R-spondin-1 induces Axin degradation via the LRP6-CK1ε axis.

R-spondins (RSPOs) are secreted signaling molecules that potentiate the Wnt/ß-catenin pathway by cooperating with Wnt ligands. RSPO1 is crucial in tissue development and tissue homeostasis. However, the molecular mechanism by which RSPOs activate Wnt/ß-catenin signaling remains elusive. In this study, we found that RSPOs could mediate the degradation of Axin through the ubiquitin-proteasome pathway. The results of Co-IP showed that the recombinant RSPO1 protein promoted the interaction between Axin1 and CK1ε. Either knockout of the CK1ε gene or treatment with the CK1δ/CK1ε inhibitor SR3029 caused an increase in Axin1 protein levels and attenuated RSPO1-induced degradation of the Axin1 protein. Moreover, we observed an increase in the number of associations of LRP6 with CK1ε and Axin1 following RSPO1 stimulation. Overexpression of LRP6 further potentiated Axin1 degradation mediated by RSPO1 or CK1ε. In addition, recombinant RSPO1 and Wnt3A proteins synergistically downregulated the protein expression of Axin1 and enhanced the transcriptional activity of the SuperTOPFlash reporter. Taken together, these results uncover the novel mechanism by which RSPOs activate Wnt/ß-catenin signaling through LRP6/CK1ε-mediated degradation of Axin.

Binding and stabilizating effect of RNA triplex poly(U)⋠poly(A)*poly(U) by enantiomers of ruthenium(II) polypyridyl complex [Ru(bpy)2(dppx)]2.

Two chiral ruthenium(II) polypyridyl complexes, Λ-[Ru(bpy)2(dppx)]2+ (bpy = 2,2'-bipyridine, dppx = 7,8-dimethyldipyridophenazine; Λ-1) and Δ-[Ru(bpy)2(dppx)]2+ (Δ-1) have been synthesized and characterized in this work. Interactions of Λ-1 and Δ-1 with the RNA triplex poly(U)⋅poly(A)*poly(U) have been investigated by various biophysical techniques. Spectrophotometric titrations and viscosity measurements suggested that enantiomers Λ-1 and Δ-1 bind with the triplex through intercalation, while the binding strengths of the two enantiomers toward the triplex differed only slightly from each other. Fluorescence titrations showed that although enantiomers Λ-1 and Δ-1 exhibited molecular "light switch" effects toward the triplex, the effect of Δ-1 was more marked. Furthermore, Furthermore, thermal denaturation showed that the two enantiomers have significantly different stabilizing effects on the triplex. The obtained results indicate that the racemic complex [Ru(bpy)2(dppx)]2+ is similar to a non-specific metallointercalator for the triplex investigated in this study, and chiralities of Ru(II) polypyridine complexes have an important influence on the binding and stabilizing effects of enantiomers toward the triplex. Two chiral ruthenium(II) polypyridyl complexes, Λ-[Ru(bpy)2(dppx)]2+ (bpy = 2,2'-bipyridine, dppx = 7,8-dimethyldipyridophenazine; Λ-1) and Δ-[Ru(bpy)2(dppx)]2+ (Δ-1) have been synthesized and characterized in this work. Interactions of Λ-1 and Δ-1 with the RNA triplex poly(U)⋅poly(A)*poly(U) have been investigated by various biophysical techniques. The obtained results indicate that the racemic complex [Ru(bpy)2(dppx)]2+ is similar as a non-specific metallointercalator for the triplex investigated in this study, and chiralities of Ru(II) polypyridine complexes have an important influence on the binding and stabilizing effects of enantiomers toward the triplex.

Interactions of arene ruthenium(II) complexes [η6-(C6H6)Ru(pprip)Cl]+ and [η6-(C6H6)Ru(H2iiP)Cl]+ with RNA triplex poly(U)•poly(A)*poly(U).

