Shigeaki Morita

Perturbation-Correlation Moving-Window Two-Dimensional Correlation Spectroscopy

A new method of analysis, perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy, is proposed. For a spectral data set collected under an external perturbation, this method provides a pair of synchronous and asynchronous two-dimensional correlation spectra plotted on a plane between a spectral variable (e.g., wavenumber) axis and a perturbation variable (e.g., temperature) axis. One of the advantages of this new correlation analysis method is that complicated spectral variation along the perturbation direction can be monitored. It has been found that the synchronous and asynchronous PCMW2D correlation spectra are similar to the first perturbation derivative and negative second perturbation derivative spectra of the original data, respectively. To demonstrate the potential of PCMW2D correlation spectroscopy, it has been applied to temperature-dependent infrared (IR) spectra of a poly(vinyl alcohol) (PVA) film. The thermal behavior of the PVA film has been revealed by the PCMW2D correlation analysis. Two characteristic cross-peaks are observed in the synchronous PCMW2D correlation spectra generated from the temperature-dependent IR spectra between the crystalline phase C–O stretching band at 1141 cm−1 and the melting temperature of 209 °C and between the amorphous phase C–O stretching band at 1095 cm−1 and another specific temperature of 233 °C. This specific temperature of 233 °C corresponds to the thermal degradation temperature due to the elimination of the hydroxyl group attached to the main chain.

Temperature-dependent structural changes in hydrogen bonds in microcrystalline cellulose studied by infrared and near-infrared spectroscopy with perturbation-correlation moving-window two-dimensional correlation analysis

Temperature-dependent structural changes in hydrogen bonds (H-bonds) in microcrystalline cellulose (MCC) were investigated by infrared (IR) and near-infrared (NIR) spectroscopy. The O–H stretching fundamentals and their first overtone bands were employed to explore the structural changes. In order to analyze the overlapping OH bands due to various H-bonds, perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy was applied to the IR and NIR data. Typical spectral variation temperatures were visualized by the PCMW2D correlation analysis. Structural changes in the strong H-bonds in MCC gradually occur in the temperature region of 25–130 °C, and they become greater above 130 °C. Both OH groups with H-bonds of intermediate strength and very weak H-bonds arise from the structural change of strong H-bonds in the temperature region of 40–90 °C, whereas the appearance of the latter OH groups with very weak H-bonds gradually becomes dominant above 90 °C. It is revealed from the present study that the glass transition at 184 °C induces the changes in the H-bonds in the Iβ and the O3–H3…O5 intrachain H-bonds. Band assignments for the O–H stretching first overtone vibration region are proposed based on the results of the PCMW2D correlation analyses.

A Study on Water Adsorption onto Microcrystalline Cellulose by Near-Infrared Spectroscopy with Two-Dimensional Correlation Spectroscopy and Principal Component Analysis

Water adsorption onto microcrystalline cellulose (MCC) in the moisture content (Mc) range of 0.2–13.4 wt % was investigated by near-infrared (NIR) spectroscopy. In order to distinguish heavily overlapping O–H stretching bands in the NIR region due to MCC and water, principal component analysis (PCA) and generalized two-dimensional correlation spectroscopy (2DCOS) were applied to the obtained spectra. The NIR spectra in four adsorption stages separated by PCA were analyzed by 2DCOS. For the low Mc range of 0.2–3.1 wt %, a decrease in the free or weakly hydrogen-bonded (H-bonded) MCC OH band, increases in the H-bonded MCC OH bands, and increases in the adsorbed water OH bands are observed. These results suggest that the inter- and intrachain H-bonds of MCC are formed by monomeric water molecule adsorption. In the Mc range of 3.8–7.1 wt %, spectral changes in the NIR spectra reveal that the aggregation of water molecules starts at the surface of MCC. For the high Mc range of 8.1–13.4 wt %, the NIR results suggest that the formation of bulk water occurs. It is revealed from the present study that approximately 3–7 wt % of adsorbed water is responsible for the stabilization of the H-bond network in MCC at the cellulose–water surface.

Variable-temperature Fourier transform infrared spectroscopic investigations of poly(3-hydroxyalkanoates) and perturbation-correlation moving-window two-dimensional correlation analysis. Part I: Study of non-annealed and annealed poly(3-hydroxybutyrate) homopolymer.

