• Volume 117, Issue 2

      March 2005,   pages  71-201

    • Recent Advances in Bio-inorganic Chemistry

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    • Meso-functionalized octamethoxyporphyrins: A new class of nonasubstituted porphyrins

      Pradeepta K Panda V Krishnan

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      Octamethoxyporphyrin containing multiple-donor substituents has been functionalized for the first time. A large number of its mono-meso-substituted derivatives with substituents such as nitro, amino, N-methylamino, formyl, hydroxymethyl, oxime, cyano and carboxy functional groups have been synthesized and characterized. They form a new class of nonasubstituted porphyrins. Crystallographic studies on the cyano derivative show that the -C N group is in conjugation with the prophyrin π-system. The calculated optical transition energies and the electron densities on the imino nitrogens of the synthesised porphyrins using AMI calculations correlate well with the experimentally observed data. Meso-substituted porphyrins are found to be essentially planar.

    • Metal ion coordination in ‘R’ and ‘T’ state hybrid hemoglobins as revealed by optical, EPR and sulphhydryl reactivity studies

      S Ramasamy Swarnalatha Venkateshrao J M Rifkind P T Manoharan

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      The sulphhydryl environment in various mixed-metal hybrid hemoglobins, viz. α2(Cu)-β2(FeCO), α2(FeCO)-β2(Cu), α2(Cu)-β2(Ni), α2(Ni)-β2(Cu), was studied by reacting them with the sulphhydryl reagent, 4,4′-dithiodipyridine (4-PDS). The reactivity was compared with that of HbCO, NiHb and CuHb. It is found that there exists a correlation between conformational change and metal ion environment, not only at the extreme R and T states but also the intermediate conformations. EPR examinations of these hybrids show that both in R state-[Cu(II)-Fe(II)] and T state-[Cu(II)-Ni(II)] hybrids at neutral pH and in the absence of IHP, CuPPIX, irrespective of the subunit in which it is present, has a mixed-metal ion environment: Species 1, a five-coordinated Cu2+ complex with strong proximal histidine bond and species 2, a four-coordinated complex without any covalent linkage with Nε F8-histidine.

    • Core-modified octaphyrins: Syntheses and anion-binding properties

      Rajneesh Misra Venkataramanarao G Anand Harapriya Rath Tavarekere K Chandrashekar

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      In this paper, a brief review of the syntheses, characterization and anion-binding properties of core-modified octaphyrins is presented. It has been shown that the core-modified octaphyrins exhibit aromaticity both in solution and in solid state, confirming the validity of the (4n + 2) Huckel rule for larger π-electron systems. Solid-state binding characteristics of TFA anions of two core-modified octaphyrins are also described.

    • Synthesis, photophysical and metal ion signalling behaviour of mono- and di-azacrown derivatives of 4-aminophthalimide

      N B Sankaran M Sarkar A Samanta

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      Synthesis, photophysical behaviour and metal ion signalling ability of 3-component systems, I and II, comprising a 4-aminophthalimido moiety as fluorophore, a dimethylene spacer and two different azacrown receptors, are reported. The fluorescence quantum yields and lifetimes of both the systems have been found to be significantly lower than that of the parent fluorophore indicating the occurrence of photoinduced electron transfer (PET) between the terminal moieties. PET is found to be more efficient in II, presumably due to the presence of more than one electron-donating centre in the receptor moiety. Fluorescence decay behaviour of the systems suggests a through-space nature of PET. The systems exhibit off-on fluorescence signalling in the aprotic media in the presence of several metal ions, some of which are well known for their fluorescence quenching abilities. Diazacrown derivative, II, appears to be a somewhat better signalling system than the monoazacrown derivative, I.

    • Fixation of CO2 in air: Synthesis and crystal structure of a μ3-CO3-bridged tricopper(II) compound

      Jhumpa Mukherjee V Balamurugan Maninder Singh Hundal Rabindranath Mukherjee

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      A novel trinuclear copper(II) compound [{(L3)Cu(OClO3)}33-OCO2)][ClO4] has been synthesised using an N-tridentate symmetrical pyridylalkylamine ligand, N-methyl-N,N-bis(2-pyridylmethyl) amine (L3). The structure of the complex has been determined by X-ray crystallography; it is found to crystallise in the hexagonal space group P63/m with a = 13·936(2), b = 13·936(2), c = 14·895(3) Å, α = β = 90°, γ = 120°. The complex possesses a 6̅ symmetry axis passing through the carbon atom of the triply bridging carbonate ion, with the three symmetry related copper ions connected to one another through the oxygen atoms from the bridging carbonato group, giving an equilateral triangular array of copper centres. Each copper ion has distorted square pyramidal environment with the basal plane formed by three nitrogen atoms of the ligand L3 and the oxygen atom of the bridging carbonato group. The apical position at each copper is provided by the weak oxygen coordination from the perchlorate ion.

