Total Reflectance FTIR Spectroscopy Research Articles

Photoactivable Nonsymmetrical Bifunctional Linkers for Protein Immobilization on Attenuated Total Reflectance FTIR Optical Devices

AbstractThe photosensitive 4‐azido‐2,3,5,6‐tetrafluoro‐1‐benzoyl core has been connected to maleimide‐, chloroacetyloxy‐, or succinimidyl carbonate motifs through various spacers to furnish a series of bifunctional linkers. One linker (7a) has been used for the construction of a biosensor for β‐lactam antibiotic detection by attenuated total reflectance FTIR (ATR‐FTIR) spectroscopy.

Molecular Orientation of Enzymes Attached to Surfaces through Defined Chemical Linkages at the Solid–Liquid Interface

The immobilization of enzymes on solid supports is widely used in many applications, including biosensors, antifouling coatings, food packaging materials, and biofuel cells. Enzymes tend to lose their activity when in contact with a support surface, a phenomenon that has been attributed to unfavorable orientation and (partial) unfolding. In this work, specific immobilization of 6-phospho-β-galactosidase (β-Gal) on a self-assembled monolayer (SAM) containing maleimide end groups and oligo(ethylene glycol) spacer segments was achieved through a unique cysteinyl residue. A systematic means to characterize the interfacial orientation of immobilized enzymes has been developed using a combination of sum frequency generation vibrational spectroscopy and attenuated total reflectance FTIR-spectroscopy. The possible orientations of the immobilized β-Gal were determined and found to be well-correlated with the tested activity of β-Gal. This study will impact the development of an increasingly wide range of devices that use surface-immobilized enzymes as integral components with improved functions, better sensitivity, enhanced stability, and longer shelf life.

Authentication of the Botanical and Geographical Origin of Distillers Dried Grains and Solubles (DDGS) by FT-IR Spectroscopy

Distillers dried grains and solubles (DDGS) were investigated with attenuated total reflection FT-IR spectroscopy both directly in their solid state and as the isolated oils (fat fractions). The collected spectra were evaluated in a first step with principal component analysis (PCA) according to the botanical origin (corn, rice, wheat) and the geographical origin (Canada, China, European Union, India, United States) of the DDGS. In a second step, statistical models were constructed for the characterization of the botanical and geographical origin using linear discriminant analysis (LDA) and soft independent modeling of class analogy (SIMCA). For this purpose, the botanical origin was investigated more deeply for corn and wheat as the most important raw materials used for DDGS production. Also, the geographical origin was investigated exemplary for corn DDGS, derived from China and the United States. Models were validated by a randomized batchwise procedure and showed satisfactory classification rates, in most cases better than 80% correct classification.

Impact of Bran Addition on Water Properties and Gluten Secondary Structure in Wheat Flour Doughs Studied by Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy

ABSTRACTThe aim of this work was to elucidate the underlying physical mechanism(s) by which bran influences whole grain dough properties by monitoring the state of water and gluten secondary structure in wheat flour and bran doughs containing 35–50% moisture and 0–10% added bran. The system was studied with attenuated total reflectance (ATR) FTIR spectroscopy. Comparison of the OH stretch band of water in flour dough with that in H2O‐D2O mixtures having the same water content revealed the formation of two distinct water populations in flour dough corresponding to IR absorption frequencies at 3,600 and 3,200 cm–1. The band intensity at 3,200 cm–1, which is related to water bound to the dough matrix, decreased and shifted to lower frequencies with increasing moisture content of the dough. Addition of bran to the dough caused redistribution of water in the flour and bran dough system, as evidenced by shifts in OH stretch frequency in the 3,200 cm–1 region to higher frequencies and a reduction in monomeric water (free water). This water redistribution affected the secondary structure of gluten in the dough, as evidenced by changes in the second‐derivative ATR‐FTIR difference spectra in the amide I region. Bran addition caused an increase in β‐sheet content and a decrease in β‐turn (β‐spiral) content. However, this bran‐induced transconformational change in gluten was more significant in the 2137 flour dough than in Overley flour dough. This study revealed that when bran is added to flour dough, water redistribution among dough components promotes partial dehydration of gluten and collapse of β‐spirals into β‐sheet structures. This transconformational change may be the physical basis for the poor quality of bread containing added bran.

