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Transition metal single-atom catalysts (SACs) have been regarded as possible alternatives to platinum-based materials due to their satisfactory performance of the oxygen reduction reaction (ORR). By contrast, main-group metal elements are rarely studied due to their unfavorable surface and electronic states. Herein, a main-group Sn-based SAC with penta-coordinated and asymmetric first-shell ligands is reported as an efficient and robust ORR catalyst. The introduction of the vertical oxygen atom breaks the symmetric charge balance, modulating the binding strength to oxygen intermediates and decreasing the energy barrier for the ORR process. As expected, the prepared Sn SAC exhibits outstanding ORR activity with a high half-wave potential of 0.912 V (vs RHE) and an excellent mass activity of 13.1 A mg Sn -1 at 0.850 V (vs RHE), which surpasses that of commercial Pt/C and most reported transition-metal-based SACs. Additionally, the reported Sn SAC shows excellent ORR stability due to the strong interaction between Sn sites and the carbon support with oxygen atom as the bridge. The excellent ORR performance of Sn SAC was also proven by both liquid- and solid-state zinc-air battery (ZAB) measurements, indicating its great potential in practical applications.

We theoretically monitor the photoinduced ππ* → n π* internal conversion process in 4-thiouracil (4TU), triggered by an optical pump. The element-sensitive spectroscopic signatures are recorded by a resonant X-ray probe tuned to the sulfur, oxygen, or nitrogen K-edge. We employ high-level electronic structure methods optimized for core-excited electronic structure calculation combined with quantum nuclear wavepacket dynamics computed on two relevant nuclear modes, fully accounting for their quantum nature of nuclear motions. We critically discuss the capabilities and limitations of the resonant technique. For sulfur and nitrogen, we document a pre-edge spectral window free from ground-state background and rich with ππ* and n π* absorption features. The lowest sulfur K-edge shows strong absorption for both ππ* and n π*. In the lowest nitrogen K-edge window, we resolve a state-specific fingerprint of the ππ* and an approximate timing of the conical intersection via its depletion. A spectral signature of the n π* transition, not accessible by UV-vis spectroscopy, is identified. The oxygen K-edge is not sensitive to molecular deformations and gives steady transient absorption features without spectral dynamics. The ππ*/ n π* coherence information is masked by more intense contributions from populations. Altogether, element-specific time-resolved resonant X-ray spectroscopy provides a detailed picture of the electronic excited-state dynamics and therefore a sensitive window into the photophysics of thiobases.

The aggregation and structural conversion of normal prion peptide (PrP C ) into the pathogenic scrapie form (PrP Sc ), which can act as a seed to enhance prion amyloid fiber formation, is believed to be a crucial event in prionopathies. Previous research suggests that the prion monomer may play an important role in oligomer generation during disease pathogenesis. In the present study, extensive replica-exchange molecular dynamics (REMD) simulations were conducted to explore the conformational characteristics of the huPrP (125-160) monomer under the histidine tautomerism effect. Investigating the structural characteristics and fibrilization process is challenging because two histidine tautomers [N ε2 -H (ε) and N δ1 -H (δ)] can occur in the open neutral state. Molecular dynamics (MD) simulation outcomes have shown that the toxic εδ and δδ isomer (containing several and broader local minima) had the highest α-helix structures, with contents of 21.11% and 21.01%, respectively, and may have a strong influence on the organizational behavior of a monomeric prion. The amino acids aspartate 20 (D20)-asparagine 29 (N29) and isoleucine 15 (I15)-histidine 16 (H16), D20-arginine 27 (R27) as well as N29 formed α-helix with the highest probabilities in the δδ and εδ isomer, accordingly. On the basis of our findings, we propose the histidine tautomerization hypothesis as a new prion accumulation mechanism, which may exist to induce the formation of prion accumulates. Overall, our tautomerism hypothesis constitutes a promising perspective for enhancing understanding of prion disease pathobiology and may help in the design of a good inhibitor.

