14 research outputs found
Monolayer Properties of 1,3-Diamidophospholipids
While nature provides an endless
variety of phospholipids presenting
hydrolyzable ester linkages for the 1,2-positioned hydrocarbon tails,
we designed and synthesized 1,3-diamidophospholipids which contain
stable fatty acid amides. These new phospholipids form faceted unilamellar
vesicles with mechanosensitive properties. Aiming to understand the
mechanism responsible for this behavior at a molecular level, we investigated
the 1,3-diamidophospholipid family in monolayers, a simplified model
membrane system. Langmuir isotherms combined with <i>in situ</i> grazing incidence X-ray diffraction (GIXD), specular X-ray reflectivity
(XR), and infrared reflectionâabsorption spectroscopy (IRRAS)
allowed the characterization of the monolayers from a structural and
thermodynamical point of view. The existence of strong headgroup interactions
due to the formation of a hydrogen-bonding network was clearly revealed
by IRRAS and by the high rigidity of the monolayers. GIXD showed that
only the longer chain compounds of the series (Pad-PC-Pad (1,3-dipalmitamidopropan-2-phosphocholine)
and Sad-PC-Sad (1,3-distearamidopropan-2-phosphocholine) were able
to form ordered monolayers. The chains are strongly tilted in a rigid
lattice formed due to these hydrogen-bonding interactions between
the headgroups. The thermodynamical analysis leads to a critical temperature
of the monolayer which is clearly different from the main phase transition
temperature in bulk, indicating that there must be a different structural
arrangement of the 1,3-diamidophospholipids in monolayers and in bilayers
Interaction of DNA with Cationic Lipid Mixturesî¸Investigation at Langmuir Lipid Monolayers
Four
different binary lipid mixtures composed of a cationic lipid
and the zwitterionic colipids DOPE or DPPC, which show different DNA
transfer activities in cell culture models, were investigated at the
soft air/water interface to identify transfection efficiency determining
characteristics. Langmuir films are useful models to investigate the
interaction between DNA and lipid mixtures in a two-dimensional model
system by using different surface sensitive techniques, namely, epifluorescence
microscopy and infrared reflectionâabsorption spectroscopy.
Especially, the effect of adsorbed DNA on the properties of the lipid
mixtures has been examined. Distinct differences between the lipid
composites were found which are caused by the different colipids of
the mixtures. DOPE containing lipid mixtures form fluid monolayers
with a uniform distribution of the fluorescent probe in the presence
and absence of DNA at physiologically relevant surface pressures.
Only at high nonphysiological pressures, the lipid monolayer collapses
and phase separation was observed if DNA was present in the subphase.
In contrast, DPPC containing lipid mixtures show domains in the liquid
condensed phase state in the presence and absence of DNA in the subphase.
The adsorption of DNA at the positively charged mixed lipid monolayer
induces phase separation which is expressed in the morphology and
the point of appearance of these domains
The Complete Phase Diagram of Monolayers of Enantiomeric <i>N</i>âStearoyl-threonine Mixtures with Preferred Heterochiral Interactions
Langmuir monolayers
of chiral amphiphiles are well-controlled model
systems for the investigation of phenomena related to stereochemistry.
Here, we have investigated mixed monolayers of one pair of enantiomers
(l and d) of the amino-acid-based amphiphile N-stearoyl-threonine. The monolayer characteristics were
studied by pressureâarea isotherm measurements and grazing
incidence X-ray diffraction (GIXD) over a wide range of mixing ratios
defined by the d-enantiomer mole fraction xD. While the isotherms provide insights into thermodynamical
aspects, such as transition pressure, compression/decompression hysteresis,
and preferential homo- and heterochiral interactions, GIXD reveals
the molecular structural arrangements on the Ă
ngstroĚm
scale. Dominant heterochiral interactions in the racemic mixture lead
to compound formation and the appearance of a nonchiral rectangular
lattice, although the pure enantiomers form a chiral oblique lattice.
Miscibility was found to be limited to mixtures with 0.27 ⲠxD Ⲡ0.73, as well as to both outer edges
(xD Ⲡ0.08 and xD Ⳡ0.92). Beyond this range, coexistence of oblique
and rectangular lattices occurs, as is clearly seen in the GIXD patterns.
