Infrared spectra of aqueous

The tiny absorbance values associated with quantitative near-infrared spectroscopy render these measurements extremely sensitive to slight variations in spectrometer alignment. Indeed, slight differences in incident radiant power between the sample and reference spectra create small positive or negative offsets along the absorbance axis. Such offsets are commonly observed for near-infrared spectra of aqueous solutions, as is apparent in the spectra presented in Figure 13.3. 

Another consequence of the strong absorption properties of water is the spectral impact of the displacement of water by dissolved solutes. Generally, in absorption spectroscopy, the solvent is selected not to absorb over the wavelength range of interest. When the absorption properties of the solvent are negligible, any displacement of solvent molecules from the optical path by the dissolution of solute molecules has a negligible effect on the measured spectrum. For near-infrared spectra of aqueous solutions, however, the absorption spectrum depends heavily on the degree of water displacement by solutes in the sample. 

CXE2C1, C1E3C1, and CXE4C1 were commercially supplied, while CxEsCx and CxEgCx were prepared by the Williamson ether synthesis. The infrared spectra of aqueous solutions of these compounds were measured for various concentrations at room temperature by using a horizontal ATR accessory with a ZnSe prism. Tibe lowest concentration studied was a mole fraction of approximately 0.005. The spectra were recorded on a JASCO FT/IR-7300 spectrometer. Each of the spectra was obtained by the coaddition of 200 scans at a resolution of 4... 

Methods for measuring the infrared spectra of aqueous solutions or suspensions of humic substances are discussed later in this chapter. 

Jones and Penneman " made an extensive infrared study of the equilibria of cyano complexes in aqueous solution. (For aqueous infrared spectroscopy, see Sec. 111-9.) Figure 111-35 shows the infrared spectra of aqueous silver cyano complexes obtained by changing the ratio of Ag to CN" ions. Table 111-35 lists the frequencies and extinction coefficients from which equilibrium constants can be calculated. Chantiy and Plane studied the same equilibria using Raman spectroscopy. 

Bunzl (1967) used the shift of the 0.97 pm band of water in the infrared spectra of aqueous tetraalkylammonium bromides at 10-70 °C to establish their structural temperatures. The differences AT = T — Tstr for 1 m solutions at 35 °C are 11-14 K, not showing a clear dependence on the nature of the cation, ranging from (CH3)4N+ to (C4H9)4N+. The temperature dependence of the differences does show cation size... 

Bunzl KW (1967) Near-infrared spectra of aqueous solutions of some tetra-n-alkylammonium bromides. J Phys Chem 71 1358-1363... 

Even though the number of the normal vibrations in a molecule is 3N-6, where N is the number of atoms in a molecule, the nucleic acids give no more than 50 well-defined absorption bands in the mid-infrared region 400-4000 cm . Vibrational spectroscopy is sensitive to conformational changes in biopolymers brought about by metal ions and it can be used to obtain information about the structure in both the solid and solution states. The spectra obtained with a Fourier transform infrared spectrometer are studied with differential techniques and the absorption of the H2O can be digitally subtracted from the solution spectra. Infrared spectra of aqueous solutions can be examined now with FT-IR techniques as opposed to the old prism and grating instruments. The spectra obtained with an FT-IR are handled with differential techniques and the data are treated with a computer. 

M.J.D. Low and R.T. Yang, "The Measurement of Infrared Spectra of Aqueous Solutions Using Fourier Transform Spectroscopy". Spectrochimica Acta, 29A, 1761 (1973). 

Figure 5. Infrared spectra of aqueous dipalmitoyl phosphatidylsulfocholine membranes recorded six hours after the sample preparation (trace A) and after being kept at 5°C for six days (trace B). Superimposed is the difference spectrum (B-A) which reflects the changes resulting from the incubation.

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh . ... 

Substituted 2-amino-l-thia-3,4-diazoles have been studied by Testa et Comparison of ultraviolet and infrared spectra of the parent compound (197 198) with those of its four possible methylated derivatives indicated that 197 predominates in aqueous solution and... 

Iron(II) complexes are often included in studies when complexes are prepared from a large number of different metal ions. 2-formylpyridine thiosemicarbazone, 5, forms brown [Fe(5)2A2] (A = Cl, Br) when prepared in ethanol and [Fe(5-H)2] from aqueous alcohol solution [156], All of these complexes are diamagnetic. The resonance Raman and infrared spectra of [Fe(5-H)2] were examined in detail [130] and coordination occurs via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. There is appreciable d-d sulfur-to-iron(II) Jt-bonding. Solution studies of iron(II) complexes of some 5-substituted-2-formylpyridine thiosemicarbazones have been reported [157], but no solids... 

The phosphorus analogue of pyrrole, phosphole, has a degree of aromatic character, according to molecular orbital calculations and nmr spectra (Brown, 1962 Chuchman et al., 1971). 1-Methyl-phosphole has a p/fg-value of 0-5 (Quin et al., 1969), much higher than that of pyrrole. It polymerizes rapidly in aqueous acid. The site of protonation of 1,2,5-triphenylphosphole is phosphorus according to the infrared spectra of some of its stable salts (Chuchman et al., 1971). 

Tabb, D. L., Koenig, J. L. Infrared Spectra of Globular Proteins in Aqueous Solution, in Analytical Applications of FT-IR to Molecular and Biological Systems, Durig, J. R. (Ed.) D. Reidel 1980, p. 241... 

It is not possible to dissolve the asphaltenes in water by treatment of the halo derivatives with aqueous sodium hydroxide or with aqueous sodium sulfite (II). The hydrolyzed products remained insoluble even in a strongly alkaline solution. The decreased (H + Cl)/C ratios and the increased O/C ratios of the products relative to those of the parent halo-asphaltenes indicate that partial reaction occurs. The infrared spectra of the products showed a broad band centered at 3450 cm 1, a region assigned to the presence of hydroxyl groups in the products, but it was not possible to establish conclusively the presence of sulfonic acid group(s) in the product from the sodium sulfite reaction by assignment of infrared absorption bands to this particular group. 

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