Single-Chain Bolaphospholipids

Investigation of keratolytic impact of synthetic bolalipids on skin penetration of a model hydrophilic permeant

Synthetic single-chain bolalipids (SSCBs) are novel excipients in drug delivery, with potential as stabilizers or solubilizers. However, their impact on skin barrier function has not been comprehensively studied. Therefore, two SSCBs (PC-C24-PC and PC-C32-PC) were studied in aqueous systems for their impact on penetration of a model permeant into porcine skin. Concentrations of 0.05 - 5 % w/w were tested; PC-C24-PC formulations were low-viscosity liquids while PC-C32-PC formed viscous dispersions to gels at room temperature. Formulations were compared for their ability to enhance sodium fluorescein penetration (SF, 0.1 % w/w) into skin via tape stripping. Using NIR-densitometry, the effect of SSCB formulations on corneocyte cohesion was evaluated. Data were compared with phospholipid mixture Lipoid S-75, sodium dodecyl sulfate (SDS), and polyethylene glycol 12-hydroxystearate (PEG-HS), and distilled water as negative control. Contrary to the hypothesis, both SSCBs failed to increase SF penetration into the stratum corneum, but rather showed a significant decrease in penetration depth compared to water. Both SSCBs exhibited a keratolytic effect at 5 % w/w, leading to substantial removal of proteins from the skin surface. Consequently, SSCBs may not enhance penetration of hydrophilic drugs into skin, but could be used as keratolytic agents.

Hierarchical Assembly of l-Phenylalanine-Terminated Bolaamphiphile with Porphyrin Show Tunable Nanostructures and Photocatalytic Properties

Demands related to clean energy and environmental protection promote the development of novel supramolecular assemblies for photocatalysis. Because of the distinctive aggregation behaviors, bolaamphiphiles with two hydrophilic end groups could be theoretically the right candidates for the fabrication of high-performance photocatalysis. However, photocatalytic applications based on bolaamphiphilic assemblies were still rarely investigated. Especially, the relationship between diverse assembled nanostructures and the properties for different applications is urgently needed to be studied. Herein, we demonstrate that using the hierarchical assembly of bolaamphiphiles could correctly induce the porphyrin supramolecular architectures with much better photocatalytic performances than the aggregations containing 450 times of the porphyrin molecules, even though both molecular structures as well as the J-aggregations of porphyrin building blocks are same in two different systems. Thus, the co-assembly of l-phenylalanine terminated bolaamphiphile (Bola-F) and the porphyrin containing four hydroxyl groups (tetrakis-5,10,15,20-(4-hydroxyphenyl)porphyrin) can form microtube in methanol and forms fibers/spheres in methanol/water mixture. For catalyzing the photodegradation of rhodamine B, the small amount of J-aggregated porphyrin within Bola-F microtubes show much better photocatalytic performance comparing with that of huge porphyrin J-aggregations in fibers/spheres. The supramolecular assemblies as well as the photocatalysis were thoroughly characterized by different spectroscopies and electron microscopy. It is demonstrated that the co-assembly with bolaamphiphiles could inhibit the energy transfer of porphyrin aggregation and subsequently benefit the electron transfer and corresponding photocatalysis under photo-irradiation. This work is not only useful for further understanding the hierarchically supramolecular assembly but also provides a new strategy for making novel functional supramolecular architectures based on the assembly of bolaamphiphiles and porphyrins.

Room temperature chiral reorganization of interfacial assembly of achiral double-decker phthalocyanine

Chiral reorganization with amplification of the Cotton effect is achieved at room temperature and atmospheric pressure in the solid-state.

(Cryo)Transmission Electron Microscopy of Phospholipid Model Membranes Interacting with Amphiphilic and Polyphilic Molecules

Lipid membranes can incorporate amphiphilic or polyphilic molecules leading to specific functionalities and to adaptable properties of the lipid bilayer host. The insertion of guest molecules into membranes frequently induces changes in the shape of the lipid matrix that can be visualized by transmission electron microscopy (TEM) techniques. Here, we review the use of stained and vitrified specimens in (cryo)TEM to characterize the morphology of amphiphilic and polyphilic molecules upon insertion into phospholipid model membranes. Special emphasis is placed on the impact of novel synthetic amphiphilic and polyphilic bolalipids and polymers on membrane integrity and shape stability.

