IR Correlation Spectroscopy Research Articles

Distinction of the Microcrystalline Celluloses from Eurycoma longifolia and Mannihot esculenta by Two-dimensional Correlation and Second Derivative IR Spectroscopy

Distinction of the Microcrystalline Celluloses from Eurycoma longifolia and Mannihot esculenta by Two-dimensional Correlation and Second Derivative IR Spectroscopy

A temperature-adjustable in situ infrared diffuse reflectance spectroscopy system for catalysts.

We introduce an innovative in situ infrared diffuse reflection rapid detection system, endowed with a temperature regulation function. This system is adept at conducting rapid infrared spectra scanning as well as simulating the catalytic environment of diverse reaction systems. The infrared absorption spectra of four kinds of Pt-based catalysts under vacuum conditions across a wide temperature spectrum ranging from -180 to 300 °C are obtained and analysed through IR correlation spectroscopy. A key finding is the notable variance in peak intensity within Pt/CeO2/CNT catalysts, highlighting a robust adsorption capacity for oxygen-containing groups at lower temperatures and a marked desorption at higher temperatures. By enabling rapid and accurate assessments of catalyst behavior under varying temperatures, it not only accelerates the evaluation process but also provides valuable insights that can guide the synthesis of more efficient catalysts.

Two-Dimensional Correlation IR Spectroscopy of Humic Substances of Chernozem Size Fractions of Different Land Use

Diffuse reflectance FTIR measurements with two-dimensional correlation spectroscopy (2D-COS) are used for accurate band identification of chernozem comprising soil organic matter (SOM), including humic substances and mineral silicate matrix. Samples of different land use (native steppe, shelterbelt, bare fallow, and arable land) of a long-term field experiment were compared. Homospectral 2D-COS maps for size fractions obtained by wet fractionation were built, and the fraction size was used as a correlation-building variable (external perturbation) of 2D-COS. Synchronous 2D-COS maps are characterized by main correlation regions at 4000–3600 (hydrogen bonds), 1800–1150 (SOM), and 1100–200 cm−1 (quartz matrix). SOM range can be used as a signature of the samples distinguishing two pairs, native steppe–bare fallow and arable land–shelterbelt, by correlations at 1340–1320 cm−1 (CH2) and 1670 cm−1 (aromatic –C=C–). Asynchronous 2D-COS maps show bands at 3690–3620, 2930–2830, in the range of 1640–1250 (8 bands), 1160, 1070, 797, 697, 505, and 400 cm−1, the latter 5 indicate the increasing proportion of silicate to quartz in small fractions. The manifestation of asynchronous correlation bands at 1650, 1580–1560, 1444, 1340, and 1250 cm−1, which have no major contribution from inorganic soil components, are due to carbonyl, carboxylate, and aromatic C–C; their appearance order (accumulation of corresponding substances in larger factions) is different for each land use. The proposed approach provides the identifying SOM components with enough reliability for SOM IR bands that are weaker compared to mineral matrix bands in original IR spectra.

Characterization of the phase transition mechanism of P(NiPAAm-co-AAc) copolymer hydrogel using 2D correlation IR spectroscopy

A thermo-responsive polymer, poly(N-isopropylacrylamide) (PNiPAAm), was copolymerized with acrylic acid (AAc) in this study. Its phase transitions during the heating and cooling processes were investigated using IR spectroscopy, principal component analysis (PCA), and two-dimensional correlation spectroscopy (2D-COS). During the heating process, the hydrogen bonding between side chain in P(NiPAAm-co-AAc) copolymer hydrogel and H2O was broken first, and then the formation of the intramolecular interaction in P(NiPAAm-co-AAc) copolymer hydrogel occurred. However, unlike the heating process, intensities of bands in the CH stretching region were changed before those in the CO stretching including the NH bending region during the cooling process. The results indicate that the phase transition of P(NiPAAm-co-AAc) copolymer hydrogel is an irreversible process at the molecular levels.

2D IR Correlation Spectroscopy in the Determination of Aggregation and Stability of KH Domain GXXG Loop Peptide in the Presence and Absence of Trifluoroacetate.

