Two-dimensional Near-infrared Correlation Research Articles

Water absorption by polyamide (PA) 6 studied with two-trace two-dimensional (2T2D) near-infrared (NIR) correlation spectroscopy

The application of two-trace two-dimensional (2T2D) correlation spectroscopy to dry-treated and wet-treated PA 6 is presented to elucidate the molecular-level variation of the polymer system induced by the water absorption. A substantial level of decrease in Young modulus are observed when the PA 6 is subjected to a wet treatment. Fine details of the change in the corresponding spectral feature are examined by 2T2D near-infrared (NIR) correlation spectroscopy. The observed correlation pattern in the asynchronous correlation spectra reveals that the water molecule absorbed by the PA 6 works as a plasticizer to increase the chain mobility by disintegrating the H-bonded bridge between the PA chains especially in the amorphous region. The disintegration of the H-bonding network, in turn, deteriorate the elastic property of the PA 6. On the other hand, the increased chain mobility also triggers chain-folding of the PA chains, eventually leading to the development of additional crystalline structure. Consequently, the absorption of the water molecules essentially induces the populational change in the crystalline and amorphous structures as well as the disruption of the H-bonding between the amorphous chains.

Rheo-optical two-dimensional (2D) near-infrared (NIR) correlation spectroscopy for probing strain-induced molecular chain deformation of annealed and quenched Nylon 6 films

A rheo-optical characterization technique based on the combination of a near-infrared (NIR) spectrometer and a tensile testing machine is presented here. In the rheo-optical NIR spectroscopy, tensile deformations are applied to polymers to induce displacement of ordered or disordered molecular chains. The molecular-level variation of the sample occurring on short time scales is readily captured as a form of strain-dependent NIR spectra by taking an advantage of an acousto-optic tunable filter (AOTF) equipped with the NIR spectrometer. In addition, the utilization of NIR with much less intense absorption makes it possible to measure transmittance spectra of relatively thick samples which are often required for conventional tensile testing. An illustrative example of the rheo-optical technique is given with annealed and quenched Nylon 6 samples to show how this technique can be utilized to derive more penetrating insight even from the seemingly simple polymers. The analysis of the sets of strain-dependent NIR spectra suggests the presence of polymer structures undergoing different variations during the tensile elongation. For instance, the tensile deformation of the semi-crystalline Nylon 6 involves a separate step of elongation of the rubbery amorphous chains and subsequent disintegration of the rigid crystalline structure. Excess amount of crystalline phase in Nylon 6, however, results in the retardation of the elastic deformation mainly achieved by the amorphous structure, which eventually leads to the simultaneous orientation of both amorphous and crystalline structures.

Hydrogen/deuterium (H/D) exchange of gelatinized starch studied by two-dimensional (2D) near-infrared (NIR) correlation spectroscopy

Hydrogen/deuterium (H/D) exchange of gelatinized starch was probed by in-situ near-infrared (NIR) monitoring coupled with two-dimensional (2D) correlation spectroscopy. Gelatinized starch undergoes spontaneous H/D exchange in D2O. During the substitution, the exchange rate essentially becomes different depending on solvent accessibility of various parts of the molecule. Thus, by analyzing the change in the NIR feature observed during the substitution, it becomes possible to sort out local structure and dynamics of the system. 2D correlation analysis of the time-dependent NIR spectra reveals the presence of different local structure of the starch, each having different solvent accessibility. For example, during the H/D exchange, the D2O is first absorbed by starch molecules especially around the surface area between the starch and water, where the water molecules are weakly interacted with the starch molecules. This absorption is quickly followed by the development of HDO species. Further absorption of the D2O results in the penetration of the molecules inside the starch and eventually develops the relatively strong interaction between the HDO and starch molecules because of the presence of dominant starch molecules.

