Molecular Light Switch Research Articles

Highly Reversible Supramolecular Light Switch for NIR Phosphorescence Resonance Energy Transfer.

Although purely organic room‐temperature phosphorescence (RTP) has drawn widespread attention in recent years, regulatable phosphorescence resonance energy transfer (PRET) supramolecular switch is still rare. Herein, single molecular dual‐fold supramolecular light switches, which are constructed by phenylpyridinium salts modified diarylethene derivatives (DTE‐Cn, n = 3, 5) and cucurbit[8]uril (CB[8]) are reported. Significantly, biaxial [3]pseudorotaxane displayed efficiently reversible RTP after binding with CB[8] and the phosphorescence quenching efficiency is calculated up to be 99%. Furthermore, the binary supramolecular assembly can coassemble with Cy5 to form ternary supramolecular assembly showing efficiently PRET, which is successfully applied in switchable near infrared (NIR) mitochondria‐targeted cell imaging and photocontrolled data encryption. This supramolecular strategy involving energy transfer provides a convenient approach for phosphorescent application in biology and material fields.

Substituent effects on the interactions of ruthenium(II) polypyridyl complexes [Ru(bpy)2(6-R-dppz)]2+ (R = hydroxy and fluorine) with the RNA triplex poly(rU)·poly(rA) × poly(rU)

Two new ruthenium(II) polypyridyl complexes, [Ru(bpy)2(6-OH-dppz)]2+ (Ru1, bpy = 2,2′-bipyridine, 6-OH-dppz = 6-hydroxydipyrido[3,2-a:2′,3′-c]phenazine) and [Ru(bpy)2(6-F-dppz)]2+ (Ru2, 6-F-dppz = 6-fluorodipyrido[3,2-a:2′,3′-c]-phenazine), have been synthesized and characterized in this work. The interactions of Ru1 and Ru2 with the RNA triplex poly(rU)·poly(rA) × poly(rU) have been investigated by spectroscopic and viscometric techniques. Spectral titrations and viscosity experiments show that the binding modes of Ru1 and Ru2 to the triplex are intercalation, with the binding affinity for Ru2 being greater than that for Ru1. Fluorescence titrations indicate that Ru2, unlike Ru1, can act as a “molecular light switch” for the triplex. Furthermore, thermal denaturation experiments suggest that Ru1 and Ru2 stabilize the Hoogsteen base-paired strand (third-strand) of the triplex without significant differences, while the two complexes exhibit different selective stabilizing effects toward the triplex. In contrast to Ru1, Ru2 shows a preference for stabilizing the template duplex under the conditions used in this study. Results of the present work demonstrate that the electronic effects of substituents on the main ligands can significantly affect the binding and stabilization effects of Ru(II) polypyridyl complexes toward the RNA triplex poly(rU)·poly(rA) × poly(rU).

Synthesis and Characterization of Ru(II) Polypyridyl Complexes with 2-(4-Methylbenzoate)-1H-imidazo[4,5-f][1,10]phenantroline Ligand, and Their DNA Binding, Photocleavage, Physico-Chemical Properties, and Cytotoxicity

In search for efficient chemotherapeutic agents, we have synthesized a novel MBIP 2-(4-methylbenzoate)-1H-imidazo[4,5-f][1,10]phenantroline and its Ru(II) polypyridyl complexes of the general formula [Ru(N–N)2(L)]2+ (where N–N = phen (1,10-phenanthroline), bpy (2,2ʹ-bipyridine), dmb (4,4ʹ-dimethyl-2,2ʹ-bipyridine), and L = MBIP. All complexes have been characterized by analytical and spectroscopic methods. Physico-chemical properties of the synthesized complexes such as stability and lipophilicity have been studied. Interaction of Ru(II) complexes with calf-thymus DNA (CT-DNA) has been explored by different spectrophotometric methods. Spectral and viscosity data indicate that all the complexes are probably involved in intercalative binding with DNA. These complexes can cleave pBR322 DNA efficiently via oxidative pathway involving singlet oxygen under photoirradiation. The DNA molecular light switch on and off performance of Ru(II) complexes has been studied. According to antimicrobial activity assays the complexes are potential agents against gram positive and gram negative bacteria. In vitro cytotoxicity has been evaluated by MTT assay against HeLa cell lines, being compared to cisplatin. The live cell imaging and lipophilicity results have revealed that the complexes can possibly cross the cell membranes and accumulate in the nucleus. The cellular localization of Ru(II) complexes determined by their lipophilicity can probably affect their anticancer efficacy and mechanism of action.