As an intrinsic origin cause, histidine behaviors play a critical role in protein misfolding processes. Generally, the English (H6R) mutation will disrupt H6 interactions. However, the structural properties of Aβ40 H6R and Aβ42 H6R under the complex influence of a histidine tautomeric effect and an H6R mutation remain unclear. Therefore, we performed a replica exchange molecular dynamics simulation to unveil such structural properties. Our result showed that the H6R substitute could promote the generation of β-sheet structures in comparison to the wild type. Three β-strand structure properties were observed in Aβ40 (rδδ), Aβ42 (rεε), Aβ42 (rεδ), and Aβ42 (rδδ) with β-sheet contents of 47.5%, 37.2%, 46.9%, and 38.6%, respectively, and the dominant conformational properties of Aβ40 (rδδ), Aβ42 (rεε), Aβ42 (rεδ), and Aβ42 (rδδ) had top conformational states of 86.0%, 73.2%, 67.0%, and 56.5%, respectively. Further analysis confirmed that R6 had different mechanisms for controlling the conformational features in Aβ40 H6R and Aβ42 H6R. In the Aβ40 systems, H14 H-bond networks played a critical role in controlling the structural properties. However, in the Aβ42 systems, R6 was more important because it was directly involved in the β-strand formation and maintained the β-sheet between the N-terminus and the central hydrophobic core region. Our current study helps to elucidate the histidine tautomeric behaviors in H6R mutations, which will present opportunities to understand the correlation between with/without H6 and the Aβ40/Aβ42 H6R misfolding mechanisms.

Histidine tautomerism is considered a crucial component that affects the constitutional and accumulation characteristics of the tau 267-312 monomer in the neutral condition, which are connected with the pathobiology of Alzheimer's disease (AD). Interpreting the organizational characteristics and accumulation procedure is a challenging task because two tautomeric conformations (the N ε -H or N δ -H tautomer) can occur in the open neutral condition. In the current work, replica-exchange molecular dynamics (REMD) simulations were performed to investigate the structural properties of the tau 267-312 monomer considering the histidine tautomeric effect. Based on the simulation outcomes, the histidine 268 (H268) (δ)-H299 (δ) (δδ) isomer had the highest β-sheet content with a value of 26.2%, which acquires a sheet-governing toxic conformer with the first abundant conformational state of 22.6%. In addition, δδ displayed notable antiparallel β-sheets between lysine 8 (K8)-asparagine 13 (N13) and valine 40 (V40)-tyrosine 44 (Y44) as well as between K32-H33 and V40-Y44 (β-meander supersecondary structure), indicating this tautomeric isomer may exist to stimulate tau oligomerization. Furthermore, H299 was found to play an essential role in the structural stabilization of the δδ isomer compared with H268. The present research will aid in obtaining insight into the organizational and accumulation properties of tau protein in the presence of histidine tautomerism to control AD.

Oxygen vacancies in TiO 2 nanoparticles are important for charge carrier dynamics, with recent studies reporting contradictory results on TiO 2 nanoparticle photocatalytic activity. We demonstrate that ground state multiplicity, defect levels, and formation energies depend strongly on vacancy location. Quantum dynamics simulations show that charges are trapped within several picoseconds and recombine over a broad range of time scales from tens of picoseconds to nanoseconds. Specifically, nanoparticles with missing partially coordinated surface oxygens showed fast recombination, while nanoparticles with missing highly coordinated subsurface oxygens or singly coordinated oxygens at tips showed slow recombination, even slower than in the pristine system. The results are rationalized by energy gaps and electron-hole localization, the latter determining nonadiabatic coupling and quantum coherence time. The diverse charge recombination scenarios revealed by the nonadiabatic dynamics simulations rationalize the contradictory experimental results for photocatalytic activity and provide guidelines for rational design of nanoscale metal oxides for solar energy harvesting and utilization.

Microporous organic polymer nanoparticles bearing tetraphenylethylene moieties (MOPTs) were prepared in the presence of poly(vinylpyrrolidone) (PVP). The PVP was entrapped into the microporous network of MOPT to form MOPT-P and played the roles of size control, porosity enhancement, and surface property management. MOPT materials without PVP showed superhydrophobicity with a water contact angle of 151°. In comparison, the MOPT-P showed excellent water compatibility. Moreover, due to the aggregation-induced emission property of tetraphenylethylene moieties, the MOPT-P showed emission and excellent emission-based sensing of nitrophenols in water with K sv values in the range of 1.26 × 10 4 ∼ 3.37 × 10 4 M -1 . It is noteworthy that the MOPT-P used water only as a sensing medium and did not require additional organic solvents to enhance water dispersibility of materials. The MOPT-P could be recovered and reused for the sensing at least five times.

