M. Thirumal

University of Delhi, Old Delhi, NCT, India

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Publications (27)54.95 Total impact

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    ABSTRACT: Bifunctional chelate, 6,6'-(2-aminoethylazanediyl)bis(methylene)dipicolinicacid (H2pentapa-en-NH2), has been synthesized and labeled with 99mTc with specific activity of 135−140 MBq/μmol in >95% yield. The in vitro stability of the labeled chelate in both PBS and human serum shows only <5% dissociation at 24 h. The in vivo distribution pattern of the labeled chelator in normal as well as EAT tumor bearing BALB/c mice suggested renal as the major route of excretion with <2% ID/g uptake in other organs. The target specificity of the chelate towards tumor was introduced by conjugating two molecules of methionine. The conjugated H2pentapa-en-met2 was synthesized in >85% yield and labeled with 99mTc in 96.2% radiochemical yield with specific activity of 110−125 MBq/μmol. The conjugate probe exhibited high serum stability (>94% at 24 h). The in vivo blood kinetic studies of radiocomplexes of H2pentapa-en-NH2 and its methionine conjugated derivative exhibited fast clearance with t1/2(F) = 32 ± 0.14 min, t1/2(S) = 4 h 20 min ± 0.21 min and t1/2(F) = 27 ± 0.3 min, t1/2(S) = 4 h 01 min ± 0.11 min, respectively. In vivo scintigraphy and ex vivo biodistribution studies in EAT tumor bearing mice demonstrated high retention of H2pentapa-en-met2 at the site of tumor with tumor to muscle ratio of 6.52 at 1 h, indicating the high specificity of 99mTc-pentapa-en-met2 toward tumors.
    RSC Advances 01/2015; 5(43):33963-33973. DOI:10.1039/C4RA13690J · 3.84 Impact Factor
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    ABSTRACT: Purpose Tumor cells are known to have an elevated requirement for methionine due to increased protein synthesis and trans-methylation reactions. A methionine based macrocyclic tumor imaging system, DO3A-Act-Met, has been designed to provide a novel platform for tumor imaging via modalities, PET/MRI using metal ions, 68Ga and 157Gd. Methods Synthesis of DO3A-Act-Met was confirmed through NMR and mass spectrometric techniques. Cytotoxicity of complexes was evaluated using MTT assay whereas receptor binding and trans-stimulation studies were performed on EAT and U-87 MG cell lines. Tumor targeting was assessed through imaging and biodistribution experiments on U-87 MG xenograft model. Results DO3A-Act-Met was synthesized and radiolabeled with 68Ga in high radiochemical purity (85-92%). The receptor binding assay on EAT cells predicted high binding affinity with Kd of 0.78 nM. Efflux of 35S-L-methionine trans-stimulated by extracellular DO3A-Act-Met on U-87MG cells suggested an L-system transport. MR studies revealed a longitudinal relaxivity of 4.35 mM−1 s−1 for Gd-DO3A-Act-Met and a 25% signal enhancement at tumor site. The biodistribution studies in U-87MG xenografts validated tumor specificity. Conclusion DO3A-Act-Met, a methionine conjugated probe is a promising agent for targeted molecular imaging, exhibiting high specificity towards tumor owing to its essential role in proliferation of cancer cells mediated through LAT1.
    Pharmaceutical Research 08/2014; 32(3). DOI:10.1007/s11095-014-1509-x · 3.95 Impact Factor
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    ABSTRACT: Expanding the light-harvesting range and suppressing the quick recombination of photogenerated charge carriers are of paramount significance in the field of photocatalysis. One possible approach to achieve wide absorption range is to synthesize type-II core/shell heterostructures. In addition, this system also shows great promise for fast separation of charge carriers and low charge recombination rate. Herein, following the surface functionalization method using 3-mercaptopropionic acid (MPA) as a surface functionalizing agent, we report on designing NaNbO3/CdS type-II core/shell heterostructures with an absorption range extending to visible range and explore the opportunity towards degradation of methylene blue (MB) dye as a model pollutant under visible light irradiation. Combined with a collection of characterizations including X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), UV-vis diffuse reflectance spectrum (DRS), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy, support the growth of CdS shell onto NaNbO3 nanorods. The resulting core/shell heterostructures unveiled high surface areas, enhanced light harvesting and appreciably increased photocatalytic activity towards MB degradation compared to individual counterparts and the photocatalytic standard, Degussa P25 under visible light irradiation. The remarkably enhanced photocatalytic activity of core/shell heterostructures could be interpreted in terms of efficient charge separation owing to core/shell morphology and resulting type-II band alignment between NaNbO3 and CdS, which creates a step like radial potential favoring the localization of one of the carriers in the core and the other in the shell. A plausible mechanism for the degradation of MB dye over NaNbO3/CdS core/shell heterostructures is also elucidated using active species scavenger's studies. Our findings imply that hydroxyl radicals (OH˙) plays crucial role in dictating the degradation of MB under visible light. This work highlights the importance of core/shell heterostructures in leading towards new paradigms for developing highly efficient and reusable photocatalysts for the destructive oxidation of recalcitrant organic pollutants. Keywords: NaNbO3, CdS, Photocatalysis, Type-II band alignment, Methylene blue, Core/shell, Herterostructures.
