Polarized light scattering from sickle hemoglobin polymers

Stirring effects on the spontaneous formation of chirality in the homoassociation of diprotonated meso-tetraphenylsulfonato porphyrins

Homoassociates of the achiral title porphyrins in acid solutions show spontaneous symmetry breaking, which can be detected by circular dichroism (CD). The CD spectra are due to differential scattering and differential absorption contributions, the relative significance of which is related to the shape and size of the homoassociate. When an earlier model, designed for the association of these diprotonated porphyrins (J aggregates with the geometry of stepped sheets of intramolecular-stabilised zwitterions), was applied to an exciton-coupling point-dipole approximation, the folding of the one-dimensional homoassociates explained the CD signals detected. An effect of the vortex direction, caused by stirring or rotary evaporation, upon the exciton chirality sign was detected. In the case of H2TPPS3, the number of experiments performed gave a statistical significance to this effect. This vortex effect can be attributed to enhancement of the chirality fluctuations that originate in the diffusion-limited aggregation to high-molecular-weight homoassociates. In this sense, the phenomenon could be general for supramolecular systems that are obtained under kinetic control, and its detection would be possible when inherent chiral chromophores were being generated in the association process.

Sickle hemoglobin polymer melting in high concentration phosphate buffer

Sickle cell hemoglobin (HbS) prepared in argon-saturated 1.8 M phosphate buffer was rapidly mixed with carbon monoxide (CO)-saturated buffer. The binding of CO to the sickle hemoglobin and the simultaneous melting of the hemoglobin polymers were monitored by transmission spectroscopy (optical absorption and turbidity). Changes in the absorption profile were interpreted as resulting from CO binding to deoxy-HbS while reduced scattering (turbidity) was attributed to melting (depolymerization) of the HbS polymer phase. Analysis of the data provides insight into the mechanism and kinetics of sickle hemoglobin polymer melting. Conversion of normal deoxygenated, adult hemoglobin (HbA) in high concentration phosphate buffer to the HbA-CO adduct was characterized by an average rate of 83 s-1. Under the same conditions, conversion of deoxy-HbS in the polymer phase to the HbS-CO adduct in the solution phase is characterized by an average rate of 5.8 s-1 via an intermediate species that grows in with a 36 s-1 rate. Spectral analysis of the intermediate species suggests that a significant amount of CO may bind to the polymer phase before the polymer melts.