Trends in Fourier transform infrared spectroscopic imaging

Fourier transform infrared (FTIR) spectroscopic imaging is a relatively new method that has received great attention as a new field of analytical chemistry. The greatest benefit of this technique lies in the high molecular sensitivity combined with a spatial resolution down to a few micrometers. Another advantage is the ability to probe samples under native conditions, which allows new insights into samples without the need for fixation, stains, or an additional marker. Advances in instrumentation have made FTIR spectroscopic imaging the tool of choice for an increasing number of applications. The main applications are in the bioanalytical chemistry of cells and tissue, polymers, and recently as well as in homeland security. This report gives a short overview of current developments and recent applications. Figure FTIR image of a polymer blend reveals the chemical composition. Online Abstract Figure (365 KB).     

Nature of water in nacre: a 2D Fourier transform infrared spectroscopic study

In this work, the interactions of aragonite and organic matrix in nacre with water are investigated using two-dimensional (2D) Fourier transform infrared (FTIR) spectroscopy. The 2D-FTIR analysis revealed four bands in the OH stretching region at around 3550, 3445, 3272 and 3074 cm(-1). Two additional bands were found at around 3616 and 3282 cm(-1) after deconvolution of the nacre spectrum. The bands at around 3616 and 3550 cm(-1) are assigned to asymmetric and symmetric OH stretching of partially hydrogen bonded water molecules. The bands at around 3445 and 3272 cm(-1) are assigned to asymmetric and symmetric OH stretching of water molecules fully hydrogen bonded with surrounding water molecules. Presence of above bands in the nacre spectrum suggests that water, in form of clusters, is present in protein matrix and aragonite pores. Water may also hydrogen bond with the organic matrix. The bands observed at 3282 and 3074 cm(-1) are assigned to asymmetric and symmetric OH stretching of water molecules, chemisorbed on surfaces of aragonite platelets. Polarization experiments suggest that H-O-H plane of water molecules is along to c-axis of aragonite platelets.     

Fourier transform infrared spectroscopic study of the photocatalytic degradation of cancerous cells on titanium dioxide

The method of attenuated total internal reflection Fourier transform IR spectroscopy has been used to study the oxidation kinetics of the biomolecular components of the eukaryotic cancerous HeLa cells initiated by the photogenerated charges on TiO₂. It was shown that the organic material of the cells on the porous film of the TiO₂ nanoparticles was mineralized in a such way that the TiO₂ surface was purified. The basic organic groups of Amide-I, Amide-II and phosphate were oxidized at different rates. Amide-II oxidized most rapidly, then followed Amide-I. The phosphate was the most resistant to oxidation.     

A Fourier transform infrared spectroscopic study of Mg-rich, Mg-poor and acid leached palygorskites

The FTIR spectra of pure magnesium-rich (Mg-rich) and magnesium-poor (Mg-poor) palygorskites, before and after short-term (<7 h) and long-term (360 h) acid leaching are presented here. Comparison of decomposition spectra of Mg-rich and Mg-poor palygorskites clearly shows that the absorption peaks related to pairs of octahedral cation differ depending on the octahedral site occupancy. Short-term acid leaching of palygorskites results in significant changes to FTIR absorption bands near 1200 and 790 cm-1. As the acid attack progresses, the band at 1200 cm-1 shifts to lower wavenumbers, whilst the band at 790 cm-1, which here is assigned to SiU-O-SiD symmetrical stretching vibration, shifts to higher wavelengths. Longer-term leaching of palygorskites results in the disappearance of 900-1200 cm-1 absorption bands, showing that the palygorskite has largely decomposed to amorphous silica. Assignments of several other bands have been made as follows: several vibrations relate to OH, i.e. 847 cm-1, hygroscopic water (1635 cm-1), Si-O vibrations 1100, 611-621, 470-481 cm-1, etc. appear in the FTIR spectra of 360 h acid leached palygorskite. Three bands near 1100, 611-621 and 470-481 cm-1 relate to Si-O vibration of an ideal hexagonal (Si2O5)n sheet.     

Fourier transform infrared spectroscopic studies of the secondary structure and thermal denaturation of CaATPase from rabbit skeletal muscle

Fourier transform i.r. spectroscopy has been used to monitor structural alterations induced by thermal denaturation of the intrinsic membrane protein CaATPase in aqueous media. The protein has been isolated, purified and studied in five forms:

• 1.(i) In its native lipid environment after isolation from rabbit sarcoplasmic reticulum, both in H₂O and D₂O suspensions.
• 2.(ii) After both mild and extensive tryptic digestion has cleaved those residues external to the membrane bilayer.
• 3.(iii) Reconstituted in vesicle form with bovine brain sphingomyelin.

