Excited-State Proton Transfer in Nonaqueous Solvent

Excited-state proton transfer from pyranine to urea in methanol solution was studied by using both steady-state quenching and fluorescence lifetime measurements at room temperature. Proton transfer initially requires a urea monomer to form a protonated urea monomer, which is then solvated by methanol. The experimental data demonstrates the emission that would be attributed to an encounter pair. A set of rate constants is obtained on the basis of a simple kinetic model.     

Study on the concentration difference heat pump using fusion and freezing processes of acetic acid-acetamide system

The concentration difference heat pump using fusion and freezing processes to generate a cold fluid has been investigated. This heat pump system utilizes the acetic acid-acetamide pair as working material, and consists of a cold fluid generating and a separation process. The operation at the cooling capacity of 3.52 kW (1 ton of refrigeration) has been investigated in this study. At the cold fluid generating process, solid acetic acid at 15°C is fused into an acetamide solution at 15°C, such that the temperature and the concentration of acetamide of the solution decreases. This dilute solution at lower temperature can be used to generate a cold fluid. The lowest attainable temperature of the solution has been investigated experimentally, and also calculated from the energy balance equation. The decreasing rates of the temperature have also been studied. At the separation process, continuous distillation is adopted to concentrate the dilute solution sent from the cold fluid generating process. The data which support the possibility of separation by continuous distillation are presented. The energy demand at the separation process is investigated theoretically.     

基于光子晶体的物质的量浓度测量研究

利用平面波展开法对二维光子晶体在H极化下的光子带隙进行数值计算。考虑了溶液温度和物质的量浓度对光子带隙的影响。结果表明,以半乳糖和木糖的水溶液作为空气孔中介质材料,当溶液物质的量浓度一定时,光子带隙随溶液温度的变化而改变;而当溶液温度一定时,光子带隙随溶液物质的量浓度发生变化。较高物质的量浓度和较高温度的溶液更容易形成光子带隙。在某些情况下,木糖的光子带隙大于半乳糖的光子带隙。     

Scaling of spatial correlations in cooperative sequential adsorption with clustering

We examine solvable cooperative sequential adsorption models on a linear lattice where adsorption rates produce strong clustering or island formation. We show that the spatial pair correlations in this regime assume a scaled form for separations comparable to a characteristic length (which diverges in the strong clustering limit). This scaled form is also determined directly from consideration of appropriate solvable continuum grain growth models.     

Chemical effect of swirling jet-induced cavitation: degradation of rhodamine B in aqueous solution

The chemical effect of swirling jet-induced cavitation was investigated with the decomposing reaction of rhodamine B in aqueous solution. It was found that rhodamine B in aqueous solution can be degraded with swirling jet-induced cavitation and the degradation can be described by a pseudo-first-order kinetics. The effects of operating conditions such as pressure, temperature, initial concentration of rhodamine B, pH of water on the degradation rate of rhodamine B were discussed. It was found that the degradation rate of rhodamine B increased with increasing pressure and decreased with increasing initial concentration. It was also found that the degradation of rhodamine B was strongly dependent of temperature and pH of aqueous solution. The oxidation efficiency of swirling jet-induced cavitation for rhodamine B degradation was discussed and compared with ultrasonic cavitation. The result indicated that the swirling jet-induced cavitation is more energy efficient as compared to sonochemical cavitation.     

Laser-induced back-side wet etching of fused silica with an aqueous solution containing organic molecules

The laser-induced back-side wet etching of fused silica with aqueous solutions of pyranine (8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt) is reported. KrF and XeF excimer lasers were employed as light sources. Well-defined line-and-space and grid micropatterns, free of debris and microcracks, were obtained. Compared with other organic solutions, the aqueous pyranine etching medium etches more slowly but produces a higher quality etched surface. With the KrF laser, the etch rate ranged from 0.02 to 0.12 nm pulse^-1, depending on the dye concentration and the fluence of the laser. The etch rate decreased dramatically when the XeF laser was employed, which was partially attributed to the lower absorption efficiency of the aqueous pyranine solution at the XeF laser wavelength. Received: 20 November 2001 / Accepted: 21 November 2001 / Published online: 2 May 2002     

