No abstract

mInteraction between the guanine-cytosine base pair and the episulfonium form of sulfur mustard (HDf) or the aziridinium form of nitrogen mustard (HN2+) was studied using the ab initio LCAO-MO method at the HF/6-31G level. The alkylation mechanism on the guanine N7 was analyzed by using a supermolecular modeling. Our stereostructural results associated with the molecular electrostatic potentials and highest occupied/lowest unoccupied molecular orbital (HOMO-LUMO) properties show that in vacuum the alkylation of the N7 of guanine by HDt in the agressive episulfonium form is a direct process without a transition state and of which the pathway is determined. Our study shows that interaction of guanine with the aziridinium form of HN2+ necessitates a transition state for the N7 alkylation route. When the N7 guanine alkylation by HD+ or HN2' is achieved, about half of a positive charge moves from the alkylator toward the guanine in both cases. 0 1996 John Wiley & Sons, Inc.

The free Val-Pro-Gly-Gly tetrapeptide belonging to the Proline-rich sequences of elastin has been studied both theoretically and experimentally. The molecular modelisation was carried out using AM1 and ab initio quantum computations while the conformation in solution was ascertained by circular dichroism spectroscopy performed on the synthesized tetrapeptide. Experimental and theoretical investigations lead to the conclusion that the most probable structure is constituted by a type II beta-turn.

No abstract

Interaction between Guanine and the episulfonium form of Sulfur mustard (HD) was studied using the ab initio LCAO-MO method at the HF/6-31G level. The alkylation mechanism on guanine-N7 was analyzed by using a supermolecular modeling. Our stereostructural results associated with the molecular electrostatic potentials and HOMO-LUMO properties, show that in vacuum the alkylation of the N7 of guanine by HD in the aggressive episulfonium form is a direct process without transition state and of which the pathway is determined.