Luminescence Titrations Research Articles

Photophysical and Chiroptical Properties of the Enantiomers of N,N'-Bis(1-phenylpropyl)-2,6-pyridinecarboxamide and their Chiral 9-Coordinate Ln3+ Complexes.

The R,R and S,S enantiomers of N,N'-bis(1-phenylpropyl)-2,6-pyridinedicarboxamide, L(Et), react with Ln3+ ions (Ln = La, Eu, Gd, and Tb) to give stable [Ln((R,R)- and (S,S)-L(Et))3]3+ in anhydrous acetonitrile solution, as evidenced by various spectroscopic measurements, including NMR and luminescence titrations. In addition to the characteristic Eu3+ and Tb3+ luminescence bands, the steady-state and time-resolved luminescence spectra of the aforementioned complexes show the residual ligand-centered emission of the 1ππ* to 3ππ* states, indicating an incomplete intersystem crossing (ISC) transfer from the 1ππ* to 3ππ* and ligand-to-Ln3+ energy transfer, respectively. The high circularly polarized luminescence (CPL) activity of [Eu(L(Et))3]3+ confirms that using a single enantiomer of L(Et) induces the preferential formation of one chiral [Eu(L(Et))3]3+ complex, consistent with the [EuL 3]3+ complexes formed with other ligands derived from a 2,6-pyridine dicarboxamide moiety. Furthermore, the CPL sign patterns of complexes with (R,R) or (S,S) enantiomer of L(Et) are consistent with the CPL sign pattern of related [LnL 3]3+ complexes with the (R,R) or (S,S) enantiomer of the respective ligands in this family.

Formation of Heteropolynuclear Lanthanide Complexes Using Macrocyclic Phosphonated Cyclam-Based Ligands.

Ligands L1 and L2, respectively based on a cyclam and a cross-bridged cyclam scaffold functionalized at N1 and N8 by 6-phosphonic-2-methylene pyridyl groups, are described. While complexation of lanthanide (Ln) cations with L2 was not possible, a family of complexes has been prepared with L1, of the general formulae [LnL1H2]Cl (Ln3+ = Lu, Tb, Yb) or [LnL1H] (Ln3+ = Eu). The solution, structural, potentiometric, and photophysical data for these novel ligands and their complexes have been investigated, including a solid-state study by X-ray diffraction (L1, L2, and [EuL1H]), 1H NMR complexation investigations (Lu3+), as well as UV-vis absorption and luminescence spectroscopy in water and D2O (pH ≈ 7). L1 forms 1:1 metal-ligand stoichiometric octadentate complexes in solution. Importantly, the pyridyl phosphonate functions are capable of simultaneous chelation to the metal center and of interaction with a second metal center. 1H NMR (Lu3+) and spectrophotometric titrations of the isolated [TbL1]- complex by EuCl3 salts demonstrated the formation of high-order (hetero)polymetallic species in aqueous solution (H2O, pH = 7). Global analysis of the luminescence titration experiment points to the formation of 4:1, 3:1, and 3:2 [TbL1]/Eu heteropolynuclear assemblies, exhibiting a strong preference to forming [TbL1]3Eu2 at increased europium concentrations, with energy transfer occurring between the kinetically inert terbium complex and added europium cations.

Combined Experimental and Density Functional Theoretical Studies of Am3+ and Eu3+ Extraction and Complexation with Different Nitrilotriacetamide (NTA) Derivatives

AbstractN,N,N′,N′,N“,N”‐hexaalkylnitrilotriacetoamide (HRNTA) derivatives were found to be promising for the separation of trivalent actinides from lanthanides, which is a burning topic in the back end of the nuclear fuel cycle. In the present work, separation of Am3+ from Eu3+ was studied using the N,N,N’,N’,N’’,N’’‐hexa‐2‐ethylhexylnitrilotriacetamide (H2EHNTA) derivative and the role of the diluent medium to control the extractable complex was demonstrated. The effect of alkyl chain length and branching in the alkyl chain of different HRNTA (R=methyl, n‐butyl, n‐hexyl, n‐dodecyl and 2‐ethylhexyl) derivatives on their complexation with Eu3+ were investigated using steady‐state and time‐resolved luminescence studies. Different species formed at different ligand to metal ratios were identified from the luminescence titration experiments and their lifetime values measured. The experimental results were corroborated with the help of density functional theoretical (DFT) calculations on Am3+ and Eu3+ complexes of HRNTA derivatives with varying alkyl chain length and branching.

