Interaction of sesamol (3,4-methylenedioxyphenol) with tyrosinase and its effect on melanin synthesis

Sesamin, sesamolin (lignans) and sesamol - from sesame seed (Sesamum indicum L.) - are known for their health promoting properties. We examined the inhibition effect of sesamol, a phenolic degradation product of sesamolin, on the key enzyme in melanin synthesis, viz. tyrosinase, in vitro. Sesamol inhibits both diphenolase and monophenolase activities with midpoint concentrations of 1.9 μM and 3.2 μM, respectively. It is a competitive inhibitor of diphenolase activity with a K_i of 0.57 μM and a non-competitive inhibitor of monophenolase activity with a K_i of 1.4 μM. Sesamol inhibits melanin synthesis in mouse melanoma B16F10 cells in a concentration dependant manner with 63% decrease in cells exposed to 100 μg/mL sesamol. Apoptosis is induced by sesamol, limiting proliferation. This study of the chemistry and biology of lignans, in relation to the mode of action of bioactive components, may open the door for drug applications targeting enzymes.     

DNA interaction studies of ethylenediaminetetraaceticacid food additive and selenium effect in DNA cleavage-inhibition

The interaction of native calf thymus DNA with ethylenediaminetetraaceticacid (EDTA) in Tris-HCl buffer at pH?=?7.8 (at this pH EDTA forms a disodium salt) was investigated. EDTA is widely used in medicine, food technology, and the chemical industry. The DNA binding mode of EDTA was monitored by absorption spectrophotometry, circular dichrosim, viscometry, and gel electrophoresis. Ultraviolet spectra of DNA showed small hyperchromicity with increase in EDTA concentration. The circular dichrosim signals at 245 and 280?nm indicated structural changes in DNA structure, and no significant effect on DNA viscosity was observed in the presence of increasing amounts of EDTA. Results are indicative of an outside, nonintercalative binding mode of EDTA to DNA. Moreover, gel electrophoresis studies showed considerable oxidative cleavage of plasmid DNA by EDTA. Mechanistic aspects of the chemical nuclease reactions were investigated using the OH radical quencher dimethylsulfoxide. In the presence of selenium, DNA cleavage by EDTA was inhibited.     

DNA binding studies of tartrazine food additive

The interaction of native calf thymus DNA with tartrazine in 10?mM Tris-HCl aqueous solution at neutral pH 7.4 was investigated. Tartrazine is a nitrous derivative and may cause allergic reactions, with a potential of toxicological risk. Also, tartrazine induces oxidative stress and DNA damage. Its DNA binding properties were studied by UV-vis and circular dichroism spectra, competitive binding with Hoechst 33258, and viscosity measurements. Tartrazine molecules bind to DNA via groove mode as illustrated by hyperchromism in the UV absorption band of tartrazine, decrease in Hoechst-DNA solution fluorescence, unchanged viscosity of DNA, and conformational changes such as conversion from B-like to C-like in the circular dichroism spectra of DNA. The binding constants (K(b)) of DNA with tartrazine were calculated at different temperatures. Enthalpy and entropy changes were calculated to be +37 and +213 kJ mol(-1), respectively, according to the Van't Hoff equation, which indicated that the reaction is predominantly entropically driven. Also, tartrazine does not cleave plasmid DNA. Tartrazine interacts with calf thymus DNA via a groove interaction mode with an intrinsic binding constant of 3.75?×?10(4) M(-1).     

