pH effect on protein G orientation on gold surfaces and characterization of adsorption thermodynamics

The pH effect on adsorbed antibody-binding protein (protein G) orientation on gold (Au) and its adsorption thermodynamic characteristics were investigated using quartz crystal microbalance (QCM) and X-ray photoelectron spectroscopy (XPS). The adsorbed protein G orientation was measured by binding response of two antibody-antigen systems: the model bovine serum albumin (BSA) and the foodborne pathogen E. coli O157:H7. Surface coverage was not significantly affected by pH, but its orientation was. The most properly oriented protein G for antibody binding was achieved at near-neutral pH. Adsorption was verified by XPS measurements using nitrogen (N) 1s, oxygen (O) 1s, and Au 4p peak heights. Adsorption energetics were determined by van't Hoff and Langmuir kinetic analyses of adsorption data obtained at 296, 303, and 308 K. Large characteristic entropy change of protein adsorption was observed (ΔS° = 0.52 ± 0.01 kcal/mol·K). The adsorption process was not classical physisorption but exhibited chemisorption characteristics based on significant enthalpy change (ΔH° = -25 ± 6 kcal/mol).     

流动注射在线氧化荧光法结合透析采样研究盐酸硫利达嗪与牛血清白蛋白的结合作用

利用流动注射在线氧化结合在线透析采样技术建立了荧光法测定血浆中游离盐酸硫利达嗪的新方法, 并将其应用于盐酸硫利达嗪与牛血清白蛋白作用机制的研究. 将盐酸硫利达嗪与牛血清白蛋白以不同比例混合并在37 ℃下培养, 以流动注射透析采样技术从混合液中分离出游离盐酸硫利达嗪, 在线氧化为强荧光化合物后测定其浓度; 应用Scrathard方程分析所测数据, 求得盐酸硫利达嗪和牛血清白蛋白的结合常数为1.2×104 L/mol, 结合位点数为0.98; 根据热力学参数推断, 盐酸硫利达嗪与牛血清白蛋白之间以疏水作用力为主; 进一步基于荧光猝灭现象和Fster非辐射能量转移理论, 得到盐酸硫利达嗪小分子与牛血清白蛋白之间的能量转移效率(E=0.497)和结合距离(r0=3.27 nm).     

Ligand bonding and dynamics on colloidal nanocrystals at room temperature: the case of alkylamines on CdSe nanocrystals

With CdSe nanocrystals stabilized with very weak ligands (pyridine) as the starting materials, NMR techniques were applied to distinguish the bonded and free alkylamine ligands in an equilibrated adsorption/desorption system for the CdSe-amine nanocrystal-ligand pair. NMR and photoluminescence (PL) measurements were further correlated to identify the linear relationship between PL intensity and the surface ligand coverage of the amine-coated CdSe nanocrystals. For 3.5 nm CdSe nanocrystals and octylamine ligands, the chemical equilibrium constant (K) of the CdSe-amine nanocrystal-ligand adsorption/desorption process was found to be around 50-100, and the corresponding Delta(r)G(o) was calculated as 9.8-11.5 kJ/mol. With a proposed mathematic method, the corresponding chemical kinetic constants for the desorption (kd) and adsorption (ka) processes were measured to be 0.01 s(-1) and 0.5 L mol(-1) s(-1), respectively. K, kd, and ka obtained here are generally 2-4 magnitudes different from those estimated in literature. Analysis indicates that these constants are well consistent with the existing experimental observations.     

