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Machine learning and artificial intelligence are increasingly gaining in prominence through image analysis, language processing, and automation, to name a few applications. Machine learning is also making profound changes in chemistry. From revisiting decades-old analytical techniques for the purpose of creating better calibration curves, to assisting and accelerating traditional in silico simulations, to automating entire scientific workflows, to being used as an approach to deduce underlying physics of unexplained chemical phenomena, machine learning and artificial intelligence are reshaping chemistry, accelerating scientific discovery, and yielding new insights. This review provides an overview of machine learning and artificial intelligence from a chemist’s perspective and focuses on a number of examples of the use of these approaches in computational chemistry and in the laboratory.

Complete active space self-consistent field (CASSCF) and multireference configuration interaction with Davidson correction (MRCI+Q) calculations have been carried out for lawrencium fluoride (LrF) and lawrencium oxide (LrO) molecules, detailing 19 and 20 electronic states for LrF and LrO, respectively. For LrF, two dissociation channels were considered, Lr(

The importance of spin-orbit effects on the predictions of energetic properties of actinide compounds has been considered for 18 different density functionals, comparing the spin-orbit and non-spin-orbit ("standard") forms of density functional theory (DFT). A set of enthalpies of formation for 66 small actinide (Th-Am) compounds-the An66 set, for which experimental data are available-have been investigated. The set includes actinide halides, oxides, and oxohalides in the general form AnOmXn, where n = 0-6, m = 0-3, and X = F, Cl, Br, or I. The impact of basis set choice was investigated, and to help account for the impact of relativity, the Stuttgart general and segmented contracted atomic natural orbital (ANO) basis sets paired with small core relativistic effective core potentials (RECP) as well as all-electron calculations utilizing the third-order Douglas-Kroll-Hess were considered.

The determination of gas phase thermochemical properties of per- and polyfluoroalkyl substances (PFAS) is central to understanding the long-range transport behavior of PFAS in the atmosphere. Prior gas-phase studies have reported the properties of perfluorinated sulfonic acid (PFOS) and perfluorinated octanoic acid (PFOA). Here, this study reports the gas phase enthalpies of formation of short- and long-chain PFAS and their precursor molecules determined using density functional theory (DFT) and ab initio approaches. Two density functionals, two ab initio methods and an empirical method were used to compute enthalpies of formation with the total atomization approach and an isogyric reaction. The performance of the computational methods employed in this work were validated against the experimental enthalpies of linear alkanoic acids and perfluoroalkanes. The gas-phase determinations will be useful for future studies of PFAS in the atmosphere, and the methodological choices will be helpful in the study of other PFAS.

The f-block ab initio correlation consistent composite approach was used to predict the dissociation energies of lanthanide sulfides and selenides. Geometry optimizations were carried out using density functional theory and coupled cluster singles, doubles, and perturbative triples with one- and two-component Hamiltonians. For the two-component calculations, relativistic effects were accounted for by utilizing a third-order Douglas–Kroll–Hess Hamiltonian. Spin–orbit coupling was addressed with the Breit–Pauli Hamiltonian within a multireference configuration interaction approach. The state averaged complete active space self-consistent field wavefunctions obtained for the spin–orbit coupling energies were used to assign the ground states of diatomics, and several diagnostics were used to ascertain the multireference character of the molecules.

The utility of a range of computational chemistry approaches for the prediction of the regioselectivity for hydroformylation processes and metal-ligand dissociation in a model organometallic system is considered to provide insight about computational strategies for use in catalysis. The hydroformylation reactions investigated are the Rh-catalyzed hydroformylation of terminal alkenes with triarylphosphine and chelating diphosphine ligands. As well, the dissociation of water from a Pt complex is considered to probe method effects on metal-ligand bonding. Several density functional theory (DFT) approaches and ab initio methods are considered. We demonstrate that the quality of the basis set selected for the calculations can play a vital role in the prediction of even the product distribution, and that correcting for basis set superposition error (BSSE) can be very important. As well, the study demonstrates a broad range of predictions achievable using a variety of DFT approaches, which is, as discussed, a manifestation of the challenges that are encountered for calculations involving transition metal molecular species, illustrating the critical need to gauge computational chemistry methods.

