Publications by authors named "Rama Mohana Rao Dumpala"

9 Publications

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Experimental and theoretical approach to probe the aquatic speciation of transuranic (neptunyl) ion in presence of two omnipresent organic moieties.

Chemosphere 2021 Jun 22;273:129745. Epub 2021 Jan 22.

Radiochemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.

Pyrazines are omnipresent in nature and have their occurrence in plants, microbes, food supplies, marine arenas. The present studies aimed at aquatic speciation of the neptunyl ion (NpO) with two pyrazine compounds namely pyrazine monocarboxylic acid (PMC) and pyrazine dicarboxylic acid (PDC). Absorption spectrophotometry was used to probe the stability, speciation and spectral properties for the complexation process. NpO forms a more stable complex with PMC than PDC for 1:1 (ML), while for 1:2 (ML) the opposite trend is observed. The extent of shift in λ which is also an indicator for the strength of complexation, reflected similar trends for the complexation process. Isothermal titration calorimetry was employed to determine the enthalpies of complex formation, which is found to be endothermic. The complexation process is entropy driven. Linear free energy correlations were established to retrieve the coordination modes of the complexes. The variation in peak potentials (the cyclic voltammograms) with change in pH and metal to ligand ratio were explored to understand redox speciation, electron transfer kinetics and Eh-pH characteristics for the interaction of NpO with pyrazine carboxylate ligands. Density functional theory calculations were employed to optimize the geometries and to calculate the bond distances and partial charges on key atoms of the optimized geometries. The theoretical calculations helped to reveal the contributions from two different configurations of the same geometry towards the optical absorption. The bond distances and partial charges estimated theoretically helped to understand the aqueous interactions at the molecular level.
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http://dx.doi.org/10.1016/j.chemosphere.2021.129745DOI Listing
June 2021

Characterization of Thorium-Pyrazinoic acid complexation and its decorporation efficacy in human cells and blood.

Chemosphere 2021 May 4;271:129547. Epub 2021 Jan 4.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai, 400094, India.

Thorium (Th) exposure to the human beings is a radiochemical hazard and the chelation therapy by suitable drugs is the major prevention approach to deal with. The present studies aimed at usage of pyrazinoic acid (PCA), which is a prodrug to treat tuberculosis, for its usage as decorporating agent for thorium from human body. The present studies provide a comprehensive knowledge on the chemical interaction and biological efficacy of pyrazinoic acid (PCA) for decorporation of Thorium from the human body. The thermodynamic parameters for Th-PCA speciation are determined by both experiment and theory. The potentiometric data analysis and Electro-Spray Ionization Mass Spectrometry (ESI-MS) studies revealed the formation of ML (i = 1-4) species with the decrease in stepwise stability constants. All the species formations are endothermic reactions and are predominantly entropy-driven. Biological experiments using human erythrocytes, whole blood and normal human lung cells showed cytocompatibility and decorporation ability of PCA for Thorium. Density functional calculations have been carried out to get insights on interaction process at molecular level. The experimental results and theoretical predictions found to be in line with each other. Present findings on complexation of Th by PCA and its evaluation in human cells and blood would further motivate determination of its safety levels and decorporation efficacy in animal models.
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http://dx.doi.org/10.1016/j.chemosphere.2021.129547DOI Listing
May 2021

Stabilization of uranyl(v) by dipicolinic acid in aqueous medium.

Dalton Trans 2021 Feb 13;50(4):1486-1495. Epub 2021 Jan 13.

The Environmental research group, R&D, Tata Steel, Jamshedpur, Jharkhand 831001, India.

Preparation of a stable U(v) complex in an aqueous medium is a challenging task owing to its disproportionation nature (conversion into more stable U(vi) and U(iv) species) and sensitivity to atmospheric oxygen. The stable uranyl (UO)/dipicolinic acid (DPA) complex ([UO(DPA)(OH)(HO)]) was formed at pH 10.5-12.0, which was confirmed by potentiometric and spectrophotometric titrations, and NMR, ESI-MS and EXAFS spectroscopy. The complex [UO(DPA)(OH)(HO)] can be electrochemically reduced on the Pt electrode at -0.9 eV (vs. Ag/AgCl) to [UO(DPA)(OH)(HO)] in aqueous medium under an anaerobic environment. According to cyclic voltammetric analysis, a pair of oxidation and reduction waves at E' = -0.592 V corresponds to the [UO(DPA)(OH)(HO)]/[UO(DPA)(OH)(HO)] redox couple and the formation of [UO(DPA)(OH)(HO)] was confirmed by the electron stoichiometry (n = 0.97 ± 0.05) of the reduction reaction of [UO(DPA)(OH)(HO)]. The pentavalent uranyl complex [UO(DPA)(OH)(HO)] was further characterized via UV-vis-NIR absorption spectrophotometry and X-ray absorption (XANES and EXAFS) spectroscopy. The [UO(DPA)(OH)(HO)] complex is stable at pH 10.5-12.0 in anaerobic water for a few days. DFT calculation shows the strong complexing ability of DPA stabilizing the unstable oxidation state U(v) in aqueous medium.
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http://dx.doi.org/10.1039/d0dt03961fDOI Listing
February 2021

Accountancy for intrinsic colloids on thorium solubility: The fractionation of soluble species and the characterization of solubility limiting phase.

