Solids, infrared spectroscopy

The polymer concentration profile has been measured by small-angle neutron scattering from polymers adsorbed onto colloidal particles [70,71] or porous media [72] and from flat surfaces with neutron reflectivity [73] and optical reflectometry [74]. The fraction of segments bound to the solid surface is nicely revealed in NMR studies [75], infrared spectroscopy [76], and electron spin resonance [77]. An example of the concentration profile obtained by inverting neutron scattering measurements appears in Fig. XI-7, showing a typical surface volume fraction of 0.25 and layer thickness of 10-15 nm. The profile decays rapidly and monotonically but does not exhibit power-law scaling [70]. 

Still another type of adsorption system is that in which either a proton transfer occurs between the adsorbent site and the adsorbate or a Lewis acid-base type of reaction occurs. An important group of solids having acid sites is that of the various silica-aluminas, widely used as cracking catalysts. The sites center on surface aluminum ions but could be either proton donor (Brpnsted acid) or Lewis acid in type. The type of site can be distinguished by infrared spectroscopy, since an adsorbed base, such as ammonia or pyridine, should be either in the ammonium or pyridinium ion form or in coordinated form. The type of data obtainable is illustrated in Fig. XVIII-20, which shows a portion of the infrared spectrum of pyridine adsorbed on a Mo(IV)-Al203 catalyst. In the presence of some surface water both Lewis and Brpnsted types of adsorbed pyridine are seen, as marked in the figure. Thus the features at 1450 and 1620 cm are attributed to pyridine bound to Lewis acid sites, while those at 1540... 

Physical properties of A-4-thiazoline-2-one and derivatives have received less attention than those of A-4-thiazoline-2-thiones. For the protomeric equilibrium, data obtained by infrared spectroscopy favors fbrm 51a in chloroform (55, 96, 887) and in the solid state (36. 97. 98) (Scheme 23). The same structural preference is suggested by the ultraviolet spectroscopy studies of Sheinker (98), despite the fact that previous studie.s in methanol (36) suggested the presence of both 51a and... 

Infrared spectroscopy is routinely used for the analysis of samples in the gas, liquid, and solid states. Sample cells are made from materials, such as NaCl and KBr, that are transparent to infrared radiation. Gases are analyzed using a cell with a pathlength of approximately 10 cm. Longer pathlengths are obtained by using mirrors to pass the beam of radiation through the sample several times. 

Porro, T. J. Pattacini, S. C. Sample Handling for Mid-Infrared Spectroscopy, Part 1 Solid and Liquid Sampling, Spectroscopy 1993, 8(7), 40-47. 

In this chapter, three methods for measuring the frequencies of the vibrations of chemical bonds between atoms in solids are discussed. Two of them, Fourier Transform Infrared Spectroscopy, FTIR, and Raman Spectroscopy, use infrared (IR) radiation as the probe. The third, High-Resolution Electron Enetgy-Loss Spectroscopy, HREELS, uses electron impact. The fourth technique. Nuclear Magnetic Resonance, NMR, is physically unrelated to the other three, involving transitions between different spin states of the atomic nucleus instead of bond vibrational states, but is included here because it provides somewhat similar information on the local bonding arrangement around an atom. 

Some of the techniques included apply more broadly than just to surfaces, interfaces, or thin films for example X-Ray Diffraction and Infrared Spectroscopy, which have been used for half a century in bulk solid and liquid analysis, respectively. They are included here because they have by now been developed to also apply to surfaces. A few techniques that are applied almost entirely to bulk materials (e.g.. Neutron Diffraction) are included because they give complementary information to other methods or because they are referred to significantly in the 10 materials volumes in the Series. Some techniques were left out because they were considered to be too restricted to specific applications or materials. 

Deprotonation of H2O2 yields OOH , and hydroperoxides of the alkali metals are known in solution. Liquid ammonia can also effect deprotonation and NH4OOH is a white solid, mp 25° infrared spectroscopy shows the presence of NH4+ and OOH ions in the solid phase but the melt appears to contain only the H-bonded species NH3 and H202. " Double deprotonation yields the peroxide ion 02 , and this is a standard route to transition metal peroxides. 

C. Ethoxycarbonylmethyl Derivatives Infrared spectroscopy indicates that equilibria of type 313 314 (R = Me, R Ac and R == Ac, R — Me) favor structure 314 in the solid state for similar work on l,4-oxazin-2-one derivatives, see references 388 and 388a. Structure 315 has also been suggested on the basis of infrared evidence. ... 

Novotny et al. [41] used p-polarized reflection and modulated polarization infrared spectroscopy to examine the conformation of 1 -1,000 nm thick liquid polyperfluoropropy-lene oxide (PPFPO) on various solid surfaces, such as gold, silver, and silica surfaces. They found that the peak frequencies and relative intensities in the vibration spectra from thin polymer films were different from those from the bulk, suggesting that the molecular arrangement in the polymer hlms deviated from the bulk conformation. A two-layer model has been proposed where the hlms are composed of interfacial and bulk layers. The interfacial layer, with a thickness of 1-2 monolayers, has the molecular chains preferentially extended along the surface while the second layer above exhibits a normal bulk polymer conformation. 

