Synthesis and properties of titanomagnetite (Fe3−xTixO4) nanoparticles: A tunable solid-state Fe(II/III) redox system

Titanomagnetite (Fe_3−xTi_xO₄) nanoparticles were synthesized by room temperature aqueous precipitation, in which Ti(IV) replaces Fe(III) and is charge compensated by conversion of Fe(III) to Fe(II) in the unit cell. A comprehensive suite of tools was used to probe composition, structure, and magnetic properties down to site-occupancy level, emphasizing distribution and accessibility of Fe(II) as a function of x. Synthesis of nanoparticles in the range 0 ? x ? 0.6 was attempted; Ti, total Fe and Fe(II) content were verified by chemical analysis. TEM indicated homogeneous spherical 9-12 nm particles. μ-XRD and Mössbauer spectroscopy on anoxic aqueous suspensions verified the inverse spinel structure and Ti(IV) incorporation in the unit cell up to x ? 0.38, based on Fe(II)/Fe(III) ratio deduced from the unit cell edge and Mössbauer spectra. Nanoparticles with a higher value of x possessed a minor amorphous secondary Fe(II)/Ti(IV) phase. XANES/EXAFS indicated Ti(IV) incorporation in the octahedral sublattice (B-site) and proportional increases in Fe(II)/Fe(III) ratio. XA/XMCD indicated that increases arise from increasing B-site Fe(II), and that these charge-balancing equivalents segregate to those B-sites near particle surfaces. Dissolution studies showed that this segregation persists after release of Fe(II) into solution, in amounts systematically proportional to x and thus the Fe(II)/Fe(III) ratio. A mechanistic reaction model was developed entailing mobile B-site Fe(II) supplying a highly interactive surface phase that undergoes interfacial electron transfer with oxidants in solution, sustained by outward Fe(II) migration from particle interiors and concurrent inward migration of charge-balancing cationic vacancies in a ratio of 3:1.     

Synthesis and MMA polymerization of chiral ansa-zirconocene ester enolate complexes with C2- and Cs-ligation

A series of chiral ansa-zirconocene ester enolate complexes incorporating C₂- or C_s-symmetric ligands, including neutral rac-(EBI)ZrCl[OC(OⁱPr)CMe₂] (1), rac-(EBI)Zr(OTf)[OC(OⁱPr)CMe₂] (2), rac-(EBI)Zr(OTf)[OC(OMe)C(Me)CH₂C(Me₂)C(OⁱPr)O] (3), [Me₂C(Cp)(Flu)]ZrMe[OC(OⁱPr)CMe₂] (4), and cationic [Me₂C(Cp)(Flu)]Zr⁺(THF)[OC(OⁱPr)CMe₂][MeB(C₆F₅)₃]⁻ (5), have been synthesized. Within the neutral C₂-ligated zirconocene ester enolate series, the chloride derivative 1 is inactive toward any methyl methacrylate (MMA) additions, the methyl derivative rac-(EBI)ZrMe[OC(OⁱPr)CMe₂] adds cleanly only 1 equiv. of MMA, and the triflate derivative 2 can add either 1 equiv. of MMA to form the single-MMA-addition product 3 or multiple equivalents of MMA to form P(MMA). Unlike the C_s-ligated methyl cation [Me₂C(Cp)(Flu)ZrMe]⁺, which is inactive for MMA polymerization under various conditions, the C_s-ligated ester enolate cation 5 is moderately active for polymerization of MMA and N,N-dimethylacrylamide at ambient temperature; the resulting P(MMA) has a high molecular weight of M_n = 388 000 Da but a low syndiotacticity of [rr] = 64%, and the polymerization conforms to a chain-end control mechanism.     

PREDICTING GULL/HUMAN CONFLICTS WITH MATHEMATICAL MODELS: A TOOL FOR MANAGEMENT

Abstract Gulls are highly adaptable animals that thrive in proximity to humans. Although gulls enjoy legal protection in North America, England, and Europe, they often conflict with human interests by spreading disease, transporting contaminants, fouling public areas with droppings, and colliding with aircraft. Of particular concern are aggregates of “loafing” gulls that gather on parking lots, rooftops, and airport runways. Loafing in birds is a general state of immobility that involves behaviors such as sleeping, sitting, standing, resting, preening, and defecating. The ability to predict the incidence of aggregated loafing provides a first step toward the amelioration of bird/human conflicts. We used mathematical models to predict the aggregate loafing behavior of gulls as a function of environmental conditions and tested model portability across years, phase of breeding cycle, loafing location, and species. Because groups of loafing birds quickly reassemble after disturbance, algebraic models for the steady‐state dynamics can be obtained from the differential equations using time‐scale analysis. The accessible management tool requires data collection on an appropriate time scale and information‐theoretic model selection from a suite of alternative algebraic models.     

固体核磁共振技术在气体水合物研究中的应用

气体水合物是在低温高压条件下由气体和水形成的笼型化合物,主要有I型,II型和H型3种晶体结构,而固体核磁共振（solid state NMR）是测定其水合指数、笼占有率等结构参数的重要手段. 该文综述了固体核磁共振技术的原理及其在水合物研究中的应用,着重介绍固体核磁共振在水合物结构表征、气体组分的鉴定、结构转化、以及在水合物生成/分解动力学过程监测方面的研究进展. 同时,对其实验方法及测试条件也进行了详细的探讨.     

