Dipyrenylphosphatidylcholines as membrane fluidity probes. Relationship between intramolecular and intermolecular excimer formation rates

Abstract

In the intramolecular excimeric membrane probe, dipyrenylphosphatidylcholine (dipyn PC), pyrene moieties are linked to the terminal carbons of the two acyl chains, each of which contains n carbons. We show here how the probe intramolecular excimer production rate, K, may be determined from the excimer/monomer intensity ratio, rl, by making use of the fluorescence titrations of the related monopyrenyl probe, pyn PC, analyzed according to the milling crowd model. rl and the rate K of dipy10 PC in four model membrane systems were measured over a wide temperature range and both parameters are shown to be sensitive functions of the lateral fluidity of the host matrix. A model for relating the intramolecular and intermolecular excimer formation rates is proposed according to which both processes are limited by the reorientational rate of the pyrene moiety. Above the fluid-gel transition temperature, Tc, the diffusion rate (f) of the monopyrenyl probe (pyn PC) is accordingly related to K by: pE approximately K/(K + 1/2f + tau -1M), where pE is the probability of excimer formation between nearest neighbor pyn PC probes, and tau M is the monomer lifetime. Values of pE derived in this way are found to be consistent with pE values derived from the milling crowd analysis of fluorescence yield titration experiments. K for dipy10 PC in DMPC multibilayers ranges from 0.21 x 10(7) s-1 at 10 degrees C in the gel phase, to 5.7 x 10(7) s-1 at 60 degrees C in the fluid phase, whereas the lateral diffusion coefficient, D, for py10 PC in the same bilayers ranged from 8 to 34 microns2 s-1, when calculated with D = fL2/4, L being the average lipid-lipid spacing of the host membrane. Above Tc and at the same reduced temperature, (T - Tc)/Tc, both f for py10 PC, and K for dipy10 PC were found to have relative magnitudes in the order: DPPC greater than DMPC greater than POPC greater than DOPC. This and the similarity of the activation energies for f and K suggest that the rotation of the the pyrene moiety is the rate-limiting step for both the lateral mobility of py10 PC and intramolecular excimer formation in dipy10 PC.

Lateral Organization of Pyrene-labeled Lipids in Bilayers as Determined from the Deviation from Equilibrium between Pyrene Monomers and Excimers

“…2 are in good agreement with previous data on the "order parameter" along phospholipid acyl chains (1, 2) and therefore lend support to a major contribution of steric restriction. Our previous data on a similar system suggest that the steric factor should be more important than the diffusion rate (Table III in Ref. 18), in agreement with the suggestion that the rotational energy barrier to excimer formation is higher than the translational one (35,36). Fig.…”

Nanoscale Ultrasound‐Switchable FRET‐Based Liposomes for Near‐Infrared Fluorescence Imaging in Optically Turbid Media

“…During noninertial cavitation, gas bubbles pre‐existing in the fluid can oscillate or move, which generates small cavities and creates free volume in the lipid bilayer. The increased free volume can facilitate quicker lateral diffusion of the lipids . Noninertial cavitation also involves the nucleation of gas bubbles in the hydrophobic region of lipid bilayers, which supports the hypothesis that US leads to volumetric changes in liposomes.…”

Liquid chromatographic determination of polyamines in human urine based on intramolecular excimer‐forming fluorescence derivatization using 4‐(1‐pyrene)butanoyl chloride

“…As seen, at present elution conditions using the linear gradient, a full separation of the derivatives was achieved within 20 min. All polyamine-PBC derivatives gave single peaks, which were completely separated from the intermolecular excimer peaks (Nohta et al, 2000;Vauhkonen et al, 1990) of PBC reagent and its hydrolysis product, 4-(1-pyrene)-butyric acid. No peaks for the polyamines were observed when monitoring fluorescence of their respective monomeric PBC derivatives at 375 nm [ Fig.…”