bis-Schiff Base Research Articles

ZnO–TiO2 Nanoparticles Coated by the Dioxomolybdenum (VI) bis-Schiff Base Complex for Catalytic Oxidation of Sulfides

The oxygenation processes for the organic compounds have great applications in fine organic fabrications. To speed up progress in the industrialization of such oxidation systems, a monometallic dioxomolybdenum (VI) bis-Schiff base complex (MoO2L2) was synthesized through coordination of easily accessible 4-hydroxyiminophenol ligand (HL) with cis-MoO22+ ion in an octahedral geometry. The structural conformation of MoO2L2 and its coordinated ligand (HL) was determined using modern spectrophotometric tools. A heterogeneous catalyst (MoO2L2@ZnO–TiO2) was successfully prepared by immobilization of MoO2L2 on the surface of ZnO–TiO2 nanostructured particles through the deprotonation of 4-OH group in its coordinated ligand. Various analytical techniques were used to examine the surface morphology and internal structure features of ZnO–TiO2 and MoO2L2@ZnO–TiO2 nanocomposites. To study the catalytic efficiency of MoO2L2 and MoO2L2@ZnO–TiO2-based catalysts, they were employed in the oxygenation process of Ph2S (diphenyl sulfide) and MePhS (methylphenyl sulfide) using the most environmentally friendly oxidant (an aqueous H2O2) under an aerobic environment. A high degree of selectivity was observed for the productivity of diphenyl sulfoxide (Ph2SO) and methylphenyl sulfoxide (MePhSO), with some contamination of overoxidation side products (Ph2SO2 and MePhSO2). The catalytic oxidative ability was not observably superior for the heterogeneous coated catalyst by ZnO–TiO2 over its homogeneous one (MoO2L2) due to the less redox activity of ZnO and TiO2 nanoparticles in the catalytic cycles for the oxygen-transfer mechanism. Both catalysts were successfully recycled, in which the homogeneous catalyst sustained its high catalytic potential for up to three cycles, while the heterogeneous catalyst was able to be reused up to six times.

An in-silico Evaluation of Some Schiff bases for Their Potency Against SARS-CoV-2 Main Protease, PASS Prediction and ADMET Studies

SARS-CoV-2 has created an agonizing pandemic situation all over the world. The inhibition of SARS-CoV-2 main protease (Mpro) by the blockage of viral replication is considered an important drug target to the many researchers working to discover specific drugs for COVID-19 treatment. Schiff bases being documented to possess antimicrobial properties might be investigated as the candidate against COVID-19. Bioactivities of some symmetrical bis-Schiff bases were evaluated using computational studies on the basis of binding affinity, PASS prediction and ADMET study. On the basis of binding affinity, it is concluded that among eighteen tested ligands 2, 5, 8, 16, 17 showed excellent, ligands 4, 6, 18 showed good and the remaining ligands showed moderate inhibition against SARS-CoV-2 Mpro (6LU7) compared to a prescribed anti-Covid-19 drug, hydroxychloroquine (HCQ). PASS prediction revealed some of Schiff bases to have good anti-carcinogenic, anti-tuberculosis, antifungal, and antiviral activities. ADMET study predicted them to be non-toxic and harmless indicating that Schiff bases may act as a promising drug candidate for the treatment of COVID-19.

A study of mononuclear 3d transition metal bis-Schiff base complexes: Synthesis, characterization, and evaluation of their antibacterial activity

