Interaction of unfolded lysozyme with hexa(oxyethylene) dodecylether

Reduced lysozyme at pH 2.5 bound hexa(oxyethylene) dodecylether in two steps and the bound amount of the surfactant reached as much as 0.5–0.6 mole per mole amino acid residue in the cooperative binding step. Circular dichroism (CD) spectra suggested a change in the polypeptide main-chain conformation as a result of the surfactant binding, but little or no organization of the tertiary structure. The interaction most likely took place between the hydrocarbon tail of the surfactant and the hydrophobic domain of reduced lysozyme. Alkylated lysozyme, obtained from the reaction with iodoacetamide, gave an essentially identical binding isotherm to that of reduced lysozyme, but different CD results were obtained for each of them.This research was partially supported by a grant-in-aid for scientific research (No. 02403004) from the Ministry of Education, Science, and Culture, Japan, and also by Nippon Oil & Fats Co., Ltd.     

The interaction of anionic azo dyes with hen egg-white lysozyme: 2

In continuation of our preceding study, this report describes pH and ionic strength dependences of the binding constants of six anionic azo dyes to lysozyme, the competitive binding of the dyes with the substrate analogues of lysozyme and the change in the circular dichroism of lysozyme by the dye binding. The binding constants were obtained from the difference spectra of visible absorption. With an increase in pH from 5.0 to 7.0 the constants for the dyes (1st of the two modes of the binding of a dye named D3) are reduced. The increase in ionic strength from 0.1 to 0.2 also reduces the values of the constant. Competitive binding was found between D3 and the analogues, but not for the other dyes. The change in the circular dichroism due to the electronic perturbation of tryptophyl residues in lysozyme was found. From these evidences, Lys 33 in lysozyme is pinpointed as the most credible binding site for the dyes (1st mode binding of D3). An unspecified location near the subsiteB in lysozyme is addressed for 2nd mode binding of D3.     

Kinetics of adsorption and desorption of sodium alkyl sulfates to and from nylon particles

The desorption rate of surfactant ions from nylon particles was investigated at the concentrations below the critical micelle concentration by applying the stopped-flow method. A mixing cell of stopped-flow spectrophotometer was modified with platinum electrodes for electric conductivity detection. The change in electric conductivity with time in the desorption process was monitored by a memory-recorder system. The surfactants used were sodium decyl, sodium dodecyl, sodium tetradecyl, and sodium hexadecyl sulfates. The desorption rate was independent of the surfactant concentration and the rate constants were obtained by applying the first-order reaction scheme. The adsorption rate constants were estimated from the experimental desorption rate constants and equilibrium constants assuming the second-order kinetics. The desorption rate constants were determined to be 1–6 sec^–1 and the adsorption rate constants to be 2–8×10⁴ mol^–1 dm³ sec^–1; the former decreased and the latter increased with increasing number of carbon atoms in alkyl chain of the surfactants.     

羟基功能化离子液体与溶菌酶相互作用的研究

采用荧光光谱和紫外吸收光谱研究了羟基功能化离子液体1-(1,2-二羟基丙基)-3-甲基咪唑氯盐([2,3-dhpmim]Cl)、1-(1,2-二羟基丙基)-3-甲基咪唑四氟硼酸盐([2,3-dhpmim]BF4)、1-(1,2-二羟基丙基)-3-甲基咪唑六氟磷酸盐([2,3-dhpmim]PF6)与溶菌酶的相互作用。研究发现此3种离子液体对溶菌酶的荧光猝灭均为静态猝灭;同步荧光显示离子液体与溶菌酶肽链上的色氨酸残基作用,色氨酸残基微环境发生改变;结合常数和结合位点数按照[2,3-dhpmim]Cl、[2,3-dhpmim]BF4、[2,3-dhpmim]PF6顺序依次增大,并随温度的升高而增大。     

Interaction of Carrier Protein with Potential Metallic Drug Candidate N-Glycoside ‘GATPT’: Validation by Multi-Spectroscopic and Molecular Docking Approaches

Lysozyme is often used as a model protein to study interaction with drug molecules and to understand biological processes which help in illuminating the therapeutic effectiveness of the drug. In the present work, in vitro interaction studies of 1-{(2-hydroxyethyl)amino}-2-amino-1,2-dideoxy-d-glucose triphenyl tin (IV) (GATPT) complex with lysozyme were carried out by employing various biophysical methods such as absorption, fluorescence, and circular dichroism (CD) spectroscopies. The experimental results revealed efficient binding affinity of GATPT with lysozyme with intrinsic binding (K_b) and binding constant (K) values in the order of 10⁵ M⁻¹. The number of binding sites and thermodynamic parameters ΔG, ΔH, and ΔS at four different temperatures were also calculated and the interaction of GATPT with lysozyme was found to be enthalpy and entropy driven. The CD spectra revealed alterations in the population of α–helical content within the secondary structure of lysozyme in presence of GATPT complex. The morphological analysis of the complex with lysozyme and lysozyme-DNA condensates was carried out by employing confocal and SEM studies. Furthermore, the molecular docking studies confirmed the interaction of GATPT within the larger hydrophobic pocket of the lysozyme via several non-covalent interactions.     

