Hydrophobic interactions in context

The finding that immobilized ions can alter the strength of hydrophobic interactions between molecules suggests a strategy for tuning hydrophobicity to optimize molecular recognition and self-assembly processes. See Letter p.347 Immobilized ions tune hydrophobic interactions The so-called hydrophobic effect is the basis of many well-known interfacial, colloidal and biophysical phenomena, including the immiscibility of oil and water and the beading of water on nonpolar surfaces. It arises as a result of the structuring of water near non-polar surfaces, but although we understand hydrophobic interactions in simple systems, most biologically and technologically relevant structures are another matter. These more complex systems are characterized by intricate patterns of non-polar, polar and charged domains in close proximity. Derek Ma and colleagues now show that cations placed near a non-polar domain strongly modulate its hydrophobic interactions, with some cations doubling the strength of the interactions, whereas others eliminate it. The findings imply that in addition to established strategies for optimizing molecular recognition or self-assembly, judicious placing of charged groups near hydrophobic domains can also be used to tune the hydrophobic forces driving such processes.