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991.
Internal residual stresses arise in glass-ceramics upon cooling down from the crystallization temperature. These stresses are due to the thermal expansion and the elastic mismatch between the crystalline and glassy phases. Therefore, the mechanical properties of glass-ceramics are likely to depend not only on their composition and microstructure but also on the type (tension or compression) and magnitude of these residual stresses. In this work, we critically review the most commonly used theoretical models concerning residual stresses in glass-ceramics and glass-matrix composites, taking into consideration the effects of crystallized volume fraction, crystal shape and thermal expansion anisotropy. We also discuss most of the reported measurements of residual stresses in these dual-phase materials using different techniques, such as X-ray diffraction, nuclear magnetic resonance, Raman and fluorescence spectroscopy, and indentation. The available models and experimental results regarding spontaneous microcracking due to residual stresses are also discussed. Finally, guidelines for future work are suggested. 相似文献
992.
Javier de Abajo Jos G. de la Campa Angel Alegría Jos M. Echave 《Journal of Polymer Science.Polymer Physics》1997,35(2):203-212
Two different series of poly(ester imide)s, which are distinguished from each other in the orientation of the ester linkages and show well-differentiated thermotropic behavior, are investigated by means of model calculations and dielectric relaxation spectroscopy. Model calculations show that the orientation of the ester linkages has a strong influence on the rotational energy barriers. The dielectric relaxation spectra of both series shows three relaxation regions in the temperature range between 100 and 400 K that have been identified as the α-, β- and γ-relaxation processes. A difference of about two orders of magnitude between the characteristic rates of the γ-relaxation is the main feature observed in the dielectric response. However, the β-relaxation shows very similar behavior for both series. The differences in the relaxation behavior in the solid state are interpreted on the basis of the rotational barriers deduced from the model calculation results. © 1997 John Wiley & Sons, Inc. 相似文献
993.
994.
Post-translational modifications (PTMs) of adeno-associated virus (AAV) capsid proteins tune and regulate the AAV infective life cycle, which can impact the safety and efficacy of AAV gene therapy products. Many of these PTMs induce changes in protein charge heterogeneity, including deamidation, oxidation, glycation, and glycosylation. To characterize the charge heterogeneity of a protein, imaged capillary isoelectric focusing (icIEF) has become the gold standard method. We have previously reported an icIEF method with native fluorescence detection for denatured AAV capsid protein charge heterogeneity analysis. Although well suited for final products, the method does not have sufficient sensitivity for upstream, low-concentration AAV samples, and lacks the specificity for capsid protein detection in complex samples like cell culture supernatants and cell lysates. In contrast, the combination of icIEF, protein capture, and immunodetection affords significantly higher sensitivity and specificity, addressing the challenges of the icIEF method. By leveraging different primary antibodies, the icIEF immunoassay provides additional selectivity and affords a detailed characterization of individual AAV capsid proteins. In this study, we describe an icIEF immunoassay method for AAV analysis that is 90 times more sensitive than native fluorescence icIEF. This icIEF immunoassay provides AAV stability monitoring, where changes in individual capsid protein charge heterogeneity can be observed in response to heat stress. When applied to different AAV serotypes, this method also provides serotype identity with reproducible quantification of VP protein peak areas and apparent isoelectric point (pI). Overall, the described icIEF immunoassay is a sensitive, reproducible, quantitative, specific, and selective tool that can be used across the AAV biomanufacturing process, especially in upstream process development where complex sample types are often encountered. 相似文献
995.
Francesco Cardoni;Moreno Meneghetti;Lucio Litti; 《Journal of Raman spectroscopy : JRS》2024,55(1):6-14
Terpenoids play a major role in agriculture, given their fungicidal and herbicidal actions, as well as their favorable toxicological, ecotoxicological, and environmental profiles. Despite all these advantages, terpenoids are reported to be unstable in direct sunlight and atmospheric conditions, so both commercial suppliers and scientific literature foresee their protection by encapsulation. The so-called microcapsules (μCaps) are therefore of high relevance as drug-delivery vectors, but very few techniques focus on their surface as well as on their morphological characterization. Indeed, these aspects are of great importance, given that their surface chemistry governs both their colloidal stability and mechanism of action. Common analysis techniques, such as chromatographic and mass-spectrometric ones, are destructive, require sample preparation, and do not result in the complete morphological characterization of the microcapsules. Micro-Raman spectroscopy, in conjunction with the surface-enhanced Raman spectroscopy (SERS) effect, offers a valuable alternative method of investigation capable of achieving a complete and non-destructive morphological characterization of the terpenoid-encapsulating systems, the dimensions of which fall within the micrometric range. In addition, the SERS effect can be exploited by fabricating the microcapsules with gold nanostars (AuNSs) modified with chitosan and a SERS reporter (Nile Blue A). Thanks to the high contrast provided by the SERS signals of this tag, it was possible to localize and confirm the chitosan in the morphology of the microcapsules. The results of this study shed new light on the possibility of analyzing terpenoid-encapsulating microcapsules and possibly other kinds of encapsulates brought by using Raman spectroscopy and by exploiting the SERS effect. 相似文献
996.