Two arene ruthenium(II) complexes [η6-(C6H6)Ru(pprip)Cl]PF6 (Ru1; pprip = 2-(3-phenyl-1H-pyrazol-4-yl)-imidazolo[4,5-f][1,10]phenanthroline) and [η6-(C6H6)Ru(H2iiP)Cl]PF6 (Ru2; H2iiP = 2-(indole-3-yl)-imidazolo[4,5-f][1,10]phenanthroline) have been synthesized and characterized in this work. Binding properties of Ru1 and Ru2 with the triplex RNA poly(U)•poly(A)*poly(U) were investigated by spectrophotometry and spectrofluorometry as well as viscosimetry. Analysis of spectroscopic titrations and viscosity measurements show that the two complexes bind with the triplex through intercalation, while the binding affinity for Ru2 toward the triplex is stronger than that for Ru1. Melting experiments indicate that the stabilizing effects of Ru1 and Ru2 toward the triplex differ from each other. Under the conditions used herein, Ru1 only stabilizes the Hoogsteen base-paired strand (third strand) without affecting stabilization of the Watson-Crick base-paired strand (the template duplex) of the triplex, while Ru2 stabilizes both the template duplex and the third strand. Although the two complexes prefer to stabilizing the third strand rather than the template duplex, the third-strand stabilization effect of Ru2 is stronger than that of Ru1. The obtained results of this work reveal that the planarity of the intercalative ligands plays an important role in the triplex stabilization by arene Ru(II) complexes.

Interaction of ruthenium(⠡) polypyridyl complexes [Ru(phen)2(L)]2+ (L = PIP, p-HPIP and m-HPIP) with RNA poly(A)•poly(U): Each complex unexpectedly exhibiting a destabilizing effect on RNA.

To further explore the binding properties of Ru(Ⅱ) polypyridine complexes with RNA, three Ru(Ⅱ) complexes [Ru(phen)2(PIP)]2+ (Ru1), [Ru(phen)2(p-HPIP)]2+ (Ru2), and [Ru(phen)2(m- HPIP)]2+ (Ru3) have been synthesized and characterized in this work. The binding properties of three Ru(Ⅱ) complexes with RNA duplex poly(A)•poly(U) have been investigated by spectral and viscosity experiments. These studies all support that these three Ru(Ⅱ) complexes bind to poly RNA duplex poly(A)•poly(U) by intercalation, and Ru1 without substituents has a stronger binding affinity for poly(A)•poly(U). Interestingly, the thermal melting experiments show that these three Ru(Ⅱ) complexes all destabilize RNA duplex poly(A)•poly(U), and the destabilizing effect can be explained by the conformational changes of duplex structure induced by intercalating agents. To the best of our knowledge, this work report for the first time a small molecule capable of destabilizing an RNA duplex, which reflects that the substitution effect of intercalated ligands has an important influence on the affinity of Ru(Ⅱ) complexes to RNA duplex, and that not all Ru(Ⅱ) complexes show thermal stability effects on an RNA duplex.

Biophysical insights into the interaction of two enantiomers of Ru(II) complex [Ru(bpy)2(7-CH3-dppz)]2+ with the RNA poly(U-A⁎U) triplex.

To determine the factors affecting the stabilization of RNA triple-stranded structure by chiral Ru(II) polypyridyl complexes, a new pair of enantiomers, ∆-[Ru(bpy)2(7-CH3-dppz)]2+ (∆-1; bpy = 2,2'-bipyridine, 7-CH3-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) and Λ-[Ru(bpy)2(7-CH3-dppz)]2+ (Λ-1), have been synthesized and characterized in this work. Binding properties of the two enantiomers with the RNA poly(U-A⁎U) triplex (where "-" denotes the Watson - Crick base pairing and "⁎" denotes the Hoogsteen base pairing) have been studied by spectroscopy and hydrodynamics methods. Under the conditions used in this study, changes in absorption spectra of the two enantiomers are not very different from each other when bound to the triplex, although the binding affinity of ∆-1 is higher than that of Λ-1. Fluorescence titrations and viscosity experiments give convincing evidence for a true intercalative binding of enantiomers with the triplex. However, melting experiments indicated that the two enantiomers selectively stabilized the triplex. The enantiomer ∆-1 stabilize the template duplex and third-strand of the triplex, while it's more effective for stabilization of the template duplex. In stark contrast to ∆-1, Λ-1 stabilizes the triplex without any effect on the third-strand stabilization, suggesting this one extremely prefers to stabilize the template duplex rather than third-strand. Besides, the triplex stabilization effect of ∆-1 is more marked in comparison with that of Λ-1. The obtained results suggest that substituent effects and chiralities of Ru(II) polypyridyl complexes play important roles in the triplex stabilization. Complexes Λ/Δ-[Ru(bpy)2(7-CH3-dppz)]2+ (Λ/Δ-1; bpy = 2,2'-bipyridine, 7-CH3-dppz = 7-methyl-dipyrido[3,2-a,2',3'-c]phenazine) were prepared as stabilizers for poly(U-A ∗ U) triplex. Results suggest the triplex stabilization depends the chiral structures of Λ/Δ-1, indicating that [Ru(bpy)2(7-CH3-dppz)]2+ is a non-specific intercalator for poly(U-A ∗ U) investigated in this work.