Per- and polyfluoroalkyl substances (PFASs) are a class of environmentally persistent industrial compounds that disrupt various metabolic pathways. Among the protein receptors to which PFASs bind, the human pregnane X receptor (hPXR) is found to be a host for a variety of long- and short-chain PFASs that lead to its overactivation. Overactivation of hPXR is linked to potential endocrine disruption, oxidative stress, hepatic steatosis, and adverse drug interactions. In this study, molecular dynamics (MD) is used to study the binding between hPXR and a number of PFAS compounds, including alternatives whose activity on hPXR has not been experimentally tested. This is the first-time MD is used to study the interactions between PFASs and hPXR, showing how relative binding free energies of PFASs relate to hPXR agonism. Binding free energy calculations, hydrogen bond analysis, per-residue decomposition calculations, and alanine scanning studies are done to provide further insight. Activities on hPXR for several short-chain and alternative PFAS compounds to long-chain PFASs that have yet to be reported will also be considered. These short-chain and alternative species include perfluorobutane sulfonic acid (PFBS), Gen-X (trade name for 2,3,3,3-tetrafluoro-2-heptafluoropropoxy propanoic acid), ADONA (trade name for 4,8-dioxa-3H-perfluorononanoic acid), and 6:2 fluorotelomer carboxylic acid (6:2 FTCA). The study shows key aspects of PFAS recognition on the hPXR, the link between PFAS binding to hPXR and the hPXR activity change observed upon the PFAS exposure, and the potential effects of alternative PFASs on hPXR activity.

Understanding the electronic structure of coordinatively unsaturated transition-metal compounds and predicting their physical properties are of great importance for catalyst design. Bond dissociation energy De and bond length re are two of the fundamental quantities for which good predictions are important for a successful design strategy. In the present work, recent experimentally measured bond energies and bond lengths of VX diatomic molecules (X = C, N, S) are used as a gauge to consider the utility of a number of electronic structure methods. Single-reference methods are one focus because of their efficiency and utility in practical calculations, and multireference configuration interaction (MRCISD) methods and a composite coupled cluster (CCC) method are a second focus because of their potential high accuracy. The comparison is especially challenging because of the large multireference M diagnostics of these molecules, in the range 0.15-0.19. For the single-reference methods, Kohn-Sham density functional theory (KS-DFT) has been tested with a variety of approximate exchange-correlation functionals. Of these, MOHLYP provides the bond dissociation energies in best agreement with experiments, and BLYP provides the bond lengths that are in best agreement with experiments; but by requiring good performance for both the De and re of the vanadium compounds, MOHLYP, MN12-L, MGGA_MS1, MGGA_MS0, O3LYP, and M06-L are the most highly recommended functionals. The CCC calculations include up to connected pentuple excitations for the valence electrons and up to connected quadruple excitations for the core-valence terms; this results in highly accurate dissociation energies and good bond lengths. Averaged over the three molecules, the mean unsigned deviation of CCC bond energies from experimental ones is only 0.4 kcal/mol, demonstrating excellent convergence of theory and experiments.

The multi-configuration electron–nuclear dynamics for open shell systems with a spin-unrestricted formalism is described. The mean fields are evaluated using second-order reduced density matrices for electronic and nuclear degrees of freedom. Applications to light-element diatomics including equilibrium geometries, electronic energies, dipole moments, and absorption spectra are presented. The von Neumann entropies for different spin states of a LiH molecule are compared.

The Born–Oppenheimer approximation is the fundamental approximation in the quantum-mechanical description of molecules, and holds true in most applications for ground-state properties and to a less...

Computational chemistry provides a powerful route to determine thermochemical properties. For transition metal thermochemistry, typically, high-level quantum methodologies are required. Ab initio c...

Michigan State University, East Lansing, Michigan. Eastern Washington University, BS, chemistry, 1990; University of Minnesota, PhD, chemical physics, 1995. Francis P. Garvan-John M. Olin Medal, AC...

