Schiff Base Research Articles

Polymeric Schiff base containing phenylhydrazine and 2-thiobarbituric acid: Synthesis, characterization, antibacterial and antifungal studies

Polymeric Schiff base ligand (MFT) derived from 2-hydroxyacetophenone, phenylhydrazine, formaldehyde, and 2-thiobarbituric acid was synthesized via condensation reaction. The synthesized MFT ligand was complexed with the metal acetates of Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) to form a polymeric Schiff base-metal complexes. The ligand and its metal polychelates were characterized by Fourier transform infra red (FT-IR), Ultraviolet-visible spectroscopy (UV-vis.), X-ray diffraction (XRD), Proton nuclear magnetic resonance spectroscopy (1H NMR), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX) and Electron paramagnetic resonance spectroscopy (EPR). The EPR spectrum of MFT-Cu(II) supported a distorted octahedral or square-planar geometry. The synthesized materials were also screened against bacterial (S. aureaus, S. mutans, B. cereus, S. pyrogenes, S. viridans, S. epidermids, C. xerosis, E. coli, K. pneumonia, P. vulgaris, P. aeruginosa) and fungal strains (A. niger, F. oxysporum, and A. oryzea). Moreover, the MFT-Zn(II) complex have demonstrated good thermal stability, as well as strong antibacterial and antifungal activities compared to the ligand and other metal polychelates.

Computational Studies and Antimicrobial Activity of 1-(benzo[d]oxazol-2- yl)-3,5-diphenylformazan Derivatives.

Due to the biological importance of the benzoxazole derivatives, some 1- (benzo[d]oxazol-2-yl)-3,5-diphenyl-formazans 4a-f were synthesized and screened for in-silico studies and in-vitro antibacterial activity. The benzo[d]oxazole-2-thiol (1) was prepared by reacting with 2-aminophenol and carbon disulfide in the presence of alcoholic potassium hydroxide. Then 2-hydrazinylbenzo[d] oxazole (2) was synthesized from the reaction of compound 1 with hydrazine hydrate in the presence of alcohol. Compound 2 was reacted with aromatic aldehydes to give Schiff base, 2-(2- benzylidene-hydrazinyl)benzo[d]oxazole derivatives 3a-f. The title compounds, formazan derivatives 4a-f, were prepared by a reaction of benzene diazonium chloride. All compounds were confirmed by their physical data, FTIR, 1H-NMR, and 13CNMR spectral data. All the prepared title compounds were screened for in-silico studies and in-vitro antibacterial activity on various microbial strains. Molecular docking against the 4URO receptor demonstrated that molecule 4c showed a maximum dock score of (-) 8.0 kcal/mol. MD simulation data reflected the stable ligand-receptor interaction. As per MM/PBSA analysis, the maximum free binding energy of (-) 58.831 kJ/mol was exhibited by 4c. DFT calculation data confirmed that most of the molecules were soft molecules with electrophilic nature. The synthesized molecules were validated using molecular docking, MD simulation, MMPBSA analysis, and DFT calculation. Among all the molecules, 4c showed maximum activity. The activity profile of the synthesized molecules against tested micro-organisms was found to be 4c>4b>4a>4e>4f>4d.

Construction of multifunctional hydrogel containing pH-responsive gold nanozyme for bacteria-infected wound healing

Nanozymes have become promising alternative antibacterial agents for bacteria-infected wounds. In this study, fucoidan-confined gold nanoparticles (Fuc@AuNPs) are developed by in situ reduction, and stabilized by sulfate groups of fucoidan. Fuc@AuNPs exhibit pH-responsive catalytic activity that can mimic oxidase (OXD) under acidic bacterial infection conditions and mimic superoxide dismutase (SOD) under normal physiological conditions. The OXD-like catalytic activity of Fuc@AuNPs generates active singlet oxygen (1O2), exhibiting effective antibacterial properties against both Gram-negative E. coli and Gram-positive S. aureus. Fuc@AuNPs and aldehyde grafted saponin incorporate with chitosan to form a hybrid hydrogel. This hydrogel exhibits superior mechanical, adhesive, and self-healing properties due to electrostatic complex coacervation networks and dynamic covalent Schiff base reactions. Animal experiments show that the hydrogel aids S. aureus-infected skin wound healing by reducing bacterial infection and promoting granulation tissue formation without causing excessive ROS-induced inflammation. This study presents the design of multifunctional nanozymes and bioactive hydrogels as a promising wound healing dressing for biomedical applications.

