title: Isomerization dynamics of photochromic spiropyran molecular switches in phospholipid bilayers.
abstract: Transient absorption spectroscopy was used to investigate the dynamics of the photochromic indolinobenzospiropyran reaction in toluene solution and in phosphatidylcholine bilayers (1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)). After excitation with UV light, colorless (R/S)-2-(3',3'-dimethyl-6-nitro-3'H-spiro[chromene-2,2'-indol]-1'-yl)ethanol derivatives are converted to colored merocyanine products in high yield; Phi = 0.45 in DMPC liposomes. We find that the reaction occurs in the bilayer aliphatic region in the gel (P(beta)(')) and liquid (L(alpha)) phases. The Arrhenius activation energy for the isomerization in DMPC bilayers was approximately 3.5 times larger in the liquid phase (L(alpha), E(a) = 26.0 +/- 1.0 kJ mol(-1)) than that in the gel phase (P(beta)('), E(a) = 7.3 +/- 1.6 kJ mol(-1)). Analysis of the isomerization rate constant temperature dependence allows an estimation of the bilayer viscosity and free volume properties in the L(alpha) phase.
authors.affiliation: Department of Chemistry, Virginia Commonwealth University, 1001 West Main Street, Richmond, Virginia 23284-2006, USA.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Wohl
authors.forename: Darius
authors.initials: D
authors.lastname: Kuciauskas
mesh_terms: D001578:Benzopyrans / Q000737:chemistry*; D007211:Indoles / Q000737:chemistry*; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D015394:Molecular Structure; D009574:Nitro Compounds / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D010777:Photochemistry; D012996:Solutions / Q000737:chemistry; D013237:Stereoisomerism; D013696:Temperature; D013997:Time Factors; D014050:Toluene / Q000737:chemistry
chemical_list: D001578:Benzopyrans; D007211:Indoles; D008051:Lipid Bilayers; D009574:Nitro Compounds; D010743:Phospholipids; D012996:Solutions; C088184:spiropyran; D014050:Toluene