Binding constants Ka (M−1), determined by fluorescence titration, and deduced free energy of association −ΔGO (kcal/mol, in parentheses) for IgGs specific for LPS of V. cholerae O1 serotype Ogawa, with synthetic analogs of the methyl α-glycoside of the terminal residue, and the presumed antigenic determinant of the Ogawa O-SP