Interaction of a New Fluorescent Probe with DNA and its Use in Determination of DNA

In this paper we reported a metal complex 1-Zn (2,5-di-[2-(3,5-bis(2-pyridylmethyl)amine-4-hydroxy-phenyl)-ethylene]-pyrazine-Zn) as a fluorescent probe sensing DNA. The result of the competitive experiment of the probe with ethidium bromide (EB) to bind DNA, absorption spectral change and polarization change in the presence and absence of DNA revealed that interaction between the probe and DNA was via intercalation. Ionic strength experiment showed the existence of electrostatic interaction as well. Scatchard plots also confirmed the combined binding modes. The fluorescence enhancement of the probe was ascribed to highly hydrophobic environment when it bound the macromolecules such as DNA, RNA or denatured DNA. The binding constant between the probe and DNA was estimated as 3.13 × 10⁷ mol⁻¹ L. The emission intensity increase was proportional to the concentration of DNA. Based on this, the probe was used to determine the concentration of calf thymus DNA (ct-DNA). The corresponding linear response ranged from 2.50 × 10⁻⁷ to 4.75 × 10⁻⁶ mol L⁻¹, and detection limit was 1.93 × 10⁻⁸ mol L⁻¹ for ct-DNA.     

A Study of the Interaction Between Malachite Green and Lysozyme by Steady-State Fluorescence

The interaction of a N-methylated diaminotriphenylmethane dye, malachite green, with lysozyme was investigated by fluorescence spectroscopic techniques under physiological conditions. The binding parameters have been evaluated by fluorescence quenching methods. The results revealed that malachite green caused the fluorescence quenching of lysozyme through a static quenching procedure. The thermodynamic parameters like ΔH and ΔS were calculated to be −15.33 kJ mol⁻¹ and 19.47 J mol⁻¹ K⁻¹ according to van’t Hoff equation, respectively, which proves main interaction between malachite green and lysozyme is hydrophobic forces and hydrogen bond contact. The distance r between donor (lysozyme) and acceptor (malachite green) was obtained to be 3.82 nm according to Fӧrster’s theory. The results of synchronous fluorescence, UV/vis and three-dimensional fluorescence spectra showed that binding of malachite green with lysozyme can induce conformational changes in lysozyme. In addition, the effects of common ions on the constants of lysozyme-malachite green complex were also discussed.     

Interaction of Thyroxine with 7 Hydroxycoumarin: A Fluorescence Quenching Study

The interaction between thyroxine hormone and 7 hydroxycoumarin (7HC) was investigated using fluorescence quenching method. The experimental results showed that thyroxine could quench the fluorescence of 7HC by forming the 7HC–thyroxine complex with static quenching. The apparent binding constants (K) between 7HC and thyroxine were determined to be 1.51 × 10⁴ (297 K) and 9.06 × 10³ (310 K). The binding sites (n) 0.98 ± 0.1. The thermodynamic parameters showed that the interaction between 7HC and thyroxine was driven mainly by hydrogen bonding interactions and van der Waals force. Calibration for thyroxine, based on quenching titration data, was linear in the concentration range 2.0 × 10⁻⁸ to 3.0 × 10⁻⁷ mol/l. The relative standard deviation was 2.58% for 2.0 × 10⁻⁷ mol/l thyroxine (n = 4) and the 3σ limit of detection was 3.42 × 10⁻⁸ mol/l in cationic surfactant CTAB medium.     

Fluorescence Quenching Reaction of Polyvinylpyrrolidone-Eosin Y System for the Determination of Polyvinylpyrrolidone

In pH 1.8 ∼ 2.8 weak acid medium, polyvinylpyrrolidone (PVP) and Eosin Y reacted to form complex that could result in Eosin Y (EY) fluorescence quenching. The maximum quenching wavelength was at 542 nm. The fluorescence quenching (ΔF) was proportional to the concentration of polyvinylpyrrolidone in a certain range. The linear range, the correlation coefficient and the detection limit were 0.33 ∼ 2.0 μg•mL⁻¹, 0.9994 and 99.6 ng•mL⁻¹, respectively. The influences of the coexistence substances were tested and the results showed that the method had good selectivity. Therefore, a new method based on fluorescence quenching of eosin Y by PVP for the determination of trace PVP was developed. The method was sensitive, simple and rapid, which was applied to the determination of trace PVP in the beer with satisfactory results. The reaction mechanism was also discussed.     

