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Akhil R. Chakravarty - One of the best experts on this subject based on the ideXlab platform.
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photocytotoxic activity of copper ii and zinc ii complexes of curcumin and acridinyl Dipyridophenazine
ChemistrySelect, 2019Co-Authors: Nandini Mukherjee, Abinaya Raghavan, Santosh Podder, Shamik Majumdar, Arun Kumar, Dipankar Nandi, Akhil R. ChakravartyAbstract:Copper(II) and zinc(II) beta-diketonates of N,N-donor ligands, viz. Cu(dppz)(cur)](NO3) (1), Cu(acdppz)(cur)](NO3) (2), Cu(acdppz) (acac)](NO3) (3), Zn(dppz)(cur)](NO3) (4) and Zn(acdppz)(cur)] (NO3) (5), where dppz is dipyrido3,2-a:2',3'-c]phenazine, acdppz is 11-(9-acridinyl)dipyrido3,2-a:2',3'-c]phenazine, cur and acac are mono-deprotonated curcumin (Hcur) and acetyl acetone (Hacac), were synthesized, characterized and their photocytotoxicity studied. An analogue of complex 3, viz. Cu(acdppz) (acac)(H2O)]Cl 1/2 (NO3) 1= 2 (3a), structurally characterized by X-ray crystallography, has a cationic complex in square-pyramidal geometry with CuN2O3 core with an axial aqua ligand. Complexes 1, 2, 4 and 5 displayed emission at similar to 520 nm (lambda(exc): 430 nm) in dimethyl sulfoxide (DMSO) giving a fluorescence quantum yield value within 0.01-0.06. The complexes, in contrast to free curcumin, were fairly stable in cellular media up to 36 h, with no apparent degradation of the bound curcumin. The complexes were photocytotoxic (IC50: 0.3 4.5 mu M) in human cervical cancer (HeLa), breast cancer (MCF-7) and liver cancer (HepG2) cells. The apoptotic cell death is due to reactive oxygen species formation. Complexes 2 and 5 showed significant uptake in HeLa cells, localizing predominantly in the cytoplasm. Mechanistic data from the pUC19 DNA photocleavage study suggest involvement of acridine and curcumin in photo-generation of singlet oxygen and hydroxyl radicals as the ROS in light of 400-700 nm.
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Photocytotoxic ternary copper(II) complexes of histamine Schiff base and pyridyl ligands
Journal of Chemical Sciences, 2016Co-Authors: Samya Banerjee, Arun Kumar, Akanksha Dixit, K Sesha Maheswaramma, Basudev Maity, Sanjoy Mukherjee, Anjali A Karande, Akhil R. ChakravartyAbstract:Ternary copper(II) complexes of salicylaldehyde-histamine Schiff base (HL) and pyridyl ligands, viz. [Cu(bpy)(L)](ClO_4) ( 1 ) and [Cu(dppz)(L)](ClO_4) ( 2 ), where bpy is 2,2 ′ $^{\prime }$ -bipyridine (in 1 ) and dppz is dipyrido[3,2-a:2 ′ $^{\prime }$ ,3 ′ $^{\prime }$ -c]phenazine (in 2 ), were synthesized, characterized and their DNA binding, photo-activated DNA cleavage activity and photocytotoxicity studied. The 1:1 electrolytic one-electron paramagnetic complexes showed a d - d band near 670 nm in aqueous DMF (1:1 v/v). The crystal structure of complex 1 showed the metal in CuN_4O distorted square-pyramidal geometry. Complex 2 intercalatively binds to calf-thymus (ct) DNA with a binding constant ( K _b) of ∼10 ^5 M^−1. It exhibited moderate chemical nuclease activity but excellent DNA photocleavage activity in red light of 647 nm forming •OH radicals. It showed remarkable photocytotoxicity in human cervical cancer cells (HeLa) giving IC_50 of 1.6 μ M in visible light (400-700 nm) with low dark toxicity. The photo-induced cell death is via generation of oxidative stress by reactive oxygen species. Graphical Abstract Schiff base copper(II) complex of Dipyridophenazine shows remarkable photocytotoxic effect in HeLa cells in visible light (400-700 nm) with reduced dark toxicity via apoptotic pathway. The complex intercalatively binds to ct-DNA, exhibits moderate chemical nuclease activity but excellent DNA photocleavage activity in red light of 705 nm forming •OH radicals.