Binding properties of two ruthenium(II) polypyridyl complexes [Ru(bpy)2(dppz-Br)]2+ and [Ru(dmb)2(dppz-Br)]2+ with the RNA poly(U)•poly(A)*poly(U) triplex.

Two ruthenium(II) polypyridyl complexes containing different ancillary ligands, [Ru(bpy)2(dppz-Br)]2+ (Ru1; bpy = 2,2'-bipyridine dppz-Br = 7-Br-dipyrido[3,2-a,2',3'-c]-phenazine) and [Ru(dmb)2(dppz-Br)]2+ (Ru2; dmb = 4,4'-dimethyl-2,2'-bipyridine), have been synthesized and characterized. Binding properties of Ru1 and Ru2 with the RNA poly(U)•poly(A)*poly(U) triplex have been investigated by UV-Vis spectroscopy, fluorescence spectroscopy, viscosity measurements as well as circular dichroism and thermal denaturation. Spectrophotometric studies together with viscosity measurements suggest that both Ru1 and Ru2 bind with the triplex by intercalation mode, and the melting experiments demonstrate that the two complexes can effectively enhance the triplex stabilization. However, results indicate that Ru1 stabilizes the third-strand and Watson-Crick base-paired duplex of the triplex without obvious selectivity. In contrast, Ru2 prefers to bind with the third strand rather than the Watson-Crick base-paired duplex of the triplex to a some extent under the same conditions used in this study, thereby significantly stabilizing the third strand. The obtained results of this study suggest that slight differences in the ancillary ligands bpy and dmb should be the main factor affecting the binding interactions of the two complexes with the triplex.

Binding Differences of Two Homochiral [Ru(bpy)2dppz]2+ Complexes with poly(U)·poly(A)*poly(U) Triplex RNA.

The first investigation of chiral ruthenium(II) complexes Δ- and Λ-[Ru(bpy)2dppz]2+ and triplex RNA poly(U)·poly(A)*poly(U) was carried out, which showed that Δ enantiomer displayed significant ability in stabilizing model triplex RNA.

Interactions of octahedral ruthenium(II) polypyridyl complexes with the RNA triplex poly(U)•poly(A)*poly(U) effect on the third-strand stabilization.

Stable triplexes play key roles in many biological processes. Due to the Hoogsteen base pairing, triplexes are, however, thermodynamically less stable than the corresponding duplexes. The poor stabilization of these structures limits their practical applications under physiological conditions. To understand the factors effect on the stabilization of RNA triplexes by octahedral ruthenium(II) complexes, the interactions of [RuL2(uip)](2+) {where L = 2,2'-bipyridine (bpy) or 1,10-phenanthroline phen, uip = 2-(5-uracil)-1H-imidazo[4,5-f][1,10]phenanthroline} with the RNA triplex poly(U)•poly(A)*poly(U) are examined by spectrophotometry, spectrofluorometry, circular dichroism, and viscosimetry in this work. The main results obtained here suggest that the third-strand stabilization depends on the hydrophobicity effects of ancillary ligands bpy and phen.

Binding properties of Ru(II) polypyridyl complexes with poly(U)·poly(A)*poly(U) triplex: the ancillary ligand effect on third-strand stabilization.

