Internal Reflection Spectroscopy Research Articles

Dialysis culture as an indicator of changes in water resources

Data of monitoring of the state of the aquatic ecosystem obtained during registration of changes in spatial and temporal parameters of whole cells and their external structures using internal reflection spectroscopy are considered. Dialysis culture of microalgae with a controlled “external environment” was used as a bioindicator.

Investigation of the Interaction of γ-Al2O3 with Aqueous Solutions of Dimethyl Methylphosphonate Using Infrared Multiple Internal Reflection Spectroscopy

The interaction of dilute solutions of dimethyl methylphosphonate (DMMP) in H(2)O with thin porous layers of γ-Al(2)O(3) has been studied under steady-state conditions using infrared multiple-internal-reflection spectroscopy. Upon the initial introduction of the DMMP solution to a previously H(2)O-saturated surface, DMMP diffuses into the porous layer and displaces weakly hydrogen-bonded H(2)O molecules. This is accompanied by hydrolysis of the γ-Al(2)O(3) to form Al(OH)(3) and/or AlO(OH). The P═O group of DMMP interacts predominantly with H(2)O and gives no clear indication of bonding to the oxide surface itself, from which it is inferred that the displacement of weakly adsorbed H(2)O results from the interaction of acidic Al-OH sites with the methoxy O atoms of DMMP. No hydrolysis of the DMMP, either in solution or in contact with the oxide, was detectable under the present conditions. The results have practical implications in the decontamination of materials following exposure to toxic reagents related to DMMP.

Methodology for determination of the state of microbial culture by degree of spatial organization of whole cells and their external structures

The proposed methodology for determination of biosystems state is based on registration of changes in the space-time parameters of cells and their external structures in a population of microorganisms from different taxonomic groups by the method of noninvasive layer-by-layer analysis using internal reflection spectroscopy. The dependence between the state of an organism and the changes in spatial organization of whole cells and their surface layers have been revealed. The proposed method allows estimation of the character and degree of dynamics of biosystem variations irrespective of the kind of influence. This method can be used for assessing the state of other organisms by the differences between values A for the surface structures and cells of these organisms.

Average Orientation of a Molecular Rotor Embedded in a Langmuir–Blodgett Monolayer

A molecular rotor in which a naphthalene rotator is attached through a silicon atom to three fatty acid chains has been synthesized, and Langmuir-Blodgett techniques were used to deposit on silica surfaces monolayers of its calcium salt, both neat and diluted with stearic acid salts. The monolayer films have been characterized by ellipsometry and Fourier transform infrared (FT-IR) grazing-incidence attenuated total internal reflection (GATR) spectroscopy on Si-SiO(2) and by UV-vis absorption spectroscopy on SiO(2). The measurements were combined with calculations of the electronic (INDO/S) and vibrational (DFT) transition moment directions to deduce the average orientation of the rotor molecules, including the naphthalene ring, relative to the surface. In both neat and mixed films, the naphthalene ring is found to preferentially tilt toward the surface, enough that its rotation is most likely hindered. A comparable picture was obtained from molecular mechanics calculations on a mixed film of the naphthalene rotor and stearic acid.

Efficiency of different light sources to polymerise composite material

The aim of this in vitro study is to examine the polymerisation efficacy of three different polymerisation units through simulated three different ceramic restorations (5 mm in diameter and 2 mm in height) by determining the degree of monomer conversion of a composite luting material. The curing efficiency was observed with Fourier transform infrared micromultiple internal reflectance spectroscopy after 24 h of polymerisation. The degree of conversion was calculated as a percentage of experimentally polymerised versus maximally polymerised composite. The degree of conversion values varied with the light source (light emitting diode, high intensity halogen and conventional halogen) (p<0·05) and the ceramic system (Cercon, IPS Empress 2 and Cerec) (p<0·05).

