title: Interactions of Enolizable Barbiturate Dyes.
abstract: The specific barbituric acid dyes 1-n-butyl-5-(2,4-dinitro-phenyl) barbituric acid and 1-n-butyl-5-{4-[(1,3-dioxo-1H-inden-(3 H)-ylidene)methyl]phenyl}barbituric acid were used to study complex formation with nucleobase derivatives and related model compounds. The enol form of both compounds shows a strong bathochromic shift of the UV/Vis absorption band compared to the rarely coloured keto form. The keto-enol equilibria of the five studied dyes are strongly dependent on the properties of the environment as shown by solvatochromic studies in ionic liquids and a set of organic solvents. Enol form development of the barbituric acid dyes is also associated with alteration of the hydrogen bonding pattern from the ADA to the DDA type (A=hydrogen bond acceptor site, D=donor site). Receptor-induced altering of ADA towards DDA hydrogen bonding patterns of the chromophores are utilised to study supramolecular complex formation. As complementary receptors 9-ethyladenine, 1-n-butylcytosine, 1-n-butylthymine, 9-ethylguanidine and 2,6-diacetamidopiridine were used. The UV/Vis spectroscopic response of acid-base reaction compared to supramolecular complex formation is evaluated by (1)H NMR titration experiments and X-ray crystal structure analyses. An increased acidity of the barbituric acid derivative promotes genuine salt formation. In contrast, supramolecular complex formation is preferred for the weaker acidic barbituric acid.
authors.affiliation: Technische Universität Chemnitz, Department of Polymer Chemistry, 09107, Chemnitz, Germany), Fax: (+49) 371-531-21239.
authors.forename: Alexander
authors.initials: A
authors.lastname: Schade
authors.affiliation: Technische Universität Chemnitz, Department of Polymer Chemistry, 09107, Chemnitz, Germany), Fax: (+49) 371-531-21239.
authors.forename: Katja
authors.initials: K
authors.lastname: Schreiter
authors.affiliation: Technische Universität Chemnitz, Department of Inorganic Chemistry, 09107, Chemnitz, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Rüffer
authors.affiliation: Technische Universität Chemnitz, Department of Inorganic Chemistry, 09107, Chemnitz, Germany.
authors.forename: Heinrich
authors.initials: H
authors.lastname: Lang
authors.affiliation: Technische Universität Chemnitz, Department of Polymer Chemistry, 09107, Chemnitz, Germany), Fax: (+49) 371-531-21239. stefan.spange@chemie.tu-chemnitz.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Spange
mesh_terms: D001463:Barbiturates / Q000737:chemistry*; D004396:Coloring Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006860:Hydrogen Bonding; D007192:Indenes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D009574:Nitro Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D012997:Solvents / Q000737:chemistry; D014466:Ultraviolet Rays
chemical_list: C000610129:1-n-butyl-5-(2,4-dinitro-phenyl)barbituric acid; C000610130:1-n-butyl-5-(4-((1,3-dioxo-1H-inden-(3 H)-ylidene)methyl)phenyl)barbituric acid; D001463:Barbiturates; D004396:Coloring Agents; D007192:Indenes; D009574:Nitro Compounds; D012997:Solvents
keywords: UV/Vis spectroscopy; barbituric acid; keto-enol tautomerism; molecular recognition; nucleobases; solvatochromism