Controlling the shape and size of crystalline solids is critical for the production of many fine chemicals, pharmaceuticals and foods, and is also important in drug delivery and release, and for technologies as diverse as bio/photo catalysis, thin-film solar cells, and antibacterial fabrics.We report the preparation of organic crystals of thiamethoxam (TMX) with a regular, micron-sized, tetragonal bipyramid shape by combinations of directed biological additives that specifically bind to the crystal surface and change the degree of supersaturation during crystal growth. Filamentous M13 bacteriophage was used as a versatile platform for presenting and selecting material-specific peptides with high affinity for TMX. Crystal morphology was manipulated with TMX-binding M13 bacteriophage displaying heptapeptide ASTLPKA coat proteins as a biological adsorbant. The mechanism by which crystal morphology was altered suggests an influence of the phage on the driving force for crystallization (an equilibrium effect) and/or the rate at which dissolved molecules precipitate on growing crystal faces (a kinetic effect). We also present data from de-supersaturation experiments suggesting that both phenomena were affected by the presence of the phage additives. Further, we varied the concentration of M13 type bacteriophage expressing heptapeptide ASTLPKA coat proteins to understand the characteristics of the adsorption behavior of phage to TMX crystals. It is shown that a modified Langmuir isotherm describes the adsorption isotherm of phage onto TMX crystals by introducing a concentration dependent factor. The phage adsorption data was also well-fitted to Satake-Yang model, which quantifies the extent of binding in terms of the binding constant (Ku) and the cooperativity parameter (u) via least-square-error fitting. This analysis suggested a cooperative binding between neighboring phage as well as site-specific binding with TMX surface. Such specific binding of M13 bacteriophage to solid surfaces could lead to the targeted manipulation of surface chemistry in colloidal suspensions in potentially complex mixtures.

Effects of a phage-display peptide on the growth of thiamethoxam (TMX) organic crystals

247th National Meeting (2014)

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