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.

D‐π‐A Molecular Probe to Unveil the Role of Solute‐Solvent Hydrogen Bonding in Solvatochromism, Location Specific Preferential Solvation and Synergistic Effect in Binary Mixtures

“…To understand the contribution of different aspects of solute‐solvent intermolecular interactions, spectral shift of this chromophoric dye observed in 20 different pure solvents is correlated with solvent property parameters using linear solvation energy relationship (LSER) multiparametric approaches . Two most widely employed LSER i. e. Kamlet‐Taft and Catalan equations, which considers solvent properties such as, HBD acidity, HBA basicity, dipolarity and polarizability have been used in the present study . To study the major contribution from any other solvent polarity parameters such as dipole moment, dielectric constant, electron pair donor/acceptor capabilities, hydrophobicity/hydrophilicity etc.…”

Kinetics of Electrophilic Alkylations of Barbiturate and Thiobarbiturate Anions

“…Another type of barbituric acid dyes is available by nucleophilic aromatic substitution of electron-withdrawing group (EWG) para -substituted aromatic fluoro compounds with barbiturate anions (Scheme b) . Such barbiturate dyes can switch between the keto- and enol-form depending on the environment. , The enol formation is associated with a color development because a push–pull dye is generated with the barbiturate substituent as electron-donating group (EDG). , Accordingly, the BA moiety can serve either as EWG (a) or EDG (b) as illustrated in Scheme .…”

“…Therefore, barbiturate dyes are useful as switchable chromophores with fluctuating hydrogen-bonding pattern (Scheme b). , This feature provides the BA moiety as a valuable substituent for manifold applications in molecular recognition of nucleic bases and related compounds. ,, Usually, the BA moiety is introduced by the synthetic procedures illustrated in Scheme , where the barbiturate anion undergoes a nucleophilic attack on the electrophilic carbon atom of the substrate. A successful synthesis significantly depends on the nucleophilic reactivity of C-5 of the barbiturate anion in conjunction with an appropriate electrophilic reagent.…”

Enantioselective Catalytic Transformations of Barbituric Acid Derivatives

“…These achievements currently allow several unique addition and annulation reactions towards the construction of high valued chiral heterocycles from barbituric acid derivatives along with innovative enantioselective developments.Catalysts 2019, 9, 131 2 of 27 antidiabetic [13] or antituberculosis properties (Figure 1e-f) [14]. Besides medicinal chemistry, the photophysical properties of barbituric acid derivatives were exploited in colorimetric or heat detection [15], and provided promising dyes or fluorogenic probes to name a few [16,17]. Catalysts 2018, 8, x FOR PEER REVIEW 2 of 30 45 46be much more prone to deprotonation by soft bases than dimedone 3 or non-cyclic homologues, such as malonate 4, for instance.…”

“…Catalysts 2019, 9, 131 2 of 27 antidiabetic [13] or antituberculosis properties (Figure 1e-f) [14]. Besides medicinal chemistry, the photophysical properties of barbituric acid derivatives were exploited in colorimetric or heat detection [15], and provided promising dyes or fluorogenic probes to name a few [16,17]. Catalysts 2018, 8, x FOR PEER REVIEW 2 of 30 45 46…”