Critical Aggregation Concentration Research Articles

Unlocking the Potential of Mannosylerythritol Lipids: Properties and Industrial Applications

Mannosylerythritol lipids (MELs), one of the most promising biosurfactants (BS), are glycolipids produced by yeasts or fungi, which have great environmental performance and high compatibility with the human body. MELs, besides working as typical surfactants, can form diverse structures when at or above the critical aggregation concentration (CAC), reduce the surface tension of water and other solutions, and be stable over a wide range of conditions. Among others, MELs present antimicrobial, antitumor, antioxidant and anti-inflammatory activities and skin and hair repair capacity, which opens possibilities for their use in applications from cosmetics and pharmaceutics to bioremediation and agriculture. However, their market share is still low when compared to other glycolipids, due to their less developed production process and higher production cost. This review gathers information on the potential applications of MELs mentioned in the literature since 1993. Furthermore, it also explores the current strategies being developed to enhance the market presence of MELs, in parallel with the ones developed for rhamnolipids and sophorolipids.

Self-Aggregation, Enhanced Guest-Binding Behavior, and Anion-Induced Agglutination of Cyclophane Dimers Linked with Florescent Perylene Diimide.

Cationic, anionic, and nonionic cyclophane dimers, 1a, 1b, and 1c, covalently linked with fluorescent perylene diimide were synthesized, respectively, as a host for aggregation-induced multivalent effects on guest-binding. These PDI-linked cyclophane dimers 1a and 1b, especially 1c, formed self-aggregates in H2O-rich solvents through π-stacking interactions. Critical aggregation concentrations of 1a, 1b, and 1c in H2O were 4.0 × 10-6, 4.0 × 10-6, and less than 0.1 × 10-6 M, respectively. The self-aggregates of the PDI-linked cyclophane dimers in H2O were several hundred nanometers in size by DLS and TEM measurements. In an aggregated state, 1a exhibited guest-binding abilities toward hydrophobic guests, such as 6-p-toluidinonaphthalene-2-sulfonate and 6-anilino-naphthalene-2-sulfonate. Moreover, anion-induced agglutination of 1a was observed upon the addition of phosphate ions, and its effectiveness was as follows: ATP > ADP > H2P2O72- > AMP ≈ PO43- > HPO42- > H2PO4-. The contribution of the adenine base of the nucleotides as a guest moiety used for effective agglutination was confirmed by 1H NMR spectroscopy.

Colloidal interactions between nanochitin and surfactants: Connecting micro- and macroscopic properties by isothermal titration calorimetry and rheology

This study elucidates the intricate interactions between chitin nanocrystals (ChNC) and surfactants of same hydrophobic tail (C12) but different head groups types (anionic, cationic, nonionic): sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and polyoxyethylene(23)lauryl ether (Brij-35). Isothermal Titration Calorimetry (ITC) and rheology are used to study the complex ChNC-surfactant interactions in aqueous media, affected by adsorption, self-assembly and micellization. The ITC results demonstrate that the surfactant head group significantly influences the dynamics and nature of the involved phenomena. Cationic DTAB's reveal minimal interaction with ChNC, non-ionic Brij-25's interact moderately at low concentrations driven by hydrophobic effects while SDS's interacts strongly and show complex interaction patterns that fall across four distinct regimes with SDS addition. We attribute such behavior to initiate through electrostatic attraction and terminate in surfactant micelle formation on ChNC surfaces. ITC also elucidates the impact of ChNC concentration on key parameters including critical aggregation concentration (CAC) and saturation concentration (C2). Dynamic rheological analysis indicates the molecular interactions translate to non-linear variations in the elastic modulus (G') upon SDS addition mirroring that observed in ITC experiments. Such a direct correlation between molecular interactions and macroscopic rheological properties provides insights to aid in the creation of nanocomposites with tailored properties.

