Positron lifetimes in phospholipid dispersions

Packing and mobility of hydrocarbon chains in phospholipid lyotropic liquid crystalline lamellar phases and liposomes: characterisation by positron annihilation lifetime spectroscopy (PALS)

“…This trend in lifetime agrees well with past studies [34][35][36]49 with a Dt oPs of 400 ps consistent with that reported by both McGrath et al 35 and Jean et al, 34 although the absolute lifetime values differ. Whilst these systems have previously been studied in the literature, interpretation and comparison of results is difficult, as the evolution of instrumentation and data analysis methods over the decades has made it difficult to directly compare the available data sets.…”

“…A discontinuity in the PALS lifetime, t 4 that corresponds to the melting transition has been observed, with t 4 increasing from ca. 35 Specifically, at the pre-transition a constant oPs lifetime t 4 B 3 ns was observed, increasing to t 4 B 3.4 ns for the L a phase. This trend in lifetime agrees well with past studies [34][35][36]49 with a Dt oPs of 400 ps consistent with that reported by both McGrath et al 35 and Jean et al, 34 although the absolute lifetime values differ.…”

“…This bound state is referred to as a ''positronium'' that may exist in two ground states, i.e. [31][32][33][34][35][36][37] However studies of this nature have been sparse, with many of the observations conflicting due to differences in data analysis and experimental design, so that it is difficult to extract physicochemically-meaningful comparative information from these studies. 12 oPs is of the greatest interest as the primary mechanism of annihilation is via ''pick-off'' with electrons in low electron density regions.…”

Positron annihilation lifetime spectroscopy (PALS): a probe for molecular organisation in self-assembled biomimetic systems

“…McGrath and co-workers 23 have also determined positron lifetimes for several phosphatidylcholine lipid dispersions demonstrating the sensitivity of t oPs to the fluidity of the lipid for lipids with chain lengths n = 12, 16, 18 for which the lifetime parameters at temperatures above the gel-liquid crystalline transition t oPs = 3.3 ns compared to 2.8 ns in the gel phase. McGrath and co-workers 23 have also determined positron lifetimes for several phosphatidylcholine lipid dispersions demonstrating the sensitivity of t oPs to the fluidity of the lipid for lipids with chain lengths n = 12, 16, 18 for which the lifetime parameters at temperatures above the gel-liquid crystalline transition t oPs = 3.3 ns compared to 2.8 ns in the gel phase.…”

Ortho-positronium Quenching in Benzene Solutions of Iron(III) Dithiocarbamates

“…The fivecoordinate halogenobis(diethyldithiocarbamato) iron (III) complexes, which are paramagnetic and hardly reducible, were also tested for the effect on the o-Ps quenching. Unlike the six-coordinate iron(III) dithiocarbamates, they only slightly affected the o-Ps lifetime, indicating that the spin-conversion process of o-Ps quenching is much less important than the oxidation process.Positronium, which is the bound state of a positron with an electron, has attracted increasing attention from many researchers and the positron annihilation as a nuclear probe has been widely applied to the study of the chemical [ 1 -6 ], miceller [ 7 -9 ], and biological systems [10][11][12]. The variation of the intensity of the long-lived component of positronium against the inhibitor concentration in systems of organic solutions has recently been successfully explained in terms of the spur model [13][14][15].…”