Much of the pioneering work which led to the discovery of efficient catalysts for modern Industrial catalytic processes was performed at a time when advanced analytical Instrumentation was not available. Insights Into catalytic phenomena were achieved through gas adsorption, molecular reaction probes, and macroscopic kinetic measurements. Although Sabatier postulated the existence of unstable reaction Intermediates at the turn of this century. It was not until the 1950 s that such species were actually observed on solid surfaces by Elschens and co-workers (2.) using Infrared spectroscopy. Today, scientists have the luxury of using a multitude of sophisticated surface analytical techniques to study catalytic phenomena on a molecular level. Nevertheless, kinetic measurements using chemically specific probe molecules are still the... 

In the case of selective oxidation catalysis, the use of spectroscopy has provided critical Information about surface and solid state mechanisms. As Is well known( ), some of the most effective catalysts for selective oxidation of olefins are those based on bismuth molybdates. The Industrial significance of these catalysts stems from their unique ability to oxidize propylene and ammonia to acrylonitrile at high selectivity. Several key features of the surface mechanism of this catalytic process have recently been descrlbed(3-A). However, an understanding of the solid state transformations which occur on the catalyst surface or within the catalyst bulk under reaction conditions can only be deduced Indirectly by traditional probe molecule approaches. Direct Insights Into catalyst dynamics require the use of techniques which can probe the solid directly, preferably under reaction conditions. We have, therefore, examined several catalytlcally Important surface and solid state processes of bismuth molybdate based catalysts using multiple spectroscopic techniques Including Raman and Infrared spectroscopies, x-ray and neutron diffraction, and photoelectron spectroscopy. 

The specific requirement for a vibration to give rise to an absorption in the infrared spectrum is that there should be a change in the dipole moment as that vibration occurs. In practice, this means that vibrations which are not centrosymmetric are the ones of interest, and since the symmetry properties of a molecule in the solid state may be different from those of the same molecule in solution, the presence of bands may depend on the physical state of the specimen. This may be an important phenomenon in applying infrared spectroscopy to the study of AB cements. 

J. Pritchard, Reflection-absorption infrared spectroscopy, in Chemical Physics of Solids and Their Surfaces, Eds M. W. Roberts and J. M. Thomas, Chemical Society, London, 1978, Vol. 7, p. 157. 

Figure 7.10 Typical optical arrangements employed for detection of (a) vapour phase (b) liquid phase and (c) solid chromatographic phases. After White [167], Reprinted from R. White (ed.), Chromatography/Fourier Transform Infrared Spectroscopy and Its Applications Marcel Dekker Inc., New York, NY (1990), by courtesy of Marcel Dekker Inc.

There is great interest in developing molecular precursors for boron-nitrogen polymers and boron nitride solid state materials, and one general procedure is described in this report. Combinations of B-trichloroborazene and hexamethyldisilazane lead to formation of a gel which, upon thermolysis, gives hexagonal boron nitride. The BN has been characterized by infrared spectroscopy, x-ray powder diffraction and transmission electron microscopy. 

First-order phase transitions can be detected by various thermoanalytical techniques, such as DSC, thermogravimetric analysis (TGA), and thermomechanical analysis (TMA) [31]. Phase transitions leading to visual changes can be detected by optical methods such as microscopy [3], Solid-solid transitions involving a change in the crystal structure can be detected by X-ray diffraction [32] or infrared spectroscopy [33], A combination of these techniques is usually employed to study the phase transitions in organic solids such as drugs. 

Varenne, A., Salmain, M., Brisson, C., and Jaouen, G. (1992) Transition metal carbonyl labeling of proteins. A novel approach to a solid-phase two-site immunoassay using Fourier transform infrared spectroscopy. Bioconjugate Chem. 3, 471-476. 

Another technique that has been employed for studying certain types of changes in solids is infrared spectroscopy, in which the sample is contained in a cell that can be heated. By monitoring the infrared spectrum at several temperatures, it is possible to follow changes in bonding modes as the sample is heated. This technique is useful for observing phase transitions and isomerizations. When used in combination, techniques such as TGA, DSC, and variable-temperature spectroscopy make it possible to learn a great deal about dynamic processes in solids. 

The topics of polymorphism and pseudopolymorphism dominate the majority of publications that deal with utilizing infrared spectroscopy for the physical characterization of pharmaceutical solids. Typically, in each of the publications, IR spectroscopy is only one technique used to characterize the various physical forms. It is important to realize that a multidisciplinary approach must be taken for the complete physical characterization of a pharmaceutical solid. Besides polymorphism, mid- and near-IR have been utilized for identity testing at the bulk and formulated product level, contaminant analysis, and drug-excipient interactions. A number of these applications will be highlighted within the next few sections. 

Infrared spectroscopy has been widely used for the qualitative and quantitative characterization of polymorphic and pseudopolymorphic compounds of pharmaceutical interest. Since solid state IR can be used to probe the nature of (pseudo)polymorphism on the molecular level, this method is particularly useful in instances where full crystallographic characterization of (pseudo)poly-morphism was not found to be possible. Recently, a significant number of publications have appeared that discuss where a multidisciplinary, spectroscopic... 

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