Structural analysis of transient reaction intermediate in formic acid dehydrogenation catalysis using two-dimensional IR spectroscopy

Cyclopentadienone Diphosphine Ruthenium Complex: A Designed Catalyst for the Hydrogenation of Carbon Dioxide to Methanol

The development of homogeneous metal catalysts for the efficient hydrogenation of carbon dioxide (CO2) into methanol (CH3OH) remains a significant challenge. In this study, a new cyclopentadienone diphosphine ligand (CPDDP ligand) was designed, which could coordinate with ruthenium to form a Ru-CPDDP complex to efficiently catalyze the CO2-to-methanol process using dihydrogen (H2) as the hydrogen resource based on density functional theory (DFT) mechanistic investigation. This process consists of three catalytic cycles, stage I (the hydrogenation of CO2 to HCOOH), stage II (the hydrogenation of HCOOH to HCHO), and stage III (the hydrogenation of HCHO to CH3OH). The calculated free energy barriers for the hydrogen transfer (HT) steps of stage I, stage II, and stage III are 7.5, 14.5, and 3.5 kcal/mol, respectively. The most favorable pathway of the dihydrogen activation (DA) steps of three stages to regenerate catalytic species is proposed to be the formate-assisted DA step with a free energy barrier of 10.4 kcal/mol. The calculated results indicate that the designed Ru-CPDDP and Ru-CPDDPEt complexes could catalyze hydrogenation of CO2 to CH3OH (HCM) under mild conditions and that the transition-metal owning designed CPDDP ligand framework be one kind of promising potential efficient catalysts for HCM.

Direct observation of conformations of a high-mobility n-type low-bandgap copolymer in solutions and solid films

The aggregation morphologies of conjugated polymers in solutions and solid films are important for their optoelectronic applications. Due to the amorphous state of the polymers, it remains a great challenge to determine their conformations in either liquids or solids. Herein, a ps/fs synchronized 2D IR technique is applied to investigate the molecular conformations of a high-mobility n-type low-bandgap copolymer, N2200, dissolved in CHCl₃ and CCl₄, and in solid films cast from both solutions by the vibrational cross-angle method. In CCl₄, the polymer forms more aggregates and folds more and the backbone dihedral angle of C-C(NDI)/C-S(Thiophene) of its average conformation is about 10° more distorted than that in CHCl₃ and the most stable conformation for a free molecule. Anti-intuitively, the solid films cast from both solutions have the same molecular conformation, and the conformation is similar to that of the polar CHCl₃ rather than the conformation of the less polar CCl₄. The results imply that the interaction between the polymer backbones is probably stronger than its interaction with CCl₄, which can naturally guide the rearrangement of polymer chains during the evaporation of solvent molecules. This work also implies that the balance and competition between the polymer/polymer interaction and the polymer/solvent interaction seem to be the dominant factors responsible for what morphology can form in a solid film cast from solution. It is not always true that different molecular conformations must exist in solid films grown from different solutions with different polarity or different extents of aggregates with different conformations.

Nanofibrous scaffolds based on bacterial cellulose crosslinked with oxidized sucrose

In this work, oxidized sucrose (OS), which is a safe bio-based and non-toxic polyaldehyde, was used as a crosslinker in defibrillated bacterial cellulose (BC) sponges obtained by freeze-drying. For mimicking the proteins' crosslinking, BC was first modified with an aminosilane to partially replace the OH groups on the BC surface with more reactive amino groups. Further, the aminosilane-grafted bacterial cellulose (BCA) was crosslinked with OS in different concentrations and thermally cured. Functionalized bacterial celluloses showed a good thermal stability, comparable to that of unmodified cellulose and much improved mechanical properties. A threefold increase in the compression strength was obtained for the BCA scaffold after crosslinking and curing. This was correlated with the uniform pore structure emphasized by the micro-CT and SEM analyses. The OS-crosslinked BCA scaffolds were not cytotoxic and showed a porosity of around 80 %, which was almost 100 % open porosity. This study shows that the crosslinking of aminated BC scaffolds with OS allows the obtaining of 3D cellulose structures with good mechanical properties and high porosity, suitable for soft tissue engineering. The results recommend this new method as an innovative approach to obtaining biomaterial scaffolds that mimic the natural extracellular matrix.

A network percolation-based contagion model of flood propagation and recession in urban road networks

In this study, we propose a contagion model as a simple and powerful mathematical approach for predicting the spatial spread and temporal evolution of the onset and recession of floodwaters in urban road networks. A network of urban roads resilient to flooding events is essential for the provision of public services and for emergency response. The spread of floodwaters in urban networks is a complex spatial-temporal phenomenon. This study presents a mathematical contagion model to describe the spatial-temporal spread and recession process of floodwaters in urban road networks. The evolution of floods within networks can be captured based on three macroscopic characteristics-flood propagation rate ([Formula: see text]), flood incubation rate ([Formula: see text]), and recovery rate ([Formula: see text])-in a system of ordinary differential equations analogous to the Susceptible-Exposed-Infected-Recovered (SEIR) model. We integrated the flood contagion model with the network percolation process in which the probability of flooding of a road segment depends on the degree to which the nearby road segments are flooded. The application of the proposed model is verified using high-resolution historical data of road flooding in Harris County during Hurricane Harvey in 2017. The results show that the model can monitor and predict the fraction of flooded roads over time. Additionally, the proposed model can achieve 90% precision and recall for the spatial spread of the flooded roads at the majority of tested time intervals. The findings suggest that the proposed mathematical contagion model offers great potential to support emergency managers, public officials, citizens, first responders, and other decision-makers for flood forecast in road networks.

Rhodapentalenes: Pincer Complexes with Internal Aromaticity

Pincer complexes are a remarkably versatile family benefited from their stability, diversity, and tunability. Many of them contain aromatic organic rings at the periphery, and aromaticity plays an important role in their stability and properties, whereas their metallacyclic cores are not aromatic. Herein, we report rhodapentalenes, which can be viewed as pincer complexes in which the metallacyclic cores exhibit considerable aromatic character. Rhodapentalenes show good thermal stability, although the rhodium-carbon bonds in such compounds are fragile. Experimental and computational studies suggest that the stabilization of rigid CCC pincer architectures together with an intrinsic aromaticity is vital for these metallacyclic rhodium species. Dearomatization-aromatization reactions, corresponding to metal-ligand cooperation of classical aromatic pincer complexes, were observed in this system. These findings suggest a new concept for pincer chemistry, the internal aromaticity involving metal d-orbitals, which would be useful for exploiting the nature of construction motif and inspire further applications.