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61.
The solid sample inhomogeneity is a weak point of traditional MALDI deposition techniques that reflects negatively on quantitative analysis. The recently developed sieve-based device (SBD) sample deposition method, based on the electrospraying of matrix/analyte solutions through a grounded sieve, allows the homogeneous deposition of microcrystals with dimensions smaller than that of the laser spot. In each microcrystal the matrix/analyte molar ratio can be considered constant. Then, by irradiating different portions of the microcrystal distribution an identical response is obtained. This result suggests the employment of SBD in the development of quantitative procedures. For this aim, mixtures of different proteins of known molarity were analyzed, showing a good relationship between molarity and intensity ratios. This behaviour was also observed in the case of proteins with quite different ionic yields. The power of the developed method for quantitative evaluation was also tested by the measurement of the abundance of IGPP[Oxi]GPP[Oxi]GLMGPP (m/z 1219) present in the collagen-α-5(IV) chain precursor, differently expressed in urines from healthy subjects and diabetic-nephropathic patients, confirming its overexpression in the presence of nephropathy. The data obtained indicate that SBD is a particularly effective method for quantitative analysis also in biological fluids of interest. 相似文献
62.
A matrix-free, high sensitivity, nanostructured silicon surface assisted laser desorption/ionization mass spectrometry (LDI-MS) method fabricated by metal-assisted etching was investigated. Effects of key process parameters, such as etching time, substrate resistance and etchant composition, on the nanostructured silicon formation and its LDI-MS efficiency were studied. The results show that the nanostructured silicon pore depth and size increase with etching time, while MS ion intensity increases with etching time to 300 s then decreases until 600 s for both low resistance (0.001–0.02 Ω cm) and high resistance (1–100 Ω cm) silicon substrates. The nanostructured silicon surface morphologies were found to directly affect the LDI-MS signal ion intensity. By characterizing the nanostructured silicon surface roughness using atomic force microscopy (AFM) and sample absorption efficiency using fluorescence microscopy, it was further demonstrated that the nanostructured silicon surface roughness was highly correlated to the LDI-MS performance. 相似文献
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64.
Melania Bednarek Przemysaw Kubisa 《Journal of polymer science. Part A, Polymer chemistry》2005,43(17):3788-3796
The cationic copolymerization of ε‐caprolactone with ethylene oxide (EO) under the conditions of activated monomer polymerization, that is, with a low‐molecular‐weight diol as an initiator and BF3 etherate as a catalyst, was studied. To ensure the uniform composition of the resulting copolymers (telechelic oligodiols), the copolymerization was conducted with incremental feeding of the EO comonomer, which was more reactive in the cationic process. 1H NMR analysis of samples isolated at different stages of the copolymerization indicated that the average composition of the copolymer was indeed nearly constant over the course of the copolymerization. Matrix‐assisted laser desorption/ionization time‐of‐flight spectra of the products revealed, however, that for the same degree of polymerization, macromolecules containing different numbers of EO units were present. The observed distribution was compared with the distribution simulated under the assumption that the probability of incorporating a given unit depended only on the feed composition (nearly constant during the copolymerization). With this assumption, a good agreement between the observed and simulated spectra was obtained. This indicated that, even when the optimum conditions for the formation of a uniform copolymer were created, the individual macromolecules differed in composition because of the statistical character of the copolymerization. The results of differential scanning calorimetry analysis were compatible with such a conclusion; two melting peaks appeared on differential scanning calorimetry curves when a sample was heated immediately after fast cooling, and this may indicate the presence of different types of crystallites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3788–3796, 2005 相似文献
65.
