1. Current address: Institut National de la Recherche Agronomique, rue de la Géraudière, F-44072 Nantes, France
2. Correspondence should be addressed to this author.
3. On a leave of absence from the Institute of Chemistry, Center of Chemical Research of the Slovak Academy of Sciences, 84238, Bratislava, Czechoslovakia
4. On a leave of absence from the Department of Chemistry, Polytechnic University, 333 Jay Street, Brooklyn, NY 11201