Coordination chemistry and bioactivity of Ni2+, Cu2+, Cd2+ and Zn2+ complexes containing bidentate Schiff bases derived from S-benzyldithiocarbazate and the X-ray crystal structure of bis[S-benzyl-β-N-(5-methyl-2-furylmethylene)dithiocarbazato]cadmium(II)

Exploration of Antiproliferative Activity and Apoptosis Induction of New Nickel(II) Complexes Encompassing Carbazole Ligands

To attest the effectiveness of nickel complexes as anticancer drug candidates with minimum side effects, the present investigation describes the facile synthesis and anticancer activities of nickel(II) complexes enriched with three derivatives of carbazolone-based benzhydrazone ligands(L) having a [Ni(L)₂] composition. Analytical and spectral techniques were used to characterize the synthesized Ni(II) complexes. The single-crystal X-ray diffraction performed for complex 4 confirmed the square planar geometry with a [Ni(κ²-N,O-L)₂] arrangement. The MTT assay was carried out for the complexes to determine in vitro cytotoxicity against cancerous human-cervical carcinoma, human-colon carcinoma, and non-cancerous L929 (fibroblast) cells. All three complexes exhibited good toxicity against the cancer cells with a low IC₅₀ concentration. Complex 4, containing -OCH₃ fragment, exhibits high lipophilicity and revealed exceptional cytotoxicity against cancer cells. AO-EB fluorescent staining indicated apoptosis-associated cell morphological changes after exposure to complex 4. The apoptosis induction was further confirmed by a HOECHST-33342 fluorescent staining technique via chromosomal condensation and nuclear fragmentation. Further, reactive oxygen species (ROS) and mitochondrial membrane potential (MMP) mechanistic studies revealed that complex 4 can raise ROS levels and reduce MMP and promote mitochondrial dysfunction-mediated apoptotic cell death. Further, stimulation of late apoptosis by complex 4 in cervical cancer cells was quantitatively differentiated through the staining of phosphatidylserine externalization by flow cytometry. Furthermore, the ELISA analysis confirmed that complex 4 induced apoptosis through caspase activation.

MTHPP monoacetic ester: unexpected formation, zinc metalation, thermal and photophysical properties

In the current investigation we report an unexpected methyl esterification occurred during the coupling reaction of mTHPP monoacetic acid 2 with 3-amino-1,2,4-triazole in the presence of HBTU/DIPEA. The mechanism of this unexpected methyl esterification was studied, and the structure of the formed methyl ester 5 was confirmed by the means of 1H, 13C NMR in addition to (MALDI-TOF and ESI-HRMS) spectrometry. The formation of 5 during the coupling reaction was also chemically supported by an alternative synthetic method involving a direct monosubstitution reaction of mTHPP 1 with methyl bromoacetate. We also investigated the metalation of 5 with zinc and studied the thermal properties along with differential scanning calorimetry (DSC) of the zinc porphyrin 6. The photophysical properties of porphyrin methyl ester 5 and its zinc complex 6 were also investigated.

Graphical Abstract

A pair of carbazate derivatives as novel Schiff base ligands: DFT and POM theory supported spectroscopic and biological evaluation

Schiff bases are mentioned as strongly important molecular scaffolds of industrial and medicinal purposes. Due to wide range applications of carbazate derivatives herein synthesis and characterization of a new Schiff base ligand, (E)-ethyl 2-(4-methoxybenzylidene)hydrazinecarboxylate and 4-(nitrobenzaldehyde)ethylcarbazate are reported. The compound was characterized on the basis of experimental and density functional theory calculations (using the B3LYP and 6-31 G(d,p)formalism combination). Among characterization techniques elemental analysis, FT-IR, UV-Vis and NMR spectroscopic evaluations were mainly employed to carry out the formulation of the compound. In addition to computational validation of characterization other significant molecular parameters were also evaluated including geometry optimization, frontier molecular orbital analysis (FMO) and Columbic interaction of different constituent atoms of the title compound. A good agreement has been found between DFT and experimental outcomes confined to prove the structure of the compound. Moreover, molecular docking and antimicrobial studies have proven the Schiff base as an effective bioactive compound.Communicated by Ramaswamy H. Sarma.