Deciphering the interaction of food additive,vanillin with DNA: A biophysical and computational study

Communicated by Ramaswamy H. Sarma     

DNA interaction studies of tridentate bridged Ru(II)-Pt(II) mixed-metal supramolecules

Reported herein are studies of the concentration and temperature dependent interactions with DNA of the stereochemically defined mixed-metal supramolecular complexes, [(tpy)Ru(tppz)PtCl](PF₆)₃ and [ClPt(tppz)Ru(tppz)PtCl](PF₆)₄ (tpy = 2,2′:6′,2′′-terpyridine and tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine). These metal complexes couple a ruthenium based light absorber (LA) to the bioactive platinum sites (BAS) using a tridentate bridging ligand (BL). The complexes exhibit intense Ru → tppz(π∗) metal to ligand charge transfer (MLCT) transitions in the visible region and adopt a square planar geometry around the Pt(II) center. The effect of incubating these metal complexes with DNA on the subsequent migration of DNA through an agarose gel was found to be more dramatic than that observed for the well known anticancer drug, cis-[Pt(NH₃)₂Cl₂] (cisplatin). This effect was enhanced with increased incubation temperature. Unwinding of supercoiled plasmid DNA was found to be more pronounced for the trimetallic complex, [ClPt(tppz)Ru(tppz)PtCl](PF₆)₄, than for the bimetallic complex, [(tpy)Ru(tppz)PtCl](PF₆)₃.     

Spectroscopic studies on the interaction of quercetin-terbium(III) complex with calf thymus DNA

The interaction of native calf thymus DNA (CT-DNA) with quercetin-terbium(III) [Q-Tb(III)] complex at physiological pH was monitored by UV absorption spectrophotometry, circular dichroism, fluorescence spectroscopy, and viscosimetric techniques. The complex displays binding properties to the CT-DNA and was found to interact with CT-DNA through outside binding, demonstrated by a hypochromic effect of Q-Tb(III) on the UV spectra of CT-DNA and the calculated association constants (K). Also, decrease in the specific viscosity of CT-DNA, decrease in the fluorescence intensity of Q-Tb(III) solutions in the presence of increasing amounts of CT-DNA, and detectable changes in the circular dichroism spectrum of CT-DNA are other evidences to indicate that Q-Tb(III) complex interact with CT-DNA through outside binding.     

Interaction studies of copper complex containing food additive carmoisine dye with human serum albumin (HSA): Spectroscopic investigations

In this study, the interaction between human serum albumin (HSA) and a copper complex of carmoisine dye; [Cu(carmoisine)₂(H₂O)₂], was studied in vitro using multi‐spectroscopic methods. It was found that the intrinsic fluorescence of HSA was quenched by the addition of the [Cu(carmoisine)₂(H₂O)₂] complex and the quenching mechanism was considered as static quenching by formation of a [Cu(carmoisine)₂(H₂O)₂]–HSA complex. The binding constant was about 10⁴ M^?1 at room temperature. The values of the calculated thermodynamic parameters (ΔH < 0 and ΔS > 0) suggested that both hydrogen bonds and the hydrophobic interactions were involved in the binding process. The site marker competitive experiments revealed that the binding of [Cu(carmoisine)₂(H₂O)₂] to HSA primarily occurred in subdomain IIIA (site II) of HSA. The results of circular dichroism (CD) and UV–vis spectroscopy showed that the micro‐environment of amino acid residues and the conformation of HSA were changed after addition of the [Cu(carmoisine)₂(H₂O)₂] complex. Finally, the binding of the [Cu(carmoisine)₂(H₂O)₂] complex to HSA was modelled by a molecular docking method. Excellent agreement was obtained between the experimental and theoretical results with respect to the binding forces and binding constant.     

Design,synthesis, MTT assay,DNA interaction studies of platinum(II) complexes

The square planar Pt(II) complexes of the type [Pt(Lⁿ)(Cl₂)] (where Lⁿ = L^1?3 = thiophene-2-carboxamide derivatives and L^4?6 = thiophene-2-carbothioamide derivatives) have been synthesized and characterized by physicochemical and various spectroscopic studies. MIC method was employed to inference the antibacterial potency of complexes in reference to free ligands and metal salt. Characteristic binding constant (K_b) and binding mode of complexes with calf thymus DNA (CT-DNA) were determined using absorption titration (0.76–1.61 × 10⁵ M^?1), hydrodynamic chain length assay and fluorescence quenching analysis, deducing the partial intercalative mode of binding. Molecular docking calculation displayed free energy of binding in the range of –260.06 to –219.63 kJmol^?1. The nuclease profile of complexes towards pUC19 DNA shows that the complexes cleave DNA more efficiently compared to their respective metal salt. Cytotoxicity profile of the complexes on the brine shrimp shows that all the complex exhibit noteworthy cytotoxic activity with LC₅₀ values ranging from 7.87 to 15.94 μg/mL. The complexes have been evaluated for cell proliferation potential in human colon carcinoma cells (HCT 116) and IC₅₀ value of complexes by MTT assay (IC₅₀ = 125–1000 μg/mL).     