Chemosphere 2021 Apr 24;269:129327. Epub 2020 Dec 24.

Homi Bhabha National Institute, Training School Complex, Anushaktinagar, Mumbai, 400094, India.

The extensive hydrolysis of tetravalent actinides leads to polynuclear formations through oxygen bridging facilitating the formation of colloids as end products. The pH, ionic strength has phenomenal effects on Thorium colloids formation. The quantitative estimation of colloids facilitates the fraction of soluble fraction into ionic, polymeric and colloidal forms of thorium. The colloids accountability and precipitate characterization explains the discrepancies in estimated solubility limits. The supernatants of long equilibrated (∼3 years) saturated thorium solution under various pH (5- 11) and ionic strengths (0-3 M NaClO) were analysed by Inductively Coupled Plasma Mass Spectrometer (ICP-MS) and Ion Chromatography (IC) to determine total and ionic thorium respectively. Laser Induced Breakdown Detection (LIBD) was employed to determine the colloid size and concentrations. The precipitates were characterized by calorimetry and XRD to determine the solubility limiting phase. The results of pH, IC, ICP-MS, and LIBD measurements on the aged thorium samples are discussed with regard to the mechanism of the formation of thorium colloids. The results revealed the formation of colloids having particle size (10-40 nm) at concentrations (10-10 particles/mL). The colloids accountancy resulted in estimated solubility products to 2-4 orders lower than their inclusion as soluble thorium. The soluble thorium was fractionated quantitatively into ionic, polymeric and colloidal forms of thorium. The precipitates formed are found to be semi amorphous.
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http://dx.doi.org/10.1016/j.chemosphere.2020.129327DOI Listing
April 2021

Aquatic interaction of uranium with two naturally ubiquitous pyrazine compounds: Speciation studies by experiment and theory.

Chemosphere 2020 Jun 6;249:126116. Epub 2020 Feb 6.

Chemical Engineering Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.

The present studies interpret the speciation of uranyl (UO) with the most ubiquitous class of natural species named pyrazines in terms of stability, speciation and its identification, thermodynamics, spectral properties determined by a range of experimental techniques and further evidenced by theoretical insights. UO forms ML and ML kind of species with a qualitative detection of ML species, while the ESI-MS identified the formation of all the complexes including ML. Both the ligands act as bidentate chelators with a difference in ring size and coordinating atoms in the complex formed. The ML complexes involve the third ligand participation as monodentate via carboxylate only due to the restricted coordination number and space around the UO ion to accommodate three ligand molecules in its primary coordination sphere. All the complexes are found to be endothermic and purely entropy driven formations. The complex formations showed redshift in the absorption spectra and the shift was further enhanced from ML to ML formation. The UO ion redox properties are used to explore the redox potential and heterogeneous electron-transfer kinetic parameters as a function of pH and concentration of UO in presence of pyrazine carboxylates. Interestingly, the cyclic voltammograms identified the ligands also as redox sensitive. The theoretical calculation gave inputs to understand the complex formation at the molecular level with major emphasis on geometry optimization, energetics, bonding parameters, molecular orbital diagrams and bond critical point analyses. The experimental observations in combination with theoretical addendum provided detailed knowledge on the interaction of UO with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylates.
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http://dx.doi.org/10.1016/j.chemosphere.2020.126116DOI Listing
June 2020

Reduction in Coordination Number of Eu(III) on Complexation with Pyrazine Mono- and Di-Carboxylates in Aqueous Medium.

Inorg Chem 2019 Aug 31;58(16):11180-11194. Epub 2019 Jul 31.

Chemical Engineering Division , Bhabha Atomic Research Centre , Mumbai 400085 , India.

The denticity, flexibility, and steric hindrance of the ligand are key factors in deciding the mode and number of coordination around a metal ion on complex formation. The thermodynamic aspects of lanthanide complexation with various multidentate ligands provides a significant insight into understand the coordination chemistry of lanthanides in framing the relevant metal organic networks for the applications in biological, biochemical and medical aspects. The pyrazine carboxylic acids are known to form many structurally important complexes and further can form chelates with coordination number of eight for europium in which more water molecules can be knocked out from the primary coordination sphere than demanded by denticity of the ligand. The present studies aimed at ESI-MS characterization and determination of the thermodynamic parameters (log β, Δ, Δ, and Δ), luminescence properties of europium complexes with pyrazine-2-carboxylate and pyrazine-2,3-dicarboxylate in aqueous solutions by experiment as well as theory. Time resolved luminescence spectroscopy supported by DFT calculations are carried out to optimize the stable geometries of the complexes with various modes of binding and coordination. Furthermore, the thermodynamic parameters estimated theoretically have been used to trace the path of complex formation.
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http://dx.doi.org/10.1021/acs.inorgchem.9b01772DOI Listing
August 2019

Complexation of thorium with pyridine monocarboxylate-N-oxides: Thermodynamic and computational studies.

