Simple method for the preparation of DNA-poly(o-methoxyaniline) hybrid: structure, morphology, and uncoiling of poly(o-methoxyaniline) on the DNA surface

The DNA-poly(o-methoxyaniline) (POMA) hybrid is prepared by mixing aqueous solutions of POMA [emeraldine salt (ES), doping level [Cl]/[N] = 0.52] and sodium salt of DNA (Na-DNA) and is then freeze-dried after 4 days. Three different compositions (WDNA = 0.25, 0.5, and 0.75, WDNA is the weight fraction of DNA) of the hybrids are prepared. The SEM pictures show a gradation in morphology; for example, for WDNA = 0.75, fibrils are present but, at lower DNA concentration, a fibrillar network structure of the hybrid is observed. The circular dichroism (CD) spectra of the hybrid solutions indicate unchanged DNA conformation and WAXS patterns indicate intact crystal structure of DNA in the hybrid. The UV-vis spectra suggest no denaturation of DNA during the blending process. The UV-vis spectra of the hybrids in aqueous medium show a gradual red shift of the pi band to polaron band transition with time. The plots of these wavelengths with time are sigmoidal, indicating the autocatalytic nature of the process. With an increase in the temperature, the rate of the red shift of the above peak is faster. Arrhenius analysis of the rate (1/tau700 where tau700 is the time required to reach the absorption maximum at the wavelength 700 nm) yields straight lines for the three hybrid compositions with activation energy values of 13-15 kcal/mol. These values are almost equal to the activation energy values of conformational transition of other polymers, supporting the red shift in UV-vis spectra occurs from conformational transition. DNA offers a surface where POMA gets adsorbed and the stable conformational transition resulting in the uncoiling of the POMA chain occurs through repulsive interaction among bound radical cations of POMA (ES) on the DNA surface. The conductivity of the hybrids is on the order of 10(-6) S/cm, and the I-V characteristic curves indicate the semiconducting nature of the hybrids.     

Formation of silver nanoparticles in deoxyribonucleic acid-poly(o-methoxyaniline) hybrid: a novel nano-biocomposite

A novel nano-biocomposite of silver and poly(o-methoxy aniline) (POMA)/DNA hybrid has been prepared by adding DNA solution to an aqueous solution of POMA (emeraldine base, EB) and AgNO(3) mixture. The mixture was aged for 10 days and was freeze-dried to form the hybrid nanocomposite (weight fraction of DNA = 0.75). FESEM pictures show a fibrillar network morphology of the biomolecular hybrid with silver nanoparticles on its surface. The TEM picture also corroborates silver nanoparticle formation in the biomolecular hybrid, and the denser population of nanoparticles in the TEM micrograph as compared to that in the SEM micrograph indicates that the nanoparticles are present inside the fibrils in greater proportion. The dc conductivity value of the hybrid indicates that POMA (EB) is doped by silver ion and the doped POMA form complexes with DNA through electrostatic interaction of the radical cation of POMA (emeraldine salt form, ES) and the DNA anion. During the doping process and Ag nanoparticle formation, a fluctuation of the pi band to polaron band transition peak occurs together with a complementary fluctuation of the polaron band to pi* band transition peak. After 53 h of aging, the former shows a slow but continuous red shift with aging time. This has been attributed to the slow uncoiling of POMA on the DNA surface. The conformation and crystal structure of DNA remain intact during the nano-biocomposite formation. The dc conductivity value of the nano-biocomposite is almost the same as that of the pure POMA-DNA hybrid at the same composition, but the I-V characteristic curve of the nano-biocomposite is somewhat different showing an insulating region on low applied voltage. At higher applied voltage, it shows a semiconducting property characterizing the large band gap semiconducting behavior of the nano-biocomposite.     

