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1.
In this study, both α-chitin powders and nanofibers were successfully dissolved in 20 wt% NaOH solutions at low temperatures. Elemental analysis confirmed that this NaOH-freezing treatment did not cause deacetylation of chitin. After heating and neutralizing with water, chitin hydrogels could be prepared. X-ray diffraction and field emission scanning electron microscope data demonstrated that these two hydrogels formed typical regenerated microporous structures with low crystallinity, which was caused by the dissolution process. Based on this result, cold ethanol was used for α-chitin nanofibers during the initial stages of neutralization, which effectively prevented the dissolution and decrease in crystallinity and was even able to preserve the continuous network structure of original nanofiber. This gelation behavior seems to be attributed to interdigitation and aggregation between neighboring nanofibers in cold alkali solution leading to the shrinkage of the hydrogel. In general, by avoiding the dissolution process, highly crystalline hydrogel based on α-chitin nanofibers was prepared by a simple NaOH treatment without use of any other chemical solvents or cross-linking agents. We expect this new type of hydrogel could be promoted to wide applications and research studies as novel green nanomaterials. 相似文献
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Cellulose - 2,2,6,6-tetramethylpiperidine-1-oxyl-radical (TEMPO) oxidation is a classical method to obtain carboxyl chitin nanomaterials, but when the traditional TEMPO/NaBr/NaClO (TBN) oxidation... 相似文献
4.
Ying Shah Zhou Dong Zhi Yang Jun Nie 《中国化学快报》2007,18(1):118-120
Crosslinked chitosan-based nanofibers were successfully prepared via electrospinning technique with heat mediated chemical crosslinking followed.The structure,morphology and mechanical property of nanofibers were characterized by attenuated total reflection-Fourier transform infrared spectroscopy(ATR-FTIR),scanning electron microscopy(SEM),Instron machine,respec- tively.The results showed that,nanofibers exhibited a smooth surface and regular morphology,and tensile strength of nanofibers improved with increasing of triethylene glycol dimethacrylate(TEGDMA)content. 相似文献
5.
Attempts to substantially increase the relative proportion of β-lactose octaacetate in products of acetylation of α-lactose monohydrate using various acetylation protocols failed. Nevertheless, the revised protocol for isolation and crystallization, based on the classical work by Hudson and Johnson, rendered preparation of β-lactose octaacetate less labor intensive. It is proposed that the melting point and [α]D value are not reliable criteria of purity of β-lactose octaacetate, which can be confidently determined by 1H NMR spectroscopy. 相似文献
6.
M. K. Grachev S. V. Sipin L. O. Kononov E. E. Nifant′ev 《Russian Chemical Bulletin》2009,58(1):223-229
An approach to the synthesis of amphiphilic glycophospholipids based on β-cyclodextrin (β-CD) was proposed. Distinctive features
of the proposed method are the use of highly efficient trivalent phosphorus derivatives in the first steps of the synthesis
and the regioselective monophosphorylation of nonprotected β-CD. The efficiency of using 13С NMR spectroscopy for the determination
of the position and number of phospholipid residues introduced into the CD composition was shown. 相似文献
7.
Kahina Si-Ahmed Fairouz Tazerouti Ahmed Y. Badjah-Hadj-Ahmed 《Analytical and bioanalytical chemistry》2009,395(2):507-518
In order to study the effect of the nature and the length of the spacer, three mixed 10-undecenoate/phenylcarbamate derivatives
of β-cyclodextrin have been prepared and linked to allylsilica gel by means of a radical reaction. The chiral recognition
ability of the resulting materials, when used as liquid chromatography chiral stationary phases (CSPs), was evaluated using
heptane and either 2-propanol or chloroform as organic mobile-phase modifiers. A large variety of racemic compounds have been
separated successfully on these CSPs (mainly pharmaceuticals and herbicides). Optimization of these separations was discussed
in terms of mobile-phase composition and structural patterns of the injected analytes. The efficiencies of the three prepared
materials were compared to those of previously described perphenylated-β-cyclodextrin column and to analogous cellulose derivative-based
CSPs.
Schematic illustration of the b-cyclodextrin/mandelic acid inclusion complex 相似文献
8.
. Oxidation of β-hydroxy thioethers with MnO2-aqu. 35%/HCl in methanol gives β-hydroxy sulfoxides in high yields. 相似文献
9.
