FTIR reflection spectroscopic studies

Upon air drying of aminosilane modified silica, samples often get a bright yellow colour. This was also observed upon drying of aqueous APTS solutions. Naviroj et al.12 intended to use FTIR spectroscopy to study the aminosilane structure in aqueous solution at various pH. For spectroscopic analysis, hydrolyzed APTS was casted onto an AgBr plate, dried and analyzed. The spectrum showed varying features according to the drying atmosphere. The spectra did therefore not reflect the solute conformation, but the structure of the dried material. 

The experimental aspects of ex situ FUR spectroscopic studies of sensitive electrodes (e.g., Li and Ca surfaces) using a purged spectrometer (not in a glove box) have been described in detail in Refs. 36-38, 92, and 93. Briefly, it is possible to analyze thin surface films on active metal, using a reflectance mode, while the active surface is in contact with a KBr or NaCl polished window. In Refs. 37 and 38, a possible organization of the measurement chamber of an FTIR spectrometer for such measurements is described. It should be noted, however, that the performance of such measurements when the spectrometer is placed in the glove box is much more elegant and easier. 

The use of infrared spectroscopy in the Earth and environmental sciences has been widespread for decades however, until development of the attenuated total reflectance (ATR) technique, the primary use was ex situ material characterization (Chen and Gardella, 1998 Tejedor-Tejedor et al., 1998 Degenhardt and McQuillan, 1999 Peak et al., 1999 Wijnja and Schulthess, 1999 Aral and Sparks, 2001 Kirwan et al., 2003). For the study of environmental systems, the strength of the ATR-Fourier transform infrared (FTIR) technique lies in its intrinsic surface sensitivity. Spectra are collected only from absorptions of an evanescent wave with a maximum penetration depth of several micrometers from the internal reflection element into the solution phase (Harrick, 1967). This short optical path length allows one to overcome any absorption due to an aqueous phase associated with the sample while maintaining a high sensitivity to species at the mineral-water interface (McQuillan, 2001). Therefore, ATR—FTIR represents a technique capable of performing in situ spectroscopic studies in real time. 

Spectroscopic studies of liquid interfaces provide important information about the composition and structure of the interfacial region. Early work was mainly carried out at the solid liquid interface and involved techniques such as neutron and X-ray diffraction, and reflection FTIR spectroscopy. More recently, powerful techniques have been developed to study the liquid liquid and liquid gas interfaces. These studies are especially important because of their relevance to biological systems such as cell membranes. The techniques described here are second-harmonic generation (SHG) and vibrational sum frequency spectroscopy (VSFS). They are both second-order non-linear optical techniques which are specific to the interfacial region. Since the second-order effects involve signals of low intensity, they rely on high-power lasers. 

Diffuse Reflectance FTIR Spectroscopic Study of Base Desorption from Thermally Treated Silica... 

In addition to simultaneous in situ spectroscopic studies, accompanying ex situ investigations also provide valuable information about the specific interaction of the substrates (imines and respective hydrogenation products) with both the chiral modifier (P-acid) and the solid catalyst. Thus, FTIR spectroscopic analysis of the catalyst after adsorption of the imine points to a strong interaction of the latter with the catalyst surface, in particular with the support, which is reflected by marked band shifts. It could be shown that the surface of the catalyst is mainly covered by the imine after use in the hydrogenation reaction, besides some small quantities of the product [11]. 

Spectroscopic studies at variable temperatures have become an important tool for the characterization of the physical structure of polymers. Especially in combination with thermoanalytical DTA or DSC measurements short-time spectroscopic FTIR investigations in controlled heating or cooling experiments provide a detailed picture of the structural changes as a function of temperature. Any variations of spectroscopic parameters such as intensity, wavenumber position and band shape directly reflect the temperature dependence of the vibrational behaviour of the investigated polymer as a consequence of changes in the inter- and intramolecular interactions and the state of order The vibrational spectra of polymers recorded in selected... 

Infrared spectroscopic studies of macromolecules became increasingly powerful with the development of Fourier transform techniques [44, 47, 48, 59-67]. (See Chap. 1 for a description of an FTIR spectrometer.) FTIR measurements can be used to probe changes in the bonding or interactions of individual amino acid side chains in proteins. Bacteriorhodopsin provides an illustration. When bacterio-rhodopsin is illuminated, its protonated retinylidine Schiff base chromophore isomerizes and then transfers a proton to a group in the protein. FTIR measurements showed the formation of an absorption band at 1,763 cm in addition to a set of absorption changes attributable to the chromophore [63, 68]. In bacteriorhodopsin that was enriched in [4- C]-aspartic acid the band appeared at 1,720 cm and an additional shift to 1,712 cm was obtained when the sovent was replaced by D2O. These observations indicated that the band reflected C=0 stretching of a protonated aspartic acid, leading to identification of a particular aspartic acid residue as the H" acceptor for deprotonation of the chromophore. 

