7 research outputs found
Synthesis of Novel Asymmetrical Single-Chain Phosphoglycol-Based Bolaamphiphiles
<div><p></p><p>The synthesis of long-chain 1,ω-diols with orthogonal cleavable protecting groups can be effectively performed with the use of the Grignard coupling reaction, successfully leading to the preparation of novel <i>asymmetrical</i> single-chain phosphoglycol-based bolaamphiphiles—a side-product that always occurred during the synthesis of <i>symmetrical</i> bolalipids.</p>
<p>[Supplementary materials are available for this article. Go to the publisher's online edition of <i>Synthetic Communications</i>® for the following free supplemental resource(s): Full experimental and spectral details.]</p>
</div
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-(ζ)-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
Functionalization of Bolalipid Nanofibers by Silicification and Subsequent One-Dimensional Fixation of Gold Nanoparticles
In the present work, we describe the successful stabilization
of
bolalipid nanofibers by sol–gel condensation (silicification)
of tetraethoxysilane (TEOS) or 3-mercaptopropyltriethoxysilane (MP-TEOS),
respectively, onto the nanofibers. The conditions for an effective
and reproducible silicification reaction were determined, and the
silicification process was pursued by transmission electron microscopy
(TEM). The resulting bolalipid–silica composite nanofibers
were characterized by means of differential scanning calorimetry (DSC),
TEM, <sup>13</sup>C, and <sup>31</sup>P NMR spectroscopy. Finally,
the novel silicified bolalipid nanofibers were used as templates for
the fixation of 5 and 2 nm AuNPs, respectively, resulting in one of
the rare examples of one-dimensional AuNP arrangements in aqueous
suspension
Highly Asymmetrical Glycerol Diether Bolalipids: Synthesis and Temperature-Dependent Aggregation Behavior
In the present work, we describe
the synthesis and temperature-dependent
aggregation behavior of two examples of a new class of highly asymmetrical
glycerol diether bolaphospholipids. The bolalipids contain a long
alkyl chain (C32) bound to glycerol in the <i>sn</i>-3 position,
carrying a hydroxyl group at the ω position. The C16 alkyl chain
in the <i>sn</i>-2 position either possesses a racemic methyl
branch at the 10 position of the short alkyl chain (lipid <b>II</b>) or does not (lipid <b>I</b>). The <i>sn</i>-1 position
of the glycerol is linked to a zwitterionic phosphocholine moiety.
The temperature-dependent aggregation behavior of both bolalipids
was studied using differential scanning calorimetry (DSC), Fourier-transform
infrared (FTIR) spectroscopy, and X-ray scattering. Aggregate structures
were visualized by transmission electron microscopy (TEM). We show
that both bolalipids self-assemble into large lamellar sheetlike aggregates.
Closed lipid vesicles or other aggregate structures such as tubes
or nanofibers, as usually found for diglycerol tetraether lipids,
were not observed. Within the lamellae the bolalipid molecules are
arranged in an antiparallel (interdigitated) orientation. Lipid <b>I</b>, without an additional methyl moiety in the short alkyl
chain, shows a lamellar phase with high crystallinity up to a temperature
of 34 °C, which was not observed before for other phospholipids
New Micellar Transfection Agents
Two novel micelle-forming amino-functionalized
lipids (OT6 and
TT6) bearing two alkyl chains connected to a large positively charged
hexavalent headgroup, which might be interesting polynucleotide transferring
agents with the advantage of an easy and reproducible production of
micelle dispersions, have been characterized. The critical micelle
concentration (cmc) of both lipids has been determined by two different
methods, namely, isothermal titration calorimetry (ITC) and 1,6-diphenyl-1,3,5-hexatriene
(DPH) fluorescence experiments. In addition, the lipid dispersions
were studied as a function of temperature using differential scanning
calorimetry (DSC), dynamic light scattering (DLS), Fourier-transform
