Hydrogelation of cyclic peptide amphiphile, colistin, through formation of hierarchically organized structure

Colistin (Col) is an cationic amphiphilic molecule having a cyclic peptide moiety as a hydrophilic group. Because of such a unique molecular architecture, self-assembled structure of Col should be much different from that of a linear amphiphilic peptide. Especially, effect of pH on self-assembly in aqueous Col solution is interesting because inter- and intra-ring interactions of Col should be affected with pH change. Thus, in this study, we investigated self-assembly of Col in aqueous solution with various pH by using small-angle X-ray scattering (SAXS) with synchrotron light source. Please click Additional Files below to see the full abstract

Structures and dynamic viscoelastic properties of micelles of mixtures of surfactin with cationic surfactant in aqueous solution

Surfactin sodium salt (SFNa) consisting of a long alkyl chain and cyclic peptide is a biosurfactant produced by Bacillus subtilis. SFNa is expected to be a useful material in cosmetics, medical field, and so on because it shows unique surface activities such as significant reduction of surface tension at extremely dilute concentration. In our previous study, we found SF formed monodisperse spherical micelles with low aggregation number in aqueous solution [1]. In addition, the aggregation number of SF micelles was discretely changed with varying salt concentration. However, such small changes of micelle structures cause slight change in viscoelasticity of the micelle solution. In the case that SF is used in detergent, tuning viscoelastic properties of its solution is requested. To tune the viscoelastic properties, tuning the structures of micelles should be important Mixing of anionic and cationic surfactant is one of the effective method to tune the structures of micelles. Therefore, addition of a cationic surfactant to anionic SFNa is expected to cause drastic change in viscoelastic properties owing to structural changes of SF micelles. Thus, in this study, we investigate the structures of micelles consisting of anionic SFNa and cetyltrimethyl ammonium bromide (CTAB) as a cationic surfactant and their viscoelasticity related to the structures of micelles. SFNa was provided by Kaneka Corporation and CTAB was dissolved at desired surfactant concentration, mole fraction of SFNa (XSF) and ratio of cation to anion (C/A) in aqueous NaCl solution. For the resulting SFNa-CTAB micelle solutions, visual observation, small angle X-ray scattering (SAXS) and dynamic viscoelastic analyses measurements were performed. We found that viscosity of aqueous solutions of SFNa-CTAB micelles are increased with increasing SF content in XSF \u3c 0.2 and CTAB content in 0.65 XSF \u3e 0.5. Therefore, it should be considered that structures of mixed micelles in these regions are much different from those of SFNa or CTAB micelles. Figure 1 shows SAXS profiles of SF-CTAB micelles at XSF = 0.1 (Red) and 0.6 (Blue). It could be confirmed scattering intensities in both systems are proportional to q-1 at low q range. Therefore, SF-CTAB mixtures form worm-like micelles at XSF = 0.1 and 0.6. However, SAXS profiles of these micelles are much different in high q region. Consequently, these micelles have different interiors. Thus, to investigate the effect of such structural difference of micelles on viscoelastic properties, dynamic viscoelastic measurements were performed. Figure 2 shows concentration dependences of the terminal relaxation times (τs) of SFNa-CTAB micelles at XSF = 0.1 and 0.6 obtained from the analyses for frequency dependence of storage and loss moduli by using Maxwell model. The τSs of these micelles are almost constant against micelle concentrations. This result means the entanglements of worm-like micelles of SFNa-CTAB mixtures are regarded as transient networks. References 1. Fujii, S. et al., Scientific Reports 2017, 7, 44494. 2. Naruse, K. et al., J. Phys. Chem. B. 2009, 113, 10222-10229 Please click Additional Files below to see the full abstract

Study on relation between spatial distribution and release rate of hydrophobic compounds incorporated in polymer micelles with anomalous small angle X-ray scattering

Amphiphilic block copolymers in aqueous solution undergo self-assembly into polymer micelles composed of hydrophobic core and hydrophilic shell. The polymer micelles can solubilize hydrophobic compounds in aqueous solution by incorporating them in the hydrophobic core. Therefore, they have been expected to be a drug career in drug delivery system (DDS). In DDS, controlling of the drug release behavior and retention stability are critical issues. However, tuning release rate and stability of retention of drug molecules is significantly difficult. Since the hydrophobic molecules must pass through the hydrophobic cores and hydrated corona layers to go out the polymer micelles, their release properties should strongly depend on spatial distribution of drug molecules in polymer micelles. Therefore, to elucidate the relation between spatial distribution of drug molecules and release properties of drug molecules is of significant importance to design a novel DDS. Thus, the aim of this study is to clarify the relation between spatial distribution of hydrophobic compounds in polymer micelles and their release and retention property. Poly(methyl methacrylate)-block-poly(N,N-(dimethylamino)ethyl methacrylate) (Poly-1) as amphiphilic block copolymer was synthesized by reversible addition-fragmentation radical polymerization. The weight- and number-average molecular weights of the resulting Poly-1 were 1.6104 g mol-1 and 1.9104 g mol-1, respectively. Three kinds of compounds (9-bromofluorene (BrF), 4-bromobenzyl alcohol (BrBzOH), 4-bromophenol (BrPh)) were employed as bromine-labeled hydrophobic compounds. Poly-1 and a hydrophobic compound were mixed at 10 wt% of a hydrophobic compound against Poly-1. Please click Additional Files below to see the full abstract

カイゴウセイ コウブンシ コンゴウケイ ノ ソウキョドウ ニカンスル ケンキュウ

博士（工学）東京農工大