Temperature-triggered fusion of vesicles composed of right-handed and left-handed amphiphilic helical peptides

Vesicles prepared from a mixture of (Sar)(25)-b-(L-Leu-Aib)(6) (SLL) and (Sar)(25)-b-(D-Leu-Aib)(6) (SDL) fused with themselves upon heating to 90 °C. The vesicles also fused with (Sar)(28)-b-(L-Leu-Aib)(8) vesicles upon heating to 90 °C. The temperature-triggered fusion was due to the phase transition of the mixed membrane of SLL and SDL at 90 °C and should be driven by the bending energy stored in the stereocomplex membrane upon taking a vesicular structure.     

Aggregation behavior of organic‐soluble semi‐aromatic polyimides in N‐methylpyrrolidone systems

Aggregation behavior of the organic‐soluble semi‐aromatic polyimides, whose degrees of imidization range from 69 to 96%, obtained using 4,4′‐oxydianiline, 4,4′‐diamino‐3,3′dihydroxybiphenyl, and bicyclo[2.2.2]‐oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA) in N‐methylpyrrolidone (NMP), NMP/cyclohexanone, and NMP/γ‐butyrolactone (BCDA‐based polyimides) were studied by static light scattering (SLS) and dynamic light scattering (DLS). The DLS analyses for the multirelaxation modes demonstrated the specific character unlike flexible polymers that the single BCDA‐based polyimide chains first associate with each other to form small clusters in the dilute region, and then expand to large aggregates by the entanglements between the small clusters with an increasing concentration into the semi‐dilute region. Given the semi‐aromatic structure of BCDA‐based polyimides weakening the charge transfer (CT) interaction between the diamine and the dianhydride unit, it is concluded that the unique aggregation behavior of BCDA‐based polyimides is dominated by the balance between the driving force for the “organic solubility” given by both the increase in bulkiness and the decrease in the CT interaction, and that for the “organic insolubility” derived from both the hydrogen‐bonded interaction of the phenolic hydroxyl groups and the π–π interaction of the phenyl rings. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Combinatorial Synthesis of Deoxyhexasaccharides Related to the Landomycin A Sugar Moiety,Based on an Orthogonal Deprotection Strategy

In this report, we describe the stereoselective synthesis of a combinatorial library comprised of 16 deoxyhexasaccharides that are related to a landomycin A sugar moiety, based on an orthogonal deprotection strategy. The use of an olivosyl donor containing a benzyl ether at the C3 position and benzoyl ester at the C4 position, and the olivosyl donor, a naphthylmethyl ether, and a p‐nitrobenzylethyl or benzyl sulfonyl ester enabled the synthesis of a set of four diolivosyl units containing a hydroxyl group at the C3 or C4 position by a simple glycosylation and deprotection procedure. Using a phenylthio 2,3,6‐trideoxyglycoside, α‐selective glycosidation proceeded without anomerization of the 2,6‐dideoxy‐β‐glycosides. In addition, alkylhydroquinone and levulinoyl groups were found to be an effective set of orthogonal protecting groups for the anomeric position and a hydroxyl group. The coupling of all combinations of trisaccharide units in a β‐selective manner was accomplished by activation of the glycosyl imidate with I₂ and Et₃SiH. No cleavage of the acid‐labile 2,3,6‐trideoxyglycoside was observed under the conditions used for the reactions. Finally, all of the protected hexasaccharides were deprotected by hydrolysis of the esters, microwave (MW) assisted cleavage of the 2‐trimethylsilylethoxymethoxy (SEM) ether, and a Birch reduction.     

