Moving-window Two-dimensional Correlation Spectroscopy Research Articles

Composition and structure analysis of different depths in the stratum corneum using confocal Raman microscopy combined with two-dimensional correlation spectroscopy

The chemical composition and structure of the stratum corneum (SC) play a crucial role in the skin barrier function. Therefore, accurately determining the SC thickness and studying the changes in lipid and keratin structure and distribution within it are key aspects of skin barrier research. Currently, there are limited analytical tools and data analysis methods available for real-time and online studies of SC composition and structural changes. In this study, we focus on depth as a perturbation and employ confocal Raman microscopy combined with moving-window two-dimensional correlation spectroscopy (MW2D) technique to investigate the SC thickness. Additionally, we employ confocal Raman microscopy combined with perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) to precisely characterize the stratification of the SC. Furthermore, the two-dimensional correlation spectroscopy (2DCOS) method is utilized to examine the content of various conformations in the keratin secondary structure within the SC, as well as the subtle interrelationships between lipid and keratin structures.

Interactions between cellulose and lignin during pyrolysis: Evolutions of condensed-phase functional groups and gas-phase volatile fraction

Understanding cellulose-lignin interactions during biomass pyrolysis is important to improve the overall product distribution and quality. In the current study, the condensed-phase cellulose-lignin interactions during biomass pyrolysis from 100° to 600°C were systematically investigated with in-situ diffuse reflectance infrared Fourier transform spectroscopy and modified perturbation correlation moving-window two-dimensional correlation spectroscopy. It was found that compared to the individual component pyrolysis, the decomposition peak, evident by thermogravimetric analysis, of cellulose-lignin co-pyrolysis became wider and shifted to higher temperature range. The cellulose-lignin interactions further promoted the formations of char, and H2O, CH3/CH2, CO, aromatic-containing compounds. With simultaneous IR identification of gaseous products and condensed-phase remaining, the detailed interaction mechanism was elucidated as: 1) hydrogen donation from cellulose hydroxyl to lignin Cα could promote the lignin rearrangement at low temperature range through quinone methide structure; 2) the reactive species from homolytic cracking of lignin could abstract hydrogen from CH/CH2 groups of cellulose to generate phenolic compounds; 3) dehydration reactions of cellulose was therefore enhanced to promote char formation.

PCMW2D and 2D Raman correlation spectroscopy evidence for presence of spin-phonon coupling in hexagonal LuMnO3

Two-dimensional correlation spectroscopy (2D-COS) and perturbation-correlation moving window two-dimensional correlation spectroscopy (PCMW2D) analysis are performed on the temperature-dependent Raman spectra of hexagonal LuMnO3 single crystal. Under the resonance with the on-site Mn d-d transitions, the correlation between the phonons which are relate to the vibration of Mn ions’ bonds and spin-excitation peaks suggest a strong spin-phonon coupling in LuMnO3. The PCMW2D results clearly show that the significant change in phonons and spin-excitation peaks occurs around the Néel temperature and the spin reorientation transition. The multiple components in the broad spin-excitation peaks also suggest variations in spin symmetries in the ground state. Furthermore, we propose that the 2D-COS and PCMW2D Raman correlation spectroscopies provide a simple and powerful method for investigating the couplings and the transitions, which would be very important for understanding systematically the magnetoelectric properties of multiferroic materials.

Applying second derivative synchronous fluorescence spectroscopy combined with Gaussian band fitting to trace variations of DOM fractions along an urban river

