Structural transition of glucagon in the concentrated solution observed by electrophoretic and spectroscopic techniques

Glucagon, a polypeptide hormone consisting of 29 amino acid residues, tends to form gel-like fibrillar aggregates, and the glucagon fibril, as well as other pathologically related fibrils including prion, amylin, and beta-amyloid, have been found to be cytotoxic through the activation of apoptotic signaling pathways. To understand the aggregation properties of glucagon fibril, we have characterized and compared the physicochemical properties of glucagon, secretin, a member of the glucagon superfamily, and amylin using analytical techniques including capillary electrophoresis (CE), circular dichroism (CD), FT-IR, FT-Raman, transmission electron microscopy (TEM), and beta-sheet-imaging probe. Aging treatment of glucagon resulted in the formation of fibrillar aggregates in time- and concentration-dependent manner, and FT-IR and FT-Raman analyses showed the spectral shift of amide I band, suggesting the conformational changes from alpha-helix to beta-sheet structure. Interestingly, secretin, having high sequential and secondary structural homology with glucagon, did not generate the fibrillar aggregates at the conditions tested. In addition, we evaluated the association state of glucagon at various pHs raging from pH 2.0 to 3.5 using CE. Based on the CE data, the rate constants of glucagon aggregation were calculated to be 0.002 +/- 0.004/h and 0.080 +/- 0.011/h for aging at pH 2.0 and 3.5, respectively, suggesting the pH dependence of self-association. CE showed the potential to separate and detect the glucagon aggregates and intermediates during aging process.     

Eleven new 2-pyrones from a Fungi Imperfecti, Trichurus terrophilus, found in a screening study guided by immunomodulatory activity

In a screening study on immunomodulatory fungal constituents, eleven new 2-pyrones tentatively named TT-1 (1), and TT-2-11 (2-11) have been isolated from a Fungi Imperfecti, Trichurus terrophilus, and designated rasfonin (1), and trichurusin B-K (2-11), respectively. Compounds 1-4 exhibited considerably high immunosuppressive activities, and compounds 8-11 have shown moderate ones. The structure-activity relationships of these constituents have also been discussed.     

Compounds structurally related to tamoxifen as openers of large-conductance calcium-activated K+ channel

We found that a variety of compounds containing partial structures of tamoxifen showed activity as chemical modulators of large-conductance calcium-activated K+ channels (BK channels).     

Two new triterpenoids from the seeds of blackberry (Rubus fructicosus)

Two new ursane-type triterpenoids (1, 2) attached to isopropylidenedioxy group were isolated from the seeds of blackberry (Rubus fructicosus L., Rosaceae) along with two known ursane-type triterpenoids, 2,3-O-isopropylidenyl-2α,3α,19α-trihydroxyurs-12-en-28-oic acid (3) and 1β-hydroxyeuscaphic acid (4). The chemical structures of 1 and 2 were determined to be 2,3-O-isopropylidene-1β,2β,3β,19α-tetrahydroxyurs-12-en-28-oic acid and 1,2-O-isopropylidene-1β,2α,3α,19α-tetrahydroxyurs-12-en-28-oic acid, respectively, based on spectroscopic data. Additionally, their cytotoxic activity towards HL-60 human leukaemia cells was evaluated. Among them, 3 demonstrated a clear cytotoxic activity with 72.8 μM of IC₅₀ value.     

Accurate mass measurement in nano-electrospray ionization mass spectrometry by alternate switching of high voltage between sample and reference sprayers

An electrospray dual sprayer, which generates separate sample and reference sprays by alternately switching the high voltage between the two sprayers, is described. The technique permits accurate mass measurements in nano-electrospray ionization mass spectrometry (ESI-MS) to be obtained using a quadrupole/orthogonal acceleration time-of-flight mass spectrometer (Q-TOF). Similar to the method employed with a dual ESI source (Wolff JC et al., Anal. Chem. 2001; 73: 2605), the two sprays are orthogonal with respect to each other, but can be independently sampled without any baffle between these sprays. The reference sprayer is used in the original configuration of the ESI source and was optimized for a 1-2 muL/min flow, whereas the sample sprayer can be either a conventional glass capillary or a borosilicate tip of the type used for nano-ESI. Both sprayers can be positioned close to the cone so as to give maximum ion currents. The sample and reference sprays are independently generated by raising the potentials on the sample and reference sprayers to 1.4 and 3.0 kV, respectively; the high voltages can be rapidly turned on and off in ca. 1 ms. A nano-ESI-MS or nano-flow LC/ESI-MS experiment using a Q-TOF coupled with the above system gave mass accuracies within 3 ppm for measurements of ions up to m/z 1000 using subpicomole samples.     

Theoretical study of O2-H2O: potential energy surface, molecular vibrations, and equilibrium constant at atmospheric temperatures

The intermolecular potential energy surface of O(2)-H(2)O was investigated at ab initio MP2 and MRSDCI levels using the aug-cc-pVTZ basis set. The vibrational levels were evaluated by numerically solving the Schr?dinger equations for the nuclear motions with the ab initio potential functions using one- to three-dimensional finite-element methods. On the basis of the calculated partition functions, the equilibrium constant of the complex, K(p), was studied. The K(p) values at atmospheric temperatures of 200-300 K were found to be 1-2 orders of magnitude less than previous estimates from the harmonic oscillator approximation.     

