Search

A well-defined, biologically relevant Mn(ii) complex is found to catalyse the aerobic oxidative cleavage of a wide range of diverse 1,2-diols to afford valuable carbonyl compounds and five-membered heterocycles under irradiation of visible light.

Reported here is a new protocol for the decarboxylative oxygenation of carboxylic acids using a non-heme manganese catalyst under blue light irradiation with O2 as the sole oxidant.

The oxidative cleavage of C═C double bonds with molecular oxygen to produce carbonyl compounds is an important transformation in chemical and pharmaceutical synthesis. In nature, enzymes containing the first-row transition metals, particularly heme and non-heme iron-dependent enzymes, readily activate O2 and oxidatively cleave C═C bonds with exquisite precision under ambient conditions. The reaction remains challenging for synthetic chemists, however. There are only a small number of known synthetic metal catalysts that allow for the oxidative cleavage of alkenes at an atmospheric pressure of O2, with very few known to catalyze the cleavage of nonactivated alkenes. In this work, we describe a light-driven, Mn-catalyzed protocol for the selective oxidation of alkenes to carbonyls under 1 atm of O2. For the first time, aromatic as well as various nonactivated aliphatic alkenes could be oxidized to afford ketones and aldehydes under clean, mild conditions with a first row, biorelevant metal catalyst. Moreover, the protocol shows a very good functional group tolerance. Mechanistic investigation suggests that Mn-oxo species, including an asymmetric, mixed-valent bis(μ-oxo)-Mn(III,IV) complex, are involved in the oxidation, and the solvent methanol participates in O2 activation that leads to the formation of the oxo species.

Chemical recycling is one of the most promising technologies that could contribute to circular economy targets by providing solutions to plastic waste; however, it is still at an early stage of development. In this work, we describe the first light-driven, acid-catalyzed protocol for chemical recycling of polystyrene waste to valuable chemicals under 1 bar of O2. Requiring no photosensitizers and only mild reaction conditions, the protocol is operationally simple and has also been demonstrated in a flow system. Electron paramagnetic resonance (EPR) investigations and density functional theory (DFT) calculations indicate that singlet oxygen is involved as the reactive oxygen species in this degradation process, which abstracts a hydrogen atom from a tertiary C–H bond, leading to hydroperoxidation and subsequent C–C bond cracking events via a radical process. Notably, our study indicates that an adduct of polystyrene and an acid catalyst might be formed in situ, which could act as a photosensitizer to initiate the formation of singlet oxygen. In addition, the oxidized polystyrene polymer may play a role in the production of singlet oxygen under light.

We present a new concept to passively steer the antenna radiation beam to a fixed direction by utilizing the liquid fluidity behavior due to gravity. Completely different from existing technologies, the proposed antenna does not require any additional mechanical structures, phase shifting circuitry, liquid pumps, tunable elements, or their associated components. By properly designing the structure and resonant mode of the liquid dielectric resonator, the proposed passive antenna can automatically steer the radiation beam to the fixed and desired direction for communication upon physical reorientation of the antenna. An antenna prototype has been proposed with a fundamental resonant band of 1.4–1.8 GHz by using new liquid materials, while its passive beam-steering feature has been experimentally verified. This simple, elegant, and low-cost antenna has combined the gyroscopic correction, gravity, and beam steering into one for the first time, presenting significant implications for radio communications and radar systems that demand an adaptive antenna beam in certain directions.

This article presents a new type of hybrid antenna that combines the multiresonant modes produced by a liquid dielectric resonator antenna (DRA) and a magnetoelectric (ME) dipole. Such a combination could not be easily realized by using conventional solid dielectrics due to fabrication and air-gap problems. An aperture-fed ME dipole for 4.1–5.3 GHz is firstly designed using a standard structure and a relatively small dimension. Then, a hybrid antenna is built by loading the ME-dipole with an aperture-fed cylindrical liquid DRA. Without increasing the antenna size and/or modifying the ME-dipole structure significantly, the hybrid antenna has realized a much wider bandwidth from 2.45 to 5.3 GHz after loading the liquid material. Moreover, it is found that the resonances of the ME-dipole are not simply shifted to lower frequencies after using the dielectric loading, it has strategically combined the multiple resonances of the electric dipole, magnetic dipole, DRA, and feeding slot. The mode combination principle and design guideline have been presented. As an example, a prototype of the proposed hybrid antenna has achieved a 73.5% fractional bandwidth with an electrical size of $0.66\times 0.66\times 0.16\,\, \boldsymbol {\lambda }_{\mathbf {0}}^{3}$ at the center frequency (3.88 GHz), over 5 dBi (up to 7 dBi) broadside gain, total efficiency >80%, and beamwidth around 80°–120° across the frequency band. The proposed hybrid antenna has advantages in terms of wide bandwidth, smaller size, and simple structure compared with other ME-dipoles and traditional wideband antennas. The idea of this antenna design could be extended to other ME-dipole and DRA structures.