<p>In this study, we have outlined a conventional and user-friendly procedure for the production of <em>(E)-1-(((5-ethyl-1,3,4-thiadiazol-2-yl)imino)methyl)naphthalen-2-ol </em><em>(HL-1)</em> and <em>(E)-1-((thiazol-2-ylimino)methyl)-naphthalen-2-ol</em> (HL-2) by the reaction of heterocyclic amine, aldehyde in the presence of ethanol as a solvent and acid as the catalyst. The synthesis of new HL-1 and HL-2 may be accomplished with ease using this approach, which is also very efficient. In the presence of dipositive Co, Ni, and Cu metal complexation, HL-1 and HL-2 were carried out in the presence of metal: ligand (1:2). HL-1, HL-2, and metal complexes are characterized with the assistance of UV/visible, FT-IR, Mass, and <sup>1</sup>H NMR spectroscopy respectively. Furthermore, the ligands mentioned above (HL-1 and HL-2) and their metal complexes were tested for the antimicrobial study and showed an excellent inhibitory zone. These investigations indicated that HL1<strong>-</strong>Co (II), HL-1Cu (II), complexes and ligands HL-2Co (II), and HL-1Ni(II) had positive effects on <em>Escherichia coli</em> causing severe stomach cramps (Gram-negative- MTCC 1610) and positive impact on <em>Staphylococcus aureus</em> (Gram-positive MTCC<strong>-</strong>96) due to skin infections.</p>

Synthesis, in vitro thymidine phosphorylase inhibitory activity and molecular docking study of novel pyridine-derived bis-oxadiazole bearing bis-schiff base derivatives

The current study has afforded twelve analogs (4a-l) of pyridine-derived bis-oxadiazole containing bis-schiff base and subsequently evaluated for their potential to inhibit thymidine phosphorylase(in vitro). All the synthesized analogs were structurally elucidated using various spectroscopic tools including NMR and HREIMS. All synthesized scaffolds showed varied range of inhibitory potential with IC50values ranging from 5.19 ± 1.10 to 36.18 ± 4.60 μM in comparison to 7-deazaxanthine (IC50 = 30.28 ± 2.10 μM) as a standard drug. All analogs (except analog 4 l which displayed less potency than standard drug) showed improved potency having IC50 values of 19.73 ± 2.30, 16.14 ± 1.20, 18.93 ± 1.60, 22.78 ± 1.80, 30.47 ± 3.70, 5.19 ± 1.10, 23.13 ± 1.90, 21.56 ± 2.50, 4.88 ± 1.10, 26.63 ± 2.90 and 6.67 ± 1.10 respectively.Results obatined were compared to standard 7-deazxanthine drug with IC50 values of 30.28 ± 2.10 μM. Structure-activity relationship (SAR) studies revealed that analogs bearing –NO2, -CF3, –OH and –Cl moieties at various position of aryl part showed many folds more potency than standard 7-deazaxathine standard drug. In order to determine the potential mode of interactions with thymidine phosphorylase active sites, the most active analogs 4f (bearing 3-CF3& 5-NO2), 4i (bearing 3-OH & 5-NO2), and 4 k (bearing 2-OH &5-NO2) were further subjected to molecular docking study. The results confirmed that these active analogs adopted numerous important interactions including hyrognen bonding, pi-donor hydrogen bond, pi-pi T shaped, pi-pi stacking, pi-alkyl, pi-anion, pi-sigma, halogen (flourine) and numerous Vander Waals interactions with the amino acid of enzyme being targeted.

Synthesis and Characterization of New Bis-Schiff Bases Linked to Various Imide Cycles

This research includes the synthesis of new bis-Schiff bases linked to different imide cycles. There were some steps involved in the synthesis of the novel Schiff bases with succinimide, phthalimide, tetrachlorophthalimide, and tetrabromophthalimide cycles. The first step involved the preparation of 4,4`-bis[(4-aminophenyl) methyl benzylidene]tolidine (1) via the condensation reaction of 3,3'-dimethyl-(1,1'-biphenyl)-4,4'-diamine with 4-amino acetophenone. In the second step, compound 1 reacted with various cyclic anhydrides, affording bis-amic acid Schiff bases 2-5. In the third step, the products 2-5 were dehydrated using the fusion method to produce the target bis-imidyl Schiff bases 6-9. This work also involved the synthesis of bis-imidyl Schiff base 10 directly by fusion of compound 1 with 1,8-naphthalic anhydride. The prepared compounds were characterized depending on their FT-IR, 1H NMR, and 13C NMR spectra. The newly synthesized target compounds are expected to be very active biologically since their molecules are essential components of two active groups (imine and imide).

