Micellar Membrane Research Articles

Self-immolation Assisted Morphology Transformation of Prebiotic Lipidated-cationic Amino Acids: Electro-droplet Mediated C-C Coupling Reaction to Synthesize Macromolecules.

Compartmentalization protected biomolecules from the fluctuating environments of early Earth. Although contemporary cells mostly use phospholipid-based bilayer membranes, the utility of non-bilayer compartments was not ruled out during the prebiotic and modern eras. In the present study, we demonstrated the prebiotic synthesis of lipidated cationic amino acid-based amphiphiles [lauryl ester of lysine (LysL); ornithine (OrnL); and 2,4-diamino butyric acid (DabL)] using model dry-down reaction. These amphiphiles self-assemble into micellar membranes. However, the OrnL and DabL-based micelles undergo pH-responsive transformation to lipid droplet-like morphologies, a modelcompartment in the prebiotic Earth. These cationic droplets encapsulated prebiotic molecules (isoprene) and assisted electron transfer reaction to synthesize isoprenoid derivatives at primitive Earth conditions. The self-assembly of prebiotic amphiphiles, their transformation to droplet compartments, and droplet-assisted C-C bond formation reaction might have helped the evolution to synthesize various biomolecules required for the origin of life.

Cover Feature: Precise Proton Mapping near Ionic Micellar Membranes with Fluorescent Photoinduced‐Electron‐Transfer Sensors (Chem. Eur. J. 36/2019)

Cover Feature: Precise Proton Mapping near Ionic Micellar Membranes with Fluorescent Photoinduced‐Electron‐Transfer Sensors (Chem. Eur. J. 36/2019)

Precise Proton Mapping near Ionic Micellar Membranes with Fluorescent Photoinduced-Electron-Transfer Sensors.

One of the challenges for fluorescent sensors is to reduce their target environment size from a micrometer scale, such as biological cells, to a nanometer scale. Proton maps near membranes are of importance in bioenergetics and are the first goal in nanometer-scale analysis with fluorescent sensors. Thirty-three fluorescent photoinduced-electron-transfer pH sensors bearing an environment-sensitive benzofurazan fluorophore and having different hydrophobicity/hydrophilicity and hydrogen-bonding abilities were prepared. These sensors were scattered in nanospaces associated with anionic and cationic micelles as model membranes to indicate proton availability and polarity in local spaces. Gathering the data from the sensors allowed the successful drawing of proton maps near anionic and cationic micelles, in which electrostatic attraction/repulsion of protons by the charged head groups of micelles and dielectric suppression of protons were clearly observed.

Diselenolane‐Mediated Cellular Uptake: Efficient Cytosolic Delivery of Probes, Peptides, Proteins, Artificial Metalloenzymes and Protein‐Coated Quantum Dots

Cyclic oligochalcogenides are emerging as powerful tools to penetrate cells. With disulfide ring tension maximized, selenium chemistry had to be explored next to enhance speed and selectivity of dynamic covalent exchange on the way into the cytosol. We show that diseleno lipoic acid (DiSeL) delivers a variety of relevant substrates. DiSeL-driven uptake of artificial metalloenzymes enables bioorthogonal fluorophore uncaging within cells. Binding of a bicyclic peptide, phalloidin, to actin fibers evinces targeted delivery to the cytosol. Automated tracking of diffusive compared to directed motility and immobility localizes 79 % of protein-coated quantum dots (QDs) in the cytosol, with little endosomal capture (0.06 %). These results suggest that diselenolanes might act as molecular walkers along disulfide tracks in locally denatured membrane proteins, surrounded by adaptive micellar membrane defects. Miniscule and versatile, DiSeL tags are also readily available, stable, soluble, and non-toxic.

Symmetrical Permeable Membranes Consisting of Overlapped Block Copolymer Cylindrical Micelles for Nanoparticle Size Fractionation

Free-standing symmetrical porous membranes consisting of uniform cylindrical micelles were prepared from a polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer following a process combining self-assembly and nonsolvent-induced phase separation (SNIPS). The fabricated membranes displayed an impressive ultrastructure by the overlapping of the cylindrical micelles throughout the whole membrane profile (∼65 μm). The effects of copolymer molecular weight and membrane-formation condition on membrane morphology were investigated and discussed in detail. It was concluded that the cylindrical micellar membranes could be obtained in a wide window of fabrication conditions as low molecular weight of PS-b-P4VP was used as the raw material. The permeation tests indicated that the water permeability of the symmetrical membranes reached 400 L/(h m2 bar) in neutral condition, which was comparable to that of the block copolymer (BCP) isoporous membrane reported in the literature. Significantly, the permea...

