The effect of pyrene labelling on the thermal stability of actin filaments

The ability of actin to form filaments is fundamental to its biological function and often characterised by various methods in vitro. One of the most frequently used methods capitalises on the observation that the fluorescence emission of a pyrene label on the Cys-374 residue of actin is enhanced by a factor of ∼20 during polymerisation. This method inherently involves the chemical modification of actin monomers with pyrene. It was reported earlier that the pyrene labelling of actin monomers has only small effect on the polymerisation and depolymerisation rates of actin, indicating that the method is suitable to characterise the effect of actin-binding proteins or peptides on the polymerisation kinetics.In our present work we tested the effect of the pyrene labelling on the thermal denaturation of actin filaments by using the method of differential scanning calorimetry (DSC). By recording the heat denaturation profiles of unlabelled and pyrene labelled actin filaments we observed that pyrene labelling shifted the melting point (T_m) of actin filaments from 66 to 68 °C. A similar effect was detected in the presence of equimolar concentration of phalloidin where the T_m shifted from 79 to 82 °C. We concluded that the observed pyrene labelling induced differences of the thermal denaturation of actin filaments were small. The DSC results, therefore, confirmed that the methods based on the measurements of pyrene intensity during actin polymerisation are suitable to characterise the polymerisation kinetics of actin under in vitro conditions.     

Untersuchung der Reaktivität und Sinterungsaktivität von Eisen(III)-oxid mittels der Diffusion radioaktiver Edelgase

Various methods for introduction of radioactive noble gases into solids are reviewed and also the diffusion of radioactive noble gases in α-iron(III)oxide, labelled by different methods. The HAHN emanation and ion bombardment methods have been used. Different noble gas diffusion processes have been shown to occur during heating the type of which is influenced by the kind of labelling conditions. The values of the activation energy of the noble gas diffusion are compared. Lattice defects including the amorphous state of Fe^IIIoxide are produced by ion bombardment. On the basis of the diffusion behaviour of radon, being studied by the emanation method, the “activity” of Fe^III oxide prepared by heating of different iron salts and sintered at various temperatures has been estimated. It is shown that the emanation method can be used for the study of the sintering of ferric oxide. On the basis of the solid state reaction ZnO + Fe₂O₃ the reactivity of ferric oxide in dependence on its thermal history has been investigated.     

New rapid methods of labelling by radioiodine

New methods for labelling of organic molecules by iodine radionuclides have been developed on the basis of a detailed study of processes occurring during radioiodination. Kits were preparations of iodinated radiophyarmaceuticals (e. g. hippurate, Bengal Rose, sulfobromophythalein). Further iodogene-impregnated filters were developed for labelling of non-iodinated compounds, especially proteins. Their use and preparation is quite simple and easy.     

Developments of the spin labelling study of polymers at interfaces

The spin labelling method has been used in a large variety of situations, in the broad field of polymers at solid interfaces. The relevance of the method is confirmed on linear neutral chains of poly (ethylene oxide) (PEO) in well defined situations and compared with the simple theoretical calculations of a mean field theory or some scaling arguments. Both theories have their own strengths and weaknesses. Then the fact, that polymers at solid liquid interfaces are three components systems, is considered and successively the effect of varying the polymer architecture, the solid surface and the solvent is studied. In all these cases specific results are obtained by Electron Paramagnetic Resonance (EPR) showing the usefulness and the versatility of the method.     

Analysis of the oxidation of cellulose fibres by titration and XPS

The purpose of this study was to evaluate the effect of selective oxidation on the surface properties of cotton cellulose fibres. Four different methods to evaluate the accessibility, nature and content of ionisable acidic groups (charge) in the fibres were applied: potentiometric and conductometric titrations, polyelectrolyte adsorption and X-ray photoelectron spectroscopy (XPS). The results from this combination of methods show that two processes take place when the oxidation method is applied: elimination of low molecular mass non-cellulosic compounds and formation of new acidic groups in the cellulose chains. Which of these processes is predominating depends on oxidation time, but the first one is initially more important. Polyelectrolyte adsorption and XPS show that the surface concentration of acidic groups is considerably lower than the bulk concentration, i.e. during oxidation the content of carboxyl groups in the surface region decreases, while it increases in amorphous regions. The decrease is due to the dissolution of low molecular weight compounds; the increase is due to the formation of new acidic groups. The use of titration methods in combination with XPS appears to be a very useful tool for identification of the formation and distribution of ionic groups in cotton fibres and their surfaces.     

