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Mülheim (Ruhr), Germany

Blusch L.K.,University of Gottingen | Blusch L.K.,University of British Columbia | Mitevski O.,University of Gottingen | Martin-Diaconescu V.,MPI fur Chemische Energiekonversion | And 4 more authors.
Inorganic Chemistry | Year: 2014

The Siamese-twin porphyrin (1H4) is a redox noninnocent pyrazole-expanded porphyrin with two equivalent dibasic {N4} binding sites. It is now shown that its selective monometalation can be achieved to give the nickel(II) complex 1H2Ni with the second {N4} site devoid of a metal ion. This intermediate is then cleanly converted to 1Ni 2 and to the first heterobimetallic Siamese-twin porphyrin 1CuNi. Structural characterization of 1H2Ni shows that it has the same helical structure previously seen for 1Cu2, 1Ni2, and free base 1H6 2+. Titration experiments suggest that the metal-devoid pocket of 1H2Ni can accommodate two additional protons, giving [1H4Ni]2+. Both bimetallic complexes 1Ni 2 and 1CuNi feature rich redox chemistry, similar to the recently reported 1Cu2, including two chemically reversible oxidations at moderate potentials between -0.3 and +0.5 V (vs Cp2Fe/Cp 2Fe+). The locus of these oxidations, in singly oxidized [1Ni2]+ and [1CuNi]+ as well as twice oxidized [1CuNi]2+, has been experimentally derived from comparison of the electrochemical properties of the complete series of complexes 1Cu2, 1Ni2, and 1CuNi, and from electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS) (Ni and Cu K edges). All redox events are largely ligand-based, and in heterobimetallic 1CuNi, the first oxidation takes place within its Cu-subunit, while the second oxidation then occurs in its Ni-subunit. Adding pyridine to solutions of [1Ni2] + and [1CuNi]2+ cleanly converts them to metal-oxidized redox isomers with axial EPR spectra typical for NiIII having significant dz21 character, reflecting close similarity with nickel complexes of common porphyrins. The possibility of selectively synthesizing heterobimetallic complexes 1MNi from a symmetric binucleating ligand scaffold, with the unusual situation of three distinct contiguous redox sites (M, Ni, and the porphyrin-like ligand), further expands the Siamese-twin porphyrin's potential to serve as an adjustable platform for multielectron redox processes in chemical catalysis and in electronic applications. © 2014 American Chemical Society. Source

Salunke-Gawali S.,University of Pune | Pawar O.,University of Pune | Nikalje M.,University of Pune | Patil R.,University of Pune | And 3 more authors.
Journal of Molecular Structure | Year: 2014

Four analogues of 2-bromo-3-(n-alkylamino)-1,4-napthoquinone (where n-alkyl is methyl in L-1Br, ethyl in L-2Br, propyl in L-3Br and butyl in L-4Br) are synthesized and characterized. A reaction mechanism is proposed for the formation of L-1Br to L-4Br from the starting material 2,3-dibromo-1,4- naphthoquinone. The νNH frequency in the FT-IR spectra is affected by the intramolecular hydrogen bonding in L-1Br to L-4Br and is observed 3267 cm-1 in L-2Br. A shift of 25 cm-1 is observed in the νCBr frequency in all the compounds as compared to 2,3-dibromo-1,4-naphthoquinone (627 cm-1). A broad charge transfer band is observed between 400 and 600 nm in the UV-Vis spectra, which imparts red colour to all the compounds. Molecular structures of L-2Br and L-3Br were studied by single crystal X-ray diffraction studies. Molecules of L-2Br crystallize in Pca21, whereas the molecule L-3Br crystallizes in the P-1 space group. Molecules of L-2Br forms a polymeric chain through NHâO interaction and forms beautiful butterfly like arrangement of molecules when viewed down the 'a' axis. Ladder like polymeric chain of molecules is observed in L-3Br via CHâO and NHâO interactions. Every alternating neighbouring chains of L-3Br, show stacking interactions between the quinonoid rings of the molecules, however this interaction is not observed in L-2Br. © 2013 Elsevier B.V. All rights reserved. Source

Pal S.,National Institute of Science Education and Research NISER | Konkimalla V.B.,National Institute of Science Education and Research NISER | Kathawate L.,University of Pune | Rao S.S.,University of Pune | And 4 more authors.
RSC Advances | Year: 2015

