Solid-Phase Molecular Recognition of Cytosine Based on Proton-Transfer Reaction
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- Portalone, G. & Colapietro, M. J Chem Crystallogr (2009) 39: 193. doi:10.1007/s10870-008-9457-0
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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) Å, V = 2534.7 (3) Å3. CytMal crystallizes in the triclinic system, space group P − 1, a = 6.7767 (9), b = 12.063 (2), c = 12.937 (3) Å, α = 78.58 (2), β = 75.87 (2), γ = 75.63 (1)°, V = 982.8 (3) Å3. 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···O, N–H···N and O–H···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.