Fluorescence and Electrochemical Sensing of Pesticides Methomyl, Aldicarb and Prometryne by the Luminescent Europium-3-Carboxycoumarin Probe

This work describes the application of time resolved fluorescence in microtiterplates and electrochemical methods on glassy carbon electrode for investigating the interactions of europium-3-carboxycoumarin with pesticides aldicarb, methomyl and prometryne. Stern-volmer studies at different temperatures indicate that static quenching dominates for methomyl, aldicarb and prometryne. By using Lineweaver-Burk equation binding constants were determined at 303 K, 308 K and 313 K. A thermodynamic analysis showed that the reaction is spontaneous with ΔG being negative. The enthalpy ΔH and the entropy ΔS of reactions were all determined. A time-resolved (gated) luminescence-based method for determination of pesticides in microtiterplate format using the long-lived europium-3-carboxycoumarin has been developed. The limit of detection is 4.80, 5.06 and 8.01 μmol L⁻¹ for methomyl, prometryne and aldicarb, respectively. This is the lowest limit of detection achieved so far for luminescent lanthanide-based probes for pesticides. The interaction of the probe with the pesticides has been investigated using cyclic voltammetry (CV), differential pulse polarography (DPP), square wave voltammetry (SWV) and linear sweep voltammetry (LSV) on a glassy carbon electrode in I = 0.1 mol L⁻¹ p-toluenesulfonate at 25 °C. The diffusion coefficients of the reduced species are calculated. The main properties of the electrode reaction occurring in a finite diffusion space are the quasireversible maximum and the splitting of the net SWV peak for Eu(III) ions in the ternary complex formed . It was observed that the increase of the cathodic peak currents using LSV is linear with the increase of pesticides concentration in the range 5 × 10⁻⁷ to 1 × 10⁻⁵ mol L⁻¹. The detection limit (DL) were about 1.01, 2.23 and 1.89 μmolL⁻¹ for aldicarb, methomyl and prometryne, respectively. In order to assess the analytical applicability of the method, the influence of various potentially interfering species was examined. Influence of interfering species on the recovery of 10 μmol L⁻¹ pesticides has been investigated.     

Binding of Quercetin to Lysozyme as Probed by Spectroscopic Analysis and Molecular Simulation

The binding of quercetin to lysozyme (LYSO) in aqueous solution was investigated by fluorescence spectroscopy, UV-vis absorption spectroscopy and molecular simulation at pH 7.4. The fluorescence quenching of LYSO by addition of quercetin is due to static quenching, the binding constants, K _a , were 3.63 × 10⁴, 3.31 × 10⁴ and 2.85 × 10⁴ L·mol⁻¹ at 288, 298 and 308 K, respectively. The thermodynamic parameters, enthalpy change, ∆H, and entropy change, ∆S, were noted to be −7.56 kJ·mol⁻¹ and 61.07 J·mol⁻¹·K⁻¹. The results indicated that hydrophobic interaction may play a major role in the binding process. The distance r between the donor (LYSO) and acceptor (quercetin) was determined as 3.34 nm by the fluorescence resonance energy transfer. The synchronous fluorescence spectroscopy showed the polarity around the tryptophan residues increased and the hydrophobicity decreased. Furthermore, the study of molecular simulation indicated that quercetin could bind to the active site (a pocket made up of 24 amino-acid residues) of LYSO mainly via hydrophobic interactions and that there were hydrogen interactions between the residues (Gln 57, Ile 98) of LYSO and quercetin. The accessible surface area (ASA) calculation verified the important roles of tryptophan (Trp) residues during the binding process.     

Solid Substrate–Room Temperature Phosphorimetry for the Determination of Trace Terbutaline Sulfate Based on Its Inhibition Oxidation of Rhodamine 6G by Sodium Periodate

