In Silico Screening of CO-Dipeptide Interactions for Bioinspired Carbon Capture.

Carbon capture, sequestration and utilization offers a viable solution for reducing the total amount of atmospheric CO concentrations. On an industrial scale, amine-based solvents are extensively employed for CO 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.

Multiscale Modeling of Vinyl-Addition Polynorbornenes: The Effect of Stereochemistry.

Vinyl-addition polynorbornenes are candidates for designing high-performance polymers due to unique characteristics, which include a high glass transition temperature associated with a rigid backbone. Recent studies have established that the processability and properties of these polymers can be fine-tuned by using targeted substitutions. However, synthesis with different catalysts results in materials with distinct properties, potentially due to the presence of various stereoisomers that are difficult to quantify experimentally.

Ligand engineering of tetra N-heterocyclic carbenes for boosting catalytic aziridination.

A comprehensive computational study on the underlying reactivity of iron tetra-NHC complexes for C + N aziridination catalysis is presented. A library of 18 unique iron tetra-NHC complexes was constructed, and a computational screening was performed on the reaction barriers associated with the rate-determining step (formation of an open chain radical intermediate). Thermodynamic barriers were computed along with a variety of steric and electronic properties, including the percentage of buried volume, orbital energies and ETS-NOCV analysis, which were used to identify key characteristics related to reactivity.

Disparate reactivity of a chiral iron(II) tetracarbene complex with organic azides.

A chiral tetra-NHC iron(II) complex and its disparate reactivity with multiple organic azides is reported. Both aryl and alkyl azides react with the iron(II) complex yielding three distinct products: an iron(IV) imide, an iron(IV) tetrazene, and a surprising and unprecedented double imide insertion complex.

Electronic Structure and Ligand Effects on the Activation and Cleavage of N on a Molybdenum Center.

Dinitrogen fixation under ambient conditions remains a challenge in the field of catalytic chemistry due to the inertness of N. Nitrogenases and heterogeneous solid catalysts have displayed remarkable performance in the catalytic conversion of dinitrogen to ammonia. By introduction of molybdenum centers in molecular complexes, one of the most azophilic metals of the transitional metal series, moderate ammonia yields have been attained.

Exploration of the Two-Electron Excitation Space with Data-Driven Coupled Cluster.

Computational cost limits the applicability of post-Hartree-Fock methods such as coupled-cluster on larger molecular systems. The data-driven coupled-cluster (DDCC) method applies machine learning to predict the coupled-cluster two-electron amplitudes () using data from second-order perturbation theory (MP2). One major limitation of the DDCC models is the size of training sets that increases exponentially with the system size.

Three-Center M-H-B Bonds Are Strong Field Interactions. Synthesis and Characterization of M(CHNMeBH) Complexes of Titanium, Chromium, and Cobalt.

We describe new compounds of stoichiometry M(CHNMeBH) (M = Ti, Cr, and Co), each of which contains three chelating boranatodimethylaminomethyl (BDAM) ligands. In all three compounds, the BDAM anion, which is isoelectronic and isostructural with the neopentyl group, is bound to the metal center at one end by a metal-carbon σ bond and at the other by one three-center M-H-B interaction. The crystal structures show that the d titanium(III) compound is trigonal prismatic (or eight-coordinate, if two longer-ranged M···H interactions with the BH groups are included), whereas the d chromium(III) compound and the d cobalt(III) compounds are both -octahedral.

Data-Driven Refinement of Electronic Energies from Two-Electron Reduced-Density-Matrix Theory.

The exponential computational cost of describing strongly correlated electrons can be mitigated by adopting a reduced-density matrix (RDM)-based description of the electronic structure. While variational two-electron RDM (v2RDM) methods can enable large-scale calculations on such systems, the quality of the solution is limited by the fact that only a subset of known necessary -representability constraints can be applied to the 2RDM in practical calculations. Here, we demonstrate that violations of partial three-particle (T1 and T2) -representability conditions, which can be evaluated with knowledge of only the 2RDM, can serve as features in a machine-learning (ML) protocol for improving energies from v2RDM calculations that consider only two-particle (PQG) conditions.

Theoretical Investigation of Actinide Ligation in Aqueous and Organic Phase for Nuclear Waste Treatment.

The generation of radioactive waste has a prominent negative impact on the use of nuclear energy due to potential health concerns and cost of waste storage. This potential impact continues to rise as the quantity of waste increases due to the increasing growth in energy demand. One of the leading contributions to the radioactivity of this waste is due to the presence of actinides.

Accurate Interaction Energies of CO with the 20 Naturally Occurring Amino Acids.

We have performed a series of highly accurate calculations between CO and the 20 naturally occurring amino acids for the investigation of the attractive noncovalent interactions. Different nucleophilic groups present in the amino acid structures were considered (α-NH , COOH, side groups), and the stronger binding sites were identified. A database of accurate reference interactions energies was compiled as computed by explicitly-correlated coupled-cluster singles-and-doubles, together with perturbative triples extrapolated to the complete-basis-set limit.

Computational investigation of functionalized carbenes on dinitrogen activation.

Activation of the dinitrogen triple bond is a crucial step in the overall fixation of atmospheric nitrogen into usable forms for industrial and biological applications. Current synthetic catalysts incorporate metal ions to facilitate the activation and cleavage of dinitrogen. The high price of metal-based catalysts and the challenge of catalyst recovery during industrial catalytic processes has led to increasing interest in metal-free catalysts.

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main-Group-Element Catalysis.

