2023 年 72 巻 5 号 p. 489-499
Currently, numerous fascinating molecular assemblies are used in food, cosmetics, and pharmaceuticals. Sugar-based amphiphiles are representative constituents of these molecular assemblies. Despite numerous studies on these generic compounds, many aspects remain unexplored even in aqueous systems. In this review, molecular assembly studies of sugar-based amphiphiles in aqueous systems are summarized. First, recent advances in molecular assembly studies, including the glassy state of lyotropic and thermotropic liquid crystalline (LC) phases, modulated crystal phases, and coagels consisting of nanofibers of alkyl β-D-glycosides, are presented. Second, research on thermotropic LC phases under desiccated conditions of trehalose fatty acid monoesters to clarify the fundamental behaviors of the glassy state and their use as stabilizers of glass-forming surfactants for pharmaceutical applications are discussed. Several effective X-ray analytical approaches are included to identify or clarify these phenomena, unknown or unsolved for a long time. Third, a comprehensive analysis of vitamin E (tocopherol)-cyclodextrin in aqueous systems is presented. Along with these topics, the importance of investigating stabilizer-free functional components, considered minor components, is highlighted. These unveiled phenomena or concepts will contribute to the development of nanoarchitectonics covering the self-assembly and selforganization of soft molecules.
Oleoscience is the study of oil and is a discipline closely related to our daily lives and the achievement of sustainable development goals (SDGs) 1) . The formulations of food, cosmetics, and pharmaceuticals have been significantly supported by the molecular assembly and self-organization of oleochemicals or biochemicals. These products involve the concept of nanoarchitectonics, the architecture of functional materials using nanoscale units based on the principles of nanotechnology 2) , 3) .
Sugars or carbohydrates are a promising option in transitioning from oil-based chemical resources to achieve SDGs. Recently, numerous advanced materials, such as sugar-based ionic liquids 4) , sugar-based polymers 5) , 6) , oligosaccharide-based gellaters 7) , cyclodextrin (CD)-based metal-organic frameworks 8) have been prepared. However, one of the most important compounds in sugar-based materials for SDGs are sugar-based amphiphiles, which have been industrially used 9) , 10) , 11) , 12) , 13) . Various sugar-based amphiphiles are constituents of oleochemicals or biochemicals, and a significant amount of effort has been invested in investigating their various molecular assemblies 10) , 11) , 12) , 13) , 14) , including absorption films 15) , emulsions 9) , 16) , 17) , forms 18) , 19) , vesicles, micelles 20) , 21) , liquid crystals (LCs), gels, crystals, and complexes with other molecules 22) , and the resulting self-organization such as nanotubes 23) .
Phase behavior studies have been a central research topic in the colloidal science field, where the aforementioned molecular assembly has been investigated in detail. Phase diagrams have helped us to understand how molecules behave as a function of concentration, temperature, or pressure, as defined by thermodynamics. To date, the phase diagrams of aqueous systems with sugar-based amphiphiles, such as sugar-based surfactants 10) , 11) and CD and their derivatives 12) , have been extensively described. Currently, there are many commercially available products based on these materials 11) , 12) , 13) , and phase studies of such materials in aqueous systems are essential for evaluating their usefulness. In addition, in the case of insoluble molecular assemblies, fascinating self-organization objects have sometimes been formed 12) , 14) , 23) .
Sugar-based surfactants consisting of sugar moieties and hydrocarbon tails exhibit excellent surface activity and molecular assembling abilities, such as micelles and LC phases 10) , 11) , 15) , 24) , 25) , 26) . The type of LC phase highly depends on its molecular structure, water concentration, and temperature. Despite numerous phase studies, fewer complete phase diagrams are available for sugar-based surfactant aqueous systems than for nonionic polyoxyethylene surfactant/water systems in terms of high-concentration and/or low-temperature regions. As the addition of oligosaccharide-based surfactants, such as sucrose fatty acid monoesters, exhibits an excellent stabilizing effect on therapeutic proteins during the freeze-drying process 27) , it is crucial to precisely understand the unknown state in their phase diagrams to predict the molecular behaviors in the process.
