Seenivasan Rajagopal

Highly dispersed silica-supported nanocopper as an efficient heterogeneous catalyst : application in the synthesis of 1,2,3-triazoles and thioethers

In this paper, we report the synthesis of amine modified SiNPs (silica nanoparticles) by a sol–gel method and the role of synthesized SiO2 as a solid support for the nanocatalyst CuNPs (copper nanoparticles). The nanocatalyst is characterized by XRD, HRTEM, BET, AFM, SEM, EDX, UV-vis, FT-IR and TGA techniques. The Cu/SiO2 (catalyst A) serves as an efficient heterogeneous nanocatalyst exhibiting high catalytic activity for the synthesis of a series of 1,4-disubstituted-1,2,3-triazoles and thioethers. The catalyst A can be recycled and reused several times without any significant loss of catalytic activity as proved by XRD and HRTEM techniques.

Mechanism of oxidation of organic sulphides by oxo(salen)manganese(v) complexes

Abstract The kinetics of oxygen atom transfer from several cationic oxo(salen)manganese(V) [salen = N,N′-ethylenebis(salicylidineaminato)] complexes to organic sulphides have been studied spectrophotometrically in acetonitrile at 25 °C. The reaction follows an overall second-order kinetics, first-order each in sulphide and oxomanganese(V) complex. Electronic-substrate and electronicoxidant effect studies reveal that the single electron transfer from sulphide to the oxo complex is the rate-controlling step. The redox potentials of the couple MnV/MnIV have been estimated by applying Marcus theory to the experimentally observed rate constants.

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.

Excited state electron transfer reactions of tris(4,4′-dialkyl-2,2′-bipyridine)ruthenium(II) complexes with phenolate ions: structural and solvent effects

Abstract The reductive quenching of three *RuL 3 2+ complexes (L≡4,4′-dialkyl-2,2′-bipyridine) by several substituted phenolate ions was investigated by the luminescence quenching technique. The decrease in the quenching constant k q with an increase in the size of the ligand is explained in terms of a change in Δ G and the electron transfer distance. The ϱ values obtained for the reactions of the three RuL 3 2+ complexes with phenolate ions are in accordance with the reactivity-selectivity principle. The influence of the solvent on the photoredox reaction of Ru(bpy) 3 2+ (bpy, 2,2′-bipyridine) reveals that, in addition to the bulk properties, the change in solvent reorganization energy (λ o ) and solvent longitudinal relaxation time (τ L ) influence the values of the quenching rate constants.

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.

Steric effects in the photoinduced electron transfer reactions of ruthenium(II)-polypyridine complexes with 2,6-disubstituted phenolate ions

The rate constants (kq) for the photoinduced electron transfer reactions of Ru(II)-polypyridyl complexes (Ru(NN)32+) with 2,6-disubstituted phenolate ions in aqueous acetonitrile are highly sensitive to change in the bulkiness of the ligand in Ru(NN)32+ as well as the phenolate ion. The decrease in kq value with the increase in the size of the ligand in Ru(NN)32+ and the phenolate ion is ascribed to the decrease in the electronic coupling matrix element, ∣HDA ∣, between the donor and acceptor with the increase in the electron transfer distance. The hydrophobic interaction or possible π–π stacking between the pyridine rings of Ru(NN)32+ and the aryl moiety of ArO− leads to less steric effect.

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.

Oxidation of organic sulfides with clay-supported iodosylbenzene as oxygen donor

Abstract Alkyl, aryl and diaryl sulfides afford excellent yields of sulfoxides with PhIO supported on natural (montmorillonite, KSF and bentonite clay) as well as cation-exchanged clays of K10-montmorillonite in acetonitrile suspension and also in solid state. A ligand coupling mechanism for this facile oxidation is proposed.

Electron transfer reactions of iron (III) - polypyridyl complexes with organic sulphides

Abstract The redox reactions of FeL 3 3+ (where L = 2,2 ′ -bipyridine, 4,4 ′ -dimethyl-2,2 ′ -bipyridine and 1,10-phenanthroline) with alkyl aryl sulphides in aqueous methanol have been studied by the spectrophotometric technique. The comparison of the experimental rate constant data with the values estimated from Marcus cross-reaction relationship led to the conclusion that the single electron transfer from sulphide to FeL 3 3+ is the rate controlling step. The kinetic data yield 1.0 × 10 7 M −1 s −1 for the ArSR/ArS + . R self-exchange rate constant at 25°C. The reactions of iron(III)-polypyridyl complexes with alkyl aryl sulphides in aqueous methanol proceed through electron transfer mechanism and form sulphoxides as products.

p-Sulfonatocalix[4]arene as a carrier for curcumin

The encapsulation of curcumin using p-sulfonatocalix[4]arene (p-SC4) is an attempt to increase the bioavailability of curcumin by increasing water solubility. The degradation of curcumin due to the basicity of p-SC4 is circumvented by maintaining the pH at 3 using 2% hydrochloric acid. The interaction is studied using UV-visible absorption, emission, transient absorption and excited state lifetime methods. The encapsulation of curcumin with p-SC4 increases the excited lifetime of curcumin, as well as the lifetime of the transients (triplet state of curcumin and phenoxyl radical of curcumin) produced upon irradiation. The mode of interaction is studied using 1H NMR and ROESY spectral techniques. The stability of curcumin in the presence of p-SC4 and the 2:1 ratio of p-SC4 binding with curcumin is established using HR-MS and MALDI-TOF analysis. The amount of enhancement in solubility is studied using the HTLC technique.