2D Correlation Spectroscopy Research Articles

Two-Dimensional Correlation Analysis of Hydrogen-Bonded Systems: Basic Molecules

This review provides information on application of two-dimensional (2D) correlation spectroscopy to studies of the molecular structure and hydrogen bonding in basic molecules and their binary mixtures with water. The first part of this review is an introduction to 2D correlation analysis and includes detailed description how to calculate the synchronous and asynchronous spectra from the raw experimental data. An appropriate pretreatment is widely discussed and the MATLAB codes to perform these operations are given. In the second part, the applications of 2D correlation spectroscopy for explorations of basic molecules like aliphatic alcohols, N-methylacetamide (NMA), diols, amino alcohols, carboxylic acids, and water in the pure liquid phases are reviewed. Finally, the 2D correlation studies of binary mixtures of basic molecules with water are discussed. It has been shown that an application of 2D correlation analysis to the complex spectra makes it possible to obtain the information not readily seen in the original data.

Order–order, lattice disordering, and order–disorder transition in SEBS studied by two-dimensional correlation infrared spectroscopy

The temperature-dependent transitions of polystyrene-block-poly(ethylene-co-1-butene)-block-polystyrene block copolymer (SEBS) at high temperature were studied using infrared spectroscopy combined with two-dimensional (2D) correlation spectroscopy. The order–order transition (OOT), the lattice disordering transition (LDT), and the order–disorder transition (ODT) of SEBS were explored with a linear temperature increment ranging from 100 to 220 °C. AFM was employed to study the surface morphology of SEBS and to identify the correlation intensity peaks in the MW2D spectra. The OOT was determined around 152 °C. The LDT appears around 170 °C. The ODT was also successfully determined around 202 °C. It is gained that the key driver of the OOT is the movements of –CH2– in the main chains of EB blocks. In the LDT, the movements of groups are simultaneous and the SEBS molecular chains move as a whole. In the ODT, it shows the driver is the movements of –CH2– in the main chains of EB blocks.

Generalized two-dimensional correlation near-infrared spectroscopy and principal component analysis of the structures of methanol and ethanol

Liquid state methanol and ethanol under different temperatures have been investigated by FT-NIR (Fourier transform nearinfrared) spectroscopy, generalized two-dimensional (2D) correlation spectroscopy, and PCA (principal component analysis). First, the FT-NIR spectra were measured over a temperature range of 30–64 (or 30–71) °C, and then the 2D correlation spectra were computed. Combining near-infrared spectroscopy, generalized 2D correlation spectroscopy, and references, we analyzed the molecular structures (especially the hydrogen bond) of methanol and ethanol, and performed the NIR band assignments. The PCA method was employed to verify the results of the 2D analysis. This study will be helpful to the understanding of these reagents.

High-resolution two-dimensional correlation spectroscopy in inhomogeneous fields: New application of intermolecular zero-quantum coherences

A new pulse sequence is proposed based on intermolecular zero-quantum coherences (iZQCs) to obtain high-resolution two-dimensional (2D) correlation spectroscopy (COSY) in inhomogeneous fields via three-dimensional (3D) acquisition. This sequence extends the high-resolution iZQC approaches from one dimension to two dimensions. Since the iZQC evolution periods in the new sequence are insensitive to the field inhomogeneities, high-resolution COSY spectra can be recovered from inhomogeneous fields by projecting the 3D data onto the indirectly acquired 2D plane. Theoretical expressions were derived according to the distant dipolar field treatment combined with product operator formalism. Both the experimental observations and computer simulations are consistent with the theoretical predictions. The new sequence thus provides an attractive way to eliminate the influences of field inhomogeneity on the conventional COSY methods, which may be useful for the study of chemical and biological materials.

Moving-window 2D correlation spectroscopy in studies of fluphenazine–DPPC dehydrated film as a function of temperature

