title: Fast relaxation dynamics of the cardiotonic drug milrinone in water solutions.
abstract: The fast relaxation dynamics of 1,6-dihydro-2-methyl-6-oxo-3,4'-bipyridine-5-carbonitrile (milrinone, MIR), a cardiotonic drug, has been characterized in water solutions at different pH. In acidic media, a blue emission reflects a charge-transfer state in the cation (C) leading to a more stabilized structure with an emission lifetime of 90 ps. The emission lifetimes of the keto (K) and anion (A) structures are approximately 65 and 310 ps, respectively. Reasons for efficient nonradiative channels are discussed in terms of hydrogen-bonding interactions, intramolecular charge transfer (ICT), and twisting motion. A blue nanosecond-emission observed in almost all the studied pH range is suggested to be due to relaxed K due to an ICT reaction. B3LYP (6-31+G**) calculations showed that, in a water cavity, K is more stable than the enol form by 7 kcal/mol, and the ICT may take place within the pyridone moiety. At the physiological pH, the inotropic K structure is the dominant species (approximately 100%).
authors.affiliation: Departamento de Química Física, Sección de Químicas, Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha, Avda. Carlos III, S.N., 45071, Toledo, Spain.
authors.forename: Maged
authors.initials: M
authors.lastname: el-Kemary
authors.forename: Juan Angel
authors.initials: JA
authors.lastname: Organero
authors.forename: Abderrazzak
authors.initials: A
authors.lastname: Douhal
mesh_terms: D002316:Cardiotonic Agents / Q000737:chemistry*; D005453:Fluorescence; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D020105:Milrinone / Q000737:chemistry*; D015394:Molecular Structure; D012996:Solutions; D013053:Spectrophotometry; D014867:Water / Q000737:chemistry*
chemical_list: D002316:Cardiotonic Agents; D012996:Solutions; D014867:Water; D020105:Milrinone