Ishani Majumder

Solvent dependent ligand transformation in a dinuclear copper(II) complex of a compartmental Mannich-base ligand: synthesis, characterization, bio-relevant catalytic promiscuity and magnetic study

An “end-off” pentadentate compartmental ligand HL has been synthesized by Mannich base condensation using p-cresol and 2-benzyl amino ethanol and structurally characterized. A dinuclear copper(II) complex, namely [Cu2(L)(μ-OH)(H2O)(ClO4)2], has been prepared by treating HL with Cu(ClO4)2·6H2O in methanolic solution with the aim of investigating its catalytic promiscuity. Single crystal structural analysis reveals that the Cu–Cu separation is 2.9 A. Catecholase activity of the complex has been investigated in anhydrous DMSO as well as in a DMSO–water mixture with progressively increasing the quantity of water up to a 1 : 1 volume ratio in order to assess the bio compatibility of the catalyst using 3,5-DTBC as a model substrate. In anhydrous DMSO the catalytic activity reaches its peak and decreases with increasing water concentration, a feature most likely due to insolubility of 3,5-DTBQ, the product formed in the catalysis, in water. The complex also shows excellent phosphatase-like activity by exploiting the Lewis acidity, the necessary requirement for that activity, under different pH. Thorough investigation reveals that no activity is observed at pH 6 but the activity increases with increasing pH and attains a maximum at pH 9. A variable temperature magnetic study shows that the two Cu centers are antiferromagnetically coupled at low temperature with a J value of −78.63 ± 1.30 cm−1. In acetonitrile medium the complex shows very exciting behavior. A new transformed ligand is generated that has been assigned as a Schiff-base ligand, 2,6-bis-[(2-hydroxy-ethylimino)-methyl]-4-methylphenol. The genesis of the new ligand is a consequence of dealkylation from HL followed by oxidation. This oxidation is counterbalanced by reduction of Cu(II) to Cu(I) as is evidenced from isolation of [Cu(MeCN)4](ClO4) from the mixture followed by X-ray structural characterization of the species.

A Deep Insight into the Photoluminescence Properties of Schiff Base CdII and ZnII Complexes

A tridentate N,N,O donor ligand 2,4-dichloro-2-[(2-piperazine-4-yl-ethylimino)-methyl]-phenol (HL) was designed, and eight new ZnII and CdII complexes, namely, [Zn(LH)(SCN)2] (1), [Zn(LH)(N3)2] (2), [Zn(LH)(NO2)2] (3), [Zn(LH)(dca)(OAc)] (4), [Cd2(LH)2(SCN)4] (5), [Cd(LH)(N3)2] (6), [Cd(LH)(NO2)2] (7), and [Cd(LH)(dca)(OAc)] (8) [where dca = dicyanamide anion] were synthesized. Five of them (1, 2, 4, 5, 7) were structurally characterized through single-crystal X-ray diffraction analysis. H-Bonding interactions are found to be the major stabilizing factor for crystallization in the solid state. Experimental and computational studies were performed in cooperation to provide a rationalization of the photoluminescence properties of those complexes. The quantum yields are anion-dependent, with enhanced efficiencies in the following order: LH < Cd-SCN(5) < Cd-dca(8) < Cd-N3(6) < Cd-NO2(7) < Zn-dca(4) < Zn-N3(2) < ZnNO2(3) < ZnSCN(1). By using quantum chemical calculations we rationalized the above trends. Moreover, the diverse lifetimes observed for those eight complexes were also quantitatively explained by considering the subtle competition between different photo-deactivation pathways.

Fluorometric detection of nitroaromatics by fluorescent lead complexes: A spectroscopic assessment of detection mechanism

Three Schiff base ligands such as 2‑[(2‑Hydroxy‑3‑methoxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL1), 2‑[(2‑Hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL2), 2‑[(3,5‑Dichloro‑2‑hydroxy‑benzylidene)‑amino]‑2‑hydroxymethyl‑propane‑1,3‑diol (HL3) have been synthesized by condensation of aldehydes (such as 3,5‑Dichloro‑2‑hydroxy benzaldehyde, 2‑Hydroxy‑benzaldehyde, and 2‑Hydroxy‑3‑methoxy‑benzaldehyde) with Tris‑(hydroxymethyl)amino methane and characterized by IR, UV-vis and 1H NMR spectroscopy. Then all these three ligands have been used to prepare Pb(II) complexes by reaction with lead(II) acetate tri-hydrate in methanol. In view of analytical and spectral (IR, UV-vis and Mass) studies, it has been concluded that, except HL2, other two ligands form 1:1 metal complexes (1 and 3) with lead. Between two complexes, complex 3 is highly fluorescent and this property has been used to identify the pollutant nitroaromatics. Finally, the quenching mechanism has been established by means of spectroscopic investigation.

Bioactive Heterometallic CuII–ZnII Complexes with Potential Biomedical Applications

A series of multinuclear heterometallic Cu–Zn complexes of molecular formula [(CuL)2Zn(dca)2] (1), [(CuL)2Zn(NO3)2] (2), [(CuL)2Zn2(Cl)4] (3), and [(CuL)2Zn2(NO2)4] (4) have been synthesized by reacting [CuL] as a “metalloligand (ML)” (where HL = N,N′-bis(5-chloro-2-hydroxybenzylidene)-2,2-dimethylpropane-1,3-diamine) and by varying the anions or coligands using the same molar ratios of the reactants. All of the four products including the ML have been characterized by infrared and UV–vis spectroscopies and elemental and single-crystal X-ray diffraction analyses. By varying the anions, different structures and topologies are obtained which we have tried to rationalize by means of thorough density functional theory calculations. All of the complexes (1–4) have now been applied for several biological investigations to verify their therapeutic worth. First, their cytotoxicity properties were assessed against HeLa human cervical carcinoma along with the determination of IC50 values. The study was extended with extensive DNA and protein binding experiments followed by detailed fluorescence quenching study with suitable reagents to comprehend the mechanistic pathway. From all of these biological studies, it has been found that all of these heterometallic complexes show more than a few fold improvement of their therapeutic values as compared to the similar homometallic ones probably because of the simultaneous synergic effect of copper and zinc. Among all of the four heterometallic complexes, complex 3 exhibits highest binding constants and IC50 values suggest for their better interaction toward the biological targets and hence have better clinical importance.