Chemphyschem最新文献

The thermal conductivity of many materials depends on temperature due to several factors, including variation of heat capacity with temperature, changes in vibrational dynamics with temperature, and change in volume with temperature. For proteins some, but not all, of these influences on the variation of thermal conductivity with temperature have been investigated in the past. In this study, we examine the influence of change in volume, and corresponding changes in vibrational dynamics, on the temperature dependence of the thermal conductivity. Using a measured value for the coefficient of thermal expansion and recently computed values for the Grüneisen parameter of proteins we find that the thermal conductivity increases with increasing temperature due to change in volume with temperature. We compare the impact of thermal expansion on the variation of the thermal conductivity with temperature found in this study with contributions of heat capacity and anharmonic coupling examined previously. Using values of thermal transport coefficients computed for proteins we also model heating of water in a protein solution following photoexcitation.

The Cover Feature depicts the H₂-induced structural transformation of truncated bipyramid Pt₁₂⁻ into the cuboctahedral cage structure Pt₁₂H₂₄⁻. The structure was deduced by a combination of trapped-ion electron diffraction and density functional theory by comparing the scattering function from experiment and theory. The Pt cage structure is stabilized by the formation of Pt−H−Pt two-electron, three-centre bridge bonds and spherical aromaticity. More information can be found in the Research Article by D. Schooss and co-workers (DOI: 10.1002/cphc.202400649).

The Front Cover picture shows nitrogen-functionalized graphene with metal cations. In this study, the structure of model NG, which consists of 174 carbon atoms, armchair edges, and various functional groups on the edges, was calculated. More information can be found in the Research Article by R. Sekiya and T. Haino (DOI: 10.1002/cphc.202400792).

The Cover Feature shows how dimethyl carbonate creates a unique AOT reverse micelle system, different from conventional hydrocarbon solvents. Even at maximum water content, the structure of the confined water differs from that of bulk water, strongly affecting the interfacial properties. More information can be found in the Research Article by F. Moyano and co-workers (DOI: 10.1002/cphc.202400617).

The benzopyrone molecule coumarin is a popular fluorescent scaffold, but how chemical modifications affect its properties is not well understood. We investigated this using halogenated 7-hydroxycoumarin, unsubstituted 4-methylumbiliferone, and ortho-chloro and bromo substitutions on the phenolic ring. Charge density data from X-Ray diffraction and computational methods revealed that halogenation at the ortho position significantly reduced quantum yield (QY). Specifically, 7-hydroxycoumarin (1) had a QY of 70 %, while ortho-chloro (2) and ortho-bromo (3) had QYs of 61 % and 30 %, respectively. Experimental data showed that these molecules excited similarly, but the electrostatic potential and dipole moments indicated that 2 and 3 dissipated excitation energy more easily due to charge separation. The heavy-atom effect of Cl and Br did not fully explain the QY reductions, suggesting other radiative decay processes were involved. By incorporating spin-orbit coupling (SOC) effects, we estimated intersystem crossing (ISC) and phosphorescence rates, providing theoretical QYs of 78 % for 1, 59 % for 2, and 15 % for 3. The large deviation for 3 was attributed to its higher SOC potential derived in computational calculations. Our overall findings indicate that 3's reduced QY results from a mix of SOC-induced ISC and charge dissipation due to the electronegativity of Br atom, while 2's reduction is primarily due to charge separation caused by Cl alone. Further studies are needed to validate this approach with other scaffolds.

CeO₂/CuO heterojunction composite catalysts were synthesized using a one-step method, achieving the introduction of Ce species on nanoscale copper oxide (CuO) particles during the hydrothermal process. CeO₂ is primarily encapsulated the auxiliary catalyst CuO in the form of nanoparticles. On one hand, this protects the nanostructure of the substrate from damage and prevents the agglomeration of CuO nanoparticles. On the other hand, the bimetallic synergistic effect between Ce and Cu effectively improves the conductivity and catalytic activity of the catalyst, significantly enhancing the selectivity of the catalyst for electrochemical reduction of CO₂ to C₂H₄, while effectively suppressing the competing hydrogen evolution reaction (HER). By regulating the amount of CeO₂ introducing, a series of CeO₂/CuO composite catalysts were designed. The results showed that the 15 % CeO₂/CuO catalyst exhibited the best selectivity and catalytic activity for C₂H₄. At a low overpotential of -1.2 V, the 15 % CeO₂/CuO catalyst demonstrated a current density of 14.2 mA cm^-2 and achieved a Faradaic efficiency for ethylene as high as 65.78 %, which is 2.85 times the current density (j=4.98 mA cm^-2) and 3.27 times the Faradaic efficiency for ethylene (FE_C2H4=20.13 %) of the undoped catalyst at the same potential. This work provides a feasible basis for achieving efficient CO₂RR to C₂ products, and even multi-carbon products.

