Effect of metal oxidation state on FRET: a Cu(I) silent but selectively Cu(II) responsive fluorescent reporter and its bioimaging applications

Copper(II) and copper(I) complexes of a newly designed and crystallographically characterized Schiff base (HL) derived from rhodamine hydrazide and cinnamaldehyde were isolated in pure form formulated as Cu(L)(NO3)] (L-Cu) (1) and Cu(HL)(CH3CN)(H2O)]ClO4 (HL-Cu) (2), and characterized by physicochemical and spectroscopic tools. Interestingly, complex 1 but not 2 offers red fluorescence in solution state, and eventually HL behaves as a Cu(II) ions selective FRET based fluorosensor in HEPES buffer (1 mM, acetonitrile-water: 1/5, v/v) at 25 degrees C at biological pH with almost no interference of other competitive ions. The dependency of the FRET process on the +2 oxidation state of copper has been nicely supported by exhaustive experimental studies comprising electronic, fluorimetric, NMR titration, and theoretical calculations. The sensing ability of HL has been evaluated by the LOD value towards Cu(II) ions (83.7 nM) and short responsive time (5-10 s). Even the discrimination of copper(I) and copper(II) has also been done using only UV-Vis spectroscopic study. The efficacy of this bio-friendly probe has been determined by employing HL to detect the intercellular distribution of Cu(II) ions in HeLa cells by developing image under fluorescence microscope.

2-(Phenylazo)pyridineplatinum(II) Catecholates Showing Photocytotoxicity, Nuclear Uptake, and Glutathione-Triggered Ligand Release

Platinum(II) complexes Pt(pap)(an-cat)] (1) and Pt(pap)(py-cat)] (2) with 2-(phenylazo)pyridine (pap), 4-2-(anthracen-9-ylmethylene)amino]ethyl]benzene-1,2-diol (H(2)an-cat), and 4-2-(pyren-1-ylmethylene)amino]ethyl]benzene-1,2-diol (H2py-cat) were prepared, and their photoinduced cytotoxicity was studied. The complexes were found to release catecholate ligand in the presence of excess glutathione (GSH), resulting in cellular toxicity in the cancer cells. The catecholate complex Pt(pap)(cat)] (3) was prepared and used as a control. Complex 3, which is structurally characterized by X-ray crystallography, has platinum(II) in a distorted square-planar geometry. The complexes are redox-active, showing responses near 0.6 and 1.0 V versus SCE in N,N-dimethylformamide/0.1 M tetrabutylammonium perchlorate corresponding to a two-step catechol oxidation process and at -0.3 and -1.3 V for reduction of the pap ligand. Complex 1 showed remarkable light-induced cytotoxicity in HaCaT (human skin keratinocytes) and MCF-7 (human breast cancer) cells, giving IC50 value of similar to 5 mu M in visible light of 400-700 nm and >40 mu M in the dark. The 2',7'-dichlorofluorescein diacetate (DCFDA) assay showed the generation of reactive oxygen species (ROS), which seems to trigger apoptosis, as is evident from the annexin V-fluorescein isothiocyanate (FITC)/propidium iodide (PI) assay. The fluorescence microscopic images showed significant nuclear localization of the complexes and free ligands. A mechanistic study revealed possible reduction of the coordinated azo bond of pap by cellular GSH, releasing the catecholate ligand and resulting in remarkable photochemotherapeutic action of the complexes.

Synthesis, crystal structure and spectroscopic and electrochemical properties of bridged trisbenzoato copper-zinc heterobinuclear complex of 2,2 `-bipyridine

The synthesis of the heterobinuclear copper-zinc complex CuZn(bz)(3)(bpy)(2)]ClO4 (bz = benzoate) from benzoic acid and bipyridine is described. Single crystal X-ray diffraction studies of the heterobinuclear complex reveals the geometry of the benzoato bridged Cu(II)-Zn(II) centre. The copper or zinc atom is pentacoordinate, with two oxygen atoms from bridging benzoato groups and two nitrogen atoms from one bipyridine forming an approximate plane and a bridging oxygen atom from a monodentate benzoate group. The Cu-Zn distance is 3.345 angstrom. The complex is normal paramagnetic having mu(eff) value equal to 1.75 BM, ruling out the possibility of Cu-Cu interaction in the structural unit. The ESR spectrum of the complex in CH3CN at RT exhibit an isotropic four line spectrum centred at g = 2.142 and hyperfine coupling constants A(av) = 63 x 10(-4) cm(-1), characteristic of a mononuclear square-pyramidal copper(II) complexes. At LNT, the complex shows an isotropic spectrum with g(parallel to) = 2.254 and g(perpendicular to) =2.071 and A(parallel to) = 160 x 10(-4) cm(-1). The Hamiltonian parameters are characteristic of distorted square pyramidal geometry. Cyclic voltammetric studies of the complex have indicated quasi-reversible behaviour in acetonitrile solution. (C) 2014 Elsevier B.V. All rights reserved.

The beta hairpin structure within ribosomal protein S5 mediates interplay between domains II and IV and regulates HCV IRES function

Translation initiation in Hepatitis C Virus (HCV) is mediated by Internal Ribosome Entry Site (IRES), which is independent of cap-structure and uses a limited number of canonical initiation factors. During translation initiation IRES-40S complex formation depends on high affinity interaction of IRES with ribosomal proteins. Earlier, it has been shown that ribosomal protein S5 (RPS5) interacts with HCV IRES. Here, we have extensively characterized the HCV IRES-RPS5 interaction and demonstrated its role in IRES function. Computational modelling and RNA-protein interaction studies demonstrated that the beta hairpin structure within RPS5 is critically required for the binding with domains II and IV. Mutations disrupting IRES-RPS5 interaction drastically reduced the 80S complex formation and the corresponding IRES activity. Computational analysis and UV cross-linking experiments using various IRES-mutants revealed interplay between domains II and IV mediated by RPS5. In addition, present study demonstrated that RPS5 interaction is unique to HCV IRES and is not involved in 40S-3 ` UTR interaction. Further, partial silencing of RPS5 resulted in preferential inhibition of HCV RNA translation. However, global translation was marginally affected by partial silencing of RPS5. Taken together, results provide novel molecular insights into IRES-RPS5 interaction and unravel its functional significance in mediating internal initiation of translation.