Synchronous fluorescence spectroscopy (SFS) combined with Gaussian band fitting, two-dimensional correlation (2D-COS) and perturbation-correlation moving-window two-dimensional (PCMW2D) can provide an excellent mothed to extract fluorescent components of dissolved organic matter (DOM) and reveal its variations in an urban river. Fifteen water samples were collected from the Anyanghe River, which flew across the town, urban, and rural regions. Five peaks (peak1 tyrosine-like, peak2 tyrosine-like, peak3 tryptophan-like, peak4 microbial humic-like, peak5 fulvic-like) were extracted using the Gaussian Amp model from the SFS in the river, while the peak1 only occurred in the rural region. The microbial humic-like in the town region accounting for 50.02 % was the representative substance. The tyrosine-like dominated in the rural regions, for its percentage range was 62.26 %-75.78 %. The average percnetage of tyrosine-like (29.77 %) in the urban region was similar to that of the tryptophan-like (21.86 %), microbial humic-like (25.56 %), and fulvic-like (22.82 %). Based on the two-dimensional correlation, the variation order of DOM fractions in the town and urban regions was tryptophan → tyrosine → microbial humic → fulvic, and the variation order in the rural region was tyrosine → tryptophan → microbial humic → fulvic. This indicated that the changing trend of DOM fractions existed from the labile protein-like to the stable humus in the whole river. According to the perturbation-correlation moving-window two-dimensional correlation spectroscopy, the spectral intensity of tyrosine-like should be linear increase in the town and urban regions, and concave increase in the rural region. The spectral intensity trend of tryptophan-like mainly was linear increase in the whole river. And the intensity of microbial humic-like showed the rough convex increase in the whole river. The trend of the fulvic-like in the town and rural regions was similar to the microbial humic-like. However the fulvic-like intensity in the urban region exhibited a trend from the concave increase to the convex increase, which was obviously different from the tyrosine-like, tryptophan-like and microbial humic-like. This attribute that the untreated domestic sewage in the urban region could discharge into the river. Therefore, for small amounts of samples, the SFS combined with Gaussian band fitting, 2D-COS and PCMW2D can be used as a powerful tool to investigate fluorescent components of DOM, and reveal their variations along the river.

Applying EEM-PARAFAC combined with moving-window 2DCOS and structural equation modeling to characterize binding properties of Cu (II) with DOM from different sources in an urbanized river

Dissolved organic matter (DOM) in aquatic environment distinctly affects the behavior and fate of heavy metals via complexation, while the interfacial mechanisms and processes are still lacking in detail. Here, Cu (II) binding characteristics of DOM originated from hilly (NDOM), rural (RDOM) and urban (UDOM) regions in an urbanized river was explored by fluorescence excitation-emission matrix spectroscopy (EEM) combined with principal component coefficients, parallel factor analyses (PARAFAC), moving-window two-dimensional correlation spectroscopy (MW2DCOS) and structural equation modeling (SEM). Eight components were extracted from the titrants through EEM-PARAFAC, i.e., phenol-like substance (C1), tyrosine-like substance (C2), visible tryptophan-like substance (C3), ultraviolet tryptophan-like substance (C4), recent biological production (C5), wastewater-derived organic matter (C6), microbial humic-like substance (C7) and fulvic-like substance (C8). Interestingly, NDOM only contained C1, C3, C5 and C8, while nearly all components were found in RDOM (except for C2) and UDOM (except for C4). The f value of C1 (1.239) in NDOM was much higher than those in RDOM (0.134) and UDOM (0.115), so was of C8. It indicated that phenol-like and fulvic-like derived from autochthonous sources exhibited great binding ratios in the complexation with Cu (II). Moreover, C3 and C5 from UDOM exhibited higher f values (0.591 and 1.983) than those from NDOM and RDOM, suggesting that Cu (II) has a great binding capacity on protein-like from domestic and industrial wastewater. The MW2DCOS revealed that phenol-like and protein-like in NDOM and RDOM were essential for the binding of 160 μmol L−1 Cu (II), whereas fulvic-like in NDOM and UDOM could react significantly with 10 μmol L−1 Cu (II). Based on SEM, Cu (II) concentration had a negative direct effect on the fluorescence intensity of C7 or C8, whereas it showed an indirect positive effect on C7 or C8 through influencing C5, so was C6. It suggested that Cu (II) showed an indirect positive effect on the C8. This study might present a further comprehend of the environmental behaviors of Cu (II) in rivers.

Experimental and theoretical study on the evolution of functional groups in cellulose char during oxidative pyrolysis

Oxidative pyrolysis of biomass is a promising substitute technology for conventional pyrolysis and is also crucial to the related degradation process of biomass materials such as aging, combustion, fire hazard, etc. The intertwining of heterogeneous oxidation and homogeneous oxidation of biomass and its derivative muffles the detailed mechanism of oxidative pyrolysis. To unravel the mechanism of heterogeneous oxidation in the cellulose condensed phase, the real-time evolution of functional groups in cellulose char during oxidative pyrolysis was probed by the in situ diffuse reflectance infrared Fourier transform technology, which is further analyzed by a homemade semi-quantitative analysis program based on the perturbation-correlation moving-window two-dimensional correlation spectroscopy and two-dimensional correlation spectroscopy. The experimental results show the obvious promotion effects of O2 on the direct oxidation of hydroxyls to unconjugated CO and the cleavage of COC in the development stage between the temperatures of the initiation and the maximum rate of weight loss, resulting in the lowered thermostability and devolatilization of cellulose. At elevated temperatures, the hydroxyls and CO were further oxidized by O2 into carboxyls, and released at around 450 °C in the last decline stage, performing the second peak of the derivative thermogravimetry curve for oxidative pyrolysis. Through density functional theory calculation of the hydroxyl oxidation, a low-temperature oxidation mechanism competitive with the transglycosylation and other dehydration reactions was proposed. Its rate is determined by the initiating H abstraction, which highly depends on the spin density (population) for the transition state and pyrolysis temperature.