Comparative studies of solid‐state synthesized poly(o‐methoxyaniline) and poly (o‐toluidine)

Poly(o‐methoxyaniline) (POMA) and poly(o‐toluidine) (POT) salts doped with different acids (methanesulphonic acid (MeSA), trifluoroacetic acid (TFA), and hydrochloric acid (HCl)) were synthesized by using solid‐state polymerization method. The polymers were characterized by Fourier transform infrared (FTIR) spectra, ultraviolet–visible (UV–Vis) spectrometry, X‐ray diffraction (XRD), cyclic voltammetry (CV), and conductivity measurements. Transmission electron microscopy (TEM) was done to study the morphologies of POMA and POT salts. The FTIR and UV‐Vis absorption spectra revealed that the reduced phase was predominant in POMA salts, and the pernigraniline phase was predominant in POT salts. It was found that POMA salts displayed higher doping level and conductivity. In contrast, POT salts were lower at doping levels and conductivity. In accordance with these results, the electrochemical activity was also found to be lower in POT salts. The XRD patterns showed that the POMA salts displayed higher crystallinity than POT salts. The results from TEM revealed that the morphologies of POMA salts were different from those of POT salts. Copyright © 2008 John Wiley & Sons, Ltd.     

Studies on optical absorption and photoluminescence of thioglycerol-stabilized CdS quantum dots

Nanoparticles of CdS were prepared at 303 K by aqueous precipitation method using CdSO4 and (NH4)2S in presence of the stabilizing agent thioglycerol. Adjustment of the thioglycerol (T) to ammonium sulphide (A) ratio (T:A) from 1:25 to 1:3.3 was done during synthesis and nanoparticles of different size were obtained. The prepared colloids were characterized by UV-vis and photoluminescence (PL) spectroscopic studies. Prominent first and second excitonic transitions are observed in the UV-vis spectrum of the colloid prepared with a T:A ratio of 1:3.3. Particle size analysis was done using XRD, high resolution TEM and dynamic light scattering and found to be approximately 3 nm. UV-vis and PL spectral features also agree with this particle size in colloid with T:A of 1:3.3. The band gap of CdS quantum dots has increased from the bulk value 2.4-2.9 eV. PL spectra show quantum size effect and the peak is shifted from 628 to 556 nm when the ratio of T:A was changed from 1:25 to 1:3.3. Doping of CdS with Zn2+ and Cu2+ is found to enhance the PL intensity. PL band shows blue-shift and red-shift on doping with Zn2+ and Cu2+, respectively. UV and PL spectral features of the CdS/Au hybrid nanoparticles obtained by a physical mixing of CdS and Au nanoclusters in various volume ratios is also discussed. Au red-shifts and rapidly quenches the PL of CdS. An additional low energy band approximately 650 nm is observed in the UV visible spectrum of the hybrid nanoparticles.     

Involvement of Long‐Lived Intermediate States in the Complex Folding Pathway of the Human Telomeric G‐Quadruplex

The energy landscapes of human telomeric G‐quadruplexes are complex, and their folding pathways have remained largely unexplored. By using real‐time NMR spectroscopy, we investigated the K⁺‐induced folding of the human telomeric DNA sequence 5′‐TTGGG(TTAGGG)₃A‐3′. Three long‐lived states were detected during folding: a major conformation (hybrid‐1), a previously structurally uncharacterized minor conformation (hybrid‐2), and a partially unfolded state. The minor hybrid‐2 conformation is formed faster than the more stable hybrid‐1 conformation. Equilibration of the two states is slow and proceeds via a partially unfolded intermediate state, which can be described as an ensemble of hairpin‐like structures.     

Preparation of size-controlled, highly populated, stable, and nearly monodispersed Ag nanoparticles in an organic medium from a simple interfacial redox process using a conducting polymer