CD is a cyclic oligosaccharide that typically consists of six, seven, or eight glucose units. CDs form inclusion complexes with various hydrophobic compounds owing to the presence of a hydrophobic internal cavity. In CD studies, the so-called Higuchi and Conner phase diagrams have been extensively used to understand the types of inclusion complexes 12) . Depending on the host and guest compounds that form inclusion complexes, the concentration dependency varies significantly. One forms a soluble inclusion and the other forms a dispersion of the complex. Although numerous studies have been reported in this regard, systematic studies on aqueous systems are lacking. In particular, the type of combination that determines the water solubility of inclusion species remains unclear.
In this review article, the following phase study topics are summarized (Fig. 1). In topic (i), research on the molecular assembly of alkyl glycosides/water binary systems “under high-concentration and/or low-temperature conditions,” which is a continuation of basic phase research 28) , 29) , is presented. In topic (ii), research on the molecular assembly “under desiccated conditions” of trehalose fatty acid monoesters is presented to clarify the fundamental characteristic behavior of the glass transition of glycolipids and their applications. Finally, in topic (iii), research on vitamin E (α-tocopherol; α-Toc) complex with various CDs “in the absence of organic solvents” for biological applications is presented. In addition, some unique behaviors of stabilizer-free functional materials, such as vitamin E and vitamin C derivative (ascorbic palmitate), are discussed. In these studies, several molecular organizations, such as nanofibers and aligning nanofilms, have been introduced. These studies should be included in soft nanoarchitectonics, which is the nanoarchitectonics of soft materials; therefore, the novel concept connecting nanoarchitectonics with this review content is described in the conclusion section.
Summary of molecular assembly and relating concept descried in this review.
Alkyl glycoside is an amphiphilic compound consisting of sugar and hydrocarbon chains via glycosidic bonds. Many phase diagrams of alkyl glycoside aqueous systems have been prepared by various researchers 10) , 11) , 13) , 24) , 25) , 26) . Among these, many phase diagrams of octyl β-D-glucoside (C8Glc) / water binary systems and octyl β-D-thioglucoside (C8SGlc) /water binary systems have been published until now because of their utility in the protein engineering field such as protein solubilization and crystallization 30) . Fundamental studies relating to their phase diagrams have shown that there are lyotropic LC phases such as hexagonal (H1), cubic (Q), fluid lamellar (Lα), and lamellar gel (Lβ) phases as well as crystal (Cr) phases. However, phase behavior at low temperatures and under high drying or desiccating conditions has typically remained unclear.
When constructing a phase diagram using rapid cooling through differential scanning calorimetry (DSC) and polarized microscopy observation, lyotropic LCs become a glassy state over a wide range of C8Glc or C8SGlc concentrations (Fig. 2a) 31) , 32) . The glass transition temperature (T g) is the temperature at which material enters the glassy state upon cooling. In addition, when the specific heat change (ΔCp) obtained from the T g curve is plotted against C8Glc or C8SGlc concentrations, a correlation with the phase transition temperature and enthalpy change (ΔH) curves for the first-order phase transition such as LC-isotropic liquid (IL), so-called of clearing point (T c), is observed (Fig. 2b). Thus, it was proposed that the variation behavior might be determined by whether water is continuous or not in Lα. Although Seki and Kodama reported in 1981 that a glass transition occurs only at a specific concentration in dioctadecylammonium chloride aqueous systems 33) , C8Glc and C8SGlc/water binary systems were good candidates for generalizing the glass transition behavior of low-molecular-weight surfactants aqueous systems.