Arsenic(III) sorption on nanostructured cerium incorporated manganese oxide (NCMO): a physical insight into the mechanistic pathway

Arsenic(III) sorption was investigated with nanostructured cerium incorporated manganese oxide (NCMO). The pH between 6.0 and 8.0 was optimized for the arsenic(III) sorption. Kinetics and equilibrium data (pH=7.0±0.2, T=303±1.6 K, and I=0.01 M) of arsenic(III) sorption by NCMO described, respectively, the pseudo-second order and the Freundlich isotherm equations well. The sorption process was somewhat complicated in nature and divided into two different segments, initially very fast sorption followed by slow intraparticle diffusion process. Sorption reaction of arsenic(III) on NCMO was endothermic (ΔH°=+13.46 kJ mol(-1)) and spontaneous (ΔG°=-24.75 to -30.15 kJ mol(-1) at T=283-323 K), which took place with increasing entropy (ΔS°=+0.14 kJ mol(-1)K(-1)) at solid-liquid interface. Energy of arsenic(III) sorption estimated by analyzing the equilibrium data using the D-R isotherm model was 15.4 kJ mol(-1), indicating the ion-exchange type mechanism. Raman, FT-IR, pH effect, desorption, etc. studies indicated that arsenic(III) was oxidized to arsenic(V) during the sorption process.     

Surface induced changes in coumarin solvation and photochemistry at polar solid/liquid interfaces

Steady state and time-resolved fluorescence measurements compare the photophysical properties of Coumarin 152 (C152) and Coumarin 461 (C461) in bulk methanol solution and adsorbed to silica/vapor and silica/methanol interfaces. C152 and C461 share the same structure except for a -CF(3) (C152) or -CH(3) (C461) group at the molecule's 4-position. This modest structural difference leads to markedly different emission behavior in bulk solution and different organization when adsorbed to silica surfaces. Steady state emission spectra of C152 and C461 adsorbed to silica surfaces from bulk methanol solutions show that the two solutes have similar surface activities (ΔG(ads) of -29.0 kJ/mol and -30.8 kJ/mol for C152 and C461, respectively) and that the interface itself has a polarity similar to that of short chain alcohols. Both solutes appear to form multilayers at higher bulk concentrations given observed linear growth in fluorescence emission intensities. At higher C152 surface concentrations a second emissive state appears at longer wavelengths, whereas the emission of C461 remains dominated by a single feature. Time dependent emission of C152 and C461 adsorbed to the silica/methanol interface shows that the silica surface inhibits C152's fast, nonradiative pathway inferred from bulk solution measurements but the fluorescence lifetime of adsorbed C461 remains unchanged from bulk solution limits. These findings are discussed in terms of the interface's ability to restrict C152 isomerization into a nonradiative, twisted intramolecular charge-transfer (TICT) state, despite the fact that this conformation represents an energetic minimum in polar solvation environments.     

基于头孢他啶测定的CQDs内标型比率荧光探针的构建

以天然生物质蒲公英为碳源,加入乙二胺,通过一步水热法合成氨基化蒲公英碳量子点(DE-CQDs).该DE-CQDs可与罗丹明6G(Rh6G)通过静电吸附作用形成具有特征双发射信号的DE-CQDs/Rh6G复合物.单一激发波长343 nm下,BR缓冲溶液pH 3.0时,复合物DE-CQDs/Rh6G于425 nm和550 ...     

Intensity enhancement of weak O2 a1Δg → X3Σg(-) emission at 1270 nm by collisions with foreign gases

Collision-induced near-IR emission of O(2) a(1)Δ(g) was investigated in O(2)/M (M = Ar, Kr, Xe, N(2), or CO(2)) gas mixtures, where the total pressure ranged from 10 to 100 atm, and gaseous O(2) dimol was excited with a pulsed dye laser at 630 nm through the simultaneous two-electron transition to prepare O(2) in the a(1)Δ(g) state. The a(1)Δ(g) → X(3)Σ(g)(-) emission intensity around 1270 nm increased with the number density of foreign gas (M) under constant O(2) number density. Emission enhancement efficiencies were in the order Xe > CO(2) > O(2) > Kr > N(2) > Ar; they are controlled by collisional enhancement during the near-IR emission at 1270 nm but not during photoabsorption at 630 nm. Efficiencies were converted into bimolecular rate constants to enhance the radiative a → X transition for the added gases. The rate constants were estimated as quadratically dependent on the molar refraction (or polarizability) of collision gas. The self-quenching rate constant was determined from the Stern-Volmer plot of the emission lifetimes measured in pure O(2).     

