Multiphoton ionization translational spectroscopy (MITS) of I2

A new technique is introduced based on the measurement of kinetic energies and angular distributions of fragments in multiphoton ionization of molecule Both positive and negative ions are measured as well as neutrals. Information is obtained about highly excited repulsive states and about the multiphot ionization process itself. Examples are reported for MPI of I₂. In a one-laser experiment dissociative autoionization is observed. In a two-laser experiment processes are distinguised, that have different intermediate states. Lifetimes of those states are measured. Information is also obtained ab an ion pair formation process, leading to a reinterpretation of potential curves.     

The polarization phenomena of spherical molecules

The calculation of the polarizabilities of spherical molecules is discussed in the light of the average excitation energy approximation to perturbation theory. It is shown that whilst information about the energy in external fields can always be obtained from polarization phenomena, some information about the unperturbed wave function also can be obtained from magnetic susceptibility and Cotton–Mouton effect measurements. In the case of argon such information was found to agree with the results of self-consistent-field calculations. Predictions of the Cotton–Mouton constants of krypton and xenon are made.     

First prebiotic generation of a ribonucleotide from adenine, D-ribose and trimetaphosphate

Adenosine monophosphate isomers are obtained by self-assembling of adenine, D-ribose and trimetaphosphate in aqueous solution in good yields. This generation of a ribonucleotide from its three molecular components occurs in a one-pot reaction at room temperature for about 30-40 days and with high chemio-, regio-, and stereo-selectivity. Similar results are obtained with guanine. A mechanism is also proposed.     

Total internal reflection imaging of microorganism adhesion using an oil immersion objective

In this paper, we report the results of total internal reflection microscopy investigations of the interaction of two types of microorganisms: Saccharomyces cerevisiae and Escherichia coli with substrates. It is shown that with this method qualitative and quantitative information about cells-substrate interaction can be obtained. One can easily make a difference between attached and non-attached as well as between dead and alive cells, and more generally can follow the dynamics of the process of cells' attachment to substrates. Quantitative information about the cell size and cell-substrate distance is obtained by using a model in which yeast cells and bacteria are approximated by ellipsoids, and multiple reflections of the evanescent waves between the cells and the substrate are neglected.     

Thermal behaviour of emulsions studied by differential scanning calorimetry

This article is a review about the ways in which solidification and the melting may occur within emulsions submitted to steady cooling and heating performed in a differential scanning calorimeter. Simple, multiple and mixed emulsions are considered. Due to nucleation phenomena creating supercooled and supersaturated liquids, the DSC curves obtained during cooling and heating are quite different. The influence of a solute in the disperse phase is described in detail. Some implications about the instabilities of emulsions due to mass transfer phenomena are described.     

Conformational disorder in the propagating radical of dimethacrylate polymers

Photopolymerization of methacrylic monomers yields samples with trapped radicals that are easily detected by electron paramagnetic resonance (EPR) spectroscopy. Despite its simplicity, there is no general agreement about the interpretation of this spectrum, in particular, about the role of methylene β protons. An extensive ENDOR study of the propagating radical in photopolymerized dimethacrylates has been carried out in order to obtain detailed information about methylene hyperfine couplings and, thus, about radical conformation. It is shown that literature models are not able to reproduce the ENDOR results and that only accurate fitting of ENDOR spectra obtained by saturating the EPR spectrum at different positions gives reliable information about radical conformation, thanks to the exploitation of conformational selectivity. It turns out that most radicals are in the minimum energy conformation, but any possible conformation is assumed by non negligible fractions of radical.     