用于检测水环境中银离子浓度的荧光适体传感器研究

银凭借其独特的性能,在医疗材料、摄影、电子、成像等行业中应用广泛.然而,银离子被列为最具毒性的重金属离子之一,会对环境以及人类的生命健康造成严重威胁.为了灵敏、特异性的检测水环境中的银离子浓度,利用纳米金的优良光学猝灭性以及双链核酸适体捕获银离子能力更强的优点,结合荧光能量共振转移原理,提出一种用于检测水环境中银离子浓...     

CdTe量子点-罗丹明B荧光共振能量转移猝灭法测定金银花中的微量铜

研究CdTe量子点(供体)和罗丹明B(受体)之间荧光共振能量转移的最佳条件,建立了荧光共振能量转移猝灭法测定金银花中微量铜的新方法.采用十六烷基三甲基溴化铵,在pH 6.00的Tris-HCl缓冲液中,Cu2+能对能量转移体系中罗丹明B荧光峰强猝灭从而测定铜的含量.Cu2+浓度在1.3×10-4～3.1×10-2 μg...     

Macroions in salty water with multivalent ions: giant inversion of charge

Screening of a strongly charged macroion by oppositely charged colloidal particles, micelles, or short polyelectrolytes is considered. Because of strong lateral repulsion such multivalent counterions form a strongly correlated liquid at the surface of the macroion. This liquid provides correlation-induced attraction of multivalent counterions to the macroion surface. As a result even a moderate concentration of multivalent counterions in the solution inverts the sign of the net macroion charge. We show that at high concentration of monovalent salt the absolute value of inverted charge can be larger than the bare one. This giant inversion of charge can be observed in electrophoresis.     

熔融Cu55团簇在Cu(010)表面上凝固过程的分子动力学模拟

采用基于嵌入原子方法的分子动力学,模拟了熔融Cu55团簇在Cu衬底(010)表面上以两个不同降温速率降温过程中结构的变化.模拟结果表明,降温速率对团簇结构的变化有很大影响.较快的降温速率使得降温过程中团簇原子具有较低的能量;较慢的降温速率有助于高温时位于衬底内的原子向衬底表面扩散,排列形成面心立方结构.     

Analytical study of stretched ultra-lean premixed flames within porous inert media

It has been shown both theoretically and experimentally that combustion within porous inert media can extend the flammability limits of reactant mixtures for unstretched stationary premixed flames. However little attention has been given to flames within porous media submitted to stretch conditions. This work presents a closed form approximate analytical solution for the problem of ultra-lean premixed flames within porous inert media subjected to small stretch rates in an impinging flow configuration against a constant temperature wall. The solution is obtained using the method of matched asymptotic expansions taking advantage of the large difference between the solid- and gas-phase thermal conductivities. The model allows for thermal nonequilibrium between the phases and is able to predict the flame temperature, velocity and position as function of the stretch rate. The results show that within porous media low stretch rates may increase the flame temperature, further extending the lean flammability limit of the reactant mixture when compared to planar flames. The model is restricted to low porosities, low stretch rates, low heat losses and intense interphase heat transfer.     

核酸适配体纳米金共振散射光谱检测血清中钾离子

在pH7.0的Na2HPO4-NaH2PO4缓冲溶液中,纳米金与适配体(aptamer)结合形成较稳定的aptamer-Au复合物,且不被NaCl聚集。在85℃水浴中,K+与aptamer作用后折叠形成稳定的G-四分体结构复合物且释放出纳米金。在高浓度盐作用下,纳米金聚集成较大粒径的纳米金颗粒,导致体系563nm处的共振散射强度增大,其平均粒径为120nm。文章研究了K+ -随机单链DNA1(ssDNA1)-纳米金、K+ -ssD-NA2-纳米金和K+ -aptamer-纳米金体系的共振散射光谱特性,并用圆二色光谱技术证明了核酸适配体结构的变化。考察了pH、NaCl浓度、aptamer浓度、纳米金用量以及Cu2+、Mg2+、Pb2+、Ca2+、Al3+、Zn2+Fe3+等常见重金属离子等对测定K+的影响,结果显示这些离子不干扰测定,该法具有较好的选择性。在选定条件下,K+浓度在0.67～3350μmol·L-1范围与共振散射峰值ΔI呈良好的线性关系,回归方程、相关系数、检出限分别为ΔI=0.167c-0.7,0.9932,0.3μmol·L-1 K+。该法用于血清样品分析,结果与离子选择电极法一致。     