激发态分子内质子转移(ESIPT)发色团修饰的树枝形聚合物合成及光物理研究

设计合成了0～4代外围修饰激发态分子内质子转移(ESIPT)发色团的聚酰胺-胺树枝形聚合物G0～G4,化合物结构经过IR,1H NMR,13C NMR和MS表征.稳态光谱研究表明,树枝形聚合物在四氢呋喃溶液中形成了聚集体,发色团酮式发光随着化合物代数增大呈先增加后减小的变化.质子化树枝形聚合物G1-H～G4-H能溶于水,并在水中形成20 nm左右的聚集体,发色团在聚集体疏水区中构象受限,仅发射酮式发光,并且发光强度受树枝形聚合物分子大小的影响.     

同步荧光光谱法研究丹参素-牛血清白蛋白体系的光增强效应

采用紫外光谱法和同步荧光光谱法研究了丹参素与牛血清白蛋白的结合特性.体系的紫外光谱显示,丹参素与牛血清白蛋白(BSA)之间发生了相互作用并生成新的复合物,同步荧光光谱则表明,丹参素对BSA存在荧光增强效应.随着丹参素浓度的增加,Δλ=15 nm时体系荧光强度明显增强,最大发射波长为285 nm,且不随浓度增加而发生变化...     

Enhancement of optical conductivity in the ultra-violet region of Cs doped ZnO sol gel thin films

Nano crystalline cesium (Cs) doped ZnO thin films were deposited on glass substrate by sol gel spin coating method with 1–3 mol.% doping concentration and different annealing temperatures. The deposited films were characterized by X-ray diffraction (XRD), Hall Effect, Photoluminescence (PL) and UV–Visible studies. XRD measurements reveal that all the samples abound in the wurtzite structure with polycrystalline nature. An increase in crystalline size from 19.60 to 44.54 nm is observed with the increase of doping concentration. Electrical conductivity of Cs doped ZnO films were observed from Hall effect measurements and the maximum carrier concentration obtained is 7.35 × 10¹⁸ cm^?3. The near band emission (384 nm) peak intensity increases with the increase of Cs doping concentration and a maximum intensity 55,280 was observed for CZ3 film from PL spectrum. Also a low energy near infrared (NIR) emission peak centered at 1.62 eV appears for the Cs doped ZnO films. The average transmission of CZ film is 88 % and the absorption edge is red shifted with the increase of Cs doping concentration and also the optical conductivity increases in the UV region.     

硅烷化活性炭的吸附性质

本工作测定了25℃和35℃时硅烷化活性炭自水溶液中吸附苯甲酸和苯甲醛的等温线;计算了吸附过程的ΔGⅲ,ΔHⅲ和ΔSⅲ;用Hill-deBoer方程处理了实验结果。所得结果表明:(1)随硅烷化时间延长,苯甲酸和苯甲醛的吸附量(mol.m^-^2)明显增加;-ΔGⅲ和-ΔHⅲ略有升高,ΔSⅲ为正值;(2)吸附分子之间的相互作用很弱,吸附分子与活性炭表面间的作用随硅烷化程度增加而加大;(3)芳香化合物可能是以苯环吸附在炭表面上的。     