Syntheses, crystal structures, dye degradation and luminescence sensing properties of four coordination polymers

Four coordination polymers based on the pyridyl-carboxyl ligand have been solvothermally synthesized and characterized. The heterogeneous catalytic oxidation activities of 1–3 and luminescence titration experiments for 4 have been studied.

Synthesis, Characterization and Biological Studies of Nickel ( Ii) and Zinc ( Ii) Complexes with Mono - and Di - Bromo Substituted Schiff Base Ligands

Transition metal complexes of nickel(II) and zinc(II) with 5-bromo- N -(8-quinolyl)salicylaldimine (HqsalBr, HL 1 ) and 3,5-dibromo- N -(8-quinolyl)salicylaldimine (HqsalBr 2 , HL 2 ) have been synthesized and successfully characterized using several techniques: IR, 1 H-NMR, mass spectrometry and thermogravimetric analysis (TGA). The molecular structures of nickel(II) and zinc(II) complexes with HL 2 were determined by single crystal X-Ray crystallography. Ligands HL 1 and HL 2 both act as a tridentate ligand and coordinate to metal ion center via deprotonated hydroxyl oxygen atom, nitrogen of azomethine functional group and nitrogen of quinoline substituent. The interaction of these complexes with DNA was investigated using calf thymus DNA (CT-DNA) in which the studies by electronic absorption and luminescence titrations reveal that DNA binding mode of the complexes is intercalation. All the synthesized complexes provide great values of binding constant (K b ) and these results are consistent with the quenching capability defined by quenching constant values (K q ). Amongst the synthesized complexes, zinc(II) with ligand HL 2 complex, [Zn(qsalBr) 2 ], exhibits the most superior ability in the interaction with CT-DNA and the verification mode of binding by the competitive reaction with ethidium bromide (EB) also indicates the strongest intercalation by such complex. Additionally, ligands and complexes were also examined in anti-lung cancer activity against A549 cell line and compared with standard compounds, Etoposide and Cisplatin.

INDUCTION OF C-MYC G-QUADRUPLEX DNA AND CYTOTOXICITY OF A CALIX[]ARENE-CONTAINING BINUCLEAR RUTHENIUM(II) COMPLEX

Herein, a binuclear ruthenium(II) complex modified by calix[4]arene group has been prepared. The complex as potential inducer and stabilizer of c-myc G-quadruplex DNA and antitumor reagent were studied. Observations revealed that the complex could bind to c-myc Pu27 and Pu22 DNA strongly with constants of 1.18 × 107 (Pu27) and 4.13 × 106 M-1 (Pu22) via groove mode as determined from absorption and luminescence titrations, as well as CD spectra. Results of continuous variation analysis confirmed that the complex interacted with c-myc G-quadruplex DNA through a 1:1 binding stoichiometry. As verified by PCR-stop assay, the replication of c-myc DNA was effectively blocked by the complex with the complete inhibition at the complex concentration of 4.0 μM both for Pu27 and Pu22, suggesting that the complex could efficiently induce the formation of c-myc G-quadruplex DNA. The appearance of blue TMB solution in the visual experiment also proved that the sequences of Pu27 and Pu22 could fold into G-quadruplex under the induction of the complex. Nevertheless, the complex was found to exhibit weak stabilization ability on c-myc G-quadruplex DNA according to FRET assay, which increased the melting point of c-myc DNA only 3-3.5 °C. The experiments on Topoisomerase inhibition and cytotoxicity of the complex showed that it acted as an inhibitor of TopoI and exhibited moderate anticancer activity against MCF-7 and Huh-7 tumor cells.

One Metal-Organic Framework with one open nitrogen site as luminescence detections for Fe3+ and Cr2O72-

One new Cd-based Metal-Organic Framework (MOF), {[Cd(cpnc)(H2O)]}n (1), has been synthesized and characterized based on a bidentate carboxylate ligand, H2cpnc, (H2cpnc = (6-(4-carboxyphenyl) nicotinic acid). The Cd cations were connected by cpnc2− ligands to form a rare 6-c rob 3D network. In addition, the effects of different organic reagents and ions on the fluorescence properties of the compound 1 have been studied. The luminescence titration experiments show that a significant quenching of fluorescence intensity can be observed after addition of Fe3+ and K2Cr2O7.

