Assessing radical scavenging capacity of Sempervivum tectorum L. leaf extracts: An integrated high-performance thin-layer chromatography/in silico/chemometrics approach

Abstract

High-Performance Thin-Layer Chromatography (HPTLC)-radical scavenging capacity (RSC) assays are standard techniques for the separation and identification of antioxidants from complex mixtures. HPTLC coupled with DPPH· visualization of chromatograms allows for the detection of individual antioxidants. However, other HPTLC-RSC assays that recognize compounds exhibiting different mechanisms of radical-scavenging activity are rarely reported. In this study, we developed an integrated approach that combines five HPTLC-RSC assays, principal component analysis (PCA) and quantum chemical calculations to assess the antioxidant capacity of Sempervivum tectorum L. leaf extracts. Two HPTLC assays - potassium hexacyanoferrate(III) total reducing power assay (TRP) and total antioxidant capacity by phosphomolybdenum method (TAC) - were developed for the first time. The method supports a more in-depth study of the RSC of natural products, as it compares the radical scavenging fingerprints of S. tectorum leaf extracts and recognizes differences in their individual bioactive constituents. Kaempferol, kaempferol 3-O-glucoside, quercetin 3-O-glucoside, caffeic acid, and gallic acid were identified as the compounds that discriminate HPTLC-RSC assays according to their mechanism of action and capture the similarities between 20 S. tectorum samples. Additionally, DFT calculations on M06–2X/6–31+G(d,p) level were applied to map thermodynamic feasibility of hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms of the identified compounds. Based on experimental and theoretical results, a combination of HPTLC-ABTS and HPTLC-TAC assays were proposed as the optimal method for mapping the antioxidants from S. tectorum. This study represents a step forward in identifying and quantifying individual antioxidants from complex food and natural product matrices in a more rational manner.