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mitochondria targeting photocytotoxic oxidovanadium iv complexes of curcumin and acridinyl Dipyridophenazine in visible light
Zeitschrift für anorganische und allgemeine Chemie, 2014Co-Authors: Samya Banerjee, Puja Prasad, Akhtar Hussain, Imran Khan, Paturu Kondaiah, Akhil R. ChakravartyAbstract:Oxidovanadium(IV) complexes, VO(acac)(L)Cl] (1), VO(cur)(L)Cl] (2), and VO(scur)(L)Cl] (3) {acac = acetylacetonate, cur = curcumin monoanion, scur = diglucosylcurcumin monoanion, L = 11-(9-acridinyl)dipyrido3, 2-a:2',3'-c]phenazine (acdppz)}, were prepared and characterized. The complexes are non-electrolytic in DMF and 1:1 electrolytic in aqueous DMF. The one-electron paramagnetic complexes showed a d-d band near 725 nm in aqueous DMF and green emission near 520 nm in aqueous DMSO. The complexes exhibited an irreversible V-IV/V-III redox response near -0.85 V versus SCE in aqueous DMF. The complexes showed good binding strengths to calf thymus DNA (K-b: 3.1x10(5)-9.6x10(5) M-1) and efficient pUC19 DNA photocleavage activity in red light of 705 and 785 nm by singlet oxygen (O-1(2)) pathway. Complexes 1 and 2 exhibited significant photocytotoxicity (IC50: 0.1-1.0 M) in visible light (400-700 nm) with low dark toxicity (IC50: >20 M) in HeLa and HaCaT cells. Complex 3 was cytotoxic in both light and dark. DNA ladder formation experiments indicated cell death via apoptotic pathway. Confocal microscopy done with 1 and 2 revealed primarily cytosolic localization of the complexes with significant presence of the complex in the mitochondria as evidenced from the imaging data using mitotracker red.
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cellular uptake and remarkable photocytotoxicity of pyrenylter pyridine oxovanadium iv complexes of Dipyridophenazine bases
Inorganica Chimica Acta, 2012Co-Authors: Bhabatosh Banik, Kumar Somyajit, Debasis Koley, Ganesh Nagaraju, Akhil R. ChakravartyAbstract:Pyrenylterpyridine (pytpy) oxovanadium(IV) complexes VO(pytpy)(L)]Cl-2 (1-6) of the Dipyridophenazine bases (L), viz., dipyrido-6,7,8,9-tetrahydrophenazine (dpqC in 1), dipyrido3,2-a:2',3'-c]phenazine-2-carboxylic acid (dppzc in 2), dipyrido3,2-a:2',3'-c]phenazine-11-sulfonic acid (dppzs in 3), 7-aminodipyrido3,2-a:2',3'-c]phenazine (dppza in 4), benzo-i]dipyrido3,2-a:2',3'-c]phenazine (dppn in 5) and dipyrido3,2-a:2',3'-c]phenazine (dppz in 6) were prepared, characterized and their DNA binding, photocleavage activity and photocytotoxicity studied. The complexes which showed a d-d band near 750 nm in DMF are efficient binders to calf thymus DNA (K-b: 3.2 x 10(5)-2.9 x 10(6) M-1). The complexes showed significant pUC19 DNA cleavage in near-IR light of 785 nm forming center dot OH radicals and photocytotoxicity in HeLa cells in visible light with the benzo-i] dipyrido3,2-a:2',3'-c]phenazine complex 5 showing a remarkably low IC50 value of 0.036 mu M. Flow-cytometric analysis shows a high sub-G1 phase cell cycle arrest in HeLa cells by the complexes on photo-irradiation. The photocytotoxicity correlates well with the hydrophobicity, photosensitizing ability and DNA binding propensity of the complexes. (C) 2012 Elsevier B.V. All rights reserved.
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remarkable photocytotoxicity of curcumin in hela cells in visible light and arresting its degradation on oxovanadium iv complex formation
Chemical Communications, 2012Co-Authors: Samya Banerjee, Puja Prasad, Akhtar Hussain, Imran Khan, Paturu Kondaiah, Akhil R. ChakravartyAbstract:Curcumin (Hcur) as a cellular imaging and PDT agent shows remarkable photocytotoxicity in HeLa cells in visible light of 400–700 nm giving IC50 = 8.2 ± 0.2 μM and its degradation is arrested on formation of photocytotoxic Dipyridophenazine (dppz) complex [VO(cur)(dppz)Cl] (IC50 = 3.3 ± 0.4 μM), while both are less toxic in the dark.
