Aggregation behavior of amphiphilic D-pi-A molecules bearing recognition group

Aggregation behavior of two amphiphilic D-pi -A molecules bearing barbituric acid as both recogniton group and electron-drawing substituent, 5-(4-dodecyl oxybenzylidene)-(1H, 3H)-2,4,6-pyrimidine trione (PB12) and 5-(4-N,N-didodecyl aminobenzylidene)-(1H,3H)-2,4,6-pyrimidine trione (AB(12)) was studied by UV-visible, fluorescence, and surface voltaic spectroscopies (SPS). The experimental results indicate that PB12 tends to form J-aggregate and AB(12) tends to form H-aggregate under increasing concentration. An intramolecular twisted charge transfer (TICT) emission around 500 nm is observed when J-aggregate is formed between PB12 molecules, and an excimer emission around 600 nm is observed when H-aggregate is formed between AB(12) molecules.

Tuning the aggregation of polyimide thin films by modification of their molecular interactions

Thin films of an organo-soluble polyimide based on 1,4-(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and 2,2'-dimethyl-4,4'-methylene dianiline (DMMDA) have been studied. A prism coupler was used to measure the refractive indices. The average refractive indices of thin films prepared by annealing at different temperatures and times were chosen to characterize the condensation states of thin films. Thin films annealed at 200 degrees C show irreversible changes in physical properties, eg solubility. FTIR spectroscopy showed that the chain structures of the above thin films remained unchanged. It is proposed that specific molecular interactions induce the irreversible changes revealed by fluorescence spectroscopy. (C) 2000 Society of Chemical Industry.

Fluorescence and aggregation behavior of a polyimide in solutions

The UV-visible absorption and fluorescence spectra of a soluble polyimide, YS-30, in several organic solvents were measured over a wide range of concentration. The experimental results show that there exist both intramolecular and intermolecular electron donor acceptor interactions for YS-30 molecules. The fluorescence behavior of YS-30 in N,N-dimethylacetamide and in chloroform solutions is similar in general, except that its ground-state intermolecular charge transfer emission is more obvious in N,N-dimethylacetamide solution. This difference is attributed to the greater extent of disruption of the chain packing by solvent or/and the more efficient radiationless energy dissipation process from the excited state complexes to chloroform. The intensity ratio of intermolecular charge transfer emission to intramolecular charge transfer emission is used to characterize the state of aggregation of YS-30 molecules in solutions. The plot of this ratio versus concentration indicates the existence of two critical concentrations. It is also found from the same plot that the decrease of coil size is very pronounced during the initial stage of shrinkage.

Synchronous fluorescence spectra of hemoglobin: A study of aggregation states in aqueous solutions

The synchronous fluorescence spectra of hemoglobin solutions are reported for the first rime. The main fluorescence peaks observed in the spectra are assigned. The effect of the concentration of hemoglobin solution on the spectra is studied. Characteristic fluorescence peaks due to the dimer and tetramer of hemoglobin molecules are recognized. (C) 1998 Academic Press.

The aggregation state of polyimide

The aggregation slate of polyimide in solution and in the solid state were studied using the NMR and fluorescence techniques. The experiment results show that the decay of spin-spin relaxation of polyimides with concentration can be described as a single exponential, biexponential, triexponential, biexponential profile. Meanwhile, the intensities of fluorencence spectra increase rapidly with the concentration, and some peaks have a red-shift. Based upon these experiment results, it can be concluded that polyimide in solution is very flexible, and there are several critical concentrations at which polyimide has distinctly different aggregation states. The existence of intermolecular charge transfer interaction between polyimide chains has been proved, and the interaction has a profound effect on the glass transition temperature, T-g, and the dynamic mechanical modulus of polyimide. (C) 1997 Elsevier Science Ltd.

Study on the microstructure and properties of nanosized stannic oxide powders

Stannic oxide xerogel was prepared by a forced hydrolysis method using SnCl4 as the precursor. The average grain sizes of the nanosized stannic oxide powders varied with the sintering temperatures. The powders were characterized by several different physico-chemical techniques. TEM was employed for the direct observation on grain sizes, shape and state of aggregation of the particles. XRD technique was used for the determination of the crystalline structure. Microstructural parameters of average crystallite size () and mean-square root microstrain (epsilon(2)>(1/2)) for the samples were calculated from the broadened values of the half-peak intensity of XRD. The atomic ratio between oxygen and tin in the surface region of the particles was estimated through the analysis of XPS. Attributing to lots of oxygen vacancies in the surface region of the nanoparticulates and the 'trapped electrons' in the vacancies, an ESR signal was observed in the sample sintered at 300 degrees C for 2 h. FTIR of the powders showed that intensity of the transverse optical mode of Sn-O stretching vibration increased with the sintering temperature while the bending vibration of O-Sn-O showed a blue shift. For Raman spectra, very important spectral characteristics such as variations of intensity and width of the bands were observed. A new Raman vibrational band located at 572 cm(-1) was identified in the samples of nanosized stannic oxide powders. Variation of these spectroscopic properties were strongly affected by grain size, shape and state of aggregation of the nanosized particulates.

