However, the deoxygenated hemoglobin monomers bind two protons upon dimerization. You should use the equilibrium expression above and the Hill Plot of rHb below to decide. Yes, the curve changes from weak to strong binding and has a region of slope greater than 1. This mutant is not cooperative and is a monomer incapable of dimerization. It is always in the strong binding state.
More protons push the equilibrium to the right.
Dimerization is incompatible with oxygen binding. High pH would favor oxygen binding by reducing dimerization. The dimerization interface has four glutamic acids, two from each subunit. This cluster of negative charges is stabilized by the uptake of one proton per pair of Glu across the interface and by nearby arginine residues. The pKa of the interface Glutamic acids is 6.0.