Search Results (86)

The use of radiosensitizers is a beneficial approach in cancer radiotherapy treatment. However, the enhancement of radiation effects on cancer cells by radiosensitizers involves several different mechanisms, reflecting the chemical nature of the radiosensitizer. G-quadruplex (G4) DNA ligands have emerged in recent years as a potential new class of radiosensitizers binding to specific DNA sequences. Recently, we have shown that the Re(I) tricarbonyl complex PDF-Pz-Re and its pyrazolyl-diamine chelator PDF-Pz, carrying a N-methylated pyridostatin (PDF) derivative, act as G4 binders of various G4-forming DNA and RNA sequences. As described in this contribution, these features prompted us to evaluate PDF-Pz-Re and PDF-Pz as radiosensitizers of prostate cancer PC3 cells submitted to concomitant treatment with Co-60 radiation. The compound RHPS4 was also tested, as this G4 ligand was previously shown to exhibit strong radiosensitizing properties in other cancer cell lines. The assessment of the resulting radiobiological effects, namely through clonogenic cell survival, DNA damage, and ROS production assays, showed that PDF-Pz-Re and PDF-Pz were able to radiosensitize PC3 cells despite being less active than RHPS4. Our results corroborate that G4 DNA ligands are a class of compounds with potential interest as radiosensitizers, deserving further studies to optimize their radiosensitization activity and elucidate the mechanisms of action. Full article

In recent years, extensive attention has been paid to advanced oxidation processes (AOPs) with peracetic acid (PAA), a widely used disinfectant, using transition metal ions for the degradation of organic contaminants within water environments. Mn(II) has been widely used as an effective homogeneous transition metal catalyst for oxidant activation, but it has shown poor performances with PAA. Since the stability of manganese species can be enhanced through the addition of ligands, this study systematically investigated a novel AOP for the oxidation of carbamazepine (CBZ) using an Mn(II)/PAA system with several different ligands added. The reactive species were explored through UV-vis spectrometry, scavengers, and probe compounds. The results suggest that Mn(III)–ligand complexes and other high-valent Mn species (Mn(V)) were generated and contributed obviously toward efficient CBZ oxidation, while radicals like CH₃CO₂^• and CH₃CO₃^• were minor contributors. The oxidation efficiency of Mn(II)/PAA/ligands depended highly on ligand species, as ethylene diamine tetraacetic acid (EDTA) and oxalate (SO) could promote the oxidation of CBZ, while pyrophosphate (PPP) showed modest enhancement. The results obtained here might contribute to the removal of residue pharmaceuticals under manganese-rich waters and also shed light on PAA-based AOPs that could help broaden our present knowledge of manganese chemistry for decontamination in water treatment. Full article

The copper(II) complexes of general formula [Cu(^GL2^H,H)(Cl)] (A4–A6, G = NO₂, H and OMe, respectively), bearing NNO tridentate Schiff base ligands (^GL2^H,H)⁻ derived from the mono-condensation of 1,3-diaminopropane and G-substituted salicylaldehydes, are here reported. The elongation of the diamine with one additional carbon atom with respect to the triad derived from ethylenediamine [Cu(^GL1^H,H)(Cl)] (A1–A3, G = NO₂, H and OMe, respectively) led to different synthetic procedures, with the difficult isolation of A6 that could be obtained only in few crystals suitable for X-ray diffractions. Operating in acidic conditions to promote the coordination of chloride and expulsion of pyridine from the complex [Cu(^GL2^H,H)(py)](ClO₄) (G = NO₂) allows for obtaining A4. On the other hand, structural rearrangement occurs when G = H, yielding the dinuclear species [Cu₂(μ-saltn)(^HL2^H,H)](ClO₄)⋅0.5MeOH (D5⋅0.5MeOH) instead of the desired A5, which can be obtained by avoiding the use of HCl and operating in the excess of LiCl. Finally, A4 and A5 were investigated as cytotoxic agents against malignant (MDA-MB-231 and 22-Rv1) and healthy (HaCaT) cell lines, and the ability of the most promising A5 to be internalized and interact with cellular targets was studied. Full article

Three new asymmetrically coordinated lanthanide derivatives based on the bicompartmental salen-type ligands N,N′-bis(3-ethoxysalicylidene)propylene-1,3-diamine (H₂EtOsalpr) and 3-ethoxysalicylaldehyde (HEtvain) have been synthesized and structurally and photophysically characterized. All the compounds show dimeric structures of the general formula [Ln(H₂EtOsalpr)(NO₃)₂(Etvain)]₂ (Ln = Nd, Eu, Dy), with each salen-type ligand bridging two lanthanide ions. The Etvain ligand comes from the H₂EtOsalpr decomposition being coordinated to the corresponding lanthanide. The Nd(III) derivative shows fluorescence emission in the NIR region, but for the Eu(III) and Dy(III) compounds, only a broad band, attributed to the ligand emission, was observed. Full article

