Luminescent platinum(II) complexes with functionalized N-heterocyclic carbene or diphosphine selectively probe mismatched and abasic DNA

mer-M(CO)3(PNP)0/+ pincer complexes (M = W(0) or Re(I); PNP = 4,5-bis(diphenylphosphino)acridine): synthesis, spectroscopy and anti-Kasha emission

Two isoelectronic and isostructural W(0) and Re(I) complexes mer-W(CO)3(PNP) (1) and [mer-Re(CO)3(PNP)]Cl (2) (PNP = 4,5-bis(diphenylphosphino)acridine) were synthesized and characterized by X-ray diffraction, infrared, electronic absorption and emission spectroscopy, and cyclic voltammetry. Structures of these complexes show a metal center bonded to the pincer ligand and two axial CO and one equatorial CO ligands. DFT calculations showed that the LUMOs of both complexes are the lowest energy π* orbitals localized in the acridine part of the ligand. The HOMO of 1 is dominated by the dπ orbital of W(0) while the HOMO of 2 has a substantial contribution from the highest energy π orbital of the acridine ring. TD-DFT calculations were performed to assist assignment of the UV-vis absorption spectra. The UV-vis absorption spectrum of 1 shows a very low energy W → π* (acridine) metal-to-ligand-charge-transfer (MLCT) absorption band that ranges from visible (500 nm) to near-infrared (>900 nm) regions and an intense acridine π → π* absorption band at 410 nm. There is a blue-green window in the ∼450-500 nm range between the π → π* and W → π*(acridine) MLCT absorptions. The absorption spectrum of 2, dominated by intense π → π* absorptions, shows no distinct low energy MLCT band. Complex 1 is luminescent, displaying acridine-based ππ* fluorescence at 501 nm which is anti-Kasha as it is higher in energy than the lowest energy excited state.

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Metals in Cancer Research: Beyond Platinum Metallodrugs

The discovery of the medicinal properties of platinum complexes has fueled the design and synthesis of new anticancer metallodrugs endowed with unique modes of action (MoA). Among the various families of experimental antiproliferative agents, organometallics have emerged as ideal platforms to control the compounds' reactivity and stability in a physiological environment. This is advantageous to efficiently deliver novel prodrug activation strategies, as well as to design metallodrugs acting only via noncovalent interactions with their pharmacological targets. Noteworthy, another justification for the advance of organometallic compounds for therapy stems from their ability to catalyze bioorthogonal reactions in cancer cells. When not yet ideal as drug leads, such compounds can be used as selective chemical tools that benefit from the advantages of catalytic amplification to either label the target of interest (e.g., proteins) or boost the output of biochemical signals. Examples of metallodrugs for the so-called "catalysis in cells" are considered in this Outlook together with other organometallic drug candidates. The selected case studies are discussed in the frame of more general challenges in the field of medicinal inorganic chemistry.

Synergistic binding of actinomycin D and echinomycin to DNA mismatch sites and their combined anti-tumour effects

Combination cancer chemotherapy is one of the most useful treatment methods to achieve a synergistic effect and reduce the toxicity of dosing with a single drug. Here, we use a combination of two well-established anticancer DNA intercalators, actinomycin D (ActD) and echinomycin (Echi), to screen their binding capabilities with DNA duplexes containing different mismatches embedded within Watson-Crick base-pairs. We have found that combining ActD and Echi preferentially stabilised thymine-related T:T mismatches. The enhanced stability of the DNA duplex-drug complexes is mainly due to the cooperative binding of the two drugs to the mismatch duplex, with many stacking interactions between the two different drug molecules. Since the repair of thymine-related mismatches is less efficient in mismatch repair (MMR)-deficient cancer cells, we have also demonstrated that the combination of ActD and Echi exhibits enhanced synergistic effects against MMR-deficient HCT116 cells and synergy is maintained in a MMR-related MLH1 gene knockdown in SW620 cells. We further accessed the clinical potential of the two-drug combination approach with a xenograft mouse model of a colorectal MMR-deficient cancer, which has resulted in a significant synergistic anti-tumour effect. The current study provides a novel approach for the development of combination chemotherapy for the treatment of cancers related to DNA-mismatches.