Uranyl (VI) complexes from hydrazone based Schiff bases derived from the condensation of benzene-1,3-di- or benzene-1,3,5-tricarbohydazide and hydroxyaromatic aldehydes

Uranyl (VI) complexes from hydrazone based Schiff bases derived from the condensation of benzene-1,3-di- or benzene-1,3,5-tricarbohydazide and hydroxyaromatic aldehydes

Synthesis and Biological Studies of Schiff Bases Derived from 4-methyl 7-Ethylcoumarin

New 7-ethyl-4-methyl coumarin derivatives bearing an azo methene group (C=N) were synthesized by a four-step process. The reaction between 7-ethylphenol and ethyl acetoacetate in the presence of sulfuric acid afforded 7-ethyl-4-methylcoumarin 1 in 90% yield. Nitration conditions (nitric acid and sulfuric acid) were then applied to product 1 to produce 6-nitro-7-ethyl-4-methycoumarin 2 and 8-nitro-4-methyl-7-ethylcoumarin 3. The temperature, the amount of starting materials, and the time of reaction were essential factors in obtaining a high yield of isomer 2 compared to the second isomer 3. The nitro groups at compounds 2 and 3 were then reduced with iron metal in an acidic medium to form the corresponding amino compounds 4 and 5, which were converted to Schiff base derivatives 6-17 via reaction with different substituted aromatic aldehydes. The synthesized compounds were characterized by FT-IR, 1H NMR, and 13C NMR spectroscopy. Evaluating the biological activities of the synthetic compounds was carried out against two bacteria: gram-positive bacteria (Staphylococcus aureus) and gram-negative bacteria (Escherichia coli) at 1×10-3 M; compound 15 showed a broad spectrum against these two types of bacteria compared to Vancomycin and Amikacin and against fungi compared to nystatin as a standard drug, but compound 7 showed stronger activities against fungi than the other synthesized compounds. In contrast, the rest of the compounds showed moderate activity against fungi compared with the same standard drag; in the antioxidant study, some new compounds showed powerful antioxidants compared with ascorbic acid as a stander reference by calculating the IC50. Compound 8 showed very good results as an antioxidant agent compared with the same standard.

Preparation, characterization and biological studies of azo dye Schiff base metal complexes derived from 2-aminothiophenol

Preparation, characterization and biological studies of azo dye Schiff base metal complexes derived from 2-aminothiophenol

Microwave Assisted Synthesis, Docking and Antimicrobial Studies of Tetrazole linked N-Acyl Hydrazone Derivatives

Novel Schiff bases of 2-(1H-tetrazole-5-yl)acetohydrazide were synthesized by employing microwave assisted green synthesis using substituted aldehydes. The structural characterization of the synthesized compounds was done by elemental, FT-IR, 1H NMR and mass spectrometry. The antimicrobial activity was investigated against Gram-positive and negative bacteria such as Staphylococcus aureus, Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. The ADME properties and protein binding studies of the test compounds were computed by using SwissADME and AutoDock software. Among all the compounds, compound HNTAC demonstrated stronger binding affinity (-10.37 kcal/mol) than the control cefazolin (-7.2 kcal/mol) for 4OR7. The excellent results of antimicrobial, molecular docking and ADME (in silico) studies enhanced the potential of the compounds under study as candidates for further research exploration.