Site preference and elastic properties of ternary alloying additions in B2 YAg alloys by first-principles calculations

First-principles calculations were preformed to study the site preference behavior and elastic properties of 3d (Ti–Cu) transition-metal elements in B2 ductility YAg alloy. In YAg, Ti is found to occupy the Y sublattice whereas V, Cr, Co, Fe, Ni and Cu tend to substitute for Ag sublattice. Due to the addition of 3d transition metals, the lattice parameters of YAg is decreased in the order: V<Cu<Cr<Ni<Co<Fe<Ti. The calculated elastic constants show that Cr, Fe, Co and Cu can improve the ductility of YAg alloy, and Fe is the most effective element to improve the ductility of YAg, while Ti, Ni and V alloying elements can reduce the ductility of YAg alloy, especially, V transforms ductile into brittle for YAg alloy. In addition, both V and Ni alloying elements can increase the hardness of YAg alloy, and Y₈Ag₇V is harder than Y₈Ag₇Ni.     

依赖于时间的光场与四能级原子的相互作用

研究了依赖于时间的单模光场与N 型四能级原子的相互作用系统,分析了原子布居的时间演化特性.结果表明,由于受到时间脉冲的调制,原子粒子数布居最后会处于一个稳定的状态.     

Boosting the Catalase-Like Activity of SAzymes via Facile Tuning of the Distances between Neighboring Atoms in Single-Iron Sites

A nanozyme with neighboring single-iron sites (Fe₂-SAzyme) was introduced as a bioinspired catalase mimic, featuring excellent activity under varied conditions, twice as high as that of random Fe₁-SAzyme and ultrahigh H₂O₂ affinity as that of bioenzymes. Surprisingly, the interatomic spacing tuning between adjacent iron sites also suppressed the competitive peroxidase pathway, remarkably increasing the catalase/peroxidase selectivity up to ~6 times compared to Fe₁-SAzyme. This dramatically switched the catalytic activity of Fe-SAzymes from generating (i.e. Fe₁-SAzymes, preferably mimicking peroxidase) to scavenging ROS (i.e. Fe₂-SAzymes, dominantly mimicking catalase). Theoretical and experimental investigations suggested that the pairwise single-iron sites may serve as a robust molecular tweezer to efficiently trap and decompose H₂O₂ into O₂, via cooperative hydrogen-bonding induced end-bridge adsorption. The versatile mechano-assisted in situ MOF capsulation strategy enabled facile access to neighboring M₂-SAzyme (M=Fe, Ir, Pt), even up to a 1000 grams scale, but with no obvious scale-up effect for both structures and performances.     

Highly Efficient Decomposition of Perfluorocarbons for over 1000 Hours via Active Site Regeneration

Tetrafluoromethane (CF₄), the simplest perfluorocarbon (PFC), has the potential to exacerbate global warming. Catalytic hydrolysis is a viable method to degrade CF₄, but fluorine poisoning severely restricts both the catalytic performance and catalyst lifetime. In this study, Ga is introduced to effectively assists the defluorination of poisoned Al active sites, leading to highly efficient CF₄ decomposition at 600 °C with a catalytic lifetime exceeding 1,000 hours. ²⁷Al and ⁷¹Ga magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) showed that the introduced Ga exists as tetracoordinated Ga sites (Ga_IV), which readily dissociate water to form Ga−OH. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density function theory (DFT) calculations confirmed that Ga−OH assists the defluorination of poisoned Al active sites via a dehydration-like process. As a result, the Ga/Al₂O₃ catalyst achieved 100 % CF₄ decomposition keeping an ultra-long catalytic lifetime and outperforming reported results. This work proposes a new approach for efficient and long-term CF₄ decomposition by promoting the regeneration of active sites.     

A De Novo-Designed Type 3 Copper Protein Tunes Catechol Substrate Recognition and Reactivity

De novo metalloprotein design is a remarkable approach to shape protein scaffolds toward specific functions. Here, we report the design and characterization of Due Rame 1 (DR1), a de novo designed protein housing a di-copper site and mimicking the Type 3 (T3) copper-containing polyphenol oxidases (PPOs). To achieve this goal, we hierarchically designed the first and the second di-metal coordination spheres to engineer the di-copper site into a simple four-helix bundle scaffold. Spectroscopic, thermodynamic, and functional characterization revealed that DR1 recapitulates the T3 copper site, supporting different copper redox states, and being active in the O₂-dependent oxidation of catechols to o-quinones. Careful design of the residues lining the substrate access site endows DR1 with substrate recognition, as revealed by Hammet analysis and computational studies on substituted catechols. This study represents a premier example in the construction of a functional T3 copper site into a designed four-helix bundle protein.     

Boosting Alkaline Hydrogen Evolution Reaction through Water Structure Manipulation

In the past, the design of efficient electrocatalyst materials for alkaline hydrogen evolution reaction (HER) was mostly focused on tuning the adsorption properties of reaction intermediates. A recent breakthrough shows that the performance can be improved by manipulating water structure at the electrode-electrolyte interface using atomically localized electric fields. The new approach was realized by using IrRu dizygotic single-atom sites and led to a significantly accelerated water dissociation and an overall improved alkaline HER performance. Supported by extensive data from advanced modeling, characterization, and electrochemical measurements, the work delivers an intricate examination of the interaction between water molecules and the catalyst surface, thereby enriching our understanding of water dissociation kinetics and offering new insights to boost overall alkaline HER efficiency.