    ACS Applied Materials & Interfaces 07/2014; 6(15). DOI:10.1021/am503055n · 6.72 Impact Factor
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    ABSTRACT: Calcium concentration modulation both inside and outside cell is of considerable interest for nervous system function in normal and pathological conditions. MRI has potential for very high spatial resolution at molecular/cellular level. Design, synthesis and evaluation of Gd-DO3A-AME-NPHE, a calcium responsive MRI contrast agent is presented. The probe is comprised of a Gd(3+)-DO3A core coupled to iminoacetate coordinating groups for calcium induced relaxivity switching. In the absence of Ca(2+) ions, inner sphere water binding to the Gd-DO3A-AME-NPHE is restricted with longitudinal relaxivity, r1 = 4.37 mM(-1) s(-1) at 4.7 T. However, addition of Ca(2+) triggers a marked enhancement in r1 = 6.99 mM(-1) s(-1) at 4.7 T (60% increase). The construct is highly selective for Ca(2+) over competitive metal ions at extracellular concentration. The r1 is modulated by changes in the hydration number (0.2 to 1.05), which was confirmed by luminescence emission lifetimes of the analogous Eu(3+) complex. T1 phantom images establish the capability of complex of visualizing changes in [Ca(2+)] by MRI.
    European Journal of Medicinal Chemistry 05/2014; 82C:225-232. DOI:10.1016/j.ejmech.2014.05.046 · 3.43 Impact Factor
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    ABSTRACT: Herein, an efficient synthetic approach to a furopyrazine scaffold with four points of diversity, starting from 2(1H)-pyrazinones, with dipeptomimetic properties, is presented. R-groups corresponding to amino acid side chains were introduced during the 2(1H)-pyrazinone and subsequent furopyrazine formation. The furopyrazine scaffold was further functionalized with an amino- and a carboxy-terminus resulting in a conformationally restricted dipeptidomimetic scaffold. The carboxy-terminus was introduced via a chemoselective vinylation of the 7-position followed by oxidative cleavage, while the amino-terminus was obtained via Buchwald–Hartwig amidation of the 2-position of the scaffold. The versatility of the synthetic method was demonstrated by the synthesis of a small library of diversely substituted furopyrazines having various amino acid side chains on the four points of diversity. Evaluation with an X-ray structure of the scaffold and computational analysis supports the exploitation of the furopyrazine scaffold as a restricted dipeptide mimic, which can mimic the two central residues of a β-turn.