Fourier deconvolution techniques have been used to enhance the resolution of the intrinsically overlapped Amide I and Amide II spectral regions. Large spectral alterations apparent in the deconvoluted spectra occur in these regions upon thermal denaturation of the protein which are consistent with the formation of a large proportion of β-antiparallel sheet form. The alteration parallels the loss in ATPase activity. A mild tryptic digestion increases slightly the proportion of α-helix and/or random coil secondary structure. A thermal transition to a form containing a high proportion of β structure is still evident. Extensive tryptic digestion nearly abolishes the alpha helical plus random coil secondary structure, while producing a high proportion of β form which is resistant to further thermally induced structural alterations.Studies of CaATPase reconstituted into vesicles with bovine brain sphingomyelin reveal a higher proportion of β structure than the native enzyme, with further introduction of β structure on thermal denaturation. Both the utility of deconvolution techniques and the necessity for caution in their application are apparent from the current experiments.     

Combined Fourier transform infrared and Raman spectroscopic studies of some carbonyl-diphosphine-indenyl-iron cations

The Fourier transform infrared and Raman spectra of the cations [η⁵-C₉H₇Fe(CO)_n dppa]⁺ (n = 1, 2; dppa=bisdiphenylphosphinoalkane, where alkane=methane, ethane, butane, hexane and octane) and [{η⁵-C₉H₇Fe(CO)₂}₂-μ-dppa]²⁺ indicate that the alkyl chain lengths have effects on the structures of the bidentate cations resulting in increased back-donation to carbonyl groups as the chain length increases. In contrast the alkyl chain lengths have no similar effects in the unidentate mononuclear and bridged cations.     

Fourier transform infrared spectroscopic determination of cypermethrin and deltamethrin in emulsifiable concentrate formulations

Fourier tranform infrared (FT-IR) spectroscopic method has been developed for determination of cypermethrin and deltamethrin in emulsifiable concentrate formulations. The known concentration of formulation was subjected to preparative thin layer chromatography and the active ingradient zone was scrapped from the plate. Pyrethroids were eluted from the adsorbent with chloroform and estimated by measuring the ester carbonyl absorption band at 1749 cm(-1) in cypermethrin and at 1743 cm(-1) in deltamethrin using base line technique. Recoveries of cypermethrin and deltamethrin from commercial and laboratory prepared formulations were 90 to 97% in both the cases. The validity of FT-IR method was confirmed by comparing the results with standard HPLC method.     

Fourier transform infrared spectroscopic study of water-in-supercritical CO2 microemulsion as a function of water content

Fourier transform infrared (FT-IR) spectrum of water-in-supercritical CO(2) microemulsion was measured at 60 degrees C and 30.0 MPa over a wide range of water/CO(2) ratio from 0.0 to 1.2 wt % to study the distribution of water into CO(2), interfacial area around surfactant headgroup, and core water pool. The microemulsion was stabilized by sodium bis(1H,1H,2H, 2H-heptadecafluorodecyl)-2-sulfosuccinate [8FS(EO)(2)] equimolarly mixed with sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate [FC6HC4] or with poly(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether [TMN-6]. The signal area of the O-H stretching band of water suggested that the number of water molecules in the microemulsion increases linearly with the water/CO(2) ratio, except for a slow initial increase below 0.4 wt % due to a part of water dissolved in CO(2). The amount of water in CO(2) was evaluated by decomposing the bending band of water into two components, one at lower frequency ascribed to water in CO(2) and the other at higher frequency to water in the microemulsion. The decomposition confirmed that CO(2) is saturated with water at the water content of 0.4 wt %. It was also revealed, from the symmetric SO stretching frequency of the surfactant, that the sulfonate headgroup is completely hydrated at the water/CO(2) ratio of 0.4-0.5 wt %. The results demonstrated that water is introduced preferentially into CO(2) and the interfacial area at small water content, and then is loaded into the micelle core after the saturation of CO(2) with water and the full hydration of the surfactant headgroup.     

Fourier transform infrared spectroscopic and theoretical study of water interactions with glycine and its N-methylated derivatives

In this study we attempt to explain the molecular aspects of amino acids' hydration. Glycine and its N-methylated derivatives: N-methylglycine, N,N-dimethylglycine, and N,N,N-trimethylglycine were used as model solutes in aqueous solution, applying FT-IR spectroscopy as the experimental method. The quantitative version of the difference spectra method enabled us to obtain the solute-affected HDO spectra as probes of influenced water. The spectral results were confronted with density functional theory calculated structures of small hydration complexes of the solutes using the polarizable continuum model. It appears that the hydration of amino acids in the zwitterionic form can be understood allowing a synchronized fluctuation of hydrogen bonding between the solute and the water molecules. This effect is caused by a noncooperative interaction of water molecules with electrophilic groups of amino acid and by intramolecular hydrogen bond, allowing proton transfer from the carboxylic to the amine group, accomplishing by the chain of two to four water molecules. As a result, an instantaneous water-induced asymmetry of the carboxylate and the amino group of amino acid molecule is observed and recorded as HDO band splitting. Water molecules interacting with the carboxylate group give component bands at 2543 ± 11 and 2467 ± 15 cm(-1), whereas water molecules interacting with protons of the amine group give rise to the bands at 2611 ± 15 and 2413 ± 12 cm(-1). These hydration effects have not been recognized before and there are reasons to expect their validity for other amino acids.     

