Characterization of lactate-guanidinium and lactate-lactate interactions in aqueous solution by spectropolarimetry

Spectropolarimetry has been used to quantify the lactate-guanidinium and lactate-lactate equilibrium interactions in aqueous solution. Association constants for the lactate-guanidinium and lactate-lactate formations are 6.11 dm(3) mol(-1) and 1.12 dm(3) mol(-1), respectively, in aqueous solution; 6.11 dm(3) mol(-1) is a high value for an electrostatic interaction in water. This stability, however, cannot account for the extremely strong lactate-protein binding, observed earlier by NMR spectroscopy. The molar rotation coefficients for both the heteroassociation and homoassociation complexes are also calculated. The homoassociative lactate-lactate binding is the first such interaction, whose constant has been determined by spectropolarimetry in aqueous solution.