Determination of Methanol in Alcoholic Beverages by Two-Dimensional Near-Infrared Correlation Spectroscopy

ABSTRACTAn innovative method for the determination of concentration of methanol in white spirit was proposed using two-dimensional near-infrared (NIR) correlation spectroscopy in combination with multivariate calibration. A total of 38 white spirit samples were adulterated with level of methanol varying from 0.1 to 10%. A one-dimensional NIR spectra of all samples were collected. Spectral characteristics of white spirit adulterated with methanol were studied based on one-dimensional NIR spectra and two-dimensional NIR correlation spectra. The origin of 4396 cm−1 peak of methanol was verified in terms of the existence or absence of cross-peaks in synchronous and asynchronous two-dimensional NIR correlation spectra. For comparison, the quantitative analysis models were constructed to determine content of methanol in white spirit using synchronous two-dimensional NIR correlation spectra and traditional one-dimensional NIR spectra, respectively. The prediction statistics criteria for synchronous two-dimensional NIR correlation spectra using N-way partial least squares, average relative error and root mean square error, were 2.97 and 0.064%, respectively. For traditional one-dimensional NIR spectra using partial least squares method, average relative error and root mean square error of prediction were 5.3 and 0.079%, respectively. Comparison results show that the proposed new method has stronger predictive ability and can provide better results than traditional one-dimensional NIR spectra using partial least squares.

Multiple-Perturbation Two-Dimensional Near-Infrared Correlation Study of Time-Dependent Water Absorption Behavior of Cellulose Affected by Pressure

Transient water absorption by cellulosic samples manufactured under varying pressure was monitored by near-infrared spectroscopy to explore the absorption behavior affected by the pressure. A substantial level of variation of the spectral features was induced by the water absorption and changes in the pressure. The detail of the spectral changes was analyzed with a multiple-perturbation, two-dimensional (2D) correlation method to determine the underlying mechanism. The 2D correlation spectra indicated that the compression of the cellulose increased the packing density of the samples, preventing the penetration of water. In addition, the compression substantially disintegrated its crystalline structure and eventually resulted in the development of inter- and intrachain hydrogen-bonded structures arising from an interaction between the water and cellulose. Consequently, the cellulose samples essentially underwent an evolutionary change in the polymer structure as well as in the packing density during the compression. This structural change, in turn, led to the seemingly complicated absorption trends, depending on the pressure.

Pressure-induced variation of cellulose tablet studied by two-dimensional (2D) near-infrared (NIR) correlation spectroscopy in conjunction with projection pretreatment

Projection two-dimensional (2D) correlation analysis, achieved by selectively eliminating specific portion of dynamic spectra synchronized with the projecting vector, was used to study compression-induced variation of cellulose tablet monitored by near-infrared (NIR) spectroscopy and water sorption test. The increased density of the tablet by compression provided apparent variation of spectral intensity much larger than those caused by the change in the cellulosic structure. The direct calculation of 2D NIR correlation spectra from the raw spectra generated a relatively uninformative synchronous correlation spectrum and a very noisy asynchronous correlation spectrum due to the predominant intensity variation arising from the light scattering. In contrast, significant correlation features were elucidated without being hampered by the baseline fluctuation when the projection-corrected NIR spectra were constructed by the projection onto the space spanned orthogonal to the baseline change. Fine features of the compression-induced variation of the system were also elucidated by 2D hetero-correlation analysis based on the NIR spectra and water sorption profiles. The 2D correlation analysis revealed that the compression produces a disordered amorphous component of cellulose. The development of mobile amorphous phase results in a more tightly packed matrix with less porosity, which in turn prevents the penetration of water into the tablet and delays the water sorption.

Spectroscopic and Quantitative Chemometric Analysis of the Epoxidised Oil/Amine System

The competitiveness between the oxirane functional group and the ester functional group present in a derivative epoxidised oil was studied by monitoring a model system which involved epoxidised oleic oil and aniline (1:1). The reaction was carried out under isothermal conditions at 95°C and monitored in situ by near infrared (NIR) spectroscopy. This system is taken as a model of the curing process in the manufacture of epoxy resins from triglycerides and diamines. Conventional spectroscopic analysis and generalised two-dimensional NIR correlation spectroscopy analysis have led to the conclusion that, even though the formation of secondary amines by ring-opening of the oxirane group as a consequence of the nucleophilic attack of the aniline is prior, the formation of amides as a consequence of the ester group reactivity is a competitive reaction. The presence of the two aforementioned reactions is also in accordance with the significant number of factors found when the spectra data matrix was analysed by evolving factor analysis. By applying multivariate curve resolution–alternating least squares to the NIR spectra obtained during the reaction, it has been possible to obtain the concentration and the spectra profiles of each chemical species involved in the reaction. The performance of the model was assessed by two parameters: alternating least squares lack of fit (lof = 1.67 %) and explained variance ( R2 = 99.68%). The recovered spectra of the generated products have the characteristic bands associated with the two postulated reactions.

