Perturbation-correlation 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.

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.

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.

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.

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.

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.