When 1.00 mol l⁻¹ I⁻ is used as ion perturber, rhodamine 6G (Rh 6G) can emit strong and stable room temperature phosphorescence (RTP) on filter paper substrate in KHC₈H₄O₄–HCl buffer solution (pH = 3.50), heated at 70 °C for 10 min. NaIO₄ can oxidize Rh 6G, which makes the RTP signal quench. Terbutaline sulfate (TBS) can inhibit NaIO₄ from oxidizing Rh 6G, which makes the RTP signal of Rh 6G enhance sharply. The content of TBS is linear correlation to ΔIp of the system. Based on the facts above, a new inhibition solid substrate-room temperature phosphorimetry (SS-RTP) for the determination of trace TBS has been established. The linear range of this method is 0.0104–2.08 pg spot⁻¹ (corresponding concentration: 0.026–5.2 ng ml⁻¹, with a sample volume of 0.4 μl) with a detection limit (L.D.) of 2.6 fg spot⁻¹ (corresponding concentration: 6.5 × 10⁻¹² g ml⁻¹), and the regression equation of working curve is ΔIp = 2.040 + 54.54 m_TBS (pg spot⁻¹), n = 6, correlation coefficient is 0.9994. For the samples containing 0.0104 pg spot⁻¹ and 2.08 pg spot⁻¹ TBS, the relative standard deviation (RSD) are 3.8% and 2.3% (n = 8), respectively, indicating good precision. This method has been applied to determination of trace TBS in the practical samples with satisfactory results. The reaction mechanism of NaIO₄ oxidizing Rh 6G to inhibit SS-RTP for the determination of trace TBS is also discussed.     

Biophysical Studies on the Interactions of a Classic Mitochondrial Uncoupler with Bovine Serum Albumin by Spectroscopic,Isothermal Titration Calorimetric and Molecular Modeling Methods

The interaction between a classic uncoupler (2,4-dinitrophenol, DNP) and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy under the physiological conditions. The fluorescence quenching constants were calculated by the Stern-Volmer equation, and based upon the temperature dependence of quenching constants, it was proved that DNP caused a static quenching of the intrinsic fluorescence of BSA. Owing to the static quenching mechanism, different associative binding constants at various temperatures were determined and thus the thermodynamic parameters, namely enthalpy (ΔH = −21.12 kJ mol⁻¹) and entropy changes (ΔS = 23.51 J mol⁻¹ K⁻¹) could be calculated based on the binding constants. Moreover, the enthalpy and entropy changes are consistent with the “Enthalpy-Entropy Compensation” equation obtained from our previous work. The negative enthalpy and positive entropy indicated that the electrostatic interactions played a major role in DNP-BSA binding process. Site marker competitive displacement experiments were carried out by using fluorescence and isothermal titration calorimetry (ITC) methods. These results showed that DNP bound with high affinity to Sudlow’s site I (subdomain IIA) of BSA. The distance (r = 3.78 nm) between donor (BSA) and acceptor (DNP) was obtained according to the mechanism of fluorescence resonance energy transfer (FRET). Furthermore, the results of synchronous fluorescence and circular dichroism (CD) spectroscopic studies indicated that the microenvironment and the secondary conformation of BSA were altered. The above results were supported by theoretical molecular modeling methods.     

Fluorescence Enhancement of the Silver Nanoparticales – Curcumin - Cetyltrimethylammonium Bromide-nucleic Acids System and its Analytical Application

It is found that silver nanoparticles (AgNPs) can further enhance the fluorescence intensity of curcumin (CU) - cetyltrimethylammonium bromide (CTAB) – nucleic acids and improve its anti-photobleaching activity. Under optimum conditions, the enhanced fluorescence intensity is proportion to the concentration of nucleic acids in the range of 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for fish sperm DNA (fsDNA), 2.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for calf thymus DNA (ctDNA), 1.0 × 10⁻⁸–1.0 × 10⁻⁶ g mL⁻¹ for yeast RNA (yRNA), and their detection limits (S/N = 3) are 8.0 ng mL⁻¹, 10.5 ng mL⁻¹ and 5.8 ng mL⁻¹, respectively. This method is used for determining the concentration of DNA in actual sample with satisfactory results. The interaction mechanism is also studied.     

Study of interaction of a fluorescent probe with DNA

The zinc complex of 2-[2-(3, 5-bis(2-pyridylmethyl)aminomethyl-4-hydroxy-phenyl) ethylene]-5-methylpyrazine (1) could bind with the calf thymus deoxyribonucleic acid (ct-DNA). The binding behaviors between them were studied by fluorescence and absorption spectral assay. The absorption titration of 1-Zn with ct-DNA showed no bathochromic shift and hypochromic effect. No anisotropy increase was observed when ct-DNA was added to 1-Zn solution. They both proved the lack of intercalation interaction between 1-Zn and ct-DNA. The ionic strength experiment, Scatchard plot, study of interaction between 1-Zn and denatured ct-DNA all revealed that the interaction mode between 1-Zn and ct-DNA was electrostatic interaction. Binding constant was estimated to be 7.96×10⁴ L moL⁻¹.     