Post-curing conversion kinetics as functions of the irradiation time and increment thickness

Objective:This study evaluated the variation of conversion degree (DC) in the 12 hours following initial photoactivation of a low-shrinkage composite resin (Venus Diamond).Material and Methods:The conversion degree was monitored for 12 hours using Attenuated Total Reflection (ATR) F-TIR Spectroscopy. The composite was placed in 1 or 2 mm rings and cured for 10 or 20 seconds with a LED lamp. ATR spectra were acquired from the bottom surface of each sample immediately after the initial photoactivation (P=0), 30 minutes (P=0.5) and 12 hours after photoactivation (P=12) in order to obtain the DC progression during the post-curing period. Interactions between thickness (T), irradiation time (I) and post-curing (P) on the DC were calculated through ANOVA testing.Results:All the first order interactions were statistically significant, with the exception of the T-P interaction. Furthermore, the shift from P=0 to P=0.5 had a statistically higher influence than the shift from P=0.5 to P=12. The post-curing period played a fundamental role in reaching higher DC values with the low-shrinkage composite resin tested in this study. Moreover, both the irradiation time and the composite thickness strongly influenced the DC.Conclusions:Increased irradiation time may be useful in obtaining a high conversion degree (DC) with a low-shrinkage nano-hybrid composite resin, particularly with 2 mm composite layers.

Modular synthesis, spectroscopic characterization and in situ functionalization using “click” chemistry of azide terminated amide containing self-assembled monolayers

A general and modular synthetic route is developed for the synthesis of azidoalkylthiol molecules, which contain an amide functional group, from common and easily available precursors. SAMs (self-assembled monolayers) formed by these amide containing azidoalkylthiols are characterised by attenuated total reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy, contact angle goniometry and surface enhanced Raman spectroscopy. Signature peaks are identified in the data which allows direct observation of all the functional groups on Au electrodes bearing these monolayers. The terminal azide group is functionalised with electroactive ferrocene group in situ, using “click” chemistry. An alkyne bearing heme derivative is covalently attached using the same technique resulting in O2 reducing electrodes.

Rapid Determination of Free Fatty Acid Content in Waste Deodorizer Distillates Using Single Bounce-Attenuated Total Reflectance-FTIR Spectroscopy

A simple, rapid, economical, and environmentally friendly analytical method was developed for the quantitative assessment of free fatty acids (FFAs) present in deodorizer distillates and crude oils by single bounce-attenuated total reflectance-FTIR spectroscopy. Partial least squares was applied for the calibration model based on the peak region of the carbonyl group (C=O) from 1726 to 1664 cm(-1) associated with the FFAs. The proposed method totally avoided the use of organic solvents or costly standards and could be applied easily in the oil processing industry. The accuracy of the method was checked by comparison to a conventional standard American Oil Chemists' Society (AOCS) titrimetric procedure, which provided good correlation (R = 0.99980), with an SD of +/- 0.05%. Therefore, the proposed method could be used as an alternate to the AOCS titrimetric method for the quantitative determination of FFAs especially in deodorizer distillates.

The effect of low-pressure air plasma treatment on the wettability and surface energy of polyvinyl chloride films

Low-pressure plasma in a RF discharge of air is employed to introduce a polar function to a polyvinyl chloride surface to enhance the wettability and activation. A clear increase in the surface energy of the surface of a polymer due to air plasma treatment was observed. The surfaces become highly hydrophilic after treatment. The effect of plasma treatment on the morphology and wettability of the surfaces were characterized by using a static contact angle measurement and attenuated total reflection-FTIR spectroscopy.

