Zachary (Ira) Mathe

All Publications

• Trends in benzene inverse sandwich complexes of the alkaline-earth metals Mg, Ca, Sr and Ba CHEMICAL SCIENCE Jedrzkiewicz, D., Morasch, M., Townrow, O. P. E., Rosch, B., Langer, J., Mathe, Z., Harder, S. 2025; 16 (38): 17793-17802

  Abstract

  Mechanochemical reduction of β-diketiminate (BDI) barium iodide precursors with K/KI resulted in the first barium inverse sandwich complexes containing the benzene dianion in yields of up to 54%. This most challenging isolation of highly reactive (BDI)Ba-(C6H6)-Ba(BDI) complexes, completes the family of heavier benzene inverse sandwich complexes and allows for a comparison of trends in the series from Mg, Ca, Sr to Ba. Syntheses, stabilities, structures, electronic states and reactivities of the full range are compared. Crucial for isolation of the Ba inverse sandwich complexes are the tBu-substituents in the ligand backbone which push the bulky aryl rings towards the large Ba metal cations. These secondary Ba⋯(π-Ar) interactions result in an unexpected high stability. Another trend is found for the ring puckering in the bridging benzene2- dianion which steadily increases from Ba to Mg. DFT calculations show the general ionic character of (BDI)Ae-(C6H6)-Ae(BDI) complexes (Ae = Mg, Ca, Sr, Ba) and reveal only small energy differences between closed-shell singlet or open-shell triplet states. The most reactive (BDI)Ba-(C6H6)-Ba(BDI) complexes could be considered the first BaI synthons. They reduce a range of polyaromatic hydrocarbons, H2 or even convert (BDI)MgI precursors into well-known (BDI)Mg-Mg(BDI) complexes. Reactions with heavier (BDI)AeI (Ae = Ca, Sr) gave (BDI)Ae-(C6H6)-Ae(BDI) and (BDI)BaI.

  View details for DOI 10.1039/d5sc05373k

  View details for Web of Science ID 001562827000001

  View details for PubMedID 40918721

  View details for PubMedCentralID PMC12409674

• Combined X-Ray Emission Spectroscopy at Phosphorus and Nickel: Detecting Subtle Changes in Catalyst Electronic Structure at High Resolution SMALL Mathe, Z., Debeer, S. 2025; 21 (37): e2505199

  Abstract

  Valence-to-core X-ray emission spectroscopy (VtC XES) is widely used to characterize valence electronic structure, especially of transition metal systems in homogeneous and bioinorganic catalysis. Although metal K-edge VtC XES has proved useful, its observable information content is limited by the large lifetime broadening of the metal 1s core hole, and its practical application is limited by small VtC emission probability and thus low count rates. Ligand VtC XES in transition metal complexes, though largely unexplored, offers a higher resolution and potential for broad applications in catalysis research. Here, P VtC XES is introduced for catalysts with phosphine ligands, perhaps the most important class of spectator ligands in homogeneous catalysis. P VtC XES is sensitive to subtle changes in electronic structure, with difference spectra that are well-reproduced by density functional theory (DFT) calculations, indicating that DFT can not only provide insight into the physical origins of spectral features but can also facilitate the identification of unknown species. Comparison to Ni VtC XES, as well as previously published X-ray absorption data, establishes the high resolution and complementary benefits of the technique. The potential of P VtC XES as a metal- and spin-agnostic tool for experimentally assessing electronic structure and mechanisms in phosphine-coordinated catalysts is highlighted.

