Attenuated Total Reflection Fourier Transform Infrared Spectroscopy Results Research Articles

Detection of Sialic Acid to Differentiate Cervical Cancer Cell Lines Using a Sambucus nigra Lectin Biosensor.

Pap smear screening is a widespread technique used to detect premalignant lesions of cervical cancer (CC); however, it lacks sensitivity, leading to identifying biomarkers that improve early diagnosis sensitivity. A characteristic of cancer is the aberrant sialylation that involves the abnormal expression of α2,6 sialic acid, a specific carbohydrate linked to glycoproteins and glycolipids on the cell surface, which has been reported in premalignant CC lesions. This work aimed to develop a method to differentiate CC cell lines and primary fibroblasts using a novel lectin-based biosensor to detect α2,6 sialic acid based on attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and chemometric. The biosensor was developed by conjugating gold nanoparticles (AuNPs) with 5 µg of Sambucus nigra (SNA) lectin as the biorecognition element. Sialic acid detection was associated with the signal amplification in the 1500-1350 cm-1 region observed by the surface-enhanced infrared absorption spectroscopy (SEIRA) effect from ATR-FTIR results. This region was further analyzed for the clustering of samples by applying principal component analysis (PCA) and confidence ellipses at a 95% interval. This work demonstrates the feasibility of employing SNA biosensors to discriminate between tumoral and non-tumoral cells, that have the potential for the early detection of premalignant lesions of CC.

The Effect of Surface Treatments on Zirconia Bond Strength and Durability.

To evaluate the effects of airborne particle abrasion (APA) combined with MDP-containing resin cement, a glass-ceramic spray deposition (GCSD) method on the shear bond strengths (SBSs) and durability of 3 mol% yttrium oxide-stabilized zirconia ceramic (3Y-TZP) compared with lithium disilicate glass ceramics (LDGC). 3Y-TZP disks were randomly treated as follows: for Group APA+MDP, 3Y-TZP was abrased using 50 μm Al2O3 particles under 0.1 Mpa and bonded with MDP-containing resin cement; for Group GCSD, 3Y-TZP was treated with the GCSD method, etched by 5% HF for 90 s, silanized and bonded with resin cement without MDP. Group LDGC was bonded as the Group GCSD. X-ray diffraction (XRD), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDX) were used to analyze the surface chemical and micro-morphological changes of the ceramics before bonding. The bonded ceramic specimens were randomly divided into subgroups, and the SBSs were determined before and after 10,000 thermocycling. The SBSs were analyzed with a one-way ANOVA analysis. Failure modes were determined with optical microscopy and SEM. The XRD, ATR-FTIR and XPS results identified the formation of lithium disilicate and zirconium silicate on 3Y-TZP after GCSD. The SEM micrographs revealed that 3Y-TZP surfaces were roughened by APA, while 3Y-TZP with GCSD and LDGC surfaces could be etched by HF to be porous. The APA treatment combined with MDP-containing resin cement produced the high immediate zirconia shear bond strengths (SBSs: 37.41 ± 13.51 Mpa) that was similar to the SBSs of the LDGC (34.87 ± 11.02 Mpa, p > 0.05), but, after thermocycling, the former dramatically decreased (24.00 ± 6.86 Mpa, maximum reduction by 35.85%) and the latter exhibited the highest SBSs (30.72 ± 7.97 Mpa, minimum reduction by 11.9%). The 3Y-TZP with GCSD treatment displayed the lower zirconia SBSs before thermocycling (27.03 ± 9.76 Mpa, p < 0.05), but it was similar to the 3Y-TZP treated with APA and MDP containing resin cement after thermocycling (21.84 ± 7.03 vs. 24.00 ± 6.86 Mpa, p > 0.05). The APA combined with MDP-containing resin cement could achieve the high immediate zirconia SBSs of those of the LDGC, but it decreased significantly after thermocycling. The GCSD technique could yield the immediate zirconia SBSs similar to those of LDGC before thermocycling, and long-term zirconia SBSs were similar to those of 3Y-TZP treated with APA followed by MDP-containing resin cement after thermocycling. Hence, the GCSD technique could enrich zirconia surface treatments and is an alternative to zirconia surface pretreatment for 3Y-TZP bond durability.

A conductive catecholate-based framework coordinated with unsaturated bismuth boosts CO2 electroreduction to formate.

