T. Daniel Thangadurai

Graphene Quantum Dot Solid Sheets: Strong blue-light-emitting & photocurrent-producing band-gap-opened nanostructures

Graphene has been studied intensively in opto-electronics, and its transport properties are well established. However, efforts to induce intrinsic optical properties are still in progress. Herein, we report the production of micron-sized sheets by interconnecting graphene quantum dots (GQDs), which are termed ‘GQD solid sheets’, with intrinsic absorption and emission properties. Since a GQD solid sheet is an interconnected QD system, it possesses the optical properties of GQDs. Metal atoms that interconnect the GQDs in the bottom-up hydrothermal growth process, induce the semiconducting behaviour in the GQD solid sheets. X-ray absorption measurements and quantum chemical calculations provide clear evidence for the metal-mediated growth process. The as-grown graphene quantum dot solids undergo a Forster Resonance Energy Transfer (FRET) interaction with GQDs to exhibit an unconventional 36% photoluminescence (PL) quantum yield in the blue region at 440u2009nm. A high-magnitude photocurrent was also induced in graphene quantum dot solid sheets by the energy transfer process.

Multispectroscopic and bioimaging approach for the interaction of rhodamine 6G capped gold nanoparticles with bovine serum albumin

Binding interaction of Bovine Serum Albumin (BSA) with newly prepared rhodamine 6G-capped gold nanoparticles (Rh6G-Au NPs) under physiological conditions (pHu202f7.2) was investigated by a wide range of photophysical techniques. Rh6G-Au NPs caused the static quenching of the intrinsic fluorescence of BSA that resulted from the formation of ground-state complex between BSA and Rh6G-Au NPs. The binding constant from fluorescence quenching method (Kau202f=u202f1.04u202f×u202f104u202fLu202fmol-1; LoDu202f=u202f14.0u202fμM) is in accordance with apparent association constant (Kappu202f=u202f1.14u202f×u202f101u202fM-1), which is obtained from absorption spectral studies. Förster resonance energy transfer (FRET) efficiency between the tryptophan (Trp) residue of BSA and fluorophore of Rh6G-Au NPs during the interaction was calculated to be 90%. The free energy change (ΔGu202f=u202f-23.07u202fkJ/mol) of BSA-Rh6G-Au NPs complex was calculated based on modified Stern-Volmer Plot. The time-resolved fluorescence analysis confirmed that quenching of BSA follows static mechanism through the formation of ground state complex. Furthermore, synchronous and three-dimensional fluorescence measurement, Raman spectral analysis and Circular Dichroism spectrum results corroborate the strong binding between Rh6G-Au NPs and BSA, which causes the conformational changes on BSA molecule. In addition, fluorescence imaging experiments of BSA in living human breast cancer (HeLa) cells was successfully demonstrated, which articulated the value of Rh6G-Au NPs practical applications in biological systems.

Fluorenone based fluorescent probe for selective “turn-on” detection of pyrophosphate and alanine

To sense biologically important entities with different size and dimensions, a fluorenone based fluorescent receptor was designed and synthesized. Probe 1 displayed a distinct fluorescence enhancement emission at 565nm for pyrophosphate and 530nm for alanine in polar solvent. The fluorescence titration experiments confirm 1:1 stoichiometric ratio with high-binding constant and very low limit of detection (LoD) values. Receptor 1 showed a highly selective and sensitive recognition to HP2O73- and to alanine over other competitive anions and amino acids. In addition, the fluorescence lifetime measurement and reversible binding study results support the practical importance of 1.

Novel Heterocyclic Schiff Base, (Z)-4-((2-((2-Aminophenyl)disulfanyl)phenylimino) (Phenyl)Methyl)-3-Methyl-1-Phenyl-1H-Pyrazol-5-ol Crystals for Enzymatic Studies

Graphical Abstract A new dithio Schiff base was synthesized and characterized by spectroscopic (FT-IR, UV-Vis, H1-NMR, and C13-NMR) and X-ray diffraction studies. Molecular interactions (inter and intra) between the neutral entities are discussed. Schiff base ligand, (Z)-4-((2-((2-aminophenyl)disulfanyl)phenylimino)(phenyl)methyl)-3-methyl-1-phenyl-1H-pyrazol-5-ol (1), was synthesized by the reaction between 2-phenyl-4-benzoyl-5-methyl-pyrazolin-3-one and 2-amino thio phenol (1:2 molar ratio). The structural elucidation was done by spectroscopic (FT-IR, UV-Vis, H1-NMR, C13-NMR) and X-ray diffraction studies. Single crystal X-ray diffraction studies revealed that 1 has monoclinic system with space group P21/c with a = 15.654 (4) Å, b = 12.848 (4) Å, c = 14.219 (4) Å; α = 90°, β = 113.65 (6)°, γ = 90°, and Z = 4. The possible intramolecular (C-H···N) and intermolecular (C-H···O, C-H···S, N-H···O) interactions of 1 were also been discussed.