Ligands for Abasic Site-containing DNA and their Use as Fluorescent Probes

Apurinic and apyrimidinic sites, also referred to as abasic or AP sites, are residues of duplex DNA in which one DNA base is removed from a Watson-Crick base pair. They are formed during the enzymatic repair of DNA and offer binding sites for a variety of guest molecules. Specifically, the AP site may bind an appropriate ligand as a substitute for the missing nucleic base, thus stabilizing the abasic site-containing DNA (AP-DNA). Notably, ligands that bind selectively to abasic sites may be employed for analytical and therapeutical purposes. As a result, there is a search for structural features that establish a strong and selective association of a given ligand with the abasic position in DNA. Against this background, this review provides an overview of the different classes of ligands for abasic site-containing DNA (AP-DNA). This review covers covalently binding substrates, namely amine and oxyamine derivatives, as well as ligands that bind to AP-DNA by noncovalent association, as represented by small heterocyclic aromatic compounds, metal-organic complexes, macrocyclic cyclophanes, and intercalator-nucleobase conjugates. As the systematic development of fluorescent probes for AP-DNA has been somewhat neglected so far, this review article contains a survey of the available reports on the fluorimetric response of the ligand upon binding to the AP-DNA. Based on these data, this compilation shall present a perspective for future developments of fluorescent probes for AP-DNA.

Luminescent and Photofunctional Transition Metal Complexes: From Molecular Design to Diagnostic and Therapeutic Applications

There has been emerging interest in the exploitation of the photophysical and photochemical properties of transition metal complexes for diagnostic and therapeutic applications. In this Perspective, we highlight the major recent advances in the development of luminescent and photofunctional transition metal complexes, in particular, those of rhenium(I), ruthenium(II), osmium(II), iridium(III), and platinum(II), as bioimaging reagents and phototherapeutic agents, with a focus on the molecular design strategies that harness and modulate the interesting photophysical and photochemical behavior of the complexes. We also discuss the current challenges and future outlook of transition metal complexes for both fundamental research and clinical applications.

DNA-Templated Modulation in the Photophysical Properties of a Fluorescent Molecular Rotor Auramine O by Varying the DNA Composition

This work delineates an integrative approach combining spectroscopic and computational studies to decipher the association-induced fluorescence properties of a fluorescent molecular rotor, viz., auramine O (AuO), after interacting with 20-mer duplex DNA having diverse well-matched base pairs. While exploring the scarcely explored sequence-dependent interaction mechanism of AuO and DNA, we observed that DNA could act as a conducive scaffold to the formation of AuO dimer through noncovalent interactions at lower molecular density. The photophysical properties of AuO depend on the nucleotide compositions as described from sequence-dependent shifting in the emission and absorption maxima. Furthermore, we explored such DNA base pair-dependent fluorescence spectral characteristics of AuO toward discriminating the thermodynamically most stable single nucleotide mismatch in a 20-mer sequence. Our results are interesting and could be useful in developing analogues with further enhanced emission properties toward mismatched DNA sequences.

Stepwise Access of Emissive Ir(III) Complexes Bearing a Multi-Dentate Heteroaromatic Chelate: Fundamentals and Applications

Three multi-dentate coordinated chelates LnH₂ (n = 1, 2, and 3), comprising a linked 1-(pyridin-2-yl)ethylbenzene and one pyrazolyl pyridine unit and showing either tridentate or tetradentate coordination modes, are successfully designed and synthesized. Dinuclear Ir(III) complexes [Ir(κ⁴-Ln)(μ-Cl)]₂ bearing tetradentate coordinated κ⁴-Ln chelate (2a, n = 1; 2b, n = 2; 2c, n = 3) were next obtained en route from the respective intermediate [Ir(κ³-LnH)Cl(μ-Cl)]₂ bearing the tridentate coordinated κ³-LnH chelate (1a, n = 1; 1b, n = 2; 1c, n = 3). Next, mononuclear Ir(III) complexes Ir(κ⁴-Ln)(thd) (3a, n = 1; 3b, n = 2; 3c, n = 3) with the tetradentate chelate were obtained upon treatment of 2 with 2,2,6,6-tetramethyl-3,5-heptanedione (thd)H in the presence of K₂CO₃. Concurrently, methylation of 2c in the presence of MeI and ⁿBu₄NCl afforded tridentate Ir(κ³-L3HMe)Cl₃ (4) and, next, can be converted to tetradentate Ir(κ⁴-L3Me)Cl₂ (5) by further cyclometalation and HCl elimination in refluxing diethylene glycol monoethyl ether solution. The Ir(III) complexes 3a, 4, and 5 were unambiguously identified using spectroscopic methods, together with single-crystal X-ray structural analyses on Ir(III) derivatives 3a, 4, and 5. Their photophysical and ,electrochemical properties and device fabrication properties were also investigated and compared with results from theoretical studies.