  View details for DOI 10.1002/smll.202505199

  View details for Web of Science ID 001516633700001

  View details for PubMedID 40567103

  View details for PubMedCentralID PMC12444823

• Coupling experiment and theory to push the state-of-the-art in X-ray spectroscopy NATURE REVIEWS CHEMISTRY Mathe, Z., Maganas, D., Neese, F., DeBeer, S. 2025; 9 (7): 436-453

  Abstract

  X-ray spectroscopy plays a pivotal role in understanding the geometric and electronic structures of countless molecules and materials, from homogeneous and heterogeneous catalysts to biological active sites. The element-selectivity of X-ray spectroscopy allows for phenomena at specific photoabsorbers to be investigated. Since the early 2000s, experimental sophistication has progressed, with increasing applications of X-ray emission spectroscopy and two-dimensional photon-in-photon-out spectroscopies, such as resonant inelastic X-ray scattering. Although advanced X-ray spectroscopic methods increase selectivity and information content, the spectra obtained present major challenges for both qualitative and quantitative interpretation. To maximize the insight gained from X-ray spectroscopy, close coupling of experiment and theory is essential. Herein, we present the theoretical and experimental aspects of X-ray spectroscopy, with an emphasis on molecular systems and how an integrated approach with a solid foundation in molecular electronic structure theory enables new modes of inquiry into (bio)chemical catalysis.

  View details for DOI 10.1038/s41570-025-00718-2

  View details for Web of Science ID 001499140500001

  View details for PubMedID 40447841

  View details for PubMedCentralID 8245202

• Inserting Three-Coordinate Nickel into [4Fe-4S] Clusters ACS CENTRAL SCIENCE Fataftah, M. S., Wilson, D. W. N., Mathe, Z., Gerard, T. J., Mercado, B. Q., DeBeer, S., Holland, P. L. 2024; 10 (10): 1910-1919

  Abstract

  Metalloenzymes can efficiently achieve the multielectron interconversion of carbon dioxide and carbon monoxide under mild conditions. Anaerobic carbon monoxide dehydrogenase (CODH) performs these reactions at the C cluster, a unique nickel-iron-sulfide cluster that features an apparent three-coordinate nickel site. How nature assembles the [NiFe3S4]-Feu cluster is not well understood. We use synthetic clusters to demonstrate that electron transfer can drive insertion of a Ni0 precursor into an [Fe4S4]3+ cluster to assemble higher nuclearity nickel-iron-sulfide clusters with the same complement of metal ions as the C cluster. Initial electron transfer results in a [1Ni-4Fe-4S] cluster in which a Ni1+ ion sits outside of the cluster. Modifying the Ni0 precursor results in the insertion of two nickel atoms into the cluster, concomitant with ejection of an iron to yield an unprecedented [2Ni-3Fe-4S] cluster possessing four three-coordinate metal sites. Both clusters are characterized using magnetometry, electron paramagnetic resonance (EPR), Mössbauer, and X-ray absorption spectroscopy and supported by DFT computations that are consistent with both clusters having nickel in the +1 oxidation state. These results demonstrate that Ni1+ is a viable oxidation state within iron-sulfur clusters and that redox-driven transformations can give rise to higher nuclearity clusters of relevance to the CODH C cluster.

  View details for DOI 10.1021/acscentsci.4c00985

  View details for Web of Science ID 001328626500001

  View details for PubMedID 39463842

  View details for PubMedCentralID PMC11503493

• Three-Coordinate Nickel and Metal-Metal Interactions in a Heterometallic Iron-Sulfur Cluster JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Wilson, D. W. N., Fataftah, M. S., Mathe, Z., Mercado, B. Q., DeBeer, S., Holland, P. L. 2024; 146 (6): 4013-4025

