Oxygen local ordering

Let us fix attention on a particular H20 molecule A in the interior of water (if we wish to identify this molecule we can suppose that it contains a nucleus of the oxygen isotope 01S) and let us consider the water molecules which happen to be nearest neighbors of this molecule at the moment. These molecules have been in contact with A for different lengths of time. Since all the molecules in the liquid wander about, there was a time when none of these molecules was in contact with A. Further, if we could now begin to watch these molecules, we should find that, after the lapse of different periods of time, they become separated from A and each is replaced by another molecule. Similar remarks can be made about the molecules which come into contact with any chosen molecule. We can now raise the question—-What is the rate of turnover of this process The rate depends on the degree of local order and disorder, which in turn depends on the strength and character of the forces between adjacent molecules. 

These phenomena suggest the existence of local variations of the oxygen content, giving rise to local ordering of the oxygens and oxygen vacancies in the central plane of copper atoms. 

The EXAFS spectroscopy results strongly confirm the existence of local order in the mineral part of lead isooctane reverse micelles in dodecane and reveal quantitative information concerning the first and second coordination shells. The radial distribution functions (RDFs) exhibit peaks at around 0.19 nm, corresponding to the first shell of oxygen atoms and at around 0.35 nm corresponding to the shell of lead. Analytical transmission electron microscopy (ATEM) indicates the size of the mineral core of the micelles (1-1.5 nm) and the discoid shape of the particles when the micelles aggregate (Mansot et al. 1994). 

Oxygen K-edge NEXAFS spectroscopy gives valuable informations on the local order of ice. " To gain knowledge on the structure of cold condensed ice films, we have undertaken the NEXAFS study of a porous amorphous ice film before and after a XUV (3-900 eV) irradiation, followed by an annealing to 150 K. 

The simplest way to create a local ordered structure within a polypeptide chain made up of amide linkages would be to form hydrogen bonds between residues which are close to one another in the amino acid sequence. As seen from Figure 3.9, this would involve either the second, third, fourth, or fifth NH group from the C=0 of the first amino acid residue. In the 2.2y ribbon description, 2.2 refers to the number of residues per turn and the subscript 7 to the number of atoms between the main chain carbonyl oxygen and the amide... 

A 2D-IR spectroscopic study on dissociation and hydrogen bonds of Nylon 12 over a temperature range of 30-150 C showed gradual weakening of inter- and intramolecular associative interactions and a decrease of local order leading to the eventual fusion. (167). The asynchronous 2D-NIR spectra indicate that the amide groups with a free carbonyl oxygen appear first, and then unassociated free amide and amide with free NH follow as the temperature is increased (174). 

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