2D Correlation Analysis Research Articles

The sequence of changes observed during degradation process of paper by the use of UV/VIS and FTIR spectrometry with application of the PCA and 2D correlation method for forensic purposes

As paper is the base for (printed) documents-including bogus documents-it is often the subject of forensic investigations. Its properties depend on interactions between and within cellulose chains, mainly assigned to inter-and intramolecular hydrogen bonds. During paper degradation, the degree of polymerization of the cellulose chain changes. Vibrational spectroscopy has already been widely applied to resolve cellulose structure, crystalline phases and hydrogen bonds networks. The aim of the present research was to evaluate the possibility of differentiating between degraded papers by spectroscopic techniques.Five paper samples were artificially aged in a climatic chamber under 65% relative humidity in air at 90 °C for various periods up to 35 days. The conditioned samples – of differing durations of ageing – were then analyzed using infrared and UV/VIS spectroscopy.It was observed that the paper samples differed in the range 1000–1120 cm−1, 2860-2950 cm−1 and 1300-1380 cm−1 in infrared as a function of time of aging. Differences were also found in UV/VIS spectra, concerning bands of intensity of ca. 280 and 350 nm. 2D correlation analysis as well as the PCA method have allowed to distinguish between selected paper samples, through the specificity of the aging process that runs in them.

Fluorescent Properties of Three Carboxyarylphosphonate Polymers with Unusual Polynuclear Zinc(II) Units

Three novel carboxyarylphosphonate polymers {[Zn2(PCP)(H2PCP)(phen)2]·H2O}n (1), [Zn(HPCP)(4,4′‐bipy)]n (2), and [Zn3(MCP)2(2,2′‐bipy)]n (3) [PCP3– = p‐O2C(C6H4)CH2PO33–, MCP3– = m‐O2C(C6H4)CH2PO33– and phen = phenanthroline] were synthesized and characterized by single‐crystal X‐ray diffraction. Compound 1 features a butterfly‐shaped dimer consisting of [Zn4P4O10] tetranuclear units, which are further linked by hydrogen bonds and π–π stacking interactions into a 3D supramolecular framework. In 2, there is an infinite P–O–Zn inorganic 2D (4,4) layer with the phosphonate moieties of HPCP2– and unidentate 4,4′‐bipy ligands vertically sticking out. As for 3, the novel [Zn6P4O12] hexanuclear units with “chair“ conformation are tetrahedrally bridged by eight MCP3– to generate a 2D double‐layer, in which the windows are occupied by 2,2′‐bipy molecules. Additionally, 2D correlation analysis of FTIR with thermal perturbation of 3 were discussed. Compounds 1–3 exhibit intense solid state fluorescent emissions. Thermogravimetric analyses suggested the very high stability.

Determination of Phosphorylation and Deprotonation Induced Higher Order Structural Transitions in αs-Caseins.

One extremely sensitive and highly successful application of Raman spectroscopy is the structural characterization of proteins. Understanding higher order structure and its effect on protein stability is essential not only for biopharmaceutical and food manufacturing but also for the understanding of diseases that result from the misfolding of proteins including diabetes type II, Alzheimer's, and Parkinson's disease. Due to the large amount of structural information available in Raman spectra, even small alterations in protein conformations including increased exposure of binding regions or changes in geometry of secondary structural elements can be identified. In this study, we demonstrate the unique sensitivity of Raman spectroscopy to subtle structural transitions in an intrinsically open, flexible protein, αs-casein, in response to phosphorylation and deprotonation. Through the application of 2D correlation analysis two separate transition phases have been identified from pH 6-9 and pH 10-12 for both phosphorylated and dephosphorylated αs-casein. However, the actual structural changes observed in each pH range differed considerably between the phosphorylated and dephosphorylated αs-casein. Furthermore, the presence of the phosphorylated serine residues is demonstrated to have a shielding effect during deprotonation of the protein.

Study of matrix-filler interaction of polypropylene/silica composite by combined infrared (IR) spectroscopic imaging and disrelation mapping

We demonstrate a Fourier transform infrared (FTIR) spectroscopic imaging combined with two-dimensional (2D) correlation analysis to elucidate matrix-filler interaction of polymer composites. Composite of maleic anhydride grafted polypropylene (MAPP) and silica sphere (SS) was fabricated. The FTIR image and disrelation map derived from sets of FTIR spectra suggest that the maleic anhydride groups in MAPP surround the SS surface and interact with the silanol on the surfaces of SS via hydrogen bonding. This clear link between MAPP and SS indicates that MAPP can be utilized as a suitable amphiphilic compatibilizer for an SS filler when it is mixed with hydrophobic polymer. FTIR imaging analysis was then further extended to categorize the interfacial states of more complicated polymer composites consisting of polypropylene (PP)/SS containing MAPP as a compatibilizer. Probing the interfacial chemical state using FTIR imaging revealed the interaction between MAPP and SS to contribute to improved elastic modulus of PP/MAPP/SS.