Proteoglycans are a family of complex glycoproteins with glycosaminoglycan chains such as heparan sulfate (HS) attached to the core protein backbone. Due to the high structural heterogeneity of HS in nature, it is challenging to decipher the respective roles of the HS chain and the core protein on proteoglycan functions. While the sulfation patterns of HS dictate many activities, the core protein can potentially impact HS functions. In order to decipher this, homogeneous proteoglycan glycopeptides are needed. Herein, we report the first successful synthesis of proteoglycan glycopeptides bearing multiple aspartic acids in the core peptide and O- and N-sulfations in the glycan chain, as exemplified by the syndecan-4 glycopeptides. To overcome the high acid sensitivities of sulfates and base sensitivities of the glycopeptide during synthesis, a new synthetic approach has been developed to produce a sulfated glycan chain on a peptide sequence prone to the formation of aspartimide side products. The availability of the structurally well-defined synthetic glycopeptide enabled the investigation of their biological functions including cytokine, growth factor binding and heparanase inhibition. Interestingly, the glycopeptide exhibited context dependent enhancement or decrease of biological activities compared to the peptide or the glycan alone. The results presented herein suggest that besides varying the sulfation patterns of HS, linking the HS chain to core proteins as in proteoglycans may be an additional approach to modulate biological functions of HS in nature., Attaching heparan sulfate glycan on a peptide backbone can modulate biological functions of the glycan.

This paper provides a 4th manifestation of a new tradition by which the editors of Comments on Inorganic Chemistry wish to lead by example, whereby we start publishing original research content that, nonetheless, preserves the Journal’s identity as a niche for critical discussion of contemporary literature in inorganic chemistry. (For the 1st, 2nd and 3rd manifestations, see: a) Otten, B. M.; Melancon, K. M.; Omary, M. A. “All That Glitters is Not Gold: A Computational Study of Covalent vs Metallophilic Bonding in Bimetallic Complexes of d10 Metal Centers – A Tribute to Al Cotton on the 10th Anniversary of His Passing,” Comments Inorg. Chem. 2018, 38, 1–35; b) Yaseen, W. K.; Sanders, S. F.; Almotawa, R. M.; Otten, B. M.; Bhat, S.; Alamo, D. C.; Marpu, S. B.; Golden, T. D.; Omary, M. A. “Are Metal Complexes “Organic”, “Inorganic”, “Organometallic”, or “Metal-Organic” Materials? A Case Study for the Use of Trinuclear Coinage Metal Complexes as “Metal-Organic Coatings” for Corrosion Suppression on Aluminum Substrates”, Comments Inorg. Chem. 2019, 39, 1–26; and c) Smith, J. B.; Otten, B. M.; Derry, P. J.; Browning, C.; Bodenstedt, K. W.; Sandridge, J. H.; Satumtira, N. T.; Zilaie, M.; Payne, J.; Nuti, R.; Omary, M. A.; Smucker, B. W. “Luminescent, Redox-Active (Dithiolato)Bis(Imine)Platinum(II) Divergent Complexes with Exchangeable Imine Ligands: An Experimental/Computational Study versus Their (Diimine)(Dithiolato)Platinum(II) Convergent Congeners”, Comments Inorg. Chem. 2019, 39, 188–215.) Herein, the dinuclear complexes {Cu[3,5-(CF3)2Pz](µ-dppm)}2 and {Cu[3,5-(CF3)2Pz](µ-dppm)}2•3THF were studied structurally, spectroscopically and via density functional theory (DFT). They were synthesized by reacting bis(diphenylphosphino)methane (dppm) with the cyclic trinuclear complex {μ-[3,5-(CF3)2Pz]Cu}3 to effect nuclearity reduction. Two forms of crystalline solids, {Cu[3,5-(CF3)2Pz](µ-dppm)}2 and {Cu[3,5-(CF3)2Pz](µ-dppm)}2•3THF have been obtained using different recrystallization conditions. The {Cu[3,5-(CF3)2Pz](µ-dppm)}2 complex was found through DFT computations to undergo a distortion from a Y-shaped coordination sphere in the S0 ground state toward a T-shape in the T1 photoexcited, lowest-lying, phosphorescent state. The distortion also causes the copper-copper bond length to contract and form an excimer bond (dCu-Cu = 2.577 Å). Experimentally, the presence of THF in the crystal was found to cause a blue shift, effecting a change in emission color from teal to blue to the naked eye, with a near-unity quantum yields (93%), rendering the latter solid suitable for inorganic LED applications but not OLEDs, as thin films exhibit a reduced quantum yield. Crystallographic evidence suggests that THF leads to a more compact lattice that makes the complexes more rigid and thus hinder the excited state distortions vs unsolvated crystals. Greater distortion leads to a lower energy radiative emission and thus a red shift in the emission color. Films were also studied and found to undergo further red shifting as a result of less rigidity in the media and more surface molecules susceptible to distortion, hence manifesting the luminescence rigidochromism optical phenomenon in the solid state as opposed to the traditional manifestation in frozen vs fluid solution. Photobleaching was studied in both the film and powder to assess photostability, which was superior in neat vs doped solids, which is also favorable for LED applications.