Toward MRI and Optical Detection of Zwitterionic Neurotransmitters: Near-Infrared Luminescent and Magnetic Properties of Macrocyclic Lanthanide(III) Complexes Appended with a Crown Ether and a Benzophenone Chromophore.

Thanks to their versatile magnetic and luminescence features, lanthanide complexes have gained a central position in biomedical imaging as magnetic resonance imaging (MRI) contrast agents and optical imaging probes. In addition, appropriate chemical design allows modification of the magnetic relaxation properties of GdIII complexes and the optical properties of visible- or near-infrared (NIR)-emitting lanthanide chelates upon interaction with various biomarkers, which makes them ideal candidates for the creation of responsive agents. In this Forum Article, we demonstrate such design principles as well as the difficulties encountered in the context of neurotransmitter (NT) detection. Lanthanide(III) complexes of a macrocyclic ligand incorporating a benzophenone chromophore and a monoazacrown ether (LnL3) have been synthesized as responsive probes to monitor amino acid NTs either in MRI (Ln = Gd) or in NIR optical detection (Ln = Nd or Yb). The parameters characterizing the water exchange and rotational dynamics of the gadolinium(III) complex were assessed by 17O NMR and 1H NMRD. In the presence of zwitterionic NTs, the inner-sphere water molecule is replaced by the carboxylate function of the NTs in the gadolinium(III) complex, leading to a decrease of the longitudinal relaxivity from 6.7 to 2-2.5 mM-1 s-1 (300 MHz and 37 °C). The apparent affinity constants range from Ka = 35 for γ-aminobutyric acid (GABA) to 80 M-1 for glycine and glutamate, and there is no selectivity with respect to hydrogen carbonate (Ka = 232; pH 7.4). The gadolinium(III) complex interacts with human serum albumin (HSA), resulting in a 60% increase in the relaxivity (20 MHz, 37 °C) in the absence of NTs. The HSA-bound complex, however, was revealed to be less responsive to NTs because of displacement of the GdIII-bound water by HSA, which was confirmed by the hydration number calculated from luminescence lifetimes of the HSA-bound europium(III) complex. The creation of an imaging agent suitable for NIR detection of NTs for an enhanced sensitivity in biological systems using the benzophenone (BP) moiety as the sensitizer of lanthanide luminescence was also attempted. Upon excitation at 300 nm of the BP chromophore in aqueous solutions of NdL3 and YbL3, characteristic NIR emissions of NdIII and YbIII were observed because of 4F3/2 → 4IJ (J = 9/2-13/2) and 2F5/2 → 2F7/2 transitions, respectively, indicating that this chromophore is a suitable antenna. Despite these promising results, luminescence titrations of NdIII and YbIII complexes with NTs were not conclusive because of chemical conversion of the ligand triggered by light, preventing quantitative analysis. The observed photochemical reaction of the ligand is strongly dependent on the nature of the lanthanide chelated; it is considerably slowed down in the presence of NdIII and EuIII.

Unfolding the complexation and extraction of Am3+ and Eu3+ using N-heterocyclic aromatic diphosphonic acids: a combined experimental and DFT study.

Phosphonate based ligands are well known for the extraction of 'f' block elements. Three N,O-donor N-heterocyclic aromatic diphosphonate ligands were evaluated in the present work for the extraction/separation studies of Am3+ and Eu3+. Complexation studies in aqueous medium using luminescence titration indicated the formation of anionic complexes in the case of Eu3+. Two phase liquid-liquid extraction studies were, therefore, carried out by employing Aliquat-336 as the liquid anion exchanger. The results indicated the formation of a species with a metal-ligand stoichiometry of 1 : 3 in the case of pyridine-2,6-diphosphonic acid (PyPOH). In the case of 2,2'-bipyridine-6,6'-diphosphonic acid (BipyPOH), however, a 1 : 2 complex was extracted and 1,10-phenanthroline-2,9-diphosphonic acid (PhenPOH) extracts the Am3+ and Eu3+ ions by forming both 1 : 2 and 1 : 3 complexes. Formation of these kinds of anionic complexes was further confirmed using electrospray ionization mass spectrometry (ESI-MS). DFT calculations predicted the structure of the anionic complexes. The non-selectivity of these kinds of ligands between Am3+ and Eu3+ was attributed to the presence of unfavorable covalent interactions in the metal-ligand bonds.

