Addition of 1-alkyl-3-methylimidazolium (C(n)-mim) cations 3-5 to a mixture of bis-phosphonium cation 2 and sodium p-sulfonatocalix[4]arene (1) in the presence of lanthanide ions results in the selective binding of an imidazolium cation into the cavity of the calixarene. The result is a multi-layered solid material with an inherently flexible interplay of the components. Incorporating ethyl-, n-butyl- or n-hexyl-mim cations into the multi-layers results in significant perturbation of the structure, the most striking effect is the tilting of the plane of the bowl-shaped calixarene relative to the plane of the multi-layer, with tilt angles of 7.2, 28.9 and 65.5 degrees , respectively. The lanthanide ions facilitate complexation, but are not incorporated into the structures and, in all cases, the calixarene takes on a 5- charge, with one of the lower-rim phenolic groups deprotonated. ROESY NMR experiments and other (1)H NMR spectroscopy studies establish the formation of 1:1 supermolecules of C(n)-mim and calixarene, regardless of the ratio of the two components, and indicate that the supermolecules undergo rapid exchange on the NMR spectroscopy timescale.
Micro- and macroscopic studies of nucleation and growth processes of MnAlPO-5 nanosized crystals under ionothermal synthesis conditions are reported herein. The samples treated at 150 °C were extracted from the reaction mixture at various stages of crystallization, and characterized by XRD; SEM; thermogravimetric analysis (TGA); (31)P and (27)Al solid-state magic angle spinning (MAS) NMR, Raman, UV/Vis, and X-ray fluorescence spectroscopy (XRF). The starting raw materials (alumina, manganese, and phosphorous) were dissolved completely in the ionic liquid and transformed into an amorphous solid after 5 h of ionothermal treatment. This amorphous solid then undergoes structural changes over the following 5-25 h, which result in an intermediate phase that consists of octahedral Al species linked to the manganese and phosphate species. The first MnAlPO-5 nuclei on the surface of the intermediate can be observed after 50 h ionoheating. These nuclei further grow, as the surface of the intermediate is in full contact with the ionic liquid, to give crystalline MnAlPO-5 nanoparticles with a mean diameter of 80 nm. The crystals become fully detached from the intermediate and are then liberated as discrete particles after 90 h heating. The transformation process from amorphous to intermediate and then to the crystalline MnAlPO-5 nanoparticles shows that nucleation starts at the solid-liquid interface and continues through surface-to-core reversed-growth until the entire amorphous solid is transformed into discrete nanocrystals.
Oligostilbenoids are polyphenols that are widely distributed in nature with multifaceted biological activities. To achieve biomimetic synthesis of unnatural derivatives, we subjected three resveratrol analogues to oligomerization by means of one-electron oxidants. Upon varying the metal oxidant (AgOAc, CuBr(2), FeCl(3)6 H(2)O, FeCl(3)6 H(2)O/NaI, PbO(2), VOF(3)), the solvent (over the whole range of polarities), and the oxygenated substitution pattern of the starting material, stilbenoid oligomers with totally different carbon skeletons were obtained. Here we propose to explain the determinism of the type of skeleton produced with the aid of hard and soft acid/base concepts in conjunction with the solvating properties of the solvents and the preferred alignment by the effect of pi stacking.
Three solid materials, [Pb(HL)(SCN)2 ]⋅CH3 OH (1), [Pb(HL)(SCN)2 ] (2), and [Pb(L)(SCN)]n (3), were obtained from Pb(SCN)2 and an unsymmetrical bis-pyridyl hydrazone ligand that can act both as a bridging and as a chelating ligand. In all three the lead center is hemidirectionally coordinated and is thus sterically optimal for participation in tetrel bonding. In the crystal structures of all three compounds, the lead atoms participate in short contacts with thiocyanate sulfur or nitrogen atoms. These contacts are shorter than the sums of the van der Waals radii (3.04-3.47 Å for Pb⋅⋅⋅S and 3.54 Å for Pb⋅⋅⋅N) and interconnect the covalently bonded units (monomers, dimers, and 2D polymers) into supramolecular assemblies (chains and 3D structures). DFT calculations showed these contacts to be tetrel bonds of considerable energy (6.5-10.5 kcal mol(-1) for Pb⋅⋅⋅S and 16.5 kcal mol(-1) for Pb⋅⋅⋅N). A survey of structures in the CSD showed that similar contacts often appear in crystals of Pb(II) complexes with regular geometries, which leads to the conclusion that tetrel bonding plays a significant role in the supramolecular chemistry of Pb(II) .
A dinuclear gold(I) pyrrolidinedithiocarbamato complex (1) with a bidentate carbene ligand has been constructed and shows potent in vitro cytotoxic activities towards cisplatin-resistant ovarian cancer cells A2780cis. Its rigid scaffold enables a zinc(II)-based metal-organic framework (Zn-MOF) to be used as a carrier in facilitating the uptake and release of 1 in solutions. Instead of using a conventional dialysis approach for the drug-release testing, in this study, a set of transwell assay-based experiments have been designed and employed to examine the cytotoxic and antimigratory activities of 1@Zn-MOF towards A2780cis.
