Mangalampalli Ravikanth

Indian Institute of Technology Bombay, Mumbai, Mahārāshtra, India

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Publications (128)323.74 Total impact

  • Yogita Pareek, M. Ravikanth
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    ABSTRACT: Review: synthesis of functionalized thiaporphyrins and their use in the construction of several covalently and non-covalently linked thiaporphyrin-based arrays; 62 refs.+ subrefs.
    ChemInform 07/2014; 45(28).
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    ABSTRACT: Unsymmetrical 22-oxacorrole containing two aryl groups and one pyrrole group at the meso position was synthesized by condensing one equivalent of 16-oxatripyrrane with one equivalent of meso aryl dipyromethane under mild acid-catalyzed conditions followed by oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). This [3+2] condensation approach was expected to yield meso-free 25-oxasmaragdyrin but unexpectedly afforded unsymmetrical meso-pyrrole-substituted 22-oxacorrole. We demonstrated the versatility of the reaction by synthesizing four new meso-pyrrole-substituted 22-oxacorroles. The reactivity of α-position of meso-pyrrole was tested by carrying out various functionalization reactions such as bromination, formylation, and nitration and obtained the functionalized meso-pyrrole-substituted 22-oxacorroles in decent yields. The X-ray structure obtained for one of the functionalized meso-pyrrole substituted 22-oxacorrole revealed that the macrocycle was nearly planar and the meso-pyrrole was in the perpendicular orientation with respect to the macrocyclic plane. The meso-pyrrole-substituted 22-oxacorroles absorb strongly in 400–700 nm region with one strong Soret band and four weak Q bands. The 22-oxacorroles are strongly fluorescent and showed emission maxima at ≈650 nm with decent quantum yields and singlet-state lifetimes. The 22-oxacorroles are redox-active and exhibited three irreversible oxidations and one or two reversible reduction(s). A preliminary biological study indicated that meso-pyrrole corroles are biocompatible.
    Chemistry 07/2014; · 5.93 Impact Factor
  • Yogita Pareek, Vellanki Lakshmi, Mangalampalli Ravikanth
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    ABSTRACT: Three covalently linked dyads such as porphyrin-ferrocene, porphyrin-BODIPY and porphyrin-sapphyrin containing one hydroxyphenyl group at the meso-position of porphyrin were synthesized by coupling the trans-functionalized porphyrin building block, 5-(4-hydroxyphenyl)-10-(4-iodophenyl)-15,20-diphenyl porphyrin, with the ethynyl functionalized redox/chromophore building block under mild Pd(0) coupling conditions. The dyads were then reacted with SnTTP(OH)2 in benzene in a 2 : 1 ratio at reflux temperature for 12 hours followed by simple alumina column chromatographic purification which afforded three pentads containing three different types of redox/chromophore components in 62-80% yields. The pentads are very stable and freely soluble in all common organic solvents. The pentads formation were confirmed by MALDI-TOF mass spectrometry and 1D and 2D NMR studies. Absorption and electrochemical studies suggested that the three components in pentads retain their independent characteristic features without significant alterations in their properties thus acting like supramolecular assemblies. The steady state fluorescence studies indicated a possibility of energy/electron transfer among the three types of components in pentads.
    Dalton Transactions 03/2014; · 3.81 Impact Factor
  • Avanish Dvivedi, Yogita Pareek, Mangalampalli Ravikanth
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    ABSTRACT: A simple, one-step, supramolecular strategy was adopted to synthesize Sn(IV) -porphyrin-based axially bonded triads and higher oligomers by using meso-pyridyl Sn(IV) porphyrin, meso-hydroxyphenyl-21,23-dithiaporphyrin, and Ru(II) porphyrin as building blocks and employing complementary and non-interfering Sn(IV) O and Ru(II) ⋅⋅⋅N interactions. The multiporphyrin arrays are stable and robust and were purified by column chromatography. (1) H, (1) H-(1) H COSY and NOESY NMR spectroscopic studies were used to unequivocally deduce the molecular structures of Sn(IV) -porphyrin-based triads and higher oligomers. Absorption and electrochemical studies indicated weak interaction among the different porphyrin units in triads and higher oligomers, in support of the supramolecular nature of the arrays. Steady-state fluorescence studies on triads indicated the possibility of energy transfer in the singlet state from the basal Sn(IV) porphyrin to the axial 21,23-dithiaporphyrin. However, the higher oligomers were weakly fluorescent due to the presence of heavy Ru(II) porphyrin unit(s), which quench the fluorescence of the Sn(IV) porphyrin and 21,23-dithiaporphyrin units.
