Cyclodextrin-based supramolecular polynitroxides with good solubility in water, good cytocompatibility and long in vivo lifetime have been synthesized and tested for the in vivo magnetic resonance imaging of glioma.

Abstract

This paper reports the synthesis, characterization and in vivo application of water-soluble supramolecular contrast agents (Mw: 5–5.6 kDa) for MRI obtained from β-cyclodextrin functionalized with different kinds of nitroxide radicals, both with piperidine structure (CD2 and CD3) and with pyrrolidine structure (CD4 and CD5). As to the stability of the radicals in presence of ascorbic acid, CD4 and CD5 have low second order kinetic constants (≤0.05 M⁻¹ s⁻¹) compared to CD2 (3.5 M⁻¹ s⁻¹) and CD3 (0.73 M⁻¹ s⁻¹). Relaxivity (r₁) measurements on compounds CD3-CD5 were carried out at different magnetic field strength (0.7, 3, 7 and 9.4 T). At 0.7 T, r₁ values comprised between 1.5 mM⁻¹ s⁻¹ and 1.9 mM⁻¹ s⁻¹ were found while a significant reduction was observed at higher fields (r₁≈0.6-0.9 mM⁻¹ s⁻¹ at 9.4 T). Tests in vitro on HEK293 human embryonic kidney cells, L929 mouse fibroblasts and U87 glioblastoma cells indicated that all compounds were non-cytotoxic at concentrations below 1 μmol mL⁻¹. MRI in vivo was carried out at 9.4 T on glioma-bearing rats using the compounds CD3-CD5. The experiments showed a good lowering of T₁ relaxation in tumor with a retention of the contrast for at least 60 mins confirming improved stability also in vivo conditions.

The mechanism and activity of CO₂ reduction at single-atom M−N₂ sites is investigated using density functional theory calculations. The asymmetric *O*CO tends to split into the *CO intermediate and the *OH intermediate at the single-atom M−N₂ sites. The intermediate (*CO or *OH) acts as a ligand to induce high activity at the M sites.

Abstract

Single-atom M−N₂ (M=Fe, Co, Ni) catalysts exhibit high activity for CO₂ reduction reaction (CO₂RR). However, the CO₂RR mechanism and the origin of activity at the single-atom sites remain unclear, which hinders the development of single-atom M−N₂ catalysts. Here, using density functional theory calculations, we reveal intermediates-induced CO₂RR activity at the single-atom M−N₂ sites. At the M−N₂ sites, the asymmetric *O*CO configuration tends to split into *CO and *OH intermediates. Intermediates become part of the active moiety to form M−(CO)N₂ or M-(OH)N₂ sites, which optimizes the adsorption of intermediates on the M sites. The maximum free energy differences along the optimal CO₂RR pathway are 0.30, 0.54, and 0.28 eV for Fe−(OH)N₂, Co−(CO)N₂, and Ni−(OH)N₂ sites respectively, which is lower than those of Fe−N₂ (1.03 eV), Co−N₂ (1.24 eV) and Ni−N₂ (0.73 eV) sites. The intermediate modification can shift the d-band center of the spin-up (minority) state downward by regulating the charge distribution at the M sites, leading to less charge being accepted by the intermediates from the M sites. This work provides new insights into the understanding of the activity of single-atom M−N₂ sites.

Electron capture by H₂O⁺ into a resonance just above ist B̃ state sparks a fast elongation of the OH bond while the neutral molecule goes to the linear geometry. The competition between autoionization and dissociation on the potential energy surface of the neutral state determines the proportion of dissociative recombination and dissociative excitation that the system experiences.

Abstract

We have investigated the dissociation of a resonant state that can be formed in low energy electron scattering from H₂O⁺. We have chosen the second triplet resonance above the state of H₂O⁺ whose autoionization mainly produces H₂O⁺ ( ). We have considered both dissociation of the resonant state itself, dissociative recombination (DR), or the dissociation of the H₂O⁺ cation after autodetachment, dissociative excitation (DE). The time-evolution of a wave packet on the potential energy surfaces of the resonance and cationic states shows, for the initial conditions studied, that the probability for DR is about 38 % while the probability for DE is negligible.