Ruthenium(II) polypyridyl complex [Ru(phen)2dppz-idzo]2+ as a colorimetric molecular "light switch" and powerful stabilizer for the RNA triplex poly(U)·poly(A)*poly(U).

The interaction of [Ru(phen)2dppz-idzo]2+ (phen = 1,10-phenanthroline, dppz-idzo = dppz-imidazolone) with triplex RNA poly(U)·poly(A)*poly(U) was carried out by using spectroscopic and viscometric techniques in this work. Luminescent titrations suggest that [Ru(phen)2dppz-idzo]2+ shows better selectivity for poly(U)·poly(A)*poly(U) compared with poly(U)·poly(A) and poly(U), this complex exhibits a "light switch" effect with an emission enhancement factor of about 123 in the presence of poly(U)·poly(A)*poly(U). Significantly, this "light switch" behavior could even be observed by the naked eye under irradiation with UV light. To our knowledge, [Ru(bpy)2dppz-idzo]2+ is the first small molecule able to serve as a colorimetric molecular "light switch" for the triplex poly(U)·poly(A)*poly(U). Combined with the spectral and viscometric results as well as [Ru(phen)2dppz-idzo]2+ stabilizing the template duplex poly(U)·poly(A), we speculate that [Ru(phen)2dppz-idzo]2+ prefers to bind with the Hoogsteen base-paired strand (the third strand) of the triplex, thus the intercalating [Ru(phen)2dppz-idzo]2+ stabilizing the third strand is more marked in comparison with the Watson-Crick base-paired duplex of the triplex. The results obtained here may be useful for understanding the interaction of triplex RNA poly(U)·poly(A)*poly(U) with small molecule, particularly ruthenium(II) complexes.

Mononuclear copper(II) complexes with 2-thiophene carboxylate and N-N donors; DNA interaction, antioxidant/anti-inflammatory and antitumor activity

Redox-active compounds such as copper-phenanthroline are known as artificial/chemical nucleases with a great impact and potential for their applications as metallotherapeutics. In that vein, the mononuclear copper(II) complexes [Cu(L)2(bipy)] (1), [Cu(L)2(bipy)(H2O)] (2) and [Cu(L)2(phen)(H2O)] (3), where L = 2-thiophene carboxylate, bipy = 2,2΄-bipyridine and phen = 1,10-phenanthroline, have been prepared and pharmacochemically studied, while the crystal structure of 1 is also reported. All the tested complexes preferably bind to CT-DNA via minor groove as resulted from UV spectroscopy studies, luminescent titration, EB competition assays and viscosity measurements. Complexes 2 and 3 in aqua behave like a “light switch” for DNA. The intensity enhancement, with the increase of DNA concentration, reached about 3–fold for 2 and 10-fold for 3. In vitro antioxidant activity of compounds 1–3, was evaluated using two different antioxidant assays: a) interaction with 1,1-diphenyl-2-picryl-hydrazyl (DPPH) stable free radical and b) inhibition of lipid peroxidation. Moreover, their inhibitory activity on soybean lipoxygenase (LOX) was evaluated for their anti-inflammatory potency. The tested complexes showed good activity on both lipid peroxidation and soybean LOX inhibition while complex 2 exhibited the best antioxidant/anti-inflammatory activity. A computational analysis over the LOX protein structure 1JNQ was performed, in an effort to support their possible mode of action. The cytotoxicity of the complexes was determined and their efficacy against several human cancer cell lines (ovarian, OAW-42; lung, A549; colon, HT29; breast, MDA-MB-231; kidney, Caki-2; and cervical, Hela) and human non-tumor cell lines (lung, MRC-5; and breast, MTSV1-7) were evaluated. The best cytotoxic activity was appeared for complex 3. In silico, computational methods support antiestrogen activity of the administered complexes on normal breast cells.