Near Infrared Spectrometric Investigations on the behaviour of Lactate.

In patients with life-threatening illnesses, the metabolic production and disposal of lactate are impaired, which leads to a build-up of blood lactate. In critical care units, the changes in lactate levels are measured through intermittent, invasive, blood sampling and in vitro assay. Continuous monitoring is lacking, yet such monitoring could allow early assessment of severity and prognosis to guide therapy. Currently, there is no routine means to measure lactate levels continuously, particularly non-invasively. The motivation of this study was to understand the interaction of lactate with light in the Near Infra Red (NIR) region of the electromagnetic spectrum. This was to create an opportunity to explore the possibility of a non-invasive sensing technology to monitor lactate continuously.In vitro studies were performed using solution samples with varying concentration levels of sodium lactate in isotonic Phosphate Buffer Solution (PBS) at constant pH (7.4). These samples were prepared using stoichiometric solution compositions and spectra for each sample were taken using a state-of-the-art spectrometer in the NIR region. The spectra were then analysed qualitatively by 2D correlation analysis, which identified the regions of interest. Further analysis of these regions using linear regression at four randomly selected wavelengths showed bathochromic shifts, which, moreover, showed systematic variation correlating with lactate concentration.

Temperature-dependent near-infrared spectroscopy for studying the interactions in protein aqueous solutions

Temperature-dependent near-infrared spectroscopy has been developed for studying quantitative and structural analysis, as well as the molecular interactions. Taking the advantage of the temperature effect on hydrogen bonding, the technique has shown its potential in analyzing the interactions in aqueous solutions. In our recent studies, the structural changes in homo-oligopeptides K5 (penta-lysine), D5 (penta-aspartic acid), and protein (ovalbumin) aqueous solutions were studied by temperature-dependent near-infrared spectroscopy. The thermodynamics and their interaction with water were analyzed with the help of the chemometric methods including continuous wavelet transform, independent component analysis, two-dimensional (2D) correlation analysis, and Gaussian fitting. The results show that the oligopeptide in aqueous solution improves the thermal stability of the water species, and K5 has stronger interaction with water than D5. In the gelation of ovalbumin, the change of the water species with two hydrogen bonds (S2) follows the same phases as the protein. S2 maintains the stability of the protein in native and molten globule states, and the weakening of the hydrogen bond in S2 by high temperature results in the destruction of the hydration shell and makes the ovalbumin clusters form a gel structure.

Water as a probe for serum–based diagnosis by temperature– dependent near–infrared spectroscopy

Diagnosis based on the compositional variation of biological liquids such as serum has drawn much attention. For exploring the potential diagnostic information from serum samples, temperature–dependent near–infrared (NIR) spectroscopy was developed to obtain the spectral change of water reflecting the interactions in serum solution, and chemometric methods were employed to mine the information from the temperature–dependent NIR spectra. The spectra of 68 healthy controls, 42 patients with the type II diabetes and 16 patients with coronary heart disease were measured and analyzed by chemometric calculations. Continuous wavelet transform (CWT) was used to enhance the resolution of the spectra. From the processed spectra, the information of non–hydrogen–bonded (NHB), weakly hydrogen–bonded (WHB) and strongly hydrogen–bonded (SHB) water species was observed. For explaining the variation of the spectra with temperature, two–dimensional (2D) correlation analysis was adopted. A clear difference in SHB/NHB ratio in the synchronous maps was found between the spectra of the patients and the controls. 86.8% of the controls and 98.3% of the patients can be correctly identified. Furthermore, combining the maps of the synchronous and asynchronous analysis, the correlation between SHB and WHB water species was discovered to have an ability to discriminate the patients of diabetes and heart disease with an accuracy of 83.7% and 75.0%, respectively. Therefore, water may be a probe for providing diagnostic information by temperature–dependent NIR spectroscopy.