Selenomethionine contents of NIST wheat reference materials

Values of the total selenium and selenomethionine (Semet) content of four wheat-based reference materials have been obtained by gas chromatography-stable isotope dilution mass spectrometry methods. The total Se method is an established one, and the results obtained with it are consistent with previously-assigned values. The Semet method (previously reported by our laboratory) is based on reaction with CNBr. Our data indicate that the four wheat samples (wheat gluten, durum wheat, hard red spring wheat, and soft winter wheat), though having a 30-fold range in total Se content, all have about 45% of their total Se values in the form of selenomethionine. Investigation of the CNBr-based method suggests that additional experiments are needed to verify that all selenomethionine in the wheat samples is accounted for, but also indicates that the values obtained are within 15% of the true values. As the form in which Se occurs in foods and dietary supplements is important from a nutritional perspective, adding information about Se speciation to total Se values in appropriate reference materials makes these materials more valuable in relevant analytical work.     

Thermofraktographie zur Schnellanalyse von Kunststoffen. 3. Mitteilung

When heating vinyl polymers within the temperature gradient of 50–450° C, they are fragmented in certain temperature ranges to defined products. These products are fractionated on the TLC-layer and subsequently chromatographed. Based on the thermofractograms obtained identification of the starting material can be made. From polyvinyl esters, e.g., the corresponding acid is obtained and copolymers yield the different acids. Thermolysis of polyvinyl carbazole yields vinyl carbazole and vinyl pyrrolidone and pyrrolidone are obtained from polyvinyl pyrrolidone. Polymethacrylate is fragmented to the corresponding methacrylate, and acrylate if obtained from polyacrylate. Evaluation of the thermofractograms leads in part to new conceptions about structures and cleavage mechanisms of such polymers.     

Ultraviolet spectrophotometric determination of copper in copper ores by flow-injection analysis

A flow-injection analysis (FIA) method for the ultraviolet spectrophotometric determination of copper in copper ores is described. The ore samples are dissolved in concentrated perchloric acid, the excess acid is neutralized with ammonia solution, and the resulting solution is used for the determination of copper. The UV-FIA system is based on the reaction of copper (II) ions with pyrophosphate and subsequent measurement of the absorbance of the dipyrophosphatocuprate (II) complex at 240 nm. The main factors which control the formation of this complex and the FIA variables influencing the system are discussed. The calibration graph is linear from 2-50 ppm copper. At a sampling rate of about 70 samples h(-1) with 50 mul sample injections, precision was about 1% relative standard deviation. Results obtained compare well with those obtained by atomic absorption spectrometry.     

用俄歇能谱和X射线能谱研究板状碘溴化银微晶中的碘离子的空间分布

本文制备了一系列不同碘含量的板状碘溴化银微晶(微晶大小约为3微米)。运用扫描透射电镜和X射线能谱仪(EDS)对单个微晶进行了分析和研究,半定量地测定了碘离子在板状微晶中的面分布;运用扫描俄歇微区棵针(SAM)和二次电子像、离子溅射剥层技术对微晶进行了表面及其纵深的碘离子的点分析,根据EDS和SAM的结果,可以得到板状碘溴化银微晶中的碘离子的空间分布。实验结果表明在板状缺溴化银微晶中,在其中心部位的碘含量最高;越靠近横向边缘的位置,碘含量越低。且在制备碘溴化银微晶时,如果pAg值较高,将会使在制备早期加入的碘离子通过不断的重结晶向微晶表面扩散,得到的微晶不是夹心结构的碘溴化银微晶。     

聚乙烯链构象熵的研究

采用旋转异构态模型，考虑近程二级相互作用和远程自回避相互作用，在金钢石格点上模拟聚乙烯链，用完全计算法研究了它的构象熵。我们得到聚乙烯链的我象熵现温度及链长的函数关系式。发现在约２００Ｋ温度以上，聚乙烯链的构象的熵随温度沽小不明显，在约２００Ｋ以下，构象熵随温度迅速减小，约在４２Ｋ的构象熵为零。我们还以现，该链的构象熵近似地与链长成正比。     