A water-soluble TbIII complex as a temperature-sensitive luminescent probe

The water soluble [Tb(dipicCbz)3]3− (dipicCbz = 4-(9H-carbazol-9-yl-)pyridine-2,6-dicarboxylato) complex was isolated and evaluated as a temperature sensor in water. The 1:3 (TbIII:dipicCbz2−) stoichiometry in solution was confirmed by luminescence titration and high-resolution mass spectrometry. The quantum yield of sensitized emission is 3.8% ± 0.4% at 25.0 ± 0.1 °C, and the emission intensity depends on the temperature in the range of 5–70 °C with a relative thermal sensitivity of 3.4% °C−1 at 35 °C and temperature resolution < 0.01 °C in the range of 30–40 °C. The reversibility of this behavior was demonstrated for three heating–cooling cycles. Calculations of the energy gap between donor and acceptor show that the temperature dependence of the emission intensity is due to back-energy transfer from the Tb 5D4 excited state to the triplet and twisted intramolecular charge transfer (TICT) states of the dipicCbz. The assignment of one of the energy levels as a TICT state was confirmed by the temperature-dependent behavior of the phosphorescence band.

A Cyclic‐RGD Dinuclear TbIII Macrocyclic Complex as a Tumor Integrin‐Selective Luminescent Probe

To develop small molecular integrin‐selective luminescent imaging probes, we have prepared the binary dipicolinate (DPA) TbIII dinuclear macrocyclic complex, Tb2(cRGDfK‐ODO2A‐dimer) (DPA)22– or complex I, and reference ligands and TbIII complexes which were purified by HPLC and characterized by NMR, mass spectrometry and luminescence spectroscopy. Luminescence titrations of the structural and bonding model Tb2(m‐ODO2A‐dimer)2+ complex by DPA2– ion confirmed the molecular formula of the adduct was Tb2(m‐ODO2A‐dimer)(DPA)22–, and the first binary binding constant was determined to be log K1 = 5.76. At pH 7.4, complex I showed 300 times luminescence enhancement at 544 nm (λex = 278 nm) as compared to that without adding DPA, and was found to bind to αvβ3 integrin and human glioblastoma U87MG tumor cells in both specific and non‐specific modes, via luminescence spectroscopic and confocal cell imaging competition studies. This makes complex I and its future optimized derivatives potentially feasible for preclinical bioimaging applications, particularly in the time‐resolved mode.

Multispectroscopic DNA-Binding studies and antimicrobial evaluation of new mixed-ligand Silver(I) complex and nanocomplex: A comparative study

A novel mixed-ligand Ag(I) complex, , has been synthesized and characterized by the elemental analysis, IR spectroscopy and 1HNMR. In the formula, dian and phen are N-(4,5-diazafluoren-9-ylidene)aniline and 1,10-phenanthroline, respectively. This complex also has been prepared at nano size by sonochemical technique and characterized by the FTIR and scanning electron microscopy (SEM). To evaluate the biological preferences of the Ag(I) complex and nanocomplex and verify the relationships between the structure and biological function, in vitro DNA binding and antibacterial experiments have been carried out. DNA-complex interaction has been pursued by electronic absorption titration, luminescence titration, competitive binding experiment, effect of ionic strength, thermodynamic studies, viscometric evaluation and circular dichroism spectroscopy in the physiological pH. Each compound displays significant binding trend to the CT-DNA. The mode of binding to the CT-DNA probably is a moderate intercalation mode with the partial insertion of the planar ligands between the base stacks of double-stranded DNA. The relative viscosities and circular dichroism spectra of the CT-DNA with the complex solutions, confirm the intense interactions of the Ag(I) complex and nanocomplex with DNA. An in vitro antibacterial test of the complex and nanocomplex on a series of the Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis) and the Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) shows a remarkable antibacterial feature of the Ag(I) complex. The MIC values (minimum inhibitory concentration) of the compounds compare with silver nitrate and silver sulfadiazine. The bacterial inhibitions of the Ag(I) complex and nanocomplex are agreed to their DNA binding affinities.