Thermally Induced Dissociation Nature of Pure 2-Pyrrolidinone via Near-Infrared Correlation Spectroscopy Analysis

The temperature-dependent dissociation behavior of 2-pyrrolidinone in the pure liquid state was investigated via perturbation-correlation moving-window two-dimensional (PCMW2D) correlation spectroscopy and two-dimensional near-infrared (2D-NIR) correlation spectroscopy. Absorption bands in the region of 6900-6000 cm(-1) assigned to the first overtones of stretching modes of NH groups provided detailed information about the dissociation process from 25 degrees C to 95 degrees C. On the basis of PCMW2D analysis, the sequence of dissociation events occurring during the temperature variation were elucidated in two temperature ranges (25-60 degrees C and 65-95 degrees C). Specific dissociation order of the hydrogen bond under temperature perturbation was disclosed by 2D-NIR correlation spectroscopy. As temperature increased, the dissociation of larger oligomers occurred firstly with the generation of smaller oligomers, which were then consumed later by the decomposition of hydrogen bonds. The dissociation of stable cyclic dimers occurred mainly at higher temperature through gradually weakened hydrogen-bonding of NH groups.

Two-dimensional near-infrared correlation spectroscopy study the methanol in acidic pH region

The effect of pH on the structure of methanol was investigated by FT-NIR (Fourier transform near-infrared) spectroscopy and generalized two-dimensional (2D) correlation spectroscopy. pH perturbed 2D correlation spectra are calculated for the spectra in the 5500–4000, 7500–5500 cm −1 regions at different pH values. We observed that the stretching of CH 3 was shifted because of the direct interaction of the CH 3 group of methanol with the OH group of water, the change of free OH is more sensitive to pH than the cyclic dimmer and CH·O.

Physico-chemical description of bread dough mixing using two-dimensional near-infrared correlation spectroscopy and moving-window two-dimensional correlation spectroscopy

NIR spectroscopy presents a huge interest in exploring chemical changes during dough mixing. The aim of the present study is to investigate the potential of 2D correlation spectroscopy (2D COS) and moving-window 2D (MW2D) correlation spectroscopy to explore the time dependence of NIR spectral responses during wheat flour dough mixing. NIR spectra were continuously recorded (between 1400 and 2325 nm) during mixing of bread type-dough (based on flour, water and yeast), using an FT-NIR spectrometer with a deported probe. The probe was positioned inside the mixer in contact with the dough. The 2D spectra calculated using raw and second derivative NIR spectra were interpreted in terms of physico-chemical events. Nine different industrial flours were used as raw material to validate the analysis. The results obtained using the 2D COS and the MW2D methods give the possibility to ascribe chemical vibrations (starch, water and gluten) to NIR absorbance changes occurring during dough mixing. The analysis of the NIR spectra identified wavelength shift associated to both dough “free water” and protein secondary structure modifications. During this study, only the MW2D method allowed to identify clearly the time dependence of physico-chemical mechanisms from NIR variation bands.

Application of two-dimensional near-infrared correlation spectroscopy to the discrimination of Chinese herbal medicine of different geographic regions

Fructus Lycii is a traditional Chinese medicinal herb. The objective of this paper was to apply two-dimensional (2D) near-infrared (NIR) correlation spectroscopy to the discrimination of Fructus Lycii of four different geographic regions. Generalized 2D-NIR correlation spectroscopy was able to enhance spectral resolution, simplify the spectrum with overlapped bands, and provide information about temperature-induced spectral intensity variations that was hard to obtain from one-dimensional NIR spectroscopy. The 2D synchronous and asynchronous spectra showed remarkable differences within the range of 4950–5700 cm −1 between samples of different geographic regions. Using NIR instead of IR made the 2D approach more convenient and fast, and it can be applied to more area like process control. This approach can also be applied analogously to the discrimination of other Chinese herbal medicine of different geographic regions.