The binding properties of [RuL(2)(mip)](2+) {where L is 1,10-phenanthroline (phen) or 4,7-dimethyl-1,10-phenanthrollne (4,7-dmp) and mip is 2'-(3",4"-methylenedioxyphenyl)imidazo[4',5'-f][1,10]phenanthroline} with regard to the triplex RNA poly(U)·poly(A)*poly(U) were investigated using various biophysical techniques and quantum chemistry calculations. In comparison with [Ru(4,7-dmp)(2)(mip)](2+), remarkably higher binding affinity of [Ru(phen)(2)(mip)](2+) for the triplex RNA poly(U)·poly(A)*poly(U) was achieved by changing the ancillary ligands. The stabilization of the Hoogsteen-base-paired third strand was improved by about 10.9 °C by [Ru(phen)(2)(mip)](2+) against 6.6 °C by [Ru(4,7-dmp)(2)(mip)](2+). To the best of our knowledge, [Ru(phen)(2)(mip)](2+) is the first metal complex able to raise the third-strand stabilization of poly(U)·poly(A)*poly(U) from 37.5 to 48.4 °C. The results reveal that the ancillary ligands have an important effect on third-strand stabilization of the triplex RNA poly(U)·poly(A)*poly(U) when metal complexes contain the same intercalative ligands.

Binding properties of a molecular "light switch" ruthenium(II) polypyridyl complex toward double- and triple-helical forms of RNA.

To further develop new luminescent probes for RNA, a new ruthenium(II) polypyridyl complex [Ru(dmb)2dppz-idzo]2+ (dmb = 4,4'-dimethyl-2,2'-bipyridine, dppz-idzo = dppz-imidazolone) has been synthesized and characterized in this study. Binding properties of [Ru(dmb)2dppz-idzo]2+ to RNA duplex poly(A) · poly(U) and triplex poly(U) · poly(A) ∗ poly(U) have been explored by spectroscopic techniques and viscometry experiments. The binding modes of [Ru(dmb)2dppz-idzo]2+ to RNA duplex and triplex are intercalation as revealed from spectral titrations and viscosity experiments, while the binding strength of this complex to duplex structure is significantly greater than that of triplex structure. Fluorescence titrations indicate that [Ru(dmb)2dppz-idzo]2+ can act as a molecular "light switch" for both duplex poly(A) · poly(U) and triplex poly(U) · poly(A) ∗ poly(U), while [Ru(dmb)2dppz-idzo]2+ is more sensitive to poly(A) · poly(U) compared to poly(U) · poly(A) ∗ poly(U) and poly(U). Therefore, this complex can distinguish between RNA duplex, triplex and poly(U), and can as luminescent probes for the three RNAs used in this study. In addition, thermal denaturation studies show that [Ru(dmb)2dppz-idzo]2+ is able to significantly increase the Stabilization of RNA duplex and triplex. The results obtained in this study may contribute to further understanding of the binding of Ru(II) complexes with different structural RNAs.

Quantitative study on the three-dimensional defense of Puzhuang Suo-Fort ancient wall and the moat.

The spatial layout of the coastal forts defense system of the Ming Dynasty of China has been studied in a relatively comprehensive way. Nonetheless, ancient defense mechanisms have not been fully revealed. Previous studies have focused more on the macro and meso levels. Studies into its microscopic construction mechanism need to be enhanced. This research attempts to quantify and validate the rationality of the ancient microscopic defense mechanism, using the ancient defense mechanism of Pu Zhuang Suo-Fort in Zhejiang Province as an instance. This study concentrates on the distribution of firepower strength beyond the walls of coastal defense forts, as well as the effect of wall height on firepower defense capabilities. There is a specific firepower attenuation area near the walls due to the firing blind area in the coastal forts defense system. And the construction of the moat plays an additive role in its defensive capability. Meanwhile, the height of the fort wall will also affect the range of the firing blind zone under Yangmacheng. In theory, there is a reasonable height range of the wall and a proper position of the moat. This height range can meet both good economy and defensive capabilities. In turn, the position of the moats and the height of the walls can verify the rationality of the construction mechanism of the coastal forts' defense system.

First ruthenium(II) polypyridyl complex as a true molecular "light switch" for triplex RNA structure: [Ru(phen)2(mdpz)]2+ enhances the stability of Poly(U)·Poly(A)*Poly(U).

Stabilization of triple helical structures is extremely important for carrying out their biological functions. Nucleic acid triple helices may be formed with DNA or RNA strands. In contrast to many studies in DNA, little has been reported concerning the recognition of the RNA triplex by transition-metal complexes. In this article, [Ru(phen)(2)(mdpz)](2+) (Ru1) is the first metal complex able to enhance the stability of the RNA triplex Poly(U)·Poly(A)*Poly(U) and serve as a prominent molecular "light switch" for the RNA triplex.

