Abstract
The formation of inclusion complexes between alkylsulfonate guests and a cationic pillar[5]arene receptor in water was investigated by NMR and ITC techniques. The results show the formation of host-guest complexes stabilized by electrostatic interactions and hydrophobic effects with binding constants of up to 107 M−1 for the guest with higher hydrophobic character. Structurally, the alkyl chain of the guest is included in the hydrophobic aromatic cavity of the macrocycle while the sulfonate groups are held in the multicationic portal by ionic interactions.
Highlights
Supramolecular chemistry is a topic of great interest to the scientific community that wants to take advantage of non-covalent interactions, such as van der Waals forces, hydrogen bonds, π-π stacking interaction, electrostatic interactions, or hydrophobic/hydrophilic interactions, with the aim of implementing and explaining increasing complexity systems [1,2,3]
These results indicate that octylsulfonate is incorporated into the magnetic shielding region of the pillararene aromatic cavity with the sulfonate group pointing towards the trimethylammonium groups of the host
Previous results from our group have shown that toluenesulfonate binding constant to pillararene decreases from 1.37 × 106 M−1 to 3.18 × 104 M−1 by increasing the host concentration from 0.01 to 0.1 mM [53]. This behavior is due to BF4 − complexation by the pillararene, which difficult the entrance of the guest
Summary
Supramolecular chemistry is a topic of great interest to the scientific community that wants to take advantage of non-covalent interactions, such as van der Waals forces, hydrogen bonds, π-π stacking interaction, electrostatic interactions, or hydrophobic/hydrophilic interactions, with the aim of implementing and explaining increasing complexity systems (bottom-up approach) [1,2,3]. We know about the electrostatic interactions between the charged groups of the pillar[5]arene and the ionic substrates, the role played by hydrophobic/hydrophilic interactions must be explored in detail In this context, fundamental studies on the interaction between charged pillararene receptors and model amphiphilic compounds are of utmost importance for the intended pharmaceutical applications in relation to these macrocycles. Pillararenes-based systems comprising amphiphilic guests offer complexes between a cationic pillar[5]arene and charged amphiphilic compounds, ing strategies for the development of novel stimuli-responsive drug-delivery systemswhich keepingprecision the head group constant,initsdrug hydrophobicity can be modulated by modifying the whichbyimprove and efficiency delivery [60,61,62,63,64,65,66].
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