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Complexation Studies of Zwitterionic Amino Acids with Crown and Guanidinium Compounds Using Titration Calorimetry by M Czekalla; H Stephan; B Habermann; J Trepte; K Gloe; F.P Schmidtchen is a Materials Science article available to read on EtoBox.

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Log K, ÁG, ÁH, and TÁS were determined by titration calorimetry for the reaction of amino acids in their zwitterionic form with bicyclic guanidinium salts as anchor groups for the carboxylate and crown compounds as ammonium binding moiety in methanol at 258C. Under the experimental conditions chosen, bicyclic guanidines show very low enthalpic contribution (<À2 kJ mol À1 ) due to their strong solvation by methanol. The complexation of the ammonium form of amino acids is strongly in ̄uenced by the ring size, nature and position of donor atoms of the macrocyclic crown compound investigated. The highest enthalpic contribution accompanied by a negative entropic term was obtained with 18-crown-6. The substitution of ether oxygen by both amine and pyridine nitrogen leads to a decrease of enthalpic contribution. The introduction of bulky substituents into the macrocyclic ring system increases the reaction entropy. Yielding a medium value of complexation enthalpy and a slightly positive value of TÁS the highest stability constant was observed with pyridino 18crown-6. # 1998 Elsevier Science B.V.

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Author

M Czekalla; H Stephan; B Habermann; J Trepte; K Gloe; F.P Schmidtchen

Publisher

Elsevier Science; Elsevier ; Elsevier BV (ISSN 0040-6031)

Published

1998

Language

EN

Field

Materials Science (Physical Sciences)