DNA interaction studies of a platinum(II) complex containing L-histidine and 1,10-phenanthroline ligands

The aim of this study was developing coordination complexes that can be used as inorganic medicinal agents. The water soluble [Pt(phen)(His)]NO(3)·3H(2)O complex in which phen=1,10-phenantheroline and His=L-histidine was synthesized and characterized using physicochemical methods. Binding interaction of this complex with calf thymus (CT) DNA was investigated by emission, absorption, circular dichroism, and viscosity measurement techniques. Upon addition of CT-DNA, changes were observed in the characteristic ultraviolet-visible (UV-Vis) bands (hypochromism) of the complex. The complex binds to CT-DNA in an intercalative mode. The calculated binding constant, K(b), was 8 ± 0.2 × 10(4) M(-1). In addition, circular dichroism (CD) study showed that the phenanthroline ligand was inserted between the base pair stack of the double-helical structure of DNA. Also, the fluorescence spectral characteristics showed an increase in fluorescence intensity of the platinum complex in the presence of increasing amounts of DNA solution. The experimental results showed that the platinum complex binds to DNA via intercalative and hydrogen bonding mode.     

Spectroscopic studies of interaction of chlorobenzylidine with DNA

Electronic absorbance and fluorescence titrations are used to probe the interaction of chlorobenzylidine with DNA. The binding of chlorobenzylidine to DNA results in hypochromism, a small shift to a longer wavelength in the absorption spectra, and emission quenching in the fluorescence spectra. These spectral characteristics suggest that chlorobenzylidine binds to DNA by an intercalative mode. This conclusion is reinforced by fluorescence polarization measurements. Scatchard plots constructed from fluorescence titration data give a binding constant of 1.3 x 10(5) M(-1) and a binding site size of 10 base pairs. This indicates that chlorobenzylidine has a high affinity with DNA. The intercalative interaction is exothermic with a Van't Hoff enthalpy of -143 kJ/mol. This result is obtained from the temperature dependence of the binding constant. The interaction of chlorobenzylidine with DNA is affected by the pH value of the solution. The binding constant has its maximum at pH 3.0. Upon binding to DNA, the fluorescence from chlorobenzylidine is quenched efficiently by the DNA bases and the fluorescence intensity tends to be constant at high concentrations of DNA when the binding is saturated. The Stern-Volmer quenching constant obtained from the linear quenching plot is 1.6 x 10(4) M(-1) at 25 degrees C. The measurements of the fluorescence lifetime and the dependence of the quenching constant on the temperature indicate that the fluorescence quenching process is static. The fluorescence lifetime of chlorobenzylidine is 1.9 +/- 0.4 ns.     

