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131.
Maria Lluïsa Maspoch Haritz Eder Ferrando José Ignacio Velasco 《Macromolecular Symposia》2003,194(1):295-304
Filled PA6 are important representatives of engineering plastics used in automotive components. Nowadays, the demand of plastic recycled grades is increasing in this branch of industry but polymer recycling can undergo thermomechanical degradation processes with the results of a poor secondary material, regarding its properties. In this paper an investigation of thermal, mechanical (tensile, flexural and impact tests) and rheological properties of a sample of recycled and filled PA6, is reported as a function of the number of reprocessing operations (3 times) and of the fraction of recycled material (15, 30 and 50%) added to the virgin material. Recycled PA6, used in this study, comes from fibre grade production waste. Material was filled with 20% glass beads and 10% glass fibre, according to the specifications of the application, mainly to obtain a lower shrinkage in the end product. This work also shows that the mineral fraction, not being degraded during the injection process, allows better recyclability to the filled material. The properties of the recycled material remain below the virgin, and the best combination of both appears to be the mixture with 30w.% recycled fraction, which shows a lost of properties similar to 3 reprocessing operations. 相似文献
132.
Dr. Félix Sancenón Lluís Pascual Mar Oroval Dr. Elena Aznar Prof. Ramón Martínez-Máñez 《ChemistryOpen》2015,4(4):418-437
Silica mesoporous supports (SMSs) have a large specific surface area and volume and are particularly exciting vehicles for delivery applications. Such container-like structures can be loaded with numerous different chemical substances, such as drugs and reporters. Gated systems also contain addressable functions at openings of voids, and cargo delivery can be controlled on-command using chemical, biochemical or physical stimuli. Many of these gated SMSs have been applied for drug delivery. However, fewer examples of their use in sensing protocols have been reported. The approach of applying SMSs in sensing uses another concept—that of loading pores with a reporter and designing a capping mechanism that is selectively opened in the presence of a target analyte, which results in the delivery of the reporter. According to this concept, we provide herein a complete compilation of published examples of probes based on the use of capped SMSs for sensing. Examples for the detection of anions, cations, small molecules and biomolecules are provided. The diverse range of gated silica mesoporous materials presented here highlights their usefulness in recognition protocols. 相似文献
133.
Annals of Operations Research - 相似文献
134.
David C Companys E Galceran J Garcés JL Mas F Rey-Castro C Salvador J Puy J 《The journal of physical chemistry. B》2007,111(35):10421-10430
This work presents a new methodology aimed at obtaining the stepwise stability constants corresponding to the binding of ions (or other small molecules) to macromolecular ligands having a large number of sites. For complexing agents with a large number of sites, very simple expressions for the stepwise stability constants arise. Such expressions are model-independent; that is, they allow the determination of the stepwise stability constants without making any previous assumption of the detailed complexation mechanism. The formalism is first presented for a single complexing ion and further extended to competitive systems where the competing ions can display, in general, different stoichiometric relationships. These ideas are applied to the analysis of experimental titrations corresponding to competitive binding of calcium ions to poly(acrylic acid) for different pH values and ionic strengths. Intrinsic stability constants were estimated from the stepwise stability constants (by removing the corresponding statistical factor), and split into specific and electrostatic contributions (by means of the Poisson-Boltzmann equation). After this treatment, the specific proton binding energies showed almost no dependence on the coverage and ionic strength. Likewise, for the range of concentrations studied, the specific component of the intrinsic stability constants of the calcium ions, calculated assuming bidentate binding of Ca to neighboring groups of a linear chain, is almost independent of the calcium and proton coverage and ionic strength. 相似文献
135.
J. Oscar C. JimÉnez‐halla Eduard Matito LluÍs Blancafort Juvencio Robles Miquel Solà 《Journal of computational chemistry》2009,30(16):2764-2776
In this work, we analyze the geometry and electronic structure of the [XnM3]n?2 species (M = Be, Mg, and Ca; X = Li, Na, and K; n = 0, 1, and 2), with special emphasis on the electron delocalization properties and aromaticity of the cyclo‐[M3]2? unit. The cyclo‐[M3]2? ring is held together through a three‐center two‐electron bond of σ‐character. Interestingly, the interaction of these small clusters with alkali metals stabilizes the cyclo‐[M3]2? ring and leads to a change from σ‐aromaticity in the bound state of the cyclo‐[M3]2? to π‐aromaticity in the XM3? and X2M3 metallic clusters. Our results also show that the aromaticity of the cyclo‐[M3]2? unit in the X2M3 metallic clusters depends on the nature of X and M. Moreover, we explored the possibility for tuning the aromaticity by simply moving X perpendicularly to the center of the M3 ring. The Na2Mg3, Li2Mg3, and X2Ca3 clusters undergo drastic aromaticity alterations when changing the distance from X to the center of the M3 ring, whereas X2Be3 and K2Mg3 keep its aromaticity relatively constant along this process. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2009 相似文献
136.
