Amitabha Datta

Monomeric, Dimeric, and Trimeric Calcium Compounds Containing Substituted Pyrrolyl and Ketiminate Ligands: Synthesis and Structural Characterization

A series of monomeric, dimeric, and trimeric calcium compounds containing substituted pyrrolyl or ketiminate ligands were synthesized, and characterized by NMR spectroscopy and single crystal X-ray diffractometry. The reaction of Ca[N(SiMe(3))(2)](2)(THF)(2) with 1 equiv of [C(4)H(3)NH(2-CH(2)NEt(2))] in toluene generates the dimeric complex, [Ca{N(SiMe(3))}[mu-eta(1):eta(5)-{C(4)H(3)N(2-CH(2)NEt(2))}]](2) (1) in which two substituted pyrrolyl ligands bind two Ca centers in a eta(1) and eta(5) fashion. The reaction between Ca[N(SiMe(3))(2)](2)(THF)(2) and 2 equiv of [C(4)H(3)NH(2-CH(2)NEt(2))] in THF yields a monomeric calcium compound Ca[C(4)H(3)N(2-CH(2)NEt(2))](2)(THF)(2) (2) that exhibits a facial octahedral geometry on the central Ca atom. Similarly, the reactions of Ca[N(SiMe(3))(2)](2)(THF)(2) with 1 and 2 equiv of OCMeCHCMeNHAr (Ar = 2,6-diisopropylphenyl) generate [Ca(OCMeCHCMeNAr){N(SiMe(3))(2)}](2) (3) and [Ca(mu-OCMeCHCMeNAr)(OCMeCHCMeNAr)](2) (4), respectively. In 3, the Ca atom possesses a distorted tetrahedral geometry where as in 4, a square plane is developed by the two calcium atoms with the bridging participation of two oxygen atoms from two ketiminate ligands. The in situ reaction of OCMeCHCMeNHAr, Ca[N(SiMe(3))(2)](2)(THF)(2), and isopropyl alcohol results in a trimeric calcium alkoxide compound Ca(3)(mu-OCMeCHCMeNAr)(2)(OCMeCHCMeNAr)(mu(3)-O-(i)Pr)(2)(mu(2)-O-(i)Pr) (5). Compounds 1, 2, and 5 showed good catalytic activity in the ring-opening polymerization of epsilon-caprolactone and l-lactide.

A Ni(II) dinuclear complex bridged by end-on azide-N and phenolate-O atoms: spectral interpretation, magnetism and biological study

A potential tetradentate monoanionic N2O2 chelator, HL, derived from the condensation of o-vanillin and N,N-dimethylethylenediammine, has been reacted with nickel perchlorate and sodium azide to yield the dinuclear Ni(II) complex [Ni(L)(μ1,1-N3)Ni(L)(OH2)2]·ClO4 (1), where L = Me2N(CH2)2NCH–C6H3(O−)(OCH3). The complex has been characterized by X-ray diffraction analysis and different spectroscopic techniques. The coordination geometry around the Ni(II) centres is a distorted octahedron, with the azide ligand and the phenolato oxygen atom bridging in μ1,1 and μ2 mode, respectively. The EPR spectra, recorded at liquid nitrogen temperature (77 K) and room temperature (298 K), show g factors of 2.080 and 2.085, in agreement with the structure determined by X-ray diffraction analysis. The VTM study confirms that there are ferromagnetic interactions between the bridging binuclear Ni(II) ions (S = 1). The evaluation of cytotoxic effects on different human cancer cell lines (A-549, MCF-7 and CaCo-2) suggests that both the ligand and complex 1 have potential anticancer properties. Furthermore, they also exhibit anti-mycobacterial activity against M. tuberculosis H37Rv (ATCC 27294) and M. tuberculosis H37Ra (ATCC 25177) strains. Molecular docking of HL with the enoyl acyl carrier protein reductase of M. tuberculosis H37Rv (PDB ID: 4U0K) has been examined, showing that HL forms two hydrogen bonds with Lys165 (1.94 and 2.53 A) in its best docked pose.