Luminescent 2D + 2D → 2D Interpenetrated Zn(II)-Coordination Polymer Based on Reduced Schiff Base Tricarboxylic Acid and Bis(imidazole) Ligand for Detection of Picric Acid and Fe3+ Ions

New bifunctional luminescent coordination polymer, formulated as {[Zn(μ-HCIP)(μ-pbix)]·2H2O}n (1) (H3CIP = 5-(4-carboxybenzylamino)isophthalic acid, pbix: 1,4-bis(imidazol-1ylmethyl)benzene), was synthesized under solvothermal conditions by using reduced Schiff base and neutral pbix ligands and characterized by IR spectroscopy, elemental analysis, single-crystal and powder X-ray diffraction, and thermal analysis. X-ray results indicated that the HCIP ligand acted as a bidentate bridging ligand and was partly deprotonated in 1. Complex 1 exhibited a 2D + 2D → 2D interpenetrated structure with sql topology. Complex 1 displayed high emission at the solid state. Luminescence titration experiments showed that complex 1 dispersed in dimethylformamide (DMF) detected the picric acid in the presence of other interfering nitroaromatic compounds with a detection limit of 56.46 ppb. In addition, complex 1 displayed highly sensitive and selective detection toward Fe3+ ion in the presence of other interfering metal ion...

Asymmetric bimetallic ruthenium(II) complexes selectively sense cyanide in water through significant modulation of their ground and excited state properties

This paper deals with anion recognition and sensing aspects of a new family of asymmetric bimetallic Ru(II) complexes derived from a heteroditopic bridging ligand (tpy-Hbzim-dipy) consisting of both bipyridine and terpyridine chelating sites covalently connected via phenyl-imidazole spacer. The recognition event was visualized in both organic as well as aqueous medium through different optical channels and spectroscopic techniques by taking profit of metal ligand interaction in the complexes. Absorption, and both steady state and time-resolved emission spectroscopic measurements were carried out as a function of pH in order to determine the ground- and excited state pKa values of the complexes. The complexes act as sensors for F−, CN−, AcO−, S2−, H2PO4− and P2O74− in acetonitrile without much selectivity. By contrast, the selectivity increased to a great extent in aqueous medium and all the four complexes act as chromogenic and fluorogenic sensors CN−, S2−, and P2O74−. Equilibrium/binding constants of the interaction process and detection limits of the complexes towards selected anions were determined from UV–vis absorption and luminescence titration profiles and the values were found to lie in order of 106M−1 and 10−9M, respectively. In addition to the steady state luminescence spectral changes, the excited-state lifetimes of the complexes were also modulated to a great extent by the selected anions which can lead to the utility of the complexes as suitable lifetime-based sensors for selected anions. Finally, test strips were also fabricated based on the metalloreceptors for their probable use as efficient test kits to detect CN−, S2−, and P2O74− in pure water for field measurements that do not require any equipment.

A “turn on” fluorescent probe based on Tb(III) complex for the detection of organophosphorus pesticides

The abuse of organophosphate pesticides and chemical-warfare agents has made severe effects on human and animal health. Consequently, it is vital to develop sensitive and selective strategies for the detection of organophosphates. In this work, the Tb(III) complex— TbL 3+ , consisting of a 1,4,7-triazacyclononane derivative as ligand was synthesized. As TbL 3+ contains no aromatic groups (function as an antenna), its intrinsic luminescence is thus minimized. The coordination of cyanophos to TbL 3+ could largely sensitize its luminescence ( I / I 0=55) because the energy of the triplet state of benzene is slightly higher in energy than the 5D4 of Tb(III). The detection limit for cyanophos was determined as 59 nmol/L. High resolution mass spectrum measurements, luminescence titration experiment and luminescence lifetime measurements reveal that TbL 3+ is bound with two cyanophos molecules and one methanol molecule. However, other organophosphates such as profenofos, chlopyrifos, dimethoate, diazinon, phoxim, fenthion, methyl parathion and dichlorvos almost did not induce any changes on luminescence intensity under the same conditions. By this work, we prepared a new luminescence probe for cyanophos with good selectivity and sensitivity.

