bis-Schiff Base Research Articles

Cyclic Carbonate Synthesis from Epoxides and CO2 Catalyzed by Aluminum-Salen Complexes Bearing a nido-C2B9 Carborane Ligand.

The active and well-designed Schiff base ligands are considered "privileged ligands". The so-called salen ligands, i.e., the tetradentate [O, N, N, O] bis-Schiff base ligands, have also found broad applications in many homogeneous catalytic reactions. Modification of the salen ligands has concentrated on altering the substituents in the phenolate rings and variations in the diamine backbones. Herein, o-carborane-supported salen ligands (2) were designed and prepared. A series of aluminum-salen complexes (3·(sol)2), which were supported by the nido-C2B9 carborane anions, were synthesized. These Al(III) complexes showed high activities (TOF up to 1500 h-1) in catalyzing the cycloaddition of epoxides and CO2 at atmospheric pressure and near room temperature. Complexes 3·(sol)2 are one of the rare examples of Al-based catalysts capable of promoting cycloaddition at 1 bar pressure of CO2. Density functional theory (DFT) studies combined with the catalytic results reveal that the catalytic cycles occur on two axial sites of the Al(III) center.

Anticancer activity of four trinuclear cobalt complexes bearing bis(salicylidene)-1,3-propanediamine derivatives

Schiff base and its complexes are being paid more and more interests for their great prospects in biological applications. We reported here four cobalt(II) complexes [Co3(L1)2(HCOO)2] (1), [Co3(L2)2(HCOO)2(CH3OH)2]·2CH3OH (2), [Co3(HL3)2(OAc)2(DMF)2] (3) and [Co3(HL4)2(HCOO)2(DMF)2]·2H2O (4) bearing the bis-Schiff base ligand of bis(5-bromosalicylidene)-1,3-propanediamine (H2L1), bis(5-bromosalicylidene)-2-methyl-1,3-propanediamine (H2L2), bis(5-chlorosalicylidene)-2-hydroxyl-1,3-propanediamine (H3L3) and bis(5-bromosalicylidene)-2-hydroxyl-1,3-propanediamine (H3L4), respectively. The anti-tumor activities of the four titled complexes were screened on a series of tumor cell lines. After an overall consideration of their cytotoxicity on cancer cells and normal cells in comparison to those for cisplatin, complex 3 shows the best anticancer effect among the four titled complexes. It revealed the influence of anti-cancer effects of the substitution groups of H, Me and OH, as well as Cl and Br. Anticancer selectivity was also found for complex 3 on different cancer cell lines with the lowest IC50 value on T-24 cells. Complex 3 induces cell apoptosis through mitochondrial pathway as demonstrated by increasing the level of reactive oxygen species, decreasing mitochondrial membrane potential, activating caspase 3/9 and arresting cell cycle in G1 phase.

Bis-Schiff base functionalized Fe3O4 nanoparticles for the sensitive fluorescence sensation of copper ions in aqueous medium

A fluorimetric nanosensor based on the bis-Schiff base fluorophore functionalized Fe3O4 nanoparticles (Fe3O4@SiO2-Saloph) has been constructed for the sensation of aqueous Cu2+ ions. The final nanohybrid was thoroughly characterized by various analytical techniques. The characterization data confirmed the successful introduction of the fluorophore and the highly superparamagnetic nature of the nanoparticles. The fluorescence measurement showed that the fluorescence of the nanosensor was pH-dependent. Notably, the fluorescence was significantly reduced after the addition of Cu2+ ions at pH 6.0, and the linear concentration range for Cu2+detecting was 0.03−1 mg/L. The detection limit was measured to be 5.4 μg/L, showing the excellent sensitivity for Cu2+detection. Besides, the nanoparticles exhibited higher selectivity to Cu2+ over other studied interfering cations. Furthermore, the nanosensor demonstrated excellent sensing reversibility and practical applicability in actual water samples. Finally, the adsorption isotherm study suggested that a monolayer complexion of Cu2+ formed on the material surface.

