Designed Peptoids as Tunable Modifiers of Zeolite Crystallization

Peptides are among the most efficient classes of crystal growth modifiers for a wide range of natural and synthetic systems owing to their unmatched design space that affords the opportunity to construct highly specific sequences to tailor crystal growth. In the case of zeolite crystallization, the high pH and temperature of common synthesis conditions renders peptides ineffective for such applications. Here, we introduce peptoids as a biomimetic platform for the rational design of zeolite growth modifiers. The chemical robustness of peptoids coupled with their facile and efficient synthesis on solid support, which enables the generation of versatile sequences with diverse chemical functionality, make these materials ideal for the relatively harsh conditions of zeolite crystallization. A library of peptoids incorporating combinations of alcohol, amine, ether, and aromatic functional moieties were synthesized and tested in growth solutions of zeolite L (LTL type), a common commercial material. Our findings reveal that peptoids are potent modifiers of zeolite L crystallization. Syntheses with 1 wt % are often sufficient to suppress nucleation, indicating a strong interaction between peptoids and the amorphous precursors formed during the early stages of zeolite L synthesis. Chemical analysis reveals that a significant fraction of peptoid remains intact at pH 13 and 160 °C, though peptoid degradation occurs with prolonged hydrothermal treatment. Time-resolved analysis of products removed from zeolite L growth mixtures reveals that amines interact more favorably than alcohols with precursors/crystals. Our studies also confirm that peptoids can be tailored to either increase or decrease the length-to-width aspect ratio of cylindrical zeolite L crystals through the insertion of hydrophilic or hydrophobic groups, respectively. The mechanisms of peptoid action are discussed within the context of complex nonclassical pathways of zeolite crystallization. Moreover, this study provides the first testing and validation of peptoids as zeolite growth modifiers, thus opening new avenues in the future to extend this general platform to other zeolite framework types and related materials grown under conditions that are too severe for biomolecules.