Binding of cationic surfactants to humic substances

Abstract

Commercial surfactants are introduced into the environment either through waste products or site-specific contamination. The amphiphilic nature of both surfactants and humic substances (HS) leads to their mutual attraction especially when surfactant and HS are oppositely charged.Binding of the cationic surfactants dodecyl-pyridinium chloride (DPC) and cetyl-or hexadecyl- binding to HS is due both to electrostatic and hydrophobic attraction and that the fate of HS in aqueous environmental systems can be strongly affected by cationic surfactants.

Quaternary ammonium compounds in soil: implications for antibiotic resistance development

“…Due to their amphiphilic nature, however, QAACs form micelles once their critical micelle concentration is reached (Table 1). This is a property not only affecting the efficiency of many surfactant-related applications, but also responsible for a dynamic equilibrium of surfactant molecules in micelles and surfactant molecules in cellular membranes that can result eventually in cell membrane dissolution, thus causing biocidal effects (Ishiguro et al 2007). From Table 1, it is clear that alkyltrimethylammonium compounds (ATMAC) and DADMACs, show correlations exist between increasing hydrophobicity and decreasing critical micelle concentration.…”

Humic substance charge determination by titration with a flexible cationic polyelectrolyte

“…The obtained humic acid was freeze dried and denoted as purified Aldrich humic acid (PAHA). PAHA was used for the detailed study because it is readily available and binding studies of inorganic ions (Milne et al, 2003), surfactants (Traina et al, 1996;Ishiguro et al, 2007) and polyelectrolytes (Kam and Gregory, 2001;Ishiguro et al, 2007) show that its physical behavior is qualitatively the same as that of other HA.…”

“…The obtained HS charge densities are collected in Table 2; they apply at the given KCl concentration and the average pH IEP values of the samples. These charge densities have been summarized before by Ishiguro et al (2007) without a discussion of the experiments. In general there is only a fair agreement with the values derived from proton titrations (see Table 2), but a precise comparison is only possible for PAHA and SFA.…”

“…The charge density of HS depends on the pH and at the pH conditions in most natural waters HS are negatively charged (Milne et al, 1995;Ritchie and Perdue, 2003). The charge density of humic particles is a dominant factor for the interactions of HS with: (1) heavy metal ions (Milne et al, 2003;Koopal et al, 2005;Merdy et al, 2006), (2) oppositely charged polyelectrolytes (Bolto et al, 1999;Kam and Gregory, 2001;Hankins et al, 2006), (3) proteins (Tan et al, 2008(Tan et al, , 2009), (4) cationic surfactants Yee et al, 2006;Ishiguro et al, 2007) and (5) mineral surfaces Filius et al, 2000;Saito et al, 2004;Weng et al, 2005). Therefore, for a good understanding of these interactions reliable information on charge characteristics of HS is of vital importance.…”

“…Colloid titrations of HS with cationic surfactants have been made by Ishiguro et al (2007). Cationic surfactants with a C 16 aliphatic chain, such as hexadecyl (cetyl) pyridinium chloride, are most suited as they bind very strongly to HS at very low surfactant concentrations.…”