Protein secondary structure and stability determined by combining exoproteolysis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

In the post-genomic era, several projects focused on the massive experimental resolution of the three-dimensional structures of all the proteins of different organisms have been initiated. Simultaneously, significant progress has been made in the ab initio prediction of protein three-dimensional structure. One of the keys to the success of such a prediction is the use of local information (i.e. secondary structure). Here we describe a new limited proteolysis methodology, based on the use of unspecific exoproteases coupled with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), to map quickly secondary structure elements of a protein from both ends, the N- and C-termini. We show that the proteolytic patterns (mass spectra series) obtained can be interpreted in the light of the conformation and local stability of the analyzed proteins, a direct correlation being observed between the predicted and the experimentally derived protein secondary structure. Further, this methodology can be easily applied to check rapidly the folding state of a protein and characterize mutational effects on protein conformation and stability. Moreover, given global stability information, this methodology allows one to locate the protein regions of increased or decreased conformational stability. All of this can be done with a small fraction of the amount of protein required by most of the other methods for conformational analysis. Thus limited exoproteolysis, together with MALDI-TOF MS, can be a useful tool to achieve quickly the elucidation of protein structure and stability.     

Review of time lag permeation technique as a method for characterisation of porous media and membranes

The time lag permeation technique has proven to bean effective method for characterisation. Because of the simple nature of the permeation experiment, transport parameters can be directly obtained from experimental data hence avoiding the intensive mathematical treatment required by other techniques. The method has historically been applied to diffusion and adsorption in porous membranes and diffusion in polymer membranes. Since its origins in 1920, interest in the time lag method has expanded because of its value in characterising simple permeation processes and also complex systems of diffusion with simultaneous adsorption and surface diffusion. This review focuses on presenting the asymptotic solution of the mass balance diffusion equations and includes applications of time lag analysis, in order to give a critical and broad perspective of this method as a tool for characterisation. It includes much of the previously published literature in order to show that for most cases the asymptotic solution of the transport equations is simple, and for more complex cases that an analytical solution is possible hence avoiding cumbersome numerical techniques.     

Time‐Resolved Synchrotron Radiation Excited Optical Luminescence: Light‐Emission Properties of Silicon‐Based Nanostructures

The recent advances in the study of light emission from matter induced by synchrotron radiation: X‐ray excited optical luminescence (XEOL) in the energy domain and time‐resolved X‐ray excited optical luminescence (TRXEOL) are described. The development of these element (absorption edge) selective, synchrotron X‐ray photons in, optical photons out techniques with time gating coincide with advances in third‐generation, insertion device based, synchrotron light sources. Electron bunches circulating in a storage ring emit very bright, widely energy tunable, short light pulses (<100 ps), which are used as the excitation source for investigation of light‐emitting materials. Luminescence from silicon nanostructures (porous silicon, silicon nanowires, and Si–CdSe heterostructures) is used to illustrate the applicability of these techniques and their great potential in future applications.     

The Excited‐State Dynamics of Phycocyanobilin in Dependence on the Excitation Wavelength

The primary light‐induced processes of phycocyanobilin were studied by means of transient‐grating spectroscopy, whereby the excitation wavelength was varied over the spectral region of the ground‐state absorption. On the basis of the results obtained, both the rate of the photoreaction in phycocyanobilin and the ratio of the decay of different excited‐state species via two decay channels depend on the excitation wavelength. Furthermore, the formation of the photoreaction product is also dependent on the pump color. These data support a recently established model for the primary photoprocesses in phycocyanobilin. In addition, phycocyanobilin protonated at the basic pyrrolenine‐type nitrogen atom was included in the transient absorption study. The decay behavior was found to be almost unchanged when compared with the unprotonated form, and this suggests that protonation of the tetrapyrrole ring structure has no effect on the overall photochemistry.     

反应注射成型聚氨酯互穿聚合物网络研究——刚性网络对于体系形态及性能的影响

用微型反应注射成型机制备了以聚氨酯(PU)为弹性相的两类同步互穿聚合物网络(SIN),其刚性相分别采用保留仲羟基的乙烯基酯树脂(VERH)以及封闭仲羟基的乙烯基酯树脂(VERA)。用傅里叶变换红外光谱在线跟踪了这类互穿网络的生成过程,发现刚性网络抑制了PU网络中硬段有序结构的形成,两个网络间有一定程度的互穿,而两个网络间的化学键作用进一步削弱氢键强度。自旋—自旋弛豫时间的测定进一步表明网络间存在一定的互穿以及刚性相对于PU硬段结晶的抑制作用。材料的力学性能与其SIN的形态有关。VERA网络对PU表现出明显的增强作用,而由VERH网络形成的SIN则由于体系相分离进程受到严重阻碍而使材料性能恶化。     

Polystyrene prepared by reactive extrusion: kinetics and effect of processing parameters

The conversion and residence time were investigated during the bulk polymerization of styrene in a twin screw extruder. It was found that polymerization mainly occurred in the zone between 400 and 1000 mm along the screw axis in the extruder, corresponding to the residence time of the reactants ranging from 1 to 4 min in the extruder. Furthermore, the processing conditions (feed rate, screw rotation rate) and average molecular weight of the polymer have a great effect on the residence time. Based on dimensionless analysis, a model of the residence time has been built‐up, which has been confirmed by the results of realistic measurements. A kinetic model of the polymerization has also been established under the assumption that the screw extruder can be regarded as an ideal plug flow reactor. Copyright © 2004 John Wiley & Sons, Ltd.     

