Ding constant Kb of L-[Ru(phen)2(p-HPIP)]2+, D[Ru(phen)2(p-HPIP)]2+, and L/D-[Ru(phen)2(p-HPIP)]2+ were calculated at KL-Ru = 9.36105 M21, KD-Ru = 7.26105 M21, and KL/D-Ru = 9.16105 M21, respectively. Although the binding constant obtained from luminescence titration via the Scatchard method is different from that obtained from absorption, both sets of binding constants show that the two complexes can effectively intercalate into the DNA base pairs and that the binding ability of L-[Ru(phen)2(p-HPIP)]2+ to the quadruplex is higher than that of D-[Ru(phen)2(p-HPIP)]2+. Circular dichroism spectra. Circular dichroism (CD) spectroscopy was used to MedChemExpress 60940-34-3 investigate the conformational properties of the enantiomeric chiral molecules in relation to the telomeric Gquadruplex. In the absence of salt, the CD spectrum of HTG21 at room temperature exhibited a negative band at 238 nm as well as a major positive band at 257 nm, which probably corresponds to the signal of the HTG21 random coil (characterized by a positive peak at 257 nm). A minor negative band at 280 nm and a positive band near 295 nm were also observed (Figures 4a?c, black line) [39]. A significant change in the CD spectrum was observed upon addition of L-[Ru(phen)2(p-HPIP)]2+ to the aqueous HTG21 solution (Figure 4a). The bands at 257 nm gradually disappeared with the addition of the complex, eventually MedChemExpress ASP015K leading to theChiral Ru Complexes Inhibit Telomerase ActivityFigure 3. Emission spectral traces of the complexes. A)L-[Ru(phen)2(p-HPIP)]2+, b)D-[Ru(phen)2(p-HPIP)]2+, c)L/D-[Ru(phen)2(p-HPIP)]2+. d)Relative emission strength of L-[Ru(phen)2(p-HPIP)]2+, D-[Ru(phen)2(p-HPIP)]2+, and L/D -[Ru(phen)2(p-HPIP)]2+ in Tris/KCl buffer (100 mM KCl, 10 mM Tris HCl, pH 7.4) with increasing ratios of [HTG21]/[Ru] = 0,2.5, [Ru] = 4 mM. These results are mean values of at least three independent experiments. d)Relative emission strength of L-[Ru(phen)2(p-HPIP)]2+, D-[Ru(phen)2(p-HPIP)]2+,and L/D -[Ru(phen)2(p-HPIP)]2. doi:10.1371/journal.pone.0050902.gappearance of a major negative band at 260 nm as well as a significant increase in the band intensity at 295 nm. Meanwhile, a new, strong, positive band gradually appeared near 270 nm. These two changes are consistent with the induction of the G-rich DNA by L-[Ru(phen)2(p-HPIP)]2+ to form the G-quadruplex structure. Thus, all the complexes can convert G-quadruplex from a linear to a hybrid structure. The HTG21 oligonucleotide formed the parallel G-quadruplex structure in the presence of K+ (Figures 4d?f, black line) [40]. The CD spectrum of this structure in the absence of 1407003 any compound shows a strong positive band at 290 nm, a small positive band at 260 nm, and a minor negative band at 234 nm. The CD spectrum changed upon L-[Ru(phen)2(p-HPIP)]2+ titration to the above solution, showing an enhancement of the maximum band at 290 nm as well as a suppression of the band at 260 nm. A strong, positive, induced CD signal also appeared at 270 nm. The band at 260 nm was gradually suppressed and formed a negative band until the ratio of L-[Ru(phen)2(p-HPIP)]2+ to HTG21 reached 4:1 (Figure 4d). This result indicates the formation of a mixture of anti-parallel and parallel conformations, possibly including hybrid-type forms, as well. This interpretation is further supported by the recent observation of a co-existing equilibrated mixture of antiparallel, hybrid, and parallel topologies of telomeric repeats in native conditions [41]. The results