Identification of major metal complexing compounds in Blepharis aspera

Verbascoside and isoverbascoside, present at 0.7% and 0.2% (w/w dryweight), were identified to be major compounds that could contribute to the metal complexation in Blepharis aspera collected in Botswana, Africa. The metallophyte B. aspera has high ability to cope with a high level of metal accumulation. The presence of metal complexing compounds and/or antioxidants can prevent oxidative reactions in lipids, proteins and DNA that take place due to the metal accumulation. On-line liquid chromatography–solid phase extraction–nuclear magnetic resonance (LC–SPE–NMR) was applied for the identification, while electrospray-mass spectrometry (ESI-MS) and UV-vis spectroscopy was used to assess whether these compounds can complex with metals. It was found that verbascoside and isoverbascoside may form complexes with nickel, iron (verbascoside only) and copper. Thus, the presence of verbascoside and isoverbascoside can explain the survival of B. aspera in mineral-rich areas.