Trifluoroacetate (TFA) is a strong anion byproduct of solid-phase peptide synthesis. Fourier transform infrared (FT-IR) spectroscopy can be used to ascertain the presence of this excipient in peptide samples for quality assessment. TFA absorbs as a strong sharp peak (1675 cm-1) within the amide I' band of the spectral region. A peptide sample and the TFA excipient can be studied simultaneously by FT-IR and 2D IR correlation spectroscopies. In addition, these techniques are able to determine the effect of TFA on the stability of the peptide. Herein, we describe the spectroscopic characterization of the GXXG loop peptide (GXXGlp), which is present in KH domain containing proteins. The sequence of the Homo sapiens Krr1 GXXGlp is evolutionarily conserved (165KRRQRLIGPKGSTLKALELLTNCY189) and has been associated with ssDNA interaction and ribosome biogenesis. Our goal was to determine the structural elements present in this peptide and evaluate whether TFA affects the stability of GXXGlp during thermal stress. We observed differences in the molecular behavior of the synthetic peptide in the presence and absence of TFA at various peptide concentrations. Finally, 2D IR correlation spectroscopy was used for the determination of the unfolding process, mechanism and extent of peptide aggregation, and the effect of TFA on the stability of the peptide. This spectroscopic method can be applied to the characterization of any synthetic peptide.

Detection of diluted contaminants on chicken carcasses using a two-dimensional scatter plot based on a two-dimensional hyperspectral correlation spectrum

A two-dimensional (2D) scatter plot method based on the 2D hyperspectral correlation spectrum is proposed to detect diluted blood, bile, and feces from the cecum and duodenum on chicken carcasses. First, from the collected hyperspectral data, a set of uncontaminated regions of interest (ROIs) and four sets of contaminated ROIs were selected, whose average spectra were treated as the original spectrum and influenced spectra, respectively. Then, the difference spectra were obtained and used to conduct correlation analysis, from which the 2D hyperspectral correlation spectrum was constructed using the analogy method of 2D IR correlation spectroscopy. Two maximum auto-peaks and a pair of cross peaks appeared at 656 and 474 nm. Therefore, 656 and 474 nm were selected as the characteristic bands because they were most sensitive to the spectral change induced by the contaminants. The 2D scatter plots of the contaminants, clean skin, and background in the 474- and 656-nm space were used to distinguish the contaminants from the clean skin and background. The threshold values of the 474- and 656-nm bands were determined by receiver operating characteristic (ROC) analysis. According to the ROC results, a pixel whose relative reflectance at 656 nm was greater than 0.5 and relative reflectance at 474 nm was lower than 0.3 was judged as a contaminated pixel. A region with more than 50 pixels identified was marked in the detection graph. This detection method achieved a recognition rate of up to 95.03% at the region level and 31.84% at the pixel level. The false-positive rate was only 0.82% at the pixel level. The results of this study confirm that the 2D scatter plot method based on the 2D hyperspectral correlation spectrum is an effective method for detecting diluted contaminants on chicken carcasses.

Determination of phosphatase activity in osteoblasts by IR and two-dimensional correlation IR spectroscopy