Unusual degradation behavior of citric acid-crosslinked gelatin in vitro and in vivo

The aim of this study was to evaluate the biodegradability and biocompatibility of gelatin matrices designed for drug-eluting stents (DESs). The matrices were prepared by crosslinking alkali-treated gelatin (AlGelatin) with a citric acid-based crosslinker, trisuccinimidyl citrate (TSC), to form AlGelatin-TSC. The biodegradation behavior of the matrices was evaluated in vitro and in vivo. An in vitro enzymatic degradation test showed that AlGelatin-TSC prepared at a TSC concentration of 20 mM is the most stable in collagenase solution compared to AlGelatin-TSC prepared at TSC concentrations higher or lower than 20 mM. Then, AlGelatin-TSC were implanted subcutaneously in rats to evaluate their biodegradability and tissue reaction in vivo. Similar to the in vitro degradation behavior, AlGelatin-TSC with TSC concentration of 20 mM exhibited the lowest biodegradable rate in vivo among all AlGelatin-TSC. In addition, strong inflammation and calcification were not observed for AlGelatin-TSC at any TSC concentration. From an analysis of the crosslinking density of the resulting AlGelatin-TSC, the lowest biodegradability of AlGelatin-TSC with TSC concentration of 20 mM was due to the highest crosslinking density of the matrix. These results suggest that AlGelatin-TSC is suitable for use as matrices in DESs because of its excellent biocompatibility and biodegradability.     

Acceleration of nickel diffusion by high tensile stress in cold-worked type 316 stainless steel at 450°C

The effect of tensile stress on diffusion was studied by the diffusion couple method. A diffusion couple was prepared by electroless plating a nickel thin layer on the round notch surface of a compact tension-type specimen of 20% cold-worked Type 316 stainless steel. The couple was diffused at 450°C for 4003?h under the maximum tensile stress of 553?MPa in the load direction. A rapid diffusion coefficient of nickel in the Type 316 stainless steel was observed at the high tensile stress zone that was 6.5 times faster than that at the low-stress zone.     

Magnetic properties of high-Bs Fe–Cu–Si–B nanocrystalline soft magnetic alloys

In the present study, the magnetic properties and microstructures of newly developed Fe–Cu–Si–B alloys prepared by annealing the melt-spun ribbon have been studied. The average size and number density of nanocrystalline grains were about 20 nm and 10²³–10²⁴ m⁻³, respectively. The saturation magnetic flux density B_s for the present alloy is more than 1.8 T, that is about 10% larger than that of Fe-based amorphous alloys. Moreover, core loss P of the present alloy is about half of that of Si-steel up to B=1.7 T.     

Measurement of sound-pressure distribution in replicas of the oral cavity.

The spatial distributions of sound pressure in artificial oral cavities were measured to examine the characteristics of wave propagation in the vocal tract. The measurement was performed with plaster replicas of the oral cavity, and pure tones were used as the driving signals to obtain both amplitude and phase distributions at varied frequencies. Plane-wave propagation, which has been widely assumed for speech production models, was examined from the measured spatial distributions of sound pressure. Trajectories of media particles and vectorial maps of acoustic intensity, which can be computed from the measured pressure distributions, were also presented to visualize the acoustic field in the oral cavity. The results showed that at certain frequencies there existed points where sound pressure was absolutely zero, with the phase spatially circulating around them. Up to about 4 kHz, except at these certain frequencies, the wave front was almost one-dimensional, though an amplitude gradient was seen in the vertical direction.     

Effect of acoustical damping with a porous absorptive layer in the cavity to reduce the structure-borne sound radiation from a double-leaf structure

Structure-borne sound radiation from a double-leaf structure with a porous absorptive layer in the cavity is studied theoretically as well as experimentally. The study is for establishing a countermeasure to reduce the structure-borne noise radiated from an interior leaf into rooms and for clarifying its reduction effect. The sound field radiated from a double-leaf elastic plate with layers of arbitrary media in the cavity set into vibration by a point force excitation is theoretically analyzed. The effect of the bulk vibration of an absorptive layer is also considered by a simple model into the present theory. Radiation reduction of an inner-layer derived from the theory is experimentally validated. Parametric studies reveal that increasing the ratio of an absorptive layer thickness to the cavity depth is effective to reduce the structure-borne sound radiation but high flow resistivity of the absorbent material is not necessarily required. A practical equation to predict the mass-air-mass resonance frequency for absorbent cavity case is given in a simple form.