A computational study with density functional theory (DFT) is carried out on the reaction between methyl sulfinyl chloride (MSC) and methanol in the presence of trimethylamine, a process which is a general model for two different methods used in practice for the obtention of chiral sulfoxides through dynamic kinetic resolution. Two mechanistic options are considered: in one of them, chloride is initially displaced by the base (ion pair mechanism), whereas in the other, chloride stays bound to sulfur until its final displacement by methoxy (neutral mechanism). In both cases, the approach of the alcohol to sulfur is coupled with a hydrogen transfer from methanol to the oxo group of MSC in a single concerted transition state. The presence of a trimethylamine molecule facilitates substantially the reaction by reducing the nucleophilic substitution barrier by more than 10 kcal/mol through the formation of a N-H bond with the hydrogen atom being transferred. The neutral mechanism presents a free energy barrier lower than the ion pair alternative and is thus preferred. 相似文献
Bismuth mixed oxide powders were prepared by oxalate coprecipitation process. The thermal decomposition behaviour of the coprecipitate
precursors has been followed by thermal analysis (TG-DTA) and FTIR spectroscopy. During the decomposition of the precursor,
several intermediates species were detected and a mechanism of formation of mixed oxide by this method is proposed. After
the thermal treatment, the precursor obtained of suggested formula Ca3[Bi6O6(C2O4)4(OH)3NO3]0.5H2O, has led to the formation of CaBi2O4 at shorter reaction time than the traditional ceramic method. In order to consolidate the results, the coprecipitation in
absence of oxalic precipitant under the same conditions was examined. XRD and scanning electron spectroscopy were used to
study particles sizes and morphology. 相似文献
The authors describe an electrochemical sensor for the breast cancer marker α-lactalbumin (αLA). It is based on the use of printed single-walled carbon nanotube (SWCNT) electrodes that were modified with polycatechol. Impedance-derived electrochemical capacitance spectroscopy (ECS) is applied for detection at an applied potential of ?0.14 V vs. Ag/AgCl reference electrode. The electrode was prepared in a two-step process. First, a dispersion of SWCNTs was drop-cast onto the surface of a poly(ethylene terephthalate) substrate to act as the working electrode. Next, catechol was electrochemically polymerized on the SWCNTs, prior to the immobilization of lysozyme. The strong interaction between lysozyme and αLA induced changes in the redox capacitance which are detected by ECS. The latter shows the device to be capable of detecting αLA in the 20 to 80 ng·mL?1 concentration range. The limit of detection is 9.7 ng·mL?1 at an S/N ratio of 3. The device was used to detect αLA in human blood serum with good recovery results.
Graphical abstract A sensitive biosensor for αLA was prepared by modifying SWCNT electrode with polycatechol and lysozyme. The electrochemical capacitance spectroscopy was used for the first time to selectively detect αLA in the blood in the range from 20 to 80 ng·mL?1.