Generalized two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy were applied to explore the melting behavior of non-annealed and annealed poly(3-hydroxybutyrate) (PHB) homopolymer as studied by variable-temperature Fourier transform infrared (FT-IR) spectroscopy. The absorption band of the C=O stretching vibration was employed to investigate the structural changes during the heating process (30–200 °C). Non-annealed PHB showed a recrystallization process in the temperature range 30–120 °C. In the asynchronous 2D correlation spectrum we clearly captured the existence of two components in the crystallinity-sensitive wing of the C=O stretching mode: a well-ordered crystalline state at lower wavenumbers (1718 cm−1) and a less ordered crystalline state at higher wavenumbers (1724 cm−1). These crystallinity-sensitive bands at 1718 and 1724 cm−1, which are not readily detectable in the one-dimensional (1D) FT-IR spectra, share asynchronous cross-peaks with bands at around 1737 and 1747 cm−1 assignable to the C=O stretching absorptions due to the amorphous components. In the case of the melting process of non-annealed PHB in the temperature range 120–200 °C, it is helpful to use the PCMW2D correlation analysis, which indicates the recrystallization between 40 and 110 °C by the shift of the C=O stretching band from 1726 cm−1 to 1722 cm−1 and the sharp change to the broad amorphous C=O stretching absorption at 1747 cm−1 at the melting temperature of PHB around 190 °C. For an annealed sample of PHB only the melting behavior was observed in the PCMW2D correlation analysis by the sharp transition from the crystalline to the amorphous C=O stretching band.

Thermal Degradation of Poly(3-hydroxybutyrate) and Poly(3-hydroxybutyrate- co -3-hydroxyhexanoate) in Nitrogen and Oxygen Studied by Thermogravimetric–Fourier Transform Infrared Spectroscopy

The thermal degradation behavior of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P(HB-co-HHx), HHx = 12 mol%) has been studied under different environmental conditions by thermogravimetric analysis (TGA) Fourier transform infrared (FT-IR) spectroscopy. It is reported that at higher temperature (>400 °C) carbon dioxide and propene are formed from the decomposition product crotonic acid in a nitrogen atmosphere, whereas in an oxygen atmosphere propene oxidizes in a further step to carbon dioxide, carbon monoxide and hydrogen. It was also found that PHB and P(HB-co-HHx) have a similar thermal degradation mechanism. The analysis of the FT-IR-spectroscopic data was performed with 2D and perturbation-correlation moving-window 2D (PCMW2D) correlation spectroscopy.

Variable-Temperature Fourier Transform Infrared Spectroscopic Investigations of Poly(3-Hydroxyalkanoates) and Perturbation-Correlation Moving-Window Two-Dimensional Correlation Analysis. Part II: Study of Poly(ε-Caprolactone) Homopolymer and a Poly(3-Hydroxybutyrate)—Poly(ε-Caprolactone) Blend

In the present study, variable-temperature Fourier transform infrared (FT-IR) spectra of a poly(ε-caprolactone) (PCL) homopolymer and a poly(3-hydroxybutyrate) (PHB)-poly(ε-caprolactone) (PCL) blend were analyzed by generalized two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy. The C=O stretching vibration bands of PCL and PHB were employed to explore the structural changes in the PCL homopolymer and the PHB–PCL blend during the heating process. For the melting of PCL homopolymer in the temperature range of 50 to 70 °C, we observed in the synchronous and asynchronous 2D correlation spectra one crystalline (1724 cm−1) and one amorphous (1737 cm−1) C=O stretching vibration band, which are also detectable in the one-dimensional FT-IR spectra. This result was also confirmed by PCMW2D correlation spectroscopy. During the heating process of the PHB–PCL blend in the temperature range 30–200 °C, the PCMW2D correlation analysis provided detailed information. Thus, in the synchronous PCMW2D correlation spectrum the melting of PCL was observed in the temperature region between 30 and 70 °C. The recrystallization of PHB in the blend in the temperature range 70–120 °C was accompanied by a shift of the C=O stretching band from higher wavenumber (1724 cm−1) corresponding to an imperfect crystalline state to the lower wavenumber (1721 cm−1) characteristic of a well-ordered crystalline state. In the temperature range 120–200 °C the melting process of PHB in the blend is captured by a sharp transition from the crystalline (1722 cm−1) to the amorphous (1747 cm−1) C=O stretching band.

Release mechanisms of acetaminophen from polyethylene oxide/polyethylene glycol matrix tablets utilizing magnetic resonance imaging.