An ionic liquid (IL) is used to make antennas for the first time. Unlike water, the proposed material has a large liquid range (-69.8 °C-350 °C), a relative permittivity of 3, an extremely low dielectric loss, and very stable thermophysical material properties. It can be used for liquid dielectric resonator antennas (DRAs) or as a loading material for performance enhancement. Importantly, the proposed liquid loading scheme is relatively simple and of low cost, but it can markedly improve the antenna performance. As design examples, a liquid-loaded wideband linearly polarized (LP) monopole antenna with an omnidirectional radiation pattern is first presented. Then, the LP antenna is modified to a wideband circularly polarized (CP) antenna with boresight radiation. These antenna examples demonstrate a frequency coverage of 1.25-5 GHz, a wide CP bandwidth, a relatively high gain (>4 dBi), high radiation efficiency >85%, and an electrical size of 0.42 λ0 x0.42λ0 x0.17λ0. The experimental results show that the liquid loading works well under a wide range of temperatures. It effectively reduces the antenna electrical size by 40% and improves the impedance matching by 5 dB. Therefore, the proposed liquid loading scheme can be applied to a variety of antenna/RF designs.

A cyclometalated rhodium complex has been shown to perform highly selective and efficient reduction of aldehydes, deriving the hydrogen from methanol. With methanol as both the solvent and hydrogen donor under mild conditions and an open atmosphere, a wide range of aromatic aldehydes were reduced to the corresponding alcohols, without affecting other functional groups.

A novel broadband circularly polarized (CP) antenna using organic ionic liquid resonators is presented in this communication for the first time. The antenna is excited by inserting a new feeding structure into the liquid which is relatively simple but significantly improves the bandwidth and CP performance of traditional single probe-fed dielectric resonator antennas (DRAs). The proposed liquid antenna is loaded with a metasurface (MS) to further improve the impedance matching and CP characteristics. A design example of the proposed antenna shows a relatively wide fractional impedance bandwidth and CP bandwidth of 51.4% and 34.2%, respectively. In addition, the proposed liquid DRA has a reduced structural complexity and a compact size compared with the conventional DRAs with a similar performance. The design methodology presented in this communication can be further exploited for a range of new liquid DRA designs and expand the design freedom and flexibility of such antennas which may have significant implications in future antenna designs using the new liquid materials.

We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H2 outside of the usual Lewis acid/base chemistry described by the concept of “frustrated Lewis pairs” (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly‐hindered boranes: tris(3,5‐dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway for the first time. This radical–based, redox pathway involves homolytic cleavage of H2, in contrast to conventional models of FLP chemistry which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids.

A series of homo- and hetero-tri(aryl)boranes incorporating pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl, and pentachlorophenyl groups, four of which are novel species, have been studied as the acidic component of frustrated Lewis pairs for the heterolytic cleavage of H2. Under mild conditions eight of these will cleave H2; the rate of cleavage depending on both the electrophilicity of the borane and the steric bulk around the boron atom. Electrochemical studies allow comparisons of the electrophilicity with spectroscopic measurements of Lewis acidity for different series of boranes. Discrepancies in the correlation between these two types of measurements, combined with structural characterisation of each borane, reveal that the twist of the aryl rings with respect to the boron-centred trigonal plane is significant from both a steric and electronic perspective, and is an important consideration in the design of tri(aryl)boranes as Lewis acids.

We show by a combination of diffraction and spectroscopic methods that CuH produced by borohydride reduction of a CuII salt consists of a core of CuH with the Wurtzite structure and a shell of water. We also demonstrate that the shell is exchangeable for ethanol., Copper(I) hydride (cuprous hydride, CuH) was the first binary metal hydride to be discovered (in 1844) and is singular in that it is synthesized in solution, at ambient temperature. There are several synthetic paths to CuH, one of which involves reduction of an aqueous solution of CuSO4·5H2O by borohydride ions. The product from this procedure has not been extensively characterized. Using a combination of diffraction methods (X-ray and neutron) and inelastic neutron scattering spectroscopy, we show that the CuH from the borohydride route has the same bulk structure as CuH produced by other routes. Our work shows that the product consists of a core of CuH with a shell of water and that this may be largely replaced by ethanol. This offers the possibility of modifying the properties of CuH produced by aqueous routes.