Single-Molecule Studies of the Na+/K+-ATPase

The Na+/K+-ATPase, a membrane-associated ion-motive ATPase, uses energy from the hydrolysis of ATP to move Na+ out of and K+ into cells. We have labeled ATPase isolated from duck supraorbital salt glands with Cy3-maleimide (Cy3-ATPase). We have previously found that the fluorescence of Cy3-ATPase decreases in the presence of ATP (Biochim Biophys Acta 2009; 1794:1549-1557). We found there that the kinetics of this ATP decrease exhibited negative cooperativity. To determine whether this behavior is due either to interaction between protomers or is an intrinsic property of monomers, we examined the fluorescence of the labeled enzyme solubilized in the nonionic detergent C12E8 in the absence and presence of varying concentrations of ATP using single-molecule total internal reflection spectroscopy (SM-TIRF). We found that: (i) our Cy3-maleimide labeling protocol yielded a significant fraction of singly-labeled protein; and (ii) even with solubilization, a significant fraction of the protein exhibited aggregation. A preliminary analysis of the data from single (non-aggregating) molecules using a hidden Markov model (HMM) suggests a difference in the single-molecule dynamics of the enzyme in the presence and absence of ATP. The implication of these observations will be discussed.

Study of lubricating compositions based on polyorganosiloxanes involving azomethine metalocomplexes

Azomethine complexes of copper, nickel, cobalt, and zinc are demonstrated to favor selective transfer in the medium of polyorganosiloxanes. In studies of the friction surfaces with the use of methods of optical and scanning electron microscopy, energy-dispersion electron probe X-ray microanalysis, and infrared frustrated total internal reflection spectroscopy, the formation of a transition-metal and tribopolymer film containing polyorganosiloxane fragments is found.

Comparative analysis of space-time organization of biological systems in periodic and dialyzed cultures of Synechococcus sp. PCC 6301

Data on biopolymers, their distribution, and spatial order in whole cells and in a certain cell layer of the cyanobacterium Synechococcus sp. PCC 6301 culture grown under periodic and dialysis conditions were obtained by the method of internal reflection spectroscopy. The fundamental distinction between the types of culture behavior under these cultivation conditions was shown. A similar approach can be used for standard specification of limiting concentrations in laboratory conditions, test object standardization, and creation of a culture with maximum possible adaptation to variable environmental conditions.

Instrumental measurement of bitter taste in red wine using an electronic tongue

An electronic tongue (ET) based on potentiometric chemical sensors was assessed as a rapid tool for the quantification of bitterness in red wines. A set of 39 single cultivar Pinotage wines comprising 13 samples with medium to high bitterness was obtained from the producers in West Cape, South Africa. Samples were analysed with respect to a set of routine wine parameters and major phenolic compounds using Fourier transform infrared-multiple internal reflection spectroscopy (WineScan) and high-performance liquid chromatography, respectively. A trained sensory panel assessed the bitterness intensity of 15 wines, 13 of which had a bitter taste of medium to high intensity. Thirty-one wine samples including seven bitter-tasting ones were measured by the ET. Influence of the chemical composition of wine on the occurrence of the bitter taste was evaluated using one-way analysis of variance. It was found that bitter-tasting wines had higher concentrations of phenolic compounds (catechin, epicatechin, gallic and caffeic acids and quercetin) than non-bitter wines. Sensitivity of the sensors of the array to the phenolic compounds related to the bitterness was studied at different pH levels. Sensors displayed sensitivity to all studied compounds at pH 7, but only to quercetin at pH 3.5. Based on these findings, the pH of wine was adjusted to 7 prior to measurements. Calibration models for classification of wine samples according to the presence of the bitter taste and quantification of the bitterness intensity were calculated by partial least squares-discriminant analysis (PLS-DA) regression. Statistical significance of the classification results was confirmed by the permutation test. Both ET and chemical analysis data could discriminate between bitter and control wines with the correct classification rates of 94% and 91%, respectively. Prediction of the bitterness intensity with good accuracy (root mean square error of 2 and mean relative error of 6% in validation) was possible only using ET data.