A computational scheme for evaluating the phosphorescence quantum efficiency: applied to blue-emitting tetradentate Pt(II) complexes

Phosphorescent organic light-emitting diodes (PhOLEDs) are leading candidates for displays or lighting technologies. Recently, blue phosphorescent tetradentate Pt(II) complexes have been attracting extensive attention due to their high phosphorescence quantum efficiency and numerous chemical structures on account of flexible ligand frames and modifications. Using quantum chemistry coupled with our thermal vibration correlation function (TVCF) formalism, we investigated the triplet excited state energy surface and the decay processes involving both direct vibrational relaxation and minimum energy crossing point (MECP) via the transition state (³TS) to the ground state (S₀) for 16 recently experimentally reported blue-emitting tetradentate Pt(II) emitters containing fused 5/6/6 metallocycles. We found that (i) in most cases, the direct vibrational relaxation deactivations dominated the triplet non-radiative decay because either the ³TS is too high or the MECP is not reachable. Hence, results from the TVCF formalism agreed well with the experiments for the phosphorescence quantum efficiency; (ii) only when both ³TS and MECP are low, for instance, for PtON1-oMe, deactivations via MECP dominated the triplet non-radiative decay.

Understanding the ancillary ligand effect on luminescent cyclometalated Ir(III) complex as a reporter for 2-acetylaminofluorene DNA(AAF-dG) adduct

Mutagenic agents such as aromatic amines undergo metabolic activation and produce DNA adducts at C8 position of guanine bases. N-2-acetylaminofluorene (AAF) generates different mutational outcomes when placed at G₁, G₂, and G₃ of a NarI sequence (-G₁G₂CG₃CC/T-). These outcomes are dictated by the conformations adopted by these adducts. Detection of such lesions is of considerable interest owing to their hazardous effects. Here, we report the synthesis of three cyclometalated [Ir(L)₂dppz]⁺ complexes (L = 2-phenylpyridine (ppy) 1; benzo[h]quinoline (bhq) 2; 2-phenylquinoline (pq) 3; dppz = dipyrido[3,2-a:2',3'-c]phenazine) and their interaction with AAF adducted NarI DNA. Remarkably, complexes 1 and 2 displayed dominant ³LC transition characteristic of polar environment despite binding to the adducted sites. On the other hand, complex 3 binds to NarI sequences and behaves as a luminescent reporter for AAF-modified DNA. The results reported here emphasize that molecular light switching phenomenon can be stimulated by switching ancillary ligands and might act as potential probes for covalent-DNA defects.

Dual-Emissive Tris-Heteroleptic Ruthenium Complexes: Tuning the DNA-Triggered Ratiometric Emission Response by Ancillary Ligands

Three tris-heteroleptic mononuclear Ru(II) complexes with dual fluorescence and phosphorescence-[Ru(dpma)(bpy)(phen)]²⁺ (1²⁺), [Ru(dpma)(bpy)(dppz)]²⁺ (2²⁺), and [Ru(dpma)(phen)(dppz)]²⁺ (3²⁺)-have been designed and used as ratiometric light-response probes for DNA, where dpma is di(pyrid-2-yl)(methyl)-amine, bpy is 2,2'-bipyridine, phen is 1,10-phenanthroline, and dppz is dipyridophenazine, respectively. Single crystals of complex 2(PF₆)₂ have been obtained and studied by X-ray analysis. The interactions of these complexes with different DNAs are investigated by means of spectroscopic methods, viscosity measurements, and molecular modeling. In the presence of calf thymus DNA, complexes 2(PF₆)₂ and 3(PF₆)₂ show the emergence of a new lower-energy phosphorescence emission band; meanwhile, the higher-energy fluorescence emission band is essentially unchanged, functioning as an intrinsic internal reference. These two complexes exhibit stronger preference for calf thymus DNA over single-strand DNA (d(A)₁₆ and d(C)₁₆). In contrast, no binding interaction between 1(PF₆)₂ and calf thymus DNA is observed. The intrinsic binding constants (K_b) of 2(PF₆)₂ and 3(PF₆)₂ with calf thymus DNA are determined to be (1.4 ± 0.4) × 10⁵ and (9.5 ± 0.15) × 10⁴ M^-1, respectively. In addition, these spectroscopic results are compared with those of the prototype complex [Ru(bpy)₂(dppz)]²⁺ (4²⁺), and density functional theory and time-dependent density functional theory calculations are employed to elucidate these experimental findings.