表面活性剂对纤维素接枝共聚物溶液粘度性质的影响

研究了阴离子十二烷基硫酸钠(SDS)、阳离子十六烷基三甲基溴化铵(CTAB)和非离子聚乙二醇辛基苯基醚(OP)等三种不同类型的表面活性剂对疏水化水溶性两性纤维素接枝共聚物(CGAO)溶液粘度性质的影响.结果表明,在SDS和OP的临界胶束浓度(cmc)附近，CGAO溶液粘度最大，SDS引起CGAO粘度的变化大于OP；即使在CTAB的cmc附近，随着CTAB浓度的增加，CGAO的粘度一直呈下降趋势；非疏水改性的纤维素接枝共聚物的溶液粘度随SDS或CTAB浓度的增加而下降，但几乎不随OP浓度的增大而变化.此外，通过凝胶渗透色谱法测得的保留时间证实了SDS、CTAB和OP与CGAO之间的疏水缔合作用.     

Multi-turn time-of-flight mass spectrometers with electrostatic sectors

The mass resolution of a time-of-flight (TOF) mass spectrometer is directly proportional to its total flight pathlength. Multi-turn or multi-passage ion optical geometries are necessary to obtain fight distances of sufficient length within reasonable size limitations. We have investigated ion optics for a multi-turn TOF mass spectrometer with electrostatic sectors. The concept of 'perfect' focusing conditions is introduced. Furthermore, a new type of multi-turn TOF mass spectrometer, the MULTUM Linear plus, was developed. It consists of four cylindrical electric sectors and 28 electric quadrupole lenses. It has a vacuum chamber 60 x 70 x 20 cm in size. Mass resolution is demonstrated to increase according to the number of ion cycles. A mass resolution of 350 000 (m/z = 28, FWHM) was achieved after 501.5 cycles. The MULTUM Linear plus analyzer is not simple, however; 28 electric quadrupole lenses are used. In order to reduce the number of ion optical parts, an improved multi-turn TOF mass spectrometer, the MULTUM II, consisting of only four toroidal electric sectors, was also developed. The possibility of tandem mass spectrometric applications using multi-turn TOF mass spectrometers is also discussed.     

Preparation of Silica-Silk Fibroin-Polyurethane Composite Films via a Sol-Gel Route

A tetraethoxysilane (TEOS)-derived sol aged for 0 h–6 h at room temperature was mixed with a polyurethane (PU) matrix. A composite of silk fibroin (SF) powders and acrylamide (AAm) was dispersed in the sol-PU mixture and dried isothermally at temperatures between 25°C and 120°C to obtain composite films. Three competitive reactions take place, i.e., those between silica-silica, SF-PU and silica-organic phases, during formation of the composite films. These reactions determine the properties such as morphology and homogeneity of the composite films. IR absorption bands for amide groups (–CONH–), C=O (amide I, 1730 cm^–1) and N–H (amide II, 1530 cm^–1) become larger with decreasing aging time of TEOS-derived sol, or increasing drying temperature. DTA exothermic peak due to the thermal decomposition of SF-AAm composite, on the composite films prepared from the 0 h-aged sol or dried at more than 50°C, shifts toward higher temperature by 44 K or more than 63 K respectively, as compared to the SF-AAm composite. Shorter aging time of TEOS-derived sol and higher drying temperature increased the extent of dispersibility, among SF-AAm composite, PU and silica, to bring a composite film more homogeneous.     

从静态应力松弛实验求材料准松弛时间谱的一种数值计算方法

避开繁琐困难的函数求解过程，采用数值计算方法，从常规的静态应力松弛实验，直接求被测材料的松弛单元的表现松弛强度．主松弛时间τ０由单－ＭＡＸＷＥＬＬ模型求得，其他松弛时间分别约取为１０（－２）·τ０，１０（－１）·τ０，１０１·τ０，１０３·τ０。应力松弛万程取５参数模型，记为谱的强度ａｉ（或Ａｉ）通过多元线性回归，由最小二乘法确定．对一种天然橡胶试样在不同温度下的松弛曲线进行处理，回归值与原始实验值吻合良好，不同温度下的松弛单元对总松弛的贡献，反映出温度对松弛过程的活化作用．