A Minimal Load-and-Lock RuII Luminescent DNA Probe

Threading intercalators bind DNA with high affinities. Here, we describe single-molecule studies on a cell-permeant luminescent dinuclear ruthenium(II) complex that has been previously shown to thread only into short, unstable duplex structures. Using optical tweezers and confocal microscopy, we show that this complex threads and locks into force-extended duplex DNA in a two-step mechanism. Detailed kinetic studies reveal that an individual stereoisomer of the complex exhibits the highest binding affinity reported for such a mono-intercalator. This stereoisomer better preserves the biophysical properties of DNA than the widely used SYTOX Orange. Interestingly, threading into torsionally constrained DNA decreases dramatically, but is rescued on negatively supercoiled DNA. Given the "light-switch" properties of this complex on binding DNA, it can be readily used as a long-lived luminescent label for duplex or negatively supercoiled DNA through a unique "load-and-lock" protocol.

Natural DNA Intercalators as Promising Therapeutics for Cancer and Infectious Diseases

Cancer and infectious diseases are one of the greatest challenges of modern medicine. An unhealthy lifestyle, the improper use of drugs, or their abuse are conducive to the increase of morbidity and mortality caused by these diseases. The imperfections of drugs currently used in therapy for these diseases and the increasing problem of drug resistance have forced a search for new substances with therapeutic potential. Throughout history, plants, animals, fungi and microorganisms have been rich sources of biologically active compounds. Even today, despite the development of chemistry and the introduction of many synthetic chemotherapeutics, a substantial part of the new compounds being tested for treatment are still of natural origin. Natural compounds exhibit a great diversity of chemical structures, and thus possess diverse mechanisms of action and molecular targets. Nucleic acids seem to be a good molecular target for substances with anticancer potential in particular, but they may also be a target for antimicrobial compounds. There are many types of interactions of small-molecule ligands with DNA. This publication focuses on the intercalation process. Intercalators are compounds that usually have planar aromatic moieties and can insert themselves between adjacent base pairs in the DNA helix. These types of interactions change the structure of DNA, leading to various types of disorders in the functioning of cells and the cell cycle. This article presents the most promising intercalators of natural origin, which have aroused interest in recent years due to their therapeutic potential.

DNA threading intercalation of enantiopure [Ru(phen)2bidppz]2+ induced by hydrophobic catalysis

The enantiomers of a novel mononuclear ruthenium(ii) complex [Ru(phen)2bidppz]2+ with an elongated dppz moiety were synthesized. Surprisingly, the complex showed no DNA intercalating capability in an aqueous environment. However, by the addition of water-miscible polyethylene glycol ether PEG-400, self-aggregation of the hydrophobic ruthenium(ii) complexes was counter-acted, thus strongly promoting the DNA intercalation binding mode. This mild alteration of the environment surrounding the DNA polymer does not damage or alter the DNA structure but instead enables more efficient binding characterization studies of potential DNA binding drugs.

Electrochemical investigations of DNA-Intercalation potency of bisnitrophenoxy compounds with different alkyl chain lengths

In this study, the binding tendency of bisnitrophenoxy compounds (BN) having different methylene (-CH₂-)_n spacer groups (n = 8-11) with fish sperm double stranded deoxyribonucleic acid (dsDNA) was explored. Cyclic voltammetry (CV) was used to evaluate various kinetic and binding parameters (K_s,h, D_o, K _b and binding site sizes). Performed electrochemical studies designated strong contact of these symmetric molecules with dsDNA in threading intercalation mode of binding. The number (n) of methylene spacer group in the molecular structure of bisnitrophenoxy compounds, e.g., BN-8 (1-nitro-4-(8-(4-nitrophenoxy)octyloxy)benzene, was observed to have a strong influence on their binding affinity. Decreased peak current values and positively shifted peak potentials recorded via cyclic voltammetry clearly depicted that bisnitrophenoxy compounds can intercalate with dsDNA. Results demonstrated the following order of binding constants; K _b (M^-1): BN-8 (2.32 × 10⁴) < BN-9 (5.73 × 10⁴) < BN-10 (8.97 × 10⁴) < BN-11 (17.34 × 10⁴). The order of increasing binding sites from BN-8 (0.13) to BN-11 (1.38), revealed the maximum threading intercalation strength by bisnitrophenoxy compound having the longest methylene spacer (n = 11). Thermodynamic studies augmented the strong binding of BN-11 with dsDNA as compared to BN-8 because of the long-chain, -CH₂- spacer in its structure. The spontaneity of dsDNA-binding was revealed by the negative ΔG values for interaction of all the compounds. Moreover, binding parameters from thermodynamic and kinetic studies also corresponded to the threading intercalation mode of interaction, which itself points to the potency of the envisioned drug-like molecules.

