Moving-window Two-dimensional Correlation 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.

Research on the secondary structure and hydration water around human serum albumin induced by ethanol with infrared and near-infrared spectroscopy

Given the role of ethanol played in the precipitation of various proteins, it is of great significance for the refined purification of proteins to understand the mechanism of protein secondary structure and hydration effect under the ethanol perturbation. Infrared (IR) spectroscopy and near-infrared (NIR) spectroscopy combined with chemometrics and aquaphotomics were utilized to get a generalized picture of the second structure of human serum albumin (HSA) and the surrounding hydrogen bond network of water after perturbation with different concentrations of ethanol ranging from 0% to 45% (v/v). The two-dimensional correlation (2DCOS) and moving window two-dimensional correlation analysis (MW-2DCOS) of IR spectroscopy provide evidence that the native structure of HSA was stabilized by the formation of α-helical structure at a low concentration of ethanol. However, the formation of intermolecular β-sheet structure by increasing ethanol is an important reason for the aggregation and precipitation of HSA. The analysis of NIR spectroscopy with the McCabe-Fisher method and aquaphotomics showed that free hydrogen bonded water was dynamic and fluctuating, 0%-20% ethanol could enhance the hydrogen bonded water cluster while the increasement of ethanol from 20% to 45% would lead to the formation of weak hydrogen bonded water cluster. These measurements provide a novel perspective on the relationship between ethanol and HSA, which is useful for maintaining activity and improving purity during the purification of proteins or other biological macromolecules.

Binding characteristics of Pb and Zn to low-temperature feces-based biochar-derived DOM revealed by EEM-PARAFAC combined with general and moving-window two-dimensional correlation analyses.

Pyrolysis carbonization of human feces has shown potential for converting feces biomass into a soil amendment. However, little is known about the interactions of DOM derived from feces-based biochar produced at low-temperature with heavy metals (HMs). In this study, the binding properties of Pb(II) and Zn(II) with DOM derived from feces-based biochar produced at low pyrolysis temperatures were investigated using EEM-PARAFAC combined with general, and moving-window two-dimensional correlation analyses (2D-COS). The results revealed that DOM from biochar produced at 280°C exhibited a higher Pb(II) and Zn(II) affinity and more binding sites than DOM produced at 380°C. The fulvic-like and humic-like components exhibited obvious fluorescence quenching after the heavy metal addition, and the complexes formed with Pb(II) and Zn(II) were more stable. C-H groups exhibited the fastest response to Pb(II) and Zn(II) binding in the FB280 DOM, while the COO- groups of carboxylic acids in the FB380 DOM exhibited the fastest response to Pb(II) and Zn(II). Moreover, the mutation concentration range of components and functional groups in DOM, as analyzed by MW2D-COS, was greater for Zn(II) than for Pb(II). These results provide a more detailed molecular-level understanding of the interaction mechanisms between heavy metals and feces-based biochar-derived DOM and the effect of HM concentration on DOM binding. Further, these results will help to provide a reasonable reference for feces management and feces-based biochar in controlling soil HMs.

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.

Mechanism of cellulose regeneration from its ionic liquid solution as revealed by infrared spectroscopy

