Different Schiff Bases-Structure, Importance and Classification

Antimicrobial starch-based cryogels and hydrogels for dual-active food packaging applications

The present study reports on the valorisation of starch waste biomass to produce dual-active cryogels and hydrogels able to adsorb water and deliver antimicrobial substances for fresh food packaging applications. Starch hydrogels were prepared by oxidation with sodium metaperiodate in water and mild conditions, while cryogels were obtained by freeze-drying process. To explore the role of starch composition on the final properties of materials, two starches differing in amylose/amylopectin ratio, were evaluated. The prepared materials were microstructurally and morphologically characterized by FTIR and NMR spectroscopy (1D, 2D, and DOSY experiments), and SEM microscopy. To provide the materials with active properties, they were loaded with antimicrobial molecules by absorption, or by crosslinking via Schiff-base reaction. All materials demonstrated high water absorption capacity and ability to deliver volatile molecules, including diacetyl and complex mixtures like mint essential oil. The release profiles of the adsorbed molecules were determined through quantitative NMR spectroscopy over time. The antibacterial activity was successfully demonstrated against Gram-positive bacterial strains for unloaded cryogels and hydrogels, and after loading with diacetyl and essential oil. The developed materials can be regarded as part of active pads for food packaging applications capable to control moisture inside the package and inhibit microbial contamination.

Photocatalyzed Synthesis of a Schiff Base via C-N Bond Formation: Benzyl Alcohol as Sustainable Surrogates of Aryl Aldehydes

The advancement of photocatalytic techniques has enabled green chemical synthesis through visible-light-mediated photochemical oxidation under mild conditions. A novel approach under visible-light conditions was facilitated by eosin-Y for the reaction between substituted benzyl alcohols and anilines, resulting in the synthesis of diverse Schiff bases. This innovative method is emphasized for its environmentally friendly nature, lack of metal catalysts, cost-effectiveness, and nontoxic characteristics.

Investigation on synthesized sulfonamide Schiff base with DFT approaches and in silico pharmacokinetic studies: Topological, NBO, and NLO analyses

The sulfonamide Schiff base (C16H14N4O3S) was successfully synthesized and experimentally ascertained. The main purpose of this research is to investigate the geometry of the aforesaid molecule using both experimental and density functional theory (DFT) techniques and determine its drug likeness characteristics, docking ability as an insulysin inhibitor, and its NLO property. For the computational investigations the DFT approaches were utilized at the B3LYP level with the 6-311G+(d,p) basic set. The experimental results of the compound (such as FT-IR, UV-Vis, and 1H NMR) were compared with simulated data. The both results were well and consistent with previously related published data. The obtained spectral results confirm the formation of the Schiff base compound. Both π-π* and n-π* interactions were found in experimental and computational UV-Vis spectra, as well as in the natural bond orbital (NBO) study. The molecular, electronic, covalent, and non-covalent interactions were analyzed using DFT studies. Both experimental and simulation results revealed that the compound is successfully formed and relatively stable. The compound with a lower band gap showed high chemical reactivity. The medicinal characteristics of the compound were evaluated using in silico medicinal methods. The investigated compound was also followed Pfizer, Golden Triangle, GSK as well as Lipinski's rules. Therefore, the compound has more favorable absorption, distribution, metabolism, excretion, and toxicity (ADMET) profile and it can be used as non-toxic oral drug candidate. The compound was exhibited good insulysin inhibitory activity and it has almost eighteen times higher non-linear optical properties than urea and three times higher than potassium dihydrogen phosphate (KDP).

Synthesis, quantum chemical calculations, in silico and in vitro bioactivity of a sulfonamide-Schiff base derivative

The sulfonamide Schiff base compound (E)-4-((4-(dimethylamino)benzylidene)amino)-N-(5-methylisoxazol-3-yl)benzenesulfonamide was successfully prepared and fully characterized. The foremost objective of this study was to explore the molecular geometry of the aforementioned compound and determine its drug likeness characteristics, docking ability as an insulysin inhibitor, anticancer and antioxidant activities. The molecular structure of this compound was optimized using the B3LYP/6-311G+(d,p) level of theory. The compound was completely characterized utilizing both experimental and DFT approaches. Molecular electrostatic potential, frontier molecular orbitals, Fukui function, drug likeness, and in silico molecular docking analyses of this compound were performed. Wave functional properties such as localized orbital locator, electron localization function and non-covalent interactions were also simulated. The compound was screened for anticancer and antioxidant activities using in vitro technique. The observed FT-IR, UV-Vis, and 1H NMR results compared with simulated data and both results were fairly consistent. The experimental and computational spectral findings confirm the formation of the Schiff base compound. Both π-π* and n-π* transitions were observed in both experimental and computational UV-Vis spectra. The examined compound followed to Pfizer, Golden Triangle, GSK, and Lipinski's rules. Consequently, it possesses a more favorable absorption, distribution, metabolism, excretion, and toxicity (ADMET) profile, making it a suitable candidate for non-toxic oral drug use. Moreover, the compound exhibited promising insulysin inhibition activity in an in silico molecular docking. The compound showed in vitro anticancer activity against A549 cancer cells with an IC50 value of 40.89 μg/mL and moderate antioxidant activity.

Recent applications of coinage metal nanoparticles passivated with salicylaldehyde and salicylaldehyde-based Schiff bases

Salicylaldehyde (SD) and its derivatives are effective precursors for generating coinage metal (gold, silver, and copper) nanoparticles (NPs). These NPs have a variety of potential environmental applications, such as in water purification and sensing, and those arising from their antibacterial activity. The use of SD and its derivatives for synthesizing coinage NPs is attractive due to several factors. First, SD is a relatively inexpensive and readily available starting material. Second, the synthetic procedures are typically simple and can be carried out under mild conditions. Finally, the resulting NPs can be tailored to have specific properties, such as size, shape, and surface functionality, by varying the reaction conditions. In an alkaline solution, the phenolate form of SD was converted to its quinone form, while ionic coinage metal salts were converted to zero-valent nanoparticles. The capping in situ produced quinone of coinage metal nanoparticles generated metal-enhanced fluorescence under suitable experimental conditions. The formation of iminic bonds during the formation of Schiff bases altered the properties (especially metal-enhanced fluorescence) and applications.