Enzyme distribution and secondary structure of sol–gel immobilized glucose oxidase by micro-attenuated total reflection FT-IR spectroscopy

Glucose oxidase (GOD) immobilized into sol–gel matrices was studied by using Micro-Attenuated Total Reflection Fourier Transform Infrared (micro-ATR FT-IR) spectroscopy in order to characterize enzyme distribution and secondary structure in systems with valuable potentialities in amperometric and optical biosensing. Spectra were acquired in the 4000–600cm−1 frequency region and the analysis of specific fingerprints in the FT-IR spectra evidenced that the enzyme was actually immobilized in the matrix. The enzyme spatial distribution was obtained by examining the amide I and amide II band region of spectra from defined sample positions. The deconvolution of the amide I band in terms of lorentzian functions provided information on the secondary structure of the immobilized GOD. By this approach a macroscopic preservation of GOD activity upon immobilization was evidenced along with the existence of some matrix sites with locally inactivated GOD. To our knowledge this is the first example of point-by-point characterization of conformational changes of immobilized enzyme by means of micro-ATR infrared spectroscopy, thus confirming that this technique can be usefully employed for a non- or minimally-invasive detailed micro-characterization of catalytic supports in order to improve their functionality.

Synthesis and Mechanical Properties of Organic–Inorganic Hybrid Materials from Lignin and Polysiloxanes

The preparation of silica-containing organic-inorganic hybrid materials composed of kraft lignin, alkoxysilanes, and organic linkers was investigated. 3-Glycidyloxypropyltrimethoxysilane, 3-(triethoxysilyl)propylisocyanate (IPTES), and bis(trimethoxysilyl)hexane were selected as the most promising linkers. The best materials obtained showed improved mechanical and thermal properties compared with lignin itself. The reaction of the hydroxyl groups with IPTES and the sol-gel reaction between the organic linker molecules were studied by attenuated total reflectance FTIR and solid-state ²⁹Si magic-angle spinning NMR spectroscopy. The homogeneous composition was demonstrated by electron microscopy and energy-dispersive X-ray spectroscopy mapping. The mechanical properties were investigated by microindentation and dynamic mechanical thermal analysis.

Understanding the Interfacial Processes at Silicon–Copper Electrodes in Ionic Liquid Battery Electrolyte

The interfacial processes at an amorphous silicon−copper (Si−Cu) electrode in the ionic liquid electrolyte of 1 M lithium bis(trifluoromethanesulfonyl)imide/1-methyl-1-propylpyrrolidinium bis- (trifluoromethylsulfonyl)imide (LiTFSI/Py1,3TFSI) during initial charge− discharge cycle are studied by characterizing the solid electrolyte interphase (SEI) composition at different states of charge using ex situ attenuated total reflection FTIR spectroscopy combined with X-ray photoelectron spectroscopy. The analyses data reveal that in the very early stage of charge (1.5 V vs Li/Li + ), alkylated Si and ester-containing species first form by the reductive decomposition of Py1,3 ion, and LiF salt and Si−F bond- containing compound first form by the decomposition of TFSI anion, respectively. TFSI decomposition is observed to begin with the C−F cleavage, which was proposed as the cleavage of N−S bond in the previous reports. Charging to lower voltage thickens the SEI layer, but lithiation of silicon results in damage or destabilization of the existing SEI probably due to changes in structural volume together with particle morphology. The SEI layer is however reversibly rebuilt in the course of delithiation. The data provide a basic understanding of the SEI formation mechanism on the silicon-based anodes in ionic liquid electrolyte for less flammable batteries.

Hierarchical Organization of Ferrocene–Peptides

Hierarchical self-assembly of disubstituted ferrocene (Fc)-peptide conjugates that possess Gly-Val-Phe and Gly-Val-Phe-Phe peptide substituents leads to the formation of nano- and micro-sized assemblies. Hydrogen-bonding and hydrophobic interactions provide directionality to the assembly patterns. The self-assembling behavior of these compounds was studied in solution by using (1)H NMR and circular dichroism (CD) spectroscopies. In the solid state, attenuated total reflectance (ATR) FTIR spectroscopy, single-crystal X-ray diffraction (XRD), powder X-ray diffraction (PXRD), and scanning electron microscopy (SEM) methods were used. Spontaneous self-assembly of Fc-peptides through intra- and intermolecular hydrogen-bonding interactions induces supramolecular assemblies, which further associate and give rise to fibers, large fibrous crystals, and twisted ropes. In the case of Fc[CO-Gly-Val-Phe-OMe](2) (1), molecules initially interact to form pleated sheets that undergo association into long fibers that form bundles and rectangular crystalline cuboids. Molecular offsets and defects, such as screw dislocations and solvent effects that occur during crystal growth, induce the formation of helical arrangements, ultimately leading to large twisted ropes. By contrast, the Fc-tetrapeptide conjugate Fc[CO-Gly-Val-Phe-Phe-OMe](2) (2) forms a network of nanofibers at the supramolecular level, presumably due to the additional hydrogen-bonding and hydrophobic interactions that stem from the additional Phe residues.