Dissolution followed by regeneration is a typical processing route to cellulose, which triggers much attention in the research of regeneration mechanism, especially for the new solvent ionic liquids (ILs). It has been known that H-bond (HB) interaction between IL and anti-solvent through double diffusion triggers the cellulose regeneration. The structural change including H-bonds transformation mainly during regeneration process is still unclear, however. In the present work, a device for in situ characterization of infrared spectroscopy was set up to monitor the cellulose regeneration from microcrystalline cellulose (MCC)/1-ethyl-3-methylimidazolium acetate ([Emim]Ac) solution. With the help of time-dependent infrared spectroscopy combined with two-dimensional spectral analysis, that is perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and generalized two-dimensional correlation spectroscopy (2DCOS), the mechanism of cellulose regeneration from MCC/[Emim]Ac solution as water diffusion was revealed. We proposed a two-stage model. The diffusion of the free [Emim]Ac and water contributes to the structural changes occurred at the former stage. Water interacts with free IL to form HB W-IL in one hand, and with non-H bonded hydroxyl groups on cellulose to form HB C-W in another hand. HB C-IL is destroyed as water diffusion further at the later stage. Continuous HB C-W is constructed, accompanied by more HB W-IL formation between released anion of [Emim]Ac and water. No crystallization or aggregation of cellulose other than improved regularity of the chain arrangement is revealed by infrared spectroscopy. This study provides a new testing technique for the characterization of H-bonds structures of cellulose on the one hand. On the other hand, it is conductive to the in-depth understanding of the regeneration mechanism of cellulose in ionic liquid systems. 1. A device for in situ characterization of infrared spectroscopy was set up for the research on the cellulose regeneration from MCC/[Emim]Ac solution. 2. Two dimensional spectral analysis including perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and generalized two-dimensional correlation spectroscopy (2DCOS) was used to monitor the H-bonds changes during regeneration process. 3. The characteristic bands located at 3128, 3190, 3367, and 3557 cm −1 was assigned to the H-bonds between water (W), ionic liquid (IL), and cellulose (C), that is HB W-W , HB W-IL , HB C-IL , and HB C-W successfully. 3. A two-stage model involving destruction and reconstruction of H-bonds was proposed for the cellulose regeneration mechanism. HB C-W and HB W-IL are formed on the basis of the destruction of HB C-IL and HB W-W .

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.

Binding characteristics of copper onto biochar-derived DOM using general, heterospectral and moving-window two-dimensional correlation analyses

Dissolved organic matter released from biochar (biochar-derived DOM, BDOM) could dominate the environmental behavior and fate of trace metals by forming BDOM-metal complexes. Here general, heterospectral as well as moving-window (MW) two-dimensional correlation spectroscopy (2DCOS) analyses of synchronous fluorescence and Fourier transform infrared spectra were employed to explore the heterogeneous binding characteristics between sludge BDOM and Cu(II). The results revealed that Cu-BDOM binding first occurred in the fulvic-like (368–380 nm), then humic-like (428 nm) fluorescent fractions, followed by infrared groups of phenolic hydroxyl groups, carboxylate, COH of polysaccharide groups, CC of aromatic carbon, CH of aliphatics and COC of aliphatic ethers. The binding affinity of the hydrophilic groups was stronger than that of hydrophobic groups in BDOM towards Cu(II). Fluorescence components in BDOM played a decisive role in the binding of Cu(II) with trace concentration (1 μM), while infrared functional groups made a substantial contribution in the complexation of Cu(II) with higher concentration (10–100 μM). The concentration of final configuration transformation point (11.7 μmol/mg in this study) by MW2DCOS analysis was suggested as an actual binding threshold that was helpful for evaluating their environmental behaviors.

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.

The effects of pH on the structure of polystyrene-nano manganese dioxide composites

Loading nano manganese dioxide (NMO) on the surface of polymers change the pH of point zero charge (pHPZC) of the dioxide. In this work, a polystyrene-NMO composite was prepared and the effects of pH from 1 to 14 on its structural and morphological properties were investigated. Moving-window, and perturbation-correlation moving-window two-dimensional correlation spectroscopies were used to analyze the pH-dependent Fourier transform infrared spectra of the composite. The auto correlation showed a peak value around pH=4 corresponding to the pHPZC of the composite, and another peak value around pH=9, which was assigned to change in the NMO structures. X-ray diffraction patterns and scanning electron microscopy further confirmed the changes at both pH=4 and pH=9 that were accompanied by a change in the morphology and crystalline structures of the composite. Moving-window and perturbation-correlation moving-window two-dimensional correlation spectroscopies are powerful tools in finding overlapped, weak, and hidden peaks along the spectral direction and could be used to locate the pHPZC of solid materials.

Binding Characteristics of Copper Onto Biochar-Derived Dom Using General, Heterospectral and Moving-Window Two-Dimensional Correlation Analyses

Binding Characteristics of Copper Onto Biochar-Derived Dom Using General, Heterospectral and Moving-Window Two-Dimensional Correlation Analyses

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.

