Changes in Fluorescent Emission Due to Non‐covalent Interactions as a General Detection Procedure for Thin‐Layer Chromatography

Abstract

Changes in fluorescence emission due to non-covalent analyte-fluorophore interactions in silica gel plates are studied and used as a general detection procedure for thin-layer chromatography (TLC). The presence of the analyte modifies the microenvironment of the fluorophore and thus changes the balance between radiative (k(r)) and non-radiative (k(nr)) emission constants. A model is proposed for analyte-fluorophore induced electrostatic interactions, which depend on analyte polarizability and are responsible for fluorescence enhancements. As consequence of these induced interactions, the analyte creates an apolar environment that prevents non-fluorescent decay mechanisms, decreasing k(nr). On the other hand, the effect of an increase in refractive index on k(r) is investigated, as it contributes to some extent to fluorescence enhancements in silica gel medium. Changes in fluorescence emission should be regarded as a general property of fluorophores in the presence of analytes, and criteria that fluorophores should meet to be used as sensitive TLC probes are discussed here.

A Hyphenated Technique based on High-Performance Thin Layer Chromatography for Determining Neutral Sphingolipids: A Proof of Concept

“…Long-chain, non-fluorescent, saturated hydrocarbons (C24, C28, C32) provide strong increases in primuline emission without any change in emission wavelength. For the alkane homologous series, fluorescence response is a function of chain length, i.e., hydrocarbon polarizability, as demonstrated for other fluorophores [32][33][34]. This effect of chain length was also observed for neutral lipids and SLs using berberine as a fluorophore [12].…”

“…A model based on weak, non-specific, induced dipole electrostatic interactions between the analyte and fluorophore has been proposed. For a given fluorophore and a homologous series of compounds, emission intensity depends on analyte polarizability (αi) [32,33]. The analyte provides an apolar environment that prevents nonradiative de-excitation pathways.…”

“…More light has now been shed on the mechanism of fluorescence induction. Fluorophores such as primuline increase their emission in the presence of molecules bearing hydrocarbon chains [31,32] as a result of dipolar-induced, non-specific interactions between the fluorophore and analyte in a silica gel medium [33,34]. Cationic fluorophores, such as berberine or coralyne, show good examples of this behavior in the presence of saturated hydrocarbons [33,35] and also of SLs [12].…”

“…The longer the alkyl chain, the higher the fluorescent response. A model has been proposed to explain increases in emission [32,33]. The application of this effect to HPTLC-scanning densitometry is referred to as FDIC [12,34].…”

Resonance driven regioselective demethylation of berberine. Microwave assisted synthesis of berberrubine and its assessment as fluorescent chemosensor for alkanes

“…A model was proposed 3,5 for this ion-induced dipole interaction, which accounted for experimental results. As the intensity enhancement will also be proportional to the interaction energy, we have, for an ionic probe P and analyte i (alkane)…”