Release mechanism of acetaminophen (AAP) from extended-release tablets of hydrogel polymer matrices containing polyethylene oxide (PEO) and polyethylene glycol (PEG) were achieved using flow-through cell with magnetic resonance imaging (MRI). The hydrogel forming abilities are observed characteristically and the layer thickness which is corresponding to the diffusion length of AAP has a good correlation with the drug release profiles. In addition, polymeric erosion contribution to AAP releasing from hydrogel matrix tablets was directly quantified using size-exclusion chromatography (SEC). The matrix erosion profile indicates that the PEG erosion kinetic depends primarily on the composition ratio of PEG to PEO. The present study has confirmed that the combination of in situ MRI and SEC should be well suited to investigate the drug release mechanisms of hydrogel matrix such as PEO/PEG.

New Method for Spectral Data Classification: Two-Way Moving Window Principal Component Analysis

Two-way moving window principal component analysis (TMWPCA), which considers all possible variable regions by using variable and sample moving windows, is proposed as a new spectral data classification method. In TMWPCA, the similarity between model function and the index obtained by variable and sample moving windows is defined as “fitness”. For each variable region selected by a variable moving window, the fitness is obtained through the use of a model function. By maximizing the fitness, an optimal variable region can be searched. A remarkable advantage of TMWPCA is that it offers an optimal variable region for the classification. To demonstrate the potential of TMWPCA, it has been applied to the classification of visible–near-infrared (Vis-NIR) spectra of mastitic and healthy udder quarters of cows measured in a nondestructive manner. The misclassification rate of TMWPCA has been compared with those of other chemometric methods, such as principal component analysis (PCA), soft independent modeling of class analogies (SIMCA), and principal discriminant variate (PDV). TMWPCA has yielded the lowest misclassification rate. The result indicates that TMWPCA is a powerful tool for the classification of spectral data.

Phase Angle Description of Perturbation Correlation Analysis and its Application to Time-Resolved Infrared Spectra:

A method of spectral analysis, phase angle description of perturbation correlation analysis, is proposed. This method is based on global phase angle description of generalized two-dimensional (2D) correlation spectroscopy, proposed by Shin-ichi Morita et al., and perturbation-correlation moving-window 2D (PCMW2D) correlation spectroscopy, proposed by Shigeaki Morita et al. For a spectral data set collected under an external perturbation, such as time-resolved infrared spectra, this method provides only one phase angle spectrum. A phase angle of the Fourier frequency domain correlation between a spectral intensity (e.g., absorbance) variation and a perturbation variation (e.g., scores of the first principle component) as a function of spectral variable (e.g., wavenumber) is plotted. Therefore, a degree of time lag of each band variation with respect to the perturbation variation is directly visualized in the phase angle spectrum. This method is applied to time-resolved infrared spectra in the O–H stretching region of the water sorption process into a poly(2-methoxyethyl acrylate) (PMEA) film. The time-resolved infrared (IR) spectra show three broad and overlapping bands in the region. Each band increases toward saturated water sorption with different relaxation times. In comparison to conventional methods of generalized 2D correlation spectroscopy and global phase angle mapping, the method proposed in the present study enables the easier visualization of the sequence as a degree of phase angle in the spectrum.

Multivariate Curve Resolution Analysis on the Multi-Component Water Sorption Process into a Poly(2-methoxyethyl Acrylate) Film:

In our previous study, sorption process of water into a biocompatible polymer film, poly(2-methoxyethy 1 acrylate) (PMEA) was monitored by time-resolved in situ attenuated total reflection infrared (ATR-IR) spectroscopy [S. Morita, et al., Langmuir 23, 3750 (2007)]. In the present study, noisy and heavily overlapped O–H stretching vibrational bands of diffusing water have been analyzed from the series spectra where the spectral shapes change irregularly with time. In spite of these complications, a powerful spectral analysis technique, multivariate curve resolution (MCR) by means of alternating least squares (ALS), yielded smooth and meaningful pure component spectra and detailed kinetic sorption profiles of each component, excluding noise. Ordinary smoothing techniques and Gaussian curve fitting would not achieve these significant results. The quantification of the kinetic parameters such as amplitudes (a) and relaxation time constants (τ) is significant for the systematic development of biocompatible materials and also for revealing the mechanisms of biocompatibility of a material. Moreover, the ratios of coefficients of each component at saturation corresponded well to the values obtained by Tanaka et al. measured by gravimetric analysis. This study is the first to report the detailed concentration profile of each water component whose sorption kinetics is discussed comprehensively.