John Kelly - One of the best experts on this subject based on the ideXlab platform.
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reversal of a single base pair step controls guanine photo oxidation by an intercalating ruthenium ii Dipyridophenazine complex
Angewandte Chemie, 2015Co-Authors: Paraic M Keane, James P Hall, Christine J Cardin, Michael Towrie, Fergus E Poynton, Igor V Sazanovich, Thorfinnur Gunnlaugsson, Susan J Quinn, John KellyAbstract:Small changes in DNA sequence can often have major biological effects. Here the rates and yields of guanine photo-oxidation by Λ-[Ru(TAP)2(dppz)]2+ have been compared in 5′-{CCGGATCCGG}2 and 5′-{CCGGTACCGG}2 using pico/nanosecond transient visible and time-resolved IR (TRIR) spectroscopy. The inefficiency of electron transfer in the TA sequence is consistent with the 5′-TA-3′ versus 5′-AT-3′ binding preference predicted by X-ray crystallography. The TRIR spectra also reveal the differences in binding sites in the two oligonucleotides.
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enantiomeric conformation controls rate and yield of photoinduced electron transfer in dna sensitized by ru ii Dipyridophenazine complexes
Journal of Physical Chemistry Letters, 2015Co-Authors: Paraic M Keane, James P Hall, Christine J Cardin, Michael Towrie, Fergus E Poynton, Ian P Clark, Igor V Sazanovich, Thorfinnur Gunnlaugsson, Susan J Quinn, John KellyAbstract:Photosensitized oxidation of guanine is an important route to DNA damage. Ruthenium polypyridyls are very useful photosensitizers, as their reactivity and DNA-binding properties are readily tunable. Here we show a strong difference in the reactivity of the two enantiomers of [Ru(TAP)2(dppz)]2+, by using time-resolved visible and IR spectroscopy. This reveals that the photosensitized one-electron oxidation of guanine in three oligonucleotide sequences proceeds with similar rates and yields for bound Δ-[Ru(TAP)2(dppz)]2+, whereas those for the Λ enantiomer are very sensitive to base sequence. It is proposed that these differences are due to preferences of each enantiomer for different binding sites in the duplex.
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x ray crystal structure of rac ru phen 2dppz 2 with d atgcat 2 shows enantiomer orientations and water ordering
Journal of the American Chemical Society, 2013Co-Authors: James P Hall, Sara Ruiz Morte, Patrick Mcintyre, Katrin Buchner, Hanna Beer, David J Cardin, John A Brazier, Graeme Winter, Daniel Cook, John KellyAbstract:We report an atomic resolution X-ray crystal structure containing both enantiomers of rac-[Ru(phen)2dppz]2+ with the d(ATGCAT)2 DNA duplex (phen = phenanthroline; dppz = Dipyridophenazine). The first example of any enantiomeric pair crystallized with a DNA duplex shows different orientations of the Λ and Δ binding sites, separated by a clearly defined structured water monolayer. Job plots show that the same species is present in solution. Each enantiomer is bound at a TG/CA step and shows intercalation from the minor groove. One water molecule is directly located on one phenazine N atom in the Δ-enantiomer only.
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transient spectroscopy of Dipyridophenazine metal complexes which undergo photo induced electron transfer with dna
Coordination Chemistry Reviews, 2011Co-Authors: Jayden A Smith, Michael W George, John KellyAbstract:Abstract This review considers transient spectroscopic studies of electron transfer reactions between nucleic acids and the excited states of transition metal complexes containing Dipyridophenazine or related ligands and focuses mainly on complexes of ruthenium, chromium and rhenium. Particular emphasis is placed on systems where transient UV/visible and/or infrared absorption spectroscopy have been employed.