Bismuth-based metal-organic frameworks (Bi-MOFs) have received attention in electrochemical CO2-to-formate conversion. However, the low conductivity and saturated coordination of Bi-MOFs usually lead to poor performance, which severely limits their widespread application. Herein, a conductive catecholate-based framework with Bi-enriched sites (HHTP, 2,3,6,7,10,11-hexahydroxytriphenylene) is constructed and the zigzagging corrugated topology of Bi-HHTP is first unraveled via single-crystal X-ray diffraction. Bi-HHTP possesses excellent electrical conductivity (1.65 S m-1) and unsaturated coordination Bi sites are confirmed by electron paramagnetic resonance spectroscopy. Bi-HHTP exhibited an outstanding performance for selective formate production of 95% with a maximum turnover frequency of 576 h-1 in a flow cell, which surpassed most of the previously reported Bi-MOFs. Significantly, the structure of Bi-HHTP could be well maintained after catalysis. In situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) confirms that the key intermediate is *COOH species. Density functional theory (DFT) calculations reveal that the rate-determining step is *COOH species generation, which is consistent with the in situ ATR-FTIR results. DFT calculations confirmed that the unsaturated coordination Bi sites acted as active sites for electrochemical CO2-to-formate conversion. This work provides new insights into the rational design of conductive, stable, and active Bi-MOFs to improve their performance towards electrochemical CO2 reduction.

Thermal Modification and Alkyl Ketene Dimer Effects on the Surface Protection of Deodar Cedar (Cedrus deodara Roxb.) Wood

The aim of this research was to evaluate the multiple effects of both thermal modification and alkyl ketene dimer (AKD) on the deodar cedar (Cedrus deodara Roxb.) wood surface, before and after an irradiation test. The physical and chemical changes that occurred on the cedar wood samples due to the combined effect of these modifications were evaluated by measuring their wettability and colour and using attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The surface analysis by XPS showed the expected variability among the sampled layers for unmodified and thermally modified cedar wood samples and a uniform composition after the AKD coverage, regardless of their pre-treatments. The FTIR spectra before the irradiation test showed that the hydrophobicity of the samples was ensured by the formation of carbonyl groups originating from the reaction between the AKD and hydroxyl groups of cellulose, which is related to the presence of the absorption band between 1700 cm−1 and 1750 cm−1. Markedly, after the irradiation test, a degradation of the amorphous cellulose component occurred, showing that photoisomerisation to the enolic form took place. Overall, although uniform AKD coverage was derived from the surface analysis and wetting test, the combined ATR-FTIR results and colour measurements showed that it could not provide permanent protection to the underlying wood structure due to its own tendency to degrade mainly in colour over time, under the action of UV rays and atmospheric agents.

Artificial deterioration of vegetable-tanned leather under synergistic effect of temperature and humidity

• The synergistic effect of temperature and relative humidity on the deterioration of mimosa-tanned leather was investigated. • The changes in structure and thermal properties of artificially aged mimosa-tanned leather were systematically studied. • The TG-FTIR technique was employed to analyze the deterioration with the evolved gaseous products during thermal degradation. The deterioration of mimosa-tanned leather artificially aged at 80 °C and 60% relative humidity (RH) for up to 32 days was investigated. The changes in thermal properties, morphology, and structure were analyzed by thermogravimetric analyzer (TGA), polarized light microscopy (PLM), scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and X-ray diffraction (XRD). The results showed that the mimosa-tanned leather was deteriorated with a decrease in hydroxyproline content. After the artificial aging treatment, the thermal resistance of the mimosa-tanned leather was reduced. This result was further confirmed by PLM observations that the shrinkage temperature of the collagen fibers decreased with increasing aging time. The evolved gaseous products from the TGA were detected by TGA-FTIR to characterize the deterioration caused by aging. After aging, the evolution yield of nitrogen-containing products such as NH 3 , HNCO, and pyrrole decreased, while the evolution yield of CO 2 increased. According to the ATR-FTIR, XRD, and SEM results, the orientation and structural integrity of the collagen fibers were destroyed by artificial aging.

Evaluation of the Physico-Chemical Properties of Liposomes Assembled from Bioconjugates of Anisic Acid with Phosphatidylcholine.