Gemini表面活性剂在合成纳米乳液中的应用

以过硫酸铵为引发剂,通过种子微乳液聚合的方法研究了阴离子型Gemini表面活性剂在形成涂料或胶粘剂用乳液中的功能。研究发现阴离子型Gemini表面活性剂在微乳液聚合中是高效的乳化剂,可以提供典型的粒径控制及良好的乳液稳定性,只需1%左右就可以得到固含量45%左右的透明纳米级聚丙烯酸酯乳液,并维持平均粒径在31nm左右。     

Application of IPF Theory to the Study of lonization Equilibrium

This article is a theoretical study about ionization equilibrium. Taking the ionization equilibrium of acetic acid in a series of MeOH-water mixtures as an example, we calculated the ionization constant Ka according to the IPF theory, the Born theory and the vander Waals theory, respectively. The results indicate that the values obtained by the IPF theory are in best accordance with those from literatures. A brief discussion about the theories is given at the end.     

DNA closed nanostructures: a structural and Monte Carlo simulation study

DNA nanoconstructs are obtained in solution by using six unique 42-mer DNA oligonucleotides, whose sequences have been designed to form a pseudohexagonal structure. The required flexibility is provided by the insertion of two non-base-paired thymines in the middle of each sequence that work as flexible hinges and constitute the corners of the nanostructure when formed. We show that hexagonally shaped nanostructures of about 7 nm diameter and their corresponding linear open constructs are formed by self-assembly of the specifically designed linear oligonucleotides. The structural and dynamical characterization of the nanostructure is obtained in situ for the first time by using dynamic light scattering (DLS), a noninvasive method that provides a fast dynamic and structural analysis and allows the characterization of the different synthetic DNA nanoconstructs in solution. A validation of the LS results is obtained through Monte Carlo (MC) simulations and atomic force microscopy (AFM). In particular, a mesoscale molecular model for DNA, developed by Knotts et al., is exploited to perform MC simulations and to obtain information about the conformations as well as the conformational flexibilities of these nanostructures, while AFM provides a very detailed particle analysis that yields an estimation of the particle size and size distribution. The structural features obtained by MC and AFM are in good agreement with DLS, showing that DLS is a fast and reliable tool for characterization of DNA nanostructures in solution.     

Gravimetric determination and radiochemical separation of palladium(II) with ethyl-α-isonitrosoacetoacetate

The use of ethyl-ga-isonitrosoacetoacetate (HEINA) for determination of palladium is reported. Pd can be estimated quantitatively from 0.5M to 2M HCl solution. Accurate results are obtained in 1M solution with an accuracy better than 1%. Decontamination values against platinum metals and other metals usually associated with Pd are greater than 10⁵. The time required for gravimetric determination is about an hour, for radiochemical separation about 25 min and the recovery is better than 90%.     

The insertion of carbon oxysulfide into some organo-metallic amines

The structures of the products obtained when carbon oxysulfide is allowed to react with organometallic amines of germanium, pholphorus, and arsenic are determined and the effect of changing hardness of the organo-metallic center is discussed. Free energies of activation for rotation about the carbonylnitrogen bond in the products are determined.     

Exciton dynamics of GaSe nanoparticle aggregates

Time-resolved and static spectroscopic results on GaSe nanoparticle aggregates are presented to elucidate the exciton relaxation and diffusion dynamics. These results are obtained in room-temperature TOP/TOPO solutions at various concentrations. The aggregate absorption spectra are interpreted in terms of electrostatic coupling and covalent interactions between particles. The spectra at various concentrations may then be interpreted in terms of aggregate distributions calculated from a simple equilibrium model. These distributions are used to interpret concentration-dependent emission anisotropy kinetics and time-dependent emission spectral shifts. The emission spectra are reconstructed from the static emission spectra and decay kinetics obtained at a range of wavelengths. The results indicate that the aggregate z axis persistence length is about 9 particles. The results also show that the one-dimensional exciton diffusion coefficient is excitation wavelength dependent and has a value of about 2 x 10(-5) cm(2)/s following 406 nm excitation. Although exciton diffusion results in very little energy relaxation, subsequent hopping of trapped electron/hole pairs occurs by a Forster mechanism and strongly red shifts the emission spectrum.     

