Unexpected Roles of Guest Polarizability and Maximum Hardness, and of Host Solvation in Supramolecular Inclusion Complexes: A Dual Theoretical and Experimental Study
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- 作者：René ; Castro ; Marcelo J. Berardi ; Emilio Có ; rdova ; Mariluz Ochoa de Olza ; Angel E. Kaifer ; and Jeffrey D. Evanseck
- 刊名：Journal of the American Chemical Society
- 出版年：1996
- 出版时间：October 23, 1996
- 年：1996
- 卷：118
- 期：42
- 页码：10257 - 10268
- 全文大小：305K
- 年卷期：v.118,no.42(October 23, 1996)
- ISSN：1520-5126
文摘
The origin of differential binding affinity and structuralrecognition between the inclusion complexes ofcyclobis(paraquat-p-phenylene),14+, and 1,4-substituted phenyl or4,4'-substituted biphenyl derivatives has beenjointly determined by spectrometric techniques and ab initio andsemiempirical molecular orbital methods. Theunusual boxed geometry and tetracationic charge distribution in14+ are key molecular features which producestrongintermolecular interactions with guest and solvent molecules.Solvation was addressed by including up to 12acetonitrile molecules in the theoretical model, which realigned thepredicted gas-phase supramolecular structuresand energies into excellent agreement with experiment. Thecomputed complexation enthalpies, 
Hbind, fromthesemiempirical molecular orbital PM3 method are on average within 1kcal/mol of the experimental free energybinding data collected from absorption spectroscopy in acetonitrile.In addition, the computed geometric penetrationand positioning of 14+/benzidine and14+/4,4'-biphenol complexes are consistentwith that reported from NMR NOEdata. The partitioning of self-consistent field complexationenergies from both classical and quantum forces hasbeen determined by using Morokuma's variational energy decompositiontechnique. It was determined that theprimary basis for the molecular recognition between 1,4-substitutedphenyl guests and 14+ is short-rangestabilizingelectrostatic forces complemented by small amounts of polarizabilityand charge-transfer. In contrast, the recognitionforce between 4,4'-substituted biphenyl guests and14+ is dominated by polarizability with asmall contribution fromelectrostatics. Therefore, the balance between molecularpolarizability and electrostatics controls thedifferentialbinding affinity and structural recognition with14+. For the first time, we report thatindividual molecular propertiesof substituted guests correlate with the binding energies ofcorresponding 14+ inclusion complexes.Direct correlationsbetween the 14+ binding energies and thecomputed molecular polarizability, maximum hardness, softness,andelectronegativity of the guest have been identified. It is nowplausible to consider the design and construction ofnew supramolecular assemblies based upon a few select molecularproperties of the constituent molecules.
Hbind, fromthesemiempirical molecular orbital PM3 method are on average within 1kcal/mol of the experimental free energybinding data collected from absorption spectroscopy in acetonitrile.In addition, the computed geometric penetrationand positioning of 14+/benzidine and14+/4,4'-biphenol complexes are consistentwith that reported from NMR NOEdata. The partitioning of self-consistent field complexationenergies from both classical and quantum forces hasbeen determined by using Morokuma's variational energy decompositiontechnique. It was determined that theprimary basis for the molecular recognition between 1,4-substitutedphenyl guests and 14+ is short-rangestabilizingelectrostatic forces complemented by small amounts of polarizabilityand charge-transfer. In contrast, the recognitionforce between 4,4'-substituted biphenyl guests and14+ is dominated by polarizability with asmall contribution fromelectrostatics. Therefore, the balance between molecularpolarizability and electrostatics controls thedifferentialbinding affinity and structural recognition with14+. For the first time, we report thatindividual molecular propertiesof substituted guests correlate with the binding energies ofcorresponding 14+ inclusion complexes.Direct correlationsbetween the 14+ binding energies and thecomputed molecular polarizability, maximum hardness, softness,andelectronegativity of the guest have been identified. It is nowplausible to consider the design and construction ofnew supramolecular assemblies based upon a few select molecularproperties of the constituent molecules.