Lamiaceae carbohydrates. 1. Pectinic substances and hemicelluloses from <Emphasis Type="Italic">Mentha x piperita</Emphasis>

Pectinic substances from the aerial part of Mentha x piperita were isolated and characterized and found to be a mixture of β-(1→4)-glucogalactan (MPG) and two α-(1→4)-rhamnopolygalacturonans (MPP′-1 and MPP′-2). It was shown that the pectin and its components exhibited membrane-stabilizing, antiatherogenic, and antioxidant activity. Hemicelluloses from M. piperita were a lignocarbohydrate complex. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 411–416, September–October, 2007.     

Comments on the electronic properties of cyclopropane,cyclobutane, and cyclohexane

Spectral quantities of cyclopropane, cyclobutane, cyclohexane, and of several derivatives, have been calculated by a semiempirical all-valence electron SCF-CI MO method. In cyclopropane, HOMO is practically localized in the carbon-frame, and LVMO is purely so. In cyclobutane, these two MO's are based on C-H bonds, while cyclohexane holds an intermediate position. Despite the overall similarity-experimental and computed-of the spectra of these molecules, assignments are non-parallel. Like cyclopropane, cyclobutane can extend conjugation, but to a diminished degree; cyclohexane behaves in this respect like an acyclic alkane. An interpretation of this gradation, in terms of the nature of high-lying MO's, is proposed.     

Effect of hydrophobic amino acids on the conformational change of decapeptides in micellar environments

A series of peptides containing various hydrophobic amino acids [methionine (Met), leucine (Leu), norleucine (Nle), phenylalanine (Phe), 2-aminooctanoic acid (Aoc), and 2-aminodecanoic acid (Ade)] were synthesized and their conformations were studied using circular dichroism (CD) spectroscopy in different solvents such as water, methanol, and aqueous solution of ammonium tetradecanesulfonate. Peptides containing hydrophobic amino acids with linear side chains formed xh31x0n8e/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-sheets in water and methanol. Electrostatic interaction between the charged side chain (lysine) and a micelle consisting of an anionic surfactant, ammonium tetradecanesulfonate, is necessary for the formation of xh31x0n8e/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-helices in micellar environments. The conformational transition from xh31x0n8e/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-helix to xh31x0n8e/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-sheet structure required moderate hydrophobicity and linear side chains. This conformational transition depended on the surfactant concentration.     

Kraftfeldrechnungen an linearen Oligopyrrolen: 2,2′-Bipyrrol, 2,2′-Furylpyrrol und Prodigiosen

Using a specific force field model, relative stabilities of 2,2x1g4t80pn6r/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-bipyrrole and 2,2x1g4t80pn6r/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-furylpyrrole conformers as well as of prodigiosene tautomers, configurations, and conformations, are studied. 2,2x1g4t80pn6r/xxlarge8242.gif" alt="prime" align="BASELINE" BORDER="0">-Bipyrrole adopts anantiperiplanar conformation in accord with other theoretical calculations and experimental findings. Its rotational barrier calculated by this method compares favourably to the one derived by other means. For the parent prodigiosene the (Z)sp,sp arrangement is found to be the most stable one. The two possible tautomers within its dipyrrin fragment do not show a significant energy difference.

     

Studies of solvent effects

The effect of water on the conformational preferences of acetylcholine has been studied within the x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">discretex233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0">, the x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">continuumx233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> and the combined x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">discrete-continuumx233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> models described in parts I and II of this series. All the models lead to the conclusion that the trans-gauche form which is, following refined quantum-mechanical computations, the intrinsically preferred one and the one observed in the crystal of acetylcholine and of a number of analogues should remain also the preferred conformation in water. This result agrees with NMR studies. The results of the empirical discrete model used here compare favorably to those obtained by an ab initio x233/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">super-moleculex233/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> treatment. The continuum model utilized here represents a net improvement above such models utilized in other works.     

Calculations of the electronic structures of cage molecules using free-electron orbitals as a basis

A non-empirical molecular orbital method, particularly suitable for calculations on cage-like molecules, is described. The method uses as basis functions the set of free-electron functions which are the solutions of Schrödinger's equation for an electron confined between two concentric, spherical potential energy barriers. Application of the theory to the SCF calculation of the energies of the delocalized electrons in benzene and tetrasulphur tetranitride shows that the model is capable of interpreting the properties of such systems. However, it does highlight a difficulty in the calculation of excited state energies with one-centre models which appears to be largely unrecognized.Extension of the method to a consideration of all the valence electrons, using P₄ as an example, reveals problems the origin of which is an inadequate treatment of the core electrons. It is suggested that these problems may best be dealt with by use of a suitable pseudo potential.     

A new approach to 6-deoxy-D-allofuranose- and 6-deoxy-L-talofuranose derivatives from 1,2:5,6-di-O-isopropylidene α-D-glucofuranose

3-O-Acetyl-1,2-O-isopropylidene-x5k268606h31/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene-x5k268606h31/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy-x5k268606h31/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene-x5k268606h31/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-L-talofuranose (6) was also prepared stereoselectively from2 b via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene-x5k268606h31/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-D-allofuranose (4 a) and -x5k268606h31/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet.     

Monte‐Carlo simulation of spatial distribution of characteristic x‐rays in multi‐film targets: source size of Al Kα x‐rays in W/Al film targets

A Monte‐Carlo simulation approach has been applied to describe the spatial distribution of characteristic x‐rays in W/Al film targets of different combinations of film thicknesses for the optimal design of a small‐sized x‐ray source having a high x‐ray intensity. The result has led to optimal combinations of W and Al film targets for 100 kV electrons, e.g. W(1 µm)/Al(20 µm), W(3 µm)/Al(15 µm) and W(5 µm)/Al(8 µm). These Al/W targets could be used as x‐ray sources for a medical instrument currently under development. Copyright © 2004 John Wiley & Sons, Ltd.     

Classical theory of vibration energy transfer in collinear collisions

Classical theory of collisions is cast in a form which also includes the uncertainty principle. This theory is used for analyzing the vibration energy transfer in the collinear collision which approximates the He-H₂ system. The results are compared with the quantum calculations and several classical and semiclassical approaches. Very good agreement with quantum theory is found, for all the parameters investigated.     

Phytoecdysteroids of Plants of the Silene Genus. 2-Deoxyecdysterone-25-Acetate from Silene wallichiana

The new ecdysteroid 2-deoxyecdysterone-25-acetate was isolated from roots of Silene wallichiana Klotzsch.