Synthesis and Characterization of Some Oxazolidine and Thiazolidine Derivatives and Study of their Antioxidants Activity

In this work, the preparation of some new oxazolidine and thiazolidine derivatives has been conducted. This was done over two steps; the first step included the synthesis of Schiff bases A1-A5 in 72-88% yields by the condensation of isonicotinic acid hydrazide and aldehydes. The second step includes the cyclization of derivatives A1-A5 with glycolic acid and thioglycolic acid to obtain the desired products, oxazolidine derivatives B1-B5 (44-60% yields) and thiazolidine derivatives C1-C5 (41-61% yields), respectively. The structure of the prepared compounds was characterized using FT-IR, 1H NMR, and 13C NMR spectroscopy. Some of the produced compounds were tested for antioxidant properties.

A silica gel-supported schiff base palladium nanocatalyst for sonogashira cross-coupling and synthesis of an anti-cancer chemotherapeutic agent

This work outlines the synthesis of a low-cost reusable silica gel-supported Schiff-base palladium nanocatalyst and its application in the synthesis of anti-cancer agent Eniuracil via the Sonogashira reaction. Silica gel was functionalized with amino containing silyl followed by the generation of a Schiff base through reaction with 1,10-phenanthroline-2,9-dicarboxaldehyde. Palladium was then coupled in the presence of hydrazine hydrate, resulting in the formation of the silica gel-supported Schiff-base palladium nanocatalyst (Si@SBPdNPs 3). Successful palladium incorporation was confirmed through Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses. Scanning Electron Microscope (SEM) images revealed spherical silica gel particles and Transmission Electron Microscopy (TEM) analysis indicated an average palladium nanoparticle size of 5.92 ± 0.1 nm. The Inductively Coupled Plasma (ICP) and Energy Dispersive X-ray (EDX) data confirmed the anchoring of 0.27 mol% of palladium to the Schiff-base in the catalyst. The industrial efficacy of the catalysts is demonstrated through its application in carbon-to-carbon bond formation between aryl halides and aromatic alkyne via the Sonogashira reaction. Furthermore, the catalyst proved effective in the synthesis of the anti-cancer agent Eniuracil, a vital component in fluoropyrimidine-based chemotherapy. The catalyst exhibited reusability without significant loss of productivity, demonstrating its robustness in C C bond formation in organic synthesis.

Bidentate [C,N] and Tridentate [C,N,S] Palladium Cyclometallated Complexes as Pre-Catalysts in Cross-Coupling Reactions.

Treatment of halide substituted bidentate [C,N] and tridentate [C,N,S] Schiff base ligands with palladium(II) acetate or with lithium tetrachloropalladate, as appropriate, afforded through C-H activation of the organic ligand, the dinuclear (1 a, 1 b) and mononuclear (1 c, 1 d, 1 e) palladacycles, respectively. Reaction of the μ-acetate dinuclear complexes with aqueous sodium chloride in a metathesis process, gave the μ-chloride dinuclear complexes (2 a, 2 b). Treatment of the latter with triphenylphosphine or with bis(diphenylphosphino)methane (dppm)/ammonium hexafluorophosphate in complex/ phosphine 1 : 2 ratio, gave the phosphine derivatives (3 a, 3 b, 4 a, 4 b). Reaction of 1 c and of 1 e with triphenylphosphine/silver perchlorate and dppm/silver perchlorate, respectively, gave compounds 2 c and 2 e with removal of the chloride ligand by precipitation of the silver halide. The compounds were characterized by microanalysis (CHN), IR and 1H and 31P{1H} NMR spectroscopy. The crystal structures of three complexes, 4 a, 1 c and 1 e were studied by single-crystal X-ray diffraction. Furthermore, the performance of the palladacycles were tested as pre-catalysts, namely Suzuki-Miyaura cross-coupling reaction and those furnishing the better results are also reported.

