Synthesis and Moessbauer spectra of octaethylporphyrin ferrous complexes

Dolphin, David; Sams, J. R.; Tsin, Tsang Bik; Wong, Kit L. Tang

doi:10.1021/ja00438a037

Cited by 116 publications

(81 citation statements)

References 4 publications

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“…At higher temperature, the isomer shift decreases with temperature due to the second‐order Doppler shift,61 with typical data suggesting a decrease in δ of 0.03 mm s −1 per 100 K 62. The isomer shifts of deoxyMb and deoxyhemoglobin (deoxyHb) vary from 0.92–0.93 mm s −1 at 4.2 K to 0.86 mm s −1 at 195 K 63.…”

Section: Resultsmentioning

confidence: 85%

O₂ Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

Kepp

2013

ChemPhysChem

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This paper reports the computed O2 binding to heme, which for the first time explains experimental enthalpies for this process of central importance to bioinorganic chemistry. All four spin states along the relaxed Fe-O2-binding curves were optimized using the full heme system with dispersion, thermodynamic, and scalar-relativistic corrections, applying several density functionals. When including all these physical terms, the experimental enthalpy of O2 binding (-59 kJ mol(-1)) is closely reproduced by TPSSh-D3 (-66 kJ mol(-1)). Dispersion changes the potential energy surfaces and leads to the correct electronic singlet and heptet states for bound and dissociated O2. The experimental activation enthalpy of dissociation (~82 kJ mol(-1)) was also accurately computed (~75 kJ mol(-1)) with an actual barrier height of ~60 kJ mol(-1) plus a vibrational component of ~10 and ~5 kJ mol(-1) due to the spin-forbidden nature of the process, explaining the experimentally observed difference of ~20 kJ mol(-1) in enthalpies of binding and activation. Most importantly, the work shows how the nearly degenerate singlet and triplet states increase crossover probability up to ~0.5 and accelerate binding by ~100 times, explaining why the spin-forbidden binding of O2 to heme, so fundamental to higher life forms, is fast and reversible.

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Section: Resultsmentioning

confidence: 85%

O₂ Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

Kepp

2013

ChemPhysChem

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“…In addition to the calculations on complex 1 discussed above, the work by Chan and co‐workers in ref. [] features an investigation of the relative spin‐state energies of Fe(II) porphyrin (complex 2 in Figure ) whose experimentally determined spin triplet ground state is challenging to reproduce computationally . The starting point of this study was a spin‐quintet ROHF calculation on a single D 2 h symmetric structure.…”

Section: Mononuclear Transition Metal Complexesmentioning

confidence: 99%

Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group

Roemelt

Pantazis

2019

Advcd Theory and Sims

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The accurate and reliable calculation of different electronic states in transition metal systems is a persistent challenge for theoretical chemistry. The widespread use of density functional theory for computing the relative energies of states with different spin in transition metal complexes not only has not discouraged, but often, owing to its limitations, has motivated the development and refinement of first-principles wavefunction-based methods, including both single-reference and multireference approaches. A significant boost for the latter has been the emergence of the density matrix renormalization group (DMRG) as a reliable tool in applied quantum chemistry. By enabling the use of larger active spaces than conventionally possible, DMRG has opened up areas of transition metal chemistry that were previously inaccessible to multireference approaches. The present perspective provides an overview of representative studies that make use of DMRG methods and discusses recent applications to spin-state energetics of transition metal systems. These range from mononuclear to exchange-coupled systems that define an important emerging field of DMRG applications. Major achievements are highlighted and potential pitfalls are identified with a view toward future methodological developments as well as extensions in the applicability of DMRG-based approaches to problems of spin-state energetics and exchange-coupling in transition metal chemistry.

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“…Perhaps, the most surprising result in this broad spectrum is that two selected CI methods (SHCISCF and ACISCF) show a discrepancy on the order of 20 kcal/mol. This is troublesome because the experimental spin energy gap is unavailable and the only available information is that the ground state is a triplet [69][70][71][72][73][74][75][76] . This broad spectrum does not necessarily indicate that the accuracy of MR methods differs within a…”

Section: Essential Time-reversal Symmetry Breakingmentioning

confidence: 99%

Utilizing Essential Symmetry Breaking in Auxiliary-Field Quantum Monte Carlo: Application to the Spin Gaps of the C₃₆ Fullerene and an Iron Porphyrin Model Complex

Malone

Morales

2020

J. Chem. Theory Comput.

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We present three distinct examples where phaseless auxiliary-field Quantum Monte Carlo (ph-AFQMC) can be reliably performed with a single-determinant trial wavefunction with essential symmetry breaking. We first utilized essential time-reversal symmetry breaking with ph-AFQMC to compute the triplet-singlet energy gap in the TS12 set. We found statistically better performance of ph-AFQMC with complexrestricted orbitals than with spin-unrestricted orbitals. We then showed the utilization of essential spin symmetry breaking when computing the single-triplet gap of a known biradicaloid, C 36 . ph-AFQMC with spin-unrestricted Hartree-Fock (ph-AFQMC+UHF) fails catastrophically even with spin-projection and predicts no biradicaloid character. With approximate Brückner orbitals obtained from regularized orbital-optimized second-order Møller-Plesset perturbation theory (κ-OOMP2), ph-1 arXiv:2001.05109v1 [physics.chem-ph] 15 Jan 2020 AFQMC quantitatively captures strong biradicaloid character of C 36 . Lastly, we applied ph-AFQMC to the computation of the quintet-triplet gap in a model iron porphyrin complex where brute-force methods with a small active space fail to capture the triplet ground state. We show unambiguously that neither triplet nor quintet is strongly correlated using UHF, κ-OOMP2, and coupled-cluster with singles and doubles (CCSD) performed on UHF and κ-OOMP2 orbitals. There is no essential symmetry breaking in this problem. By virtue of this, we were able to perform UHF+ph-AFQMC reliably with a cc-pVTZ basis set and predicted a triplet ground state for this model geometry. The largest ph-AFQMC in this work correlated 186 electrons in 956 orbitals.Our work highlights the utility, scalability, and accuracy of ph-AFQMC with a single determinant trial wavefunction with essential symmetry breaking for systems mainly dominated by dynamical correlation with little static correlation. LLNL-JRNL-801427-DRAFT

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Synthesis and Moessbauer spectra of octaethylporphyrin ferrous complexes

Cited by 116 publications

References 4 publications

O₂ Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

O₂ Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group

Utilizing Essential Symmetry Breaking in Auxiliary-Field Quantum Monte Carlo: Application to the Spin Gaps of the C₃₆ Fullerene and an Iron Porphyrin Model Complex

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Synthesis and Moessbauer spectra of octaethylporphyrin ferrous complexes

Cited by 116 publications

References 4 publications

O2 Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

O2 Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

Multireference Approaches to Spin‐State Energetics of Transition Metal Complexes Utilizing the Density Matrix Renormalization Group

Utilizing Essential Symmetry Breaking in Auxiliary-Field Quantum Monte Carlo: Application to the Spin Gaps of the C36 Fullerene and an Iron Porphyrin Model Complex

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O₂ Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

O₂ Binding to Heme is Strongly Facilitated by Near‐Degeneracy of Electronic States

Utilizing Essential Symmetry Breaking in Auxiliary-Field Quantum Monte Carlo: Application to the Spin Gaps of the C₃₆ Fullerene and an Iron Porphyrin Model Complex