New Class of Aggregates in Aqueous Solution:  An NMR, Thermodynamic, and Dynamic Light Scattering Study

• Published in: Langmuir 2006-07, Vol.22 (14), p.6031-6041
• Main Authors: Sanna, Cecilia, La Mesa, Camillo, Mannina, Luisa, Stano, Pasquale, Viel, Stéphane, Segre, Annalaura
• Format: Article
• Language: English
• Subjects: Chemistry; Exact sciences and technology; General and physical chemistry
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la060118e

We investigated the aggregation properties of two classes of aromatic and hydrophobic compounds, namely chloroacetamides and ethyl 3-phenyl-2-nitropropionates, in moderately concentrated aqueous solution (millimolar range). The identification of all species present in solution under specific experimental conditions was performed by 1D and 2D NMR, pulsed gradient spin−echo NMR, and dynamic light scattering techniques. Some physical−chemical properties (viscosity, surface tension, and colligative properties) of the aqueous solutions were also determined. Both classes of compounds behave quite similarly:  in solution, three distinct species, namely a monomeric species, small and mobile aggregates, and large and stiff aggregates, are observed. The results give insight into a new class of aggregates, held together by π−π interactions, which show an unusual associative behavior in water.