About Me |
---|
Dr. Rabindra Nath Pradhan received his MSc. Degree from Utkal University (2012). Then he qualified UGC-JRF in Joint CSIR?UGC National Eligibility Test (June 2012) and GATE (2013). After that, he joined for Ph.D. in the Indian Institute of Technology, Bhubaneswar under Dr. Akhilesh Kumar Singh, obtained degree in 2019, on the topic entitled as “T1 and ParaCEST-Based Molecular Contrast Agents for MRI”. After completed his degree he joined as an Assistant Professor in chemistry, in the Regional Institute of Education Bhubaneswar (NCERT). His current interests are focused on design and synthesis of different macrocyclic and acyclic ligands and their corresponding metal complexes to explore their desired contrast ability towards MRI. |
Sl. No. | Title | Issuer |
---|
Fe(II) and Ni(II) paraCEST contrast agents containing the di-pyridine
macrocyclic ligand 2,2?,2?-(3,7,10-triaza-1,5(2,6)-dipyridinacycloundecaphane-3,7,10-
triyl)triacetamide (DETA) are reported here. Both [Fe(DETA)]2+ and [Ni-
(DETA)]2+ complexes were structurally characterized. Crystallographic data revealed
the seven-coordinated distorted pentagonal bipyramidal geometry of the [Fe-
(DETA)]·(BF4)2·MeCN complex with five coordinated nitrogen atoms from the
macrocyclic ring and two coordinated oxygen atoms from two amide pendant arms.
The [Ni(DETA)]·Cl2·2H2O complex was six-coordinated in nature with a distorted
octahedral geometry. Four coordinated nitrogen atoms were from the macrocyclic
ring, and two coordinated oxygen atoms were from two amide pendant arms.
[Fe(DETA)]2+ exhibited well-resolved sharp proton resonances, whereas very broad
proton resonances were observed in the case of [Ni(DETA)]2+ due to the long
electronic relaxation times. The CEST peaks for the [Fe(DETA)]2+ complex showed
one highly downfield-shifted and intense peak at 84 ppm with another shifted but less intense peak at 28 ppm with good CEST
contrast efficiency at body temperature, whereas [Ni(DETA)]2+ showed only one highly shifted intense peak at 78 ppm from the
bulk water protons. Potentiometric titrations were performed to determine the protonation constants of the ligand and the
thermodynamic stability constant of the [M(DETA)]2+ (M = Fe, Co, Ni, Cu, Zn) species at 25.0 °C and I = 0.15 mol·L?1 NaClO4.
Metal exchange studies confirmed the stability of the complexes in acidic medium in the presence of physiologically relevant anions
and an equimolar concentration of Zn(II) ions.
Two macrocyclic triamide octadentate chelator scaffolds L1 and L2 were synthesized, characterized by several
spectroscopic techniques, and their pKa values were determined by potentiometric titration. Using these ligands,
two water soluble paramagnetic Eu(III) complexes, [EuL1(OH2)](NO3)3·H2O (EuL1) and [EuL2(OH2)](NO3)3·H2O
(EuL2) were synthesized and characterized in the solid state and in solution. Single crystal X ray diffraction
measurement of [EuL1(OH2)](NO3)3.H2O (EuL1) reveals octadentate binding of the ligand to Eu(III) and ninth
coordination being completed by an oxygen atom of a solvent molecule (H2O). X-ray diffraction data of
[EuL2(OH2)](NO3)3·H2O (EuL2) were severely disordered and hence its chloride analogue
[EuL2(DMF)]Cl3·H2OMeOH (EuL2-Cl) was synthesized and characterized using single-crystal X-ray diffraction
measurements. The crystal data of [EuL2(DMF)](Cl)3·H2OMeOH (EuL2-Cl) reveal octadentate binding of the
ligand to Eu(III), with the ninth coordination being completed by an oxygen atom of a solvent molecule (DMF).
Luminescence measurements confirm the presence of a water molecule coordinated to Eu(III) in aqueous solution.
The stability of the Eu(III) complexes was investigated using spectrophotometric molar ratio method.
Cyclic voltammetry studies obtained from aqueous solutions of the Eu(III) complexes show reversible one
electron reduction processes at the glassy carbon electrode with E1/2=?0.799 V and ?0.777 V (versus Ag/
AgCl) for the complexes of L1 and L2.
The successful synthesis of new pyrimidine based organic ligands with terminal carboxylate and oxime functional
groups, followed by their employment in metallogrid self-assembly has yielded three tetranuclear [Ni4(L1)4]
?2CH3CN?4CH3OH·4H2O (1), [Cu4(HL1?)4]?8CH3OH·28H2O (2) and [Ni4(H2L2)4](CF3SO3)8?4CH3NO2·8H2O (3),
[2×2] metallogrid complexes. The complexes have been well characterized by elemental analyses, IR spectra,
UV-vis spectra and X-ray structural analyses. Variable temperature magnetic measurements/studies done on these
three complexes followed by magnetic data fitting suggest that all the three complexes are dominated by intramolecular
antiferromagnetic exchange coupling.