Inhibitory effects and mechanisms of high molecular-weight phlorotannins from Sargassum thunbergii on ADP-induced platelet aggregation

We evaluated the effects of high molecular-weight phlorotannins from Sargassum thunbergii (STP) on ADP-induced platelet aggregation and arachidonic acid (AA) metabolism in New Zealand white rabbits and Wistar rats. The inhibition of STP on platelet aggregation was investigated using a turbidimetric method, and the levels of the terminal products of AA metabolism were measured using the corresponding kits for maleic dialdehyde (MDA), thromboxane B-2 (TXB2) and 6-keto-prostaglandin F-1 alpha (6-keto-PGF(1 alpha)) by colorimetry and radioimmunoassay, as appropriate. We found that STP could inhibit ADP-induced platelet aggregation, and the inhibitory ratio was 91.50% at the STP concentration of 4.0 mg/mL. Furthermore, STP markedly affected AA metabolism by decreasing the synthesis of MDA (P < 0.01) and increasing the synthesis of 6-keto-PGF(1 alpha), thus changing the plasma TXB2/6-keto-PGF(1 alpha) balance when the platelets were activated (P < 0.01). Therefore, STP altered AA metabolism and these findings

Influence of albumen on aggregation and O-2 evolution of protoplasm from Bryopsis hypnoides Lamourou

The extruded protoplasm from the coenocytic green alga, Bryopsis hypnoides Lamouroux, was able to reform a cell wall and develop further into a mature alga in seawater. In this paper, the influence of albumen on the ability of aggregation and on the photosynthesis of protoplasm was examined. Results show that the protoplasm of B. hypnoides could aggregate in either albumen or chicken egg, which is similar to that in seawater. However unlike in seawater, the aggregation from B. hypnoides in albumen and chicken egg failed to develop into a mature individual. Interestingly, the protoplasm of B. hypnoides could maintain its photosynthetic O-2 evolution in albumen and chicken egg, while the time in chicken egg was longer than that in albumen.

An N-shape thermal front in the western South Yellow Sea in winter

An N-shape thermal front in the western South Yellow Sea (YS) in winter was detected using Advanced Very High Resolution Radiation (AVHRR) Sea Surface Temperature data and in-situ observations with a merged front-detecting method. The front, which exists from late October through early March, consists of western and eastern wings extending roughly along the northeast-southwest isobaths with a southeastward middle segment across the 20-50 m isobaths. There are north and south inflexions connecting the middle segment with the western and eastern wings, respectively. The middle segment gradually moves southwestward from November through February with its length increasing from 62 km to 107 km and the southern inflexion moving from 36.2A degrees N to 35.3A degrees N. A cold tongue is found to coexist with the N-shape front, and is carried by the coastal jet penetrating southward from the tip of the Shandong Peninsula into the western South YS as revealed by a numerical simulation. After departing from the coast, the jet flows as an anti-cyclonic recirculation below 10 m depth, trapping warmer water originally carried by the compensating Yellow Sea Warm Current (YSWC). A northwestward flowing branch of the YSWC is also found on the lowest level south of the front. The N-shape front initially forms between the cold tongue and warm water involved in the subsurface anti-cyclonical recirculation and extends upwards to the surface through vertical advection and mixing. Correlation analyses reveal that northerly and easterly winds tend to be favorable to the formation and extension of the N-shape front probably through strengthening of the coastal jet and shifting the YSWC pathway eastward, respectively.

Elliptic Object Detection Based on Shape Preserving and Active Contour

本文通过形状约束方程(组)与一般主动轮廓模型结合,将目标形状与主动轮廓模型融合到统一能量泛函模型中,提出了一种形状保持主动轮廓模型即曲线在演化过程中保持为某一类特定形状。模型通过参数化水平集函数的零水平集控制演化曲线形状,不仅达到了分割即目标的目的,而且能够给出特定目标的定量描述。根据形状保持主动轮廓模型,建立了一个用于椭圆状目标检测的统一能量泛函模型,导出了相应的Euler-Lagrange常微分方程并用水平集方法实现了椭圆状目标检测。此模型可以应用于眼底乳头分割,虹膜检测及相机标定。实验结果表明,此模型不仅能够准确的检测出给定图像中的椭圆状目标,而且有很强的抗噪、抗变形及遮挡性能。

Ultrasonic synthesis of silica-alumina nanomaterials with controlled mesopore distribution without using surfactants

A novel sol-gel process has been developed for the synthesis of amorphous silica-aluminas with controlled mesopore distribution without the use of organic templating agents, e.g., surfactant molecules. Ultrasonic treatment during the synthesis enables production of precursor sols with narrow particle size distribution. Atomic force microscopy analysis shows that these sol particles are spherical in shape with a narrow size distribution (i.e., 13-25 nm) and their aggregation during the gelation creates clusters containing similar sized interparticle mesopores. A nitrogen physiadsorption study indicates that the mesoporous materials containing different Si/Al ratios prepared by the new synthesis method has a large specific surface area (i.e., 587-692 m(2)/g) and similar pore sizes of 2-11 nm. Solid-state Al-27 magic angle spinning (MAS) NMR shows that most of the aluminum is located in the tetrahedral position. A transmission electron microscopy (TEM) image shows that the mesoporous silica-alumina consists of 12-25 nm spheres. Additionally, high-resolution TEM and electron diffraction indicate that some nanoparticles are characteristic of a crystal, although X-ray diffraction and Si-29 MAS NMR analysis show an amorphous material.