infrared (FT-IR) spectroscopy, and cryo-transmission electron microscopy
(cryo-TEM). The OT6 and TT6 micelles effectively complex DNA as determined
by ITC and DSC measurements. In addition, DLS and ζ-potential
measurements were performed to determine lipoplex formulations that
exhibit colloidal stability. Finally, the structures of OT6/DNA complexes
were investigated by means of X-ray scattering and TEM
Impact of Headgroup Asymmetry and Protonation State on the Aggregation Behavior of a New Type of Glycerol Diether Bolalipid
In
the present work, we describe the synthesis and the temperature-dependent
aggregation behavior of a new class of asymmetrical glycerol diether
bolalipids. These bolalipids are composed of a membrane-spanning alkyl
chain with 32 carbon atoms (C32) in the <i>sn</i>-3 position,
a methyl-branched C16 alkyl chain in the <i>sn</i>-2 position,
and a zwitterionic phosphocholine headgroup in the <i>sn</i>-1 position of a glycerol moiety. The long C32 alkyl chain is terminated
either by a second phosphocholine (<b>PC-Gly(2C16Me)C32-PC</b>) or by a phosphodimethylethanolamine
headgroup (<b>PC-Gly(2C16Me)C32-Me</b><sub><b>2</b></sub><b>PE</b>). The temperature- and pH-dependent aggregation behavior
of both lipids was studied using differential scanning calorimetry
(DSC), Fourier transform infrared (FTIR) spectroscopy, small-angle
X-ray scattering (SAXS), and small-angle neutron scattering (SANS)
experiments. The morphology of the formed aggregates in an aqueous
suspension was visualized by transmission electron microscopy (TEM).
We show that <b>PC-Gly(2C16Me)C32-PC</b> and <b>PC-Gly(2C16Me)C32-Me</b><sub><b>2</b></sub><b>PE</b> at pH 5 self-assemble into
large lamellar aggregates and large lipid vesicles. Within these structures,
the bolalipid molecules are probably assembled in a monolayer with
fully interdigitated chains. The lipid molecules seem to be tilted
with respect to the layer normal to ensure a dense packing of the
alkyl chains. A temperature increase leads to a transition from a
lamellar gel phase to the liquid-crystalline phase at about 28–30
°C for both bolalipids. The lamellar aggregates of <b>PC-Gly(2C16Me)C32-Me</b><sub><b>2</b></sub><b>PE</b> started to transform into
nanofibers when the pH value of the suspension was increased to above
11. At pH 12, these nanofibers were the dominant aggregates
Synthesis, Characterization, and Nanoencapsulation of Tetrathiatriarylmethyl and Tetrachlorotriarylmethyl (Trityl) Radical DerivativesA Study To Advance Their Applicability as in Vivo EPR Oxygen Sensors
Tissue oxygenation
plays an important role in the pathophysiology
of various diseases and is often a marker of prognosis and therapeutic
response. EPR (ESR) is a suitable noninvasive oximetry technique.
However, to reliably deploy soluble EPR probes as oxygen sensors in
complex biological systems, there is still a need to investigate and
improve their specificity, sensitivity, and stability. We reproducibly
synthesized various derivatives of tetrathiatriarylmethyl and tetrachlorotriarylmethyl
(trityl) radicals. Hydrophilic radicals were investigated in aqueous
solution mimicking physiological conditions by, e.g., variation of
viscosity and ionic strength. Their specificity was satisfactory,
but the oxygen sensitivity was low. To enhance the capability of trityl
radicals as oxygen sensors, encapsulation into oily core nanocapsules
was performed. Thus, different lipophilic triesters were prepared
and characterized in oily solution employing oils typically used in
drug formulations, i.e., middle-chain triglycerides and isopropyl
myristate. Our screening identified the deuterated ethyl ester of
D-TAM (radical <b>13</b>) to be suitable. It had an extremely
narrow single EPR line under anoxic conditions and excellent oxygen
sensitivity. After encapsulation, it retained its oxygen responsiveness
and was protected against reduction by ascorbic acid. These biocompatible
and highly sensitive nanosensors offer great potential for future
EPR oximetry applications in preclinical research