Abstract
This article reports measurements of the concentration distribution of two model proteins adsorbed from aqueous solution by two different high surface area carbons, using small angle neutron and X-ray scattering (SANS and SAXS). The proteins investigated were bovine serum albumin (67 kDa), and bovine pancreatic trypsin inhibitor (BPTI), also known under the name aprotinin (6.5 kDa). The two carbon substrates were C1, an open structured carbon aerogel derived from a resorcinol–formaldehyde polymer aerogel, and C2, a commercial nanoporous carbon from MAST Carbon (UK). Although both C1 and C2 possess a high proportion of pores that are either closed or inaccessible to low temperature nitrogen vapour, the size distribution of the accessible pores is broad enough to accommodate BSA molecules. In C1, which is hydrophobic, the BSA molecules migrate individually into pores that are compatible with their size, whereas BPTI forms clusters having the same size as BSA. With C2, the hydrophilic internal surface limits the adsorption efficiency. The strong adhesion of proteins to hydrophilic surfaces prevents diffusion of either molecule into the micro- and nanopores. In this sample both BSA and BPTI form large clusters. These observations have relevance to biomedical applications, such as haemoperfusion or as a medium for protein storage.
Highlights
The way in which biomolecules adsorb and migrate on solid surfaces, notably on porous substrates, is the focus of converging interests from investigations into protein conformation, [1,2,3,4] physical adsorption processes,[5,6,7] and medical applications.[8,9] Activated carbons are a class of porous substrates that have been widely employed for many centuries as general adsorbents
In the same carbon at pH 2.8, the extended conformation adopted in free solution by BSA at low pH does not occur: in the basic environment of carbon C1 the indirect polyelectrolyte character of this molecule induced by the pH disappears as the excess proton amount is transferred to the pore walls
For the smaller bovine pancreatic trypsin inhibitor (BPTI) molecule, the aggregation number is of the order of 10 in C1, and more than an order of magnitude greater in C2
Summary
The way in which biomolecules adsorb and migrate on solid surfaces, notably on porous substrates, is the focus of converging interests from investigations into protein conformation, [1,2,3,4] physical adsorption processes,[5,6,7] and medical applications.[8,9] Activated carbons are a class of porous substrates that have been widely employed for many centuries as general adsorbents They are invaluable as adsorbents of small molecules in numerous applications related to public health, such as drinking water purification, personnel protection, etc. Treatment of patients suffering from acute poisoning, drug overdose, hepatic coma, or metabolic disturbances removes toxins from the bloodstream by circulating the patient’s blood through an adsorbent, usually activated carbon or resins Such haemoperfusion procedures extract small to medium sized molecules that tend to be more difficult to remove by conventional haemodialysis.
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