We are reporting Co(II) and Ni(II) complexes of a pyridine containing aromatic macrocyclic triamide ligand,
3,6,9,15-tetraazabicyclo(9.3.1)pentadeca-1(15),11,13-triene-3,6,9-triacetamide (TPTA), as paramagnetic
chemical exchange saturation transfer (paraCEST) MRI contrast agents. The synthesis and characterization
of TPTA and its complexes are reported. The solution chemistry and solid-state structure of Co(II) and
Ni(II) complexes are studied. Crystallographic data show that the [Co(TPTA)]·Cl2·2H2O complex (sevencoordinate,
all four N atoms of ring and three amide O atoms) has a distorted pentagonal bipyramidal
geometry, however the [Ni(TPTA)Cl]·Cl·0.25H2O complex (six-coordinate, all four N atoms of the ring,
one amide O and one chloride ion) adopts a distorted octahedral geometry. Notably the two pendent
amide arms are not coordinated in the [Ni(TPTA)Cl]+ complex and one chloride ion fulfils its sixth coordination.
The CEST effect of [Co(TPTA)]2+ and [Ni(TPTA)Cl]+ amide protons is observed at 57 ppm and
78 ppm downfield of the bulk water proton respectively in a buffer solution containing 20 mM
N-(2-hydroxyethyl)piperazine-N’-ethanesulfonic acid and 100 mM NaCl at pH 7.4 at 37 °C on a
9.4 T NMR spectrometer. The effects of CEST intensity and exchange rate constant with variation of pH of
the solution were studied. The CEST effect and exchange rate constant for the amide protons of the
[Co(TPTA)]2+ complex have been monitored in HEPES buffer, fetal bovine serum (FBS), rabbit serum and
4% agarose gel (w/w). The stability of the [Co(TPTA)]2+ complex in aqueous solution towards oxidation
was verified by cyclic voltammetry measurement. The stability of [Co(TPTA)]2+ has further been monitored
in the presence of biologically relevant ions including HPO4
2?, CO32?, and Zn2+ and under acidic
conditions.
The self-assembly of two pyridine hydrazone based tritopic ligands appended with terminal
carboxylate groups with CuII and NiII have been investigated. These polytopic ligands with tridentate
coordination pockets were designed to produce homoleptic [3 × 3] grid complexes on reaction with transition
metals.Despite the formation of anticipated metallogrids as the final self-assembly outcome, metal ion geometric
preferences and ligand flexibility lead to the formation of tetranuclear clusters in the self-assembly process with
CuII and NiII metal ions. These results illustrate the dynamic nature of the metal–ligand interactions and flexible
nature of the ligand backbone in coordination self-assembly. The synthesis, structure and magnetic properties
of three tetraanuclear species {[Cu4(H2L1b)2(OTf)4(OH)2(H2O)2]·6H2O}n (1), [Ni4(L2a)2(OCH3)4]·4H2O
(2), [Cu4(L2b)2(OTf)4(H2O)4]·6H2O (3) involving two tritopic ligands with central pyridine framework are
described.
tWe have developed a novel coumarin-based chemosensor H2L with ICT character bearing the hydra-zone of substituted phenol, synthesized by the condensation of 2-hydroxy-4-methylbenzohydrazidewith 3-acetylcoumarin. The fluorescence spectra of the receptor H2L demonstrated that the sensor couldselectively recognize Al3+over other metal ions and the detection limit was found in the micromolarconcentration range. Sensing capability of the receptor for Al3+was reversible. Cu2+complex of H2L wasstructurally characterized which gave the basis for possible structure of Al3+complex of H2L. The TurnOn fluorescence of H2L is based on intramolecular charge transfer (ICT), chelation enhanced fluorescence(CHEF) and C N isomerization to serve as fluorescent chemosensor in DMF-water solvent mixture. Thereceptor H2L showed a remarkably red-shifted absorption spectrum in the presence of Al3+in DMF.B3LYP-SCRF/6-31G* density functional theory explains the ICT mechanism.
A new unsymmetrical ditopic ligand H2L was used to synthesize two [2 × 2] grid type tetranuclear trivalent
and mixed-valent FeIII
4 , FeII
2FeIII
2 complexes, respectively. Both complexes [FeIII
4 (L’)4] (1) and [FeII
2FeIII
2 (L)4]
(BF4)2·2CH3CN (2) have been X-ray structurally characterized. The magnetic properties of complexes 1
and 2 show dominant antiferromagnetic coupling. Mössbauer studies were carried out to confirm the
electronic states of the iron centres. The structural properties of the two complexes are diverse though
they have been synthesized from the same ligand but under different conditions. In 1, all the Fe(III) metal
centres are coordinated by two pairs of parallel but oppositely aligned ligand strands arranged in a ‘headto-
tail’ fashion, whereas in 2, Fe(II) and Fe(III) metal centres are coordinated by two pairs of parallel aligned
ligand strands arranged in a ‘head-to-head’ fashion.