Reduced Maxwell-Bloch equations with anisotropic dipole momentum

We develop the inverse scattering transform for the recently found integrable system of reduced Maxwell-Bloch equations with two components of polarization and with an anisotropic dipole momentum. The model describes few-cycle pulses of optical or other field propagations. We find that the existence of a nontrivial group of symmetry of the corresponding Lax pair leads to a particular form of the inverse scattering transform equations. We show that solutions can be expressed in terms of the solution of a matrix Riemann-Hilbert problem formulated for the complex plane with a nontrivial group of automorphisms.     

Electroporative Adjustment of pH in Living Yeast Cells: Ratiometric Fluorescence pH Imaging

A number of vital cell functions including modulation of signaling pathways and regulation of the cellular transport critically depends on the cytoplasmic pH. Many pathological cellular changes are related to the abnormal cytosolic pH as well. Reliable and well-calibrated methods for quantification of the cytosolic pH are therefore of high importance. The pH calibration is particularly difficult in walled cells since standard methods fail. In this report we evaluated the new electroporative calibration method of the cytosolic pH in yeasts by the fluorescence microscopy. The calibration was done on living cells using pyranine as a ratiometric pH-sensitive probe. The probe was electroporatively delivered to the cytosol. We have shown that unlike the measurements in suspension the fluorescence microscopy reveals cell subpopulations with different sensitivity to the pH calibration. While the majority of the cells were well calibrated, there was found subpopulation of uncalibrated cell as well as singular cells exhibiting anomalous pH calibration due to the staining of acidic organelles. Resolution of cell subpopulations helps to achieve better pH calibration compared to the calibration in cuvette on a cell suspension.     

巯基苯并咪唑在银电极表面的自组装吸附特性及表面增强拉曼光谱

采用循环伏安法处理Ag电极,得到活化的具有表面增强拉曼光谱(SERS)效应的粗糙Ag表面,进一步采用激光拉曼光谱探讨了2-巯基苯并咪唑(MBI)在其表面的自组装分子层的吸附特性。实验表明,在活性Ag表面的MBI自组装分子层能够产生理想的SERS效应,其强度随探针分子MBI浓度的增加先提高后减弱,达到一定浓度时因受其空间位阻等因素的影响,增强效应减弱。MBI在1×10^-6 mol·L^-1 浓度时增强效果最大。拉曼增强效应随着体系酸度的变化有着明显不同,在强酸性条件下的增强效应明显优于中性和碱性条件。MBI分子存在两种不同的异构体和在不同酸度下存在3种不同的存在形态,并形成动态平衡。pH <2时,MBI分子主要以硫酮式MBI⁺存在,并以巯基上的S:与活性Ag以配位方式吸附成键,其整个大π键平面垂直地吸附于Ag表面,产生相对较大的SERS信号。pH >2时,由于硫酮式和硫醇式与活性Ag的键合方式和能力不同,硫醇式上的S与Ag以S-Ag共价方式同时双键侧上的N以配位方式协同参与吸附成键,比硫酮式MBI⁺的单纯配位吸附要强,因而形成了竞争吸附,表现为SERS在pH=2~3.7之间的急剧下降。MBI硫醇式由于以S-Ag、N-Ag键的协同吸附,形成了倾斜侧卧式垂直吸附,而使拉曼增强效应相对减弱。     