Platinum(II) N-heterocyclic carbene complexes arrest metastatic tumor growth

Vimentin is a cytoskeletal intermediate filament protein that plays pivotal roles in tumor initiation, progression, and metastasis, and its overexpression in aggressive cancers predicted poor prognosis. Herein described is a highly effective antitumor and antimetastatic metal complex [Pt^II(C^N^N)(NHC^2Bu)]PF₆ (Pt1a; HC^N^N = 6-phenyl-2,2'-bipyridine; NHC= N-heterocyclic carbene) that engages vimentin via noncovalent binding interactions with a distinct orthogonal structural scaffold. Pt1a displays vimentin-binding affinity with a dissociation constant of 1.06 µM from surface plasmon resonance measurements and fits into a pocket between the coiled coils of the rod domain of vimentin with multiple hydrophobic interactions. It engages vimentin in cellulo, disrupts vimentin cytoskeleton, reduces vimentin expression in tumors, suppresses xenograft growth and metastasis in different mouse models, and is well tolerated, attributable to biotransformation to less toxic and renal-clearable platinum(II) species. Our studies uncovered the practical therapeutic potential of platinum(II)‒NHC complexes as effective targeted chemotherapy for combating metastatic and cisplatin-resistant cancers.

Metal complexes as optical probes for DNA sensing and imaging

Transition and lanthanide metal complexes have rich photophysical properties that can be used for cellular imaging, biosensing and phototherapy. One of the applications of such luminescent compounds is the detection and visualisation of nucleic acids. In this brief review, we survey the recent literature on the use of luminescent metal complexes (including Re^I, Ru^II, Os^II, Ir^III, Pt^II, Eu^III and Tb^III) as DNA optical probes, including examples of compounds that bind selectively to non-duplex DNA topologies such as quadruplex, i-motif and DNA mismatches. We discuss the applications of metal-based luminescent complexes in cellular imaging, including time-resolved microscopy and super-resolution techniques. Their applications in biosensing and phototherapy are briefly mentioned in the relevant sections.

Differentiating a Least-Stable Single Nucleotide Mismatch in DNA Via Metal Ion-Mediated Base Pairing and Using Thioflavin T as an Extrinsic Fluorophore

Monitoring the DNA dynamics in solution has great potential to develop new nucleic acid-based sensors and devices. With spectroscopic approaches, both at the ensemble average and single-molecule resolution, this study is directed to differentiate a single nucleotide mismatch (SNM) via a metal ion-stabilized mismatched base-pairing (C-Ag⁺-C/C-Cu²⁺-T) (C = cytosine, T = thymine) and site-selective extrinsic fluorophore, specifically, Thioflavin T (ThT). This is the first approach of its kind where dynamic quantities like molecular diffusion coefficients and diffusion times have been utilized to distinguish the least-stable SNM (CC & CT) formed by the most discriminating nucleobase, specifically, cytosine in a 20-mer duplex DNA. Additionally, this work also quantifies metal ions (Ag⁺ and Cu²⁺) at lower concentrations using fluorescence correlation spectroscopy. Our results can provide greater molecular-level insights into the mismatch-dependent metal-DNA interactions and also illuminate ThT as a new fluorophore to monitor the dynamics involved in DNA-metal composites.

Chiral molecular imprinted sensor for highly selective determination of D-carnitine in enantiomers via dsDNA-assisted conformation immobilization