Roderic P. Quirk Young J. Kim Ya Guo Chrys Wesdemiotis Mark A. Arnould 《Journal of polymer science. Part A, Polymer chemistry》2006,44(8):2684-2693
Hydroxyl chain‐end functionalizations of polymeric organolithium compounds with oxetane (trimethylene oxide) were studied in benzene at 25 °C. Functionalizations of poly(styryl)lithium and polystyrene‐oligo‐butadienyllithium proceed efficiently to form the corresponding ω‐hydroxypropyl‐functionalized polymers in 98 and 97% isolated yields, respectively. No nonfunctional polymer (≤1–2%) was detected by thin layer chromatography (TLC) analysis for either polymer. All functionalized polymers were characterized by 13C and 1H NMR analyses; no evidence for oxetane oligomerization at the chain end was observed. The MALDI‐TOF mass spectrum of ω‐hydroxypropylpolystyrene was consistent with the expected structure without any detectable oligomerization of oxetane. A small, but detectable series of peaks corresponding to nonfunctional polystyrene was also observed in the MALDI‐TOF mass spectrum. The functionalization of the adduct of 1,1‐diphenylethylene and PSLi produced the corresponding ω‐hydroxypropyl‐functionalized polymer in only 86% isolated yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2684–2693, 2006 相似文献
66.
67.
Guirong Pan James E. Mark Dale W. Schaefer 《Journal of polymer science. Part A, Polymer chemistry》2003,41(24):3314-3323
Four polyhedral oligomeric silsesquioxane (POSS) cages with vinyl groups were linked to a central siloxane core by hydrosilylation. The goal was to obtain filler particles of sizes between those of the POSS cages themselves and the much larger silica particles typically used to reinforce elastomers. The hydrosilylation reaction was monitored with Fourier transform infrared spectroscopy and proton nuclear magnetic resonance, and the resulting structure was confirmed by mass spectrometry. Simply blending these POSS-based fillers into silanol-terminated poly(dimethylsiloxane) (PDMS) had little effect on the mechanical properties, but bonding them to PDMS provided considerable reinforcement. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3314–3323, 2003 相似文献
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69.
A novel melt transurethane polycondensation route for polyurethanes under solvent‐free and nonisocyanate condition was developed for soluble and thermally stable aliphatic or aromatic polyurethanes. The new transurethane process was investigated for A + B, A‐A + B, and A‐A + B‐B (A‐urethane and B‐hydroxyl) ‐type condensation reactions, and also monomers bearing primary and secondary urethane or hydroxyl functionalities. The transurethane process was confirmed by 1H and 13C NMR, and molecular weight of the polymers were obtained as Mn = 10–15 × 103 and Mw = 15–45 × 103 g/mol. The mechanistic aspects of the melt transurethane process and role of the catalyst were investigated using model reactions, 1H NMR, and MALDI‐TOF‐MS. The model reactions indicated the occurrence of 97% reaction in the presence of catalyst, whereas its absence gave only less than 2% of the product. The polymer samples were subjected for end‐group analysis using MALDI‐TOF‐MS, which confirms the Ti‐catalyst mediated nonisocyanate pathway in the melt transurethane process. Almost all the polyurethanes were stable up to 280 °C, and the Tg of the polyurethanes can be easily fine‐tuned from ?30 to 120 °C by using appropriate diols in the melt transurethane process. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2445–2458, 2008 相似文献
70.
Norris JL Hangauer MJ Porter NA Caprioli RM 《Journal of mass spectrometry : JMS》2005,40(10):1319-1326
Although cleavable detergents were first synthesized a number of years ago, they have only recently been successfully applied to problems involving biological molecules. Recent reports have demonstrated that these compounds are useful for applications involving both 2D PAGE and mass spectrometry. However, most cleavable surfactants have utilized acid-labile functional groups to affect cleavage. In applications where extreme pH is required, acid cleavable detergents have limited usefulness. We report the synthesis of fluoride cleavable silane compounds and photolabile cinnamate esters as cleavable detergents having alternative cleavage chemistries than previously reported cleavable detergents. These compounds were applied to whole cell analysis using MALDI mass spectrometry, and it was demonstrated that their use results in an increase in the number of proteins analyzed by increasing protein solubility. 相似文献