N/N=C(\C(=O)Nc1ccc([N+](=O)[O-])cc1)C(C1=Nc2cc([N+](=O)[O-])ccc2NC1)[N+](=O)[O-]
Molecules with a polar surface area of greater than 140 angstroms squared (Å2) tend to be poor at permeating cell membranes. What's the psa of this molecule?