Solubilization mechanism of α-glycosylated naringin based on self-assembled nanostructures and its application to skin formulation

We previously reported that α-glycosylated naringin (naringin-G), synthesized by enzyme-catalyzed transglycosylation, can enhance the solubility of poorly water-soluble compounds without surface-active property. However, the solubilization mechanism has not been fully elucidated. In this study, the solubilization mechanism of naringin-G was investigated using nuclear magnetic resonance (NMR) spectroscopy, and its application in skin formulations was further investigated. 1H NMR and dynamic light scattering measurements at various concentrations confirmed the self-assembled nanostructures of naringin-G above a critical aggregation concentration of approximately 2.2 mg/mL. Two-dimensional 1H–1H nuclear Overhauser effect spectroscopy and solubility tests revealed that flavone with poor water solubility, could be solubilized in its self-assembled structure with a stoichiometric relationship with naringin-G. When naringin-G was included in the skin formulation, the permeated amount and permeability coefficient (Papp) of flavones improved up to four times with increasing amounts of naringin-G. However, flavone solubilization by adding an excessive amount of naringin-G resulted in a decreased permeated amount and Papp of flavones, indicating the interplay between the apparent solubility and skin permeability of flavones. Naringin-G, which forms a nanoaggregate structure without exhibiting surface-active properties, has the potential to enhance the solubility and skin permeation of poorly water-soluble compounds.

Self‐assembled nanoparticles based on pullulan‐g‐poly(Z‐L‐lysine) for controlled drug delivery: Synthesis, characterization and preliminary studies on the encapsulation of indomethacin

AbstractNovel biocompatible systems suitable for the controlled release of active ingredients are under the spotlight within the last few years. The present investigation focuses on the preparation of nanoparticles (NPs) based on the amphiphilic copolymer pullulan‐graft‐poly(Z‐L‐lysine) bearing different amounts of lysine (10, 20, and 30 wt%), and on the evaluation of their ensuing viability to encapsulate the hydrophobic nonsteroidal anti‐inflammatory drug indomethacin (INDO). The copolymers are synthesized by ring‐opening polymerization, characterized by NMR and FTIR, and their critical aggregation concentration is determined by fluorescence. The NPs are prepared with and without INDO using different copolymer/solvent ratios and INDO/copolymer ratios. The hydrodynamic diameter and polydispersity of the NP suspensions are monitored by dynamic light scattering for 30 days. Their sizes vary between 208 and 338 nm, and some reach the micrometric range (19–73 μm). INDO‐free NPs are identified as spherical‐shaped by atomic force microscopy. Two formulations are tested in terms of encapsulation efficiency (EE = 43%–89%), and the drug crystallinity (DC = 7%–27%) which is determined by differential scanning calorimetry, indicating a reduction with respect to pristine INDO. The results suggest that the copolymers prepared herewith have potential to be applied as carriers for new drug delivery systems of class II drugs.

Study on the aggregation nature of sodium cocoyl glycinate and sodium hyaluronate mixture in aqueous and NaCl solutions

AbstractThe mixed system of sodium cocoyl glycinate and sodium hyaluronate (HA) with different mass concentrations and relative molecular weights was investigated by the surface tension method. All the curves of surface tension versus logarithm of concentration (γ‐lgc curves) of sodium cocoyl glycinate‐HA mixed system displayed the properties of double platform. The critical micelle concentration (cmc) of sodium cocoyl glycinate was 1.690 g/L at 25°C. The two inflection points of the γ‐lgc curves corresponding to the cocoyl glycine‐HA mixed system were cac (the critical aggregation concentration) and cmce (the extended cmc of sodium cocoyl glycinate), and cac < cmce < cmc. With the change of the mass concentration and relative molecular weight of HA, the cac values were almost constant. However, cmce increased with the increase of the mass concentration of HA at the same HA molecular weight. For the HA of molecular weight of 800 and 260000 Da, the mass concentration of HA increased from 0.05 to 0.4 g/L, and the cmce value increased from 1.199 to 1.390 g/L and 1.102 to 1.330 g/L, respectively. When the mass concentration of HA remained the same, the change in the relative molecular weight of HA had little effect on the cmce value. For the mixed system of sodium cocoyl glycine −0.1 g/L HA, when the concentration of NaCl was 2 g/L, the salt enhancement effect was dominant. When the concentration of NaCl was 4 to 8 g/L, the salt weakening effect was dominant. It is indicated that HA can improve the chemical properties of sodium cocoyl glycinate at a certain concentration, thus improving the cleaning, foaming, and foam stability of sodium cocoyl glycinate.

