1. Chemo AC, Vrije Universiteit Brussel, Laarbeeklaan 103, B-1090 Brussel, Belgium (V.C., J.V.-A., B.W., D.J.-R., FD., L.P., R.P., D.-L.M.); and Shell International Chemicals B.V, Shell Research and Technology Centre, Amsterdam, P.O. Box 38 000, 1030 BN Amsterdam, The Netherlands (O.E.D.)