    ChemInform 04/2012; 68(14):3019–3029. DOI:10.1016/j.tet.2012.02.022
  • Meganathan Thirumal · Peter K. Davies
    Journal of Materials Science 07/2011; 46(13):4715-4718. DOI:10.1007/s10853-011-5455-2 · 2.37 Impact Factor
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    ABSTRACT: A phosphonate derivative 10'-bis(acetamido)-ethane-bis[1,4,7-tri(methylene phosphonic acid)-1,4,7,10-tetraazacyclododecane] (DO3P-AME-DO3P), was synthesized with 90% yield in high purity. It was labeled with (99m)Tc in 97.5% efficiency and specific activity of 112-250 MBq/μmol. The binding affinity of (99m)Tc-DO3P-AME-DO3P towards bone minerals was tested in vitro by using hydroxy apatite as a bone model with absorption of 93% during the first hour of the experiment. Receptor binding assay on human bone cell line SAOS-2 demonstrated K(d) value of 1.07 nM. Cell binding studies of DO3P-AME-DO3P on osteoblasts and osteoclasts cells performed in vitro displayed preferential affinity of the compound towards osteoclast (167.95 ± 3.56% dose/mg protein). The serum stability of (99m)Tc complex was found to be 96.8% after 24 h. Blood kinetics of (99m)Tc-DO3P-AME-DO3P performed on normal rabbits showed fast clearance with t(1/2)(F) = 15 min ± 0.014 min and t(1/2)(S) = 4 h 3 min ± 0.09 min. Biodistribution studies carried out in normal BALB/c mice showed bone-to-blood ratio of 20 and bone-to-muscle ratio of 33. The bone tissue demonstrated highest concentration of bound radioactivity with 10.73% ID/g at 1 h post injection. The protonation and stability constants were determined by pH-potentiometry titrations. The stability constants of DO3P-AME-DO3P with Lu(III), Sm(III), and Ho(III) were 19.7, 21.8, and 20.2 determined by "out of cell" method. The excellent bone seeking properties of DO3P-AME-DO3P make it a candidate of choice for SPECT imaging and preferential uptake of the compound in osteoclasts in comparison to osteoblasts; BMM and BMC can be used to understand the pathway of pathogenesis of osteoporosis and skeletal metastases.
    Bioconjugate Chemistry 02/2011; 22(2):244-55. DOI:10.1021/bc100382c · 4.82 Impact Factor
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    ABSTRACT: A bis-polyazamacrocycle, 10'-bis(acetamido)ethane-bis[1,4,7-tri(carboxymethane)-1,4,7,10-tetraazacyclododecane] (DO3A-AME-DO3A) was synthesized for application in magnetic resonance imaging. The efficacy of DO3A-AME-DO3A as non ionic magnetic contrast agent was tested by performing relaxometric studies on its gadolinium complex. The longitudinal relaxivity, r(1) and transverse relaxivity, r(2) values were found to be 5.84 mM(-1)s(-1) and 6.82 mM(-1)s(-1), per Gd(III) at pH 7.0, 37 °C. The luminescence properties of europium complex of DO3A-AME-DO3A were investigated in aqueous medium. The lifetime of Eu(2)-DO3A-AME-DO3A in water was found to be 0.786 ms. Emission and luminescence lifetime measurements on the europium complex of DO3A-AME-DO3A gives a hydration number of q = 1.9. The reaction enthalpy and entropy were found to be, ΔH(0) = -(6.2 ± 2) kJ mol(-1), ΔS(0) = - (1.8 ± 0.4) kJ mol(-1)K(-1), and K(Eu)(298) = (1.8 ± 0.1).
    Dalton Transactions 02/2011; 40(13):3346-51. DOI:10.1039/c0dt01370f · 4.20 Impact Factor
  • M. Thirumal · A. K. Ganguli
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 05/2010; 33(18). DOI:10.1002/chin.200218022
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    Ashok K. Ganguli · Shikha Nangia · Meganathan Thirumal · Pratibha L. Gai
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    ABSTRACT: Using molten salt route (with NaCl/KCl as the salt) we have been able to synthesize a new form of magnesium tantalate at 850°C. Powder X-ray diffraction data could be indexed on an orthorhombic unit cell with lattice parameters, ‘a’ = 15.36(1) Å, ‘b’ = 13.38(1) Å and ‘c’ = 12.10(1) Å. High resolution transmission electron microscopy and electron diffraction studies confirm the results obtained by X-ray studies. Energy dispersive X-ray spectroscopy helps ascertain the composition of MgTa2O6. The title compound shows a dielectric constant of ∼24 with a low dielectric loss of 0.006 at 100 kHz at room temperature. Dielectric constant is nearly unchanged with rise in temperature while the loss shows a very marginal increase (0.007 at 300°C).
    Journal of Chemical Sciences 06/2006; 118(1):37-42. DOI:10.1007/BF02708763 · 1.22 Impact Factor
  • M. Thirumal · P. K. Davies
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    ABSTRACT: The hexagonal perovskite, Ba8ZnTa6O24, was prepared in single-phase form and was found to be a stable secondary phase, formed as a result of the loss of ZnO from Ba(Zn1/3Ta2/3)O3 microwave dielectrics. The experimental and calculated X-ray patterns of Ba8ZnTa6O24 indicate it is isostructural with Ba8Ta6NiO24 with an 8H (cchc)2 close-packed BaO3 stacking sequence and the lattice parameters, a=10.0825(14), c=19.0587(38)Å. High-density ceramics of Ba8ZnTa6O24 could be prepared at temperatures considerably lower (1400°C) than those used to sinter pure Ba(Zn1/3Ta2/3)O3, and exhibit very good microwave dielectric properties with ɛ=30.5, Qf=62 300, and τf=+36 ppm/°C at 8.9 GHz.