Preparation and characterization of a novel amphiphilic nanocarrier based on enzymatic polymerization-derived α-1,3-glucan for efficient quercetin encapsulation

AbstractBiodegradable nanocarriers based on polysaccharide-derived amphiphilic copolymers are promising candidates to enhance drug solubility and stability. This study aimed to design a novel amphiphilic carrier based on enzymatic polymerization-derived exopolysaccharides, α-1,3-glucan. Glycosyltransferase I from Streptococcus mutans was used to synthesize α-1,3-glucan, and the amphiphilic α-1,3-glucan-graft-poly(ε-caprolactone) (Glucan-g-PCL) copolymer was synthesized via a homogeneous ring-opening polymerization (ROP) in ionic liquid, 1-butyl-3-methylimidazolium chloride. The chemical structures and physical properties of Glucan-g-PCL copolymer were characterized by FT-IR, 1H NMR, XRD, and TGA. The self-assembly behavior of the amphiphilic α-1,3-glucan derivative was investigated by fluorescence probe. The results showed that Glucan-g-PCL exhibited a low critical aggregation concentration (CAC) and formed core-shell structured nanostructure via self-assembly. Quercetin (Qu), a hydrophobic active component, was successfully encapsulated within the Glucan-g-PCL micelle-like nanostructure, showing efficient encapsulation and dispersion in water. Qu/Glucan-g-PCL micelle-like nanostructure (Qu/M) was characterized by DLS, TEM, FT-IR, and XRD. FT-IR and XRD analyses showed that Qu was present in an amorphous state in the formulation and without any chemical reactions during the sample preparation procedures. In addition, the antioxidant properties of the Qu/M were investigated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method, and significantly improved antioxidant activity was observed for Qu/M compared to Qu/water. The utilization of Glucan-g-PCL nanostructure encapsulation opens up new possibilities for enhancing and expanding the practical applications of quercetin and α-1,3-glucan. Graphic Abstract

Influence of cationic dimeric and trimeric-type surfactants on the aggregation behavior of water-soluble phthalocyanine: A combined experimental and computational study

The aggregation behavior of the water-soluble phthalocyanine, namely zinc 2,9,16,23–tetra(tert–butyl)–29H,31H–phthalocyanine tetrasulphonic acids (ZnPcS4), has been examined in the presence of dimeric and trimeric-type cationic surfactants and their conventional counterpart cetyltrimethylammonium bromide (CTAB). The absorption and fluorescence studies of ZnPcS4 in water showed a different feature than that in methanol suggesting the formation of aggregated ZnPcS4 in an aqueous medium. The fluorescence studies of ZnPcS4 in the presence of examined dimeric-type cationic surfactants showed lower critical aggregation concentration (CAC = 0.62–13.6 µM) compared to that of CTAB (CAC = 16 µM). It was found that the position of the substituents affected the critical micelle concentration (CMC) value, and the ortho-dimeric surfactant had a lower CMC value compared to those surfactants with meta, and para-dimeric surfactant. It was interesting to see that the CMC for the dimeric surfactant with two groups at the para position (13.6 µM) decreased significantly (0.04 µM) by removing the (O-CH2) groups attached to the benzene which can be explained by structural parameters determined by theoretical calculations. By changing the surfactants from dimers to cationic trimers surfactants, a significant decrease in the CAC values was observed (0.04 µM for Trimer-12 with two dodecyl groups and 0.39 µM for Trimer-8 with two octyl groups). This finding indicates that the increase in tail length by four methylene groups of Trimer-12 compared to Trimer-8 results in a decrease in CAC by about one order of magnitude. These new findings suggest that the trimeric-type cationic surfactants are remarkably superior to conventional and dimeric-type surfactants, which could have a profound impact on many applications of ZnPCS4 including, but not limited to, medical, organic electronics, light harvesting, photonics, and optical sensors.

Synthesis of PEG-Polycycloether Block Copolymers: Poloxamer Mimics Containing a Rigid Helical Block.