Luteolin (3',4',5,7-tetrahydroxyflavone), a type of flavonoid found in medicinal herbs and vegetables, has been of great interest due to its antioxidative, anti-inflammatory, and anticarcinogenic effects. Despite these beneficial biological properties, the ease with which luteolin forms molecular crystals in conventional aqueous formulations has hampered much wider applications. In this study, we introduce an oil-in-water (O/W) nanoemulsion vehicle system for enhanced follicular delivery of luteolin. The luteolin-loaded nanoemulsion, which had an average hydrodynamic size of approximately 290 nm, was produced by the assembly of poly(ethylene oxide)- block -poly(ε-caprolactone) and lecithin at the O/W interface. The luteolin-loaded nanoemulsion showed outstanding stability against drop coalescence and aggregation. This was confirmed from the slight drop size increase after repeated freeze-thaw cycling and long-term storage. Moreover, in vivo hair growth evaluation demonstrated that the luteolin-loaded nanoemulsions fabricated in this study possessed the hair growth-promotion activity, which is comparable with the case of using a luteolin solution in an organic solvent.

A bioinspired synthesis of chiral 3,4-dihydropyranones via S-to-O acyl-transfer reactions is described. Asymmetric Michael addition-lactonization reactions of β,γ-unsaturated α-keto esters with thioesters are catalyzed by proline-derived urea, providing 3,4-dihydropyranones and spiro-3,4-dihydrocoumarin-fused 3',4'-dihydropyranones in high yield (up to 94%) with excellent stereoselectivities (up to >20:1 dr, 99% ee) under catalyst loadings as low as 1 mol %.

Real-time time-dependent density functional theory (RT-TDDFT) provides a practical algorithm for propagating a many-electron system driven by external laser fields. The fields are included nonperturbatively in the propagation, and the molecular reduced single-electron density operator and various spectroscopic and diffraction signals can be computed directly, avoiding the expensive calculation of many-body states. Nonlinear optical signals contain contributions of multiple pathways. A phase cycling protocol is implemented in order to separate these pathways. Simulations of XUV four-wave mixing signals in the CO molecule are compared with ab initio sum-over-states calculations.

With the advancement of intense ultrafast X-ray sources, it is now possible to create a molecular movie by following the electronic dynamics in real time and real space through time-resolved X-ray diffraction. Here we employ real-time time-dependent density functional theory (RT-TDDFT) to simulate the electronic dynamics after an impulse core or valence ionization in the glycine-phenylalanine (GF) dipeptide. The time-evolving dipole moment, the charge density, and the time-resolved X-ray diffraction signals are calculated. The charge oscillation is calculated for 7 fs for valence ionization and 500 as for core ionization. The charge oscillation time scale is comparable to that found in a phenylalanine monomer (4 fs) [ Science 2014 , 346 , 336 ] and is slightly longer because of the elongated glycine chain. Following valence ionization, the charge migration across the GF is mediated by the delocalized lone-pair orbitals of oxygen and nitrogen of the electron-rich amide group. The temporal Fourier transform of the dipole moment provides detailed information on the charge migration dynamics and the molecular orbitals involved. Heterodyne-detected attosecond X-ray diffraction signals provide the magnitude and phase of the scattering amplitude in momentum space and can thus be inverted to yield the charge density in real space.

Motivated by the enormous importance of nanoscale TiO 2 in a wide range of photocatalytic applications and the ill-understood high activity of the commercial nano-TiO 2 photocatalysts, we provide a predictive map of how the anatase-rutile level alignment varies from the smallest nanoparticles (NPs) to the bulk. Specifically, we compute the size dependence of the energies of vacuum-referenced electronic levels in a range of realistically structured rutile and anatase TiO 2 NPs employing accurate all-electron density functional calculations. In agreement with most recent work, a staggered type II anatase level alignment is predicted for the bulk phases, which we further find to persist into the regime of large NPs. We predict that other level alignments will emerge when the diameter of the TiO 2 NPs is reduced below ∼15 nm. Our results suggest how experiment could test the widely debated importance of the bulk-like type II anatase level alignment for enhanced photoactivity of nano-TiO 2 .

The self-assembly powder (SAP) with varying Nafion content was synthesized and characterized by XRD, XPS, HRTEM, and mapping. It is observed that the oxygen from oxygen functional groups transfers to the surface of Pt and generate PtO during the process of self-assembly with the mechanism of micro galvanic cell, where Pt, carbon black, and Nafion act as the anode, cathode and electrolyte, respectively. The appearance of PtO on the surface of Pt leads to a turnover of Nafion structure, and therefore more hydrophilic sulfonic groups directly contact with Pt, and thus the triple-phase boundary (TPB) has been expanded.

As significantly expressed during cell division, polo-like kinase 1 (PLK1) plays crucial roles in numerous mitotic events and has attracted interest as a potential therapeutic marker in oncological drug discovery. We prepared two small molecular fluorescent probes, 1 and 2, conjugated to SBE13 (a type II PLK1 inhibitor) to investigate the PLK1-targeted imaging of cancer cells and tumors. Enzymatic docking studies, molecular dynamics simulations, and in vitro and in vivo imaging experiments all supported the selective targeting and visualization of PLK1 expressing cells by probes 1 and 2, and probe 2 was successfully demonstrated to image PLK1-upregulated tumors with remarkable signal-to-background ratios. These findings represent the first example of small-molecule based fluorescent imaging of tumors using PLK1 as a target, which could provide new avenues for tumor diagnosis and precision therapeutics.