Liquid-phase isobutane alkylation with butenes over aluminum chloride complexes synthesized in situ from activated aluminum and tert-butyl chloride

The liquid-phase interaction between isobutane and butenes at 303 K and 2.5–3.0 MPa has been investigated using activated aluminum (Al*)-tert-butyl chloride (TBC) model system (TBC: Al* = 0.35−4 mol/mol). It has been demonstrated by attenuated total reflection FT-IR (ATR-FT-IR) spectroscopy that the catalytically active aluminum chloride complexes forming in situ in the hydrocarbon medium vary in composition. Alkylation as such takes place at equimolar proportions of the reactants (TBC: Al* = 1: 1) and butenes feed 1mass flow rate of 5 h−1 per gram of Al*. According to ATR-FT-IR data, the most abundant aluminum complexes resulting under these conditions are the AlCl4− and Al2Cl7− ions and, probably, the molecular complex AlCl3 · sec-C4H9Cl. In a fourfold excess of TBC over Al* at butenes mass feed rate of 2.5 h−1, isobutane undergoes self-alkylation. In this case, the Al2Cl7− ion is not detected and the most abundant complexes are AlCl4−, Al3Cl10− and the molecular species AlCl3 · tert-C4H9Cl. It is hypothesized that the Al2Cl7− ion plays the key role in the liquid-phase alkylation of isobutane with butenes.

Chemometric Processing of Pharmaceutical Essential Oil Fingerprints—Comparison of GC, HPLC, TLC, IR Spectroscopy, and Differential Scanning Calorimetry

Fifteen essential oils of pharmaceutical grade were fingerprinted by five techniques: TLC, GC, HPLC, attenuated total reflectance FTIR spectroscopy, and differential scanning calorimetry (DSC). Denoising and baseline removal was found to be a crucial step for correct comparative analysis. Standardization of the signal was not necessary in the presented case; however, it should be considered and checked in each case. Due to small variance explained by first two principal components (below 50%) and outlying observations, the main analysis was performed by Euclidean dendrograms. It was found that almost all techniques besides DSC find real chemical similarities; however, DSC can be used as an additional tool. The similarities among the five techniques were also compared and discussed.

The Development of Modulated, Quasi-Isothermal and Ultraslow Thermal Methods as a Means of Characterizing the α to γ Indomethacin Polymorphic Transformation

While polymorphism remains a key issue within the pharmaceutical and related industries, the understanding of the transformation process itself remains relatively poorly understood. In this study we use a combination of conventional and modulated temperature differential scanning calorimetry (MTDSC), quasi-isothermal MTDSC (Qi-MTDSC) and ultraslow heating rate MTDSC as a novel means of investigating the temperature-induced α to γ transformation in indomethacin, using hot stage microscopy and variable temperature attenuated total reflectance FTIR spectroscopy as supportive techniques. In particular, we utilize the ability of MTDSC to measure subtle heat capacity changes through the transformation, we examine the use of Lissajous analysis of the modulated heating signal itself (both scanning and quasi-isothermal) and finally we investigate the use of ultraslow heating rates (down to 0.04 °C/min) so as to facilitate examination of the melt-crystallization process at a scanning rate whereby kinetic hindrance becomes negligible. Indomethacin was prepared in the metastable α and stable γ forms using standard approaches. Samples were studied using conventional DSC, Qi-MTDSC (involving holding and modulating the sample at a series of incremental temperature steps) and ultraslow MTDSC. All studies were conducted using a Q-1000 MTDSC using crimped pans, following standard calibration procedures. Conventional DSC at 10 °C/min showed the expected single melting responses for the α and γ forms, while MTDSC at slower rates indicated the presence of a melt-crystallization process. Quasi-isothermal studies allowed the heat capacity to be estimated as a function of time, while the associated Lissajous analysis demonstrated distortion of the elliptical response as a result of the kinetic events involved. Ultraslow heating resulted in superimposition of the melting and crystallization processes, resulting in a discrete thermal event that was enthalpically equivalent to the difference between the two processes. It is suggested that these combined thermal methods allow the conversion to be profiled in a manner which facilitates both kinetic and thermodynamic analysis of the transformation.

