6 research outputs found
Analysis of the Hydration Process and Rotational Dynamics of Water in a Nafion Membrane Studied by <sup>1</sup>H NMR Spectroscopy
<sup>1</sup>H NMR spectroscopy is employed to reveal the hydration
process of a Nafion membrane by measuring both the chemical shift
and the spin–lattice relaxation time. In a former study, the
hydration process was suggested to comprise two steps: the molecular
adsorption of water on the sulfonic acid groups and wetting with liquid
water. The present study has revealed the first step can further be
divided into two steps. By introducing a new experimental technique,
the quantitatively reliable NMR measurements of protons (<sup>1</sup>H) of water involved in the polymer membrane are realized. In addition,
a new analytical procedure is developed using a reciprocal concentration
on a saturation–adsorption model, and the hydration is clearly
revealed to have three individual steps. Both the chemical shift and
the relaxation time plots against the reciprocal concentration exhibit
three linear parts with apparently different slopes. Of great interest
is that the initial hydration is divided into two stages: the first
hydration is a very strong adsorption of water probably on the hydroxyl
group of the sulfonic acid group, and the second one is a relatively
weak adsorption on another site of the sulfonic acid group. The third
hydration is readily assigned to excess bulk (liquid-like) water as
expected. These adsorption processes are readily correlated with the
rotational motion of water by converting the spin–lattice relaxation
time to the rotational correlation time
Surface Selection Rule of Infrared Diffuse Reflection Spectrometry for Analysis of Molecular Adsorbates on a Rough Surface of a Nonabsorbing Medium
The surface selection rule (SSR)
for discussing the molecular orientation
in a thin film adsorbed on a rough surface is determined by analyzing
a surface monolayer by defining the angle of incidence and polarizations.
As the standard sample, a highly organized self-assembled monolayer
(SAM) on a rough alumina surface is employed. By introducing crossed-Nicol
polarizers in the incident and detection paths, the specular reflection
and diffuse reflection components are readily separated. To fully
understand the spectra of the SAM, a new idea is proposed that the
incidental light can be excluded from the discussion when the angle
of incidence is small, which is named the pseudotransmission (pd-Tr)
model. Another important idea is that a part of a spectrum is degraded
in the signal-to-noise ratio by the suppression of incidental light
on the rough surface via a deconstructive interference, which can
experimentally be revealed by the crossed-Nicol measurements of single-beam
spectra depending on the angle of incidence. Through the experiments
of all the combinations of polarizations and angles of incidence,
the pd-Tr model and the light suppression are found to be an important
base to fully understand the SSR of molecular adsorbates on a rough
surface of a nonabsorbing medium
Study of Perfluoroalkyl Chain-Specific Band Shift in Infrared Spectra on the Chain Length
The CF<sub>2</sub> symmetric stretching vibration (ν<sub>s</sub>(CF<sub>2</sub>)) band of a perfluoroalkyl (Rf) group in an
infrared (IR) spectrum exhibits a unique character, that is, an apparent
high wavenumber shift with increasing the chain length, which is an
opposite character to that of the CH stretching vibration band of
a normal alkyl chain. To reveal the mechanism of the unusual IR band
shift, two vibrational characters of an Rf chain are focused: (1)
a helical conformation of an Rf chain, (2) the carbon (C) atoms having
a smaller mass than the fluorine (F) atom dominantly vibrate as a
coupled oscillator leaving F atoms stay relatively unmoved. These
indicate that a “coupled oscillation of the skeletal C atoms”
of an Rf chain should be investigated considering the helical structure.
