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Efficient modulation of hydrogen-bonding interactions by remote substituents.
Sung-Youn Chang1, Hung Sop Kim, Kyoung-Jin Chang
1Center for Bioactive Molecular Hybrids and Department of Chemistry, Yonsei University, Seoul 120-749, South Korea.
Organic Letters
|January 16, 2004
Summary
Macrocycle substituents significantly impact binding affinity for adipamide guests. Electron-withdrawing groups enhance binding, while electron-donating groups decrease it, offering insights into molecular recognition.
Area of Science:
- Supramolecular chemistry
- Organic chemistry
- Chemical thermodynamics
Background:
- Macrocycles are versatile hosts in supramolecular chemistry.
- Understanding guest-host interactions is crucial for designing molecular recognition systems.
- Tetralactam macrocycles offer a tunable scaffold for binding studies.
Purpose of the Study:
- To synthesize a series of tetralactam macrocycles with varying substituents.
- To investigate the binding affinities of these macrocycles for an adipamide guest.
- To elucidate the influence of substituents on binding thermodynamics.
Main Methods:
- Synthesis of diverse tetralactam macrocycles.
- 1H NMR titration experiments in CDCl3.
- Determination of association constants and binding free energies (ΔΔG).
Main Results:
- Association constants varied significantly based on substituents (up to ΔΔG = 3.4 kcal/mol).
- Electron-donating groups (OMe, NMe2) reduced binding affinity.
- Electron-withdrawing groups (Cl, NO2) enhanced binding affinity.
Conclusions:
- Substituent effects play a critical role in the binding affinity of tetralactam macrocycles.
- Secondary repulsions and intramolecular hydrogen bond perturbations rationalize the observed trends.
- These findings provide valuable data for the rational design of host molecules for specific guests.