Proton MRD Profile Analysis in Intracellular Hemoglobin Solutions: A Three Sites Exchange Model Approach

The Three Sites Exchange Model (3SEM) was properly used to describe Proton ( 1 H) Magnetic Relaxation Dispersion ( 1 HMRD) in intracellular samples of hemoglobin A (HbA) and hemoglobin S (HbS) at 310 K. The HbA and HbS samples were obtained from whole blood of voluntary donors and patients, respectively, and processed by classical methods (centrifugation, decanting and freezing–thawing cycles). The 1 HMRD profiles (20 kHz–60 MHz) were obtained using a Fast Field Cycling NMR Relaxometer (Stelar FFC 2000 Spinmaster) and Minispec relaxometers (Mq20, Mq60). The 3SEM used includes the contribution of labile protons from the structure of the protein; and the contribution of the cross relaxation to dispersion was estimated as: at least one order of magnitude lower than the total dispersion. Two dispersions were found: one of them properly describing the hemoglobin rotational correlation time and another one probably related to internal and/or hydrated water molecules with effective correlation times higher than 1 ns and main residence times less than the rotational correlation time of the protein. The use of the 3SEM creates the conditions to properly explain proton magnetic relaxation during the HbS polymerization process.