Dimensional Correlation Analysis Research Articles

The effect of pH on the bonding of Cu2+ and chitosan-montmorillonite composite

Based on the contradict statements on the mechanisms of the bonding between metal ions and chitosan based adsorbent, this paper present studies on the Cu2+ adsorption by the chitosan-montmorillonite composite. The in situ attenuated total reflectance Fourier transform infrared spectroscopy and two dimensional correlation analysis were used to record the spectra during the adsorption and the pH perturbation, and analyze the interaction sequence of the groups related to the adsorption, respectively. The results showed that the bonding with −NH3+ might attribute the adsorption capacity greater than that with hydroxyl. The hydroxyl of chitosan (or composite) take part in the Cu2+ adsorption at pH 3.0–5.0 and were more active at lower pH. The amino replaced hydroxyl as the bonding sites with the change of −NH3+ to −NH2 by proton exchange when pH was near 5.0.

Studies of reorganization of the molecules during smectic A–smectic C phase transition using infrared spectroscopy and generalized two-dimensional correlation analysis

The FT-IR spectra of the 4-hexyloxybenzylidene-4′-dodecyloxyaniline (6BA12) were studied as a function of temperature to describe reorganization of spatial distribution of molecules during various liquid crystal phase transitions: isotopic liquid (IL) – nematic (N), nematic – smectic A (SmA), smectic A – smectic C (SmC), smectic C – smectic I (SmI). The main focus is on the SmA-SmC and SmC-SmI transitions. Two dimensional correlation analysis (2D-IR) of IR spectra has been used to check changes of the arrangement and specific interactions of molecules during phase transitions. A moving-window autocorrelation analysis has been applied to locate transition points basing on the spectroscopic data.

Vibrational spectroscopic analysis of a metal/carbon nanotube coating interface and the effect of its interaction with albumin

Multi-walled carbon nanotubes (MWCNTs) as a modifying phase on the titanium support can be potentially used for medical purposes as a material for the production of implants or implantable electrodes or for applications for cardiac surgery. Developing better blood compatible biomaterials must be connected with the condition of their anti-thrombogenic characteristic. A carbon nanotube layer was formed on a titanium plate coated in half with MWCNTs to have admission to: MWCNTs coating, to the Ti/MWCNTs interface region at the MWCNTs coating edge and finally to the Ti support. The Raman measurements were performed in two different locations: in the interface/edge region of the titanium and MWCNTs coating and in the center of the MWCNTs layer. For each of these positions, measurements in two different depths were performed: on the sample top surface of the MWCNT layer and near the bottom of the MWCNTs layer, i.e. at the titanium support interface. The studied sample regions differ in G-, D- and D′-mode structural characteristics as dispersion, crystallinity, the size of the arranged domains, and the distance between the point defects. The phase boundary region is more disordered and exposed to a greater surface tension. These features influence the interactions with albumin which represented the material behavior in contact with the tissue. The MWCNTs coating is hydrophilic (contact angle ∼55°), in the border area this value increases to ∼60°, then Ti support is hydrophobic (∼98°). Two dimensional correlation analysis allows us to unravel albumin-MWCNTs' interaction. The cross-peaks show a contribution from G+ and G− carbon nanotubes bands and protein secondary structure demonstrating the formation of a film on the surface of the test sample and indicate the change of the albumin conformation during adhesion.

Applications of FTIR spectroscopy in environmental studies supported by two dimensional correlation analysis

