Attenuated total reflection adsorption

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

Some attention has also been paid to the simultaneous adsorption of sulfate anions and organic compounds. Futamata [44] has detected coadsorption of water molecules and sulfate species with uracil on polycrystalline gold electrode, applying attenuated total reflection-infrared spectroscopy. The adsorbed sulfate species appeared either as S04 or HS04, depending on the pH of the electrolyte solution. Skoluda... 

The attenuated total reflection (ATR) Fourier transform infrared spectroscopic (FT-fR) studies of Gendreu, Jakobsen, and others79 have the potential for direct determination of conformational changes during the adsorption process due to shifts in the infrared absorption bands. Sakurai et al. 80,81), have used ATR-FT1R, as well as CD, to probe conformational changes upon adsorption. 

In the various sections of this chapter, I will briefly describe the major characteristics of FT-IR, and then relate the importance of these characteristics to physiochemical studies of colloids and interfaces. This book is divided into two major areas studies of "bulk" colloidal aggregates such as micelles, surfactant gels and bilayers and studies of interfacial phenomena such as surfactant and polymer adsorption at the solid-liquid interface. This review will follow the same organization. A separate overview chapter addresses the details of the study of interfaces via the attenuated total reflection (ATR) and grazing angle reflection techniques. 

Fourier-transformed infrared spectroscopy (FT1R), either in the transmission mode(70), the grazing incidence reflection (GI) mode(7,5) or the attenuated total reflection (ATR) mode(7,2), has been the most widely used experimental tool for the characterization and structure determination of SA monolayers. GI-IR is especially useful in determining the molecular orientation in the film structures because it senses only the vibrational component perpendicular to the substrate surface(7,5). Polarized ATR-IR can also be used to study molecular orientation(7,77). McKeigue and Gula-ri(72) have used ATR-IR to quantitatively study the adsorption of the surfactant Aerosol-OT. 

In an effort to gain a better understanding of the initial fouling step leading to bacterial attachment and biofilm formation, we have investigated the adsorption of protein and polysaccharides onto thin metallic films and uncoated internal reflection elements from flowing solutions using attenuated total reflectance spectroscopy. The preliminary results will be described in this paper. 

Adsorption of the enzymes subtilisin BPN and lysozyme onto model hydrophilic and hydrophobic surfaces was examined using adsorption isotherm experiments, infrared reflection-absorption spectroscopy (IRRAS), and attenuated total reflectance (ATR) infrared (IR) spectroscopy. For both lysozyme and BPN, most of the enzyme adsorbed onto the model surface within ten seconds. Nearly an order-of-magnitude more BPN adsorbed on the hydrophobic Ge surface than the hydrophilic one, while lysozyme adsorbed somewhat more strongly to the hydrophilic Ge surface. No changes in secondary structure were noted for either enzyme. The appearance of carboxylate bands in some of the adsorbed BPN spectra suggests hydrolysis of amide bonds has occurred. 

Bertolucci, Jantzef, and Chamberlain (8) report briefly on their work using single-reflection, attenuated, total-reflection, infrared spectroscopy to study the mechanism of adsorption on hydroxy-apatite crystals of citric acid, tartaric acid, sodium citrate, oxytetracycline hydrochloride, and glycine. This work has been of interest to many chemists, but it also has particular pertinency to current research on dental adhesives and the effect of pretreatment of the tooth cavity wall. 

Adsorption of CN on a silver metal film was reported by Hatta et al. [112], using multiple internal reflection in an ATR (attenuated total reflection) prism configuration. Basically the same features were observed by Hatta et al. as in the external reflection approach, namely a potential-dependent band located between 2100 and 2118 cm assigned to the adsorbed CN ion and another band located at 2143 cm , assigned to the Ag(CN)2 complex. The feature at 2167 cm was not observed, because of the limited potential range used in this experiment to avoid the dissolution of the silver film [112]. 

Attenuated Total Reflectance FTIR (ATR-FTIRf) is a method that has been applied by a number of workers for the study of protein conformation. ATR has been used for monitoring adsorption of proteins or blood components to sur ces (1,2), and for the structural analysis of proteins dried onto an IRE (thin film) (3,4). It has also been used for exploring the effects of solution conditions on the structure of proteins irreversibly adsorbed to an IRE (5,6,7), and has been shown to be usefel for studying the secondary structure and ligand binding properties of membrane proteins (8,9). 

