CAPS, cyclohexylaminopropane sulfonic acid, is a surfactant. CAPS can be used as biological buffer (0.05 M, pH 11) for dialysis[1][2].
CAPS surfactant bears a single neyative charge since the amine is not ionized at high pH[1].
[1]. Bedard P R, et al. Ion Interaction: The Energetics and Mechanism of The Competitive Behavior Between Two Similarly Charged Molecules. 1. The Effect of Ionic Strength, Acetonitrile and Surfactant Concentration[J]. Journal of Liquid Chromatography, 1985, 8(13):2417-2443.
[2]. Oberley TD, et al. The effect of the dimeric and multimeric forms of fibronectin on the adhesion and growth of primary glomerular cells. Exp Cell Res. 1983 May;145(2):265-76.