Tris-heteroleptic ruthenium(II) polypyridyl complexes: Synthesis, structural characterization, photophysical, electrochemistry and biological properties

Three water-soluble tris-heteroleptic ruthenium(II) polypyridyl complexes [Ru(bpy)(phen)(bpg)]2+ (1), [Ru(bpy)(dppz)(bpg)]2+ (2), and [Ru(phen)(dppz)(bpg)]2+ (3) (where bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2′,3′-c] phenazine, bpg = 4b,5,7,7a-tetrahydro-4b,7a-epiminomethanoimino-6H-imidazo[4,5-f] [1,10] phenanthroline-6,13-dione) have been synthesized and characterized. Molecular structures of complexes 1 and 3 are confirmed by single crystal X-ray structure determination. Interaction of complexes 1–3 with DNA is explored by various spectroscopic techniques. The complexes 1–3 show solvent dependent photophysical properties. Complexes 2 and 3 show extensive “molecular light switch” effect for DNA. The complexes 1–3 are low toxic towards HeLa (human cervical cancer) and HL-60 (human promyelocytic leukemia) cell lines. Further, the cellular uptake of complexes 2 and 3 by cells shows that complexes mainly localised on the nucleus of the cells.

Light-induced complex formation of bacteriophytochrome RpBphP1 and gene repressor RpPpsR2 probed by SAXS.

Bacteriophytochrome proteins (BphPs) are molecular light switches that enable organisms to adapt to changing light conditions through the control of gene expression. Canonical type 1 BphPs have histidine kinase output domains, but type 3 RpBphP1, in the bacterium Rhodopseudomonas palustris (Rps. palustris), has a C terminal PAS9 domain and a two‐helix output sensor (HOS) domain. Type 1 BphPs form head‐to‐head parallel dimers; however, the crystal structure of RpBphP1ΔHOS, which does not contain the HOS domain, revealed pseudo anti‐parallel dimers. HOS domains are homologs of Dhp dimerization domains in type 1 BphPs. We show, by applying the small angle X‐ray scattering (SAXS) technique on full‐length RpBphP1, that HOS domains fulfill a similar role in the formation of parallel dimers. On illumination with far‐red light, RpBphP1 forms a complex with gene repressor RpPpsR2 through light‐induced structural changes in its HOS domains. An RpBphP1:RpPpsR2 complex is formed in the molecular ratio of 2 : 1 such that one RpBphP1 dimer binds one RpPpsR2 monomer. Molecular dimers have been modeled with Pfr and Pr SAXS data, suggesting that, in the Pfr state, stable dimeric four α‐helix bundles are formed between HOS domains, rendering RpBphP1functionally inert. On illumination with light of 760 nm wavelength, four α‐helix bundles formed by HOS dimers are disrupted, rendering helices available for binding with RpPpsR2.

Design of an Ultrafast G Protein Switch Based on a Mouse Melanopsin Variant.

