2 research outputs found
Acylated Carrageenan Changes the Physicochemical Properties of Mixed Enzyme–Lipid Ultrathin Films and Enhances the Catalytic Properties of Sucrose Phosphorylase Nanostructured as Smart Surfaces
Control over the
catalytic activity of enzymes is important to
construct biosensors with a wide range of detectability and higher
stability. For this, immobilization of enzymes on solid supports as
nanostructured films is a current approach that permits easy control
of the molecular architecture as well as tuning of the properties.
In this article, we employed acylated carrageenan (AC) mixed with
phospholipids at the air–water interface to facilitate the
adsorption of the enzyme sucrose phosphorylase (SP). AC stabilized
the adsorption
of SP at the phospholipid monolayer, as detected by tensiometry, by
which thermodynamic parameters could be inferred from the surface
pressure–area isotherm. Also, infrared spectroscopy applied
in situ over the monolayer showed that the AC–phospholipid
system not only permitted the enzyme to be adsorbed but also helped
conserve its secondary structure. The mixed monolayers were then transferred
onto solid supports as Langmuir–Blodgett (LB) films and investigated
with transfer ratio, quartz crystal microbalance, fluorescence spectroscopy,
and atomic force microscopy. The enzyme activity of the LB film was
then determined, revealing that although there was an expected reduction
in activity in relation to the homogeneous environment the activity
could be better preserved after 1 month, revealing enhanced stability
Molecular-Level Modifications Induced by Photo-Oxidation of Lipid Monolayers Interacting with Erythrosin
Incorporation into
cell membranes is key for the action of photosensitizers
in photomedicine treatments, with hydroperoxidation as the prominent
pathway of lipid oxidation. In this paper, we use Langmuir monolayers
of 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphocholine (DOPC)
and 1,2-dipalmitoyl-<i>sn</i>-glycero-3-phosphocholine (DPPC)
as cell membrane models to investigate adsorption of the photosensitizer
erythrosin and its effect on photoinduced lipid oxidation. From surface
pressure isotherms and polarization-modulated infrared reflection–absorption
spectroscopy (PM-IRRAS) data, erythrosin was found to adsorb mainly
via electrostatic interaction with the choline in the head groups
of both DOPC and DPPC. It caused larger monolayer expansion in DOPC,
with possible penetration into the hydrophobic unsaturated chains,
while penetration into the DPPC saturated chains was insignificant.
Easier penetration is due to the less packed DOPC monolayer, in comparison
to the more compact DPPC according to the monolayer compressibility
data. Most importantly, light irradiation at 530 nm made the erythrosin-containing
DOPC monolayer become less unstable, with a relative surface area
increase of ca. 19%, in agreement with previous findings for bioadhesive
giant vesicles. The relative area increase is consistent with hydroperoxidation,
supporting the erythrosin penetration into the lipid chains, which
favors singlet oxygen generation close to double bonds, an important
requirement for photodynamic efficiency