The cmc-value of a bolalipid with two phosphocholine headgroups and a C24 alkyl chain: Unusual binding properties of fluorescence probes to bolalipid aggregates

Bolalipids with a long alkyl chain and two phosphocholine polar groups self-assemble in water into two different types of aggregate structures, namely helical nanofibers at low temperature and two types of micellar aggregates at higher temperature. We tried to determine the critical aggregation concentration (cac) or critical micellar concentration (cmc) of the bolalipid tetracosane-1,24-bis(phosphocholine) (PC-C24-PC) by using different fluorescent probes. The use of pyrene or pyrene derivatives as fluorophores failed, whereas the probes 1,8-ANS and particularly bis-ANS gave consistent results. The structure of the bolalipid aggregates obviously hinders partitioning or binding of pyrene derivatives into the micellar interior, whereas 1,8-ANS and bis-ANS can bind to the surface of the aggregate structures. The observed large increase in fluorescence intensity of bis-ANS indicates that binding to the hydrophobic surface of the aggregates leads to a reduction of the dye mobility. However, binding of bis-ANS is relatively weak, so that the determination of a cac/cmc-value is difficult. Simulations of the intensity curves for PC-C24-PC lead to estimates of the cac/cmc-value of 0.3-1.0×10^-6M, depending on the structure of the aggregates. Single molecule fluorescence correlation spectroscopy was used to determine the mobility of bis-ANS as a function of concentration of PC-C24-PC. The dye diffusion time and the molecular brightness are lower at low bolalipid concentration, when only free dye is present, and increase at higher concentration when bis-ANS is bound to the aggregates. The experimental cac/cmc-values are higher than those estimated, using an incremental method for the change in Gibbs free energy for micellization with n-alkyl-phosphocholines with only one polar group as a comparison. Apparently, for PC-C24-PC in micellar or fibrous aggregates, more CH₂ groups are exposed to water than in a conventional micelle of an n-alkyl-phosphocholine.

Carbamate-Based Bolaamphiphile as Low-Molecular-Weight Hydrogelators

A new bolaamphiphile analog featuring carbamate moieties was synthesized in six steps starting from thymidine. The amphiphile structure exhibits nucleoside-sugar polar heads attached to a hydrophobic spacer via carbamate (urethane) functions. This molecular structure, which possesses additional H-bonding capabilities, induces the stabilization of low-molecular-weight gels (LMWGs) in water. The rheological studies revealed that the new bolaamphiphile 7 stabilizes thixotropic hydrogels with a high elastic modulus (G′ > 50 kPa).

Control of stem-cell behavior by fine tuning the supramolecular assemblies of low-molecular-weight gelators

Controlling the behavior of stem cells through the supramolecular architecture of the extracellular matrix remains an important challenge in the culture of stem cells. Herein, we report on a new generation of low-molecular-weight gelators (LMWG) for the culture of isolated stem cells. The bola-amphiphile structures derived from nucleolipids feature unique rheological and biological properties suitable for tissue engineering applications. The bola-amphiphile-based hydrogel scaffold exhibits the following essential properties: it is nontoxic, easy to handle, injectable, and features a biocompatible rheology. The reported glycosyl-nucleoside bola-amphiphiles (GNBA) are the first examples of LMWG that allow the culture of isolated stem cells in a gel matrix. The results (TEM observations and rheology) suggest that the supramolecular organizations of the matrix play a role in the behavior of stem cells in 3D environments.