The primary goal of optogenetics is the light-controlled noninvasive and specific manipulation of various cellular processes. Herein, we present a hybrid strategy for targeted protein engineering combining computational techniques with electrophysiological and UV/visible spectroscopic experiments. We validated our concept for channelrhodopsin-2 and applied it to modify the less-well-studied vertebrate opsin melanopsin. Melanopsin is a promising optogenetic tool that functions as a selective molecular light switch for G protein-coupled receptor pathways. Thus, we constructed a model of the melanopsin Gq protein complex and predicted an absorption maximum shift of the Y211F variant. This variant displays a narrow blue-shifted action spectrum and twofold faster deactivation kinetics compared to wild-type melanopsin on G protein-coupled inward rectifying K+ (GIRK) channels in HEK293 cells. Furthermore, we verified the in vivo activity and optogenetic potential for the variant in mice. Thus, we propose that our developed concept will be generally applicable to designing optogenetic tools.

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.

Conformation Specific Binding of [Ru(phen)2(dppz)]2+ with Mono‐ and Cluster Arylamine‐DNA Adducts

AbstractThe development of any probe to detect cluster adducts requires an in depth understanding on the binding affinity of probes to these adducts. In this context, we attempted to study the interaction of known DNA molecular switch [Ru(phen)2(dppz)]2+ with mono‐ and cluster DNA adducts in 16‐mer NarI sequence (5′‐CTCTCG1G2CG3CCATCAC‐3′) where guanine bases are modified with N‐acetyl‐2‐aminofluorene(AAF). Luminescence studies show that [Ru(phen)2(dppz)]2+ (phen: 1,10‐phenanthroline and dppz: dipyrido[3,2‐a:2′,3′‐c]phenazine) binds to AAF adduct at G1 and G3 which possesses minor‐groove(W) and stacked conformation(S) exhibit two fold enhancement while G2 with major groove B‐conformer exhibit 1.6 fold enhancement when compared to control. In diadducts, RuII binds to G2G3 AAF adduct lower than that of other two diadducts G1G3 and G1G2. With triadducts, phenazine moiety of RuII complex adopts canted geometry to the DNA due to the very unstable structure at the adducted site. From microscale thermophoretic data, the kd of RuII was determined and found to be consistent with luminescence data. The present study provides an overall insight of role of conformation of AAF structure embedded in different sequence context that dictates the sensitivity of the DNA molecular light switch, in turn, facilitates in developing highly efficient probe to distinguish these cluster adducts.

Ultrafast in cellulo photoinduced dynamics processes of the paradigm molecular light switch [Ru(bpy)2dppz]2+

An in cellulo study of the ultrafast excited state processes in the paradigm molecular light switch [Ru(bpy)2dppz]2+ by localized pump-probe spectroscopy is reported for the first time. The localization of [Ru(bpy)2dppz]2+ in HepG2 cells is verified by emission microscopy and the characteristic photoinduced picosecond dynamics of the molecular light switch is observed in cellulo. The observation of the typical phosphorescence stemming from a 3MLCT state suggests that the [Ru(bpy)2dppz]2+ complex intercalates with the DNA in the nucleus. The results presented for this benchmark coordination compound reveal the necessity to study the photoinduced processes in coordination compounds for intracellular use, e.g. as sensors or as photodrugs, in the actual biological target environment in order to derive a detailed molecular mechanistic understanding of the excited-state properties of the systems in the actual biological target environment.

SYNTHESIS, CHARACTERIZATION AND DNA BINDING ACTIVITY OF A POTENTIAL DNA INTERCALATOR

A novel complex, [Ru(dppz)2(p-MOPIP)]2+ (dppz = dipyrido-[3,2-a:20,30-c]phenazine, p-MOPIP = 2-(4-methoxyphenyl) imidazo[4,5-f][1,10]phenanthroline) has been synthesized and characterized by elemental analysis, 1H Nuclear Magnetic Resonance spectroscopy, mass spectrometry, Fourier Transform Infrared analysis, Ultra Violet visible and fluorescence spectroscopy. Herein, the complex was designed by adding p-MOPIP as an intercalating ligand and dppz as the ancillary ligand. The DNA binding properties of the complex with Calf Thymus DNA (CT-DNA) were investigated using spectroscopic methods. The UV-visible absorption band observed at 460 nm corresponded to the metal-to-ligand charge transfer (MLCT) while bands at 358 and 281 nm corresponded to intra-ligand (IL) π-π* transitions of the ligand scaffold in p-MOPIP and dppz. The intrinsic binding constant, Kb for this complex was 1.67 x 106 M-1 and this suggested that this complex, [Ru(dppz)2(p-MOPIP)]2+ bound to DNA via the intercalative mode. Interestingly, the interaction of this complex with CT-DNA also had a ‘molecular light switch’ effect.