    Chemistry 03/2014; · 5.93 Impact Factor
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    ABSTRACT: New multiple photosynthetic reaction centers were constructed from cyclophosphazene decorated multiporphyrin chromophores and a fulleropyrrolidine having a pyridine ligand (). The excited state electron transfer in the self-assembled donor-acceptor assembly was investigated by using steady state absorption and emission, time-resolved emission spectroscopy and nanosecond laser flash photolysis. The effect of metal (Zn(2+)) coordination to porphyrin units in the multiporphyrin arrays on cyclophosphazine scaffold () was studied by comparing with metal free porphyrin assembly on a cyclophosphazene scaffold (). In , the decrease of absorption and fluorescence intensity and the lowering of the amplitude of longer fluorescence lifetime with increase of concentration reflect the formation of a ground state complex with an association constant of ∼14 910 M(-1). When compared to the metal-free complex , the metal-coordinated derivative exhibited shortening of the singlet and triplet state lifetimes and lowering of the singlet and triplet quantum yields. The cause of the decrease of the triplet quantum yields by insertion of zinc metal is discussed along with the possible non-planarity of the porphyrin ring. From the fluorescence lifetime measurements for the mixture, it is proposed that self-assembly of the donor-acceptor complex leads to charge separated species with a rate constant of 7.1 × 10(9) s(-1). The decrease of triplet state intensity and lifetime of the in the complex from the nanosecond transient absorption studies support the occurrence of intermolecular electron transfer in the triplet state.
    Physical Chemistry Chemical Physics 03/2014; · 3.83 Impact Factor
  • Tejinder Kaur, Avijit Ghosh, Palanisamy Rajakannu, Mangalampalli Ravikanth
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    ABSTRACT: The hexacoordinated rhenium(I) complex of 5,10,15,20-tetra-p-tolyl-21,23-dithiaporphyrin was synthesized, and the crystal structure analysis revealed the unusual binding mode of rhenium(I) to two thiophene sulfur atoms and one of the pyrrole nitrogen atoms of the porphyrin macrocycle.
    Inorganic Chemistry 02/2014; · 4.59 Impact Factor
  • Emandi Ganapathi, Way‐Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: An alternate synthetic route was developed for tetraaryl 27-thiasapphyrins by condensation of meso-aryl dipyrromethanes with 2,5-bis(p-tolylhydroxymethyl)thiophene under acid-catalyzed conditions. Previously, 27-thiasapphyrins have been prepared by a multistep synthesis using 2,2′-bipyrrole as the key precursor. In our strategy, the pyrrole–pyrrole bond was generated to form 27-thiasapphyrins by oxidative coupling of meso-aryl dipyrromethane and 2,5-bis(p-tolylhydroxymethyl)thiophene, and the desired 27-thiasapphyrins were isolated in 8–12 % yields. The crystal structure of one of the 27-thiasapphyrins indicates that the macrocycle is almost planar and the thiophene sulfur atom is in the plane whereas the four pyrrole nitrogen atoms slightly deviate from the plane defined by four meso carbon atoms. Absorption spectroscopy showed four well defined Q bands in 590–770 nm and one strong Soret band in 470–480 nm region for 27-thiasapphyrins. The 27-thiasapphyrins are stable under redox conditions and undergo two-to-three reversible oxidations and one-to-two reversible reductions. The macrocycles are weakly fluorescent with low quantum yields and singlet state lifetimes.
    Asian Journal of Organic Chemistry. 02/2014;
  • Vellanki Lakshmi, Tamal Chatterjee, Mangalampalli Ravikanth
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    ABSTRACT: A simple synthetic route was developed for the decomplexation of F-BODIPYs (fluorine-substituted boron–dipyrromethenes) to afford dipyrrins in high yields. This was achieved by treating the F-BODIPYs with different Lewis acids such as ZrCl4, TiCl4, AlCl3, Sc(OTf)3, or SnCl4 in CH3CN/CH3OH under refluxing conditions. This synthetic strategy was efficient for different types of F-BODIPYs such as meso-aryl-substituted BODIPYs, 3-pyrrolyl BODIPYs, functionalized 3-pyrrolyl BODIPYs, π-extended pyrrolyl BODIPYs, sterically crowded BODIPYs, and the BF2 complex of 25-oxasmaragdyrin.
