pH-sensitive response of a highly photoluminescent MoS2 nanohybrid material and its application in the nonenzymatic detection of H2O2

Analytical and Bioanalytical Chemistry - The mechanism behind the variation in the photoluminescence (PL) of a MoS2 nanohybrid material with pH was investigated. Highly fluorescent MoS2 quantum...     

Understanding the Photoluminescence Mechanism of Nitrogen‐Doped Carbon Dots by Selective Interaction with Copper Ions

Doped fluorescent carbon dots (CDs) have drawn widespread attention because of their diverse applications and attractive properties. The present report focusses on the origin of photoluminescence in nitrogen‐doped CDs (NCDs), which is unraveled by the interaction with Cu²⁺ ions. Detailed spectroscopic and microscopic studies reveal that the broad steady‐state photoluminescence emission of the NCDs originates from the direct recombination of excitons (high energy) and the involvement of defect states (low energy). In addition, highly selective detection of Cu²⁺ is achieved, with a detection limit of 10 μm and a dynamic range of 10 μm –0.4 mm . The feasibility of the present sensor for the detection of Cu²⁺ in real water samples is also presented.     

Reactions of Organic Ions at Ambient Surfaces in a Solvent-Free Environment

Solvent-free ion/surface chemistry is studied at atmospheric pressure, specifically pyrylium cations, are reacted at ambient surfaces with organic amines to generate pyridinium ions. The dry reagent ions were generated by electrospraying a solution of the organic salt and passing the resulting electrosprayed droplets pneumatically through a heated metal drying tube. The dry ions were then passed through an electric field in air to separate the cations from anions and direct the cations onto a gold substrate coated with an amine. This nontraditional way of manipulating polyatomic ions has provided new chemical insights, for example, the surface reaction involving dry isolated 2,4,6-triphenylpyrylium cations and condensed solid-phase ethanolamine was found to produce the expected N-substituted pyridinium product ion via a pseudobase intermediate in a regiospecific fashion. In solution however, ethanolamine was observed to react through its N-centered and O-centered nucleophilic groups to generate two isomeric products via 2H-pyran intermediates. The O-centered nucleophile reacted less rapidly to give the minor product. The surface reaction product was characterized in situ by surface enhanced Raman spectroscopy, and ex situ using mass spectrometry and H/D exchange, and found to be chemically the same as the major pyridinium solution-phase reaction product.     

Unusual coordination mode of tetradentate Schiff base cobalt(III) complexes

Contrary to the stereotype, Jacobsen's catalyst, chiral (salcy)Co(III)OAc adopts an unusual binding mode. The tetradentate {ONNO} ligand does not form a square plane but wraps cobalt in a cis-β fashion while acetate is chelating.     

Nanoparticles-chemistry, new synthetic approaches, gas phase clustering and novel applications

In this paper, an overview of the synthesis, chemistry and applications of nanosystems carried out in our laboratory is presented. The discussion is divided into four sections, namely (a) chemistry of nanoparticles, (b) development of new synthetic approaches, (c) gas phase clusters and (d) device structures and applications. In ‘chemistry of nanoparticles’ we describe a novel reaction between nanoparticles of Ag and Au with halocarbons. The reactions lead to the formation of various carbonaceous materials and metal halides. In ‘development of new synthetic approaches’ our one-pot methodologies for the synthesis of core-shell nanosystems of Au, Ag and Cu protected with TiO₂ and ZrO₂ as well as various polymers are discussed. Some results on the interaction of nanoparticles with biomolecules are also detailed in this section. The third section covers the formation of gas phase aggregates/clusters of thiol-protected sub-nanoparticles. Laser desorption of H₂MoO₄, H2WO₄, MoS₂, and WS₂ giving novel clusters is discussed. The fourth section deals with the development of simple devices and technologies using nanomaterials described above.     

Selective and Wash‐Resistant Fluorescent Dihydrocodeinone Derivatives Allow Single‐Molecule Imaging of μ‐Opioid Receptor Dimerization

μ‐Opioid receptors (μ‐ORs) play a critical role in the modulation of pain and mediate the effects of the most powerful analgesic drugs. Despite extensive efforts, it remains insufficiently understood how μ‐ORs produce specific effects in living cells. We developed new fluorescent ligands based on the μ‐OR antagonist E‐p‐nitrocinnamoylamino‐dihydrocodeinone (CACO), that display high affinity, long residence time and pronounced selectivity. Using these ligands, we achieved single‐molecule imaging of μ‐ORs on the surface of living cells at physiological expression levels. Our results reveal a high heterogeneity in the diffusion of μ‐ORs, with a relevant immobile fraction. Using a pair of fluorescent ligands of different color, we provide evidence that μ‐ORs interact with each other to form short‐lived homodimers on the plasma membrane. This approach provides a new strategy to investigate μ‐OR pharmacology at single‐molecule level.     

Dual-wavelength laser induced breakdown spectroscopic technique for emission enhancement in vacuum

A novel approach of dual-wavelength LIBS with a single Nd³⁺:YAG laser is proposed and demonstrated for lunar-simulant analysis in high vacuum conditions. Laser ablation was performed at 355 nm/532 nm wavelength, and subsequently, the plasma was reexcited with the fundamental (1064 nm) wavelength. The interpulse delay was adjusted by varying the optical path length. A significant line intensity enhancement up to a factor of 3 was observed for many of the dominant emission lines of the lunar simulant sample. A theoretical model for understanding the mechanism behind the intensity improvements of dual-wavelength configurations is also discussed. Experimentally observed plasma temperature was comparable with theoretically estimated plasma temperature of silicon, which is the major constituent of lunar simulant.     

Quantum Dots (QDs) Based Fluorescent Sensor for the Selective Determination of Nimesulide

Fluorescent PET (Photoinduced Electron Transfer) has been of particular growth in recent times. A novel PET based fluorescent sensor using unmodified CdSe quantum dots (QDs) has been developed for the trace determination of Nimesulide (NIM). The sensor is based on the selective fluorescence quenching of quantum dots by NIM in presence of other NSAIDs and is found that intensity of quenching is linearly related to NIM concentration in the range 8.2?×?10^?7 – 4.01?×?10^?5?M. The mechanism of interaction is discussed. Finally, the potential application of the proposed method for the trace determination of NIM in pharmaceutical formulation is demonstrated.     

Local dynamic mechanical analysis

While new materials with tailored properties appear every day, the need of appropriate characterization tools is still an important concern. Analyses of thin films on thick substrate are often highly influenced by the substrate properties. A dynamical nanoindentation system has been designed and built through the integration of a nanoindenter head equipped with capacitive displacement sensing, scanning probe microscope with related XYZ scanning electronics and an additional transducer for sample actuation. Our Local-Dynamic Mechanical Analysis (L-DMA) setup allows for both, tip and sample modulation mode what somehow contrasts with commercially available systems. This issue allows for direct comparison between both techniques and therefore for consistent quantitative mechanical measurements. The system offers two distinctive measurement techniques, local mechanical spectroscopy and mechanical imaging modes. Bulk materials as well as thin films of ceramics and polymers have been used for testing and validating the setup. The instrument has been modeled in sample modulation mode and experimental results obtained for different materials were compared with simulation data.