Publications by authors named "Werner Kaminsky"

110 Publications

Increasing reactivity by incorporating π-acceptor ligands into coordinatively unsaturated thiolate-ligated iron(II) complexes.

Inorganica Chim Acta 2021 Sep 30;524. Epub 2021 Apr 30.

The Department of Chemistry, University of Washington, Box 351700 Seattle, WA 98195-1700, United States.

Reported herein is the structural, spectroscopic, redox, and reactivity properties of a series of iron complexes containing both a π-donating thiolate, and π-accepting -heterocycles in the coordination sphere, in which we systematically vary the substituents on the -heterocycle, the size of the -heterocycle, and the linker between the imine nitrogen and tertiary amine nitrogen. In contrast to our primary amine/thiolate-ligated Fe(II) complex, [Fe(SN(tren))] (), the Fe(II) complexes reported herein are intensely colored, allowing us to visually monitor reactivity. Ferrous complexes with R = H substituents in the 6-position of the pyridines, [Fe(SN(6-H-DPPN)] () and [Fe(SN(6-H-DPEN))(MeOH)] () are shown to readily bind neutral ligands, and all of the Fe(II) complexes are shown to bind anionic ligands regardless of steric congestion. This reactivity is in contrast to and is attributed to an increased metal ion Lewis acidity assessed via aniodic redox potentials, E, caused by the π-acid ligands. Thermodynamic parameters (ΔH, ΔS) for neutral ligand binding were obtained from -dependent equilibrium constants. All but the most sterically congested complex, [Fe(SN(6-Me-DPPN)] (), react with O. In contrast to our Mn(II)-analogues, dioxygen intermediates are not observed. Rates of formation of the final mono oxo-bridged products were assessed via kinetics and shown to be inversely dependent on redox potentials, E, consistent with a mechanism involving electron transfer.
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http://dx.doi.org/10.1016/j.ica.2021.120422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8301228PMC
September 2021

Hierarchical nanosheets built from superatomic clusters: properties, exfoliation and single-crystal-to-single-crystal intercalation.

Chem Sci 2020 Aug 3;11(39):10744-10751. Epub 2020 Aug 3.

Department of Chemistry, University of Washington Seattle Washington 98195 USA

Tuning the properties of atomic crystals in the two-dimensional (2D) limit is synthetically challenging, but critical to unlock their potential in fundamental research and nanotechnology alike. 2D crystals assembled using superatomic blocks could provide a route to encrypt desirable functionality, yet strategies to link the inorganic blocks together in predetermined dimensionality or symmetry are scarce. Here, we describe the synthesis of anisotropic van der Waals crystalline frameworks using the designer superatomic nanocluster Co(py)CoSeL (py = pyridine, L = PhPN(Tol)), and ditopic linkers. Post-synthetically, the 3D crystals can be mechanically exfoliated into ultrathin flakes (8 to 60 nm), or intercalated with the redox-active guest tetracyanoethylene in a single-crystal-to-single-crystal transformation. Extensive characterization, including by single crystal X-ray diffraction, reveals how intrinsic features of the nanocluster, such as its structure, chirality, redox-activity and magnetic profile, predetermine key properties of the emerging 2D structures. Within the nanosheets, the strict and unusual stereoselectivity of the nanocluster's Co edges for the low symmetry (α,α,β) isomer gives rise to in-plane structural anisotropy, while the helically chiral nanoclusters self-organize into alternating Δ- and Λ-homochiral rows. The nanocluster's high-spin Co edges, and its rich redox profile make the nanosheets both magnetically and electrochemically active, as revealed by solid state magnetic and cyclic voltammetry studies. The length and flexibility of the ditopic linker was varied, and found to have a secondary effect on the structure and stacking of the nanosheets within the 3D crystals. With these results we introduce a deterministic and versatile synthetic entry to programmable functionality and symmetry in 2D superatomic crystals.
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http://dx.doi.org/10.1039/d0sc03506hDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8162370PMC
August 2020

Robust Synthetic Route toward Anisotropic Metal-Organic Cages with Tunable Surface Chemistry.

