Studies of interaction between a new synthesized minor-groove targeting artificial nuclease and DNA

Nuclease plays an important role in molecular biology, such as DNA sequencing. Synthetic polyamide conjugates can be considered as new tool in the selective inhibition of gene expression and as potential drugs in anticancer or antiviral chemotherapy. In this paper, a new synthesized minor-groove targeting artificial nuclease, oligopyrrol-containing peptide, was reported. It was found that this new compound can bind DNA in AT-riched minor groove with high affinity and site specificity. DNA binding behavior was determined by UV-vis and circular dichroism (CD) methods. It was indicated that compound 6 can enhance the Tm of oligomer DNA from 51.8 to 63.5 degrees C and possesses large binding constant (Kb=8.83x10(4)L/mol).     

Synthesis of new piperazine derived Cu(II)/Zn(II) metal complexes, their DNA binding studies, electrochemistry and anti-microbial activity: Validation for specific recognition of Zn(II) complex to DNA helix by interaction with thymine base

New 3,4:9,10-dibenzo-2,11-dihydroxy-1,12-bispiperazine-5,8-dioxododecane complexes [C₂₄H₃₆N₄O₆Cu] (1), [C₂₄H₃₂N₄O₄Zn] (2) have been synthesized and characterized by elemental analysis, IR, NMR, Mass, EPR, UV–vis spectroscopy and molar conductance measurements. The complexes are non-ionic in nature and possess octahedral geometry around Cu²⁺, Zn²⁺ central metal ions. The binding studies of 1 and 2 with calf thymus DNA (CT-DNA) were investigated by UV–vis, fluorescence, cyclic voltammetery and viscosity measurements. The calculated binding constant K_b for 1 and 2 obtained from UV–vis absorption studies was 7.6 × 10³ M⁻¹, 80.8 × 10⁴ M⁻¹, respectively. The intrinsic binding constants were also estimated to be 7.0 × 10⁴ M⁻¹ and 7.53 × 10⁵ M⁻¹ for 1 and 2, respectively by using emission titrations. These experimental results suggest that complexes are groove binders and interact to CT-DNA with different affinities. Both the complexes in presence and absence of CT-DNA show quasireversible wave corresponding to Cu^II/Cu^I and Zn^II/Zn^I redox couple. The changes in E_1/2, ΔE, I_pa/I_pc ascertain the interaction of 1 and 2 with CT-DNA. Further, decrease in viscosity of CT-DNA with increasing concentration of complexes was observed. In vitro, antimicrobial activity against fungi A. brassicicola, A. niger and bacteria E. coli, P. aeruginosa of complexes were carried out, which indicate that complex 2 is more active against both fungal and bacterial strains as shown by % inhibition data.     

Thermodynamic and spectrographic studies on the interactions of ct-DNA with 5-fluorouracil and tegafur

The interactions of calf thymus deoxyribonucleic acid (ct-DNA) with two antitumour drugs (5-fluorouracil and tegafur) in aqueous buffer solution (pH 7.40) have been investigated using nano-watt-scale isothermal titration calorimetry (ITC), circular dichroism (CD), ultraviolet absorption (UV) and fluorescence spectroscopy. Thermodynamic parameters, i.e., binding proportions and constants, standard changes of enthalpy (ΔH°), Gibbs free energy (ΔG°) and entropy (ΔS°) have been derived from the calorimetric data. The binding ratios of 5-fluorouracil and tegafur with base pairs in ct-DNA are 1:3 and 1:4, respectively. The thermodynamic parameters have been discussed according to the influence of drugs on molecular structure of the DNA shown spectrogram. The results indicate that molecule of 5-fluorouracil or tegafur can intercalate itself into the intra-molecular space formed by DNA double helix and cause some changes in the secondary structure of DNA molecule.     

Study on the interaction of puerarin with lysozyme by spectroscopic methods

The interaction between lysozyme (LYSO) and puerarin has been studied at three temperatures (294, 302 and 310K) through/using fluorescence spectroscopy and circular dichroism (CD). The LYSO fluorescence was quenched by the binding of puerarin to LYSO. The binding constants and the number of binding sites can be calculated from the data obtained from fluorescence quenching experiments. According to the van't Hoff equation, the standard enthalpy change (DeltaH degrees ) and standard entropy change (DeltaS degrees ) for the reaction were calculated to be 17.47kJ/mol and 163.5J/molK. It indicated that the hydrophobic interactions play a main role in the binding of puerarin to LYSO. In addition, the distance between puerarin (acceptor) and tryptophan residues of LYSO (donor) was estimated to be 1.47nm on the basis of fluorescence energy transfer. The changes of LYSO secondary structure in the presence of puerarin were observed from CD spectroscopy.     