Two-dimensional near-infrared correlation temperature studies of an amorphous polyamide

Near-infrared spectra of a totally amorphous polyamide measured over the temperature range 25–200°C was analyzed using generalized two-dimensional (2D) correlation spectroscopy. At least, five distinct bands at 5690, 5810, 5900, 5980 and 6010 cm −1 were identified in the region of the CH overtones (5200–6200 cm −1). Among them, two bands at 5810 (aliphatic) and 6010 cm −1 (aromatic) are found to be very sensitive to the temperature-induced structural changes of the polyamide under examination. In the ν(NH) overtone region (6300–6800 cm −1), the asynchronicity of the bands assigned to the vibrations of the free and hydrogen-bonded NH groups indicate a complicated dissociation mechanism and the existence of different hydrogen-bonded species in the investigated totally amorphous polyamide sample. Owing to the spectral resolution enhancement in 2D correlation spectra, a splitting of the first overtone of the free NH stretching vibration into two components at 6780 (totally free) and 6740 cm −1 (free-end) can be observed.

Studies on the structure of water using two-dimensional near-infrared correlation spectroscopy and principal component analysis.

The structure of water molecules in the pure liquid state has been subjected to extensive research for several decades. Questions still remain unanswered, however, and no single model has been found capable of explaining all the anomalies of water. In the present study, near-infrared spectra of water in the temperature region 6-80 degrees C have been analyzed by use of principal component analysis and two-dimensional correlation spectroscopy in order to study the dynamic behavior of a band centered around 1,450 nm at room temperature, which is due to the combination of symmetric and antisymmetric O-H stretching modes (first overtone) of water. It has been found that the wavelengths 1,412 and 1,491 nm account for more than 99% of the spectral variation, representing two major water species with weaker and stronger hydrogen bonds, respectively. A third species located at 1438 nm, whose concentration was relatively constant as a function of temperature, is also indicated. A somewhat distorted two-state structural model for water is suggested.

1P048二次元近赤外相関分光法による卵白アルブミンの酸変性過程の研究 : 水和状態と二次構造変化の同時観測

1P048二次元近赤外相関分光法による卵白アルブミンの酸変性過程の研究 : 水和状態と二次構造変化の同時観測

Time-resolved near-infrared and two-dimensional near-infrared correlation spectroscopic studies of the polymerization process of silane coupling agents. Dynamic behavior of water molecules in the 3-aminopropyltriethoxysilane-ethanol-water system

The polymerization behavior of 3-aminopropyltriethoxysilane, a process initiated by water molecules, has been examined using time-resolved near-IR and 2D near-IR correlation spectra. By deconvolution of the time-resolved near-IR spectra, the existence of the component bands at 5189, 5265 and 5300 cm−1, whose intensities decrease markedly as the reaction proceeds, has been confirmed in the 5000–5400 cm−1 region. The band at 5189 cm−1 has been assigned to water molecules, while those at 5265 and 5300 cm−1 have been assigned to the strongly and weakly associated silanol groups, respectively. The kinetics of the hydrolysis of the ethoxy groups and of the formation of a siloxane bond have been analyzed using the time-dependent integral intensities of these three bands and the mechanisms of the reactions have been discussed. Evidence for this polymerization process is also clearly evident in the 2D near-IR correlation spectra.

Time-resolved near-infrared and two-dimensional near-infrared correlation spectroscopic studies on polymerization of the silane coupling agent perfluorooctyltrimethoxysilane

The polymerization behavior of perfluorooctyltrimethoxysilane (PFOS) in ethanol, which is acid-catalyzed by 0.25 M HCl, has been examined using time-resolved near-IR and 2D near-IR correlation spectra. In the time-resolved near-IR spectra, the bands at 5164 and 4825 cm−1 have been assigned to the combination bands of water and ethanol OH groups, respectively. It has been found that the absorbance variation of the two near-IR bands occurs in a two-step process. The absorbance of the 5164 cm−1 band rapidly decreases in the initial step but increases exponentially in the second step, while that of the 4825 cm−1 band rapidly increases both in the initial step and, exponentially, in the second step. These results indicate that the time-dependent absorbance variation of the two near-IR bands reflects the polymerization process of PFOS, in which consumption and release of water molecules and release of methanol in the two-step process occur as a consequence of the acid-catalyzed hydrolysis of methoxy groups and the formation of silanols (SiOH) to form a siloxane bond. It has also been found that this polymerization process is distinctly reflected in the 2D near-IR correlation spectra.