Inorg Chem 2021 Jun 11;60(11):7602-7606. Epub 2021 May 11.

Department of Chemistry, University of Washington, Seattle, Washington 98195-1700, United States.

Metal-organic cages with well-defined interior cavities and tunable surface chemistry serve as attractive building blocks for new types of soft nanoporous materials. While a compositionally diverse repertoire of metal-organic cages exists, the vast majority feature highly symmetric cores. Here, we report a robust, generalizable synthetic route toward anisotropic copper paddlewheel-based cages with tunable pendant amide groups. An isostructural family with increasingly hydrophobic surface properties has been synthesized and characterized by single-crystal X-ray diffraction, gas sorption analysis, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and H NMR digestion experiments. The metal-organic cages reported here may enable a deeper study of how anisotropy influences the long-range structure and emergent function of soft nanoporous materials.
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http://dx.doi.org/10.1021/acs.inorgchem.1c00466DOI Listing
June 2021

A Cyclic Ruthenium Benzylidene Initiator Platform Enhances Reactivity for Ring-Expansion Metathesis Polymerization.

J Am Chem Soc 2021 May 7;143(19):7314-7319. Epub 2021 May 7.

Ring-expansion metathesis polymerization (REMP) has shown potential as an efficient strategy to access cyclic macromolecules. Current approaches that utilize cyclic olefin feedstocks suffer from poor functional group tolerance, low initiator stability, and slow reaction kinetics. Improvements to current initiators will address these issues in order to develop more versatile and user-friendly technologies. Herein, we report a reinvigorated tethered ruthenium-benzylidene initiator, , that utilizes design features from ubiquitous Grubbs-type initiators that are regularly applied in linear polymerizations. We report the controlled synthesis of functionalized cyclic poly(norbornene)s and demonstrate that judicious ligand modifications not only greatly improve kinetics but also lead to enhanced initiator stability. Overall, is an adaptable platform for the study and application of cyclic macromolecules via REMP.
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http://dx.doi.org/10.1021/jacs.1c03491DOI Listing
May 2021

Tuning the Electronic Structure of Atomically Precise Sn/Co/Se Nanoclusters via Redox Matching of Tin(IV) Surface Sites.

Inorg Chem 2021 May 11;60(9):6135-6139. Epub 2021 Apr 11.

Department of Chemistry, University of Washington, Seattle, Washington 98195, United States.

A new strategy is reported to tailor the electronic properties of a superatomic metal chalcogenide cluster by redox matching the cluster core with surface tin(IV) sites. Two ternary clusters (SnR)CoSeL (R = Me, Bu) are synthesized by salt metathesis from the hexalithiated salt [Li(py)]CoSeL and RSnCl. Cyclic and differential-pulse voltammetry studies reveal that the tristannylated clusters feature two new, near-degenerate, electronic states within the highest occupied molecular orbital-lowest unoccupied molecular orbital gap of the CoSe core, which are attributed to the reduction of a surface tin site. Single-crystal X-ray diffraction analysis reveals that no Sn···Se coordination is present in the solid state. The single-crystal X-ray structure of the hexalithiated salt starting material is reported for the tetrahydrofuran (THF) adduct variant [Li(THF)]CoSeL.
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http://dx.doi.org/10.1021/acs.inorgchem.1c00313DOI Listing
May 2021

CO Hydrogenation Catalyzed by a Ruthenium Protic N-Heterocyclic Carbene Complex.

Inorg Chem 2021 Apr 29;60(8):5996-6003. Epub 2021 Mar 29.

Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, United States.

