Carboxylic acid line shapes

Special Situations Line Shapes of Carboxylic Acids... 

In conclusion, note that the quality of the theoretical SD with respect to the experimental line shape is not as good for crystalline adipic acid as for the gaseous and liquid carboxylic acids studied above. The reason is that if Fermi resonances seem to be unavoidable in order to reproduce all features of the experimental line shapes and to conserve a good stability of the basic physical parameters when changing the temperature, however, the way in which the Fermi resonances are taken into account is very sentitive to the used adiabatic and exchange approximations [82]. 

This section was devoted to the applications of the theoretical model previously presented to experimental line shapes of carboxylic acids. 

Cyclic dimers of carboxylic acids represent important model systems forming two coupled intermolecular hydrogen bonds [Fig. 15.1 (d), inset of Fig. 15.4]. The linear vibrational spectra of carboxylic acid dimers have been studied in detail, both in the gas and the liquid phase, and a substantial theoretical effort has been undertaken to understand the line shape of their 0-H and/or O-D stretching bands. In contrast, there have been only a few experiments on the nonlinear vibrational... 

Once the iron is inside the sphere, a site of mineral nu-cleation is located—step 2 in the biomineralization process. Although the site(s) of nucleation are not known, the walls are lined with carboxylic acids from aspartate and glutamate residues. These are the probable sites of nucleation. After nucleation, the mineral begins to form. The shape is controlled by the protein shell. Studies of the resulting mineral are consistent with octahedrally coordinated iron(III) ions joined by bridging oxide and/or hydroxide ions. A mineral termed ferrihydrite has a similar postulated structure. Because ferritin is used for iron storage agents, the supramolecular structures described in step 4 of Section III.B are not formed. 

Let us now place the carbonyl atom of citric acid in the center of such a tetrahedron and draw the line of valences. The hydroxyl is placed above, the carboxyl below, and the two acetic groups to the left and right of a plane passing through the center. Let us now represent the enzyme as a large protein molecule with an active center shaped to accept the citric acid molecule, and by way of an example, consider its effect on aconitase. 

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