Fourier transform infrared spectroscopy study of nanostructured nickel oxide

Nanostructured nickel oxide having different average particle sizes ranging from 3 to 16 nm were synthesized and Fourier transform infrared (FTIR) spectra of the samples were recorded in the far infrared (IR) region. The spectra were found to be dominated by surface mode absorptions with no distinct absorption corresponding to the bulk transverse optical mode. IR absorption coefficient, alpha, for the nanostructured NiO samples were calculated as a function of frequency using a macroscopic approach devised by Fuchs. The effects of crystalline geometry, numerical values of optical constants, filling factor and increased damping on the spectral features of the samples were analyzed. Though the simulations approximately reproduced the occurrence of a shoulder in the experimental spectra, the most intense peak in the simulated spectra was found to be about 50 cm(-1) above the corresponding experimentally observed peak. It was shown that the experimentally observed absorption maximum of all the samples were in close agreement with that determined using a microscopic theory based on the rigid ion model. The weak absorption peaks in the frequency region 60-100 cm(-1) appearing in the spectra of all the samples were identified as surface induced transverse acoustical modes, omegaTA, which became IR active due to the breakdown of translational symmetry in the nanocrystallites.     

Fourier transform infrared study of segmental orientation in polymer blends

The effect of the macromolecular plasticizer poly(-methyl--n-propyl--propiolactone), PMPPL, on the orientation of poly(vinyl chloride), PVC, has been studied by FTIR spectroscopy. The addition of PMPPL to PVC does not change significantly the degree of orientation of PVC segments. In blends, PMPPL chains are more oriented when the matrix is richer in PVC but the PMPPL orientation function always remains smaller than that of PVC segments.     

Fourier transform infrared study of uniaxially oriented atactic polystyrene

Infrared measurements of the dichroic ratio of atactic polystyrene absorption bands provide a valuable method of determination of the overall orientation of chains as well as the particular orientation of the trans conformational segments. The orientation process produces the alignment of the chains as well as an increase in the amount of trans conformational segments. A linear relationship is observed between birefringence and dichroic ratio for the absorption bands characteristic of overall orientation. A value of 35° ± 3° is obtained for the angle between the normal to the plane of the benzene ring and the chain axis from both infrared and birefringence determinations.     

Fourier transform approach to potential harmonics

Because of the high degeneracy of hyperspherical harmonics, a method is needed for selecting the most important ones for inclusion in hyperangular basis sets. Such a method was developed by M. Fabre de la Ripelle, who showed that the most important harmonics are λ-projections of the product of the potential and a zeroth-order wave function; and he gave these the name, “potential harmonics.” In the present study we develop Fourier-transform-based methods for generating potential harmonics and for evaluating matrix elements between them. These methods are illustrated by a small calculation on three-body Coulomb systems with a variety of mass ratios. © 1997 John Wiley & Sons, Inc.     

The study of a single BGC823 cell using Fourier transform infrared microspectroscopic imaging

In order to investigate gastric cancer at cellular and sub-cellular level, a single human gastric adenocarcinoma BGC823 cell was studied by an infrared microscope equipped with a focal plane array (FPA) detector. The spectra showed difference between the nucleus and the endoplasmic reticulum (ER) of the BGC823 cell. The peak of vasPO2- was shifted to a higher wavenumber at the nucleus compared with that at the ER. The height ratios of 2954 cm(-1)/2922 cm(-1) (CH3/CH2) and 1088 cm(-1)/1539 cm(-1) (DNA/amide II) of the nucleus were significantly higher than those of the ER. Furthermore, chemical images reveal the intensity distributions of lipids, proteins and DNA of the single BGC823 cell, and the intense absorptions of proteins and DNA were observed in the nuclear region of the cell while the intense absorption of lipids was found in the ER region of the cell. The Fourier transform infrared (FTIR) microspectroscopic imaging result indicates the study of the single gastric cancer cell at sub-cellular level can be beneficial for knowing gastric cancer more which will be of great importance for the study and diagnosis of gastric cancer. The result also suggests that FPA is a useful tool in the study of a single cell and may be a powerful tool for study and diagnosis of gastric cancer.     