Fischer et al. [101] investigated the simultaneous quantification of the content of several additives in PVC with an in-line diffuse reflectance probe. The signal from diffuse reflectance can be affected by a number of physical properties of the sample, rather than just its chemical make up. This makes obtaining quantitative data very difficult. Chemometric analysis showed the possibility of detecting even small amounts of additives (3%) with an absolute prediction error of 0.3%. Step-scan PA-FTIR spectroscopic studies were used to study surfactant exudation and film formation in PS-nBA latex films [102]. 

To put things into perspective, we. can broadly classify these analytical methods into bulk, dry surface, and in situ interfacial techniques. This chapter focuses on the last category, illustrating two in situ techniques used to study anion binding at the goethite (a-FeOOH)-water interface titration calorimetry and cylindrical internal reflection-Fourier transform infrared (CIR-FTIR) spectroscopy. In fact, CIR-FTIR could prove to be extremely powerful, since it allows direct spectroscopic observation of ions adsorbed at the mineral-water interface. 

New developments in spectroscopic techniques have made it possible to obtain Raman spectra and more recently also FTIR spectra of oligomer crystals. The crystal area used for FTIR studies with all reflecting Cassegrain type microscopes is about 30 x 30 um, while the laser beam focused through the microscope covers about 5 j,m in diameter. Several examples of IR and Raman crystal studies, some of them correlating with X-ray crystal diffraction studies, are listed in Sec. 4.7.1.3.5. 

A consistent description of the structure of alkanethiol monolayers on gold has emerged from an array of spectroscopic and diffraction studies. X-ray photoelectron spectroscopic (XPS) studies support the presence of anisotropically chemisorbed alkanethiolates on gold [24-29]. Ellipsometric measurements [24-27, 30], capacitance studies [30] and XPS measurements [31] confirm monolayer film thickness. Fourier transform infrared external reflective spectroscopy (FTIR-ERS) shows that the chains tilt at about 30° off the surface normal, and the plane containing the carbon backbone is twisted out of the plane of tilt by about 50° [25-27, 30, 32, 33]. 

FTIR is another surface-sensitive spectroscopic tool to analyze biomedical polymers since sample preparation is very simple for this technique. FTIR spectra should be recorded in reflection mode instead of transmission mode in order to analyze the functional groups present on polymer surfaces. ATR-FTIR has been apphed to study in vitro mineralization of porous starch scaffolds cultured in bone marrow stromal cells harvested from Wistar rats. Mineral deposition in in vitro cultures is usually followed by von Kossa stain or Alizarin red stain or by calcium uptake. These methods provide erroneous results because the scaffold matrix itself can take up some calcium from the medium. ATR-FTIR is devoid of the limitation and provides reliable information on the mineralization process. In the... 

In situ FTIR and diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) studies deal mainly with photocatalytic oxidation or reduction of nitric oxide (NO) as important pollutant and green house gas as well as the depollution or selective oxidation of organics such as olefinic, aliphatic, aromatic, and oxygenated hydrocarbons. 

A newly developed thermal micro attenuated total reflection (ATR)/FTIR spectroscopic system with curve fitting program was used forthe quantitative investigation of molecular interactions in aqueous solutions of poly(N-isopropylacrylamide) (PNIPAAM). The lower critical solution temperature (LCST) in water of the PNIPAAM studied was found to be about 33C by cloud point measurement, DSC and the thermal micro ATR/FTIR spectroscopic system. The results from the new spectroscopic system with curve fitting program indicated that intermolecular interactions might predominate between PNIPAAM and water at temperatures below the LCST but above the LCST, PNIPAAM molecules in water were aggregated because of intramolecular interactions within the PNIPAAM molecules and the hydrophobic interactions in the system. 35 refs. 

It is very hard to identify surface species formed on lithium in contact with polymeric electrolytes, because it is difficult to remove the polymeric matrices from the Li surfaces for spectroscopic measurements. It is possible to study the surface chemistry of Li electrodes in contact with polymeric electrolytes by in situ FTIR spectroscopy using internal reflectance mode (Figure 2). We recently studied the surface chemistry of Li electrodes in two types of polymeric electrolytes ... 

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