The aim of this work was the evaluation of the physico-chemical properties of a new type of liposomes that are composed of DPPC and bioconjugates of anisic acid with phosphatidylcholine. In particular, the impact of modified anisic acid phospholipids on the thermotropic parameters of liposomes was determined, which is crucial for using them as potential carriers of active substances in cancer therapies. Their properties were determined using three biophysical methods, namely differential scanning calorimetry (DSC), steady-state fluorimetry and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Moreover, temperature studies of liposomes composed of DPPC and bioconjugates of anisic acid with phosphatidylcholine provided information about the phase transition, fluidity regarding chain order, hydration and dynamics. The DSC results show that the main phase transition peak for conjugates of anisic acid with phosphatidylcholine molecules was broadened and shifted to a lower temperature in a concentration- and structure-dependent manner. The ATR-FTIR results and the results of measurements conducted using fluorescent probes located at different regions in the lipid bilayer are in line with DSC. The results show that the new bioconjugates with phosphatidylcholine have a significant impact on the physico-chemical properties of a membrane and cause a decrease in the temperature of the main phase transition. The consequence of this is greater fluidity of the lipid bilayer.

Highly Characteristic Adsorption Based on Single Crystal {001}-TiO2 Surface Molecular Recognition Promotes Enhanced Oxidation.

Exploring the adsorption and selective removal mechanism of target pollutants on the catalytic interface is an important research topic in the field of environmental sewage treatment. However, the molecular recognition based on the surface of single crystals is still unclear. Single crystal molecularly imprinted TiO2 (001-MI-TiO2) with a highly exposed {001} plane was prepared by a hydrothermal method to characteristically adsorb and degrade phenol. The kinetics of phenol oxidation on 001-MI-TiO2 was 12.93 times that of polycrystal nonimprinted TiO2. The phenol adsorption quantity of 001-MI-TiO2 was 1.68 times that of the polycrystal molecularly imprinted TiO2 (MI-TiO2). Compared with MI-TiO2, the significantly increased removal of phenol on 001-MI-TiO2 mainly attributed to the enhanced adsorption quantity and better photocatalytic performance. The recognition mechanism of phenol on the 001-MI-TiO2 during the adsorption process was studied using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), which indicated enhanced adsorption of phenol when compared with MI-TiO2. The recognition between the phenol molecule and the imprinted sites mainly relied on the hydrogen bond between the π bond of the benzene ring and the hydroxyl group on the surface of TiO2. Besides, the interferent ATR-FTIR results showed that the single crystal surface can significantly reduce noncharacteristic adsorption, indicating good selectivity for the targets. In addition, the degradation intermediates during the photocatalytic process were further analyzed by in situ infrared technology.

Optimization of induction parameters, structure quality assessment by ATR-FTIR and in silico characterization of expressed recombinant polcalcin in three different strains of Escherichia coli

The inhalation of Chenopodium album (C. album) pollen, especially polcalcin (Che a 3), has been reported as a significant source of allergic respiratory symptoms. This study was conducted to characterize biophysical differences of recombinant polcalcin come from three different Escherichia coli strains using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), optimize recombinant polcalcin expression, and linear B-cell epitopes identification using in silico methods. ATR-FTIR results of purified proteins showed spectra intensity variance in the amide I region, while there were no changes in pick position and shape of the bands. SHuffle® T7 Express was selected for subsequent optimization due to ability in the correction of the mis-oxidized bonds and promotes proper folding which was validated by ATR-FTIR analysis results. Then, Response Surface Methodology was performed to optimize critical factors including induction temperature, duration of induction, and concentration of inducer. The best partitioning conditions were achieved in 1.5 mM IPTG for 10.97 h at 29.9 °C. Finally, prediction of polcalcin B-cell epitopes was carried out which indicated the presence of 4 different epitopes. Together, the results may help to the development of diagnostic approaches and also vaccine manufacture for desensitization and modulation of the allergic response in patients.

Study on the role of n-SiO2 incorporation in thermo-mechanical and microstructural properties of ambient cured FA-GGBS geopolymer matrix

The effect of Nano silica (seed) addition on the early period of geopolymer formation in the alkali mediated FA + GGBS reaction, was analyzed by Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Experimentation on different dosages of NS (0–3%), in the 80% FA and 20% GGBS (precursor material) activated through NaOH and Na2SiO3 (MR:1.1). The seed (NS) added in the system triggering the nucleation that reduce the induction period by formation of more geo polymeric gel in the early period of 12–72 h that was evident from ATR-FTIR results and it was pronounced at the NS dose of 2.5% that yield rapid increase in strength development to an extend of 50% gain as curing age increased from 1 day to 3 days, thereafter at slower rate upto 365 days. The weight change and strength characteristics of mortars after heat treatment in the temperature range of 30–800 °C studied showed that seeded mortar did not show any visible cracks/deterioration. Thermal conductivity and thermal stability using TGA/DTA and SEM microscopic examination studied.