基于双发射免标记核酸探针的比率型荧光传感器用于银的检测

构建了一种新型免标记的双发射荧光比率核酸探针(GelRed/[G40]/Tb^3+)并用于Ag+的检测。对于GelRed/[G40]/Tb^3+探针,GelRed作为一种核酸染料嵌入到单链DNA-[G40]中,形成的GelRed/[G40]作为稳定的内置参照标准,在激发波长290 nm处,发射荧光强度固定不变的红色荧光(发射波长为635 nm),而[G40]/Tb^3+作为敏感的响应信号,随着Ag^+浓度的增加,产生的绿色荧光逐渐增强(发射波长为545 nm),[G40]/Tb3+与GelRed/[G40]发射的荧光强度比值也发生相应的改变,从而实现对Ag^+的定量检测。在优化的实验条件下,[G40]/Tb^3+与GelRed/[G40]荧光强度比值和Ag^+浓度在0~7.5μmol/L的范围内具有较好的线性关系,Ag^+检出限为0.156μmol/L。本传感器在10 min内就可完成对Ag^+的分析。方法已用于自来水样中Ag^+的检测,与ICP-MS法检测结果一致。     

Preparation and surface characterization of polymer nanoparticles designed for incorporation into hybrid materials

We prepared water dispersions of poly(n-butyl methacrylate-st-butyl acrylate) crosslinked core-shell nanoparticles functionalized with different amounts of trimethoxisilane (TMS) groups in the outer shell. The purpose of the TMS groups is to chemically bind the rubbery particles to a nanostructured silica network, using sol-gel copolymerization. Here, we present nanoparticles containing 13 mol % and 30 mol % of TMS groups in the outer shell and compare their surface morphology with particles that do not contain TMS. The particles are prepared by a two-step seeded emulsion polymerization technique at neutral pH. In the first step, we obtained crosslinked seed particles (44 nm in diameter) by a batch process. In the second step, we used a semi-continuous emulsion polymerization technique under starved feed conditions to obtain monodispersed particles of controlled composition and size (ca. 100 nm in diameter). Fluorescence decay measurements were performed in situ on the dispersions, using a pair of cationic dyes adsorbed onto the surface of the nanoparticles: rhodamine 6G as the energy transfer donor and malachite green carbinol hydrochloride as the acceptor. The kinetics of F?rster resonance energy transfer (FRET) between the dyes is sensitive to the donor-acceptor distance, allowing us to obtain the binding distribution of the dyes at the nanoparticle surface. For the unmodified nanoparticles, we found a dye distribution that corresponds to an average interface thickness of delta = (5.2 +/- 0.2) nm. For the samples containing 13 mol % and 30 mol % of TMS groups in the outer shell we obtained broader interfaces, with widths of delta = (6.2 +/- 0.2) nm and delta = (6.5 +/- 0.1) nm respectively. This broadening of the distribution with the surface modification is interpreted in terms of the increase in free volume of the shell caused by the TMS groups. Finally, we studied the effect of temperature on the water-polymer interface fuzziness, in order to evaluate the accessibility of the TMS groups during the sol-gel synthesis of nanostructured hybrid materials.     

Behavior of β-amyloid 1-16 at the air-water interface at varying pH by nonlinear spectroscopy and molecular dynamics simulations

The adsorption and aggregation of β-amyloid (1-16) fragment at the air-water interface was investigated by the combination of second harmonic generation (SHG) spectroscopy, Brewster angle microscopy (BAM), and molecular dynamics simulations (MD). The Gibbs free energy of surface adsorption was measured to be -10.3 kcal/mol for bulk pHs of 7.4 and 3, but no adsorption was observed for pH 10-11. The 1-16 fragment is believed not to be involved in fibril formation of the β-amyloid protein, but it exhibits interesting behavior at the air-water interface, as manifested in two time scales for the observed SHG response. The shorter time scale (minutes) reflects the surface adsorption, and the longer time scale (hours) reflects rearrangement and aggregation of the peptide at the air-water interface. Both of these processes are also evidenced by BAM measurements. MD simulations confirm the pH dependence of surface behavior of the β-amyloid, with largest surface affinity found at pH = 7. It also follows from the simulations that phenylalanine is the most surface exposed residue, followed by tyrosine and histidine in their neutral form.     

