Hook, Line, and Sinker! Spectroscopic Studies of Bi-Modular Mono- and Bis-1,8-naphthalimide-Ru(bpy)3-conjugates as DNA "Light Switches".

Bi-chromophoric ruthenium polypyridyl complexes comprising one or two nitro-1,8-naphthalimide groups are shown to be effective DNA binders with off-on light switching properties. The binding to DNA was investigated using a combination of studies such as UV-visible absorption and emission titrations, thermal denaturation, and circular dichroism spectroscopy. The DNA affinity was shown to be sensitive to both the linker length and the number of naphthalimides (one vs two) contained in these systems and binding constants ranging from 106 to 107 M-1 for salmon testes DNA. The strong DNA binding is attributed to the combination of naphthalimide intercalation and the electrostatic interaction of the ruthenium complex. Large emission enhancements from the metal to ligand charge transfer (MLCT) emission arising from the metal complex were observed upon DNA binding, which was attributed to the interruption of intramolecular electron transfer quenching processes. Moving the nitro substitution from the 4-position to the 3-position is found to result in modification of the DNA binding and the resulting optical properties. The off-on light switch phenomena reported demonstrate the potential of these complexes to act as DNA probes.

Synthesis, Characterization, and Biological Profiling of Ruthenium(II)-Based 4-Nitro- and 4-Amino-1,8-naphthalimide Conjugates.

We report the synthesis, photophysical characterization, and biological evaluation of four DNA-binding ruthenium(II) polypyridyl 4-nitro- and 4-amino-1,8-naphthalimide conjugates. A meta arrangement around the ring connecting the 1,8-naphthalimide to a bipyridine ligand creates a cleft, the result of which renders the shape of the complex complementary to that of DNA. We have demonstrated that each complex exhibits water solubility and a distinctive set of photophysical properties that has allowed the nature of their interaction with DNA to be probed by various ground- and excited-state titrations. Furthermore, by varying the ancillary ligands, we also demonstrate their ability to act as DNA photocleavers, where all compounds have been found to cleave supercoiled DNA with high efficiency. Detailed cellular uptake experiments revealed that the conjugates accumulate in the cytoplasm and nucleus of HeLa cells, showing characteristic red metal-to-ligand charge-transfer emission, and also exhibit photoactivated cytotoxicity within the cells upon irradiation at 450 nm. A comparison between the meta and para arrangements of the 1,8-naphthalimide moiety relative to the Ru(II) center suggests increased DNA binding in the case of the meta arrangement; however, bipyridine-4-amino-1,8-naphthalimide conjugates appear to show superior phototoxicity in comparison to their 4-nitro derivatives.

Unexpected DNA binding properties with correlated downstream biological applications in mono vs. bis-1,8-naphthalimide Ru(II)-polypyridyl conjugates.

The synthesis, spectroscopic characterisation and biological evaluation of mono- and bis-1,8-naphthalimide-conjugated ruthenium(ii)-polypyridyl complexes is presented. Spectroscopic DNA titrations, together with denaturation studies, show strong binding of both species to DNA through the naphthalimide arms. Linear and circular dichroism (LD and CD) spectroscopy reveal close association of the Ru(bpy)3(2+) core with DNA in the case of the mono-naphthalamide complex, [Ru(bpy)2(bpy-NAP)](2+). Significantly, binding by the second naphthalimide arm in the [Ru(bpy)2(bpy-NAP2)](2+) complex is found to displace the Ru(bpy)3(2+) centre from the DNA backbone. This 'negative allosteric effect' is found to have a dramatic influence on the photoinduced damage of plasmid DNA, and the viability of HeLa cancer cells upon photoactivation. Overall the study clearly maps and correlates the relationship between molecular structure, in vitro binding and activity, and in cellulo function.

Highly effective DNA photocleavage by novel "rigid" Ru(bpy)(3)-4-nitro- and -4-amino-1,8-naphthalimide conjugates.

The synthesis of the two novel 1,8-naphthalimideruthenium conjugates Ru-Nap-NO(2) and Ru-Nap-NH(2) and their photophysical evaluation upon interaction with DNA is reported. Significant changes were seen in both the absorption and emission spectra upon interaction of both conjugates with DNA, from which large binding constants were determined. Moreover, highly efficient DNA cleavage was observed upon irradiation for 5 min, during which supercoiled DNA was converted to nicked and linear DNA by Ru-Nap-NH(2).

Synthesis and pharmacological studies of new hybrid derivatives of fentanyl active at the mu-opioid receptor and I2-imidazoline binding sites.

Two series of fentanyl-derived hybrid molecules bearing potent I2-imidazoline binding site (IBS) ligands (i.e., guanidine and BU224 moieties) linked with an aliphatic (m=2, 3, 4, 6, 7, 8, 9 and 12 methylene units) or aromatic spacer were prepared. Their affinities for the mu-opioid receptors and for the I2-IBS were determined through competition binding studies on human postmortem brain membranes. Whereas the BU224 hybrid molecules bound to the mu-opioid receptor and the I2-IBS in the micromolar to low micromolar range, the alkaneguanidine series exhibited remarkable affinities in the nanomolar range for both receptors. [35S]GTPgammaS functional assays were performed on human postmortem brain membranes with selected ligands from each series (4f and 8g) showing the highest dual affinity for the mu-opioid receptor and I2-IBS affinities. Both compounds displayed agonist properties: at the mu-opioid receptor for the alkaneguanidine derivative 4f (spacer: six methylene units) and at a G-protein coupled receptor (GPCR) which remains to be determined for 8g. The lack of analgesic properties of 4f in vivo (i.e., hot plate and writhing tests in mice), discordant with the good in vitro binding data (Ki mu=1.04+/-0.28 nM, Ki I2=409+/-238 nM), may possibly be due to the low intrinsic efficacy of the compound. Alternatively, a low access to the central nervous system for this kind of hybrid molecules cannot be ruled out. Two new compounds reported here (9f and 13), which were not dual acting, are worth mentioning for their outstanding binding affinities; 9f bound to the mu-opioid receptor with a picomolar affinity (Ki=0.0098+/-0.0033 nM), whereas 13 presented an I2-IBS affinity (Ki=18+/-11 nM) similar to the reference compound BU224.