The effect of incorporating fluphenazine (FPh) into the dipalmitoylphosphatidylcholine (DPPC) multibilayers was studied by means of two-dimensional correlation spectroscopy (2DCOS) applied to attenuated total reflection (ATR) infrared spectra. DPPC is used as a model membrane that mimics the organization of lipids in biological membranes and their interaction with FPh. ATR-IR spectra for both DPPC dry film alone and the film doped with FPh were recorded as a function of temperature to provide information about the interaction between FPh molecules and DPPC lipid. The chain-melting phase-transition temperature changes are strictly correlated with the conformational order of the lipid hydrocarbon chains. To gain deeper insight into the accompanying spectral changes, we employed moving-window 2D correlation spectroscopy. Subdividing all the measurements from 10 to 90 °C into 20° subsets enables a detailed identification of spectral features induced by embedding FPh into DPPC multilayers. Moving-window analysis of the power spectra for the ν asym,symCH 2, δ sCH 2, and δ rCH 2 vibrations provides evidence that FPh is embedded in the region between the bilayers, penetrating their hydrophilic part, which destabilizes the interchain interaction. Above 60 °C the FPh–DPPC system reaches the liquid crystalline phase with the well-established location of FPh. A further temperature increase to 90 °C has little effect on the intrachain conformational order and the packing character of the FPh–DPPC system in the liquid crystalline phase. In addition, FPh hinders the formation of large domains. Comparison of the moving-window analysis done by using slice spectra for DPPC and FPh-doped DPPC dry film for ν asym,symCH 2, νC O, and ν sym PO 2 - shows that the interaction between the DPPC and FPh molecules is accompanied by very distinct spectral changes located in a both lower and narrower temperature range than those observed in pure DPPC film.

Interactions in two-component liposomes studied by 2D correlation spectroscopy

The effect of dipping amphiphilic ICPANs (1-Alkylaminium, N-[2-[3-[3,5-bis(1,1-dimethylethyl)-4-hydroxyphenyl]-1-oxopropoxy]ethyl]-N,N-dimethyl-, bromide) homologues, characterized by varying alkyl chain length ( n = 8, 10, 12, and 16), into large multilamellar vesicles (MLVs) of dipalmitoylphosphatidylcholine (DPPC) was studied. Attenuated total reflectance infrared (ATR-IR) spectroscopy combined with 31P-NMR enabled observing a cut-off effect for the longest homologue. By employing two-dimensional correlation spectroscopy (2DCOS) for monitoring spectral changes induced by the heating process, detailed information about structural changes was obtained. They confirmed the substantial reorganization in the structure of the interfacial region in the ICPAN-C16/DPPC vesicles compared with the shorter homologues, where mainly the alkyl chains experience significant trans-to-gauche reorganization. Absorbance changes around 1400 cm −1 assigned to the symmetric deformation mode δ sym ( +N(CH 3) 3) are a good marker of changes in vesicle shape and are sensitive to the percentage of DPPC molecules directly interacting with the surface of the ATR crystal. This study clearly demonstrates the potential of 2DCOS in investigating interactions in two-component liposomes.

Net analyte signal based two-dimensional (NAS 2D) correlation near infrared spectroscopy

A new method of analysis, based on the net analyte signal presented by Lorber is proposed for the two-dimensional correlation near infrared spectroscopy. A spectra data set under the static perturbation of concentration was collected. NAS is manipulated for removing the information that was unrelated to a certain analyte. To demonstrate the potential of NAS 2D correlation spectroscopy, a set of concentration-dependent near infrared spectra of Sinomenine Hydrochloride in methanol was used as an example. The results show that NAS 2D, reconstructed from a series of principal factors can extract more subtle and useful spectra features, and make the band assignment explicable for structure analysis.

Characterization of fungal degraded lime wood by FT-IR and 2D IR correlation spectroscopy

Abstract The action of soft-rot fungus Chaetomium globosum has been studied. The decayed lime wood samples were observed for different periods of exposure. The degree of decay was determined by weight loss which was of 50.4% after 133 days. The samples were analyzed by FT-IR and 2D IR correlation spectroscopy. The intensity bands assigned to different vibrations from cellulose and hemicelluloses show a decrease, while the intensities of the bands assigned to C–O vibrations due to the formation of oxidized structures increase. At the same time, the intensity of the band assigned to C–O in metoxyl groups from lignin shows a decrease with increasing exposure time. The differences between reference and decayed wood spectra were examined in detail using 2D correlation spectroscopy and the second derivative analysis for two exposure time periods — of 0–70 days and 70–133 days. The formation of reactive species due to oxidation reactions induced by enzymes and the demethoxylation of the lignin structure was evidenced.