Jorge‐Aarn Rangel‐Mndez Manlio‐Joaquin Graniel‐Sabido Juan‐Francisco Snchez‐Cruz Rosa Moo‐Puc 《Biomedical chromatography : BMC》2019,33(4)
To date, several methods for the quantification of tamoxifen and its metabolites have been developed, most of which employ liquid chromatography tandem–mass spectrometry (LC–MS/MS). These methods are highly sensitive and reproducible, but are also time‐consuming and require expensive equipment; one of their main disadvantages is matrix ionization effects. A more viable option, particularly in developing countries, is high‐performance liquid chromatography coupled with UV or fluorescence detection. We developed and validated a method for simultaneous quantification of tamoxifen, endoxifen and 4‐hydroxytamoxifen based on high‐performance liquid chromatography with fluorescence detection in a reverse‐phase column. The method is rapid (16 min plus 5 min of column re‐equilibrium), accurate (80–100%) and precise (0.23–6.00%), and does not require any additional irradiation process. Sample pretreatment consists of protein precipitation with acetonitrile under alkaline conditions, employing only 200 μL plasma. The validated method's wide range allowed quantification of steady‐state levels in patients under standard tamoxifen treatment (20 mg/day). This assay is ready for application in clinical studies and routine quantification of tamoxifen, endoxifen and 4‐hydroxytamoxifen in healthcare institutions. 相似文献
997.
Mykola Telychko Jie Su Aurelio Gallardo Yanwei Gu Jesús I. Mendieta‐Moreno Dongchen Qi Anton Tadich Shaotang Song Pin Lyu Zhizhan Qiu Hanyan Fang Ming Joo Koh Jishan Wu Pavel Jelínek Jiong Lu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18764-18770
The ability to use mechanical strain to steer chemical reactions creates completely new opportunities for solution‐ and solid‐phase synthesis of functional molecules and materials. However, this strategy is not readily applied in the bottom‐up on‐surface synthesis of well‐defined nanostructures. We report an internal strain‐induced skeletal rearrangement of one‐dimensional (1D) metal–organic chains (MOCs) via a concurrent atom shift and bond cleavage on Cu(111) at room temperature. The process involves Cu‐catalyzed debromination of organic monomers to generate 1,5‐dimethylnaphthalene diradicals that coordinate to Cu adatoms, forming MOCs with both homochiral and heterochiral naphthalene backbone arrangements. Bond‐resolved non‐contact atomic force microscopy imaging combined with density functional theory calculations showed that the relief of substrate‐induced internal strain drives the skeletal rearrangement of MOCs via 1,3‐H shifts and shift of Cu adatoms that enable migration of the monomer backbone toward an energetically favorable registry with the Cu(111) substrate. Our findings on this strain‐induced structural rearrangement in 1D systems will enrich the toolbox for on‐surface synthesis of novel functional materials and quantum nanostructures. 相似文献
998.
The concentration polarization phenomena and its effects represent one of the main challenges for the optimal operation of many nanofluidic systems. A numerical investigation of the different electric current transition regimes observed during the concentration polarization phenomena in nanochannels is performed. This included a 2D‐axisymmetric simulation of the nanofluidic system (reservoir‐nanochannel‐reservoir). From these simulations, a novel mechanism is discovered that explains that different current transition regimes. This driving mechanism involves the applied electric field penetration while the convective flow mechanism is found to be negligible. This differs with the classical statement that the mixing process with less depleted areas initiated by an electrokinetic vortex instability starts the overlimiting regime. Additionally, the numerical approach allows us to identify new characteristics of the linear‐limiting transition such as source‐like and saddle‐like points of the electric field streamlines. The three voltage–current regimes (linear, limiting and overlimiting) are explained by observing and quantifying changes in electric field, potential, ion concentration and ion concentration gradients within the system. 相似文献
999.
Ivan A. Gagarinov Tiehai Li Na Wei Javier Sastre&#x;Torao Robert P. de&#x;Vries Margreet A. Wolfert Geert‐Jan Boons 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(31):10657-10662
We describe a chemoenzymatic strategy that can give a library of differentially fucosylated and sialylated oligosaccharides starting from a single chemically synthesized tri‐N‐acetyllactosamine derivative. The common precursor could easily be converted into 6 different hexasaccharides in which the glucosamine moieties are either acetylated (GlcNAc) or modified as a free amine (GlcNH2) or Boc (GlcNHBoc). Fucosylation of the resulting compounds by a recombinant fucosyl transferase resulted in only modification of the natural GlcNAc moieties, providing access to 6 selectively mono‐ and bis‐fucosylated oligosaccharides. Conversion of the GlcNH2 or GlcNHBoc moieties into the natural GlcNAc, followed by sialylation by sialyl transferases gave 12 differently fucosylated and sialylated compounds. The oligosaccharides were printed as a microarray that was probed by several glycan‐binding proteins, demonstrating that complex patterns of fucosylation can modulate glycan recognition. 相似文献
1000.