New Fluorescent Antitumour Cisplatin Analogue Complexes. Study of the Characteristics of their Binding to DNA by Flow Injection Analysis

The flow injection technique is applied to study the binding to DNA of new platinum complexes—E₁: ethylenediaminechlorocholylglycinateplatinum(II): [PtCl(CG)(en)], C₅₄H₉₂O₁₂Pt and E₂: ethylenediaminebischolylglycinateplatinum(II): [Pt(CG)₂(en)], C₂₈H₅₀ClN₃O₆Pt—derived from cisplatin in which the exchangeable ligands were replaced by bile acids, such that these anticancer drugs have less toxicity and less resistance is developed towards them. Both compounds are fluorescent and their fluorescence is enhanced when they form adducts with DNA, a property that is extremely useful for monitoring the cytotoxic activity and their mechanisms of action. The binding parameters to DNA of E₁ [apparent intrinsic binding constant K_E1: (11.2 ± 0.4) × 10³ M⁻¹ and maximum number of binding sites per nucleotide, n _E1: 0.121 ± 2 × 10⁻³) and E₂ (K_E2: 9.2 ± 0.7) × 10³ M⁻¹ and n _E2 0.098 ± 2 × 10⁻³] were determined following the Scatchard method and the type of binding was studied experimentally through the modifications introduced by each of the compounds into the ethidium bromide–DNA bond.     

A Novel Fluorescent Silver Ion Biosensor Based on Nucleic Acid Molecular “Light Switch”

As one of nucleic acid molecular “light switch”, Ru(bipy)₂(dppx)²⁺ is a good probe for the determination of double-helical DNA, which displays intense fluorescence when double-helical DNA is present. However, the fluorescence of Ru(bipy)₂(dppx)²⁺ is quenched when Ag⁺ is added to the Ru(bipy)₂(dppx)²⁺-DNA system. Based on the quenching of the fluorescence of Ru(bipy)₂(dppx)²⁺-DNA system by Ag⁺, a simple, rapid and specific method for Ag⁺ determination was proposed. In the optimum conditions, Ag⁺ concentration versus Ru(bipy)₂(dppx)²⁺ fluorescence intensity gave a linear response in the range from 0.2 to 6.0 μM with a detection limit (3σ) of 3.2 × 10⁻⁸ M. The proposed method has been applied to determine the Ag⁺ in water samples and sulfadiazine silver cream successfully. Because of the intense fluorescence of Ru(bipy)₂dppx²⁺ when DNA is present, the interaction between Ag⁺ and DNA was confirmed by fluorescence microscopy and the phenomenon of the fluorescence images agreed well with the results. The possible mechanism of the reaction was also discussed by circular dichroism spectra and isothermal titration calorimetry.     

Lower Bounds for an Integral Involving Fractional Laplacians and the Generalized Navier-Stokes Equations in Besov Spaces

When estimating solutions of dissipative partial differential equations in L^p-related spaces, we often need lower bounds for an integral involving the dissipative term. If the dissipative term is given by the usual Laplacian −Δ, lower bounds can be derived through integration by parts and embedding inequalities. However, when the Laplacian is replaced by the fractional Laplacian (−Δ)^α, the approach of integration by parts no longer applies. In this paper, we obtain lower bounds for the integral involving (−Δ)^α by combining pointwise inequalities for (−Δ)^α with Bernstein's inequalities for fractional derivatives. As an application of these lower bounds, we establish the existence and uniqueness of solutions to the generalized Navier-Stokes equations in Besov spaces. The generalized Navier-Stokes equations are the equations resulting from replacing −Δ in the Navier-Stokes equations by (−Δ)^α.     

Thermodynamics, Conformation and Active Sites of the Binding of Zn–Nd Hetero-bimetallic Schiff Base to Bovine Serum Albumin

