TY - JOUR
T1 - Understanding the complexation of aliphatic and aromatic acids guests with octa acid
AU - Choudhury, Rajib
AU - Ramamurthy, Vaidhyanathan
N1 - Publisher Copyright:
Copyright © 2017 John Wiley & Sons, Ltd.
Copyright:
Copyright 2018 Elsevier B.V., All rights reserved.
PY - 2018/5
Y1 - 2018/5
N2 - In this study, inclusion of 10 guest molecules, adamantyl and naphthyl carboxylic acids with different structural and electronic properties, within a synthetic cavitand octa acid was probed by isothermal calorimetry, 1D and 2D 1H nuclear magnetic resonance spectroscopy, and molecular dynamic simulations. Under the condition of the experiments (pH ~ 8.7), the guests were included as carboxylate anions with the polar anionic head group facing water and hydrophobic carbon skeleton buried within the cavitand, forming 1:1 host to guest complexes. Importance of weak interactions between the guest and the cavitand interior is reflected in the measured negative ΔH values. Although ΔH was negative for all guests, ΔS was positive for adamantyl guests and negative for naphthyl guests. Quite likely the difference in hydrophobicity between the 2 sets of molecules and the strength of interaction between the guest and the host are responsible for the sign difference in ΔS between the 2 series. The importance of steric factor during inclusion of naphthyl carboxylic acids within octa acid cavity is brought out by the difference in thermodynamic parameters between the 1- and 2-substituted naphthyl carboxylic acids; 2-naphthyl carboxylic acids that can penetrate deeply have larger −ΔH and 1-naphthyl carboxylic acids that can only enter the cavity in an angle have smaller −ΔH. As expected, based on the well-known concept of “enthalpy-entropy compensation,” the molecules that have large −ΔH are accompanied by large −ΔS.
AB - In this study, inclusion of 10 guest molecules, adamantyl and naphthyl carboxylic acids with different structural and electronic properties, within a synthetic cavitand octa acid was probed by isothermal calorimetry, 1D and 2D 1H nuclear magnetic resonance spectroscopy, and molecular dynamic simulations. Under the condition of the experiments (pH ~ 8.7), the guests were included as carboxylate anions with the polar anionic head group facing water and hydrophobic carbon skeleton buried within the cavitand, forming 1:1 host to guest complexes. Importance of weak interactions between the guest and the cavitand interior is reflected in the measured negative ΔH values. Although ΔH was negative for all guests, ΔS was positive for adamantyl guests and negative for naphthyl guests. Quite likely the difference in hydrophobicity between the 2 sets of molecules and the strength of interaction between the guest and the host are responsible for the sign difference in ΔS between the 2 series. The importance of steric factor during inclusion of naphthyl carboxylic acids within octa acid cavity is brought out by the difference in thermodynamic parameters between the 1- and 2-substituted naphthyl carboxylic acids; 2-naphthyl carboxylic acids that can penetrate deeply have larger −ΔH and 1-naphthyl carboxylic acids that can only enter the cavity in an angle have smaller −ΔH. As expected, based on the well-known concept of “enthalpy-entropy compensation,” the molecules that have large −ΔH are accompanied by large −ΔS.
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U2 - 10.1002/poc.3795
DO - 10.1002/poc.3795
M3 - Article
AN - SCOPUS:85037998279
VL - 31
JO - Journal of Physical Organic Chemistry
JF - Journal of Physical Organic Chemistry
SN - 0894-3230
IS - 5
M1 - e3795
ER -