Phase behavior studies of octyl β-D-glucoside (C8Glc). Hot scientific topic represented by each figure are described around alphabetical number. (a) Global phase diagram of C8Glc-aqueous system containing the nonequilibrium parameters such as ice nucleation curve (T in), devitrification curve (T dev) and glass transition temperature curves (T g and T g’) 31) , 32) , 34) , 35) . Lα: Lamellar fluid, Q: Cubic, H: Hexagonal, IL: Isotropic liquid. (b) Schematic illustration of fluid lamellar (Lα) liquid crystalline (LC) system motifs for C8Glc-aqueous system categorized by thermodynamic parameters, ΔC p, ΔH and T C 31) , 32) , ΔC p; heat capacity change at glass transition temperature (T g), T C; clearing point where Lα LC phase become IL, ΔH; Enthalpy change at T C. (c) Relationships of alkyl chain length number (n) and various temperatures, T c, T m and T g, for anhydrous n-alkyl β-D-glucoside (CnGlc) 38) . (d) Schematic illustration of the crystal parameters of C8Glc 41) . (e) Temperature-dependent peak intensities of Cr and LC for C8Glc 41) .
Furthermore, a so-called supplemented phase diagram, which introduces Tg’, a glass transition temperature curve in the unfrozen phase after the ice has formed, was described for C8Glc and C5Glc, respectively 34) , 35) . The phase diagram shows that when the aqueous solution is cooled, after ice formation below the liquidus curve, the unfrozen phase would be concentrated to the intersection of the T g and T g’ curves and become a glassy state. Namely, for C8Glc aqueous systems, the unfrozen system should be vitrified in an LC state of approximately 90 wt%, inhibiting further ice formation (Fig. 2a) 34) . For C5Glc aqueous systems, freezing the aqueous solution resulted in the formation of a glassy state of approximately 90 wt% micellar solutions in the unfrozen system 35) . In the presence of an electrolyte such as NaCl and KCl, detailed analysis became difficult, but the persistence of the lyotropic behavior of C8Glc without precipitation in a freezing state was confirmed by simultaneous X-ray diffraction (XRD)-DSC measurements and low-temperature XRD analysis 32) , 36) , 37) .
The observation of the glass formation of alkyl β-D-glucoside (CnGlc) in the freeze-concentration state suggested that CnGlc would also exhibit glass transition in the anhydrous state. To investigate this, anhydrous CnGlc (chain length, n=1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12) with various alkyl chain lengths were prepared, and their glass-forming properties compared (Fig. 2c) 31) , 38) . The results showed that all CnGlc exhibited glass transition in the anhydrous state; T g decreases for chain lengths of 1-5 for IL states, and does not change for chain lengths above six in the Lα state. Regarding the lack of a distinct contribution to or the effect of the elongation of the alkyl chain length on T g, it was proposed that the glass formation in Lα LCs may be partially vitrified only around their sugar moieties, and therefore, the contribution of alkyl chains may be too small to detect or may be insignificant 38) . A further clarification study of this partial glassy system is described in section 3.
On the other hand, the understanding of Cr phase behaviors is also significant in phase diagram studies, and CnGlc crystallizes. To date, many crystal structures of glycolipids have been analyzed by single-crystal X-ray structural analysis 39) , 40) ; however, the single-crystal structural analysis of alkyl β-D-glycosides has not been performed because of the difficulty in preparing a single crystal with adequate size for single-crystal structural analysis. Nevertheless, when grazing incidence XRD measurements with two-dimensional detectors (2D-GI-XD) using a perpendicularly aligning Cr film were applied for CnGlc (n=7, 8), the formation of incommensurate smectic C (SmC) phases, corresponding to an intermediate phase, i.e., the ripple phase with two large crystal-lattice constants comparable to the lengths of their bilayer structures was confirmed (Fig. 1d) 41) . In addition, temperature-dependent 2D-GI-XD analysis identified a solid-to-solid phase transition as the starting temperature, which begins to form solid-solution-like behavior consisting of a Cr phase and an LC phase (Fig. 2e). In addition, the formation of an incommensurate smectic A (SmA) phase, corresponding to the so-called ribbon phase, was confirmed for octyl β-D-galactoside (C8Gal) hemihydrate crystal through 2D-GI-XD analysis (Fig. 3, right) 42) , 43) . These modulated lamellar Cr structures such as incommensurate SmC and SmA phases have never been observed in glycolipid crystal studies. Thus, it is expected that these novel findings overturn the previous consensus on glycolipids, which were formulated without the knowledge of the Cr phase behavior of alkyl β-D-glycosides; the formation of a modulated structure is reported in the LC state 44) . More recently, a more sophisticated crystal structure consisting of a cubic Cr phase has been reported for CnGlu (n=4, 5), with critical packing parameters (CPPs) less than 0.33, whereas C6Glc with a CPP of 0.42 formed a modulated lamellar Cr structure similar to C7Glc and C8Glc with similar CPP values 45) .
