Modulation of Nuclearity in CuII -MnII Complexes of a N2 O2 Donor Ligand Depending upon Carboxylate Anions: Structures, Magnetic Properties and Catalytic Oxidase Activities.

Three new hetero-metallic copper(II)-manganese(II) complexes, [(CuL)2 Mn3 (C6 H5 CO2 )6 ] (1), [(CuL)2 Mn(CH3 CO2 )2 ] (2), and {[(CuL)2 Mn(C6 H5 CH2 CO2 )2 ] ⋅ 2CH3 CN} (3), have been synthesized using [CuL] as ''metalloligand'' (where H2 L=N,N'-bis(2-hydroxynaphthyl-methylidene)-1,3-propanediamine). Single-crystal structural analyses show an almost linear penta-nuclear structure for complex 1 where a square planar [CuL] unit is connected to each of the two terminal MnII ions of a linear, centrosymmetric [Mn3 (benzoate)6 ] unit through the double phenoxido bridges. Both complexes 2 and 3 possess a linear tri-nuclear structure where two terminal square-pyramidal [CuL] units are bonded to the central MnII ion through double phenoxido oxygen atoms along with a syn-syn bridging acetate (for 2)/phenyl acetate (for 3). All three complexes exhibit catecholase, and phenoxazinone synthase-like activities under aerial conditions. For catecholase like activity, the turnover numbers (kcat ) are 595, 40, and 205 h-1 whereas, for phenoxazinone synthase like activity, the turnover numbers are 25, 4, and 11 h-1 for complexes 1-3, respectively. The mechanism of both catalytic oxidase activities is proposed on the basis of mass spectral evidences. Variable-temperature (2-300 K) dc molar magnetic susceptibility measurements of 1 reveal antiferromagnetic interactions between the Cu-Mn centres (J1 =-29.3 cm-1 ), and also between the Mn-Mn centres of the [Mn3 (benzoate)6 ] unit (J2 =-0.68 cm-1 ). On increasing the magnetic field at 2 K, its ground spin state changes from S=3/2 to S=5/2 at 4 T, attributable to the low value of J2 which makes the excited spin states close in energy with the ground spin state. Complexes 2 and 3 show antiferromagnetic coupling interactions between the Cu-Mn pairs with J values of -9.51, and -5.32 cm-1 , respectively.

DNA Damage and Apoptosis Induction in Cancer Cells by Chemically Engineered Thiolated Riboflavin Gold Nanoassembly.

Herein we have engineered a smart nuclear targeting thiol-modified riboflavin-gold nano assembly, RfS@AuNPs, which accumulates selectively in the nucleus without any nuclear-targeting peptides (NLS/RGD) and shows photophysically in vitro DNA intercalation. A theoretical model using Molecular Dynamics has been developed to probe the mechanism of formation and stability as well as dynamics of the RfS@AuNPs in aqueous solution and within the DNA microenvironment. The RfS@AuNPs facilitate the binucleated cell formation that is reflected in the significant increase of DNA damage marker, γ-H2AX as well as the arrest of most of the HeLa cells at the pre-G1 phase indicating cell death. Moreover, a significant upregulation of apoptotic markers confirms that the cell death occurs through the apoptotic pathway. Analyses of the microarray gene expression of RfS@AuNPs treated HeLa cells show significant alterations in vital biological processes necessary for cell survival. Taken together, our study reports a unique nuclear targeting mechanism through targeting the riboflavin receptors, which are upregulated in cancer cells and induce apoptosis in the targeted cells.