Transform Infrared Reflection Absorption Spectroscopy Research Articles

Regio-selective lipase catalyzed hydrolysis of oxanorbornane-based sugar-like amphiphiles at air–water interface: A polarized FT-IRRAS study

Interfacial hydrolysis of oxanorbornane-based amphiphile (Triol C16) by Candida rugosa lipase was investigated using real-time polarized Fourier transform-infrared reflection absorption spectroscopy (FT-IRRAS). The kinetics of hydrolysis was studied by analyzing the ester carbonyl ν(CO) stretching vibration band across the two dimensional (2D) array of molecules at the confined interface. In particular, we demonstrate Triol C16 to form Michaelis-Menten type complex, like that of lipid-substrate analogues, where the Triol C16 head group remained accessible to the catalytic triad of the lipase. The enzyme-induced selective cleavage of the ester bond was spectroscopically monitored by the disappearance of the intense ν(CO) resonance at 1736cm−1. Consequently, the in situ spectroscopic measurements evidenced selective ester hydrolysis of Triol C16 yielding Tetrol C2OH and Palmitic acid, which remained predominantly in the undissociated form at the interface. The conformation sensitive amide I (majorly ν(CO)) and the interfacial water reorganization suggested 2D ordering of the enzyme molecules following which interfacial reactions were employed towards probing the enzyme kinetics at the air/water interface. The investigation demonstrated further the potential of IRRAS spectroscopy for real-time monitoring the hydrolytic product formation and selectivity at biomimetic interfaces.

Aging effects of plasma polymerized ethylenediamine (PPEDA) thin films on cell-adhesive implant coatings

Thin plasma polymer films from ethylenediamine were deposited on planar substrates placed on the powered electrode of a low pressure capacitively coupled 13.56MHz discharge. The chemical composition of the plasma polymer films was analyzed by Fourier Transform Infrared Reflection Absorption Spectroscopy (FT-IRRAS) as well as by X-ray photoelectron spectroscopy (XPS) after derivatization of the primary amino groups. The PPEDA films undergo an alteration during the storage in ambient air, particularly, due to reactions with oxygen. The molecular changes in PPEDA films were studied over a long-time period of 360days. Simultaneously, the adhesion of human osteoblast-like cells MG-63 (ATCC) was investigated on PPEDA coated corundum blasted titanium alloy (Ti-6Al-4V), which is applied as implant material in orthopedic surgery. The cell adhesion was determined by flow cytometry and the cell shape was analyzed by scanning electron microscopy. Compared to uncoated reference samples a significantly enhanced cell adhesion and proliferation were measured for PPEDA coated samples, which have been maintained after long-time storage in ambient air and additional sterilization by γ−irradiation.

Molecular Recognition of Arginine by Supramolecular Complexation with Calixarene Crown Ether Based on Surface Plasmon Resonance

Arginine plays an important role in cell division and the functioning of the immune system. We describe a novel method by which arginine can be identified using an artificial monolayer based on surface plasmon resonance (SPR). The affinity of arginine binding its recognition molecular was compared to that of lysine. In fabrication of an arginine sensing interface, a calix[4]crown ether monolayer was anchored onto a gold surface and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. The interaction between arginine and its host compound was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Recognition of calix[4]crown monolayer was assessed by the selective binding of arginine. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of arginine under aqueous conditions.

Controlling Liquid Crystal Alignment Using Photocleavable Cyanobiphenyl Self-Assembled Monolayers

We report on the development of novel cyano-biphenyl-based thiolate self-assembled monolayers designed to promote homeotropic alignment of calamitic liquid crystals. The molecules developed contain an ortho-nitrobenzyl protected carboxylic acid group that on irradiation by soft UV (365 nm) is cleaved to yield carboxylic acid groups exposed at the surface that promote planar alignment. Using a combination of wetting, X-ray photoelectron spectroscopy, Fourier transform-infrared reflection absorption spectroscopy, and ellipsometry we show that high photolysis yields (>90%) can be achieved and that the patterned SAMs are suitable for the controlled alignment of calamitic liquid crystals. This study further shows that such photo-patterned SAMs can be used to control the formation of focal conic domains (FCDs) in the smectic-A phase in terms of positioning and size confinement on surfaces.