Mutational activations of the oncogene BRAF (especially BRAF V600E) result in a poor prognosis for colon cancer patients and are associated with chemoresistance rendering them refractory to treatment. The development of novel bioactive compounds with specific targeting abilities under such conditions is an urgent need in drug discovery. In this report we synthesize and characterize three fluorescent benzo[α]phenoxazine compounds (10R-benzo[α]phenoxazine-5-one, 1B; R = Cl, 2B; R = CH3, 3B; R = H) and their anticancer activities are evaluated in a COLO205 cell line. All three compounds with a log P value around 2 were cell permeable. However, 2B and 3B showed specific cytotoxicity in a malignant COLO205 cell line with a BRAF mutation (V600E) in comparison to a non-malignant wild-type BRAF HEK293T cell line. From further cell-based assays (cell cycle analysis, DNA fragmentation and caspase activation), we conclude that 2B and 3B treatment-induced selective cell death by inducing cell cycle arrest at the G0/G1 phase and caspase-mediated apoptosis (activation of the intrinsic and extrinsic pathways) are present only in BRAF V600E COLO205 cells. Further studies in the drug discovery pipeline might help develop these benzo[α]phenoxazines as promising chemotherapeutics for such refractory mutated cancers. © The Royal Society of Chemistry 2015. Source

Pal S.,National Institute of Science Education and Research NISER | Jadhav M.,University of Pune | Weyhermuller T.,MPI fur Chemische Energiekonversion | Patil Y.,Indian Institute of Science | And 5 more authors.
Journal of Molecular Structure | Year: 2013

Side chain homologated derivatives of 2-chloro-3-(n-alkylamino)-1,4- naphthoquinone {n-alkyl: pentyl; L-5, hexyl; L-6, heptyl; L-7 and octyl; L-8} have been synthesized and characterized by elemental analysis, FT-IR, 1H NMR, UV-visible spectroscopy and LC-MS. Compounds, L-4, {n-alkyl: butyl; L-4}, L-6 and L-8 have been characterized by single crystal X-ray diffraction studies. The single crystal X-ray structures reveal that L-4 and L-8 crystallizes in P21 space group, while L-6 in P21/c space group. Molecules of L-4 and L-8 from polymeric chains through C AH- • O and NAH- • O close contacts. L-6 is a dimer formed by NAH- • O interaction. Slipped π-π stacking interactions are observed between quinonoid and benzenoid rings of L-4 and L-8. Orientations of alkyl group in L-4 and L-8 is on same side of the chain and polymeric chains run opposite to one another to form zip like structure to the alkyl groups. Antiproliferative activities of L-1 to L-8{n-alkyl: methyl; L-1, ethyl; L-2, propyl; L-3 and butyl; L-4} were studied in cancer cells of colon (COLO205), brain (U87MG) and pancreas (MIAPaCa2) where L-1, L-2 and L-3 were active in MIAPaCa2 (L-1 = L-2 > L-3) and COLO205 (L-2 = L-3 > L-1) and inactive in U87MG. From antiproliferative studies with compounds L-1 to L-8 it can be concluded that homologation of 2-chloro-3-(n-alkylamino)-1,4-napthoquinone with saturated methyl groups yielded tissue specific compounds such as L-2 (for MIAPaCa2) and L-3 (for COLO205) with optimal activity. © 2013 Elsevier Ltd. All rights reserved. Source

Ware A.P.,University of Pune | Patil A.,University of Pune | Khomane S.,University of Pune | Weyhermuller T.,MPI fur Chemische Energiekonversion | And 2 more authors.
Journal of Molecular Structure | Year: 2015

Abstract Naphthoquinone based redox active chemosensor 1; 2-(2'-aminomethylpyridine)-3-chloro-1,4-naphthoquinone ligand has been synthesized and characterized. Chemosensor 1 crystallizes in monoclinic space group P21/n. Molecules showed intramolecular N-H⋯O and N-H⋯N, intermolecular N-H⋯O, C-H⋯O and slipped π-π stacking interactions. Chemosensor 1 showed orange colored solution in methanol and specifically detects Cu2+ ions by deprotonation of N-H. The deprotonation of amino N-H can also be achieved by mild base viz. triethylamine and chemosensor 1 can be used to detect several metal ions for example Ni2+, Mn2+ etc. that could observed by naked eye. Color changes observed were monitored by UV-visible and fluorescence spectra. Chemosensor 1 could provide either bidentate or tridentate coordination sites to metal ions. Redox nature of chemosensor 1 was evaluated by cyclic voltammetry studies. Electronic transition wavelengths of chemosensor 1 ligand have been evaluated in methanol, water and triethylamine by TD-DFT studies and comparative studies were performed with experimental results. © 2015 Elsevier B.V. All rights reserved. Source

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