Charge Characteristics of Submicron Heterogeneities in Aqueous Solutions of Low-Molecular Weight Organics

Abstract

The submicron heterogeneities (SMHs), spontaneously forming in aqueous solutions of different organic molecules, have been studied. The studied molecules included TBA alcohol (7 mol %); glucose monosaccharide (200 mM); sucrose disaccharide (200 mM); and seven amino acids of different types: nonpolar glycine (100 mM), hydrophobic valine (50 mM), aromatic phenylalanine (50 mM), sulfur-containing methionine (50 mM), polar serine (50 mM), glutamic acid (50 mM), and basic arginine (50 mM). The presence of SMНs with sizes of 0.1–1 µm was confirmed in all these solutions, including all types of amino acids, which may be of particular interest for biology. The values of the SMH ζ-potential were also found; they vary from –20 to –5 mV for the aforementioned solutions. These values are insufficient for maintaining the SMH stability due to the Coulomb barrier; hence, there are additional stability factors, related to the SMH hydrophility. This fact disproves the version about the hydrophobic character of SMH, discussed in the literature (at least, for the investigated solutions). SMHs disappear as a result of filtering and do not form again for several hours in all solutions, except the TBA solution, where they arise for less than 1 min.