Understanding how water and its solutes behave in confined environments is critical for understanding biological, geological and interfacial systems in terms of its influence on intracellular processes, surface catalysis, and membranes. In the following study we examined how changing size of AOT/water/isooctane reverse micelles (confinement) affects the pK&lt;sub abp="629"&gt;a value of essential organic and biomolecules, such as ascorbic acid, phenol, and catechols, that can coordinate to metal ions. A knowledge of this behavior is critical for the understanding of coordination processes that occur at membrane surfaces. By varying the size of &lt;i abp="630"&gt;w&lt;sub abp="631"&gt;o ( = [H&lt;sub abp="632"&gt;2O]/[AOT]), hence the size of reverse micelles, from 20 to 5 we examined how ascorbic acid (vitamin C) and other similar molecules (phenol and catechols) are affected by confinement. Changing the size of a reverse micelle is accomplished by simply increasing or decreasing the amount of water in the solution The &lt;sup abp="633"&gt;1H-NMR spectra of the solute were recorded as a function of pH. The chemical shift patterns generated titration curves for each micelle size and the pK&lt;sub abp="634"&gt;a was determined from these plots. It was found that the pKa for some molecules varied whereas for others it remained constant. The results indicate that confinement near an interface does not impact the apparent pKa value for ascorbic acid. The pK&lt;sub abp="635"&gt;as of norepinephrine, epinephrine, and catechol are also reported and conclusions are proposed regarding the observed pK&lt;sub abp="636"&gt;a trends.

Effect of confinement on the acidity of organic and bio ligands

253rd National Meeting (2017)

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