Synthesis, structural elucidation and optical activity of symmetric Schiff base-functionalized ferrocenes: Synergetic experimental and DFT insights

A number of Schiff base functionalized derivatives (3a-c) was synthesized from the conventional dehydration of ferrocenecarboxaldehyde and diamine precursors in acetonitrile as a solvent at ambient conditions. IR, UV–Vis, elemental analysis, 1H- and 13CNMR were used to elucidate the novel bis-Schiff base compounds. The nature of electronic absorptions was tracked using Time-Dependent Density-Functional Theory (TD-DFT). The molecular electrostatic potential illuminated that the target compounds are sharing relatively akin electronic distributions. In order to determine the electrophilic and nucleophilic sites, surface analysis of the structures was examined for this purpose. These sites are expected to possess an indispensable role to stabilize and robust the structures via typical hydrogen bonding and non-classical CH···π interactions. Type and influence of solvents on absorption spectra were pursued for the selected model (3a), in which aprotic solvents showed negative solvatochromism (more stable ground state), whereas protic solvents delivered positive solvatochromism (more stable excited state). For example, the metal-to-ligand charge transfer band displayed a gradual shift of the λmax (12 nm) when the type of solvent was switched from polar aprotic (ethyl acetate) to polar protic (methanol) due to the formation of hydrogen bonding, causing bathochromic shift. Eventually, the computationally resulting energy gap of the new products (ΔE) were found to be −4.258 (3a), −4.022 (3b) and −3.105 (3c) eV. These values were compared and found to be in a close level with produced figures from the spectra of density of states and with experimentally determined values using Tauc approach.

Synthesis of Conjugated bis-Schiff Base and Their Complexes as Dye-Sensitizer for Dye Sensitized Solar Cell (DSSC) Application

Schiff base and their metal complexes have been widely used as photovoltaic materials due to their excellent π-electron transfer properties along the molecule. A total of eleven conjugated symmetrical bis-Schiff base and their complexes with different π-spacers have been synthesized and spectroscopically characterized in order to investigate their conversion efficiency in dye-sensitizer solar cells (DSSC). All compounds were either substituted with hydroxy (-OH) or methoxy (-OMe) as the electron donor and difluoro boron (BF2) as the electron acceptor or without any substituent. All compounds were applied as dye-sensitizer in DSSC using titanium (IV) oxide (TiO2) coated on a fluoride doped tin oxide glass as the working electrode and electric paint containing carbon black, whereas graphene coated indium tin oxide glass as the counter electrode. The power conversion efficiencies of the eleven bis-Schiff bases were compared to N3 Dye as the benchmark standard. The results showed that the compound with aromatic ring bridge as the π-spacer and -OMe substituent gave the highest efficiency at 0.0691% whereas the compound with aromatic ring and BF2 gave the lowest efficiency at 0.0012%.

Synthesis, In Vitro α-Glucosidase Inhibitory Activity and Molecular Docking Study of New Benzotriazole-Based Bis-Schiff Base Derivatives

This study was carried out to synthesize benzotriazole-based bis-Schiff base scaffolds (1-20) and assess them in vitro for α-glucosidase inhibitory potentials. All the synthetics analogs based on benzotriazole-based bis-Schiff base scaffolds were found to display an outstanding inhibition profile on screening against the α-glucosidase enzyme. The synthetic scaffolds showed a varied range of inhibition profiles having IC50 values ranging from 1.10 ± 0.05 µM to 28.30 ± 0.60 µM when compared to acarbose as a standard drug (IC50 = 10.30 ± 0.20 µM). Among the series, fifteen scaffolds 1-3, 5, 6, 9-16, 18-20 were identified to be more potent than standard acarbose, while the five remaining scaffolds 4, 7, 8, 16, and 17, also showed potency against the α-glucosidase enzyme but were found to be less potent than standard acarbose. The structure of all the newly synthesized scaffolds was confirmed using different spectroscopic techniques such as HREI-MS and 1H- and 13C- NMR spectroscopy. To find a structure-activity relationship, molecular docking studies were carried out to understand the binding mode of the active inhibitors with the active sites of the enzyme and the results supported the experimental data.

