Enhancement of Fluorescence in Thin-Layer Chromatography Induced by the Interaction between n-Alkanes and an Organic Cation

Abstract

Fluorescence enhancement of a broad variety of solutes has been used extensively in TLC although no thorough explanation has been proposed. In this work, we try to understand it and explore new applications to which it can be put. In this way, alkanes can be quantitatively determined by fluorescence scanning densitometry using silica gel plates impregnated with berberine sulfate. Molecular simulation and analysis of molecular orbitals allows this phenomenon to be explained in this case and lays the groundwork to explain fluorescence enhancements produced by other molecules. A ion-molecule interaction between alkanes and berberine sulfate is responsible for the enhancement of fluorescence produced by alkanes. Computational results suggest that the surrounding alkane molecules provide an apolar environment to the berberine cation, thus enhancing the intensity of the fluorescence signal. This proposed explanation has been tested by extending the fluorescence determination to other compounds. These include biologically interesting saturated and unsaturated fatty acids, steroids and derivatives, prostaglandins, ceramides, galactocerebrosides, as well as terpenes, and polypropylene glycols. In addition, according to the proposed explanation, the properties required for alternative impregnants to berberine are discussed.

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

“…In our previous work, [2][3][4][5] we showed that non-specific induced electrostatic interactions between fluorescent probes and hydrocarbon chains of analytes are responsible for emission increases in the case of different FDIC probes, such as cations (berberine and coralyne) and a zwitterion (Reichardt's dye). As Debye's equation [4,9] suggests the possibility of using neutral FDIC probes with a permanent dipolar moment, we have now studied another cationic probe (coptisine) and a neutral dipolar fluorophore (Nile red) as TLC-FDIC probes with a homologous series of nonpolar (n-alkanes) and polar analytes (n-alcohols).…”

“…Many fluorescent molecules (probes) change their emission intensity [1][2][3][4][5] in the presence of a large number of compounds (analytes). The extent and sign of the change depends on the chemical nature of the analyte, whether fluorescent or not.…”

“…[2] For example, DE is À7.04 and À7.50 kcal mol À1 for berberine-dodecane (C 12 ), and berberinetetradecane (C 14 ), respectively. Recently, we optimized the geometries of complexes formed by berberine cation and some lipids by molecular mechanics calculations.…”

Separation of amino acids, their derivatives and enantiomers by impregnated TLC

“…An explanation for fluorescence enhancement on impregnated plates due to an ion-molecule interaction between analyte (alkane molecules) and the impregnating reagent (berberine cation) has recently been proposed (Cossio et al, 2000).…”

“…It has been found that impregnation of silica gel by means of metal ions or other anions improves the separation of organic compounds and impregnation by organic ligands improves the separation of metal ions. Recently, quantitative determination of alkanes by fluorescence scanning densitometry using silica gel plates impregnated with berberine sulphate has been reported (Cossio et al, 2000). TLC studies on separation of amino acids on copper sulphate and polyamide mixed silica gel layers (Srivastava et al, 1984a) using MeOH-BuOAc-HOAcpyridine, separation of synthetic dyes on copper sulphate and ammonium molybdate impregnated silica layers , separation of certain metal ions on 8-hydroxyquinoline and dibenzoylmethane impregnated layers (Srivastava et al, 1984b), separation of rare earths on HDEHP-TOPO impregnated cellulose plates , improved separation of several PTH-amino acids on Fe 2 , Co 2 , Ni 2 and Zn 2 impregnated silica gel plates (Bhushan and Reddy, 1987a, b), and separation of antihistamines (Bhushan and Joshi, 1996) and vitamins (Bhushan and Parshad, 1999) on plates impregnated with metal ions are a few examples from the literature.…”