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structure determination of an intercalating ruthenium Dipyridophenazine complex which kinks dna by semiintercalation of a tetraazaphenanthrene ligand
Proceedings of the National Academy of Sciences of the United States of America, 2011Co-Authors: James P Hall, John Kelly, Kyra Osullivan, Abeer Naseer, Jayden A Smith, Christine J CardinAbstract:Abstract We describe a crystal structure, at atomic resolution (1.1 A, 100 K), of a ruthenium polypyridyl complex bound to duplex DNA, in which one ligand acts as a wedge in the minor groove, resulting in the 51° kinking of the double helix. The complex cation Λ-[Ru(1,4,5,8-tetraazaphenanthrene)2(Dipyridophenazine)]2+ crystallizes in a 1∶1 ratio with the oligonucleotide d(TCGGCGCCGA) in the presence of barium ions. Each complex binds to one duplex by intercalation of the Dipyridophenazine ligand and also by semiintercalation of one of the orthogonal tetraazaphenanthrene ligands into a second symmetrically equivalent duplex. The result is noncovalent cross-linking and marked kinking of DNA.
Jacqueline K Barton - One of the best experts on this subject based on the ideXlab platform.
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crystal structure of δ ru bpy 2dppz 2 bound to mismatched dna reveals side by side metalloinsertion and intercalation
Nature Chemistry, 2012Co-Authors: Hang Song, Jens T Kaiser, Jacqueline K BartonAbstract:DNA mismatches represent a novel target in the development of diagnostics and therapeutics for cancer, because deficiencies in DNA mismatch repair are implicated in cancers, and cells that are repair-deficient show a high frequency of mismatches. Metal complexes with bulky intercalating ligands serve as probes for DNA mismatches. Here, we report the high-resolution (0.92 A) crystal structure of the ruthenium ‘light switch’ complex Δ-[Ru(bpy)_(2)dppz]^(2+) (bpy = 2,2′-bipyridine and dppz = Dipyridophenazine), which is known to show luminescence on binding to duplex DNA, bound to both mismatched and well-matched sites in the oligonucleotide 5′-(dCGGAAATTACCG)_(2)-3′ (underline denotes AA mismatches). Two crystallographically independent views reveal that the complex binds mismatches through metalloinsertion, ejecting both mispaired adenosines. Additional ruthenium complexes are intercalated at well-matched sites, creating an array of complexes in the minor groove stabilized by stacking interactions between bpy ligands and extruded adenosines. This structure attests to the generality of metalloinsertion and metallointercalation as DNA binding modes.
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Crystal structure of Δ-[Ru(bpy)_2dppz]^2+ bound to mismatched DNA reveals side-by-side metalloinsertion and intercalation
Nature Chemistry, 2012Co-Authors: Hang Song, Jens T Kaiser, Jacqueline K BartonAbstract:DNA mismatches represent a novel target in the development of diagnostics and therapeutics for cancer, because deficiencies in DNA mismatch repair are implicated in cancers, and cells that are repair-deficient show a high frequency of mismatches. Metal complexes with bulky intercalating ligands serve as probes for DNA mismatches. Here, we report the high-resolution (0.92 Å) crystal structure of the ruthenium ‘light switch’ complex Δ-[Ru(bpy)_2dppz]^2+ (bpy = 2,2′-bipyridine and dppz = Dipyridophenazine), which is known to show luminescence on binding to duplex DNA, bound to both mismatched and well-matched sites in the oligonucleotide 5′-(dCGGAAATTACCG)_2-3′ (underline denotes AA mismatches). Two crystallographically independent views reveal that the complex binds mismatches through metalloinsertion, ejecting both mispaired adenosines. Additional ruthenium complexes are intercalated at well-matched sites, creating an array of complexes in the minor groove stabilized by stacking interactions between bpy ligands and extruded adenosines. This structure attests to the generality of metalloinsertion and metallointercalation as DNA binding modes. A ‘light switch’ ruthenium complex is known to show enhanced luminescence in the presence of DNA mismatches — emerging targets for cancer diagnostics and therapeutics — but the way it interacts with DNA has remained unclear. Now, metalloinsertion into and metallointercalation at the minor groove of the double helix have been unambiguously observed in a high-resolution crystal structure.