Fabrication of PP-g-PEGMA-g-heparin and its hemocompatibility: From protein adsorption to anticoagulant tendency

We described a two-step process to fabricate the heparinized polypropylene (PP) film using cyanuric chloride (CC) as a trifunctional reagent and poly (ethylene glycol) methacrylate (PEGMA) as a spacer. The modified PP films were characterized by attenuated total reflectance FT-IR and X-ray photoelectron spectroscopy; the content of PEGMA and heparin were determined by gravimetric method and a toluidine blue assay, respectively. For the PP-g-PEGMA films, it was found that small size protein BSA tended to adsorb on the surface of low molecular weight monomer grafted PP, whereas big spindle-shaped fibrinogen tended to adsorb on the surface of high molecular weight monomer grafted PP. We gave a definition of anti-protein adsorptive factor r with two model proteins, albumin and fibrinogen. The results by platelet adhesion and plasma recalcification time (PRT) experiments indicated that the factor r could be used to quantitatively evaluate the anticoagulant tendency of PP-g-PEGMA modified films. For the PP-g-PEGMA-g-heparin modified films, the surface was proved to have a high bioactivity by the adsorption of AT III assay and very low platelet adhesion. It indicated that immobilization of heparin on the PP film with PEGMA as a spacer was an effective way to improve the hemocompatibility of PP.

In Situ ATR FTIR Study of Dextrin Adsorption on Anatase TiO2

The adsorption of two dextrin-based polymers, a regular wheat dextrin (TY) and a carboxymethyl-substituted (CM) dextrin, onto an anatase TiO(2) particle film has been studied using in situ attenuated total reflection (ATR) FTIR spectroscopy. Infrared spectra of the polymer solutions and the polymer adsorbed at the anatase surface were acquired for two solution conditions: pH 3 and pH 9; below and above the isoelectric point (IEP) of anatase, respectively. Comparison of the polymer solution spectra and the adsorbed layer spectra highlighted a number of spectral differences that were attributed to involvement of the carboxyl group of CM Dextrin interacting with the anatase surface directly and the adsorption of oxidized dextrin chains in the case of regular dextrin (TY) at high pH. The adsorption/desorption kinetics were determined by monitoring spectral peaks of the pyranose ring of both polymers. Adsorption equilibrium was not established for Dextrin TY for many hours, whereas CM Dextrin reached equilibrium in its adsorption within 60 min. The extent of desorption of Dextrin TY (observed by flowing a background electrolyte dextrin-free solution) was extensive at both pH values, which reflects the poor affinity and binding of the polymer on anatase. In contrast, CM Dextrin underwent almost no desorption, indicating a high affinity between the carboxyl groups of the polymer and the anatase surface.

Effect of Particle Size and Composition on CO-Tolerance at Pt–Ru/C Catalysts Analyzed by In Situ Attenuated Total Reflection FTIR Spectroscopy

