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Lichtenberg C.,ETH Zurich | Viciu L.,ETH Zurich | Vogt M.,ETH Zurich | Rodriguez-Lugo R.E.,ETH Zurich | And 8 more authors.
Chemical Communications | Year: 2015

A low-valent trinuclear iron complex with an unusual linear Fe(i)-Fe(ii)-Fe(i) unit is presented. It is accessed in a rational approach using a salt metathesis reaction between a new anionic Fe(i) containing heterocycle and FeCl2. Its electronic structure was studied by single crystal XRD analysis, EPR and Mössbauer spectroscopy, and magnetic susceptibility measurements. © The Royal Society of Chemistry 2015.

Blusch L.K.,University of Gottingen | Craigo K.E.,University of Michigan | Martin-Diaconescu V.,MPI fur Chemische Energiekonversion | McQuarters A.B.,University of Michigan | And 6 more authors.
Journal of the American Chemical Society | Year: 2013

The Siamese-twin porphyrin (2H4) is a unique pyrazole-expanded porphyrin providing two adjacent cavities each offering an {N4} binding motif. It was previously found to form stable dicopper(II) or dinickel(II) complexes where both metal ions are nested in a porphyrin-like environment. This work addresses the rich redox chemistry of the dicopper complex 2Cu2 that originates from the redox synergy of two proximate metal ions in combination with the potentially non-innocent expanded porphyrin ligand. Complementing previous X-ray crystallographic and SQUID data for solid material, the electronic structure of parent 2Cu2 in solution was now investigated by MCD and EPR spectroscopy. This allowed the assignment of UV-vis absorptions and confirmed the drastic twist of the molecule with ferromagnetically coupled copper(II) ions. 2Cu2 was found to exhibit multiple redox events in the potential range from -2.4 to +1.7 V versus Fc/Fc+, and singly oxidized [2Cu2]+ as well as doubly oxidized [2Cu2]2+ were characterized in detail by various analytical and spectroscopic methods. [2Cu2]+ was found by EPR spectroscopy and DFT calculations to have an S = 1/2 ground state, while [2Cu2]2+ is diamagnetic. Single crystal X-ray crystallography of [2Cu2(acetone)2](BF4) 2 revealed that the 2Cu2 core is structurally invariant upon two-fold oxidation, while XAS measurements at the Cu K-edge for 2Cu 2 and [2Cu2(acetone)2](BF4) 2 showed that the copper ions remain in the +2 oxidation state throughout. The combined experimental and computational evidence identified the Siamese-twin porphyrin as a multi-electron redox-active ligand with hidden non-innocence. Each ligand subunit upon oxidation forms a ligand-centered radical, though the spin vanishes because of covalency and strong antiferromagnetic coupling between the ligand radical and the proximate metal ion. Complexes of the Siamese-twin porphyrin may thus serve as a valuable bioinspired platform that combines both metal-ligand and two-metal-ion cooperativities for use in multi-electron processes. © 2013 American Chemical Society.

Morgenstern B.,Saarland University | Neis C.,Saarland University | Zaschka A.,Saarland University | Romba J.,Saarland University | And 2 more authors.
Inorganic Chemistry | Year: 2013

cis-[CoL2]3+ (1a3+), trans-[CoL 2]3+ (2a3+), cis-[Co(MeL)2] 3+ (1b3+), and trans-[Co(MeL)2]3+ (2b3+), L = 1,4-diazepan-6-amine (daza) and MeL = 6-methyl-1,4-diazepan-6-amine (Medaza), were allowed to react as templates in acetonitrile with paraformaldehyde and triethylamine. Several CoIII complexes, where two adjacent amino groups of two ligand moieties are interlinked by an oxidimethaneamine bridge, were obtained. Connection of a primary with a secondary amino group (prim-sec bridging) was found to be predominant. The singly and doubly bridged daza- and Medaza-derivatives 7a 3+, 9a3+ and 7b3+, 9b3+ were characterized by crystal-structure analysis. The bridging process resulted in a slight lengthening of the mean Co-N distance, a red shift of the A 1g-T1g transition, and an increase of the Co III/CoII reduction potential. Several minor components, which could be only partially separated by chromatographic methods, were also formed. The daza-derivatives 6a3+ (prim-prim bridged) and 10a 3+ (bidentate coordination of one daza frame) formed in small quantities. The Medaza derivatives 3b3+ and 4b3+ (trans configuration of the Medaza frames, with additional pending carbinolamino groups), and 8b3+ (with a methylideneimino group) represent intermediates of the condensation process. Their structure was again corroborated by X-ray diffraction. All bridged species (6a3+, 7a 3+, 7b3+, 8b3+, 9a3+, 9b 3+, and 10a3+) exhibited exclusively a cis orientation of the two diazepane frames, even if the trans configured 2a3+ or 2b3+ were used as starting materials. Molecular mechanics calculations indicate that in the bridged species with a trans configuration steric strain is substantially more pronounced. In alkaline aqueous media, 9a3+ and 9b3+ revealed a complete degradation of the bridges whereby the original 1a3+ and 1b3+ reformed. The pseudo-first-order rate constant kobs of the degradation reaction was found to depend linearly on OH- concentration. The degradation of the first bridge is about 100 times faster than the degradation of the second. The mechanism of formation and degradation of such oxidimethaneamine bridges is discussed. © 2013 American Chemical Society.

