Sesquiterpene Lactones and Flavonoids from <Emphasis Type="Italic">Artemisia albida</Emphasis>

The five known lactones matricarin, austricin, canin, and achillin guaianolides and argolide germacranolide and the two flavonoids eupatilin and its 7-O-methyl ester were isolated for the first time from the aerial part of Artemisia albida Willd. The structure of eupatilin was confirmed by an x-ray structure analysis. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 568–570, November–December, 2005.     

Sesquiterpene Lactones from <Emphasis Type="Italic">Stizolophus balsamita</Emphasis> and Their Biological Activity

Four sesquiterpene lactones with the germacrane structure were isolated from the aerial part of Stizolophus balsamita. X-ray structure analyses showed that two of them were previously known balsamin derivatives. A third was a crystalline isomorphous mixture of the known lactone stizolin and 11,13-dihydrostizolin in a 53:47 ratio. The biological activities of the balsamin derivatives were investigated. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 454–457, September–October, 2005.     

Mechanisms of viscosity of polyacids and polybases in the region of pronounced polyelectrolyte effect

The dependence of viscosity of dilute solutions containing high-and low-molecular-mass electrolytes on solute concentrations was studied for completely and partially ionizing polyelectrolytes used as an example. The viscosity of solutions of the completely ionizing polyelectrolytes is described by the generalized Fuoss relationship derived earlier. However, the viscosity of solutions of the incompletely ionizing polyelectrolytes may substantially deviate from the relations derived on the basis of this expression. On the basis of the electrostatic theory of swelling, it was shown that the region of the distinct polyelectrolyte effect corresponds to practically complete volume filling by macromolecular coils. The viscosity of a polyelectrolyte solution is determined by two factors, the electrostatic interaction of coils that occur at a distance on the order of the Debye length apart from one another and the coil deformability. The former factor can completely be described through the similarity criterion corresponding to the generalized Fuoss law, and the latter factor requires that a change in the electrostatic persistence length should be taken into account, as this quantity is directly affected by the degree of charging of the macromolecule backbone.     

Extraction of Chemical Speciation and Molar Absorption Coefficients with Well-Posed Solutions of Beer's Law

The performance of different types of solutions of Beer's law was evaluated on a suite of synthetic uv-vis spectra generated at various degrees of random error. Solutions making use of absorbance matrices filtered from random noise were the most successful at retrieving the properties of chemical species at larger errors. Repeated automated simulations, however, indicated that such solutions display a number of occurrences associated with poor fits to the synthetic data. Solutions to Beer's law starting from the raw absorbance matrices including random errors produced more consistent sets of values of rather poorer quality. A bootstrap statistical analysis of the repeated simulations showed the median quality of the fit (e.g., sum-of-squares of the deviations) nonetheless to be far superior for solutions making use of error/noise filtration. These resulting absorbance matrices when reduced dimensionality, moreover, gave better values of the molar absorption coefficients and formation constant if solved numerically using orthogonal-triangular (QR) factorizations. These solutions are therefore recommended for the extraction of spectroscopic and thermodynamic/kinetic properties of chemical species from spectroscopic data, however, not without a rigorous validation of the model. All the solutions to Beer's law are provided in the computational language of Matlab 7.0 and may be readily implemented for any quantitative spectroscopic analyses.     

Intermacromolecular interactions involving linear and network polyacids and nonionic polymers

Interactions between linear and network polymers are studied in the case when one component is a polyacid and the other component is an uncharged polymer. It is shown that, under different reaction conditions, swelling or contraction of the polymer network can be observed for the same pair of reagents. It is found that, during consideration of the formation of an interpolymer complex between network and linear polymers, a distinction should be made between a semi-interpenetrating network and a hydrogel with a modified surface. The latter forms under conditions when the linear polymer practically does not penetrate the network and the complexation occurs predominantly on the sample surface.     

Interpolymer complex formation of some nonionogenic polymers with linear and crosslinked polyacrylic acid

The formation of interpolymer complexes on the surface of crosslinked poly (acrylic acid) with some nonionogenic polymers is compared with the complex formation in analogous linear polymer systems. The behavior of these systems is compared with that of complexes of two oppositely charged polyelectrolytes. The concentration redistribution of the linear polymer in the system polyelectrolyte network-polymer solution and the degree of swelling of this network in these solutions were determined. © 1994 John Wiley & Sons, Inc.