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71.
We showed previously that poly(L-lactide)-grafted dextran could form biodegradable nanogels in water. In this paper, various properties of Dex-g-PLLA nanogels were compared with Dex-Chol (dextran-cholesterol conjugate) nanogels to investigate the effects of hydrophobic units. Dex-g-PLLA nanogels exhibited significantly lower CAC and higher colloidal stability, indicating a strong tendency to form nanogels. We prepared lysozyme-loaded Dex-g-PLLA nanogels, and they exhibited a sustained release of lysozyme for 1 week without denaturation in PBS at 37 degrees C. The Dex-g-PLLA nanogels therefore have great potential as a delivery vehicle for therapeutic protein. 相似文献
72.
Soonchul Kang Hironobu Hayashi Tomokazu Umeyama Dr. Yoshihiro Matano Prof. Nikolai V. Tkachenko Prof. Helge Lemmetyinen Prof. Hiroshi Imahori Prof. 《化学:亚洲杂志》2008,3(12):2065-2074
Trifluoroacetic acid‐catalyzed condensation of pyrrole with electron‐deficient and sterically hindered 3,5‐bis(trifluoromethyl)benzaldehyde results in the unexpected production of a series of meso‐3,5‐bis(trifluoromethyl)phenyl‐substituted expanded porphyrins including [22]sapphyrin 2 , N‐fused [22]pentaphyrin 3 , [26]hexaphyrin 4 , and intact [32]heptaphyrin 5 together with the conventional 5,10,15,20‐tetrakis(3,5‐bis(trifluoromethyl)phenyl)porphyrin 1 . These expanded porphyrins are characterized by mass spectrometry, 1H NMR spectroscopy, UV/Vis/NIR absorption spectroscopy, and fluorescence spectroscopy. The optical and electrochemical measurements reveal a decrease in the HOMO–LUMO gap with increasing size of the conjugated macrocycles, and in accordance with the trend, the deactivation of the excited singlet state to the ground state is enhanced. 相似文献
73.
Kiyonaga T Fujii M Akita T Kobayashi H Tada H 《Physical chemistry chemical physics : PCCP》2008,10(43):6553-6561
TiO(2) particle-supported Au nanoparticles (NPs) with varying sizes and good contact (Au/TiO(2)) were prepared under a constant loading amount by the deposition-precipitation method. The Fermi energy of Au NPs loaded on TiO(2) at the photostationary state (E(F)') was determined in water by the use of S/S(2-) having specific interaction with Au as a redox probe. The E(F)' value goes up as the mean size of Au NPs (d) increases at 3.0 相似文献
74.
Sakai K Umezawa S Tamura M Takamatsu Y Tsuchiya K Torigoe K Ohkubo T Yoshimura T Esumi K Sakai H Abe M 《Journal of colloid and interface science》2008,318(2):440-448
The adsorption and micellization behavior of novel sugar-based gemini surfactants (N,N(')-dialkyl-N,N(')-digluconamide ethylenediamine, Glu(n)-2-Glu(n), where n is the hydrocarbon chain length of 8, 10 and 12) has been studied on the basis of static/dynamic surface tension, fluorescence, dynamic light scattering (DLS) and cryogenic transmission electron microscope (cryo-TEM) data. The static surface tension of the aqueous Glu(n)-2-Glu(n) solutions measured at the critical micelle concentration (cmc) is observed to be significantly lower than that of the corresponding monomeric surfactants. This suggests that the gemini surfactants, newly synthesized in the current study, are able to form a closely packed monolayer film at the air/aqueous solution interface. The greater ability in the molecular association is supported by the remarkably (approximately 100-200 times) lower cmc of the gemini surfactants compared with the corresponding monomeric ones. With a combination of the fluorescence and DLS data, a structural transformation of the Glu(n)-2-Glu(n) micelles is suggested to occur with an increase in the concentration. The cryo-TEM measurements clearly confirm the formation of worm-like micelles of Glu(12)-2-Glu(12) at the concentration well above the cmc. 相似文献
75.
76.
There has been a great interest in developing photoswitchable magnetic materials because of their possible applications for future high-density information storage media. In fact, however, the examples reported so far did not show ferromagnetic behavior at room temperature. From the viewpoint of their practical application to magnetic recording systems, the ability to fix their magnetic moments such that they still exhibit room-temperature ferromagnetism is an absolute requirement. Here, we have designed reversible photoswitchable ferromagnetic FePt nanoparticles whose surfaces were coated with azobenzene-derivatized ligands. On the surfaces of core particles, reversible photoisomerization of azobenzene in the solid state was realized by using spacer ligands that provide sufficient free volume. These photoisomerizations brought about changes in the electrostatic field around the core-FePt nanoparticles. As a result, we have succeeded in controlling the magnetic properties of these ferromagnetic composite nanoparticles by alternating the photoillumination in the solid state at room temperature. 相似文献
77.