Presented in this paper are experimentally measured relative complex permittivities as a function of frequency for a representative range of ionic liquids, comprising 64 imidazolium, choline, phosphonium, ammonium, pyrrolidinium, pyridinium and piperidinium cations with a variety of anions. The measurement was conducted using a coaxial probe technique at room temperature from almost DC (0 Hz) to 18 GHz with a high level of accuracy. The real parts of the complex permittivities have been summarized in table format with both the real and imaginary parts presented as individual spectra for each ionic liquid. It is found that an increase in the molecular weight results in a decrease in overall permittivity and this is true over multiple series of ionic liquids. Additives such as water are shown to have a profound effect on the complex permittivity. The measured data is useful for a wide range of applications, such as electronic devices, chemical synthesis and materials.

Synthetic analogues of marine sponge guanidine alkaloids showed in vitro antiparasitic activity against Leishmania (L.) infantum and Trypanosoma cruzi. Guanidines 10 and 11 presented the highest selectivity index when tested against Leishmania. The antiparasitic activity of 10 and 11 was investigated in host cells and in parasites. Both compounds induced depolarization of mitochondrial membrane potential, upregulation of reactive oxygen species levels, and increased plasma membrane permeability in Leishmania parasites. Immunomodulatory assays suggested an NO-independent effect of guanidines 10 and 11 on macrophages. The same compounds also promoted anti-inflammatory activity in L. (L.) infantum-infected macrophages cocultived with splenocytes, reducing the production of cytokines MCP-1 and IFN-γ. Guanidines 10 and 11 affect the bioenergetic metabolism of Leishmania, with selective elimination of parasites via a host-independent mechanism.

A range of guanidinium catalysts was prepared in six or seven synthetic steps and applied to the phase transfer alkylation of a glycinate Schiff's base in 21–86% ee as well as the phase transfer epoxidation of some chalcones in 85–94% ee. Using a spectrophotometric method, pKa values in the range 13.2–13.9 in DMSO have been determined for some of the catalysts highlighting an increase in basicity relative to achiral tetramethylguanidine (pKa=13.0) and a mechanism involving the protonated guanidinium ion as a phase transfer catalyst is proposed. The use of two of the catalysts for the addition of nucleophiles in Michael addition reactions was investigated and both were found to be effective catalysts. A counterion effect was apparent in these reactions, but no enantioselectivity was observed.

The salts, [Ph(2)B{OCH(2)CH(2)N(Me)(CH(2))(n)}(2)][Ph(4)B(3)O(3)](n = 4,5), were prepared in moderate yields in MeOH solution from reaction of Ph(2)BOBPh(2) with [N(CH(2))n(Me)(CH(2)CH(2)OH)][OH] and PhB(OH)(2) in a 1:2:4 ratio. The reactions also lead to Ph(3)B(3)O(3). Both salts were characterized by NMR ((1)H, (13)C, (11)B) IR, and single-crystal XRD studies. The salts are comprised of cationic monoborates (zwitterionic, 2N(+) and 1B(-)) and tetraphenylboroxinate anions. (C) 2009 Elsevier B.V. All rights reserved.

CuH is a material that appears in a wide diversity of circumstances ranging from catalysis to electrochemistry to organic synthesis. There are both aqueous and nonaqueous synthetic routes to CuH, each of which apparently leads to a different product. We developed synthetic methodologies that enable multigram quantities of CuH to be produced by both routes and characterized each product by a combination of spectroscopic, diffraction and computational methods. The results show that, while all methods for the synthesis of CuH result in the same bulk product, the synthetic path taken engenders differing surface properties. The different behaviors of CuH obtained by aqueous and nonaqueous routes can be ascribed to a combination of very different particle size and dissimilar surface termination, namely, bonded hydroxyls for the aqueous routes and a coordinated donor for the nonaqueous routes. This work provides a particularly clear example of how the nature of an adsorbed layer on a nanoparticle surface determines the properties.

A structural, spectroscopic, and computational investigation of Stryker’s reagent, [HCu{P(C6H5)3}]6, and its isotopomers has provided new insights into the complex. Neutron diffraction shows that the hydrides are best described as edge bridging rather than face bridging. The combination of infrared and inelastic neutron scattering spectroscopies has allowed the location of most of the modes associated with the hydrides and their assignments. The structural and spectroscopic conclusions are supported by the ab initio studies of the complex.