Precise probe design based ESIPT coupled AIE mechanism toward endogenous cyanide in food detection and bioimaging

Cyanide (CN–) is one of the strongest and fastest-acting toxic substances, and its excessive presence will cause great harm to the environment, food and human health. Although several fluorescent probes that recognize CN– have been extensively reported, developing the fluorescent probe with aggregation-induced emission (AIE) and large Stokes shift is still an extremely difficult problem due to lack of effective strategies. Thus, continuing efforts to seek novel, structurally distinct and functionally specific structures with large Stokes shift and AIE features are highly anticipated. Herein, we design and synthesize a novel asymmetric bis-Schiff base block (named as HPBC) based on the excited state intramolecular proton transfer (ESIPT) and AIE mechanism. Benefiting from restriction of intramolecular rotation and –CN electron-withdraw nature promoting the ESIPT effect of HPBC in the recognition system, HPBC shows large Stokes shift (243 nm), high selectivity, rapid identification of CN– and AIE effects. Excitingly, the limit of detection (LOD) was calculated to be 1.32 × 10-7 M, which was much lower than the 1.9 × 10-6 M specified by the World Health Organization and better than other previously reported probes. More importantly, further investigations demonstrated that the molecule we designed was successfully applied to sense endogenous CN– in food samples and the low cytotoxicity of HPBC was allowed to discover CN– in C. elegans, mice and HeLa cells. Overall, this work provides a new viewpoint of the rational design and synthesis of fluorescent probe toward CN– with AIE and large Stokes shift features, and triggers the discovery of new functions and properties of biological materials, which would open a new frontier for probes.

Evaluation and molecular modelling of bis-Schiff base derivatives as potential leads for management of diabetes mellitus.

Developing a medication to cure and manage diabetes mellitus complications is of interest in medicinal chemistry. Toward this end, six bis-biphenyl-salicylaldehyde Schiff base derivatives have been evaluated for their α-glucosidase inhibition, antiglycation and anti-inflammation potentials. Four compounds (compounds 2-5) showed an excellent α-glucosidase inhibitory effect superior to that produced by acarbose. Additionally, the docking study revealed that these compounds are anchored within the binding pocket of α-glucosidase via hydrogen bonding, π-stacking and hydrophobic interactions, comparable to a high number of hydrogen bonding involved in anchoring acarbose. Interestingly, all tested compounds showed varying degrees of antiglycation activity with superior activity for two of them (compound 1 and compound 6) compared to the standard rutin. Moreover, the results indicated an outstanding anti-inflammatory activity for two compounds (compounds 1 and 6) compared to ibuprofen.

Bis(thiophen-2-yl-methylene) Benzene-1, 4-Diamine as Fluorescent Probe for the Detection of Fe3+ in Aqueous Samples.

A Schiff base bis(thiophen-2-yl-methylene)benzene-1, 4-diamine (L) was synthesized and used for selective and sensitive detection of Fe3+. L exhibited enhanced fluorescence response at excitation of 365nm and emission wavelength of 440nm for Fe3+. The formation of a 1:1 complex between L and Fe3+ was suggested by Job's plot by fluorescence titration and from optimized structures using Density functional theory (DFT). The fluorescence intensity was directly proportional to concentration of Fe3+ (R2 = 0.999) with the detection limit of 3.8 × 10-7M and the binding constant of 1.20 × 104M-1 at pH = 6.0. The probe was used to detect Fe3+ in different water samples with the percentage recovery of 99.7-103%. The interference of the other cations are < 5%.

Metal Based Bioactive Nitrogen and Oxygen Donor Mono and Bis Schiff Bases: Design, Synthesis, Spectral Characterization, Computational Analysis and Antibacterial Screening.

The scientific interest in developing the advanced metal based compounds to inhibit and control bacterial infections is continuously rising. Keeping in view their pharmacological significance, two new bioactive symmetrical phenylenediamine mono- and bis-Schiff bases, 2-{[(4-aminophenyl)imino]methyl}-6-methoxyphenol (L1) and 2,2'-{benzene-1,2-diylbis[nitrilomethylylidene]}bis(6-methoxyphenol) (L2) have been synthesized and characterized by using physical techniques, spectral methods, elemental and DFT based computational analysis with B3LYP/6-311++G(d, p) basis set. Furthermore, the synthesized ligands were complexed with VO, Mn, Co, Ni, Cu and Zn ions in ratio [M:L,1:2 and 1:1], respectively. All the complexes exhibited significant antibacterial action against all tested bacterial strains. But overall, the zinc complexes possessed higher antibacterial activity. These results concluded that metal complexes might be promising induction in the upcoming time for medical purposes.

