Potential benefits of triethylamine as n-electron donor in the estimation of forskolin by electronic absorption and emission spectroscopy.

Diterpenoid forskolin was isolated from Coleus forskolii. The electronic absorption and emission studies of forskolin were investigated in various solvents with an aim to improve its detection limits. The two chromophores present in the diterpenoid are not conjugated leading to the poor absorption and emission of UV light. The absorption and fluorescence spectra were solvent specific. In the presence of a monodentate ligand, triethylamine the detection of forskolin is improved by 3.63 times in ethanol with the fluorescence method and 3.36 times in DMSO by the absorption spectral method. The longer wavelength absorption maximum is blue shifted while the lower energy fluorescence maximum is red shifted in the presence of triethylamine. From the wavelength of fluorescence maxima of the exciplex formed between excited forskolin and triethylamine it is concluded that the order of reactivity of hydroxyl groups in the excited state forskolin is in the reverse order to that of the order of the reactivity of hydroxyl groups in its ground state.

Synthesis and fluorescence study of naphthalimide-coumarin, naphthalimide-luminol conjugates.

Fluorescent naphthalimide-coumarin and naphthalimide-luminol conjugates were prepared by nucleophilic substitution reaction. The synthesized conjugates were characterized by (1)H-NMR, (13)C-NMR, mass and IR spectra. The absorption and fluorescence of these conjugates revealed that naphthalimide-luminol conjugates are more fluorescent than the naphthalimide-coumarin conjugates. In proton accepting DMSO solvent the fluorescence of the conjugates was quenched, while in proton donating ethanol solvent enhanced fluorescence was noticed. Based on the excitation maxima and fluorescence maxima it was found that in naphthalimide-coumarin conjugates coumarin acting as donor and naphthalimide acting as acceptor where as in naphthalimide-luminol conjugates naphthalimide acts as donor and luminol acts as acceptor.

2-Hexylaminoethylamidonaphthalimide as Cu2+ sensor.

New fluorescent hexylaminoalkylamidonaphthalimides were synthesized and their fluorescence was investigated in different solvents. The fluorescence intensity of hexylaminoalkylamidonaphthalimides is directly related to the number of carbons in the intervening chain between the naphthalimide and n-hexylamine. Among the hexylaminoalkylamidonaphthalimides, 2-hexylaminoethylamidonaphthalimide was developed into a new fluorogenic probe. The bidentate 2-hexylaminoethylamidonaphthalimide acted as fluorescent chemosensor with a high selectivity and suitable affinity towards Cu(2+) in aqueous medium (pH 7.4). This technique of detection of Cu(2+) is highly sensitive and can detect 0.1 µM range.

Dye induced quenching of firefly luciferase-luciferin bioluminescence.

The quenching of firefly bioluminescence (BL) in presence of xanthene dyes and tetratolylporphyrin was investigated. The BL intensity was quenched with an altered decay pattern in presence of xanthene dyes and tetratolylporphyrin. The electronic absorption spectra indicate that there is no significant interaction occurring between the dyes and the BL components in the ground state. The BL quenching decay rate and fluorescence quenching studies of luciferin by the dyes suggest an energy transfer through an exciplex, involving oxyluciferin, in the excited state and the dyes, in the ground state. The bimolecular quenching rate constant (K(q)) values obtained from fluorescence studies varied between 7.7 x 10(12) and 19.8 x 10(12)M(-1)s(-1). The magnitude of the bimolecular quenching rate constants confirmed the complex formation between dye and excited oxyluciferin. The exciplex subsequently undergoes a non-radiative decay to the ground state via a combination of heavy atom induced and Förster-type energy transfer. The decay rate constants in presence and in absence of dyes vary between 7.47 x 10(-4) and 7.6 x 10(-2)s(-1). In the presence of dyes the effective decay rate constants (k(eff)) increased while the lifetime of light emitting species decreased. The kinetic studies in presence of singlet oxygen scavengers, like beta-carotene and NaN(3), prove that there is no significant quenching of the firefly BL due to the formation of singlet oxygen.