Self-assembly of different single-chain bolaphospholipids and their miscibility with phospholipids or classical amphiphiles

A variety of bolalipids with a single long alkyl chain and two identical headgroups self-assemble in aqueous solutions into helical entangled nanofibers leading to the formation of a hydrogel. An increase in temperature usually leads to the break-up of the fiber structure into micellar aggregates. In this paper the question is addressed whether bolalipids of different lengths or different headgroup structures can form mixed fibers. Also, the stability of the fiber aggregation of bolalipids in mixtures with phospholipids forming lamellar bilayers is discussed. Here, the question whether single-chain bolalipids can be incorporated into phospholipid bilayers to stabilize bilayer membranes is important, as possibly lipid vesicles used for drug delivery can be improved. Finally, the stability of the fiber aggregate against solubilisation by common surfactants was studied. The paper addresses the question which type of aggregate structure dominates the self-assembly of bipolar and monopolar amphiphiles in aqueous suspension.

Collapsed bipolar glycolipids at the air/water interface: effect of the stereochemistry on the stretched/bent conformations

This article describes a comparative study of several bipolar lipids derived from tetraether structures. The sole structural difference between the main two glycolipids is a unique stereochemical variation on a cyclopentyl ring placed in the middle of the lipids. We discuss the comparative results obtained at the air/water interface on the basis of tensiometry and ellipsometry. Langmuir-Blodgett depositions during lipid film compressions and decompressions were also analyzed by AFM. The lactosylated tetraether (bipolar) lipid structures involved the formation of highly stable multilayers, which are still present at 10 mN m(-1) during decompression. This study suggests also that the stereochemistry of a central cyclopentyl ring dramatically drives the conformation of the corresponding bipolar lipids. Both isomers (trans and cis) adopt a U-shaped (bent) conformation at the air/water interface but the trans cyclopentyl ring induces a much more frustration within this type of conformation. Consequently, this bipolar lipid (trans-tetraether) undergoes a flip of one polar head-group (lactosyl) leading to a stretched conformation during collapse.

Tuning the aggregation behaviour of single-chain bolaamphiphiles in aqueous suspension by changes in headgroup asymmetry

The self-assembly process in aqueous suspension of two new asymmetrical single-chain bolaamphiphiles, namely 32-{[hydroxy(2-hydroxyethoxy)phosphinyl]oxy}dotriacontane-1-yl-{2-[N-(3-dimethylaminopropyl)-N,N-dimethylammonio]ethylphosphate} (DMAPPC-C32-POH) and 32-hydroxydotriacontane-1-yl-{2-[N-(3-dimethylaminopropyl)-N,N-dimethylammonio]ethylphosphate} (DMAPPC-C32-OH), was studied as a function of temperature using transmission electron microscopy, differential scanning calorimetry, FT-IR-spectroscopy, small angle neutron and small angle X-ray scattering to determine whether the asymmetry of the molecule induces the formation of types of aggregates other than the well characterized helical nanofibres of structurally similar symmetrical single-chain bolaamphiphiles with identical headgroups. DMAPPC-C32-POH in acetate buffer at pH 5 can still form nanofibres, i.e. the asymmetry does not induce the formation of other aggregate structures. However, the fibres display a tendency to break more easily and to form irregular, circular structures. This is also reflected by the rheological properties of the suspension that reveal decreased strain resistance at pH 5. In aqueous suspensions at pH 10, where the headgroups of the molecule are negatively charged, only short fibre segments are formed and no gel formation occurs. At higher temperature these fibres convert into micellar aggregates as observed before for symmetrical bolalipids with large headgroups. In contrast, in aqueous suspensions of DMAPPC-C32-OH, a bolalipid where the size difference of the headgroups is much larger, lamellar structures are formed at pH 10 where the headgroup of the molecule is zwitterionic. At low temperature, the molecules are packed in an orthorhombic lattice with interdigitated chains and a repeat distance between lamellae of 6.2 nm is observed. An increase in temperature leads to a lamellar phase with hexagonal packing of the chains. The chains become liquid-crystalline only at very high temperature above 90 °C. At low pH, when the headgroup of the molecule becomes positively charged, some short elongated micellar aggregates are seen besides sheet-like structures. A temperature increase leads to a similar sequence of transformations of the chain packing until formation of a liquid-crystalline lamellar phase at a temperature close to 90 °C. The results show that the aggregation behaviour of single-chain bolaamphiphiles can not only be tuned by changes in chain length or size of both headgroups but also by the difference in headgroup size and charge in asymmetric bolaamphiphiles.