Syntheses, characterization, crystal structures and Jack bean urease inhibitory property of NiII, CdII, CuII and FeIII complexes with bis-Schiff bases

Four new nickel(II), cadmium(II), copper(II) and iron(III) complexes, [Ni3(L1)2(μ2-η1:η1-CH3COO)2] (1), [Cd2(L1)2(CH3OH)2] (2), [Cu(L2)] (3) and [Fe2(L3)2(μ2-OCH3)2] (4), where L1, L2 and L3 are the dianionic form of N,N'-bis(5-fluorosalicylidene)-1,3-propanediamine (H2L1), N,N'-bis(3,5-difluorosalicylidene)-1,3-propanediamine (H2L2) and N,N'-bis(4-fluorosalicylidene)-1,3-propanediamine (H2L3), respectively, were prepared. The compounds have been characterized by physico-chemical methods. The structures of the metal complexes were also confirmed by single crystal X-ray diffraction. The Ni atoms in complex 1 are in square pyramidal and octahedral coordination environments. The Cd atoms in complex 2 are in an octahedral coordination environment. The Cu atom in complex 3 is in a tetrahedrally distorted square planar coordination environment. The Fe atoms in complex 4 are in an octahedral coordination environment. The Jack bean urease inhibitory assay indicated that the copper complex displays good activity.

Synthesis, Crystal Structures and Antibacterial Activities of N,N'-Ethylene-bis(3-bromosalicylaldimine) and Its Copper(II) and Cobalt(III) Complexes.

A bis-Schiff base N,N'-ethylene-bis(3-bromosalicylaldimine) (H2L) was prepared from 3-bromosalicylaldehyde and ethane-1,2-diamine. With H2L as ligand, a new copper(II) complex [CuL] (1) and a new cobalt(III) complex [CoL(NCS)(DMF)] (2) were prepared and characterized by physico-chemical methods and single crystal X-ray analysis. X-ray analysis indicates that the Cu atom in complex 1 is in square planar coordination, and the Co atom in complex 2 is in octahedral coordination. The compounds were tested in vitro for their antibacterial activities on Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas fluorescens. Both complexes have effective activities on the bacteria.

Synthesis and antitumor activities of five Cu(II) complexes of bis(5-halosalicylidene)-1,3-propanediamine derivatives.

The development of metal complexes of Schiff base has attracted much attention due to their DNA binding properties and extensive biological activities. We reported here five copper(II) complexes [Cu(L1)] (1), [Cu(L2)] (2), [Cu(L3)] (3), [Cu2(L4)(OAc)] (4), and [Cu2(L5)(HCOO)] (5) bearing the bis-Schiff base ligands of bis(5-chlorosalicylidene)-1,3-propanediamine (H2L1), bis(5-chlorosalicylidene)-2-methyl-1,3-propanediamine (H2L2), bis(5-bromosalicylidene)-2-methyl-1,3-propanediamine (H2L3), bis(5-chlorosalicylidene)-2-hydroxyl-1,3-propanediamine (H3L4), and bis(5-bromosalicylidene)-2-hydroxyl-1,3-propanediamine (H3L5), respectively. The single crystal X-ray diffraction analysis results revealed that complexes 1-3 present mononuclear structures and complexes 4 and 5 show dinuclear structures. It was also shown that all of these complexes are stable under physiological conditions. The in vitro antitumor activities of the five complexes were evaluated. Anticancer selectivity was also found for complex 2 on different cell lines with the lowest IC50 value on Hela cells. Further mechanistic studies showed that the three mononuclear Cu(II) complexes can induce apoptosis through the mitochondrial pathway by decreasing mitochondrial membrane potential and increasing the reactive oxygen species (ROS) and Ca2+ levels. They can activate caspase-3 and caspase-9, and can also regulate the expression of pro-apoptotic protein and anti-apoptotic protein in cells. All of these results showed that complex 2 is a potential anticancer drug.

