Oxamate and pyruvate are isoelectronic molecules. They both quench tryptophan fluorescence with Stern–Volmer constants of 16 and 20 M–1, respectively, which are comparable to that of arcrylamide, a ...commonly used probe for protein structure. On the other hand, it is well known that neither the carboxylate group of these molecules nor the amide group is a good quencher. To find the mechanism of the quenching by oxamate and pyruvate, density functional theory computations with a polarizable continuum model, solvation based on density, and explicit waters, were performed. Results indicate that both molecules can be an electron acceptor via photoinduced electron transfer. There are two requirements. First, the carboxylate and amide moieties must be in direct contact to bring about noticeable quenching. The conjugation between the amide (or the keto) group and the carboxylate group leads to a lower π* orbital, which is the lowest unoccupied molecular orbital (LUMO), and can then accept an electron from the excited tryptophan. Second, since oxamate and pyruvate ions have high electron density, hydrogen bonds with waters, which can be simulated by an explicit water model, are essential. Their LUMO energies are strongly influenced by water in aqueous solution. The above findings demonstrate how tryptophan fluorescence gets quenched in aqueous solution. The findings may be important in dealing with those problems where frontier orbitals are considered, especially with molecules having high electron density.
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Upon excitation at 308 nm, 4-biphenyl carbonyl azide (4-BpCON3) shows unusually fast decay of transient absorption associated with the first excited singlet state, with time constants of several ps ...in MeOH, acetonitrile, and CHCl3. In cyclohexane and cyclohexene, the lifetimes are ca. 0.3 ps, which is in stark contrast to the lifetimes of hundreds of ps in the case of 2-naphthoyl azide. Furthermore, photolysis at 266 and 308 nm brought about the same yields of nitrene and isocyanate products. To understand these findings, we also applied ultrafast transient absorption spectroscopy to the structurally related molecule, fluorene-2-carbonyl azide (F2CON3), in which the two phenyl rings are fixed in a plane by a methylene group. Both carbonyl azides (biphenyl and fluorenyl) have very short lived excited states in different solvents, indicating that the twisting of phenyl rings is not the reason for the fast decay. Theoretical studies using time dependent density functional theory (TDDFT), especially with PBE0 and CAM-B3LYP functionals, suggest that excited-state potential energy surface crossings lead to the efficient and fast decomposition of carbonyl azides upon photoexcitation. Especially, the decay of the Franck-Condon state to the S1 state with π(CON3)-π*(N3') transition character, where -N3 is in a bent conformation (∠NNN = ca. 125°), is the key step. Finally, a model is presented to explain solvent dependence, different decaying rates, and other experimental findings.
Currently, the fabrication of low cost and high efficiency electrocatalysts is a hotspot in the study of water splitting. Herein, plasma spray (PS) was used to induce a microcosmic explosion (
me
) ...on Ni mesh to modify the nanoscale Ni for the preparation of
me
-PS-NM electrodes with excellent hydrogen evolution. We also demonstrated that oxygen evolution could be significantly enhanced after the
me
-PS-NM electrodes were doped with Fe
3+
. Both electrodes formed a system exhibiting superior activity and stability for overall water splitting without noble metals.
We have induced a microcosmic explosion on the substrate surface by plasma-spraying to design an economical and efficient electrode for overall water splitting.
NiFe layered double hydroxide (NiFe LDH) is a promising material with multiple functions. In this communication, a novel method is used to prepare NiFe LDH. This synthesis method is achieved
via
...galvanic-cell corrosion between nickel and iron substrates in aqueous solutions containing a halogen group anion (
e.g.
, Cl) at ambient temperature. The as-prepared NiFe LDH electrodes are developed as electrocatalysts for the oxygen evolution reaction (OER) and exhibit excellent catalytic activities and durability. This work provides an energy-efficient, cost-effective, and scaled-up corrosion engineering approach for manufacturing NiFe LDH materials.
NiFe LDH is prepared
via
galvanic-cell corrosion between nickel and iron substrates in aqueous solutions containing a halogen group anion (
e.g.
, Cl) at ambient temperature.
Recently, production of hydrogen (H
2
) through the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) has acquired great attention because it is more environmentally friendly and ...energy-saving. Herein, an approach of water activation was developed for
in situ
growth of NiMo LDH nanosheet arrays on NiMo foam without using any binder or pressurizing or heating steps. The obtained NiMo foam electrodes showed exceptional catalytic activity and durability for both the UOR and HER. This work offers a new standpoint on designing electrodes with high activation for efficient and sustainable hydrogen production coupled with urea organic oxidation.
A simple water-activation strategy was adopted to rapidly synthesize an efficient and stable electrode featuring
in situ
autologous catalyst-substrate characteristics.