Poloxamers are amphiphilic block copolymers consisting of poly(ethylene glycol) (PEG) and poly(propylene glycol) segments. Their self-assembly and interfacial properties are tied to the relative hydrophilicity and hydrophobicity of each block and can therefore be adjusted by changing block lengths. Here, a series of PEG-polycycloether block copolymers is synthesized that have the same structure as a poloxamer, but they encompass a rigid polycyclic backbone as the hydrophobic block. A variety of polymer structures are synthesized, for example diblock or triblock architectures, with/without olefinic units, atactic or isotactic backbone, and different block lengths. Due to their amphiphilicity, self-assembly into spherical aggregates (diameters ranging from 64 to 132nm) at low concentrations (critical aggregation concentration as low as 0.04mgmL-1) is observed in water. Low surface tensions (as low as 26.7 mNm-1) are observed as well as the formation of stable high internal phase emulsions (HIPEs) irrespective of the oil/water ratio. This contrasts with the properties of the commonly used poloxamers P188 or P407 and illustrates the significance of the rigid polycycloether block. These new colloidal properties offer new prospects for applications in emulsion formulations for biomedicine, cosmetics, and the food industry.

Environmental colloid behaviors of humic acid - Cadmium nanoparticles in aquatic environments

Humic acid (HA), a principal constituent of natural organic matter (NOM), manifests ubiquitously across diverse ecosystems and can significantly influence the environmental behaviors of Cd(II) in aquatic systems. Previous studies on NOM-Cd(II) interactions have primarily focused on the immobilization of Cd(II) solids, but little is known about the colloidal stability of organically complexed Cd(II) particles in the environment. In this study, we investigated the formation of HA-Cd(II) colloids and quantified their aggregation, stability, and transport behaviors in a saturated porous media representative of typical subsurface conditions. Results from batch experiments indicated that the relative quantity of HA-Cd(II) colloids increased with increasing C/Cd molar ratio and that the carboxyl functional groups of HA dominated the stability of HA-Cd(II) colloids. The results of correlation analysis between particle size, critical aggregation concentration (CCC), and zeta potential indicated that both Derjaguin-Landau-Verwey-Overbeek (DLVO) and non-DLVO interactions contributed to the enhanced colloidal stability of HA-Cd(II) colloids. Column results further confirmed that the stable HA-Cd(II) colloid can transport fast in a saturated media composed of clean sand. Together, this study provides new knowledge of the colloidal behaviors of NOM-Cd(II) nanoparticles, which is important for better understanding the ultimate cycling of Cd(II) in aquatic systems.

Probing berberine syringate-bovine serum albumin interactions by multi-spectroscopic, conductimetric, volumetric and molecular docking methods

In this paper, a new berberine-based salt berberine syringate ([BBR][SA]) was synthesized and [BBR][SA]-bovine serum albumin (BSA) interactions were investigated by various techniques like UV–visible absorption, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), volumetry and conductimetry. Using the experimental values of density and conductivity, the specific volume of BSA and the critical aggregation concentration of [BBR][SA] were derived. From the variation trends of specific volume for BSA with [BBR][SA] concentrations, it was observed the predominate ionic interaction/dehydration effect at small [BBR][SA] concentration and the non-polar interaction/hydration phenomenon at higher [BBR][SA] concentration for the binding of [BBR][SA] with BSA, as well as hydration shell structure changes at different temperatures in the medium with different pH values. Aggregation of [BBR][SA] is slowed by increasing concentration of BSA and temperature. The thermodynamic parameters of aggregation process have been exploited to gain more information on the interaction of [BBR][SA] with BSA. UV–vis absorption, multiple fluorescence spectroscopy (steady-state spectroscopy, synchronous fluorescence, three-dimensional fluorescence), and FT-IR have been utilized to understand the interaction mechanisms and binding strength between the two molecules. [BBR][SA] quenches the fluorescence of BSA through static quenching mechanism. The 1:1 complex between [BBR][SA] and BSA with a strong affinity was formed. The changes in microenvironment and conformation of BSA caused by [BBR][SA] were revealed by synchronous fluorescence spectra, 3D fluorescence maps and FT-IR. The binding average distance from [BBR][SA] to BSA (2.83 nm) was obtained based on the theory of Förster energy transfer. Competitive binding experiment confirms [BBR][SA] binding to Sudlow site I (sub-domain IIA) of BSA. In addition, molecular docking was generated to provide valuable information about the available binding sites of [BBR][SA] on BSA and the types of binding forces.