Development of surface plasmon resonance immunosensor for the novel protein immunostimulating factor

The immunostimulating factor (ISTF) plays an important role in immunopathologic changes associated with Actinobacillus actinomycetemcomitans where it is located in the outer cell membrane. We describe a novel method by which ISTF can be monitored using a protein chip system based on surface plasmon resonance (SPR). The affinity of ISTF to its monoclonal antibodies and other proteins was compared. In fabrication of an ISTF immunosensor, a calix[4]crown ether monolayer was anchored onto a gold surface for use as an artificial protein linker system, and then characterized by Fourier Transform infrared reflection absorption spectroscopy, atomic force microscopy, and cyclic voltammetry. Anti-ISTF was immobilized onto the monolayer, and the interaction between ISTF and its antibodies was investigated by SPR. The calix[4]crown ether was found to assemble as a monolayer on the gold surface. Orientation and accessibility of anti-ISTF were assessed by the selective binding of ISTF. Modification of the SPR chip with the calix[4]crown monolayer provides a reliable and simple experimental platform for investigation of isolated proteins under experimental conditions resembling those of their native environment.

Synthesis and DNA binding behavior of a naphthalene diimide derivative carrying two dicobalt hexacarbonyl complexes as an infrared DNA probe

Synthetic naphthalene diimide probe 1 having two dicobalt hexacarbonyl complexes at its substituent termini, which forms a stable threading intercalate complex with double stranded DNA, could utilized in the detection of the target DNA hybridized with DNA probe immobilized on a gold surface using Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR RAS) technique. Naphthalene diimide having two dicobalt hexacarbonyl complexes at its substituent termini 1 was designed and synthesized as an infrared probe for double stranded DNA. Spectrophotometric and viscometric DNA binding studies of 1 and naphthalene diimide having two acetylene moieties 2 as its precursor were carried out to prove their threading intercalation binding modes. Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR RAS) measurements were achieved for DNA-immobilized on a gold surface before and after hybridization with complementary DNA strand. Distinguished absorption peaks assigned to the dicobalt hexacarbonyl complexes were obtained in the case of the formation of double stranded DNA after treatment with 1 . This result revealed that 1 can be used as an infrared probe for monitoring double stranded DNA.

Photopatterned Thiol Surfaces for Biomolecule Immobilization

The ability to pattern small molecules and proteins on artificial surfaces is of importance for the development of new tools including tissue engineering, cell-based drug screening, and cell-based sensors. We describe here a novel "caged" thiol-mediated strategy for the fabrication of planar substrates patterned with biomolecules using photolithography. A thiol-bearing phosphoramidite (3-(2'-nitrobenzyl)thiopropyl (NBTP) phosphoramidite) was synthesized and coupled to a hydroxyl-terminated amorphous carbon substrate. A biocompatible oligo(ethylene glycol) spacer was used to resist nonspecific adsorption of protein and DNA and enhance flexibility of attached biomolecules. Thiol functionalities are revealed by UV irradiation of NBTP-modified surfaces. Both the surface coupling and photodeprotection were monitored by Polarization Modulation Fourier Transform Infrared Reflection Absorption Spectroscopy (PM-FTIRRAS) and X-ray Photoelectron Spectroscopy (XPS) measurements. The newly exposed thiols are chemically very active and react readily with a wide variety of groups. A series of molecules including biotin, DNA, and proteins were attached to the surfaces with retention of their biological activities, demonstrating the utility and generality of the approach.