In the present study, therefore, the coupled oscillation of the Rf
chain dependent on the chain length is investigated by Raman spectroscopy,
which is suitable for investigating a skeletal vibration. The Raman-active
ν<sub>s</sub>(CF<sub>2</sub>) band is found to be split into
two bands, the splitting is readily explained by considering the helical
structure and length with respect to group theory, and the unusual
peak shift is concluded to be explained by the helical length
Impact of Kinetically Restricted Structure on Thermal Conversion of Zinc Tetraphenylporphyrin Thin Films to the Triclinic and Monoclinic Phases
The
powerful combination of p-polarized multiple-angle incidence
resolution spectroscopy (pMAIRS) and grazing incidence X-ray diffraction
(GIXD) is applied to the structural characterization of zinc tetraphenylporphyrin
(ZnTPP) in vapor-deposited films as a function of the deposition rate.
The deposition rate is revealed to have an impact on the initial film
structure and its conversion by thermal annealing. The pMAIRS spectra
reveal that a fast deposition rate yields a kinetically restricted
amorphous film of ZnTPP having a “face-on orientation”,
which is readily discriminated from another “randomly oriented”
amorphous film generated at a slow deposition rate. In addition, the
GIXD patterns reveal that the film grown at a slow deposition rate
involves a minor component of triclinic crystallites. The different
initial film structure significantly influences the thermal conversion
of ZnTPP films. The randomly oriented amorphous aggregates with the
triclinic crystallite seeds are converted to the thermodynamically
stable phase (monoclinic) via the metastable triclinic phase. The
kinetically restricted structure, on the other hand, is followed by
a simple thermal conversion: the molecules are directly converted
to the monoclinic one rather than the triclinic one
Transient Reciprocating Motion of a Self-Propelled Object Controlled by a Molecular Layer of a <i>N</i>‑Stearoyl‑<i>p</i>‑nitroaniline: Dependence on the Temperature of an Aqueous Phase
The mode-bifurcation of a self-propelled
system induced by the
property of a <i>N</i>-stearoyl-<i>p</i>-nitroaniline
(C<sub>18</sub>ANA) monolayer developed on an aqueous phase was studied.
A camphor disk was placed on a C<sub>18</sub>ANA monolayer, which
indicated a characteristic surface pressure–area (π–<i>A</i>) isotherm. A camphor disk transiently exhibited reciprocating
motion at a higher surface density of C<sub>18</sub>ANA. The amplitude
of the reciprocating motion increased with an increase in the temperature
of the aqueous phase below 290 K, but reciprocating motion varied
to irregular motion over 290 K. The temperature-dependent reciprocating
motion is discussed in terms of the π–<i>A</i> curve for C<sub>18</sub>ANA depending on the temperature. The interaction
between C<sub>18</sub>ANA molecules was measured by Fourier transform
IR spectrometry and Brewster-angle microscopy. As an extension of
the study, the trajectory of reciprocating motion could be determined
by writing with a camphor pen on the C<sub>18</sub>ANA monolayer
Robust Surface Plasmon Resonance Chips for Repetitive and Accurate Analysis of Lignin–Peptide Interactions
We have developed novel surface plasmon
resonance (SPR) sensor
chips whose surfaces bear newly synthesized functional self-assembled
monolayer (SAM) anchoring lignin through covalent chemical bonds.
The SPR sensor chips are remarkably robust and suitable for repetitive
and accurate measurement of noncovalent lignin–peptide interactions,
which is of significant interest in the chemical or biochemical conversion
of renewable woody biomass to valuable chemical feedstocks. The lignin-anchored
SAMs were prepared for the first time by click chemistry based on
an azide–alkyne Huisgen cycloaddition: mixed SAMs are fabricated
on gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethylene
oxide) disulfides and then reacted with azidated milled wood lignins
to furnish the functional SAMs anchoring lignins covalently. The resulting
SAMs were characterized using infrared reflection–absorption,
Raman, and X-ray photoelectron spectroscopies to confirm covalent
immobilization of the lignins to the SAMs via triazole linkages and
also to reveal that the SAM formation induces a helical conformation
of the ethylene oxide chains. Further, SPR measurements of the noncovalent
lignin–peptide interactions using lignin-binding peptides have
demonstrated high reproducibility and durability of the prepared lignin-anchored
sensor chips