Cellulose - In this study, alkali and alkaline earth metal chlorides with different cationic radii (LiCl, NaCl, and KCl, MgCl2, and CaCl2) were used to gain insight into the behavior of cellulose... 相似文献
It is shown by construction that the only restriction on theintegral cohomology ring of a finitely presented asphericalgroup is that it has dimension at most 2. 相似文献
Precipitation or coprecipitation of polyelectrolytes has been largely investigated. However, the precipitation of polyelectrolytes via addition of charged and non‐charged surfactants has not been systematically studied and reported. Consequently, the aim of this work is to investigate the effect of different surfactants (anionic, cationic, non‐charged and zwitterionic) on the precipitation of cationic and anionic polymethylmethacrylate polymers (Eudragit). The surfactants effect has been investigated as a function of their concentration. Special attention has been dedicated to the CMC range and to the colloidal characterization of the formed dispersions. Moreover, the effect of salt (NaCl) and pH was also addressed. It is pointed out that non‐ionic and zwitterionic surfactants do not interact with charged Eudragit E100 and L100. For oppositely charged Eudragit E100/SDS and Eudragit L100/CTAB, precipitation occurs, and the obtained dispersions have been characterized in terms of particle size distribution and zeta potential. It was established that the binding of SDS molecules to Eudragit E100 polymer chains is made through the negative charges of the surfactant heads under the CMC value whereas binding of CTAB to Eudragit L100 chains is made at a CTAB concentration 5 times above its CMC. For Eudragit E100/SDS system, a more acidic medium induces aggregation. A same result was observed for the Eudragit L100/CTAB at a more basic pH. Moreover, it was observed that increasing salt concentration (higher than 100 mM) led to aggregation as generally observed for polycations/anionic surfactant systems. 相似文献
Dyestuff substances in textile wastewaters are harmful pollutants which pose serious disposal challenges. A solar photocatalytic treatment combining degradation of structurally diverse dyes (Rhodamine B, Reactive Orange 16 or Auramine O) and energetic valorisation by H2 production on systematically varied M/TiO2 (M=Au, Ag, Cu or Pt) is herein explored. Bleaching was efficient in all cases, and especially rapid for azo (>98 % after 2 h) as compared to poly-heterocyclic chromophores. Interestingly, dye degradation rates were similar to literature results under aerobic conditions, whereby no energy recovery is possible. Due to the recalcitrant dye structures, H2 production becomes markedly sensitive to metal co-catalyst chemistry and morphology. The occurrence of active metallic, i. e. M(0), surfaces in sufficiently large nanoparticles are key to ensurie initial H2 evolution. An increase in Au domain sizes from 101 up to 102 nm ranges resulted in 10-fold site-specific catalytic activity (TOF) enhancement, whereas growth of Pt nanoparticles well above the sub-nanometric regime was essential for efficient H2 production. In quest of using affordable metallic elements, bleaching and sustained H2 evolution was proven after prolonged irradiation using Cu/TiO2, owing to the in situ reduction of the copper co-catalyst. In summary, anaerobic photoreforming can be as efficient as the more common aerobic approach, also allowing energy recovery in the form of waste-derived hydrogen. 相似文献
In this work, we propose a new algorithm to improve existing techniques used in the field of spectroscopic data regression analysis. In particular, it combines the power of nonlinear kernel regressors (kernel ridge regression [KRR], kernel principal component regression [KPCR], and Gaussian process regression [GPR]) with an optimization based on nondominated sorting multi-objective genetic algorithm (NSGAII) to filter the residual outliers in the prediction space and leverage points in the features space. The proposed algorithm, contrary to most existing robust algorithms, simultaneously optimizes many complementary objectives for an automatic adaptation and thus a better outliers detection. It is well known that the elimination of outliers greatly improves the regression model. It is thus the aim of this work to develop a new robust regression algorithm. It has been applied on five different datasets, and the results are compared to both classical nonlinear regression methods and the commonly used robust regression methods robust continuum regression (RCR), partial robust M-regression (PRM), robust principal component regression (RPCR), robust PLSR (RSIMPLS), and locally weighted regression (LWR). They show that the proposed algorithm outperforms the classical nonlinear regression methods and is a promising competitor to the robust methods outperforming most of them. Even though the results obtained are only from five datasets, this algorithm can be considered an interesting contribution for improving data analysis in the field of chemometrics. 相似文献
Synthetic dyes have become an integral part of many industries such as textiles, tannin and even food and pharmaceuticals. Industrial dye effluents from various dye utilizing industries are considered harmful to the environment and human health due to their intense color, toxicity and carcinogenic nature. To mitigate environmental and public health related issues, different techniques of dye remediation have been widely investigated. However, efficient and cost-effective methods of dye removal have not been fully established yet. This paper highlights and presents a review of recent literature on the utilization of the most widely available biopolymers, specifically, cellulose, chitin and chitosan-based products for dye removal. The focus has been limited to the three most widely explored technologies: adsorption, advanced oxidation processes and membrane filtration. Due to their high efficiency in dye removal coupled with environmental benignity, scalability, low cost and non-toxicity, biopolymer-based dye removal technologies have the potential to become sustainable alternatives for the remediation of industrial dye effluents as well as contaminated water bodies. 相似文献