In this paper, we report the joint use of FTIR spectroscopy and two dimensional correlation analysis (2DCORR) applied to the identification of the aggregation pathways of natural organic matter (i.e. humic substance) extracted from marine sediments and in the second case of study, to the comparison of the molecular modifications caused by the actions of different pollutants on a marine algae used as biomarker of environmental quality. In the first application, the extractable humic substance (HS) from sediments was ultra-filtered to obtain seven sub-fractions of HS with molecular weight (mw) < 1kDa and > 100kDa. After the examination of FTIR spectra of each sediment samples, 2DCORR was applied to examine the molecular mechanism of the aggregation process. This approach allows to differentiate the role played by carbohydrates, lipids and proteins during the evolution of the aggregation process. Carbohydrates are significant in any phase of the aggregation while proteins though significant in any phase of the aggregation seem to play a role strictly related to polymerisation reaction with carbohydrates. Lipids play a completely different role in the aggregation process with respect to carbohydrates and proteins because they are significant only in sub-fractions of HS with mw < 1 kDa and mw > 5 kDa, so suggesting that their role is the so called cross-linking action (i.e. bridge among lower mw aggregate), already observed in the aggregation of terrestrial HS. In the second application of FTIR spectroscopy and 2DCORR, the acetone extracts of Dunaliella tertiolecta prepared according to the ISO standard protocol for toxicity test, were examined in presence of several inorganic and organic pollutants to study the molecular modifications caused by pollutant actions in algal cells. This approach allows to differentiate the molecular mechanisms of toxic action for the observed pollutants. Heavy metals such as Hg, Zn, Cr (VI) and Cu cause modifications of carbohydrate lipid and nucleic acid contents and structural modifications (i.e. inter and intra molecular hydrogen bonds) of these biomolecules simultaneously. Glycols compounds cause modifications of carbohydrates lipids and nucleic acids contents and structural modifications too as observed for heavy metals but without an evident simultaneity between the two types of modification. At last, surfactants cause modifications of carbohydrates lipids and nucleic acid contents only. These experimental results suggest that the use of FTIR spectroscopy with 2DCORR analysis is a potential tool for evaluating toxic effects in the study of environmental quality of marine samples.

Two Dimensional Correlation Analysis of Fourier Transform Ion Cyclotron Resonance Mass Spectra of Dissolved Organic Matter: A New Graphical Analysis of Trends

Two-dimensional (2D) correlation analysis was applied to 20 Fourier transform ion cyclotron resonance mass spectra (FTICR-MS) of ultrafiltered dissolved organic matter samples from a salinity transect of the lower Chesapeake Bay. We were able to investigate the chemical changes in the dissolved organic matter pool at the molecular level and classify the individual peaks based on their biogeochemical reactivity. The power of this technique is its ability to be used on either the presence/absence of the individual peaks or their normalized magnitudes. The presence or absence of the peaks are utilized to identify the reactivity and correlation between peaks that plot in different regions of the van Krevelen diagram, whereas the normalized magnitudes are used to correlate the changes among individual peaks. One of the promising advantages of 2D correlation of FTICR-MS data is the ability to associate the variations of the individual peaks with the changes in the functional groups that are measured by other spectroscopic techniques. This approach takes us one step further from identifying molecular formulas to proposing chemical structures.

Thermal ageing behavior of styrene–butadiene random copolymer: A study on the ageing mechanism and relaxation properties

Thermal oxidative ageing process of commercial available styrene–butadiene random copolymer (SBR) has been studied by the combination use of in-situ collected dynamic FTIR spectrum and two dimensional correlation analysis. The modification on the viscoelastic properties were studied by dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). It was found that the degradation took place predominantly in the aliphatic segment at the allylic position, giving rise to a maximum absorption at 1725 cm−1 in the carbonyl stretching region. The initiation process occurring in the aromatic parts produced acetophenone end groups as evidenced by the shoulder peak at 1679 cm−1. A series of oxygenated species were identified in the dynamic spectrum including anhydrides, lactones, peracids, aliphatic ketones and unsaturated carbonyl species. However, the band of unsaturated carbonyl species at 1695 cm−1 varied nonmonotonously, first increase sharply and then decreased. Concerning the concentration of double bonds, a detailed analysis revealed the different evolving trend between benzylic and aliphatic vinyls. The former showed an increment whereas the later were found to decrease, resulting in the broadening at 1638 cm−1. Furthermore, the relative generation rates of different carbonyls were ranked by two dimensional correlation analysis together with two shoulder peaks at 1713 and 1679 cm−1 identified subtly in the asynchronous spectrum. On the basis of the above spectroscopic results, the mechanisms of thermal degradation were proposed.The relaxation behavior of thermally degraded SBR was studied by DMA and DSC. Both of the two techniques evidenced an increasing and broadening Tg, suggesting the crosslinking reaction dominated thermal degradation. After checking the normalized spectra, it is found that all of the relaxation curves (irrespective of storage modulus, loss modulus or loss tangent) get widen over ageing. Two parameters, steepness (S) and wideness index (W) were defined in normalized storage modulus plot to make a quantitative discussion. The S reduced whereas the W rose up after degradation. The broader glass transition zone after ageing was attributed to the more heterogeneous relaxation environment and the wider size distribution of motion units participating in the transition.