Thermal curing behavior of benzoxazine functional polysilsesquioxane nanospheres

Benzoxazine functional polysilsesquioxane (Bz-PSQ) nanoparticles were synthesized using a simple sol-gel method in this work, which is characterized by scanning electron microscopy (SEM) and show a uniform spherical morphology. The benzoxazine functional structure of nanospheres was studied by Fourier transform infrared spectroscopy (FTIR) and water contact angle measurement. The curing kinetics and curing behavior of benzoxazine structure in nanoshperes were investigated by differential scanning calorimeter (DSC) and In situ FTIR. The activation energy of the curing reaction is 148.0 ± 14.1 kJ mol−1 for Kissinger and 149.4 ± 13.4 kJ mol−1 for Ozawa method, respectively. Differential FTIR spectra and 2D correlation analysis were utilized to discern the sequence of molecular variations during the curing process and the possible polymerization mechanism of benzoxazine structure was proposed as well.

Crystallization Behavior of Poly(Tetramethylene Oxide) Influenced by the Crystallization Condition of Poly(Butylene Succinate) in Their Copolymers

The effect of crystallization conditions of poly(butylene succinate) (PBS) component on the crystallization of poly(tetramethylene oxide) (PTMO) component in their segment block copolymer, with a higher PTMO content (PTMO mass fraction is 67%), was investigated by DSC and temperature-dependent FTIR. It is found that the isothermal crystallization time (tIC) of PBS has an effect on the crystallization behavior of PTMO component. Perturbation correlation move-window two-dimensional (PCMW2D) correlation analysis and generalized 2D correlation analysis (2DIR) were performed to explore the origin of this phenomenon. The PCMW2D and 2DIR results show that the correlation intensity peak observed at around 20 °C for PTMO is due to the PTMO chains movements forced by the PBS chains folded movements. If tIC of PBS at temperature of 20 °C is prolonged, more PTMO components are incorporated in the region between PBS lamellae and the peak at -7.6 °C (belonging to less-constricted PTMO chains) changes smaller and even disappears, while the peak at -16.3 °C belonging to more-constricted PTMO chains gets bigger. A crystallization model was also established in this study. The results of tensile testing showed that tensile strength slightly increased and elongation at break decreased with increasing heat treatment time at 40 °C.

Enthalpy-Driven Transition of Liquid Crystalline Textures of Poly(2-cyano-p-phenylene terephthalamide) in N,N-Dimethyl Acetamide/Lithium Chloride

The solution of poly(2-cyano-p-phenylene terephthalamide) (CY-PPTA) in N,N-dimethyl acetamide/lithium chloride exhibited a concentration-dependent transition of liquid crystalline textures from nematic-rich to cholesteric-rich with increasing concentration above the critical concentration. The 2D correlation analysis of the FTIR spectra revealed that the dipolar interactions between cyano groups of the polymer increased as concentration increased. The polarized cyano group withdrew the delocalized π-electrons in the C-N bond of the amide group of the polymer, increasing its single bond character. The molecular simulation based on this spectroscopic evidence proposed a change of molecular shapes of CY-PPTA from linear rigid rod to semi-rigid helix. The semi-rigid helical conformation where the single bond character was prevalent over the delocalized one in the C-N bond would develop a cholesteric liquid crystalline texture.

Dual morphology titanium dioxide for dye sensitized solar cells

Anatase TiO2 displaying dual morphologies were synthesized with a simple chemical route via a single step. A strong correlation between the dye sensitized solar cell (DSSC) device performance and the obtained dual morphologies are highlighted using relevant evidences from UV–vis and diffuse reflectance spectroscopy (DRS), Raman analysis, field emission scanning electron microscope, high resolution transmission electron microscope, current-voltage characteristics and impedance analysis. Structural investigation revealed that the interested medium in this work employed for the synthesis of TiO2 produced different types of dual morphologies such as nanospheres with nanoparticles (NSNP), microsphere decorated with nanoparticles (μSNP) and nanoparticles with stone like features (NPS). UV–vis and DRS results indicated the ability of the materials to assist with diffused reflectance and optical absorption of the screen printed photoanodes. In addition, an investigation of Raman vibrational characteristics was carried out in detail using synchronous and asynchronous 2D correlation analysis. The high intense Eg anatase mode of Raman spectrum was simulated using a phonon confinement model and its normalized spectra are compared with an experimental data. The resultant performances in the DSSCs were not indicative by the material properties; so, the charge transfer resistance (Rct) and recombination properties of the photoanode were investigated. These results showed that the Nyquist plot of NSNP possesses the smallest diameter, which reveals that the device based on NSNP offers the lowest Rct value that accounts for the higher conversion efficiencies when compared with the DSSC device based on photoanodes μSNP and NSP. It can be concluded that the improved power conversion efficiency shown by photoanode fabricated using NSNP has the dual role of optimum surface area for dye loading and light scattering centres. These properties, when optimized along with the offered pathway for electrolyte diffusion to the dye degeneration with less Rct, could lead to better photoelectric conversion efficiency.