Cold-crystallization and physical stability of glassy carbamazepine

Physical stability as well as isothermal and non-isothermal cold-crystallization of quench-cooled drug carbamazepine (CBZ) was studied using powder X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FT-IR). Three phase transitions on heating were reported: glass softening (∼329 K), cold-crystallization (∼389 K) and melting (∼463 K). XRD results and evaluation of DSC data using Adam-Gibbs model extended to the glassy state revealed, that the amorphous sample of CBZ remains physically stable for 8 h at room temperature (i.e. about 30 K below glass transition temperature). Isothermal XRD measurements showed that amorphous CBZ is prone to rapid nucleation even about 50 K below the glass transition, but crystal growth is considerably slowed down in such conditions. Fragility parameter m was calculated and quench-cooled CBZ was identified as moderately fragile glass. FT-IR measurements coupled with moving-window two-dimensional correlation spectroscopy proved that changes in vibrational dynamics accompanied all phase transitions. Considerable strengthening of hydrogen bonding was observed during cold crystallization.

Comprehensive utilization of agricultural wastes by combined wet torrefaction and pyrolysis

Wet torrefaction (WT) is promising to convert moist biomass into hydrophobic fuel with higher heating value and energy density. The current study investigated the comprehensive utilization of biomass with combined wet torrefaction and pyrolysis. Characterizations of both torrefied solid and liquid were achieved to understand the evolution of physicochemical properties during WT. The composition analysis showed that the torrefied liquid was a promising candidate for furfural and organic acid production, and could affect the WT solid properties as well. Torrefied solid products with less reactive ash, larger surface area, and higher crystallinity were obtained. And the AAEM removal by WT could be enhanced with corncob due to its hemicellulose abundance. Followed by WT, techniques including TGA, py-GC/MS and py-in-situ DRIFT were used for pyrolysis investigation of torrefied solids. It was found that WT could change the activation energy of cellulose decomposition mainly due to the removal of AAEMs. The energy required for levoglucosan production could be mildly reduced, resulted from enlarged pore structure and better cellulose accessibility. Because of the removal of reactive AAEMs and enhanced product transportation, levoglucosan yield reached 55 wt% based on cellulose content, even with some inert AAEMs left in torrefied solids. The yields of phenols without methoxyl groups were also enhanced by WT. The perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) analysis of the in-situ DRIFT results further proved that WT could significantly change the pyrolysis pathway of cellulose from dehydration and condensation to hydrogen bond dissociation and glycosidic bond cleavage.

In situ evolution of functional groups in char during cellulose pyrolysis under the catalysis of KCl and CaCl2

A combination of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) and two-dimensional correlation spectroscopy (2D-COS) was used to reveal the catalytic mechanism of KCl and CaCl2 on cellulose char evolution during slow pyrolysis. Pretreatments of the one-dimensional spectra ensure the semi-quantitative analysis of the evolution of functional groups in pyrolysis char, which invoked principal component analysis followed by a Butterworth filter for denoising and extended multiplicative scatter correction. Through the differential processing of the absolute changes, the char evolution product was divided into ‘char rearrangement’ and ‘char devolatilization’ processes containing a high contribution from chemical reactions and physical migration, respectively. The ‘char rearrangement’ of cellulose pyrolysis consists of four stages, i.e. the budding, development, climax and decline stages, which were dominated by H-bond network reconfiguration, the consumption of C–O–C and OH, homogeneous devolatilization and aromatization, respectively. The uppermost influence of the two salts on the pyrolysis is the relationship alteration of C–O–C cleavage, dehydration reactions and ‘char devolatilization’. For neat, KCl-loaded and CaCl2-loaded cellulose, the unsaturated bonds were formed in the light reaction intermediate, heavy reaction intermediates and cellulose chain, respectively. Especially, the cleavage of most C–O–C following dehydration reactions conduced a shoulder peak in the differential thermogravimetry curve before the maximum weight loss rate of CaCl2-loaded sample. Due to the alteration, the pyrolysis was advanced but slowed down by the high content of unsaturated bonds in char. This study provides a powerful tool for the in situ semi-quantitative analysis of char evolution during the non-catalytic and catalytic thermo-chemical conversion of solid fuels and waste, and the results benefit to both biomass pyrolysis mechanism revelation and industrial production of biochar.