Fourier transform infrared study of the gel form of isotactic polystyrene

Infrared spectra of isotactic polystyrene gel films are observed to be significantly different from those of amorphous and crystalline polymer, indicating that the gel form is in a different conformation than the usual 3₁ helical crystal structure. Computer-assisted subtraction indicates that approximately 35% of the chains participate in the gel component, effectively ruling out structural defects as the origin of the ordered gel component.     

Fourier transform infrared study of the effects of irradiation on polyethylene

Fourier transform infrared spectra have been obtained for polyethylene irradiated in oxygen and nitrogen atmospheres. The spectra before and after irradiation have been compared by digital subtraction. The difference spectra are indicative of changes caused by irradiation. Crosslinking and chain scission reactions produce the observed changes.     

Single-drop micro-extraction and diffuse reflectance Fourier transform infrared spectroscopic determination of chromium in biological fluids

The present paper deals with a new micro-extraction procedure for selective separation of Cr(VI) in the form of a metaloxy anionic species namely dichromate (Cr₂O₇²⁻) with N¹-hydroxy-N¹,N²-diphenylbenzamidine (HOA) in to dichloromethane and its subsequent and rapid diffuse reflectance Fourier transform infrared spectroscopic (DRS-FTIR) determination employing potassium bromide matrix. The diffuse reflectance Fourier transform infrared spectroscopy gives both qualitative and quantitative information about the dichromate. The determination of chromium is based on the analytical peak selection, among the various vibrational peaks, at 902 cm⁻¹. The micro-extraction was based on the liquid-liquid solvent extraction (LLSE) principle. The dichromate binds with the nitrogen and oxygen atoms of N¹-hydroxy-N¹,N²-diphenylbenzamidine (HOA) and forms 1:2, Cr(VI):HOA complex in 0.1 mol L⁻¹ HCl medium. The formation of above complex, in the acidic medium, is confirmed by the appearance of chocolate-brown color in the micro-extract. The speciation studies of Cr(III) and Cr(VI) is done by conversion of Cr(III) into Cr(VI) utilizing H₂O₂ as an oxidizing agent. The chemistry of pure dichromate and that of its HOA complex is discussed. The limit of detection (LoD) and the limit of quantification (LoQ) of the method are found to be 0.01 μg g⁻¹ Cr₂O₇²⁻ and 0.05 μg g⁻¹ Cr₂O₇²⁻, respectively. The standard deviation value and the relative standard value at a level of 10 μg Cr₂O₇²⁻/0.1 g KBr for n = 10 is found to be 0.26 μg Cr₂O₇²⁻ and 2.6%, respectively. The relative standard deviation (n = 8 and 6) for the determination of dichromate (Cr₂O₇²⁻) in real human biological fluid samples is observed to be in the range 3.1-7.8%.     

Fourier transform infrared study of two truxene-based discotic liquid crystals

We have used FTIR absorption to study the crystalline and liquid-crystalline phases of 2,3,7,8,12,13-hexa-n-tetradecanoyloxy-truxene (HATX) and 2,3,7,8,12,13-hexa(4-n-undecyloxybenzoyloxy)truxene (HBTX). Both materials show pronounced changes in the CH₂ stretching mode frequencies at their melting points. In addition, HATX shows a transition at about 20°C below the nominal melting point in which the alkyl tails gain significant disorder. Benzene stretching modes and the CH₂ deformation modes show subtle changes at the D_rd → N transition of HBTX and at the D_rd → D_hd transition of HATX.     

Fourier transform infrared study of low-temperature CO adsorption on CuMgAl-hydrotalcite

Single-phase CuMgAl ternary hydrotalcite with (Cu+Mg)/Al atomic ratio of 3.0 and Cu/Mg atomic ratio of 1.0 was synthesized by coprecipitation. Thermoanalytical studies of this sample showed transformations in three stages in the temperature range up to ca. 900 K yielding mainly CuO phase. In situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopic measurements showed the presence of carbonates even after calcination of the sample at 973 K. The genesis of Cu+ sites during thermal treatment in vacuo at different temperatures for this sample was followed by IR spectroscopy of CO adsorbed at low temperature. Essentially no Cu+ sites are present on a sample calcined at 723 K, consistent with X-ray photoelectron spectroscopic (XPS) data. However, sample subjected to activation (1 h of O2 treatment at 723 K followed by 1 h of evacuation at the same temperature) upon CO adsorption at 85 K unambiguously showed the presence of Cu+ sites. 12CO-13CO coadsorption studies confirmed the presence of dicarbonyls, which are converted to linear Cu+-CO species during evacuation at 85 K. Concentration of the accessible Cu+ sites increased with the increase in activation temperature up to 873 K and decreased with a further temperature rise. The copper sites on the sample are heterogeneously distributed and their distribution depends on the activation temperature. Two routes of reduction of Cu2+ to Cu+ are proposed: (i) autoreduction during evacuation and (ii) reduction by CO.