A novel “turn-on” fluorescent sensor based on Tetraphenylethylene-planarized bis-Schiff base for dual-state TFA detection

Fast and effective volatile acid trifluoroacetic acid (TFA) sensing is urgently demanded environmental safety. Herein, a novel “turn-on” fluorescent chemosensor of tetraphenylethylene (TPE)-planarized bis-Schiff-base was designed and facilely synthesized. The bi-Schiff-based TPE derivative contains two symmetrical terminal naphthalene rings making it nonluminescence. While it exhibited obvious “turn on” fluorescent emission and a real-time visual color changes upon TFA both in solution and vapor phases, respectively. The test paper color change was reversible by the fuming of NH3. Photoluminescence (PL), ultraviolet-visible (UV–vis) absorption spectra and density functional theory (DFT) calculations were employed to investigate the acidichromism mechanism. The fluorescent sensor shows high selectivity and sensitivity for TFA detection. The design of TPE-planarized provide a new strategy for AIE-active “turn-on/off” fluorescence sensors.

Synthesis, spectroscopic characterization (FT-IR, NMR, UV-Vis), DFT study, antibacterial and antioxidant in vitro investigations of 4,6-bis((E)-1-((3-(1H-imidazol-1-yl)propyl)imino)ethyl)benzene-1,3-diol

A new bis-Schiff base derived from N-(3-Aminopropyl)imidazole and 4, 6-diacetylresorcinol was obtained. The bis Schiff base RS was characterized through mass spectrometry, elemental analysis, infrared, UV-Vis, 1H and 13C NMR spectroscopy. The B3LYP method was used to calculate the optimized structure of the molecule through density functional of theory (DFT) using the 6-31G (d, p) basis set. The 1H and 13C NMR chemical shifts with respect to TMS were calculated using the (GIAO) method in DMSO‑d6 and compared with the experimental data. In addition, the frontier molecular orbitals, electronic properties and the molecular electrostatic potential (MEP) of RS were investigated using DFT calculations. The compound showed significant antibacterial activity against Staphylococcus aureus. The DPPH free radical scavenging assay was used to evaluate the antioxidant activity. The effective concentration (EC50) showed that the compound has a good antioxidant activity.

Synthesis, characterization, superoxide dismutase, and antimicrobial activities of Co (II) complexes with Schiff base ligand and their hybrid proteins

AbstractMetal complexes have been reported to possess excellent free radical scavenging and antimicrobial properties. In the present study, seven linear trinuclear complexes were synthesized based on bis Schiff base ligand and complexes 1, 3–7 are reported for the first time. Their structure was characterized by IR spectroscopy and single crystal diffraction. BSA was used as carrier to hybridize the synthesized complexes to construct hybrid proteins. The interaction between metal complex and BSA was studied by UV–Vis spectrophotometry and fluorescence spectroscopy. Static quenching was the main mechanism identified for the interaction between metal complex and BSA. In the superoxide dismutase (SOD) activity test, IC50 values of complexes and hybrid proteins range between 2.89 and 26.53 μM, with hybrid proteins demonstrating a stronger activity than the complexes. Among all the complexes studied, complex 5 exhibited the strongest inhibition against Candida albicans (MIC 12.5 μg ml−1) and Cryptococcus neoformans (MIC 6.5 μg ml−1).

Structures, fluorescence, and superoxide radical scavenging activities of two cd–Ln (Ln = Gd, Er) coordination polymers with an open-chain ether Schiff base and isonicotinate

Two Cd–Ln coordination polymers (CPs), with the open-chain ether Schiff base bis(5-bromine-3-methoxysalicylidene)-3-oxapentane-1,5-diamine (H2L), {[CdLnL(OAc)(NO3)(CH3OH)(isonicotinate)]·(3CH2Cl2)}n (Ln = Gd (1) and Er (2)), have been synthesized by the interfacial diffusion method. The structure analysis reveals that both CPs 1 and 2 are infinite one-dimensional zigzag coordination polymers, which are formed by isonicotinate bridging CdLnL cluster units. The fluorescence properties of H2L, 1 and 2 in the solid-state were studied. Compared with the free H2L, the fluorescence peaks of the two Cd–Ln CPs have undergone a significant blue shift (about 80 nm) and enhancement. This is due to the increased rigidity of the ligand after coordination of the metal ions with the ligand, which reduces the energy loss of thermal vibration. The fluorescence enhancement of 1 is greater than that of 2, which may be caused by the lanthanide contraction. Moreover, the results of experiments in vitro indicate that H2L, 1 and 2 have good ability to scavenge superoxide radical and that 1 and 2 are higher than free H2L, where their IC50 value is in the range 12.5–21.4 μM.

