Synthesis and physicochemical, DFT, thermal and DNA-binding analysis of a new pentadentate N3S2 Schiff base ligand and its [CuN3S2]2+ complexes

A Preliminary Investigation of Thermally Stable Schiff Base Metal Complexes for Hyperthermia: Synthesis and Biological Evaluation

A novel Schiff base ligand (L), bearing N2O2 donor sites, was derived from the condensation of 5-chloromethylisophthaldehyde and phenylpropanolamine (PPA). Mononuclear Co(II), Cu(II), and Zn(II) complexes were synthesized and were characterized by FTIR, UV-Vis, 1H NMR, ESI-mass spectroscopy, molar conductance, and thermal and electrochemical studies. The thermal investigation revealed that the complexes were stable up to 150-250 °C and began to degrade in stages, resulting in the development of respective metal oxides. The Coats-Redfern integration method was used to calculate the kinetic and thermodynamic parameters, the energy of activation (Ea), and changes in enthalpy (∆H), entropy (∆S), and free energy (∆G) for each step of the degradation processes. For stage I decomposition, the calculated activation energy values of the complexes follow the order of Ea [Cu(L)] > Ea [Co(L)(H2O)2] > Ea [Zn(L)]. The influence of the temperature on the efficacy of antioxidant activities of the complexes with DPPH assay, ABTS assay, and hydroxy radical assay was investigated at various concentrations using ascorbic acid (AA) as the reference. Antioxidant activity was assessed at multiple temperatures to ascertain whether these complexes may be applied in radiation therapy enhanced with hyperthermia and found to be stable. Subsequently, the Cu(II) complex (C2) demonstrated a greater cytotoxicity (IC50 = 5.16 µM) than Co(II), Zn(II), and conventional cisplatin when in vitro cytotoxicity was evaluated against the MCF-7 cell line using the MTT method. Analyses of the thermal stability and ROS scavenging ability of complexes have demonstrated that these complexes have potential in hyperthermic radiation therapy.

Theoretical and experimental investigation of mixed-ligand metal(II) Schiff base complexes using maleic acid as the auxiliary ligand

This work is focused on the synthesis of several transition metal complexes [ML(MA)], where M = Copper (II), Zinc (II), Cobalt (II) and Nickel (II), MA = maleic acid and L = Schiff base generated from benzene-1,2-diamine [o-phenylenediamine] and 4-chlorobenzaldehyde. The characterization using Fourier-Transform Infrared, Nuclear Magnetic Resonance spectroscopy, Ultraviolet-Visible spectra, Mass, Electro Paramagnetic Resonance and elemental analysis confirm the square planar geometry of the complexes. The in vitro antimicrobial potential of the complexes has been tested by the broth dilution method and the antioxidant method has been done by free radical scavenging analysis. The in vitro methods reveal the outstanding biological characteristics of the copper complexes. The molecular structure of the ligand and its metal (II) complexes has been optimized using Density Functional Theory studies performed by the Gaussian-09 software and their parameters have been discussed. Natural Bond Orbital and Frontier Molecular Orbital analyses have assessed the presence of a metal-ligand bond in complexes. In addition, molecular docking studies have also been performed on antiviral activity of all the complexes using a viral protein and their interacting amino acids.

Synthesis, characterization, in vitro, in silico and in vivo investigations and biological assessment of Knoevenagel condensate β-diketone Schiff base transition metal complexes

A novel Schiff base ligand was synthesized by the Knoevenagel condensation of β-diketone (obtained from substituted Curcumin and Cuminaldehyde) and 4-amino antipyrine. Metal complexes were made from this Schiff base by reacting with metal salts such as Cu(II), Ni(II), Ru(III), VO(IV), and Ce(IV). Physicochemical approaches such as UV-Vis, FT-IR, NMR, EPR, and Mass spectroscopy were used to determine the geometry of the complexes. The thermodynamic stability and biological accessibility of the complexes were investigated using density functional theory (DFT) calculations at the B3LYP/6-31G(d) level. A molecular docking analysis was also performed on 1BNA receptor. Both the Schiff base ligand and metal complexes interacted well to this protein receptor. All metal complexes have a significant potential to bind to CT DNA via the intercalation mechanism. All the in vivo and in vitro screening studies showed that the complexes exhibit higher activities than the free Schiff base.Communicated by Ramaswamy H. Sarma.

Aminothiazole-Linked Metal Chelates: Synthesis, Density Functional Theory, and Antimicrobial Studies with Antioxidant Correlations

During the current study, the new aminothiazole Schiff base ligands (S1 ) and (S2 ) were designed by reacting 1,3-thiazol-2-amine and 6-ethoxy-1,3-benzothiazole-2-amine separately with 3-methoxy-2-hydroxybenzaldehyde in good yields (68-73%). The ligands were characterized through various analytical, physical, and spectroscopic (FT-IR, UV-Vis, 1H and 13C NMR, and MS) methods. The ligands were exploited in lieu of chelation with bivalent metal (cobalt, nickel, copper, and zinc) chlorides in a 1:2 (M:L) ratio. The spectral (UV-Vis, FT-IR, and MS), as well as magnetic, results suggested their octahedral geometry. The theoretically optimized geometrical structures were examined using the M06/6-311G+(d,p) function of density function theory. Their bioactive nature was designated by global reactivity parameters containing a high hardness (η) value of 1.34 eV and a lower softness (σ) value of 0.37 eV. Different microbial species were verified for their potency (in vitro), revealing a strong action. The Gram-positive Micrococcus luteus and Gram-negative Escherichia coli gave the highest activities of 20 and 21 mm for compounds (8) and (7), respectively. The antifungal activity against the Aspergillus niger and Aspergillus terreus species gave the highest activities of 20 and 18 mm for compounds (7) and (6), respectively. The antioxidant activity, evaluated as DPPH and ferric reducing power, gave the highest inhibition (%) as 72.0 ± 0.11% (IC50 = 144 ± 0.11 μL) and 66.3% (IC50 = 132 ± 0.11 μL) for compounds (3) and (8), respectively. All metal complexes were found to be more biocompatible than free ligands due to their chelation phenomenon. The energies of LUMOs had a link with their activities.