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61.
Ron Janzon Jürgen Puls Andreas Bohn Antje Potthast Bodo Saake 《Cellulose (London, England)》2008,15(5):739-750
Different paper grade pulps were extracted with nitren in order to produce dissolving pulps and polymeric xylan. The yield
and molecular structure of the extracted pulps were investigated by carbohydrate analysis and HPSEC combined with fluorescence
labelling in order to additionally monitor the carbonyl and carboxyl group profiles of the pulps. The supramolecular structure
of selected pulps were further studied by solid state 13C-CP/MAS-NMR and wide-angle X-ray scattering (WAXS). These supramolecular data of nitren extracted pulps were compared to
samples extracted with NaOH and a conventional dissolving pulp in order to classify the properties of nitren extracted pulps.
Nitren extraction results in selective xylan removal without noticeable degradation or oxidation of the cellulose fraction.
The resulting dissolving pulps have high molar masses, a narrow molar mass distribution and the typical contents of carbonyl
and carboxyl groups. The supramolecular structure of cellulose is less affected by nitren compared to strong NaOH, and the
resultant dissolving pulps still have the cellulose I structure.
All laboratories are members of the European polysaccharide network of excellence EPNOE. 相似文献
62.
Deng Y Wang Y Holtz B Li J Traaseth N Veglia G Stottrup BJ Elde R Pei D Guo A Zhu XY 《Journal of the American Chemical Society》2008,130(19):6267-6271
As drug delivery, therapy, and medical imaging are becoming increasingly cell-specific, there is a critical need for high fidelity and high-throughput screening methods for cell surface interactions. Cell membrane-mimicking surfaces, i.e., supported lipid bilayers (SLBs), are currently not sufficiently robust to meet this need. Here we describe a method of forming fluidic and air-stable SLBs through tethered and dispersed cholesterol groups incorporated into the bottom leaflet. Achieving air stability allows us to easily fabricate SLB microarrays from direct robotic spotting of vesicle solutions. We demonstrate their application as cell membrane-mimicking microarrays by reconstituting peripheral as well as integral membrane components that can be recognized by their respective targets. These demonstrations establish the viability of the fluidic and air-stable SLB platform for generating content microarrays in high throughput studies, e.g., the screening of drugs and nanomedicine targeting cell surface receptors. 相似文献
63.
Antipina MN Dobner B Konovalov OV Shapovalov VL Brezesinski G 《The journal of physical chemistry. B》2007,111(49):13845-13850
In order to be used in versatile DNA delivery systems, novel cationic lipids were synthesized. The head groups of the new compounds represented by monoamines or oligoamines can be charged or uncharged depending on the environmental pH. Since their pK values are unknown, the protonation properties of these lipids have been studied in a wide pH range. In our experiments, the amphiphilic molecules were organized as a Langmuir monolayer at the air-water interface. Total reflection X-ray fluorescence (TRXF) was used to determine the 2D concentration of bromide counterions bound to a positively charged (protonated) Langmuir monolayer. The protonation rate of the novel cationic lipids was estimated by comparing the fluorescence intensity with that of dioctadecyldimethylammonium bromide monolayers as a reference. TRXF investigations were supplemented with results of film-balance measurements, grazing incidence X-ray diffraction, and X-ray reflectivity data. The results obtained display that the monolayers of all studied compounds are completely uncharged at pH values above 10. In the investigated pH region, the highest protonation rate of the monolayers is observed at pH 3. The influence of the monolayer packing density on the protonation properties is clearly shown. 相似文献
64.
The dissociation and formation of water on the Rh(111) and Ni(111) surfaces have been studied using density functional theory with generalized gradient approximation and ultrasoft pseudopotentials. Calculations have been performed on 2x2 surface unit cells, corresponding to coverages of 0.25 ML, with spot checks on 3x3 surface unit cells (0.11 ML). On both surfaces, the authors find that water adsorbs flat on top of a surface atom, with binding energies of 0.35 and 0.25 eV, respectively, on Rh(111) and Ni(111), and is free to rotate in the surface plane. Barriers of 0.92 and 0.89 eV have to be overcome to dissociate the molecule into OH and H on the Rh(111) and Ni(111) surfaces, respectively. Further barriers of 1.03 and 0.97 eV need to be overcome to dissociate OH into O and H. The barriers for the formation of the OH molecule from isolated adsorbed O and H are found to be 1.1 and 1.3 eV, and the barriers for the formation of the water molecule from isolated adsorbed OH and H are 0.82 and 1.05 eV on the two surfaces. These barriers are found to vary very little as coverage is changed from 0.25 to 0.11 ML. The authors have also studied the dissociation of OH in the presence of coadsorbed H or O. The presence of a coadsorbed H atom only weakly affects the energy barriers, but the effect of O is significant, changing the dissociation barrier from 1.03 to 1.37 and 1.15 eV at 0.25 or 0.11 ML coverage on the Rh(111) surface. Finally, the authors have studied the dissociation of water in the presence of one O atom on Rh(111), at 0.11 ML coverage, and the authors find a barrier of 0.56 eV to dissociate the molecule into OH+OH. 相似文献
65.
