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.

Development of luminescent sensors based on transition metal complexes for the detection of nitroexplosives.

The detection of chemical explosives is a major area of research interest and is essential for the military as well as homeland security to counter the catastrophic effects of global terrorism. In recent years, tremendous effort has been devoted to the development of luminescent materials for the detection of explosives in the vapor, solution, and solid states with a high degree of selectivity and sensitivity and a rapid response time. Apart from the wide range of organic fluorescent chemosensors, transition metal complexes play a prominent role in the sensing of nitroaromatic explosives owing to their rich photophysical characteristics. This review briefly summarizes the salient features of the design and preparation of transition metal (Zn(ii), Ir(iii), Pd(ii), Pt(ii), Re(i) and Ru(ii)) complexes/metallacycles/metallosupramolecules with emphasis on their photophysical properties, sensing behavior, mechanism of action, and the driving forces for detecting explosives and future prospects and challenges. Most of the probes that have been reported to date act as "turn-off" luminescent sensors because their emission (intensity, lifetime, and quantum yield) is eventually quenched upon sensing with nitroaromatic compounds (NACs) through photo-induced electron or energy transfer. These unique properties of transition metal complexes in response to explosives open up new vistas for the development of real world applications such as on-site detection, in-field security, forensic research, etc.

Electron Transfer Studies of Ruthenium(II) Complexes with Biologically Important Phenolic Acids and Tyrosine.

The ruthenium(II) complexes having 2,2'-bipyridine and phenanthroline derivatives are synthesized and characterized. The photophysical properties of these complexes at pH 12.5 are studied. The electron transfer reaction of biologically important phenolic acids and tyrosine are studied using absorption, emission and transient absorption spectral techniques. Semiclassical theory is applied to calculate the rate of electron transfer between ruthenium(II) complexes and biologically important phenolic acids.

A Spectroscopy Approach for the Study of the Interaction of Oxovanadium(IV)-Salen Complexes with Proteins.

Oxovanadium(IV)-salen complexes bind with bovine serum albumin (BSA) and ovalbumin (OVA) strongly with binding constant in the range 10(4)-10(7) M(-1) at physiological pH (7.4) confirmed using UV-visible absorption, fluorescence spectral and circular dichroism (CD) study. CD results show that the binding of oxovanadium(IV) complexes induces the conformational change with the loss of α-helicity in the proteins. Docking studies indicate that mode of binding of oxovanadium(IV)-salen complexes with proteins is hydrophobic in nature.

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

Alkoxy bridged binuclear rhenium(I) complexes are used as a probe for the selective and sensitive detection of aggregation of ß-amyloid fibrils that are consorted with Alzheimer's 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 ß-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.

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.

Ruthenium nanocatalysis on redox reactions.

Nanoparticles have generated intense interest over the past 20 years due to their high potential applications in different areas such as catalysis, sensors, nanoscale electronics, fuel and solar cells and optoelectronics. As the large fractions of metal atoms are exposed to the surface, the use of metal nanoparticles as nanocatalysts allows mild reaction conditions and high catalytic efficiency in a large number of chemical transformations. They have emerged as sustainable heterogeneous catalysts and catalyst supports alternative to conventional materials. This review focuses on the synthesis, characterization and catalytic role of ruthenium nanoparticles (RuNPs) on the redox reactions of heteroatom containing organic compounds with the green reagent H2O2, a field that has attracted immense interest among the chemical, materials and industrial communities. We intend to present a broad overview of Ru nanocatalysts for redox reactions with an emphasis on their performance, stability and reusability. The growth in the chemistry of organic sulfoxides and N-oxides during last decade was due to their importance as synthetic intermediates for the production of a wide range of chemically and biologically active molecules. Thus design of efficient methods for the synthesis of sulfoxides and N-oxides becomes important. This review concentrates on the catalysis of RuNPs on the H2O2 oxidation of organic sulfides to sulfoxides and amines to N-oxides. The deoxygenation reactions of sulfoxides to sulfides and reduction of nitro compounds to amines are fundamental reactions in both chemistry and biology. Here, we also highlight the catalysis of metal nanoparticles on the deoxygenation of sulfoxides and sulfones and reduction of nitro compounds with particular emphasis on the mechanistic aspects.