Study on the effect of temperature on the conformation of cross-linked collagen by two-dimensional infrared correlation spectroscopy

The Fourier transform infrared spectroscopy and two dimensional correlation analysis method were applied to study a denaturing process of uncross-linked collagen and cross-linked collagen during varying temperature. It was found that the intensity of typically characteristic absorptions of collagen decreased and its peak shifted to low frequency, The amide II central absorbance peak moved to a lower frequency by about 10 cm(-1), which indicated that the inter-chain hydrogen bonds which stabilized the triple helix conformation of collagen were disrupted during thermal denaturation, resulting in a conformational change. The intensity of auto-peak at 1 515 cm(-1) was maximum, which suggested that the temperature had a big impact on amide II. In comparison with uncross-linked collagen, the intensity of cross-peaks of cross-linked collagen was weaker, which demonstrated that the effect of temperature on the structure of cross-linked collagen was smaller, and the thermal stability properties of collagen solution could be improved by cross-linking. While the order of second structure changes of cross-linked collagen was different. These fundamental data should provide available information for understanding the relationship between the structure and function of cross-linked collagen.

Analysis of CO 2–NH 3 reaction dynamics in an aqueous phase by PCA and 2D IR COS

Both carbamation and bicarbonation are of prime importance in the absorption reactions of CO 2 in an aqueous NH 3 solution, as they are related to the CO 2 working capacity, regeneration energy, and the critical problem of blocking the gas pathway for the CO 2 capture process. Herein, the influence of reaction temperature on the CO 2 and NH 3 reaction in an aqueous solution is demonstrated by a principal component analysis (PCA) and a two dimensional correlation analysis (2D IR COS) obtained from FT-IR, dependent on the reaction time. In contrast to the reaction at 298 K, conversion of the dominant reaction from carbamation to bicarbonation and respective conformational changes were observed at 278 K by PCA and 2D IR COS. The PCA results elucidate that two major reactions following the dependence of reaction time were divided into two regions, I and II. The turnover point was subsequently tracked in these two regions, where precipitation of ammonium bicarbonate occurred due to the limitation of solubility at this turning point. The interrelation and sequential variation of conformations in regions I and II were investigated by synchronous and asynchronous 2D correlation analyses. The combination of PCA and 2D IR COS provides a powerful and useful analytic method to capture and monitor the dynamics of complex chemical reactions.

Isothermal crystallization behavior of water in poly(vinyl methyl ether) aqueous solution investigated by infrared and two-dimensional infrared correlation spectroscopy

Isothermal crystallization behavior of water at −30 °C in PVME aqueous solution with the PVME concentration in the range of 40–60 wt% was investigated in detail by time-dependent infrared spectroscopy and two dimensional correlation analysis. The result suggests that when the PVME concentration is between 40 and 60%, the crystallization rate decreases with increasing PVME concentration, and the crystallization of water in low temperature is kinetically controlled. Of particular interest is that the so-called “unfrozen bound water” can be frozen slowly when PVME aqueous solution is annealed at a suitable low temperature. The crystallization mechanism of water in PVME/water system is elucidated by 2D correlation analysis.