Compounds based on the [3 × 3] nonamanganese(II)
square grid motif and featuring additional manganese(II) ions
linked to the grid core were isolated through a strict self-assembly grid through a Mn–O bond. The same reaction carried out with
H2L2 affords an unprecedented 2D polymeric structure [Mn11-
(L2?)6(H2O)8][Mn(H2O)6]·24H2O, in which each nonamanganese
grid is connected to its four neighbors through tetraaquomanganese(
II) centers, again linked to the carboxylate functions.
The two compounds also contain [Mn(H2O)6]2+ complexes in
the lattice. These metallogrid-based compounds, for which DC
magnetic data were collected and analysed in detail, emphasize
the rich binding affinity and bridging versatility of the used
ligands, which provide access to both discrete complexes and
extended polymeric assemblies.
approach. Extended tritopic picolinic dihydrazide ligands
were used, which contain terminal ester groups and differ in
the R substituent on the para position of the central pyridine
ring (H2L1, R = OCH3; H2L2, R = H). Upon reaction with
Mn(OAc)2·4H2O, the ligand H2L1 undergoes hydrolysis and
spontaneous self-assembly to afford [Mn10(L1?)6(H2O)5]-
[Mn(H2O)6]2·11H2O, where a pentaaquomanganese(II) unit is
connected to one of the terminal carboxylate functions of the
We herein report a structurally characterized Schiff base ligand, L, formed by the condensation of 1,1-bis-[2-
hydroxy-3-acetyl-5-methylphenyl]methane with 2-picolyl amine. It utilizes the three signalling
mechanisms, ESIPT, chelation enhanced fluorescence (CHEF) and C]N isomerization, to serve as a
“Turn-On” fluorescence chemosensor for Al3+. L has high selectivity for Al3+ in MeOH. The reversible
nature of this chemosensor makes it cost effective. It joins the rare family of ditopic fluorescent
chemosensors. When this Schiff base receptor was treated with Al3+ salt in MeOH, the fluorescence
intensity abruptly increased. Other metal ions did not show such a significant effect on the fluorescence.
The detection limit for this chemosensor was found to be 0.7 mM.
Synthesis of a macrocyclic compound is a great challenge in the field of synthetic chemistry. A
macrocyclic tri-toslyte compound (L) was designed and synthesized by using different types of chemical
reactions. NMR, Mass, Uv-Vis spectroscopy confirmed that the synthesized compound was formed in
pure form. The single crystal X-ray diffraction measurements reveal that the compound (L) is macrocyclic
with tri-tosylate group attached to the three nitrogen atoms of the macrocyclic backbone.
Di-pyridine containing macrocyclic ligand 3,7-diaza-1,5(2,6)-dipyridinacyclooctaphane (L) is reported
here. The ligand was synthesized through multi steps organic synthesis and its Cu(II) complex[Cu(L)].Cl2
was also successively synthesized. Both the ligands and complex were characterized by standard
spectroscopic technique in both solid phase as well as solution phase. Crystal data reveals that the
[Cu(L)].Cl2 is six coordinated distorted octahedral geometry with four nitrogen donor of macrocyclic ring
and two chlorine atom.
The study of nanotechnology is quite interesting today. It has extensive use in cutting-edge physics, chemistry, engineering, and biological sciences. It served as a stepping stone for the direction that will utilize nanotechnology for a variety of applications in the future. There have been numerous advances in nanoscience and nanotechnology recently that will transform our way of life. Starting with disease detection, treatment, and prevention in many facets of human existence and extending to technical advancements like nanomedicine. Silver nanoparticles (AgNPs) are among the most important and fascinating nanomaterials among the many nanotechnological devices and nanoparticles. It has many beneficial biomedical uses. AgNPs are significant in nanomedicine.
The study of nanotechnology is quite interesting today. It has extensive use in cutting-edge physics, chemistry, engineering, and biological sciences. It served as a stepping stone for the direction that will utilize nanotechnology for a variety of applications in the future. There have been numerous advances in nanoscience and nanotechnology recently that will transform our way of life. Starting with disease detection, treatment, and prevention in many facets of human existence and extending to technical advancements like nanomedicine. Silver nanoparticles (AgNPs) are among the most important and fascinating nanomaterials among the many nanotechnological devices and nanoparticles. It has many beneficial biomedical uses. AgNPs are significant in nanomedicine.