Substituent effects in double-helical hydrogen-bonded AAA-DDD complexes.

Area of Science:

• Supramolecular Chemistry
• Organic Chemistry
• Chemical Physics

Background:

• Hydrogen-bond arrays are fundamental building blocks in supramolecular chemistry.
• Designing self-assembling systems with tunable properties is a key challenge.
• Double-helical complexes offer unique structural and functional possibilities.

Purpose of the Study:

• To synthesize and characterize two series of hydrogen-bond arrays (DDD and AAA).
• To investigate the effect of chemical substituents on the stability of resulting double-helical complexes.
• To establish quantitative relationships between substituent properties and complex stability.

Main Methods:

• Synthesis of DDD and AAA hydrogen-bond arrays.
• Formation of triply-hydrogen-bonded double-helical complexes in solution (CDCl3).
• Spectroscopic analysis and determination of association constants.
• Correlation of stability with Hammett substituent constants.

Main Results:

• Successfully synthesized DDD and AAA arrays forming double-helical complexes.
• Electron-withdrawing groups on DDD arrays increased association constants up to 30-fold.
• Electron-donating groups on AAA arrays similarly enhanced complex stabilities.
• Stability variations were quantitatively modeled using free energy relationships (R(2) > 0.96).
• Complex stabilities were tunable over three orders of magnitude (>20 kJ mol(-1)).

Conclusions:

• Chemical modification of hydrogen-bond arrays provides a powerful strategy for controlling supramolecular complex stability.
• Quantitative structure-property relationships were established for predicting and optimizing complex formation.
• This work demonstrates significant control over self-assembly through rational substituent design.