Synthesis and Reversible Hydration of a Pseudoprotein, a Fully Organic Polymeric Desiccant by Multiple Single-Crystal-to-Single-Crystal Transformations

A diphenylalanine derivative, N3-Phe-Phe-NHCH2CCH, was designed for topochemical azide-alkyne cycloaddition (TAAC) polymerization. This dipeptide adopted -sheet arrangement as designed, in its crystals, but the azide and alkyne were not fitly aligned for their topochemical reaction. However, the voids present around these groups allowed them to attain a reactive geometry upon heating and their consequent TAAC polymerization to a pseudoprotein in a single-crystal-to-single-crystal (SCSC) fashion. This motion led to the creation of channels in the product crystal and it absorbed water from the surroundings to fill these channels as H-bonded water wire. The pseudoprotein undergo reversible hydration/dehydration in SCSC fashion many times under mild conditions: hydration at low relative humidity and dehydration at low temperature. Vapor sorption analyses suggest that this fully organic polymer might be useful as an energy-efficient desiccant material for controlling indoor humidity.