GOSSYPOL CLATHRATES: STRUCTURE AND THERMAL BEHAVIOR OF GOSSYPOL SOLVATES WITH TWO PICOLINE ISOMERS

Gossypol forms stable solvates with 4- and 2-picolines at room temperature. The solvates are investigated by single crystal X-ray diffraction and thermal analysis. Solvate crystals of gossypol with 4-picoline (1) have the 1: 3 composition (gossypol: 4-picoline) and crystallize in the P2(1)/c space group. This substance is isostructural to a trisolvate of gossypol with pyridine. Solvate crystals of gossypol with 2-picoline (2) have the 1: 4 composition (gossypol: 2-picoline) and crystallize in the P-1 space group. The unit cell parameters for the investigated structures are as follows: 1 monoclinic crystals, C30H30O8 center dot 3C(6)H(7)N, a = 10.7530(1) angstrom, b = 20.7834(3) angstrom, c = 19.1166(2) angstrom, beta = 95.537(1)degrees, V = 4252.32(9) angstrom(3), M = 797.92, Z = 4, d(x) = 1.246 g/cm(3), and R = 0.0489 for 4102 reflections; 2 triclinic crystals, C30H30O8 center dot 4C(6)H(7)N, a = 11.467(1) angstrom, b = 14.962(2) angstrom, c = 15.570(3) angstrom, alpha = 75.62(1)degrees, beta = 69.83(1)degrees, gamma = 79.58(1)degrees, V = 2414.6(7) angstrom(3), M = 891.04, Z = 2, d(x) = 1.226 g/cm(3), and R = 0.0528 for 3779 reflections. The results of the single crystal XRD and thermal analysis confirm that gossypol with 4-picoline forms a trisolvat, and a tetrasolvate with 2-picoline. The transition from 4-picoline to 2-picoline proves to change the type of the host-guest association from one-dimensional to zero-dimensional, i.e., to lead to a new crystal structure. Desolvation of compound 2 begins at a lower temperature than that for compound 1, which is explained by their different crystal structures.