Effect of Mobile Phase pH* on Chromatographic Behaviour in Chiral Ligand-Exchange Thin-Layer Chromatography (CLETLC) of Amino Acid Enantiomers

The enantiomers of some amino acids have been separated on commercial chiral TLC plates in reversed-phase mode. The effect of the pH* of the aqueous-organic mobile phase on the retention and mobility of the enantiomers and on selectivity was investigated. It was shown that for most of the amino acids investigated the highest enantioselectivity was obtained at pH* 3–4 or 6–7. The drift and disturbance of the baseline on the chromatograms were also much smaller at pH* 3–4 and 6–7.     

Tetraphenylporphyrins monosubstituted with a crown ether in one phenyl ring. Synthesis and characterization

Summary The synthesis and spectroscopic characterization of seven new tetraphenyl-porphyrins (1–7) derivatized with 12-crown-4, 14-crown-4, 15-crown-5, or 18-crown-6 ether units inortho orpara position of one of the phenyl rings is described.

---

In einem Phenylring mit Kronenethern monosubstituierte Tetraphenylporphyrine. Synthese und Charakterisierung

Zusammenfassung Die Synthese und die spektroskopische Charakterisierung sieben neuer Tetraphenylporphyrine (1–7), die mit 12-Krone-4, 14-Krone-4, 15-Krone-5 oder 18-Krone-6 in derortho-oderpara-Position eines Phenylrings substituiert sind, werden beschrieben.

     

Untersuchung der Wechselwirkung von Eiweißen mit Polysacchariden im Wassermedium

Zusammenfassung Die komplexe Koazervation im SystemG-A-H₂O kann als zweistufiger Prozeß aufgefaßt werden. Das erste Stadium ist die Bildung des elektrisch neutralen Komplexes zwischen G und A unter Einfluß der elektrostatischen Anziehungskräfte. Die Stöchiometrie der gewonnenen Verbindung wird durch die Äquivalenz der Makroionen bestimmt.Nur elektrisch neutrale Komplexe können die neue Phase, d. h. das komplexe Koazervat bilden. Deshalb muß die Zusammensetzung der koazervaten Phase von p_H abhängen und bei Veränderung des Verhältnisses der Polymere im Gemisch unveränderlich bleiben.Bei einem Verhältnis der Polymere, kleiner als das stöchiometrische, ist die Bildung geladener Komplexe möglich.Den Prozeß der komplexen Koazervation kann man mittels der Methode der Trübungsmessung bei C_s<6·10^{–3 g}/100 g untersuchen. Hierbei ist die optische Dichte proportional der Menge des komplexen Koazervats oder des elektrisch neutralen Komplexes im System.     

Optimization of stepwise gradient elution in reversed-phase chromatography

Summary Equations describing multi-step gradient elution with a mobile phase of constant composition in each step were derived. These equations useful for calculating the retention volumes in both gradient HPLC and TLC were derived on the basis of the relationship between the isocratic capacity factor and the volume fraction of the organic modifier. The validity of the equations was experimentally verified in a LiChrosorbRP-18-water/methanol system for 11 methyl- and chlorobenzenes and phenols. A satisfactory agreement between the theoretical and experimental k′ values was found.     

Binary and ternary chromium(III) complexes with cellular reductants and DNA components isolated from redox type systems. Part 1. Chromium(VI)–cysteine–adenine (adenosine,ATP)

The reduction of CrO₃ with an excess of L-cysteine and its interaction with DNA fragments (adenine, adenosine) and ATP nucleotide was studied by analysis of the isolated solid products. The precipitates were characterised by elemental analyses, FAB mass spectral data, spectroscopic methods (u.v.–vis., f.i.r., i.r.) and magnetic measurements. The Cr^III complexes obtained appear to be various Cr^III cysteinate and adenine or ATP (but not adenosine) ternary species of the addition type bound through the hydrogen bonding network.     