Kinetic studies on Cro repressor-operator DNA interaction

The six operators of phage lambda and their consensus sequence were synthesized as 21 base-pair DNAs and their interactions with Cro repressor were studied using a filter binding assay. The measured equilibrium dissociation constants suggest that Cro has the highest affinity to the consensus operator (KD = 1.2 X 10(-12) M) and then the OR3 operator (KD = 2.0 X 10(-12) M), after that the affinity becomes lower in the following order: OR1, OL1, OL2, OL3, OR2. The competition experiments show that Cro forms the most stable complex with the consensus operator (t1/2 = 150 min), which is followed by the complex with OR3 (t1/2 = 70 min), OR1, OL1, OL2, OL3 and OR2. The association rate constants (ka) were also measured. They are approximately the same (2 X 10(8) to 4 X 10(8) m-1 s-1) for the consensus, OR3, OR2 and OR1 operators. These experiments have thus shown that the sequence difference in the operator affects the dissociation (KD and kd) but not the association (ka) process. The operators' binding strengths relative to OR1 are 14 (for consensus operator), 7.6 (OR3), 0.73 (OL1), 0.42 (OL2), 0.16 (OL3) and 0.1 (OR2). Seven different lengths of OR-containing DNA fragments were prepared. Measurement of kinetic parameters shows that the affinity of Cro to operator DNA (measured by KD) is essentially constant and independent of the DNA length, while the association and dissociation rate constants increase as the DNA length increases. This is consistent with the idea that Cro locates and leaves its operator via a two-step mechanism. It appears that Cro binds first at an arbitrary site on DNA, then is transferred to its operator site by a facilitated mechanism. The process is reversed when Cro dissociates from the operator. Most of our data fit to the theoretical expression formulated by Berg, Winter & von Hippel for the sliding mechanism. We conclude that Cro slides along the DNA to locate and leave the operator.     

DNA interaction and cytotoxicity studies of new ruthenium(II) cyclopentadienyl derivative complexes containing heteroaromatic ligands

Four ruthenium(II) complexes with the formula [Ru(η⁵-C₅H₅)(PP)L][CF₃SO₃], being (PP = two triphenylphosphine molecules), L = 1-benzylimidazole, ; (PP = two triphenylphosphine molecules), L = 2,2′bipyridine, ; (PP = two triphenylphosphine molecules), L = 4-Methylpyridine, ; (PP = 1,2-bis(diphenylphosphine)ethane), L = 4-Methylpyridine, , were prepared, in view to evaluate their potentialities as antitumor agents. The compounds were completely characterized by NMR spectroscopy and their crystal and molecular structures were determined by X-ray diffraction. Electrochemical studies were carried out giving for all the compounds quasi-reversible processes. The images obtained by atomic force microscopy (AFM) suggest interaction with pBR322 plasmid DNA. Measurements of the viscosity of solutions of free DNA and DNA incubated with different concentrations of the compounds confirmed this interaction. The cytotoxicity of compounds 1234 was much higher than that of cisplatin against human leukemia cancer cells (HL-60 cells). IC₅₀ values for all the compounds are in the range of submicromolar amounts. Apoptotic death percentage was also studied resulting similar than that of cisplatin.     

Binding studies on aluminum(III)-albumin interaction

The present paper reports a quantitative investigation on the binding of aluminum to human serum albumin. Equilibrium dialysis and a general thermodynamic approach have been used to determine the binding parameters. Two aluminum binding sites have been identified on the albumin molecule, involving sites with single and double occupancy modes. The binding properties of these two distinct sites appear to undergo reciprocal influences, suggesting a possible interaction between the corresponding protein moieties. Both coordination modes proceed from weak interactions, as shown by the binding energies calculated.     

Reevaluation of interaction of cis-dichloro(ethylenediamine)platinum(II) with DNA

Intrastrand cross-links represent the majority of modifications in DNA resulting from interaction with the cancer chemotherapeutic drug cis-diamminedichloroplatinum(II) (cis-DDP). These adducts were recently characterized although several discrepancies remained to be resolved. In these studies, [3H]-cis-dichloro(ethylenediamine)platinum(II) (cis-DEP) was used because of the convenience of the radiolabel; this analogue produces adducts at identical sites in DNA as cis-DDP. Both drugs platinate the following sequences in DNA: GG, 65%; AG, 25%; GNG, 6%. The adduct at AG sequences invariably has adenine on the 5'-terminus of the dimer. The present enzyme digestion protocol included P1 nuclease, which produced complete digestion rather than as previously reported. The frequency of platination at GG was too high to be explained by an initial monofunctional platination at any guanine. However, direct bifunctional attack preferentially at GG was obviated because monofunctional adducts could be trapped with thiourea at short time periods. After short incubations, with cis-DEP and removal of unreacted drug, the monofunctional adducts slowly rearranged to bifunctional adducts. It is suggested that this evolution of adducts may result from the drug "walking" along the double helix, a phenomenon that does not appear to occur in single-stranded DNA.     

