The Molecular Basis of Growth Control in Guanine Crystals.

Precise control over crystal morphology is a longstanding challenge in materials science, as crystal shape governs optical, mechanical, and electronic properties. In contrast, living organisms achieve remarkable control over crystal morphology, though the underlying mechanisms are not fully understood. Among the most common organic materials are guanine crystals, notable for their plate-like morphology and high anisotropic refractive index, arising from the stacking of hydrogen-bonded molecular layers along the (100) plane. Here we show that simple synthetic polymers not only reproduce this biogenic plate-like form in vitro but also expand the accessible morphology space to prisms and needles by systematically varying i) multivalent interactions, ii) functional-group identity, and iii) polarity and hydrogen-bonding capacity. Using microscopy, spectroscopy, and molecular dynamics simulations, we find that carbonyl-bearing polymers selectively adsorb to the (100) stacking face, cap layer addition along the a-axis, and yield large plates indistinguishable from biogenic crystals. In contrast, reducing carbonyl polarity, increasing steric-bulk, or introducing highly-polar groups redirect adsorption and produces bulkier prisms or slender needles. Simulations corroborate facet selectivity, identify contact motifs involving carbonyl oxygens and adjacent methylenes. Together, these findings provide design principles for sculpting organic crystals and suggest analogous interactions exploited by biological scaffolds to orchestrate guanine assembly.