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oxidative damage by ruthenium complexes containing the Dipyridophenazine ligand or its derivatives a focus on intercalation
Inorganic Chemistry, 2002Co-Authors: Sarah Delaney, Matthias Pascaly, Pratip K Bhattacharya, Jacqueline K BartonAbstract:Interactions with DNA by a family of ruthenium(II) complexes bearing the dppz (dppz = Dipyridophenazine) ligand or its derivatives have been examined. The complexes include Ru(bpy)_2(dppx)^(2+) (dppx = 7,8-dimethylDipyridophenazine), Ru(bpy)_2(dpq)^(2+) (dpq = dipyridoquinoxaline), and Ru(bpy)_2(dpqC)^(2+) (dpqC = dipyrido-6,7,8,9-tetrahydrophenazine). Their ground and excited state oxidation/reduction potentials have been determined using cyclic voltammetry and fluorescence spectroscopy. An intercalative binding mode has been established on the basis of luminescence enhancements in the presence of DNA, excited state quenching, fluorescence polarization values, and enantioselectivity. Oxidative damage to DNA by these complexes using the flash/quench method has been examined. A direct correlation between the amount of guanine oxidation obtained via DNA charge transport and the strength of intercalative binding was observed. Oxidative damage to DNA through DNA-mediated charge transport was also compared directly for two DNA-tethered ruthenium complexes. One contains the dppz ligand that binds avidly by intercalation, and the other contains only bpy ligands, that, while bound covalently, can only associate with the base pairs through groove binding. Long range oxidative damage was observed only with the tethered, intercalating complex. These results, taken together, all support the importance of close association and intercalation for DNA-mediated charge transport. Electronic access to the DNA base pairs, provided by intercalation of the oxidant, is a prerequisite for efficient charge transport through the DNA π-stack.
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Dipyridophenazine complexes of os ii as red emitting dna probes synthesis characterization and photophysical properties
Inorganic Chemistry, 1999Co-Authors: Erik R Holmlin, Jacqueline K BartonAbstract:Polypyridyl complexes of Os(II) bearing one Dipyridophenazine (dppz) derivative and two ancillary ligands derived from bipyridine (bpy) or phenanthroline (phen) exhibit emission maxima at ∼740 nm and average excited-state lifetimes in the 10 ns range upon binding to DNA by preferential intercalation of the dppz ligand. A family of [Os(L^1)(L^2)(L^3)]^(2+) and [Os(L^1)_2(L^2)]^(2+) complexes with simple modifications in the ancillary phen or bpy ligands (L^1 and L^3) as well as the intercalating dppz ligand (L^2) was prepared. By cyclic voltammetry, electron-donating substituents on the ancillary ligands lowered the Os(3+/2+) reduction potential but did not affect the reduction potential of the dppz ligand. A methyl substituent at the 7-, 8-, or 6-position of the dppz ligand shifted the phenazine reduction toward the negative but did not affect the Os(3+/2+) potential. Absorption titrations indicated intercalative binding to DNA with high affinity (K_B ∼10^6 M^(-1)) for the family of complexes, although at high ratios (50:1) of base pairs to metal, complexes with ancillary 4,7-dimethylphenanthroline or 4,4‘-dimethylbipyridine ligands exhibit less hypochromism (26−27%) in the π−π* transition on the dppz ligand compared to complexes with 5,6-dimethylphenanthroline (30−37%) or the parent phen (31−35%). By steady-state and time-resolved emission spectroscopy, complexes bound to DNA by intercalation with substituents on the 4,7- or 4,4‘-positions of the ancillary phen or bpy displayed lower quantum yields for emission (Φ_(em)) compared to complexes with the parent phen, while complexes with methyl substituents on the dppz ligand had the greatest Φ_(em). Studies with poly d(AT), poly d(GC), and mixed-sequence DNA revealed that the emission yields are also sequence-dependent. Comparative luminescence studies in CH_2Cl_2 demonstrated that these effects arise from a combination of (i) the inherent sensitivity of the excited state to ligand structure and (ii) perturbations in DNA binding geometry introduced by substituents on the ancillary and intercalating ligands. Our results clarify the relationships between ligand architecture and emission yield and lifetime in the presence and absence of DNA and illustrate the utility of dppz complexes of Os(II) as luminescent probes for DNA.