Bulky NCN aryl-diamides featuring methyl groups in the benzyl positions were synthesized with the aim of creating a new class of meta-xylene-based trianionic pincer ligands where the common decomposition pathway of metal pincer complexes via C-H activation is prevented. Sterically demanding substituents on the ligands furthermore provide steric protection of the metal centre and can help prevent the dimerization of the complexes. While a double deprotonation of the ligands and the formation of a dilithium salt was straightforward, difficulties were encountered when attempting to deprotonate the ipso-CH proton on the central aryl ring to yield trianionic ligands. This stands in contrast to related pincer ligands without methyl groups in the benzylic positions. Experimental and theoretical investigations led to the conclusion that the challenges encountered when attempting the third deprotonation are likely caused by an interplay of increased electron density at the nitrogen atoms and steric hindrance. Both effects originate in the introduction of methyl groups in the benzylic positions, which make the targeted proton less accessible. These results provide further insight into the impact of methyl groups in the benzyl positions on both steric and electronic properties of NCN pincer ligands, which may find utility in coordination chemistry applications where metalation can be achieved by direct C-H activation rather than requiring triple deprotonation. Full article

2,5-furandicarboxaldehyde (DFF) is one of the most promising biomass-based building blocks for the synthesis of biobased polymers. DFF can be obtained from 5-hydroxymethylfurfural (HMF), a fructose derivate, and it is a key molecule in the sequence of reactions of furan chemistry to develop biobased plastics. In this frame, four manganese(III)–Schiff base complexes 1–4 have been obtained. The general formula for the complexes, MnLⁿ(OCN)(H₂O/CH₃OH)_m (Lⁿ being the Schiff base ligands L¹–L⁴, formed as the result of the condensation of different substituted hydroxybenzaldehydes with diverse diamines, and m = 1–3), has been confirmed by characterization through different analytical and spectroscopic techniques. X-ray crystallographic studies for 1 and 2 showed tetragonally distorted octahedral structures, where the Schiff base was placed in the equatorial coordination positions of the Mn(III) ion. Complexes 1 and 2 behaved as efficient catalysts in the oxidation of HMF to DFF in an electrolytic reaction at pH 8.5, with phosphate buffer at room temperature, with conversion rates of 70–80%. On the other hand, complexes 3 and 4, where the axial position was sterically less accessible, yielded only an 11% conversion of HMF to DFF. The results indicate that a correct selection of metal complexes allows the development of a new efficient way to obtain DFF. Full article

A series of colorful binuclear Schiff bases derived from the different diamine bridges including 1,2- ethylenediamine (bis-Et-SA, bis-Et-4-NEt₂, bis-Et-5-NO₂, bis-Et-Naph), 1,2-phenylenediamine (bis-Ph-SA, bis-Ph-4-NEt₂, bis-Ph-5-NO₂, bis-Ph-Naph), dicyano-1,2-ethenediamine (bis-CN-SA, bis-CN-4-NEt₂, bis-CN-5-NO₂, bis-CN-Naph) have been designed and prepared. The optical properties of these binuclear Schiff base ligands were fully determined by UV–Vis absorption spectroscopy, fluorescence emission spectroscopy, and time-dependent-density functional theory (TD-DFT) calculations. The inclusion of D-A systems and/or π-extended systems in these binuclear Schiff base ligands not only enables adjustable RGB light absorption and emission spectra (300~700 nm) but also yields high fluorescence quantum efficiencies of up to 0.84 in MeCN solution. Then, with the ESIPT (excited-state intramolecular proton transfer) property, fluorescence analysis showed that the probe bis-Et-SA and bis-Ph-SA could recognize Zn²⁺ via the “turn on” mode in the MeCN solution. During the detection process, bis-Et-SA and bis-Ph-SA demonstrate rapid response and high selectivity upon the addition of Zn²⁺. The coordination of Zn²⁺ with the oxygen atom and Schiff base nitrogen atom in a tetrahedral geometry is confirmed by Job’s plot, FT-IR, and ¹H NMR spectroscopy. In addition, the paper test and Hela cells were successfully carried out to detect Zn²⁺. Moreover, the sensitivity of bis-Et-SA and bis-Ph-SA is much better than that of those Schiff base ligands containing only one chelating unit [O^N^N^O]. Full article