New silver(I) complex with diazafluorene based ligand: Synthesis, characterization, investigation of in vitro DNA binding and antimicrobial studies

A novel diazafluorene based complex with silver, [Ag(dian)2]NO3, where dian is N-(4,5-diazafluoren-9-ylidene)aniline, has been prepared and characterized by elemental analysis, IR spectroscopy, 1HNMR, UV–Vis spectroscopy and cyclic voltammetry. In order to explore the relationship between the structure and biological properties, DNA binding propensity and in vitro antibacterial property have also been studied. The mode of DNA-complex interaction has been investigated by electronic absorption titration, luminescence titration, competitive binding experiment, effect of ionic strength, thermodynamic studies, viscometric evaluation, circular dichroism spectroscopy and cyclic voltammetry. The results reveal that the complex binds to CT-DNA in a moderate intercalation capability with the partial insertion of a planar dian ligand between the base stacks of double-stranded DNA with binding constant (Kb) of 2.4 × 105 M−1. The viscosities and CD spectra of the DNA provide strong evidence for the intercalation. An in vitro antibacterial efficacy of the Ag(I) complex on a series of Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis) and Gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa) indicates that the complex exhibits a marked antibacterial activity. The minimum inhibitory concentrations of the complex indicate that it exhibits much higher antibacterial effect on standard bacterial strains of Escherichia coli and Staphylococcus aureus than those of silver nitrate, silver sulfadiazine. The bacterial inhibitions of the silver(I) complex are closely agreed to its DNA binding affinities.

Cationic Amphiphilic Tris-Cyclometalated Iridium(III) Complexes Induce Cancer Cell Death via Interaction with Ca2+-Calmodulin Complex.

In our previous paper, we reported on the preparation of some cationic amphiphilic Ir complexes (2c, 2d) containing KKGG peptides that induce and detect cell death of Jurkat cells. Mechanistic studies suggest that 2c interacts with anionic molecules and/or membrane receptors on the cell surface to trigger an intracellular Ca2+ response, resulting in the induction of cell death, accompanied by membrane disruption. We have continued the studies of cell death of Jurkat cells induced by 2c and found that xestospongin C, a selective inhibitor of an inositol 1,4,5-trisphosphate receptor located on the endoplasmic reticulum (ER), reduces the cytotoxicity of 2c, suggesting that 2c triggers the release of Ca2+ from the ER, leading to an increase in the concentration of cytosolic Ca2+, thus inducing cell death. Moreover, we synthesized a series of new amphiphilic cationic Ir complexes 5a-c containing photoreactive 3-trifluoromethyl-3-phenyldiazirine (TFPD) groups, in an attempt to identify the target molecules of 2c. Interestingly, it was discovered that a TFPD group functions as a triplet quencher of Ir complexes. It was also found that 5b is useful as a turn-on phosphorescent probe of acidic proteins such as bovine serum albumin (BSA) (pI = 4.7) and their complexation was confirmed by luminescence titrations and SDS-PAGE of photochemical products between them. These successful results allowed us to carry out photoaffinity labeling of the target biomolecules of 5b (2c and analogues thereof) in Jurkat cells. A proteomic analysis of the products obtained by the photoirradiation of 5b with Jurkat cells suggests that the Ca2+-binding protein "calmodulin (CaM)" is one of target proteins of the Ir complexes. Indeed, 5b was found to interact with the Ca2+-CaM complex, as evidenced by luminescence titrations and the results of photochemical reactions of 5b with CaM in the presence of Ca2+ (SDS-PAGE). A plausible mechanism for cell death induced by a cationic amphiphilic Ir complex is discussed on the basis of our results.

English

Three novel ruthenium(II) complexes of the general formula [Ru(II)(bpy)2L]2+ were synthesized, where L = 1,10-phenanthroline derivatives of position 2 imidazole having 3,4-didecyloxy-phenyl (ddip), 3,4-ditetradecyloxy-phenyl (dtip) and 3,4-dihexadecyloxy-phenyl (dhip). All complexes were characterized by elemental analysis, 1H-NMR and ESI-MS. Their photophysical properties have also been studied by UV-visible spectroscopy and fluorescence spectroscopy. The complexes exhibit Ru(II) metal centered emission at approximately 610 nm in acetonitrile solution at room temperature. DNA binding studies were carried out by UV-visible titration, luminescence titration and viscosity studies. The results indicated that [Ru(bpy)2(ddip)]2+ binds to CT-DNA by partial intercalation mode, while [Ru(bpy)2(dtip)]2+ and [Ru(bpy)2(dhip)]2+ bind intercalatively via extended ligands.