We describe the hydrogenation of CO to formate catalyzed by a Ru(II) bis(protic N-heterocyclic carbene, p-NHC) phosphine complex [Ru(bpy)(MeCN)(P(p-NHC))](PF) (). Under catalytic conditions (20 μmol catalyst, 20 bar CO, 60 bar H, 5 mL THF, 140 °C, 16 h), the activity of is limited only by the amount of KPO present in the reaction, yielding a nearly 1:1 ratio of turnover number (TON) to equivalents of KPO (relative to ), with the highest TON = 8040. Additionally, analysis of the reaction solution post-run reveals the catalyst intact with no free ligand observed. Stoichiometric studies, including examination of unique carbamate and hydride complexes as relevant intermediates, were carried out to probe the operative mechanism and understand the importance of metal-ligand cooperativity in this system.
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http://dx.doi.org/10.1021/acs.inorgchem.1c00417DOI Listing
April 2021

Inorganic clusters as metalloligands: ligand effects on the synthesis and properties of ternary nanopropeller clusters.

Dalton Trans 2020 Nov;49(45):16464-16473

University of Washington, Department of Chemistry, Seattle, WA 98195, USA.

Redox-active multimetallic platforms with synthetically addressable and hemilabile active sites are attractive synthetic targets for mimicking the reactivity of enzymatic co-factors toward multielectron transformations. To this end, a family of ternary clusters featuring three edge metal sites anchored on a [Co6Se8] multimetallic support via amidophosphine ligands are a promising platform. In this report, we explore how small changes in the stereoelectronic properties of these ligands alter [Co6Se8] metalloligand formation, but also substrate binding affinity and strength of the edge/support interaction in two new ternary clusters, M3Co6Se8L6 (M = Zn, Fe; L(-) = Ph2PN(-)iPr). These clusters are characterized extensively using a range of methods, including single crystal X-ray diffraction, electronic absorption spectroscopy and cyclic voltammetry. Substrate binding studies reveal that Fe3Co6Se8L6 resists coordination of larger ligands like pyridine or tetrahydrofuran, but binds the smaller ligand CNtBu. Additionally, investigations into the synthesis of new [Co6Se8] metalloligands using two aminophosphines, Ph2PN(H)iPr (LH) and iPr2PN(H)iPr, led to the synthesis and characterization of Co6Se8LH6, as well as the smaller clusters Co4Se2(CO)6LH4, Co3Se(μ2-PPh2)(CO)4LH3, and [Co(CO)3(iPr2PN(H)iPr)]2. Cumulatively, this study expands our understanding on the effect of the stereoelectronic properties of aminophosphine ligands in the synthesis of cobalt chalcogenide clusters, and, importantly on modulating the push-pull dynamic between the [Co6Se8] support, the edge metals and incoming coordinating ligands in ternary M3Co6Se8L6 clusters.
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http://dx.doi.org/10.1039/d0dt02416cDOI Listing
November 2020

Probing CO Generation through Metal-Assisted Alcohol Dehydrogenation in Metal-2-(arylazo)phenol Complexes Using Isotopic Labeling (Metal = Ru, Ir): Synthesis, Characterization, and Cytotoxicity Studies.

Inorg Chem 2020 Oct 30;59(20):15526-15540. Epub 2020 Sep 30.

Department of Chemistry, National Institute of Technology, Rourkela 769008, Odisha, India.

The reaction of 2-{2-(benzo[1,3]dioxol-5-yl)- diazo}-4-methylphenol (HL) with [Ru(PPh)Cl] in ethanol resulted in the carbonylated ruthenium complex [RuL(PPh)(CO)] (), wherein metal-assisted decarbonylation via in situ ethanol dehydrogenation is observed. When the reaction was performed in acetonitrile, however, the complex [RuL(PPh)(CHCN)] () was obtained as the main product, probably by trapping of a common intermediate through coordination of CHCN to the Ru(II) center. The analogous reaction of HL with [Ir(PPh)Cl] in ethanol did not result in ethanol decarbonylation and instead gave the organoiridium hydride complex [IrL(PPh)(H)] (). Unambiguous evidence for the generation of CO via ruthenium-assisted ethanol oxidation is provided by the synthesis of the C-labeled complex, [Ru(PPh)L(CO)] () using isotopically labeled ethanol, CHCHOH. To summarize all the evidence, a ruthenium-assisted mechanistic pathway for the decarbonylation and generation of alkane via alcohol dehydrogenation is proposed. In addition, the in vitro antiproliferative activity of complexes - was tested against human cervical (HeLa) and human colorectal adenocarcinoma (HT-29) cell lines. Complexes - showed impressive cytotoxicity against both HeLa (half-maximal inhibitory concentration (IC) value of 3.84-4.22 μM) and HT-29 cancer cells (IC values between 3.3 and 4.5 μM). Moreover, the complexes were comparatively less toxic to noncancerous NIH-3T3 cells.
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http://dx.doi.org/10.1021/acs.inorgchem.0c02563DOI Listing
October 2020

