Optical properties of in situ doped and undoped titania nanocatalysts and doped titania sol-gel nanofilms

In this paper we present spectroscopic properties of doped and undoped titanium dioxide (TiO₂) as nanofilms prepared by the sol-gel process with rhodamine 6G doping and studied by photoacoustic absorption, excitation and emission spectroscopy. The absorption spectra of TiO₂ thin films doped with rhodamine 6G at very low concentration during their preparation show two absorption bands, one at 2.3 eV attributed to molecular dimmer formation, which is responsible for the fluorescence quenching of the sample and the other at 3.0 eV attributed to TiO₂ absorption, which subsequently yields a strong emission band at 600 nm. The electronic band structure and optical properties of the rutile phase of TiO₂ are calculated employing a fully relativistic, full-potential, linearized, augmented plane-wave (FPLAPW) method within the local density approximation (LDA). Comparison of this calculation with experimental data for TiO₂ films prepared for undoped sol-gels and by sputtering is performed.     

Spectrophotometric determination of uranium with 5-(2′-carboxyphenyl)azo-8-quinolinol in the non-ionic micellar medium of Triton X-100

Triton X-100, a non-ionic surfactant, has been used to sensitize the reaction of 5-(2-carboxyphenyl)azo-8-quinolinol with uranium in aqueous medium at pH 5.2–6.1 to form a wine red coloured complex. The micellar sensitization results in two and a half-times enhanced molar absorptivity enabling the determination of uranium in rock samples at ppm level, stability of the complex enhanced from 4 hours to at least 72 hours. Extraction of the complex is avoided making the procedure simple, rapid and easy in operation. The molar absorptivity and Sandell's sensitivity of the complex are 1.50·10⁴l·mol^–1·cm^–1 and 15.9 ng·cm^–2, respectively, at _max=568 nm. Beer's law is obeyed over the range 0–3.3 g·ml^–1 of uranium. An amount as low as 0.19 g·ml^–1 of uranium could be determined satisfactorily within a relative standard deviation of ±1.3%. The limits of determination and practical quantitation are 0.29 and 1.80 ppm, respectively. The method was applied to the determination of uranium in soil, stream sediment and rock samples.     

Molecular orbital calculations on the conformation of nucleic acids and their constituents

The conformational properties of the furanose ring of purine- and pyrimidine--nucleosides and-nucleotides are studied quantum-mechanically with the help of the PCILO method, using the pseudorotational concept. The computations point to the existence of two stable conformational zones centered around the C(3)-endo and C(2)-endo conformations which in the isolated furanose ring are separated by barriers of the order of 4 kcal/mole. In nucleosides one of the barriers (the one running through the O(1)-exo-C(2)-exo path) becomes very high. A detailed study is made of the relation between the phase angle of pseudorotation, P, and the torsion angle about the glycosyl bond, _CN. A very satisfactory agreement with the available experimental data is observed.

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Zusammenfassung Die Konformationseigenschaften des Furanoserings in -Nucleosiden und Nucleotiden von Purin und Pyrimidin werden nach der PCILO-Methode unter Berücksichtigung der pseudorotatorischen Betrachtungsweise studiert. Die Rechnung läßt auf die Existenz zweier stabiler Konformationszonen schließen, die in der Umgebung der C(2)-endo und der C(3)-endo Konformationen liegen, und die im isolierten Furanosering durch Energiebarrieren der Größenordnung von 4 kcal/mol voneinander getrennt sind. In Nucleosiden wird eine der Barrieren (die durch den Weg O(1)-exo-C(2)-exo gekennzeichnete) sehr hoch. Die Relation zwischen dem Phasenwinkel der Pseudorotation, P, und dem Drehwinkel um die Glycosylbindung, _CN, wird einer eingehenden Untersuchung unterworfen. Man beobachtet eine sehr zufriedenstellende Übereinstimmung mit den verfügbaren experimentellen Daten.

