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排序方式: 共有370条查询结果,搜索用时 15 毫秒
311.
Jia Bin Yeo Jun Ho Jang Young In Jo Jeong Woo Koo Ki Tae Nam 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2024,136(2):e202316020
Utilizing CO2-derived formaldehyde derivatives for fuel additive or polymer synthesis is a promising approach to reduce net carbon dioxide emissions. Existing methodologies involve converting CO2 to methanol by thermal hydrogenation, followed by electrochemical or thermochemical oxidation to produce formaldehyde. Adding to the conventional methanol oxidation pathway, we propose a new electrochemical approach to simultaneously generate formaldehyde derivatives at both electrodes by partial methanol oxidation and the direct reduction of CO2. To achieve this, a method to directly reduce CO2 to formaldehyde at the cathode is required. Still, it has been scarcely reported previously due to the acidity of the formic acid intermediate and the facile over-reduction of formaldehyde to methanol. By enabling the activation and subsequent stabilization of formic acid and formaldehyde respectively in methanol solvent, we were able to implement a strategy where formaldehyde derivatives were generated at the cathode alongside the anode. Further mechanism studies revealed that protons supplied from the anodic reaction contribute to the activation of formic acid and the stabilization of the formaldehyde product. Additionally, it was found that the cathodic formaldehyde derivative Faradaic efficiency can be further increased through prolonged electrolysis time up to 50 % along with a maximum anodic formaldehyde derivative Faradaic efficiency of 90 %. 相似文献
312.
Huiqi Yeo Dimitrios P. Balagiannis Jean H. Koek Jane K. Parker 《Molecules (Basel, Switzerland)》2022,27(19)
The shift in consumer landscape towards vegan, vegetarian and flexitarian diets has created an unprecedented challenge in creating meat aroma from plant-based alternatives. The search for potential vegan solutions has thus led to a renewed interest in authentic meat flavour profiles. To gain a better understanding of the qualitative odour differences between boiled beef and boiled chicken, aroma extracts were isolated using Likens-Nickerson simultaneous distillation-extraction (SDE), selected expressly because the in-situ heating of the sample facilitates the capture of aroma intermediates during the cooking process, thereby mimicking the cooking of meat in stocks and stews. The extracts were then analysed by Gas Chromatography-Mass Spectrometry (GC-MS) and GC-Olfactometry (GC-O). Most of the volatiles identified in this study were sulfur-containing compounds, such as sulfides, thiols, mercaptoaldehydes and mercaptoketones, which are derived from the Maillard reaction. Meanwhile, lipid oxidation results in the formation of unsaturated aldehydes, such as alkenals and alkadienals. Families of thiazoles and 3-thiazolines were found in the extracts. Two novel 3-thiazolines (5-ethyl-2,4-dimethyl-3-thiazoline and 2-ethyl-4,5-dimethyl-3-thiazoline) which may also contribute to the meaty aroma were identified in this work and synthesised from their respective aldehyde and mercaptoketone precursors. 相似文献
313.
Somodi F Werner S Peng Z Getsoian AB Mlinar AN Yeo BS Bell AT 《Langmuir : the ACS journal of surfaces and colloids》2012,28(7):3345-3349
A two-step method has been developed for precise size and composition control of bimetallic Pt-In nanoparticles. Very small (1.62 nm) PtIn seed nanoparticles with 1:1 metal ratio were prepared in the absence of capping agents followed by growth of Pt on their surface in the presence of oleyl amine as reducing and stabilizing agent. Nanoparticles with bulk compositions of Pt(4)In, Pt(3)In, and Pt(2)In could be synthesized with average diameter smaller than 3 nm. TEM, EDX, and XPS provided evidence for homogeneous growth without separate nucleation of pure platinum nanoparticles in the reaction solution. Pt(3)In nanoparticles were deposited onto SiO(2) surface by incipient wetness impregnation. Temperature-induced changes in the particle surface were monitored by in situ IR spectroscopy and CO adsorption. It was found that surface alloy composition of the particles could be tuned by using oxidizing or reducing atmospheres. 相似文献
314.
Songyi Seo Mi-Kyung Kim Ryul-I Kim Yeongju Yeo Koung Li Kim Wonhee Suh 《Experimental & molecular medicine》2020,52(10):1744
Dipeptidyl peptidase-4 (DPP-4) inhibitors are used for the treatment of type 2 diabetes mellitus (DM). Recent studies have shown that beyond their effect in lowing glucose, DPP-4 inhibitors mitigate DM-related microvascular complications, such as diabetic retinopathy. However, the mechanism by which pathological retinal neovascularization, a major clinical manifestation of diabetic retinopathy, is inhibited is unclear. This study sought to examine the effects of evogliptin, a potent DPP-4 inhibitor, on pathological retinal neovascularization in mice and elucidate the mechanism by which evogliptin inhibits angiogenesis mediated by vascular endothelial growth factor (VEGF), a key factor in the vascular pathogenesis of proliferative diabetic retinopathy (PDR). In a murine model of PDR, an intravitreal injection of evogliptin significantly suppressed aberrant retinal neovascularization. In human endothelial cells, evogliptin reduced VEGF-induced angiogenesis. Western blot analysis showed that evogliptin inhibited the phosphorylation of signaling molecules associated with VEGF-induced cell adhesion and migration. Moreover, evogliptin substantially inhibited the VEGF-induced activation of adenosine 5′-diphosphate ribosylation factor 6 (Arf6), a small guanosine 5′-triphosphatase (GTPase) that regulates VEGF receptor 2 signal transduction. Direct activation of Arf6 using a chemical inhibitor of Arf-directed GTPase-activating protein completely abrogated the inhibitory effect of evogliptin on VEGF-induced activation of the angiogenic signaling pathway, which suggests that evogliptin suppresses VEGF-induced angiogenesis by blocking Arf6 activation. Our results provide insights into the molecular mechanism of the direct inhibitory effect of the DPP-4 inhibitor evogliptin on pathological retinal neovascularization. In addition to its glucose-lowering effect, the antiangiogenic effect of evogliptin could also render it beneficial for individuals with PDR.Subject terms: Vascular diseases, Growth factor signalling 相似文献
315.
