Mercury emissions and partitioning from Indian coal-fired power plants.

In India coal combustion is the single largest source of emission of mercury which is a wide-spread persistent global toxicant, travelling across international borders through air and water. As a party to the Minamata convention, India aims to monitor and reduce Hg emissions and stricter norms are introduced for mercury emissions from power plants (30 µg/Nm3for flue gas in stack). This paper presents the results obtained during the experimental studies performed on mercury emissions at four coal-fired and one lignite-fired power plants in India. The mercury concentration in the feed coal varied between 0.12-0.27 mg/Kg. In the mercury mass balance, significant proportion of feed coal mercury has been found to be associated with fly ash, whereas bottom ash contained very low mercury. 80%-90% of mercury was released to air through stack gas. However, for circulating fluidised bed boiler burning lignite, about 64.8% of feed mercury was found to get captured in the fly ash and only 32.4% was released to air. The mercury emission factor was found to lie in the range of 4.7-15.7 mg/GJ.

Mercury in Indian Thermal Coals.

In India, coal utilization in power generation, constitutes as the single largest source of mercury emissions. This study presents mercury content in Indian sub-bituminous and bituminous coals that are primarily used as fuel in large-scale electricity generation facilities. A total of 165 number of coal samples have been collected from the major coal producing regions of the country. Along with the mercury content, other chemical parameters like moisture, ash, volatile matter, total Sulphur and gross calorific value were also analyzed. Mercury concentrations of these coals were found to be between 3 and 554 µg/kg, with an average of 175 µg/kg. Variation of the mercury content with the rank parameters like volatile matter, carbon content, ash and total Sulphur were also assessed. No significant correlations were observed with the rank parameters but a general trend of increasing mercury with ash content is discernible.

Fluorescent chemodosimeter for quantification of cystathionine-γ-synthase activity in plant extracts and imaging of endogenous biothiols.

A new reagent for quantification of CgS in plant extracts using a generalized methodology suitable for recognition of homocysteine (Hcy) with luminescence ON response.

A Switch-On NIR Probe for Specific Detection of Hg2+ Ion in Aqueous Medium and in Mitochondria.

A new 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based probe molecule (L) is synthesized for specific binding to Hg2+ ion in physiological condition with an associated luminescence ON response in the near-IR region of the spectrum. Appropriate functionalization in the 5-position of each of two pyrrole moieties with styryl functionality in a BODIPY core helped us in achieving the extended conjugation and a facile intramolecular charge transfer transition with a narrow energy gap for frontier orbitals. This accounted for a poor emission quantum yield for the probe molecule L. Binding to Hg2+ helped in interrupting the facile intramolecular charge transfer (ICT) process that was initially operational for L. This resulted in a hypsochromic shift of absorption band and a turn-on luminescence response with λMaxEms of 650 nm on specific binding to Hg2+. Observed spectral changes are rationalized based on quantum chemical calculations. Interestingly, this reagent is found to be localized preferentially in the mitochondria of the live human colon cancer (Hct116) cells. Mitochondria is one of the major targets for localization of Hg2+, which actually decreases the mitochondrial membrane potential and modifies various proteins having sulfudryl functionality(ies) to cause cell apoptosis. Considering these, ability of the present reagent to specifically recognize Hg2+ in the mitochondrial region of the live Hct116 cells has significance.

A fluorescent probe for bisulfite ions: its application to two-photon tissue imaging.

A benzoxazinone based fluorescent probe for the specific and efficient detection of bisulfite ions in aqueous medium is described. The probe formed a bisulfite/sulphite adduct with an associated turn-on fluorescence response in the red wavelength region. No interference was observed in the detection process from all possible competing anions and molecules, including cyanide ion, cysteine, homocysteine and glutathione. In addition, the probe showed a fast response time, low detection limit, and cell membrane permeability. Furthermore, the probe was two-photon excitable, enabling imaging of endogenous bisulfite ions in HeLa cells as well as in deep tissues from different organs of mouse.

Fluorescent probes for the detection of cyanide ions in aqueous medium: cellular uptake and assay for ß-glucosidase and hydroxynitrile lyase.

A chemodosimteric reagent (1) for the efficient detection of cyanide species (CN- and/or HCN) in aq. medium as well as under physiological conditions has been described. Selective reaction of the cyanide species with this reagent in the presence of all common interfering anions, amino acids and glutathione (GSH) led to the generation of the corresponding cyanohydrin derivative. The formation of the cyanohydrin derivative of the probe is associated with a visually detectable change in solution fluorescence in aq. buffer medium with 1.9 µM NaCN, the threshold limit set by WHO for the safe drinking water and this makes this fluorogenic sensor an ideal candidate for in-field applications. An apparent switch on the luminescence response, ultralow detection limit, low response time, cell membrane permeability and insignificant toxicity are key features of a probe molecule, which gives it a distinct edge over previously reported chemodosimetric reagents for the detection of cyanide species (CN- or HCN) in an aqueous environment. This methodology could be used for developing a generalized and efficient fluorescence-based assay for crucial enzymes like ß-glucosidase and hydroxynitrile lyase. Furthermore, spectrally-resolved fluorescence microscopy measurements on single-cells revealed that this sensor molecule could also be used for imaging the cellular uptake of cyanide species from aq. solution contaminated with NaCN. Our results confirmed that statistical analysis of integrated intensity and transition energy obtained from the emission spectra collected over various microscopic sub-cellular regions can potentially be used to discriminate the effects of local cellular environments and that due to cyanide detection.