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novel Dipyridophenazine complexes of ruthenium ii exploring luminescent reporters of dna
Journal of the American Chemical Society, 1992Co-Authors: Richard M Hartshorn, Jacqueline K BartonAbstract:A series of ruthenium(II) complexes have been prepared which contain two phenanthroline ligands and a third bidentate ligand which is one of a set of derivatives of the parent dipyrido[3,2-a:2',3'c]phenazine (DPPZ) ligand. The spectroscopic properties of these complexes in the presence and absence of DNA have also been characterized. The derivatives have been prepared by condensation of different diaminobenzenes or diaminopyridines with the synthetic intermediate bis(1,10-phenanthroline)(1,10-phenanthroline-5,6-dione)ruthenium(II). [Ru(phen)_2DPPz](2+), like [Ru(bpy)_2DPPz]^(2+), acts as a molecular "light switch" for the presence of DNA, displaying no detectable photoluminescence in aqueous solution but luminescing brightly on binding to DNA. None of the DPPZ derivatives prepared show comparable "light switch" enhancements, since some luminescence may be detected in aqueous solution in the absence of DNA. For some complexes, however, luminescence enhancements of a factor of 20-300 are observed on binding to DNA. For these and the parent DPPZ complexes, the large enhancements observed are attributed to a sensitivity of the ruthenium-DPPZ luminescent charge-transfer excited state to quenching by water; although these complexes show little or no luminescence in water, appreciable luminescence is found in acetonitrile. Other derivatives show little solvent sensitivity in luminescence, and these, like Ru(phen)_3^(2+), display moderate enhancements (20-70%) on binding to DNA. [Ru(phen)_2DPPz]^(2+) and its derivatives all show at least biexponential decays in emission. Two binding modes have been proposed to account for these emission characteristics: a perpendicular mode where the DPPZ ligand intercalates from the major groove such that the metal-phenazine axis lies along the DNA dyad axis, and another, side-on mode where the metal-phenazine axis lies along the long axis of the base pairs.
M Swaminathan - One of the best experts on this subject based on the ideXlab platform.
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a recyclable solid acid catalyst sulfated titania for easy synthesis of quinoxaline and Dipyridophenazine derivatives under microwave irradiation
Bulletin of the Chemical Society of Japan, 2011Co-Authors: B Krishnakumar, M SwaminathanAbstract:TiO2–SO42−, prepared by sol–gel method has been used for the synthesis of quinoxaline and dipyridophenizine derivatives under microwave irradiation. High-resolution transmission electron microscope...
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Solvent free synthesis of quinoxalines, Dipyridophenazines and chalcones under microwave irradiation with sulfated Degussa titania as a novel solid acid catalyst
Journal of Molecular Catalysis A-chemical, 2011Co-Authors: B Krishnakumar, M SwaminathanAbstract:Abstract Sulfated TiO2–P25 (Degussa titania) has been prepared by sol–gel method using H2SO4 and characterized by FT-IR, XRD, FE-SEM, EDS, HR-TEM, XPS, DRS and BET surface area measurements. Sulfate loading by H2SO4 increases the Lewis acidity of Degussa tiatania. This catalyst gives an excellent yield with less reaction time and is an inexpensive and easily recyclable solid acid catalyst for the synthesis of quinaxalines, Dipyridophenazines and chalcones under microwave irradiation.
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a recyclable and highly effective sulfated tio2 p25 for the synthesis of quinoxaline and Dipyridophenazine derivatives at room temperature
Journal of Organometallic Chemistry, 2010Co-Authors: B Krishnakumar, M SwaminathanAbstract:Abstract Sulfated TiO 2 -P25 has been prepared using H 2 SO 4 and used for the synthesis of quinoxaline and Dipyridophenazine derivatives. Sulfate loading by H 2 SO 4 increases the Lewis acidity of TiO 2 -P25. This catalyst gives excellent yield with less reaction time and it is an inexpensive, easily recyclable catalyst for this reaction.
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an efficient protocol for the green synthesis of quinoxaline and Dipyridophenazine derivatives at room temperature using sulfated titania
Catalysis Communications, 2010Co-Authors: B Krishnakumar, R Velmurugan, S Jothivel, M SwaminathanAbstract:Abstract Biologically active quinoxalines and Dipyridophenazines were efficiently synthesized in excellent yield and less reaction time using inexpensive, easily recyclable sulfated titania (TiO 2 –SO 4 2− ). TiO 2 –SO 4 2− , prepared by sol–gel method, was characterized by XRD, FT-IR and SEM techniques to confirm the sulfate loading. TiO 2 –SO 4 2− has more acidic sites when compared to TiO 2 (prepared )and TiO 2 –P25. Synthesis of quinoxalines with this catalyst can also be carried out in water.
Keith C Gordon - One of the best experts on this subject based on the ideXlab platform.