    • Synthesis, characterisation of few N-substituted 1,8-naphthalimide derivatives and their copper(II) complexes

      Nilotpal Barooah Chandan Tamuly Jubaraj B Baruah

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      A few 1,8-naphthalimide derivatives with phenyl (1), benzyl (2), 3,4-dimethoxyphenyl ethyl (3), 4-pyridyl (4), 2-hydroxy ethyl (5), 4-pyridylmethyl (6) groups attached to the nitrogen atom are synthesized and characterized. Cyclic voltammograms of all these compounds show one-electron reversible redox cycle ( −1·24 V to −1·18 V) due to formation of anion radicals. However, in the case of (5), quenching of this redox process occurs when polyhydroxy-aromatic compounds such as 1,3-dihydroxy benzene and 1,3,5-trihydroxybenzene are added. Copper complexes, namely bis-{N-(4-pyridylmethyl)1,8-naphthalimide} copper (II) perchlorate (8), bis-{N-(4-pyridylmethyl)1,8-naphthalimide}copper (II) perchlorate (9) and bis-{N-(4-pyridylmethyl)phthalimide} copper (II) perchlorate (10) are synthesized and characterised. The complexes (8) and (9) show reversible redox couple of the ligand without any significant interaction with the redox active copper (II) centre.

    • Effect of copper-sulphur bond on the DNA photo-cleavage activity of 2-(methylthio)ethylpyridine-2-carbaldimine copper(II) complexes

      Tarkeshwar Gupta Ashis K Patra Shanta Dhar Munirathinam Nethaji Akhil R Chakravarty

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      The binding and photo-induced DNA cleavage activity of a binary complex [CuL2](ClO4)2 (1) and the in situ generated ternary complexes [CuLB](ClO4)2 from 1 (B: 1,10-phenanthroline, phen, 2; dipyrido[3,2-d: 2′,3′-f]quinoxaline, dpq, 3) are studied, where L is a N2S-donor tridentate Schiff base 2- (methylthio)ethylpyridine-2-carbaldimine. Complex 1, structurally characterized by X-ray diffraction study, has six-coordinate meridional geometry showing CuN4S2 coordination. The Cu-N bond lengths are in the range of 1·968(3) to 2·158(4) Å. The Cu-S bond lengths of 2·599(2) and 2·705(2) Å are significantly long indicating weak covalent interaction between copper and sulphur atoms. The thiomethyl groups are cis to each other giving S-Cu-S angle of 75·82(5)°. The Cu-N(pyridyl) bond distances are longer than the Cu-N(imine) bonds. The complexes are redox active and display a quasi-reversible cyclic voltammetric response assignable to the Cu(II)/Cu(I) couple near 0·0 V vs SCE in DMF-Tris buffer (1: 4 v/v) using 0·1 M KCl as supporting electrolyte. Electronic spectra of the complexes show a d-d band in the range 630 to 700 nm in DMF along with higher energy charge transfer bands. While complex 1 is a poor binder to DNA, the ternary complexes show good DNA binding propensity. The photo-nuclease activity of 13 is studied using UV and visible wavelengths. The DNA cleavage activity at 365 nm follows the order: 3 > 2 > 1. The cleavage reaction involves the formation of singlet oxygen as the reactive species in a type-II process.

    • Synthesis and characterization of a chiral dimeric copper(II) complex: Crystal structure of [Cu2(μ-Cl)2(HL)2]·H2O(H2L = S-(−)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol)

      Chullikkattil P Pradeep Panthapally S Zacharias Samar K Das

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      Synthesis and characterization of an optically active binuclear dichloro-bridged copper(II) complex [Cu2(μ-Cl)2(HL)2]·H2O 1 (H2L = S-(−)-2-[(2-hydroxy-1-phenyl-ethylimino)-methyl]-phenol) of a Schiff-base derived from salicylaldehyde and (S)-(+)-2-phenylglycinol are described. Compound 1 crystallizes in the orthorhombic chiral P212121 space group with Z = 4, a = 10·21(2), b = 11·574(3), c = 25·364(9). Each copper shows square pyramidal geometry with O2NCl2 coordination and the Cu2Cl2 core geometry adopts a butterfly shape. Crystals of 1 were further characterized by elemental analysis, IR, UV-visible and EPR spectroscopy and circular dichroism (CD) studies.

