Preparation of trimethylsilyl derivatives of amino acids and peptides for peptide synthesis

Russian Chemical Bulletin -     

Liquid chromatography of cardiac glycosides

Summary LC was used for the separation of several cardiac glycosides with water-alcohol eluents on a silanised silica column. The influence of temperature and composition of the eluent on the retention time, the retention volumes of the glycosides, the selectivity and the capacity factor of the column were studied. Higher temperature and a higher ethanol content in the eluent reduce the retention time, the selectivity and the capacity factor but the efficiency of the column increases. The best separation of six glycosides studied was obtained at 50°C, the ethanol content in the eluent being about 30%.     

Silochroms as adsorbents and supports in liquid chromatography

The use of macroporous silica gels, silochroms, with homogeneous geometrical structure as adsorbents and supports for liquid stationary phases in liquid chromatography is described.

The selectivity of separation and retention volumes of silochroms depend strongly on the degree of hydroxylation of the surface and on the nature of the mobile phase. In optimizing the parameters, rapid and complete separation of strongly polar isomers and biological active substances and drugs is obtained.

The dependence of retention volumes and column efficiency on the amount of liquid phase, covered on silochrom, has been investigated.     

Magnetocaloric effect in (La<Subscript>0.6</Subscript>Ca<Subscript>0.4</Subscript>)<Subscript>0.9</Subscript>Mn<Subscript>1.1</Subscript>O<Subscript>3</Subscript>

The results of investigations of the magnetization, susceptibility, and magnetic-field-induced changes in the entropy of polycrystalline manganite (La_0.6Ca_0.4)_0.9Mn_1.1O₃ near the magnetic phase transition have been presented. Magnetic measurements have been carried out at temperatures in the range from 210 to 310 K in magnetic fields of up to 9 T. The magnetocaloric effect has been revealed by measuring the magnetic-field dependences of magnetization. The magnitude of the magnetocaloric effect is compared with similar results obtained for other manganites.     

Structure and defects at Y2BaCuO5 interfaces in melt-textured YBa2Cu3Ox superconductors

Y₂BaCuO₅ (211) inclusions are prominent microstructural features found in melt-textured YBa₂Cu₃O_x (123) superconductors. These particles are of interest because the 123/211 interfaces and the interface-associated defects have been proposed to be flux pinning centers. In addition, the 211 particles are believed to be heterogeneous nucleation centers of dislocation which can increase the critical current density of 123. Unfortunately, only limited studies have been performed on these particles to ascertain their roles in flux pinning. In this investigation, 211 particles, the interfacial structure and defects in undeformed and mechanically deformed melt-textured 123 have been studied by transmission electron microscopy. It was found that there appears to be a preferred orientation between large oblong 211 particles and the 123 matrix. In addition, while the 123/211 interfaces in undeformed 123 are sharp and relatively undistorted, the interfaces in deformed 123 samples are much thicker. Also, the distribution of strained regions and dislocations around oblong 211 particles in undeformed 123 is nonuniform; the interfaces of low surface curvature are relatively free of defects while the surfaces of high curvature are abundant in dislocations. In contrast, the 123/211 interfaces in deformed 123 samples contain high density of dislocations regardless of interface curvature.     

Analysis of Two-Dimensional Optical Fields Using an Additional Shift

A solution to the phase problem in optics is considered within the context of registration and analysis of two-dimensional stationary optical fields transformed by the object under study or fields forming an image. To obtain information on amplitude and phase distributions of the light field analyzed, a method of registration of two intensity distributions is used. The first distribution corresponds directly to the amplitude distribution. The other is formed for the sum of the initial field and the field shifted along a certain direction. The intensity distributions obtained allow one to calculate the two-dimensional structure of the field under study. It is noteworthy that the method requires no iteration procedures in solving the problem. This leads to speeding up of the processing and analysis of the information. Two variants of optical schemes for the analysis of light fields are considered. The first one corresponds to registration of the image of the analyzed plane and the second to registration of the spectrum of the spatial frequencies.     

Reaction of arylenedioxytrihalophosphoranes with acetylenes 11. Electronic effect of the substituent in arylacetylene on the reaction rate

The reactions of 2,2,2-trichlorobenzo-1,3,2-dioxaphosphole and its benzo-substituted derivatives with arylacetylenes containing strong +M-donors and -M-acceptors afford benzo[e]-1,2-oxaphosphinine 2-oxides (phosphacoumarins) in high yields. Studies by the competitive reaction method showed that the reaction rate is sensitive to the electronic nature of the substituent in arylacetylene. Thus, the introduction of +M-donors into the phenyl ring of arylacetylene leads to an increase in the reaction rate, whereas the introduction of -M-acceptors results in its substantial decrease. The molecular and supramolecular structures of selected 2-hydroxyphosphacoumarins and substituted vinylphosphonate, which is generated by the cleavage of the P-heterocycle, were studied by X-ray diffraction.     

Formation of the cage-like phosphoranes with the P-C and P-N bonds in the reactions of 2-(2-benzylidenamino)phenoxy-4-tert-butylbenzo-1,3,2-dioxaphosphol with ethyl mesoxalate and ethyl trifluoropyruvate

The reaction of 2-(2-benzylidenamino)phenoxy-4-tert-butylbenzo-1,3,2-dioxaphosphol with ethyl mesoxalate and ethyl trifluoropyruvate resulted in the formation of tricyclic phosphoranes with the P-C and P-N bonds. The adduct emerged from the initial reaction of the P^III derivative with the activated ketone (1: 1), further underwent the transformation via the intramolecular reaction involving the benzylideniminoaryl substituent, which resulted in the formation of the cage-like phosphoranes.     

Dimephosphone analogues. 3. Molecular and crystal structure of dimephosphone pyridinoylhydrazones exhibiting antiphthisic activity

Molecular and crystal structures of dimephosphone nicotinoylhydrazone and dimephosphone isonicotinoylhydrazone exhibiting antiphthisic activity are studied. In contrast to aroylhydrazones of arylaldehydes, existing in the crystalline state as a mixture of two amide conformers, the studied hydrazones exist in the crystalline state in the single geometrical form E _C=N E _N-N Z _N-C(O).