Kinetic studies of interaction between acridine orange and DNA

The interaction between acridine orange (AO) and deoxyribonucleic acid (DNA) was studied by the stopped-flow method. The spectral change of AO due to interaction with DNA was followed over the wavelength range 350–600 nm at various concentration ratios of DNA phosphate to dye. The spectral change observed by the stopped-flow method was found distinctly different from that, during the dead-time, leading to a conclusion that the binding of AO to the outside of DNA occurs much faster than the intercalation into base pairs of DNA. The dependence of the rate of reaction on the reactant concentration and on the salt, concentration of the solution was also studied. The results are consistent with the mechanism that the intercalation proceeds via the outside bound state.     

Cu(0) as the reaction additive in purge-free ATRP-assisted DNA detection

We report here the use of Cu(0) as a reducing reagent to eliminate dissolved oxygen-induced ATRP catalyst oxidation and radical chain termination. It eliminates the need for an inert environment as in a conventional ATRP reaction and allows DNA detection to be conducted in a purge-free fashion. 2-Hydroxyethylmethacrylate (HEMA) is the model monomer in our study, and Cu(I)/2,2'-dipyridyl-based complexes are used as the reaction catalyst. The amount of polymer chains grafted on the substrate upon reaction termination is quantified by measuring the final film thicknesses using ellipsometry. Synthesis of PHEMA films atop both small molecules and ssDNA in the presence of a limited amount of air at room temperature is achieved by adding Cu(0) as the reducing reagent. No compromised DNA detection sensitivity is noticed, though a 10:1 ratio of Cu(0):Cu(I) is required to achieve optimal polymer growth. Successful employment of Cu(0) as the reducing agent eliminates the cumbersome purging process in ATRP and renders the ATRP-assisted DNA sensing method more portable, simpler, and more time-efficient.     

NMR studies of chromomycin A3 interaction with DNA

The binding of chromomycin A3 to calf thymus DNA and poly(dG-dC) has been studied by 13C and 1H NMR with emphasis on the mode of binding, the role of Mg2+, and pH effects. The most prominent changes in the DNA base pair 13C NMR resonances upon complexation with chromomycin were observed for G and C bases, consistent with the G-C preference exhibited by this compound. Comparison of the 13C spectrum of DNA-bound chromomycin A3 with that of DNA-bound actinomycin D, a known intercalator, showed many similarities in the base pair resonances. This suggested the possibility that chromomycin A3 binds via an intercalative mechanism. 1H NMR studies in the imino proton, low-field region of the spectrum provided additional evidence in support of this binding mode. In the low-field spectrum of chromomycin A3 bound to calf thymus DNA, a small shoulder was observed on the upfield side of the G-C imino proton peak. Similarly, in the chromomycin A3 complex with poly(dG-dC), a well-resolved peak was found upfield from the G-C imino proton peak. These results are expected for ligands that bind by intercalation. Furthermore, in both the calf thymus and poly(dG-dC) drug complexes (in the presence of Mg2+) a broad peak was also present downfield (approximately 16 ppm from TSP) from the DNA imino protons. This was attributed to the C-9 phenolic hydroxyl proton on the chromomycin chromophore. Visible absorbance spectra at different pH values showed that the role of Mg2+ in the binding of chromomycin A3 to DNA is more than simple neutralization of the drug's anionic change.     

The interaction of Rh(II) and Rh(III) with DNA

The interaction of Rh2(II)(acetate)4, cis-[Rh(III)(en)2Cl2] Cl (en = ethylenediamine) and [Rh(III) (NH3)5Cl]Cl2 with calf thymus DNA has been studied at various r values [formula; see text] and interaction times. Electronic spectra, melting and cooling curves and sedimentation data indicate no interaction of the acetate complex with DNA, except in the case of a high r value and long interaction time. The other two complexes have been found to interact with the phosphate groups, thus stabilizing the macromolecule.