Synthesis, Structural and Physicochemical Properties of Water-Soluble Mixed-Ligand Diruthenium Complexes Containing Anilinopyridinate Bridging Ligands

A series of water-soluble Ru₂⁵⁺ complexes of the type Ru₂(O₂CCH₃)₃(L)Cl where L = 2,3,4,5,6-F₅ap, 2,4,6-F₃ap, 2-Fap, ap, 2-Meap, 2,6-Me₂ap, or 2,4,6-Me₃ap, where ap is the anilinopyridinate anion, have been characterized as to their structural and physicochemical properties in H₂O and DMSO. Five of the newly synthesized complexes were structurally characterized, and the Ru-Cl bond lengths range from 2.477 to 2.544 Å while the Ru-Ru bond lengths range from 2.2838 to 2.2935 Å. The UV-vis spectra of each compound are characterized by three absorption bands in both H₂O and DMSO, the intensity and position of which vary with both the type of bridging ligand and the solvent. The seven examined Ru₂⁵⁺ complexes exist as 1:1 electrolytes in water, and each undergoes a reversible one-electron reduction assigned to Ru₂⁵⁺/Ru₂⁴⁺ in both investigated solvents. A second irreversible reduction attributed to Ru₂⁴⁺/Ru₂³⁺ is also observed for each compound at more negative potentials in DMSO. A linear free energy relationship exists between the sum of the Hammett substituent constants (Σσ) on the ap-type bridging ligand and the wavenumber of an absorption band for the Ru₂⁵⁺ complexes. A linear relationship is also seen between Σσ and measured E_1/2 values for the Ru₂⁵⁺/Ru₂⁴⁺ process in water containing 0.1 M KCl, but little to no effect is seen between the specific bridging ligand and the structural features of the investigated compounds.

Recent Developments in the Interactions of Classic Intercalated Ruthenium Compounds: [Ru(bpy)₂dppz]2+ and [Ru(phen)₂dppz]2+ with a DNA Molecule

[Ru(bpy)₂dppz]²⁺ and [Ru(phen)₂dppz]²⁺ as the light switches of the deoxyribose nucleic acid (DNA) molecule have attracted much attention and have become a powerful tool for exploring the structure of the DNA helix. Their interactions have been intensively studied because of the excellent photophysical and photochemical properties of ruthenium compounds. In this perspective, this review describes the recent developments in the interactions of these two classic intercalated compounds with a DNA helix. The mechanism of the molecular light switch effect and the selectivity of these two compounds to different forms of a DNA helix has been discussed. In addition, the specific binding modes between them have been discussed in detail, for a better understanding the mechanism of the light switch and the luminescence difference. Finally, recent studies of single molecule force spectroscopy have also been included so as to precisely interpret the kinetics, equilibrium constants, and the energy landscape during the process of the dynamic assembly of ligands into a single DNA helix.

A luminescent on–off probe based calix[4]arene linked through triazole with ruthenium(ii) polypyridine complexes to sense copper(ii) and sulfide ions

The supramolecular sensor Ru2L was designed by joining a bis-ruthenium(ii) polypyridyl complex with a p-tert-butyl calix[4]arene platform through a 1,2,3-triazole linker and used for sensing of copper(ii) and sulfide ions by fluorescence.

Bimetallic Ru(ii) and Os(ii) complexes based on a pyrene-bisimidazole spacer: synthesis, photophysics, electrochemistry and multisignalling DNA binding studies in the near infrared region

We report in this paper the synthesis, characterization, photophysical and electrochemical properties, and detailed DNA binding affinities of two homobimetallic Ru(ii) and Os(ii) complexes derived from a new bridging ligand consisting of two pyridyl-imidazole coordinating units rigidly coupled with a central pyrene moiety. The structure of the diruthenium complex was confirmed by X-ray crystallography. Both complexes exhibit luminescence at room temperature from their ³MLCT states, with lifetimes of τ₁ = 12.6 ns and τ₂ = 48.8 ns for the Ru(ii) complex (1) and τ₁ = 23.7 ns for the Os(ii) complex (2). For 2, the luminescence maximum stretches to the NIR region, which is suitable for potential biological applications. Both complexes exhibit two successive one-electron reversible metal-centered oxidations in the positive potential window. Computational studies employing DFT and TD-DFT methods were also performed to assign the experimentally observed optical spectral bands in the complexes. The binding affinities of the complexes towards DNA were thoroughly investigated through a variety of techniques, viz. absorption, luminescence, excited state lifetime, circular dichroism, thermal denaturation, viscosity measurement, and relative DNA binding studies using ethidium bromide. Finally, molecular docking studies were also carried out to visualize the modes of interaction between the complexes and DNA.