Hydrogels Based on Proteins Cross-Linked with Carbonyl Derivatives of Polysaccharides, with Biomedical Applications

Adding carbonyl groups into the hydrogel matrix improves the stability and biocompatibility of the hydrogels, making them suitable for different biomedical applications. In this review article, we will discuss the use of hydrogels based on polysaccharides modified by oxidation, with particular attention paid to the introduction of carbonyl groups. These hydrogels have been developed for several applications in tissue engineering, drug delivery, and wound healing. The review article discusses the mechanism by which oxidized polysaccharides can introduce carbonyl groups, leading to the development of hydrogels through cross-linking with proteins. These hydrogels have tunable mechanical properties and improved biocompatibility. Hydrogels have dynamic properties that make them promising biomaterials for various biomedical applications. This paper comprehensively analyzes hydrogels based on cross-linked proteins with carbonyl groups derived from oxidized polysaccharides, including microparticles, nanoparticles, and films. The applications of these hydrogels in tissue engineering, drug delivery, and wound healing are also discussed.

Exploration of Calocybe indica mushroom phenolic acid-kidney bean protein complex: Functional properties, amino acid profiles, in-vitro digestibility, and application in vegan product development

The study evaluates the interaction between Calocybe indica mushroom polyphenols (phenolic acid) and kidney bean protein (KBPM), aiming to enhance vegan food quality. The mushrooms exhibited a carbohydrate content of 3.65%, an antioxidant activity of 55.04 ± 0.17%, and a phenolic content of 4.86 mg GAE/g. Caffeic and cinnamic acids were identified through high-pressure liquid chromatography. Various concentrations of KBPM were tested at phenolic acid concentrations of 0.025, 0.050, 0.1, 0.2, 0.4, 0.8, and 1%, among these, KBPM 0.2 demonstrated the highest binding efficiency of 99.40 ± 0.05%. Notably, this complex improved the protein's functional properties, such as solubility by 11.43%, water and oil holding capacities by 10.62% and 22.04%, and emulsion capacity and stability by 3.69% and 5.83%, respectively, compared to the native protein. The protein-phenolic acid complex also enhanced thermal stability, surface charge, amino acid content, and reduced particle size compared to native protein. These enhancements also improved protein digestibility and sensory attributes in a fruit-based smoothie.

Dynamic Covalent Bond-Based Polymer Chains Operating Reversibly with Temperature Changes

Dynamic bonds can facilitate reversible formation and dissociation of connections in response to external stimuli, endowing materials with shape memory and self-healing capabilities. Temperature is an external stimulus that can be easily controlled through heat. Dynamic covalent bonds in response to temperature can reversibly connect, exchange, and convert chains in the polymer. In this review, we introduce dynamic covalent bonds that operate without catalysts in various temperature ranges. The basic bonding mechanism and the kinetics are examined to understand dynamic covalent chemistry reversibly performed by equilibrium control. Furthermore, a recent synthesis method that implements dynamic covalent coupling based on various polymers is introduced. Dynamic covalent bonds that operate depending on temperature can be applied and expand the use of polymers, providing predictions for the development of future smart materials.

Discovery of new Schiff bases of the disalicylic acid scaffold as DNA gyrase and topoisomerase IV inhibitors endowed with antibacterial properties

DNA gyrase and topoisomerase IV show great potential as targets for antibacterial medicines. In recent decades, various categories of small molecule inhibitors have been identified; however, none have been effective in the market. For the first time, we developed a series of disalicylic acid methylene/Schiff bases hybrids (5a-k) to act as antibacterial agents targeting DNA gyrase and topoisomerase IV. The findings indicated that the new targets 5f-k exhibited significant antibacterial activity against Gram-positive and Gram-negative bacteria, with efficacy ranging from 75% to 115% of the standard ciprofloxacin levels. Compound 5h demonstrated the greatest efficacy compared to the other compounds tested, with minimum inhibitory concentration (MIC) values of 0.030, 0.065, and 0.060 μg/mL against S. aureus, E. coli, and P. aeruginosa. 5h had a MIC value of 0.050 μg/mL against B. subtilis, which is five times less potent than ciprofloxacin. The inhibitory efficacy of the most potent antibacterial derivatives 5f, 5h, 5i, and 5k against E. coli DNA gyrase was assessed. The tested compounds demonstrated inhibitory effects on E. coli DNA gyrase, with IC50 values ranging from 92 to 112 nM. These results indicate that 5f, 5h, 5i, and 5k are more effective than the reference novobiocin, which had an IC50 value of 170 nM. Compounds 5f, 5h, 5i, and 5k were subjected to additional assessment against E. coli topoisomerase IV. Compounds 5h and 5i, which have the highest efficacy in inhibiting E. coli gyrase, also demonstrated promising effects on topoisomerase IV. Compounds 5h and 5i exhibit IC50 values of 3.50 µM and 5.80 µM, respectively. These results are much lower and more potent than novobiocin's IC50 value of 11 µM. Docking studies demonstrate the potential of compound 5h as an effective dual inhibitor against E. coli DNA gyrase and topoisomerase IV, with ADMET analysis indicating promising pharmacokinetic profiles for antibacterial drug development.