Insight into oxidation and adsorption treatment of algae-laden water: Algal organic matter transformation and removal

The efficacy of applying gas phase surface discharge non-thermal plasma (NTP) combined with anion-exchange processes for algae-laden water treatment was evaluated. The excitation-emission matrix fluorescence and parallel factor analyses coupled with two-dimensional correlation spectroscopy (2DCOS), hetero-2DCOS, and perturbation correlation moving window two-dimensional correlation spectroscopy of ATR-FTIR and synchronous fluorescence spectra were used to elucidate variation in the functional groups and algal organic matter (AOM) conformations during the NTP oxidation process. The intracellular compounds released from the lysis of algal cells could be effectively degraded and mineralized, which was accompanied by a rapid decrease in chlorophyll a, turbidity, and particle size. The organic nitrogen could be instantly converted to NH4+-N during NTP oxidation and then oxidized to NO3−-N with negligible NO2−-N accumulation, resulting in a continuous increase in NO3−-N. The final concentration of the toxin microcystin-LR was far lower than the standard for drinking water (1.0 μg/L). The chromophoric functional groups were destroyed over time, and the aromatic carbon was gradually converted to aliphatic carbon via NTP oxidation. The transition times of functional groups and fluorescent fractions were all in the range of 10–20 min. In the post-NTP treatment, the L20 resin could remove 38.4% of DOC, 83.4% of NO3−-N, 73.2% of TN, and 63.8% of TP in the treatment loading of 600 resin volume and exhibited high reusability during 10 adsorption–desorption cycles. Overall, NTP oxidation combined with resin adsorption might be a potential candidate to address algae-laden water and minimize its adverse effects thereafter.

Protein-sugar interaction between Asini Corii Colla (donkey-hide gelatin) and Lycii Fructus (goji berry) evaluated by temperature-resolved ATR-FTIR and moving-window two-dimensional correlation spectroscopy

Using Lycii Fructus extract (LFE) as a complementary ingredient to ameliorate the poor taste of Asini Corii Colla (ACC) is a promising way to produce ACC-based formula dietary supplements with pleasant taste and combinational functionalities. However, the possible interactions between ACC proteins and LFE sugars should be concerned. Temperature-resolved ATR-FTIR and moving-window two-dimensional correlation spectroscopy (MW2D-COS) were employed in this research to examine the heat-induced changes of ACC-LFE mixtures with different mass ratios. When the mixture containing LFE half of or equal to ACC, the lyophilized LFE sugars acted as amorphous matrix to stabilize the secondary structures of ACC proteins and raised the protein transition temperature from 125 °C (pure ACC) to 133 °C and 138 °C. But the interactions between LFE sugars and ACC proteins in the mixture containing LFE twice as much as ACC are complex, which decrease the protein transition temperature to about 115 °C. Therefore, the ACC-to-LFE mass ratio is crucial to the stabilization and functionality of ACC-LFE formula dietary supplements. This research also shows the potential of temperature-resolved ATR-FTIR and MW2D-COS in assessing the formula compatibilities of food or pharmaceutical preparations.

Hydrogen bonding in micro-phase separation of poly(polyamide 12-block-polytetrahydrofuran) alternating block copolymer: Enthalpies and molecular movements

The role of hydrogen bonds to the micro-phase separation process of poly(polyamide 12-block-polytetrahydrofuran) alternating block copolymer upon cooling (170–15°C) was investigated by in situ FTIR spectra combined with scaling moving-window two-dimensional correlation spectroscopy (scaling-MW2D) and the generalized 2D correlation analysis. The micro-phase separation process of polyamide elastomer was found to be composed of two processes via the combination of scaling-MW2D and differential scanning calorimetry (DSC). The first process (process A, 138–80°C) is the initial process of the micro-phase separation of the polyamide elastomer, and the second process (process B, 80–35°C) is the completion process of the micro-phase separation. The method of calculating the generation enthalpy of hydrogen bonds from in situ FTIR was also successfully established via Van’t Hoff analysis, and the above two processes were further confirmed through the enthalpy of hydrogen bonding. The generalized 2D correlation analysis was performed for these two processes. The results of 2D correlation analysis revealed that the impetus for the process A was the generation of the disordered hydrogen bonds between the CO and N–H groups in the PA12 blocks, the PA12 crystallization induced by the formation of the ordered hydrogen bonds is the key step of the process B.