A study of rearrangement processes in the mass spectra of substituted benzophenones which provide a guide to orientation

An investigation of the mass spectra of substituted benzophenones has shown that a number of rearrangement processes are operative. The rearrangements have been shown to involve solely the ortho-substituents to the carbonyl group and in many cases the carbonyl oxygen atom itself participates in the processes. Deuterium labelling experiments combined with data obtained from accurate mass and metastable analysis have enabled the probable mechanisms of rearrangement and fragmentation to be elucidated. An understanding of these processes should greatly assist in the location of substituents in unknown benzophenones.     

Optimizing fitting parameters in thermogravimetry

This study presents an alternative to simple estimation of parametric fitting models used in thermal analysis. The addressed problem consists in performing an alternative optimization method to fit thermal analysis curves, specifically TG curves and their first derivatives. This proposal consists in estimating the optimal parameters corresponding to fitting kinetic models applied to thermogravimetric (TG) curves, using evolutionary algorithms: differential evolution (DE), simulated annealing and covariance matrix adapting evolutionary strategy. This procedure does not need to include a vector with the initial values of the parameters, as is currently required. Despite their potential benefits, the application of these methods is by no means usual in the context of thermal analysis curve’s estimation. Simulated TG curves are obtained and fitted using a generalized logistic mixture model, where each logistic component represents a thermal degradation process. The simulation of TG curves in four different scenarios taking into account the extent of processes overlapping allows us to evaluate the final results and thus to validate the proposed procedure: two degradation processes non-overlapped simulated using two generalized logistics, two processes overlapped, four processes non-overlapped and four processes overlapped two by two. The mean square error function is chosen as objective function and the above algorithms have been applied separately and together, i.e., taking the final solution of the DE algorithm is the initial solution of the remaining. The results show that the evolutionary algorithms provide a good solution for adjusting simulated TG curves, better than that provided by traditional methods.     

Study of water transpiration features of sweet pepper using a thermal imaging system and non-destructive quality monitoring during post-harvest storage

Summary Sweet pepper is susceptible to relatively fast quality changes and its quality is influenced strongly by water or mass losses mainly due to transpiration processes during post-harvest. The aim of this study was the investigation of different storage conditions' effect on quality maintenance of pepper using surface thermal imaging, measurement of overall static stiffness and low-mass impact stiffness as non-destructive methods. Post-harvest keeping quality of pepper samples increased and unfavourable quality degradation was prevented under low, non-chilling temperatures together with the use of LDPE-packaging film resulted in high quality and fresh appearance after more than two weeks long storage period.     

Mass spectrometric study of hexamethyldisilazane and some of its N-substituted derivatives

The electron-impact-induced decomposition of the title compounds has been investigated in detail. Deuterium labelling was used to study the mechanisms of fragmentation and the structures of ions generated. Hydrogen, methyl and phenyl group migrations to one of the silicon atoms were observed as significant secondary processes. These processes are usually γ-transitions, from which it is inferred that these rearrangements occur via 4-membered cyclic transition complexes.     

High resolution mass spectrometry.—II Some substituted benzothiazoles

The mass spectra of nineteen substituted benzothiazoles have been recorded and the identity of the various ions in the mass spectra has been established by high resulution (accurate) mass measurement. Deuterium labelling has been used to elucidate the fragmentation processes of these compounds. The parent compound of the series, benzothiazole, exhibits the loss of hydrogen cyanide and carbon monosulphide from the parent ion as the most important decomposition pathways. The hydrogen atom concerned in the loss of hydrogen cyanide is shown to originate from the 2-position of benzothiazole, while in 2-substituted benzothiazoles, different mechanisms are apparent for the loss of hydrogen cyanide, and these are clarified by deuterium labelling. Some substituted benzothiazoles can lose sulphur from their molecular ions, a process which does not occur in benzothiazole itself. The substituted benzothiazoles undergo many other types of fragmentations, in some cases retaining the substituent, and in other cases losing it prior to collapse of the thiazole ring.     

Adventages and limits on usage of thermal methods in complex systems

In order to increase the nutrition value of bread, one of the most commonly used foodstuff all over the world, different additives are used in bread processing. In this paper we describe the thermal changes in bread and that of with 0.5% crude soybean lecithin additive. Their thermal stability has been investigated by TG, DSC and EGD methods. The thermal changes were also followed of soy products, lecithin and lysine, ingredients used as bread additives in order to check if they may suffer any thermal degradation during the baking process. The data obtained can be of use only for qualitative conclusions. According to the obtained data at the usual bread baking temperature only the additives in crust may partly decompose while in the crumb, at lower temperatures the additives, due to baking, are not damaged. The thermal methods give a possibility for rapid estimation of processes induced by heat effects in additives during the baking, and they are suitable to detect the changes during the bread-making procedure. However, they are neither suitable to provide any quantitative data on these changes nor facts affecting the nutrition value and of the bread.     

