| Autor: |
Nizhnik YP; BioStone, 2815 Exchange Blvd., Southlake, TX 76092, USA., Hansen E; Department of Chemistry, Ball State University, Muncie, IN 47306, USA., Howard C; Department of Chemistry, Ball State University, Muncie, IN 47306, USA., Zeller M; Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA., Rosokha SV; Department of Chemistry, Ball State University, Muncie, IN 47306, USA. |
| Abstrakt: |
4-Nitroquinoline-N-oxide (NQO) and 4-nitropyridine-N-oxide (NPO) are important precursors for the synthesis of substituted heterocycles while NQO is a popular model mutagen and carcinogen broadly used in cancer research; intermolecular interactions are critical for their reactions or functioning in vivo. Herein, the effects of the coordination of N-oxide's oxygen atom to Lewis acids on multicenter donor-acceptor bonding were explored via a combination of experimental and computational studies of the complexes of NQO and NPO with a typical π-electron donor, pyrene. Coordination with ZnCl 2 increased the positive electrostatic potentials on the surfaces of these π-acceptors and lowered the energy of their LUMO. Analogous effects were observed upon the protonation of the N-oxides' oxygen or bonding with boron trifluoride. The interaction of ZnCl 2 , NPO, or NQO and pyrene resulted in the formation of dark co-crystals comprising π-stacked Zn-coordinated N-oxides and pyrene similar to that found with protonated or (reported earlier) BF 3 -bonded N-oxides. Computational studies indicated that the coordination of N-oxides to zinc(II), BF 3 , or protonation led to the strengthening of the multicenter bonding of the nitro-heterocycle with pyrene, and this effect was related both to the increased electrostatic attraction and molecular-orbital interactions in their complexes. |