Fracture of tendon collagen

A study of rat-tail tendon fibers, about 200 μ in diameter, by scanning electron microscopy of fractured specimens reveals that these crimped fibers are largely made up of cylindrical units, about 10 μ in diameter. These, in turn, are made up of the well-known collagen fibrils, ca. 0.1 μ in diameter, which have been observed previously by transmission electron microscopy and small-angle x-ray diffraction. Both the 10-μ and 0.1-μ cylindrical units were found to be arranged parallel to the macroscopic fiber axis rather than helically about it, as has been often proposed in the past. Significant improvement in resolution of the fracture surfaces was obtained by dehydration of the tendon. Microscopy of undehydrated tendon fibers undergoing solubilization by dilute aqueous acetic acid confirmed the results obtained by fractography.     

Predictions of molecular geometries and electronic spectra of complex unsaturated molecules from MC-LCAO-MO method with particular reference to triplet-triplet transitions of naphthalene

An MC-LCAO-MO approach which has been proposed for open-shell systems of unsaturated hydrocarbons having degenerate MO's is applied to naphthalene, calculating its molecular geometry and electronic spectrum. The results are compared with those obtained by the usual semi-empirical SCF-CI method and with experiment. As for benzene, anthracene, phenanthrene and triphenylene, the bond lengths and the -electron energies in their ground states are calculated in the same manner. Most of the calculated bond lengths are in fairly good agreement with experiment. The total -electron energies of the ground states obtained by the MC-LCAO-MO and SCF-CI methods agree within about 0.01 eV when CI is included and within about 0.1 eV when CI is not invoked. It is found that the electronic spectrum of naphthalene obtained by the present method is in good agreement with that derived from the SCF-CI method and also explains most part of experiments. A detailed discussion is given on the calculated triplet-triplet absorption spectrum and its intensity distribution of naphthalene.     

A new high frequency dynamic mechanical analysis system: An approach to direct high frequency testing of tire tread rubber

Dynamic Mechanical Analysis (DMA) systems are measurement devices for obtaining master curves and complex modules of viscoelastic materials, such as rubbers. The conventional DMAs measurement systems in market have several limitations, which restrict their ability for operating at high frequencies. Thus, Williams, Landel and Ferry (WLF) relation is used to produce master curves and predict the material properties at high frequencies. In conventional DMAs, experiments are done in a range of temperatures, and then a master curve is made for a chosen reference temperature by shifting the measurements data to high frequencies. Therefore, the obtained results, which are not based on direct measurements, can be inaccurate. In order to overcome this problem a new simple shear high-frequency DMA (HFDMA) system is designed and built to directly measure the dynamic mechanical properties of viscoelastic material at high frequencies and the strain levels sufficient for tire manufacturers. The new HFDMA can be used to test any viscoelastic materials which have glass transmission temperature (Tg) lower than room temperature (about 23 °C) such as the Styrene-butadiene rubber (SBR). The SBR is the base material for tire tread. The designing process of this new HFDMA is presented in this paper. The rubber specimen shape is chosen by taking into account the shear elastic wave effect, bending, buckling effect and heat generation in the specimen. The repeatability test is accomplished to ensure that the results obtained from the new HFDMA are repeatable and the repeatability uncertainty is about 0.04%. The new HFDMA is validated by comparing to the direct test results of conventional DMA at 100 Hz. The direct high frequency (5 kHz) complex shear modulus and damping factor are compared with the master curve of the conventional DMA developed by the use of WLF relation for SBR. This comparison revealed that the complex shear modulus and damping factor of the SBR obtained from the HFDMA at 5 kHz and 0.05% strain amplitude are about 7% and 6.5% higher than those obtained from the conventional DMA, respectively.