Spectroscopic examination hydration

Inspection of the proposed nitration mechanism (Scheme 1) reveals that the mononitrate dipositive lanthanide species [Ln(H20)x(N03)](0Tf)2 (1) is the key intermediate. An independent preparation and characterisation of such a species enables possible indentification of 1 directly in situ in the reaction mixture. Additionally, spectroscopic examination of these salts may provide some evidence for our working model. We have developed a novel preparation of these mixed salts by simple metathesis of lanthanide chlorides with the requisite quantities of silver nitrate and silver triflate in water (Scheme 3).17 The resulting hydrated salts were white or lightly coloured (pink, green or yellow) solids which were found to be stable indefinitely at room temperature in the solid state. 

Carerl et al ( ) have carried out a careful infrared spectroscopic examination of the hydration of lysozyme. Figure 3 compares the spectroscopic results with heat capacity measurements. The principal conclusions are the following 1) the first two steps in the hydration process. Regions IV and HI, are seen in the Infrared measurements. The discontinuity at 0.07 li observed in the dependence on hydration of the carboxylate, amide, and water bands (Figure 3), corresponds to the juncture of Regions IV and III. 2) The Increase in carboxylate intensity within Region IV means that proton redistribution follows... 

Surface spectroscopic examination of hydrated frozen silicone polymers is useful in the study of polymer structure as a function of hydration. Most surface spectroscopies utilize an ultrahigh vacuum, which is a hydrophobic environment. By freezing a polymer into its hydrated configuration and then examining it a UHV environment, it is possible to examine qualitatively and quantitatively the chemical structure of the hydrated polymer. This allows understanding of the hydrated polymer structure following plasma treatment and further refinement of the plasma chemical process. 

Section 2.2.1 summarizes the spectroscopic measurements that have been performed to examine the dynamics of water molecules in hydrate versus ice networks. Sections 2.2.2 and 2.2.3 provide a brief overview of the mechanical and thermal properties, respectively, of hydrates compared to ice. Characterization of these properties will aid in facilitating the accurate interpretation of data obtained from in situ detection measurements of natural hydrates. These natural hydrates occur in sediments in permafrost and marine environments. The hydrate mechanical and thermal properties are also important in the evaluation of the location and distribution of natural hydrates in sediments. (Further details are given in Chapter 7—Hydrates in the Earth.)... 

The range of IR bands that can be utilized to assess hydration alludes to the pervasiveness of water absorbance in an IR spectrum Water is a strong IR absorber and thus can pose a particular difficulty in the spectral examination of aqueous samples. The advent of computer-interfaced FT systems allowing spectral manipulation (such as band subtraction) can circumvent these difficulties, as can the use of specialized accessories such as ATR elements [3] and even alternative vibrational spectroscopic techniques, e.g., FT-Raman spectroscopy. FT-Raman spectroscopy, providing complementary information to IR, has in recent years been employed for the characterization of human SC [185-190] and model SC lipids [191], as well as for the noninvasive monitoring of topically applied compounds [192] and the in vitro evaluation of SC-enhancer interactions [193]. 

Several further species of Flindersia have been examined for alkaloids and other extractives and the chemistry of this genus has been reviewed (118). The only new alkaloid found was iflflaiamine ([a] n — 0.6° hydrate, mp 62°-63° picrate, mp 207°-209°), the sole alkaloid of the wood of Flindersia ifflaiana F. Muell. (119), which is a dihydrofuroquinoline (XX). Its structure was largely elucidated by spectroscopic measurements. Its UV- and IR-spectra showed it to be a 2-alkoxy-4-quinolone, and the NMR-spectrum showed the presence of three C-methyl groups and one A-methyl (attached to aromatic ring N), a 1,2-disubstituted benzene ring, and other evidence supporting the 2-alkoxy-4-quinolone structure. 

It was stated earlier that the vast majority of pharmaceutical solvates are hydrates. There are a few studies, however, in which other solvates of drugs have been studied. Ghosh et al. (27) examined a range of dialkylhydroxypyridones (iron chelators with possible application for the treatment of anemias) and compared their structures to their corresponding formic acid solvates. TGA was able to monitor the loss of formic acid, providing complementary information for spectroscopic studies that in turn were able to provide a molecular-level explanation for the desolvation profiles. 

In situ thermal transitions were also described by Taylor et al., who examined the isothermal dehydration behavior of trehalose dihydrate [29]. For small particle size fractions (<45 fjLm), heating at 80°C caused loss of peak definition until, at 210 min, amorphous material was present. In contrast, a larger particle size fraction (>425 fim) converted to the crystalline anhydrous form of the material. The kinetics of this conversion was probed from the Raman data using peak height ratios with time a two-stage rearrangement was indicated. A broader consideration of pharmaceutical hydrates, including their characterization by several techniques (NMR, Raman spectroscopy, and isothermal calorimetry) can be found in the literature [30] as can a review of the use of spectroscopic techniques for the characterization of polymorphs and hydrates [31]. 

Ever since Franklin and Gosling [1] examined the first fibers of DNA it has been known that DNA occurs in vivo in hydrated form. Experiments involving sedimentation equilibrium studies [2-4], isopiestic measurements [5], gravimetric [6], X-ray fiber diffraction, infrared [7-9] and NMR spectroscopic investigations [10-12] lead to the conclusion that DNA is heavily hydrated. The hydration is not homogeneous around the DNA and can be described in the terms of two discrete lays representing primary and secondary hydration shells. 

The ketene hydration reaction has been examined recently by time-resolved spectroscopic tech-niques. ° Intermediate enols have been directly observed in solution, although this is not generally the case because ketene hydration is usually slower than enol tautomerization. The hydration rate constants of representative groups of ketenes " " in aqueous solutions have been obtained and their reactivities rationalized. 

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