In this paper, a novel approach was established on the basis of a molecularly imprinted technique with the aid of double-stranded deoxyribonucleic acid (dsDNA) embedded in a molecularly imprinted polymer (MIP) membrane as a new functional unit with chiral recognition for highly specific chiral recognition. The chiral molecules were immobilized and anchored in the cavities of the MIP membrane on the basis of the three-dimensional structure of a molecule determined by the functional groups, spatial characterization of the cavities of MIPs, and the spatial orientation with dsDNA embedded in MIPs. D-carnitine was selected as an example of a chiral molecular template, which intercalated into dsDNA immobilized on the gold electrode surface to form dsDNA-D-carnitine complex, and then the complex was embedded in the MIP during electropolymerization. After elution, the stereo-selective cavities were obtained. Our findings have shown that AAAA-TTTT base sequence had high affinity for D-carnitine intercalation. Combined with the electrochemical detection method, MIP sensor was prepared. The selectivity of the MIP sensor to ultratrace D-carnitine was significantly improved; the sensor had remarkable stereo-selectivity and highly chiral specific recognition to D-carnitine, and L-carnitine with a concentration of 10,000 times D-carnitine did not interfere with the detection of D-carnitine in the assay of raceme. The sensor also exhibited high sensitivity to ultratrace D-carnitine determination with a linear response to the concentration of D-carnitine in the range of 3.0 × 10^-16 mol/L to 4.0 × 10^-13 mol/L, with a detection limit of 2.24 × 10^-16 mol/L. The mechanism of chiral recognition was studied, and result showed that apart from the recognition effect of imprinted cavities, dsDNA provided chiral selectivity to the spatial orientation of chiral molecules via the intercalation of chiral molecules with dsDNA and electrostatic interaction with groups of DNA base.

Interplay between Cellular Metabolism and the DNA Damage Response in Cancer

Metabolism is a fundamental cellular process that can become harmful for cells by leading to DNA damage, for instance by an increase in oxidative stress or through the generation of toxic byproducts. To deal with such insults, cells have evolved sophisticated DNA damage response (DDR) pathways that allow for the maintenance of genome integrity. Recent years have seen remarkable progress in our understanding of the diverse DDR mechanisms, and, through such work, it has emerged that cellular metabolic regulation not only generates DNA damage but also impacts on DNA repair. Cancer cells show an alteration of the DDR coupled with modifications in cellular metabolism, further emphasizing links between these two fundamental processes. Taken together, these compelling findings indicate that metabolic enzymes and metabolites represent a key group of factors within the DDR. Here, we will compile the current knowledge on the dynamic interplay between metabolic factors and the DDR, with a specific focus on cancer. We will also discuss how recently developed high-throughput technologies allow for the identification of novel crosstalk between the DDR and metabolism, which is of crucial importance to better design efficient cancer treatments.

In vivo anticancer activity of a rhodium metalloinsertor in the HCT116 xenograft tumor model

Mismatch repair (MMR) deficiencies are a hallmark of various cancers causing accumulation of DNA mutations and mismatches, which often results in chemotherapy resistance. Metalloinsertor complexes, including [Rh(chrysi)(phen)(PPO)]Cl₂ (Rh-PPO), specifically target DNA mismatches and selectively induce cytotoxicity within MMR-deficient cells. Here, we present an in vivo analysis of Rh-PPO, our most potent metalloinsertor. Studies with HCT116 xenograft tumors revealed a 25% reduction in tumor volume and 12% increase in survival with metalloinsertor treatment (1 mg/kg; nine intraperitoneal doses over 20 d). When compared to oxaliplatin, Rh-PPO displays ninefold higher potency at tumor sites. Pharmacokinetic studies revealed rapid absorption of Rh-PPO in plasma with notable accumulation in the liver compared to tumors. Additionally, intratumoral metalloinsertor administration resulted in enhanced anticancer effects, pointing to a need for more selective delivery methods. Overall, these data show that Rh-PPO inhibits xenograft tumor growth, supporting the strategy of using Rh-PPO as a chemotherapeutic targeted to MMR-deficient cancers.

Switch-on effect on conformation-specific arylamine-DNA adduct by cyclometalated Ir(III) complexes

Arylamines are known to form covalent-DNA adducts upon metabolic activation. These covalent adducts adopt different conformational attributes, viz., major groove (B), stacked (S), and minor groove (W), and lead to different types of mutations. The conformation depends on the flanking and next flanking bases at the 3' position of the adduct. Early detection of these conformations by simple probes is an ideal and challenging task. Here, we have reported two Ir(III)-based cyclometalated complexes, viz., [Ir(ppy)₂(imiphen)]⁺ (1) (ppy: 2-phenylpyridine; imiphen: 2-(1H-imidazol-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) and [Ir(ppy)₂(furphen)]⁺ (2) (furphen: 2-(furan-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) and its interaction with N-acetyl-2-aminofluorene-dG (AAF-dG). The sequences used in this work are NarI sequence (-CG₁G₂CG₃CX-) in which Gs are modified with AAF and X is either C or T. Luminescence studies reveal that the Ir(III) complexes bind to AAF-dG adduct with high specificity toward G₁ and G₃ compared to G₂ and unmodified control. The selectivity also depends on the next flanking base as cytosine favors G₃^AAF, while thymine favors G₁^AAF in complex 1 and vice versa for complex 2. The quenching studies confirm that Ir(III) complexes bind with AAF-dG sequences through the minor groove. The outcome of this work reveals that the switch-on effect by the complexes can be utilized for determining the conformational heterogeneity of the adduct and also for similar covalent-DNA adducts.