A novel, label-free fluorescent aptasensor for cocaine detection based on a G-quadruplex and ruthenium polypyridyl complex molecular light switch

A [Ru(bpy)2(bqdppz)]2+ ligand with high selectivity towards G-quadruplex was synthesized and introduced to serve as a prominent molecular light switch via specifically recognizing the cocaine aptamer-involved G-quadruplex.

PH and DNA luminescence switching, DNA photocleavage and cytotoxic properties of two thiophene-containing ruthenium(II) complexes

Two new Ru(II) complexes, [Ru(Htip)3]Cl2 (1) and [Ru(Htip)2(dppz)]Cl2 (2), were synthesised and were characterised. The ground- and excited-state acid–base properties of 1 and 2 were studied and demonstrated that 1 acted as a pH-induced “on–off–on” luminescence switch. The binding behaviours of 1 and 2 to calf thymus DNA were studied with absorption and emission spectroscopy, DNA viscosities and density functional theory calculations. 2 was found to act as a DNA molecular light switch and as an efficient photocleaver of pUC 18 DNA. The cytotoxicities of the complexes were evaluated with the MTT method and it was found that 1 displayed apparent anticancer activity against MCF-7 cell, whereas 2 exhibited more potent and wider-spectrum antitumor activities against all cancer cell lines tested.

基于钌多吡啶类配合物的DNA分子光开关及生物传感研究

There is a great interest in the development of small molecules that can target and regulate DNA. In this review, we summarize the recent development of DNA molecular light switch based on ruthenium(Ⅱ) polypyridyl complexes, which include the principle of DNA molecular light switch, light switch of different DNA conformations as well as the methods of cycling the switch. The application of ruthenium(Ⅱ) polypyridyl complexes for label-free DNA-based sensing is highlighted too.

Label-free fluorescent DNA sensor for the detection of silver ions based on molecular light switch Ru complex and unmodified quantum dots

Using molecular light switch Ru complex Ru(bpy)(2)(dppz)(2+) and CdTe quantum dots (QDs), we have designed a label-free DNA fluorescent sensor for the detection of Ag(+) in aqueous solution.

Indication of critical micelle concentration of nonionic surfactants with large emission change using water-soluble conjugated polymer as molecular light switch

A new near-infrared water-soluble conjugated polymer, i.e. poly [2,5-di (propyloxysulfonate)-1,4-phenylene-ethynylene-9,10-anthrylene] (PPEASO3) was synthesized to investigate its interaction with surfactants. It was found that PPEASO3 has only a weak fluorescence emission at about 670nm due to its self-aggregation in water and in aqueous solution containing a low concentration of nonionic surfactants, i.e. below their critical micelle concentration (CMC). However, a dramatic fluorescence enhancement with a large emission blue-shift (>40nm) was found once the concentration of nonionic surfactants reached the CMC (especially for Triton X-100). An orange fluorescence could be observed even with naked-eyes under UV-lamp, which gave a direct indication for the micelle forming process and provided a simple method for the CMC determination of the nonionic surfactants. The CMC values determined by this method were in good agreement with those obtained by other techniques. The dramatic emission change observed could be ascribed to the intensive hydrophobic interaction between PPEASO3 and surfactants micelle, which greatly disrupts the aggregation of the polymer and increase the fluorescence efficiency of PPEASO3.