Synthesis, crystal structures and biological activity of trinuclear nickel(II) and copper(II) complexes derived from N,N'-bis(4-bromosalicylidene)-1,3-pentanediamine

The self-assembly reaction of the bis-Schiff base N,N'-bis(4-Bromosalicylidene)-1,3-pentanediamine (H2L) with nickel chloride and sodium azide in methanol afforded a new phenolate and end-on azide bridged trinuclear nickel complex [Ni3L2(μ1,1-N3)2(CH3OH)2]2CH3OH (1). The reaction of H2L with copper acetate produced a new phenolate and acetate bridged trinuclear copper complex [Cu3L2(CH3COO)2] (2). The complexes were characterized by elemental analysis, IR and UV-Vis spectroscopy. The crystal structures of the complexes have been determined by X-ray crystallography. In complex 1, the Ni atoms are in octahedral coordination, while in complex 2, the Cu atoms are in square pyramidal and octahedral coordination. The Schiff base ligand coordinates to the metal atoms through the two phenolate O and two imine N atoms. The antimicrobial activities of the complexes were assayed and evaluated.

Preparation of a bis-Schiff base immobilized mesoporous SBA-15 nanosensor for the fluorogenic sensing and adsorption of Cu2.

An inorganic-organic chemosensing material (MS-NSP) was developed by anchoring the bis-Schiff base fluorophore onto the channel surface of a SBA-15 mesoporous silica surface with a quaternary ammonium linker. The mesostructure, morphology, and spectral features of MS-NSP were systematically described. The nanohybrid could be implemented as a multifunctional fluorescent nanosensor for Cu2+ ions. A good linearity was observed over the concentration range from 0 to 4 mM, and the lower Cu2+ detection limit by MS-NSP was found to be 0.19 μM. Additionally, the fluorescence response of MS-NSP was remarkably specific for Cu2+ ions compared to other competitive ionic species. Moreover, the MS-NSP can also be utilized as an adsorbent for the effective elimination of Cu2+ from an aqueous solution. The kinetic features of adsorption were well described by the pseudo-second-order model and the sorption isotherm was in agreement with the Langmuir model. The theoretical maximum adsorption amount of Cu2+ ions was determined at 58.5 mg g-1. Finally, the interaction of MS-NSP and Cu2+ was investigated using theoretical calculations. Overall, the material in the present study is useful for both the sensitive detection and effective extraction of Cu2+ ions.

Structural and magnetic studies of six-coordinated Schiff base Dy(iii) complexes

The tuning of slow magnetic relaxation of six-coordinated Dy(iii) complexes was achieved through chloride and bis-Schiff bases bearing different spacers.

Electronic Structure of Two New Bis-Schiff Base Ligands using DFT Method

Two bis-Schiff Bases 1 and 2 are ligands that can coordinate with manganese metal to form stable complexes and have biological activity. Thermodynamic parameters, HOMO-LUMO energy levels and FTIR spectra of two ligands have been computed using B3LYP/6-311++G(d,p) functional of the DFT calculations. Both ligands are favored thermodynamically, and the ligand 1 has been shown to be more stable than ligand 2. The Polarizability values of two ligands have been investigated. The results refer that ligand 2 interacts earlier than ligand 1 to the metal ion. The FTIR spectra of two ligands have been evaluated. All results show the good agreement between the theoretical and experimental data.

Synthesis of Bis (Benzoyl Acetone Ethylene Diimine) Schiff Base Complex of Nickel (II) Supported on Magnetite Silica Nanoparticles (Fe3O4@SiO2/Schiff-Base of Ni(II)) and Using It as an Efficient Catalyst for Green Synthesis of 1-Amidoalkyl-2-Naphthols

Synthesis of Bis (Benzoyl Acetone Ethylene Diimine) Schiff Base Complex of Nickel (II) Supported on Magnetite Silica Nanoparticles (Fe3O4@SiO2/Schiff-Base of Ni(II)) and Using It as an Efficient Catalyst for Green Synthesis of 1-Amidoalkyl-2-Naphthols

Synthesis of New Series Bis-3-Chloro-β-Lactam Derivatives from Symmetrical Bis-Schiff Bases as Effective Antimicrobial Agents with Molecular Docking Studies

Endeavoring to find a new type of antimicrobial agents, a new sequence of bis-Schiff bases and bis-3-cholro-β-lactams are synthesized. An astonishing class of strained compounds is part of the symmetrical bis-Schiff bases that has widespread applications and building blocks for the combination of bis-3-cholro-β-lactams antibiotics. Bis-3-cholro-β-lactams are synthesized through (Staudinger) [2+2] ketene-imine cycloaddition reaction. Structures of the produced compounds are deduced by 1H, 13C-NMR, and FT-IR spectroscopies. All produced compounds are shown moderate to good antimicrobial activity compared to human pathogenic bacteria strains (Escherichia coli and Staphylococcus aureus), also compared to Aspergillus Niger and Trichophyton mentagrophytes fungi through the broth microdilution technique. A molecular docking study is used for showing the active sides and binding affinity of the products with the target proteins or receptors of E. coli (PDB ID: 3GI9).