The reducing property of an organically soluble conducting polymer (poly(o-methoxyaniline), POMA) is used to prepare monodisperse, size-controlled, highly populated, and highly stable silver nanoparticles in an organic medium through an interfacial redox process with an aqueous AgNO3 solution. The transition of emeraldine base (EB) to the pernigraniline base (PB) form of POMA occurs during nanoparticle formation, and the nitrogen atoms of POMA(PB) stabilize Ag nanoparticles by coordination to the adsorbed Ag(+) on the nanoparticle surface. The conductivity of the nanocomposite is on the order of 10(-11) S/cm, indicating that no doping of POMA occurs under the preparation conditions. The nanoparticles are free of excess oxidant and external stabilizer particles. The POMA (EB) concentration tailors the size of nanoparticles, and at its higher concentration (0.01% POMA with 0.01 N AgNO3), very dense Ag nanoparticles (6 x 10(15) particles/m(2)) of almost uniform size and shape are produced. The rate constant and Avrami exponent values of the nanoparticle formation are measured from the time-dependent UV-vis spectra using the Avrami equation. The Avrami exponent (n) values are close to 1, indicating 2D athermal nucleation with the circular shape of the nuclei having diffusion-controlled growth. The rate constant values are almost independent of AgNO3 concentration but are strongly dependent on POMA concentration. The higher rate constant with increasing POMA(EB) concentration has been attributed for the lowering of nanoparticle size due to increased nucleation density.     

离子液体中纳米TiO2/聚3-甲基噻吩复合膜的制备及性质研究

采用溶胶凝胶法制成了纳米TiO₂电极, 在离子液体中将其应用于3-甲基噻吩的电化学聚合, 采用循环伏安法(CV), 在线紫外可见光谱(UV-Vis), 扫描电镜(SEM)和电化学阻抗谱(EIS)对TiO₂/聚3-甲基噻吩(TiO₂/PMT)复合膜进行了表征并研究了其电化学性质. 实验证明, 不论是用循环伏安法, 恒电位, 还是恒电流方法, 都能在电极上得到聚3-甲基噻吩(PMT)膜, 并伴随有明显的掺杂和去掺杂过程. 对应的在线紫外可见光谱上, 也出现了氧化和还原两种不同的吸收状态, 还原(去掺杂)过程中在480 nm处有一个吸收峰, 而氧化(掺杂)过程中此峰消失, 取而代之的是一个可见光区的逐渐增强的吸收. PMT膜是p型半导体, TiO₂是n型半导体, 两者之间能够形成p-n异质结, 使光电转换效率得以提高. SEM给出了TiO₂电极和聚合物修饰的TiO₂的形貌图, 电极的交流阻抗谱则从一个角度说明了聚合物膜修饰电极的导电性.     

Thioether moiety functionalization of mesoporous silica films for the encapsulation of highly dispersed gold nanoparticles

Highly dispersed gold nanoparticles within mesoporous thin films (MTFs) have been synthesized through a newly developed controllable strategy, in which (1,4)-bis(triethoxysilyl)propane tetrasufide (BPTS) organosiloxane coupling agent was co-assembled with tetraethyl orthosilicate (TEOS) to form organic groups functionalized mesoporous composite films followed with oxidization, ion-exchange with Au(en)₂Cl₃ (en: 1,2-ethanediamine) compound and calcination under hydrogen/nitrogen mixing atmosphere. Small-angle X-ray diffraction (XRD) characterization indicated that up to 10 mol% of BPTS could be incorporated into mesoporous hybrid films, and that would not breakup the structural integrity and long-range periodicity. The loaded gold nanoparticles were uniformly distributed due to the molecular level homogenous mixing of the BPTS precursor with TEOS, and its concentration could be controlled via the original ratio of BPTS to TEOS. The nanoparticles had a narrow size distribution with diameters in the size range of 3-7 nm through transmission electron microscopy (TEM) observation and underwent a slight size increase with the higher gold load level. An overall increase in the absorption intensity, a red shift of absorption peak, together with a comparatively narrower bandwidth could be observed at higher gold concentration within composite films from UV-vis spectra. Wide-angle XRD, TEM, X-ray photoelectron spectroscopy (XPS) and UV-vis spectra characterizations all agreed on the fact that the gold loading level could be controlled by the amount of BPTS in the starting sol for preparing MTFs.     

