Immobilization kinetics and mechanism of bovine serum albumin on diatomite clay from aqueous solutions

Abstract

Abstract In this research, adsorption properties of bovine serum albumin (BSA) on diatomite clay, which is an oxide mineral, were studied as a function of BSA, sodium phosphate buffer and protein concentration and pH and the thermodynamic parameters of adsorption process were investigated. The BSA adsorption experiment onto diatomite clay indicated that the BSA solution reached the maximum adsorption value at pH 5.5. It was observed that the maximum adsorption capacity (qm) of the data obtained from the adsorption studies showed a great dependence on pH. The maximum amount of adsorption in adsorption experiments can be considered as points where the electrostatic interaction for pH is appropriate. Both structural and electrostatic interaction in regions outside of the isoelectric point may have caused a decrease in BSA absorbance. The structural influences were associated with different conformational states that while BSA molecules accept changes with pH, electrostatic effects can be observed in BSA molecules behaved like soft particles. In this case, it is not possible to explain the independence of the qm–pH curves of the amount of adsorption. The protein molecules at this point are very stable. Because this value is close to the isoelectric point of serum albumin. The surface structural change of BSA and diatomite clay was studied. For this, Fourier transform infrared spectroscopy (FTIR) spectroscopy values were compared before and after the experiment. The diatomite samples used as support material were characterized by FTIR, scanning electron microscopy, thermogravimetric analysis and Brunauer Emmett–Teller surface area analysis. The thermodynamic functions such as enthalpy, entropy, Gibbs free energy and activation energy were investigated in their experimental work. The thermodynamic parameters such as Gibbs free energy (ΔG*), E a, ΔH* and ΔS* were calculated as − 67.45, 15.41, − 12.84 kJ mol−1 and − 183.28 J mol−1 K−1 for BSA adsorption, respectively. We can deduce that the adsorption process from the data obtained from the thermodynamic parameters is spontaneous and exothermic. The adsorption of the process was investigated using Eyring and Arrhenius equations, and its adsorption kinetic found to be coherent with the pseudo-second-order model. As a result, we reached that the diatomite clay is a suitable adsorbent for the BSA. Experimental results showed that diatomite clay has the potency to be used for rapid pretreatment in the process of identifying proteins.

Keywords

• Adsorption
• Diatomite clay
• Thermodynamic
• Protein