Dynamic Interfacial Properties and Foamability of DoTAB/SiO2 Mixtures

The interaction between nanoparticles and cationic surfactants is an exciting and emerging field in interfacial science. This area of research holds significant promise, linking fundamental principles to practical applications in a variety of industries, including chemical processes, biomedical applications and the petroleum industry. This study explores the interaction between dodecyltrimethylammonium bromide (DoTAB) and silica (SiO2) nanoparticles, investigating their influence on dynamic interfacial properties and foam characteristics. Through equilibrium and dynamic surface tension measurements, along with examining the dilational visco-elasticity behavior, this research reveals the complex surface behavior of DoTAB/SiO2 mixtures compared to individual surfactant solutions. The foamability and stability experiments indicate that the addition of SiO2 significantly improves the foam stability. Notably, stable foams are achieved at low SiO2 concentrations, suggesting a cost-effective approach to enhancing the foam stability. This study identifies the optimal stability conditions for 12 mM DoTAB solutions, emphasizing the crucial role of the critical aggregation concentration region. These findings offer valuable insights for designing surfactant-nanoparticle formulations to enhance foam performance in various industrial applications.

The aggregation behaviors of organic radicals in polar fluorinated arenes

AbstractPolar fluorinated arenes can promote organic free radical reactions, which have attracted scientists’ interest in recent years. However, it is still unknown how these solvents interact weakly with organic radical molecules to influence their reactivity. In this study, we investigated how organic free radicals aggregate in five polar fluorocarbon solvents, and demonstrated that different substituents can influence their aggregation behaviors. In these solvents, small organic radicals with simple substituents maintain a homogeneous solution; however, radicals with substituents that form intermolecular hydrogen bonds or with long‐chain aliphatic hydrocarbons tend to aggregate in them, whereas substituents of long‐chain aliphatic hydrocarbons tend to promote aggregation better. The critical aggregation concentrations of these aggregates are measured by concentration‐dependent UV–visible spectroscopy. Their topological morphologies are all spherical based on TEM. The compactness and rotational motivation speed of radical molecules within these aggregates are determined by EPR spectroscopy. The particle sizes of these aggregates are determined by analyzing their cyclic voltammograms. Most excitingly, electrochemical experiments reveal that the aggregation behaviors of free radical molecules with intermolecular hydrogen bonds can significantly increase their catalytic rate for electro‐oxidizing benzyl alcohol in such a solvent. The results of this study indicate that in polar fluorinated arenes organic radical molecules’ aggregation behaviors are related to their structures. This may provide guidelines for regulating organic radical reactivity in these solvents in the future.

Nucleotide‐Protocell Interactions: A Reciprocal Relationship in Prebiotically Pertinent Environments

AbstractSpontaneous interactions between nucleotides and lipid membranes are likely to have played a prominent role in the emergence of life on Earth. However, the effect of nucleotides on the physicochemical properties of model protocellular membranes is relatively less understood. To this end, we aimed to discern the effect of canonical nucleotides on the properties of single‐chain amphiphile membranes under prebiotically relevant conditions of multiple wet‐dry cycles. Furthermore, the change in the critical aggregation concentration of the membranes and their stability in the presence of nucleotides was also investigated in astrobiologically relevant analogue environments. We report that different nucleotides, lipid headgroups, and the ionic makeup of the system affect lipid‐nucleotide interactions, and these, in turn, modulate the effect of nucleotides on the membrane properties. Specifically, the presence of AMP, UMP, and CMP promoted self‐assembly of oleic acid membranes and increased their stability against certain prebiotically relevant selection pressures. This study takes us a step towards an appreciable understanding of how nucleotides might have shaped the protocellular landscape of the prebiotic Earth.