A novel binuclear hydrazone-based Cd(II) complex is a strong pro-apoptotic inducer with significant activity against 2D and 3D pancreatic cancer stem cells

A novel binuclear Cd complex (1) with hydrazone-based ligand was prepared and characterized by spectroscopy and single crystal X-ray diffraction techniques. Complex 1 reveals a strong pro-apoptotic activity in both human, mammary adenocarcinoma cells (MCF-7) and pancreatic AsPC-1 cancer stem cells (CSCs). While apoptosis undergoes mostly caspase-independent, 1 stimulates the activation of intrinsic pathway with noteworthy down regulation of caspase-8 activity in respect to non-treated controls. Distribution of cells over mitotic division indicates that 1 caused DNA damage in both cell lines, which is confirmed in DNA interaction studies. Compared to 1, cisplatin (CDDP) does not achieve cell death in 2D cultured AsPC-1 cells, while induces different pattern of cell cycle changes and caspase activation in 2D cultured MCF-7 cells, implying that these two compounds do not share similar mechanism of action. Additionally, 1 acts as a powerful inducer of mitochondrial superoxide production with dissipated trans-membrane potential in the majority of the treated cells already after 6 h of incubation. On 3D tumors, 1 displays a superior activity against CSC model, and at 100 μM induces disintegration of spheroids within 2 days of incubation. Fluorescence spectroscopy, along with molecular docking show that compound 1 binds to the minor groove of DNA. Compound 1 binds to the human serum albumin (HSA) showing that the HSA can effectively transport and store 1 in the human body. Thus, our current study strongly supports further investigations on antitumor activity of 1 as a drug candidate for the treatment of highly resistant pancreatic cancer.

Synthesis, characterization and biological evaluation of transition metal complexes derived from N, S bidentate ligands

Two bidentate NS ligands were synthesized by the condensation reaction of S-2-methylbenzyldithiocarbazate (S2MBDTC) with 2-methoxybenzaldehyde (2MB) and 3-methoxybenzaldehyde (3MB). The ligands were reacted separately with acetates of Cu(II), Ni(II) and Zn(II) yielding 1:2 (metal:ligand) complexes. The metal complexes formed were expected to have a general formula of [M(NS)2] where M = Cu2+, Ni2+, and Zn2+. These compounds were characterized by elemental analysis, molar conductivity, magnetic susceptibility and various spectroscopic techniques. The magnetic susceptibility measurements and spectral results supported the predicted coordination geometry in which the Schiff bases behaved as bidentate NS donor ligands coordinating via the azomethine nitrogen and thiolate sulfur. The molecular structures of the isomeric S2M2MBH (1) and S2M3MBH (2) were established by X-ray crystallography to have very similar l-shaped structures. The Schiff bases and their metal complexes were evaluated for their biological activities against estrogen receptor-positive (MCF-7) and estrogen receptor-negative (MDA-MB-231) breast cancer cell lines. Only the Cu(II) complexes showed marked cytotoxicity against the cancer cell lines. Both Schiff bases and other metal complexes were found to be inactive. In concordance with the cytotoxicity studies, the DNA binding studies indicated that Cu(II) complexes have a strong DNA binding affinity.

Synthesis and Spectroscopic and Biological Activities of Zn(II) Porphyrin with Oxygen Donors

Results of investigation of the physicochemical properties of zinc complexes containing substituted phenols as axial ligand having general formula [X-Zn-t(p-CH₃) PP] [where X = different phenolates as axial ligand] in impurity-free organic solvent are presented. The four-coordinated zinc porphyrin accepts one axial ligand in 1 : 1 molar ratio to form five-coordinated complex, which is purified by column chromatography and characterized by physicochemical, biological evaluation and TGA/DTA studies. Absorption spectra show two principal effects: a red shift for phenols bearing substituted electron releasing groups (−CH₃, −NH₂) and blue shift for phenols bearing electron withdrawing groups (−NO₂, −Cl) relative to Zn-t(p-CH₃) PP, respectively. ¹H NMR spectra show that the protons of the phenol ring axially attached to the central metal ion are merged with the protons of the porphyrin ring. Fluorescence spectra show two fluorescence peaks in the red region with emission ranging from 550 nm to 700 nm. IR spectra confirm the appearance of Zn-N_Por and Zn-O vibrational frequencies, respectively. According to the thermal studies, the complexes have a higher thermal stability and the decomposition temperature of these complexes depends on the axial ligation. The respective complexes of X-Zn^II-t(p-CH₃) PP were found to possess higher antifungal activity (up to 90%) and higher in vitro cytotoxicity against human cancer cells lines.