Two-dimensional correlation analysis of Raman microspectroscopy of subcellular interactions of drugs in vitro.

Two-dimensional (2D) correlation analysis is explored to data mine the time evolution of the characteristic Raman microspectroscopic signatures of the subcellular responses of the nucleoli of human lung cancer cells to the uptake of doxorubicin. A simulated dataset of experimental control spectra, perturbed with systematically time-dependent spectral changes, constituted by a short-term response which represents the initial binding of the drug in the nucleolus, followed by a longer term response of the organelle metabolism, is used to validate the analysis protocol. Applying 2D correlation analysis, the in phase, synchronous correlation coefficients are seen to contain contributions of both response profiles, whereas they can be independently extracted from the out of phase, asynchronous correlation coefficients. The methodology is applied to experimental data of the uptake of doxorubicin in human lung cell lines to differentiate the signatures of chemical binding and subsequent cellular response.

Tensile deformation of polyamide (PA) 6 probed by rheo-optical near-infrared (NIR) spectroscopy

A rheo-optical near-infrared (NIR) spectroscopy, based on the combination of NIR spectroscopy and mechanical analysis, was applied to polyamide (PA) 6 samples consisting of bundled amorphous chains. Sets of strain-dependent NIR spectra as well as tensile stress of dried and wet treated PA 6 samples were collected during the mechanical elongation of the samples. The spectra were then subjected to two-dimensional (2D) correlation analysis to elucidate fine features of the spectral changes. An asynchronous correlation peak develops between the bands at 2355 and 2300 nm due to the combination modes of CH2 groups arising from the rubbery amorphous chain and rigid crystalline lamella of the dried PA 6, respectively. It therefore indicates that during the tensile deformation, the orientation of the amorphous chain is induced first to cause the elastic deformation. Further elongation results in the rotation of the crystalline lamella connected with the amorphous chain. This correlation intensity apparently increases by the wet treatment, suggesting that water molecule in the PA 6 disrupts the H-bonding interaction between the adjacent polymer chains and thus makes the polymer more flexible. Accordingly, it is likely the H-bonding between the polymer chains works in a manner somewhat similar to cross-linked polymers, which substantially effects on the mechanical property of the PA 6.

Generalized Two-dimensional Correlation Analysis for Unimodal Waveforms Modeled by Quadratic Polynomials.

We describe further potential of generalized 2D correlation analysis, aiming to realize the automation of the sequential order determination of signal variations. By modeling unimodal waveforms using quadratic functions, we can analytically express 2D correlation functions to yield an index to determine the sequential order. Based on the obtained results, we find an exception for determining the sequential order of signal variations. To resolve the exception, we suggest an extended way of interpreting the sequential order of signal intensity changes.

Secondary structure assessment of formulated bevacizumab in the presence of SDS by deep ultraviolet resonance Raman (DUVRR) spectroscopy

A deep-ultraviolet resonance Raman (DUVRR) spectroscopic method has been used to study the secondary structural changes of a therapeutic monoclonal antibody (mAb), bevacizumab (Avastin™) under a chemical stress: the presence of sodium dodecyl sulfate (SDS). The results demonstrate that DUVRR spectroscopy can assay the higher order structure of the formulated protein in a sensitive and selective manner. The SDS-induced partially unfolding of the mAb was probed by DUVRR spectroscopy where the amide I, II and III spectral features showed conformational changes between beta-sheet, alpha-helix and random coil forms. A chemometric model was also built to analyze the spectral changes occurring with protein-SDS interactions. The analysis showed there are different stages of mAb-SDS interaction as the SDS concentration increases. In addition, a two-dimensional (2D) correlation analysis was applied to the DUVRR spectra to visualize the secondary structure changes of bevacizumab under stresses. As an addition to the chemometric model, the 2D correlation mapping method suggested different transitions between secondary structure motifs were occurring at different SDS concentrations. Overall, chemometric and 2D analysis provided complimentary information, and show the potential of coupling DUVRR with advanced statistical methods in revealing complex structural information in formulated protein pharmaceuticals.

Detailed Cyclization Pathways Identification of Polyacrylonitrile and Poly(acrylonitrile-co-itaconic acid) by in Situ FTIR and Two-Dimensional Correlation analysis

In situ Fourier transform infrared spectroscopy (in situ FTIR) and two-dimensional (2D) correlation analysis were applied to investigate the cyclization pathways of polyacrylonitrile homopolymer (P...