J Chem Thermodyn 2018 Jul 8;122:13-22. Epub 2018 Mar 8.

Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India.

The feed wastes and waste water treatment plants are the major sources for the entry of N-oxides into the soils then to aquatic life. The complexation of actinides with potentially stable anthropogenic ligands facilitate the transportation and migration of the actinides from the source confinement. The present study describes the determination of thermodynamic parameters for the complexation of Th(IV) with the three isomeric pyridine monocarboxylates (PCNO) namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO). The potentiometric and isothermal calorimetric titrations were carried out to determine the stability and enthalpy of the formations for all the Th(IV)-PCNO complexes. Th-PANO complexes are more stable than Th-NANO and Th-IANO complexes which can be attributed to chelate formation in the former complexes. Formation of all the Th-PCNO complexes are endothermic and are entropy driven. The geometries for all the predicted complexes are optimized the energies, bond distances and charges on individual atoms are obtained using TURBOMOLE software. The theoretical calculation corroborated the experimental determinations.
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http://dx.doi.org/10.1016/j.jct.2018.02.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7094258PMC
July 2018

Structural, luminescence, thermodynamic and theoretical studies on mononuclear complexes of Eu(III) with pyridine monocarboxylate-N-oxides in aqueous solution.

Spectrochim Acta A Mol Biomol Spectrosc 2018 Feb 9;190:150-163. Epub 2017 Sep 9.

Radioanalytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai 400085, India; Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India.

The mononuclear complexes formed by Eu(III) with three isomeric pyridine monocarboxylate-N-oxides namely picolinic acid-N-oxide (PANO), nicotinic acid-N-oxide (NANO) and isonicotinic acid-N-oxide (IANO) in aqueous solutions were studied by potentiometry, luminescence spectroscopy and isothermal titration calorimetry (ITC) to determine the speciation, coordination, luminescence properties and thermodynamic parameters of the complexes formed during the course of the reaction. More stable six membered chelate complexes with stoichiometry (ML, i=1-4) are formed by Eu(III) with PANO while non chelating ML and ML complexes are formed by NANO and IANO. The stability of Eu(III) complexes follow the order PANO>IANO>NANO. The ITC studies inferred an endothermic and innersphere complex formation of Eu(III)-PANO and Eu(III)-IANO whereas an exothermic and outer-sphere complex formation for Eu(III)-NANO. The luminescence life time data further supported the ITC results. Density functional theoretical calculations were carried out to optimize geometries of the complexes and to estimate the energies, structural parameters (bond distances, bond angles) and charges on individual atoms of the same. Theoretical approximations are found to be in good agreement with the experimental observations.
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http://dx.doi.org/10.1016/j.saa.2017.09.013DOI Listing
February 2018

Stability, speciation and spectral properties of NpO complexes with pyridine monocarboxylates in aqueous solution.

Spectrochim Acta A Mol Biomol Spectrosc 2017 Jun 6;181:13-22. Epub 2017 Mar 6.

Radioanalytical Chemistry Division, Bhabha Atomic Research Center, Trombay, Mumbai 400085, India.

Neptunyl ion as NpO is the least reacting and most mobile radioactive species among all the actinides. The picolinic acid used for decontamination is co-disposed along with the radioactive waste. Thus, in long term storage of HLW, there is high possibility of interaction of actinides and long lived fission products with the picolinate and can cause migration. The complexation of NpO with the three structural isomers of pyridine monocarboxylates provides an insight to explore the role of hetero atom (nitrogen) with respect to key binding moiety (carboxylate). In the present study, the log β values, speciation and spectral properties of NpO complexes with pyridine monocarboxylates viz. picolinate, nicotinate and isonicotinate, have been studied at 298K in 0.1M NaClO medium using spectrophotometry. The complexation reactions involving protonated ligands are always accompanied by protonation/deprotonation process; thus, the protonation constants of all the three pyridine monocarboxylates under same conditions were also determined by potentiometry. The spectrophotometric data analysis for complexation of NpO with pyridine monocarboxylates indicated the presence of ML and ML complexes with log β values of 2.96±0.04, 5.67±0.08 for picolinate, 1.34±0.09, 1.65±0.12 for nicotinate and 1.52±0.04, 2.39±0.06 for isonicotinate. The higher values of log β for picolinate were attributed to chelation while in other two isomers, the binding is through carboxylate group only. Density Functional Theory (DFT) calculations were carried out to get optimized geometries and electrostatic charges on various atoms of the complexes and free pyridine monocarboxylates to support the experimental data. The higher stability of NpO nicotinate and isonicotinate complexes compared to simple carboxylates and the difference in log β between the two is due to the charge polarization from unbound nitrogen to the bound carboxylate oxygen atoms.
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http://dx.doi.org/10.1016/j.saa.2017.03.013DOI Listing
June 2017