Sandhya Y. Rane

Thermal Studies of Metal-quinone Complexes Role of Aqua Coligations with Copper(II) in Coordination of 2-hydroxy-1,4-naphthoquinone

Copper(II) complexes of lawsone (2-hydroxy-1,4-naphthaquinone, Lw) with variety of aqua ligation viz. Cu-1, [Cu(Lw)2(H2O)]2; Cu-2, [Cu(Lw)2(H2O)2] and Cu-3, [Cu(Lw)2(H2O)2]2 have been synthesized. The role of water as counter ligand on coordination propensity of redox active lawsone in naphthoquinone/naphthosemiquinone (NQ/NSQ) forms is quantified by studies of pyrolytic reactions, using non-isothermal TG and DTA techniques, coupled with IR studies. Mixed (NQ) (NSQ) ligation in Cu-1 and Cu-3 required energy of activation, Ea ∼67 kJ mol−1 of (NQ) and ∼41 kJ mol−1 of (NSQ). Comparable energies of aqua ligand (∼43 kJ mol−1) with NSQ ligand in Cu-1 and Cu-3, dictate charge distributions in lawsone coordinations. A large difference between Ea of aqua and p-NQ ligand indicates coordination of lawsone in its fully oxidised quinone form in Cu-2. From thermoanalytical studies schematic oxidative decomposition mechanisms are proposed for Cu-1 and Cu-3. From pyrolytic reactions enthalpies are estimated by DTA technique.

Antioxidant and anticancer activities of supramolecularly controlled magnetostructural halo-oximes of lawsone

Crystal engineering based on halogen bonding together with host–guest interactions of water molecules via H-bonding, stabilizing supramolecular architecture in chloro 1, bromo 2 and iodo 3oximes of lawsone, is discussed. 1 and 2 crystallize in orthorhombic, non-centrosymmetric space group Pna21 while 3 crystallizes in monoclinic P21/n space group. Non-covalent competitive interactions of asymmetric solvation and halogen bonding can have a large influence on the spin distribution in 1, 2 and 3 derivatives of spin carrier lawsone live polymer as revealed by single crystal X-ray and EPR studies. The significant C3–Cl/Br⋯O, C3–Cl/Br⋯H, O–H⋯OC, C–H⋯π and π⋯π interactions have been identified in the molecular assemblies leading to net magnetostructures of halo-oximes. Dimer-of-dimer-type tetrameric radical assembly of 3 and interacting bi- and monoradical chain on 21 axis in 1 and 2 have been identified. The proton-coupled electron transfers possibly govern the antioxidant nature in halooximes of spin carrier lawsone in terms of oxygen reduction to water molecules. Such activity is found to be directly proportional to the spin (radical) concentrations in 1 to 3 and increases in order 1 < 2 < 3 according to halogen bonding effect. The antioxidant chemical DPPH assays for scavenging of such free radicals result in similar trend of increasing order like 1 < 2 < 3, but the chemical in vitro as well as ex vivoSOD antioxidant activities and biological anticancer activity on MCF-7, Hela and HL-60 cell lines show the increasing order 3 < 2 < 1 according to H-bonding effect. This probably could be attributed to the conversion of superoxide radical ions into H2O2, which leads to greater oxidative stress leading to apoptosis.

Temperature Effect on Ancillary μ‐Carbonato Ligand Modes in Hydroxy Naphthoquinonato Copper(II) Complex: An EPR Spectroscopic and Magnetic Coupling Evidences

Thermal, magnetic and electrochemical properties of the complex 1, [Cu2 (μ‐CO3) (ONQ)2 (4HNQ)2] are discussed [where ONQ=2‐oxido‐1, 4‐napthoquinone and 4HNQ=4‐hydroxy‐1, 2‐naphthoquinone]. The coordination of the ligand is in tautomeric forms viz. ONQ and 4HNQ in 1. The carbonate anion acts as a bridge between two Cu (II) centers showing bidentate (μ‐η1‐η1‐CO3 2‐) coordination mode with distorted square based pyramidal geometry for each Cu(II) ion. Temperature‐dependent zero field splitting (zfs) interactions (D and E) are resolved from X‐ (300K and 77 K) and Q‐band (300K) EPR spectra. At 300K, E>D and at 77K, D>E. It reveals temperature dependent modes of coordination viz. syn‐anti and anti‐anti of ancillary ligand in 1. Variable temperature magnetic susceptibility (SQUID) measurements show a weak antiferromagnetic coupling between the two Cu (II) centers. The susceptibility data was best fitted with HDVV model and the coupling constant found to be J=−4.8 cm−1 with agreement factor R=2.41*10−8. Metal based redox couple assigned at E½=+0.18 V with ΔE=0.125 V corresponds to two electrons transfer in the Cu (II)⇔Cu (0) redox couple.

Cu(II) conjugation along the transformation of a vitamin K3 derivative to a dinaphthoquinone methide radical

1,1′-Methide-bi-vitamin K3 (B) has been isolated as a dinaphthoquinone methide radical (DNQM) by the transformation of 1-imino(acetylhydrazino)-vitamin K3 (A). The transformation follows a biomimetic activation pathway mediated via Cu(II) ion catalyzed oxidative coupling. Single crystal X-ray and electron spin resonance (ESR) experiments combined with density functional calculations elucidate the “resonance structure” of the DNQM radical (B). Fluorescence investigations reveal that DNQM facilitates interaction with the cysteine residue. As compared to the parent substrate, B shows a depletion in the level of GSH, triggering apoptosis in HeLa cells.