Dinuclear metal complexes: multifunctional properties and applications

Dinuclear metal complexes have enabled breakthroughs in OLEDs, photocatalytic water splitting and CO₂reduction, DSPEC, chemosensors, biosensors, PDT and smart materials.

Cooperative recognition of T:T mismatch by echinomycin causes structural distortions in DNA duplex

Small-molecule compounds that target mismatched base pairs in DNA offer a novel prospective for cancer diagnosis and therapy. The potent anticancer antibiotic echinomycin functions by intercalating into DNA at CpG sites. Surprisingly, we found that the drug strongly prefers to bind to consecutive CpG steps separated by a single T:T mismatch. The preference appears to result from enhanced cooperativity associated with the binding of the second echinomycin molecule. Crystallographic studies reveal that this preference originates from the staggered quinoxaline rings of the two neighboring antibiotic molecules that surround the T:T mismatch forming continuous stacking interactions within the duplex. These and other associated changes in DNA conformation allow the formation of a minor groove pocket for tight binding of the second echinomycin molecule. We also show that echinomycin displays enhanced cytotoxicity against mismatch repair-deficient cell lines, raising the possibility of repurposing the drug for detection and treatment of mismatch repair-deficient cancers.

FeII4L4 Tetrahedron Binds to Nonpaired DNA Bases

A water-soluble self-assembled supramolecular Fe^II₄L₄ tetrahedron binds to single stranded DNA, mismatched DNA base pairs, and three-way DNA junctions. Binding of the coordination cage quenches fluorescent labels on the DNA strand, which provides an optical means to detect the interaction and allows the position of the binding site to be gauged with respect to the fluorescent label. Utilizing the quenching and binding properties of the coordination cage, we developed a simple and rapid detection method based on fluorescence quenching to detect unpaired bases in double-stranded DNA.

Synthesis, structure and density functional theory calculations of a novel photoluminescent trisarylborane-bismuth(III) complex

A novel trisarylborane-Bi(III) complex, tris(4-(dimesitylboryl)phenyl)bismuthine [Bi(PhBMes₂ )₃ ], in which (Ph = phenyl, and Mes = mesityl), was synthesized via the reaction of bismuth (III) chloride (BiCl₃ ) with three equivalents of lithiated (4-bromophenyl)- dimesitylborane [BrPhBMes₂ ]. The new trisarylbismuthine was characterized by elemental analysis, ultraviolet-visible (UV-vis) spectroscopy, and NMR (¹ H and ¹³ C) spectroscopy. The molecular structure of Bi(PhBMes₂ )₃ in the solid state was determined using single-crystal X-ray diffraction analysis, which showed short intermolecular C-H···H-C contact. The complex is a fluorescent emitter (λ_max  = 395 nm) at room temperature and a phosphorescent emitter (λ_max  = 423 nm) at 77 K, which displayed a long lifetime of 495 ms. The UV-vis transitions were investigated using density function theory (DFT) and time-dependent (TD)-DFT calculations. Natural bond orbital analysis showed that the bismuth (III) center was mainly Lewis acidic in nature.

Cellular Target of a Rhodium Metalloinsertor is the DNA Base Pair Mismatch

Defects in DNA mismatch repair (MMR) are commonly found in various cancers, especially in colorectal cancers. Despite the high prevalence of MMR-deficient cancers, mismatch-targeted therapeutics are limited and diagnostic tools are indirect. Here, we examine the cytotoxic properties of a rhodium metalloinsertor, [Rh(phen)(chrysi)(PPO)]²⁺ (RhPPO) in 27 diverse colorectal cancer cell lines. Despite the low frequency of genomic mismatches and the non-covalent nature of the RhPPO-DNA lesion, RhPPO is on average five times more potent than cisplatin. Importantly, the biological target and profile for RhPPO differs from that of cisplatin. A fluorescent metalloinsertor, RhCy3, was used to demonstrate that the cellular target of RhPPO is the DNA mismatch. RhCy3 represents a direct probe for MMR-deficiency and correlates directly with the cytotoxicity of RhPPO across different cell lines. Overall, our studies clearly indicate that RhPPO and RhCy3 are promising anticancer and diagnostic probes for MMR-deficient cancers, respectively.