Surface modification of chitosan/PEO nanofibers by air dielectric barrier discharge plasma for acetylcholinesterase immobilization

There are different methods to modify polymer surfaces for biological applications. In this work we have introduced air-dielectric barrier discharge (DBD) plasma at atmospheric pressure as an economical and safe method for modifying the surface of electrospun chitosan/PEO (90/10) nanofibers for acetylcholinesterase (AChE) immobilization. According to the contact angle measurement results, the nanofibers become highly hydrophilic when they are exposed to the DBD plasma for 6min in compared to unmodified membrane. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) results reveal hydroxyl, CO and NH3+ polar groups increment after 6min plasma treatment. Contact angle measurements and ATR-FTIR results are confirmed by X-ray photoelectron spectroscopy (XPS). AChE at pH 7.4 carries a negative charge and after immobilization on the surface of plasma-treated nanofibrous membrane attracts the NH3+ group and more enzyme activity is detected on the plasma-modified nanofibers for 6min in compared to unmodified nanofibers. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) are used for the surface topography and morphology characterization. The results have proved that air-DBD plasma is a suitable method for chitosan/PEO nanofibrous membrane modification as a biodegradable and functionalized substrate for enzyme immobilization.

Coupled redox transformation of chromate and arsenite on ferrihydrite.

The redox chemistry of chromate (Cr(VI)) and arsenite (As(III)) on the iron oxyhydroxide, ferrihydrite (Fh), was investigated. Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS) were used to determine the composition of the adsorbed layer on Fh during and after exposure to solution-phase Cr(VI) and As(III). The individual exposure of Cr(VI) or As(III) on Fh resulted in the adsorption of the respective species, and there was no change in the oxidation state of either species. In contrast, exposure of Fh simultaneously to Cr(VI) and As(III) led to an adsorbed layer that was primarily Cr(III) and As(V). This redox transformation occurred over various experimental conditions at pH 3, 5, and 7 and in the presence or absence of O2, as demonstrated by in situ ATR-FTIR results. A similar redox transformation was not observed at a solution of pH 9, due to minimal Cr(VI) adsorption. Postreaction XPS showed that the majority of adsorbed arsenic existed as As(V) at pH 3, 5, and 7, while As(III) was the main species detected at pH 9. At pH 3 the redox chemistry between Cr(VI) and As(III) led to a As(V) product surface loading of ∼600 mmol/kg. Experiments performed in the absence of dissolved O2 resulted in less As(V) on the surface compared to experiments in which O2 was present for equivalent reaction times.

Developing a rapid and sensitive method for determination of trans-fatty acids in edible oils using middle-infrared spectroscopy

Several countries have adopted labelling policy concerning the declaration of trans fatty acids (TFAs) content in the nutritional facts panel of processed food. Consequently, the food industry requires rapid methods to measure low levels of TFAs. This paper reports the development of a rapid method to determine TFAs <1% in edible oils (palm, peanut, soybean and sunflower) and oils/fat samples extracted from finished products using attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Traditional linear regression and Partial Least Squares (PLS) statistical tools were applied to model the spectroscopic data. The calibration models of edible oils/fat samples showed a coefficient-of-correlation ⩾0.982 and standard error of prediction (SEP) between 0.03% and 0.06%. The ATR-FTIR results of extracted oils/fat are in good agreement with the capillary gas chromatography with flame ionisation detector (GC/FID). This study has demonstrated that ATR-FTIR technique can be used to rapidly determine trans fatty acids <1% in oils/fat.