Electrocatalytic proton reduction to form dihydrogen (H ) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main-group-element-based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (-4.

Electrocatalytic Hydrogen Evolution Using A Molecular Antimony Complex under Aqueous Conditions: An Experimental and Computational Study on Main-Group Element Catalysis.

Electrocatalytic hydrogen gas production is considered a potential pathway towards carbon-neutral energy sources. However, the development of this technology is hindered by the lack of efficient, cost-effective, and environmentally benign catalysts. In this study, a main-group-element-based electrocatalyst, SbSalen, is reported to catalyze the hydrogen evolution reaction (HER) in an aqueous medium.

Potent Anti-Inflammatory, Arylpyrazole-Based Glucocorticoid Receptor Agonists That Do Not Impair Insulin Secretion.

Glucocorticoids (GCs) are widely used in medicine for their role in the treatment of autoimmune-mediated conditions, certain cancers, and organ transplantation. The transcriptional activities GCs elicit include transrepression, postulated to be responsible for the anti-inflammatory activity, and transactivation, proposed to underlie the undesirable side effects associated with long-term use. A GC analogue that could elicit only transrepression and beneficial transactivation properties would be of great medicinal value and is highly sought after.

σ-Donation and π-Backdonation Effects in Dative Bonds of Main-Group Elements.

The nature of donor-acceptor interactions is important for the understanding of dative bonding and can provide vital insights into many chemical processes. Here, we have performed a computational study to elucidate substantial differences between different types of dative interactions. For this purpose, a data set of 20 molecular complexes stabilized by dative bonds was developed (DAT20).

Redox states of dinitrogen coordinated to a molybdenum atom.

Chemical structures bearing a molybdenum atom have been suggested for the catalytic reduction of N at ambient conditions. Previous computational studies on gas-phase MoN and MoN species have focused only on neutral structures. Here, an ab initio electronic structure study on the redox states of small clusters composed of nitrogen and molybdenum is presented.

Nature of the Short Rh-Li Contact between Lithium and the Rhodium ω-Alkenyl Complex [Rh(CHCMeCHCH═CH)].

We describe the preparation of the bis(η,η-2,2-dimethylpent-4-en-1-yl)rhodate(I) anion, -[Rh(CHCMeCHCH═CH)], and the interaction of this species with Li both in solution and in the solid state. For the lithium(diethyl ether) salt [Li(EtO)][Rh(CHCMeCHCH═CH)], VT-NMR and H{Li} NOE NMR studies in toluene- show that the Li cation is in close proximity to the d orbital of rhodium. In the solid-state structure of the lithium(12-crown-4) salt [Li(12-crown-4)][Li{Rh(CHCMeCHCH═CH)}], one lithium atom is surrounded by two [Rh(CHCMeCHCH═CH)] anions, and in this assembly there are two unusually short Rh-Li distances of 2.

A Carbodiimide-Mediated P-C Bond-Forming Reaction: Mild Amidoalkylation of -Nucleophiles by Boc-Aminals.

The first example of a carbodiimide-mediated P-C bond-forming reaction is described. The reaction involves activation of β-carboxyethylphosphinic acids and subsequent reaction with Boc-aminals using acid-catalysis. Mechanistic experiments using P NMR spectroscopy and DFT calculations support the contribution of unusually reactive cyclic phosphinic/carboxylic mixed anhydrides in a reaction pathway involving ion-pair "swapping".

Climate Change Adaptation Studies as a tool to ensure airport's sustainability: The case of Athens International Airport (A.I.A.).

A.I.A (Athens International Airport) is the first major transportation infrastructure in Greece.

Transferable MP2-Based Machine Learning for Accurate Coupled-Cluster Energies.

Machine learning methods have enabled the low-cost evaluation of molecular properties such as energy at an unprecedented scale. While many of such applications have focused on molecular input based on geometry, few studies consider representations based on the underlying electronic structure. Directing the attention to the electronic structure offers a unique challenge that allows for a more detailed representation of the underlying physics and how they affect molecular properties.

Direct Identification of Mixed-Metal Centers in Metal-Organic Frameworks: Cu(BTC) Transmetalated with Rh Ions.

Raman spectroscopy was used to establish direct evidence of heterometallic metal centers in a metal-organic framework (MOF). The Cu(BTC) MOF HKUST-1 (BTC = benzenetricarboxylate) was transmetalated by heating it in a solution of RhCl to substitute Rh ions for Cu ions in the dinuclear paddlewheel nodes of the framework. In addition to the Cu-Cu and Rh-Rh stretching modes, Raman spectra of (CuRh)(BTC) show the Cu-Rh stretching mode, indicating that mixed-metal Cu-Rh nodes are formed after transmetalation.

Selecting Quantum-Chemical Methods for Lanthanide-Containing Molecules: A Balance between Accuracy and Efficiency.

An analysis of how different density functionals, basis sets, and relativistic approximations affect the computed properties of lanthanide-containing molecules allows one to determine which method provides the highest accuracy. Historically, many different density functional methods have been employed to perform calculations on lanthanide complexes and so herein is a detailed analysis of how different methodological combinations change the computed properties of three different families of lanthanide-bearing species: lanthanide diatomic molecules (fluorides and oxides) and their dissociation energies; larger, molecular complexes and their geometries; and lanthanide bis(2-ethylhexyl)phosphate structures and their separation free energies among the lanthanide series. The B3LYP/Sapporo/Douglas-Kroll-Hess (DKH) method was shown to most accurately reproduce dissociation energies calculated at the CCSDT(Q) level of theory with a mean absolute deviation of 1.