Xavier Sala Isabel Romero Montserrat Rodríguez Lluís Escriche Antoni Llobet 《Angewandte Chemie (International ed. in English)》2009,48(16):2842-2852
Water into oxygen : A good catalyst for converting water into oxygen is seen as an essential part of any sustainable solar‐energy conversion scheme. Some success has been achieved using molecular complexes as catalysts and the key factors influencing their performance are discussed. The necessity of generating a solid‐state catalytic system is presented and the first attempts to generate supported molecular water‐oxidation catalysts are analyzed.
137.
Mallol R Rodríguez MA Heras M Vinaixa M Plana N Masana L Morris GA Correig X 《Analytical and bioanalytical chemistry》2012,402(7):2407-2415
The sizes of certain types of lipoprotein particles have been associated with an increased risk of cardiovascular disease.
However, there is currently no gold standard technique for the determination of this parameter. Here, we propose an analytical
procedure to measure lipoprotein particles sizes using diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY). The
method was tested on six lipoprotein fractions, VLDL, IDL, LDL1, LDL2, HDL2, and HDL3, which were obtained by sequential ultracentrifugation from four patients. We performed a pulsed-field gradient experiment
on each fraction to obtain a mean diffusion coefficient, and then determined the apparent hydrodynamic radius using the Stokes–Einstein
equation. To validate the hydrodynamic radii obtained, the particle size distribution of these lipoprotein fractions was also
measured using transmission electron microscopy (TEM). The standard errors of duplicate measurements of diffusion coefficient
ranged from 0.5% to 1.3%, confirming the repeatability of the technique. The coefficient of determination between the hydrodynamic
radii and the TEM-derived mean particle size was r
2 = 0.96, and the agreement between the two techniques was 85%. Thus, DOSY experiments have proved to be accurate and reliable
for estimating lipoprotein particle sizes. 相似文献
138.
The potential energy surface for the intramolecular excited state hydrogen transfer (IESHT) in ortho-phthalaldehyde (OPA), which generates an enol ketene, has been studied with ab initio calculations (MS-CASPT2//CASSCF). The goal of our study is to establish the mechanistic factors that make the primary phototautomerization step irreversible. Similar to what we recently described for ortho-nitrobenzaldehyde (NBA) (Migani et al., Chem. Commun., 2011, 47, 6383-6385), the IESHT in OPA is characterized by the relocation of two electrons from the in-plane to the out-of-plane orbital system. Consistent with this, OPA has the same IESHT mechanism as NBA. The first step of ketene formation is the hydrogen transfer, which starts on an (n, π*) state. The reaction coordinate goes through a conical intersection with the ground state and leads to a biradical intermediate with a bent ketene moiety. The second step is the linearization of the ketene moiety, which is associated to a change in the electronic configuration from biradical to ketene. Because of the electron relocation, the reverse transfer is similar to a Woodward-Hoffmann forbidden process with a sizeable barrier. This makes the tautomerization irreversible and allows the ketene to react further to biphthalide and benzaldehyde. Together with our previous NBA study, we establish the electronic relocation mechanism as a new mechanism for IESHT. This mechanism explains the different reactivity of OPA and NBA compared to organic photoprotectors, where the IESHT is reversed on a very short time scale. 相似文献
139.
140.
Groen JC Maldonado L Berrier E Brückner A Moulijn JA Pérez-Ramírez J 《The journal of physical chemistry. B》2006,110(41):20369-20378
The effects of alkaline treatment on the mesoporosity development and iron speciation in Fe-MFI zeolites have been investigated. To this end, a variety of samples derived from different synthetic routes and having distinct Si/Al ratios and Fe content were treated in NaOH solutions and characterized by N2 adsorption, SEM, TEM, UV/vis spectroscopy, and EPR. The alkaline treatment induces a significant intracrystalline mesoporosity development by framework silicon extraction and promotes disintegration of oligomeric iron species. Iron in framework positions has shown to provoke mesopore formation, whereas nonframework iron species suppresses silicon leaching and lowers the extent of extra porosity. 相似文献