316.
Choi I Kim YK Min DH Lee S Yeo WS 《Journal of the American Chemical Society》2011,133(42):16718-16721
We report on a new surface modification method for grafting a "dynamic" property for on-demand activation of the click reaction. Our approach utilizes the acetylene group masked with dicobalt hexacarbonyl, Co(2)(CO)(6), which is not reactive toward the click reaction. Electrochemical treatment reveals the acetylene group on the selected region, which is then used as a chemical handle for surface functionalization via the click reaction with an azide-containing molecule. Electrochemical and chemical conversions on the surface were verified by cyclic voltammetry, X-ray photoelectron spectroscopy, and fluorescence spectroscopy. We have demonstrated immobilization of an azide-modified RGD peptide and promotion of cell adhesion/migration to the region of electrochemical induction. 相似文献
317.
Qi Hang Low Nicholas Wei Xian Loo Federico Calle‐Vallejo Boon Siang Yeo 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(8):2278-2282
The electrocatalytic CO2 reduction reaction (CO2RR) can dynamise the carbon cycle by lowering anthropogenic CO2 emissions and sustainably producing valuable fuels and chemical feedstocks. Methanol is arguably the most desirable C1 product of CO2RR, although it typically forms in negligible amounts. In our search for efficient methanol‐producing CO2RR catalysts, we have engineered Ag‐Zn catalysts by pulse‐depositing Zn dendrites onto Ag foams (PD‐Zn/Ag foam). By themselves, Zn and Ag cannot effectively reduce CO2 to CH3OH, while their alloys produce CH3OH with Faradaic efficiencies of approximately 1 %. Interestingly, with nanostructuring PD‐Zn/Ag foam reduces CO2 to CH3OH with Faradaic efficiency and current density values reaching as high as 10.5 % and ?2.7 mA cm?2, respectively. Control experiments and DFT calculations pinpoint strained undercoordinated Zn atoms as the active sites for CO2RR to CH3OH in a reaction pathway mediated by adsorbed CO and formaldehyde. Surprisingly, the stability of the *CHO intermediate does not influence the activity. 相似文献
318.
Dr. Tam D. Nguyen Ori Geuli Loo Pin Yeo Prof. Shlomo Magdassi Prof. Daniel Mandler Prof. Alfred Iing Yoong Tok 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16573-16581
The electrophoretic deposition (EPD) of graphene-based materials on transparent substrates is highly potential for many applications. Several factors can determine the yield of the EPD process, such as applied voltage, deposition time and particularly the presence of dispersion additives (stabilisers) in the suspension solution. This study presents an additive-free EPD of graphene quantum dot (GQD) thin films on an indium tin oxide (ITO) glass substrate and studies the deposition mechanism with the variation of the applied voltage (10–50 V) and deposition time (5–25 min). It is found that due to the small size (≈3.9 nm) and high content of deprotonated carboxylic groups, the GQDs form a stable dispersion (zeta-potential of about −35 mV) without using additives. The GQD thin films can be deposited onto ITO with optimal surface morphology at 30 V in 5 min (surface roughness of approximately (3.1±1.3) nm). In addition, as-fabricated GQD thin films also possess some interesting physico-optical properties, such as a double-peak photoluminescence at about λ=417 and 439 nm, with approximately 98 % visible transmittance. This low-cost and eco-friendly GQD thin film is a promising material for various applications, for example, transparent conductors, supercapacitors and heat conductive films in smart windows. 相似文献
319.
320.
In this paper, a luminous ratio was applied to evaluate four types of material surfaces; anodized aluminium, stainless steel, poly-butylene tetra-phthalate (PBT), and phenol formaldehyde, marked using a Nd:YAG laser. The luminous ratio was based on the spectral reflectance readings obtained from a spectrophotometer and computed for the case of scotopic (low illumination) and photopic (normal illumination) viewing. The method of using luminous ratios was able to produce quantitative results that determined visibility differences under photopic and scotopic viewing for stainless steel and phenol formaldehyde. The method revealed optimal marking speeds for all the materials studied; with the optimal speed found to be highest for PBT and lowest for stainless steel. By comparing the absolute luminous ratio differences at the respective optimal marking speeds, the method also revealed that markings on phenol formaldehyde and anodized aluminium had the highest and lowest visibility, respectively. 相似文献