Coagel studies of octyl β-D-galactoside (C8Gal). (Left) Phase diagram of C8Gal-aqueous system below 30 wt％ C8Gal concentration 46) . IL: Isotropic liquid. T K; Krafft boundary temperature. (Middle) Optical microscopy image of 10 wt％ C8Gal-water mixture hydrogel. (Right) Schematic illustration of the crystal parameters of C8Gal hemihydrate crystal 42) .
C8Gal is the isomer of C8Glc and shows a high Krafft boundary temperature (T K) in water binary systems (Fig. 3, left) 26) . Conversely, the typical precipitate of alkyl glycosides such as alkyl α-glucoside and dodecyl β-D-glucoside exhibited typical coagel formation with a so-called macroscopically separated state 46) . However, the precipitation of C8Gal-formed hydrogel is because of the persistence of the liquid phase without the liquid-liquid phase prior to and during the coagel formation in the aqueous system 46) . Typically, alkyl glycosides likely forms a phase separated state comprising two different liquid compositions, but C8Gal did not. Optical-microscopy, atomic force microscopy, field-emission scanning electron microscopy, and powder XRD (PXRD) analyses of the xerogel of C8Gal revealed that the hydrogel is formed by nanofiber-like crystals consisting of hemihydrate of modulated SmA Cr, the so-called ribbon Cr phase (Fig. 3). Because the formation of nanofiber-based coagel is unique for C8Gal, consisting of galactose and normal octanol, the modification of the hydrogel by cryogenic treatment has been subsequently explored 47) . As a result, two effective cryogenic methodologies for changing the physicochemical properties of C8Gal Cr phases have been proposed. One is a hyperfast cooling at 30°C/min, and the other is freeze-thaw treatment with the addition of appropriate electrolytes. These methods can rapidly crystallize ice before the formation of hydrogels or inhibit the formation of hydrogels before ice crystallize. According to the simultaneous XRD-DSC measurements, the size of the crystals prepared by the abovementioned cryogenic treatments decreased, decreasing the T K and Δ H K of C8Gal/water hydrogels, respectively.
Trehalose fatty acid monoester (CnTre), consisting of trehalose moiety and alkyl chains, is an oligosaccharide-based surfactant that can be commercially available from Dojindo Lab (Kumamoto, Japan). Because of the symmetrical structure of the trehalose structure, the precise synthesis of the identified structure of trehalose fatty acid mono ester is significantly easier than that of sucrose fatty acid monoester, the most industrially manufactured sugar ester (Fig. 4a) 48) , 49) . They have excellent surface-active properties 49) , and recently, the unique performance as a cancer cell recognition 50) has been proposed. On the other hand, trehalose is an excellent component for pharmaceutical excipients 51) , 52) , and therefore, it was expected that trehalose amphiphiles would also exhibit excellent properties as excipients.