Saliva as a Diagnostic Tool for Early Detection of Exercise-Induced Oxidative Damage in Female Athletes

Although blood still remains the most commonly utilized medium to detect increased levels of oxidative damage induced by exercise, saliva diagnostics have gained increasing popularity due to their non-invasive nature and athlete-friendly collection process. Given that the contribution of various phases of the menstrual cycle to the levels of oxidative damage may differ, the aim of this study was to evaluate an agreement between salivary and plasmatic levels of lipid peroxidation products in female swimmers in both the follicular (F) and luteal (L) phases of the menstrual cycle at rest and following exercise. Twelve well-trained female swimmers aged 19.6 ± 1.1 years old were examined. We measured diene conjugates (DCs), triene conjugates (TCs), and Schiff bases (SBs) in lipids immediately after their extraction from both saliva and blood plasma. All female swimmers were studied two times each, in the two different phases of one menstrual cycle, before and after high-intensity interval exercise (HIIE). Salivary and plasmatic levels of DCs, TCs, and SBs significantly increased post-exercise compared to pre-exercise, in both the F and L phases. A high positive correlation was observed between the concentrations of DCs, TCs, and SBs in the saliva and blood plasma of participants in the F and L phases, both at rest and following HIIE. Ordinary least products regression analysis indicates that there was no proportional and differential bias in the data. The Bland-Altman method also declares that there was no differential bias, since the line of equality was within the 95% confidence interval of the mean difference between salivary and plasmatic levels of DCs, TCs, and SBs in female swimmers, in both the F and L phases, before and after HIIE. There was also no proportional bias in the Bland-Altman plots. Thus, this is the first study to report a high agreement between the quantifications of DCs, TCs, and SBs in the saliva and blood plasma of female swimmers in both the F and L phases, at rest and following HIIE.

Unveiling potent Schiff base derivatives with selective xanthine oxidase inhibition: In silico and in vitro approach

This research describes the synthesis by an environmentally-friendly method, microwave irradiation, development and analysis of three novel and one previously identified Schiff base derivative as a potential inhibitor of bovine xanthine oxidase (BXO), a key enzyme implicated in the progression of gout. Meticulous experimentation revealed that these compounds (10, 9, 4, and 7) have noteworthy inhibitory effects on BXO, with IC50 values ranging from 149.56 µM to 263.60 µM, indicating their good efficacy compared to that of the standard control. The validation of these results was further enhanced through comprehensive in silico studies, which revealed the pivotal interactions between the inhibitors and the catalytic sites of BXO, with a particular emphasis on the imine group (-C = N-) functionalities. Intriguingly, the compounds exhibiting the highest inhibition rates also showcase advantageous ADMET profiles, alongside encouraging initial assessments via PASS, hinting at their broad-spectrum potential. The implications of these findings are profound, suggesting that these Schiff base derivatives not only offer a new vantage point for the inhibition of BXO but also hold considerable promise as innovative therapeutic agents in the management and treatment of gout, marking a significant leap forward in the quest for more effective gout interventions.

Metallosalen modified carbon nitride a versatile and reusable catalyst for environmentally friendly aldehyde oxidation

The development of environmentally friendly catalysts for organic transformations is of great importance in the field of green chemistry. Aldehyde oxidation reactions play a crucial role in various industrial processes, including the synthesis of pharmaceuticals, agrochemicals, and fine chemicals. This paper presents the synthesis and evaluation of a new metallosalen carbon nitride catalyst named Co(salen)@g-C3N4. The catalyst was prepared by doping salicylaldehyde onto carbon nitride, and subsequently, incorporating cobalt through Schiff base chemistry. The Co(salen)@g-C3N4 catalyst was characterized using various spectroscopic techniques including Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Infrared Spectroscopy (IR), and Thermogravimetric Analysis (TGA). Furthermore, after modification with salicylaldehyde, the carbon nitride component of the catalyst exhibited remarkable yields (74-98%) in oxidizing various aldehyde derivatives (20 examples) to benzoic acid. This oxidation reaction was carried out under mild conditions and resulted in short reaction times (120-300 min). Importantly, the catalyst demonstrated recyclability, as it could be reused for five consecutive runs without any loss of activity. The reusable nature of the catalyst, coupled with its excellent yields in oxidation reactions, makes it a promising and sustainable option for future applications.

Spin-labeling Insights into How Chemical Fixation Impacts Glycan Organization on Cells

As new methods to interrogate glycan organization on cells develop, it is important to have a molecular level understanding of how chemical fixation can impact results and interpretations. Site-directed spin labeling technologies are well suited to study how the spin label mobility is impacted by local environmental conditions, such as those imposed by cross-linking effects of paraformaldehyde cell fixation methods. Here, we utilize three different azide-containing sugars for metabolic glycan engineering with HeLa cells to incorporate azido glycans that are modified with a DBCO-based nitroxide moiety via click reaction. Continuous wave X-band electron paramagnetic resonance spectroscopy is employed to characterize how the chronological sequence of chemical fixation and spin labeling impacts the local mobility and accessibility of the nitroxide-labeled glycans in the glycocalyx of HeLa cells. Results demonstrate that chemical fixation with paraformaldehyde can alter local glycan mobility and care should be taken in the analysis of data in any study where chemical fixation and cellular labeling occur.

Synthesis and Primary Activity Assay of Novel Benitrobenrazide and Benserazide Derivatives

Schiff bases attract research interest due to their applications in chemical synthesis and medicinal chemistry. In recent years, benitrobenrazide and benserazide containing imine moiety have been synthesized and characterized as promising inhibitors of hexokinase 2 (HK2), an enzyme overexpressed in most cancer cells. Benserazide and benitrobenrazide possess a common structural fragment, a 2,3,4-trihydroxybenzaldehyde moiety connected through a hydrazone or hydrazine linker acylated on an N' nitrogen atom by serine or a 4-nitrobenzoic acid fragment. To avoid the presence of a toxicophoric nitro group in the benitrobenrazide molecule, we introduced common pharmacophores such as 4-fluorophenyl or 4-aminophenyl substituents. Modification of benserazide requires the introduction of other endogenous amino acids instead of serine. Herein, we report the synthesis of benitrobenrazide and benserazide analogues and preliminary results of inhibitory activity against HK2 evoked by these structural changes. The derivatives contain a fluorine atom or amino group instead of a nitro group in BNB and exhibit the most potent inhibitory effects against HK2 at a concentration of 1 µM, with HK2 inhibition rates of 60% and 54%, respectively.

