Conformational study of galphimines A and B.

A conformational study has been performed for galphimines A and B, which differ from each other only in an acetate moiety on ring B of galphimine A. Mechanical molecular calculations showed that the predominant conformers in a Boltzman distribution are those which establish an intramolecular hydrogen bond between the hydroxyls on rings A and B, keeping a similar conformation on the rest of the molecule. The existence of these conformers was confirmed by NMR spectroscopy in (D6) DMSO solution. Furthermore, an unbound hydrogen conformation was found. These types of conformations very probably coexist in solution, for both types of galphimines A and B. Additional experiments suggest that the acetate group on galphimine A does not distort rings B and A, neither does it disturb the intramolecular hydrogen bond formation that also shows galphimine B. Finally, it does not present a steric effect on ring A to avoid any type of interaction of the functional groups on this ring with the biological receptor. The acetate group, which is responsible for the lost of activity of galphimine A very probably prevent that the hydroxyls OH4 and OH7 from interacting, either in a hydrogen bounded or free form, with the receptor, indicating the importance that these hydroxyls play in the biological activity of the molecule.

(Tetrakis(2-pyridylmethyl)ethylenediamine)iron(II) perchlorate. Study of density functional methods.

On the basis of the data obtained by X-ray diffraction, the properties of two independent crystallographic subsystems in the [Fe(tpen)](ClO4)2.2/3H2O complex are studied in detail with the density functional method B3LYP. The energies of singlet, triplet, and quintet states at different temperatures are obtained, the influences of geometry on energy changes are analyzed, the regularity of the spin-state interconversions is investigated, and the effect of the triplet and action of the anion on spin crossover are discussed. This investigation demonstrates that (1) the energy difference between the high-spin state and singlet state decreases as the Fe-N distance and geometric distortion increase, (2) the spin-equilibrium system is predominantly in low-spin form below room temperature and the proportion of high-spin state rapidly increases above room temperature, (3) one of the two cation sites has a greater presence of the high-spin content, (4) the triplet state may be responsible for the fast rate of spin-state interconversions, and (5) the B3LYP method proves to be very adequate to study the spin-state transition of this complex.