    Journal of the American Ceramic Society 05/2005; 88(8):2126 - 2128. DOI:10.1111/j.1551-2916.2005.00426.x · 2.61 Impact Factor
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    P.K Davies · A Borisevich · M Thirumal
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    ABSTRACT: The synthesis of new families of perovskites with a 1:2 ordered Ba(Zn1/3Ta2/3)O3-type structure was investigated. The compound La(Li1/3Ti2/3)O3 was prepared with a 1:2 ordered arrangement of Li and Ti and is the first reported titanate with this type of structure. A new family of ordered perovskites, (Sr2/3La1/3)(Li1/3Ta2/3)O3 and (Sr2/3La1/3)(Li1/3Nb2/3)O3, were also prepared with a 1:2 layered order of Li+ and B5+ cations. All three compounds exhibit dielectric constants >25 and Q.f values >20,000. Studies were also made on the phase stability of Zn-deficient compositions of BZT. The hexagonal perovskite, Ba8ZnTa6O24, was isolated in single-phase form and was found to be the stable phase formed as a result of the loss of ZnO from BZT. Ba8ZnTa6O24 can be sintered to high density at temperatures considerably lower than pure BZT and exhibits very good microwave properties. In particular at GHz frequencies ε=30.5, Q.f=62,000, and τf=+36 ppm/°C.
    Journal of the European Ceramic Society 01/2003; 23(14-23):2461-2466. DOI:10.1016/S0955-2219(03)00156-0 · 2.95 Impact Factor
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    ABSTRACT: Oxides belonging to the families Ba3ZnTa2−xNbxO9 and Ba3MgTa2−xNbxO9 were synthesized by the solid state reaction route. Sintering temperatures of 1300°C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425°C hexagonally ordered structures were obtained for Ba3MgTa2−xNbxO9 over the entire range (0≤x≤1) of composition, while for Ba3ZnTa2−xNbxO9 the ordered structure exists in a limited range (0≤x≤0.5). The dielectric constant is close to 30 for the Ba3ZnTa2−xNbxO9 family of oxides while the Mg analogues have lower dielectric constant of ∼18 in the range 50 Hz to 500 kHz. At microwave frequencies (5–7 GHz) dielectric constant increases with increase in niobium concentration (22–26) for Ba3ZnTa2−xNbxO9; for Ba3MgTa2−xNbxO9 it varies between 12 and 14. The “Zn” compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the “Mg” analogues.
    Materials Research Bulletin 11/2002; 37(14):2321–2334. DOI:10.1016/S0025-5408(02)00933-9 · 2.29 Impact Factor
  • M. Thirumal · AK Ganguli
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    ABSTRACT: Oxides of the type, Ba3-xSrxZnNb2O9 (0 ≤x ≤3), were synthesized by the solid state route. Oxides calcined at 1000°C show single cubic phase for all the compositions. The cubic lattice parameter (a) decreases with increase in Sr concentration from 4.0938(2) forx = 0 to 4.0067(2) forx = 3. Scanning electron micrographs show maximum grain size for thex = 1 composition (∼ 2 μm) at 1200°C. Disks sintered at 1200°C show dielectric constant variation between 28 and 40 (at 500 kHz) for different values of x with the maximum dielectric constant atx = 1.
    Bulletin of Materials Science 08/2002; 25(4). DOI:10.1007/BF02704116 · 0.87 Impact Factor
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    M. Thirumal · A. K. Ganguli
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    ABSTRACT: Oxides of the type, Sr3Zn1-xMgxNb2O9 (0 less than or equal to x less than or equal to 1) have been obtained by the ceramic method. These oxides crystallize in the hexagonal cell corresponding to ordered triple perovskites. Sintered disks show nearly frequency-independent dielectric constant for all the compositions. Compositions sintered at 1425degreesC yield dielectric constant of 20-22 at similar to6 GHz, with quality factor ranging from 1300 to 1500. Sr3Zn0.5Mg0.5Nb2O9 shows a very low temperature coefficient of resonant frequency (tau(f)) of +4 ppm/degreesC.
