Improved methods for structural analyses of glycosaminoglycans (GAGs) are required to understand their functional roles in
various biological processes. Major challenges in structural characterization of complex GAG oligosaccharides using liquid
chromatography-mass spectrometry (LC-MS) include the accurate determination of the patterns of sulfation due to gas-phase
losses of the sulfate groups upon collisional activation and inefficient on-line separation of positional sulfation isomers
prior to MS/MS analyses. Here, a sequential chemical derivatization procedure including permethylation, desulfation, and acetylation
was demonstrated to enable both on-line LC separation of isomeric mixtures of chondroitin sulfate (CS) oligosaccharides and
accurate determination of sites of sulfation by MSn. The derivatized oligosaccharides have sulfate groups replaced with acetyl groups, which are sufficiently stable to survive
MSn fragmentation and reflect the original sulfation patterns. A standard reversed-phase LC-MS system with a capillary C18 column
was used for separation, and MSn experiments using collision-induced dissociation (CID) were performed. Our results indicate that the combination of this
derivatization strategy and MSn methodology enables accurate identification of the sulfation isomers of CS hexasaccharides with either saturated or unsaturated
nonreducing ends. Moreover, derivatized CS hexasaccharide isomer mixtures become separable by LC-MS method due to different
positions of acetyl modifications. 相似文献
Increasing evidence indicates that sulfur-containing molecules can play important roles in the activity of platinum anticancer drugs. Although nuclear DNA is retained to be the ultimate target, these platinum compounds can readily react with a variety of other substrates containing a soft donor atom, such as proteins, peptides, and low molecular weight biomolecules, before reaching DNA. In a recent study it was demonstrated that the DNA platination rate of a trans-geometry antitumor drug was dramatically enhanced by methionine binding, thus suggesting that the thioether could serve as a catalyst for DNA platination. In this work we performed detailed studies on the reactions of a widely investigated and very promising trans-platinum complex having two iminoethers and two chlorido ligands, trans-EE, with methionine (Met) and guanosine 5'-monophosphate (GMP). The results show that in the reaction of trans-EE with methionine the bisadduct is the dominant species in the early stage of the reaction. The reaction is also influenced by chloride concentration: at low NaCl the bis-methionine adduct is formed in preference, whereas the monoadduct is favored at high NaCl concentration. Not only the monomethionine complex, trans-PtCl(E-iminoether)(2)(AcMet), but also the bis-methionine adduct, trans-Pt(E-iminoether)(2)(AcMet)(2), which has already lost both leaving chlorides, can react with GMP to form the ternary platinum complex trans-Pt(E-iminoether)(2)(AcMet)(GMP). The latter reaction discloses the possibility of direct coordination to DNA of a platinum-protein adduct, in which the two carrier ligands remain intact; this is not the case of cis-oriented platinum complexes, like cisplatin, for which formation of a ternary complex is usually accompanied by loss of at least one carrier ligand. Interestingly, isomerization from S to N coordination of one methionine takes place in the bis-methionine complex at neutral pH, while the monoadduct appears to be stable. The shift from S to N coordination of one methionine in the trans-bis-methionine adduct can easily account for the obtainment of the cis isomer in the bis-chelated Pt(Met-S,N)(2) end product. 相似文献
Sigma Delta (\(\Sigma \Delta \)) quantization, a quantization method first surfaced in the 1960s, has now been widely adopted in various digital products such as cameras, cell phones, radars, etc. The method features a great robustness with respect to quantization noises through sampling an input signal at a Super-Nyquist rate. Compressed sensing (CS) is a frugal acquisition method that utilizes the sparsity structure of an objective signal to reduce the number of samples required for a lossless acquisition. By deeming this reduced number as an effective dimensionality of the set of sparse signals, one can define a relative oversampling/subsampling rate as the ratio between the actual sampling rate and the effective dimensionality. When recording these “compressed” analog measurements via Sigma Delta quantization, a natural question arises: will the signal reconstruction error previously shown to decay polynomially as the increase of the vanilla oversampling rate for the case of band-limited functions, now be decaying polynomially as that of the relative oversampling rate? Answering this question is one of the main goals in this direction. The study of quantization in CS has so far been limited to proving error convergence results for Gaussian and sub-Gaussian sensing matrices, as the number of bits and/or the number of samples grow to infinity. In this paper, we provide a first result for the more realistic Fourier sensing matrices. The main idea is to randomly permute the Fourier samples before feeding them into the quantizer. We show that the random permutation can effectively increase the low frequency power of the measurements, thus enhance the quality of \(\Sigma \Delta \) quantization. 相似文献
Transition Metal Chemistry - An improved procedure is described herein for the synthesis of triangular Ag(I) 3,5-bis(trifluoromethyl)pyrazolate ({[3,5-(CF3)2Pz]Ag}3), which involves initial... 相似文献
In this study, three different volume expansion ratios of expanded graphite (EG) are prepared and investigated to enhance the heat transfer efficiency of the sodium acetate trihydrate (SAT) composites. A series of SAT composite phase change materials (CPCMs) with EG were prepared. The influence of volume expansion ratio and mass fraction of EG on thermodynamic characteristics of SAT CPCMs was examined, including thermal conductivity, phase change temperature, enthalpy, latent heat storage and release time, and the degree of supercooling. Results showed that SAT CPCMs can be absorbed adequately by EG, and EG could enhance the heat transfer efficiency effectively. But it also brought some problems with the addition of all the three volume expansion ratios of EG, such as the poor enthalpy and serious supercooling. Particularly, the situation gets worse with the increase in mass and expansion ratio of EG. Therefore, it is better to choose the EG with proper expansion ratio or reduce the proportion of the EG which possesses higher expansion ratio. Besides, thermal cycling test and thermogravimetric analysis revealed that the SAT CPCMs with 3 mass% EG showed a good thermal stability.