Induced circular dichroiism spectra of benz[b]anthracene included inβ-cyclodextrin

The assignment of the absorption spectra of benz[b]anthracene (1) is reported by measuring the induced circular dichroism spectra of the -cyclodextrin complex with1. It is concluded from the signs of the induced circular dichroism bands that the first absorption band (20.4–30.9×10³ cm^–1) has the transition dipole moment perpendicular to the long axis and the second absorption band (30.9–37.2×10² cm^–1) has the transition dipole moment parallel to the long axis of1. Our assignments are in complete agreement with earlier assignments. The induced circular dichroism spectra exhibit Cotton splittings at 19.1×10³ and 42.8×10³ cm^–1. It can be concluded from Cotton splittings of the induced circular dichroism spectra that the association of two 1:1 inclusion complexes forms a ground-state dimer.     

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.     

硫堇与寡核苷酸结合序列选择性的光谱研究

用UV-Vis吸收光谱、荧光光谱、圆二色谱以及核磁共振光谱等手段研究了硫堇(TH)与两个不同序列寡核苷酸的作用。TH与寡核苷酸作用后的吸收光谱和荧光光谱产生了明显的减色红移和荧光猝灭效应。分别计算了TH与[oligo d(GC)]2和[oligo d(AT)]2作用的荧光猝灭常数和结合常数,结果表明TH与GC序列的结合能力比与AT序列更强。通过TH与[oligo d(GC)]2作用后双螺旋链构象变化以及TH质子的1HNMR谱峰明显变宽,进一步说明TH与寡核苷酸结合的序列选择性。     

Characterization of p-hydroxybenzoic acid methylester physi- and chemiadsorbates on silica by IR and UV-spectroscopy

Physiadsorbates and chemiadsorbates of p-hydroxybenzoic acid methylester (pHBAME) on colloidal and porous silicas were studied by IR and UV spectroscopy. In the IR spectra of self-supporting discs of the adsorbates, typical features were detected which allow differentiation between the physi- and the chemiadsorbed state: a strong absorption band at 1417 cm^–1 characterizes the chemiabsorbate. Dehydration by annealing and rehydration of the adsorbates proceeded also in a different way, indicated by absorption bands both in the carbonyl group and in the ring vibration frequency range. In the UV spectra the absorption maximum of the chemiadsorbate occured at 250 nm and that of the physiadsorbate at 255.5 nm (from cyclohexane suspensions of the adsorbates).Dedicated to Prof. Dr. Paul Heinz List on the occasion of his 65^th birthday.     

Interaction of poly(L-glutamic acid) with cationic surfactants carrying different head groups

Three cationic surfactants carrying a common hydrocarbon tail (dodecyl group) interact differently with fully ionized poly(L-glutamic acid)(PGA), depending on the type of their ionic head groups. Decrease of pH occurred in the order; dodecylammonium chloride (DAC) > dodecyldimethylammonium chloride (DDAC) > dodecyltrimethylammonium chloride (DTAC). The-helix of PGA was strongly induced by the addition of DAC and DDAC but weakly by DTAC. The induction was inhibited when NaCl concentration was greater than 0.05 M. In the solid state, proton transfer through hydrogen bonds from ionic heads of DDAC to carboxylate groups of the polypeptide was observed. Distortion of circular dichroism spectra occurred at high mixing ratios of surfactant to polymer, due to the aggregation of-helices, as confirmed by light scattering measurements and infrared absorption spectra.     

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.     

Infrared and raman studies on the phase structure of barium ethyl(octyl)phosphate-water system

Barium ethyl(alkyl)phosphates, as new simple surfactants ((C₂H₅O)(RO)-PO ₂ ^– )₂Ba²⁺ with various chain length ofR, were synthesized. The infrared spectra in the CH stretching region were measured for these surfactants in the solid state and in aqueous solution, and assignments were made. In particular, the ordering and environment of octyl chains in the different phases of the barium ethyl(octyl)phosphate-water system were studied by the Fourier-transform-infrared and Raman spectra. The CH stretching bands in the infrared spectra reflected the ordering and environment of octyl chains in each phase. The Raman band connected to the PO ₂ ^– symmetric stretching mode was sensitively shifted. This was caused by the change of aggregation structures with different Ba²⁺...PO ₂ ^– interaction. The infrared band arising from the PO ₂ ^– antisymmetric stretching mode was insensitive to the phase structures. The C–C stretching region in the infrared spectra was used to discuss the ordering of each phase.     