New V, VO, VO, and VO Systems: Exploring their Interconversion in Solution, Protein Interactions, and Cytotoxicity.

Inorg Chem 2020 Oct 11;59(19):14042-14057. Epub 2020 Sep 11.

Department of Chemistry, National Institute of Technology, Rourkela, 769008 Odisha, India.

The synthesis and characterization of one oxidoethoxidovanadium(V) [VO(L)(OEt)] () and two nonoxidovanadium(IV) complexes, [V(L)] ( and ), with aroylhydrazone ligands incorporating naphthalene moieties, are reported. The synthesized oxido and nonoxido vanadium complexes are characterized by various physicochemical techniques, and their molecular structures are solved by single crystal X-ray diffraction (SC-XRD). This revealed that in the geometry around the vanadium atom corresponds to a distorted square pyramid, with a ON coordination sphere, whereas that of the two nonoxido V complexes and corresponds to a distorted trigonal prismatic arrangement with a ON coordination sphere around each "bare" vanadium center. In aqueous solution, the VO moiety of undergoes a change to VO species yielding [VO(L)] (), while the nonoxido V-compounds and are partly converted into their corresponding VO complexes, [VO(L)(HO)] ( and ). Interaction of these VO, VO, and V systems with two model proteins, ubiquitin (Ub) and lysozyme (Lyz), is investigated through docking approaches, which suggest the potential binding sites: the interaction is covalent for species and , with the binding to Glu16, Glu18, and Asp21 for Ub, and His15 for Lyz, and it is noncovalent for species , , and , with the surface residues of the proteins. The ligand precursors and complexes are also evaluated for their antiproliferative activity against ovarian (A2780) and prostate (PC3) human cancer cells and in normal fibroblasts (V79) to check the selectivity of the compounds for cancer cells.
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http://dx.doi.org/10.1021/acs.inorgchem.0c01837DOI Listing
October 2020

A Non-fullerene Acceptor with Enhanced Intermolecular π-Core Interaction for High-Performance Organic Solar Cells.

J Am Chem Soc 2020 Sep 26;142(36):15246-15251. Epub 2020 Aug 26.

Department of Chemistry, City University of Hong Kong, Kowloon 999077, Hong Kong.

Understanding the molecular structure and self-assembly of thiadiazole-derived non-fullerene acceptors (NFAs) is very critical for elucidating the origin of their extraordinary charge generation and transport properties that enable high power conversion efficiencies to be achieved in these systems. A comprehensive crystallographic study on a state-of-the-art NFA, Y6, and its selenium analog, , has been conducted which revealed that the π-core interaction induced by benzo[2,1,3]thiadiazole S-N-containing moieties plays a significant role in governing the molecular geometries and unique packing of Y6 and to ensure their superior charge-transport properties. Moreover, benefitting from the red-shifted optical absorption via selenium substitution, photovoltaic devices based on a PM6::PCBM ternary blend delivered an exceptionally high short-circuit current of 27.48 mA/cm and a power conversion efficiency of 17.08%.
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http://dx.doi.org/10.1021/jacs.0c07083DOI Listing
September 2020

Comparison of two MnMn-bis-μ-oxo complexes {[Mn(N(6-Me-DPEN))](μ-O)} and {[Mn(N(6-Me-DPPN))](μ-O)}.