Pham VC Jossang A Sévenet T Nguyen VH Bodo B 《The Journal of organic chemistry》2007,72(25):9826-9829
Myrobotinol (1) was isolated from the leaves of Myrioneuron nutans (Rubiaceae) and its structure determined from spectral data, including mass spectrometry and 2D NMR. This compound presents a new hexacyclic alkaloid skeleton including a 1,3-oxazine and aminal functionality. The absolute configuration of myrobotinol was established by using Mosher's method. A plausible biosynthetic pathway starting from L-lysine via Delta-piperideine was proposed for this hexacyclic alkaloid. 相似文献
66.
Antipina MN Schulze I Dobner B Langner A Brezesinski G 《Langmuir : the ACS journal of surfaces and colloids》2007,23(7):3919-3926
Cationic liposomes/DNA complexes can be used as nonviral vectors for direct delivery of DNA-based biopharmaceuticals to damaged cells and tissues. In order to obtain more effective and safer liposome-based gene transfection systems, the new cationic lipid 2-amino-3-hexadecyloxy-2-(hexadecyloxymethyl)propan-1-ol (AHHP) was synthesized. In this paper we report on the synthesis of AHHP and investigations of its physical-chemical properties. Langmuir monolayers of AHHP were studied at the air/buffer interface by film balance measurements, grazing incidence X-ray diffraction (GIXD), and infrared reflection absorption spectroscopy (IRRAS). Structure and thermotropic phase behavior of AHHP in aqueous dispersion were examined by small-angle and wide-angle X-ray scattering (SAXS/WAXS) and differential scanning calorimetry (DSC). The results show clear differences in structure and phase behavior of AHHP, both in the monolayer system and in aqueous dispersions, in dependence on the subphase pH due to protonation or deprotonation of the primary amine in the lipid head group. Thermodynamic data derived from pi-A isotherms provide information about the critical temperature (Tc), which is in rough agreement with the temperature of the lipid phase transition from gel to fluid state (Tm) found by X-ray and calorimetry studies of AHHP aqueous dispersions. The packing properties of the molecules in mono- and bilayer systems are very similar. DNA couples to the monolayer of the new lipid at low as well as at high pH but in different amounts. The DNA coupling leads to an alignment of adsorbed DNA strands indicated by the appearance of a Bragg peak. The distance between aligned DNA strands does not change much with increasing monolayer pressure. 相似文献
67.
Endoglucanases were used as a selective tool to determine the substituent distribution along the chains of partially substituted cellulose acetates. Unsubstituted segments are intensively fragmented while highly substituted segments are only slightly degraded or not affected at all. Two different procedures were developed to perform a preparative separation of the fragments by size exclusion chromatography. One system is based on a direct separation of the fragmentation products using pyridine : water (9 : 1) as an eluent. The isolated fragments can be analysed regarding to their DS values by ATR/FTIR spectroscopy or by hydrolysis and HPLC. The second system is based on deutero-acetylation of endoglucanase fragmented samples. The complete acetylation of all OH groups enables a chromatographic separation in chloroform. Afterwards the isolated fragments can be analysed regarding to their partial DS values by 1H-NMR spectroscopy. 相似文献
68.
Heiko Winter Abdellatif Barakat Bernard Cathala Bodo Saake 《Macromolecular Symposia》2005,232(1):74-84
The sorption of arabinoxylan (AX) on bacterial cellulose was investigated by adding AX to the culture medium of Gluconacetobacter xylinus. The starting AX material was produced by alkaline extraction of oat spelts. To investigate the impact of varying AX quality, the residual lignin was reduced by ClO2 bleaching. Furthermore, bleached and unbleached xylans were subjected to xylanase hydrolysis in order to produce fractions of varying molar mass. Of all samples only the water soluble fractions were used for sorption experiments. A reduced molar mass resulted in a lower sorption of AX to the cellulose, while the lignin content increased the sorption of AX on bacterial cellulose. The sorption of AX resulted in a reduction of bacterial cellulose crystallinity and cellulose Iα content. In combined treatments of AX with xyloglucan and β-glucan no synergistic effect of those polysaccharides on the AX sorption was found. 相似文献
69.
70.