Analysis of platinum-based anticancer injections cisplatin and carboplatin in blood serum and urine of cancer patients by photometry, fluorometry, liquid chromatography using a Schiff-base as derivatizing reagent

Photometric, fluorometric and liquid chromatographic methods were proposed to analyze Pt(II) from cis-platin and carbo-platin injections after derivatization with reagent 2-oxo-propanoic acid N-phenylhydrazonecarbothioamide. The reagent reacted with metals Au(III), Ag(I), Mn(II), Pt(II), Mo(VI), V(V/IV) to develop their characteristic colors in the pH range 3-12 and were extracted in organic solvent trichloromethane. The photoluminescent behavior of ligand and its metal complexes was investigated to correlate the emission pattern. Liquid chromatographic method was also proposed to analyze cis-platin and carbo-platin anti-cancer drugs based on the pre-column derivatizing platinum(II) with ligand. The complex of platinum was separated and eluted from HPLC column Microsorb C-18, (150 cm x 4.6 mm i.d, 5 µm) comprising eluents - tetrabutyl ammonium bromide (1 mM)-sodium acetate (1 mM)-acetonitrile-water-methanol (02:02:06:22:68 v/v/v/v/v). Metals Au(III), Ag(I), Mn(II), V(IV/V), Mo(VI) were also separated completely. The linear calibration range 0.5-2.5 µg/mL was observed following Beer's law with detection limit of 150.00 ng/mL Pt(II). The determination of cis-platin and carbo-platin injections by photometric, fluorometric and chromatographic methods showed RSD (n = 3) 1.14-3.12, 0.98-2.84, 0.92-2.72% respectively. The developed methods were employed to analyze cis-platin in samples of serum and urine of cancer patients undergoing chemotherapy and platinum amounts were observed within 45.0-86.0, 49.0-91.0, 42.0-84.0 ng/mL and 82.0-398, 81.0-389, 74.0-391 ng/mL with relative standard deviation (RSD) (n = 4) of 2.28-3.88, 2.40-3.82, 2.52-3.82% and 2.52-3.91, 2.44-3.94, 1.98-3.24% by liquid chromatographic, fluorometric and photometric techniques respectively.

Design, preparation and characterization of magnetic nanoparticles functionalized with chitosan/Schiff base and their use as a reusable nanocatalyst for the green synthesis of 1H-isochromenes under mild conditions

In this study, a Schiff base complex magnetic nanocatalyst was designed and prepared. The structure of the Fe3O4@CS-SB-CaMgFe2O4 nanocatalyst was characterized using FT-IR spectroscopy, XRD, VSM, FE-SEM, EDX, elemental mapping, BET, and TGA techniques. The synthesis of 1H-isochromene compounds has attracted the attention of chemists due to their biological and medicinal properties. The 1H-isochromene derivatives were synthesized in the presence of the Fe3O4@CS-SB-CaMgFe2O4 nanocatalyst with excellent efficiency and short reaction time as well as according to the rules of green chemistry. This reaction was carried out using Fe3O4@CS-SB-CaMgFe2O4 as a catalyst to develop a simple method with low activation energy at room temperature under optimal conditions. This catalyst provides a promising route for the synthesis of 1H-isochromene multiple times through its recyclability without significant loss of catalytic activity. This nanocatalyst possesses several advantages, including cost-effectiveness, facile separation, environmental friendliness, and recyclability, for the efficient production of 1H-isochromenes. The obtained compounds were further analyzed using spectroscopic techniques, such as melting point, FT-IR, 1H NMR, and 13C NMR analyses, to confirm their structures. The spectra of the synthesized compounds were recorded and analyzed, and a plausible mechanism for their synthesis was proposed. The characterization results and structural elucidation provide valuable insights into the preparation of these compounds.

Recent advances in the antioxidant activity of metal-curcumin complexes: a combined computational and experimental review

Curcumin, an extensively studied phytochemical compound, has gained attention for its potential therapeutic applications across a spectrum of diseases. Its notable attributes include its relatively high tolerability within the human body and its perceived absence of adverse side effects. This review article presents a comprehensive overview of the antioxidant effects exhibited by complexes formed by curcumin and curcumin derived ligands with metals like Mn, Cu, Fe, Zn, Ga and In, which leads to toxic effects beyond a certain limit, based on both experimental and theoretical findings. Additionally, the discussion delves into metal-curcumin complexes characterized by stoichiometries of 1:1 and 1:2, exploring their geometric arrangements and corresponding antioxidant activity, as highlighted in recent studies. These complexes hold the promise of improving curcumin's solubility, stability, and bioavailability, potentially augmenting its overall therapeutic potential and expanding its scope for medical applications.

Recent Advances on the Antimicrobial Activities of Schiff Bases and their Metal Complexes: An Updated Overview

Schiff bases represent a valuable class of organic compounds, synthesized via condensation of primary amines with ketones or aldehydes. They are renowned for possessing innumerable applications in agricultural chemistry, organic synthesis, chemical and biological sensing, coating, polymer and resin industries, catalysis, coordination chemistry, and drug designing. Schiff bases contain imine or azomethine (-C=N-) functional groups which are important pharmacophores for the design and synthesis of lead bioactive compounds. In medicinal chemistry, Schiff bases have attracted immense attention due to their diverse biological activities. This review aims to encompass the recent developments on the antimicrobial activities of Schiff bases. The article summarizes the antibacterial, antifungal, antiviral, antimalarial, and antileishmanial activities of Schiff bases reported since 2011.