Activation energies for the thermodegradation process of an epoxy-diamine system

The study of the degradation of a polymer is important because it can determine the upper temperature limit, the mechanism of a solid-state process, and the life-time for this system. Since the behavior of thermosets is affected by the selection of the curing cycle, it is important to investigate the changes which take place during the thermal degradation of these materials when a change on the sequence of time and temperature is introduced during the curing reaction. In this work, the thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) cured through different sequences of time and temperature was studied by thermogravimetric analysis in order to determine the reaction mechanism of the degradation processes, and also to check the influence of the curing cycle on this mechanism. Values obtained using different kinetic methods were compared to the value obtained by Kissinger’s method (differential method which do not require a knowledge of the n-order reaction mechanism), and to that obtained through Flynn–Wall–Ozawa method in a previous work.     

Photooxidation of acetone on TiO2(110): conversion to acetate via methyl radical ejection

It is generally held that radicals form and participate in heterogeneous photocatalytic processes on oxide surfaces, although understanding the mechanistic origins and fates of such species is difficult. In this study, photodesorption and thermal desorption techniques show that acetone is converted into acetate on the surface of TiO2(110) in a two-step process that involves, first, a thermal reaction between acetone and coadsorbed oxygen to make a surface acetone-oxygen complex, followed second by a photocatalytic reaction that ejects a methyl radical from the surface and converts the acetone-oxygen complex into acetate. Designation of the photodesorption species to methyl radicals was confirmed using isotopically labeled acetone. The yield of photodesorbed methyl radicals correlates well with the amount of acetone depleted and with the yield of acetate left on the surface, both gauged using postirradiation temperature programmed desorption (TPD). The thermal reaction between adsorbed acetone and oxygen to form the acetone-oxygen complex exhibits an approximate activation barrier of about 10 kJ/mol. A prerequisite to this reaction is the presence of surface Ti3+ sites that enable O2 adsorption. Creation of these sites by vacuum reduction of the surface prior to acetone and oxygen coadsorption results in an initial spike in the acetone photooxidation rate, but replenishment of these sites by photolytic means (i.e., by trapping excited electrons at the surface) appears to be a slow step in a sustained reaction. Evidence in this study for the ejection of organic radicals from the surface during photooxidation catalysis on TiO2 provides support for mechanistic pathways that involve both adsorbed and nonadsorbed species.     

The Differential Calorimetric Study of the Reactivity of Unstable Compounds

The detection of unstable intermediates in chemical, photochemical, and radiation-chemical reactions can be greatly facilitated by the use of thermoanalytical methods. Special advantages are offered by differential thermal analysis (DTA), since it permits fast, easy investigation, from about ?150°C upward in some cases, over a wide temperature range. In this way processes that under normal conditions follow one another with immeasurable rapidity can be separated on the basis of their different temperature dependences. The great sensitivity of the method also allows the use of very dilute solutions, so that the studies can be confined to unimolecular processes. The value of the method for the determination of energetic and kinetic data is illustrated by its application to the photochemically obtanable, unstable, ozonide-like epidioxydihydrofurans.     

在确定的热力学状态下测量气体导热系数与黏度

气体的导热系数和黏度是重要的热物性参数,其数值大小取决于所处的热力学状态。在目前的导热系数和黏度主要测量方法中,待测工质在测量时需经历非定常的过程或处于具有物性梯度的非平衡态之下,使得待测工质的物性在时间或者空间上不处于一个确定的热力学状态。本文利用圆柱定程干涉法,通过分析气体导热系数和黏度导致的声波能量耗散,结合气体输运理论中对稀疏气体的描述,探索了在确定的热力学状态下同时测量气体导热系数和黏度的方法,并以氩(Ar)为例进行了实验验证。测量结果与已有文献一致性较好,初步证实了方法的可行性。     

Kinetic study of thermal processing of glycerol by thermogravimetry

Over the past years, the production of biodiesel has significantly increased in Brazil due to its obligatory use in the composition of diesel for vehicle use. As a result, in the most ordinary processes, a hundred thousand tons of glycerol is produced as by-product per 1 billion liters of biodiesel. Glycerol has already been widely studied. Nonetheless, the quantity produced today demands new proposals for uses, such as a fuel. In this aim, the authors studied the kinetics of the thermal processing of glycerol. In this research, thermogravimetry (TG), derivative thermogravimetry (DTG), and differential thermal analysis (DTA) were used to provide the experimental data. Kinetic parameters were calculated by Kissinger method for the global process observed during the heating of the samples from the room temperature up to 600 °C, both in open and in sealed crucibles (with a little hole). Kinetic data were also determined at different isoconversion conditions during heating, by applying Ozawa–Flynn–Wall and Blazejowski methods to TG data. Results show that glycerol heated from 30 to 600 °C, under normal pressure, does not experience simple volatilization. The activation energies calculated at different conversion degrees by these methods show that only volatilization occurs when the mass loss of glycerol is lower than 40% and that for higher conversion degrees, partial thermal decomposition and/or dissociation of glycerol are occurring as well. These facts are also confirmed by the volatilization enthalpies estimated using another method developed by Blazejowski based on Van’t Hoff equation.     