Oxidation state and proton doping level in copolymers of 2-aminobenzoic acid and 2-methoxyaniline

UV-vis spectra of homopolymers and copolymers of 2-aminobenzoic acid (OAB) and 2-methoxyaniline (OMA) were analyzed in order to obtain information about the oxidation state and proton doping level of these polymers. Dimethyl sulfoxide (DMSO) was used as a solvent in which protonated forms of polyanilines are preserved and a mixture of N-methyl-2-pyrrolidone and triethylamine (0.5 %) as a solvent (NMP/TEA) in which polyanilines are assumed to be non-protonated. Polymers were prepared in the emeraldine salt form, externally doped with HCl. It was found that only external doping is eliminated in NMP/TEA while internal doping by carboxylate groups bound in OAB units remains operative. Since doped quinoid units do not contribute to the quinoid band (Q-band at 630 nm), the intensity ratio of the Q-band and benzenoid band (B-band at 320 nm) cannot be simply correlated with the oxidation state of poly(OMA-co-OAB) copolymers in contrast to poly(OMA) and polyaniline. Spectra of copolymers with less than 60 % of OMA units as well as those of poly(OAB) in DMSO and NMP/TEA are almost identical due to internal doping, which is proposed to lead to structures in which main-chain protons are coulombically bound with immobile carboxylate anions. In the spectra of copolymers with less than 60 % of OMA units, a well-resolved band occurs at 500 nm, which can be ascribed to alternating or close-to-alternating sequences of OMA and OAB units.     

Ordered supramolecular assembly of bis[3,4,1 2,13,21,22,30, 31-octa(dodecylthio)-2,3-naphthalocyaninato] erbium at the air/water interface

The supramolecular assembly of bis[3, 4, 12, 13, 21, 22, 30, 31-octa(dodecylthio)-2, 3-naphthalocyaninato] erbium complex (Er[Nc(SC₁₂H25)₈]₂) was fabricated at the air/water interface by Langmuir monolayer technique. Surface pressure-area isotherm indicates that stable monolayer is formed. The monolayer morphology on mica was investigated by atomic force microscopy (AFM). Columnar domains of ca. 100 nm X (20–30) nm appearing in the micrograph have ordered orientation. Polarized UV-vis spectra and small-angle X-ray diffraction pattern show that the macrocycles tilt in the monolayer. The orientation angle of the naphthalocyanine ring with respect to the substrate was found to be ca. 54°. Each monolayer is ca. 3.53 nm thick. The columnar domain comprises 4–6 rows of columnar supramolecular assemblies where the molecules stack face-to-face.     

铱(IV)离子与人血丙种球蛋白的作用研究

在0.1 mol•L^－1醋酸-醋酸钠(pH 5.0)体系中, 采用紫外吸收光谱、荧光光谱及同步荧光光谱法研究了人血丙种球蛋白(gamma seroglobulinum humanum, 简称GSH)与铱(IV)离子的相互作用. 结果表明, Ir(IV)离子使人血丙种球蛋白的构象发生了改变, α-螺旋含量减少, 并且用同步荧光光谱发现Ir(IV)离子与人血丙种球蛋白的作用位点更接近于色氨酸, 从而使色氨酸残基的疏水性略有减小. 荧光光谱结果表明Ir(IV)对人血丙种球蛋白内源荧光(342 nm)产生了较强的荧光猝灭作用, 根据不同温度下Ir(IV)对人血丙种球蛋白的荧光猝灭作用, 证明了这种荧光猝灭为静态猝灭机制, 计算了其结合常数和结合位点数, 从而得出了静电作用力为其主要的作用力.     