  Abstract

  Biological multielectron reactions often are performed by metalloenzymes with heterometallic sites, such as anaerobic carbon monoxide dehydrogenase (CODH), which has a nickel-iron-sulfide cubane with a possible three-coordinate nickel site. Here, we isolate the first synthetic iron-sulfur clusters having a nickel atom with only three donors, showing that this structural feature is feasible. These have a core with two tetrahedral irons, one octahedral tungsten, and a three-coordinate nickel connected by sulfide and thiolate bridges. Electron paramagnetic resonance (EPR), Mössbauer, and superconducting quantum interference device (SQUID) data are combined with density functional theory (DFT) computations to show how the electronic structure of the cluster arises from strong magnetic coupling between the Ni, Fe, and W sites. X-ray absorption spectroscopy, together with spectroscopically validated DFT analysis, suggests that the electronic structure can be described with a formal Ni1+ atom participating in a nonpolar Ni-W σ-bond. This metal-metal bond, which minimizes spin density at Ni1+, is conserved in two cluster oxidation states. Fe-W bonding is found in all clusters, in one case stabilizing a local non-Hund state at tungsten. Based on these results, we compare different M-M interactions and speculate that other heterometallic clusters, including metalloenzyme active sites, could likewise store redox equivalents and stabilize low-valent metal centers through metal-metal bonding.

  View details for DOI 10.1021/jacs.3c12157

  View details for Web of Science ID 001160893200001

  View details for PubMedID 38308743

  View details for PubMedCentralID PMC10993082

• Access to a Labile Monomeric Magnesium Radical by Ball-Milling ANGEWANDTE CHEMIE-INTERNATIONAL EDITION Jedrzkiewicz, D., Mai, J., Langer, J., Mathe, Z., Patel, N., DeBeer, S., Harder, S. 2022; 61 (15): e202200511

  Abstract

  In order to isolate a monometallic Mg radical, the precursor (Am)MgI⋅(CAAC) (1) was prepared (Am=tBuC(N-DIPP)2 , DIPP=2,6-diisopropylphenyl, CAAC=cyclic (alkyl)(amino)carbene). Reduction of a solution of 1 in toluene with the reducing agent K/KI led to formation of a deep purple complex that rapidly decomposed. Ball-milling of 1 with K/KI gave the low-valent MgI complex (Am)Mg⋅(CAAC) (2) which after rapid extraction with pentane and crystallization was isolated in 15 % yield. Although a benzene solution of 2 decomposes rapidly to give Mg(Am)2 (3) and unidentified products, the radical is stable in the solid state. Its crystal structure shows planar trigonal coordination at Mg. The extremely short Mg-C distance of 2.056(2) Å indicates strong Mg-CAAC bonding. Calculations and EPR measurements show that most of the spin density is in a π* orbital located at the C-N bond in CAAC, leading to significant C-N bond elongation. This is supported by calculated NPA charges in 2: Mg +1.73, CAAC -0.82. Similar metal-to-CAAC charge transfer was calculated for M0 (CAAC)2 and [MI (CAAC)2 + ] (M=Be, Mg, Ca) complexes in which the metal charges range from +1.50 to +1.70. Although the spin density of the radical is mainly located at the CAAC ligand, complex 2 reacts as a low-valent MgI complex: reaction with a I2 solution in toluene gave (Am)MgI⋅(CAAC) (1) as the major product.

  View details for DOI 10.1002/anie.202200511

  View details for Web of Science ID 000757421100001

  View details for PubMedID 35108440

  View details for PubMedCentralID PMC9306460

• Phosphorus Kβ X-ray emission spectroscopy detects non-covalent interactions of phosphate biomolecules <i>in situ</i> CHEMICAL SCIENCE Mathe, Z., McCubbin Stepanic, O., Peredkov, S., DeBeer, S. 2021; 12 (22): 7888-7901

  Abstract

  Phosphorus is ubiquitous in biochemistry, being found in the phosphate groups of nucleic acids and the energy-transferring system of adenine nucleotides (e.g. ATP). Kβ X-ray emission spectroscopy (XES) of phosphorus has been largely unexplored, with no previous applications to biomolecules. Here, the potential of P Kβ XES to study phosphate-containing biomolecules, including ATP and NADPH, is evaluated, as is the application of the technique to aqueous solution samples. P Kβ spectra offer a detailed picture of phosphate valence electronic structure, reporting on subtle non-covalent effects, such as hydrogen bonding and ionic interactions, that are key to enzymatic catalysis. Spectral features are interpreted using density functional theory (DFT) calculations, and potential applications to the study of biological energy conversion are highlighted.