光谱法研究Cu2+与肌红蛋白的相互作用

用紫外吸收光谱、荧光光谱、同步荧光光谱及圆二色(CD)谱研究了Cu2+与肌红蛋白(Mb)的相互作用. 结果发现, Cu2+使Mb的紫外吸收增强, 峰位蓝移, 说明Cu2+与Mb发生了较强的相互作用; Mb的特征荧光峰猝灭, 且随着温度升高猝灭常数Ksv降低, 表明Cu2+对Mb的荧光猝灭机制属于静态猝灭; 计算了不同温度下的结合常数和结合位点数; 由van′t Hoff方程计算出ΔH和ΔS分别为-11.60 kJ/mol和33.77 J·(mol·K)-1, 得出二者之间的作用力主要为静电力; 并依据Förster非辐射能量转移理论确定了给体-受体间的结合距离r=2.56 nm. 同步荧光光谱表明, Cu2+对Mb的构象产生影响, 使色氨酸残基的疏水性下降. CD光谱测得加入Cu2+后, 二级结构发生改变, 使α-螺旋含量降低.     

Fluorometric investigation on the interaction of oleanolic acid with bovine serum albumin

The interactions between oleanolic acid and bovine serum albumin (BSA) have been studied by fluorescence, circular dichroism (CD), UV–vis absorption and Fourier transform infrared spectroscopy (FTIR) under physiological conditions. Spectroscopic analysis of the emission quenching at different temperatures has revealed that the quenching mechanism of bovine serum albumin by oleanolic acid is static quenching mechanism. The binding sites number n and binding constants K are obtained at various temperatures. The distance r between oleanolic acid and the protein is evaluated according to the theory of Forster energy transfer. The results by FTIR, CD and UV–vis absorption spectra experiment indicate that the secondary structures of protein have been perturbed in the presence of oleanolic acid. The thermodynamic parameters ΔH⁰, ΔG⁰, and ΔS⁰ are calculated according to van’t Hoff equation, which indicates that the hydrogen bonds and van der-waals are the intermolecular forces stabilizing the complex. Molecular modeling studies the interaction BSA with oleanolic acid.     

白藜芦醇与DNA相互作用的研究

在pH=7.4的Tris-HCI缓冲溶液中,采用紫外光谱、荧光光谱及粘度法研究了白藜芦醇与小牛胸腺DNA(ctDNA)的相互作用。在生理条件下,白藜芦醇可以与ctDNA相互作用形成复合物,运用双倒数法求出了白藜芦醇与ctDNA相互作用的热力学参数。白藜芦醇能有效猝灭吖啶橙(AO)-DNA体系的荧光,猝灭方式为生成复合物的静态猝灭。粘度法实验证明ctDNA溶液的粘度随着白藜芦醇浓度的增加而增大。结果表明,白藜芦醇与DNA发生了较强的相互作用,其键合模式为经典的插入方式。     

利福布汀与人血清白蛋白相互作用的光谱研究

用荧光光谱法和圆二色谱法研究了利福布汀(RB)与人血清白蛋白(HSA)的相互作用. 结果表明, RB与HSA之间的相互作用主要是疏水作用, 作用机制是静态猝灭与动态猝灭的结合. 其结合常数(Ka)在106数量级, 说明RB和HSA有很强的结合. 此外, 探讨了金属离子(Cu2+, Zn2+, Mg2+ 和Ca2+)对RB与HSA结合常数的影响. 同步荧光光谱和圆二色谱数据表明, RB可导致HSA的构象改变.     

温度对中性红与小牛胸腺DNA相互作用的影响

用光谱法和电化学法研究了温度对中性红 (NR)与小牛胸腺DNA (CTDNA)相互作用的影响 ,在低温下和在低浓度下NR嵌入到CTDNA碱基内部 ,NR的显色团嵌入G -C碱基对并与核酸双螺旋的对称轴垂直 (γ =90°) ,当温度升高时 ,部分NR从DNA双螺旋中脱出 ,嵌入的NR发色团的长轴转变为与DNA双螺旋的对称轴成 45°角 (γ =45°)。     

Study on the Interaction of Nd3+ with Human Serum Albumin at Molecular Level

Neodymium is applied widely in agriculture to improve crop nutrition and incidentally in fertilizers, yet little is known of its effect on the biological function of human serum albumin (HSA). The interaction of Nd³⁺ to HSA has been investigated mainly by fluorescence spectra, UV–vis absorption spectra and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of HSA by Nd³⁺ was a static quenching process and the binding constant is 5.71 × 10⁴ L mol^‐1 and the number of binding sites is 1 at 292 K. The thermodynamic parameters (ΔH⁰ = ‐20.79 kJ mol^‐1, ΔG⁰ = ‐26.58 kJ mol^‐1, and ΔS⁰ = 19.85 J mol^‐1 K^‐1) indicate that electrostatic effect between the protein and Nd³⁺ is the main binding force. The distance r = 2.91 nm between donor (HSA) and acceptor (Nd³⁺) was obtained according to Förster's nonradiative energy transfer. In addition, UV–vis, CD and synchronous fluorescence results showed that the addition of Nd³⁺ changed the conformation of HSA.     