Phase-Specific Raman Analysis of n-Alkane Melting by Moving-Window Two-Dimensional Correlation Spectroscopy.

We use moving-window two-dimensional correlation spectroscopy (MW-2DCOS) for phase-specific Raman analysis of the n-alkane (C21H44) during melting from the crystalline solid phase to the intermediate rotator phase and to the amorphous molten phase. In MW-2DCOS, individual peak-to-peak correlation analysis within a small subset of spectra provides both temperature-resolved and spectrally disentangled Raman assignments conducive to understanding phase-specific molecular interactions and chain configurations. We demonstrate that autocorrelation MW-2DCOS can determine the phase transition temperatures with a higher resolving power than commonly-used analysis methods including individual peak intensity analysis or principal component analysis. Besides the enhanced temperature resolving power, we demonstrate that asynchronous 2DCOS near the orthorhombic-to-rotator transition temperature can spectrally resolve the two overlapping peaks embedded in the Raman CH2 twisting band in the orthorhombic phase, which had been only predicted but not observed due to thermal broadening near the melting temperature.

A new way to interpret perturbation-correlation moving-window two-dimensional correlation spectroscopy: probing the dynamic interaction of ionic liquid 1-ethyl-3-methylimidazolium acetate to absorb atmospheric water.

A rule to interpret perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) was developed. Compared with Morita's rule, this proposed rule retains the ability to obtain interval features (i.e., monotonicity, concavity, and convexity) and adds the function to quickly and accurately determine both tipping points (i.e., local extrema and inflection points). It could be described as follows: the local extrema and inflection point could be determined by the zero point with an opposite sign on its left and right side in ΠΦ (synchronous PCMW2D) and ΠΨ (asynchronous PCMW2D), respectively. Specifically, a negative left (right) side and a positive right (left) side of point indicates a local minimal (maximal) value. By using the rule to interpret ΠIR (PCMW2D infrared spectroscopy) of 1-ethyl-3-methyl-imidazolium acetate [EMIM][Ac]-atmospheric water (H2O) as a function of time, we found that the atmospheric water was absorbed only into the bulk of [EMIM][Ac] before 150 min by hydrogen-bonding interaction, only onto the surface of [EMIM][Ac] after 330 min by van der Waals force, and both to the bulk and surface of [EMIM][Ac] between 150 and 330 min by hydrogen-boding and van der Waals force simultaneously. The proportion of bulk water sorption and surface water sorption to [EMIM][Ac] was about 4 and 96%, respectively.

Tracking the curing process of automotive paint by moving-window two-dimensional infrared correlation spectroscopy and principal component analysis

Moving-window two-dimensional correlation spectroscopy (MW2DCOS) and principal component analysis (PCA) were combined to interpret the time serial infrared spectra. The curing process of an automotive paint sample was tracked by attenuated total reflection Fourier transform infrared spectroscopy. Score plots of the first and second principal components showed that the curing process contained three stages. Meanwhile, the loading spectra indicated that the solvent was a mixture of aromatic compounds. Absorption peaks which changed significantly in each stage were revealed by auto-peak MW2DCOS. Furthermore, point-line and point-point MW2DCOS demonstrated the time-resolved relationship between absorption peaks from toluene, xylene and resin. In summary, the evaporation of toluene was the first stage of the curing process of this automotive paint sample. Next, the mixture of o-xylene, m-xylene and p-xylene began to evaporate in the second stage. After the evaporation of the solvent, the solid paint membrane was formed. For the interpretation of the time serial spectra, PCA is useful to estimate the number of significant chemical components and to find out the important turning points of the process, while MW2DCOS can show the changes of the spectral peaks and the relationship between them step by step. The combination of PCA and MW2DCOS is very interesting to extract and display the time-resolved information in the time serial spectra.