NO dissociation and N 2 production in the presence of co-adsorbed S 18O 2 and D 2 on Pt(3 3 2)

NO dissociation and subsequent N 2 production in the presence of co-adsorbed S 18O 2 and D 2 on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Reduction of NO by D (D 2 is adsorbed dissociatively on Pt surfaces) proceeds to a limited extent, because this reaction is rate-controlled by NO dissociation and the supply of D atoms at the higher surface temperatures at which NO dissociation becomes significant (350 K and higher). NO–D reaction is suppressed in the presence of S 18O 2, depending significantly on the S 18O 2 coverage and the competition between the reactions NO–D and S 18O 2–D. When the supply of D 2 is limited, e.g., 0.1 L in this study, the presence of S 18O 2 suppresses the NO–D reaction. With a sufficient supply of D 2, e.g., 0.4 L and higher, D-atom competing reactions do not play a role any more because the reactions of both NO and S 18O 2 with D proceed only to a very limited extent. As such, generation of O atoms from S 18O 2 dissociation is the main reaction that leads to the suppression in NO dissociation and consequently, N 2 production. It is also concluded that the presence of S 18O 2 does not seriously poison the active sites on the Pt surface, providing that there is a sufficient D supply to remove O atoms from both NO dissociation and S 18O 2 dissociation.

Interactions between S 18O 2 and NO on the surface of stepped Pt(3 3 2)

Interactions between S 18O 2 and NO on the surface of stepped Pt(3 3 2) were studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) combined with thermal desorption spectroscopy (TDS). Adsorbed S 18O 2 does not seem to have a preference for step sites on Pt(3 3 2). As such, the presence of S 18O 2 molecules following exposures of ⩽1.6 L does not significantly block the subsequent adsorption of NO (⩽0.8 L) on these step sites. Adsorbed S 18O 2 molecules undergo dissociation (S 18O 2(a) → S 18O(a) + 18O(a)) as the surface temperature is increased to 250 K and above, but the resultant 18O(a) further reacts with sulfur oxides (S 18O 2(a) and S 18O(a)) to form S 18O x ( x > 2) species at ∼400 K and above. The S 18O x species desorb as S 18O 2. Even though the presence of co-adsorbed S 18O 2 suppresses NO dissociation and subsequent N 2 production, this effect is not significantly enhanced with increasing the exposures of S 18O 2 in the range ⩽1.6 L; N 2 desorption is still detectable at an exposure of 1.6 L S 18O 2, at which a considerable amount of S 18O 2 desorption is detected.

Exploring the mechanism of NO–C 2H 4 reactions on the surface of stepped Pt(3 3 2)

Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS), thermal desorption spectroscopy (TDS), and auger electron spectroscopy (AES), were employed to explore the mechanism of NO reduction in the presence of C 2H 4 on the surface of stepped Pt(3 3 2). Both NO–Pt and C 2H 4–Pt interactions are enhanced when NO and C 2H 4 are co-adsorbed on Pt(3 3 2). As a result, C 2H 4 is dissociated at surface temperatures as low as 150 K, and the N–O stretch band is weakened. The presence of post-exposed C 2H 4 leads NO desorption from steps to decrease significantly, but the same effect on NO desorption from terraces becomes appreciable only at higher post-exposures of C 2H 4, e.g., 0.6 L and 1.2 L, and proceeds to a much slighter extent. Auger spectra indicate that as a result of the reaction with O from NO dissociation, the amount of surface C species is greatly reduced when NO is post-exposed to a C 2H 4 adlayer. It is concluded that reduction of NO in the presence of C 2H 4 proceeds very effectively on the surface of the Pt(3 3 2), through a mechanism of NO dissociation and subsequent O removal. Following this mechanism, the significant dissociation of adsorbed NO molecules on steps at surface temperatures below 400 K, and subsequent rapid reaction between the resultant O and C-related species, accounts for the considerable amount of N 2 desorption at temperatures below 400 K.