Tuning of multiple luminescence outputs and white-light emission from a single gelator molecule through an ESIPT coupled AIEE process.

A unique example of an ESIPT coupled AIEE process, associated with a single molecule (1), is utilized for generating multiple luminescent colors (blue-green-white-yellow). The J-aggregated state of 1 forms a luminescent gel in THF and this luminescent property is retained even in the solid state.

A novel fluorescence probe for estimation of cysteine/histidine in human blood plasma and recognition of endogenous cysteine in live Hct116 cells.

A new Cu(II)-complex is used as a "Turn-On" luminescence probe for specific detection of endogenous Cys in live Hct116 cells and Cys present in human blood plasma without any interference from other amino acids, especially GSH and Hcy. Difference in the mechanistic pathway for Cys and His recognition is discussed.

Hydrogen bonding interaction between active methylene hydrogen atoms and an anion as a binding motif for anion recognition: experimental studies and theoretical rationalization.

Two new reagents, having similar spatial arrangements for hydrogen atoms of the active methylene functionalities, were synthesized and interactions of such reagents with different anionic analytes were studied using electronic spectroscopy as well as by using (1)H and (31)P NMR spectroscopic methods. Experimental studies revealed that these two reagents showed preference for binding to F(-) and OAc(-). Detailed theoretical studies along with the above-mentioned spectroscopic studies were carried out to understand the contribution of the positively charged phosphonium ion, along with methylene functionality, in achieving the observed preference of these two receptors for binding to F(-) and OAc(-). Observed differences in the binding affinities of these two reagents toward fluoride and acetate ions also reflected the role of acidity of such methylene hydrogen atoms in controlling the efficiencies of the hydrogen bonding in anion-Hmethylene interactions. Hydrogen bonding interactions at lower concentrations of these two anionic analytes and deprotonation equilibrium at higher concentration were observed with associated electronic spectral changes as well as visually detectable change in solution color, an observation that is generally common for other strong hydrogen bond donor functionalities like urea and thiourea. DFT calculations performed with the M06/6-31+G**//M05-2X/6-31G* level of theory showed that F(-) binds more strongly than OAc(-) with the reagent molecules. The deprotonation of methylene hydrogen atom of receptors with F(-) ion was observed computationally. The metal complex as reagent showed even stronger binding energies with these analytes, which corroborated the experimental results.

New chemodosimetric probe for the specific detection of Hg2+ in physiological condition and its utilisation for cell imaging studies.

A dithiane derivative of BODIPY is synthesized. This new reagent could be used for the specific and instantaneous detection of Hg(2+) in physiological condition. This dithiane reagent reacts specifically with Hg(2+) to regenerate the parent BODIPY-aldehyde with consequential change in visually detectable optical responses and this provides the possibility of using this reagent as a colorimetric probe or as a fluorescent biomarker/imaging reagent. Further, non-covalent interactions could be utilized for formation of an inclusion complex with biologically benign ß-cyclodextrin for enhancing its solubility in aqueous environment and this included adduct could be used as a fluorescent marker and imaging reagent for Hg(2+). Uptake of Hg(2+) ions in live HeLa cells, exposed to a solution having Hg(2+) ion concentration as low as 2 ppb, could also be detected by confocal laser microscopic studies.

Role of metal ion in specific recognition of pyrophosphate ion under physiological conditions and hydrolysis of the phosphoester linkage by alkaline phosphatase.

Complexes synthesized from Zn(II), Cu(II), and Cd(II), using a dipicolyl amine derivative (L), showed unique specificity toward pyrophosphate ion (PPi or P4O7(4-)) among all other common anionic analytes, including different biologically significant phosphate ion (PO4(3-), H2PO4(2-)) or phosphate-ion-based nucleotides, such as AMP, ADP, ATP, and CTP. However, the relative affinities of PPi toward these three metal complexes were found to vary and follow the order K(a)(L.Zn-PPi) > are given in units of (a)(L.Cu-PPi) ≥ K(a)(L.Cd-PPi). Luminescence responses of the receptor L were substantial on binding to Zn(2+) and Cd(2+), while relatively a much smaller luminescence response was observed in the presence of Cu(2+). Luminescence responses of L.M-PPi (M is Zn(2+), Cd(2+), and Cu(2+)) were further modified on binding to the PPi ion. This could be utilized for quantitative detection of PPi in physiological condition as well as for developing a real time "turn-on" (for L.Zn and L.Cu) and "turn-off" (for L.Cd) fluorescence assay for evaluating the enzymatic activity of alkaline phosphatase (ALP). Experimental results revealed how the subtle differences in the binding affinities between PPi and M in L.M (M is Zn(2+), Cd(2+), and Cu(2+)), could influence the cleavage of the phosphoester linkage in PPi by ALP. The DFT calculations further revealed that the hydrolytic cleavage of the metal ion coordinated phosphoester bond is kinetically faster than that for free PPi and thus, rationalized the observed difference in the cleavage of the phosphoester bond by an important mammalian enzyme such as ALP in the presence of different metal complexes.