Topological Dynamics of Micelles Formed by Geometrically Varied Surfactants.

The molecular architecture of sugar-based surfactants strongly affects their self-assembled structure, i.e., the type of micelles they form, which in turn controls both the dynamics and rheological properties of the system. Here, we report the segmental and mesoscopic structure and dynamics of a series of C16 maltosides with differences in the anomeric configuration and degree of tail unsaturation. Neutron spin-echo measurements showed that the segmental dynamics can be modeled as a one-dimensional array of segments where the dynamics increase with inefficient monomer packing. The network dynamics as characterized by dynamic light scattering show different relaxation modes that can be associated with the micelle structure. Hindered dynamics are observed for arrested networks of worm-like micelles, connected to their shear-thinning rheology, while nonentangled diffusing rods relate to Newtonian rheological behavior. While the design of novel surfactants with controlled properties poses a challenge for synthetic chemistry, we demonstrate how simple variations in the monomer structure can significantly influence the behavior of surfactants.

Complex by design: Hydrotrope-induced micellar growth in deep eutectic solvents.

HYPOTHESIS: The self-assembly of ionic surfactants in deep eutectic solvents has recently been demonstrated, opening up new possibilities in terms of the development of formulated products and templating of nanostructured materials. As it occurs in an aqueous environment, the solvophobic effect drives the formation of micelles in these solvents and specific-ion interactions alter the resulting structures. We hypothesized that the presence of hydrotropic salts would greatly affect the micellar structure in deep eutectic solvents, ultimately leading to the formation of worm-like aggregates. EXPERIMENTS: A systematic investigation performed on hydrotrope-surfactant assemblies in neat and hydrated 1:2 choline chloride:glycerol is presented. The effect of choline salicylate on the micellization of hexadecyltrimethylammonium chloride at different hydrotrope-to-surfactant ratios was probed by contrast variation small-angle neutron scattering. FINDINGS: Here the first investigation on salt-induced micellar growth in deep eutectic solvents is presented. The microscopic characterization of the system shows that the micelle-hydrotrope interaction in pure and hydrated deep eutectic solvents results in a significant increase in micelle elongation. The condensation of the hydrotrope on the micelle, which alters the effective monomer packing, leads to the formation of worm-like micelles with tunable morphology and flexibility. The results presented here present new possibilities in terms of self-assembly and co-assembly in neoteric solvents, where micelle morphology can be controlled through surfactant-salt interactions.

Molecular structure of maltoside surfactants controls micelle formation and rheological behavior.

HYPOTHESIS: The anomeric configuration (α or ß) of n-hexadecyl-d-maltopyranoside (C16G2) has been shown to affect the morphology of the micelle, from elongated for α-C16G2 to worm-like micelles for ß-C16G2. The entanglement of worm-like micelles often leads to strong modifications of the rheological behavior of the system and, as such, the anomeric configuration of C16G2 could also provide the possibility of controlling this. Furthermore, mixing these surfactants are hypothesized to result in mixed micelles allowing to finely tune the rheology of a system containing these sustainable surfactants. EXPERIMENTS: The rheology of α- and ß-C16G2, and mixtures of those, was determined by rotational and oscillatory rheology at different temperatures and surfactant concentrations. Micelle structure and composition for these systems were characterized using contrast variation small-angle neutron scattering and small-angle X-ray scattering. The results from these were connected in order to elaborate a molecular understanding of the rheological response of the system. FINDINGS: The self-assembly of these surfactants have been found to result in different rheological properties. ß-C16G2 show a high viscosity with a non-Newtonian viscoelastic behavior, which was linked to the formation of worm-like micelles. In contrast, α-C16G2 self-assembled into short cylindrical micelles, resulting in a Newtonian fluid with low viscosity. Furthermore, mixtures of these two surfactants lead to systems with intermediate rheological properties as a result of the formation of micelles with intermediate morphology to those of the pure anomers. These results also show that the rheological properties of the system can be tuned to change the micelle morphology, which in turn depends on the anomeric configuration of the surfactant. Also, surfactant concentration, temperature of the system, and micelle composition for surfactant mixtures provide control over the rheological properties of the system in a wide temperature range. Therefore, these results open new possibilities in the development of sustainable excipients for formulation technology, where the characteristics of the system can be easily tailored through geometric variations in the monomer structure whilst maintaining the chemical composition of the system.

Tail unsaturation tailors the thermodynamics and rheology of a self-assembled sugar-based surfactant.