Synthesis of Schiff Bases Based on Chitosan and Heterocyclic Moiety: Evaluation of Antimicrobial Activity

Schiff bases of chitosan (CS) were prepared by reaction of four different heterocyclic compounds, namely, 1,3-dimethyl-2,4,6-trioxohexahydropyrimidine-5-carbaldehyde (M1), 3-acetyl-2H-chromen-2-one (M2), 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (M3), and 4-oxo-4H-chromene-3-carbaldehyde (M4), with CS using thermal and ultrasound approaches. CS Schiff base formation was confirmed by using FT-IR, XRD, and TGA. Characteristic data show that amino groups in chitosan reacted with the functional group in the heterocyclic compound to form the Schiff base. CS Schiff bases show thermal stability more than pure CS. The antimicrobial activity of Schiff bases was tested against +ve Gram bacteria and -ve Gram bacteria. The result shows that Schiff bases prepared by temperature and ultrasound methods possess high antimicrobial activity against +ve Gram bacteria and -ve Gram bacteria; in comparison, Schiff bases produced by the ultrasound method have higher antimicrobial activity. The Schiff base (CSM4U), prepared by the ultrasound method by reaction of CS with 4-oxo-4H-chromene-3-carbaldehyde, exhibited higher antimicrobial activity than Gentamicin as an antibacterial agent. The inhibition range caused by CSM4U was between 19 and 27 mm. Moreover, CSM4U also acted as an antifungal agent, causing an inhibition zone of 21 mm for both Candida albicans and Candida tropicalis, which was higher than that of Terbinafine.

Stimuli-Responsive Polymer-Based Nanosystems for Cancer Theranostics

Stimuli-responsive polymers can respond to internal stimuli, such as reactive oxygen species (ROS), glutathione (GSH), and pH, biological stimuli, such as enzymes, and external stimuli, such as lasers and ultrasound, etc., by changing their hydrophobicity/hydrophilicity, degradability, ionizability, etc., and thus have been widely used in biomedical applications. Due to the characteristics of the tumor microenvironment (TME), stimuli-responsive polymers that cater specifically to the TME have been extensively used to prepare smart nanovehicles for the targeted delivery of therapeutic and diagnostic agents to tumor tissues. Compared to conventional drug delivery nanosystems, TME-responsive nanosystems have many advantages, such as high sensitivity, broad applicability among different tumors, functional versatility, and improved biosafety. In recent years, a great deal of research has been devoted to engineering efficient stimuli-responsive polymeric nanosystems, and significant improvement has been made to both cancer diagnosis and therapy. In this review, we summarize some recent research advances involving the use of stimuli-responsive polymer nanocarriers in drug delivery, tumor imaging, therapy, and theranostics. Various chemical stimuli will be described in the context of stimuli-responsive nanosystems. Accordingly, the functional chemical groups responsible for the responsiveness and the strategies to incorporate these groups into the polymer will be discussed in detail. With the research on this topic expending at a fast pace, some innovative concepts, such as sequential and cascade drug release, NIR-II imaging, and multifunctional formulations, have emerged as popular strategies for enhanced performance, which will also be included here with up-to-date illustrations. We hope that this review will offer valuable insights for the selection and optimization of stimuli-responsive polymers to help accelerate their future applications in cancer diagnosis and treatment.

Crystal Structure, Hirshfeld Surface Analysis, and Biological Activities of Schiff-Base Derivatives of 4-Aminoantipyrine

Eight Schiff bases, synthesized by the reaction of 4-aminoantipyrine with different cinnamaldehydes, were studied in the solid state by using vibrational spectroscopy (IR) and X-ray diffraction techniques. The analysis was extended to the solution phase through ultraviolet-vis, fluorescence spectroscopy, and cyclic voltammetry. Finally, the crystal structures of four compounds (3b, 3d, 3g, and 3h) were determined and studied. In addition to the experimental study, theoretical calculations using the semiempirical method PM6/ZDO were performed to understand better the compound's molecular properties, UV-vis, and infrared spectra. The primary difference is the angular conformation of the terminal phenyl rings around the corresponding linking C-N and C-C σ-bonds. Furthermore, as a result of extended bonding, the > C=N- azomethine group-containing Cpyr-N=(CH)-(CR)=(CH)-Cbz chain (with R=H for 3b, 3d, and 3h, and R=CH3 for 3g) is planar, nearly coplanar, with the mean plane of the pyrazole ring. Hirshfeld surface (HS) analysis was used to investigate the crystal packing and intermolecular interactions, which revealed that intermolecular C-H···O and C-H···N hydrogen bonds, π···π stacking, and C-H···π and C=O···π interactions stabilize the compounds. The energy contributions to the lattice energies of potential hydrogen bonds were primarily dispersive and repulsive. All derivatives were tested in vitro on LPS-stimulated mouse macrophages to assess their ability to suppress the LPS-induced inflammatory responses. Only a slight reduction in the level of NO production was found in activated macrophages treated with 3h. Additionally, the derivatives were tested for antimicrobial activity against several clinical bacteria and fungi strains, including three biofilm-forming microorganisms. Nevertheless, only Schiff base 3f showed interesting antibacterial activities with minimum inhibitory concentration (MIC) values as low as 15.6 μM against Enterobacter gergoviae. On the other hand, Schiff base 3f and, to a lesser extent, 3b and 3h showed antifungal activity against clinical isolates of Candida. The lowest MIC value was for 3f against Candida albicans (15.6 μM). It is interesting to note that the same Schiff bases exhibit the highest activity in both biological evaluations.

Strategies for Improving Selectivity and Sensitivity of Schiff Base Fluorescent Chemosensors for Toxic and Heavy Metals

Toxic cations, including heavy metals, pose significant environmental and health risks, necessitating the development of reliable detection methods. This review investigates the techniques and approaches used to strengthen the sensitivity and selectivity of Schiff base fluorescent chemosensors designed specifically to detect toxic and heavy metal cations. The paper explores a range of strategies, including functional group variations, structural modifications, and the integration of nanomaterials or auxiliary receptors, to amplify the efficiency of these chemosensors. By improving selectivity towards targeted cations and achieving heightened sensitivity and detection limits, consequently, these strategies contribute to the advancement of accurate and efficient detection methods while increasing the range of end-use applications. The findings discussed in this review offer valuable insights into the potential of leveraging Schiff base fluorescent chemosensors for the accurate and reliable detection and monitoring of heavy metal cations in various fields, including environmental monitoring, biomedical research, and industrial safety.

