Experimental and theoretical study of 3-carboxy-5,6-benzocoumarin

Photophysical properties of 7-(diethylamino)coumarin-3-carboxylic acid in the nanocage of cyclodextrins and in different solvents and solvent mixtures

The photophysical properties of 7-(diethylamino) coumarin-3-carboxylic acid (7-DCCA) were studied in cyclodextrins (α, β, γ,-CDs), different neat solvents and solvent mixtures by using steady state absorption, emission and time-resolved fluorescence spectroscopy. We have observed that with gradual increase in concentration of β-CD the fluorescence quantum yield and lifetime decreased in a regular pattern whereas with gradual increase in concentration of γ-CD the fluorescence quantum yield and lifetime gradually increased. With addition of urea, the fluorescence quantum yield and lifetime of 7-DCCA in CDs increased. Binding constant calculation shows that 7-DDCA forms 1:1 complex with β-CD and with γ-CD it forms 1:1 and 1:2 (guest:host) inclusion complex. We proposed that the dye molecule formed capping complex with β-CD by means of hydrogen bonding and after addition of urea the hydrogen bonding network broke down and part of dye molecule entered inside the cavity of β-CD. The photophysics of 7-DCCA was studied in dioxane-water mixture and ethylene glycol-acetonitrile mixture to know the effect of polarity and viscosity of the media. The photophysics of 7-DCCA was also studied in different neat solvents. It was found that the photophysics of 7-DCCA depended on the structural feature of the solvents and solvent mixtures.

Spectrofluorimetric study of the interaction of ciprofloxacin with amino acids in aqueous solution following solvatochromic studies

Complexation of a fluoroquinolone derivative (ciprofloxacin), L, and some amino acids has been studied using spectrofluorimetric method. Results indicated that ciprofloxacin have a greater tendency to form a 1:1 complex with aspartic acid and arginine than the other tested molecules. The fluorescence of ciprofloxacin exhibits quenching process while it has been titrated with these amino acids. Formation constant values (K(f)) for complex formed between ciprofloxacin and amino acids were also calculated. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were studied too. Possible reasons for the observed stability sequence were discussed based on the structures proposed for the resulting complexes. Besides the solution studies, solvatochromic properties of the ciprofloxacin are discussed by studying its spectra in a selection of different solvents.

Experimental and theoretical study of the interaction of 3-carboxy-5,6-benzocoumarin with some 1,2,3,4,5,6,7,8-octahydroacridines and the corresponding N-oxides

The interaction of 3-carboxy-5,6-benzocoumarin (BzCum) with 1,2,3,4,5,6,7,8-octahydroacridine (OHA), 9-amino-1,2,3,4,5,6,7,8-octahydroacridine (H(2)N-OHA) and the corresponding N-oxides (OHA-NO and H(2)N-OHA-NO) was studied by fluorescence (steady state, time resolved) and absorption spectroscopy. The analysis of the fluorescence data in terms of Stern-Volmer plots indicated a predominant dynamic quenching for OHA and OHA-NO, and a more complex process for H(2)N-OHA and H(2)N-OHA-NO. The dynamic process was assigned to a photoinduced electron transfer (PET) from the acridine derivatives to the excited state of BzCum. The application of the Rehm-Weller-Marcus theory leads to a good agreement with literature data and allows for the estimation of the solvent organization energy. The presence of the PET mechanism was also supported by DFT results. The absorption spectra evidence the formation of a ground state complex assigned to a hydrogen bond complex involving the carboxylic hydrogen of BzCum.

Theoretical and experimental study of the inclusion complexes of the 3-carboxy-5,6-benzocoumarinic acid with cyclodextrins

The 3-carboxy-5,6-benzocoumarinic acid (BzCum) presents important emission properties that could make it suitable to be used as a fluorescence marker for proteins. Since the guest-cyclodextrin interaction can be used as a model for the ligand-protein interaction, the host-guest complexes of BzCum with alpha-, beta-, gamma-, 2-hydroxypropyl-beta-cyclodextrin (2-HP-beta-CD) and 2-hydroxypropyl-gamma-cyclodextrin (2-HP-gamma-CD) were investigated by means of steady-state fluorescence measurements. As the guest may exist either in anionic or in neutral form, the experiments were performed at two different pH values, 9.48 and 2.11. The association constants and the stoichiometry of the complexes were estimated by non-linear regression analysis. A theoretical study of the complexes was made using molecular mechanics (MM) calculation methods. The electrostatic and van der Waals contributions to the energy were estimated and a discussion was made on this basis.

Crystal structure and photoluminescence of 7-(N,N'-diethylamino)-coumarin-3-carboxylic acid

The structure of 7-(N,N'-diethylamino)-coumarin-3-carboxylic acid (DCCA) was verified by single crystal X-ray crystallography. The UV-vis absorption and fluorescence of DCCA were discussed. The compound exhibits strong blue emission under ultraviolet light excitation. The molecular structure of DCCA was optimized using density function theory (DFT) at B3LYP/6-31G level, showing that the optimized geometers parameters are in good agreement with experiment data. In addition, the HOMO and LUMO levels of DCCA were deduced.