Background: Cytosine is a biologically important compound owing to its natural occurrence as a component of nucleic acids. Cytosine plays a crucial role in DNA/RNA base pairing, through several hydrogen-bonding patterns, and controls the essential features of life as it is involved in genetic codon of 17 amino acids. The molecular recognition among cytosines, and the molecular heterosynthons of molecular salts fabricated through proton-transfer reactions, might be used to investigate the theoretical sites of cytosine-specific DNA-binding proteins and the design for molecular imprint. Results: Reaction of cytosine (Cyt) and 5-fluorocytosine (5Fcyt) with 5-nitrouracil (Nit) in aqueous solution yielded two new products, which have been characterized by single-crystal X-ray diffraction. The products include a dihydrated molecular salt (CytNit) having both ionic and neutral hydrogen-bonded species, and a dihydrated cocrystal of neutral species (5FcytNit). In CytNit a protonated and an unprotonated cytosine form a triply hydrogen-bonded aggregate in a self-recognition ion-pair complex, and this dimer is then hydrogen bonded to one neutral and one anionic 5-nitrouracil molecule. In 5FcytNit the two neutral nucleobase derivatives are hydrogen bonded in pairs. In both structures conventional N-(HO)-O-center dot center dot center dot, O-(HO)-O-center dot center dot center dot, N-H+center dot center dot center dot N and N-(HN-)-N-center dot center dot center dot intermolecular interactions are most significant in the structural assembly. Conclusion: The supramolecular structure of the molecular adducts formed by cytosine and 5-fluorocytosine with 5-nitrouracil, CytNit and 5FcytNit, respectively, have been investigated in detail. CytNit and 5FcytNit exhibit widely differing hydrogen-bonding patterns, though both possess layered structures. The crystal structures of CytNit (Dpk(a) = -0.7, molecular salt) and 5FcytNit (Dpk(a) = -2.0, cocrystal) confirm that, at the present level of knowledge about the nature of proton-transfer process, there is not a strict correlation between the Dpk(a) values and the proton transfer, in that the acid/base pk(a) strength is not a definite guide to predict the location of H atoms in the solid state. Eventually, the absence in 5FcytNit of hydrogen bonds involving fluorine is in agreement with findings that covalently bound fluorine hardly ever acts as acceptor for available Bronsted acidic sites in the presence of competing heteroatom acceptors.

Solid-phase molecular recognition of cytosine based on proton-transfer reaction. Part II. supramolecular architecture in the cocrystals of cytosine and its 5-Fluoroderivative with 5-Nitrouracil / Portalone, Gustavo. - In: CHEMISTRY CENTRAL JOURNAL. - ISSN 1752-153X. - STAMPA. - 5:1(2011), pp. 51-51. [10.1186/1752-153x-5-51]

Solid-phase molecular recognition of cytosine based on proton-transfer reaction. Part II. supramolecular architecture in the cocrystals of cytosine and its 5-Fluoroderivative with 5-Nitrouracil

PORTALONE, Gustavo
2011

Abstract

Background: Cytosine is a biologically important compound owing to its natural occurrence as a component of nucleic acids. Cytosine plays a crucial role in DNA/RNA base pairing, through several hydrogen-bonding patterns, and controls the essential features of life as it is involved in genetic codon of 17 amino acids. The molecular recognition among cytosines, and the molecular heterosynthons of molecular salts fabricated through proton-transfer reactions, might be used to investigate the theoretical sites of cytosine-specific DNA-binding proteins and the design for molecular imprint. Results: Reaction of cytosine (Cyt) and 5-fluorocytosine (5Fcyt) with 5-nitrouracil (Nit) in aqueous solution yielded two new products, which have been characterized by single-crystal X-ray diffraction. The products include a dihydrated molecular salt (CytNit) having both ionic and neutral hydrogen-bonded species, and a dihydrated cocrystal of neutral species (5FcytNit). In CytNit a protonated and an unprotonated cytosine form a triply hydrogen-bonded aggregate in a self-recognition ion-pair complex, and this dimer is then hydrogen bonded to one neutral and one anionic 5-nitrouracil molecule. In 5FcytNit the two neutral nucleobase derivatives are hydrogen bonded in pairs. In both structures conventional N-(HO)-O-center dot center dot center dot, O-(HO)-O-center dot center dot center dot, N-H+center dot center dot center dot N and N-(HN-)-N-center dot center dot center dot intermolecular interactions are most significant in the structural assembly. Conclusion: The supramolecular structure of the molecular adducts formed by cytosine and 5-fluorocytosine with 5-nitrouracil, CytNit and 5FcytNit, respectively, have been investigated in detail. CytNit and 5FcytNit exhibit widely differing hydrogen-bonding patterns, though both possess layered structures. The crystal structures of CytNit (Dpk(a) = -0.7, molecular salt) and 5FcytNit (Dpk(a) = -2.0, cocrystal) confirm that, at the present level of knowledge about the nature of proton-transfer process, there is not a strict correlation between the Dpk(a) values and the proton transfer, in that the acid/base pk(a) strength is not a definite guide to predict the location of H atoms in the solid state. Eventually, the absence in 5FcytNit of hydrogen bonds involving fluorine is in agreement with findings that covalently bound fluorine hardly ever acts as acceptor for available Bronsted acidic sites in the presence of competing heteroatom acceptors.
2011
01 Pubblicazione su rivista::01a Articolo in rivista
Solid-phase molecular recognition of cytosine based on proton-transfer reaction. Part II. supramolecular architecture in the cocrystals of cytosine and its 5-Fluoroderivative with 5-Nitrouracil / Portalone, Gustavo. - In: CHEMISTRY CENTRAL JOURNAL. - ISSN 1752-153X. - STAMPA. - 5:1(2011), pp. 51-51. [10.1186/1752-153x-5-51]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11573/387371
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