    • Synthesis and crystal structure of 5-(4′-carboxyphenyl)-10,15,20-tri(4′-t-butylphenyl)porphinato zinc(II) complex

      P Bhyrappa C Arunkumar J J Vittal

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      Synthesis and crystal structure of 5-(4′-carboxyphenyl)-10,15,20-tri(4′-t-butylphenyl)porphinato zinc(II) have been presented. The title complex shows interesting hydrogen-bonded dimeric structure in the solid state.

    • Fluorescence-enhancement with different ionic inputs in a cryptand-based multi-receptor signalling system

      Bamaprasad Bag Parimal K Bharadwaj

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      Two molecules of a laterally non-symmetric aza cryptand have been attached to 9,10-dimethylanthracene to obtain a multi-receptor fluorescent signalling system in the “receptor-spacer-fluorophore-spacer-receptor” format. In the absence of a metal ion, weak fluorescence is observed upon excitation of the anthryl group owing to efficient photo-induced electron transfer (PET) of the lone pair of N attached to the anthryl group. However, when a metal salt is added, the lone pair is engaged, thus in blocking of the PET and leading to recovery of fluorescence to different extents depending upon the nature of the metal ion.

    • Mixed-ligand complexes of ruthenium(II) incorporating a diazo ligand: Synthesis, characterization and DNA binding

      Megha S Deshpande Avinash S Kumbhar

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      Mixed-ligand complexes of the type [Ru(N-N)2(dzdf)]Cl2, where N-N is 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen) and 9-diazo-4,5-diazafluorene (dzdf), have been synthesized and characterized by elemental analysis, UV-Vis, IR and NMR spectroscopy. Binding of these complexes with calf thymus DNA (CT-DNA) has been investigated by absorption spectroscopy, steady-state emission spectroscopy and viscosity measurements. The experimental results indicate that the size and shape of the intercalating ligands have marked effect on the binding affinity of the complexes to CT-DNA. The complex [Ru(phen)2(dzdf)]Cl2 binds with CT-DNA through an intercalative binding mode, while the complex [Ru(bpy)2(dzdf)]Cl2 binds electrostatically.

    • Fluorescence properties of meso-tetrafurylporphyrins

      Iti Gupta M Ravikanth

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      Fluorescence properties of meso-tetrafurylporphyrins with N4, N3S and N2S2 porphyrin cores are studied by both steady-state and time-resolved fluorescence techniques and compared with the corresponding meso-tetraarylporphyrins. The study shows that the replacement of six-membered aryl groups with five-membered furyl groups at meso-positions alter the fluorescence properties considerably, as reflected in the large red shifts and broadening of fluorescence bands with reduction in quantum yields and singlet excited-state lifetimes. However, zinc(II) derivatives of meso-tetrafurylporphyrin and mesotetraarylporphyrin did not show significant differences in their emission properties.

    • Rhodium and iridium complexes of N-(2′-hydroxyphenyl)pyrrole-2-aldimine: Synthesis, structure, and spectral and electrochemical properties

      Semanti Basu Indrani Pal Ray J Butcher Georgina Rosair Samaresh Bhattacharya

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      Reaction of N-(2′-hydroxyphenyl)pyrrole-2-aldimine (H2L) with [M(PPh3)3Cl] (M = Rh, Ir) affords complexes of type [M(PPh3)2(L)Cl]. Structures of both complexes have been determined by X-ray crystallography. In both complexes, the N-(2′-hydroxyphenyl)pyrrole-2-aldimine ligand is coordinated to the metal centre, via dissociation of the acidic protons, as a dianionic tridentate N,N,O-donor. The M(L)Cl fragment constitutes an equatorial plane with the metal at the centre and the two PPh3 ligands occupying axial positions. The complexes are diamagnetic (low-spin d6, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry of the [M(PPh3)2(L)Cl] complexes shows reversible M(III)-M(IV) oxidation near 0·5 V vs SCE and quasi-reversible ligand-centred oxidative response near 1·0 V vs SCE.

    • Biocatalysis by metallated cyclotriphosphazenes: L2Zn(NO3)2 {L = spiro-N3P3[O2C12H8][N(CH3)NH2]} as a synthetic phosphoesterase and nuclease

      Vadapalli Chandrasekhar Venkatasubbiah Krishnan Ramachandran Azhakar C Madhavaiah Sandeep Verma

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      Catalytic activity of [L2.Zn][NO3]2] (L = spiro-N3P3[O2C12H8][N(CH3)NH2]) towards the hydrolysis of two phosphodiesters, [bis(p-nitrophenyl)phosphate, bNPP] and [2-(hydroxypropyl)-p-nitrophenyl phosphate, hNPP] has been examined. While the rate of hydrolysis of the former is accelerated over a million-fold, the rate of hydrolysis of the latter also is enhanced considerably. Detailed kinetic evaluation of these reactions has been carried out and all the kinetic parameters including the Michaelis-Menten parameters are reported. The catalyst [L2.Zn][NO3]2] has also been found to be an effective nuclease. Relaxation of supercoiled plasmid DNA, pBR322, occurs in presence of [L2.Zn][NO3]2 without the need for any exogenous reagents.

