Vibrational sum frequency spectroscopy (VSFS) is a nonlinear optical process.
The sum frequency signal is proportional to the square of second order nonlinear
susceptibility, which is proportional to the average of polarizabilities of molecules,
which is related to molecular orientation. Since the polarizabilities of molecules in bulk
phase will be canceled out, a sum frequency signal can only be generated from interfaces
where the inversion symmetry is broken. Because of its interfacial specificity, VSFS has
been applied to study many interfacial phenomena. In this dissertation we investigated
various biological interfaces with VSFS. Fibrinogen adsorption was studied at the
protein/solid interface in combination with atomic force microscopy (AFM),
immunoassay, and VSFS. Astonishing changes in the interfacial water orientation
accompanied by the pH changes provided fibrinogen’s adsorption mechanism up to the
amino acid level. Enzymatic fragmentation of fibrinogen revealed that the adsorption
property of fibrinogen was mainly from the alpha C fragments of the protein. Mimicking of the fibrinogen binding site with polypeptides was successfully performed
and showed very similar properties of fibrinogen adsorption.
Protein stability is sensitive to the salts in solutions. The ability of ions to
stabilize protein was ordered by Hofmeister in 1888 and the order is SO4
2- ≅ HPO4
2- > F-
> Cl- > Br- > NO3
- > I- (≅ ClO4
-) > SCN-. Even though the phenomenon was observed in
various biological systems, the origin of those ionic effects is still not well understood.
We studied ion effects on alkyl chain ordering and interfacial water structure for
octadecylamine, dimethyldidodecylammonium bromide, and dilauroylphosphotidyl
choline monolayers. Because of its ability to probe a hydrophobic moiety and interfacial
water at the same time, VSFS provided further information to understand the Hofmeister
series. We found that the Hofmeister effect is a combinatorial effect of screening
effects, ion binding, and dispersion forces.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1708 |
| Date | 02 June 2009 |
| Creators | Lim, Soon Mi |
| Contributors | Cremer, Paul S. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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