The emission control of harmful compounds and greenhouse gases and the development of alternative, sustainable fuel sources is a major focus in current research. A solution for this problem lies in the development of efficient catalytic materials. Here, gas phase model systems represent prominent examples for obtaining fundamental insights on reaction properties of prospective catalytic systems. In this work, we review results from studies of tantalum clusters and their oxides in the gas phase and discuss insights with a potential relevance for applied systems. We focus on reactions that are essential for sustainable chemistry in the future. In detail, we address the activation of methane, which may enable the transformation of a greenhouse gas to a chemical feedstock, and we discuss the activation of NH₃, which may function as an alternative energy carrier whose unwanted emission needs to be curbed in future applications. Finally, we consider the activation of N₂ as a third reaction, since reducing the high energy demand of ammonia synthesis still bears significant challenges. While tantalum may be an interesting catalytic material, the discussed studies may also serve as benchmark for investigations of other materials.

The formulation of safe electrolytes for supercapacitors based on phosphazene used as a flame-retardant (FR) is carried out. 3 molecules are used: hexafluorocyclotriphosphazene (FR1), (ethoxy)pentafluorocyclotriphosphazene (FR2) and pentafluoro(phenoxy)cyclotriphosphazene (FR3). A comparative study on the efficacy from a safety point of view is performed to determine the minimum percentages of each to be used in a conventional acetonitrile (ACN)/1.0 M tetraethylammonium tetrafluoroborate (Et₄NBF₄) electrolyte to make it non-flammable. Flammability tests have shown that 5 %FR1, 15 %FR2 or 20 %FR3 are required to do that. The FTIR coupled to the TGA as well as the measurements of surface tensions and contact angles showed that the FRs tend to protect the surface of the electrolyte. The transport properties always remain good, superior to PC/1.0 M Et₄NBF₄ for example, and the electrochemical stability windows determined in 3-electrode cells with platinum or activated carbon are at least 2.5 V. The cycling performances are also interesting because the AC|AC EDLCs made in this study are compatible with these FRs, which makes it possible to operate devices providing energies and powers of 23.0 Wh kg^-1 and 3.7 kW kg^-1 with the electrolytes based on FR1 or FR2 between 0 and 2.5 V.

Highly emissive Zn-Ag-In-S nanocrystals have attracted attention as derivatives of I-III-VI₂-type nanocrystals without the use of toxic elements. The wide tunability of their luminescence wavelengths is attributed to the controllable bandgap of the solid solution between ZnS and AgInS₂. However, enhancement of the photoluminescence quantum yield (PL-QY) depending on the chemical composition has not been elucidated. Here, the luminescence mechanisms of Zn-Ag-In-S nanocrystals were studied from the perspective of ZnS doped with Ag and In, although previous research has proposed a hypothesis that Zn is a radiative recombination centre in the AgInS₂ host. The Zn-Ag-In-S nanocrystals were synthesized by systematically varying the Zn, Ag, and In contents. The nanocrystals exhibit a structure in which a part of the Zn in the cubic ZnS is substituted with Ag and In. Luminescence was ascribed to a donor-acceptor pair (DAP) recombination between electrons trapped in In donors and holes trapped in Ag acceptors. The composition-dependent enhancement of PL-QYs was attributed to an increase in donor and acceptor concentrations. The DAP characteristics were maintained over a wide range of Ag and In contents because of the localized character of the band edge states dominated by Ag and In orbitals, as suggested formerly by simulation.

Carbon capture, sequestration and utilization offers a viable solution for reducing the total amount of atmospheric CO₂ concentrations. On an industrial scale, amine-based solvents are extensively employed for CO₂ capture through chemisorption. Nevertheless, this method is marked by the high cost associated with solvent regeneration, high vapor pressure, and the corrosive and toxic attributes of by-products, such as nitrosamines. An alternative approach is the biomimicry of sustainable materials that have strong affinity and selectivity for CO₂. Bioinspired approaches, such as those based on naturally occurring amino acids, have been proposed for direct air capture methodologies. In this study, we present a database consisting of 960 dipeptide molecular structures, composed of the 20 naturally occurring amino acids. Those structures were analyzed with a novel computational workflow presented in this work that considers certain interaction sites that determine CO₂ affinity. Density functional theory (DFT) and symmetry-adapted perturbation theory (SAPT) computations were performed for the calculation of CO₂ interaction energies, which allowed to limit our search space to 400 unique dipeptide structures. Using this computational workflow, we provide statistical insights into dipeptides and their affinity for CO₂ binding, as well as design principles that can further enhance CO₂ capture through cooperative binding.