Plasmon Hybridization in Individual Gold Nanocrystal Dimers: Direct Observation of Bright and Dark Modes

We apply a nanomanipulation technique to assemble pairs of monodispersed octahedral gold nanocrystals (side length, 150 nm) along their major axes with a varying tip-to-tip separation (25-125 nm). These pairs are immobilized onto indium tin oxide coated silica substrates and studied as plasmonic dimers by polarization-selective total internal reflection (TIR) microscopy and spectroscopy. We confirm that the plasmon coupling modes with the scattering polarization along the incident light direction result from the transverse-magnetic-polarized incident light, which induces two near-field-coupled dipole moments oriented normal to the air-substrate interface. In such cases, both in-phase (antibonding) and antiphase (bonding) plasmon coupling modes can be directly observed with the incident light wave vector perpendicular and parallel to the dimer axis, respectively. The observation of antiphase plasmon coupling modes ("dark" plasmons) is made possible by the unique polarization nature of the TIR-generated evanescent field. Furthermore, with decreasing nanocrystal separation, the plasmon coupling modes shift to shorter wavelengths for the incident light perpendicular to the dimer axis, whereas relatively large red shifts of the plasmonic coupling modes are found for the parallel incident light.

Mild and Selective Oxidation of Cellulose Fibers in the Presence of N-Hydroxyphthalimide

The oxidation reaction of regenerated cellulose fibers mediated by N-hydroxyphthalimide (NHPI) and various cocatalysts at room temperature for different time intervals and various amounts of low concentration sodium hypochlorite solution has been investigated to produce oxidized cellulose (OC), a biocompatible and bioresorbable polymer. The results revealed that the nonpersistent phthalimide-N-oxyl (PINO) radical generated in situ from NHPI in both, metallic or metal-free systems, is a powerful agent in this kind of transformation. Moreover, the reaction converts highly selectively C(6) primary hydroxyl groups to carboxylic groups under mild reaction conditions and shorter reaction times than previously reported. The amounts of negatively charged groups in OC were determined by means of potentiometric titration. Further characterization of the products were accomplished by using Fourier transform infrared spectroscopy/attenuated total internal reflection spectroscopy (FT-IR/ATR), environmental scanning electron microscopy (ESEM), and X-ray and energy-dispersive X-ray (EDX) spectroscopy. Notably, water retention values of the oxidized fibers increased by 30% in comparison with the original nonoxidized sample, as a result of the introduction of hydrophilic carboxylate groups.

Study of adsorption behaviors of meso-tetrakis (4-N-Methylpyridyl) porphine p-Toluenesulfonate at indium–tin-oxide electrode/solution interface by in-situ internal reflection spectroscopy and cyclic voltammetry

In situ electrochemical-absorption spectra of meso-tetrakis (4-N-Methylpyridyl) porphine p-Toluenesulfonate (TMPyP) adsorbed on the surface of an ITO (indium–tin-oxide) electrode was observed by simultaneous measurements using cyclic voltammetry (CV) and internal reflection spectroscopy. The CV experiment was performed using ITO coated on glass as the working electrode, platinum wire as the counter electrode and silver/silver chloride (Ag/AgCl) electrode as the reference electrode. It was found that, in 1 M HCl and pH = 2 Britton–Robinson solutions, TMPyP were adsorbed on ITO as P(0)H 4 2+ state and P(0)H 2 state, respectively. Moreover, when the potential was applied on the ITO electrode, the redox reactions of TMPyP in 1 M HCl were also different from those in pH = 2 Britton–Robinson solutions. The adsorption rate, desorption rate and equilibrium constants as well as the adsorption free energy of TMPyP were determined by fitting adsorption process between TMPyP and ITO using Langmuirian adsorption model. The effect of pH on the internal reflection spectra was also explored, in which it was shown that the increase of pH lead to the enhancement of the intensity of the internal reflection spectra and the blue shift of the peak position. With the increase of ionic strength of TMPyP solution, the intensity of the internal reflection spectra decreased.

