Functional Brain Imaging with Multi-Objective Multi-Modal Evolutionary Optimization

Functional brain imaging is a source of spatio-temporal data mining problems. A new framework hybridizing multi-objective and multi-modal optimization is proposed to formalize these data mining problems, and addressed through Evolutionary Computation (EC). The merits of EC for spatio-temporal data mining are demonstrated as the approach facilitates the modelling of the experts' requirements, and flexibly accommodates their changing goals

Redox Isomerism in the S3 State of the Oxygen-Evolving Complex Resolved by Coupled Cluster Theory

The electronic and geometric structures of the water-oxidizing complex of photosystem II in the steps of the catalytic cycle that precede dioxygen evolution remain hotly debated. Recent structural and spectroscopic investigations support contradictory redox formulations for the active-site Mn4CaOx cofactor in the final metastable S3 state. These range from the widely accepted MnIV4 oxo-hydroxo model, which presumes that O−O bond formation occurs in the ultimate transient intermediate (S4) of the catalytic cycle, to a MnIII2MnIV2 peroxo model representative of the contrasting “early-onset” O−O bond formation hypothesis. Density functional theory energetics of suggested S3 redox isomers are inconclusive because of extreme functional dependence. Here, we use the power of the domain-based local pair natural orbital approach to coupled cluster theory, DLPNO-CCSD(T), to present the first correlated wave function theory calculations of relative stabilities for distinct redox-isomeric forms of the S3 state. Our results enabled us to evaluate conflicting models for the S3 state of the oxygen-evolving complex (OEC) and to quantify the accuracy of lower-level theoretical approaches. Our assessment of the relevance of distinct redox-isomeric forms for the mechanism of biological water oxidation strongly disfavors the scenario of early-onset O−O formation advanced by literal interpretations of certain crystallographic models. This work serves as a case study in the application of modern coupled cluster implementations to redox isomerism problems in oligonuclear transition metal systems. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH Gmb

Orientational Jahn–Teller Isomerism in the Dark-Stable State of Nature's Water Oxidase

The tetramanganese–calcium cluster of the oxygen-evolving complex of photosystem II adopts electronically and magnetically distinct but interconvertible valence isomeric forms in its first light-driven oxidized catalytic state, S2. This bistability is implicated in gating the final catalytic states preceding O−O bond formation, but it is unknown how the biological system enables its emergence and controls its effect. Here we show that the Mn4CaO5 cluster in the resting (dark-stable) S1 state adopts orientational Jahn–Teller isomeric forms arising from a directional change in electronic configuration of the “dangler” MnIII ion. The isomers are consistent with available structural data and explain previously unresolved electron paramagnetic resonance spectroscopic observations on the S1 state. This unique isomerism in the resting state is shown to be the electronic origin of valence isomerism in the S2 state, establishing a functional role of orientational Jahn–Teller isomerism unprecedented in biological or artificial catalysis. © 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH Gmb

Reconciling Local Coupled Cluster with Multireference Approaches for Transition Metal Spin-State Energetics

Spin-state energetics of transition metal complexes remain one of the most challenging targets for electronic structure methods. Among single-reference wave function approaches, local correlation approximations to coupled cluster theory, most notably the domain-based local pair natural orbital (DLPNO) approach, hold the promise of bringing the accuracy of coupled cluster theory with single, double, and perturbative triple excitations, CCSD(T), to molecular systems of realistic size with acceptable computational cost. However, recent studies on spin-state energetics of iron-containing systems raised doubts about the ability of the DLPNO approach to adequately and systematically approximate energetics obtained by the reference-quality complete active space second-order perturbation theory with coupled-cluster semicore correlation, CASPT2/CC. Here, we revisit this problem using a diverse set of iron complexes and examine several aspects of the application of the DLPNO approach. We show that DLPNO-CCSD(T) can accurately reproduce both CASPT2/CC and canonical CCSD(T) results if two basic principles are followed. These include the consistent use of the improved iterative (T1) versus the semicanonical perturbative triple corrections and, most importantly, a simple two-point extrapolation to the PNO space limit. The latter practically eliminates errors arising from the default truncation of electron-pair correlation spaces and should be viewed as standard practice in applications of the method to transition metal spin-state energetics. Our results show that reference-quality results can be readily achieved with DLPNO-CCSD(T) if these principles are followed. This is important also in view of the applicability of the method to larger single-reference systems and multinuclear clusters, whose treatment of dynamic correlation would be challenging for multireference-based approaches.

