title: Electrochemical evidence of surfactant activity of the hepes pH buffer which may have implications on trace metal availability to cultures in vitro.
abstract: Hydrogen ion buffers are required for many different types of in vitro biological and chemical studies, but they may not be inert enough, thus interfering with the system under study. N-Hydroxyethylpiperazine-N'-ethanesulfonic acid (Hepes), a zwitterionic buffer in the 7.0-8.0 pH range, has been used in different biological studies. In this work, surfactant activity of Hepes and the buffer's capability to bind copper(II) were investigated through different electrochemical techniques: ion-selective electrode potentiometry, potentiometric stripping analysis, differential pulse anodic stripping voltammetry, normal pulse anodic stripping voltammetry, and alternating current polarography. Hepes concentrations between 0.1 (0.24 g liter-1) and 25 mmol liter-1 (6.0 g liter-1) were studied at pH 8.0 (and at pH 6.5 for comparison). At pH 8.0 Hepes displayed surfactant activity, particularly when magnitude of Hepes > 10 mmol liter-1 (2.4 g liter-1). The ability of Hepes to bind copper(II) was detected when Hepes was in large excess (magnitude of Hepes/magnitude of Cu between 10,000 and 2000). Eventual implications in the bioavailability of copper(II) are also discussed.
authors.affiliation: LAQUIPAI, Faculdade de Ciências do Porto, Portugal.
authors.forename: M T
authors.initials: MT
authors.lastname: Vasconcelos
authors.forename: M A
authors.initials: MA
authors.lastname: Azenha
authors.forename: O M
authors.initials: OM
authors.lastname: Lage
mesh_terms: D002478:Cells, Cultured; D004563:Electrochemistry; D006531:HEPES; D006863:Hydrogen-Ion Concentration; D008670:Metals / Q000737:chemistry*; D013501:Surface-Active Agents / Q000737:chemistry*
chemical_list: D008670:Metals; D013501:Surface-Active Agents; D006531:HEPES