Formation and flow behavior of micellar membranes in a T-shaped microchannel.

Understanding the formation and instability behavior of membranes is of fundamental interest and practical relevance to various biotechnological applications and self-assembly systems. Surfactant micellar membranes serve as a simple model system when surfactant molecules self-assemble into micellar structures under flow, but observing such process in real time is a major challenge due to limitations in spatiotemporal resolutions. We use a simple T-shaped microchannel to capture the formation and flow behavior of an ionic surfactant micro-micellar-membrane (μMM) when an aqueous stream of organic salt sodium salicylate (NaSal) meets a stream of cationic surfactant cetyltrimethylammonium bromide (CTAB). The μMM is shown to grow and become unstable depending on the flow rate, as characterized using micro-particle image velocimetry, fluorescence microscopy, flow birefringence, and bulk rheometry. We propose a simple model that accounts for the flow, elasticity and inertia of the μMM to analyze its flow behavior. Our experimental protocol can be easily replicated in conventional laboratories without the need of utilizing sophisticated equipment such as synchrotron small angle X-ray scattering and micro-electronics circuits. Our combined experimental and modeling results can be extrapolated to provide new insights to study the flow behavior and thermodynamic phases of lipid membranes, membrane proteins, and biological membranes.

Measurement of Local Sodium Ion Levels near Micelle Surfaces with Fluorescent Photoinduced-Electron-Transfer Sensors.

The Na(+) concentration near membranes controls our nerve signals aside from several other crucial bioprocesses. Fluorescent photoinduced electron transfer (PET) sensor molecules target Na(+) ions in nanospaces near micellar membranes with excellent selectivity against H(+). The Na(+) concentration near anionic micelles was found to be higher than that in bulk water by factors of up to 160. Sensor molecules that are not held tightly to the micelle surface only detected a Na(+) amplification factor of 8. These results were strengthened by the employment of control compounds whose PET processes are permanently "on" or "off".

Measurement of Local Sodium Ion Levels near Micelle Surfaces with Fluorescent Photoinduced‐Electron‐Transfer Sensors

AbstractThe Na+ concentration near membranes controls our nerve signals aside from several other crucial bioprocesses. Fluorescent photoinduced electron transfer (PET) sensor molecules target Na+ ions in nanospaces near micellar membranes with excellent selectivity against H+. The Na+ concentration near anionic micelles was found to be higher than that in bulk water by factors of up to 160. Sensor molecules that are not held tightly to the micelle surface only detected a Na+ amplification factor of 8. These results were strengthened by the employment of control compounds whose PET processes are permanently “on” or “off”.

PH Responsive Self‐Assembly of Cucurbit[7]urils and Polystyrene‐Block‐Polyvinylpyridine Micelles for Hydrophobic Drug Delivery

Polystyrene‐block‐polyvinylpyridine (PS‐b‐P4VP) polypseudorotaxanes with cucurbit[7]urils (CB[7]) were prepared from water soluble PS‐b‐P4VPH+ polymer and CB[7] in aqueous solution at room temperature. At acidic and neutral pH, the pyridinium block of PS‐b‐P4VP is protonated (PS‐b‐P4VPH+) pushing CB[7] to preferably host the P4VP block. At basic pH (pH 8), P4VP is not charged and thus is not able to strongly complex CB[7]. This phenomenon was verified further by monitoring the release of pyrene, a hydrophobic cargo model, from a PS‐b‐P4VPH+/CB[7] micellar membrane. Release study of UV active pyrene from the membrane at different pH values revealed that the system is only operational under basic conditions and that the host‐guest interaction of CB[7] with P4VPH+ significantly slows down cargo release.

PH-triggered micellar membrane for controlled release microchips

A pH-responsive membrane based on polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer was developed on a model glass microchip as a promising controlled polymer delivery system. The PS-b-P4VP copolymer assembles into spherical and/or worm-like micelles with styrene block cores and pyridine coronas in selective solvents. The self-assembled worm-like morphology exhibited pH-responsive behaviour due to the protonation of the P4VP block at low pH and it's deprotonation at high pH and thus constituting a switchable “off/on” system. Doxorubicin (Dox) was used as cargo to test the PS-b-P4VP membrane. Luminescence experiments indicated that the membrane was able to store Dox molecules within its micellar structure at neutral pH and then release them as soon as the pH was raised to 8.0. The performance of the cast membrane was predictable and most importantly reproducible. The physiochemical and biological properties were also investigated carefully in terms of morphology, cell viability and cell uptake.

Limited enzymatic hydrolysis of soy protein enhances cholesterol absorption inhibition in Caco-2 cells.