The interactions between N,N′-di(2-hydroxy-3-methyoxy-phenyl-1-methylene)-o-phenyldiamine-mone Zn(II), Nd(III) nitrate (2LZnNd) and bovine serum albumin (BSA) was investigated by various spectroscopic techniques under physiological conditions. It was proved that the fluorescence quenching of BSA by 2LZnNb was a result of the formation of a non-fluorescent complex with the binding constants of 3.15 × 10⁵; 2.72 × 10⁵ and 2.44 × 10⁵ M^–1 at 298 K, 304 K and 310 K, respectively. A marked increase in the fluorescence anisotropy in the proteinous environments indicates that BSA introduces motional restriction on the drug molecule. The corresponding thermodynamics parameters ΔH and ΔS were calculated to be –16.36 kJ mol^–1 and 43.48 J mol^–1 K^–1 via van’t Hoff equation. Moreover, the competitive probes experiment revealed that the binding location of 2LZnNb to BSA is in the hydrophobic pocket of site II. The effect of 2LZnNb on the conformation of BSA has been analyzed by means of CD spectrum and three-dimensional fluorescence spectra. The results indicate that the conformation of BSA molecules was changed in the presence of 2LZnNb Schiff base.     

Second-derivative Synchronous Fluorometric Method for the Simultaneous Determination of Cinnarizine and Domperidone in Pharmaceutical Preparations. Application to Biological Fluids

A rapid, simple and highly sensitive second derivative synchronous fluorometric method has been developed for the simultaneous analysis of binary mixture of cinnarizine (CN) and domperidone (DOM). The method is based upon measurement of the native fluorescence of these drugs at Δλ = 80 nm in aqueous methanol (50% V/V). The different experimental parameters affecting the native fluorescence of the studied drugs were carefully studied and optimized. The fluorescence-concentration plots were rectilinear over the range of 0.1 to 1.3 μg mL⁻¹ and 0.1–3.0 μg mL⁻¹ for CN and DOM, respectively with lower detection limits of 0.017 and 5.77 × 10⁻³ μg mL⁻¹ and quantification limits of 0.058 and 0.02 μg mL⁻¹ for CN and DOM. The proposed method was successfully applied for the determination of the studied compounds in synthetic mixtures and in commercial tablets. The results obtained were in good agreement with those obtained with reference methods. The high sensitivity attained by the synchronous fluorometric method allowed the determination of CN in real and spiked human plasma. The mean % recoveries in case of spiked human plasma (n = 3) were 96.39 ± 1.18 while that in real human plasma (n = 3) was 104.67 ± 4.16.     

Experimental study of the <Emphasis Type="Italic">πh</Emphasis><Subscript>11/2</Subscript> band in <Superscript>113</Superscript>Sb

In the present work, the excited states of ¹¹³Sb were populated in the ¹⁰⁰Mo(²⁰Ne, p6n) reaction at a beam energy of 136 MeV. States only up to 59/2⁻ were observed in the ΔJ = 2 band. Mean lifetimes for the five states (from 4460 to 7998 keV) were measured for the first time using Doppler shift attenuation method. An upper limit of the lifetime (0.14 ps) was estimated for the 9061 keV, 47/2⁻ state. The B(E2) values, derived from the present lifetime results, correspond to a large quadrupole deformation of β ₂ = 0.32. The observed reduction in the experimental B(E2) values for the 918.4 keV (spin 39/2⁻ → 35/2⁻) and 985 keV (spin 43/2⁻ → 39/2⁻) transitions may be interpreted as due to the proton alignement in the g _7/2 orbital. The dynamic moment of inertia was observed to be about half of the rigid body value at the highest observed frequency.     

Fluorescence Enhancement Effect for the Determination of Polychlorinated Biphenyls with Bovine Serum Albumin

A sensitive and selective method for the trace determination of 3, 3’, 4, 4’-tetrachlorobiphenyl (PCB77) by using bovine serum albumin (BSA) as a fluorescence probe was introduced. Under optimum conditions, the enhanced fluorescence intensity was proportional to the concentration of polychlorinated biphenyls in the range of 8.9 × 10⁻⁸–5.0 × 10⁻⁶ mol L⁻¹ for PCB77, and 5.0 × 10⁻⁷–5.0 × 10⁻⁶ mol L⁻¹ for 2, 2’, 5, 5’-tetrachlorbiphenyl (PCB52). The detection limits (S/N = 3) of PCB77 and PCB52 were 2.6 × 10⁻⁸ mol L⁻¹ and 2.9 × 10⁻⁷ mol L⁻¹, respectively. Furthermore, the fluorescence enhancement mechanism was discussed in detail. Results indicated that fluorescence enhancement of the system originated from the formation of BSA-PCBs complexes. In addition, PCBs were mainly bound to the tyrosine residues in BSA molecules.     