Synthesis, Spectral Characterisation and Pharmacological Studies on Co(II), Ni(II), Cu(II) and Zn(II) Bis-Schiff Base Complexes Derived From 4-hydroxybenzohydrazide

The transition metal(II) chelates were prepared by the reactions of bis-Schiff base ligands derived from 4-hydroxy benzohydrazide and isophthalaldehyde / o-phthaldehyde in 1:1 metal to ligand ratio. The formed ligands and their metal complexes have been investigated by the following spectroscopic tools i.e, elemental analysis, FT-IR spectra, molar conductance, 1H NMR, ESI-mass, electronic spectra, magnetic moments, ESR and thermal analyses. The low molar conductance values give the non- electrolytic nature of the metal(II) chelates. From that the spectroscopic observations of complexes having the molecular formula [M(Ln)2Cl2] (where M= Co(II), Ni(II), Cu(II) and Zn(II), n=1and 2) and act as tetradentate N2O2 donor sites of ligands. The docking results predicts that the protein with ligands having good interaction energy. All formed complexes have efficient antibacterial activity than ligand of tested pathogens. The mode of binding interaction of ct-DNA and Cu(II) complexes gives the intercalative binding with hypochromism shifts using electronic titrations method. In electrophoresis, cleavages of PUC18DNA to cleave effectively with Cu(II) complexes in the presence of hydroxyl radicals. The antioxidant assay of DPPH radical scavenging activity of tested compounds shows good results, when compared to ascorbic acid as standard. The anticancer MTT assay of Cu(II) complexes tested against MCF-7 cancerous cells gives the promising therapeutic activity.

A novel “off-on-off” fluorescent probe for sensing of Fe3+ and F− successively in aqueous solution and its application in cells

We have successfully developed a bis-schiff base fluorescent probe L, linking hemicyanine aldehyde and salicylaldehyde through hydrazine hydrate, which continuously identify Fe3+ and F− in MeCN-Tris (v/v, 2:1, 10 mM, pH 7.3) solution. The probe L showed a highly selective and sensitive fluorescence “turn-on” for Fe3+ over other metal ions accompanying with the solution color change from yellow to red. Furthermore, the resulting L-Fe3+ complex detect only F− among the common various anions. The bonding mechanisms were detected by fluorescence and absorption titrations, 1H NMR titrations, HRMS and theoretical calculations. In addition, the probe has been used for liquid colorimetry and test paper colorimetric identification of Fe3+. Moreover, the probe L was used for sequentially off-on-off fluorescence imaging of Fe3+ and F− in HeLa cells.

Synthesis, molecular modeling, and biomedical applications of oxovanadium(IV) complexes of Schiff bases as a good SARS-CoV-2 inhibitor

Oxovanadium(IV) complexes of dibasic symmetrical bis-Schiff bases synthesized from 1,6-hexanediamine and orthohydroxy aldehydes or diketones. Their formation was confirmed with the help of elemental analysis, FTIR, 1H NMR, UV-visible and mass spectra, magnetic susceptibility, and conductance measurements. Quantum mechanical calculations are indicative to the proposed structures of the complexes. Most of the ligands and complexes have considerable inhibition capacity on mycelia growth against selected pathogenic fungi and bacteria and show good antioxidant property too. Complexes showed good larvicidal activity against the mosquito larvae (Culex quinquefasciatus). Molecular docking of a Schiff base, (BzA-HD-BzAH2) with SARS-CoV-2 Mpro revealed the best binding affinity with the receptor protein compared to the approved medicine hydroxychloroquine (HCQ) and favipiravir (FVP). The ADMET analysis showed that ligand is non-carcinogenic and less toxic than standards, HCQ or FVP. However, these in silico studies proved BzA-HD-BzAH2 to be a good candidate for development as a therapeutic drug against SARS-CoV-2.