The Influence of Chemical Pre-treatment and Magnesium Surface Enrichment on Bonding of Succinic Acid Molecules to Aluminium Alloy

In the present study a combined Fourier Transform Infrared Reflection–Absorption Spectroscopy (FT-IR–RAS) and Auger electron spectroscopy (AES) analysis was performed to investigate the bonding of organic coatings to oxides formed on Al–Mg based alloys. The interfacial bonding of a model molecule, succinic acid, mimicking the functional groups used in practical coatings was studied in detail on various differently pre-treated aluminium alloy (AA5182, 4.8 wt% magnesium) surfaces. Besides these differently pre-treated alloy surfaces, also pure magnesium and aluminium were studied for reference. The surface and near-surface composition of the alloys was studied by Auger electron spectroscopy, ion-milling away the surface oxides to obtain a depth profile. The results show that after heat treatment, the oxides are as much enriched in magnesium as aluminium although the bulk concentration of magnesium is only 4.8 wt%. FT-IR–RAS shows that bonding of the succinic acid molecules takes place in a range of configurations, varying between bridging bidentates and unidentates. The relative portion of unidentates increases with the magnesium surface concentration. This is attributed to the difference in bond lengths of Mg–O and Al–O, forcing the carboxylic acid groups to stretch or to attach to only one oxide group (unidentate) instead of two (bidentate). Also the mixed OH/CO3 surface after Mg enrichment at the surface has less room for bonding with two groups, thus affecting the bonding configuration in a similar way.

The role of co-adsorbed O 2 on the catalytic reduction of NO with 13C 2H 5OH on the surface of Pt(3 3 2)

The influence of pre-dosed O 2 on the catalytic reduction of NO with 13C 2H 5OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). We show that the oxidation of 13C 2H 5OH with O 2 is a very effective reaction, occurring at 150 K and giving rise to acetate. The presence of NO does not lead to any evident oxidation of 13C 2H 5OH irrespective of the annealing temperature. For the case of O 2 + 13C 2H 5OH + NO co-adlayers, oxidation of 13C 2H 5OH also takes place at 150 K. However, no new surface species that are supposed to be an intermediate for the production of N 2 are detected. The influence of O 2 on the production and desorption of N 2 is intimately related to both O 2 and 13C 2H 5OH coverage. The presence of pre-dosed O 2 does not greatly promote N 2 desorption. In fact, N 2 desorption is suppressed quantitatively with increasing O 2 coverage, after which unreacted, or left-over O atoms appear and remain on steps. It is concluded that the presence of pre-dosed O 2 does not play a role of activating reactants in the catalytic reduction of NO with 13C 2H 5OH on the surface of Pt(3 3 2).

Elastomeric Nanoparticle Composites Covalently Bound to Al2O3/GaAs Surfaces

This article reports the modification of Al2O3/GaAs surfaces with multifunctional soft materials. Siloxane elastomers were covalently bound to dopamine-modified Al2O3/GaAs semiconductor surfaces using MPt (M = Fe, Ni) nanoparticles. The sizes of the monodisperse FePt and NiPt nanoparticles were less than 5 nm. The surfaces of the nanoparticles as well as the Al2O3/GaAs substrates were modified with allyl-functionalized dopamine that utilized a dihydroxy group as a strong ligand. The immobilization of the elastomers was performed via a hydrosilation reaction of the allyl-functionalized dopamines with the siloxane backbones. X-ray photoelectron spectroscopy (XPS) experiments confirmed the covalent bonding of the siloxane elastomers to the oxide layer on the semiconductor surface. Fourier transform-infrared reflection absorption spectroscopy (FT-IRRAS) measurements revealed that the allyl functional groups are bonded to the siloxane backbones. The FT-IRRAS data also showed that the density of the allyl groups on the surface was lower than that of the siloxane backbones. The mechanical properties of the surface-bound nanocomposites were tested using nanoindentation experiments. The nanoindentation data showed that the soft matrix composed of the elastomeric coating on the surfaces behaves differently from the inner, hard Al2O3/GaAs substrate.

