Monolayer behavior of human serum albumin (HSA) at air-water interface

Abstract

Langmuir monolayers of human serum albumin (HSA) are formed on water surface at neutral pH (≈ 7.0) in absence and presence of Ca2+ ions in aqueous subphase. Compression-decompression surface pressure (π) - specific molecular area (A) isotherm cycle for both the conditions are recorded to compare the corresponding hysteresis behaviours. It is seen from the isotherms that in pure water compression curve of HSA monolayer tries to follow the decompression curve, whereas it is almost similar in presence of Ca2+ ions. Topographical features of the HSA monolayer at the air-water interface are obtained from Brewster angle microscopy (BAM). Protein films are also deposited in Si (001) substrates at lower and higher surface pressures, i.e., at 5 and 18 mN/m and are investigated by Atomic Force Microscopy (AFM) to explore out-of-plane structure and surface morphology. Although nearly homogeneous layer is formed by the HSA protein at the air-water interface before and after interaction with calcium ions, but slight conformation variation of protein takes place in presence of ions and accordingly the elastic behavior of monolayer changes under mechanical compression and expansion.Langmuir monolayers of human serum albumin (HSA) are formed on water surface at neutral pH (≈ 7.0) in absence and presence of Ca2+ ions in aqueous subphase. Compression-decompression surface pressure (π) - specific molecular area (A) isotherm cycle for both the conditions are recorded to compare the corresponding hysteresis behaviours. It is seen from the isotherms that in pure water compression curve of HSA monolayer tries to follow the decompression curve, whereas it is almost similar in presence of Ca2+ ions. Topographical features of the HSA monolayer at the air-water interface are obtained from Brewster angle microscopy (BAM). Protein films are also deposited in Si (001) substrates at lower and higher surface pressures, i.e., at 5 and 18 mN/m and are investigated by Atomic Force Microscopy (AFM) to explore out-of-plane structure and surface morphology. Although nearly homogeneous layer is formed by the HSA protein at the air-water interface before and after interaction with calcium ions, but slight c...