2 research outputs found
Lipid Rearrangement in DSPC/DMPC Bilayers: A Neutron Reflectometry Study
Lipid translocation in membranes is still far from being
understood
and well characterized for natural cell membranes as well as for simpler
bilayer model systems. Several discrepancies with respect to its occurrence
and its characteristic time scale are present in the literature. In
the current work, the structural changes induced by lipid rearrangement
in a distearoyl-/dimyristoyl-phosphocholine binary lipid system have
been addressed by means of neutron reflectivity. It has been shown
that a fast, spontaneous compositional reorganization with lipid transfer
between the two leaflets of the bilayer takes place only when the
lipid species are both in the fluid phase. This process has been identified
as the so-called lipid flip-flop. Moreover, the influence of the preparation
protocol on the structural properties of the system has been investigated
Stacking and Branching in Self-Aggregation of Caffeine in Aqueous Solution: From the Supramolecular to Atomic Scale Clustering
The dynamical and structural properties
of caffeine solutions at
the solubility limit have been investigated as a function of temperature
by means of MD simulations, static and dynamic light scattering, and
small angle neutron scattering experiments. A clear picture unambiguously
supported by both experiment and simulation emerges: caffeine self-aggregation
promotes the formation of two distinct types of clusters: linear aggregates
of stacked molecules, formed by 2–14 caffeine molecules depending
on the thermodynamic conditions and disordered branched aggregates
with a size in the range 1000–3000 Å. While the first
type of association is well-known to occur under room temperature
conditions for both caffeine and other purine systems, such as nucleotides,
the presence of the supramolecular aggregates has not been reported
previously. MD simulations indicate that branched structures are formed
by caffeine molecules in a T-shaped arrangement. An increase of the
solubility limit (higher temperature but also higher concentration)
broadens the distribution of cluster sizes, promoting the formation
of stacked aggregates composed by a larger number of caffeine molecules.
Surprisingly, the effect on the branched aggregates is rather limited.
Their internal structure and size do not change considerably in the
range of solubility limits investigated