Catalytic reduction of NO in the presence of benzene on a Pt(3 3 2) surface

The catalytic reduction of NO in the presence of benzene on the surface of Pt(3 3 2) has been studied using Fourier transform infra red reflection-absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). IR spectra show that while the presence of benzene molecules at low coverage (e.g., following an exposure of just 0.25 L) promotes NO–Pt interaction, the adsorption of NO on Pt(3 3 2) at higher benzene coverages is suppressed. It is also shown that there are no strong interactions between the adsorbed NO molecules and the benzene itself or benzene-derived hydrocarbons, which can lead to the formation of intermediate species that are essential for N 2 production. TDS results show that the adsorbed benzene molecules undergo dehydrogenation accompanied by hydrogen desorption starting at 300 K and achieving a maximum at 394 K. Subsequent dehydrogenation of the benzene-derived hydrocarbons then begins with hydrogen desorption starting at 500 K. N 2 desorption from NO adlayers on clean Pt(3 3 2) surface becomes significant at temperatures higher than 400 K, giving rise to a peak at 465 K. This peak corresponds to N 2 desorption from NO dissociation on step sites. The presence of benzene promotes N 2 desorption, depending on the benzene coverage. When the benzene exposure is 0.25 L, the N 2 desorption peak at 459 K is dramatically increased. Increasing benzene coverage also results in the intensification of N 2 desorption at ∼410 K. At benzene exposures of 2.4 L, N 2 desorption develops as a broad peak with a maximum at ∼439 K. It is concluded that the catalytic reduction of NO by platinum in the presence of benzene proceeds by NO decomposition and subsequent oxygen removal at temperatures lower than 500 K, and NO dissociation is a rate-limiting step. The contribution of benzene to N 2 desorption is mainly attributed to providing a source of H, which quickly reacts with NO-derived atomic O, leaving the surface with more vacant sites for further NO dissociation.

NO–methanol interaction on the surface of Pt(3 3 2)

The interaction between NO and CH 3OH on the surface of stepped Pt(3 3 2) was investigated using Fourier transform infra red reflection–absorption spectroscopy (FTIR-RAS) and thermal desorption spectroscopy (TDS). At 90 K, pre-dosed CH 3OH molecules preferentially adsorb on step sites, suppressing the adsorption of NO molecules on the same sites. However, due to a much stronger interaction with Pt, at 150 K and higher, the adsorption of NO molecules on step sites is restored, giving rise to peaks closely resembling those of NO molecules adsorbed on clean Pt(3 3 2) surface. Adsorbed CH 3OH is very reactive on this surface, and is readily oxidized to formate in the presence of O 2, even at 150 K. In contrast, reactions between CH 3OH and co-adsorbed NO are slight to non-existent. There are no new peaks in association with intermediates resulting from CH 3OH–NO interactions. It is concluded that the reduction of NO with CH 3OH on Pt(3 3 2) does not proceed through a mechanism of forming intermediates.

Hybridization of Oligonucleotide-Modified Silver and Gold Nanoparticles in Aqueous Dispersions and on Gold Films

Functionalization of silver and gold nanoparticles by 12mer-thiolated homo-oligonucleotides, SA and ST (containing only adenine or thymine, respectively), and their hybridization and dehybridization in aqueous dispersions have been described. In addition, ST and SA were self-assembled onto gold films and hybridized with their complementary pairs, unlabeled or labeled by gold and silver nanoparticles. The base pairing between DNA strands and the types of oligonucleotides (adenine or thymine) attached to the nanoparticles was detected by Polarization Modulated Fourier Transform Infrared Reflection Absorption Spectroscopy (PM-FTIRRAS).

Spectroelectrochemical studies of bilayers of phospholipids in gel and liquid state on Au(111) electrode surface

