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Document Type

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Plant, Soil & Insect Sciences

Year Degree Awarded

2017

Month Degree Awarded

February

First Advisor

Baoshan Xing

Second Advisor

Richard W. Vachet

Third Advisor

Stephen Simkins

Subject Categories

Biochemistry | Environmental Health

Abstract

In the first project, we examined adsorption of bovine serum albumin (BSA) and lysozyme (LYZ) on carboxylated (CM), hydroxylated (HM) and graphitized (GM) multi-wall carbon nanotubes (CNTs). All adsorption isotherms were fitted well with Langmuir model. Maximum adsorption capacities (mg/g) followed: HM>CM>GM for both BSA and LYZ, which positively related to the surface areas of the three CNTs. However, after surface area normalization, adsorption capacity (mg/m2) followed: HM>GM>CM for BSA and GM>CM>HM for LYZ, indicating that functional groups and hydrophobicity of CNTs also contributed to protein adsorption. In addition, adsorption of LYZ (77,500-96,800 mg/g) was at least 280 times higher than BSA (124-275 mg/g) for all the three CNTs. BSA molecules on CNTs surface mainly showed a mono-layer adsorption while LYZ adsorption was through multi-layers. Moreover, BSA (0-13000 mg/L) was able to disperse the three CNTs. However, no significant dispersion was observed for all the three CNTs in the presence of LYZ at the same concentrations. The results revealed that α-helix structure of both proteins diminished after interacting with the three CNTs. This research will be helpful to clarify the mechanism of protein adsorption on functionalized CNTs, and would be of importance for using CNTs in biomedical and pharmaceutical fields.

In the second project, we studied adsorption of BSA and LYZ on graphene and graphene oxide such as flakes (FGO) and powders (PGO). Maximum adsorption capacities (mg/g) were followed: FGO>Gr>PGO for both BSA and LYZ, which is in the same order of the surface area size of each graphene. The adsorption maxima of BSA on three graphene were positively related to the concentration of sodium phosphate. However, the adsorption maxima of LYZ were in an opposite order, indicating that ionic strength could have different effect on the adsorption behavior of protein on graphene oxides. The dispersion of protein and graphene oxides hybrids was also affected by the functional groups on the surface of graphene oxides and ionic strength. From this study, BSA could disperse the GO into solution and prevent the sodium ions aggregating the GO layers by removing free sodium ions from the solution. However, LYZ could help sodium ions to aggregate the GO layers due to few sodium ions could interact with the LYZ and the two hydrophobic cores on the surface of LYZ. Furthermore, the α-helical structure of both proteins diminished after coated on the surface of graphene. However β-strand content was increasing at the same time, indicating 2-D β-strand might be more stable on the flat surface of graphene. This research will be helpful to clarify the mechanism of protein adsorption on GO, and would be of importance for using GO and Gr in biomedical, environmental and pharmaceutical fields.

PengDissertation.docx (52985 kB)
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Available for download on Thursday, February 01, 2018

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