Thermotropic liquid crystalline (LC) phase behavior studies of trehalose fatty acid monoester (CnTre). Hot scientific topic represented by each figure are described around alphabetical number. (a) Solvent-free enzymatic synthesis of CnTre via esterificaion 48) . (b) Summary of phase behavior of CnTre hydrate Cr and anhydrous CnTre LC phase (n=10, 12, 14, 16) 53) . Lα: Lamellar fluid, Q: Cubic, IL: Isotropic liquid, Cr: Crystal. (c) Schematic illustration of spin-coating of CnTre solution, representative X-ray reflectivity (XRR) profile and temperature-dependent behavior of film thickness, t 59) . (d) Structural relaxation behaviors of bilayer length, d, and t/d around glass transition of CnTre. T g (1) and T g (2) were obtained by slow and rapid cooling rates, respectively 59) .
The phase behaviors of CnTre (n=10, 12, 14, 16) exhibiting thermotropic LC and hydrate Cr under desiccated conditions have been studied (Fig. 4b) 53) . The results showed that the monohydrate crystals of CnTre undergo dehydration around 80°C to become LC states. Because the melting point (T m) of their anhydrous crystals is assumed to be much higher, the use of hydrate crystals as the initial state rather than anhydrous crystals is considered effective for the application of the hot melt method. The drug will be included in their LC phases without excess heating. C10Tre formed the cubic LC phase, C14Tre and C16Tre formed the Lα LC phase, and C12Tre can form both the cubic and Lα LC phases, respectively, depending on the thermal condition. Their cubic and Lα LC phases exhibited glass transition at T g of approximately 80°C, which was much higher than that of CnGlc. Furthermore, in the case of C16Tre, the DSC and low-temperature wide-angle X-ray scattering (WAXS) measurements showed a distinct decrease in packing length at low temperatures, which was accompanied by thermal heat despite being in the glassy state. This phenomenon, confirmed in both thermal and structural analyzes, was attributed to a phase transition between the Lβ and Lα LC states in the glassy state. To the best of our knowledge, this was the first observation of a Lβ-Lα LC phase transition in the glassy state, including in lipid science studies 53) , 54) . The phenomenon strongly supports the proposal that glycolipid can become a partial glassy state, as mentioned in section 2. In addition, the low-temperature WAXS measurement was conducted using an apparatus setup, which is often used for single-crystal structure analysis. This was useful for evaluation in the low-temperature region under N2 gas atmosphere 53) .
On the other hand, the question of whether glycolipid glasses, which result in such characteristic phenomena, are real glasses in the true sense of the word arose. Generally, various thermophysical properties change dramatically below T g 54) , 55) , 56) , 57) , 58) . Furthermore, viscosity changes dramatically near the T g, and structural relaxation is observed in response to the cooling rate. One example of structural relaxation is the volume as a function of the cooling rate. To confirm whether such structural relaxation occurs at the glass transition of glycolipids, CnTres (n=14, 16) were used for clarification. CnTre is significant because of its high T g and excellent aligning property on the substrate for their LC phases 59) , which would be significant for various applications in cosmetics and pharmaceuticals.
The glass transition behavior can be evaluated in the nanofilm state (Fig. 4c). For nanofilms consisting of free sugar such as sucrose, trehalose, and CD, thickness, t, is the thermodynamic parameter to be evaluated 60) , 61) , 62) . On the other hand, in the CnTre LC film, not only t but also the bilayer length, d, of CnTre can be determined by X-ray analysis. Thus, we were inspired to examine two structural parameters: film thickness, t, and bilayer length, d 59) . Here, t was determined by X-ray reflectivity (XRR) analysis, and d was determined by PXRD analysis. As a result, when using t/d as a structural parameter, the number of layers remains constant below T g (Fig. 4d). In other words, the film structure is highly preserved in the glassy state. In addition, the structural relaxation behaviors in terms of t, d, and t/d were confirmed as a function of the cooling rate. From these results, we concluded that the glass transition of glycolipid can be explained by the conventional glass theory 55) , 56) , 58) , 59) , whereas the formation of a partial glassy state in the LC state would become the most significant specificity of glycolipid glass.