also indicate that L-[Ru.Ding constant Kb of L-[Ru(phen)2(p-HPIP)]2+, D[Ru(phen)2(p-HPIP)]2+, and L/D-[Ru(phen)2(p-HPIP)]2+ were calculated at KL-Ru = 9.36105 M21, KD-Ru = 7.26105 M21, and KL/D-Ru = 9.16105 M21, respectively. Although the binding constant obtained from luminescence titration via the Scatchard method is different from that obtained from absorption, both sets of binding constants show that the two complexes can effectively intercalate into the DNA base pairs and that the binding ability of L-[Ru(phen)2(p-HPIP)]2+ to the quadruplex is higher than that of D-[Ru(phen)2(p-HPIP)]2+. Circular dichroism spectra. Circular dichroism (CD) spectroscopy was used to investigate the conformational properties of the enantiomeric chiral molecules in relation to the telomeric Gquadruplex. In the absence of salt, the CD spectrum of HTG21 at room temperature exhibited a negative band at 238 nm as well as a major positive band at 257 nm, which probably corresponds to the signal of the HTG21 random coil (characterized by a positive peak at 257 nm). A minor negative band at 280 nm and a positive band near 295 nm were also observed (Figures 4a?c, black line) [39]. A significant change in the CD spectrum was observed upon addition of L-[Ru(phen)2(p-HPIP)]2+ to the aqueous HTG21 solution (Figure 4a). The bands at 257 nm gradually disappeared with the addition of the complex, eventually leading to theChiral Ru Complexes Inhibit Telomerase ActivityFigure 3. Emission spectral traces of the complexes. A)L-[Ru(phen)2(p-HPIP)]2+, b)D-[Ru(phen)2(p-HPIP)]2+, c)L/D-[Ru(phen)2(p-HPIP)]2+. d)Relative emission strength of L-[Ru(phen)2(p-HPIP)]2+, D-[Ru(phen)2(p-HPIP)]2+, and L/D -[Ru(phen)2(p-HPIP)]2+ in Tris/KCl buffer (100 mM KCl, 10 mM Tris HCl, pH 7.4) with increasing ratios of [HTG21]/[Ru] = 0,2.5, [Ru] = 4 mM. These results are mean values of at least three independent experiments. d)Relative emission strength of L-[Ru(phen)2(p-HPIP)]2+, D-[Ru(phen)2(p-HPIP)]2+,and L/D -[Ru(phen)2(p-HPIP)]2. doi:10.1371/journal.pone.0050902.gappearance of a major negative band at 260 nm as well as a significant increase in the band intensity at 295 nm. Meanwhile, a new, strong, positive band gradually appeared near 270 nm. These two changes are consistent with the induction of the G-rich DNA by L-[Ru(phen)2(p-HPIP)]2+ to form the G-quadruplex structure. Thus, all the complexes can convert G-quadruplex from a linear to a hybrid structure. The HTG21 oligonucleotide formed the parallel G-quadruplex structure in the presence of K+ (Figures 4d?f, black line) [40]. The CD spectrum of this structure in the absence of 1407003 any compound shows a strong positive band at 290 nm, a small positive band at 260 nm, and a minor negative band at 234 nm. The CD spectrum changed upon L-[Ru(phen)2(p-HPIP)]2+ titration to the above solution, showing an enhancement of the maximum band at 290 nm as well as a suppression of the band at 260 nm. A strong, positive, induced CD signal also appeared at 270 nm. The band at 260 nm was gradually suppressed and formed a negative band until the ratio of L-[Ru(phen)2(p-HPIP)]2+ to HTG21 reached 4:1 (Figure 4d). This result indicates the formation of a mixture of anti-parallel and parallel conformations, possibly including hybrid-type forms, as well. This interpretation is further supported by the recent observation of a co-existing equilibrated mixture of antiparallel, hybrid, and parallel topologies of telomeric repeats in native conditions [41]. The results also indicate that L-[Ru.