熔融Cu55团簇在Cu(010)表面上凝固过程的分子动力学模拟

采用基于嵌入原子方法的分子动力学,模拟了熔融Cu₅₅团簇在Cu衬底（010）表面上以两个不同降温速率降温过程中结构的变化.模拟结果表明,降温速率对团簇结构的变化有很大影响.较快的降温速率使得降温过程中团簇原子具有较低的能量;较慢的降温速率有助于高温时位于衬底内的原子向衬底表面扩散,排列形成面心立方结构. 关键词： 团簇 凝固 分子动力学 表面     

β-修正新光度法测定痕量铜的研究

在ｐＨ５～６的缓冲溶液中,铜与对二甲氨基苄基罗丹宁反应生成红色络合物。本文应用β－修正双波长光度法测定铜,可消除过量显色剂ＰＤＲ产生的影响,明显的提高了测定的灵敏度。实验结果表明：ＲＳＤ＜２．９％,加标回收率８７．７％～１１２．０％,最低检测限０．５５μｇ／ｍＬ。本法适合于金属材料、环境水体中痕量铜的测定。     

以巯基丙酸为稳定剂的水溶性CdTe量子点的水热合成及表征

以巯基丙酸(MPA)为稳定剂,采用水热合成方法在160 ℃下合成水溶性CdTe量子点。研究了不同反应时间及反应前驱体溶液的不同pH值对合成的CdTe量子点光学性质的影响。结果表明:所制得的CdTe量子点的荧光发射波长在510~661 nm范围内连续可调,并且CdTe量子点的光学性质强烈地依赖于反应前驱体溶液的pH值,最佳pH值为9。透射电子显微镜和X射线衍射分析表明所制备的CdTe量子点的形状接近于球形,粒径分布较均匀。与回流方法制备的水溶性量子点相比,高温条件下的水热合成方法简单,反应时间短,CdTe量子点生长速度快,100 min就可生长到3.5 nm,并且所制得的CdTe量子点荧光强度高,稳定性好,荧光量子产率也较高,最高可达44.6%。     

Competition between aggregation and migration processes of a multi-species system

We propose a solvable multi-species aggregation--migration model, in which irreversible aggregations occur between any two aggregates of the same species and reversible migrations occur between any two different species. The kinetic behaviour of an aggregation--migration system is then studied by means of the mean-field rate equation. The results show that the kinetics of the system depends crucially on the details of reaction events such as initial concentration distributions and ratios of aggregation rates to migration rate. In general, the aggregate mass distribution of each species always obeys a conventional or a generalized scaling law, and for most cases at least one species is scaled according to a conventional form with universal constants. Moreover, there is at least one species that can survive finally.     

Monitoring of the Proton Electrochemical Gradient in Reconstituted Vesicles: Quantitative Measurements of Both Transmembrane Potential and Intravesicular pH by Ratiometric Fluorescent Probes

Proteoliposomes carrying reconstituted yeast plasma membrane H⁺-ATPase in their lipid membrane or plasma membrane vesicles are model systems convenient for studying basic electrochemical processes involved in formation of the proton electrochemical gradient (Δμ_H ⁺) across the microbial or plant cell membrane. Δψ- and pH-sensitive fluorescent probes were used to monitor the gradients formed between inner and outer volume of the reconstituted vesicles. The Δψ-sensitive fluorescent ratiometric probe oxonol VI is suitable for quantitative measurements of inside-positive Δψ generated by the reconstituted H⁺-ATPase. Its Δψ response can be calibrated by the K⁺/valinomycin method and ratiometric mode of fluorescence measurements reduces undesirable artefacts. In situ pH-sensitive fluorescent probe pyranine was used for quantitative measurements of pH inside the proteoliposomes. Calibration of pH-sensitive fluorescence response of pyranine entrapped inside proteoliposomes was performed with several ionophores combined in order to deplete the gradients passively formed across the membrane. Presented model system offers a suitable tool for simultaneous monitoring of both components of the proton electrochemical gradient, Δψ and ΔpH. This approach should help in further understanding how their formation is interconnected on biomembranes and even how transport of other ions is combined to it.