An enolato-bridged dinuclear Cu(II) complex with a coumarin-assisted precursor: a spectral, magnetic and biological study

A new, phenoxo-bridged CuII dinuclear complex Cu2[(L)2(DMF)2] (1) has been obtained by employing the coumarin-assisted tridentate precursor, H2L, [benzoic acid(7-hydroxy-4-methyl-2-oxo-2H-chromen-8-ylmethylene)-hydrazide]. Complex 1 has been systematically characterized by FTIR, UV-Vis, fluorescence and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 shows that the geometry around each copper ion is square pyramidal, comprising two enolato oxygen atoms belonging to different ligands (which assemble the dimer bridging the two metal centers), one imine-N and one phenolic-O atoms of the Schiff base and one oxygen atom from the DMF molecule. The temperature dependent magnetic interpretation agrees with the existence of weak ferromagnetic interactions between the bridging dinuclear Cu(II) ions. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy towards M. tuberculosis H37Rv ATCC 27294 and M. tuberculosis H37Ra ATCC 25177 strains. The cytotoxicity study on human adenocarcinoma cell lines (MCF7) suggests that the ligand and complex 1 have potential anticancer properties. Molecular docking of H2L with the enoyl acyl carrier protein reductase of M. tuberculosis H37Rv (PDB ID: 4U0K) is examined and the best docked pose of H2L shows one hydrogen bond with Thr196 (1.99 A).

A rare doubly nitrato and phenoxido bridged trimetallic CuII complex: EPR, antiferromagnetic coupling and theoretical rationalization

A rare trimetallic CuII complex, [Cu3(L)2(NO3)2] (1) has been afforded incorporating a [CuL] metalloligand, [where H2L = N,N′-bis(salicylidene)-1,3-propanediamine]. In 1, in addition to the double phenoxido bridge, the two terminal CuII atoms are linked to the central CuII by means of syn–anti bridging nitrate anions giving rise to a linear arrangement. Complex 1 exhibits strong antiferromagnetic coupling and shows an χMT value of 0.703 cm3 mol−1 K at 300 K. DFT computational studies reveal that there is a clear magneto-structural correlation between the Cu–O–Cu angle and the JCu–Cu values, which is in accordance with the experimental evidence. The biological effect of 1 on the viability of different human carcinoma cells was evaluated using MTT assay and the results indicate that this complex induces a decrease in cell-population growth of human colorectal carcinoma cells (COLO 205) with apoptosis.

A new Cu(II) three-dimensional network with 4,4′-oxybis benzoic acid: structural diversity, EPR, and magnetism

The copper derivative {[Cu4(oba)4(H2O)4]∙H2O}n (1) has been hydro(solvo)thermally synthesized by combining flexible 4,4′-oxybis benzoic acid (oba) and divalent copper nitrate. As a result of the potential coordination modes of carboxylate oxygens from the oba ligand, the aforementioned complex leads to the formation of an interesting 3D framework, as evidenced by single-crystal X-ray diffractometry. Concerning the topology in 1, the dimers [Cu2C4O8] are nodes of a 5-fold 4-connected uninodal net of the type lvt, with point symbol {42.84} and vertex symbol [4.4.84.84.88.88]. The encapsulation of the copper coordination polymer displays a moderate luminescent property. On temperature-dependent magnetic study, it reveals that the magnetic behaviour of 1 can be associated to a strong antiferromagnetic coupling between the two Cu(II) ions.

EPR and electrochemical interpretation of bispyrazolylacetate anchored Ni(II) and Mn(II) complexes: cytotoxicity and anti-proliferative activity towards human cancer cell lines

Two mononuclear NiII and MnII compounds, [Ni(bdtbpza)2(CH3OH)4] (1) and [Mn(bdtbpza)2(CH3OH)2(H2O)2] (2), are afforded by employing a ‘scorpionate’ type precursor [bdtbpza = bis(3,5-di-t-butylpyrazol-1-yl)acetate]. The single crystal X-ray structure reveals that the central metal ion (NiII for 1 and MnII for 2) is surrounded by a pair of Oacetate atoms of two bis(pyrazol-1-yl)acetate units, while four OMeOH donors for 1 and two OMeOH plus two Owater for 2 complete the first coordination sphere. Thus, both compounds exhibit a slightly distorted octahedral geometry possessing an O6 coordination environment. EPR spectra of CuII-doped 1 and of 2 recorded on the polycrystalline solids and in organic solution confirm the octahedral geometry around the metal ions and the binding of six oxygen atoms. The electrochemical study of compounds 1 and 2 shows that one electron reduction of MnII occurs at a more negative potential than NiII, indicating a lower tendency of reduction for Mn than Ni. Both compounds displayed a high cytotoxic activity against A2780 ovarian carcinoma cells and no cytotoxic activity in normal primary human fibroblasts for concentrations up to 55 μM. Notwithstanding, compound 1 is found to be the most cytotoxic towards A2780 cancer cells. The cytotoxic activity of compound 1 is correlated with the induction of apoptosis associated with a higher mitochondria dysfunction and autophagy cell death. In addition, the compounds can induce oxidative damage leading to ROS accumulation. Overall, the data presented here demonstrate that 1 has potential for further in vivo studies aiming at its future application in ovarian cancer therapy.