Thermal behavior of annealed organic glasses

The influence of annealing processes on the thermal behavior of organic glasses in the glass-transition interval has been investigated and analyzed quantitatively. In detailed annealing studies of atactic polystyrene and Aroclor 5460, the absorption of thermal energy superposed on the increase in the specific heat at the glass transition, observed with suitably chosen heating rates, was followed by the differential thermal method. It is concluded that the absorption of thermal energy observed under these conditions parallels the extent of molecular relaxation that has taken place during the annealing period. It is not necessary to postulate a first-order process to account for the energy absorption. Moreover, such a postulate leads to severe conceptual difficulties regarding the development of crystallinity in crystallizable materials. The areas and the shapes of the endotherms are considered in terms of the original physical properties of the quenched glasses and the anticipated equilibrium properties. Relationships between the extent of energy absorption and time-dependent processes such as volume relaxation are discussed.     

Evaluation of the 99mtechnetium labelling effect on Pseudomonas aeruginosa surface properties

Gamma emitter isotopes present some advantages over beta emitters as radioisotopic microbial labels. The labelling of bacteria with ^99mtechnetium (^99mTc) has recently been described. However, it was not ascertained weether the labelling process modifies microbial physicochemical surface properties important in the interaction between bacteria and eukaryotic cells. In the present study, we evaluated the effect of the labelling process on Pseudomonas aeruginosa surface charge, hydrophobicity, adherence to human buccal epithelial cells and phagocytosis by human leukocytes. No significant differences in electrophoretic mobility or cationized ferritin distribution was observed on the cell surface of labelled and unlabelled bacteria. ^99mTc labelling did not modify the hydrophobicity adhesiveness or phagocytosis of P. aeruginosa. It is concluded that bacterial labelling with ^99mTc may be a useful method for the numeration of bacteria and the analysis of their functional properties.     

Ab Initio Nonadiabatic Dynamics of Semiconductor Materials via Surface Hopping Method

Photoinduced carrier dynamic processes are without doubt the main driving force responsible for the efficient performance of semiconductor nanomaterials in applications like photoconversion and photonics. Nevertheless, establishing theoretical insights into these processes is computationally challenging owing to the multiple factors involved in the processes, namely reaction rate, material surface area, material composition etc. Modelling of photoinduced carrier dynamic processes can be performed via nonadiabatic molecular dynamics (NA-MD) methods, which are methods specifically designed to solve the time-dependent Schrodinger equation with the inclusion of nonadiabatic couplings. Among NA-MD methods, surface hopping methods have been proven to be a mighty tool to mimic the competitive nonadiabatic processes in semiconductor nanomaterials, a worth noticing feature is its exceptional balance between accuracy and computational cost. Consequently, surface hopping is the method of choice for modelling ultrafast dynamics and more complex phenomena like charge separation in Janus transition metal dichalcogenides-based van der Waals heterojunction materials. Covering latest stateof-the-art numerical simulations along with experimental results in the field, this review aims to provide a basic understanding of the tight relation between semiconductor nanomaterials and the proper simulation of their properties via surface hopping methods. Special stress is put on emerging state-ot-the-art techniques. By highlighting the challenge imposed by new materials, we depict emerging creative approaches, including high-level electronic structure methods and NA-MD methods to model nonadiabatic systems with high complexity.     

Intramolecular dynamics and conformational transition in proteins studied by biophysical labelling methods. Common and specific features of proteins from thermophylic micro-organisms

A general survey is carried out on the theoretical grounds for methods of spin, luminescence and M?ssbauer labels, as well as their application in the study of protein intramolecular dynamics. When combined, these methods allow the protein dynamics to be investigated within a wide range of correlation times (tau c = 10(2) - 10(-10) s) and amplitudes. The purposeful application of the methods to various proteins at different temperatures (30-330 K), water content, substrate addition, etc., revealed a number of dynamical processes and conformational transitions in proteins. The experiments indicated correlations between the local segmental mobility of protein globules in a nanosecond temporal scale and biochemical reactions, such as long-distance electron transfer, hydrolysis and photoreactions. The biophysical labelling methods results were analysed together with the data on dynamics obtained using complementary physico-chemical methods and theoretical calculations. Special emphasis is given to recent results on proteins from thermophylic micro-organisms. The mechanisms of protein intramolecular dynamics and their role in the stability and functions of proteins and enzymes are discussed.