Thermal induced structural changes of polyhydroxyamide by two-dimensional (2D) infrared correlation study

Two-dimensional (2D) correlation analysis of in situ FTIR spectra was used to probe the thermally induced structural changes in a poly(hydroxyamide) (PHA) precursor prepared from the reaction of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (Bis-AP-AF) with terephthaloyl chloride. Large spectral changes in the in situ FTIR spectra of the PHA precursor film were observed in the range of 200–300 °C. The thermal cyclodehydration reaction of the PHA precursor film strongly affects the spectral changes corresponding to the amide group and the adjacent phenyl ring in the Bis-AP-AF unit. The thermal cyclodehydration reaction of the PHA precursor film in the range of 240–300 °C induced the spectral changes in amide linkage before the formation of the benzoxazole ring.

Structural symmetry changes in SmB6 - 2D correlation spectroscopy and principal component analysis

2D correlation analysis (2DCOS) and principal component analysis (PCA) have been performed on temperature-dependent Raman spectra from 12 K to 300 K of SmB6 single crystals grown from Boron with a purity of 99.9% (3N) or 99.9999% (6N). Significant differences in the Raman spectra of SmB6(3N) and SmB6(6N) are observed. The Raman active T2g, Eg, and A1g modes of SmB6(3N) are broader and shift to higher wavenumbers compared with those of SmB6(6N). The results of 2DCOS and PCA on temperature-dependent Raman spectra of SmB6(3N) and SmB6(6N) give us further information. We find that all the T2g, Eg, and A1g modes of SmB6(6N) are single bands, while those of SmB6(3N) show all doublet features. The appearance of multiple bands in Raman vibrational modes of SmB6(3N) sample implies that the structure of boron octahedra of the SmB6(3N) has lower symmetry than that of SmB6(6N). Our findings in 2DCOS and PCA of the Raman spectra strongly support the differences in the behavior of SmB6(3N) and SmB6(6N).

Combined effect of transglutaminase and sodium citrate on the microstructure and rheological properties of acid milk gel

Combined effects of trisodium citrate (TSC), transglutaminase (Tgase) and heating were studied with relation to the mechanical properties of acid milk gels. Acidification of skimmed microfiltered milk samples was performed at 30 °C by addition of glucono – δ lactone to achieve final pH of 4.6 in 4 h. Increasing levels of TSC (0, 10 and 20 mM) were added to the samples, followed by addition of a constant level of Tgase (3 U/g of protein), and subsequent heating to 85 °C for 30 min. Prior to acidification, suspensions were analyzed in terms of amount of sedimentable material, hydration, hydrodynamic diameter (Dh) and ζ-potential (ζ) of the particles. Acid-induced gelation was studied using small deformation rheology followed by large deformation test. The water holding capacity of the gels (WHC) was performed at pH 4.6. Gels microstructure were investigated by confocal laser scanning microscopy at pH 4.6 and determination of mean pore size was performed by 2D-correlation analysis. Results showed that combined Tgase and TSC treatments had significant effect on rheological properties, WHC and gel microstructure. Higher stiffness of the gels was observed with Tgase and TSC at 10 mM, whereas a homogenous network distribution with smaller pore size was observed in the presence of Tgase and TSC at 20 mM.

A simple model for cell type recognition using 2D-correlation analysis of FTIR images from breast cancer tissue

Breast cancer is the second most common cancer after lung cancer. So far, in clinical practice, most cancer parameters originating from histopathology rely on the visualization by a pathologist of microscopic structures observed in stained tissue sections, including immunohistochemistry markers. Fourier transform infrared spectroscopy (FTIR) spectroscopy provides a biochemical fingerprint of a biopsy sample and, together with advanced data analysis techniques, can accurately classify cell types. Yet, one of the challenges when dealing with FTIR imaging is the slow recording of the data. One cm2 tissue section requires several hours of image recording. We show in the present paper that 2D covariance analysis singles out only a few wavenumbers where both variance and covariance are large. Simple models could be built using 4 wavenumbers to identify the 4 main cell types present in breast cancer tissue sections. Decision trees provide particularly simple models to reach discrimination between the 4 cell types. The robustness of these simple decision-tree models were challenged with FTIR spectral data obtained using different recording conditions. One test set was recorded by transflection on tissue sections in the presence of paraffin while the training set was obtained on dewaxed tissue sections by transmission. Furthermore, the test set was collected with a different brand of FTIR microscope and a different pixel size. Despite the different recording conditions, separating extracellular matrix (ECM) from carcinoma spectra was 100% successful, underlying the robustness of this univariate model and the utility of covariance analysis for revealing efficient wavenumbers. We suggest that 2D covariance maps using the full spectral range could be most useful to select the interesting wavenumbers and achieve very fast data acquisition on quantum cascade laser infrared imaging microscopes.