    European Journal of Organic Chemistry 01/2014; 2014(10):2105-2110. · 3.34 Impact Factor
  • Sheri Madhu, Mangalampalli Ravikanth
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    ABSTRACT: We synthesized benzimidazole substituted boron-dipyrromethene 1 (BODIPY 1) by treating 3,5-diformyl BODIPY 2 with o-phenylenediamine under mild acid catalyzed conditions and characterized by using various spectroscopic techniques. The X-ray structure analysis revealed that the benzimidazole NH group is involved in intramolecular hydrogen bonding with fluoride atoms which resulted in a coplanar geometry between BODIPY and benzimidazole moiety. The presence of benzimidazole moiety at 3-position of BODIPY siginificantly altered the electronic properties, which is clearly evident in bathochromic shifts of absorption and fluorescence bands, improved quantum yields, increased lifetimes compared to BODIPY 2. The anion binding studies indicated that BODIPY 1 showed remarkable selectivity and specificity toward F(-) ion over other anions. Addition of F(-) ion to BODIPY 1 resulted in quenching of fluorescence accompanied by a visual detectable color change from fluorescent pink to nonfluorescent blue. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bonding between BODIPY and benzimidazole moieties leading to (i) noncoplanar geometry between BODIPY and benzimidazole units and (ii) operation of photoinduced electron transfer (PET) from benzimidazole moiety to BODIPY unit causing quenching of fluorescence. Interestingly, when we titrated the nonfluorescent blue 1-F(-) solution with TFA resulted in a significant enhancement of fluorescence intensity (15-fold) because the PET quenching is prevented due to protonation of benzimidazole group. Furthermore, the reversibility and reusability of sensor 1 for the detection of F(-) ion was tested for six cycles indicating the sensor 1 is stable and can be used in reversible manner.
    Inorganic Chemistry 01/2014; · 4.59 Impact Factor
  • Tamal Chatterjee, Avijit Ghosh, Sheri Madhu, Mangalampalli Ravikanth
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    ABSTRACT: Stable calixoxa- and calixthiasmaragdyrins containing three methine bridges and two direct bonds connecting the five pyrrole/heterocycle rings were synthesized by [3 + 2] condensation of dipyrromethane with 16-oxatripyrrane and 16-thiatripyrrane respectively under mild acid-catalyzed conditions. The compounds were characterized by HR-MS, 1D & 2D NMR, absorption and electrochemical techniques and the structure of calixoxasmaragdyrin was solved by X-ray crystallography. The crystal structure analysis indicated that the calixoxasmaragdyrin macrocycle was highly distorted due to the flexibility introduced by one sp(3)meso-carbon. The compounds show ill-defined absorption bands and irreversible oxidation and reduction waves which were attributed to the disruption of conjugation of the macrocycle by incorporation of one sp(3)meso-carbon. The anion binding studies indicated that the calixoxasmaragdyrin exhibited specific sensing ability for the HSO4(-) ion over other anions whereas calixthiasmaragdyrins did not even show an ability to bind anions.
    Dalton Transactions 01/2014; · 3.81 Impact Factor
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    ABSTRACT: We report the synthesis of 3-amino boron-dipyrromethene (3-amino BODIPY) by treating 3-bromo boron-dipyrromethene (3-bromo BODIPY) initially with sodium azide in acetonitrile followed by triphenylphosphine(PPh3)/H2O in tetrahydrofuran in three steps under mild reaction conditions. In this reaction, 3-azido BODIPY which formed in the first step was not isolated but the 3-iminophosphorane BODIPY which formed in the second step was isolated and characterized crystallographically. The 3-amino BODIPY was characterized by various spectroscopic and X-ray analytical techniques. To test the reactivity of amine functionality on BODIPY core, we prepared 1-(meso-anisyl BODIPY)-3-phenyl urea/thiourea derivatives under simple reaction conditions. Our studies indicated that 1-(meso-anisyl BODIPY)-3-pheny thiourea can act as specific chemodosimetric sensor for Hg2+ ion and 1-(meso-anisyl BODIPY)-3-phenyl urea as colorimetric and ratiometric sensor for F− ion.
