Eththilu Babu

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.

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.

Binding and Fluorescence Resonance Energy Transfer (FRET) of Ruthenium(II)-Bipyridine-Calixarene System with Proteins—Experimental and Docking Studies

The investigation of the interaction of ruthenium(II)-bipyridine-tert-butylcalix[4]arene complexes (Rubc2 and Rubc3) with proteins (BSA and ovalbumin) using absorption, emission, excited state lifetime and circular dichroism techniques and by docking studies show that luminophore-receptor system bind strongly with proteins. An enhancement of absorption as well as emission intensity of Ru(II)-calixarene complexes in the presence of proteins, but the quenching of the emission intensity of proteins in the presence of Ru(II)-calixarene complexes are the interesting observations. The enhancement of emission intensity of Ru(II)-calixarene complex, in the presence of proteins, is due to the fluorescence resonance energy transfer (FRET) from protein to Ru(II)-calixarene complex. Among the two Ru(II)-calixarene complexes synthesized Rubc3 has more efficient binding and energy transfer than Rubc2 and BSA, with a large cavity size, has the advantage for binding over ovalbumin. Docking studies reveal that the presence of tert-butylcalix[4]arene moiety in Ru(II)-calixarene complexes facilitates binding with proteins. After the binding of Rubc2 and Rubc3 with proteins, the nearby fluorophores present in proteins are in optimal distance from the ruthenium centre for efficient FRET process to occur.

A selective, long-lived deep-red emissive ruthenium(II) polypyridine complexes for the detection of BSA

A selective, label free luminescence sensor for bovine serum albumin (BSA) is investigated using ruthenium(II) complexes over the other proteins. Interaction between BSA and ruthenium(II) complexes has been studied using absorption, emission, excited state lifetime and circular dichroism (CD) spectral techniques. The luminescence intensity of ruthenium(II) complexes (I and II), has enhanced at 602 and 613 nm with a large hypsochromic shift of 18 and 5 nm respectively upon addition of BSA. The mode of binding of ruthenium(II) complexes with BSA has analyzed using computational docking studies.

Optical Recognition of Anions by Ruthenium(II)-Bipyridine-Calix[4]Arene System

The two t-butylcalix[4]arene attached ruthenium(II)-bipyridine complexes (Rubc2 and Rubc3) has been synthesized and the anion recognition studies have been carried out using emission techniques. The binding of anions, which are sensed by the complexes, are studied by UV-visible and emission techniques. The complex Rubc2 recognizes the Cl−, H2PO4− and AcO− anions. The complex Rubc3 recognizes the Br− and AcO− anions. The AcO− quenches the emission intensity of both two complexes but the other anion increases the emission intensity of the complexes. The excited state lifetime and transient absorption studies were carried out the AcO− facilitates non radiative pathway. The other anions stabilize the excited state and facilitate the radiative pathway.

Sensitized Near-Infrared Luminescence From NdIII, YbIII and ErIII Complexes by Energy-Transfer From Ruthenium 1,3-Bis([1,10]Phenanthroline-[5,6-d]-Imidazol-2 -yl)Benzene

The luminescent ruthenium 1,3 -bis([1,10]phenanthroline-[5,6 -d]- imidazol-2 -yl)benzene (bpibH2) complex, a potentially useful bridging ligand with a vacant diimine site, has been used as ‘metallo ligand’ to make heterodinuclear d–f complexes by attachment of a {Ln(dik)3} fragment (dik = 1,3-diketonate) at the vacant site. When Ln = Nd, Yb, or Er the lanthanide centre has low-energy f–f excited states capable of accepting energy from the 3MLCT excited state of the Ru(II) centre, there is quenching in the 3MLCT luminescence of the Ru(II) centre, that affords sensitized lanthanide(III) based luminescence in the near-IR region. Nd(III) was found to be the most effective at quenching the 3MLCT luminescence of the ruthenium component because of the high density of f–f excited states of the appropriate energy which make it as effective energy-acceptor compared to Er and Yb complexes.