Periodic DFT calculations to compute the attributes of a quantum material: honeycomb ruthenium trichloride.

Quantum spin liquids (QSLs) have become prominent materials of interest in the pursuit of fault-tolerant materials for quantum computing applications. This is due to the fact that these materials are theorized to host an interesting variety of quantum phenomena such as quasi-particles that may behave as anyons as a result of the high entangled nature of the spin states within the systems. Computing the electronic and magnetic properties of these materials is necessary in order to understand the underlying interactions of the materials. In this paper, the structural, electronic, and magnetic properties including lattice parameters, bandgap, Heisenberg coupling constants, and Curie temperatures for α-RuCl3, a promising candidate for the Kitaev QSL model, are computed using periodic density functional theory. Furthermore, various parameters of the calculations (i.e. functional choice, basis set, k-point density, and Hubbard correction) are varied in order to determine what effect, if any, the computational setup has on the computed properties. The results of this study indicate that PBE functional with Hubbard corrections of 1.5-2.5 eV with a k-point density of 3.0 points per Å-1 appear to be the best parameters to compute Heisenberg coupling constants for α-RuCl3. These parameters with the addition of spin orbit coupling works well for computing Curie temperatures for α-RuCl3. Distinct differences are noted in the computations of the bulk structure vs. monolayer structures, indicating that interactions between the layers play a role in the material properties and changes to the inter-layer spacing may result in interesting and unique magnetic properties that require further investigation.

Atomistic insights into the hydrodefluorination of PFAS using silylium catalysts.

Fluorochemicals are a persistent environmental contaminant that require specialized techniques for degradation and capture. In particular, recent attention on per- and poly-fluoroalkyl substances (PFAS) has led to numerous explorations of different techniques for degrading the super-strong C-F bonds found in these fluorochemicals. In this study, we investigated the hydrodefluorination mechanism using silylium-carborane salts for the degradation of PFAS at the density functional theory (DFT) level. We find that the degradation process involves both a cationic silylium (Et3Si+) and a hydridic silylium (Et3SiH) to facilitate the defluorination and hydride-addition events. Additionally, the role of carborane ([HCB11H5F6]-) is to force unoccupied anti-bonding orbitals to be partially occupied, weakening the C-F bond. We also show that changing the substituents on carborane from fluorine to other halogens weakens the C-F bond even further, with iodic carborane ([HCB11H5I6]-) having the greatest weakening effect. Moreover, our calculations reveal why the C-F bonds are resistant to degradation, and how the silylium-carborane chemistry is able to chemically transform these bonds into C-H bonds. We believe that our results are further applicable to other halocarbons, and can be used to treat either our existing stocks of these chemicals or to treat concentrated solutions following filtration and capture.

Toward bioinspired polymer adhesives: activation assisted via HOBt for grafting of dopamine onto poly(acrylic acid).

The design of bioinspired polymers has long been an area of intense study, however, applications to the design of concrete admixtures for improved materials performance have been relatively unexplored. In this work, we functionalized poly(acrylic acid) (PAA), a simple analogue to polycarboxylate ether admixtures in concrete, with dopamine to form a catechol-bearing polymer (PAA-g-DA). Synthetic routes using hydroxybenzotriazole (HOBt) as an activating agent were examined for their ability in grafting dopamine to the PAA backbone. Previous literature using the traditional coupling reagent 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC) to graft dopamine to PAA were found to be inconsistent and the sensitivity of EDC coupling reactions necessitated a search for an alternative. Additionally, HOBt allowed for greater control over per cent functionalization of the backbone, is a simple, robust reaction, and showed potential for scalability. This finding also represents a novel synthetic pathway for amide bond formation between dopamine and PAA. Finally, we performed preliminary adhesion studies of our polymer on rose granite specimens and demonstrated a 56% improvement in the mean adhesion strength over unfunctionalized PAA. These results demonstrate an early study on the potential of PAA-g-DA to be used for improving the bonds within concrete.

Distinguishing the Protonation State of the Histidine Ligand to the Oxidized Iron-Sulfur Cluster from the MitoNEET Family of Proteins.

The iron-sulfur cluster located in the recently discovered human mitoNEET protein (and related proteins) is structurally similar to the more well-known ferredoxin and Rieske clusters. Although its biological function is uncertain, the iron-sulfur cluster in mitoNEET has been proposed to undergo proton-coupled electron transfer involving the histidine ligand to the cluster. The cluster is also released from the protein at low pH. This contribution reports density functional calculations to model the structures, vibrations, and Heisenberg coupling constants (J) for high-spin (HS), broken symmetry (BS) singlet, and extended broken symmetry (EBS) singlet states of the oxidized iron-sulfur cluster from mitoNEET. This work suggests that J values or 15 N isotopic frequency shifts may provide methods for determining experimentally whether the histidine ligand to the oxidized iron-sulfur cluster in human mitoNEET and mitoNEET-related proteins is protonated or deprotonated.

Distinguishing Protonation States of Histidine Ligands to the Oxidized Rieske Iron-Sulfur Cluster through (15) N Vibrational Frequency Shifts.

The Rieske [2Fe-2S] cluster is a vital component of many oxidoreductases, including mitochondrial cytochrome bc1; its chloroplast equivalent, cytochrome b6f; one class of dioxygenases; and arsenite oxidase. The Rieske cluster acts as an electron shuttle and its reduction is believed to couple with protonation of one of the cluster's His ligands. In cytochromes bc1 and b6f, for example, the Rieske cluster acts as the first electron acceptor in a modified Q cycle. The protonation states of the cluster's His ligands determine its ability to accept a proton and possibly an electron through a hydrogen bond to the electron carrier, ubiquinol. Experimental determination of the protonation states of a Rieske cluster's two His ligands by NMR spectroscopy is difficult, due to the close proximity of the two paramagnetic iron atoms of the cluster. Therefore, this work reports density functional calculations and proposes that difference vibrational spectroscopy with (15) N isotopic substitution may be used to assign the protonation states of the His ligands of the oxidized Rieske [2Fe-2S] complex.