Calix[n]triazoles are developed as new derivatives in the calixarene family. Calixtriazole compounds 2-4 are synthesized using an iterative convergent strategy including an inter-/intramolecular copper(I)-catalyzed azide-alkyne cycloaddition reaction. Solid-state structures are clearly refined to give 1,2-alternate and partial cone conformations for calix[4]triazole and calix[5]triazole, respectively. Theoretical studies based on density functional theory (DFT) calculations indicated that intermolecular interactions are crucial in determining the conformers of the crystals, and the most stable conformers of calix[4]triazole, calix[5]triazole, and calix[6]triazole in the monomeric forms are 1,3-alternate, 1,3-alternate, and 1,3,5-alternate, respectively.

We report an efficient and highly enantioselective hydroboration of aliphatic 1,1-disubstituted alkenes with pinacolborane using a phosphine-Cu catalyst. The method allows facile preparation of enantiomerically enriched β-chiral alkyl pinacolboronates from a range of 1,1-disubstituted alkenes with high enantioselectivity up to 99% ee. Unprecedented enantiodiscrimination between the geminal alkyl substituents was observed with functional group compatibility in the hydroboration. Furthermore, a catalyst loading as low as 1 mol % furnished the desired product without a decrease in yield or selectivity, demonstrating its efficiency in gram scale synthesis.

A major challenge in photodynamic cancer therapy (PDT) is avoiding PDT-induced hypoxia, which can lead to cancer recurrence and progression through activation of various angiogenic factors and significantly reduce treatment outcomes. Reported here is an acetazolamide (AZ)-conjugated BODIPY photosensitizer (AZ-BPS) designed to mitigate the effects of PDT-based hypoxia by combining the benefits of anti-angiogenesis therapy with PDT. AZ-BPS showed specific affinity to aggressive cancer cells (MDA-MB-231 cells) that overexpress carbonic anhydrase IX (CAIX). It displayed enhanced photocytotoxicity compared to a reference compound, BPS, which is an analogous PDT agent that lacks an acetazolamide unit. AZ-BPS also displayed an enhanced in vivo efficacy in a xenograft mouse tumor regrowth model relative to BPS, an effect attributed to inhibition of tumor angiogenesis by both PDT-induced ROS generation and CAIX knockdown. AZ-BPS was evaluated successfully in clinical samples collected from breast cancer patients. We thus believe that the combined approach described here represents an attractive therapeutic approach to targeting CAIX-overexpressing tumors.

All electron relativistic density functional theory (DFT) based calculations using numerical atom-centered orbitals have been carried out to explore the relative stability, atomic, and electronic structure of a series of stoichiometric TiO 2 anatase nanoparticles explicitly containing up to 1365 atoms as a function of size and morphology. The nanoparticles under scrutiny exhibit octahedral or truncated octahedral structures and span the 1-6 nm diameter size range. Initial structures were obtained using the Wulff construction, thus exhibiting the most stable (101) and (001) anatase surfaces. Final structures were obtained from geometry optimization with full relaxation of all structural parameters using both generalized gradient approximation (GGA) and hybrid density functionals. Results show that, for nanoparticles of a similar size, octahedral and truncated octahedral morphologies have comparable energetic stabilities. The electronic structure properties exhibit a clear trend converging to the bulk values as the size of the nanoparticles increases but with a marked influence of the density functional employed. Our results suggest that electronic structure properties, and hence reactivity, for the largest anatase nanoparticles considered in this study will be similar to those exhibited by even larger mesoscale particles or by bulk systems. Finally, we present compelling evidence that anatase nanoparticles become effectively bulklike when reaching a size of ∼20 nm diameter.