In terms of the utility development of glass transition of glycolipids, their application as a stabilizer of proteins during freeze-thaw and freeze-drying processes was considered. The effectiveness as a protein stabilizer during freeze-thaw and freeze-drying processes had been previously proposed by Izutsu et al. 27) To clarify the effectiveness of the glass formation of glycolipids, CnTre and CnGlc, which exhibit high T g of approximately 80°C and low T g of approximately 10°C, respectively, were compared 63) , 64) . As a result, a stronger retention effect was observed by increasing the alkyl chain length to preserve the enzymatic activity of L-lactate dehydrogenase (LDH) during the freeze-thaw process, indicating the importance of the surface activity of glycolipids 63) . On the other hand, the maintenance effects on the enzymatic activity of LDH depend on sugar moiety rather than the alkyl chain length for the freeze-drying process 64) . CnTre with a significantly higher T g than CnGlc was a more effective stabilizer, indicating that the stabilizing effect is strongly dependent on glass formation properties. Furthermore, the high glass-forming ability against the protein resulted in the long-term storage of the protein 64) . Thus, it was proposed that bifunctional properties such as an amphiphilic nature (a surface activity) and glass-forming capacities for glycolipid molecules are crucial for effective stabilization during the freeze-drying process and subsequent storage processes. As the film state of CnTre was effectively preserved in the glassy state 59) , it is assumed that the glassy glycolipid film formation around the protein would also be effective for stabilization during freeze-drying and subsequent storage processes.
The solubility enhancement of water-insoluble compounds by encapsulation by CDs has been reported. Owing to the presence of a hydrophobic internal cavity, CDs can form inclusion complexes with various hydrophobic guest molecules and afford additional values such as solubility, stability, and availability 4) . Furthermore, large aggregates formed by the self-assembly of CD guest complexes have been reported recently as a distinct issue affecting CD solubility. However, a systematic understanding of inclusion complexes, particularly what combination of CD host and guest compounds produced such a difference, has not been fully clarified.
Vitamin E (Tocopherol; Toc) is a representative lipophilic antioxidant, consisting of a chromanol head and a phytyl tail 65) , 66) . Recently, a comprehensive comparative study on CD-Toc complexation in aqueous systems has been reported 67) , 68) . Namely, the effects of various CDs such as α-CD, β-CD, γ-CD, 2,6-di-O-methylated β-cyclodextrin (2,6-DMCD), and randomly-methylated β-cyclodextrin (RDMCD) on aqueous systems containing inclusion complexes with Toc and 2,2,5,7,8-pentamethyl-6-chromanol (PMC) were investigated (Fig. 5). As a result, 2,6-DMCD formed a water-soluble inclusion complex with Toc and effectively enhanced its solubility, whereas β-CD and γ-CD exhibited a tendency to form large aggregates consisting of inclusion complexes in aqueous media, and α-CD neither exhibited solubility enhancement nor the development of aggregation. 2D ROESY nuclear magnetic resonance analysis showed the direct interaction between the chromanol ring and the sugar of 2,6-DMCD 68) , whereas the complexation of γ-CD was confirmed by the enhancement of fluorescence and the disappearance of asymmetrical methylene and symmetrical methyl stretching vibration in Fourier transform infrared spectra 67) . These behaviors have been interpreted as follows and summarized in Table 1; first, owing to the narrow pore size, the α-CD-Toc inclusion complex was rarely formed, and neither solubility enhancement nor stable dispersion was formed. Other CDs equipped with sufficient pore sizes could form complexes with Toc, but the solubility of Toc was not always improved. For other natural CD systems such as β-CD and γ-CD, possibly owing to the rigidity of CD molecules and the effect caused by the intermolecular hydrogen bonding, large aggregates are formed 67) . On the other hand, the solubility of inclusion complexes with methylated CD derivatives such as 2,6-DMCD and RDMCD was modified 68) . These methyl substituents may disrupt the regular hydrogen bonding network within native CD molecules and increase their ability to interact with the surrounding water molecules. However, for RDMCD, the effect of methyl substituents has been weakened, and some degree of aggregation of inclusion complexes was confirmed.
