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HPLC with cellulose Tris (3,5-DimethylPhenylcarbamate) chiral stationary phase: Influence of coating times and coating amount on chiral discrimination
No full textCoating cellulose tris (3,5-dimethylphenylcarbamate) (CDMPC) on silica gels with large pores have been demonstrated as an efficient way for the preparation of chiral stationary phase (CSP) for high-performance liquid chromatography (HPLC). During the process, a number of parameters, including the type of coating solvent, amount of coating, and the method for subsequent solvent removing, have been proved to affect the performance of the resultant CSPs. Coating times and the concentration of coating solution, however, also makes a difference to CSPs' performance by changing the arrangement of cellulose derivatives while remaining the coating amount constant, have much less been studied before, and thereby, were systematically investigated in this work. Results showed that CSPs with more coating times exhibited higher chiral recognition and column efficiency, suggesting that resolution was determined by column efficiency herein. Afterwards, we also investigated the effect of coating amount on the performance of CSPs, and it was shown that the ability of enantio-recognition did not increase all the time as the coating amount; and four of seven racemates achieved best resolution when the coating amount reached to 18.37%. At the end, the reproducibility of CDMPC-coated CSPs were further confirmed by two methods, ie, reprepared the CSP-0.15-3 and reevaluated the effect of coating times
Rhodamine-naphthalimide demonstrated a distinct aggregation-induced emission mechanism: elimination of dark-states via dimer interactions (EDDI)
No full textRhodamine B-naphthalimide (RhB-Naph) demonstrated a distinct aggregation-induced emission (AIE) mechanism, different from the restriction of intramolecular rotations or vibrations as in traditional AIE molecules. The monomers of RhB-Naph were non-emissive, due to the presence of a dark S-1 state. Upon molecular aggregation, intermolecular interactions significantly altered the electronic properties of RhB-Naph, leading to the formation of a bright S-1 state and endowing RhB-Naph with notable AIE properties. Besides, we demonstrated that RhB-Naph enabled the development of a solid-state three-color fluorescent switch upon multi-external stimuli
Promoting effects of desilication and dealumination on the catalytic performance of Al-rich HMOR for catalysing naphthalene tert-butylation with tertiary butanol
No full texttert-Butylation of naphthalene is a potential technology to produce 2,6-di-tert-butylnaphthalene (2,6-DTBN), which is a valuable raw material for the synthesis of polyethylene naphthalate (PEN). Alkaline, acid and combined alkaline-acid treatments were adopted to regulate the porosity and acidity of Al-rich HMOR zeolite. The structure, porosity and acidity of the catalysts were well characterized and the catalytic performance in the tertbutylation of naphthalene was extensively investigated. The strong acid sites were verified as the intrinsic active sites for naphthalene alkylation for the first time. Characterization results indicated that alkaline treatment could extract silicon from the framework and intra-crystalline mesopores with diameters of 3-30 nm were successfully generated in Al-rich HMOR by one-step alkaline treatment. The introduced mesopores could enhance the mass diffusion of molecules as well as the coke-resistance, despite that the high acid density in the internal surface would lead to fast coke deposition. On the other hand, the acid treatment could remove the aluminium efficiently, leading to significantly decreased strong acid sites located at the micropores and pore entrances, which reduced coke deposition in the channels and pore entrances and brought about sharp increase in the conversion rate of naphthalene per strong acid site. Thus, higher naphthalene conversion and di-tert-butyl naphthalene (DTBN) selectivity were obtained over all the post-treated samples. Besides, the high selectivity for 2,6-DTBN (2,6-/2,7-DTBN > 28.0) remained. More importantly, combined alkaline and acid treatment had synergistic effects on the improvement of the initial activity as well as the catalytic stability due to the optimized acidity and porosity
Insights into the high-temperature oxidation of methylcyclohexane
No full textReactive molecular dynamics simulations were performed under different conditions in order to investigate indetail the chemical events associated with high-temperature oxidation of methylcyclohexane (MCH). The corresponding kinetic behaviors of the major intermediates and products were systematically analyzed at the atomistic level. Thus the overall reaction scheme of MCH oxidation was established from the initial step to the final products. It was observed that the oxidation of MCH was mainly initiated by two kinds of reactions, including unimolecular decomposition and H abstraction, with the former being more important. In agreement with the available experimental results, C2H4, CH2O, CO, CO2 and H2O were found to be the major products during the oxidation process. The results revealed that center dot CH3O2, center dot CH3O and center dot C3H5O radicals were the precursors for CH2O production, which was the key intermediate to generate CO. Additionally, center dot C2H3O also had closed relationship with the formation of CO. For a better description of the combustion behavior, small oxides related to intermolecular reactions should be considered in the oxidation of MCH mechanisms. The temperature and density had a positive effect on the oxidation of MCH; it was also found that an increase of the equivalence ratio had a negligible effect on the MCH oxidation
