Physicochemical Characterization of Hydrated 4-Sulphonato-Calix[n]arenes: Thermal,Structural, and Sorption Properties |
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| Authors: | Wenzhan Yang Rahul Manek William M Kolling Marius Brits Wilna Liebenberg |
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| Institution: | 1. School of Pharmacy, The University of Louisiana at Monroe, Department of Basic Pharmaceutical Sciences , Monroe, LA, 71209, USA;2. Research Institute for Industrial Pharmacy, School of Pharmacy, North-West University , Potchefstroom, 2520, South Africa |
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| Abstract: | In this study, the thermal behavior of three hydrated water-soluble 4-sulphonato calixn]arenes was investigated. The melting points, heats of fusion, and heats of solution of the calix4]arene, calix6]arene and calix8]arene were 277, 262, and 270°C; 192, 242 and 351 kJ/mol; and 30, 58 and 63 kJ/mol, respectively. Lower heat of fusion, smaller increase in entropy and smaller heat of solution of the calix4]arene compared to the calix6]arene and calix8]arene showed that less heat was required to break up the crystal lattice of the smaller macromolecule. This apparent anomaly is rationalized in terms of smaller cooperativity of interaction between the molecules of calix4]arene in the crystal lattice, although the strength of the individual interactions is stronger as evidenced by the higher melting point. TGA analysis indicated that about 17–20% of water was associated with the calixn]arenes. Both TGA and hot stage microscopy results indicated that upon heating these molecules underwent stepwise water loss. TGA kinetics showed that the 4-sulphonato-calix8]arene lost water easier than the other two calixarenes. The moisture adsorption behavior of all calixarenes followed type II isotherms. For the same amount of material, the calix6]arene adsorbed more moisture than the calix4]arene and the calix8]arene. Moreover, dehydrated less crystalline 4-sulphonic-calixn]arenes powders are hydroscopic.  | |
| Keywords: | 4-sulphonato-calix[n]arene Melting Hydration Dehydration Moisture sorption |
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