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ABSTRACT
In this study, TiO2 nanoparticles (NPs) of different sizes were synthesized using sol gel method and calcined at different temperatures ranging from 200 to 700°C. The specific surface area of TiO2 was found to decrease with the increase in calcination temperature. It was observed that adsorption of bovine serum albumin (BSA) on TiO2 NPs obeyed the Freundlich adsorption isotherm, and the isotherm parameters were calculated from equilibrium adsorption batch experiments. The kinetics of adsorption was best fitted by pseudo-first-order kinetic model. The effect of particle dosage on BSA adsorption was also studied and it was observed that the adsorption increased with the increase in particle dosage and decrease in particle size. The conformational changes of BSA on exposure to TiO2 NPs of various sizes were investigated using circular dichroism spectropolarimetry. The results suggested that BSA underwent a distortion in the secondary structure which was quantified by the percent α-helicity. A size-dependent distortion was observed. The α-helix content changed from 32.3% for pure BSA to 21.9% when exposed to NPs calcined at 200°C (350 mg/L) and to 28.4% for NPs calcined at 700°C at the same concentration.
Nomenclature
| BSAsat | = | saturation concentration of BSA |
| qe | = | amount of adsorbed protein per weight of adsorbent (mg/g) at equilibrium |
| Ce | = | un-adsorbed protein concentration in solution at equilibrium (mg/L) |
| Q0 | = | maximum amount of the BSA per unit weight of sorbent to form a complete monolayer on the surface bound (mg/g) |
| B | = | the affinity of the binding sites (L/mg) |
| Kf | = | adsorption capacity |
| N | = | adsorption intensity |
| S | = | specific surface area of NPs (m2/g) |
| k1 | = | rate constant for pseudo-first-order adsorption kinetics (min−1) |
| k2 | = | rate constant for pseudo-second-order adsorption kinetics (g/mg/min) |
| q | = | amount of protein adsorbed at any time (mg/g) |
| MRE | = | mean residue ellipsity (cm2/mol) |
| Cp | = | molar concentration of BSA |
| N | = | number of amino acid residue |
| l | = | path length (cm) |
Acknowledgements
We thank the Central Research Facility of IIT Kharagpur for providing the required facilities. We also thank Pastor L. Solano-Flores and Anirban Banerjee for their help in characterization and material procurement. The help and support of Malini Ghosh, Kyriakos Manoli, and Ghodsieh Malekshoar are greatly acknowledged.
Supplemental data
Supplemental data for this article can be accessed on the publisher’s website.