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Name (Title):
Hidenori Noguchi (Assistant Professor)
Affiliation:
Graduate School of Science, Hokkaido University
Address:
N10-W8, Sapporo 060-0810, JAPAN
Email: noguchi@pchem.sci.hokudai.ac.jp
Home Page: http://pchem.sci.hokudai.ac.jp/index_E.html
Presentation Title:
Interfacial molecular structure at solid/liquid interfaces by surface sensitive vibrational
spectroscopies.
Abstract:
Molecular level characterization of the structure of proteins
and many other biomaterials, especially in wet conditions, are
quit important to understand how they function. We applied
surface specific vibrational spectroscopies (SFG and ATR-IR) to
investigate the structure and function of (1) interfacial water at
thermo-responsive polymer surface and (2) protein immobilized
on solid surface in buffer solution.
1. Interfacial water structure at PNIPAM surface studied by
SFG spectroscopy
Poly-N-isopropyl-acrylamide (PNIPAM) is one of the most
thoroughly investigated thermo-responsive polymers in aqueous
solution. PNIPAM has a well defined lower critical solution
temperature (LCST) around 32˚C. Bellow LCST, PNIPAM
chains are strongly hydrated with water molecules. Above the
LCST, they dehydrate and collapse to a globular form. Such
structural transition induced by temperature may have a number
of interesting possible applications. However, the detail
molecular information especially about the water molecules
around PNIPAM chains is still controversial. In this study,
temperature dependence of interfacial water structure at
Poster Session PG-3
Fig. 1 SFG spectra of OH stretch
region of PNIPAM/water interface
at several temperatures.
PNIPAM surface was investigated by SFG spectroscopy. SFG spectra in the OH stretching region
of PNIPAM/water interface are shown in Figure 1. Two broad peaks were observed at ca. 3200
cm -1 and ca. 3450 cm -1 , which are known to be due to the symmetric OH stretching of strongly
hydrogen bonded water "ice-like water" and the asymmetric OH stretching of weakly hydrogen
bonded water "liquid-like water", respectively. SFG intensity of the "liquid-like water"
component became stronger as the temperature increased from 20 to 40˚C. When the temperature
was decreased to 20˚C, SFG spectrum returned to the initial shape. These results suggest that the
PNIPAM surface reversibly change from "hydrophobic" to "hydrophilic" as the temperature
change from 20 to 40˚C.
2. Structure and function of calmodulin immobilized on a solid substrate studied by in situ
ATR-IR and SFG spectroscopies
Calmodulin (CaM), which is one of the Ca 2+ binding protein, immobilized on a chemically
modified gold surface by binding its histidine-tag to surface attached nickel-chelating nitrilotriacetic
acid (Ni-NTA), maintaining its activities. Association and dissociation of target peptide
mastoparan(MP) with the immobilized CaM was monitored in real time using in situ ATR-IR
spectroscopy by varying the concentration of MP to estimate the binding constant of MP with
immobilized CaM. The binding constant was 4 orders of magnitude smaller than homogeneous
system, suggesting that the conformational change of CaM was sterically hindered by surface
immobilization. Effect of Ca 2+ on the structure of water around CaM was also investigated by
using SFG.
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