A. C. Doriguetto

Preparation of achiral and chiral (E)-enaminopyran-2,4-diones and their phytotoxic activity.

A short and efficient approach to a range of new chiral and achiral functionalized (E)-enaminopyran-2,4-diones starting with commercially available dehydroacetic acid is described. The phytotoxic properties of these (E)-enaminopyran-2,4-diones were evaluated by their ability to interfere with the growth of Sorghum bicolor and Cucumis sativus seedlings. A different sensitivity of the two crops was evident with the (E)-enaminopyran-2,4-diones. The most active compounds were also tested against two weeds, Ipomoea grandifolia and Brachiaria decumbens. To the best of our knowledge, this is the first report describing enaminopyran-2,4-diones as potential plant growth regulators.

The effect of the cation substitution on the structural and vibrational properties of Cs2NaGaxSc1−xF6 solid solution

Raman scattering and x-ray diffration were used to characterize the structural and vibrational properties of the Cs2NaGaxSc(1-x)F6 solid solutions, for x ranging from 0.0 to 1.0. The Raman spectra, taken at room and low temperature, allow us to follow the phase evolution in detail and indicate the breaking of the local symmetry since low Ga concentration levels. Five compositions were studied by x-ray diffraction: x = 0.0, 0.2, 0.5, 0.8, and 1.0. A cubic space group, Fm3m, was found to x = 0.0 and x = 0.2 and a trigonal one was found to x = 0.5, 0.8, and 1.0. Details of both phases are presented and the correlation between x-ray diffraction and Raman scattering is discussed.

Pseudopolymorphism in hydroxybenzophenones: the dihydrate of 2,2′,4,4′‐tetrahydroxybenzophenone

A dihydrate pseudopolymorph of bis(2,4-dihydroxyphenyl)methanone, C(13)H(10)O(5)·2H(2)O, (I), was obtained during polymorphism screening of hydroxybenzophenone derivatives. This structure, in which the molecule sits on a twofold axis, was compared with the known anhydrous form of (I) [Schlemper (1982). Acta Cryst. B38, 554-559]. The role of water in the crystal assembly was established on the basis of the known monohydrate pseudopolymorph of 3,4-dihydroxybenzophenone [Landre, Souza, Corrêa, Martins & Doriguetto (2010). Acta Cryst. C66, o463-o465].

A monoclinic polymorph of the ticlopidine hydrochloride

C561 treat symptoms of allergic conditions such as rhinitis and urticara. In the Cambridge Structural Database (CSD) there is one report for the dextro isomer (REFCODE: CPHMAL10) and three reports in the Powder Diffraction File (PDF-4+: 00-041-1599, 00-042-1792, 00-050-2420). Similarly, there is one report in CSD and five in the PDF-4 for the racemic mixture. In an attempt to obtain polymorphic modifications of DexChlor, crystallization experiments were carried by slow evaporation and vapour diffusion using water, ethanol, methanol, acetone, dichloromethane and DMSO, among other solvents. The crystallization of DexChlor in acetone, by slow evaporation at 4-5 oC, produced colourless prisms. The c parameter of the unit cell of this phase is twice the corresponding value for CPHMAL10. The asymmetric unit has two crystallographically independent molecules. The geometry of one of the molecules is such that it overlaps with the molecule obtained in the previous report but the second independent molecule has a different conformation. In the new dataset, the reflections with l=2n+1 are systematically weak but nevertheless present. Transformation of the atomic positions of CPHMAL10 and re-indexing of data in the smaller cell resulted in a non-satisfactory refinement of the structure. This indicated that the small cell does not represent correctly the structure of DexChlor. Thus, DexChlor crystallizes in the monoclinic system, space group P21 with unit cell parameters a=8.8872(6), b=20.3157(14), c=11.4666(7) Å, β=104.032(4)°, V=2008.5(2) Å3, Z=4. A detailed description will be presented.

Supramolecular chemistry of anti-HIV nucleoside drugs: toward smart crystal phases and self-assembled DNA-mimicries

In-situ cryo-crystallographic techniques have been successfully applied to the determination of the crystal structures of compounds which are liquids at room temperature. It has become possible, using this approach to analyze intermolecular interactions of molecular species without the involvement of solvent either as a promoter for crystal growth or as incorporated solvatomorph [1]. 2-bromo-2chloro-1,1,1-trifluoroethane (Halothane) is a clinically used anesthetic, which has been studied earlier by in situ pressure frozen method using a diamond anvil setup. The crystals were found to belong to triclinic (space group P-1) system [2]. The crystals generated in our experiment belong to a monoclinic system (space group C2/c) with a = 18.6626(1) Å, b = 4.5759(1) Å, c = 12.4030(2) Å, β =91.85°, and V=1058.59(12) Å3, thus generates a new polymorphic form. In this structure the bromine and chlorine atoms are substitutionally disordered similar to that found in the in situ pressure frozen polymorph and the occupancies of bromine and chlorine at each site refine to 52:48 ratio. The packing is through several F....F and Cl/Br....F contacts resulting in tetrameric units as shown below.