Acta Crystallogr E Crystallogr Commun 2020 Jul 9;76(Pt 7):1042-1046. Epub 2020 Jun 9.

The Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA.

The addition of -butyl hydro-peroxide ( BuOOH) to two structurally related Mn complexes containing -bis-(6-methyl-2-pyridyl-meth-yl)ethane-1,2-di-amine (6-Me-DPEN) and -bis-(6-methyl-2-pyridyl-meth-yl)propane-1,2-di-amine (6-Me-DPPN) results in the formation of high-valent bis-oxo complexes, namely di-μ-oxido-bis-{[,-bis-(6-methyl-2-pyridylmeth-yl)ethane-1,2-di-amine]-manganese(II)}(-) bis-(tetra-phenyl-borate) dihydrate, [Mn(CHN)O](CHB)·2HO or {[Mn(N(6-Me-DPEN))](-O)}(2BPh)(2HO) () and di-μ-oxido-bis-{[,-bis-(6-methyl-2-pyridylmeth-yl)propane-1,3-di-amine]-manganese(II)}(-) bis-(tetra-phenyl-borate) diethyl ether disolvate, [Mn(CHN)O](CHB)·2CHO or {[Mn(N(6-MeDPPN))](-O)}(2BPh)(2EtO) (). Complexes and both contain the 'diamond core' motif found previously in a number of iron, copper, and manganese high-valent bis-oxo compounds. The flexibility in the propyl linker in the ligand scaffold of , as compared to that of the ethyl linker in , results in more elongated Mn-N bonds, as one would expect. The Mn-Mn distances and Mn-O bond lengths support an Mn oxidation state assignment for the Mn ions in both and . The angles around the Mn centers are consistent with the local pseudo-octa-hedral geometry.
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http://dx.doi.org/10.1107/S2056989020004557DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7336796PMC
July 2020

Selective detection of pyrophosphate anion by zinc ensemble of C-symmetric triaminoguanidine-pyrrole conjugate and its biosensing applications.

Anal Chim Acta 2020 Mar 24;1103:192-201. Epub 2019 Dec 24.

Department of Chemistry, Bharathiar University, Coimbatore, 641 046, Tamil Nadu, India. Electronic address:

A new-fangled C-symmetric triaminoguanidine-pyrrole conjugate has been constructed and utilized for sensing applications. The probe selectively detects zinc ions (Zn) by colorimetric as well as turn-on fluorescent manner. Further, the in-situ formed zinc ensemble displays turn-off fluorescence response towards the pyrophosphate anion (PPi) via displacement approach. Emissive off-on-off sensing characteristics of the probe has been successfully exploited to construct the INHIBIT logic gate, coding/decoding of messages and in vivo imaging of Zn/PPi in zebrafish larvae. Further, PPi detection characteristics of zinc ensembles were established for the sensing of PPi discharged from DNA synthesis and other biological reactions.
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http://dx.doi.org/10.1016/j.aca.2019.12.061DOI Listing
March 2020

Diversion of Catalytic C-N Bond Formation to Catalytic Oxidation of NH through Modification of the Hydrogen Atom Abstractor.

J Am Chem Soc 2020 02 7;142(7):3361-3365. Epub 2020 Feb 7.

Center for Molecular Electrocatalysis , Pacific Northwest National Laboratory , Richland , Washington 99352 , United States.

We report that (TMPRu(NH) (TMP = tetramesitylporphryin) is a molecular catalyst for oxidation of ammonia to dinitrogen. An aryloxy radical, tri--butylphenoxyl (·), abstracts H atoms from a bound ammonia ligand of (TMP)Ru(NH), leading to the discovery of a new catalytic C-N coupling to the para position of · to form 4-amino-2,4,6-tri--butylcyclohexa-2,5-dien-1-one. Modification of the aryloxy radical to 2,6-di--butyl-4-tritylphenoxyl radical, which contains a trityl group at the para position, prevents C-N coupling and diverts the reaction to catalytic oxidation of NH to give N. We achieved 125 ± 5 turnovers at 22 °C for oxidation of NH, the highest turnover number (TON) reported to date for a molecular catalyst.
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http://dx.doi.org/10.1021/jacs.9b13706DOI Listing
February 2020

Atomically Defined Nanopropeller FeCoSe(PhPNTol): Functional Model for the Electronic Metal-Support Interaction Effect and High Catalytic Activity for Carbodiimide Formation.