Binding properties of ruthenium(II) complexes [Ru(phen)2(7-R-dppz)]2+ (R = methyl or bromine) toward poly(U)•poly(A) RNA duplex.

Two Ru(II) complexes containing different substituents, [Ru(phen)2(7-CH3-dppz)]2+ (Ru1) and [Ru(phen)2(7-Br-dppz)]2+ (Ru2), have been synthesized in this study. The binding properties of Ru1 and Ru2 with the duplex RNA poly(U)•poly(A) (where "•" denotes the Watson - Crick base pairing) have been researched by biophysical techniques and viscosity measurements. Analysis of spectral titrations and viscosity measurements indicate that Ru1 and Ru2 bind to the duplex via intercalative, and the binding affinity of Ru1 with the duplex is remarkably higher than that of Ru2. Furthermore, fluorescence emission spectra demonstrates that although complexes Ru1 and Ru2 can act as molecular "light switches" for the duplex RNA, alters in fluorescence emission of Ru1 and Ru2 are prominent differences, and the effectiveness of Ru1 is more remarkable compared with that of Ru2. The melting experiments suggest that the duplex RNA stabilizing effects of Ru1 and Ru2 differ from each other, among them, complex Ru1 can obviously enhance the stability of the duplex RNA, while Ru2 has only a slightly stabilizing effect for the duplex RNA, indicating that Ru1 preferentially binds to RNA duplex over Ru2. The obtained results indicate that subtle modifications of the intercalative ligand of Ru(II) polypyridyl complex with either methyl or bromide group have a significant effect on the duplex-binding discrimination.

Binding properties of [Ru(phen)2(11-R-dppz)]2+ (R = F or CN) with poly(A)•poly(U) duplex RNA.

Two Ru(II) complexes, [Ru(phen)2(11-F-dppz)]2+ (Ru1, phen = 1,10-phenanthroline, 11-F-dppz = 11-fluorodipyrido[3,2-a:2',3'-c]phenazine) and [Ru(phen)2(11-CN-dppz)]2+ (Ru2, 11-CN-dppz = 11-cyanodipyrido[3,2-a:2',3'-c]phenazine), have been synthesized and characterized in this work. The binding properties of Ru1 and Ru2 with poly(A)•poly(U) RNA duplex have been investigated by spectroscopic methods and viscosity measurements. UV-vis absorption spectra and viscosity experiments demonstrate that the binding modes of Ru1 and Ru2 with poly(A)•poly(U) RNA duplex are intercalation, while the binding affinity for Ru2 is greater than that for Ru1. In addition, thermal denaturation studies reveal that both complexes significantly improve the stability of poly(A)•poly(U) duplex RNA. However, fluorescence titrations indicate that Ru1, unlike Ru2, can act as a molecular "light switch" for the poly(A)•poly(U) duplex RNA. The obtained results of this work indicate that the electron-withdrawing effect of substituents on the main ligands can significantly affect the binding of Ru(II) polypyridyl complexes with poly(A)•poly(U).

Research on cluster system distribution of traditional fort-type settlements in Shaanxi based on K-means clustering algorithm.

Taking the traditional fort-type settlements in Shaanxi as the research object, quantitative research methods such as K-means clustering algorithm, correlation analysis, density analysis, and nearest neighbor index are used to study their spatial distribution, formation causes, and cluster characteristics. The objective of the study is to break through the geographical limitations of fort-type settlements research and to explore the scientific methods of classifying and analyzing traditional fort-type settlements. The conclusions are: (1) The results of cluster analysis show that the fort-type settlements in Shaanxi can be divided into three categories; (2) The overall distribution of fort-type settlements in Shaanxi shows multi-point aggregation, and contains both point and linear aggregation distribution; (3) There are four typical cluster systems among the traditional fort-type settlements in Shaanxi; (4) The factors that have the greatest influence on the distribution of settlements are construction force, wall masonry, age, fortification purpose, and topographic environment. The article innovatively proposes the "cluster system" perspective and introduces mathematical algorithms and quantitative research methods to study the cluster system of the fort-type Settlements. This approach is feasible and can be applied to other settlement-related studies. At the same time, the perspective of cluster system could be used in heritage conservation, which can contribute to the restoration of architectural relics and systemic conservation on a larger scale.