Reshaping the Energy Landscape Transforms the Mechanism and Binding Kinetics of DNA Threading Intercalation

Molecules that bind DNA via threading intercalation show high binding affinity as well as slow dissociation kinetics, properties ideal for the development of anticancer drugs. To this end, it is critical to identify the specific molecular characteristics of threading intercalators that result in optimal DNA interactions. Using single-molecule techniques, we quantify the binding of a small metal-organic ruthenium threading intercalator (Δ,Δ-B) and compare its binding characteristics to a similar molecule with significantly larger threading moieties (Δ,Δ-P). The binding affinities of the two molecules are the same, while comparison of the binding kinetics reveals significantly faster kinetics for Δ,Δ-B. However, the kinetics is still much slower than that observed for conventional intercalators. Comparison of the two threading intercalators shows that the binding affinity is modulated independently by the intercalating section and the binding kinetics is modulated by the threading moiety. In order to thread DNA, Δ,Δ-P requires a "lock mechanism", in which a large length increase of the DNA duplex is required for both association and dissociation. In contrast, measurements of the force-dependent binding kinetics show that Δ,Δ-B requires a large DNA length increase for association but no length increase for dissociation from DNA. This contrasts strongly with conventional intercalators, for which almost no DNA length change is required for association but a large DNA length change must occur for dissociation. This result illustrates the fundamentally different mechanism of threading intercalation compared with conventional intercalation and will pave the way for the rational design of therapeutic drugs based on DNA threading intercalation.

Metal-mediated diradical tuning for DNA replication arrest via template strand scission

A series of M(PyED)·X (X = 2Cl-, SO42-) pyridine-metalloenediyne complexes [M = Cu(II), Fe(II), or Zn(II)] and their independently synthesized, cyclized analogs have been prepared to investigate their potential as radical-generating DNA-damaging agents. All complexes possess a 1:1 metal-to-ligand stoichiometry as determined by electronic absorption spectroscopy and X-ray diffraction. Solution structural analysis reveals a pπ Cl [Formula: see text] Cu(II) LMCT (22,026 cm-1) for Cu(PyED)·2Cl, indicating three nitrogens and a chloride in the psuedo-equatorial plane with the remaining pyridine nitrogen and solvent in axial positions. EPR spectra of the Cu(II) complexes exhibit an axially elongated octahedron. This spectroscopic evidence, together with density functional theory computed geometries, suggest six-coordinate structures for Cu(II) and Fe(II) complexes and a five-coordinate environment for Zn(II) analogs. Bergman cyclization via thermal activation of these constructs yields benzannulated product indicative of diradical generation in all complexes within 3 h at 37 °C. A significant metal dependence on the rate of the reaction is observed [Cu(II) > Fe(II) > Zn(II)], which is mirrored in in vitro DNA-damaging outcomes. Whereas in situ chelation of PyED leads to considerable degradation in the presence of all metals within 1 h under hyperthermia conditions, Cu(II) activation produces >50% compromised DNA within 5 min. Additionally, Cu(II) chelated PyED outcompetes DNA polymerase I to successfully inhibit template strand extension. Exposure of HeLa cells to Cu(PyBD)·SO4 (IC50 = 10 μM) results in a G2/M arrest compared with untreated samples, indicating significant DNA damage. These results demonstrate metal-controlled radical generation for degradation of biopolymers under physiologically relevant temperatures on short timescales.

