Published in:
Chemistry – A European Journal, 22 (2016) 16, Seite 5734-5748
Language:
English
DOI:
10.1002/chem.201504932
ISSN:
0947-6539;
1521-3765
Origination:
Footnote:
Description:
AbstractThe 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 1H 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.