    Materials Research Bulletin 01/2002; 37(1):185-191. DOI:10.1016/S0025-5408(01)00812-1 · 2.29 Impact Factor
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    ABSTRACT: Oxides belonging to the families BaâZnTa{sub 2-x}NbâOâ and BaâMgTa{sub 2-x}NbâOâ were synthesized by the solid state reaction route. Sintering temperatures of 1300 deg. C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425 deg. C hexagonally ordered structures were obtained for BaâMgTa{sub 2-x}NbâOâ over the entire range (0{
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    M. Thirumal · A. K. Ganguli
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    ABSTRACT: There are now many advanced materials, which have been discovered with unique dielectric properties having been designed with an eye to specific applications. One of the areas of current interest to the material scientist and solid state chemist is to find new materials suitable for use as dielectric resonators in microwave applications and to tailor its properties. Among them the ABO3 type perovskite oxides and the AB2O6 (columbite/trirutile) type of oxides where B is either Nb or Ta have been pursued vigorously in the recent past. There is a continuous interest to optimise the dielectric properties by suitable doping at the A-site, B-site and the B′ site of the perovskite related A(B1/3B′2/3O3) structure. In addition there is an increasing demand to discover alternate routes of synthesis, which would afford these oxides at much lower temperatures. We discuss our recent results on some of the above materials.
    Progress in Crystal Growth and Characterization of Materials 01/2002; 44(3):147-154. DOI:10.1016/S0960-8974(02)00011-6 · 1.48 Impact Factor
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    ABSTRACT: Oxides belonging to the families Ba3ZnTa2−xNbxO9 and Ba3MgTa2−xNbxO9 were synthesized by the solid state reaction route. Sintering temperatures of 1300°C led to oxides with disordered (cubic) perovskite structure. However, on sintering at 1425°C hexagonally ordered structures were obtained for Ba3MgTa2−xNbxO9 over the entire range (0≤x≤1) of composition, while for Ba3ZnTa2−xNbxO9 the ordered structure exists in a limited range (0≤x≤0.5). The dielectric constant is close to 30 for the Ba3ZnTa2−xNbxO9 family of oxides while the Mg analogues have lower dielectric constant of ∼18 in the range 50Hz to 500kHz. At microwave frequencies (5–7GHz) dielectric constant increases with increase in niobium concentration (22–26) for Ba3ZnTa2−xNbxO9; for Ba3MgTa2−xNbxO9 it varies between 12 and 14. The “Zn” compounds have much higher quality factors and lower temperature coefficient of resonant frequency compared to the “Mg” analogues.
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    M. Thirumal · A. K. Ganguli
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    ABSTRACT: Monophasic Oxides of the type MgNb2−xTaxO6 (0 ≤ x ≤ 2) have been synthesized by solid-state reactions using Mg(NO3)2·6H2O as the source of Mg. The oxides crystallize in the orthorhombic columbite structure till x = 1.75 and the tetragonal trirutile structure for pure MgTa2O6 (x = 2.0). Sintered pellets at 1200°C show dielectric constant varying between 16 to 28 for the entire range of composition at a frequency of 500 kHz. The dielectric loss is nearly constant with frequency, and varies between 0.004 and 0.01 for different compositions. The temperature coefficient of dielectric constant (τE) is 3 to −3 ppm/C (30 to 300°C). Scanning electron micrographs reveal a gradual decrease in grain size with increase in Ta concentration with size of 7 to 10 microns for the pure Nb phase sintered at 1200°C while the pure Ta phase shows a grain size of approximately 0.5 to 1 microns.
    Materials Research Bulletin 11/2001; 36(13):2421-2427. DOI:10.1016/S0025-5408(01)00706-1 · 2.29 Impact Factor

Publication Stats

154 Citations
54.95 Total Impact Points

Institutions

  • 2011–2014
    • University of Delhi
      Old Delhi, NCT, India
  • 2000–2010
    • Indian Institute of Technology Delhi
      • Department of Chemistry
      New Dilli, NCT, India
  • 2001–2006
    • Indian Institute of Technology Ropar
      • Department of Chemistry
      Rūpar, Punjab, India
  • 2003–2005
    • University of Pennsylvania
      • Department of Materials Science and Engineering
      Philadelphia, Pennsylvania, United States