Synthesis, characterization and DNA-binding characteristics of Ru(II) molecular light switch complexes

A series of four polypyridyl Ru(II) complexes such as [Ru(L)4(PIP)]2+ and [Ru(L)4PPIP]2+ where L is 4-amino pyridine and Pyridine (PIP = 2-phenylimidazo[4,5-f] [1, 10] phenanthroline), (PPIP = 2-(4′-phenoxy-phenyl) imidazo[4,5-][1, 10]phenanthroline) have been synthesized and characterized by elemental analysis, physicochemical methods such as UV–vis, IR and NMR spectroscopic techniques. The DNA-binding behavior of these complexes was investigated by electronic absorption titrations, fluorescence spectroscopy, viscosity measurements and salt-dependent studies. The experimental results indicate that all these complexes can bind to DNA through an intercalation mode, the DNA-binding affinities of these complexes follow the order [Ru(4-APy)4(PPIP)]2+(1) > [Ru(Py)4PPIP]2+(2) > [Ru(4-APy)4(PIP)]2+(3) > [Ru(Py)4PIP]2+(4). Noticeably, these complexes have been found to be efficient photosensitisers for strand scissions in plasmid DNA. Further, all four complexes screened for their antimicrobial activity indicate that the complexes show appreciable activity against Escherichia coli and Neurospora Crassa. In addition, in the presence of Co2+, the emission of DNA-[Ru(L4)PPIP/PIP]2+ can be quenched and recovered by the addition of EDTA, which exhibited the DNA “light switch” properties.

A new stable and reliable method for labeling nucleic acids of fully replicative viruses

Efficiently labeling nucleic acids of fully replicative viruses is a challenge. In this work, a 'molecular light switch' complex [Ru(phen)(2)(dppz)](2+), where phen = 1,10-phenanthroline and dppz = dipyrido[3,2-a:2',3'-c]phenazine, has been exploringly used to label vaccinia virus nucleic acid. The labeled virions exhibited strong and stable fluorescence and could be imaged at the single-virion level. Moreover, they were fully infectious and can be used to study the behaviors of invasion into their host cells. The method is general and suitable for labeling various DNA viruses.

A molecular light switch Ru complex and quantum dots for the label-free, aptamer-based detection of thrombin

A simple, label-free method for the detection of thrombin has been developed based on the conformational transition of aptamer in the presence of the target by using a molecular light switch, Ru polypyridine complex, and quantum dots as novel fluorescence probes in aqueous solution.

Pushing the limit: synthesis, photophysical and DNA binding studies of a NIR-emitting Ru(ii)-polypyridyl probe with ‘light switch’ behaviour

The new Ru(II) polypyridyl complex 1 was synthesised using microwave irradiation from the new polypyridyl ligand 2'DipyTAP', and its photophysical properties, and DNA binding abilities were investigated using various spectroscopic techniques; and 1 was shown to act as a 'NIR molecular light switch' for DNA with an emission window between 680 and 860 nm.

DNA-binding and photocleavage studies of ruthenium(II) complexes containing asymmetric intercalative ligand

A novel asymmetric ligand 2-(pyridine-2-yl)-1-H-imidazo[4,5-i]dibenzo[2,3-a:2′,3′-c]phenazine (pidbp) and its ruthenium complexes [Ru(L) 2(pidbp)] 2+ (L = bpy (2, 2′- bipyridine), phen (1, 10 – phenanthroline)), have been synthesized and characterized by elemental analysis, ES-MS, 1H NMR. Various methods support the conclusion that both Ru(II) complexes can intercalate into DNA base pairs. Complex [Ru(bpy) 2(pidbp)] 2+ 4 exhibits its DNA “molecular light switch” properties. Furthermore, the two complexes are efficient DNA-photocleavers under irradiation at 365 nm, and complex 5 exhibits a stronger DNA-photocleavage efficiency than complex 4. The mechanism of DNA cleavage is an oxidative process by generating singlet oxygen.