Glycerophosphoglycerophosphoglycerol, a special class of phospholipids containing four fatty acid chains, is widely known under its trivial name cardiolipin. This phospholipid consists of two glycerophosphoglycerol moieties linked via glycerol (Fig. 1). This leads to a conical molecule with a small, immobile head group and a large, rigid, hydrophobic tail. When packed in a membrane, these features strongly promote negative curvature. The acyl groups and the backbone glycerol groups are oriented parallel to the membrane normal, while the two phosphate groups are positioned parallel to the membrane surface. One or both phosphate groups may be deprotonated, depending on pH, leading to single- or double-charged anions (Horvath and Daum 2013).

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