Protein hydrolysates were produced by hydrolyzing isolated soy protein (ISP) with enzymes including flavourzyme, alcalase, trypsin, chymotrypsin and pepsin for 12 h, respectively. Each hydrolysate was measured its recovery and evaluated its relative cholesterol uptake (RCU, %) in Caco-2 cells. The higher the recovery represented the higher the yield. The lower the RCU revealed the higher the cholesterol absorption inhibition. The result indicated that intact ISP could further decrease its RCU by hydrolyzing with any of these enzymes. Flavourzyme-ISP hydrolysate had the lowest RCU of 37% and maintained the highest recovery of 58% than the others. The effects of limited ISP hydrolysis using flavourzyme in terms of the degree of hydrolysis (DH, %) on recovery and RCU in Caco-2 cells were also investigated. When the DH was less than 22.8%, the RCU decreased with the increase in DH. However, extensive ISP hydrolysis using flavourzyme to obtain DH higher than 28% did not guarantee enhance the cholesterol absorption inhibition but significantly (p＜0.05) decreased the recovery. According to micelle inspection using a transmission electron microscope, the hydrolysate was clearly incorporated into the micellar membrane but ISP wasn't. This finding suggested that incorporation of the hydrolysate lead to reduce cholesterol solubility during micelle preparation as well as inhibit cholesterol absorption in Caco-2 cells.

Multiplexing Sensory Molecules Map Protons Near Micellar Membranes

Hi-fi mapping: Multiplexing fluorescent sensors that simultaneously target proton concentration and polarity move to micellar nanospaces, self-regulate their positions, and report their pKa values and wavelengths, which are controlled by their local environments. Such sensory functions enable maps of proton gradients near micellar membranes to be drawn.

Aqueous solubility and membrane interactions of hydrophobic peptides with peptoid tags

Lysine tagging of hydrophobic peptides of parent sequence KKAAALAAAAALAAWAALAAAKKKK-NH(2) has been shown to facilitate their synthesis and purification through water solubilization, yet not impact on the intrinsic properties of the hydrophobic core sequence with respect to its insertion into membranes in an alpha-helical conformation. However, due to their positively charged character, such peptides often become bound to phospholipid head groups in membrane surfaces, which inhibits their transbilayer insertion and/or prevents their transport across cellular bilayers. We sought to develop more neutral peptides of membrane-permeable character by replacing most Lys residues with uncharged peptoid [N-(R)glycyl] residues, which might similarly confer water solubility while retaining membrane-interactive properties of the hydrophobic core. Several "peptoid-tagged" derivatives of the parent peptide were prepared with varying peptoid content, with five of the six Lys residues replaced with peptoids Nala and/or Nval. Conformations of these peptides measured by circular dichroism spectroscopy demonstrated that these water-soluble peptides retain the alpha-helix structure in micelles (lysophosphatidylcholine and sodium dodecyl sulfate) notwithstanding the known helix-breaking capacity of the peptoid tags. Blue shifts in Trp fluorescence spectra and quenching experiments with acrylamide confirmed that peptoid-tagged peptides insert spontaneously into micellar membranes. Results suggest that upon introduction of uncharged tags, the interaction between the membrane and the peptides is dominated by the hydrophobicity of the peptide core rather than the electrostatic interactions between the Lys and the head groups of the lipids. The overall findings indicate that peptoid residues are effective surrogates for Lys as uncharged water-solubilizing tags and, as such, provide a potentially valuable feature of design of membrane-interactive peptides.

Polar residue tagging of transmembrane peptides.

Studies that focus on packing interactions between transmembrane (TM) helices in membrane proteins would greatly benefit from the ability to investigate their association and packing interactions in multi-spanning TM domains. However, the production, purification, and characterization of such units have been impeded by their high intrinsic hydrophobicity. We describe the polar tagging approach to biophysical analysis of TM segment peptides, where incorporation of polar residues of suitable type and number at one or both peptide N- and C-termini can serve to counterbalance the apolar nature of a native TM segment, and render it aqueous-soluble. Using the native TM sequences of the human erythrocyte protein glycophorin A (GpA) and bacteriophage M13 major coat protein (MCP), properties of tags such as Lys, His, Asp, sarcosine, and Pro-Gly are evaluated, and general procedures for tagging a given TM segment are presented. Gel-shift assays on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) establish that various tagged GpA TM segments spontaneously insert into micellar membranes, and exhibit native TM dimeric states. Sedimentation equilibrium analytical centrifugation is used to confirm that Lys-tagged GpA peptides retain the native dimer state. Two-dimensional nuclear magnetic resonance (NMR) spectroscopy studies on Lys-tagged TM MCP peptides selectively enriched with N-15 illustrate the usefulness of this system for evaluating monomer-dimer equilibria in micelle environments. The overall results suggest that polar-tagging of hydrophobic (TM) peptides approach constitutes a valuable tool for the study of protein-protein interactions in membranes.