Supramolecular multivalency effects enhance imine formation in aqueous medium allowing for dynamic modification of enzymatic activity

Imine formation under physiological conditions represents a challenging reaction due to the strong propensity of aldimines to be hydrolyzed. Herein we disclose the remarkable effect of supramolecular multivalency on increasing imine stability. A family of reactive aldehydes was synthesized bearing supramolecularly-active sites within their structure. The imine formation activity for such aldehydes was evaluated and compared with model aldehydes. The reaction of the best-performing species - containing two carboxylate groups-with a set of amines showed a significant decrease in imine yields as the degree of supramolecular multivalency between sidechains decreased. The reversible conjugation of amino acid derivatives and small peptides was also assayed, with excellent selectivities for the imine formation at the Nα position even in substrates containing competing sites. Preliminary results on protein bioconjugation revealed that a model enzyme could be dynamically inhibited upon reaction with the aldehyde, with its native activity being recovered by displacing the imine bonds with a suitable chemical effector (i.e., acylhydrazide).

Dipole moment as the underlying mechanism for enhancing the immobilization of glucose oxidase by ferrocene-chitosan for superior specificity non-invasive glucose sensing

Non-invasive methods for sensing glucose levels are highly desirable due to the comfortableness, simplicity, and lack of infection risk. However, the insufficient accuracy and ease of interference limit their practical medical applications. Here, we develop a non-invasive salivary glucose biosensor based on a ferrocene-chitosan (Fc-Chit) modified carbon nanotube (CNT) electrode through a simple drop-casting method. Compared with previous studies that relied mainly on trial and error for evaluation, this is the first time that dipole moment was proposed to optimize the electron-mediated Fc-Chit, demonstrating sturdy immobilization of glucose oxidase (GOx) on the electrode and improving the electron transfer process. Thus, the superior sensing sensitivity of the biosensor can achieve 119.97 μA mM-1 cm-2 in phosphate buffered saline (PBS) solution over a wide sensing range of 20-800 μM. Additionally, the biosensor exhibited high stability (retaining 95.0% after three weeks) and high specificity toward glucose in the presence of various interferents, attributed to the specific sites enabling GOx to be sturdily immobilized on the electrode. The results not only provide a facile solution for accurate and regular screening of blood glucose levels via saliva tests but also pave the way for designing enzymatic biosensors with specific enzyme immobilization through fundamental quantum calculations.

Synthesis and Characterization of 2-(((2,7-Dihydroxynaphthalen-1-yl)methylene)amino)-3',6'-bis(ethylamino)-2',7'-dimethylspiro[isoindoline-1,9'-xanthen]-3-one and Colorimetric Detection of Uranium in Water

2-(((2,7-Dihydroxynaphthalen-1-yl)methylene)amino)-3',6'-bis(ethylamino)-2',7'-dimethyl-spiro[isoindoline-1,9'-xanthen]-3-one was synthesized using Rhodamine 6G hydrazide (prepared using literature methods) and commercially available 2,7-dihydroxynaphthalene-1-carbaldehyde via imine condensation. Structural characterization was performed using FT-IR, 1H-NMR, 13C-NMR, X-ray, and HRMS. This Schiff base shows promise as a ligand for the colorimetric analysis of uranium in water.

New platinum (II) complexes based on schiff bases: synthesis, specification, X-ray structure, ADMET, DFT, molecular docking, and anticancer activity against breast cancer

Acylpyrazolone-based Schiff base ligands (HLⁿ) and their corresponding Pt(II) complexes with the general formula [Pt(Lⁿ)(Cl)] (n = 1-3) were synthesized and characterized by different spectroscopic techniques including ¹H-NMR, ¹⁹⁵Pt-NMR, LC-Mass, FT-IR, and UV-Vis spectroscopy, as well as elemental analysis. The crystal structure of one of the Schiff base ligands was also obtained. Based on the ADMET comparative results and the bioavailability radar charts, the complexes are completely drug-like. The Schiff base complexes with a structural difference of one methyl group in ligand were used as anticancer agents against human breast cancer cell lines SKBR3 and MDA-MB-231. The IC₅₀ values after treatment by [Pt(L¹)Cl] and [Pt(L²)Cl] were obtained more than cisplatin and less than carboplatin on cancer cells MDA-MB-231 and SKBR3, while the IC₅₀ value of [Pt(L³)Cl] was more than both other complexes and clinical Pt drugs. Molecular docking data showed that the groove binding is the main interaction with DNA double strands with a minor contribution from electrostatic interactions. To investigate the structure-activity relationship, DFT computational was done. All quantum chemical parameters display the drug approaching biomacromolecule and more biological activity of [Pt(L¹)Cl] > [Pt(L²)Cl] > [Pt(L³)Cl]. So, three Schiff base platinum complexes can be suitable candidates as anticancer drugs. Schiff-base ligands (HLn) and their Pt(II) complexes ([Pt(Ln)(Cl)], n=1-3) were obtained. To investigate their biological property and main interactions with DNA, ADMET, and cytotoxicity against MDA-MB-231 and SKBR3, DFT, and Molecular docking were done.

Indole-carbohydrazide linked phenoxy-1,2,3-triazole-N-phenylacetamide derivatives as potent α-glucosidase inhibitors: design, synthesis, in vitro α-glucosidase inhibition, and computational studies

BACKGROUND

A new series of indole-carbohydrazide-phenoxy-1,2,3-triazole-N-phenylacetamide hybrids 11a-o was designed based on molecular hybridization of the active pharmacophores of the potent α-glucosidase inhibitors. These compounds were synthesized and evaluated against α-glucosidase.