农药异丙威与小牛胸腺DNA的作用研究

在生理酸度条件下,采用紫外光谱和荧光光谱法研究异丙威与小牛胸腺DNA的作用表明:DNA对异丙威的荧光有明显的猝灭作用,属于静态猝灭方式;K4[Fe(CN)6]猝灭试验发现DNA对异丙威有明显的保护作用,离子强度的改变对异丙威和异丙威-DNA体系的荧光均无明显影响;异丙威的加入使DNA的熔点升高,并且异丙威能够竞争置换EB与DNA的结合位点。上述实验也表明,异丙威以嵌插方式作用于DNA的结合位点,有可能通过形成DNA加合物的形式造成DNA损伤,从而最终导致基因突变。     

红景天苷与DNA的结合作用研究

在pH=7.4的生理酸度条件下,采用荧光光谱和紫外-可见光谱法,并结合I-效应、离子强度的影响、DNA熔点及粘度测定等实验手段,研究了红景天苷与小牛胸腺DNA的相互作用.结果表明,DNA对红景天苷的内源荧光有明显的猝灭作用,猝灭过程为静态猝灭.由荧光猝灭实验数据,计算出不同温度下红景天苷与DNA之间作用的结合常数和热力...     

Studies on the binding of nevadensin to human serum albumin by molecular spectroscopy and modeling

The binding of nevadensin to human serum albumin (HSA) in aqueous solution was investigated for the first time by molecular spectroscopy and modeling at pH 7.4. Spectrophotometric observations are rationalized in terms of a static quenching process and binding constant (K_a, K_b) and the number of binding sites (n ≈ 1) were evaluated by fluorescence quenching methods. Thermodynamic data showed that nevadensin was included in the hydrophobic cavity of HSA mainly via hydrophobic interactions. The value of 3.09 nm for the distance r between the donor (HSA) and acceptor (nevadensin) was derived from the fluorescence resonance energy transfer. Spectrophotometric techniques were also applied to investigate the structural information of HSA molecules on the binding of nevadensin and the results showed that the binding of nevadensin to HSA did not change significantly molecular conformation of HSA in our experimental conditions. Furthermore, the study of molecular modeling also indicated that nevadensin could strongly bind to the site I (subdomain IIA) of HSA mainly by a hydrophobic interaction and there are hydrogen bond interactions between nevadensin and the residues Arg-218, Arg-222, Lys-195, and Asp-451. As compared to the other flavonoids, the flavonoids containing methoxy groups which are in aromatic rings can bind to HSA with higher affinity.     

Fluorometric investigation of the interaction of bovine serum albumin with surfactants and 6-mercaptopurine

Fluorescence quenching in solutions of bovine serum albumin has been investigated in the presence of 6-mercaptopurine and ionic surfactants. Spectroscopic analysis of the emission quenching at different temperatures revealed that the quenching mechanism of bovine serum albumin by 6-mercaptopurine was dynamic quenching mechanism. The Stern–Volmer quenching model has been successfully applied, and the activation energy of the interaction between 6-mercaptopurine and bovine serum albumin as much as 4.26 kJ mol⁻¹ was calculated. The distance r between donor (bovine serum albumin) and acceptor (6-mercaptopurine) was obtained according to fluorescence resonance energy transfer (FRET). The result of synchronous fluorescence spectra shows that the conformation of bovine serum albumin has been changed at the present of 6-mercaptopurine.     

