Theoretical comparison between structural and dynamical features of Dolastatins 11 and 12 antineoplastic depsipeptides

Molecular mechanics (MM) and dynamics (MD) calculations in vacuo and in water have been performed for the natural cyclodepsipeptides Dolastatins 11 and 12 isolated from the sea hare Dolabella auricularia. The analysis of the MD trajectories for the two systems can give useful insight on the backbone structural features, side-chain and peptide-water interactions as well as on the inter- and intra-molecular hydrogen bonds. A comparison between the selected and analysed lowest energy isomers shows the different conformational behaviour of the compounds. Finally, with the aim to ascertain a structure-activity relationship for the two peptides, the interactions of both Dolastatins with water, generic hydrophobic environment, magnesium and calcium ions have been investigated by means of the GRID program.     

Kinetics of ion-pair extraction in continuous flow systems

Kinetic aspects of ion-pair extraction in continuous-flow systems have been studied. Processes have been developed by using a new methodology based on reversal of the flow direction for a preselected number of cycles and on contiuous monitoring at the detector of a plug of organic phase inserted into a carrier stream (aqueous phase) by means of a conventional injection valve. The configuration used required none of the units typically associated with this separation technique. The information obtained, with clear kinetic connotations, can also be exploited for analytical purposes. The behaviour of different ion pairs formed between ferroin and 23 anionic counter ions has been studied. Individual and joint kinetic determinations of these anions from kinetic parameters are proposed.     

An experimental and theoretical study of surface segregation in a Fe-6at.%Si bicrystal

The analysis of segregation phenomena in bicrystals is an important step for the understanding of combined effects of the elementary diffusion processes involved in the segregation in polycristalline systems. The segregation of Si and P in a Fe-6at.%Si bicrystal with a (100) and (110) surface has been investigated by means of AES (Auger electron spectroscopy). For these experiments the technique of a linearly increased temperature has been applied. Significant differences between the segregation kinetics at the two surfaces of the sample have been found on the one hand for the maximum coverage of P and on the other hand for the high temperature behaviour of Si. Additionally, model calculations based on the KTBIM (kinetic tight binding Ising model) have been performed to qualitatively describe the experimental results. It is shown, that the striking differences between the segregation behaviour at the two differently oriented surfaces can be explained by different segregation energies of P, whereas Si plays a minor role due to its relatively small segregation energy.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

On the Phase Diagram of LiF-KCI-KBr and KF-NaCI-NaBr Systems

The phase diagrams of LiF-KCl-KBr and KF-NaCl-NaBr systems have been de'er-mined by visual polythermal method with the X-ray diffraction analysis of solid phases.The thermodynamical behaviour of the molten salt solutions of these systems are estimated on the basis of the data of phase diagrams.The thermodynamical behaviour of these recipioral-salt-pair containing systems is explained by the results of the computerized simulation using Monte Carlo method.     

Prediction of rheological properties in polymer colloids

The rheological properties of concentrated suspensions, containing sterically stabilized polymer colloids, are reviewed. It is shown that the various rheological characteristics are strongly interrelated in such systems. They deviate from Brownian hard sphere behaviour, but these deviations are closely related to the interparticle potential and other colloidal characteristics like particle diffusivity. As a result the rheological properties can be predicted from the colloidal characteristics and vice versa. This is demonstrated by means of available data on well characterized model dispersions. In the experiments volume fraction, particle size, suspending medium and temperature have been changed. Data reduction schemes and scaling laws for these parameters are discussed.     

Approach to hydrophilic interaction chromatography column selection: Application to neurotransmitters analysis

This paper presents the comparison between 12 hydrophilic interaction liquid chromatography columns that are commercially available. The main factors influencing the retention and selectivity toward 12 neurotransmitters for these different HILIC systems have been studied. For additional information, the retention data have been analyzed statistically by factor analysis. Principal component analyses (PCA) were calculated to evidence different separation behaviour between the stationary phases, based on the retention data measured for three compound classes: anionic acidic compounds, cationic basic compounds and zwitterionic amino acids. Finally, a generic procedure is suggested for optimization of HILIC analyses, depending on the ionization state of the analytes.     