BODIPY appended copper(II) complexes of curcumin showing mitochondria targeted remarkable photocytotoxicity in visible light

Copper(II) complexes of BODIPY (borondipyrromethene) derivatives (L-1, L-2) and curcumin (Hcur), viz. Cu(L-1)(cur)]Cl (1) and Cu(L-2)(cur)]Cl (2), where L-1 and L-2 are the non-iodinated and diiodinated BODIPY appended dipicolylamine ligands, are prepared and characterized and their photocytotoxic activity in visible light studied. Binding to copper(II) has rendered stability to curcumin from its hydrolytic degradation in buffer medium. The complexes show mitochondrial localization in HeLa cells emphasizing the findings that both 1 and 2 are mitochondria-targeting complexes and induce cancer cell death. Complex 1 with a fluorophoric BODIPY moiety in L-1 gave IC50 values of 7.9(+/- 0.3) mu M in visible light (400-700 nm) and 29.1(+/- 0.5) mu M in the dark. Complex 2 having a diiodo BODIPY moiety in L-2 as a photosensitizer gave IC50 values of 3.8(+/- 0.2) mu M in visible light and 32.1(+/- 0.4) mu M in the dark. The PDT effect of 2 is comparable to that of Photofrin (R), an FDA approved PDT drug. Cell death follows an apoptotic pathway with the formation of reactive oxygen species (ROS).

Polypyridyl iron(II) complexes showing remarkable photocytotoxicity in visible light

Iron(II) complexes of polypyridyl ligands (B), viz. Fe(B)(2)]Cl-2 (1 and 2) of N, N, N-donor 2-(2-pyridyl)-1,10-phenanthroline (pyphen in 1) and 3-(pyridin-2-yl)dipyrido3,2-a:2',3'-c]phenazine (pydppz in 2), are prepared and characterized. They are 1:2 electrolytes in aqueous DMF. The diamagnetic complexes exhibit metal to ligand charge transfer band near 570 nm in DMF. The complexes are avid binders to calf thymus DNA giving binding constant (K (b)) values of similar to 10(6) M-1 suggesting significant intercalative DNA binding of the complexes due to presence of planar phenanthroline bases. Complex 2 exhibits significant photocytotoxicity in immortalized human keratinocyte cells HaCaT and breast cancer cell line MCF-7 giving IC50 values of 0.08 and 13 mu M in visible light (400-700 nm). Complex 2 shows only minor dark toxicity in HaCaT cells but is non-toxic in dark in MCF-7 cancer cells. The light-induced cellular damage follows apoptotic pathway on generation of reactive oxygen species as evidenced from the dichlorofluorescein diacetate (DCFDA) assay.

Photocytotoxic ternary copper(II) complexes of histamine Schiff base and pyridyl ligands

Ternary copper(Il) complexes of salicylaldehyde-histamine Schiff base (HL) and pyridyl ligands, viz. Cu(bpy)(L)](ClO4) (1) and Cu(dppz)(L)](C104) (2), where bpy is 2,2'-bipyridine (in 1) and dppz is dipyrido3,2-a:2',3'-c]phenazine (in 2), were synthesized, characterized and their DNA binding, photo-activated DNA cleavage activity and photocytotoxicity studied. The 1:1 electrolytic one-electron paramagnetic complexes showed a d-d band near 670 nm in aqueous DMF (1:1 v/v). The crystal structure of complex 1 showed the metal in CuN4O distorted square-pyramidal geometry. Complex 2 intercalatively binds to calf-thymus (ct) DNA with a binding constant (K-b) of similar to 10(5) M-1. It exhibited moderate chemical nuclease activity but excellent DNA photocleavage activity in red light of 647 nm forming (OH)-O-center dot radicals. It showed remarkable photocytotoxicity in human cervical cancer cells (HeLa) giving IC50 of 1.6 mu M in visible light (400-700 nm) with low dark toxicity. The photo-induced cell death is via generation of oxidative stress by reactive oxygen species.

Remarkable photo-induced anticancer activity of vitamin-S6 Schiff base copper(II) complexes of pyridyl bases

Vitamin-B6 (VB6) Schiff base (H2L) copper(II) complexes of pyridyl bases, viz. Cu(bpy)(L)] (1), Cu(phen)(L)] (2) and Cu(dppz)(L)] (3), where bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline and dppz is dipyrido3,2-a:2',3'c]phenazine are synthesized, characterized and their phto-induced anticancer activity studied. The non-electrolytic one electron paramagnetic complexes exhibit a d-d band near 700 nm in DMF. The dppz complex intercalatively binds to calf-thymus DNA with binding constant (K-b) values of similar to 10(6) M-1. This complex exhibits low chemical nuclease activity but excellent DNA photocleavage activity when irradiated with red light of 705 nm forming (OH)-O-center dot radical. It displays remarkable photocytotoxicity in human cervical cancer cells (HeLa) giving IC50 value of 0.9 mu M in visible light (400-700 nm) while being less toxic in darkness (IC50 : 23 mu M). The cellular uptake of the complexes seems to be via VB6 transporting membrane carrier mediated diffusion pathway. Photo-induced cell death follows apoptotic pathway involving photo-generated intracellular reactive oxygen species.