COLL Ramanathan Nagarajan  Sunday, March 16, 2014 

4 - Mechanism of selective recognition of cubic platinum nanocrystals by peptides in aqueous solution

Hadi Ramezani-Dakhel1, hr15@zips.uakron.edu, Lingyan Ruan2, Yu Huang2,3, Hendrik Heinz1. (1) Department of Polymer Engineering, University of Akron, Akron, Ohio 44325, United States, (2) Department of Materials Science and Engineering, University of California, Los Angeles, California 90095, United States, (3) California NanoSystems Institute, University of California, Los Angeles, California 90095, United States

Shape, size, and surface modification regulate functionality of metal nanocrystals in catalysts, sensors, and electrode materials. In-situ synthesis of metal nanocrystals of different shapes facilitates the exploration of new functionalities although the underlying shape-controlling mechanisms still remain poorly understood. Oligomers of naturally occurring amino acids have been employed as efficient regulating agents to engineer the structure of nanocrystals. A naturally selected, non-charged peptide named T7 (Acyl-TLTTLTN-Amide) was reported to bind to platinum nanocubes enclosed by six {100} facets and directs the formation of single crystalline platinum cubes in reductive synthesis. We explain the mechanism of specific cube recognition and of cube formation from cuboctahedral seed crystals using molecular dynamics simulation with the CHARMM-METAL force field. We found a higher mobility of water molecules near the edges of nanocubes compared to the center of the facets and a unique match of polarizable atoms in T7 (N, O, C) to the square pattern of epitaxial sites on the cube surface. Water competes strongly with the peptide anywhere on the {100} facets, yet higher mobility of water near the edges of the cube favors peptide adsorption (‒5.8±0.8 kcal/mol). These data are also in agreement with peptide desorption on extended {100} facets experimentally and a positive energy of peptide attachment in the simulation (+13±2 kcal/mol). In the synthesis of Pt nanocrystals in the presence of T7 peptides, cuboctahedral seed crystals are initially formed. The simulation of cuboctahedral seeds in contact with several peptides then shows that T7 peptide locates on {100} facets with a slight preference over {111} facets which suggests faster growth of the {111} facets and is consistent with the experimentally observed formation of cubic nanocrystals. The results therefore explain the likely mechanism of nanocrystal growth and show that force fields such as CHARMM-METAL and INTERFACE-METAL can predict selective adsorption and preferred nanocrystal shapes.


Sunday, March 16, 2014 09:35 AM
Single Molecules at Interfaces: Experiments and Simulations (08:30 AM - 11:50 AM)
Location: Dallas Convention Center
Room: D161

 

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