O(1D2-3P(2,1,0)) 630.0, 636.4, and 639.2 nm forbidden emission line intensity ratios measured in the terrestrial nightglow

The intensity ratio of the neutral oxygen "red" emission lines O(1D2-3P(2,1)) 630.0 nm to 636.4 nm has been measured in terrestrial nightglow spectra obtained from astronomical instrumentation. The observed intensity ratio, I(630.0 nm)/I(636.4 nm) = 2.997 +/- 0.016, is consistent with the value of 2.997 determined from the recent spontaneous emission coefficient calculations of Storey and Zeippen (2000), distinctly lower than the value of 3.10 calculated from those coefficients recommended by the National Institutes of Standards and Technology (NIST), and lower than the value of 3.1 measured by laboratory experiment (Kernahan and Pang, 1975). A weak emission line measured at 639.174 +/- 0.003 nm has also been observed in these spectra and identified as the highly optically forbidden transition O(1D2-3P0) 639.1773 nm of the same multiplet as the red lines. The observed intensity ratio, I(636.4 nm)/I(639.2 nm) = 1700 +/- 700, is a factor of 2 lower than that predicted by most recent theoretical calculations.     

Adsorption of anionic and cationic dyes by activated carbons, PVA hydrogels, and PVA/AC composite

The textural and adsorption characteristics of a series of activated carbons (ACs), porous poly(vinyl alcohol) (PVA) gels, and PVA/AC composites were studied using scanning electron microscopy, mercury porosimetry, adsorption of nitrogen (at 77.4 K), cationic methylene blue (MB), anionic methyl orange (MO), and Congo red (CR) from the aqueous solutions. Dye-PVA-AC-water interactions were modeled using the semiempirical quantum chemical method PM6. The percentage of dye removed (C(rem)) by the ACs was close to 100% at an equilibrium concentration (C(eq)) of less than 0.1 mM but decreased with increasing dye concentration. This decrease was stronger at C(eq) of less than 1 mM, and C(rem) was less than 50% at a C(eq) of 10-20 mM. For PVA and the PVA/AC composite containing C-7, the C(rem) values were minimal (<75%). The free energy distribution functions (f(ΔG)) for dye adsorption include one to three peaks in the -ΔG range of 1-60 kJ/mol, depending on the dye concentration range used and the spatial, charge symmetry of the hydrated dye ions and the structural characteristics of the adsorbents. The f(ΔG) shape is most complex for MO with the most asymmetrical geometry and charge distribution and adsorbed at concentrations over a large C(eq) range. For symmetrical CR ions, adsorbed over a narrow C(eq) range, the f(ΔG) plot includes mainly one narrow peak. MB has a minimal molecular size at a planar geometry (especially important for effective adsorption in slit-shaped pores) which explains its greater adsorptive capacity over that of MO or CR. Dye adsorption was greatest for ACs with the largest surface area but as molecular size increases adsorption depends to a greater extent on the pore size distribution in addition to total and nanopore surface areas and pore volume.     

Inter- and intraconfigurational transitions of Nd3+ in hexafluoroelpasolite lattices

Excitation of the 4f3 ion Nd3+ in hexafluoroelpasolite lattices by synchrotron radiation of wavelength approximately 185 nm leads to fast 4f(2)5d --> 4f3 emission below 52,630 cm(-1) and slower 4f3 --> 4f3 emission from the luminescent states (4)F(3/2) gamma8u (11 524 cm(-1)) and 2G2(9/2) gamma8u (approximately 47,500 cm(-1)). The near-infrared emission is well-resolved, and a clear interpretation of the 4I(9/2) crystal field levels and of the one-phonon vibronic sideband is given. The excitation spectrum of the 2G2(9/2) emission enables clarification of the structure of the 4f(2)5d configuration (which extends from approximately 52,000 to 128,000 cm(-1)). Detailed energy level and intensity calculations have been performed, which provide simulations of the d-f emission and the f-d excitation spectra in good agreement with experiment. It is interesting that although the 4f3 2G2(9/2) gamma8u --> 4f3 4I(J) transitions are very weak in intensity compared with transitions terminating upon higher multiplet terms, most of the 4f(2)5d (3H) 4I(9/2) gamma8g --> 4f3 emission intensity resides in the transitions to 4I(J).     