Jun Yang Chun-Rui Han Jiu-Fang Duan Ming-Guo Ma Xue-Ming Zhang Feng Xu Run-Cang Sun 《Cellulose (London, England)》2013,20(1):227-237
The unique combinations of hard and soft components with core/shell structures were proposed to synthesize high strength nanocomposite hydrogels. The elastomeric hydrogels containing rod-like cellulose nanocrystals (CNCs) core and polyacrylamide shell were made from aqueous solutions via free radical polymerization in the absence of chemical cross-links. The obtained hydrogels possessed greater tensile strength and elongation ratio when compared with chemically cross-linked counterparts. Oscillatory shear experiments indicated that CNCs interacted with polymer matrix via both chemical and physical interactions and contributed to the rubbery elasticity of the hydrogels. The nanocomposite hydrogels were more viscous than the chemical hydrogels, suggesting the addition of CNC led to the increase of energy dissipating and viscoelastic properties. The network structure model was proposed and it suggested that the high extensibilities and fracture stresses were related to the well-defined network structures with low cross-linking density and lack of noncovalent interactions among polymer chains, which may promote the rearrangements of network structure at high deformations. 相似文献
10.
Min Wu Daisuke Sawada Yu Ogawa Satoshi Kimura Masahisa Wada Shigenori Kuga 《Cellulose (London, England)》2013,20(6):2757-2763
The highly crystalline β-chitin from diatom Thalassiosira weissflogii was esterified via intercalation with succinic anhydride followed by simple heating, maintaining the original crystalline order. Due to the introduced free carboxyl groups, the chitin ester crystal showed ion exchange ability for metal cations in aq. solution. Heavy metal cations such as Pb2+ bound to the β-chitin succinate gave characteristic X-ray diffraction patterns, indicating regular alignment of metal ions. Such materials represent a new type of organometallic architecture, possibly leading to novel functionalities. 相似文献
11.
Svetlana R. Derkach Nina I. Sokolan 《Journal of Dispersion Science and Technology》2017,38(10):1427-1434
Influence of the chitosan concentration in the low-concentrated acidic hydrogels formed by (bio)polyelectrolyte chitosan–gelatin complexes (at a constant gelatin concentration of 1%) was studied by shearing in steady flow and linear oscillations. These complexes, including native gelatin, demonstrate clearly expressed viscoelastic properties. Viscoelastic properties correlated well with the non-Newtonian behavior of hydrogels (according to the Cox–Merz rule). Increasing the chitosan concentration (from 0.1% to 0.6%) results in exponential growth of the apparent viscosity, yield stress, and storage modulus. However, a further increase in chitosan concentration to 0.8% leads to a reduction in these rheological parameters due to the electrostatic repulsion of similarly charged polyelectrolyte complexes under the high concentration of these complexes. The macro-rheological properties of chitosan–gelatin gels are mainly determined by the colloidal structure of sol-precursors in solutions. The yield stress dependence on the radius of the dispersed particles is of square type. Electron photomicrographs showed that the introduction of even small quantities of chitosan leads to radical changes in the supramolecular structure of the gelatin gel. 相似文献
12.
New bimolecular sulfur-containing -phenylethylamines and N-benzyltetrahydroisoquinolines have been synthesized from formyl derivatives of diaryl sulfides. The possibility of using metals as catalysts for obtaining diaryl sulfides in the reaction of ortho-substituted benzaldehydes with SCl2 has been shown for the first time.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 731–735, September–October, 1995. Original article submitted November 11, 1994. 相似文献
13.
Zhan Lin Liwen Ji Andrew J. Medford Quan Shi Wendy E. Krause Xiangwu Zhang 《Journal of Solid State Electrochemistry》2011,15(6):1287-1294
The growing demands for reagentless hydrogen peroxide (H2O2) and β-nicotinamide adenine dinucleotide (β-NADH) sensors from food, pharmaceutical, chemical, and biochemical fields have
stimulated extensive research interest on nano-engineered Pd. In this paper, Pd/carbon composite nanofibers were prepared
by electrodepositing Pd onto electrospun carbon nanofibers to act as a catalyst toward the electrocatalytic redox reactions
of H2O2 and β-NADH. The morphology of nano-engineered Pd was controlled by selectively adjusting the electrodeposition time and potential.
Scanning electron microscopy and transmission electron microscopy results showed that nanocactus- and nanoflower-like Pd depositions
were obtained on the surface of carbon nanofibers. Electrocatalytic analysis demonstrated a high electrocatalytic activity
of the composite nanofibers for the redox of H2O2 and oxidation of β-NADH. 相似文献
14.
Bohumil Dolensky 《Journal of fluorine chemistry》2003,123(1):95-99
Nucleophilic attack of azide on 2-bromo-3-fluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1a) in aprotic solvent occurs on the 2-position to give the 2-azido derivative (2a). Reduction of azide and removal of the trityl group produces β-fluorohistidinol (6a). Elimination of HBr from 1a followed by “FBr” addition to the resulting double bond gives 2-bromo-3,3-difluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1b). Nucleophilic attack of azide followed by reduction and removal of the trityl group, as for the preparation of 6a, gives β,β-difluorohistidinol (6b). Initial attempts, under a variety of conditions, to oxidize the fluorinated histidinol precursors to carboxylic acids have not been successful. 相似文献
15.
