Photochemically induced disturbance of the alkyl chain packing in vesicular membranes.
In previous reports, we presented the synthesis and properties of double-tailed azobenzene-substituted phosphate amphiphiles (Kuiper et al. Synthesis 2003, 695 and Kuiper et al. Langmuir 2004, 20, 1152). We also reported that an ion channel can be regulated by trans-cis isomerization of these amphiphiles, which were incorporated in the membrane (Folgering et al. Langmuir 2004, 20, 6985). In the present study, the effect of trans-cis isomerization of both single- and double-tailed azobenzene-substituted amphiphiles on the aggregation and packing behavior has been studied. The phase transition temperature of a membrane and the thermal half-life times of the cis azobenzene-substituted amphiphiles in membranes have been measured. Furthermore, the synthesis and properties of single-tailed azobenzene-substituted phosphate amphiphiles are described and compared with those of the double-tailed analogues. The single-tailed azobenzene-substituted phosphates have a low solubility in water and form micelles, sheets, and crystals. In all cases the trans-cis isomerization leads to a disturbance of the chain packing. Both single- and double-tailed cis azobenzene-substituted phosphates lowered the main phase transition temperature of bilayer membranes. The effect increased when the azobenzene moiety was situated closer to the head group. Accordingly, the half-life times of the cis azobenzene group was shorter when the azobenzene group was positioned closer to the head group for both the single- and double-tailed amphiphiles. Interestingly, the thermal cis-trans isomerization of the single-tailed azobenzene-substituted phosphates was faster in a DOPC membrane than that for the free monomer in aqueous solution.
Kuiper
Johanna M
JM
Physical Organic Chemistry Unit, Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands.
Stuart
Marc C A
MC
Engberts
Jan B F N
JB
D002152:Calorimetry, Differential Scanning; D007536:Isomerism; D009682:Magnetic Resonance Spectroscopy; D008567:Membranes, Artificial; D046529:Microscopy, Electron, Transmission; D010777:Photochemistry; D013056:Spectrophotometry, Ultraviolet; D013500:Surface Tension
D008567:Membranes, Artificial