engleski

Orientational Dependence of the Affinity of Guanidinium Ions to the Water Surface

The behavior of guanidinium chloride at the surface of aqueous solutions is investigated using classical molecular dynamics simulation. It is found that the population of guanidinium ions oriented parallel to the interface is greater in the surface region than in bulk. The opposite is true for ions in other orientations. Overall, guanidinium chloride is depleted in the surface region, in agreement with the fact that addition of guanidinium chloride increases the surface tension of water. The orientational dependence of the surface affinity of the guanidinium cation appears to be related to its anisotropic hydration. To bring the ion to the surface in the parallel orientation does not require hydrogen bonds to be broken, in contrast to other orientations. The surface enrichment of parallelly oriented guanidinium indicates that its solvation is more favorable near the surface than in bulk solution for this orientation. The dependence of the bulk and surface properties of guanidinium on the force field parameters, including polarizability, is also investigated. Despite significant quantitative differences between the force fields, the surface behavior is qualitatively robust. The implications of the above findings for the behaviorof guanidinium groups near biological interfaces are demonstrated on the example of arginine side chain orientations in lysozyme.

guanidinium cation; molecular dynamics simulations; hydrogen bond; air-water interface; force fields

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