Ex situ IR data are collected on dried, diluted powder films in a low vacuum enviromnent or one purged with a dry gas such as N2. Attenuated total reflectance (ATR)-IR spectroscopy provides surface-sensitive IR measurements and can be used for in situ studies of sorption phenomena. Raman spectroscopy is a related vibrational spectroscopy that provides complimentary information to IR. It can also be used to collect vibrational spectra of aqueous samples. Typical data reduction for vibrational spectra involves subtraction of a background spectmm collected under identical conditions from the raw, averaged sample spectrum. Data analysis usually consists of an examination of changes in peak position and shape and peak fitting (Smith, 1996). These and other spectral parameters are tracked as a function of maaoscopic variables such as pH, adsorption density, and ionic strength. 

E. Zippel, M. W. Breiter, and R. Kellner, Fourier-transform Infrared, Attenuated Total Reflection Spectroscopy A Complementary Tool for the Ivestigation of the Adsorption of CO on Thin Metal Layers, J. Chem. Soc. Faraday Trans. 87, 637-642 (1991). 

This study addresses the question of how bulk polymer chemistry and surface energy affect the amount and the conformation of FN adsorbed to a series of polyurethaneureas. The technique of Fourier transform infrared spectroscopy (FTIR) coupled with attenuated total reflectance (ATR) optics was used to continuously and non-invasively measure the kinetics of FN adsorption, as well as to monitor conformational changes occuring during adsorption. 

Fourier Transform Infrared Spectroscopic and Attenuated Total Reflectance Studies of Protein Adsorption in Flowing Systems... 

Another variant of IR spectroscopic technique is known as Fourier Transform IR Attenuated Total Reflection Spectroscopy (ATR FT-IR) has been described by Poston et al. [123] to study adsorbates at the silica-solution interface. The authors reported the preparation of ZnSe internal-reflection elements coated with a porous silica layer of ca. 700 nm thick. They studied the adsorption of ethylacetate from n-heptane solutions. This technique allows the determination of IR spectra in-situ and its dependence on the solution concentration. They found a nonlinear adsorption isotherm of ethylacetate on... 

The application of IR spectroscopy to organic sorbates has been primarily limited to gas-phase a orption kinetics and gas-phase catalysis (21). The usefrilness of IR for investigating sorption/desorption processes in situ, has been demonstrated for the selectivity of conformer adsorption at mineral surfaces (22). Strong absorption of H O vibrational modes by IR radiation has been a major hindrance in the application of IR spectroscopy to study organic sorption at aqueous-mineral interfaces. Attenuated total reflectance-IR (ATR-IR) spectroscopy and the use of DjO in the aqueous phase minimizes the water absorption problem. Figure 3 details the ATR setup used in this study. Clay pastes were loaded into Teflon plaques and clamped to both sides of a vertical ATR prism. Silicon sealant around the edges of the plaques prevented water evaporation during extended data collection times (up to 2 days). The area of the D O... 

Adsorption dynamics Ruorescence spectroscopy and microscopy (including immunofluorescence, total internal reflection fluorescence) Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) Quartz crystal microbalance (Spectroscopic) eUipsometry Reflectometric interference spectroscopy... 

The present chapter gives an overview of the ap>plication of Attenuated total reflection -Infrared spectroscopy (ATR-IR) to the environmentally important mineral - aqueous electrolyte interface. At these interfaces the important adsorption processes occur that limit the availability of potentially toxic solutes. These retention processes may retard for example the migration of solutes in aquifer systems or even immobilize them on the aquifer material, which is usually a natural mineral. Selected solutes may also via a preliminary adsorption process, which weakens bonds, enhance both dissolution kinetics and the equilibrium solubihty of a given mineral. 

Couzist, A., Gulari E. (1993). Adsorption of sodium laurate from its aqueous solution onto an alumina surface. A dynamic study of the surface-surfactant interaction using attenuated total reflection Fourier transform infrared spectroscopy, Langmuir Vol. 9, 3414-3421, 0743-7463. 

Presented below is an example of structure development at the solid-liquid interface for the silica/dodecyltrimethylammonium bromide (C12TAB) system, at pH 4.0 and O.IM NaCl as the background electrolyte, obtained by Singh et aL (11). A combination of different techniques such as adsorption, zeta potential, contact angle and FT-IR attenuated total reflection (ATR) measurements, have been used in this study to clearly illustrate the structural transitions, and the structure of self-assembled surfactant films at different adsorbed amounts of the surfactants at the interface. 

---