We analyze a list heuristic for the vertex cover problem that handles the vertices in a given static order based on the degree sequence. We prove an approximation ratio of at most for a nonincreasing degree sequence, and show that no ordering can achieve an approximation ratio of less than . 相似文献
78.
Tanaka M Hayashi S Eu S Umeyama T Matano Y Imahori H 《Chemical communications (Cambridge, England)》2007,(20):2069-2071
A novel naphthyl-fused zinc porphyrin carboxylic acid has been synthesized and employed successfully in a dye-sensitized TiO2 solar cell, with a power conversion efficiency of 4.1%, which is improved by 50% relative to the unfused porphyrin reference cell. 相似文献
79.
Morishita T Harigai M Yamazaki Y Kamikubo H Kataoka M Imamoto Y 《Photochemistry and photobiology》2007,83(2):280-285
The role of the array of aromatic amino acid side chains located close to the chromophore binding loop of photoactive yellow protein (PYP) was studied using the alanine-substitution mutagenesis. Phe92, Tyr94, Phe96 and Tyr98 were replaced with alanine (F92A, Y94A, F96A and Y98A, respectively), then these mutants were characterized by UV-visible absorption spectra, circular dichroism (CD) spectra, thermal stability and photocycle kinetics. Absorption maxima of F92A, Y94A, F96A and Y98A were 444, 442, 439 and 447 nm, respectively, different to wild type (WT) at 446 nm. Far-UV CD spectra of mutants other than F92A were different from WT, indicating that Tyr94, Phe96 and Tyr98 maintain the native secondary structure of PYP. Mid-point temperatures of thermal denaturation of F92A, Y94A and F96A, estimated by the CD signal at 222 nm, were 5-10 degrees C lower than WT. Time constants of the photocycle estimated by flash-induced absorbance change were 0.36 s for WT and 1.4 s for Y98A, however, 100, 30 and 3000 times slower than WT for F92A, Y94A and F96A, respectively. Tyr98 is located in the loop region, whereas Phe92, Tyr94 and Phe96 are incorporated in the beta4 strand, showing that aromatic amino acid residues in the beta-sheet regulate the absorption spectrum, thermal stability and photocycle of PYP. Aromatic rings of Phe92, Tyr94 and Phe96 lie nearly perpendicular to the aromatic ring of Phe75 or chromophore. Possible weak hydrogen bonds between the aromatic ring hydrogen and pi-electrons of these residues are discussed. 相似文献
80.
Molecular aggregates of partially fluorinated quaternary ammonium salt gemini surfactants 总被引:1,自引:0,他引:1
Matsuoka K Yoshimura T Shikimoto T Hamada J Yamawaki M Honda C Endo K 《Langmuir : the ACS journal of surfaces and colloids》2007,23(22):10990-10994
The size and shape of novel partially fluorinated gemini surfactant 1,2-bis[dimethyl-(3-perfluoroalkyl-2-hydroxypropyl)ammonium]ethane bromide (CnFC3-2-C3CnF, where n=4, 6, and 8) were investigated in aqueous solution by means of light scattering and transmission electron microscopy (TEM). The sizes of these molecular aggregates changed with increasing carbon number of the alkyl chain and concentration. For example, the apparent hydrodynamic radius by dynamic light scattering was 18 nm at a concentration of cmcx5 for n=4, 115 nm at the cmcx15 for n=6, and 62 nm at the cmcx30 for n=8, at 298.2 K. The shapes of CnFC3-2-C3CnF aggregates drastically changed with the alkyl chain length; the aggregates were mainly in the form of large or irregular small aggregates (n=4), string-like aggregates (n=6), and vesicles (n=8). The bromide-ion activity was measured using a bromide-ion-selective electrode to determine the degree of counterion binding to the aggregates. The degree of counterion binding to aggregate was very small compared with that in the typical hydrogenated gemini surfactants. These results indicated that the small curvature of large aggregates was not influenced by an electrostatic repulsion between the cationic head groups in the case of the bulky molecular volume of fluorinated gemini surfactants. 相似文献