Effect of gelatin on micellization and microstructural behavior of amphiphilic amitriptyline hydrochloride drug solution: A detailed study

Herein we have investigated the dealings between amphiphilic antidepressant drug amitriptyline hydrochloride (AMT) and gelatin interaction using different proposed techniques. AMT is used for the treatment of mental/mood problems such as depression. Gelatin interacts with this drug alike fashions to the interaction of polymers and surfactants i.e., critical aggregation concentration (cac) and polymer saturation point (psp) were together achieved significantly. AMT and gelatin interaction starts due to the highly surface active complex formation as disclosed by decreasing of surface tension of gelatin solution by adding of AMT. It was uncovered from results that cac decreases on increasing the gelatin concentrations, whereas psp increases which is a sign of the attraction between AMT and gelatin. Thermodynamic parameters were also evaluated and discussed in detail. Fluorescence measurements were used to find the values of average aggregation numbers (N_agg) and various other parameters like Stern–Volmer constant (K_sv) and micropolarity. The nuclear magnetic resonance (¹H NMR) data suggested that AMT interacts with gelatin by the means of hydrophobic interaction. The ¹H NMR experiments explain that the extent of chemical shifts (δ) and line width (lw) increases with the increase in gelatin concentration. Secondary structure of gelatin was also examined via circular dichroism (CD) technique at different concentration of AMT. CD results confirmed that with increasing drug concentration the random coil portion of gelatin enhances. Field emission scanning electron microscope (FESEM) provided clear pictures of (drug + gelatin) interaction.     

光谱法和电化学法研究中性红与小牛胸腺DNA的相互作用

利用紫外 可见和圆二色光谱(CD)法和伏安方法,研究了小分子染料中性红(NR)与小牛胸腺DNA(CTDNA)的相互作用。实验表明在NR低浓度下,NR能嵌入至核酸双螺旋的碱基内部在G C处与核酸结合,而在较高浓度情况下,嵌入的NR分子与后来的在核酸双螺旋外部的NR分子相互作用发生聚集,从而堆积在DNA双螺旋的表面,同时使核酸的构象由B型转变为Z型。用光谱滴定的方法获得NR与CTDNA作用内部结合常数,分别为:Ka1=2 4×104mol·L-1·cm-1和Ka2=2 1×10-2mol·L-1·cm-1。     

Studies of (3-mercaptopropyl)trimethoxylsilane and bis(trimethoxysilyl)ethane sol–gel coating on copper and aluminum

Berbamine, a naturally occurring isoquinoline alkaloid extracted from Berberis sp., is the active constituent of some Chinese herbal medicines and exhibits a variety of pharmacological activities. The effects of berbamine on the structure of bovine serum albumin (BSA) were investigated by circular dichroism, fluorescence and absorption spectroscopy under physiological conditions. Berbamine caused a static quenching of the intrinsic fluorescence of BSA, and the quenching data were analyzed by application of the Stern–Volmer equation. There was a single primary berbamine-binding site on BSA with a binding constant of 2.577 × 10⁴ L mol⁻¹ at 298 K. The thermodynamic parameters, enthalpy change (ΔH⁰) and entropy change (ΔS⁰) for the reaction were −76.5 kJ mol⁻¹ and −173.4 J mol⁻¹ K⁻¹ according to the van’t Hoff equation. The results showed that the hydrogen bond and van der Waals interaction were the predominant forces in the binding process. Competitive experiments revealed a displacement of warfarin by berbamine, indicating that the binding site was located at Drug sites I. The distance r between the donor (BSA) and the acceptor (berbamine) was obtained according to the Förster non-radiation energy transfer theory. The results of three-dimensional fluorescence spectra, UV–vis absorption difference spectra and circular dichroism of BSA in the presence of berbamine showed that the conformation of BSA was changed. The results provide a quantitative understanding of the effect of berbamine on the structure of bovine serum albumin, providing a useful guideline for further drug design.     

Simple and sensitive fluorometric sensing of malachite green with native double-stranded calf thymus DNA as sensing material

A novel fluorometric sensing of malachite green is proposed in this paper. The native double-stranded calf thymus DNA was used as sensing material. In the presence of native double-stranded calf thymus DNA, malachite green could interact with the DNA, which resulted in a strong fluorescence emission. The fluorescent intensity was linear with malachite green concentration in the range of 4.0 × 10⁻¹⁰ − 1.8 × 10⁻⁷ g ml⁻¹ and the limit of detection was 2.0 × 10⁻¹⁰ g ml⁻¹. Before fluorescence measurement, the only required operation is the mixing of two solutions. So, this method is rather simple and rapid. The method is very safe for the analyst. Furthermore, the mechanism for fluorescence enhancing of native double-stranded calf thymus DNA on MG was proposed based on a series of experiments. The results suggest that the interaction between MG and calf thymus DNA is intercalation in nature.     

圆二色性测定蛋白质在超细粒子上吸附的构象变化

研究了蛋白质在超细粒子固体表面吸附过程中构象的变化;选择的吸附剂粒径很小,可以直接应用圆二色性光谱测定蛋白质吸附层的二级结构变化;研究了pH、固体吸附表面在蛋白质吸附过程中对蛋白质构象的影响,得到了较好的实验数据,为进一步进行蛋白质吸附机理的理论研究提供了基础。