V-shaped ligand 1,3-bis(1-ethylbenzimidazol-2-yl)-2-thiapropane and manganese(II), cobalt(II) and copper(II) complexes: Synthesis, crystal structure, DNA-binding properties and antioxidant activities

Deciphering the effect of hydrophobicity on protein binding interaction in cobalt(II) complexes by multispectroscopic and computational methods

In the present work, we report the synthesis, characterization of two cobalt complexes (1 and 2) and their HSA binding studies by multispectroscopic methods. Hirshfeld surfaces analysis and fingerprint plot analysis were carried out to identify intermolecular interactions viz., N-H···O, O-H···O and C-H···O linkages in crystal framework of the complexes. Density functional theory (DFT) studies were carried out to ascertain the electronic structure and molecular geometry of the complexes 1 and 2, and determine the localization of HOMO and LUMO in the complexes. A comparative in vitro interaction study of complex 1 and 2 with human serum albumin protein was carried out by employing UV-vis, fluorescence, circular dichroism, FTIR and molecular docking techniques. Interestingly, the HSA binding affinity of complex 2 was found to be more than complex 1 which was evidenced from the higher binding constant values owing to its strong hydrophobic topology. Further, a significant conformational change in microenvironment of HSA was noticed upon binding with complexes 1 and 2, nevertheless more perturbations were noticed in presence of complex 1. Molecular docking studies were carried out to validate the spectroscopic results and ascertain the preferential binding mode of complexes at the specific target site of HSA.Communicated by Ramaswamy H. Sarma.

First Cobalt(II) Spin Crossover Compound with N4S2-Donorset

Herein we report the synthesis and characterization of a novel bis-tridentate 1,3,4-thiadiazole ligand (L = 2,5-bis[(2-pyridylmethyl)thio]methyl-1,3,4-thiadiazole). Two new mononuclear complexes of the type [M^II(L)₂](ClO₄)₂ (with M = Fe^II (C1) and Co^II (C2)) have been synthesized, containing the new ligand (L). In both complexes the metal centers are coordinated by an N₄S₂-donorset and each of the two ligands is donating to the metal ion with just one of the tridentate pockets. The iron(II) complex (C1) is in the low spin [LS] state below room temperature and shows an increase in the magnetic moment only above 300 K. In contrast, the cobalt(II) complex (C2) shows a gradual spin crossover (SCO) with T_1/2 = 175 K. To our knowledge, this is the first cobalt(II) SCO complex with an N₄S₂-coordination.

Tuned structure and DNA binding properties of metal complexes based on a new 4-acylpyrazolone derivative

The structure and DNA binding performance of three transition metal compounds based on a new pyrazolone ligand were tuned effectively by changing both metal cations and anions.

Antimicrobial activities of self-assembled copper(ii), nickel(ii), and cobalt(iii) complexes combined with crystallographic, spectroscopic, DFT calculations and Hirshfeld surfaces analyses

Three 2-D and 3-D Cu(ii), Ni(ii), and Co(iii) complexes were obtained by reaction of HL1 with different metal salts. The complexes were characterized by single-crystal X-ray crystallography and spectroscopic methods, as well as Hirshfeld surface analysis and DFT studies.

Novel chemical sensor for detection Ca(II) ions based on ferutinin

A new optical chemical sensor based on medicinal compound, jaeschkeanadiol p-hydroxyben-zoate (Ferutinin), has been designed and utilized for Ca(II) ions detections. This natural optical sensor exhibits immense selectivity including fluorescence and absorption ratiometric for Ca(II) ions within precious physiological pH range. Further, the chelation process of the Ca(II) ions with the medicinal optical sensor ferutinin yields a 1:1 (metal: ligand) complex which is accompanied by fluorescence enhancement of the main emission band centered at 355 nm of the medicinal probe. The fluorescence "turn-on" effect is a clear evidence for the chelation process between ferutinin medicinal probe and Ca(II) ions and this could be simply detected. The new sensor was proposed depending on significant fluorescence mechanism, (MLCT, metal-ligand charge transfer). However, the interaction of the medicinal optical sensor with Ca(II) in presence of other cations was examined without any significant interference. Also, the new developed optical sensor consecutively exhibits low limit of detection (LOD) 1.5 nM for Ca(II) which is detected in very significant physiological pH range (pH = 7.4). Also, the probe provides high binding affinity towards Ca(II) with large binding constant K_b 5.97 × 10⁴ M^-1. As a result, this optical sensor may apply for detection Ca(II) in cell or biological samples.

Cu(I) complexes regulated by N-heterocyclic ligands: Syntheses, structures, fluorescence and electrochemical properties

Three mononuclear Cu(I) complexes, namely, [Cu(2-PBO)(PPh₃)₂]·ClO₄·2CH₂Cl₂ (1), [Cu(3-PBO)(PPh₃)₂(ClO₄)]·CH₂Cl₂ (2) and [Cu(PBM)(PPh₃)₂]·ClO₄ (3) (2-PBO = 2-(2'-Pyridyl)benzoxazole, 3-PBO = 2-(3'-Pyridyl)benzoxazole, PBM = 2-(2'-Pyridyl)benzimidazole, PPh₃ = triphenylphosphine) have been synthesized and characterized by elemental analyses, IR, ¹H NMR, ¹³C NMR, X-ray single crystal diffraction and thermal analysis. Photoluminescent investigation shows that complexes 1-3 exhibit distinct tunable light green (512 nm)-to-yellow (557 nm) photoluminescence by varying the N-heterocyclic ligands. Three complexes show intense 2-PBO-based yellow, 3-PBO-based light green and intense PBM-based bright green luminescence upon irradiation with a standard UV lamp (λ_ex = 254 nm) at room temperature. Moreover, the electrochemical properties of 1-3 have been investigated by cyclic voltammetry. The results suggest the frontier molecular orbits and the HOMO-LUMO energy gaps of these cuprous complexes are effectively adjusted through the introduction of different N-heterocyclic ligands, thus achieving the selective luminescence of the cuprous complexes.