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Notably, Toc stabilized in each system and exhibited characteristic radical scavenging behaviors (Fig. 5). These aggregated systems, particularly the γ-CD-added system, exhibited remarkable sustained effects because of the slow dynamics 67) . In contrast, the rapid scavenging effect for molecularly dissolved Toc was recognized, even for the system in which the chromanol head was directly encapsulated by CD 68) . Thus, several specific vitamin E vehicle motifs using a CD stabilizer were proposed; 2,6-DMCD dissolves Toc and allows its rapid access to radicals, whereas β-CD and γ-CD form Toc-containing aggregates and afford packaging effects, which enable them to control the radical scavenging effect in aqueous systems. These different types of vehicles developed without an organic solvent must be fascinating devices to extend the biological applications of Toc. In addition, the γ-CD-Toc complex exhibited more potent cytoprotective activity than γ-CD alone, suggesting that the γ-CD-Toc complex enters COS-7 cells and scavenges intracellular lipid radicals in a cytoprotective manner 67) .
Meanwhile, the authors investigated the behavior of various CD and Toc combinations in water in the absence of organic solvents because biological research was assumed to require a system lacking in organic solvents. However, it was confirmed that several issues arose when Toc was pre-dissolved in an organic solvent before being added to the water media 68) .
Notably, Toc readily exhibits high dispersibility in the absence of CDs or surface-active species such as surfactants and exhibited excellent ABTS radical scavenging effects, even in the dispersion state comparable to water-soluble Trolox and 2,2,5,7,8-pentamethyl-6-chromanol (PMC) 69) . Furthermore, the study on the basic thermal behavior of pure ascorbic acid 6-palmitate (ASP), a representative lipophilic vitamin C derivative, confirmed the formation of the intermediated state consisting of Cr and LC phases after cooling of the LC state obtained by heating only above T m. The temperature-dependent 2D-GI-XD analysis was effective in identifying this anomalous behavior 70) . Note that Toc and ASP were classically treated as minor components in oil and fat science. The behaviors of these functional components as minor components had been investigated extensively. However, fundamental science that traditionally treats minor components as the main phase may be rather new. Such research from different perspectives can open up new horizons.
In this review, some of the recent advances in phase behavior studies of sugar-based amphiphiles are summarized while focusing on the author’s work. Basic research on simple glycolipids, such as alkyl β-D-glucosides and octyl β-D-galactoside, has provided abundant new knowledge about the molecular assembly of glycolipids. Generalization of the glass transition behavior and formation of a modulated lamellar Cr phase have been proposed. Because of their excellent glass-forming properties, oligosaccharide-based amphiphiles, such as trehalose fatty acid monoesters, significantly advance the clarification of the glass transition of glycolipids and the exploration of their usefulness. For these molecular assembly studies, X-ray measurements, such as XRD-DSC, 2D-GI-XD, and WAXS measurements with an apparatus typically used for single-crystal X-ray structural analysis, as well as XRR and PXRD measurements with an aligning LC film, were effective. Regarding research on inclusion complex systems consisting of CDs and vitamin E, the categorization of the inclusion type was performed through comprehensive comparative studies. This review emphasizes the significance of investigating the fundamental science of traditionally regarded as minor components such as surfactants and lipophilic vitamin lipids, with the assumption that they can also be the main components. In addition, the concepts described in this review, such as the formation of a non-continuous water layer, nanofabirization without liquid-liquid phase separation, glassification in partial domain, high-alignment nanofilm of glycolipids, and nanoaggregation of CD-guest molecule compounds, may be significant for creating further fascinating nanoarchitectonics.
The author is grateful to all collaborators for their support.
There are no conflicts of interest to declare.