Cetyltrimethyl ammonium bromide‐modified attapulgite was prepared and utilized as a novel sorbent in a simple solid‐phase extraction method for the determination of vitamin A in blood serum. Several factors affecting extraction efficiency were systematically optimized, including the sampling solvent and its volume, as well as the elution solvent and its volume. Under the optimal solid‐phase extraction conditions, the adsorption capacity of vitamin A was as high as 28 mg/g according to the Langmuir isotherm model. Based on the developed solid‐phase extraction method, the level of vitamin A in 200 µL blood serum sample could be accurately determined by high‐performance liquid chromatography. The recoveries of vitamin A spiked in 10% v/v methanol aqueous solutions were in the range of 86.9–92.8%, with the relative standard deviations not more than 8.1%. The method was applied to the determination of vitamin A in serum samples from 20 pregnant women. Compared with the previously reported solid‐phase extraction methods for determination of vitamin A in serum, our developed cetyltrimethyl ammonium bromide‐modified attapulgite‐based solid‐phase extraction method used lower serum volume, omitted extra steps (i.e. evaporation and re‐dissolution), and eliminated internal standard. The results were promising for it to be used in routine monitoring during pregnancy. 相似文献
Ophiocordyceps xuefengensis (O. xuefengensis), a new species of caterpillar fungus, has been identified as the sister taxon of Ophiocordyceps sinensis (O. sinensis). The aims of the present study are to evaluate the anticancer activity and to qualitatively analyze the potential bioactive chemical constituents of O. xuefengensis and O. sinensis, comparatively. An MTT assay was used to evaluate the in vitro anticancer activities of different fractions from O. xuefengensis and O. sinensis. The results show that ethyl acetate fractions of O. xuefengensis and O. sinensis have significant in vitro anticancer activity. These two bioactive fractions were analyzed by ultra-performance liquid chromatography–electrospray ionization with quadrupole–time of flight tandem mass spectrometry technology. A total of 82 compounds and 101 compounds were identified or tentatively characterized in the bioactive fractions of O. xuefengensis and O. sinensis, respectively. Among these compounds, 68 existed in both O. xuefengensis and O. sinensis. A total of 67 compounds were reported in O. xuefengensis and 8 compounds were reported in caterpillar fungus for the first time. This is the first detailed comparative analysis of the in vitro anticancer activity and chemical ingredients between O. xuefengensis and O. sinensis. The application of this work will provide reliable fundamental pharmacological substances for the use of O. xuefengensis by Yao people. 相似文献
Hole-transporting materials with tunable structures and properties are mainly applied in organic light-emitting diodes as transport layer. But their catalytic properties as signal amplifiers in biological assays are seldom reported. In this paper, a starburst molecule, 4,4,4″-tri(N-carbazolyl)-triphenylamine (TCT), containing a triphenylamine as the central core and three carbazoles as the peripheral functional groups was designed and synthesized. Subsequently, the hole-transporting material based on the TCT polymer, poly(TCT) (PTCT), was achieved via a low-cost electrochemical method and exploited as an efficient metal-free electrocatalyst for non-enzymatic glucose detection. Here, this hole-transporting material served three purposes: electrochemical recognition (owing to hydrogen bonding interaction and the biomimetic microenvironment created by the polymer), electrocatalysis (owing to the hole-transporting capability of triphenylamine and the catalytic property of carbazole), and signal amplification (owing to energy migration along the conductive polymer backbone). The electrocatalytic and sensing performances of the sensor based on PTCT were evaluated in detail. Results revealed that the PTCT film could efficiently catalyze the oxidation of glucose at a less-positive potential (+0.20 V) in the absence of any enzymes. The response to glucose was linear in the concentration range of 1.0–6000 μM, and the detection limit was 0.20 μM. With good stability and selectivity, the proposed sensor could be feasibly applied to detect glucose in practical samples. The encouraging sensing performances suggest that the hole-transporting material is one of the promising biomimetic catalysts for electrocatalysis and relevant fields. 相似文献