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

• Published in: Angewandte Chemie International Edition Vol. 57; no. 38; pp. 12435 - 12439
• Main Authors: Mohanrao, Raja, Sureshan, Kana M.
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 17-09-2018
• Edition: International ed. in English
• Subjects: Alkynes; Channels; Chemical synthesis; Crystals; Cycloaddition; cycloadditions; Dehydration; Desiccants; Humidity; Hydration; Hygroscopic water; Low temperature; phenylalanine; Polymerization; pseudoproteins; Relative humidity; topochemical reactions; cycloadditions; phenylalanine; pseudoproteins; desiccants; topochemical reactions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201806451

A diphenylalanine derivative, N3‐Phe‐Phe‐NHCH2CCH, was designed for topochemical azide–alkyne cycloaddition (TAAC) polymerization. This dipeptide adopted β‐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.
Keeping dry: A single‐crystal‐to‐single‐crystal (SCSC) topochemical azide–alkyne cycloaddition (TAAC) polymerization of a phenylalanine‐based dipeptide to a pseudoprotein is presented. The dipeptide experienced large conformational motion to achieve the reactive orientation required for TAAC reaction. Channels were created, leading to stoichiometric absorption of water. The pseudoprotein could thus find application as a desiccant material.