Everyone knows oil and water don’t mix. It’s a simple concept, sure, but the hydrophobic interactions between fats and water are crucial to the mechanics of microbiology. The weird thing is, the base theories of chemistry suggest that there’s no reason oil and water shouldn’t mix, even though it’s obvious that’s not the case. Now there’s an explanation: a team of chemical engineers at the University of California, Santa Barbara have defined an equation that measures a compound’s hydrophobic character. It’s the first such equation of its kind.“This discovery represents a breakthrough that is a culmination of decades of research,” professor Jacob Israelachvili, who’s been researching this topic since the ’80s, said. “The equation is intended to be a tool for scientists to begin quantifying and predicting molecular and surface forces between organic substances in water.”Hydrophobic interactions, in which fat compounds are repelled from polar compounds like water and vice versa, are central to the inner workings of life. The way proteins fold, the structure of biological membranes and even the way viruses breach individual cells are all governed largely by the interactions between lipids and water. Yet as high school chem students learn, the set of weak intermolecular forces call van der Waal forces suggest that there’s no reason for the compounds not to attract each other.“According to the van der Waals theory, however, oil and water shouldn’t separate and surfactants shouldn’t form membranes, but they do,"Israelachvili said. "There has been no proven theory to account for these special hydrophobic interactions. Such behaviors are crucial for life as we know it to exist.”One of the more difficult aspects of designing the equation was first designing experimental methods to produce a good set of empirical data to work with. The team used a soap-like lipid compound called a surfactant that is light-sensitive. When floated in water and blasted with light, the surfactant’s interactions with the water were able to be measured. UCSB professor Brad Chmelka, the study’s co-author, said that the team refined the use of an instrument for measuring surface forces that was first used by Israelachvili in the ’70s.While research will have an impact on a range of industrial applications, but the team has stated that it believes the research has a wealth of important applications in biomedicine. Jean Chin, who oversees membrane structure grants at the National Institute of General Medical Sciences of the National Institutes of Health, agreed.“Cell membranes are complex and discriminating structures, allowing the transmission of various signals into cells and mediating specific interactions with bacteria and viruses,” she said. “This study, by enhancing our understanding of the role played by hydrophobic forces in membrane dynamics, will expand what we know about membrane structure and function, as well as microbial infection pathways.”The physical model for describing hydrophobic interactions has escaped researchers since the 1800s. It’s been a search made all the more frustrating by the fact that scientists and engineers have known how the interactions work, but haven’t had an equation to explain their magnitude. It’s quite the breakthrough, and in Israelachvili’s case, is the culmination of three decade’s worth of work.
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