Based on the results, a complete phase diagram with two eutectic points
at xD â 0.25 and xD â 0.75 is proposed. Moreover, N-stearoyl-threonine was found to have a strong tendency to form a
hydrogen-bonding network between the headgroups, which promotes superlattice
formation
CaCO<sub>3</sub> Mineralization under β-Sheet Forming Peptide Monolayers
In biominerals, proteins are key elements in the controlled
nucleation
and growth of the mineral phase. We report here on the coupled evolution
of the organic and inorganic structures during the nucleation and
growth of CaCO<sub>3</sub> under a monolayer of acidic β-sheet
forming peptides that mimic the natural proteins found in nacre. The
investigation is carried out using in situ analytical techniques (X-ray
diffraction and IR spectroscopy) to provide molecular scale structural
information over the whole course of the mineralization process. Mineralization
is shown to coexist with β-sheet order while inducing other
conformational changes to the peptide assembly. Peptides promote the
growth of unoriented vaterite crystals; no templating effect of the
β-sheet order is observed
Polyoxometalate Surfactants as Unique Molecules for Interfacial Self-Assembly
Whereas, commonly, Langmuir monolayers are structurally
dominated
by the aliphatic chains, we present here the first case of monolayers
where the chains merely serve anchoring at the air/water interface
and the organization is dictated by the hydrophilic head group self-assembling
in a hexagonal lattice. These head groups are polyoxometalates known
for their multifunctional potential. The chain length has been systematically
varied, allowing for a general study of the impact of the chain length
on the supramolecular structure. These model structures are studied
here by a combination of modern techniques, the leading ones being
X-ray reflectivity and grazing incidence X-ray diffraction. The quantitative
structural insights offered in this Letter might represent a starting
point for the rational design and study of a new class of emulsions,
including an organic tail and a multifunctional inorganic polar head
Investigation of Binary Lipid Mixtures of a Three-Chain Cationic Lipid with Phospholipids Suitable for Gene Delivery
In the present work, we characterize
binary lipid mixtures consisting
of a three-chain amino-functionalized cationic lipid (DiTT4) with
different phospholipids, namely, 1,2-dioleoyl-<i>sn</i>-glycero-3-phosphoethanolamine
(DOPE), 1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphoethanolamine
(DMPE), or 1,2-dimyristoyl-<i>sn</i>-glycero-3-phosphocholine
(DMPC). The mixing behavior was investigated by differential scanning
calorimetry (DSC). Additionally, aqueous dispersions of the binary
mixtures were characterized by means of dynamic light scattering (DLS),
laser Doppler electrophoresis, and transmission electron microscopy
(TEM) to get further information about particle size, charge, and
shape. The complex formation between different binary lipid mixtures
and plasmid DNA (pDNA) was investigated by zeta-(Îś)-potential
(laser Doppler electrophoresis) and DLS measurements, and the lipid/DNA
complexes (lipoplexes) were screened for efficient DNA transfer (transfection)
in cell culture. Finally, efficient lipid compositions were investigated
with respect to serum stability. This work provides a detailed characterization
of the cationic lipid mixtures as foundation for further research.
Efficient gene transfer in the presence of serum was demonstrated
for selected lipoplexes showing their capability to be used as high-potency
gene delivery vehicles
Versatility of a Glycosylphosphatidylinositol Fragment in Forming Highly Ordered Polymorphs
Glycosylphosphatidylinositols (GPIs)
are often attributed with
the ability to associate with the organized membrane microdomains.