The kinetics of erosion of polyamide films under the action of a glow discharge plasma

Infrared internal reflection and absorption spectroscopy was used to study the kinetics of erosion of AL 60/40 polyamide films under glow discharge treatment. The degree of erosion was estimated quantitatively.

Changes in the IR internal reflection and absorption spectra of AK 60/40 polyamide films after the action of a glow discharge plasma

The modification of surface layers of AK 60/40 polyamide under the action of a gas discharge plasma was studied. Measurements were performed by infrared internal reflection spectroscopy. The results were analyzed to establish possible mechanisms of the interaction of a plasma with the polymer and structural changes in the polymer.

Measurement of the thickness of thin polymer layers by infrared frustrated total internal reflection spectroscopy

A method is proposed for determining the thickness of thin (0.1–5.0 µm) polymer layers and coatings by means of infrared frustrated total internal reflection (FTIR) spectroscopy. This method is based on an analytic expression derived for the dependence of the intensities of absorption bands in IR FTIR spectra on the thickness of a polymer layer. The method is tested on model samples consisting of a thick film of polyethylene terephthalate with a layer of different thicknesses of polystyrene deposited on it. The advantage of this method is the ability to determine the thickness of thin polymer layers deposited on bulk or opaque polymer substrates.

Structure of hexafluoroisopropanol–water mixture studied by FTIR-ATR spectra and selected chemometric methods

The FTIR spectra of 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP)–water binary solutions have been obtained by means of attenuated total internal reflection (ATR) spectroscopy. The spectral properties of the system have been analyzed as a function of alcohol concentration by following methods: multivariate curve resolution based on alternating least-square procedure (MCR-ALS) preceded by evolving factor analysis (EFA), kernel analysis, and two-dimensional (2D) correlation spectroscopy. From all the information obtained by these methods the four-component model describing the aggregation of HFIP and water molecules in HFIP–water mixtures was proposed. In characterization of properties of the components not only changes in the aggregation process were taken into account but also variations in relative population of different HFIP conformations were considered. The case reported is a very good example to show how the MCR-ALS and 2D analysis could complement each other, leading to enhancement of the multicomponent data interpretation.

Comparison of Methods for Determining Specific-surface Area of Fine-grained Soils

Characteristics of fine-grained soils primarily depend on their specific-surface area and hence, reliable determination of this parameter is essential. In this context, researchers have employed quite sophisticated instruments (viz., a BET surface area analyzer, the mercury intrusion porosimetry, internal reflectance spectroscopy, X-Ray diffraction and gas pycnometer etc.) and methodologies (viz., sorption of Methylene Blue dye, Ethylene Glycol Monoethyl Ether and p-Nitrophenol) to determine specific-surface area of these soils. However, most of these methodologies are found to be quite tedious, cost and time intensive. Apart from this, the results obtained are contentious due to the inherent limitations associated with either the instruments employed or the basic assumptions made for computing the specific-surface area of the soil. Hence, it becomes mandatory to evaluate the efficiency of these methodologies for determining specific-surface area of fine-grained soils. With this in view, different types of soils were considered in this study and their specific-surface area was determined, by following different methodologies, and the results were evaluated critically. In addition, attempts were made to develop relationships between the basic properties of fine-grained soils (viz., liquid limit, cation-exchange capacity, activity, and free swell index) and the specific-surface area. These relationships will be of immense help to the practicing engineers and research fraternity.

