Infrared spectroscopy interpretation

Spectroscopy and the Electromagnetic Spectrum Infrared Spectroscopy Interpreting Infrared Spectra... 

To remove water, commercial ionic liquids used for fundamental research purposes should be dried at 60 °C in vacuo overnight. The water content should be checked prior to use. This can be done qualitatively by infrared spectroscopy or cyclovoltametric measurements, or quantitatively by Karl-Fischer titration. If the ionic liquids cannot be dried to zero water content for any reason, the water content should always be mentioned in all descriptions and documentation of the experiments to allow proper interpretation of the results obtained. 

Frequently, electrochemical information can be interpreted better in the presence of additional nonelectrochemical information. Typically, however, there is one significant restriction electrochemical and spectroscopic techniques often do not detect exactly the same mechanisms. With spectroscopic measurements (e.g., infrared spectroscopy), products that are formed by electrochemical processes may be detected. In other cases (luminescence techniques) mechanisms may be found by which charge carriers are trapped and recombine. Other techniques (electroreflection studies) allow the nature of electronic transitions to be determined and provide information on the presence or absence of an electric field in the surface of an electrode. With no traditional technique, however, is it... 

Rasmussen [82] describes a gas chromatographic analysis and a method for data interpretation that he has successfully used to identify crude oil and bunker fuel spills. Samples were analysed using a Dexsil-300 support coated open tube (SCOT) column and a flame ionisation detector. The high-resolution chromatogram was mathematically treated to give GC patterns that were a characteristic of the oil and were relatively unaffected by moderate weathering. He compiled the GC patterns of 20 crude oils. Rasmussen [82] uses metal and sulfur determinations and infrared spectroscopy to complement the capillary gas chromatographic technique. 

Enantiomers have identical chemical and physical properties in the absence of an external chiral influence. This means that 2 and 3 have the same melting point, solubility, chromatographic retention time, infrared spectroscopy (IR), and nuclear magnetic resonance (NMR) spectra. However, there is one property in which chiral compounds differ from achiral compounds and in which enantiomers differ from each other. This property is the direction in which they rotate plane-polarized light, and this is called optical activity or optical rotation. Optical rotation can be interpreted as the outcome of interaction between an enantiomeric compound and polarized light. Thus, enantiomer 3, which rotates plane-polarized light in a clockwise direction, is described as (+)-lactic acid, while enantiomer 2, which has an equal and opposite rotation under the same conditions, is described as (—)-lactic acid. 

Irrespective of the detailed interpretation of these results (25), they provide further evidence against the oft-popular notion that SERS for cyanide and other strongly coordinating adsorbates arises from specific "surface complexes" [such as Au(CN) ] (28) as distinct from the preponderant adsorbate species presumably sensed by infrared spectroscopy (also see reference 7). 

Infrared spectroscopy has often been used for obtaining structural information but, as shown in the long debate about the structure of Co4(CO)i2 in solution66,92 only partial information is generally obtained and unequivocal interpretations are rarely possible. 

The admixture of lead to platinum has a similar effect (Fig. 5). At the same time, the aromatizing activity increases up to about 1 1 Pt Pt atomic ratio 24). With even more lead it scatters aroimd somewhat lower values 66). Electron donation from lead to platinum has been proved by infrared spectroscopy, so one may wonder whether lead is present as metal in the catalyst (75). The additive effect can also be interpreted by its creating hydrogen-deficient surface sites favorable for aromatization. When more lead is present than platinum (i.e., where no more continuous platinum surface is probable), the inverse correlation between hydrogen adsorptivity and activity ceases to exist. 

MS, chemical ionization-MS, and sometimes GC/infrared spectroscopy (IR) have been used with GC/MS to obtain structural information. Examples of the use of GC/ MS for identifying new DBFs include the recent identification of iodo-acids. The iodo-acids were discovered in drinking water treated with chloramination through the use of full-scan GC/MS on the methylated extracts. Empirical formula information for both the molecular ions and the fragment ions was obtained by high-resolution electron ionization (EI)-MS, and the spectra were interpreted to yield tentative identifications of five new iodo-acids (iodoacetic acid, bromoiodoacetic acid, ( )-3-bromo-3-iodopropenoic acid, (Z)-3-bromo-3-iodopropenoic acid, and )-2-iodo-3-methylbutenedioic acid). Structural assignments were then confirmed by the match of mass spectra and GC retention times to authentic chemical standards, several of which had to be synthesized. 