The removal of impurities from gray cotton fabric by atmospheric pressure plasma treatment and its characterization using ATR-FTIR spectroscopy

Gray cotton fabric shows hydrophobic characteristics due to presence of non-cellulosic impurities in outermost layers of cotton fiber. In the present study, atmospheric pressure plasma treatment for the removal of the non-cellulosic impurities from gray cotton fabric is investigated. Gray cotton fabric is treated with air dielectric barrier discharge at different time interval, and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). Different species formed in plasma are identified using optical emission spectroscopy. The results clearly show that the plasma treatment improves wettability of gray cotton which is due to the removal of non-cellulosic impurities and due to the formation of polar carboxylate group. Removal of wax after plasma treatment is clearly reflected in ATR-FTIR spectra as disappearance of symmetric and asymmetric stretching of alkyl group at 2852.24 and 2917.81 cm−1. Further, ATR-FTIR spectroscopy provides a fast and satisfactory assessment of removal of impurities from cotton surface when untreated and plasma-treated cotton fabric is exposed to HCl vapor and subsequently spectra are collected. We observed a strong carboxyl peak is induced at 1749 cm−1 in case of untreated cotton. While for plasma-treated cotton fabrics substantial variation in the intensity of 1641 and 1749 cm−1 peak is observed with increase in plasma treatment time. The morphological changes observed by SEM are in accordance with ATR-FTIR results. The results are compared with conventionally (alkaline scouring) treated cotton fabric. The study reveals that atmospheric pressure plasma has potential to become dry and environment friendly process to improve wettability of gray cotton fabric.

Plasma deposition of a silicone-like layer for the corrosion protection of magnesium

Magnesium (Mg) and its alloys are widely used for biodegradable implant materials due to their degradability and mechanical properties similar to bone. However, the high corrosion rate and release of hydrogen gas hinder its clinical application. In this study, plasma-polymerization was used to deposit the hexamethyldisiloxane (HMDSO) polymeric films on Mg surface using low temperature radio frequency discharge plasma. The chemical and physical properties of the HMDSO films were characterized by contact angle measurements, field emission scanning electron microscope, and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). Contact angle results show that the contact angle and the plasma discharge powers are strongly correlated. ATR-FTIR results indicate that plasma-polymerized HMDSO films have a chemical structure close to polydimethylsiloxane (PDMS). The weight loss test and electrochemical impedance spectroscopy were performed immersion in 0.9% NaCl solution in order to investigate corrosion protective properties of the coating layer. It was found that HMDSO plasma-polymerized coating layer showed good anti-corrosion properties than that of untreated samples. These results that the polymeric films coated on Mg may be potentially applied for clinical use.

Characterization and formation of hydroxyapatite on Ti6Al4V coated by plasma electrolytic oxidation

In this study, Ti6Al4V alloy was coated in the solution consisting of calcium acetate (CA) and β-calcium glycerophosphate (β-Ca-GP) by plasma electrolytic oxidation (PEO) to produce hydroxyapatite and calcium apatite-based composite used as of bioactive and biocompatible materials in biomedical applications. The phase structures, surface morphologies, functional groups of molecules, chemical compositions of the surfaces and the binding energies of atoms in the coating were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS), respectively. Anatase, rutile, calcium oxide, titanium phosphide, whitlockite, tri-calcium phosphate (TCP), perovskite calcium titanate and hydroxyapatite phases on the coating were detected by XRD analysis. The surface of coatings produced by PEO method has a porous structure. The amount of amorphous hydroxyapatite is the highest value for the coating produced at 5min in XPS and ATR-FTIR results, whereas the amount of crystalline hydroxyapatite has the highest value for coating produced at 120min in XRD results.

Surface Treatment of Polypropylene Powders Using a Plasma Reactor with a Stirrer

A radio frequency argon plasma reactor with a stirrer was employed for the surface treatment of polypropylene (PP) powders. The changes in the superficial contact angle and the superficial composition of the un-treated and treated PP powders were analyzed by means of water contact angle (WCA) measurement, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The water contact angle changed from the original value of 130.2° before plasma treatment to the value of 73.6° after treatment for 5 minutes. With the increase in plasma treating time, there were a decrease in the water contact angle and an increase in the content of oxygen containing polar functional groups (i.e., C-O, C=O and O-C=O). Both XPS and ATR-FTIR results indicated that the plasma treatment led to the formation of oxygen containing polar functional groups due to oxidation on the surface of the PP powders, and the trend of variation of the water contact angle with plasma treating time was related to the concentration of oxygen atom on the treated PP powders surface. Furthermore, the aging of the plasma-treated PP powders was investigated.