Hybrid silica-PVA nanofibers via sol-gel electrospinning

We report on the synthesis of poly(vinyl alcohol) (PVA)-silica hybrid nanofibers via sol-gel electrospinning. Silica is synthesized through acid catalysis of a silica precursor (tetraethyl orthosilicate (TEOS) in ethanol-water), and fibers are obtained by electrospinning a mixture of the silica precursor solution and aqueous PVA. A systematic investigation on how the amount of TEOS, the silica-PVA ratio, the aging time of the silica precursor mixture, and the solution rheology influence the fiber morphology is undertaken and reveals a composition window in which defect-free hybrid nanofibers with diameters as small as 150 nm are obtained. When soaked overnight in water, the hybrid fibers remain intact, essentially maintaining their morphology, even though PVA is soluble in water. We believe that mixing of the silica precursor and PVA in solution initiates the participation of the silica precursor in cross-linking of PVA so that its -OH group becomes unavailable for hydrogen bonding with water. FTIR analysis of the hybrids confirms the disappearance of the -OH peak typically shown by PVA, while formation of a bond between PVA and silica is indicated by the Si-O-C peak in the spectra of all the hybrids. The ability to form cross-linked nanofibers of PVA using thermally stable and relatively inert silica could broaden the scope of use of these materials in various technologies.     

蓝色磷光材料FIrpic的发光特性

研究了掺杂浓度及热退火对磷光材料双(4,6-二氟苯基吡啶-N,C2?)吡啶甲酰合铱(FIrpic)发光性能的影响.不同掺杂浓度的薄膜及有机电致发光器件(OELDs)的发光颜色都随FIrpic浓度的增大由蓝色逐渐变化到黄绿色.纯FIrpic薄膜的吸收光谱和光致发光(PL)光谱在440-480nm范围内有明显的光谱重叠,476nm处的发光强度随FIrpic掺杂浓度增大而降低主要是由自吸收效应引起的.测量了不同激发密度下的光致发光光谱和不同掺杂浓度下的电致发光(EL)光谱,发现530nm处的发光强度随激发强度或掺杂浓度的增大而增强,证实了530nm处的发光是来源于FIrpic分子间的激基缔合物发光.通过比较热退火前后薄膜微观形貌及电致发光器件光谱的变化,进一步证实了热退火促进FIrpic分子聚集,增强了FIrpic分子间的辐射跃迁发光.通过调控FIrpic掺杂浓度和优化器件结构,并对器件进行热退火处理得到一系列发光颜色从蓝色逐渐变化到黄绿色的有机电致发光器件.     

Resonance Light Scattering Method for Study on the Interaction Between Fluorinated Surfactant Potassium Perfluorooctanesulfonate and DNA

Resonance light-scattering (RLS) characteristics of the interactions between fluorinated surfactant potassium perfluorooctanesulfonate (PFOS) with calf thymus nucleic acid (ct DNA) were studied. After DNA was added, aggregation of PFOS on the molecular surface of DNA occurred in the pH 3.5 ～6.0, which resulted in an enhanced RLS peak at 370 nm. The RLS intensity was found to be proportional to the concentration of DNA. The determination limit was 20.0 μg · L^?1. UV-visible (UV-vis) spectra and infrared (IR) spectra both proved the binding changed the confromation of DNA.     

Ordered supramolecular assembly of bis[3,4,12,13,21,22,30,31-octa(dodecylthio)-2,3-naphthalocyaninato]erbium at the air/water interface

The supramolecular assembly of bis[3, 4, 12, 13, 21, 22, 30, 31-octa(dodecylthio)-2, 3-naphthalocyaninato] erbium complex (Er[Nc(SC12H25)8]2) was fabricated at the air/water interface by Langmuir monolayer technique. Surface pressure-area isotherm indicates that stable monolayer is formed. The monolayer morphology on mica was investigated by atomic force microscopy (AFM). Columnar domains of ca. 100 nm ×(20-30) nm appearing in the micrograph have ordered orientation. Polarized UV-vis spectra and small-angle X-ray diffraction pattern show that the macrocycles tilt in the monolayer. The orientation angle of the naphthalocyanine ring with respect to the substrate was found to be ca. 54°. Each monolayer is ca. 3.53 nm thick. The columnar domain comprises 4-6 rows of columnar supramolecular assemblies where the molecules stack face-to-face.     

