Biophysics

Abstract

4-Nitroquinoline 1-oxide has attracted much attention not only because of its biological actions but also because of its particularly interesting chemical structure: thus, it has two strong polar groups, i. e. the N-oxide and nitro groups in the molecule, and for this reason 4-nitroquinoline 1-oxide is susceptible to nucleophilic attack in chemical reaction. The or-electronic energy obtained by means of the molecular orbital method reflects this property. Thus, the energy of the lowest vacant orbital of 4-nitroquinoline 1-oxide is extremely low, showing that the electron affinity of this compound is significantly large (Fig. 1 a). This also means that 4-nitroquinoline 1-oxide acts as electron acceptor in the charge transfer complex formation. Owing to the existence of the strong electron-attracting groups, negative charges are located mostly on the polar groups, resulting in a positive charge on the non-substituted benzene ring (Fig. 1 b). Electron density is greatest at position 2, and this agrees well with the fact that electrophilic substitution occurs at this position (see Chapter 2).