Solid-Phase Molecular Recognition of Cytosine Based on Proton-Transfer Reaction

The proton-transfer molecular adducts cytosine/isoorotic acid (1: 1) dihydrate (CytIsor) and cytosine/maleic hydrazide (2: 2) dihydrate (CytMal) have been studied by X-ray diffraction methods. CytIsor crystallizes in the orthorhombic system, space group Pbnb, a = 7.4859 4), b = 12.7977 (9), c = 26.4573 (16) angstrom, V = 2534.7 (3) angstrom(3). CytMal crystallizes in the triclinic system, space group P - 1, a = 6.7767 ( 9), b = 12.063 ( 2), c = 12.937 (3) angstrom, alpha = 78.58 (2), beta = 75.87 (2), gamma = 75.63 (1)degrees, V = 982.8 (3) angstrom(3). In both compounds protonation occurs at the N3 atom of the cytosine aminooxo tautomer as a result of the proton-transfer process from the acidic hydroxy groups of the counterions. In the crystal structure, both cocrystals are stabilized by a plethora of N-H center dot center dot center dot O, N-H center dot center dot center dot N and O-H center dot center dot center dot O hydrogen bonds. It is shown the ability of cytosine to form large organic assemblies, with the appropriate guest, due to solid-state recognition involving synthons based on hydrogen bonding between functional groups as sites of proton-transfer reactions.