UV-induced bursting of cell-sized multicomponent lipid vesicles in a photosensitive surfactant solution.

We study the behavior of multicomponent giant unilamellar vesicles (GUVs) in the presence of AzoTAB, a photosensitive surfactant. GUVs are made of an equimolar ratio of dioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) and various amounts of cholesterol (Chol), where the lipid membrane shows a phase separation into a DPPC-rich liquid-ordered (L(o)) phase and a DOPC-rich liquid-disordered (L(d)) phase. We find that UV illumination at 365 nm for 1 s induces the bursting of a significant fraction of the GUV population. The percentage of UV-induced disrupted vesicles, called bursting rate (Y(burst)), increases with an increase in [AzoTAB] and depends on [Chol] in a non-monotonous manner. Y(burst) decreases when [Chol] increases from 0 to 10 mol % and then increases with a further increase in [Chol], which can be correlated with the phase composition of the membrane. We show that Y(burst) increases with the appearance of solid domains ([Chol] = 0) or with an increase in area fraction of L(o) phase (with increasing [Chol] ≥ 10 mol %). Under our conditions (UV illumination at 365 nm for 1 s), maximal bursting efficiency (Y(burst) = 53%) is obtained for [AzoTAB] = 1 mM and [Chol] = 40 mol %. Finally, by restricting the illumination area, we demonstrate the first selective UV-induced bursting of individual target GUVs. These results show a new method to probe biomembrane mechanical properties using light as well as pave the way for novel strategies of light-induced drug delivery.

Revised ionic radii of lanthanoid(III) ions in aqueous solution.

A new set of ionic radii in aqueous solution has been derived for lanthanoid(III) cations starting from a very accurate experimental determination of the ion-water distances obtained from extended X-ray absorption fine structure (EXAFS) data. At variance with previous results, a very regular trend has been obtained, as expected for this series of elements. A general procedure to compute ionic radii in solution by combining the EXAFS technique and molecular dynamics (MD) structural data has been developed. This method can be applied to other ions allowing one to determine ionic radii in solution with an accuracy comparable to that of the Shannon crystal ionic radii.

Stability and instability of the isoelectronic UO2(2+) and PaO2+ actinyl oxo-cations in aqueous solution from density functional theory based molecular dynamics.

In this work, Pa(V) monocations have been studied in liquid water by means of density functional theory (DFT) based molecular dynamic simulations (CPMD) and compared with their U(VI) isoelectronic counterparts to understand the peculiar chemical behavior of Pa(V) in aqueous solution. Four different Pa(V) monocationic isomers appear to be stable in liquid water from our simulations: [PaO(2)(H(2)O)(5)](+)(aq), [Pa(OH)(4)(H(2)O)(2)](+)(aq), [PaO(OH)(2)(H(2)O)(4)](+)(aq), and [Pa(OH)(4)(H(2)O)(3)](+)(aq). On the other hand, in the case of U(VI) only the uranyl, [UO(2)(H(2)O)(5)](2)(+)(aq), is stable. The other species containing hydroxyl groups replacing one or two oxo bonds are readily converted to uranyl. The Pa-OH bond is stable, while it is suddenly broken in U-OH. This makes possible the formation of a broad variety of Pa(V) species in water and participates to its unique chemical behavior in aqueous solution. Further, the two actinyl oxocations in water are different in the ability of the oxygen atoms to form stable and extended H-bond networks for Pa(V) contrary to U(VI). In particular, protactinyl is found to have between 2 and 3 hydrogen bonds per oxygen atom while uranyl has between zero and one.