Design of a stabilized short helical peptide and its application to catalytic enantioselective epoxidation of (E)-chalcone

Stabilized short helical heptapeptides containing a combination of an α-aminoisobutyric acid as a helical promoter and l/d-serine derivatives to produce cross-linked units were synthesized. The cyclic peptide R₃,₇R-2, which had d-serine derivatives at its 3rd and 7th positions, formed a stable right-handed (P) α-helix in solution and the crystalline state. Furthermore, its N-terminal free helical peptide catalyzed the enantioselective epoxidation of (E)-chalcone to afford the epoxide in a high yield and moderate enantioselectivity.     

Molecular size fractionation of soil humic acids using preparative high performance size-exclusion chromatography

High performance size-exclusion chromatography (HPSEC) is useful for the molecular size separation of soil humic acids (HAs), but there is no method available for various HAs with different chemical properties. In this paper the authors propose a new preparative HPSEC method for various soil HAs. Three soil HAs with different chemical properties were fractionated by a Shodex OHpak SB-2004 HQ column with 10mM sodium phosphate buffer (pH 7.0)/acetonitrile (3:1, v/v) as an eluent. The HAs eluted within a reasonable column range time (12-25 min) without peak tailing. Preparative HPSEC chromatograms of these HAs indicated that non-size-exclusion effects were suppressed. The separated fractions were analyzed by HPSEC to determine their apparent molecular weights. These decreased sequentially from fraction 1 to fraction 10, suggesting that the HAs had been separated by their molecular size. The size-separated fractions of the soil HA were mixed to compare them with unfractionated HA. The analytical HPSEC chromatogram of the mixed HA was almost identical to that of the unfractionated HA. It appears that the HAs do not adsorb specifically to the column during preparative HPSEC. Our preparative HPSEC method allows for rapid and reproducible separation of various soil HAs by molecular size.     

Surface chemical analysis and chromatographic characterization of polyethylenimine-coated hydroxyapatite with various amount of polyethylenimine

Polyethylenimine (PEI) has been widely used as a coating material to produce stationary phase for ion-exchange chromatography of biomolecules. However, a precise study of the PEI coating fraction has been lacking, despite such quantification being very important for fundamental research as well as identifying further industrial applications.In this study, we produced four types of PEI-coated hydroxyapatite (PEI-HAp) with various fractions of PEI (0.16%, 0.5%, 1.0%, 1.5%) using a spray-drying system to evaluate correlations between coating fractions and the thermochemical or chromatographic behaviors of theses products. The thermal analyses of these matrices showed two exothermic peaks when the PEI coating fraction exceeded 1.0%. The one peak indicated a PEI decomposition peak and the other would indicate bond dissociation of PEI layers formed over the HAp surface as the PEI concentration increased. Furthermore, the chromatographic analysis for the surface chemical characteristics showed the correlation between coating fraction and the retention time of protein or nucleotide. Acidic or phosphorylated proteins were more strongly adsorbed as the PEI coating fraction increased when the initial coating fraction was low, but at fraction exceeding 0.5%, constant retention was observed. The retention time of nucleotides increased in proportion to the fraction of PEI added. The good selectivity of PEI-HAp may be attributable to multifunctional interactions of electrostatic and bare Ca sites on HAp, not just the amino sites of PEI. These precise studies of PEI coating fraction are our original novel contributions, which could be achieved by quantitative consideration using thermal analysis and chromatography.     

Water-soluble low-molecular-weight cellulose chains radially oriented on gold nanoparticles

Cellulose chains bearing N-lipoyl group at the reducing-end as a sulfide linker, self-assembled on the surface of gold nanoparticles (CELL2Au, CELL13Au, and CELL41Au with the number average degrees of polymerization (DP_n) of 2, 13, and 41, respectively) were prepared. CELL2Au, CELL13Au, and CELL41Au were obtained via deprotection of the cellulose triacetate (CTA) self-assembled on the surface of gold nanoparticles that are consisting of CTA chains with corresponding DP_n organized in a radial manner with head-to-tail orientation, where a head is the reducing-end, and a tail is the non-reducing-end. CELL2Au and CELL13Au were well-dispersed in water including a trace of methanol, whereas CELL41Au was not. The transmission electron microscopy (TEM) observation of CELLAus deposited on copper grids revealed that the diameters (d) of the gold cores of CELL2Au, CELL13Au, and CELL41Au were 6.1, 6.1, and 11.5 nm, respectively. Wide angle X-ray diffractgram showed that cellulose chains of CELL13Au had quite low crystallinity and exhibited additional faint diffraction pattern of cellulose II. Cellulose chains of CELL41Au were amorphous. The UV–vis measurements revealed that CELL2Au and CELL13Au were well-dispersed in water. The hydrodynamic diameters (D) of CELL2Au and CELL13Au in water were 21.8 and 55.9 nm, respectively, according to dynamic light scattering (DLS) measurements, suggesting that cellulose chains on the gold were organized in a radial manner with head-to-tail orientation. ¹H-NMR measurement revealed that low-molecular-weight cellulose chains (DP_n = 13) on the gold dissolved in water, whereas low-molecular-weight cellulose (DP_n = 13) itself did not.