Sabyasachi Sarkar

Archimedean Synthesis and Magic Numbers: “Sizing” Giant Molybdenum-Oxide-Based Molecular Spheres of the Keplerate Type

Pythagorean harmony can be found in the spherical polyoxometalate clusters described here (see illustration for an example of a structure), since there are interesting relationships between the so-called magic numbers (12, 32, 42, 72, 132) relevant for spherical viruses and the number of the building blocks in the cluster. The size of these Keplerate clusters can be tailored by varying the type of connections between the pentagons by means of different spacers.

Carbon Nano‐onions for Imaging the Life Cycle of Drosophila Melanogaster

Real-time X-ray or magnetic resonance imaging are known methods used for biomedical diagnosis. By the oral administration of barium meal, X-ray imaging can be extended for use in soft tissue imaging. The oral ingestion of a fluorescent probe is a new approach to imaging a living species. Here, water-soluble carbon nano-onions are introduced as a nontoxic, fluorescent reagent enabling Drosophila melanogaster (fruit flies) to be imaged alive. It is demonstrated that these water-soluble carbon nano-onions, synthesized from wood waste, colorfully image all the development phases of Drosophila melanogaster from its egg to adulthood. Oral ingestion of up to 4 ppm of soluble carbon nano-onions allows the optical fluorescence microscopy imaging of all the stages of the fruit fly life cycle without showing any toxic effects. The fluorescent Drosophila melanogaster excretes this fluorescing material upon the withdrawal of carbon nano-onions from its food.

A reaction based colorimetric as well as fluorescence ‘turn on’ probe for the rapid detection of hydrazine

A fluorescein based reactive probe has been designed and synthesized to detect hydrazine selectively over other common analytes. We used here 4-bromobutyrate as a masking unit of fluorescein dye. Hydrazine plays here the role of a de-masking agent to set free the fluorescein dye through a simultaneous substitution–cyclisation–elimination process. This leads to ‘turn on’ fluorescence with easily discernible color change with a fast response time (<15 minutes).

Linking Icosahedral, Strong Molecular Magnets {Mo} to Layers—A Solid‐State Reaction at Room Temperature

The by no means trivial, solid-state reaction for the condensation of {(Mo)Mo 5 } 12 Fe 30 giant spheres commences through the water ligands and leads to oxo (or hydroxo) bridging. As the discrete icosahedral units approach each other, their oxygen atom bridges ultimately form covalent bonds (Fe-Fe 3.79 A , see picture) to result in a symmetric layered structure.

A nickel(II)-sulfur-based radical-ligand complex as a functional model of hydrogenase.

A nickel(II) dithiolene complex [Ni II (L 2− )(L − .)][PPh 4 ] (1; see figure; L=1,2-dicarbomethoxyethylene dithiolate) electrocatalyzes hydrogen evolution at the lowest achievable reduction potential (−0.69 V) in CH3CN and also in aqueous medium (−0.71 V) to date. Compound 1 shows strikingly similar EPR and reduction potential values to those observed with native Ni-containing hydrogenases.

Pollutant soot of diesel engine exhaust transformed to carbon dots for multicoloured imaging of E. coli and sensing cholesterol

A convenient method for the synthesis of water soluble, fluorescent carbon dots from environmental pollutant diesel soot is described. The soot, generated from the exhaust of diesel engines as black, diesel particulate matter (DPM), is an environmental pollutant. This pollutant has been utilized as the precursor carbon source to create water soluble versions of carbon dots by chemical oxidation. The small sized water soluble carbon dots once separated display multicoloured emissions covering the green to red and extended to the near-infrared region. These have been used in imaging Escherichia coli and further used in sensing cholesterol.

