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Mesoporous silica shells were formed on nonporous spherical silica cores during the sol–gel reaction to elucidate the mechanism for the generation of secondary particles that disturb the efficient growth of mesoporous shells on the cores. Sodium bromide (NaBr) was used as a typical electrolyte for the sol–gel reaction to increase the ionic strength of the reactant solution, which effectively suppressed the generation of secondary particles during the reaction wherein a uniform mesoporous shell was formed on the spherical core. The number of secondary particles (N2nd) generated at an ethanol/water weight ratio of 0.53 was plotted against the Debye–Hückel parameter κ to quantitatively understand the Debye screening effect on secondary particle generation. Parameter κa, where a is the average radius of the secondary particles finally obtained in the silica coating, expresses the trend in N2nd at different concentrations of ammonia and NaBr. N2nd was much lower than that expected theoretically from the variation of secondary particle sizes at a constant Debye–Hückel parameter. A similar correlation with κa was observed at the high and low ethanol/water weight ratios of 0.63 and 0.53, respectively, with different hydrolysis rate constants. The good correlation between N2nd and κa revealed that controlling the ionic strength of the silica coating is an effective approach to suppress the generation of secondary particles for designing mesoporous shells with thicknesses appropriate for their application as high-performance liquid chromatography column packing materials.

A gold nanoparticle (AuNP) has a localized surface plasmon resonance peak depending on its size, which is often utilized for surface-enhanced Raman scattering (SERS). To obtain information on the cholesterol (Chol)-incorporated lipid membranes by SERS, AuNPs (5, 100 nm) were first functionalized by 1-octanethiol and then modified by lipids (AuNP@lipid). In membrane surface-enhanced Raman spectroscopy (MSERS), both signals from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and Chol molecules were enhanced, depending on preparation conditions (size of AuNPs and lipid/AuNP ratio). The enhancement factors (EFs) were calculated to estimate the efficiency of AuNPs on Raman enhancement. The size of AuNP100nm@lipid was 152.0 ± 12.8 nm, which showed an surface enhancement Raman spectrum with an EF2850 value of 111 ± 9. The size of AuNP5nm@lipid prepared with a lipid/AuNP ratio of 1.38 × 104 (lipid molecule/particle) was 275.3 ± 20.2 nm, which showed the highest enhancement with an EF2850 value of 131 ± 21. On the basis of fluorescent probe analyses, the membrane fluidity and polarity of AuNP@lipid were almost similar to DOPC/Chol liposome, indicating an intact membrane of DOPC/Chol after modification with AuNPs. Finally, the membrane properties of AuNP@lipid systems were also discussed on the basis of the obtained MSERS signals.

Fluorescence probes are usually employed to analyze pharmacokinetics of drug carriers; however, this method using usual probes is not suitable to monitor drug carriers in detail because fluorescence spectra do not change by the disruption of drug carriers. In this study, pyrene-fatty acid conjugates were investigated as probes to monitor the state of drug carriers in real time. 1-Pyrenemethanol was conjugated with fatty acids, such as lauric acid, stearic acid, and behenic acid, and the conjugates were stirred in ethanol, resulting in the formation of submicron particles; these particles exhibited excimer emission. When J774.1 and Colon 26 cells were treated with these particles, the associated fluorescence spectra shifted from excimer emission to monomer emission. Moreover, the degree of change was controlled by the type of fatty acid. These results support the design of drug carriers that can be used to monitor pharmacokinetics in real time and to control the disruption time.

The use of achiral surfactant assemblies as a reaction platform for an alkylation reaction resulted in a high enantiomeric excess. Dilauryldimethylammonium bromide (DDAB) vesicles were modified with cholesterol to promote alkylation of N-(diphenylmethylene)glycine tert-butyl ester (DMGBE) with benzyl bromide, resulting in high conversion (∼90%) and high enantioselectivity (up to 80%). The R-enantiomer was formed on using the DDAB vesicles, whereas the use of phospholipid liposomes prepared from 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) produced an excess of the S-enantiomer. Considering the chemical structures of the reaction substrates and amphiphiles as well as the membrane structures and properties of DDAB vesicles and DOPC liposomes, it is suggested that the enantiomeric excesses result from the location of the quaternary amine of the amphiphiles and the DMGBE at the outer surface of the membrane. We show that the enantioselective reaction at the surface of the self-assembly could be regulated by adjusting the chemical structures and resulting membrane properties of the self-assembly.

We first report that a highly enantioselective C–C bond formation reaction was achieved with liposomes in aqueous media. Alkylation of N-(diphenylmethylene)glycine tert-butyl ester (DMGBE) with benzyl bromide was conducted in the presence of cetyltrimethylammonium bromide micelles, resulting in a high conversion of DMGBE but little enantiomeric excess (e.e.) of the product. The same reaction was then carried out in 1,2-dioleoyl-sn-glycero-3-phosphocholine liposome suspensions, where the e.e. values were high (at least 90 % (S)), indicating that the liposome membranes can behave as the promoter of the enantioselective reaction. Changing the type of lipid to 1,2-dipalmitoyl-sn-glycero-3-phosphocholine to form a more ordered bilayer membrane lowered the reaction conversion but still maintained high e.e.% , that is, >90 (S), regardless of lipid chirality. It is indicated that multiple interactions between the DMGBE intermediate and lipid molecules promoted the migration of the intermediate into the interior of the membrane, whose bottom side (Si face) could be free for alkylation. These results suggest that liposomes can promote and regulate the alkylation of amino acid derivatives.