Morphological transformation of self-assemblies by tuning hydrophobic segment of small amphiphiles.

Hypothesis: With increasing surge in the development of supramolecular self-assemblies, it is crucial to predict the influence of amphiphilic segment in dictating the morphology of self-aggregates. This article reports the design and synthesis of low molecular weight amphiphiles with varying hydrophobicity both in the spacer unit and at the terminal moiety.

Experiments: Hydrophobicity at the spacer moiety was modulated by altering alkyl chain length and by inclusion of aromatic ring and the same was changed at hydrophobic terminal using pyrene, naphthalene, n-hexadecane having 2-aminopyridine as polar head. Microscopy and spectroscopy were used to investigate the morphologies of self-aggregated amphiphiles.

Findings: Variation of hydrophobicity of the spacer moiety either by changing the alkyl chain length (C0, C2, C6, C11 and phenyl ring) having pyrene as terminal hydrophobic unit led to the formation of only spherical vesicles in respective solvent system. Morphological transformation of self-aggregates from vesicle to fused-vesicle to gel was observed in DMSO-water upon alteration in the hydrophobic end of amphiphile from pyrene to naphthyl to C16 alkyl chain having C6 alkyl chain as spacer. Hence, the hydrophobicity at the terminal of the amphiphile has the predominant role in tuning the morphology of self-aggregates through modulation in the hydrophobic-lipophilic balance (HLB) of amphiphiles.