Determination of Surface Coverage and Orientation of Reduced Cytochrome c on a Silica Surface with Polarized ATR Spectroscopy

Linearly polarized attenuated total internal reflection (ATR) spectroscopy is used to study the adsorption properties of reduced cytochrome c to a silica surface. The adsorption equilibrium constant, surface coverage, protein orientation, effect of NaCl, and pH dependence are determined for the adsorption of reduced cytochrome c onto a silica surface. Surface coverage results (at pH 7.2) show that reduced cytochrome c packs onto the silica surface at <80% of a closely packed monolayer. The protein orientation distribution as measured by an order parameter is shown to be dependent on the surface coverage and solution pH. All of the results for the surface adsorption of reduced cytochrome c on silica are indicative of an electrostatically driven interaction. The results for reduced cytochrome c are compared to surface adsorption results for oxidized cytochrome c on silica. These results indicate that there is no significant difference in the adsorption behavior correlating to the oxidation state of this heme protein.

Relationship Between Interfacial Water Layer Adhesion Loss of Silicon/Glass Fiber–Epoxy Systems: A Quantitative Study

Water at the polymer/substrate interface is often the major cause of adhesion loss in coatings, adhesives, and fiber-reinforced polymer composites. This study critically assesses the relationship between the interfacial water layer and the adhesion loss in epoxy/siliceous substrate systems. Both untreated and silane-treated Si substrates and untreated and silane-treated E-glass fibers were used. Thickness of the interfacial water layer was measured on epoxy/Si systems by Fourier transform infrared–multiple total internal reflection (FTIR-MTIR) spectroscopy. Adhesion loss of epoxy/Si systems and epoxy/E-glass fiber composites was measured by peel adhesion and short-beam shear tests, respectively. Little water accumulation at the epoxy/Si substrate interface was observed for silane-treated Si substrates, but about 10 monolayers of water accumulated at the interface between the epoxy and the untreated Si substrate following 100 h of exposure at 24 °C. More than 70% of the initial epoxy/untreated Si system peel strength was lost within 75 h of exposure, compared with 20% loss after 600 h for the silane-treated Si samples. Shear strength loss in composites made with untreated E-glass fiber was nearly twice that of composites fabricated with silane-treated fiber after 6 months of immersion in 60 °C water. Further, the silane-treated composites remained transparent, but the untreated fiber composites became opaque after water exposure. Evidence from FTIR-MTIR spectroscopy, adhesion loss, and visual observation strongly indicated that a water layer at the polymer/substrate interface is mostly responsible for the adhesion loss of epoxy/untreated siliceous substrate systems and epoxy/untreated glass fiber composites and that FTIR-MTIR is a viable technique to reliably and conveniently assess the adhesion loss attributable to water sorption at the interface.

Study of fibrinogen adsorption on hydroxyapatite and TiO 2 surfaces by electrochemical piezoelectric quartz crystal impedance and FTIR–ATR spectroscopy

The electrochemical piezoelectric quartz crystal impedance (EQCI), a combined technique of piezoelectric quartz crystal impedance (PQCI), electrochemical impedance (EI), and Fourier transform infrared spectroscopy–attenuated total internal reflectance spectroscopy (FTIR–ATR) were used to in situ study the adsorption process of fibrinogen onto the surface of biomaterials—TiO 2 and hydroxyapatite (Ca 5(PO 4) 3OH, HAP). The equivalent circuit parameters, the resonance frequencies and the half peak width of the conductance spectrum of the two biomaterial-modified piezoelectric quartz crystal (PQC) resonances as well as the FTIR–ATR spectra of fibrinogen during fibrinogen adsorption on TiO 2 and HAP particles modified electrode surface were obtained. The adsorption kinetics and mechanism of fibrinogen were investigated and discussed as well. The results suggested that two consecutive steps occurred during the adsorption of fibrinogen onto TiO 2 and hydroxyapatite (HAP) surface. The fibrinogen molecules were firstly adsorbed onto the surface, and then the rearrangement of adsorbed fibrinogen or multi-layered adsorption occurred. The FTIR–ATR spectroscopy investigations showed that the secondary structure of fibrinogen molecules was altered during the adsorption and the adsorption kinetics of fibrinogen related with the variety of biomaterials. These experimental results suggest a way for enriching biological analytical science and developing new applications of analytical techniques, such as PQCI, EI, and FTIR–ATR.