Phosphatase activity in osteoblasts like Saos-2 cells was previously determined by measuring infrared spectra of substrates (pyrophosphate, 4-nitrophenyl phosphate, α-glucose-1-phosphate or β-Glycerophosphate), in the presence of Saos-2 cells under physiological conditions, at 37°C and pH=8. In this work, 2D correlation analysis served to resolve component bands in infrared spectra to obtain accurate values of enzymatic activity. We critically analyzed the advantages and pitfalls of 2D correlation analysis and compared their results with those obtained from infrared difference spectra. In the case of PPi substrate, 2D correlation analysis resolved well the overlapping bands associated to PPi and Pi. We obtained an average specific activity of hydrolysis of PPi by Saos-2 cells of around 133±16nmolmg−1min−1 by using peak positions determined from 2D correlation analysis as compared with the value of around 118±10nmolmg−1min−1 obtained from peak positions determined by IR difference spectra. However, in the case of 4-nitrophenyl phosphate, 2D correlation analysis, as well as infrared difference spectra, failed to resolve Pi band located at 990cm−1 from the strongly overlapped 4-nitrophenyl phosphate band located at around 980cm−1. This is explained by the fact that the 990cm−1-band increased during hydrolysis, while the 980cm−1-band decreased, cancelling each other. In the case of β-glycerophosphate, 2D IR correlation analysis confirmed the peak position of Pi within 2cm−1 as determined by infrared spectroscopy. The specific activity of hydrolysis of β-glycerophosphate as determined by both methods was identical within experimental errors. Taken together our findings indicated that each method yielded specific activity values of TNAP in osteoblast cells within 20% from each other. The combination of 2D-correlation analysis and IR spectroscopy confirmed and reinforced the interpretation of IR spectra. Both approaches are complementary and provided a solid rationale to select peak positions for accurate determination of enzymatic activity in cells.

Synthesis, structure and temperature-depended 2D IR correlation spectroscopy of an organo-bismuth benzoate with 1,10-phenanthroline

An organo-bismuth benzoate with phen as auxiliary ligand, [Bi(phen)(C6H5COO)(C6H4COO)] (1) (phen = 1,10-phenanthroline) has been hydrothermally synthesized from bismuth nitrate, 2-mercaptonbenzoic acid with phen as auxiliary ligand and characterized by single-crystal X-ray diffraction, elemental analyses, PXRD, IR spectra, TG analyses, temperature-depended 2D-IR COS (two-dimensional infrared correlation spectroscopy). Interestingly, benzoate anions in 1 came from the desulfuration reaction of 2-mercaptonbenzoic acid under hydrothermal condition. Compound 1 is a discrete organo-bismuth compound with benzoate and phen ligands. The offset face-to-face π-π stacking interactions and C–H⋯O hydrogen bonds link the isolate complex into a 3D supramolecular network. The temperature-depended 2D-IR COS indicates that the stretching vibrations of CC/CN of aromatic rings and CO bonds are sensitive to the temperature change.

IR Correlation Spectroscopy using Microgratings to be Compared with Dispersive IR Spectroscopy#

Microgratings that were designed and fabricated to generate IR absorption spectra of SF6 and NH3 on diffraction into a specific detection angle were tested by correlation spectroscopy. The micrograting diffraction provides a reference spectrum for a target molecule, and its cross‐correlation with the transmission spectrum of a gas cell is obtained by varying the diffraction angle. As our optical setup can measure the dispersive transmission spectrum and the correlation spectrum under the same conditions, the two kinds of spectra were compared directly in terms of signal‐to‐noise ratio (SNR). The SNR’s of the correlation spectra were a few times lower than those of the dispersed spectra; therefore, the correlation spectroscopy can hardly be placed above the dispersive spectroscopy with respect to the SNR. The merit of the correlation spectroscopy is that a rather small range of modulation wavelength is needed to identify the target. Therefore, the correlation spectroscopy would be more useful for such target molecules whose spectra consist of broad peaks spread throughout a wide wavelength range.

Crystallization behavior and toughening mechanism of poly(ethylene oxide) in polyoxymethylene/poly(ethylene oxide) crystalline/crystalline blends

