Cooperativity of non-covalent interactions has been extensively reported in the literature [1]. Cooperativity occurs in the well-known example of ice, where the oxygen-oxygen separation is shortened to 2.76 Å compared to 2.98 Å in the water dimer [2]. Recently, we reported a new equation for calculating total interaction energy in one noncyclic ABC triad and also new insights into cooperativity of noncovalent bonds [3]. Our next studies confirmed the expectation that the above proposed equation can be used in calculating the total interaction energy in any acyclic ABC system, regardless the nature of bonds between A, B and C fragments [4]. Our results also clearly show that whenever the fragmentation of any system into three fragments is possible we can find whether there is a cooperativity or anticooperativity between the corresponding bonds.