Dual-responsive chondroitin sulfate self-assembling nanoparticles for combination therapy in metastatic cancer cells

In this study, we developed self-assembling nanoparticles (LCPs) able to trigger the release of Chlorambucil (Chl) and Doxorubicin (DOX) to MDA-MB-231 cells by exploiting the enzyme and redox signals. The DOX loaded LCPs was prepared by the self-assembly of two chondroitin sulphate (CS) derivatives, obtained by the covalent conjugation of Lipoic Acid (LA) and Chlorambucil (Chl) to the CS backbone. After the physic-chemical characterization of the conjugates by FT-IR, 1H NMR, and determination of the critical aggregation concentration, spherical nanoparticles with mean hydrodynamic diameter of 45 nm (P.D.I. 0.24) and Z-potential of - 44 mV were obtained by water addition/solvent evaporation method. In vitro experiments for the release of Chl and DOX were performed in healthy and cancer cells, using a cell culture media to maintain the physiological intracellular conditions (pH 7.4) (and concentration of esterase and GSH. The results allowed the selective release of the payloads to be detected: Chl release of 0 and 41% were obtained after 2 h incubation in normal and in cancer cells respectively, while values of 35 (in healthy cells) and 60% (in cancer cells) were recorded for DOX release after 96 h. Finally, viability studies proved the ability of the newly proposed nanosystem to enhance the cytotoxic activity of the two drugs against cancer cells.

Physicochemical properties and biological activities of new berberine-based salts with syringic acid as well as 3,5-dimethoxybenzoic acid as anions: Effect of temperature, concentration and anion

Two novel berberine-based salts (berberine syringate ([BBR][SA]) and berberine 3,5-dimethoxybenzote ([BBR][DA])) were prepared and characterized. Their thermal stability, solubility and octanol–water partition coefficient in aqueous solution and simulated physiological fluids (simulated gastric, simulated body, simulated intestinal fluids) were determined. Self-aggregation and association behaviors of two salts in aqueous solution have been investigated by conductimetric method at different temperatures and limiting molar conductivity, critical aggregation concentration, etc for [BBR][SA] and [BBR][DA] were calculated. The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of two salts were assessed to evaluate their antibacterial effects on four strains (Staphylococcus aureus, Bacillus subtilis, Candida albicans, and Streptococcus mutans). The effect of two synthetic salts on the esterase-like activity of BSA and their cytotoxicity evaluation against B16-F10 cancer cell line were also carried out. The obtained results were evaluated with regard to the influence of such parameters as temperature, concentration and the nature of the anion.

Impact of Linker Groups on Self-Assembly, Gene Transfection, Antibacterial Activity, and In Vitro Cytotoxicity of Cationic Bolaamphiphiles.

Cationic bolaamphiphiles have gained significant attention in various research fields, including materials science, drug delivery, and gene therapy, due to their unique properties and potential applications. The objective of the current research is to develop more effective cationic bolaamphiphiles. Thus, we have designed and synthesized two cationic bolaamphiphiles (-(CH2)12(2,3-dihydroxy-N,N-dimethyl-N-(3-ureidopropyl)propan-1-aminium chloride))2 (C12(DDUPPAC)2)) and (-(CH2)12(N-(3-(carbamoyloxy)propyl)-2,3-dihydroxy-N,N-dimethylpropan-1-aminium chloride)2 (C12(CPDDPAC)2) containing urea and urethane linkages, respectively. We have investigated their self-assembly properties in water using several techniques, including surface tension, electrical conductivity, fluorescence probe, calorimetry, dynamic light scattering, and atomic force microscopy. Their biological applications, e.g., in vitro gene transfection, antibacterial activity, and cytotoxicity, were studied. Both bolaamphiphiles were observed to produce aggregates larger than spherical micelles above a relatively low critical aggregation concentration (cac). The calorimetric experiments suggested the thermodynamically favorable spontaneous aggregation of both bolaforms in water. The results of interaction studies led to the conclusion that C12(CPDDPAC)2 binds DNA with a greater affinity than C12(DDUPPAC)2. Also, C12(CPDDPAC)2 is found to act as a more efficient gene transfection vector than C12(DDUPPAC)2 in 264.7 cell lines. The in vitro cytotoxicity assay using MTT, however, revealed that neither of the bolaamphiphiles was toxic, even at higher quantities. Additionally, both bolaforms show beneficial antibacterial activity.