Abstract This study aims to design a classification technique suitable for Zhuang ethnic clothing images by integrating the concept of supply–demand matching and convolutional neural networks. ...Firstly, addressing the complex structure and unique visual style of Zhuang ethnic clothing, this study proposes an image resolution model based on supply–demand matching and convolutional networks. By integrating visual style and label constraints, this model accurately extracts local features. Secondly, the model’s effectiveness and resolution performance are analyzed through various performance metrics in experiments. The results indicate a significant improvement in detection accuracy at different annotation points. The model outperforms other comparative methods in pixel accuracy (90.5%), average precision (83.7%), average recall (80.1%), and average F 1 score (81.2%). Next, this study introduces a clothing image classification algorithm based on key points and channel attention. Through key point detection and channel attention mechanisms, image features are optimized, enabling accurate classification and attribute prediction of Zhuang ethnic clothing. Experimental results demonstrate a notable enhancement in category classification and attribute prediction, with classification accuracy and recall exceeding 90% in top-k tasks, showcasing outstanding performance. In conclusion, this study provides innovative approaches and effective solutions for deep learning classification of Zhuang ethnic clothing images.
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Purpose
The current American Joint Committee on Cancer (AJCC) staging manual uses tumor size, lymph node, and metastatic status to stage breast cancer across different subtypes. We examined the ...prognosis of triple-negative breast cancer (TNBC) versus non-TNBC within the same stages and sub-stages to evaluate whether TNBC had worse prognosis than non-TNBC.
Methods
We reviewed the National Cancer Institute Surveillance, Epidemiology, and End Results (SEER) data and identified 158,358 patients diagnosed with breast cancer from 2010 to 2012. The overall survival (OS) time and breast cancer cause-specific survival time were compared between patients with TNBC and non-TNBC in each stage and sub-stages. The results were validated using a dataset of 2049 patients with longer follow-up from our institution.
Results
Compared with patients with non-TNBC, patients with TNBC had worse OS and breast cancer cause-specific survival time in every stage and sub-stage in univariate and multivariate analyses adjusting for age, race, tumor grade, and surgery and radiation treatments in the SEER data. The worse OS time in patients with TNBC was validated in our institutional dataset.
Conclusions
Patients with TNBC have worse survival than patients with non-TNBC. The new AJCC staging manual should consider breast cancer biomarker information.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
In this paper, a facile and ultrafast two-step dipping process was developed to
in situ
form an electrocatalyst on a NiMo foam substrate without consuming extra energy. The obtained electrode showed ...a porous coral-like structure decorated with nanosheets and exhibited excellent overall water splitting properties in alkaline solution. This study provides a feasible strategy for developing an environmentally friendly and energy-efficient non-noble metal electrode for hydrogen production from water splitting.
We use an ultrafast two-step dipping strategy to fabricate a porous nanosheet array without other external forces. The practical application potential of a bifunctional water splitting electrode based on a NiMo foam substrate is studied.
Fluorescence of Reduced Nicotinamide Adenine Dinucleotide (NADH) is extensively employed in studies of oxidoreductases. A substantial amount of static and kinetic work has focused on the binding of ...pyruvate or substrate mimic oxamate to the binary complex of lactate dehydrogenase (LDH)‐NADH where substantial fluorescence quenching is typically observed. However, the quenching mechanism is not well understood limiting structural interpretation. Based on time‐dependent density functional theory (TDDFT) computations with cam‐B3LYP functional in conjunction with the analysis of previous experimental results, we propose that bound oxamate acts as an electron acceptor in the quenching of fluorescence of NADH in the ternary complex, where a charge transfer (CT) state characterized by excitation from the highest occupied molecular orbital (HOMO) of the nicotinamide moiety of NADH to the lowest unoccupied molecular orbital (LUMO) of oxamate exists close to the locally excited (LE) state involving only the nicotinamide moiety. Efficient quenching in the encounter complex like in pig heart LDH requires that oxamate forms a salt bridge with Arg‐171 and hydrogen bonds with His‐195, Thr‐246 and Asn‐140. Further structural rearrangement and loop closure, which also brings about another hydrogen bond between oxamate and Arg‐109, will increase the rate of fluorescence quenching as well.
Oxamate efficiently quenches the fluorescence of NADH in the lactate dehydrogenase (LDH) ternary complex, but not in water, through electron transfer (ET) mechanism. Oxamate interacts with LDH by forming a salt bridge with Arg‐171 and hydrogen bonds with His‐195, Thr‐246 and Asn‐140 in the encounter complex. It adds another hydrogen bond with Arg‐109 after loop closing. Such interactions decrease the energy of a charge transfer (CT) state involving the nicotinamide moiety and oxamate. Then, electron transfer from excited states of NADH to oxamate and consequent fluorescence quenching take place.
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