New organosols of ZnS and HgS in N,N-dimethylformamide and dimethyl sulfoxide. Use in the preparation of semiconductive polymer-metal sulfide composite films

Organosols of ZnS and HgS in N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) were prepared by reaction of Zn and Hg salts with H₂S. ZnS in the DMF organosol has a particle size of about 300 Å, determined by an argon laser scattering technique. The form of HgS in the organosols varies with temperature, concentration of HgS, and type of solvent;-HgS in a DMF organosol is converted into-HgS at –30 °C or above. Poly(acrylonitrile)-ZnS or -HgS composite films prepared from organosols are semiconductive, and the electrical conductivity of the film increases by a factor of 10²–10³ on exposure to moisture or alcohol vapour. Poly(acrylonitrile)--HgS composite films, prepared from heated-HgS, show electrical conductivity of a range of 10^–1–10^–2 S cm^–1 and a large electron mobility.     

Binding of benzopurpurin 4B to poly(N-vinyl-2-pyrrolidone): A spectral study on the mechanism of dye binding

The binding mechanism of benzopurpurin 4B to poly(N-vinyl-2-pyrrolidone) was studied by a spectrophotometric absorbance change method at pH 7.1 in 0.05 mol dm^–3 phosphate buffer. The results were analyzed by Scatchard, Hill, and Schwarz methods. The different shapes of the Scatchard plots indicated the varying degrees of cooperativity which depended on the percent saturation of binding sites. The Hill method elucidated the pairwise binding of the dye to polymer at the intermediate saturation and multimolecular binding both at the low and high saturations. The Schwarz method confirmed the interaction between bound dye molecules which led to cooperativity. The difference spectra of the polymer-dye complex evidenced the elucidated binding mechanism.     

Simultaneous occurrence of energy transfer and photoinduced electron transfer in interactions of hen egg white lysozyme with 4-nitroquinoline-1-oxide

The carcinogenic drug 4-nitroquinoline-1-oxide (4NQO) has been found to bind with the protein hen egg white lysozyme as evident from fluorescence quenching experiments. The binding constant and stoichiometry have been determined. The values of the thermodynamic parameters indicate that the interaction is an enthalpy-driven spontaneous phenomenon. The experimental value of change in free energy is similar to that obtained from the docking study. The far UV circular dichroism spectra show some changes in the secondary structure of protein. The high value of bimolecular quenching constant leads to the possibility of Förster resonance energy transfer (FRET). Along with FRET, the photoinduced electron transfer (PET) from tryptophan residue of protein to 4NQO has also been evident from the transient absorption spectra obtained in laser flash photolysis experiments. The simultaneous occurrence of FRET and PET is the key factor for quenching of intrinsic fluorescence of the protein as it binds with the drug.     

牛血红蛋白与双十二烷基二甲基溴化铵相互作用的光谱研究(英文)

运用荧光光谱、紫外-可见吸收光谱和圆二色谱法研究了双十二烷基二甲基溴化铵(DDAB)与牛血红蛋白(Hb)的相互作用。从紫外-可见吸收光谱观察到,随着DDAB的浓度增大,Hb在406nm处的特征吸收峰强度下降,且峰位蓝移,说明DDAB导致血红素辅基微观环境变化。由荧光光谱研究可以得出随着DDAB的浓度增大,Hb在340nm处的荧光强度逐渐增强,说明导致色氨酸荧光淬灭的血红素辅基与色氨酸的距离增大。由Scatchard方程计算了不同温度下该反应的表观结合常数、结合位点数及结合热力学参数,热力学参数的变化表明DDAB与Hb之间以疏水作用力为主。圆二色谱的研究进一步表明DDAB使Hb产生轻微的二级结构改变,α-螺旋含量增加.     