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substituent effects on the electronic properties of complexes with Dipyridophenazine and triazole ligands electronically connected and disconnected ligands
Coordination Chemistry Reviews, 2015Co-Authors: Holly Van Der Salm, Anastasia B S Elliott, Keith C GordonAbstract:Abstract Substituent effects may tune and alter the optical and electronic properties of ligands and the complexes which they comprise. We review the effect of electron-withdrawing and -donating groups on the Dipyridophenazine (dppz) framework. The observation of selected modulation of the properties associated with the phenazine or phenanthroline MOs is observed and reflected in the electrochemical and optical properties. The effect of donor groups that can give rise to ligand-centred charge-transfer optical transitions is also discussed. The effect of substituents on complexes with triazole ligands is examined; in stark contrast to the findings for dppz systems, and virtually regardless of the type of triazole ligand, substituents have only a muted effect on optical and electrochemical properties.
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intraligand charge transfer excited states in re i complexes with donor substituted Dipyridophenazine ligands
Inorganic Chemistry, 2014Co-Authors: Christopher B Larsen, Michael W George, Holly Van Der Salm, Anastasia B S Elliott, Michael G Fraser, Charlotte A Clark, Raphael Horvath, Nigel T Lucas, Keith C GordonAbstract:The donor–acceptor ligands 11-(4-diphenylaminophenyl)dipyrido[3,2-a:2′,3′-c]phenazine (dppz-PhNPh2) and 11-(4-dimethylaminophenyl)dipyrido[3,2-a:2′,3′-c]phenazine (dppz-PhNMe2), and their rhenium complexes, [Re(CO)3X] (X = Cl–, py, 4-dimethylaminopyridine (dmap)), are reported. Crystal structures of the two ligands were obtained. The optical properties of the ligands and complexes are dominated by intraligand charge transfer (ILCT) transitions from the amine to the dppz moieties with λabs = 463 nm (e = 13 100 M–1 cm–1) for dppz-PhNMe2 and with λabs = 457 nm (e = 16 900 M–1 cm–1) for dppz-PhNPh2. This assignment is supported by CAM-B3LYP TD-DFT calculations. These ligands are strongly emissive in organic solvents and, consistent with the ILCT character, show strong solvatochromic behavior. Lippert–Mataga plots of the data are linear and yield Δμ values of 22 D for dppz-PhNPh2 and 20 D for dppz-PhNMe2. The rhenium(I) complexes are less emissive, and it is possible to measure resonance Raman spectra. These d...
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structural electronic and computational studies of heteroleptic cu i complexes of 6 6 dimesityl 2 2 bipyridine with sulfur substituted Dipyridophenazine ligands
Polyhedron, 2013Co-Authors: Michael G Fraser, Holly Van Der Salm, Scott A Cameron, Jonathan E Barnsley, Keith C GordonAbstract:Abstract A series of stable heteroleptic Cu(I) complexes of 6,6′-dimesityl-2,2′-bipyridine with three sulfur-substituted Dipyridophenazine ligands, and unsubstituted dppz are synthesized and studied. The X-ray crystal structures of the complexes display coordinative flexibility of the Cu(I) metal ion and display strong intramolecular π–π stacking interactions. The coordination geometries of the Cu(I) metal centers are characterized by the τ4 parameter, and range from 0.626 for [Cu(bpy(Mes)2)(dppz(Sdec)2]BF4 to 0.757 for [Cu(bpy(Mes)2)(dppzS2CS)]BF4. Cyclic voltammetry reveals Cu(I)/Cu(II) oxidation potentials around 0.83 V for all the complexes studied, consistent with a similar coordination environment of the complexes in solution. The ligand-based reduction potentials are consistent with the electronic nature of the sulfur substituent. Resonance Raman spectroscopy and TD-DFT calculations reveal the presence of an MLCT → bipyridine transition with 488 and 514.5 nm excitation, and dppz-type chromophores ranging from UV (351 nm) to the visible (457 nm) excitation wavelengths. For [Cu(bpy(Mes)2)(dppzS2CS)]BF4 and [Cu(bpy(Mes)2)(dppz(Sdec)2]BF4 the most intense optical transition at 434 and 442 nm respectively are assigned as intraligand (IL)/MLCT transitions.