Synthesis, and biological activity of some new 1,3 – bis ( 4 – nitro benzyl -2 - aryl hydro pyrimidine

According to bright importance’s showed by pyrimidine and hydro pyrimidine derivatives a newly series of hydro pyrimidine derivatives was synthesized by three steps. The first step by synthesized bis Schiff base from reaction two equivalents of p-nitro benzaldehyde with one equivalent of 1,3-propane diamine (1,3-diaminopropane) to afford compound 1. The next step was to reduction the imine group by NaBH4 to afford compound 2. The finally step by cyclization compound 2 during reaction it with some arylaldehyde in constated acetic acid and refluxing the mixture for 24 to 72 hours to afford compounds 3a-h. The resulting compounds were characterized by FT-IR, 1H NMR, 13C NMR, moreover, their structures confirmed by elementary analysis (CHN). The antibacterial activity for newly synthesis compounds 3a-h screened using Staphylococcus aureus as Gram positive bacteria and Escherichia coli as Gram negative bacteria. Compounds 3a and 3h exhibited highest inhibition zone as well compounds 33 and 3g showed moderated antibacterial activity.

Unprecedented bi- and trinuclear palladium(II)-sodium complexes from a salophen-type Schiff base: Synthesis, characterization, thermal behavior, and in vitro biological activities

Novel bi- and trinuclear palladium(II)-sodium complexes, {[PdL]Na(NO3)(EtOH)} (1) and {[PdL]2Na}Cl (2) based on salophen-type Schiff base N,N'-(1,2-phenylene)-bis(3-methoxysalicylideneimine) (H2L) were synthesized under ambient and sonochemical conditions. Ultrasonication proved to be a more effective method for the rapid synthesis of these bi- and trinuclear complexes under mild conditions. On the basis of the molecular structure of complexes 1 and 2, each palladium atom is placed in the “inner” N2O2 compartment, and the sodium atoms are located in the “outer” O2O’2 compartment of the twofold deprotonated bis-Schiff base ligand. In both complexes, each Pd(II) ion is four coordinated showing square planar geometry, whereas the Na(I) ions in complexes 1 and 2 adopt two different geometries, namely hepta and octa coordination, respectively. In addition, the solventless thermolysis of both complexes at 500 °C was also studied by thermal gravimetric analysis (TGA). EDX and powder XRD data pointed out the presence of highly pure nanoscaled materials. Furthermore, the anticancer and antibacterial activities of bi- and trinuclear complexes were examined towards MCF-7 human breast cancer cell line and evaluated against one gram-negative strain (Escherichia coli ATCC 25922) and one gram-positive strain (Staphylococcus aureus ATCC 6538). The in vitro studies revealed that complex 2 exhibited higher anticancer activity against MCF-7 cell line as well as better antibacterial effect on the examined bacteria strains than complex 1.