Synthesis of metal-based biologically active agents from ONO-donor Schiff base ligand

Synthesis of metal-based biologically active agents from ONO-donor Schiff base ligand

AIE Active Polymeric Fluorescent Nanoaggregates from Glycogen for Sensitive Detection of Tetracycline.

Detection and monitoring of environmental contaminants such as antibiotic residues in aquatic environments is challenging. To address this, a variety of detection methods has been developed; out of which optical sensing using fluorescence is found as one of the most robust methods. However, most of the reported sensors are made from metal ions using tedious synthetic processes, on the other hand, optical sensors using biosourced polymers are rarely reported. Herein, an anionic glycogen functionalized aggregation induced emission (AIE) active system; NCMCTPN was prepared using a simple Schiff base condensation reaction of tetraphenylethene amine (TPENH2) and carboxymethyl cellulose dialdehyde (NCMCA) and its self-assembled polymeric nanoaggregates were explored for sensitive and selective turn-off fluorescence detection of a broad-spectrum tetracycline antibiotic, in an aqueous medium with a limit of detection of 127.5 ppb. The combination of factors such as inner filter effect and photoinduced electron transfer from the polymeric nanoaggregates to tetracycline through activation of a non-radiative decay process is possibly responsible for the high sensitivity of the fluorescent nanoprobe towards the antibiotic.

Optical fiber SPR Pb2+sensor with tip-printed Fabry-Perot interferometer for temperature compensation

Due to the serious biological toxicity and environmental refractory of heavy metal ions, the detection of heavy metal ions in liquids has attracted great attention. A novel fiber optic surface plasmon resonance (SPR) sensor is presented for detecting lead ions (Pb2+) with temperature compensation. The sensitivity of SPR channel to Pb2+ is up to -41.55 nm/μM and the detection limit is 7.05 nM after three parallel experiments by synthesizing Schiff base and fixing it on the sensor surface. Using femtosecond laser-induced two-photon polymerization (TPP) technology, a compact fiber-tip miniature Fabry-Perot interferometer (FPI) was printed at the end of the fiber-optic SPR sensor, thus realizing the temperature measurement in the process of detecting Pb2+. The FPI channel exhibits a linear response to temperature and remains unaffected by Pb2+ concentration, thus facilitating temperature correction. The experimental results also show that the proposed sensor has the advantages of compact structure, easy to prepare, good stability, specificity and repeatability. Therefore, this kind of sensor has great potential in various biochemical test applications, and opens up a new way to prepare compact and flexible optical sensors.

Durable colorful superhydrophobic cotton fabric constructed from modified microcrystalline cellulose prepared by Schiff base reaction

Cotton fabric is widely used for its excellent wearability but often suffers from drawbacks such as poor stain resistance, susceptibility to corrosion, and low colorfastness. Here, we introduce a novel method to create colorful superhydrophobic cotton fabric using octadecylamine-modified dialdehyde cellulose (DAC/ODA) particles as building units, which are synthesized via a Schiff base reaction and subsequently dyed with active dyes. Leveraging the film-forming ability of ODA and the affinity between cellulose materials, DAC/ODA formed a robust coating on the cotton surface, with its microstructure precisely controlled through thermal induction. The resulting fabric (DAC/ODA/Cotton) exhibited exceptional superhydrophobicity, with a water contact angle of 155° and an osmotic pressure of 426.2 mm. The uniform coverage of DAC/ODA on cotton fibers also ensured high air permeability (33.1 mm/s). Additionally, DAC/ODA/Cotton demonstrated outstanding antifouling performance against various common liquids and water can easily remove dust from its surface. Importantly, the fabric maintains its superhydrophobicity under extreme conditions such as high temperature, UV radiation, and acid-base exposure. Even after 100 abrasion cycles, no significant changes in surface morphology and color on DAC/ODA/Cotton were observed. This fluorine-free, environmentally friendly approach offers significant potential for developing multifunctional textiles and coatings with broad applications while reducing environmental impact.