    Dyes and Pigments 01/2014; 102:218–227. · 3.53 Impact Factor
  • Emandi Ganapathi, Sheri Madhu, Mangalampalli Ravikanth
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    ABSTRACT: A series of triazole bridged BODIPY-conjugates were synthesized under click reaction conditions. The 3-azido BODIPY was generated in situ by treating 3-bromo BODIPY with NaN3 in CH3CN at room temperature for 60 min and reacted with appropriate ethynyl containing chromophore/redox active unit, such as ferrocene, BODIPY, Zn(II) porphyrin, 21,23-dithiaporphyrin, BF2-smaragdyrin in the presence of CuI/DIPEA in THF/CH3CN solvent. The conjugates were purified by column chromatography and obtained pure compounds in 45–50% yields. The conjugates were characterized by HR-MS, 1D, 2D, 19F and 11B NMR and X-ray crystallography for BODIPY-ferrocene conjugate. Absorption and electrochemical studies showed features of both the moieties present in the conjugates and also support interaction between the two moieties in the conjugates. The fluorescence studies supported an efficient energy transfer from BODIPY unit to BF2-smaragdyrin unit in BODIPY–BF2-smaragdyrin conjugate but the energy transfer was not efficient in BODIPY–Zn(II) porphyrin and BODIPY–21,23-dithiaporphyrin conjugates.
    Tetrahedron. 01/2014; 70(3):664–671.
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    ABSTRACT: A multisignaling Hg(II) sensor based on a benzimidazole substituted BODIPY framework was designed, which displays excellent selectively toward Hg(II) in vitro and in vivo. Optical and fluorogenic measurements in solution reveal that the sensor can detect mercury ions at submicromolar concentrations, with high specificity. The detection of Hg(II) is associated with a blue-shift in optical spectra and a simultaneous increase in the fluorescence quantum yield of the sensor, which is attributed to a decrease in charge delocalization and inhibition of photoinduced electron transfer upon binding to Hg(II). Using several spectroscopic measurements, it is shown that the binding mechanism involves two sensor molecules, where lone pairs of the benzimidazole nitrogen coordinate to a single mercury ion. The utility of this BODIPY sensor to detect Hg(II) in vivo was demonstrated by fluorescence imaging and spectroscopy of labeled human breast adenocarcinoma cells. While average emission intensity of the sensor over a large number of cells increases with incubated mercury concentrations, spatially resolved fluorescence spectroscopy performed on individual cells reveals clear spectral blue-shifts from a subensemble of sensors, corroborating the detection of Hg(II). Interestingly, the emission spectra at various submicrometer locations within cells exhibited considerable inhomogeneity in the extent of blue-shift, which demonstrates the potential of this sensor to monitor the local (effective) concentration of mercury ions within various subcellular environments.
    Inorganic Chemistry 09/2013; · 4.59 Impact Factor
  • Hemanta Kalita, Way-Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: A series of B(OR)2-smaragdyrin complexes were synthesized by treating BF2-smaragdyrin complex with various aliphatic and aromatic alcohols in the presence of AlCl3 in CH2Cl2 at room temperature. The compounds are stable and characterized by various spectroscopic and electrochemical techniques. The X-ray structure solved for one of the B(OR)2-smaragdyrin complex showed that the macrocycle is planar and the boron atom is in tetrahedral geometry coordinated to two pyrrole nitrogens of the macrocycle and two oxygen atoms of the axial -OR groups. (1)H NMR studies indicated that the alkoxy or aryloxy groups present on the boron atom experience the macrocyclic ring current effect and appear in the up-field region. The absorption properties of B(OR)2-smaragdyrin complexes showed a strong absorption band at ∼700 nm along with other absorption bands in the 450-650 nm region like BF2-smaragdyrin complex. Since B(OR)2-smaragdyrin complexes are electron rich due to the presence of electron rich alkoxy and aryloxy groups, the B(OR)2-smaragdyrin complexes are easier to oxidize but difficult to reduce compared to BF2-smaragdyrin. The B(OR)2-smaragdyrin complexes are found to be weakly fluorescent than BF2-smaragdyrin.
    Dalton Transactions 08/2013; · 3.81 Impact Factor
  • Avijit Ghosh, Way-Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: We report the unusual formation of thiaisoporphyrins containing bridging sp(3)meso carbon between two pyrroles when 21-thiaporphyrins were reacted with PhBCl2 in dry toluene at reflux temperature.
