Molecular Engineering of Self-Assembling Diphenylalanine Analogues Results in the Formation of Distinctive Microstructures

Diphenylalanine
is one of the most studied building blocks in organic
supramolecular chemistry, forming ordered assemblies with unique mechanical,
optical, piezoelectric, and semiconductive properties. These structures
are being used for diverse applications, including energy storage,
biosensing, light emission, drug delivery, artificial photosynthesis,
and chemical propulsion. To increase the structural diversity of this
dipeptide building block, three previously unreported analogues in
which the aliphatic chain between the peptide backbone and the phenyl
ring was gradually lengthened were synthesized. Each dipeptide self-assembled
into unique microstructures, differing in morphology, which ranged
from flat plates to long microrods to flattened microplanks. The structures
were also found to possess distinctive optical properties. Furthermore,
X-ray crystallography of each of the three diphenylalanine analogues
presented distinctive molecular arrangements. The remarkable differences
between each dipeptide in the intermolecular interactions they formed
provide insight into the physicochemical mechanisms of self-assembly
and, in addition, indicate the biological significance of the single
methylene bridge of phenylalanine.