In this study, the unique crystallization behavior of poly(ethylene oxide) (PEO) in polyoxymethylene (POM)/PEO crystalline/crystalline blends was examined in detail. This study was the first to report the typical fractionated crystallization of PEO in POM/PEO blends when PEO is fewer than 30 wt.%. The delayed crystallization temperature of PEO was confirmed at about 5°C to 14°C by using differential scanning calorimetry and perturbation–correlation moving‐window 2D correlation IR spectroscopy. Wide‐angle X‐ray diffraction indicates that no new crystal structures or co‐crystals were generated in POM/PEO. The statistical calculations of scanning electron microscopy photos show that the average diameter of PEO particles is 0.227 µm to 1.235 µm and that the number of small particles is as many as 109 magnitudes per cm3. Theory analysis establishes that the delayed crystallization of PEO is a heterogeneous nucleation process and not a homogeneous nucleation process. A significant toughening effect of PEO to POM was also observed. The impact strength of POM/PEO acquires a maximum of 10.5 kJ/m2 when PEO content is 5%. The impact strength of the blend increases by 78.0% compared with pure POM. To improve the toughening effect, the best particle size is established between 0.352 and 0.718 µm, with a PEO particle spacing of 0.351 µm to 0.323 µm. The number of corresponding particles was 0.887 × 109 per cm3 to 3.240 × 109 per cm3. A PEO toughening model for POM was proposed to provide a new and effective way to solve the problem of POM toughening. Copyright © 2014 John Wiley & Sons, Ltd.

Fabrication of Microgratings and their IR Diffraction Spectra

Microgratings whose diffracted field at a fixed angle generate IR spectra of SF6 or NH3 were fabricated by MEMS techniques for the purpose of IR correlation spectroscopy. Each micrograting was composed of 1441 reflecting lines in the area of 19.2 × 19.2 mm. The depth profile of the line elements was determined with a gradient searching method that was described in our previous publication (J. Mod. Opt. 2013, 60, 324-330), and was discretized into 16 levels between 0 and 6.90 μm. The diffraction field from a given depth profile was calculated with Fraunhofer equation. The fabricated microgratings showed errors in the depth and the width within acceptable ranges. As the result, the diffracted IR spectrum of each micrograting matched well with its target reference spectrum within spectral resolution of our optical setup.

PH-induced structural changes of ovalbumin studied by 2D correlation IR spectroscopy

The secondary structural changes of pH-induced ovalbumin during the transition from native state into intermediate state were studied with the use of 2D correlation spectroscopy and principal component analysis. 2D correlation spectra constructed from the pH-dependent IR spectra of ovalbumin solution revealed the following scenario of the intensity changes with pH decrease. When pH decreased from 5.5 and 3.6 intensity of components attributed to the β-turns, the α-helical elements, and native β-sheets increased. It was caused by protonation induced changes in environment of these elements. When the protonation of the acidic groups were finalized the system adopted the intermediate structure. It was accompanied by weak structural changes that mainly included the β-turns and the α-helices. In extreme acidic conditions at pH below pH 2 the intermediate structure was no longer stable and oligomers rich in the β-sheet structure were formed.

Rapid identification of Pterocarpus santalinus and Dalbergia louvelii by FTIR and 2D correlation IR spectroscopy

Since Pterocarpus santalinus and Dalbergia louvelii, which are of precious Rosewood, are very similar in their appearance and anatomy characteristics, cheaper Hongmu D. louvelii is often illegally used to impersonate valuable P. santalinus, especially in Chinese furniture manufacture. In order to develop a rapid and effective method for easy confused wood furniture differentiation, we applied tri-step identification method, i.e., conventional infrared spectroscopy (FT-IR), second derivative infrared (SD-IR) spectroscopy and two-dimensional correlation infrared (2DCOS-IR) spectroscopy to investigate P. santalinus and D. louvelii furniture. According to FT-IR and SD-IR spectra, it has been found two unconditional stable difference at 848cm−1 and 700cm−1 and relative stable differences at 1735cm−1, 1623cm−1, 1614cm−1, 1602cm−1, 1509cm−1, 1456cm−1, 1200cm−1, 1158cm−1, 1055cm−1, 1034cm−1 and 895cm−1 between D. louvelii and P. santalinus IR spectra. The stable discrepancy indicates that the category of extractives is different between the two species. Besides, the relative stable differences imply that the content of holocellulose in P. santalinus is more than that of D. louvelii, whereas the quantity of extractives in D. louvelii is higher. Furthermore, evident differences have been observed in their 2DCOS-IR spectra of 1550–1415cm−1 and 1325–1030cm−1. P. santalinus has two strong auto-peaks at 1459cm−1 and 1467cm−1, three mid-strong auto-peaks at 1518cm−1, 1089cm−1 and 1100cm−1 and five weak auto-peaks at 1432cm−1, 1437cm−1, 1046cm−1, 1056cm−1 and 1307cm−1 while D. louvelii has four strong auto-peaks at 1465cm−1, 1523cm−1, 1084cm−1 and 1100cm−1, four mid-strong auto-peaks at 1430cm−1, 1499cm−1, 1505cm−1 and 1056cm−1 and two auto-peaks at 1540cm−1 and 1284cm−1. This study has proved that FT-IR integrated with 2DCOS-IR could be applicable for precious wood furniture authentication in a direct, rapid and holistic manner.