    Chemical Communications 08/2013; · 6.38 Impact Factor
  • Tamanna K. Khan, Martin Bröring, Sanjay Mathur, Mangalampalli Ravikanth
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    ABSTRACT: Porphyrin/metalloporphyrin derivatives are a class of chromophores possessing favorable optical and redox properties for variety of applications ranging from materials to medicine. However, one drawback of porphyrin derivatives is their relatively poor absorption in the blue-green region of the spectrum (450–550 nm). One of the approaches for improving the absorption properties of porphyrin derivatives in blue-green region is their linking with chromophores that are capable of strongly absorbing in that region. Boron-dipyrrins (BODIPYs) are highly fluorescent dyes which absorb strongly in blue-green region and possess complementary properties with porphyrins. In recent times, covalently and non-covalently linked BODIPY-porphyrin conjugates on their own and in association with other moieties such as fullerenes received lot of attention because of their use for various applications. Several synthetic strategies have been developed to synthesize simple BODIPY-porphyrin conjugates to complex photonic wires and gates. This review describes synthesis, properties and potential applications of covalently and non-covalently linked conjugates containing only BODIPY and porphyrin units as well as conjugates containing BODIPY, porphyrin and other groups such as fullerenes.
    Coordination Chemistry Reviews 08/2013; 257(s 15–16):2348–2387. · 11.02 Impact Factor
  • Avijit Ghosh, Rajesh Gonnade, Mangalampalli Ravikanth
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    ABSTRACT: Synthesis and first structural characterization of hexa coordinated rhenium(i) tricarbonyl complex of 5,20-bis(p-tolyl)-10,15-bis(p-methoxyphenyl)-21-selenaporphyrin are described. The Re(i) complex of 21-selenaporphyrin was synthesized by treating free base 21-selenaporphyrin in 1,2-dichlorobenzene with Re(CO)5Cl at reflux for 7 h and analyzed using mass, NMR, FT-IR, UV-vis and electrochemical techniques. The first structure of metal complex of 21-selenaporphyrin was determined by X-ray single crystal analysis. The crystal structure revealed that the Re(CO)3 coordinates to two of the three inner nitrogens and one selenium to produce compound . The selenophene ring bent towards the Re(i) ion and the selenium is displaced by 0.41 Å from the mean plane of 24-atoms to coordinate with Re(i) ion in η(1)-fashion. The 21-selenaporphyrin is distorted in compound compared to free base 21-selenaporphyrin. (1)H and (13)C NMR studies indicated that compound exhibits fluxional behaviour in coordination mode of binding in solution. The compound is highly stable and does not undergo decomplexation under acidic conditions. The absorption spectra showed three broad Q-bands and splitted Soret band and electrochemical studies indicated that compound is stable under redox conditions.
    Dalton Transactions 06/2013; · 3.81 Impact Factor
  • Hemanta Kalita, Way-Zen Lee, Mangalampalli Ravikanth
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    ABSTRACT: BF2-complex of meso-free 25-oxasmaragdyrin is synthesized under simple reaction conditions in high yield and the reactivity of meso-free carbon atom was demonstrated by carrying out functionalization followed by coupling reactions.
    The Journal of Organic Chemistry 05/2013; · 4.56 Impact Factor
  • Vellanki Lakshmi, Mangalampalli Ravikanth
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    ABSTRACT: A Wittig reaction was employed to synthesize conjugated BODIPYs in high yields by treating formylated BODIPYs with alkyl/aryl ylides under simple room temperature conditions. Treatment of 3,5-diformyl BODIPYs or -formyl 3-pyrrolyl BODIPY with different alkyl/aryl ylides in CH2Cl2 at room temperature for 2 h followed by straightforward column chromatographic purification on silica afforded conjugated BODIPYs in ~ 65-90% yields. This is an alternate method to Knoevenagel and Heck reactions which have been used to synthesize such conjugated BODIPYs. The method works very efficiently and we prepared 12 substituted BODIPYs including cholesterol substituted BODIPYs to demonstrate the versatility of the reaction. The spectral, electrochemical and fluorescence properties of these conjugated BODIPYs are also described.
    The Journal of Organic Chemistry 04/2013; · 4.56 Impact Factor
  • Sheri Madhu, Rajesh G Gonnade, Mangalampalli Ravikanth
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    ABSTRACT: Synthesis, characterization, spectral and electrochemical properties of 3,5-bis(acrylaldehyde) BODIPY are described. The compound exhibited higher selectivity towards cysteine/homocysteine over other amino acids as well as thiol-containing compounds as shown by absorption, emission titration experiments as well as in living cells.
    The Journal of Organic Chemistry 04/2013; · 4.56 Impact Factor