Synthesis, Antioxidant ability and Docking study for new 4,4'-((2-(Aryl)-1H-benzo[d]imidazole-1,3(2H)-diyl)bis(methylene))diphenol)

New series of 4,4'-((2-(Aryl)-1H-benzo[d]imidazole-1,3(2H)-diyl)bis(methylene))Diphenol(3a-g) was successfully synthesized from cyclization of the reduction product of bis Schiff bases (2) with aryl aldehydes bearing phenolic hydroxyl in the presence of acetic acid. The structure of these compounds was identified from FT-IR, 1H NMR, 13C NMR and EIMs. The Antioxidant capability was screened by DPPH and FRAP assays. Both assays showed antioxidant capability more than BHT as well. Compounds 3b and 3c showed antioxidant capacity slightly less than ascorbic acid. The docking study for theses compound was carried out as III DNA polymerase inhibitor. The results of docking demonstrated that the increase in hinderances around phenolic hydroxyl for the aryl attached position two for benzimidazole decrease the capability of interaction and give less bending and smaller docking score and there is inverse relationship between increasing hindrances around phenolic hydroxyl and DNA polymerase inhibition for these compounds.

Synthesis of a novel bis Schiff base chelating resin for adsorption of heavy metal ions and catalytic reduction of 4-NP

A novel CPS-AA chelating resin containing bis Schiff base was prepared by the CPS with synthetic small molecular ligands. It has been used for the adsorption of heavy metal ions in wastewater. Ft-IR spectroscopy and the 1H NMR spectrum proved the successful synthesis of Schiff base structure on the chelating resin. The results of adsorption experiments showed the maximum adsorption capacities for Cu (II), Pb (II) and Ni (II) were 3.74, 1.02, and 2.87 mmol/g respectively. The adsorption condition experiment proves that the material has excellent adsorption selectivity and reusability. The possible chelation mechanism was inferred to be four-tooth coordination, which is beneficial to the stretching of molecular chain and increases the adsorption capacity and stability of heavy metal ions. Finally, Cu-adsorbed composites (CPS-AA-Cu) were used as catalysts to explore the reduction and removal of 4-NP in an aqueous solution, and the results showed excellent catalytic performance.

Synthesis, Characterization, Antioxidant and Antibacterial Activities of Six Metal Complexes Based Tetradentate Salen Type Bis-Schiff Base

Considering the importance of metal complexes in the development of medicinal chemistry, a series of transition metal complexes of Co(II), Fe(II), Zn(II), Cu(II), and Ni(II) has been synthesized from N,N'-bis(salicylidene)-2,2-dimethyl-1,3-diaminopropane H2L Schiff base ligand. The reaction of the H2L with the selected metal ions led to tetrahedral and octahedral coordinated complexes. The structural features of the obtained metal complexes were determined using analytical techniques such as FT-IR, NMR, UV-Vis, X-ray powder diffraction, mass spectrometry, and Thermogravimetry–differential thermal (TGA/DTA) analysis. The measured conductance for obtained compounds has shown the electrolytic behavior of all obtained complexes. The synthesized ligand and corresponding complexes were screened for their antioxidant and antibacterial activities. Indeed, Co(II) and Fe(II) complexes have shown excellent antioxidant activities for DPPH radical scavenging and FRAP assays, respectively. The results obtained from the disc diffusion assay showed that Co(II), Fe(II), Zn(II), and Cu(II) complexes had displayed promising antibacterial activity against Escherichia coli and Staphylococcus aureus, while no effect has been observed on both strains for ligand H2L and its corresponding Ni(II) complex.

Synthesis and Molecular Docking Studies of New Series of Bis-Schiff Bases Thiadiazoles Derived From Disulfides and Thioethers with Potent Antibacterial Properties

Two new series of various heterocyclic bis-Schiff bases of Thiadiazoles disulfides and thioethers are synthesized. The first series was the synthesis of bis-Schiff of thiadiazole disulfides (4a-h) synthesized from their corresponding Schiff bases after oxidation by hydrogen peroxide. The second series was the synthesis of bis-Schiff base thiadiazole thioethers (7a-h). It was obtained from the reaction of bis-thiadiazole diamine (6) with different aldehyde. The diamine (6) was generated by reacting thiadiazole with dibromoethane in dimethylformamide and triethylamine as a catalyst. All of the synthesized compounds were analyzed by using FT-IR, 1H-NMR, 13C-NMR, and C-APT techniques. The synthesized compounds were screened against two gram-positive bacteria (Staphylococcus and streptococcus), and two strains of gram-negative (E. coli and klebsiella) in comparison to two standard strong antibiotic drugs (ciprofloxacin and vancomycin). Generally, all the synthesized compounds showed highly antibacterial properties, particularly, compounds (4b,4f, and 7b) which observed potent anti-bacterial properties against both gram- (positive, negative) bacteria were even higher than the standard drugs. Lastly, molecular docking studies were also applied to find the binding affinity and active sides of the products with the target proteins.