METHODS

The 15 various derivatives of indole-carbohydrazide-phenoxy-1,2,3-triazole-N-phenylacetamide scaffold were synthesized, purified, and fully characterized. These derivatives were evaluated against yeast α-glucosidase in vitro and in silico. ADMET properties of the most potent compounds were also predicted.

RESULTS

All new derivatives 11a-o (IC₅₀ values = 6.31 ± 0.03-49.89 ± 0.09 µM) are excellent α-glucosidase inhibitors in comparison to acarbose (IC₅₀ value = 750.0 ± 10.0 µM) that was used as a positive control. Representatively, (E)-2-(4-((4-((2-(1H-indole-2-carbonyl)hydrazono)methyl) phenoxy)methyl)-1H-1,2,3-triazol-1-yl)-N-(4-methoxyphenyl)acetamide 11d with IC₅₀ = 6.31 µM against MCF-7 cells, was 118.8-times more potent than acarbose. This compound is an uncompetitive inhibitor against α-glucosidase and showed the lowest binding energy at the active site of this enzyme in comparison to other potent compounds. Furthermore, computational calculations predicted that compound 11d can be an orally active compound.

CONCLUSION

According to obtained data, compound 11d can be a valuable lead compound for further structural development and assessments to obtain effective and potent new α-glucosidase inhibitors.

Promising Schiff bases in antiviral drug design and discovery

Emerging and re-emerging illnesses will probably present a new hazard of infectious diseases and have fostered the urge to research new antiviral agents. Most of the antiviral agents are analogs of nucleosides and only a few are non-nucleoside antiviral agents. There is quite a less percentage of marketed/clinically approved non-nucleoside antiviral medications. Schiff bases are organic compounds that possess a well-demonstrated profile against cancer, viruses, fungus, and bacteria, as well as in the management of diabetes, chemotherapy-resistant cases, and malarial infections. Schiff bases resemble aldehydes or ketones with an imine/azomethine group instead of a carbonyl ring. Schiff bases have a broad application profile not only in therapeutics/medicine but also in industrial applications. Researchers have synthesized and screened various Schiff base analogs for their antiviral potential. Some of the important heterocyclic compounds like istatin, thiosemicarbazide, quinazoline, quinoyl acetohydrazide, etc. have been used to derive novel Schiff base analogs. Keeping in view the outbreak of viral pandemics and epidemics, this manuscript compiles a review of Schiff base analogs concerning their antiviral properties and structural-activity relationship analysis.

Novel Biologically Active N-Substituted Benzimidazole Derived Schiff Bases: Design, Synthesis, and Biological Evaluation

Herein, we present the design and synthesis of novel N-substituted benzimidazole-derived Schiff bases, and the evaluation of their antiviral, antibacterial, and antiproliferative activity. The impact on the biological activity of substituents placed at the N atom of the benzimidazole nuclei and the type of substituents attached at the phenyl ring were examined. All of the synthesized Schiff bases were evaluated in vitro for their antiviral activity against different viruses, antibacterial activity against a panel of bacterial strains, and antiproliferative activity on several human cancer cell lines, thus enabling the study of the structure-activity relationships. Some mild antiviral effects were noted, although at higher concentrations in comparison with the included reference drugs. Additionally, some derivatives showed a moderate antibacterial activity, with precursor 23 being broadly active against most of the tested bacterial strains. Lastly, Schiff base 40, a 4-N,N-diethylamino-2-hydroxy-substituted derivative bearing a phenyl ring at the N atom on the benzimidazole nuclei, displayed a strong antiproliferative activity against several cancer cell lines (IC₅₀ 1.1-4.4 μM). The strongest antitumoral effect was observed towards acute myeloid leukemia (HL-60).

Perspectives on the Structural Design and Luminescent Behavior of Liquid Crystalline Materials Based on Copper(I) Complexes

This paper provides insight into the various studies that have been carried out to date on liquid crystalline materials based on copper(I) complexes. Although the study of copper(I) complexes with respect to their liquid crystalline property is quite limited, metallomesogens prepared with different structural components and ligands from groups such as azamacrocycles, alkythiolates, ethers, isocyanides, phenanthroline, Schiff bases, pyrazolates, phosphines, biquinolines, and benzoylthioureas are reported and summarized in this review. A special section is dedicated to the discussion of emission properties of copper(I) metallomesogens.

Ease to Challenges in Achieving Successful Synthesized Schiff Base, Chirality, and Application as Antibacterial Agent

This study reports how to overcome the challenges experienced in achieving successful synthesized Schiff base via types of Schiff base (chiral and achiral), synthesis, nature of products, and its antibacterial applications. Schiff base is a versatile ligand which is useful in asymmetric reactions to prepare chiral catalysts. It is also used in symmetric reactions to prepare achiral compounds. In line with the achiral compounds, conventional (room temperature and refluxing) and microwave irradiation methods are the two main types of methods to synthesize achiral Schiff base as reported in this review. Among various experimental approaches, this study supports the green chemistry microwave approach to synthesize Schiff base because of its benefits environmental sustainability. Problems relating to the nature of products formed from the synthesized Schiff bases were examined and resolved. Herein, the products could either be solid (crystals, powder, and precipitate), oily, or viscous (sticky) products. Some familiar characterization techniques used to identify and confirm the successful syntheses of Schiff bases, such as solubility test, melting point (MP), Fourier transform infrared (FTIR), ultraviolet-visible (UV-Vis), and nuclear magnetic resonance (NMR, 1H NMR, and 13C NMR), were discussed. In addition, the antibacterial studies on Schiff base and corresponding metal complexes confirmed their biological relevance to the human.

