Photo-responsive liposomes composed of spiropyran-containing triazole-phosphatidylcholine: investigation of merocyanine-stacking effects on liposome-fiber assembly-transition

Soft Matter. 2019 May 8;15(18):3740-3750. doi: 10.1039/c8sm02181c.

Abstract

A spiropyran-containing triazole-phosphatidylcholine (SPTPC) was synthesized through a copper-catalyzed azide alkyne cyclo-addition (CuAAC) reaction. In water, SPTPCs self-assembled and a spontaneous spiropyran-to-merocyanine (SP-to-MC) isomerization occurred, resulting in coexistence of liposomes and fibers, and switching from the spiropyran (SP) to the merocyanine (MC) isomeric structure induced a reversible transition between these molecular assemblies. Study of the self-assembly of SPTPCs and photo-induced liposome-fiber assembly-transition revealed that the presence of MC enabled additional inter-membrane interaction during self-assembly and that the MC-stacking effect was the driving force for the assembly-transition. Exposure to UV light induced switching from SP to MC, where the planar structure of MC and the confinement of MC led to enhanced MC-stacking. The effect of MC-stacking was both advantageous and disadvantageous: MC-stacking perturbed the hydrophobic phase in the bilayer membrane and facilitated the liposome-to-fiber transition, otherwise the MC-stacking retarded switching of MC to SP, and caused an incomplete recovery of MC to SP during fiber-to-liposome recovery, thus a fatigue of SP was induced by MC-stacking during the liposome-to-fiber transition cycle. To decrease the intermolecular interactions and suppress MC-stacking, photo-inert triazole-phosphatidylcholine (TPC) was incorporated to prepare two-component TPC/SPTPC-liposomes, which exhibited better recovery kinetics. The photo-adaptive behavior of TPC/SPTPC-liposomes confirmed the disturbance of bilayer membranes by inter-membrane MC-stacking and the formation of MCTPC-enriched phases in the bilayer membrane.

MeSH terms

  • Alkynes / chemistry
  • Azides / chemistry
  • Benzopyrans / chemistry*
  • Catalysis
  • Copper / chemistry
  • Indoles / chemistry*
  • Lipid Bilayers / chemistry
  • Liposomes / chemistry*
  • Nitro Compounds / chemistry*
  • Phase Transition
  • Phosphatidylcholines / chemistry*
  • Photochemical Processes*
  • Triazoles / chemistry*
  • Ultraviolet Rays

Substances

  • Alkynes
  • Azides
  • Benzopyrans
  • Indoles
  • Lipid Bilayers
  • Liposomes
  • Nitro Compounds
  • Phosphatidylcholines
  • Triazoles
  • merocyanine
  • spiropyran
  • Copper