纳米钛酸钙粉体的制备及其对水中铅和镉的吸附行为

采用柠檬酸络合溶胶-凝胶法制备了纳米钛酸钙粉体. 以X射线衍射(XRD)、透射电子显微镜(TEM)和傅立叶变换红外光谱(FTIR)对其进行了表征. 考察了该纳米粉体对水中重金属铅和镉的吸附性能, 并以镉离子为例, 系统地研究了吸附热力学和动力学. 结果表明, 该法合成的钛酸钙为钙钛矿结构的纳米粉体, 粒径大小受灼烧温度的影响, 灼烧温度越高, 粉体平均粒径越大, 600 ℃灼烧2 h条件下, 粉体的平均粒径最小, 约为20 nm. 当介质的pH值为4～8时, 钛酸钙对水中的铅和镉具有很强的吸附能力. 其对镉离子的吸附行为符合Langmuir 吸附等温模型和HO准二级动力学方程式, 吸附过程焓变(ΔH)为39.312 kJ&#8226;mol－1, 各温度下的自由能变(ΔG)均小于零, 熵变(ΔS)均为正值, 吸附过程的活化能(Ea)为20.359 kJ&#8226;mol－1. 该吸附过程是自发的吸热物理过程. 被吸附的铅和镉均可用1 mol&#8226;L－1的硝酸完全洗脱回收. 对铅和镉的富集因子均超过200. 将其应用于水中痕量铅和镉的吸附富集和测定, 回收率分别为96.3%～107.2%和93.5%～104.0%, 与石墨炉原子吸收光谱法测定结果一致.     

聚羧酸型梳状共聚物超分散剂在氟虫腈颗粒界面的吸附性能

采用紫外光谱(UV)、 傅里叶变换红外光谱(FTIR)、 X射线光电子能谱(XPS)和扫描电子显微镜(SEM)对聚羧酸型梳状共聚物超分散剂(TERSPERSE^®2700)在氟虫腈颗粒界面的吸附等温线、 吸附动力学、 吸附作用力、 吸附层厚度以及吸附状态等进行了分析. 实验结果表明, TERSPERSE^®2700分散剂在氟虫腈颗粒界面的吸附模型符合Langmuir吸附等温式, 吸附量随着温度升高而增大, 并计算了ΔG^0-, ΔH^0-和ΔS^0-. 吸附符合准一级动力学模型, 吸附速率常数随着温度升高而增大, 吸附活化能E_a=29.28 kJ/mol. 利用XPS谱图, 估算其吸附厚度约为1 nm, 表明存在吸附作用. 实验发现氟虫腈存在分子间氢键, 同时氢键也是分散剂分子与氟虫腈颗粒表面结合的重要作用力.     

Ag+存在下催化还原铬黑T及应用于Ag+检测

以铬黑T(EBT)为探针,在有Ag⁺存在的最优条件下,EBT被NaBH 4催化还原,体系在445 nm发射波长处荧光强度明显增强,基于此构建一种光学测定溶液中微量Ag⁺的方法。在最优条件下,Ag⁺浓度在(7.5×10-9~1.0×10^-6 mol·L^-1)范围内呈良好的线性关系,线性回归方程为ΔI F=5.59×10⁸ c-31(c,mol·L^-1,r=0.9966),Ag⁺的最低有效检测浓度为6.0×10^-8 mol·L^-1。在最优条件下,运用该方法对样品中Ag⁺浓度进行检测,样品中Ag⁺浓度的检测回收率在98.8%~102.4%之间,RSD=2.1%。该检测方法能够对水溶液中微量的Ag⁺进行有效定量检测,且操作简单、检测限低、灵敏度高。