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.

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.

Chadar D.,University of Pune | Rao S.S.,University of Pune | Khan A.,University of Pune | Gejji S.P.,University of Pune | And 3 more authors.
RSC Advances | Year: 2015

Synthesis and characterization of fluorescent benzo[α]phenoxazines viz., M-1B (10-chloro-6-methyl-7a,11a-dihydro-5H-benzo[α]phenoxazin-5-one), M-2B 6,10-dimethyl-7a,11a-dihydro-5H-benzo[α]phenoxazin-5-one), M-3B (6-methyl-7a,11a-dihydro-5H-benzo[α]phenoxazin-5-one) and benzo[α]phenthiazine, M-4B (6-methyl-5H-benzo[α]phenothiazin-5-one) were carried out. 1H and 13C chemical shifts were assigned from the 2DgHSQCAD NMR experiments. Compound M-1B crystallizes in the orthorhombic space group P212121, while M-2B and M-4B crystallize in the monoclinic space group P21/c. The crystal network of M-1B showed slipped π-π stacking and Cl⋯Cl interactions, while M-2B facilitated ladder like π-π stacked polymeric chains. The C⋯S contacts were observed in the crystal environment of M-4B. All these structures possess C-H⋯O interactions. Electronic structure and charge distribution in terms of molecular electrostatic potential and frontier orbital analyses based on the MO6-2X based density functional theory further showed that monomer and dimer structures are in keeping with the single crystal X-ray data and provide insights for the growth of the crystal network. Antiproliferative activity of M-1B-M-4B was determined from the MTT assay against a human breast adenocarcinoma cell line (MCF-7), human carcinoma cell line (HeLa) and normal skin cell line. All these compounds showed significant cytotoxic activity against MCF-7 and HeLa by inducing apoptosis and thus can be viewed as potential candidates for antitumor therapy. Compounds M-2B and M-4B were further found to be topoisomerase II inhibitors. This journal is © The Royal Society of Chemistry.

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.

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.

Chadar D.,University of Pune | Camilles M.,University of Pune | Patil R.,University of Pune | Khan A.,University of Pune | And 2 more authors.
Journal of Molecular Structure | Year: 2015

We would like to introduce eight analogues of n-alkylamino derivatives of vitamin K3 (2-methyl-1,4-naphthoquinone) viz, 2-(n-alkylamino)-3-methyl-1,4-naphthoquinone (where n-alkyl is methyl; LM-1, ethyl; LM-2, propyl; LM-3, butyl; LM-4, pentyl; LM-5, hexyl; LM-6, heptyl; LM-7, octyl; LM-8). All the above analogues have been successfully synthesized from vitamin K3 and characterized using different analytical techniques. Furthermore, in order to understand the mechanistic aspects of formation of LM-1 to LM-8 compounds, we could propose the mechanism. The FT-IR analysis of LM-1 to LM-8 indicate the presence of characteristic band of NH group ∼3287-3364 cm-1, the variation was attributed to extensive intramolecular hydrogen bonding interaction. The molecular structure of LM-3 compound has been confirmed by single crystal X-ray diffraction analysis. LM-3 compound crystallises in triclinic space group P1. There were four independent molecules in asymmetric unit cell and their molecular interactions observed via NH.

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.

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