Interfacial reaction of silver ultra-thin film deposited on interpenetrating polymer network substrate by liquor-phase reduction

The interfacial reaction, metal transformations, and nonmetal bond types of silver ultra-thin film deposited on polyurethane (PU) based interpenetrating polymer networks (IPN) substrate by the liquor-phase reduction at room temperatures were studied by atomic force microscope (AFM), X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The IPN substrate was prepared by dip-pulling precursors onto a silicon wafer or a glass plate, followed by solidification at room temperature. The interpenetrate structures of IPN with two crosslinked networks restricted the aggregation of silver during the reduction and deposition. The devised –OH terminal group in PU simplified the determination of reactive site in IPN and reinforced the adhesion between IPN and silver through interfacial reaction. The XPS results, which matched well with the ATR-FTIR results, verified the chemical reactive site of PU in IPN with silver in the oxide state.

Molecular interactions between magainin 2 and model membranes in situ.

In this paper, we investigated the molecular interactions of magainin 2 with model cell membranes using sum frequency generation (SFG) vibrational spectroscopy and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Symmetric 1-palmitoyl-2-oleoyl-sn-glycero-3-[Phospho-rac-(1-glycerol)] (POPG) and 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) bilayers, which model the bacterial and mammalian cell membranes, respectively, were used in the studies. It was observed by SFG that magainin 2 orients relatively parallel to the POPG lipid bilayer surface at low solution concentrations, around 200 nM. When increasing the magainin 2 concentration to 800 nM, both SFG and ATR-FTIR results indicate that magainin 2 molecules insert into the POPG bilayer and adopt a transmembrane orientation with an angle of about 20 degrees from the POPG bilayer normal. For the POPC bilayer, even at a much higher peptide concentration of 2.0 microM, no ATR-FTIR signal was detected. For this concentration on POPC, SFG studies indicated that magainin 2 molecules adopt an orientation nearly parallel to the bilayer surface, with an orientation angle of about 75 degrees from the surface normal. This shows that SFG has a much better detection limit than ATR-FTIR and can therefore be applied to study interfacial molecules with a much lower surface coverage. This magainin 2 orientation study and further investigation of the lipid bilayer SFG signals support the proposed toroidal pore model for the antimicrobial activity of magainin 2.

Ordered adsorption of coagulation factor XII on negatively charged polymer surfaces probed by sum frequency generation vibrational spectroscopy

Electrostatic interactions between negatively charged polymer surfaces and factor XII (FXII), a blood coagulation factor, were investigated by sum frequency generation (SFG) vibrational spectroscopy, supplemented by several analytical techniques including attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), quartz crystal microbalance (QCM), zeta-potential measurement, and chromogenic assay. A series of sulfonated polystyrenes (sPS) with different sulfonation levels were synthesized as model surfaces with different surface charge densities. SFG spectra collected from FXII adsorbed onto PS and sPS surfaces with different surface charge densities showed remarkable differences in spectral features and especially in spectral intensity. Chromogenic assay experiments showed that highly charged sPS surfaces induced FXII autoactivation. ATR-FTIR and QCM results indicated that adsorption amounts on the PS and sPS surfaces were similar even though the surface charge densities were different. No significant conformational change was observed from FXII adsorbed onto surfaces studied. Using theoretical calculations, the possible contribution from the third-order nonlinear optical effect induced by the surface electric field was evaluated, and it was found to be unable to yield the SFG signal enhancement observed. Therefore it was concluded that the adsorbed FXII orientation and ordering were the main reasons for the remarkable SFG amide I signal increase on sPS surfaces. These investigations indicate that negatively charged surfaces facilitate or induce FXII autoactivation on the molecular level by imposing specific orientation and ordering on the adsorbed protein molecules.

Influence of Electrostatic Interactions on the Surface Adsorption of a Viral Protein Cage

The Cowpea chlorotic mottle virus (CCMV) provides a useful protein-cage architecture that can be used for the size- and shape-constrained chemistry of nanomaterials. The control of surface assembly is necessary for the realization of many applications of these nanoscale reaction vessels. Electrostatic interactions provide a useful (and reversible) method for controlled surface assembly. CCMV absorption behavior was studied on Formvar, bare Si, Formvar-coated Si, and Si modified by aminopropyltriethoxysilane (APS). Transmission electron microscopy (TEM), atomic force microscopy (AFM), and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) were used to characterize the CCMV surface adsorption. Combined AFM and ATR-FTIR data indicated that the viral coverage on the modified surfaces was approximately 84% of the jamming limit predicted by the random sequential adsorption (RSA) model. According to the ATR-FTIR results, surface coverage was not increased at higher ionic strengths nor at a pH near the isoelectric point (pI) of the virus. The Langmuir model was used to provide a description of the kinetic absorption behavior.