Effects of urea and a nonionic surfactant on the micellization and counterion binding properties of cetyltrimethyl ammonium bromide and sodium dodecyl sulfate

Micellization characteristics and counterion binding properties of cetyltrimethyl ammonium bromide (CTAB) in presence of urea and a nonionic surfactant polyoxyethylene sorbitan monolaurate (PSML), and of sodium dodecyl sulphate (SDS) in presence of urea as well as of several mixtures of CTAB with a bile salt, sodium cholate (NaC), and sodium chloride have been studied. Both urea and PSML have increased the critical micelle concentration (CMC) of the surfactants, the former being more effective than the latter. The analysis of the results supports the pseudophase micellar model to hold over the mass action model. Pure CTAB micelles bind more counterions (96 %) than pure SDS micelles (87 %), and the decreasing effect of urea on the binding is less in case of the former than the latter. A 41 mixture of CTAB and sodium cholate (NaC) can micellize and the micelles bind 87 % bromide ion, whereas 21 and 11 mixtures do not micellize. Micelles of 11 mixture of CTAB and NaCl can bind counter bromide ions to the extent of 92 %. The limiting concentrations of urea required to effect counterion binding by CTAB and SDS micelles are 0.15 mol dm^–3 and 0.25 mol dm^–3, respectively. Such effect is shown by PSML on CTAB at a ratio 0.281. The activation energy of conduction of SDS has increased in the presence of urea up to a concentration of 4 mol dm^–3, at higher concentrations the activation energy has decreased, the effect being more for surfactant concentration above CMC than below.     

Adsorption of polyethylene glycol from aqueous solution on montmorillonite clays

Adsorption rates and capacities of polyethylene glycol (PEG) were investigated for five montmorillonite clays. The adsorption of PEG for all the montmorillonite clays was rapid, and equilibrium was attained within 30 min. The adsorption isotherms of PEG for all the montmorillonites conformed to the Freundlich equation. The adsorption heats were 7.3 and 11.6 kJ · mol^–1(mw.:2000), and 8.7 and 14.2 kJ · mol^–1(mw.:20000) for the montmorillonite and the bentonite II-Ca, respectively. Adsorption capacities for all the clay samples approached constants for the molecular weight of PEG over 2000, though they increased with the increase of molecular weight under 2000. The adsorption capacities were slightly influenced by a nearly neutral pH. The montmorillonite clays which had different interlayer cations showed quite different adsorption capacities. The bentonite II-Ca, the acid clay, and the activated clay showed large adsorption capacities that were 30–50 % of that of an activated carbon.     

Effect of spermine conjugation on the interaction of acridine with alternating purine-pyrimidine oligodeoxyribonucleotides studied by CD, fluorescence and absorption spectroscopies

We studied by electronic spectroscopies the interaction between double-stranded oligonucleotides containing either adenine-thymine or guanine-cytosine alternating sequences and N(1)-(acridin-9-yl)-1,16-diamino-4,8,13-triazahexadecane, which is a conjugated molecule formed by the covalent binding of spermine and 9-aminoacridine moieties via a trimethylene chain. Solutions containing the oligonucleotides and the conjugate, at different molar ratios, were studied by using electronic absorption, fluorescence emission and circular dichroism. Calculated association constants and fluorescence emission spectra showed that spermine conjugation induces sequence selectivity. The orientation of the intercalated acridine rings with respect to the oligonucleotide base planes was deduced from the electronic circular dichroism spectra. Evidence of the formation of spermine-induced aggregated structures, with potential applications to DNA packaging, gene therapy and anti-tumor therapy, was also achieved. Our data demonstrates that this spermine-acridine conjugate adds several specific characteristics provided by the polyamine moiety, as sequence selectivity, to the interesting properties of acridine derivatives.     

Thermodynamic and structural study of pyrene-1-carboxaldehyde/DNA interactions by molecular spectroscopy: Probing intercalation and binding properties

The binding of pyrene-1-carboxaldehyde (1-PyCHO) with ctDNA was investigated through absorption, intrinsic and induced circular dichroism, viscosity measurements and steady-state fluorescence. The binding and the number of monomer units of the polymer involved in the binding of one dye molecule (site size) have been quantified. The results indicated that the 1-PyCHO molecule binds to the ctDNA in an intercalative mode. The spectroscopic evidence of this intercalation process is also corroborated by the effect of urea, iodide-induced fluorescence quenching of pyrene-1-carboxaldehyde and competitive binding using a fluorescent intercalator, SYBR Green I (SG). The induced circular dichroism (ICD) spectra of pyrene-1-carboxaldehyde complexed with ctDNA show that pyrene-1-carboxaldehyde intercalates into ctDNA and that the intercalation orientation of pyrene to the DNA base-pairs long axis is heterogeneous. On the other hand, the intrinsic circular dichroism (CD) spectra show a stabilization of the right-handed B form of ctDNA, due to the intercalation process.