylysine and chitooligosaccharide Maillard reaction products on quality of refrigerated sea bass fillets

BACKGROUND

The Maillard reaction is a promising and safe method for obtaining chitooligosaccharide conjugates with proteins or peptides as food preservatives. This study aims to investigate the moisture state, physicochemical properties, and shelf-life of sea bass fillets treated with ε-polylysine (ε-PL) and chitooligosaccharides (COS), which are Maillard reaction products (LC-MRPs), during refrigerated storage.

RESULTS

The results of microbiological analysis and confocal laser scanning microscope (CLSM) revealed that LC-MRPs could retard microbial growth effectively. Compared with control, other treated groups could strongly retard the increase in the thiobarbituric acid (TBA) value, the K-value and the total volatile basic nitrogen (TVB-N) value, and also inhibited the softening of texture and the accumulation of biogenic amines in fish. The results of low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) indicate that LC-MRPs could delay the water migration of fillets and increase water holding capacity (WHC). Through sensory evaluation, the application of LC-MRPs increased the shelf-life of refrigerated sea bass fillets for another 9 days.

CONCLUSION

Maillard reaction products derived from chitooligosaccharides and ε-polylysine have strong potential for preserving sea bass. © 2022 Society of Chemical Industry.

Cu(II) Complexes with Proline-Derived Schiff Base Ligand: Chemical Resolution of N,C-Unprotected α-Amino Acids and Their Antibacterial Activity

An operationally simple and convenient resolution method via Cu(II) complexes was reported, efficiently providing valuable enantiopure N,C-unprotected α-amino acids. This protocol features synthetically attractive yields and a stereochemical outcome, using a recyclable Schiff base ligand and inexpensive easily accessible metal copper salts. These novel Cu(II) complexes can be obtained in an enantiopure state by means of column chromatography or recrystallization. Furthermore, all the Cu(II) complexes were evaluated for their antibacterial activities. Among them, complexes (S,2S)-3a, (S,2S)-3g, and (S,2S)-3o showed significant antibacterial activities against Staphylococcus aureus Mu50. Further biological evaluation indicated that they were effective against most of Gram-positive bacteria. It is the first study on the biological activities of transition metal complexes with this type of proline-derived Schiff base ligand.

Synthesis of novel chitosan Schiff base and its ZnO nanocomposite for removal of synthetic dye, antimicrobial, and cytotoxicity activity

In this work, a novel chitosan Schiff base 4-(2-Hydroxyaniline)pent-3-en-2-one chitosan (2-HyA-CS) and its ZnO nanocomposite (2-HyA-CS/ZnO) were sensitized and characterized by appropriate methods; FTIR, XRD, Elemental analysis, SEM, TEM and TGA. The result of characterization methods confirms the preparation of 2-HyA-CS and 2-HyA-CS/ZnO. The SEM images reveal that chitosan, 2-HyA-CS, and 2-HyA-CS/ZnO have a varied roughness and porous surfaces. The reason for this difference was attributed to the formation of Schiff base 2-HyA-CS and the presence of ZnO nanoparticles in 2-HyA-CS/ZnO. The patterns of XRD and FTIR confirm the formation of 2-HyA-CS and 2-HyA-CS/ZnO. The degree of substitution (DS) of modified chitosan 2-HyA-CS was calculated using Elemental analysis and FTIR.ATR, it was found to be 74%. The adsorption efficiency of the produced adsorbents was compared with pure chitosan to remove of Remazol Brilliant Blue R (RBBR) from an aqueous medium and antimicrobial activity. The removal percentage of RBBR by chitosan, 2-HyA-CS, and 2-HyA-CS/ZnO are 47.12%, 91.9%, and 96.56%, respectively with the following order: 2-HyA-CS/ZnO > 2-HyA-CS > chitosan. Their antimicrobial activities were studied against two Gram negative bacteria ( E. coli and P. aeruginosa), two Gram positive bacteria ( S. aureus and B. cereus) and ( C. albicans) as a yeast strain, the inhibitory zone measurements revealed that the activity of 2-HyA-CS/ZnO is excellent and higher than 2-HyA-CS and pure chitosan. The cytotoxicity of the prepared compound 2-HyA-CS and 2-HyA-CS/ZnO along with pure chitosan was estimated against two human cancer cells MCF-7 cells and HepG-2 cells, the result indicates that 2-HyA-CS/ZnO having higher Inhibitory activity against both MCF-7 and HepG-2 cells with 53.5 ± 2.86 and 27.4 ± 1.23 µg/mL respectively and 2-HyA-CS possessing moderate Inhibitory activity against both MCF-7 and HepG-2 cancer cells with IC50 = 216.5 ± 7.48 and 135.6 ± 6.49 µg/ml respectively.

Synthesis of new chitosan Schiff base and its Fe2O3 nanocomposite: Evaluation of methyl orange removal and antibacterial activity

New chitosan Schiff base (3EtO-4OH/Chit) and its 3EtO-4OH/Chit/Fe₂O₃ nanocomposite were synthesized and characterized by FTIR, ¹H NMR, XRD, TGA, DSC and SEM. The result confirmed the preparation of 3EtO-4OH/Chit and its 3EtO-4OH/Chit/Fe₂O₃ nanocomposite. The efficiency of the prepared catalysts was studied for the methyl orange (MO) removal from aqueous solution. The effect of adsorbent dose and contact time on the removal of dye has been studied. Their antibacterial activities were considered against two Gram positive (S. aureus and B. cereus) and two Gram negative (E. coli and P. aeruginosa) bacteria and the results showed that the activity of the 3EtO-4OH/Chit/Fe₂O₃ is excellent and is more than chitosan and 3EtO-4OH/Chit. Thermogravimetry studies shows that the weight loss stages and the residual value at 600 °C are different for the two compounds. DSC curve of the title compounds 3EtO-4OH/Chit and 3EtO-4OH/Chit/Fe₂O₃ is different from each other. The reason for this difference could be due to the presence of iron oxide nanoparticles in 3EtO-4OH/Chit/Fe₂O₃.

N, P-co-doped carbon dots as a dual-mode colorimetric/ratiometric fluorescent sensor for formaldehyde and cell imaging via an aminal reaction-induced aggregation process

Novel colorimetric and ratiometric fluorometric dual-mode N, P-co-doped carbon nanodots, BPEI-CDs, for highly sensitive and selective detection of formaldehyde (FA) were successfully prepared from N-(phosphonomethyl)iminodiacetic acid (PMIDA) and branched polyethyleneimine (BPEI). The treatment of FA caused a remarkable linear enhancement of ratiometric fluorescence (F_501 nm/F_408 nm) in a wide range of 0-40 μM with a detection limit (LOD) of 0.47 μM (3σ/k), along with distinct color changes from colorless to light yellow. Mechanistic study shows that this electron-rich system, formed by the cooperative roles of N and P, promoted the FA-induced Schiff bases formation reaction, which contributed to the CD aggregation-induced emission (AIE) "turn-on" response and enhancement of π-conjugation-induced bathochromic behaviors. Furthermore, N, P-co-doped BPEI-CDs were successfully applied to the determination of FA in bean sprout samples. Using the standard addition method, the recoveries ranged from 96.9 to 101.8%, and the relative standard deviation (RSD) was in the range 2.23 to 3.21%. The application for intracellular FA sensing further verified that this novel nanoprobe may offer a new venue for the design of simple, low-cost, and sensitive biosensors. Graphical abstract.