Spin-state energetics of manganese spin crossover complexes: Comparison of single-reference and multi-reference ab initio approaches

Manganese spin crossover (SCO) complexes form a small but ever expanding family of compounds with thermally accessible states of different electronic configuration and total spin. Accurate prediction of spin-state energetics is essential for the theoretical description of these systems. However, this represents a challenging problem that necessitates recourse to correlated wave function methods rather than the more approximate density functional theory (DFT). Here we present a detailed study of spin-state energetics for eight Mn(III) and Mn(II) SCO complexes using the domain-based local pair natural orbital approach to coupled cluster theory with singles, doubles, and perturbative triples, DLPNO-CCSD(T). The effects of reference determinants, basis set, triples excitations, and pair natural orbitals (PNO) thresholds are evaluated and analysed in detail, enabling us to propose a robust and efficient computational protocol based on a combined and balanced mix of extrapolation to the complete basis set and infinite PNO space limits. The results are subsequently used to evaluate multireference wavefunction-based (CASSCF/NEVPT2) and DFT approaches, highlighting their inability to provide a balanced description of spin-state energetics for these complexes. The DLPNO-CCSD(T) protocol proposed in this study can serve as a generally applicable reference-quality quantum chemical method for studying spin crossover systems. © 2021 Elsevier Lt

EPR Spectroscopy of Cu(II) Complexes: Prediction of g-Tensors Using Double-Hybrid Density Functional Theory

Computational electron paramagnetic resonance (EPR) spectroscopy is an important field of applied quantum chemistry that contributes greatly to connecting spectroscopic observations with the fundamental description of electronic structure for open-shell molecules. However, not all EPR parameters can be predicted accurately and reliably for all chemical systems. Among transition metal ions, Cu(II) centers in inorganic chemistry and biology, and their associated EPR properties such as hyperfine coupling and g-tensors, pose exceptional difficulties for all levels of quantum chemistry. In the present work, we approach the problem of Cu(II) g-tensor calculations using double-hybrid density functional theory (DHDFT). Using a reference set of 18 structurally and spectroscopically characterized Cu(II) complexes, we evaluate a wide range of modern double-hybrid density functionals (DHDFs) that have not been applied previously to this problem. Our results suggest that the current generation of DHDFs consistently and systematically outperform other computational approaches. The B2GP-PLYP and PBE0-DH functionals are singled out as the best DHDFs on average for the prediction of Cu(II) g-tensors. The performance of the different functionals is discussed and suggestions are made for practical applications and future methodological developments. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

A new reaction pathway in organophosphorus chemistry: competing SN2- and AE'-pathways for nucleophilic attack at a phosphorus-cage compound

Competition: A combination of 31P NMR spectroscopic and calculational studies have shown that nucleophilic substitution in the phosphorus-carbon cage compound ClP3(CtBu)2 occurs through competing SN2- and AE-type reaction pathways (see scheme for model compound ClP3(CH)2). The AE mechanism results in the formation of a C2v-symmetric intermediate prior to release of the chloride ion

Unusual 31P Hyperfine Strain Effects in a Conformationally Flexible Cu(II) Complex Revealed by Two-Dimensional Pulse EPR Spectroscopy

Strain effects on g and metal hyperfine coupling tensors, A, are often manifested in Electron Paramagnetic Resonance (EPR) spectra of transition metal complexes, as a result of their intrinsic and/or solvent-mediated structural variations. Although distributions of these tensors are quite common and well understood in continuous-wave (cw) EPR spectroscopy, reported strain effects on ligand hyperfine coupling constants are rather scarce. Here we explore the case of a conformationally flexible Cu(II) complex, [Cu{Ph2P(O)NP(O)Ph2-κ2O,O′}2], bearing P atoms in its second coordination sphere and exhibiting two structurally distinct CuO4 coordination spheres, namely a square planar and a tetrahedrally distorted one, as revealed by X-ray crystallography. The Hyperfine Sublevel Correlation (HYSCORE) spectra of this complex exhibit 31P correlation ridges that have unusual inverse or so-called "boomerang" shapes and features that cannot be reproduced by standard simulation procedures assuming only one set of magnetic parameters. Our work shows that a distribution of isotropic hyperfine coupling constants (hfc) spanning a range between negative and positive values is necessary in order to describe in detail the unusual shapes of HYSCORE spectra. By employing DFT calculations we show that these hfc correspond to molecules showing variable distortions from square planar to tetrahedral geometry, and we demonstrate that line shape analysis of such HYSCORE spectra provides new insight into the conformation-dependent spectroscopic response of the spin system under investigation. © 2020 American Chemical Society

Electronic properties of the S = 5/2 Mn(II) complexes [Mn{PhC(O)NP(O)PPh2}(N,N)(NO3)], (N,N) = phenanthroline, neocuproine, 2,2′-bipyridine

The synthesis, as well as the structural and electronic properties of the [Mn(O,O)(N,N)(NO3)] complexes, (O,O) = {PhC(O)NP(O)PPh2}−, (N,N) = phenanthroline (1), neocuproine (2) and 2,2′-bipyridine (3) is reported. The three complexes were structurally characterized by X-ray crystallography, and complexes 1 and 2 were shown to be closer to octahedral, whereas 3 to trigonal prismatic. The zero-field splitting parameters of these S = 5/2 systems were determined by X- and Q-band EPR spectroscopy, revealing a small but significant difference in the magnitude of |D| for complex 3 (0.18 cm−1) compared to those of 1 and 2 (0.14 and 0.12 cm−1, respectively). These differences are attributed to the structural and electronic properties of complexes 1–3. The latter were probed by DFT calculations, which showed different DSOC contributions among the three complexes. © 2021 Elsevier Lt

Genetic Etiology for Alcohol-Induced Cardiac Toxicity

10.1016/j.jacc.2018.03.462Journal of the American College of Cardiology71202293-2302JACC