Selective recognition of DNA defects by cyclometalated Ir(iii) complexes

Three different cyclometalated Ir(iii) complexes selectively bind to DNA defects.

Fluorescent organometallic rhodium(I) and ruthenium(II) metallodrugs with 4-ethylthio-1,8-naphthalimide ligands: Antiproliferative effects, cellular uptake and DNA-interaction

Fluorescent 4-ethylthio-1,8-naphthalimides containing rhodium(I) N-heterocyclic carbene (NHC) and ruthenium (II) NHC fragments were synthesised and evaluated for their antiproliferative effects, cellular uptake and DNA-binding activity. Both types of organometallics triggered ligand dependent efficient cytotoxic effects against tumor cells with the rhodium(I) NHC derivatives causing stronger effects than the ruthenium (II) NHC analogues. Antiproliferative effects could also be observed against several pathogenic Gram-positive bacterial strains, whereas the growth of Gram-negative bacteria was not substantially affected. Cellular uptake was confirmed by atomic absorption spectroscopy as well as by fluorescence microscopy indicating a general ligand dependent accumulation in the cells. An in-depth study on the interaction with DNA confirmed insertion of the naphthalimide moiety between the planar bases of B-DNA via an intercalation mechanism, as well as its stacking on top of the quartets of G-quadruplex structures. Furthermore, additional coordinative binding of the organometallic complexes to the model DNA base 9-ethylguanine could be detected. The studied compounds thus represent promising bioorganometallics featuring strong pharmacological effects in combination with excellent cellular imaging properties.

Protein staining agents from low toxic platinum(ii) complexes with bidentate ligands

Low toxic platinum(ii) complexes with bidentate ligands have been developed as novel protein staining agents.

A Rhodium-Cyanine Fluorescent Probe: Detection and Signaling of Mismatches in DNA

We report a bifunctional fluorescent probe that combines a rhodium metalloinsertor with a cyanine dye as the fluorescent reporter. The conjugate shows weak luminescence when free in solution or with well matched DNA but exhibits a significant luminescence increase in the presence of a 27-mer DNA duplex containing a central CC mismatch. DNA photocleavage experiments demonstrate that, upon photoactivation, the conjugate cleaves the DNA backbone specifically near the mismatch site on a 27-mer fragment, consistent with mismatch targeting. Fluorescence titrations with the 27-mer duplex containing the CC mismatch reveal a DNA binding affinity of 3.1 × 106 M-1, similar to that of other rhodium metalloinsertors. Fluorescence titrations using genomic DNA extracted from various cell lines demonstrate a clear discrimination in fluorescence between those cell lines that are proficient or deficient in mismatch repair. This differential luminescence reflects the sensitive detection of the mismatchrepair-deficient phenotype.

A Ruthenium(II) Complex as a Luminescent Probe for DNA Mismatches and Abasic Sites

[Ru(bpy)₂(BNIQ)]²⁺ (BNIQ = Benzo[c][1,7]naphthyridine-1-isoquinoline), which incorporates the sterically expansive BNIQ ligand, is a highly selective luminescent probe for DNA mismatches and abasic sites, possessing a 500-fold higher binding affinity toward these destabilized regions relative to well-matched base pairs. As a result of this higher binding affinity, the complex exhibits an enhanced steady-state emission in the presence of DNA duplexes containing a single base mismatch or abasic site compared to fully well-matched DNA. Luminescence quenching experiments with Cu(phen)₂²⁺ and [Fe(CN)₆]^3– implicate binding of the complex to a mismatch from the minor groove via metalloinsertion. The emission response of the complex to different single base mismatches, binding preferentially to the more destabilized mismatches, is also consistent with binding by metalloinsertion. This work shows that high selectivity toward destabilized regions in duplex DNA can be achieved through the rational design of a complex with a sterically expansive aromatic ligand.

The luminescent complex [Ru(bpy)₂(BNIQ)]²⁺ selectivity targets mismatched and abasic sites in duplex DNA and exhibits an enhanced emission intensity in the presence of these defect sites relative to well-matched base pairs.