We already observe a decrease of the CCl4 solvent shift by van der Waals forces OH…CCl4 of 1:1 complexes, induced by the H-bond of the other OH or OD group. This decrease is measured by the CCl4 solvent effect for monomers. This indicates a real negative polarization by the H-bond in 1:1 complexes on the second OH/OD. This experiment establishes the real polarization and excludes the importance of repulsions of the bases as the cause. The dependence of intermolecular forces is known on the polarizability. Our method demonstrates directly the polarization by interactions.
The anti-cooperativity of symmetric complexes B1…HOD…B1 by a strong base B1 can be reduced in unsymmetric 1:2 complexes B1…HOD…B2 by weaker bases B2. This weakening of the anti-cooperativity of the stronger base could be predicted quantitatively. Similarly, the anti-cooperativity of the weaker base B2 is strengthened in unsymmetric 1:2 complexes by stronger bases B1.
It is known that H-bonds XH…B can be strengthened by cooperativity with a second H-bond XH…XH…B. They can be weakened for water by anti-cooperativity of two H-bonds B…HOH…B. The H-bond B1…HO of 1:2 complexes B1…HOH…B2 can be weakened if the base strength of B2 is stronger than of B1 or strengthened if B2 is weaker than B1. Nature may use these possibilities in biochemistry. 相似文献