The particle size dependence of activities for the hydrogen oxidation reaction (HOR) on monodisperse Pt2Ru3 (d = 2.6, 3.6, and 4.5 nm) supported on carbon black prepared by the nanocapsule method (Pt2Ru3/C) was investigated by in situ attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy in 1% CO (H2-balance)-saturated 0.1 M HClO4. The highest CO-tolerant HOR activity at both 25 and 60 °C was observed for the smallest Pt2Ru3 particle (d = 2.6 nm), with a Pt-rich top surface and an Ru-rich core. At 25 °C, the suppression of the adsorption of CO on Ru sites was a dominant factor to maintain the electronic modification effect that weakens the bond strength of COad. The adsorption of CO on Ru at all catalysts was found to decrease markedly by increasing the temperature to 60 °C, probably because of a decrease in the bond strength of COad on Ru sites. At 60 °C, the coverage of bridged CO, θ[COB], on Pt sites was found to be lowest on the smallest Pt2Ru3 particle. Because COB blocks two active sites for the HOR, the largest number of HOR active sites can be available at the smallest particle. The effect of chemical composition on the CO-tolerance was also analyzed on Pt2Ru3/C and PtRu/C with the identical particle size d = 2.6 nm. While both catalysts exhibited nearly comparable CO-tolerance at 25 °C, Pt2Ru3/C showed higher CO-tolerance at 60 °C, which is ascribed to the lower θ[COB], probably because of an electronic effect of the Ru-rich core.

Temperature‐Responsive Polymer/Carbon Nanotube Hybrids: Smart Conductive Nanocomposite Films for Modulating the Bioelectrocatalysis of NADH

A temperature-sensitive polymer/carbon nanotube interface with switchable bioelectrocatalytic capability was fabricated by self-assembly of poly(N-isopropylacrylamide)-grafted multiwalled carbon nanotubes (MWNT-g-PNIPAm) onto the PNIPAm-modified substrate. Electron microscopy and electrochemical measurements revealed that these fairly thick (>6 μm) and highly porous nanocomposite films exhibited high conductivity and electrocatalytic activity. The morphological transitions in both the tethered PNIPAm chains on a substrate and those polymers wrapping around the MWNT surface resulted in the opening, closing, or tuning of its permeability, and simultaneously an electron-transfer process took place through the channels formed in the nanostructure in response to temperature change. By combining the good electron-transfer and electrochemical catalysis capabilities, the large surface area, and good biocompatibility of MWNTs with the responsive features of PNIPAm, reversible temperature-controlled bioelectrocatalysis of 1,4-dihydro-β-nicotinamide adenine dinucleotide with improved sensitivity has been demonstrated by cyclic voltammetry and electrochemical impedance spectroscopy measurements. The mechanism behind this approach was studied by Raman spectroscopy, in situ attenuated total reflection FTIR spectroscopy, and contact angle measurements. The results also suggested that the synergetic or cooperative interactions of PNIPAm with MWNTs gave rise not only to an increase in surface wettability, but also to the enhancement of the interfacial thermoresponsive behavior. This bioelectrocatalytic "smart" system has potential applications in the design of biosensors and biofuel cells with externally controlled activity. Furthermore, this concept might be proposed for biomimetics, interfacial engineering, bioelectronic devices, and so forth.

Impact of frying on key fatty acid ratios of canola oil

AbstractThe study was carried out to investigate the changes in saturated (SFA), monoene (MUFA), trans (TFA), and polyunsaturated (PUFA) fatty acids and the key fatty acid ratios (SFA/UFA, cis PUFA/SFA, C18:2/C16:0 and C18:3/C16:0) during potato chips frying in canola oil using single bounce attenuated total reflectance FTIR (SB‐ATR‐FTIR) spectroscopy. The data obtained from GC‐FID were used as reference. The calibration of main fat groups and their key fatty acid ratios were developed by partial least square (PLS) regression coefficients using 4000 to 650 cm−1 spectral range. FTIR PLS regression for the predicted SFA, MUFA, TFA, and PUFA were found 0.999, 0.998, 0.998, and 0.999, respectively, whereas for SFA/UFA, cis PUFA/SFA, C18:2/C16:0 and C18:3/C16:0 the regression coefficients were 0.991, 0.997, 0.996, and 0.994, respectively. We conclude that FTIR‐PLS could be used for rapid and accurate assessment of changes in the main fat groups and their key fatty acid ratios ratio during the frying process.Practical applications: FTIR‐ATR method is very simple, rapid, and environmentally friendly. No sample preparation is required and one drop of oil is enough for FTIR analysis. The proposed method could be applied for quick determination of key fatty acid ratios in the food processing industry.