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Résumé Les propriétés conformationnelles du noyau furanose des -nucleosides et nucleotides des purines et pyrimidines sont étudiées par la méthode PCILO en faisant appel au concept de la pseudorotation. Les calculs indiquent l'existence de deux zones de conformations stables, centrées autour des conformations C(2)-endo et C(3)-endo, qui sont dans le sucre isolé séparées par des barrières de l'ordre de 4 kcal/mole. Dans les nucleosides, l'une de ces barrières (celle qui passe par le chemin O(1)-exo-C(2)-exo) devient très élevée. Une étude détaillée est effectuée sur la relation entre l'angle de phase de la pseudorotation P et l'angle de torsion autour de la liaison glycosylique, _CN. Un excellent accord avec les données expérimentales disponibles est observé.

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This research was supported by the R.C.P. 173 and the A.T.P. A 655-2303 of the C.N.R.S.     

Preferred conformers in n-propanol: A PCILO study

Preferred conformers around the central C-C and C-O bonds in n-propanol have been determined using the quantum-mechanical PCILO method and compared with those observed experimentally by microwave spectroscopy. The agreement between theory and experiment is excellent, thus minimizing time consuming searches for microwave transitions corresponding to the preferred conformers.     

Molecular orbital studies on the structure of nucleoside analogs. IV. Conformation of 3-deazapurine nucleosides

Conformational properties of 3-deazapurine nucleosides (namely, 3-deazaadenosine and 3-deazaguanosine) have been investigated by the PCILO method. Both C(2′)-endo and C(3′)-endo sugar puckers have been considered and the results indicate that the conformational preferences of these nucleoside analogs are quite different from those of their parent nucleosides adenosine and guanosine, respectively. This result has been correlated in terms of the biological inactivity of these nucleoside analogs.     

Conformation of nucleoside antibiotics

Minor modifications or substitutions in the sugar or in the base part of pyrimidine and purine nucleosides have a profound effect on their biological activity. These modified nucleosides usually become antiviral, antibacterial, or cancerostatic agents and they are collectively called nucleoside antibiotics. The conformational properties of some of these nucleoside antibiotics have been studied by the PCILO method. The results obtained from such study indicate that the conformational preferences of these nucleoside antibiotics are very similar to those of their parent nucleosides and especially so in the situations that occur in aqueous solutions. The important biological significance of these results is that these nucleoside antibiotics can easily get incorporated into growing chains of DNA and RNA by mimicking their parent nucleosides and can interfere with the protein synthesis of RNA or DNA synthesis.     

Some neutral three-coordinate complexes of mercury(II) halides and pseudohalides with N-methylnicotinamide

Coordination compounds of mercury(II) chloride, bromide, cyanide and thiocyanate with N-methylnicotinamide, a potentially bidentate ligand, have been prepared. The complexesisolated have 1∶1 (metal:ligand)stoichiometry. Molecular weight measurements in molten camphor indicate that the mercury (II) chloride and bromide complexes are monomeric. Based on conductance values, molecular weight determinations and infrared spectral data, it is inferred that in the solid state in all these complexes the metal ion has a coordination number three and is bonded to the N-methylnicotinamide via its pyridine ring nitrogen, and is terminally bonded to the halogen/pseudohalogens.     

High-performance thin layer chromatography method for quantitative determination of four major anthraquinone derivatives in Rheum emodi

A high-performance thin layer chromatographic (HPTLC) method for the rapid and simple quantification of the four major anthraquinone derivatives i.e. physcion, chrysophanol, emodin and chrysophanol glycoside in Rheum emodi is described. HPTLC of anthraquinone derivatives was performed on pre-coated RP-18 F254S HPTLC plates. For achieving good separation, the mobile phase of methanol-water-formic acid (80:19:1, v/v/v) was used. The densitometric determination of anthraquinone derivatives was carried out at 445 nm in reflection/absorption mode. The calibration curves were linear in the range of 20-100 ng for physcion, 80-400 ng for chrysophanol and emodin, and 200-1000 ng for chrysophanol glycoside. The method was found to be reproducible and convenient for quantitative analysis of anthraquinone derivatives in the methanolic extract of rhizomes of R. emodi collected from three different locations of Western Himalaya, India.