Discharges in water confront low energy efficiency when used for treating surface water due to increased conductivities. Accordingly, reactive species production of single discharges was studied for different water conductivities and the dielectric time constant was identified as characteristic parameter assessing efficiency. Production efficiencies up to 6.1 g (H₂O₂) ⋅ kWh⁻¹ were achieved.

Abstract

The production of hydrogen peroxide (H₂O₂) is a key parameter for the performance of pulsed discharges submerged in water utilized as advanced oxidation process. So far, any related assessment of the underlying mechanism was conducted for the application of several hundred discharges, which did not allow for a correlation with physical processes. Moreover, the production was rarely investigated depending on water conductivity as one of the most important parameters for the development of submerged discharges. Accordingly, hydrogen peroxide generation was investigated here for individual single discharge events instigated with 100 ns high-voltage pulses in water with three different conductivities and was associated with the discharge development, i. e. spatial expansion and dissipated electrical energy. The approach necessitated the improvement of an electrochemical flow injection analysis based on the reaction of Prussian blue with H₂O₂. Hydrogen peroxide concentrations were quadratically increasing with propagation time and stable for different water conductivities. H₂O₂ production per unit volume of a discharge was constant over time with an estimated rate constant of 3.2 mol ⋅ m⁻¹ s⁻¹, averaged over the crosssectional area of all discharge filaments. However, the individually dissipated energy increased with conductivity, hence, the production efficiency decreased from 6.1 g ⋅ kWh⁻¹ to 1.4 g ⋅ kWh⁻¹, which was explained by increased resistive losses within the bulk liquid.

Ab initio quantum chemical calculations reveal the unprecedented formation of anion-anion dative bond.

Abstract

Formation of a genuine chemical bond between two similarly charged fragments is beyond expectation. Any such interaction generally lies in the realm of non-covalent interaction. Herein, formation of a strong dative covalent bond between two anionic fragments is reported for the first time. Calculation using ab initio coupled cluster theory reveals the formation of an unprecedented strong H₃Be⁻←X⁻ (X⁻=CH₃ ⁻, CN⁻, OH⁻, F⁻) dative covalent bond. The calculated bond dissociation energies in polar solvents are significant, which indicates the possibility of their experimental realization.

The adhesion of Au oxide and NPG films on a Au substrate was investigated at high voltages with respect to the crystallographic orientation. While the Au oxide films formed are homogeneous in most cases, the NPG films show a strong dependence on the crystallographic orientation. Both very thin and thick NPG films tend to exfoliate.

Abstract

Nanoporous Au (NPG) has different properties compared to bulk Au, making it an interesting material for numerous applications. To modify the structure of NPG films for specific applications, e. g., the porosity, thickness, and homogeneity of the films, a fundamental understanding of the structure formation is essential. Here, we focus on NPG prepared via electrochemical reduction from Au oxide formed during high voltage (HV) electrolysis on poly-oriented Au single crystal (Au POSC) electrodes. These POSCs consist of a metal bead, with faces with different crystallographic orientations and allow screening of the influence of crystallographic orientation on the structure formation for different facets in one experiment. The HV electrolysis is performed between 100 ms and 30 s at 300 V and 540 V. The amount of Au oxide formed is determined by electrochemical measurements and the structural properties are investigated by scanning electron and optical microscopy. We show that the formation of Au oxide is mostly independent of the crystallographic orientation, except for thick layers, while the macroscopic structure of the NPG films depends on experimental parameters such as the Au oxide precursor thickness and the crystallographic orientation of the substrate. Possible reasons for the frequently observed exfoliation of the NPG films are discussed.

Nitrogen-doped multi-walled carbon nanotubes (NMWCNTs) are synthesized. Further, sulfonic-acid-functionalized copper phthalocyanine (CuPc-SO₃ ⁻) is integrated into the NMWCNTs (NMWCNTs-CuPc-SO₃ ⁻) and characterized. The NMWCNT-CuPc-SO₃ ⁻ material is highly selective towards the four-electron oxygen reduction reaction at low overpotentials, as determined by rotating ring electrode studies.