Concatenated Two-Dimensional Correlation Analysis: A New Possibility for Generalized Two-Dimensional Correlation Spectroscopy and its Application to the Examination of Process Reversibility

We propose a new application of generalized two-dimensional (2D) correlation spectroscopy called "concatenated" 2D correlation analysis, which is useful in identifying the presence of strict similarity or very subtle difference between two spectral data sets having a similar origin. This approach is very efficient and can offer many potential applications. In this study, the detailed examination of process reversibility is explored. Two forms of concatenation, horizontal and vertical concatenation of data matrices, are introduced and the latter is discussed in detail. Concatenated 2D correlation analysis allows one to investigate directly the correlation between two independent but related spectral data sets. It can extract more detailed information, such as the comparison of effects of two different perturbations or different systems. We describe the principle of the "mirror-image concatenation" in 2D correlation analysis, which is applied to demonstrate its reliability and efficiency on three spectral models: a synthetic simulation data set; experimental Fourier transform infrared (FT-IR) spectra of the thermally induced unfolding-refolding transition of bovine pancreatic ribonuclease A (RNase A) in aqueous solution; and a set of FT-IR spectra of traditional Chinese medicines (TCM) of similar origin. The concatenated 2D correlation analysis shows its power in revealing the irreversibility of the thermally induced conformation transition of RNase A as well as the comparison of different species of TCM.

Two-dimensional correlation spectroscopy — Biannual survey 2007–2009

The publication activities in the field of 2D correlation spectroscopy are surveyed with the emphasis on papers published during the last two years. Pertinent review articles and conference proceedings are discussed first, followed by the examination of noteworthy developments in the theory and applications of 2D correlation spectroscopy. Specific topics of interest include Pareto scaling, analysis of randomly sampled spectra, 2D analysis of data obtained under multiple perturbations, evolution of 2D spectra along additional variables, comparison and quantitative analysis of multiple 2D spectra, orthogonal sample design to eliminate interfering cross peaks, quadrature orthogonal signal correction and other data transformation techniques, data pretreatment methods, moving window analysis, extension of kernel and global phase angle analysis, covariance and correlation coefficient mapping, variant forms of sample–sample correlation, and different display methods. Various static and dynamic perturbation methods used in 2D correlation spectroscopy, e.g., temperature, composition, chemical reactions, H/D exchange, physical phenomena like sorption, diffusion and phase transitions, optical and biological processes, are reviewed. Analytical probes used in 2D correlation spectroscopy include IR, Raman, NIR, NMR, X-ray, mass spectrometry, chromatography, and others. Application areas of 2D correlation spectroscopy are diverse, encompassing synthetic and natural polymers, liquid crystals, proteins and peptides, biomaterials, pharmaceuticals, food and agricultural products, solutions, colloids, surfaces, and the like.

Temperature-dependent infrared spectrum of (Bu 4N) 2[Ru(dcbpyH) 2-(NCS) 2] on nanocrystalline TiO 2 surfaces

The thermal degradation behavior of the self-assembled thin films of (Bu 4N) 2[Ru(dcbpyH) 2-(NCS) 2] (N719) anchoring on TiO 2 surfaces via its carboxylate group has been studied using temperature-dependent diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Our analysis indicate that the decomposition temperature of N719 appeared to be at ≈270 °C on TiO 2 surfaces, whereas such decompositions occurred at temperatures higher than ≈340 °C in their solid states as line with the thermal analysis data. This change was also found to be irreversible, if heated above 100 °C on TiO 2 surfaces. Our 2D correlation spectroscopy and principal component analysis (PCA) applied to the temperature-dependent DRIFT spectra supported that the thermal degradation mechanism for N719 should differ in its solid state and on TiO 2 powder surfaces. The NCS stretching vibrational intensities of the neat N719 vibrations were found to shift from 2102 to 1975 cm −1 increase with increase in temperatures, whereas similar vibration changes from 2095 to 2008 cm −1 were observed for N719 attached to TiO 2. Referring from the open-circuit potential, short-circuit, fill factor, and efficiency measurements for the N719 dye-loaded photoelectrodes depending on temperature, the NCS stretching band at ∼2008 cm −1 on TiO 2 surfaces appeared to be correlated with the thermal degradation of the DSSCs.