Photochemically active DNA-intercalating ruthenium and related complexes - insights by combining crystallography and transient spectroscopy

Recent research on the study of the interaction of ruthenium polypyridyl compounds and defined sequence nucleic acids is reviewed. Particular emphasis is paid to complexes [Ru(LL)2(Int)]2+ containing potentially intercalating ligands (Int) such as dipyridophenazine (dppz), which are known to display light-switching or photo-oxidising behaviour, depending on the nature of the ancillary ligands. X-ray crystallography has made a key contribution to our understanding, and the first complete survey of structural results is presented. These include sequence, enantiomeric, substituent and structural specificities. The use of ultrafast transient spectroscopic methods to probe the ultrafast processes for complexes such as [Ru(TAP)2(dppz)]2+ and [Ru(phen)2(dppz)]2+ when bound to mixed sequence oligonucleotides are reviewed with particular attention being paid to the complementary advantages of transient (visible) absorption and time-resolved (mid) infra-red techniques to probe spectral changes in the metal complex and in the nucleic acid. The observed photophysical properties are considered in light of the structural information obtained from X-ray crystallography. In solution, metal complexes can be expected to bind at more than one DNA step, so that a perfect correlation of the photophysical properties and factors such as the orientation or penetration of the ligand into the intercalation pocket should not be expected. This difficulty can be obviated by carrying out TRIR studies in the crystals. Dppz complexes also undergo insertion, especially with mismatched sequences. Future areas for study such as those involving non-canonical forms of DNA, such as G-quadruplexes or i-motifs are also briefly considered.

Induced-Fit Recognition of CCG Trinucleotide Repeats by a Nickel-Chromomycin Complex Resulting in Large-Scale DNA Deformation

Small-molecule compounds targeting trinucleotide repeats in DNA have considerable potential as therapeutic or diagnostic agents against many neurological diseases. Ni^II (Chro)₂ (Chro=chromomycin A3) binds specifically to the minor groove of (CCG)_n repeats in duplex DNA, with unique fluorescence features that may serve as a probe for disease detection. Crystallographic studies revealed that the specificity originates from the large-scale spatial rearrangement of the DNA structure, including extrusion of consecutive bases and backbone distortions, with a sharp bending of the duplex accompanied by conformational changes in the Ni^II chelate itself. The DNA deformation of CCG repeats upon binding forms a GGCC tetranucleotide tract, which is recognized by Ni^II (Chro)₂ . The extruded cytosine and last guanine nucleotides form water-mediated hydrogen bonds, which aid in ligand recognition. The recognition can be accounted for by the classic induced-fit paradigm.

The Structure of Linkers Affects the DNA Binding Properties of Tethered Dinuclear Ruthenium(II) Metallo-Intercalators

With the long-term aim of enhancing the binding properties of dinuclear Ru^II -based DNA light-switch complexes, a series of eight structurally related mono- and dinuclear systems are reported in which the linker of the bridging ligand has been modulated. These tethered systems have been designed to explore issues of steric demand at the binding site and the thermodynamic cost of entropy loss upon binding. Detailed spectroscopic and isothermal titration calorimetry (ITC) studies on the new complexes reveal that one of the linkers produces a dinuclear system that binds to duplex DNA with an affinity (K_b >10⁷  m^-1 ) that is higher than its corresponding monometallic complex and is the highest affinity for a non-threading bis-intercalating metal complex. These studies confirm that the tether has a major effect on the binding properties of dinuclear complexes containing intercalating units and establishes key design rules for the construction of dinuclear complexes with enhanced DNA binding characteristics.

Dissecting the Dynamic Pathways of Stereoselective DNA Threading Intercalation

DNA intercalators that have high affinity and slow kinetics are developed for potential DNA-targeted therapeutics. Although many natural intercalators contain multiple chiral subunits, only intercalators with a single chiral unit have been quantitatively probed. Dumbbell-shaped DNA threading intercalators represent the next order of structural complexity relative to simple intercalators, and can provide significant insights into the stereoselectivity of DNA-ligand intercalation. We investigated DNA threading intercalation by binuclear ruthenium complex [μ-dppzip(phen)4Ru2](4+) (Piz). Four Piz stereoisomers are defined by the chirality of the intercalating subunit (Ru(phen)2dppz) and the distal subunit (Ru(phen)2ip), respectively, each of which can be either right-handed (Δ) or left-handed (Λ). We used optical tweezers to measure single DNA molecule elongation due to threading intercalation, revealing force-dependent DNA intercalation rates and equilibrium dissociation constants. The force spectroscopy analysis provided the zero-force DNA binding affinity, the equilibrium DNA-ligand elongation Δxeq, and the dynamic DNA structural deformations during ligand association xon and dissociation xoff. We found that Piz stereoisomers exhibit over 20-fold differences in DNA binding affinity, from a Kd of 27 ± 3 nM for (Δ,Λ)-Piz to a Kd of 622 ± 55 nM for (Λ,Δ)-Piz. The striking affinity decrease is correlated with increasing Δxeq from 0.30 ± 0.02 to 0.48 ± 0.02 nm and xon from 0.25 ± 0.01 to 0.46 ± 0.02 nm, but limited xoff changes. Notably, the affinity and threading kinetics is 10-fold enhanced for right-handed intercalating subunits, and 2- to 5-fold enhanced for left-handed distal subunits. These findings demonstrate sterically dispersed transition pathways and robust DNA structural recognition of chiral intercalators, which are critical for optimizing DNA binding affinity and kinetics.