  View details for DOI 10.1039/d1sc01266e

  View details for Web of Science ID 000648622300001

  View details for PubMedID 34168842

  View details for PubMedCentralID PMC8188515

• Calcium Valence-to-Core X-ray Emission Spectroscopy: A Sensitive Probe of Oxo Protonation in Structural Models of the Oxygen-Evolving Complex INORGANIC CHEMISTRY Mathe, Z., Pantazis, D. A., Lee, H., Gnewkow, R., Van Kuiken, B. E., Agapie, T., DeBeer, S. 2019; 58 (23): 16292-16301

  Abstract

  Calcium is an abundant, nontoxic metal that finds many roles in synthetic and biological systems including the oxygen-evolving complex (OEC) of photosystem II. Characterization methods for calcium centers, however, are underdeveloped compared to those available for transition metals. Valence-to-core X-ray emission spectroscopy (VtC XES) selectively probes the electronic structure of an element's chemical environment, providing insight that complements the geometric information available from other techniques. Here, the utility of calcium VtC XES is established using an in-house dispersive spectrometer in combination with density functional theory. Spectral trends are rationalized within a molecular orbital framework, and Kβ2,5 transitions, derived from molecular orbitals with primarily ligand p character, are found to be a promising probe of the calcium coordination environment. In particular, it is shown that calcium VtC XES is sensitive to the electronic structure changes that accompany oxo protonation in Mn3CaO4-based molecular mimics of the OEC. Through correlation to calculations, the potential of calcium VtC XES to address unresolved questions regarding the mechanism of biological water oxidation is highlighted.

  View details for DOI 10.1021/acs.inorgchem.9b02866

  View details for Web of Science ID 000500650600062

  View details for PubMedID 31743026

  View details for PubMedCentralID PMC6891804

• Trapping intermediates in metal transfer reactions of the CusCBAF export pump of <i>Escherichia coli</i> COMMUNICATIONS BIOLOGY Chacon, K. N., Perkins, J., Mathe, Z., Alwan, K., Ho, E. N., Ucisik, M. N., Merz, K. M., Blackburn, N. J. 2018; 1: 192

  Abstract

  Escherichia coli CusCBAF represents an important class of bacterial efflux pump exhibiting selectivity towards Cu(I) and Ag(I). The complex is comprised of three proteins: the CusA transmembrane pump, the CusB soluble adaptor protein, and the CusC outer-membrane pore, and additionally requires the periplasmic metallochaperone CusF. Here we used spectroscopic and kinetic tools to probe the mechanism of copper transfer between CusF and CusB using selenomethionine labeling of the metal-binding Met residues coupled to RFQ-XAS at the Se and Cu edges. The results indicate fast formation of a protein-protein complex followed by slower intra-complex metal transfer. An intermediate coordinated by ligands from each protein forms in 100 ms. Stopped-flow fluorescence of the capping CusF-W44 tryptophan that is quenched by metal transfer also supports this mechanism. The rate constants validate a process in which shared-ligand complex formation assists protein association, providing a driving force that raises the rate into the diffusion-limited regime.

  View details for DOI 10.1038/s42003-018-0181-9

  View details for Web of Science ID 000461126500192

  View details for PubMedID 30456313

  View details for PubMedCentralID PMC6235853

• Renewable Additives that Improve Water Resistance of Cellulose Composite Materials JOURNAL OF RENEWABLE MATERIALS Buckley, H. L., Touchberry, C. H., McKinley, J. P., Mathe, Z. S., Muradyan, H., Ling, H., Fadadu, R. P., Mulvihill, M. J., Amrose, S. E. 2017; 5 (1): 1-13

  View details for DOI 10.7569/JRM.2016.634109

  View details for Web of Science ID 000399649600001