Molecular surface electrostatic potentials and anesthetic activity

General anesthetics apparently act through weak, noncovalent and reversible interactions with certain sites in appropriate brain proteins. As a means of gaining insight into the factors underlying anesthetic potency, we have analyzed the computed electrostatic potentials V-S(r) on the surfaces of 20 molecules with activities that vary between zero and high. Our results are fully consistent with, and help to interpret, what has been observed experimentally. We find that an intermediate level of internal charge separation is required; this is measured by Pi, the average absolute deviation of V-S(r), and the approximate window is 7 < Pi < 13 kcal mol(-1). This fits in well with the fact that anesthetics need to be lipid soluble, but also to have some degree of hydrophilicity. We further show that polyhalogenated alkanes and ethers, which include the most powerful known anesthetics, have strong positive potentials, V-S,V-max, associated with their hydrogens, chlorines and bromines (but not fluorines). These positive sites may impede the functioning of key brain proteins, for example by disrupting their normal hydrogen-bond patterns. It has indeed been recognized for some time that the most active polyhalogenated alkanes and ethers contain hydrogens usually in combination with chlorines and/or bromines.