Although metal-ion-directed self-assembly has been widely used to construct a vast number of macrocycles and cages, it is only recently that the biological properties of these systems have begun to be explored. However, up until now, none of these studies have involved intrinsically photoexcitable self-assembled structures. Herein we report the first metallomacrocycle that functions as an intracellular singlet oxygen sensitizer. Not only does this Ru2 Re2 system possess potent photocytotoxicity at light fluences below those used for current medically employed systems, it offers an entirely new paradigm for the construction of sensitizers for photodynamic therapy.
Universal access to clean water has been a global ambition over the years. Photocatalytic water disinfection through advanced oxidation processes has been regarded as one of the promising methods for breaking down microbials. The forefront of this research focuses on the application of metal-free photocatalysts for disinfection to prevent secondary pollution. Graphitic carbon nitride (g-C3 N4 ) has achieved instant attention as a metal-free and visible-light-responsive photocatalyst for various energy and environmental applications. However, the photocatalytic efficiency of g-C3 N4 is still affected by its rapid charge recombination and sluggish electron-transfer kinetics. In this contribution, two-dimensionally protonated g-C3 N4 was employed as metal-free photocatalyst for water treatment and demonstrated 100 % of Escherichia coli within 4 h under irradiation with a 23 W light bulb. The introduction of protonation can modulate the surface charge of g-C3 N4 ; this enhances its conductivity and provides a "highway" for the delocalization of electrons. This work highlights the potential of conjugated polymers in antibacterial application.
Reactions of [Rh(κ(2) -O,O-acac)(PMe3 )2 ] (acac=acetylacetonato) and α,ω-bis(arylbutadiynyl)alkanes afford two isomeric types of MC4 metallacycles with very different photophysical properties. As a result of a [2+2] reductive coupling at Rh, 2,5-bis(arylethynyl)rhodacyclopentadienes (A) are formed, which display intense fluorescence (Φ=0.07-0.54, τ=0.2-2.5 ns) despite the presence of the heavy metal atom. Rhodium biphenyl complexes (B), which show exceptionally long-lived (hundreds of μs) phosphorescence (Φ=0.01-0.33) at room temperature in solution, have been isolated as a second isomer originating from an unusual [4+2] cycloaddition reaction and a subsequent β-H-shift. We attribute the different photophysical properties of isomers A and B to a higher excited state density and a less stabilized T1 state in the biphenyl complexes B, allowing for more efficient intersystem crossing S1 →Tn and T1 →S0 . Control of the isomer distribution is achieved by modification of the bis- (diyne) linker length, providing a fundamentally new route to access photoactive metal biphenyl compounds.
This work reports the outcome of thermal grafting of 2-ethynylaniline, 3-ethynylaniline, and 4-ethynylaniline on a hydrogenated Si(100) surface. Using high-resolution XPS and AFM, it was found that the grafting of these compounds could be attributed to resonating structures that arise from the position of an electron-donating NH2 group and an electron-withdrawing acetylene group. For the ortho- and para-positioned acetylene group, surface reactions were observed to proceed predominantly via the acetylene to form a Si-C bond, whereas the meta-positioned acetylene group was found to have undergone nucleophilic grafting through the NH2 group onto the silicon surface to form a Si-N bond. Furthermore, a tert-butoxycarbonyl-protected derivative for a meta-positioned ethynylaniline was synthesized to exclusively force the reaction to react with the acetylene group and subsequent analysis confirmed that unprotected 3-ethynylaniline had indeed reacted through the nucleophilic NH2 group as hypothesized. Thus, for the first time, the interplay between resonance structures and their effects on silicon surface modifications were systematically catalogued.
Developing highly active, non-noble-metal H2 -evolution catalysts is appealing yet still remains a great challenge in the field of electrocatalytic and photocatalytic H2 production. In this work, high quality transition-metal carbonitrides M3 CN (MXene) are investigated using well-defined density functional theory (DFT) calculations. The structural configurations, H-adsorption free energy (ΔGH ) and charge transfer for bare, surface-terminated and transition-metal (TM)-modified M3 CNO2 are systematically studied. The calculated results indicate that all bare transition metal carbonitrides exhibit strong binding between H atom and catalysts. In addition, only Ti3 CNO2 and Nb3 CNO2 have the potential to be HER active catalysts based on the ΔGH results. In an attempt to overcome poor HER activity limitations, we apply O as well as OH mixed groups and TMs modification on the Ti3 CNO2 surface for tuning HER activity, and a significant improvement of HER activity is observed. Overall, this work presents in-depth investigations for transition-metal carbonitrides (MXene) and opens up new designs for robust metal carbonitrides as noble-metal-free cocatalysts for highly efficient and low-cost MXene-based nanocomposites for water splitting applications.
