Polysaccharide (PS) based nanoparticles (NP) are of great interest for biomedical applications. A key challenge in this regard is the functionalization of these nanomaterials. The aim of the present work was the development of reactive PS-NP that can be coupled with an amino group containing compounds under mild aqueous conditions. A series of cellulose phenyl carbonates (CPC) and xylan phenyl carbonates (XPC) with variable degrees of substitution (DS) was obtained by homogeneous synthesis. The preparation of PS-NP by self-assembling of these hydrophobic derivatives was studied comprehensively. While CPC mostly formed macroscopic aggregates, XPC formed well-defined spherical NP with diameters around 100 to 200 nm that showed a pronounced long-term stability in water against both particle aggregation as well as cleavage of phenyl carbonate moieties. Using an amino group functionalized dye it was demonstrated that the novel XPC-NP are reactive towards amines. A simple coupling procedure was established that enables direct functionalization of the reactive NP in an aqueous dispersion. Finally, it was demonstrated that dye functionalized XPC-NP are non-cytotoxic and can be employed in advanced biomedical applications. 相似文献
Enzymatic degradation of model cellulose films prepared by a spin-coating technique was investigated by ellipsometry. The cellulose films were prior to degradation characterized by ellipsometry, contact angle measurements, ESCA (electron spectroscopy for chemical analysis) and AFM (atomic force microscopy). At enzyme addition to preformed cellulose films an initial adsorption was observed, which was followed by a total interfacial mass decrease due to enzymatic degradation of the cellulose films. The degradation rate was found to be constant during an extended time of hours, whereafter the degradation leveled off. In parallel to the decreased interfacial mass, the cellulose degradation resulted in a thinner and more dilute interfacial film. At long degradation times, however, there was an expansion of the cellulose film. The enzyme concentration affected the degradation rate significantly, with a faster degradation at a higher enzyme concentration. The effects of pH, temperature, ionic strength and stirring rate in the cuvette were also investigated. 相似文献
We have combined the techniques of statistical and harmonic linearization to develop a linearized approximation theory for the calculation of the second-order statistics (i.e., autocorrelation functions and spectral densities) of nonlinear systems driven by both random and periodic forces. For the special case of a Duffing oscillator (a damped anharmonic oscillator with a cubic nonlinearity) driven by Gaussian white noise and by a sinusoidal force, explicit expressions for the renormalized (linearized) frequency, the autocorrelation function, and the spectral density of the oscillator displacement in terms of all the system parameters have been derived. We have determined the region of the parameter space in which the applied periodic force has a significant influence on the second-order statistics of the oscillator.This research was supported by the Office of Naval Research, by the National Science Foundation under grant No. CHE78-21460 and by a grant from Charles and Reneé Taubman. 相似文献
Supramolecular complexes of a poly(tert‐butoxystyrene)‐block‐polystyrene‐block‐poly(4‐vinylpyridine) triblock copolymers and less than stoichiometric amounts of pentadecylphenol (PDP) are shown to self‐assemble into a core–shell gyroid morphology with the core channels formed by the hydrogen‐bonded P4VP(PDP)complexes. After structure formation, PDP was removed using a simple washing procedure, resulting in well‐ordered nanoporous films that were used as templates for nickel plating.
Fructosamine-3-kinase (FN3K) mediates the regeneration of lysine from fructosamines formed on proteins as a result of the
‘early’ Maillard reaction. As fructosamines and advanced glycation endproducts derived therefrom are supposed to play an adverse
role in the development of diabetic complications, FN3K is discussed as a protein-repairing enzyme. In this study, a method
for the determination of FN3K activity in erythrocyte lysate is described which overcomes the complexity of currently known
assays. The assay is based on the FN3K-dependent conversion of the synthetic UV-active fructosamine Nα-hippuryl-Nε-(1-deoxy-D-fructosyl)lysine (BzGFruK) to Nα-hippuryl-Nε-(phosphofructosyl)lysine (BzGpFruK). The FN3K activity was quantified by measuring the formation of BzGpFruK using RP-HPLC
with UV detection. Identification of the metabolite BzGpFruK was achieved by means of UV and mass spectroscopy. The results
are related to the content of haemoglobin for standardisation. First activity measurements with a chosen number of normoglycaemic
subjects confirmed the convenient applicability of the method and showed distinctly different individual activities, as already
discovered recently. The new established assay needs only the equipment of a routine laboratory with HPLC instrumentation.
This should facilitate further studies about a possible relationship between the FN3K activity and the development of diabetic
complications. 相似文献
2H/1H isotope ratios of polyhalogenated compounds were determined by elemental analysis and isotope ratio mass spectrometry (EA-IRMS).
Initial measurements with standard EA-IRMS equipment, which used high-temperature pyrolysis to convert the organic compounds
into hydrogen, did not achieve significant signals for polychlorinated pesticides and related compounds, presumably due to
the formation of HCl instead of hydrogen. To reverse this problematic reaction, a chromium reactor was incorporated into the
element analyzer system, which scavenged Cl, forming chromium chloride and releasing hydrogen again in the form of H2. The optimized system therefore allowed the δ2H values of polyhalogenated compounds to be determined. A quality assurance program was developed based on several parameters.
(i) Each compound was analyzed using a sequence of five injections, where the first measurement was discarded. (ii) Recovery
of H (when calculated relative to acetanilide) had to be >90% for all replicates in a sequence. (iii) All δ-values within
a sequence had to vary by less than 10‰. (iv) Results had to be reproducible on another day with a different sample scheme.
Once this reproducibility had been established, variabilities in the δ2H values of organohalogen standards were investigated using the technique. The highest δ2H value of +75‰ was found for o,p′-DDD, whereas the strongest depletion in deuterium was found for Melipax (–181‰). The most important results for comparable
compounds were as follows. DDT-related compounds gave δ2H values of between +59 and +75‰ (technical DDT, o,p′- and p,p′-DDD) or in the range of approximately −1‰, indicative of the different sources/methods of producing this compound. Four
HCH isomers from the same supplier showed relatively similar hydrogen isotope distributions, whereas two lindane (γ–HCH) standards
from other sources had 39‰ less deuterium. This difference is likely due to different purification steps during the isolation
of pure lindane from the technical HCH mixture. An even greater difference was observed between the δ2H values of Toxaphene (US product dating from 1978) and Melipax (product from the former East Germany, dating from 1979),
which gave δ2H values of –101‰ and –181‰, respectively, meaning that both products were easily distinguished via δ2H-IRMS. Fractioning of hydrogen isotopes in the atmospheric water cycle was suggested as one reason for the different values.
In this theory, the water (which had different δ2H values depending on where it was taken from) was incorporated during the biosynthesis of camphene, which is the natural
product used to produce both products. These results indicate that hydrogen isotope-specific analysis can be a valuable tool
for tracing the origins of a compound in certain cases. 相似文献