An ultrasensitive NO2 sensor based on lightweight flexible organic single crystals

There is a growing interest in developing advanced organic electronic devices as viable replacements for their inorganic counterparts. This is due to the simple and low-cost processing, versatile molecular design, and ease of control of physical properties. Organic-crystalline materials have shown superior device performance and are seen as promising candidates for future flexible electronics. Despite advancements in understanding the fundamentals governing flexibility in organic single crystals, they are rarely used in electronic devices. Herein, we fabricated a device using flexible single crystals of a Schiff base with intramolecular charge-transfer states and investigated their electrical conductivity and gas-sensing capabilities. Because the properties of charge-transfer states are influenced by their proximal environment, the device is able to selectively detect the highly toxic gas NO2 under ambient conditions with a sensitivity of 3.36 × 106 % and a detection limit of 67 ppb. The flexibility of the crystals allowed their integration into flexible substrates, expanding their potential use in the realm of wearable technology and smart electronics. This makes our findings relevant to the ecosystem and public health.

Synthesis of naringenin schiff base loaded CMC/PVA scaffold as biodegradable wound care materials

Abstract The complex formula of wound care therapy includes effective treatment tactics, infection prevention, wound preconditioning, and germ therapy. By creating ideal circumstances for wound healing, wound dressings are a major factor in lowering the rate at which infections worsen. The persistence of chronic wounds as a significant healthcare challenge necessitates the creation of innovative wound-dressing techniques. This work describes a novel method for creating ternary biodegradable polymers from polyvinyl alcohol (PVA) and carboxymethylcellulose (CMC). With the addition of Naringin Schiff base, the aqueous mixture of CMC and PVA creates an ideal wound dressing material. The base of Naringin Schiff possesses strong antibacterial and antioxidant characteristics. The goal of this work is to create polymer based on polyvinyl alcohol (PVA) and carboxymethylcellulose (CMC) loaded with Naringin Schiff base for efficient wound care therapy. The 1H, 13C NMR, FT-IR, and Mass spectrometry were used to characterize the Schiff base. The Schiff Base loaded CMC/PVA film was characterized by FT-IR, AFM. Studies such as biodegradability, antimicrobial studies, water absorption capabilities, water vapour transmission rate and dressing pH of the films were also conducted. The promise of biopolymers as better wound dressing material will be highlighted in this work, allowing more efficient wound care.

Efficient one-pot strategy for fluorescent conjugated polymers derived from 8-amino-1-naphthalene-3,6-disulfonic acid: Synthesis, thermal and optical properties

Schiff base polymers, also known as poly(imines) or poly(azomethine)s, constitute a subset of conjugated polymers. The Schiff base compound was synthesized via the condensation reaction between 8-amino-1-naphthalene-3,6-disulfonic acid and 4-hydroxybenzaldehyde. Subsequently, both 8-amino-1-naphthalene-3,6-disulfonic acid and its Schiff base derivative were polymerized into a poly(naphthol) (PANAPDSA) and Schiff base polymer (PANAPDSASB) under alkaline condition using H2O2 (35 % aqueous solution) as oxidant via oxidative polycondensation (OP). The chemical structures of the synthesized compounds were approved using NMR, FT-IR, UV–Vis, element and LC-MS/MS spectroscopic techniques. The synthesized polymers exhibited lower optical and electrochemical band gaps compared to their respective monomers, suggesting their potential utility as semiconductor materials. The poly(naphthol) derivative exhibited high fluorescent emission intensity of 1000 a.u. when excited at 300 nm with a photoluminescence (PL) emission quantum yield of 13.6 % at 392 nm of emission wavelength in N,N-dimethylformamide (DMF) solution. Weight average molecular weight (Mw) values of PANAPDSA and PANAPDSASB ranged from 9500 Da to 11200 Da, with PDI values between 1.12 and 1.13. The synthesis of conjugated polymers could hold significant importance in technological advancements.