DNA intercalation optimized by two-step molecular lock mechanism

The diverse properties of DNA intercalators, varying in affinity and kinetics over several orders of magnitude, provide a wide range of applications for DNA-ligand assemblies. Unconventional intercalation mechanisms may exhibit high affinity and slow kinetics, properties desired for potential therapeutics. We used single-molecule force spectroscopy to probe the free energy landscape for an unconventional intercalator that binds DNA through a novel two-step mechanism in which the intermediate and final states bind DNA through the same mono-intercalating moiety. During this process, DNA undergoes significant structural rearrangements, first lengthening before relaxing to a shorter DNA-ligand complex in the intermediate state to form a molecular lock. To reach the final bound state, the molecular length must increase again as the ligand threads between disrupted DNA base pairs. This unusual binding mechanism results in an unprecedented optimized combination of high DNA binding affinity and slow kinetics, suggesting a new paradigm for rational design of DNA intercalators.

Delta chirality ruthenium 'light-switch' complexes can bind in the minor groove of DNA with five different binding modes

[Ru(phen)₂(dppz)]²⁺ has been studied since the 1990s due to its 'light-switch' properties. It can be used as a luminescent DNA probe, with emission switched on through DNA binding. The luminescence observed is dependent on the solvent accessibility of the pyrazine nitrogen atoms, and therefore is sensitive to changes in both binding site of the cation and chromophore orientation. The compound is also chiral, and there are distinct differences between the enantiomers in terms of the emission behaviour when bound to a variety of DNA sequences. Whilst a number of binary DNA-complex X-ray crystal structures are available, most include the Λ enantiomer and there is very little structural information about binding of the Δ enantiomer. Here, we present the first X-ray crystal structure of a Δ enantiomer bound to well-matched DNA, in the absence of the other, Λ enantiomer. We show how the binding site observed here can be related to a more general pattern of motifs in the crystallographic literature and propose that the Δ enantiomer can bind with five different binding modes, offering a new hypothesis for the interpretation of solution data.

Mechanisms of small molecule-DNA interactions probed by single-molecule force spectroscopy

There is a wide range of applications for non-covalent DNA binding ligands, and optimization of such interactions requires detailed understanding of the binding mechanisms. One important class of these ligands is that of intercalators, which bind DNA by inserting aromatic moieties between adjacent DNA base pairs. Characterizing the dynamic and equilibrium aspects of DNA-intercalator complex assembly may allow optimization of DNA binding for specific functions. Single-molecule force spectroscopy studies have recently revealed new details about the molecular mechanisms governing DNA intercalation. These studies can provide the binding kinetics and affinity as well as determining the magnitude of the double helix structural deformations during the dynamic assembly of DNA–ligand complexes. These results may in turn guide the rational design of intercalators synthesized for DNA-targeted drugs, optical probes, or integrated biological self-assembly processes. Herein, we survey the progress in experimental methods as well as the corresponding analysis framework for understanding single molecule DNA binding mechanisms. We discuss briefly minor and major groove binding ligands, and then focus on intercalators, which have been probed extensively with these methods. Conventional mono-intercalators and bis-intercalators are discussed, followed by unconventional DNA intercalation. We then consider the prospects for using these methods in optimizing conventional and unconventional DNA-intercalating small molecules.

