Molecular Electrostatic Potential Reorganization Theory to Describe Positive Cooperativity in Noncovalent Trimer Complexes

Abstract

Supramolecular self-assembly and molecular recognition processes are driven mainly by positive cooperativity in noncovalent interactions. Here, we report a large variety of hydrogen-, tetrel-, chalcogen-, pnicogen-, halogen-, aerogen-, and dihydrogen-bonded dimer and trimer complexes, computed using the MP2/6-311++G(d,p) level ab initio theory. The dimer to trimer change is associated with a positive cooperativity in all the complexes. Significant electron density reorganization occurs in monomers because of noncovalent bond formation which is quantified using the change in the molecular electrostatic potential (MESP) at bonded atoms. For a noncovalent dimer XDYA, an electron density flow is observed from the donor molecule XD to acceptor molecule YA. As a result, YA in dimer showed a tendency to form a stronger noncovalent bond with an electron-deficient center of a third molecule, whereas XD in the dimer showed a tendency to form a stronger noncovalent bond with an electron-rich center of a third molecule. The change in change-of-MESP at the donor and acceptor atoms involved in bond formation (ΔΔVn) is used as a parameter to assess the extent of electron donor–acceptor (eDA) interaction in dimers and trimers and found that ΔΔVn is directly proportional to the total binding energy. A cooperativity rule has emerged from this study which states that the electron reorganization in the dimer due to the eDA interaction always enhances its donor–acceptor interactive behavior with a third molecule toward the formation of a noncovalent trimer complex.