Do N-heterocyclic aromatic rings prefer π-stacking?

Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai, India.
Physical Chemistry Chemical Physics (Impact Factor: 4.49). 03/2011; 13(13):5514-25. DOI: 10.1039/c0cp02015j
Source: PubMed


The IR-UV double resonance spectroscopy of phenylacetylene complexes with triazine, pyrazine and pyridine in the acetylene C-H group of phenylacetylene was investigated. These spectra indicate that in the complexes of triazine, pyrazine and pyridine the acetylenic group is minimally perturbed and the predominant interaction is with the π electron density of the phenyl ring of phenylacetylene. Geometries of the complexes optimized at M06-2X/aug-cc-pVDZ and MP2/aug-cc-pVDZ levels, combined with highly accurate energy calculations at the complete basis set (CBS) limit of CCSD(T), indicate the formation of π-stacked complexes in all the three cases. Additionally, a C-H...N hydrogen-bonded complex between pyridine and phenylacetylene was also observed. The present results indicate that N-heterocyclic aromatic rings favor formation of π-stacked complexes.

Download full-text


Available from: Kwang S. Kim
  • [Show abstract] [Hide abstract]
    ABSTRACT: The structure of the phenylacetylene-dimer has been elucidated using IR-UV double resonance spectroscopy in combination with high level ab initio calculations at the CCSD(T)/CBS level. The IR spectra in the acetylenic and the aromatic C-H stretching regions indicate that the two phenylacetylene moieties are in identical environments and very similar to the phenylacetylene monomer. Calculated stabilization energies and the free energies at the CCSD(T)/CBS level favor the formation of an anti-parallel π-stacked structure. The DFT-SAPT energy decomposition analysis points out that the anti-parallel π-stacked structure maximizes electrostatic as well as the dispersion components of energy. The observed IR spectra are consistent with the anti-parallel π-stacked structure.
    No preview · Article · Aug 2011 · Physical Chemistry Chemical Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: The respective structures and stabilities of imidazole-imidazole, benzene-imidazole, and benzene-indole dimers have been investigated using different DFT-D functional, MP2, CCSD(T), and SAPT levels of theory with a medium basis set. Comparative analysis of binding energies and structural parameters of the dimers points to a preference for stacking contact or hydrogen bond in an imidazole-imidazole dimer. In contrast, a T-shaped configuration with H-π interaction is maximally advantageous for benzene-imidazole and benzene-indole dimers. High-level ab initio calculations at the CCSD(T)/CBS and DFT-SAPT levels show that classical hydrogen-bonded tilted imidazole-imidazole dimer is a global minimum structure and that it has high electrostatic energy. However, for benzene-imidazole and benzene-indole dimers, the global minimum (N-H···π) structure has high electrostatic energy as well as dispersion energy.
    No preview · Article · Feb 2012 · The Journal of Physical Chemistry A
  • [Show abstract] [Hide abstract]
    ABSTRACT: Resonant two photon ionization (R2PI), IR-UV, and UV-UV double resonance spectroscopic techniques combined with quantum chemistry calculations have been used to determine the structure of indole⋅⋅⋅thiophene dimer observed in a supersonic jet. With the help of combined experimental and theoretical IR spectra it has been found that the observed dimer has a N-H⋅⋅⋅π hydrogen bonded slanted T-shaped structure. The present study demonstrates the effect of heteroatoms present in the acceptors on the strength of the π-hydrogen bonding interactions. It was concluded by Sherrill and co-workers from their theoretical study of benzene⋅⋅⋅pyridine dimer that aromatic rings containing heteroatoms are poorest π-hydrogen bond acceptors [E. G. Hohenstein and C. D. Sherrill, J. Phys. Chem. A 113, 878 (2009)]. But the current spectroscopic investigation exhibits that five membered aromatic heterocycles are favorable π-hydrogen bond acceptors. In this study, it has also been shown that thiophene is a better π-hydrogen bond acceptor than furan. The present work has immense biological significance as indole is the chromophore of tryptophan residue in the proteins and thiophene derivatives have potential therapeutic applications. Thus, understanding the binding motif between indole and thiophene in the heterodimer studied in this work may help in designing efficient drugs.
    No preview · Article · Sep 2012 · The Journal of Chemical Physics
Show more