Synthesis and characterization of water-soluble carbon nanotubes from mustard soot

Carbon nanotubes (CNT) has been synthesized by pyrolysing mustard oil using an oil lamp. It was made water-soluble (wsCNT) through oxidative treatment by dilute nitric acid and was characterized by SEM, AFM, XRD, Raman and FTIR spectroscopy. The synthesized wsCNT showed the presence of several junctions and defects in it. The presence of curved graphene structure (sp2) with frequent sp3 hybridized carbon is found to be responsible for the observed defects. These defects along with the presence of di- and tri-podal junctions showed interesting magnetic properties of carbon radicals formed by spin frustration. This trapped carbon radical showed ESR signal in aqueous solution and was very stable even under drastic treatment by strong oxidizing or reducing agents. Oxidative acid treatment of CNT introduced several carboxylic acid group functionalities in wsCNT along with the nicking of the CNT at different lengths with varied molecular weight. To evaluate molecular weights of these wsCNTs, an innovative method like gel electrophoresis using high molecular weight DNA as marker was introduced.

Water‐Induced Formation, Characterization, and Photoluminescence of Carbon Nanotube‐Based Composites of Gadolinium(III) and Platinum(II) Dithiolenes

Understanding the nature of interactions of targeted drug-delivery vehicles, such as functionalized carbon nanotubes (f-CNTs) and their composites, with a cell or its organelles or DNA, where water is a major constituent, requires molecular-level understanding of f-CNTs with analogous chemical systems. The nature of interaction has not yet been explored within the scope of formation of giant aggregates by self-assembly processes. Crystals of platinum(II) dithiolene [Pt(mnt)2 ][PPh4 ]2 (1) and gadolinium(III) dithiolene [Gd(mnt)3 ][PPh4 ]3 (2) (mnt=maleonitrile dithiolate) form nanospheres (diameter 88 nm) and nanoflowers (400-600 nm) in acetonitrile/water and DMF/water solvent mixtures, respectively. The formation of nanospheres or nanoflowers is proposed to be a water-induced phenomenon. These nanospheres and nanoflowers interact with f-CNTs by forming either spherical supramolecular assemblies (3, diameter up to 45. 5 μm) in the case of platinum(II) dithiolene or composite flowers (4) with CNT buckling for gadolinium(III) dithiolene. Both nanostructures, (3) and (4), show emission upon excitation at a range of wavelengths (λex =385-560 nm). The fluorescence emissions of the composite materials 3 and 4 are proposed to be due to separation of energy states of the nanospheres of 1 or the nanoflowers of 2 by the energy states of the f-CNTs, leading to the possibility of new electronic transitions.

A Triphenyl Amine‐Based Solvatofluorochromic Dye for the Selective and Ratiometric Sensing of OCl− in Human Blood Cells

A new visible-light-excitable fluorescence ratiometric probe for OCl(-) has been developed based on a triphenylamine-diamiomaleonitrile (TAM) moiety. The structure of the dye was confirmed by single-crystal X-ray analysis. It behaves as a highly selective and sensitive probe for OCl(-) over other analytes with a fast response time (∼100 s). OCl(-) reacts with the probe leading to the formation of the corresponding aldehyde in a mixed-aqueous system. The detection limit of the probe is in the 10(-8) M range. The probe (TAM) also exhibits solvatofluorochromism. Changing the solvent from non-polar to polar, the emission band of TAM largely red-shifted. Moreover, the probe shows an excellent performance in real-life application in detecting OCl(-) in human blood cells. The experimentally observed changes in the structure and electronic properties of the probe after reaction with OCl(-) were studied by DFT and TDDFT computational calculations.

ESIPT based Hg2+ and fluoride chemosensor for sensitive and selective ‘turn on’ red signal and cell imaging

An excited state intramolecular proton transfer (ESIPT) enabled fluorescent sensor phenanthroline diimino phenol (PDP) for Hg2+ has been designed and synthesized. PDP acts as a dual sensor and selectively detects only Hg2+ in mixed aqueous medium and fluoride in acetonitrile medium over other competing metal ions and anions. The binding of PDP with Hg2+ is supported by DFT. The ESIPT phenomenon in PDP is favored in the presence of Hg2+, which is rarely reported, along with an intense red fluorescence suppressing other competing metal ions. Among different anionic analytes, only fluoride shows a visually detectable exciting color change from pale yellow to pink with almost similar emission characteristics. PDP also demonstrates its importance in the fluorescent imaging of Hg2+ ions in human cancer cells.