Kinetics of the aromatic hydroxylation with permonophosphoric acid

Oxidation of phenol, anisole and toluene with permonophosphoric acid in acetonitrile or water gives the corresponding ortho and para hydroxylated aromatics (HO-C₆H₄-X, X = OH, OMe, Me). The observed ortho :para ratio in a solvent acetonitrile are as follows: 5·0 with phenol, 3·5 with anisole and 2·0 with toluene. The oxidation rates for phenol and anisole in acetonitrile are expressed as: v = k″[ArH][H₃PO₅]²h_o, where h_o is the Hammett's acidity function and ArH is phenol or anisole. A mechanism involving a rate-determining attack of protonated dimeric perphosphoric acid 4 on aromatic carbon is presented and discussed.     

Influence of cyclohexane vapor on stick-slip friction between mica surfaces

Stick-slip friction between mica surfaces under cyclohexane vapor has been investigated with the Surface Force Apparatus. The dynamic shear stress decreased from 60 to 10 MPa with increasing relative vapor pressure (rvp) from 5% to 50%. Between a rvp of 50% and 80%, the shear stress remained at approximately 10 MPa, with a slight decrease on increasing the rvp. At a rvp greater than 80%, the values of shear stress were below 5 MPa. The stick-slip behavior was observed in the rvp range of 20% to saturation. When the rvp reached 20%, stick-slip appeared but faded out with sliding time. At a rvp greater than 50%, the stick-slip pattern was stable without fading. By taking into account the size of the meniscus formed by capillary condensation of the liquid around the contact area and the Laplace pressure, the dependence of shear stress and the stick-slip modulation on rvp suggests that the origin of the stick-slip observed in cyclohexane vapor is as follows: At a rvp greater than 50%, where stable sick-slip is observed, the stick-slip caused by the cyclohexane layering in the contact area is of essentially the same origin as that observed with mica surfaces sliding in bulk cyclohexane liquid. As with the bulk liquid experiment, decreasing the layer thickness (or the number of the layers) between the surfaces increases the shear stress at the onset of slip. In the vapor phase experiments, the stick-slip is enhanced by the increase of the negative Laplace pressure in the capillary condensed liquid, thereby forcing the surfaces toward each other more strongly with decreasing rvp. In the rvp range between 20% and 50%, where the fading stick-slip is observed, the condensate liquid seeps into the contact area under the influence of the applied tangential force and thus triggers the slip motion. Due to the small condensation volume, the liquid condensed around the contact area is exhausted in the process of repeating stick-slip. As the slip length is limited to the meniscus size, the stick-slip amplitude becomes smaller, and eventually the surfaces start sliding without stick-slip.     

Enhancement of MR ratios using thin oxide layers in PtMn and α-Fe2O3-based spin valves

Spin valves having thin oxide layers in the pinned and/or free layers were prepared by sputtering. MR ratios of the spin valves were increased from 8.1 to 11.9% by inserting the oxide layer into the pinned layer in Ta/PtMn/CoFe/Cu/CoFe/Ta spin valves. MR ratio of 13.9% and considerably large sheet ΔR of 2.55 Ω were obtained in the PtMn-based spin valves having the oxide layer in the pinned and free layer. Larger MR ratio of 17.3% and the sheet ΔR of 1.3 Ω were obtained in the PtMn-based dual-type spin valves having the oxide layer in both pinned layers. α-Fe₂O₃ based spin valves having thin oxide layers were also prepared. MR ratios of the spin valves were increased from 11.9 to 14.3% by inserting the oxide layer into the free layer in α-Fe₂O₃/CoFe/Cu/CoFe/Ta spin valves. The enhancement of the MR ratios may be attributed to the specular scattering effect of the conduction electrons by the thin oxide layers.     

Effect of end group chemistry on surface molecular motion of monodisperse polystyrene films

The surface molecular motion of monodisperse polystyrene (PS) with various chain end groups was investigated on the basis of temperature‐dependent scanning viscoelasticity microscope (TDSVM). The surface glass transition temperatures, T_g^ss for the proton‐terminated PS (PS‐H) films with number‐average molecular weight, M_n of 4.9k–1,450k measured by TDSVM measurement were smaller than those for the bulk one, with corresponding M_ns, and the T_g^ss for M_n smaller than ca. 50k were lower than room temperature (293 K). In the case of M_n = ca. 50k, the T_g^ss for the α,ω‐diamino‐terminated PS (α,ω‐PS(NH₂)₂) and α,ω‐dicarboxy‐terminated PS (α,ω‐PS(COOH)₂) films were higher than that of the PS‐H film. On the other hand, the T_g^s for the α,ω‐perfluoroalkylsilyl‐terminated PS (α,ω‐PS(SiC₂C^F₆)₂) film with the same M_n was much lower than those for the PS films with all other chain ends. The change of T_g^s for the PS film with various chain end groups can be explained in terms of the depth distribution of chain end groups at the surface region.