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Structural, electronic and computational studies of heteroleptic Cu(I) complexes of 6,6′-dimesityl-2,2′-bipyridine with sulfur-substituted Dipyridophenazine ligands
Polyhedron, 2013Co-Authors: Michael G Fraser, Holly Van Der Salm, Scott A Cameron, Jonathan E Barnsley, Keith C GordonAbstract:Abstract A series of stable heteroleptic Cu(I) complexes of 6,6′-dimesityl-2,2′-bipyridine with three sulfur-substituted Dipyridophenazine ligands, and unsubstituted dppz are synthesized and studied. The X-ray crystal structures of the complexes display coordinative flexibility of the Cu(I) metal ion and display strong intramolecular π–π stacking interactions. The coordination geometries of the Cu(I) metal centers are characterized by the τ4 parameter, and range from 0.626 for [Cu(bpy(Mes)2)(dppz(Sdec)2]BF4 to 0.757 for [Cu(bpy(Mes)2)(dppzS2CS)]BF4. Cyclic voltammetry reveals Cu(I)/Cu(II) oxidation potentials around 0.83 V for all the complexes studied, consistent with a similar coordination environment of the complexes in solution. The ligand-based reduction potentials are consistent with the electronic nature of the sulfur substituent. Resonance Raman spectroscopy and TD-DFT calculations reveal the presence of an MLCT → bipyridine transition with 488 and 514.5 nm excitation, and dppz-type chromophores ranging from UV (351 nm) to the visible (457 nm) excitation wavelengths. For [Cu(bpy(Mes)2)(dppzS2CS)]BF4 and [Cu(bpy(Mes)2)(dppz(Sdec)2]BF4 the most intense optical transition at 434 and 442 nm respectively are assigned as intraligand (IL)/MLCT transitions.
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synthesis and electronic properties of mononuclear osmium ii and rhenium i complexes containing ligands derived from 2 3 a 3 2 c Dipyridophenazine ppb
Polyhedron, 2004Co-Authors: Matthew I J Polson, Sarah L Howell, Amar H Flood, Anthony K Burrell, Allan G Blackman, Keith C GordonAbstract:Abstract An improved method for the synthesis of the polypyridyl ligand [2,3-a:3′,2′-c]Dipyridophenazine (ppb) is reported. In addition, the syntheses of the new ppb-based ligands L (L=[2,3-a:3′,2′-c]Dipyridophenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dimethylphenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dichlorophenazine, [2,3-a:3′,2′-c]dipyrido[1,2-e]benzophenazine, [2,3-a:3′,2′-c:3″,2″-e]tripyridoquinoxaline and [2,3-a:3′,2′-c]dipyrido-5-methylphenazine) are detailed. The complexes [Os(ppb)(bpy)2]2+ and [Os(L)(bpy)2]2+ have been synthesised and their electrochemical, electronic absorption and UV–Vis spectrochemical properties measured. Syntheses of the rhenium(I) complexes fac-[Re(L″)(CO)3Cl] (L″ = [2,3-a:3′,2′-c]Dipyridophenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dimethylphenazine, [2,3-a:3′,2′-c]dipyrido-6,7-dichlorophenazine, [2,3-a:3′,2′-c]dipyrido[1,2-e]benzophenazine) are also reported. The osmium(II) complexes [Os(L′)(bpy)2]2+ (L′ = 2,3-di-(2-pyridyl)quinoxaline, 6,7-dimethyl-2,3-di-(2-pyridyl)quinoxaline, 6,7-chloro-2,3-di-(2-pyridyl)quinoxaline, 2,3-di-(2-pyridyl)benzo[g]quinoxaline, 4-methyl-di-(2-pyridyl)quinoxaline) have also been prepared and studied. The electronic spectra of the Os and Re complexes are dominated by strong MLCT transitions. The lowest energy MLCT transitions correlate linearly with the first reduction potential for the [Os(L)(bpy)2]2+ series. Electrochemical oxidation of the [Os(L)(bpy)2]2+ and [Os(L′)(bpy)2]2+ complexes results in the appearance of LMCT transitions in the visible region while reduction of the [Os(L)(bpy)2]2+ complexes produces complex electronic spectra. Comparison with the reduced fac-[Re(L″)(CO)3Cl] complexes allows assignment of L″ − π→π* transitions in the NIR (1200–1000 nm) and red (850–700 nm) regions. The nonsymmetrical ligands [2,3-a:3′,2′-c:3″,2″-e]tripyridoquinoxaline and [2,3-a:3′,2′-c]dipyrido-5-methylphenazine both coordinate to the [Os(bpy)2]2+ unit in a stereospecific manner to give a single geometric isomer. The crystal structure of [Re(CO)3(ppb)Cl] is reported, in which the polypyridyl ligand deviates significantly from planarity.