界面聚合法合成聚邻苯二胺及其表征

邻苯二胺电聚合膜己广泛用于生物活性物质固定、电催化、腐蚀防护和电色材料研究,近期也用于制备分子印迹型化学/生物传感器[1,2]。人们已经研究了聚邻苯二胺的结构特性、性能及应用前景[3,4,5]。目前聚合物基纳米复合材料的制备方法主要有:分子自组装法、微乳液聚合法、电化学     

A facile preparation method for synthesis of silica sulfuric acid/poly(o‐methoxyaniline) core–shell nanocomposite

A new nanocomposite of poly(o‐methoxyaniline) (POMA) is introduced by overlayer formation of POMA on silica. The key appealing feature of the synthesis is the role of silica sulfuric acid (SSA) both as solid acid dopant and template in overlayer self‐assembly of POMA on silica surface. Hereon siloxide group (Si―O^?) of silica surface is replaced with dopant anion of SSA (≡Si―O―SO₃^?), which leads to formation of a overlayer of POMA on the silica surface. The composite particles are spherical in the nanoscale range of 50 nm without application of any external template (no‐template synthesis). Nanocomposite was fully characterized by various instrumentation methods: Fourier transform infrared (FT‐IR), ultraviolet–visible (UV–vis), thermogravimetric analysis (TGA), diffrential thermal analysis (DTA), elemental analysis (CHNS), energy dispersive X‐ray (EDX), X‐ray photoelectron spectroscopy (XPS) and X‐ray difraction (XRD). Based on XPS and CHNS results, it is demonstrated that the doping level of POMA is as high as 50% and for the first time the ratio of 4:2:2 is obtained for ―NH― (amine): ―HN^.+― (polarons): ?HN⁺― (bipolarons), respectively. In fact, bipolarons may also coexist with polarons with a 1:1 ratio of them. Moreover, the synthesis benefits from the perspective of green chemistry which is preparation under solid‐state (solvent‐free) condition. Copyright © 2015 John Wiley & Sons, Ltd.     

DNA-interaction studies of a copper(II) complex containing ceftobiprole drug using molecular modeling and multispectroscopic methods

Abstract

The interaction of the [Cu(cef)(phen)Cl₂] complex with calf-thymus DNA (ct-DNA) at physiological pH was investigated by UV-visible spectrophotometry, fluorescence measurement, dynamic viscosity measurements, circular dichroism spectroscopy, and molecular modeling. UV-vis spectra showed 5?nm bathochromic shift of the absorption band at 270?nm along with significant hypochromicity for the absorption band of the complex. The binding constant obtained of UV-vis (1?×?10⁵ M^?1) is more in keeping with intercalators and suggests this binding mode. Moreover, thermodynamic parameters indicated that hydrogen bond and van der Waals interactions play main roles in the binding of [Cu(cef)(phen)Cl₂] to ct-DNA. In addition, [Cu(cef)(phen)Cl₂]-DNA docked model is in approximate correlation with the experimental results.     

Synthesis, crystal structure, and DNA-binding study on the trinitrate{2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide))} gadolinium(III) complex

A 2,2'-[2,3-naphthylenebis(oxy)]-bis(N,N-diisopropyl(acetamide)) ligand (L) and its Gd(III) complex have been prepared and characterized. The crystal and molecular structure of the complex was determined by single-crystal X-ray diffraction. The interactions of complex with calf thymus DNA were investigated by UV-vis, fluorescence and viscosity measurements. Experimental results indicated that the complex can bind to DNA by intercalation modes. Its intrinsic binding constant is 1.03 x 10(6) M(-1).     

光谱法研究喜树碱与牛血清白蛋白的相互作用

采用多种光谱技术对喜树碱和牛血清白蛋白的相互作用进行了研究.结果表明喜树碱和牛血清白蛋白可形成基态复合物,引起牛血清白蛋白内源荧光猝灭.通过计算获得了二者在不同温度下的结合常数及结合位点数.根据喜树碱和牛血清白蛋白结合的热力学参数,确定了二者之间主要为疏水作用力.根据F(o)rster非辐射能量转移理论确定了喜树碱和牛血清白蛋白的作用距离.同步荧光光谱显示喜树碱主要与蛋白中色氨酸残基发生相互作用,改变其周围的局部构象.红外光谱提示喜树碱可引起蛋白的构象发生改变,α-螺旋二级结构减少.