HYPOTHESIS: The self-assembly of long-tail surfactants results in the formation of nanoscale structures, e.g. worm-like micelles, with the ability to modify the rheology of the system. However, micelle formation, and thus the alteration of the rheology, is subject to the high Krafft temperature of saturated long-tail surfactants. Hexadecylmaltosides are sustainable surfactants that, in solution, form tailorable viscoelastic fluids. The preparation of monounsaturated sugar-based surfactants is hypothesised to reduce the Krafft point compared to the saturated analogues, therefore increasing the temperature range where the surfactant remains in the micellar form. EXPERIMENTS: Here we report the synthesis and characterisation of a novel sugar-based surfactant with an unsaturated C16-tail, namely palmitoleyl-ß-d-maltoside (ß-C16-1G2). Differential scanning calorimetry was used to probe the temperature stability of the system. The rheology of ß-C16-1G2 solutions was investigated by means of rotational and oscillatory rheology, and these results were connected to the mesoscopic structure of the system as shown by small-angle neutron and X-ray scattering, and dynamic light scattering. FINDINGS: The presence of a double bond on the alkyl chain moiety leads to a depression in the Krafft point, allowing the surfactant to form a thermodynamically stable micellar solution over a wide range of temperatures, i.e. 5-95 °C. The surfactant self-assembles into worm-like micelles which, upon entanglement in the semi-dilute regime, result in the formation of a non-Newtonian, viscoelastic fluid. These observations have important implications in the development of new sustainable formulated products, enabling the preparation of surfactant phases with remarkable thermal resilience.

Enzyme-Assisted Synthesis of High-Purity, Chain-Deuterated 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine.

1-Palmitoyl-d 31-2-oleoyl-d 32-sn-glycero-3-phosphocholine (POPC-d 63) with the palmitoyl and oleoyl chains deuterium-labeled was produced in three steps from 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine, deuterated palmitic acid, and deuterated oleic anhydride. Esterification at the sn-2 position was achieved under standard chemical conditions, using DMAP to catalyze the reaction between the 2-lysolipid and oleic anhydride-d 64. Complete regioselective sn-1 acyl substitution was achieved in two steps using operationally simple, enzyme-catalyzed regioselective hydrolysis and esterification to substitute the sn-1 chain for a perdeuterated analogue. This method provides chain-deuterated POPC with high chemical purity (>96%) and complete regiopurity, useful for a variety of experimental techniques. This chemoenzymatic semisynthetic approach is a general, modular method of producing highly pure, mixed-acyl phospholipids, where the advantages of both chemical synthesis (efficiency, high yields) and biocatalytic synthesis (specificity, nontoxicity) are realized.

Perdeuterated Conjugated Polymers for Ultralow-Frequency Magnetic Resonance of OLEDs.

The formation of excitons in OLEDs is spin dependent and can be controlled by electron-paramagnetic resonance, affecting device resistance and electroluminescence yield. We explore electrically detected magnetic resonance in the regime of very low magnetic fields (<1 mT). A pronounced feature emerges at zero field in addition to the conventional spin- 1 / 2 Zeeman resonance for which the Larmor frequency matches that of the incident radiation. By comparing a conventional π-conjugated polymer as the active material to a perdeuterated analogue, we demonstrate the interplay between the zero-field feature and local hyperfine fields. The zero-field peak results from a quasistatic magnetic-field effect of the RF radiation for periods comparable to the carrier-pair lifetime. Zeeman resonances are resolved down to 3.2 MHz, approximately twice the Larmor frequency of an electron in Earth's field. However, since reducing hyperfine fields sharpens the Zeeman peak at the cost of an increased zero-field peak, we suggest that this result may constitute a fundamental low-field limit of magnetic resonance in carrier-pair-based systems. OLEDs offer an alternative solid-state platform to investigate the radical-pair mechanism of magnetic-field effects in photochemical reactions, allowing models of biological magnetoreception to be tested by measuring spin decoherence directly in the time domain by pulsed experiments.

An integrative toolbox to unlock the structure and dynamics of protein-surfactant complexes.

The interactions between protein and surfactants play an important role in the stability and performance of formulated products. Due to the high complexity of such interactions, multi-technique approaches are required to study these systems. Here, an integrative approach is used to investigate the various interactions in a model system composed of human growth hormone and sodium dodecyl sulfate. Contrast variation small-angle neutron scattering was used to obtain information on the structure of the protein, surfactant aggregates and surfactant-protein complexes. 1H and 1H-13C HSQC nuclear magnetic resonance spectroscopy was employed to probe the local structure and dynamics of specific amino acids upon surfactant addition. Through the combination of these advanced methods with fluorescence spectroscopy, circular dichroism and isothermal titration calorimetry, it was possible to identify the interaction mechanisms between the surfactant and the protein in the pre- and post-micellar regimes, and interconnect the results from different techniques. As such, the protein was revealed to evolve from a partially unfolded conformation at low SDS concentration to a molten globule at intermediate concentrations, where the protein conformation and local dynamics of hydrophobic amino acids are partially affected compared to the native state. At higher surfactant concentrations the local structure of the protein appears disrupted, and a decorated micelle structure is observed, where the protein is wrapped around a surfactant assembly. Importantly, this integrative approach allows for the identification of the characteristic fingerprints of complex transitions as seen by each technique, and establishes a methodology for an in-detail study of surfactant-protein systems.