Assessment of the results from data processing systems using a digital chromatogram simulator

A digital chromatogram simulator has been used to evaluate the performance of data handling systems. The simulator can synthesize chromatograms with any desired shape from a library of peaks based on real peak shapes. Once generated, the chromatograms can be reproduced exactly any number of times. The algorithms used in data handling systems have a significant effect on the results they produce. An object of this work was to examine how well the true size of a peak was reported when the peak was detected overlapping with other peaks. A series of experiments was therefore performed in which peaks were overlapped by different amounts and in different situations. The reported results from the data systems were compared with the results which would have been reported had the peaks been fully resolved. A significant difference was found between the overlap results and the fully resolved results, which did not have a linear relationship with the parameters tested. The chromatogram simulator was found to be a powerful tool in assessing the performance of the data systems. It offers a valuable means of evaluating the quality of the results produced by these systems.     

Flame retardant polymeric additives for polyolefines. Different role of phosphoric and boric acids as FR agents in their reaction products with triglycidyl isocyanurate

Two adducts based on triglycidyl isocyanurate and phosphoric or boric acid have been compared by means of thermogravimetric analysis to investigate their activity as flame retardants and thermostabilizing agents respect to polypropylene. Better behaviour of phosphoric acid adducts have been observed.     

Application of target factor analysis of gas chromatography. Reproduction,prediction and classification

Summary Using the method of target factor analysis (TFA) described by Malinowski and Howery a computer program has been developed to study different sets of gas chromatographic retention data. Physico-chemical, topological and uniqueness parameters have been found to be basic factors to describe solute behaviour problems. Factor analytical solutions have been used to reproduce the data matrices and to make predictions based on best sets of basic factors. The mean absolute error in the reproduction step is between 1.72 retention index units (i.u.) for a relatively simple matrix consisting of retention indices of alcohols and 7.36 i.u. for a combined data matrix of alcohol, aldehyde and ketone retention indices. TFA has also been used to classify solutes based on their retention behaviour. Alkanes have been classified from cycloalkanes, alkanes from alkenes, and alcohols from aldehydes and ketones using only their retention data and a special kind of uniqueness vector.     

Study of the Contents and Speciation of Heavy Metals in River sediments By Factor Analysis

Abstract

Heavy metals Zn, Cd, Pb, Cu, Ni and Co from two spanish river sediments have been determined by voltammetric techniques, along with % CaCO₃ and % organic matter, and the whole data set examined by means of Factor Analysis, finding a different behaviour of the metals in each river.

Heavy metal speciation in the sediments was carried out by using the Tessier's scheme: Zn and Pb were mainly associated to ‘reducible phases’, Cd and Cu bound to ‘organic matter and sulphides’, and Ni and Co were distributed between the above fractions. The ‘residual’ metals were used as pollution indicators from the rivers, finding a similar behaviour to other industrialized river systems.     

含羟基化合物及其葡萄糖醛酸苷类反相高效液相色谱法保留指数预测

采用体外孵有生物合成方法,获得葡萄糖醛酸耷类代谢物,并建立了其保留指数预测方法,在实验条件下,误差小于12％。     

Tristhienylphenylamine--extended dithiafulvene hybrids as bifunctional electroactive species

Extended hybrid conjugated systems based on a trithienylphenylamine core with 1, 2 and 3 peripheral dithiafulvenyl units have been synthesized and studied by cyclic voltammetry and UV-Vis. absorption spectroscopy. Theoretical calculations have also been undergone. The behaviour of these derivatives which depends on the number of dithiafulvene moieties grafted of the central core is cleared up. One polymer, obtained from derivative 3 presents polyelectrochromic properties.     

Diffusion coefficients and complex equilibria in solution-IV Experimental determination and manipulation of diffusion data

An experimental method for effectively measuring the change of diffusion current of a metal ion in the presence of increasing concentration of a complexing ligand is described and applied to five metal-ligand systems. The method has been applied to cases of reversible and irreversible electrochemical behaviour and is shown to provide reliable formation-curve data. The systems selected have formation constants which range over some ten orders of magnitude and in most cases the values obtained agree satisfactorily with those reported in the literature. In one case equilibrium data have been calculated for the first time.     

Thermal conductivity of argon,krypton and their mixtures at low temperatures (90-270 k)

Experimental thermal conductivity values of argon, krypton and their mixtures have been measured at 1 atm (101.325 kN/m²) in a specially designed hot-wire cell in the temperature range 90-270 K. These values are compared with the recommended values based on available data for pure systems, and with the predictions of kinetic theory based on L-J (12-6), exp-six and (11-6-8) potentials. Combination rules for predicting the interaction parameters for unlike molecules from the knowledge of parameters for like molecules have been derived for (11-6-8) potential. Two variants of the procedures based on Sutherland-Wassiljewa expressions have also been examined for mixtures.     