I. N. Topchieva I. G. Panova B. I. Kurganov V. V. Spiridonov E. V. Matukhina S. K. Filippov A. V. Lezov 《Colloid Journal》2008,70(3):356-365
A new method for the synthesis of associates of cyclodextrins (CDs) of the columnar type consisting of the precipitation of CDs from aqueous solutions into acetone at lowered temperatures is developed. It is shown that columnar structures exist in both a crystalline state and in aqueous solutions. Hydrodynamic radii and molecular masses of noncovalent columnar structures (NCSs) in aqueous solutions are determined by the dynamic and static light scattering methods. The degree of association of noncovalent columnar polymers is ~40. It is revealed the NCS associates based on β-CD are stable and their hydrodynamic radius R h is equal to 100 ± 10 nm. The kinetics of interactions of initial β-CD and NCS with poly(propylene oxide) (PPO) is studied. The pattern of kinetic curves of R h growth upon interaction between NCS and PPO indicates that the aggregation of the particles of polymer inclusion complex proceeds in the regime of reaction-limited cluster-cluster aggregation. Kinetic curves describing the interaction processes between β-cyclodextrin and PPO are characterized by the presence of induction period t 0. At t > t 0, R h ∞ t 0.56 which is typical for the diffusion-limited cluster-cluster aggregation. Schemes of the formation of polymer inclusion complexes between initial β-CD or NCS and poly(propylene oxide) are proposed. Comparison of kinetic data on the complexation of β-CD in solution in the form of associates of two types with PPO demonstrates that columnar forms of associates are reactive species acting as macroreceptors. 相似文献
16.
This paper reports the use of natural amino acids, the tripeptide β-strand mimic Hao, and the β-turn mimic δ-linked ornithine to generate water-soluble 54-, 78-, and 102-membered-ring macrolactams. These giant macrocycles were efficiently prepared by synthesis of the corresponding protected linear peptides, followed by solution-phase cyclization and deprotection. The protected linear peptide precursors were synthesized on 2-chlorotrityl chloride resin by conventional Fmoc-based solid-phase peptide synthesis. Macrocyclization was typically performed using HCTU and N,N-diisopropylethylamine in DMF at ca. 0.5 mM concentration. The macrocycles were isolated in 13-45% overall yield after HPLC purification and lyophilization. 1D, 2D TOCSY, and 2D ROESY (1)H NMR studies of the 54- and 78-membered-ring macrolactams establish that these compounds fold to form β-sheet structures in aqueous solutions. 相似文献
17.
G. A. Schwechheimer 《Russian Chemical Bulletin》1960,9(9):1570-1571
Summary A method is proposed for preparation of the -aminoethyl ether of dimethylethynylcarbinol from the -cyanoethyl ether of dimethylethynylcarbinol. 相似文献
18.
SUN JianGuo GRAETER Stefan V. TANG Jian HUANG JingHuan LIU Peng LAI YuXiao YU Lin MAJER Günter SPATZ Joachim P. & DING JianDong 《中国科学:化学(英文版)》2014,57(4):645-653
Surface patterning is very useful in biomaterial studies, yet it is not easy to prepare a micropattern with cell-adhesion contrast that is stable in a wet environment. Recently, a platform technique of transfer photolithography was invented to fabricate stable metal microarrays on the surface of a cell-adhesion resistant and mechanically biomimetic poly(ethylene glycol) hydrogel; the linker is the key chemical in such a transfer strategy. This article reports the design and synthesis of a hetero-bifunctional macromonomer linker with a thiol group at one end and an acryloyl group at the other end. The bifunctional linker was characterized by GPC and 1H NMR, and the average number of thiol groups in the bifunctional linker was detected by Ellman’s reagent. The regent stability under wet conditions was also confirmed by the model reactants. The resultant micropatterned surfaces are meaningful for future studies of cell behaviors on mechanically biomimetic matrixes. 相似文献
19.
A new β-amino acrylic acid Ni(II) complex has been developed and used for the synthesis of α-alkyl-β-amino acids via alkylation with alkyl halides under operationally convenient conditions. The pivotal α-alkylated intermediate can be converted into the corresponding α-alkyl-β-amino acids via two steps with a wide range of substituents. 相似文献
20.
We propose a dechlorination process that allows safe and environmental conversion of chlorinated fluorocarbons. Starting with dissolving a fluorocarbon in an alcohol–NaOH solution, the fluorocarbons are reacted with alcohol–NaOH solvents at room temperature and pressure. In this work, the effect of the NaOH concentration on the solubility of CCl2F2 (CFC-12), CH2F2 (HFC-32), C2HF5 (HFC-125), C2H2F4 (HFC-134a) and C2H4F2 (HFC-152a) in methanol–NaOH, ethanol–NaOH and 1-propanol–NaOH solutions was measured. The experimental salting-out effects can be explained by solvation of a few alcohol molecules on sodium ion. Setchenov coefficients were determined and found to be independent of temperature. 相似文献