GIS-based precise predictive model of mountain beacon sites in Wenzhou, China.

In ancient China, where was frequently troubled by invaders, the government set up many beacon towers for alerting and transmitting military information along the border and the coast. Many beacon sites still exist in some areas, which are generally located in dangerous places with high mountains and rough terrain, bringing great difficulties to archaeological discovery. Therefore, it is particularly important to develop a predictive model applicable to the distribution of mountain beacon sites. Taking 68 beacon sites found in Wenzhou as research samples, this study used the superimposed method of logistic regression and viewshed analysis, forming a high-precision, scientific and operational predictive model for the distribution of beacon sites, which was verified by the cross-validation method. The results showed that the beacon site predictive model simulated in this study could reduce the probability scope of site location by 90% compared with the common logistic regression predictive model, which greatly improved the accuracy and ability of site prediction. At the same time, it could also be used to understand the relationship between the known sites and their surroundings to assist in decision-making about conservation and management.

A naked-eye colorimetric molecular "light switch" based on ruthenium(II) polypyridyl complex [Ru(phen)2ttbd]2+ as binder and stabilizer for RNA duplex and triplex.

Binding of [Ru(phen)2ttbd]2+ (phen = 1,10-phenanthroline, ttbd = 4-(6-propenylpyrido-[3,2-a]- phenzain-10-yl-benzene-1,2-diamine) to the RNA triplex poly(U-A*U) (herein "-" and "*" refer to the Watson-Crick and Hoogsteen binding, respectively) and the duplex poly(A-U) have been investigated by spectral technology and viscosity method. Analysis of spectral titrations and viscosity experiments as well as melting measurements suggest that [Ru(phen)2ttbd]2+ binds to the studied RNA triplex and duplex through intercalation, while its binding constant toward the triplex is greater than the duplex. Luminescent titrations indicate that [Ru(phen)2ttbd]2+ can act as a molecular "light switch" for the two RNAs and the switch effect can be detected by the naked-eye. Moreover, the "light switch" can be repeatedly cycled off and on by adjusting the pH of the solution, whereas color change in the case of the triplex is more significant compared with the duplex. To our knowledge, [Ru(phen)2ttbd]2+ is the first small molecule capable of serving as a pH-controlled reversible visual molecular "light switch" for both the RNA triplex poly(U-A*U) and duplex poly(A-U). Thermal denaturation experiments suggest that [Ru(phen)2ttbd]2+ can obviously increase the triplex stabilization, while it stabilizing third-strand is more marked in comparison with the template duplex of the triplex, indicating this complex preferentially binds to third-strand. The obtained results may be useful for understanding the binding of Ru(II) polypyridyl complexes to RNAs.

Interaction of arene ruthenium(II) complexes [(η6-C6H6)Ru(L)Cl]PF6 (L = o-fpip and p-fpip) with the RNA triplex poly(U)*poly(A)•poly(U).

To comprehend the binding properties of η6-arene Ru(II) complexes with poly(U)*poly(A)•poly(U) triplex, two arene Ru(II) complexes with different fluorine substituent positions, [(η6-C6H6)Ru(o-fpip)Cl]PF6 (Ru1,η6-C6H6 = benzene ring, o-fpip = 2-(2'­fluorine) imidazo [4,5-f] Biver et al. (2008), Gupta et al. (2012) [1, 10] phenanthroline) and [(η6-C6H6)Ru(p-fpip)Cl]PF6 (Ru2,η6-C6H6 = benzene ring, o-fpip = 2-(4'­fluorine) imidazo [4,5-f] Biver et al. (2008), Gupta et al. (2012) [1, 10] phenanthroline), have been synthesized and characterized in this study. The binding of Ru1 and Ru2 with poly(U)*poly(A)•poly(U) triplex has been investigated by viscosity measurement and spectroscopic methods. Analysis of UV-Vis absorption spectral titrations suggests that Ru1 and Ru2 bind to the triplex through an intercalative mode, but the binding affinity of Ru2 is slightly higher than that of Ru1, which is also verified by viscosity and EB (ethidium bromide) competition measurements. Furthermore, the thermal denaturation experiment shows that Ru1 and Ru2 increase the third-strand stabilization to a similar extent. Interestingly, the two complexes have essentially no effect on the stabilization of the template duplex. Considering the structure of Ru1 and Ru2, conceivably besides the intercalation of ligand, the force stabilizing the triplex should also involve covalent binding and electrostatic interaction. The obtained results will contribute to our understanding of the interaction of arene Ru(II) complexes with the poly(U)*poly(A)•poly(U) triplex.