Homo- and Heterobimetallic Ruthenium(II) and Osmium(II) Complexes Based on a Pyrene-Biimidazolate Spacer as Efficient DNA-Binding Probes in the Near-Infrared Domain

We report in this work a new family of homo- and heterobimetallic complexes of the type [(bpy)2M(Py-Biimz)M'(II)(bpy)2](2+) (M = M' = Ru(II) or Os(II); M = Ru(II) and M' = Os(II)) derived from a pyrenyl-biimidazole-based bridge, 2-imidazolylpyreno[4,5-d]imidazole (Py-BiimzH2). The homobimetallic Ru(II) and Os(II) complexes were found to crystallize in monoclinic form with space group P21/n. All the complexes exhibit strong absorptions throughout the entire UV-vis region and also exhibit luminescence at room temperature. For osmium-containing complexes (2 and 3) both the absorption and emission band stretched up to the NIR region and thus afford more biofriendly conditions for probable applications in infrared imaging and phototherapeutic studies. Detailed luminescence studies indicate that the emission originates from the respective (3)MLCT excited state mainly centered in the [M(bpy)2](2+) moiety of the complexes and is only slightly affected by the pyrene moiety. The bimetallic complexes show two successive one-electron reversible metal-centered oxidations in the positive potential window and several reduction processes in the negative potential window. An efficient intramolecular electronic energy transfer is found to occur from the Ru center to the Os-based component in the heterometallic dyad. The binding studies of the complexes with DNA were thoroughly studied through different spectroscopic techniques such as UV-vis absorption, steady-state and time-resolved emission, circular dichroism, and relative DNA binding study using ethidium bromide. The intercalative mode of binding was suggested to be operative in all cases. Finally, computational studies employing DFT and TD-DFT were also carried out to interpret the experimentally observed absorption and emission bands of the complexes.

Ruthenium(ii) complexes with dppz: from molecular photoswitch to biological applications

The present article describes the recent advances in biological applications of the Ru-dppz systems in DNA binding, cellular imaging, anticancer drugs, phototherapy, protein aggregation detecting and chemosensors.

DNA-binding, topoisomerases I and II inhibition and in vitro cytotoxicity of ruthenium(II) polypyridyl complexes: [Ru(dppz)2L](2+) (L=dppz-11-CO2Me and dppz)

Two ruthenium(II) polypyridyl complexes, [Ru(dppz)2dppz-11-CO2Me](ClO4)2 (Ru1) and [Ru(dppz)3](ClO4)2 (Ru2), have been synthesized and characterized. The spectral characteristics of Ru1 and Ru2 were investigated by fluorescence spectroscopy and revealed that both complexes were sensitive to solvent polarity. The binding properties of the two complexes towards calf-thymus DNA (CT-DNA) have been investigated by different spectrophotometric methods and viscosity measurements, indicating that both complexes bind to CT-DNA by means of intercalation, but with different binding affinities. Topoisomerase inhibition and DNA strand passage assay demonstrates that the two complexes are dual inhibitors of topoisomerases I and IIa. On the other hand, the cytotoxicity of both complexes has been evaluated by MTT assays and Giemsa staining experiments. The main results reveal that the ester functional group has a significant effect on the DNA-binding affinities and topoisomerases inhibition effects of Ru1 and Ru2, and further advance our knowledge on the DNA-binding and topoisomerase inhibition by Ru(II) complexes.

Strong DNA deformation required for extremely slow DNA threading intercalation by a binuclear ruthenium complex

DNA intercalation by threading is expected to yield high affinity and slow dissociation, properties desirable for DNA-targeted therapeutics. To measure these properties, we utilize single molecule DNA stretching to quantify both the binding affinity and the force-dependent threading intercalation kinetics of the binuclear ruthenium complex Δ,Δ-[μ‐bidppz‐(phen)₄Ru₂]⁴⁺ (Δ,Δ-P). We measure the DNA elongation at a range of constant stretching forces using optical tweezers, allowing direct characterization of the intercalation kinetics as well as the amount intercalated at equilibrium. Higher forces exponentially facilitate the intercalative binding, leading to a profound decrease in the binding site size that results in one ligand intercalated at almost every DNA base stack. The zero force Δ,Δ-P intercalation K_d is 44 nM, 25-fold stronger than the analogous mono-nuclear ligand (Δ-P). The force-dependent kinetics analysis reveals a mechanism that requires DNA elongation of 0.33 nm for association, relaxation to an equilibrium elongation of 0.19 nm, and an additional elongation of 0.14 nm from the equilibrium state for dissociation. In cells, a molecule with binding properties similar to Δ,Δ-P may rapidly bind DNA destabilized by enzymes during replication or transcription, but upon enzyme dissociation it is predicted to remain intercalated for several hours, thereby interfering with essential biological processes.

Tri- and tetra-nuclear polypyridyl ruthenium(ii) complexes as antimicrobial agents

Tri- and tetra-nuclear polypyridylruthenium(ii) complexes have been synthesised which exhibit high levels of antimicrobial activity.