Evaluation of optimized molecular structure-antimicrobial and antioxidant efficacy relationship of Schiff bases

The synthesis, reactivity, structure, antimicrobial potential, and antioxidant property of some Schiff bases were extensively studied experimentally and theoretically using the B₃LYP method of DFT (density functional theory). Schiff bases formed with the interaction of salicylaldehyde and amino alcohols in a 1:1 molar ratio in ethanol. The physicochemical and spectroscopic investigations decide the plausible structure of these newly synthesized Schiff bases. The computational study can assess the molecular orbitals, chemical reactivity, stability, and molecular electrostatic potential of Schiff bases. The thermodynamic parameters and optimized structures of Schiff bases in the gaseous state investigated by the B₃LYP method of DFT. The evaluation of Schiff bases possesses antimicrobial resistance against gram-negative (Pseudomonas aeruginosa) and (Bacillus cereus)gram-positive bacterial strains as well as fungal strains (Candida albicans and Penicillium chrysogeum). The MIC (minimum inhibitory concentration) of all Schiff bases against Bacillus cereus was found in the range of 250 to 1200 µg. The MIC values of L₁H, L₂H, and L₃H against Penicillium chrysogeum were 400, 600, and 800 µg, respectively, whereas the MIC value of L₁H against Candida albicans was 600 µg. The free radical scavenging activity by the DPPH method was used to access potential antioxidant activity in Schiff bases.

Antioxidant and Anticancer Potential of the New Cu(II) Complexes Bearing Imine-Phenolate Ligands with Pendant Amine N-Donor Groups

Cu(II) complexes bearing NNO-donor Schiff base ligands (2a, b) have been synthesized and characterized. The single crystal X-ray analysis of the 2a complex revealed that a mononuclear and a dinuclear complex co-crystallize in the solid state. The electronic structures of the complexes are optimized by Density Functional Theory (DFT) calculations. The monomeric nature of 2a and 2b species is maintained in solution. Antioxidant activities of the ligands (1a, b) and Cu(II) complexes (2a, b) were determined by in vitro assays such as 1,1-diphenyl-2-picrylhydrazyl free radicals (DPPH^.) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) radicals (ABTS⁺). Our results demonstrated that 2a showed better antioxidant activity. MTT assays were performed to assess the toxicity of ligands and Cu(II) complexes in V79 cells. The antiproliferative activity of compounds was tested against two human tumor cell lines: MCF-7 (breast adenocarcinoma) and SW620 (colorectal carcinoma) and on MRC-5 (normal lung fibroblast). All compounds showed high cytotoxicity in the all-cell lines but showed no selectivity for tumor cell lines. Antiproliferative activity by clonogenic assay 2b showed a more significant inhibitory effect on the MCF-7 cell lines than on MRC-5. DNA damage for the 2b compound at 10 µM concentration was about three times higher in MCF-7 cells than in MRC-5 cells.

Comprehensive Empirical Model of Substitution—Influence on Hydrogen Bonding in Aromatic Schiff Bases

In this work, over 500 structures of tri-ring aromatic Schiff bases with different substitution patterns were investigated to develop a unified description of the substituent effect on the intramolecular hydrogen bridge. Both proximal and distal effects were examined using Density Functional Theory (DFT) in the gas phase and with solvent reaction field (Polarizable Continuum Model (PCM) and water as the solvent). In order to investigate and characterize the non-covalent interactions, a topological analysis was performed using the Quantum Theory of Atoms In Molecules (QTAIM) theory and Non-Covalent Interactions (NCI) index. The obtained results were summarized as the generalized, empirical model of the composite substituent effect, assessed using an additional group of simple ring-based Schiff bases. The composite substituent effect has been divided into separate increments describing the different interactions of the hydrogen bridge and the substituent: the classical substituent effect, involving resonance and induction mediated through the ring, steric increment based on substituent proximity to the bridge elements, and distal increment, derived from substitution on the distal ring.

Pincer Complexes Derived from Tridentate Schiff Bases for Their Use as Antimicrobial Metallopharmaceuticals

Within the current challenges in medicinal chemistry, the development of new and better therapeutic agents effective against infectious diseases produced by bacteria, fungi, viruses, and parasites stands out. With chemotherapy as one of the main strategies against these diseases focusing on the administration of organic and inorganic drugs, the latter is generally based on the synergistic effect produced by the formation of metal complexes with biologically active organic compounds. In this sense, Schiff bases (SBs) represent and ideal ligand scaffold since they have demonstrated a broad spectrum of antitumor, antiviral, antimicrobial, and anti-inflammatory activities, among others. In addition, SBs are synthesized in an easy manner from one-step condensation reactions, being thus suitable for facile structural modifications, having the imine group as a coordination point found in most of their metal complexes, and promoting chelation when other donor atoms are three, four, or five bonds apart. However, despite the wide variety of metal complexes found in the literature using this type of ligands, only a handful of them include on their structures tridentate SBs ligands and their biological evaluation has been explored. Hence, this review summarizes the most important antimicrobial activity results reported this far for pincer-type complexes (main group and d-block) derived from SBs tridentate ligands.

Photofunctions in Hybrid Systems of Schiff Base Metal Complexes and Metal or Semiconductor (Nano)Materials

Composite materials very often provide new catalytic, optical or other physicochemical properties not observed for each component separately. Photofunctions in hybrid systems are an interesting topic of great importance for industry. This review presents the recent advances, trends and possible applications of photofunctions of hybrid systems composed of Schiff base metal complexes and metal or semiconductor (nano)materials. We focus on photocatalysis, sensitization in solar cells (DSSC-dye sensitized solar cell), ligand-induced chirality and applications in environmental protection for Cr(VI) to Cr(III) reduction, in cosmetology as sunscreens, in real-time visualization of cellular processes, in bio-labeling, and in light activated prodrug applications.

A study of the photochemical behaviour and relaxation mechanisms of anti–syn isomerisation around quinazolinone –N–N bonds

High-resolution NMR experiments revealed that differently substituted quinazolinone-based Schiff bases undergo anti to syn isomerisation on exposure to ultraviolet light in DMSO solution.