Abstract
Infrared (IR) microspectroscopy combined with a quartz crystal
microbalance (QCM) together with an original relative humidity (RH)
control system has been developed for studying water adsorption on a
collagen film. The adsorbed water weights measured by QCM are almost
similar for wetting and drying processes at 28 ℃, indicating that the
collagen film is close to the water adsorption/desorption equilibria. A
broad OH + NH stretching band area (3000–3700 cm−1) in the IR
spectra of the collagen film increased linearly with the adsorbed weight
until about 1.2 μg/8.0 μg dry collagen film at relative humidity
(RH) = 40%, while at higher RH (60%, 80%), the band area deviates from the
linear trend to the lower side, due to viscoelasticity and others. The
OH + NH band can be simulated by four Gaussian components at 3440, 3330,
3210, and 3070 cm−1 with the relatively constant band areas of
3330 and 3070 cm−1 components due to amide A and B (NH) for
increasing and decreasing RH. Bound water (3210 cm−1 component:
short H bond) constitutes around 70% of total water
(3440 + 3210 cm−1 band areas) at RH = 4.9% but decreases to 23%
at RH = 80.3%, where free water (3440 cm−1 component: long H
bond) becomes dominant over 70%. The peak shifts of C=O stretching (Amide
I) and N–H bending (Amide II) can be understood by increasing hydrogen
bonding of water molecules (bound water) bound to peptides at lower RH.
The higher wavenumber shifts of CH stretching can be due to the loose
binding of water molecules (free water) to aliphatic chains on the
collagen surface, especially at higher RH. The present combined QCM-IR
method is useful for studying amounts and natures of water adsorbing on
biomolecules.
© 2017 The Author(s)
PDF Article
More Like This
Cited By
You do not have subscription access to this journal. Cited by links are available to subscribers only. You may subscribe either as an Optica member, or as an authorized user of your institution.
Contact your librarian or system administrator
or
Login to access Optica Member Subscription