Arumugam Ramdass

Aggregation-Induced Emission Enhancement in Alkoxy-Bridged Binuclear Rhenium(I) Complexes: Application as Sensor for Explosives and Interaction with Microheterogeneous Media

The aggregation-induced emission enhancement (AIEE) characteristics of the two alkoxy-bridged binuclear Re(I) complexes [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, C10H21) bearing a long alkyl chain with 4-(1-naphthylvinyl)pyridine (1,4-NVP) ligand are illustrated. These complexes in CH2Cl2 (good solvent) are weakly luminescent, but their intensity increased enormously by almost 500 times by the addition of poor solvent (CH3CN) due to aggregation. By tracking this process via UV-vis absorption and emission spectral and TEM techniques, the enhanced emission is attributed to the formation of nanoaggregates. The nanoaggregate of complex 2 is used as a sensor for nitroaromatic compounds. Furthermore, the study of the photophysical properties of these binuclear Re(I) complexes in cationic, cetyltrimethylammonium bromide (CTAB), anionic, sodium dodecyl sulfate (SDS), and nonionic, p-tert-octylphenoxypolyoxyethanol (TritonX-100, TX-100), micelles as well as in CTAB-hexane-water and AOT-isooctane-water reverse micelles using steady-state and time-resolved spectroscopy and TEM analysis reveals that the nanoaggregates became small and compact size.

Photoswitchable alkoxy-bridged binuclear rhenium(I) complexes – a potential probe for biomolecules and optical cell imaging

We describe the solvothermal synthesis, structural characterization, photophysics and potential applications as probes of two alkoxy-bridged binuclear Re(I) complexes, [{Re(CO)3(1,4-NVP)}2(μ2-OR)2] (1, R = C4H9; 2, R = C10H21; 1,4-NVP = 4-(1-naphthylvinyl)pyridine). Irradiation of 1 and 2 at 365 nm leads to an interesting trans-cis photoisomerization process, which was examined by 1H NMR, UV-vis, emission and time-resolved techniques. Compounds 1 and 2 exhibit photoswitchable luminescence enhancement arising from photoinduced intramolecular energy transfer from the 3MLCT state of the Re(I) chromophore to the triplet excited state of the ligand 1,4-NVP. In addition, these Re(I) complexes serve as excellent probes for the ultrasensitive detection of biological molecules, including bovine serum albumin (BSA) and a platelet derived growth factor (PDGF) binding aptamer. Our results also suggest that, since these Re(I) complexes have low cytotoxicity and fluorescence properties under physiological conditions, they could be a useful probe for optical imaging of cancer cells by confocal laser scanning microscopy.

Alkoxy bridged binuclear rhenium (I) complexes as a potential sensor for β-amyloid aggregation

Alkoxy bridged binuclear rhenium(I) complexes are used as a probe for the selective and sensitive detection of aggregation of β-amyloid fibrils that are consorted with Alzheimers disease (AD). The strong binding of the complexes is affirmed by the fluorescence enhancement and calculated binding constant value in the order of 10(5)M(-1) is obtained from the Scatchard plots. The binding of β-amyloid can be attributed to π-π stacking interaction of naphthalene moiety present in rhenium(I) complexes, and it is supported by docking studies. The selectivity is quite high towards other proteins and the formation of fibrils can be observed in the range of 30-40 nm through the AFM and TEM techniques.

Synthesis and characterization of monometallic rhenium(I) complexes and their application as selective sensors for copper(II) ions

Novel imine functionalized monometallic rhenium(I) polypyridine complexes (1–4) comprising two phenol moieties attached to 2,2′-bipyridine ligands L1–L4 have been synthesized and characterized. These complexes exhibit selective and sensitive detection towards copper(II) ions and this is observed through changes in UV-visible absorption, luminescence and time-resolved spectroscopic techniques. An enormous enhancement is observed in emission intensity, quantum yield and luminescence lifetime with the addition of copper(II) ions, and this can be attributed to the restriction of CN isomerization in the Re(I) complexes. The strong binding between copper(II) ions and these complexes reveals that the binding constant values are in the range of 1.1 × 103–6.0 × 103 M−1. The absorption spectral behavior of the complexes is supported by DFT calculations.

Kinetic study of the oxovanadium(IV)–salen-catalyzed H2O2 oxidation of phenols

The oxovanadium(IV)–salen-catalyzed H2O2 oxidation of phenols gives o-catechol and hydroquinone as the reaction products. The reaction follows Michaelis–Menten-type kinetics, and the rate is accelerated by electron-donating substituents on both the substrate and the salen ligand. This peculiar substituent effect is accounted for in terms of bond formation between peroxo group of the oxidant and the benzene ring of the substrate in the transition state. A suitable mechanism for the reaction is proposed.

Aggregation-induced emission enhancement of anthracene-derived Schiff base compounds and their application as a sensor for bovine serum albumin and optical cell imaging

Three anthracene-based Schiff base complexes, R1-R3 (R1 = (E)-N´-((anthracen-10-yl)methylene)benzohydrazide; R2 = (E)-1-((anthracen-10-yl)methylene)-4-phenylsemicarbazide; and R3 = (E)-1-((anthracen-10-yl)methylene)-4-phenylthiosemicarbazide) were synthesized from 9-anthracenecarboxaldehyde, benzohydrazide, 4-phenylsemicarbazide and 4-phenylthiosemi-carbazide respectively, and characterized by various spectral techniques. The absorption spectral characteristics of R1-R3 were bathochromically tuned to the visible region by extending the π conjugation. These target compounds were weakly fluorescent in tetrahydrofuran (THF) solution because of rapid isomerization of the C=N double bond in the excited state. However, the aqueous dispersion of R1-R3 in the THF/water mixture by the gradual addition of water up to 90% resulted in an increase in the fluorescence intensity mainly due to aggregation-induced emission enhancement (AIEE) properties. The formation of nanoaggregates of R1-R3 were confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The compounds R1-R3 are ideal probes for the fluorescence sensing of bovine serum albumin (BSA) and breast cancer cells by optical cell imaging.

Utilization of Heavy Metal Complexes as Phosphorogenic Sensors for the Detection of Amino Acids

The use of phosphorogenic heavy-metal complexes has emerged as an attractive platform for luminescence sensing and cellular imaging studies as a result of several merits including precisely arranging the coordination structures and charge-transfer characteristics. This review intends to provide the design principles and the applications of amino acids sensing based on heavy-metal complexes such as Re(I)-, Ru(II)-, Ir(III)-, and Pt(II). These metal complexes function as phosphorogenic sensors with superior activities and selectivities towards amino acids by utilizing several mechanisms, including luminescent responses of “switch-on”. Furthermore, the practical utility of long lifetime and cell permeability of these metal complexes allows to detect luminescence imaging of amino acids in living cells without interference from endogenous fluorophores.