Large-Scale Synthesis of Carbon Dots Driven by Schiff Base Reaction at Room Temperature

Photoluminescent carbon dots (CDs) have received increasing attention because of their admirable photophysical performances. The current strategies for synthesizing CDs typically require high energy consumption levels, and the ability to synthesize CDs at ambient temperature would be highly desirable. Herein, we design an energy-efficient approach to synthesize CDs through a Schiff base crosslinking between 2,5-dihydroxy-1,4-benzoquinone and tetraethylenepentamine at room temperature. The obtained CDs possess maximum photoluminescence (PL) emissions of 492 nm. Moreover, the proposed CDs possess good stability and a concentration-dependent PL and their maximum emissions can redshift from 492 to 621 nm as the CDs concentration increases. Because of their good luminescent properties, the CDs can be employed as optical probes for doxorubicin detection using the inner filter effect. This study develops a powerful approach for the large-scale synthesis of CDs with a superior performance.

Synthesis, Spectroscopic Studies, Thermal Stability and Crystal Structure of New Bidentate Schiff Base and Its Cadmium Complex

A new asymmetric bidentate Schiff base ligand was synthesized from a condensation reaction between 2,4-dichlorobenzaldehyde (C7H4Cl2O) and 1,3-pentanediamine (C5H14N2). A cadmium complex was prepared by adding Cd(II) iodide dissolved in methanol to a methanolic solution of the Schiff base ligand, in a ratio of 1:1. The ligand was characterized by elemental, spectroscopic (IR, <sup>1</sup>H NMR), and thermogravimetric analyses. The ligand structure, thermally very stable, is revealed to be bidentate with two potential N-donor sites. The crystal structure of the Schiff base was elucidated by X-ray diffraction analysis. Compound crystallizes in a monoclinic system with a space group P21/n and a number of units per unit cell Z = 4. The unit cell parameters are: a =7.3885(2), b =16.9332 (4), c = 15.5624(4), and β = 90.4306(10). In the asymmetric unit of the ligand, the benzene rings C08/C10/C09/C11/C21/C17 and C20/C15/C13/C18/C22/C24 are in trans position with the aliphatic group with respect to the bonds (C07-N05) and (C19-N06), respectively. In addition, these two aromatic rings are located in two different planes, forming an angle of 3.60º between them, given that the dihedral angle between the ring C08/C10/C09/C11/C21/C17 and the aliphatic group N05-N06 is 67.49º. The spectroscopic data of the complex reveals a mononuclear complex where the Cd(II) ion is housed in a N2I2 coordination site with a slightly distorted tetrahedral geometry. The conductance data indicate that the complex is a neutral electrolyte.

Green synthesis of starch/chitosan complex via ozone-mediated Schiff reaction: Structure, thermal behaviors and surface properties

Ozone was used as a green and environmentally friendly initiator to directly induce a Schiff base cross-linking reaction between chitosan and waxy rice starch (CS) in the present investigation. The effects of oxidation on the structure of chitosan/starch bio-based composite, along with the cross-linked structure formation via Schiff base reaction, were investigated and confirmed using FTIR, XRD, and XPS characterization techniques. The formation of new bonds (C=N) along with other attributes imparted by the cross-linking reaction were evaluated and characterized. Notably, the ozone-induced cross-linking reaction significantly altered the water retention capabilities of CS, especially in the case of aqueous ozone treatment, which significantly improved its swelling power, water holding capacities, and water adsorption. Additionally, aqueous ozone treatment facilitated the formation and stabilization of the gel network. Gaseous ozone in dry state proved more effective in promoting the formation of CN groups, leading to enhanced surface hydrophobicity, while aqueous ozone offered better oxidation uniformity for the coexistence system of chitosan and starch. This work provides a novel and environmentally friendly approach for fabricating the chitosan/starch chemically cross-linking materials through ozone-induced direct Schiff base reaction, which simplifies the preparation process of the complex and minimizing the utilization of solvents.