Studies on pH-controlled transition of myoglobin capsules from hollow to multilayered structures

Abstract

In this study, myoglobin biocapsules (lyophilisomes) of various types and sizes were prepared using a combination of freezing-annealing and immobilization. Hollow lyophilisomes of pure myoglobin below and above its isoelectric point were designed and changes in their secondary structure based on variations in pH were studied by circular dichroism spectroscopy and confocal laser scanning microscopy. The study results show that permeability and size of these capsules change as pH changes; besides, near the isoelectric point, large swollen multiwalled capsules are formed, which when exposed to buffers of lower pH exhibited a tendency to reverse to hollow structures. Adsorption of these capsules onto solid surfaces has been studied using quartz crystal microbalance and contact angle measurements. Thus, pH shift may be a useful post-preparation approach for stimuli-responsive modification of the surface roughness, porosity and permeability of pre-assembled polypeptide microcapsules.