The equilibrium geometries and spectroscopic properties of two key singlet carbenes, buta-1,3-diynylcarbene (6) and 2-methylenebicyclo[1.1.0]but-1(3)-en-4-ylidene (9), which have not been experimentally observed to date, are investigated using high-level coupled-cluster (CC) methods. The current theoretical study necessitates new experimental data on C5H2 isomers considering the relevance of these molecules to interstellar chemistry. Bent-pentadiynylidene (4) has been missing in the laboratory and the prime focus of our earlier theoretical work. The present theoretical study indicates that isomers 6 and 9 are also viable experimental targets. Apart from ethynylcyclopropenylidene (2), pentatetraenylidene (3), ethynylpropadienylidene (5), and 3-(didehydrovinylidene)cyclopropene (8), which are identified by Fourier transform microwave spectroscopy, the dipole moments of elusive 4, 6, and 9 are also nonzero (μ ≠ 0). The relative energies of these isomers, calculated at the CCSDT(Q)/CBS level of theory, with respect to linear triplet pentadiynylidene (1) reveal that they all lie within 25.1 kcal mol-1. Therefore, geometric, energetic, aromatic, and spectroscopic parameters are reported here, which may assist the efforts of molecular spectroscopists in the future. Anharmonic vibrational calculations on isomers 6 and 9 indicate that the former is loosely bound and would be challenging to be detected experimentally. Among the undetected carbenes, 9 may be considered as a potential target molecule considering its higher polarity and aromatic nature.

High level multireference calculations were performed for LuF for a total of 132 states, including four dissociation channels Lu(2D) + F(2P), Lu(2P) + F(2P), and two Lu(4F) + F(2P). The 6s, 5d, and 6p orbitals of lutetium, along with the valence 2p and 3p orbitals of fluorine, were included in the active space, allowing for the accurate description of static and dynamic correlation. The Lu(4F) + F(2P) channel has intersystem spin crossings with the Lu(2P) + F(2P) and Lu(2D) + F(2P) channels, which are discussed herein. To obtain spectroscopic constants, bond lengths, and excited states, multi-reference configuration interaction (MRCI) was used at a quadruple-ζ basis set level, correlating also the 4f electrons and corresponding orbitals. Core spin–orbit (C-MRCI) calculations were performed, revealing that 13Π0− is the first excited state closely followed by 13Π0+. In addition, the dissociation energy of LuF was determined at different levels of theory, with a range of basis sets. A balance between core correlation and a relativistic treatment of electrons is fundamental to obtain an accurate description of the dissociation energy. The best prediction was obtained with a combination of coupled-cluster single, double, and perturbative triple excitations /Douglas–Kroll–Hess third order Hamiltonian methods at a complete basis set level with a zero-point energy correction, which yields a dissociation value of 170.4 kcal mol−1. Dissociation energies using density functional theory were calculated using a range of functionals and basis sets; M06-L and B3LYP provided the closest predictions to the best ab initio calculations.