Self-assembling of oleic acid ( cis-9-octadecenoic acid) and linoleic acid ( cis-9, cis-12-octadecadienoic acid) in ethanol studied by time-dependent attenuated total reflectance (ATR) infrared (IR) and two-dimensional (2D) correlation spectroscopy

The dynamic behavior of liquid oleic and linoleic acids in ethanol has been explored by applying attenuated total reflectance (ATR) infrared (IR) spectroscopy. Fine spectral features are obtained with two-dimensional (2D) correlation spectroscopy. When the solution mixture was exposed to the open atmosphere, the complexes between the carboxylic acids and ethanol begin to dissociate and it starts the formation of dimers of the carboxylic acids. As the evaporation proceeds, the dimeric molecules undergo the self-assembling to form tightly packed quasi-smectic liquid crystal structure. The hetero-system 2D correlation spectra developed with two sets of time-dependent ATR–IR spectra of oleic and linoleic acids reveal that linoleic acid molecules aggregate faster as compared with oleic acid ones during the self-assembling mostly due to the difference in the number of the C C bonds.

An application of concatenated 2D correlation spectroscopy: Exploration of the reversibility of the temperature-induced hydration variation of poly( N-isopropylmethacrylamide) in aqueous solution

We have demonstrated an application of “concatenated” 2D correlation analysis in quantitative or semi-quantitative examination of the reversibility of the temperature-induced hydration variation of PNiPMA in water solution. Hydration reversibility of hydrophilic amide group and hydrophobic CH group are compared in different temperature ranges. The appearance of significant cross-peaks in the asynchronous spectrum calculated from the roundtrip data matrix indicates the existence of certain inter-asynchronicity between heating and cooling cycle. The contribution of different factors to the 2D asynchronous spectrum could be separated by selecting the range of the spectral dataset for concatenation. The irreversibility of the temperature-induced hydration variation in PNiPMA is not constant during the whole round trip: it is most obvious in the phase separation process, while in the range far away from that period it is nearly neglectable. The hydration variation of PNiPMA manifests significant irreversibility in the phase separation stage. The asynchronous peaks of hydrophobic CH groups are much weaker than that of hydrophilic amide group during any temperature range in the temperature round trip. The irreversibility of CH groups is not as strong as that of amide group during the round trip. It further supports the conclusion that the hydration variation of hydrophilic amide group is dominated in the temperature-induced phase separation of the polymer in water solution.

The relative error caused by reproducibility in two-dimensional correlation spectroscopy

Reproducibility is a very important issue for the construction and interpretation of two-dimensional (2D) correlation spectra. This paper introduced the way to estimate the relative error in 2D correlation spectroscopy, especially focused on the possible source of errors that may arise from the limitation of experimental reproducibility. Mainly two sources of reproducibility are examined. The first is the reproducibility of the performance of experimental apparatus, in which the baseline drift as well as the noise level of spectroscopic measurements are taken into consideration. The maximum intensities of the 2D correlation maps obtained by the measurement of a series of small fluctuations of baselines are typically only in the order of 10 −5 and 10 −7, respectively, for synchronous or asynchronous spectra, which are so small that their effect can be safely ignored. Meanwhile, the 2D correlation maps based purely on the experimental noise can also be constructed, which provides the threshold above which any correlation can be treated as meaningful. The second source of relative error is caused by the reproducibility of the experimental condition. The most commonly used perturbations for generalized 2D correlation spectroscopy are concentration and temperature. Therefore, the effect of the reproducibility of the concentration of each sample prepared, as well as the small variation of the temperature during the measurement, which may all give rise to relative error, was examined. A quantitative measure of the extent of relative error caused by this kind of reproducibility can also be analyzed by using 2D correlation maps.

Comprehensive determination of (3)J (HNHalpha) for unfolded proteins using (13)C'-resolved spin-echo difference spectroscopy.

An experiment is presented to determine 3JHNHα coupling constants, with significant advantages for applications to unfolded proteins. The determination of coupling constants for the peptide chain using 1D 1H, or 2D and 3D 1H-15N correlation spectroscopy is often hampered by extensive resonance overlap when dealing with flexible, disordered proteins. In the experiment detailed here, the overlap problem is largely circumvented by recording 1H-13C′ correlation spectra, which demonstrate superior resolution for unfolded proteins. J-coupling constants are extracted from the peak intensities in a pair of 2D spin-echo difference experiments, affording rapid acquisition of the coupling data. In an application to the cytoplasmic domain of human neuroligin-3 (hNlg3cyt) data were obtained for 78 residues, compared to 54 coupling constants obtained from a 3D HNHA experiment. The coupling constants suggest that hNlg3cyt is intrinsically disordered, with little propensity for structure.