RNA-binding of Ru(II) complexes [Ru(phen)2(7-OCH3-dppz)]2+ and [Ru(phen)2(7-NO2-dppz)]2+: The former serves as a molecular "light switch" for poly(A)•poly(U).

To further determine the factors that affect the binding properties of ruthenium(II) polypyridine complexes with RNA duplex and to find excellent RNA-binding agents, the binding properties of ruthenium(II) complexes [Ru(phen)2(7-OCH3-dppz)]2+ (Ru1, phen = 1,10-phenan- throline, 7-OCH3-dppz = 7-methoxy-dipyrido-[3,2-a,2',3'-c]-phenazine) and [Ru(phen)2(7-NO2- dppz)]2+ (Ru2, 7-NO2-dppz = 7-nitro-dipyrido-[3,2-a,2',3'-c]-phenazine) with RNA poly(A)•poly(U) duplex have been investigated by spectroscopic methods and viscosity measurements in this work. The results show that complexes Ru1 and Ru2 bind to poly(A)•poly(U) through intercalation and the binding affinity between Ru2 and poly(A)•poly(U) is greater than that of Ru1. Thermal denaturation experiments suggest that both ruthenium(II) complexes exhibit a significant stabilizing effect on poly(A)•poly(U) duplex. Moreover, fluorescence emission spectra exhibit that, deviating from Ru2, Ru1 exhibits a "light switch" effect for poly(A)•poly(U). This effect can be observed by the naked eye under UV light and adjusted by pH, meaning that Ru1 may act as a reversible pH controlled molecular "light switch". The results obtained in this work will contribute to our understanding of the significant influence of the intercalative ligand substituent effect in the binding process of ruthenium(II) complexes with RNA duplex.

Insight into achirality and chirality effects in interactions of an racemic ruthenium(II) polypyridyl complex and its Δ- and Λ-enantiomers with an RNA triplex.

RNA triplexes have a variety of potential applications in molecular biology, diagnostics and therapeutics, while low stabilization of the third strand hinders their practical utilities under physiological conditions. In this regard, achieving the third-strand stabilization by binding small molecules is a promising strategy. Chirality is one of the basic properties of nature. To clarify achirality and chirality effects on the binding and stabilizing effects of RNA triplexes by small molecules, we report for the first time the RNA interactions of an racemic ruthenium(II) polypyridyl complex [Ru(bpy)2(11-CN-dppz)]2+ (rac-Ru1) and its two enantiomers Δ/Λ-[Ru(bpy)2(11-CN-dppz)]2+ (Δ/Λ-Ru1) with an RNA triplex poly(U-A*U) (where "-" represents Watson-Crick base pairing, and "*" denotes Hoogsteen base pairing, respectively) in this work. Research shows that although rac-Ru1 and its two enantiomers Δ/Λ-Ru1 bind to the RNA triplex through the same mode of intercalation, the binding affinity for enantiomer Δ-Ru1 is much higher than that for rac-Ru1 and enantiomer Λ-Ru1. However, compared to enantiomer Λ-Ru1, the binding affinity for rac-Ru1 does not show much of an advantage, which is slightly greater than that for the former. Thermal denaturation measurements reveal both rac-Ru1 and Δ-Ru1 to have a preference for stabilizing the third strand rather than the template duplex of the RNA triplex, while Λ-Ru1 stabilizes the RNA triplex without significant selectivity. Besides, the third-strand stabilizing effects by rac-Ru1 and Δ-Ru1 are not markedly different from each other, but more marked than that by Λ-Ru1. This work shows that the binding properties of the racemic Ru(II) polypyridyl complex with the RNA triplex are not simply an average of its two enantiomers, indicating potentially complicated binding events.