Bis-Schiff Bases of Isatin Derivatives Synthesis, and their Biological Activities: A Review

Isatin is a heterocyclic molecule that belongs to one of the most important classes of organic compounds known as indolines. Isatin, isatin analogs, and their Schiff bases have recently attracted a lot of attention in medicinal chemistry. Isatin, itself, shows various biological activities such as antiviral, anticancer, antimicrobial, anti-inflammatory, analgesic, antioxidant, and anticonvulsant. Bis- Schiff bases containing isatin moiety have been known to possess a wide spectrum of pharmacological activities. This review offers up-to-date information on the most active isatin bis-Schiff bases, which would include anticancer, antimicrobial, antiviral, anticonvulsant, anti-inflammatory, and analgesic activities. These observations can lead to new molecular modifications that result in compounds with more desirable pharmacological properties

Synthesis and Evaluation of Bis-Schiff Bases of Carbohydrazide as Antioxidant and Cytotoxic Agents.

Antioxidants are known to prevent oxidative stress-induced damage to the biomolecules and thus, delay the onset of cancers and many age-related diseases. Therefore, the development of novel and potent antioxidants is justified. During this study, we synthesized symmetrical Bis-Schiff bases of carbohydrazide 1-27, and evaluated their in vitro antioxidative activity and cytotoxic activity. Among synthesized compounds, six compounds 20 (IC50 = 12.89 ± 0.02 μM), 16 (IC50 = 14.32 ± 0.43 μM), 17 (IC50 = 18.52 ± 0.83 μM), 19 (IC50 = 22.84 ± 0.62 μM), 24 (IC50 = 35.1 ± 0.82 μM) and 15 (IC50 = 40.03 ± 1.06 μM) showed an excellent 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, better than the standard butylatedhydroxyanisole (BHA) (IC50 = 44.6 ± 0.6 μM). Likewise, two compounds 16 (IC50 = 4.3 ± 1.3 μM) and 20 (IC50 = 6.6 ± 1.6 μM) showed oxidative burst scavenging activity better than the standard drug ibuprofen (IC50 = 11.2 ± 1.9 μM). Some synthesized compounds showed good to moderate toxicity against prostate cancer (PC-3) cell lines. This study has identified potent antioxidants and good cytotoxic agents with the potential to further investigate.

Bis-Schiff base linkage-triggered highly bright luminescence of gold nanoclusters in aqueous solution at the single-cluster level

Metal nanoclusters (NCs) have been developed as a new class of luminescent nanomaterials with potential applications in various fields. However, for most of the metal NCs reported so far, the relatively low photoluminescence quantum yield (QY) in aqueous solution hinders their applications. Here, we describe the utilization of bis-Schiff base linkages to restrict intramolecular motion of surface motifs at the single-cluster level. Based on Au22(SG)18 (SG: glutathione) NCs, an intracluster cross-linking system was constructed with 2,6-pyridinedicarboxaldehyde (PDA), and water-soluble gold NCs with luminescence QY up to 48% were obtained. The proposed approach for achieving high emission efficiency can be extended to other luminescent gold NCs with core-shell structure. Our results also show that the content of surface-bound Au(I)-SG complexes has a significant impact on the PDA-induced luminescence enhancement, and a high ratio of Au(I)-SG will be beneficial to increasing the photoluminescence intensity of gold NCs.