J. Workman, L. Weyer, Practical Guide to Interpretive Near-infrared Spectroscopy. Taylor Erancis, Boca Raton, FL, 2007. 

The wavelengths of IR absorption bands are characteristic of specific types of chemical bonds. In the past infrared had little application in protein analysis due to instrumentation and interpretation limitations. The development of Fourier transform infrared spectroscopy (FUR) makes it possible to characterize proteins using IR techniques (Surewicz et al. 1993). Several IR absorption regions are important for protein analysis. The amide I groups in proteins have a vibration absorption frequency of 1630-1670 cm. Secondary structures of proteins such as alpha(a)-helix and beta(P)-sheet have amide absorptions of 1645-1660 cm-1 and 1665-1680 cm, respectively. Random coil has absorptions in the range of 1660-1670 cm These characterization criteria come from studies of model polypeptides with known secondary structures. Thus, FTIR is useful in conformational analysis of peptides and proteins (Arrondo et al. 1993). 

Even though these approaches are powerful methods for determining functional sites on proteins, they are limited if not coupled with some form of structural determination. As Figure 2 illustrates, molecular biology and synthetic peptide/antibody approaches are not only interdependent, they are tied in with structural determination. Structural determination methods can take many forms, from the classic x-ray crystallography and NMR for three-dimensional determination, to two-dimensional methods such as circular dichroism and Fourier Transformed Infrared Spectroscopy, to predictive methods and modeling. A structural analysis is crucial to the interpretation of experimental results obtained from mutational and synthetic peptide/antibody techniques. 

The infrared (IR) spectra of 1,10-phenanthroline, its hydrate and perchlorate in the region 600-2000 cm-1 have been obtained, and the principal features of the spectra interpreted.66 Further studies on the IR spectra of 1,10-phenanthroline,67-69 substituted 1,10-phenanthrolines,70,71 and 1,7-phenanthroline67 have also been reported. The IR spectrum of 4,7-phenanthroline in the region 650-900 cm-1 has been analyzed, and the C—H out-of-plane deformation frequencies were compared with those of phenanthrene and benzo[/]quinoline.72 The IR spectra of salts of 1,10-phenanthroline have been taken, and the NH vibrations determined.28,73 Infrared spectroscopy has been used to detect water associated with 1,10-phenanthroline and some of its derivatives on extraction into nitromethane from aqueous solution.74 The Raman spectrum of 1,10-phenanthroline has been compared with its IR spectrum.75 Recently, the Raman and IR spectra of all ten isomeric phenanthrolines were measured in solution and solid states, and the spectra were fully discussed.76... 

The insoluble material is assumed to be the graft copolymer and this is verified by infrared spectroscopy. For grafting onto the butadiene portion of a copolymer, the C-H out-of-plane bending vibrations as well as the olefin C-H stretching vibration are most useful. The graft copolymer of acrylonitrile onto polystyrene cannot be analyzed by infrared spectroscopy since the only change would be in the C-H overtone region and these bands are too weak to permit interpretation. 

Tn the previous papers of this series (1, 2, 3, 4) calibration and repro- ducibility of gel permeation chromatography (GPC) have been extensively examined. This paper describes the application of GPC to two selected samples of linear polyethylenes, one having a narrow molecular weight distribution (NMWD) and another a broad molecular weight distribution (BMWD). These samples were distributed by the Macro-molecular Division of IUPAC (5) for the molecular characterization of commercial polymers. The average molecular weights by GPC are compared with the data obtained from infrared spectroscopy, osmotic pressure, melt viscosity, and intrinsic viscosity. Problems associated with data interpretation are discussed. 

In conclusion, the analysis of spectra properly recorded to 185 nm, or lower where possible, can give useful estimates of secondary structure content, but the content of turns and of P-structure should be interpreted with caution. Fourier transform infrared spectroscopy (FTIR) provides better estimates of the latter. When using the results of far-UV CD determination to characterize reproducibility of folding for different samples, it is important first to compare the spectra visually and to look for possible trends or factors that may explain small differences, rather than to rely solely on comparison of derived secondary structure contents. 

Infrared spectroscopy is a common analytical method used in industry and research. The reader may refer to basic texts such as (12-14) to obtain guidance in the method, instrumentation, sample preparation and interpretation of spectra. 

Overall perspectives of the results from ethene and the higher alkenes have been attempted in Sections VI.B.6 and VI.G. What has become clear, particularly in the context of hydrocarbon adsorption, is that the study of spectra on single-crystal surfaces is of great assistance in finding the correct interpretation of the more complex multispecies spectra obtained from finely divided metal catalysts. This has only become possible by the development of VEELS and RAIRS, the latter allied with the Fourier-transform methods that have also transformed the quality of the spectra from metal-particle catalysts obtained by transmission infrared spectroscopy. The use of RAIRS in turn has emphasized the general significance of the MSSR. 

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