Triterpeneglycosides of Astragalus and their genins. XXV. Cyclocanthoside D from Astragalus tragacantha

The epigeal part of the plant ofAstragalus tragacantha Habl. (Leguminosae) has yielded, together with cyclosieversigenin 3-O--D-xylopyranoside, a new glycoside of the cycloartane series — cyclocanthoside D, the structure of which has been established on the basis of chemical transformations and spectral characteristics as 24S-cycloartane-3,6,16,24,25-pentaol 16-O--D-glucopyranoside 3-O--D-xylopyranoside.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 73–76, January–February, 1988.     

Study of nuclear effects in nucleon structure functions up to and beyond the kinematic limit

An experiment on deep inelastic muon nucleon scattering in order to study the x-dependence of nucleon structure functions and their ratios over a range ofQ ²=50–200 GeV² andx= =0·4–2·0 is proposed. Such measurements performed on a number of nuclei with atomic weights from 2 to 207 provide new information for detailed studies of the EMC effect and test models explaining thex-behaviour of the nucleon structure functions and their ratios. The measurements are decisive for the proof that a quark-parton model of the nucleus describes adequately nuclear structure probed at high energies. The upgraded high luminosity BCDMS spectrometer with improved resolution in transferred energy can be used for the measurements.Dedicated to the 30th anniversary of the Joint Institute for Nuclear Research.     

On numerical study of periodic solutions of a delay equation in biological models

Some results are presented of the numerical study of periodic solutions of a nonlinear equation with a delayed argument in connection with themathematical models having real biological prototypes. The problem is formulated as a boundary value problem for a delay equation with the conditions of periodicity and transversality. A spline-collocation finite-difference scheme of the boundary value problem using a Hermitian interpolation cubic spline of the class C ¹ with fourth order error is proposed. For the numerical study of the system of nonlinear equations of the finitedifference scheme, the parameter continuation method is used, which allows us to identify possible nonuniqueness of the solution of the boundary value problem and, hence, the nonuniqueness of periodic solutions regardless of their stability. By examples it is shown that the periodic oscillations occur for the parameter values specific to the real molecular-genetic systems of higher species, for which the principle of delay is quite easy to implement.     

Silica Adsorbents with Well-Defined Peracetylated Thiosaccharide Surfaces: Synthesis and Use for Stereoselective Separations in RP and NP HPLC

New chiral silica adsorbents with well-defined peracetylated thiosaccharide (a.k.a. thiosaccharide) surfaces containing 1, 3, 7, and 13 glucose units have been synthesized through the reaction of trimethoxysilyl-derivatives of thiosaccharides with bare silica gel. As determined by FTIR, nitrogen adsorption, thermo-gravimetric analysis, and chemical analysis, the adsorbents prepared contained closely packed uniform monolayer surfaces of thiosaccharide groups grafted to silica. The chromatographic behavior of the thiosaccharide-silicas prepared has been evaluated in the HPLC separations of stereoisomers in both normal and reversed phase modes. With the exception of low grafted thiomaltodecatriose-silica, there was no effect of the size of thiosaccharide on the selectivity of the separations.     

Determination of the quantum yield of singlet-triplet conversion in complex organic compounds by the method of laser fluorimetry

The possibilities of the nonlinear laser fluorimetry method for determination of the quantum yield into the triplet state are demonstrated. The values of the absorption cross section and the triplet-state quantum yield are determined from the fluorescent saturation curves for 6-aminophenolenone and rhodamine 6G (used as a test material).     

The Adsorption of Saturated and Aromatic Hydrocarbon Vapors on Silicas with Chemically Grafted Perfluorohexyl Groups

Regardless of the nature of the modifier (mono-, bi-, and trichlorosilanes with perfluorohexyl groups or monochlorooctylsilane), the modification of silica decreased retention volumes and adsorption values of both n-alkanes and aromatic hydrocarbons. The entropy factor can play a key role in adsorption intermolecular interactions on the surface of chemically modified silicas. The modification of the surface with bi- and trichloroperfluorohexylsilanes caused the appearance of new centers more active compared with those of the initial carrier. The most oleophobic and nonpolar coatings were obtained using monochlorosilane with perfluorohexyl groups as a modifier.     

Exchange interaction and elastic 16O + 12C scattering

The effect of core exchange on the potential of interaction between the ¹⁶O and ¹²C nuclei is considered. The amplitudes corresponding to nonlocal exchange interactions are calculated in the Born approximation. It is shown that the inclusion of exchange processes leads to the growth of the elasticscattering amplitude in in the region of large scattering angles. The dependence of amplitudes on the parity of relative motion is analyzed.     

Dual reactivity of diazonium salts derived from 1-amino-2-ethynyl-9,10-anthraquinones

Diazotization of vicinal 1-amino-2-ethynyl-4-R-9,10-anthraquinones followed by a reaction with NaN₃ gave 5-hydroxy-3-R-1H-naphtho[2,3-g]indazole-6,11-diones or 3-ethynyl-5-R-6H-anthra[1,9-cd]isoxazol-6-ones, depending on the substituents at the triply bonded C atom and in position 4 of the anthraquinone framework.     

Terahertz emission from a metallic surface induced by a femtosecond optic pulse

Results of experimental and theoretical investigations on generation of terahertz radiation at the interaction of femtosecond laser pulses with a metal surface are presented. Investigations are performed with the laser pulse intensities higher compared with that used in papers [Opt. Lett.29, 2674 (2004); Opt. Lett.30, 1402 (2005)]. The most effective generation is observed for p-polarized optical pulses with incidence angles in the range 5°-10° (from the surface), depending on the kind of metal. For the copper, the exponential growth of terahertz pulse energy with the increase of optical pulse energy was registered. Theoretical interpretation for some of the experimental results is proposed based on the model of free electrons in metal.     

On the shift of a regulatory signal in models of matrix synthesis

The paper deals with the limiting properties of the matrix synthesis models that take into account the phenomenon of branching and an unspecified number of intermediate steps. Numerically, it is shown that with unlimited increase of the number of intermediate steps, there is observed a shift of the control signal along the chain synthesis. Also the shift causes the compression of the control function which is inversely proportional to the branching ratio. If branching is absent then the conjectures are proved by analogy with the available limit theorems.