Abstract

In the present work, the oxygen reduction reaction (ORR) is explored in an acidic medium with two different catalytic supports (multi-walled carbon nanotubes (MWCNTs) and nitrogen-doped multi-walled carbon nanotubes (NMWCNTs)) and two different catalysts (copper phthalocyanine (CuPc) and sulfonic acid functionalized CuPc (CuPc-SO₃ ⁻)). The composite, NMWCNTs-CuPc-SO₃ ⁻ exhibits high ORR activity (assessed based on the onset potential (0.57 V vs. reversible hydrogen electrode) and Tafel slope) in comparison to the other composites. Rotating ring disc electrode (RRDE) studies demonstrate a highly selective four-electron ORR (less than 2.5 % H₂O₂ formation) at the NMWCNTs-CuPc-SO₃ ⁻. The synergistic effect of the catalyst support (NMWCNTs) and sulfonic acid functionalization of the catalyst (in CuPc-SO₃ ⁻) increase the efficiency and selectivity of the ORR at the NMWCNTs-CuPc-SO₃ ⁻. The catalyst activity of NMWCNTs-CuPc-SO₃ ⁻ has been compared with many reported materials and found to be better than several catalysts. NMWCNTs-CuPc-SO₃ ⁻ shows high tolerance for methanol and very small deviation in the onset potential (10 mV) between the linear sweep voltammetry responses recorded before and after 3000 cyclic voltammetry cycles, demonstrating exceptional durability. The high durability is attributed to the stabilization of CuPc-SO₃ ⁻ by the additional coordination with nitrogen (Cu-N_x) present on the surface of NMWCNTs.

The Front Cover shows a two-dimensional representation of a conical intersection causing a Jahn-Teller distortion that removes the degeneracy of two electronic states. The lowest-energy potential energy surface features close-lying multi minima and saddle points for bypiramidal Cu₅ structures. As a result, Cu₅ clusters exhibit fluxional motion, a characteristic enhancing their performance as catalysts. Cover design by Katarzyna Krupka. More information can be found in the Research Article by Alexander O. Mitrushchenkov and María Pilar de Lara-Castells.

Sandwich fibrous PEG encapsulations were constructed, consisting of a protection layer, a barrier layer and a PCM-loaded layer. Selected applications of the sandwich fibrous PEG encapsulations are available by controlling the PEG types or introducing conductive particles.

Abstract

Phase change materials (PCMs) textiles have been developed for personal thermal management (PTM) while limited loading amount of PCMs in textiles reduced thermal buffering effect. In this work, we proposed a sandwich fibrous encapsulation to store polyethylene glycol (PEG) with PEG loading amount of 45 wt %, which consisted of polyester (PET) fabrics with hydrophobic coating as protection layers, polyurethane (PU) nanofibrous membranes as barrier layers and PEG-loaded viscose fabric as a PCM-loaded layer. The leakage was totally avoided by controlling weak interfacial adhesion between protection layer and melting PEG. The sandwich fibrous PEG encapsulations had an overall melting enthalpy value ranging from 50 J/g to 78 J/g and melting points ranging from 20 °C to 63 °C by using different PEGs. Besides, introduction of Fe microparticles in PCM-loaded layer enhanced thermal energy storage efficiency. We believe that the sandwich fibrous PEG encapsulation has a great potential in various fields.

The Cover Feature shows the preferred reaction mechanisms of H₂ dissociation on Cu₁₃ and defective graphene-supported Cu₁₃ clusters. The dissociation energy barrier on defective graphene-supported Cu₁₃ clusters is considerably lower compared to pure Cu₁₃ clusters, and the average adsorption energy of dissociated H atoms on defective graphene-supported Cu₁₃ clusters is also greatly enhanced. More information can be found in the Research Article by Yueru Li and Dunyou Wang.