Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)
Alycia Lewis - Central State University
Co-Author(s): Daqing Gao, Clive Chirume, Dexter Heath, and Ibrahim Katampe, Central State University, Wilberforce, OH
Hydrogen bonding interaction is the strongest among all noncovalent intermolecular forces. Thus, there is increasing interest in making use of H-bonding interactions to design and synthesize new functional polymeric materials such as stimuli-responsive and switchable supramolecular polymers. Understanding of the H-bonding pattern and strength is key in a successful assembly of noncovalent complexes. In a recent publication, we have developed a computational protocol to accurately evaluate Hbonding interactions in solution. We have reported our evaluations of the Gibbs binding free energies of more than 30 H-bonded complexes in chloroform solvent with the use of Minnesota density functional M06-2X , SMD solvent model, and the cc-pVDZ basis set.
Our previous work covered all the H-bonding patterns of both doubly and triply Hbonded complexes. Will our protocol be successfully used to evaluate the H-bonding interactions of more complicated patterns such as the quadruply H-bonded motifs? In this paper, we present our latest computational results on a redox-responsive quadruple H-bonding system synthesized by Zimmerman and coworkers. In their experimental work, a highly stable quadruply H-bonded complex between 2,7-diamido-1,8- naphthyridine (DAN) and a 7-deazaguanine urea (DeUG) was formed. The DAN unit was found to undergo reversible interconversion upon oxidizing and reducing reagents. The DAN-DeUG complex was determined to be more stronger bonded than the oxidized DAN-DeUG system by 5.0 kcal/mol (free energy) in chloroform. Our computational model have reproduced the difference of 4.6 kcal/mol in the binding strength of the two complexes in dichlomethane. The computed absolute free energies of binding of the two complexes, DAN-DeUG and DAN(oxidized)-DeUG are -9.2 and -4.6 kcal/mol which are in favorable comparison with the experimental values of -8.3 and -3.8 kcal/mol. More structural insights into the origin of the differential binding of the two forms of the quadruply H-bonded complexes will be discussed. Modeling the complexes in chloroform solvent is ongoing.
References: Gao, D., Lang, D. & Robinson, T. 2014. Computational Study of the Thermodynamic Stabilities of Hydrogen-Bonded Complexes in Solution. Theoretical Chemistry Accounts, 133:1577 (pp 1-13). Li, Y., Park, T., Quansah, J.K. & Zimmerman, S.C. 2011. Synthesis of a Redox- Responsive Quadruple Hydrogen-Bonding Unit for Applications in Supramolecular Chemistry. J. Am. Chem. Soc., 133, 17118-17121.
Funder Acknowledgement(s): This research is supported by a LSAMP grant from NSF awarded to Ohio State University, Central State University, and 10 other colleges and universities in Ohio (http://odi.osu.edu/ohio-lsamp-alliance/), and by the Ohio Supercomputer Center.
Faculty Advisor: Daqing Gao,