Among the layered transition metal dichalcogenides (TMDs) that can form stable two-dimensional crystal structures, molybdenum disulfide (MoS 2 ) has been intensively investigated because of its unique properties in various electronic and optoelectronic applications with different band gap energies from 1.29 to 1.9 eV as the number of layers decreases. To control the MoS 2 layers, atomic layer etching (ALE) (which is a cyclic etching consisting of a radical-adsorption step such as Cl adsorption and a reacted-compound-desorption step via a low-energy Ar + -ion exposure) can be a highly effective technique to avoid inducing damage and contamination that occur during the reactive steps. Whereas graphene is composed of one-atom-thick layers, MoS 2 is composed of three-atom-thick S (top) -Mo (mid) -S (bottom) layers; therefore, the ALE mechanisms of the two structures are significantly different. In this study, for MoS 2 ALE, the Cl radical is used as the adsorption species and a low-energy Ar + ion is used as the desorption species. A MoS 2 ALE mechanism (by which the S (top) , Mo (mid) , and S (bottom) atoms are sequentially removed from the MoS 2 crystal structure due to the trapped Cl atoms between the S (top) layer and the Mo (mid) layer) is reported according to the results of an experiment and a simulation. In addition, the ALE technique shows that a monolayer MoS 2 field effect transistor (FET) fabricated after one cycle of ALE is undamaged and exhibits electrical characteristics similar to those of a pristine monolayer MoS 2 FET. This technique is also applicable to all layered TMD materials, such as tungsten disulfide (WS 2 ), molybdenum diselenide (MoSe 2 ), and tungsten diselenide (WSe 2 ).

Tautomeric state of histidine is one of the factors that influence the structural and aggregation properties of amyloid β (Aβ)-peptide in neutral state. It is worth it to uncover the monomeric properties of Aβ(1-42) peptide in comparison with Aβ(1-40) peptide. Our replica-exchange molecular dynamics simulations results show that the sheet content of each tautomeric isomer in Aβ(1-42) monomer is slightly higher than that in Aβ(1-40) monomer except His6(δ)-His13(δ)-His14(δ) (δδδ) isomer, implying higher aggregation tendency in Aβ(1-42), which is in agreement with previous experimental and theoretical studies. Further analysis indicates that (εεε), (εδε), (εδδ), and (δδε) isomers prefer sheet conformation although they are in nondominating states. Particularly, it is confirmed that antiparallel β-sheets of (εδδ) were formed at K16-E22 (22.0-43.9%), N27-A30 except G29 (21.9-40.2%), and M35-I41 except G37 (24.1-43.4%). Furthermore, (εδδ) may be the easiest one to overcome structural transformation due to nonobstructing interactions between K16 and/or L17 and histidine residues. The current study will help to understand the tautomeric effect of Aβ(1-42) peptide to overcome Alzheimer's disease.

Histidine state (deprotonated, neutral, and protonated) is considered an important factor influencing the structural properties and aggregation mechanisms in amyloid β-peptides (Aβ), which are associated with the pathogenesis of Alzheimer's disease. Understanding the structural properties and aggregation mechanisms is a great challenge because two forms (the N ε -H or N δ -H tautomer) can exist in the free neutral state of histidine. Here, replica-exchange molecular dynamics simulation was performed to elucidate the changes in structure and the mechanism of aggregation influenced by tautomeric behaviors of histidine in Aβ(1-40). Our results show that sheet-dominating conformations can be found in the His6(δ)-His13(δ)-His14(δ) (δδδ) isomer with significant antiparallel sheet structures between R5-D7 and L34-G38, as well as between L17-F20 and L34-G38, implying that a new aggregation mechanism may exist to promote the generation of oligomers and/or aggregates. This work is helpful in understanding the fundamental tautomeric behaviors of neutral histidine in the process of aggregation.

We investigated the influence of size and structure on the electronic structure of TiO2 nanoparticles 0.5-3.2 nm in diameter, in both vacuum and water, using density functional theory (DFT) calculations. Specifically, we tracked the optical and electronic energy gap of a set of (TiO2)n nanoparticles ranging from small non-bulklike clusters with n = 4, 8, and 16, to larger nanoparticles derived from the anatase bulk crystal with n = 35 and 84. As the difference between these two energy gaps (the exciton binding energy) becomes negligible in the bulk, this magnitude provides an indicator of the bulklike character of the electronic structure of the nanoparticles under study. Extrapolating our results to larger sizes, we obtain a rough estimate of the nanoparticle size at which the electronic structure will begin to be effectively bulklike. Our results generally confirmed that the electronic structure of the nanoparticle ground state and excited state has a more pronounced structure dependency than size dependency within a size range of 0.5-1.5 nm. We also showed that the thermodynamic preference for the photocatalytic species is the first S1 exciton. This S1 exciton is stable under vacuum but may evolve to free charge carriers upon structural relaxation in an aqueous environment for particles 0.5-1.5 nm in size studied in the present article. An analysis of ionization potentials and electron affinities, relative to the standard reduction potential for the water splitting half-reactions, revealed the importance of considering the structural relaxation in the excited states and the presence of water for assessing the thermodynamic conditions for photocatalytic water splitting.