Vibrational Dynamics of Carbamazepine: Studies Based on Two-Dimensional Correlation Spectroscopy and X-ray Diffraction.

Fourier transform infrared spectroscopy as well as X-ray diffraction (XRD) were employed to thoroughly study phase transitions taking place during heating-cooling-heating cycle of carbamazepine (CBZ), a well known and commonly used antiepileptic drug. Both techniques revealed cold crystallization taking place during second heating. Moreover, XRD studies for the first time proved the coexistence of CBZ (form I) and iminostilbene (product of the degradation of CBZ) after a heating-cooling cycle. Moving window two-dimensional correlation (MW 2D-COS) spectroscopy and two-dimensional correlation spectroscopy were shown to be effective tools to reveal phase sequences and to provide information about the order of sequential changes of bands' intensities during each phase transition, respectively.

Study on thermal behavior of regenerated micro-crystalline cellulose containing slight amount of water induced by hydrogen-bonds transformation

Cellulose exhibit an excellent ability to adsorb water because of its strong hydrophilicity. The effect of water present in natural cellulose on the structure and thermal property has been paid attention. However, the influence is not clear on the cellulose after regeneration, in the process of which a large amount of water is usually used. In the present study, two important thermal behavior of water-loss and oxidation respectively in the temperature range of 20–165 °C and 165–300 °C was identified in the heating process of the regenerated microcrystalline cellulose (MCC) with the water content of 2.4 wt%. By using perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy combined with generalized 2D correlation spectroscopy (2DCOS), the successive changes in the physical loss of water, the initial inter- and intrachain H-bonds weakening, and the formation of the weak/free H-bonds are illustrated during the first process. While continuous development of the weak/free H-bonds network and the transition from the OH groups within H-bonds to the CO group are closely linked in the subsequent oxidation process. Furthermore, it is found that a higher crystallinity and a lower water-content can be obtained in the sample after high-temperature annealing. Thus prepared MCC go through the same two stages but with high-temperature shift of ca. 10 °C. The structural changes in H-bonds correlated to the thermal behavior mentioned above exhibit a high-temperature shift correspondingly. Temperature-dependent WAXD spectra reveals that the higher thermal stability of the sample is contributed from the structural regularity and the high crystallinity of the regenerated cellulose II improved by decreased water content. Our results indicate that water existence should be considered in the process of the preparation and industrialization of cellulose.

Plasma protein adsorption on TiO2 nanoparticles: Impact of surface adsorption on temperature-dependent structural changes

Protein adsorption on metal oxide nanoparticle surfaces is crucial to the behavior of oxide nanoparticles in biological systems. In this study, attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy was used for the first time to probe differences in the temperature-dependent conformational changes of two plasma proteins, bovine serum albumin (BSA) and fibrinogen (Fib), in solution and adsorbed on titanium dioxide nanoparticle (ca. 20 nm in diameter) surfaces. ATR-FTIR spectra and autocorrelation moving window two-dimensional correlation (MW2D) spectroscopy were used to identify the denaturation temperature range of these two proteins in aqueous solution and adsorbed. Generalized two-dimensional correlation spectroscopy (2DCOS) was done to investigate the protein unfolding pathway. The results show that the thermostability of BSA changed when adsorbed on the surface whereas there was no difference for solution phase Fib and adsorbed on TiO2. The most notable fact was that solution BSA underwent significant structural changes upon adsorption whereas adsorbed Fib did not. Upon heating adsorbed BSA, no further changes occurred while BSA in solution thermally denatured. In contrast, solution and adsorbed Fib had identical denaturation temperatures and similar sequential secondary structural changes with increasing temperature. These studies show quantitatively, for the first time, that there are differences in the temperature-dependent structural changes of proteins adsorbed on nanoparticles surfaces and these changes depend on the initial interaction with the nanoparticle surface. Overall, the results of this study provide new insights into understanding the effects of temperature on the structure of adsorbed protein on nanoparticle surfaces and the range of different behaviors that can occur.