Several novel copper (II) complexes of reduced Schiff bases containing fluoride substituents were prepared and structurally characterized by single-crystal X-ray diffraction. The complexes exhibited diverse structures, with the central atom in distorted tetrahedral geometry. The biological effects of the products were evaluated, specifically their cytotoxicity, antimicrobial, and antiurease activities, as well as affinity for albumin (BSA) and DNA (ct-DNA). The complexes showed marked cytotoxic activities in the HepG2 hepatocellular carcinoma cell line, considerably higher than the standard cisplatin. The cytotoxicity depended significantly on the substitution pattern. The best activity was observed in the complex with a trifluoromethyl group in position 4 of the benzene ring—the dichloro[(±)-trans-N,N′-bis-(4-trifluoromethylbenzyl)-cyclohexane-1,2-diamine]copper (II) complex, whose activity (IC₅₀ 28.7 μM) was higher than that of the free ligand and markedly better than the activity of the standard cisplatin (IC₅₀ 336.8 μM). The same complex also showed the highest antimicrobial effect in vitro. The affinity of the complexes towards bovine serum albumin (BSA) and calf thymus DNA (ct-DNA) was established as well, indicating only marginal differences between the complexes. In addition, all complexes were shown to be excellent inhibitors of the enzyme urease, with the IC₅₀ values in the lower micromolar region. Full article

It is generally accepted that adjacent guanine residues in DNA are the primary target for platinum antitumor drugs and that differences in the conformations of the Pt-DNA adducts can play a role in their antitumor activity. In this study, we investigated the effect of the carrier ligand cis-1,3-diaminocyclohexane (cis-1,3-DACH) upon formation, stability, and stereochemistry of the (cis-1,3-DACH)PtG₂ and (cis-1,3-DACH)Pt(d(GpG)) adducts (G = 9-EthlyGuanine, guanosine, 5′- and 3′-guanosine monophosphate; d(GpG) = deoxyguanosil(3′-5′)deoxyguanosine). A peculiar feature of the cis-1,3-DACH carrier ligand is the steric bulk of the diamine, which is asymmetric with respect to the Pt-coordination plane. The (cis-1,3-DACH)Pt(5′GMP)₂ and (cis-1,3-DACH)Pt(3′GMP)₂ adducts show preference for the ΛHT and ∆HT conformations, respectively (HT stands for Head-to-Tail). Moreover, the increased intensity of the circular dichroism signals in the cis-1,3-DACH derivatives with respect to the analogous cis-(NH₃)₂ species could be a consequence of the greater bite angle of the cis-1,3-DACH carrier ligand with respect to cis-(NH₃)₂. Finally, the (cis-1,3-DACH)Pt(d(GpG)) adduct is present in two isomeric forms, each one giving a pair of H8 resonances linked by a NOE cross peak. The two isomers were formed in comparable amounts and had a dominance of the HH conformer but with some contribution of the ΔHT conformer which is related to the HH conformer by having the 3′-G base flipped with respect to the 5′-G residue. Full article

This study aims to advance the field of green chemistry and catalysis by exploring alternatives to conventional non-renewable energy sources. Emphasis is placed on hydrogen as a potential fuel, with a focus on the catalytic properties of Ni(II) complexes when coordinated with o-phenylenediamine and diimine ligands. We report the synthesis and comprehensive characterization, with various physical and spectroscopic techniques, of three heteroleptic Ni(II) complexes: [Ni(1,10-phenanthroline)(o-phenylene diamine)] (1), [Ni(2,2-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (2), and [Ni(5,5-dimethyl-2,2-bipyridine)(o-phenylene diamine)] (3). The catalytic activity of these complexes for hydrogen evolution was assessed through photochemical studies utilizing visible light irradiation. Two distinct photosensitizers, fluorescein and quantum dots, were examined under diverse conditions. Additionally, their electrocatalytic behavior was investigated to elucidate the hydrogen evolution reaction (HER) mechanism, revealing a combined proton-coupled electron transfer (PCET)/electron-coupled proton transfer (ECPT) mechanism attributed to the chemical nature of the diamine ligand. The influence of ligand substituent position, ligand chemical nature, and photosensitizer type on catalytic performance was systematically studied. Among the complexes investigated, complex 2 demonstrated superior catalytic performance, achieving a turnover number (TON) of 3357 in photochemical experiments using fluorescein as a photosensitizer. Conversely, complex 1 exhibited the highest TON of 30,066 for HER when quantum dots were employed as the photosensitizer. Full article

This review summarizes the structural characteristics and physicochemical properties of chiral 4f and 3d-4f complexes based on enantiopure salen-type Schiff base ligands. The chirality originates from the enantiopure diamines and is imparted to the Schiff base ligands and complexes and finally to the crystal structures. The reported enantiopure Schiff base ligands derive from the condensation of aromatic aldehydes, such as salicylaldehyde and its various derivatives, and the enantiopure diamines, (1R,2R) or (1S,2S)-1,2-diamino-cyclohexane, (1R,2R) or (1S,2S)-1,2-diamino-1,2-diphenylethane, (R) or (S)-2,2′-diamino-1,1′-binaphthalene, and 1,2-diaminopropane. Full article

