Preferences in molecular orientation: multivariate statistics or chemistry?

P. Jedlovszky¹, A. Vincze², G. Horvai³

¹ Department of Colloid Chemistry, Eötvös Loránd University, Pázmány Péter stny. 1/a, H-1117 Budapest, Hungary

² Department of NBC and Environmental Security, Zrínyi Miklós National Defense University, Hungária krt. 9-11, H-1581 Budapest, Hungary

³ Department of Chemical Information Technology, Budapest University of Technology and Economics, Gellért tér 4, H-1111 Budapest, Hungary;

phone: +361 4631480; fax: +361 4633953;  E-mail: horvai@ch.bme.hu

Molecules in fluid phases may show preferential orientation in the neighbourhood of an interface and their movement (diffusion, rotation) and chemical reactions may also be quite different at the interface than in the bulk.

We have studied by different simulation techniques the orientation of water molecules and of ions near the interface. For water we have found a gradual change of orientational preferences near the interface. Surprisingly there are two preferred orientations in the outmost water layer and these preferred orientations do not depend too much on the composition of the contacting phase. Ion orientations are more difficult to be simulated at realistic concentrations yet some rough results could be obtained.

Earlier, similar studies by others gave different (but not contradicting) results. We have shown that in those earlier studies the multivariate statistics of orientation were not analyzed in sufficient depth. The interpretation of the term “preference” needs careful discussion. We show a simple strategy that leads to correct results even in complex situations.

Reference:
P. Jedlovszky, A. Vincze, G. Horvai, J. Chem. Phys. accepted