Comparison of the self-assembly and cytocompatibility of conjugates of Fmoc (9-fluorenylmethoxycarbonyl) with hydrophobic, aromatic, or charged amino acids.

The self-assembly in aqueous solution of three Fmoc-amino acids with hydrophobic (aliphatic or aromatic, alanine or phenylalanine) or hydrophilic cationic residues (arginine) is compared. The critical aggregation concentrations were obtained using intrinsic fluorescence or fluorescence probe measurements, and conformation was probed using circular dichroism spectroscopy. Self-assembled nanostructures were imaged using cryo-transmission electron microscopy and small-angle X-ray scattering (SAXS). Fmoc-Ala is found to form remarkable structures comprising extended fibril-like objects nucleating from spherical cores. In contrast, Fmoc-Arg self-assembles into plate-like crystals. Fmoc-Phe forms extended structures, in a mixture of straight and twisted fibrils coexisting with nanotapes. Spontaneous flow alignment of solutions of Fmoc-Phe assemblies is observed by SAXS. The cytocompatibility of the three Fmoc-amino acids was also compared via MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] mitochondrial activity assays. All three Fmoc-amino acids are cytocompatible with L929 fibroblasts at low concentration, and Fmoc-Arg shows cell viability up to comparatively high concentration (0.63 mM).

Synthesis and self-assembly behaviors of α-galactosyl ceramide (1,2)-polysaccharide analogue

α-Galactosyl ceramide (GalCer) as a glycolipid has been long used as a standard reference for positive control in natural killer T cell studies. The (1,2)-disaccharide analogue of GalCer attracts a special attention in the study of lysosomal glycolipid processing. This paper describes the synthesis and self-assembly behaviors of GalCer 1,2-polysaccharide analogue (PolyGalCer), having considered the 1,2-disaccharide analogue as a structural motif. The synthesis of PolyGalCer is performed via one-pot glycosidation technique of 1,2-linked oligogalactan exploiting chain polymerization of galactose-based cyclic sulfite as a monomer initiated with ceramide-based alcoholic aglycon. Through the concentration dependence of PolyGalCer solutions in water or in MeOH on the turbidity, it is found that PolyGalCer forms associates in both media. From the intersection points, the critical aggregation concentration (CAC) values of PolyGalCer in water and MeOH were estimated. To know the self-assembly and the thermal transition behaviors, we performed dynamic light scattering (DLS) analysis of the associates comprising PolyGalCer in water. The transmission electron microscopy observations of the aqueous sample solution indicate that the solution of PolyGalCer includes large spherical associates. The results clarify that the 1,2-galactan moiety of PolyGalCer skeleton contributes on the kinetic inhibition of large associate formation and the metamorphosis of associates.

Engineering π-Conjugation of Phenylalanine Derivatives for Controllable Chiral Folding and Self-Assemblies.

π-π stacking interaction is an attractive interaction that involves aromatic groups containing π-conjugated domains. It is a promising strategy for stabilizing folded structures with interesting chiroptical properties and manipulating the supramolecular chiral self-assembly process. In this study, we report the engineering of π-conjugated amino acids that utilize π-π stacking interactions to manipulate chiral folding as well as self-assembly evolution. Stepwise conjugation of phenyl, naphthyl, and pyrenyl to N-terminal phenylalanine derivatives witnessed the folding through intramolecular π-interactions in solution phase, which facilitated the formation of chiral geometry and the emergence of chiral optics. Introduction of aromatic domains efficiently lowers the critical aggregation concentration in the aqueous media. Molecular folding enables a special concentration-dependent self-assembly, whereby the supramolecular chirality accomplished inversion with the evolution of helical nanoarchitectures. This work develops a strategy to engineer π-conjugated amino acids with controllable folding behaviors, which also offers implications for the rational design of functional chiral materials.