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, ¹³C, and ³¹P 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>_<b>2</b><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>_<b>2</b><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>_<b>2</b><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 DerivativesA 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