Synthesis and complexation properties towards metal ions of new tri-substituted thiacalix[4]arenes

New thiacalix[4]arenes appended with three amide functions have been prepared. Their conformations have been solved thanks to 1H NMR 2D correlation spectroscopy (COSY) and nuclear overhauser and exchange spectroscopy (NOESY). The complexation ability of these ligands towards various metal ions (Cd2 + , Pb2 + , Pd2 + , Ni2 + , Hg2 + , Hg+, Ag+, Zn2 + and Cu2 + ) has been investigated by the UV–vis absorption and the stoichiometry of the metal–ligand complexes was determined.

Structural changes in biodegraded lime wood

The changes in structure of lime wood ( Tilia cordata Mill.) decayed by Trichoderma viride Pers. have been investigated by FT-IR and 2D IR correlation spectroscopy. Wood was exposed to fungi for different durations up to 84 days, with decay assessed through mass loss and FT-IR. A decrease of intensities bands assigned to different vibrations from cellulose and hemicelluloses, with increasing intensities of the bands assigned to C O vibrations due to formation of oxidized structures was observed; and examined in details using 2D-correlation spectroscopy and the second derivative analysis in the exposure time range of 0–35 days. The formation of reactive species due to oxidation reactions induced by enzymes was evidenced. It has been also established that after longer degradation period oligomers and oxidized structures result, and finally small fragments containing carboxyl or carbonyl groups are formed, which lead to loss of structural integrity of the lime wood.

An experimental study on the “sequential order” rules in generalized two-dimensional correlation spectroscopy

Following our theoretical analysis on the “sequential order” rules in generalized two-dimensional (2D) correlation spectroscopy (H. Huang, Anal. Chem. 79 (2007) 8281–8292), an experimental study was conducted to test the “sequential order” rules using the FT-NIR data of poly(3-hydroxybutyrate) (PHB)/poly( l-lactic acid) (PLA) blends under uniaxial elongation and parallel polarization. The local sequential order concept proposed for the generalized two-dimensional (2D) correlation spectroscopy is now more clearly stated; “the intensity change at ν1 occurs predominantly before ν2” means that the starting time of the intensity change at ν1 is prior to that at ν2. It is this local sequential order which reflects the real and intuitive sequential order between two events in generalized situations. It has been found that the integrated/ overall sequential order results obtained from the 2D correlation analysis may be contradictory to the intuitive local sequential order. In addition, different integrated/ overall sequential orders could be obtained by selection of different sampling intervals from a certain set of experimental data, or choosing different number of the contours for the same sampling interval. These new experimental findings are a perfect reinforcement to our previous theoretical study and have further demonstrated the uncertainty of applying the “sequential order” rules in generalized 2D correlation spectroscopy.

Quantitative Classification of Two-Dimensional Correlation Spectra

Two-dimensional (2D) correlation spectroscopy, which takes advantage of the apparent enhancement of spectral resolution, is known to be useful in qualitative discrimination of seemingly similar samples. The possibility of quantitative classification of 2D correlation spectra is even more desirable. Two useful parameters, namely Euclidian distance and correlation coefficient between 2D correlation spectra, are introduced for this purpose. Dry and sweet red wine samples are used to demonstrate the utility of these parameters. The distances between the 2D infrared (IR) spectra of sweet and dry red wines are roughly proportional to the differences of sugar contents in them. The result shows that the two parameters are useful measures for the quantitative evaluation of the similarity among the samples and their corresponding 2D correlation spectra.

Application of 2D correlation spectroscopy with MCR in the preparation of glycerol polyesters

The condensation of glycerol and adipic acid was studied by 2D correlation spectroscopy in combination with MCR to identify spectral changes associated with this polymerization reaction and to describe the development of structure in the polymer. This biobased polymer is being evaluated for use as a controlled release matrix where the extent of reaction is a key performance parameter. A spectroscopic technique was sought to estimate the extent of reaction and guide product development. FT-IR spectra were collected as the reaction was performed on a temperature programmable ATR assembly fitted to a Bruker Tensor 27 spectrophotometer. The resulting time series was analyzed by 2D correlation spectroscopy. Correlation maps were used to identify bands related to the formation of the polymer and multivariate curve resolution (MCR) was applied to develop a model in terms of pure components. This combined technique offers a rapid method for sample analysis and facilitates the preparation of materials to a specified extent of reaction.