Water Uptake of Poly(2-N-Alkyl-2-Oxazoline)s: Temperature-Dependent Fourier Transform Infrared (FT-IR) Spectroscopy and Two-Dimensional Correlation Analysis (2DCOS)

A library of poly(2-oxazoline)s with varying length of the alkyl side-chain has been investigated by variable-temperature Fourier transform infrared (FT-IR) spectroscopy. These polymers are suitable for studies of structure-property relationships as their cationic ring-opening polymerization and the relatively facile monomer synthesis enable a control of the molecular structure. In this contribution, the number of carbon atoms in the linear side-chain is systematically varied from a short methyl to a long nonyl group. Previous studies showed that the sample library can be split in two groups: poly(2-oxazoline)s with a short side-chain (methyl-, ethyl-, and isopropyl-) exhibit hygroscopic behavior, while those with longer side-groups (butyl- and longer) were found to be semi-crystalline. To gain further insight into the mechanisms of hydrogen bonding and crystallization, temperature-dependent infrared (IR) spectroscopy has been applied in the current study. The processes involved have been monitored by generalized two-dimensional correlation spectroscopy (2DCOS) and perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) in the C=O stretching region around 1645 cm(-1). These advanced analysis techniques provided valuable additional information on the material behavior during heating. As water is removed from the samples in the course of the heating process, it was possible to clearly distinguish between "loosely associated" and hydrogen-bonded water. Furthermore, the melting process of the semi-crystalline samples could be depicted. For the poly(2-isopropyl-2-oxazoline) even a crystallization process could be monitored in the temperature range between glass transition and melting.

Two-Step Curing Reaction of Epoxy Resin Studied by Thermal Analysis and Infrared Spectroscopy

A curing reaction of bisphenol A diglycidyl ether epoxy resin with 4,4'-diaminodicyclohexyl methane hardener was investigated by means of modulated differential scanning calorimetry (MDSC) and infrared (IR) spectroscopy. MDSC observation revealed that the curing process of the resin occurred in two steps. Mid-infrared and near-infrared spectra of the resin were measured as a function of temperature. The obtained spectra were analyzed by perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D-COS). The first step was revealed as a polymerization reaction among the oxirane group and primary and secondary amine groups, followed by etherification; the second step of the curing process occurred in the vicinity of the gelation point and was characterized by the growth of a three-dimensional cross-linking structure with tertiary amine and etherification of the hydroxyl group.

Effect of baseline drift on perturbation–correlation moving-window two-dimensional correlation spectroscopy

Effect of baseline drift on perturbation–correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy was investigated using a set of simulated spectra. It was revealed that an increase or decrease of a baseline intensity leads to a positive or negative synchronous PCMW2D correlation baseline and an increase or decrease of an actual peak intensity on the baseline drift leads to a positive or negative synchronous PCMW2D correlation peak or valley on the correlation baseline, respectively.

NIR spectroscopic study of the dissolution process in pharmaceutical tablets

In this study, water penetration and the interaction between water and a pharmaceutical excipient in a tablet were investigated using near-infrared (NIR) spectroscopy and perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW-2DCS). The penetration rate of water into a tablet was mainly dependent on the porosity of the tablet and was less dependent on the type of excipient. This behavior was well described by the Lucas–Washburn theory. The PCMW-2DCS technique revealed that there are two-staged interaction changes in NIR spectra of the water–powder interactions. The first and second changes corresponded to the water–solid interaction and the dissolution of the solid, respectively. The diffusion-controlled dissolution model by Nernst well explained these results.

Temperature-Dependent Changes in Hydrogen Bonds in Cellulose Iα Studied by Infrared Spectroscopy in Combination with Perturbation-Correlation Moving-Window Two-Dimensional Correlation Spectroscopy: Comparison with Cellulose Iβ

Our recent IR study demonstrated that hydrogen-bond structure in cellulose Ibeta drastically changes around 220 degrees C (Watanabe et al. Biomacromolecules 2006, 7, 3164). In the present study, temperature-dependent IR spectra of cellulose Ialpha from 30 to 260 degrees C were analyzed by use of perturbation-correlation moving-window two-dimensional correlation spectroscopy. It was observed that as in the case of cellulose Ibeta abrupt changes in the hydrogen-bond structure occur around 220 degrees C in cellulose Ialpha. It was also revealed that although weakly hydrogen-bonded OH groups in Ibeta are stable below 230 degrees C thermal oxidation of those in Ialpha is accelerated around 220 degrees C. In this way, the present study has clarified a difference between the thermal behavior of Ialpha and that of Ibeta at the functional group level. Our result suggests that the drastic change in the hydrogen-bond structure around 220 degrees C makes cellulose Ialpha much more unstable than Ibeta.