Modelling of the pore flow in capillary electrochromatography

Pore flow in capillary electrochromatography (CEC) on porous silica particles has been investigated. To that end the migration behaviour of narrow polystyrene (PS) standards dissolved in di-methylformamide (DMF) with lithium chloride in 1 and 10 mmol/l concentration has been measured. These data have been compared to theoretical predictions. The latter were based on a model comprising cylindrical pores of varying diameter as measured experimentally by porosimetry, while the flow in each set of pores was calculated with the expression given by Rice and Whitehead. A reasonable to good agreement between experimental and predicted data was observed, provided it was assumed that pores of differing diameter occur in series. It was found that the flow in pores with a nominal size of 100 A can be considerable compared to the interstitial flow, especially at 10 mmol/l ionic strength. It is concluded that pore flow within porous particles in CEC, of great importance for improved efficiency in both interactive and exclusion type CEC, can be predicted fairly reliably by means of the Rice and Whitehead expression.     

Thermochemistry of C60 and C70 fullerene solvates

In an effort to improve understanding of dissolution behaviour of fullerenes and their simple chemical derivatives the binary systems of C₆₀, C₇₀ and the piperazine monoadduct of [60] fullerene C₆₀ N₂C₄H₈ with a series of aromatic solvents have been studied by means of DSC. In certain systems solid solvates have been found to be the thermodynamically stable phases relative to saturated solution at room temperature. Identified solid solvates were characterized by their compositions, temperatures and enthalpies of incongruent melting transitions. The regularities in thermodynamic stability of the solvated crystals have been discussed along with dissolution properties of fullerenes and the derivative. Certain correlations have been observed.     

Photochromic chiral liquid crystalline systems containing spiro-oxazine with a chiral substituent II. Photoinduced behaviour

The photoinduced behaviour of low molecular mass liquid crystalline (LC) systems doped with the chiral photochromic spiro-oxazine, 9'-{5-(-)-menthoxyacetoxy-1,3-dihydro-1,3,3-trimethylspiro[2H-indole-2,3'-[3H]naphth-[2,1 -b][1,4]oxazine]} 4-[11-(tetrahydro-2-pyranyloxy)undecyloxy]biphenyl-4'-carboxylate (THP11SOM) was observed by means of transmittance measurements at 21°C. The experimental results revealed that the ring-opened merocyanine form of THP11SOM resulting from the photochromism first disturbed the helical planar orientation of the LC molecules and then induced a new helical pitch. The magnitudes of both the disturbance in orientation of the LC molecules and the shift in the helical pitch were significantly influenced by the concentration of THP11SOM. The photoinduced behaviour was reversible due to the photochemical and thermal back reaction of the THP11SOM. In addition, the effect of UV light on the nematic-isotropic transition temperatures of the mixtures with or without a hindered amine light stabilizer was studied.     

Multiple tandem mass spectrometry-based investigation of the behaviour of some thiazol-benzimidazolones and 2-benzimidazolylsulfanyl ethanones

The behaviour in electrospray conditions of a series of thiazol-benzimidazolones and 2- benzimidazolylsulphanyl ethanones has been studied by means of multiple tandem mass spectrometry experiments. Even though the experimental conditions were the same, different behaviour is observed for the two classes of compounds. In the case of thiazol-benzimidazolones, the formation of a protonated complex with CH3OH employed as solvent is observed, but in the case of 2-benzimidazolylsulphanyl ethanones the formation of MNa+ ions is privileged. This behaviour has been related to molecular structure. The collisionally-induced decompositions of MH+ ions have been rationalised in terms of the Stevenson-Audier and even-electron rules, as well as on the basis of proton affinity data. Thus, protonated thiazol-benzimidazolones undergo facile loss of CO and a series of different decomposition pathways involving cleavage of the thiazolone ring that reflect the structure of the neutral fragments. In contrast, the decompositions of the protonated 2-benzimidazolylsulphanyl ethanones are mainly related to the piperazine moiety, suggesting that the protonation takes place on this substructural unit.     

Der Chemische Transport ternärer intermetallischer Phasen in den Systemen Cr/Co/Ge und Co/Ta/Ge

Chemical Vapor Transport of Intermetallic Systems. 11 Chemical Vapor Transport of Ternary Intermetallic Phases in the Systems Cr/Co/Ge and Co/Ta/Ge By means of chemical vapor transport using iodine as transport agent it is possible to prepare a number of ternary intermetallic compounds in the system Co/Cr/Ge as single crystals. The transport behaviour in this ternary system is related to that in the binary systems. Some informations are given about transport phenomena in the systems Co/Cr and Co/Ta/Ge.