Jung, Yousung and Marcus, R. A. (2010) Protruding interfacial OH groups and 'on-water' heterogeneous catalysis. Journal of Physics: Condensed Matter, 22 (28). Art. No. 284117 . ISSN 0953-8984 http://resolver.caltech.edu/CaltechAUTHORS:20100720-084322628
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The key aspect of the remarkable organic catalysis that is observed to occur at the organic/water phase boundary, the so-called 'on-water' catalysis (Narayan et al 2005 Angew. Chem. 44 3275), was recently proposed to be the protruding OH groups of water molecules at the interface that interact with the transition state (TS) via hydrogen bonding and lower activation barriers (Jung and Marcus 2007 J. Am. Chem. Soc. 129 5492). In particular, the cycloaddition reaction of quadricyclane (Q) with dimethyl azodicarboxylate (DMAD) on-water was calculated to be more than 100 000 times more efficient in terms of rate constant than the neat reaction. In this paper, we review and consider a related reaction of Q with dimethyl acetylenedicarboxylate, where nitrogen, a good H-bond acceptor, in DMAD is replaced by carbon, a poor H-bond acceptor. A very low rate acceleration of acetylenedicarboxylate on-water relative to the neat reaction is obtained theoretically, as compared to DMAD on-water, due to the relatively low H-bonding ability of acetylenedicarboxylate with water at the TS relative to the reactants. We suggest that there may also be an 'intrinsic steric effect' or orientational advantage in the on-water catalysis in general, and both electronic and steric effects may be in operation for the smaller on-water catalysis for the cycloaddition reaction of quadricyclane and acetylenedicarboxylate. A preliminary quantum mechanical/molecular mechanical (QM/MM) simulation including 1264 water molecules for the on-water reaction of DMAD + Q also suggests that there are indeed approximately two–four more H-bonds between the TS and the dangling OH groups than between the reactants and the surface.
|Additional Information:||© 2010 IOP Publishing Ltd. Received 7 November 2009, in final form 6 January 2010 Published 21 June 2010. This paper is a contribution that concerns recent progresses in the field of computer simulations of water discussed at the CECAM workshop ‘Modeling and Simulation of Water at Interfaces from Ambient to Supercooled Conditions’ supported by ESF-Simbioma and CECAM. It is a pleasure to acknowledge the support of this research by the WCU program (R31-2008-000-10055-0) through the National Research Foundation of Korea, and also by the National Science Foundation and the Office of Naval Research. We would like to acknowledge the contribution of Dr Meher Prakash who first called our attention to the dramatic results found with azodicarboxylate on-water which stimulated our study of the original work. We would like to thank Professors Barry Sharpless, Valery Fokin, and Dr Arani Chandra for helpful discussions.|
|Classification Code:||PACS: 82.65.+r; 82.20.Db; 82.20.Ej; 82.30.Nr; 87.15.R-|
|Official Citation:||Yousung Jung and R A Marcus 2010 J. Phys.: Condens. Matter 22 284117 doi: 10.1088/0953-8984/22/28/284117|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||30 Jul 2010 22:23|
|Last Modified:||26 Dec 2012 12:15|
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