Observation of the phase transition in phospholipid liposomes taking advantage of the particular optical properties of octa-α-butyloxy-H2phthalocyanines

✍ Scribed by A. Zeug; A. Paul; B. Röder

• Publisher: John Wiley and Sons
• Year: 2001
• Tongue: English
• Weight: 116 KB
• Volume: 05
• Category: Article
• ISSN: 1088-4246
• DOI: 10.1002/jpp.374

✦ Synopsis

In this work we report on the influence of the polarity of the environment on the optical properties of octa-α-butyloxy-H~2~phthalocyanine ( H ~2~ PC ( OBu )~8~) in organic solvents and liposomes using steady-state absorption as well as time correlated single photon counting (TCSPC). A change was found in Q-band absorption in various solvents. Taking into account that the absorption properties of H ~2~ PC ( OBu )~8~ are modulated by the polarity of the direct surrounding, polarities inside micro-heterogeneous systems can be probed. This was demonstrated for liposomes of dipalmitoylphosphatidylcholine (DPPC), with regard to the behavior during the phase transition between the gel and liquid-crystal state. Absorption spectra of H ~2~ PC ( OBu )~8~ embedded in DPPC-liposomes have been recorded in the temperature range from 15 to 70 °C, covering the phase transition region at about 36–39 °C. The Q-band absorption at temperatures below and above the phase transition resembles those in polar and non-polar solvents, respectively. Measurements of fluorescence lifetime confirm this equivalence. We explain this behavior by a change of the localization of the dye molecules inside the membrane. For H ~2~ PC ( OBu )~8~ embedded in DPPC-liposomes we demonstrated by using optical methods that the position of the dye molecules strongly depends on the phase-state of the phospholipid. In addition, H ~2~ PC ( OBu )~8~ can be used as a probe for phase transition processes taking advantage of the specific behavior in surroundings with different polarity.