Direct Spectroscopic Evidence for an n→π* Interaction.

The n→π* interaction is an extremely weak but very important noncovalent interaction. Although this interaction is widely present in biomolecules and materials, its existence is counterintuitive and so has been debated extensively. Herein, we have reported direct spectroscopic evidence for an n→π* interaction for the first time by probing the carbonyl stretching frequency in phenyl formate using isolated gas-phase IR spectroscopy. This result also demonstrates that the conformational preference for the cis conformer of phenyl formate compared to the trans conformer arises due to the presence of the n→π* interaction in the former. The direct proof reported herein for this controversial but important noncovalent interaction should stimulate further experimental and theoretical investigation on this intriguing research topic.

[1]  Santosh K. Singh,et al.  The n → π* interaction: a rapidly emerging non-covalent interaction. , 2015, Physical chemistry chemical physics : PCCP.

[2]  Sumit Kumar,et al.  Competition between n → π(Ar)* and conventional hydrogen bonding (N-H···N) interactions: an ab initio study of the complexes of 7-azaindole and fluorosubstituted pyridines. , 2014, Physical chemistry chemical physics : PCCP.

[3]  Gail J. Bartlett,et al.  Interplay of hydrogen bonds and n→π* interactions in proteins. , 2013, Journal of the American Chemical Society.

[4]  L. Evangelisti,et al.  Lone-pair···π interaction: a rotational study of the chlorotrifluoroethylene-water adduct. , 2013, Angewandte Chemie.

[5]  R. Raines,et al.  Intimate interactions with carbonyl groups: dipole-dipole or n→π*? , 2013, The Journal of organic chemistry.

[6]  Cynthia J. Lee,et al.  Experimental and theoretical characterization of a lone pair-π complex: water-hexafluorobenzene. , 2013, Journal of Physical Chemistry A.

[7]  J. López,et al.  Unveiling the shape of aspirin in the gas phase. , 2012, Angewandte Chemie.

[8]  Sumit Kumar,et al.  Structure of 7-azaindole···2-fluoropyridine dimer in a supersonic jet: competition between N-H···N and N-H···F interactions. , 2011, The journal of physical chemistry. A.

[9]  J. López,et al.  Conformations of γ-aminobutyric acid (GABA): the role of the n→π* interaction. , 2010, Angewandte Chemie.

[10]  C. Ochsenfeld,et al.  Tuning the cis/trans conformer ratio of Xaa-Pro amide bonds by intramolecular hydrogen bonds: the effect on PPII helix stability. , 2010, Angewandte Chemie.

[11]  Amit Choudhary,et al.  n→π* Interactions in Proteins , 2010, Nature chemical biology.

[12]  R. Raines,et al.  Nature of Amide Carbonyl−Carbonyl Interactions in Proteins , 2009, Journal of the American Chemical Society.

[13]  W. Klopper,et al.  Strong N-H...pi hydrogen bonding in amide-benzene interactions. , 2009, The journal of physical chemistry. B.

[14]  J. Reedijk,et al.  Lone pair–π interactions: a new supramolecular bond? , 2008 .

[15]  Nathan R. Pillsbury,et al.  State-specific studies of internal mixing in a prototypical flexible bichromophore: Diphenylmethane. , 2008, The Journal of chemical physics.

[16]  Sebastian Höfener,et al.  Scope and limitations of the SCS-MP2 method for stacking and hydrogen bonding interactions. , 2008, Physical chemistry chemical physics : PCCP.

[17]  H. Blackwell,et al.  Local and tunable n-->pi* interactions regulate amide isomerism in the peptoid backbone. , 2007, Journal of the American Chemical Society.

[18]  M. Egli,et al.  Lone pair-aromatic interactions: to stabilize or not to stabilize. , 2007, Accounts of chemical research.

[19]  J. López,et al.  The shape of beta-alanine. , 2006, Journal of the American Chemical Society.

[20]  J. Vondrášek,et al.  Structure and IR spectrum of phenylalanyl-glycyl-glycine tripetide in the gas-phase: IR/UV experiments, ab initio quantum chemical calculations, and molecular dynamic simulations. , 2005, Chemistry.

[21]  Clark R. Landis,et al.  Valency and Bonding: Contents , 2005 .

[22]  A. Gómez-Zavaglia,et al.  Matrix isolation FTIR spectroscopic and theoretical study of methyl lactate , 2004 .

[23]  Martin Egli,et al.  Water-nucleobase "stacking": H-pi and lone pair-pi interactions in the atomic resolution crystal structure of an RNA pseudoknot. , 2003, Journal of the American Chemical Society.

[24]  Ronald T. Raines,et al.  An electronic effect on protein structure , 2003, Protein science : a publication of the Protein Society.

[25]  John L Markley,et al.  Collagen stability: insights from NMR spectroscopic and hybrid density functional computational investigations of the effect of electronegative substituents on prolyl ring conformations. , 2002, Journal of the American Chemical Society.

[26]  J. Gallivan,et al.  Can lone pairs bind to a pi system? The water...hexafluorobenzene interaction. , 1999, Organic letters.

[27]  E. D. Isaacs,et al.  Covalency of the Hydrogen Bond in Ice: A Direct X-Ray Measurement , 1999 .

[28]  G. A. Jeffrey,et al.  An Introduction to Hydrogen Bonding , 1997 .

[29]  M. Egli,et al.  Stereoelectronic effects of deoxyribose O4' on DNA conformation. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[30]  T. Zwier,et al.  Size-Specific Infrared Spectra of Benzene-(H2O)n Clusters (n = 1 through 7): Evidence for Noncyclic (H2O)n Structures , 1994, Science.

[31]  Jack D. Dunitz,et al.  Geometrical reaction coordinates. II. Nucleophilic addition to a carbonyl group , 1973 .