The Hydrophobicity Threshold for Peptide Insertion into Membranes

AbstractFor Abstract see ChemInform Abstract in Full Text.

Continuous production and simultaneous precipitation of a dipeptide in a reversed micellar membrane reactor

The dipeptide AcPheLeuNH2 was continuously synthesized from acetyl phenylalanine ethyl ester (AcPheOEt) and leucinamide (LeuNH2) by α-chymotrypsin encapsulated in TTAB/heptane/octanol reversed micelles in a ceramic membrane reactor. Simultaneous separation of the dipeptide was achieved by selective precipitation. Apart from the dipeptide, two by-products resulting from the hydrolysis and thetransesterification of AcPheOEt with the cosolvent octanol were obtained. The dipeptide was recovered with high purity (higher than 92%) due to precipitation from the complex reaction medium. The influence of the concentration of the two substrates in performance parameters of the continuous reactor such as productivity, yields, conversion degree, selectivity, and operational stability was investigated. The integration of catalysis and separation in a ceramic membrane reactor led to a one-step process for the production of a dipeptide with a high purity.

Dye-sensitized photo-oxidation of amino acids in reversed micellar membrane mimetic system

Dye-sensitized photo-oxidation of amino acids in reversed micellar membrane mimetic system

Dye-sensitized photo-oxidation of amino acids in reversed micellar membrane mimetic system

The photochemistry of a novel photosensitizer H[TBC(OiPr)4P(OH) 1, and the photo-oxidation of amino acids sensitized by H[TBC(OLPr)4P(OH)] have been investigated in the AOT/HzO/toluene reversed micellar system. Absorption and fluorescence measurements indicate that H[TBC(OiPr)4(OH)1 can interact with the reversed micelles by adsorption to the micellar surface, resulting in the disaggregation of the sensitizer and the enhancement of its photoactivity. In micellar solutions, H[TBC(OiPr)4P(OH)] can efficiently photo-generate1O2(Type II mechanism) and\( O_2^{\mathop .\limits^\_ } \) (Type 1 mechanism) as shown by stationary photolysis and ESR spin-trapping techniques. Amino acids dissolved in water pools of reversed micelles can be photo-oxidized via Type ll mechanism as sensitized by H[TBC(Oi'Pr)4P(OH) ]. The photo-oxidation of tryptophan follows the first-order kinetics, while that of tyrosine is much slower. Kinetic studies of the photodynamic behavior in this microheterogeneous system shows that the microheterogeneity can alter the mechanism and the kinetic-controlling factors of photosensitization reaction.

Dipeptide synthesis and separation in a reversed micellar membrane reactor

The synthesis of dipeptide AcPheLeuNH 2 catalyzed by α-chymotrypsin encapsulated in TTAB/octanol/heptane reversed micelles was investigated in a tubular ceramic membrane reactor, operated in a batch mode. The reaction medium conditions (TTAB concentration, buffer molarity, and pH) were optimized using a factorial design in order to achieve maximum synthesis rates. Hydrated reversed micelles permeated through the membrane together with the substrate ester, dipeptide, and by-products. However, as a result of the low solubility of the peptide in the reaction medium, selective precipitation occurred, thus enabling the complete retention of the solid product by the ultrafiltration membrane and therefore an integration of a separation step in the biotransformation process. In spite of the continuous accumulation of solids inside the reactor, constant permeation flow rates could be maintained throughout the operation. The influence of α-chymotrypsin, TTAB, and water concentration on the kinetics and mass transfer of the system was also investigated. The behavior of the system during a continuous experiment was also evaluated.

Continuous lipolysis in a reversed micellar membrane bioreactor

The enzymatic hydrolysis of olive oil using Chromobacterium viscosum lipase B encapsulated in reversed micelles of AOT in isooctane was carried out in a continous reversed micellar membrane bioreactor. A tubular ceramic membrane installed in an ultrafiltration module was used to retain the lipase and separate the products from the reaction media. Water filled micelles were supplemented to the reactor together with the substrate/solvent solution to compensate for the permeation of reversed micelles. The influence of substrate concentration, residence time and water content in the productivity and conversion of the system were investigated. A linear relationship between productivity and conversion degree was found for each substrate concentration tested. Operational stability of the bioreactor was tested in a long term operation confirming the high stability of this catalytic system.