Investigation of the electrokinetic properties of paraffin suspension. 2. In cationic and anionic surfactant solutions

Electrical phenomena at nonionogenic hydrophobic surfaces (solid or liquid) in water, electrolyte, and/or surfactant solutions still attract research. In part 1 of this paper we described the electrokinetic behavior of paraffin wax suspension in water and electrolyte solutions (NaCl or LaCl3). On the basis of the latest data of water structure near hydrophobic surfaces it was concluded that immobilized water dipoles at the interface can play an essential role in the zeta potential formation. In this paper were investigated the zeta potentials of paraffin wax in cationic surfactants cetyltrimethylammonium bromide, C16H33(CH3)3NBr, and octadecyltrimethylammonium chloride, C18H37(CH3)3NCl, and anionic surfactant sodium dodecyl sulfate, C12H25SO4Na. Also changes in wettability of the paraffin surface due to the surfactant's adsorption were studied via wetting contact angle measurements and calculation of the surface free energy. It was concluded that at a low surfactant concentration (10(-6) M) the water dipole structure still contributes to the zeta potential, but at a higher one the zeta potential is determined by the surfactant molecules' adsorption. A special role of OH- ions is also clearly seen. Moreover, a functional relationship was found between the surface free energy of the surfactant-covered paraffin surface and the zeta potential.     

Hypoxanthine,xanthine and theobromine complexes with palladium(II) and platinum(IV) chlorides

Summary Complexes of the general types Pd(L)(LH)Cl (LH=hxH, xnH, or tbH) and Pt(L)(LH)Cl₃ (LH=hxH, or xnH) are formed by boiling under reflux 21 molar mixtures of hypoxanthine (hxH), xanthine (xnH) or theobromine (tbH) and PdCl₂ or PtCl₄ in ethanol-triethyl orthoformate. These complexes appear to be linear chain polymeric species, characterized by single monoanionic L^– ligands bridging between adjacent Pd²⁺ or Pt⁴⁺ ions. Inclusion of one terminal neutral LH and one terminal chloro-ligand completes the coordination sphere in the square-planar Pd²⁺ complexes, while the Pt⁴⁺ complexes aretrans-octahedral, involving three terminal chloro and one terminal LH ligand per platinum. The possible binding sites of the bidentate bridging L^– and the unidentate terminal LH are discussed.     

Modification of the Orientation of Substitution Reactions on Thiophene and Furan Derivatives

Under normal conditions, thiophene and furan derivatives are substituted in the α position, and no convenient alternative methods for the preparation of β-substitution products have been available until now. The present article describes a method that permits the synthesis of many β-substituted thiophenes and furans. In this method, the carbonyl group in α-aldehydes or ketones of the thiophene and furan series is blocked by complex formation with an excess of aluminum chloride, so that electrophilic substitution takes place in position 4. In another useful method, the carbonyl group is blocked by acetalization. The acetals can be metalated in the ring by organolithium compounds.     

Synthesis and properties of 1-(6-methoxy)-2-benzothiazolyl)-2-pyridones

Substituted ]-(6-methoxy-2-benzothiazolyt)-2-pyridones were prepared from 2-amino-6-methoxybenzathiazate through N-(6-methoxy-2-benzothiazotyl) cyanvorearmileaznd-3-aryl-N-(6-methoxy-2-benzothiazolyt)-2-cyano-2-propenamides. The cyclization of the latter with malonodinitrile in the presence of piperidine gave the corresponding pyridones. The structures of the synthesized compounds were confirmed by¹H NMR and mass spectral data.Department of Organic Chemistry, Mass Spectrometry Laboratory, Slovak Technical University, 812 37 Bratislava, Slovakia. Published in Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1402–1404, October, 1995. Original article submitted August 24, 1995.     

Carrier influence on the paramagnetic and catalytic properties of supported titanium complexes

Alumina-silica possessing various Al₂O₃/SiO₂ ratios was used as a carrier of surface titanium complexes. The systems obtained were examined as models for the investigation of the macroligand (inorganic gel) influence on the physicochemical properties of supported transition metal complexes. The titanium complexes were prepared first by the reaction of CpTiCl₃, with the hydroxyl groups of the gel and then reduced by an excess of BuLi. The influence was established of the basic gel properties on: (a) the amount of titanium(IV) and titanium(III) complexes on the alumina-silica gel surfaces; (b) the symmetry of the surface Ti^III surface complexes; (c) the electron density around the surface-Ti^III ions, ionic or covalent bonds character in a complex; and (d) the catalytic activity in olefin hydrogenation.