Protein-Eye View of the in Meso Crystallization Mechanism.

For evolving biological and biomedical applications of hybrid protein?lipid materials, understanding the behavior of the protein within the lipid mesophase is crucial. After more than two decades since the invention of the in meso crystallization method, a protein-eye view of its mechanism is still lacking. Numerous structural studies have suggested that integral membrane proteins preferentially partition at localized flat points on the bilayer surface of the cubic phase with crystal growth occurring from a local fluid lamellar L? phase conduit. However, studies to date have, by necessity, focused on structural transitions occurring in the lipid mesophase. Here, we demonstrate using small-angle neutron scattering that the lipid bilayer of monoolein (the most commonly used lipid for in meso crystallization) can be contrast-matched using deuteration, allowing us to isolate scattering from encapsulated peptides during the crystal growth process for the first time. During in meso crystallization, a clear decrease in form factor scattering intensity of the peptides was observed and directly correlated with crystal growth. A transient fluid lamellar L? phase was observed, providing direct evidence for the proposed mechanism for this technique. This suggests that the peptide passes through a transition from the cubic QII phase, via an L? phase to the lamellar crystalline Lc phase with similar layered spacing. When high protein loading was possible, the lamellar crystalline Lc phase of the peptide in the single crystals was observed. These findings show the mechanism of in meso crystallization for the first time from the perspective of integral membrane proteins.

Using SANS with Contrast-Matched Lipid Bicontinuous Cubic Phases To Determine the Location of Encapsulated Peptides, Proteins, and Other Biomolecules.

An understanding of the location of peptides, proteins, and other biomolecules within the bicontinuous cubic phase is crucial for understanding and evolving biological and biomedical applications of these hybrid biomolecule-lipid materials, including during in meso crystallization and drug delivery. While theoretical modeling has indicated that proteins and additive lipids might phase separate locally and adopt a preferred location in the cubic phase, this has never been experimentally confirmed. We have demonstrated that perfectly contrast-matched cubic phases in D2O can be studied using small-angle neutron scattering by mixing fully deuterated and hydrogenated lipid at an appropriate ratio. The model transmembrane peptide WALP21 showed no preferential location in the membrane of the diamond cubic phase of phytanoyl monoethanolamide and was not incorporated in the gyroid cubic phase. While deuteration had a small effect on the phase behavior of the cubic phase forming lipids, the changes did not significantly affect our results.

Synthesis of Perdeuterated 1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine ([D82 ]POPC) and Characterisation of Its Lipid Bilayer Membrane Structure by Neutron Reflectometry.

1-Palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), an unsaturated acyl chain containing lipid, is often the predominant lipid in eukaryotic cell membranes in which it is crucial for the fluidity of membranes under physiological conditions. Commercially available, partially deuterated [D31 ]1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine ([D31 ]POPC) does not provide sufficient isotopic contrast for detailed structural studies of multicomponent membranes through neutron techniques. Herein, a relatively straightforward and generic chemical deuteration method is discussed for the asymmetric synthesis of perdeuterated [D31 ]1-palmitoyl-[D33 ]2-oleoyl-sn-[D5 ]glycero-[D13 ]3-phosphocholine ([D82 ]POPC) that also allows selective deuteration of any of its constituent groups. Neutron reflectivity of a [D82 ]POPC-supported bilayer was used to experimentally determine the neutron scattering length density profile of the lipid. The acyl chains of [D82 ]POPC are closely contrast-matched to heavy water, whereas the very high scattering length density of the deuterated glycerophosphocholine head groups provides good contrast to membrane-binding agents in both deuterated and non-deuterated solvent environments.

Enantioselective total syntheses of the proposed structures of prevezol B and evaluation of anti-cancer activity.

The first enantioselective total syntheses of the proposed structures of the natural product prevezol B are reported. The reported syntheses complement the previously-reported syntheses of the proposed structures of prevezol C, a stereoisomer of prevezol B. It was previously shown that the structure of the naturally occurring prevezol C had been incorrectly assigned. This work has led us to conclude that the proposed structures of prevezol B are also incorrect and major revision of both of the structures of the prevezols B and C is required. Cytotoxicity studies on the human cervical cancer cell line HeLa revealed that the synthesized prevezol B and C compounds were not active even at the highest concentration used (100 µM). However, one of the synthetic precursors was shown to have modest potency against HeLa cells (IC50 = 23.5 ± 1.8 µM).

Synthesis of the proposed structures of Prevezol C.

The first enantioselective synthesis of the proposed relative structures of Prevezol C is reported in 11 linear steps from readily available materials. The unusual syn bromohydrin was installed via a multistep sequence culminating in a diastereoselective geminal dibromide reduction. Discrepancies in the spectral data of the synthetic materials and the natural sample have led to the conclusion that the proposed structures are incorrect.