Calcium titration of Chlamydomonas reinhardtii centrin and its structural changes

Chlamydomonas reinhardtii centrin is a highly conserved calcium binding protein belonging to the EF-hand superfamily. Centrin, like other calcium binding proteins, changes conformation upon calcium binding. In addition, the calcium binding sites are comprised mainly of aspartates and glutamates which would serve as probes for a calcium binding event. 2D IR correlation spectroscopy has proven to be a valuable technique to determine the differences in the molecular behavior of the EF-hand domains within centrin. Moreover, the differences in affinity for calcium displayed by these domains were correlated to differences in the molecular behavior of these EF-hand domains when compared with each other and the full-length protein. We were able to confirm the nature of the two independent domains within centrin. Furthermore, we established the mechanism of aggregation was self-association due to adsorption of centrin to the ZnSe ATR crystal and estimated the extent of aggregation of the full-length protein.

Verification of Ganoderma (lingzhi) commercial products by Fourier Transform infrared spectroscopy and two-dimensional IR correlation spectroscopy

Ganoderma commercial products are typically based on two sources, raw material (powder form and/or spores) and extract (water and/or solvent). This study compared three types of Ganoderma commercial products using 1 Dimensional Fourier Transform infrared and second derivative spectroscopy. The analyzed spectra of Ganoderma raw material products were compared with spectra of cultivated Ganoderma raw material powder from different mushroom farms in Malaysia. The Ganoderma extract product was also compared with three types of cultivated Ganoderma extracts. Other medicinal Ganoderma contents in commercial extract product that included glucan and triterpenoid were analyzed by using FTIR and 2DIR. The results showed that water extract of cultivated Ganoderma possessed comparable spectra with that of Ganoderma product water extract. By comparing the content of Ganoderma commercial products using FTIR and 2DIR, product content profiles could be detected. In addition, the geographical origin of the Ganoderma products could be verified by comparing their spectra with Ganoderma products from known areas. This study demonstrated the possibility of developing verification tool to validate the purity of commercial medicinal herbal and mushroom products.

Transitions of monodisperse aPS studied by model-based 2D correlation infrared spectroscopy incorporating S-shaped function

In this paper, a new S-shaped function (model) called Boltzmann sigmoid was incorporated into the model-based 2D correlation infrared spectroscopy. Boltzmann sigmoid is a typical transition function, and it was found from the curve fitting of the IR spectral intensity variations of monodisperse aPS at heating. The glass transition and the liquid–liquid transition of aPS were determined by MW2D IR spectrum. The model-based 2D correlation IR spectroscopy incorporating Boltzmann sigmoid was successfully employed to investigate the mechanism of these two transitions. We found that the flip motion of the side benzene rings is earlier than the creep of the main chains of monodisperse aPS during the glass transition. Moreover, the difference of the sequential order is precisely defined as ΘE=4.5°. The movements of the main chains and the side benzene rings are completely simultaneous without a difference during the liquid–liquid transition of aPS, and the difference of the sequential order is ΘE=0°. It represents the whole movement of macromolecular chains of aPS. The liquid–liquid transition is probably a consequence of the onset of melts motions, and the slippage of chain entanglements. The difference of the effective phase angle in the model-based 2D spectra is proportional to the difference of the transition temperature at the different bands in MW2D spectra.