Resolution Enhancement and Band Assignments for the First Overtone of OH(D) Stretching Modes of Butanols by Two-Dimensional Near-Infrared Correlation Spectroscopy. 3. Thermal Dynamics of Hydrogen Bonding in Butan-1-(ol-d) and 2-Methylpropan-2-(ol-d) in the Pure Liquid States

Two-dimensional (2D) near-infrared (NIR) correlation spectroscopy was used to study the temperature-induced changes in the hydrogen bonding of butan-1-(ol-d) and 2-methylpropan-2-(ol-d) in the pure liquid phase. The similarity between the 2D correlation spectra of both studied butanols and their nondeuterated analogues proves that the isotopic substitution in the hydroxyl group affects little the dynamic properties of the hydrogen bonding. This conclusion also confirms the heterospectral analysis, performed for the spectra of the deuterated samples and their nondeuterated counterparts. In the asynchronous spectra of 2-methylpropan-2-ol and its deuterated analogue, we identified new bands at 7040 and 5226 cm-1, respectively, which are probably due to an intramolecular effect. Moreover, a heterospectral asynchronous plot develops a peak at (5286, 7085), not seen in the homospectral 2D plots of butan-1-(ol-d) and butan-1-ol, giving rise to an additional resolution enhancement. This new peak reveals different...

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies of Compatible Polymer Blends: Composition-Dependent Spectral Variations of Blends of Atactic Polystyrene and Poly(2,6-dimethyl-1,4-phenylene ether)

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies of Compatible Polymer Blends: Composition-Dependent Spectral Variations of Blends of Atactic Polystyrene and Poly(2,6-dimethyl-1,4-phenylene ether)

Application of two-dimensional near-infrared correlation spectroscopy to protein research

The purpose of the present paper is to demonstrate the potential of generalized two-dimensional (2D) near-infrared (NIR) correlation spectroscopy in studies of hydration and structure of proteins. We describe here two examples. The first example is concerned with heat denaturation process of ovalbumin in aqueous solutions and the second one deals with isomerizations with varying pH of serum albumin. New insight has been obtained into the hydration and unfolding process of secondary structures of ovalbumin and serum albumin by studying temperature- or pH-dependent correlation patterns in 2D synchronous and asynchronous spectra. Generalized 2D NIR correlation spectroscopy emphasizes spectral features not readily observable in conventional one-dimensional spectra, enabling to extract subtle but valuable structural changes concerning with the protein denaturation.

Two-Dimensional Near-Infrared Correlation Spectroscopy Studies on Composition-Dependent Spectral Variations in Ethylene/Vinyl Acetate Copolymers: Assignments of Bands Due to Ethylene Units in Amorphous, Disordered, and Orthorhombic Crystalline Phases

Generalized two-dimensional (2D) correlation spectroscopy has been applied to the study of the composition-dependent near-infrared (NIR) spectral changes in 11 different ethylene/vinyl acetate (EVA) copolymers with vinyl acetate (VA) content from 6 to 42 wt %. The 2D synchronous correlation analysis of the 11 NIR spectra has separated the bands due to ethylene units from those due to the VA units. The obtained results are consistent with those reached by the calculation of the second derivative and by chemometrics analysis reported in our previous paper. However, the 2D correlation analysis has given clearer evidence for the band separation. Two-dimensional asynchronous correlation analysis has revealed out-of-phase variations between some bands due to ethylene and some bands due to VA and has determined the order of intensity change between them. On the basis of the order of intensity change, the bands of ethylene in the orthorhombic crystalline phase have been discriminated from those in the amorphous and disordered phases. This paper discusses the potentials of three powerful techniques, 2D correlation analysis, the calculation of the second derivatives, and that of regression coefficients in chemometrics, in unraveling rather complicated NIR spectra.