Interaction of the pre-organized complex of iron(II) trimethylacetate and 1,10-phenanthroline (phen) [Fe₂(piv)₄(phen)₂] (1) (piv = (Me)₃CCO₂⁻)) with 1,6-diaminohexane (dahx) in anhydrous acetonitrile yielded a 1D coordination polymer [Fe₃O(piv)₆(dahx)_1.5]_n (2) and an organic salt of pivalic acid (H₂dahx)(piv)₂ (3). The structure of the obtained compounds was determined by single-crystal X-ray diffraction analysis. The phase purity of the complexes was determined by powder X-ray diffraction analysis. According to the single-crystal X-ray analysis, coordination polymer 2 is formed due to the binding of a triangular carboxylate core {Fe₃(μ₃-O)(μ-piv)₆} with an aliphatic diamine ligand. Thermal behavior was investigated for compounds 1 and 2 in an argon atmosphere. Full article

The aerobic photooxidation of sulfides into sulfoxides in eco-friendly solvents, notably water, at room temperature, represents a significant interest in the domain of synthetic chemistry. This study introduces four highly stable hexadentate Ir(III) complexes: [Ir(fpqen)](PF₆) (1), [Ir(btqen)](PF₆) (2), [Ir(bmpqen)](PF₆) (3), and [Ir(bnqen](PF₆) (4) (where bfpqen is N,N′-bis(2-(4-fluorophenyl)quinolin-8-yl)ethane-1,2-diamine, btqen is N,N′-bis(2-(4-tolyl)quinolin-8-yl)ethane-1,2-diamine, bmpqen is N,N′-bis(2-(4-methoxyphenyl)quinolin-8-yl)ethane-1,2-diamine, and bnqen is N,N′-bis(2-naphthylquinolin-8-yl)ethane-1,2-diamine). These complexes were synthesized utilizing an in situ inter-ligand C-N cross-coupling photoreaction of the precursors [Ir(L)₂(en)](PF₆) (L is 2-(4-fluorophenyl)quinoline, (2-(4-tolyl)quinoline, 2-(4-methoxyphenyl)quinoline or 2-naphthylquinoline, and en is 1,2-diamine) under benign conditions. This methodology furnishes a valuable and complementary approach for the in situ generation of multidentate complexes through a post-coordination inter-ligand-coupling strategy under mild conditions. Moreover, these hexadentate Ir(III) complexes exhibit pronounced catalytic activity and chemo-selectivity toward the aerobic photooxidations of sulfides into sulfoxides in aqueous media at room temperature, offering a new avenue for the sustainable synthesis of sulfoxides. Full article

The hydrodeoxygenation (HDO) of renewable fats or fatty acids into alkanes is a powerful measure to address energy and environmental crises. Molybdenum carbide-based catalysts are promising due to their platinum-like noble metal electronic properties. In this paper, Mo₂C catalysts were prepared by one-step carbonization of amine molybdenum oxide (AMO) precursors using diamines with different carbon chain lengths as ligands. The physical and chemical properties and the HDO catalytic activity of the catalysts were investigated. The results indicate that as the carbon chain of diamines in the precursor increases, the carbon content of the catalysts in the surface and bulk phase increases. The Mo₂C-12 catalyst exhibited excellent catalytic performance, with a palmitic acid conversion rate of 100% and an alkane selectivity of 96.6%, which are attributed to the smallest particle size, largest pore size, and synergistic effect of carbon. This work provides a simple and safe method for regulating the surface properties of Mo₂C catalysts. Full article

The development of catalysts has significantly advanced the progress of polyolefin materials. In particular, group 4 (Ti, Zr, Hf) non-metallocene catalysts ligated with [N,N] bidentate ligand(s) have garnered increasing attention in the field of olefin polymerization due to their structurally stability and exceptional polymerization behaviors. Ligands containing nitrogen donors are diverse and at the core of many highly active catalysts. They mainly include amidine, guanidinato, diamine, and various N-heterocyclic ligands, which can be used to obtain a series of new polyolefin materials, such as ultrahigh molecular weight polyethylene (UHWMPE), olefin copolymers (ethylene/norbornene and ethylene/α-olefin) with high incorporations, and high isotactic or syndiotactic polypropylene after coordination with group 4 metals and activation by cocatalysts. Herein, we focus on the advancements and applications of this field over the past two decades, and introduce the catalyst precursors with [N,N] ligand(s), involving the effects of ligand structure, cocatalyst selection, and polymerization conditions on the catalytic activity and polymer properties. Full article