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Does the wavelength dependent photoisomerization process of the p-coumaric acid come out from the electronic state dependent pathways?
No full textSimilar to the anion photoactive yellow protein (PYP) chromophore, the neutral form of the PYP chromophore was also found to exhibit a the wavelength-dependent photoisomerization quantum yield. The isomerization quantum yield increases with the increasing excitation energy on the S-1 state, while decreases when being excited to the S-2 state. Does this wavelength dependent product yield come out from the specific reaction pathways of the S-1 and S-2 states? This would mean that, the relaxation pathway of the S-2 state is distinct from that of the S-1 state and does not involve twisting motion. Does it break Kasha's rule by exhibiting a direct transition from the S-2 state to the ground state? The underlying mechanism needs further in. In this article, we employed the on-the-fly dynamics simulations and static electronic structure calculations to reveal the deactivation mechanism of the neutral form of the PYP chromophore. Our results indicated that the C=C twisting motion dominates the S-1 state decay process. In contrast, for the decay process of the S-2 state, an ultrafast transition from the S-2 to the S-1 state through a planar conical intersection is observed, and the excess energy activates a new reaction channel to the ground state characterized by a puckering distortion of the ring. This pathway competes with the photoisomerization channel. No direct transition from S-2 to S-0 is observed, hence Kasha's rule is valid for this process. Our calcualtions can provide a reasonable explanation of the wavelength-dependent isomerization quantum yield of neutral PYP chromophore, and we hope it can provide theoretical foundations for comparing the effect of protonation state on the dynamcal behaviors of PYP chromophore. (C) 2018 Elsevier B.V. All rights reserved
Highly effective transformation of carbohydrates to 5-Hydroxymethylfurfural with Al- montmorillonite as catalystr
No full textAluminum ion-exchanged Ca-montmorillonite with different concentrations of aluminum ion were prepared and applied in the conversion of carbohydrates to 5-hydroxymethylfurfural (HMF). It was found that two types of acid sites were present in the catalyst, Lewis acid sites for isomerization of glucose and Bronsted acid sites for dehydration of fructose. With Al-mont-10 as catalyst, the yield of HMF converted from glucose was 80.4% in a biphase system (THF: NaCl solution) at 180 degrees C for 2.5 h. Further, the catalyst also shows excellent catalytic performance in the conversion of starch and inulin, and the yield of HMF reached 60.1% and 81.6% under identical conditions, respectively
Synthesis of acetyl-substituted tetrahydrobenzofuran and tetrahydronaphthalene via cascade Diels-Alder cycloadditions and dehydration of renewable furanics
No full textA acetyl-substituted tetrahydrobenzofuran, 1-(4,5,6,7-tetrahydro-1-benzofuran-6-yl)ethenone (6-AcBZOF) and a acetyl-substituted tetrahydronaphthalene, 1-(1,2,3,4-tetrahydronaphthalen-2-yl)ethenone (2-AcTNAPH) were conveniently synthesized from renewable furanics by cascade Diels-Alder and dehydration reactions. The Diels-Alder cycloaddition of 4-(2-Furyl)-3-buten-2-one (4-FB) with ethylene followed by dehydration in presence of zeolites was studied. Sn grafted Beta zeolite exhibited high performance with 69% yield of 2-AcTNAPH starting from 4-FB. In this reaction, 6-AcBZOF was produced as intermediate. Further, it was found that this acetyl substituted tetrahydrobenzofuran could be formed in high yield, 86%, in the absence of catalyst. For the first time in the literature, we report the synthesis of a renewable acetyl-substituted tetrahydronaphthalene in high yield from biomass-derived 4-FB in a tandem approach. While a acetyl-substituted tetrahydrobenzofuran could be prepared without a catalyst, catalyst was essential for the successful synthesis of the acetyl-substituted tetrahydronaphthalene
Bridged Hybrid Monolithic Column Coupled to High-Resolution Mass Spectrometry for Top-Down Proteomics
No full textTop-down mass spectrometry (MS)-based proteomics has become a powerful tool for comprehensive characterization of intact proteins. However, because of the high complexity of the proteome, highly effective separation of intact proteins from complex mixtures prior to MS analysis remains challenging. Monolithic columns have shown great promise for intact protein separation due to their high permeability, low backpressure, and fast mass transfer. Herein, for the first time, we developed bridged hybrid bis(triethoxysilyl)ethylene (BTSEY) monolith with C8 functional groups (C8@BTSEY) for highly effective protein separation and coupled it to high-resolution MS for identification of intact proteins from complex protein mixtures. We have optimized mobile phase conditions of our monolith -based reverse-phase chromatography (RPC) for online liquid chromatography (LC)-MS analysis and evaluated separation reproducibility of the C8pBTSEY column. We further assessed the chromatographic performance of this column by separating a complex protein mixture extracted from swine heart tissue. Using our monolithic column (i.d. 100 mu m X 35 cm), we separated over 300 proteoforms (up to 104 kDa) from 360 ng of protein mixture in an 80 min one-dimensional (1D) LC run. The highly effective separation and recovery of intact proteins from this monolithic column allowed unambiguous identification of similar to 100 proteoforms including a large protein, alpha actinin2 (103.77 kDa), by online ID LC-MS/MS-analysis for the first time. As demonstrated, this C8pBTSEY column is reproducible and effective in separation of intact proteins, which shows high promise for top-down proteomics