    • Mixed-ligand copper(II) complexes of dipicolylamine and 1,10-phenanthrolines: The role of diimines in the interaction of the complexes with DNA

      S Ramakrishnan M Palaniandavar

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      Mixed-ligand copper(II) complexes of the type [Cu(dipica)(diimine)](ClO4)2, where dipica is di(2-picolyl)amine and diimine is 1,10-phenanthroline (phen), 5,6-dimethyl-1,10-phenanthroline (5,6-dmp), 2,9-dimethyl-1,10-phenanthroline (2,9-dmp) or dipyridoquinoxaline (dpq), have been isolated and characterized by analytical and spectral methods. The copper(II) complexes exhibit a broad band in the visible region around 675 nm and axial EPR spectra in acetonitrile glass (77 K) with g and A values of ∼2·22 and 185 × 10−4 cm−1 respectively, suggesting the presence of a square-based coordination geometry for the CuN5 chromophore involving strong axial interaction. The interaction of the complexes with CT DNA has been studied using absorption, emission and circular dichroic spectral methods and viscosity measurements. Absorption spectral titrations reveal that the intrinsic DNA binding affinities are dependent upon the nature of the diimine ligand: dpq > 5,6-dmp > phen > 2,9-dmp. This suggests the involvement of the diimine rather than the dipica ‘face’ of the complexes in DNA binding. An intercalative mode of DNA interaction, which involves the insertion of dpq and to a lesser extent the phen ring of the complexes in between the DNA base pairs, is proposed. However, interestingly, the 5,6-dmp complex is involved in hydrophobic interaction of the 5,6-dmp ring in the grooves of DNA. The large enhancement in the relative viscosity of DNA on binding to the dpq and 5,6-dmp complexes supports the proposed DNA binding modes. Further, remarkably, the 5,6-dmp complex is selective in exhibiting a positive-induced CD band on binding to DNA suggesting the transition of the B form of CT DNA to A-like conformation. The variation in relative emission intensities of DNA-bound ethidium bromide observed upon treatment with the complexes parallels the trend in DNA binding affinities.

    • Iron(III) porphyrin-catalysed oxidation reactions by m-chloroperbenzoic acid: Nature of reactive intermediates

      A Agarwala V Bagchi D Bandyopadhyay

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      The reaction of m-chloroperbenzoic (m-CPBA) acid with meso-tetrakis (pentafluorophenyl) porphynatoiron(III) chloride (F20TPPFe(III)Cl ) has been studied in dichloromethane and acetonitrile medium at 25 ± 1°C. The reactive intermediates formed in this reaction have been quantitatively trapped by 2,4,6-tri t-butylphenol (TTBP) in both the solvents. It has been observed that the kinetic plots of the formation of TTBP radical in dichloromethane are all multiexponential, supporting the formation of more than one reactive intermediate in this solvent. In acetonitrile solvent the formation of TTBP radical was however observed to be distinctly single exponential. Different kinds of reactive intermediates are proposed in these two solvents.

    • Porphyrin-anthraquinone dyads: Synthesis, spectroscopy and photochemistry

      P Prashanth Kumar G Premaladha Bhaskar G Maiya

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      Free-base (H2L2), copper(II) (CuL2) and zinc(II) (ZnL2) derivatives of a porphyrin-anthraquinone conjugate with an azomethine group separating the two photoactive subunits have been synthesized and characterized by mass (FAB), IR, UV-visible, 1H NMR and ESR spectroscopic techniques and also by cyclic and differential pulse voltammetric methods. Analysis of the data reveals that the spectral and electrochemical properties of the individual chromophoric entities are retained and that there is no specific π-π interaction between the porphyrin and anthraquinone subunits. H2L2 and ZnL2 are shown to exhibit substantial quenching (88–97%) of the porphyrin fluorescence compared to their corresponding monomeric analogues. An intramolecular electron-transfer mechanism is proposed for the substantial decrease in fluorescence in both derivatives. The fluorescence decays of porphyrin-anthraquinone conjugates are fit to 2/3 exponentials and indicate that multiple orientations of the porphyrin and anthraquinone groups contribute to the electron-transfer event. These results are in good agreement with steady-state fluorescence results. From the time-resolved fluorescence data, the electron-transfer rate constants are calculated, indicating kET values in the range of 1·1 × 109 to 9·9 × 1010 s−1 that are dependent upon the solvent.

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