Unique (3,8)-connected lanthanide arenedisulfonate metal-organic frameworks containing benzimidazole-5,6-dicarboxylic acid co-ligand: Syntheses, structures and luminescence

Abstract Two isostructural 3D lanthanide arenedisulfonate metal-organic frameworks (MOFs) [Ln(Hbidc)(nds)0.5(H2O)]n(Ln=Eu(1), La(2)) have been successfully synthesized by the hydrothermal reaction of lanthanide oxide with 2,6-naphthalenedisulfonate sodium (Na2nds) and an auxiliary ligand, 1H-benzimidazole-5,6-dicarboxylic acid (H3bidc). The two complexes are both constructed from 2D [Ln(Hbidc)]+ double layers pillared by nds2− ligands to generate 3D (3, 8)-connected open-framework structures with 1D long narrow channels running along the a axis. From topological point of view, the 3D framework is a (3, 8)-connected tfz-d net. The weak interactions including N–H⋯O, O–H⋯O hydrogen bonds and π–π stacking are observed in 1. The 2D IR correlation spectroscopy was applied to study the molecular interactions induced by thermal perturbation. The emission spectra of 1 exhibit the characteristic transition of 5D0→7FJ(J=0–4) of Eu(III).

Optical properties of serum albumin water solutions, containing mesoporous silicon particles

The interaction of molecules of bovine serum albumin (BSA) with silicon nanoparticles (SiNPs) was studied in water solutions of them at different pH values. The data of photon correlation spectroscopy and IR spectroscopy of studied solutions indicate the absence of interaction between BSA and SiNPs in the pH range 3–7, which is attested to by the experimentally obtained character of the pH dependence of the translational diffusion coefficient Dt and by the absence of hydrogen bonds between the protein carbonyl groups and the OH groups on the surface of mesoporous silicon nanoparticles. The obtained data may play a leading role in further in vivo application of silicon nanoparticles.

Characterization by Fourier transform infrared spectroscopy (FT-IR) and 2D IR correlation spectroscopy of a carbosilane dendrimer with peripheral ammonium groups

Fourier transform infrared spectroscopy and 2D correlation spectroscopy were used to study the microstructural changes occurring on heating of a new carbosilane dendrimer with peripheral ammonium groups. Temperature-dependent spectral variations in the 3,010–2,710, 1,530–1,170, and 1,170–625 cm−1 regions were monitored during the heating process. The dependence, on temperature, of integral absorptions and position of spectral bands was established and the spectral modifications associated with molecular conformation rearrangements, allowing molecular shape changes, were found. Before 180 °C, the studied carbosilane dendrimer proved to be stable, while at higher temperatures it oxidizes and Si–O groups appear. 2D IR correlation spectroscopy gives new information about the effect of temperature on the structure and dynamics of the system. Synchronous and asynchronous spectra indicate that, at low temperature, conformational changes of CH3 and CH3–N+ groups take place first. With increasing temperature, the intensity variation of the CH2, C–N, Si–C and C–C groups from the dendritic core is faster than that of the terminal units. This indicates that, with increasing temperature, the segments of the dendritic core obtain enough energy to change their conformation more easily as compared to the terminal units, due to their internal flexibility.

Relative stability of human centrins and its relationship to calcium binding.

Centrins are calcium binding proteins that belong to the EF-hand superfamily with diverse biological functions. Herein we present the first systematic study that establishes the relative stability of related centrins via complementary biophysical techniques. Our results define the stepwise molecular behavior of human centrins by two-dimensional infrared (2D IR) correlation spectroscopy, the change in heat capacity and enthalpy of denaturation by differential scanning calorimetry, and the relative stability of the helical regions of centrins by circular dichroism. More importantly, 2D IR correlation spectroscopy provides unique information about the similarities and differences in dynamics between these related proteins. The thermally induced molecular behavior of human centrins can be used to predict biological target interactions that have a relative dependence on calcium affinity. This information is essential for understanding why certain isoforms may be used to rescue a phenotype and therefore also for explaining the different functions these proteins may have in vivo. Furthermore, this comparative approach can be applied to the study of recombinant therapeutic protein candidates for the treatment of disease states.