Authors:Łukasz Komsta, Rafał Pietraś, Ewelina Bartuzi, Robert Skibiński and Anna Gumieniczek
Thin-layer chromatography (TLC) on two adsorbents (RP18 and CN) and with six modifiers (acetonitrile, acetone, dioxane, propan 2-ol, methanol, and tetrahydrofurane), followed by classical RM value extrapolation (previous results), was chemometrically compared with new one-run gradient high-performance liquid chromatography (HPLC) (C18, C18e, CN, and DIOL columns, acetonitrile, and methanol as modifiers) and, additionally, with seven computational algorithms (ALOGPs, AClogP, ALOGP, MLOGP, KOWWIN, XLOGP2, and XLOGP3) as a lipophilicity assessment tool on 35 model compounds with known lipophilicity. The statistical significance of intercepts and slopes of Collander equation (log P — retention dependence) and their values were compared. Whole results data set was subjected to scaled principal component analysis, which allowed exploring two main trends in these data. It can be concluded that one-run gradient HPLC does not outperform TLC in lipophilicity determination. Very good correlations were obtained between real log P and computational approaches; however, this is not a surprise for such simple molecules.
Authors:Yu. N. Sazanov, L. A. Shibaev and T. A. Antonova
The method of comparative thermal analysis has been used to determine the thermal stability of polyimides and their model compounds. The extent of defects in the investigated polyimides was determined by gas chromatography. The dependence of the extent of the defects on the chemical structure of the initial components and the supermolecular structure of the polyimides was established.
Authors:Ł. Komsta, R. Skibiński, A. Gumieniczek and A. Wojnar
The thin-layer chromatographic (TLC) retention of 35 model compounds has been investigated with ten screening mobile phases on six normal-phase and seven reversed-phase adsorbents. The retention factors formed two cubes with dimensions 35 × 10 × 6 and 35 × 10 × 7, respectively, which enabled three-way analysis by PARAFAC. A one-component PARAFAC model was optimum in both cases and two-component models performed worse. The one-component model explained 78.8% of the variance in normal-phase chromatography and 94.2% of the variance in reversed-phase chromatography. These results showed that the major variability of the retention factor (RF) can be modelled as the product of three factors related to the substance itself, the mobile phase, and the adsorbent. RF modelling was substantially better than using k or RM (rate mobility) values.
Authors:Łukasz Komsta, Patrycja Smardz, Rafał Pietraś, Robert Skibiński and Anna Gumieniczek
The retention (RM) values of nine one-point adsorption model compounds: diphenylamine, indol, 2-naphtol, 1-naphtol, 1-naphtylamine, 4-toluidine, carbazole, 4-chloraniline, and thymol were investigated on silica gel using six modifiers: acetone, dioxane, hexane, isopropanol, methylethylketone, ethyl acetate, and tetrahydrofurane (in hexane). These compounds showed small but visible curvilinearity of dependence of RMvs. modifier concentration. This curvilinearity is very similar among the investigated compounds, so relative differences of extrapolated RM are almost the same (strictly intercorrelated) regardless of the regression technique used. We have compared several robust and weighted regression methods and investigated their impact on extrapolated values. It can be concluded that one should primarily consider weighted regression with 1/x weights during retention extrapolation. It seems to be a better alternative than classical regression (better extrapolation) and also better than polynomial approaches (better stability).
Six oligomers of -aminocaproic acid (ACA) from dimer (K2) to heptamer (K7), gamma-irradiated in an oxygen-free atmosphere, were investigated by the EPR method. The oligomers were synthesized and irradiated with60Co gamma-rays in the dose range from 0 to 6.5 kGy. The formation of –CH2–CONH–CH–CH2– radical was established. The quantitative determinations of total concentrations of spins were carried out. On the basis of the present and earlier results, the competition of the reactions of detachment of hydrogen and of breaking of –CONH– bond is discussed. The particular resistance of amide bond in dimer seems to be confirmed by the measurements of kinetics of radical decay. The mass spectrometry of gamma-unirradiated ACA and ACA oligomers K2-K4 was carried out. The results indicate a minute contribution of ionic processes in the radiolysis of ACA oligomers in solid phase.
Authors:G. E. Domburg, V. N. Sergeeva and G. A. Zheibe
Compounds acting as model biphenyl and phenylcoumarane structural units in the lignin molecule (dehydrodivanillin and dehydrodiisoeugenol) were investigated by thermal analysis. The results were compared with previously obtained data on the thermal degradation of model phenylpropane monomer units of lignin. It was found that the mechanism of thermal degradation of these models and the thermal stabilities of the bonds depend on the structure. The thermal stability of the models increases in the absence of reactive functional groups in the side chain.
Authors:S. Maślanka, W. W. Sułkowski and A. Sułkowska
investigation of modelcompounds are required to perform the physico-chemical characteristics of polymers. Instrumental techniques such as NMR, dielectric spectroscopy, thermogravimetric analysis and mechanical spectroscopy are used to study the physico
Authors:Michal Baudys, Martin Zlámal, Josef Krýsa, Jaromír Jirkovský and Petr Kluson
activities have been examined with many attempts to generalize the achieved results. These attempts are often reported with azo dyes as modelcompounds. The main reason for using azo dyes as models is the simple spectral determination of their photocatalytic