Synthesis, Characterization, and Bioactivity of Schiff Bases and Their Cd(2+), Zn(2+), Cu(2+), and Ni(2+) Complexes Derived from Chloroacetophenone Isomers with S-Benzyldithiocarbazate and the X-Ray Crystal Structure of S-Benzyl- β -N-(4-chlorophenyl)methylenedithiocarbazate

Two bidentate Schiff base ligands having nitrogen sulphur donor sequence were derived from the condensation of S-benzyldithiocarbazate (SBDTC) with 2-chloroacetophenone and 4-chloroacetophenone to give S-benzyl-β-N-(2-chlorophenyl)methylenedithiocarbazate (NS2) and S-benzyl-β-N-(4-chlorophenyl)methylenedithiocarbazate (NS4) isomers. Each of the ligands was then chelated with Cd²⁺, Zn²⁺, Cu²⁺, and Ni²⁺. The compounds were characterized via IR spectroscopy and melting point while the structure of NS4 was revealed via X-ray crystallography. Finally, the compounds were screened for antimicrobial activity to investigate the effect that is brought by the introduction of the chlorine atom to the benzene ring. X-ray crystallographic analysis showed that the structure of NS4 is planar with a phenyl ring that is nearly perpendicular to the rest of the molecules. The qualitative antimicrobial assay results showed that NS4 and its complexes lacked antifungal activity while Gram-positive bacteria were generally inhibited more strongly than Gram-negative bacteria. Furthermore, NS4 metal complexes were inhibited more strongly than the ligand while the opposite was seen with NS2 ligand and its complexes due to the partial solubility in dimethyl sulfoxide (DMSO). It was concluded that generally NS2 derivatives have higher bioactivity than that of NS4 derivatives and that the Cd complexes of both ligands have pronounced activity specifically on K. rhizophila.

Bis[2,4-di-bromo-6-(N-{4-[(E)-1-(benzyl-oxy-imino)-eth-yl]phen-yl}carboximido-yl)phenolato]copper(II)

In the title complex, [Cu(C22H17Br2N2O2)2], the Cu(II) ion is four-coordinated in a trans-CuN2O2 square-planar geometry by two phenolate O and two imino N atoms from two deprotonated N,O-bidentate ligands. In the crystal, the packing of the mol-ecules is controlled by C-H⋯π and π-π inter-actions [centroid-centroid distances = 3.568 (3), 3.678 (2), 3.717 (3) and 3.799 (2) Å] and weak Br⋯Br halogen bonds [3.508 (4) Å], linking the mol-ecules into an infinite three-dimensional supra-molecular network.

2-Methyl-3-nitro-N-{(E)-[5-(4-nitro-phen-yl)furan-2-yl]methyl-idene}aniline

In the title Schiff-base type compound, C(18)H(13)N(3)O(5), the central furan ring makes dihedral angles of 12.80 (7) and 51.43 (4)° with the terminal benzene rings. The dihedral angle between the benzene rings is 45.43 (3)°. In the crystal, C-H⋯O hydrogen bonds link the mol-ecules into layers parallel to (010). In addition, there are π-π stacking inter-actions within the layer [centroid-centroid distance = 3.584 (1) Å] and between the layers [centroid-centroid distance 3.751 (1) Å].

Diaquabis{2-hydroxy-5-[(pyridin-2-yl)methylideneamino]benzoato-κ2N,N′}nickel(II) dihydrate

In the title complex, [Ni(C₁₃H₉N₂O₃)₂(H₂O)₂]·2H₂O, the Ni^II atom, located on a twofold rotation axis, is in a distorted octa­hedral geometry, defined by four N atoms from two 2-hy­droxy-5-[(pyridin-2-yl)methyl­idene­amino]­benzoate ligands and two O atoms from two water mol­ecules. In the crystal, inter­molecular O—H⋯O hydrogen bonds link the complex mol­ecules and uncoordinated water mol­ecules into a three-dimensional network. Intra­molecular O—H⋯O hydrogen bonds are present between the hy­droxy and carboxyl­ate groups.

(2Z,N'E)-N'-[(2-Hy-droxy-1-naphth-yl)methyl-idene]furan-2-carbohydrazonic acid

In the title compound, C₁₆H₁₂N₂O₃, the dihedral angle between the mean planes of the naphthalene ring system and the furan ring is 21.3 (6)°. The mol­ecular structure is stabilized by an intra­molecular O—H⋯N hydrogen bond, which generates an S(6) graph-set motif.