Photocatalytic CO2 reduction is a revolutionary approach to solve imminent energy and environmental issues by replicating the ingenuity of nature. The past decade has witnessed an impetus in the rise of two-dimensional (2D) structure materials as advanced nanomaterials to boost photocatalytic activities. In particular, the use of 2D carbon-based materials is deemed as highly favorable, not only as a green material choice, but also due to their exceptional physicochemical and electrical properties. This Review article presents a diverse range of alterations and compositions derived from 2D carbon-based nanomaterials, mainly graphene and graphitic carbon nitride (g-C3 N4 ), which have remarkably ameliorated the photocatalytic CO2 performance. Herein, the rational design of the photocatalyst systems with consideration of the aspect of dimensionality and the resultant heterostructures at the interface are systematically analyzed to elucidate an insightful perspective on this pacey subject. Finally, a conclusion and outlook on the limitations and prospects of the cutting-edge research field are highlighted.
In this work, a series of non-noble metal single-atom catalysts of Mo2 CS2 -MXene for CO2 reduction were systematically investigated by well-defined density-functional-theory (DFT) calculations. It is found that nine types of transitional metal (TM) supported Mo2 CS2 (TM-Mo2 CS2 ) are very stable, while eight can effectively inhibit the competitive hydrogen evolution reaction (HER). After comprehensively comparing the changes of free energy for each pathway in CO2 reduction reaction (CO2 RR), it is found that the products of TM-Mo2 CS2 are not completely CH4 . Furthermore, Cr-, Fe-, Co- and Ni-Mo2 CS2 are found to render excellent CO2 RR catalytic activity, and their limiting potentials are in the range of 0.245-0.304 V. In particular, Fe-Mo2 CS2 with a nitrogenase-like structure has the lowest limiting potential and the highest electrocatalytic activity. Ab initio molecular dynamics (AIMD) simulations have also proven that these kinds of single-atom catalysts with robust performance could exist stably at room temperature. Therefore, these single TM atoms anchored on the surface of MXenes can be profiled as a promising catalyst for the electrochemical reduction of CO2 .
Despite the fact that perovskite solar cells (PSCs) have a strong potential as a next-generation photovoltaic technology due to continuous efficiency improvements and the tunable properties, some important obstacles remain before industrialization is feasible. For example, the selection of low-cost or easy-to-prepare materials is essential for back-contacts and hole-transporting layers. Likewise, the choice of conductive substrates, the identification of large-scale manufacturing techniques as well as the development of appropriate aging protocols are key objectives currently under investigation by the international scientific community. This Review analyses the above aspects and highlights the critical points that currently limit the industrial production of PSCs and what strategies are emerging to make these solar cells the leaders in the photovoltaic field.
Because of their structural and compositional flexibility, perovskite oxides represent an attractive alternative electrocatalyst class to precious metals for the oxygen reduction reaction (ORR); an important reaction in fuel cells and metal-air batteries. Partial replacement of the original metal cation with another cation, namely, doping, can be used to tailor the ORR activity of perovskite, for which a metal has been exclusively used as the dopant component in the past. Herein, phosphorus is proposed as a non-metal dopant for the cation site to develop a new perovskite family with the formula of La0.8 Sr0.2 Mn1-x Px O3-δ (x=0, 0.02, 0.05, and 0.1; denoted as LSM, LSMP0.02, LSMP0.05, and LSMP0.1, respectively). Powder XRD patterns reveal that the solubility of phosphorus in the perovskite structure is around 0.05. Rotating ring-disk electrode experiments in the form of linear-sweep voltammetry scans demonstrated the best ORR performance for LSMP0.05, and also revealed close to a four-electron ORR pathway for all four compositions. A chronoamperometric test (9000 s) and 500 cycle accelerated durability test demonstrated higher durability for LSMP0.05 relative to that of LSM and the commercial 20 wt % Pt/C catalyst. The higher ORR activity for LSMP0.05 is attributed to the optimised average valence of Mn, as evidenced by combined X-ray photoelectron spectroscopy and soft X-ray absorption spectroscopy data. Doping phosphorus into perovskites is an effective way to develop high-performance electrocatalysts for ORR.
Molecular processes behind hydrogen evolution reactions can be quite complex. In macroscopic electrochemical cells, it is extremely difficult to elucidate and understand their mechanism. Gas phase models, consisting of a metal ion and a small number of water molecules, provide unique opportunities to understand the reaction pathways in great detail. Hydrogen evolution in clusters consisting of a singly charged metal ion and one to on the order of 50 water molecules has been studied extensively for magnesium, aluminum and vanadium. Such clusters with around 10-20 water molecules are known to eliminate atomic or molecular hydrogen upon mild activation by room temperature black-body radiation. Irradiation with ultraviolet light, by contrast, enables hydrogen evolution already with a single water molecule. Here, we analyze and compare the reaction mechanisms for hydrogen evolution on the ground state as well as excited state potential energy surfaces. Five distinct mechanisms for evolution of atomic or molecular hydrogen are identified and characterized.