Spectrofluorimetric Assessment of Doxycycline Hydrochloride in Pharmaceutical Tablets and Serum Sample Based on the Enhancement of the Luminescence Intensity of the Optical Sensor Sm<Superscript>3+</Superscript> Ion

A simple and sensitive spectrofluorimetric method for determination of trace amount of doxycycline hydrochloride (DC) in pharmaceutical tablets and serum samples was developed. In ammonia buffer solution of pH 8.9 the doxycycline hydrochloride can remarkably enhance the luminescence intensity of the Sm³⁺ ion in Sm³⁺- DC complex at λ_ex = 400 nm. The produced luminescence intensity of Sm³⁺- DC complex in DMSO is in proportion to the concentration of DC and used as optical sensor for its determination. The dynamic range for the determination of DC is 1 × 10⁻⁸ – 5 × 10⁻⁶ mol L⁻¹ and in case of quantum yield calculations is 7 × 10⁻⁹ – 5 × 10⁻⁶ mol L⁻¹ with detection limit of 6.5 × 10⁻¹⁰ mol L⁻¹. The enhancement mechanism of the luminescence intensity in the Sm³⁺- DC system has been also discussed. A comparison with other spectrofluorimetric methods for tetracycline derivatives in which Eu³⁺ ion is used instead of Sm³⁺ ion is also studied.     

Determination of Bioactive Matter by Affinity Adsorption Solid Substrate–Room Temperature Phosphorimetry Based on Lectin Labeled with Self-ordered Ring of Eosin Y

A new phosphorescent labeling reagent named self-ordered ring (ESOR) of eosin Y (E) was developed. And the application of the determination of bioactive matter by affinity adsorption solid substrate–room temperature phosphorimetry (AA-SS-RTP) based on ESOR labeling lectin was studied. Results showed that pink and homogeneous ESOR could be formed by E on polyamide membrane (PAM) in the presence of cetyltrimethylammonium bromide (CTAB) and ammonia water. ESOR could emit strong and stable room temperature phosphorescence (RTP) signal of E in the presence of heavy atom perturber. Specific affinity adsorption (AA) reactions could be carried out between the products of concanavalin agglutinin (Con A), triticum vulgaris lectin (WGA) labeled with ESOR and alpha-fetoprotein variant (AFP-V), alkaline phosphatase (ALP), glucose (G), respectively. Not only did the products of the affinity adsorption reactions preserve good RTP characteristic of E, but also the ΔI _p (ΔI _p = I _p2 − I _p1, I _p1 is the RTP intensity of blank reagent, I _p2 is the RTP intensity of sample) of these products was proportional to the content of AFP-V, ALP and G, respectively. According to the facts above, a new method of AA-SS-RTP for the determination of AFP-V, ALP and G was established, based on ESOR labeling lectin. Detection limits (LD) of this method were 0.040 fg spot⁻¹ for AFP-V, 0.045 fg spot⁻¹ for ALP and 0.090 fg spot⁻¹ for G. And it has been successfully applied to the determination of AFP-V in human serum as well as the survey and forecast of human diseases. This method had high sensitivity, good repeatability, long RTP lifetime and little background interference with at the long wavelength area. Meanwhile, the mechanism for the determination of trace AFP-V by AA-SS-RTP based on Con A labeled with ESOR was also discussed.     

Study of DNA Light Switch Ru(II) Complexes : Synthesis,Characterization, Photocleavage and Antimicrobial Activity

The three Ru(II) complexes of [Ru(phen)₂dppca]²⁺ (1) [Ru(bpy)₂dppca]²⁺ (2) and [Ru(dmb)₂dppca]²⁺ (3) (where phen = 1,10 phenanthroline, bpy = 2,2-bipyridine, dmb = 2 ,2-dimethyl 2′,2′-bipyridine and polypyridyl ligand containing a single carboxylate functionality dppca ligand (dipyridophenazine-11-carboxylic acid) have been synthesized and characterized. These complexes have been shown to act as promising calf thymus DNA intercalators and a new class of DNA light switches, as evidenced by UV-visible and luminescence titrations with Co²⁺ and EDTA, steady-state emission quenching by [Fe(CN)₆]⁴⁻ and KI, DNA competitive binding with ethidium bromide, viscosity measurements, and DNA melting experiments. The results suggest that 1, 2, and 3 complexes bind to CT-DNA through intercalation and follows the order 1 > 2 > 3. Under irradiation at 365 nm, the three complexes have also been found to promote the photocleavage of plasmid pBR322 DNA.