Differential capacity, chronocoulometry and Polarization Modulation Fourier Transform Infrared Reflection Absorption Spectroscopy (PM FTIRRAS) were employed to investigate spreading of small unilamellar vesicles (SUVs) of DOPC and DMPC onto a Au(111) electrode surface. The electrochemical experiments demonstrated that vesicles fuse onto the electrode surface and at E>−0.5V (SSCE) or at charge densities −10< σ M<5 μC cm −2 to form defected bilayers, directly in contact with the metal surface. The analysis of PM FTIRRA spectra in the CH stretching region showed that the DOPC bilayer is in the liquid crystalline state while the bilayer of DMPC is in the gel or in the ripple phase. The spectra were also used to determine the tilt of the acyl chains in the bilayer of DMPC as a function of the electrode potential. At E<−0.5 V (SSCE), where the bilayer is detached from the metal surface, the chains are tilted at ∼29° with respect to surface normal. When the bilayer is adsorbed at the metal surface at E>−0.5 V (SSCE), the tilt angle increases to ∼42°. The increase of the tilt angle is discussed in terms of a change in the packing of the polar head of the phospholipids molecules in the bilayer adsorbed at the electrode surface.

Carbon dioxide activation and alkali compound formation. I. Vibrational characterization of oxalate intermediates

The activation of CO 2 in thin potassium layers adsorbed on Cu(1 1 1) has been studied with time-evolved Fourier transform-infrared reflection absorption spectroscopy. The growth of thin layers by reactive evaporation of potassium in a CO 2 atmosphere permits control of the K:CO 2 stoichiometry, which strongly affects the selectivity in the formation of intermediates and the decomposition pathways of the layer. Layers grown in a CO 2 rich atmosphere exhibit the preferential growth of stoichiometric potassium oxalate K 2C 2O 4 (D 2h). The molecular identity of oxalate with D 2h symmetry is confirmed by vibrational spectra utilizing isotopic substitution methods ( 13CO 2 and C 18O 2) and by the use of isotopic mixtures of CO 2/C 18O 2 and CO 2/ 13CO 2. A comparison of the isotope data with theoretical calculations gives an estimated OCO bond angle in oxalate of 132°. Far-IR spectra obtained with synchrotron radiation indicate the equivalent interaction of all oxygen atoms with the potassium. A comparison of the vibrational data with theoretical ab initio calculations confirms the structural model of an oxalate species that is bulk coordinated with no strong directional bonding and all oxygen atoms equally interacting with potassium. At medium and low CO 2:K ratios, very complex vibrational spectra are observed, indicating the formation of an oxalate surface species with C 2v symmetry in addition to D 2h − oxalate, CO 2 − and CO 2 2− species.

Exchange Reaction of Adsorbed Formate with Gaseous Formic Acid on Ni(110) Studied by Time-Resolved Fourier Transform Infrared Reflection Absorption Spectroscopy

The dynamic behavior of adsorbed formate on Ni(110) in the presence of gaseous formic acid was studied by time-resolved infrared reflection absorption spectroscopy. The preadsorbed formate (DCOO(a)) was replaced by the postexposed formic acid (HCOOD) to form HCOO(a) on Ni(110) in the temperature region between 230 and 300 K, where the formate was stable under vacuum and no decomposition of formate was observed. It was confirmed that the preadsorbed DCOO(a) desorbed as DCOOD accompanied by formation of HCOO(a) via the deuterium atom transfer from HCOOD.

Chemisorption of CO on the Ir(111) surface: Adsorption and desorption kinetics measured with in situ vibrational spectroscopy

The kinetics of adsorption and desorption of carbon monoxide on Ir(111) have been investigated using the well-defined and carefully calibrated IR absorption peak position of the CO intramolecular stretching vibration as a nonintrusive coverage probe. Experiments were performed with time-resolved Fourier transform infrared reflection–absorption spectroscopy (TR-IRAS), which allows high-resolution measurements over a large pressure range between 1×10−8 and 1×10−5 mbar and surface temperature range between 390 and 500 K. The rate of desorption into vacuum is compared with the rate of desorption in the presence of a finite pressure of the desorbing gas. In this case, a flux-dependent enhancement of the desorption rate has been observed previously, which, if existent, should have an important impact on heterogeneously catalyzed reactions performed under high-pressure conditions. Most of these experiments, however, were performed using thermal desorption spectroscopy, a nonequilibrium method. We have been able to measure all rate parameters that are essential to describe the desorption in situ with TR-IRAS and have, thereby, clarified the disagreements that exist in the literature.