GPI fragment <b>1</b> forms a highly ordered subgel-phase structure
characterized by ordering of both headgroups and alkyl chains in thin
layers. While investigating the driving forces behind the formation
of these ordered monolayers, we have studied polymorphism of <b>1</b> under different conditions employing surface-sensitive X-ray
diffraction methods. Three distinct polymorphs of <b>1</b> (<b>I</b>, <b>II</b>, and <b>III</b>) were identified
and characterized by grazing incidence X-ray diffraction. Polymorphs <b>II</b> (a condensed monolayer structure) and <b>III</b> (highly
ordered subgel phase) coexist on an 8 M urea solution subphase allowing
for a detailed thermodynamic and kinetic analysis of the processes
leading to the formation of these polymorphs. They are enantiotropic
and can be directly interconverted by changes in temperature or lateral
surface pressure. As a consequence, polymorph <b>III</b> nuclei
of critical size (or larger) could be formed by density fluctuations
in a multicomponent system, and they could continue to exist for a
period of time even under conditions that would normally not allow
for the nucleation of polymorph <b>III</b>. The processes described
here could also lead to the formation of patches of highly ordered
structures in a disordered environment of a cell membrane suggesting
that GPIs may play a role in the formation of such domains
Synthesis and Biophysical Characterization of an Odd-Numbered 1,3-Diamidophospholipid
Nanomedicine
suffers from low drug delivery efficiencies. Mechanoresponsive
vesicles could provide an alternative way to release active compounds
triggered by the basic physics of the human body. 1,3-Diamidophospholipids
with C16 tails proved to be an effective building block for mechanoresponsive
vesicles, but their low main phase transition temperature prevents
an effective application in humans. As the main phase transition temperature
of a membrane depends on the fatty acyl chain length, we synthesized
a C17 homologue of a 1,3-diamidophospholipid: Rad-PC-Rad. The elevated
main phase transition temperature of Rad-PC-Rad allows mechanoresponsive
drug delivery at body temperature. Herein, we report the biophysical
properties of Rad-PC-Rad monolayer and bilayer membranes. Rad-PC-Rad
is an ideal candidate for advancing the concept of physically triggered
drug release
Langmuir Monolayers of an Inclusion Complex Formed by a New Calixarene Derivative and Fullerene
The design of new molecules with directed interactions
to functional
molecules as complementary building blocks is one of the main goals
of supramolecular chemistry. A new <i>p-tert</i>-butylcalixÂ[6]Âarene
monosubstituted derivative bearing only one alkyl chain with an acid
group (C6A3C) has been synthesized. The C6A3C has been successfully
used for building Langmuir monolayers at the airâwater interface.
The C6A3C molecule adopts a flatlike orientation with respect to the
airâwater interface. The molecular structure gives the molecule
amphiphilic character, while allowing the control of both the dissociation
degree and the molecular conformation at the airâwater interface.
The C63AC has been combined with pristine fullerene (C60) to form
the supramolecular complex C6A3C:C60 in 2:1 molar ratio (CFC). The
CFC complex retains the ability of C6A3C to form Langmuir monolayers
at the air/water interface. The interfacial molecular arrangement
of the CFC complex has been convincingly described by in situ UVâvis
reflection spectroscopy and synchrotron X-ray reflectivity measurements.
Computer simulations complement the experimental data, confirming
a perpendicular orientation of the calixarene units of CFC with respect
to the airâwater interface. This orientation is stabilized
by the formation of intermolecular H-bonds. The interfacial monolayer
of the CFC supramolecular complex is proposed as a useful model for
the well-defined self-assembly of recognition and functional building
blocks
Phase Behavior and Molecular Packing of Octadecyl Phenols and their Methyl Ethers at the Air/Water Interface
Noncovalent
molecular interactions, such as hydrogen bonding and
van der Waals forces, play an important role in self-assembling to
supramolecular structures. To study these forces, we chose monolayers
at the air/water interface to limit the possible arrangements of the
interacting molecules. Furthermore, monolayers provide useful tools
to understand and study interactions between molecules in a controlled
and fundamental way. The phase behavior and molecular packing of the
phenols 1-(4-hydroxyphenyl)-octadecane (<b>5a</b>), 1-(3,4-dihydroxyphenyl)-octadecane
(<b>6</b>), and 1-(2,3,4-trihydroxyphenyl)-octadecane (<b>3</b>) and their methyl ethers in monolayers at the air/water
interface have been examined by Ď/A isotherms, Brewster angle
microscopy (BAM), grazing incidence X-ray diffraction (GIXD) measurements,
and density functional theory (DFT) calculations. The phenols are
synthesized by FriedelâCrafts acylation of methoxybenzenes,
hydrogenation of the resulting aryl ketones, and cleavage of the aryl
methyl ethers. In the Ď/<i>A</i> isotherms and in
BAM, the phenols show patches of the solid condensed phase at large
molecular areas and the monolayers collapse at high pressures. Furthermore,
the dimensions of the unit cell obtained by GIXD measurements are
compatible with an arrangement of the phenyl rings that allows one
aryl ring to interact with four adjacent phenyl rings in an edge-to-face
arrangement, which leads to a significant binding energy. The experimental
data are in good agreement with DFT calculations of 2D crystalline
benzene and <i>p</i>-cresol arrangements. The enhanced monolayer
stability of phenol <b>5a</b> can be explained by hydrogen bonds
of the hydroxyl group with water and van der Waals forces between
the alkyl chains and arylâaryl interactions