J Am Chem Soc 2019 12 5;141(50):19605-19610. Epub 2019 Dec 5.

Department of Chemistry , University of Washington , Seattle , Washington 98195 , United States.

Atomically defined interfaces that maximize the density of active sites and harness the electronic metal-support interaction are desirable to facilitate challenging multielectron transformations, but their synthesis remains a considerable challenge. We report the rational synthesis of the atomically defined metal chalcogenide nanopropeller FeCoSeL (L = PhPNTol) featuring three Fe edge sites, and its ensuing catalytic activity for carbodiimide formation. The complex interaction between the Fe edges and CoSe support, including the interplay between oxidation state, substrate coordination, and metal-support interaction, is probed in detail using chemical and electrochemical methods, extensive single crystal X-ray diffraction, and electronic absorption and Mössbauer spectroscopy.
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http://dx.doi.org/10.1021/jacs.9b12473DOI Listing
December 2019

Triple hydrogen atom abstraction from Mn-NH complexes results in cyclophosphazenium cations.

Chem Commun (Camb) 2019 Nov;55(93):14058-14061

Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory P.O. Box 999, Richland, WA 99352, USA.

All hydrogen atoms of the NH3 in [Mn(depe)2(CO)(NH3)]+ are abstracted by 2,4,6-tri-tert-butylphenoxyl radical, resulting in the isolation of a rare cyclophosphazenium cation, [(Et2P(CH2)2PEt2)N]+, in 76% yield. An analogous reaction is observed for [Mn(dppe)2(CO)(NH3)]+. Computations suggest insertion of NHx into a Mn-P bond provides the thermodynamic driving force. Contextualization of this reaction provides insights on catalyst design and breaking strong N-H bonds.
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http://dx.doi.org/10.1039/c9cc06915aDOI Listing
November 2019

Chemistry of mixed-ligand oxidovanadium(IV) complexes of aroylhydrazones incorporating quinoline derivatives: Study of solution behavior, theoretical evaluation and protein/DNA interaction.

J Inorg Biochem 2019 10 22;199:110786. Epub 2019 Jul 22.

Department of Chemistry, National Institute of Technology, Rourkela, 769008, Odisha, India. Electronic address:

A series of eight hexacoordinated mixed-ligand oxidovanadium(IV) complexes [VO(L)(L)] (1-8), where L = L - L are four differently substituted ONO donor aroylhydrazone ligands and L are N,N-donor bases like 2,2'-bipyridine (bipy) (1, 3, 5 and 7) and 1,10-phenanthroline (phen) (2, 4, 6 and 8), have been reported. All synthesized complexes have been characterized by various physicochemical techniques and molecular structures of 1 and 6 were determined by X-ray crystallography. With a view to evaluate the biological activity of the VO species, the behavior of the systems VO/L, VO/L/bipy and VO/L/phen was studied as a function of pH in a mixture of HO/DMSO 50/50 (v/v). DFT calculations allowed finding out the relative stability of the tautomeric forms of the ligands, and predicting the structure of vanadium complexes and their EPR parameters. To study their interaction with proteins, firstly the ternary systems VO/L with 1-methylimidazole, which is a good model for histidine binding, were examined. Subsequently the interaction of the complexes with lysozyme (Lyz), cytochrome c (Cyt) and bovine serum albumin (BSA) was studied. The results indicate that the complexes showed moderate binding affinity towards BSA, while no interaction takes place with lysozyme and cytochrome c. This could be explained with the higher number of accessible coordinating and polar residues for BSA than for Lyz and Cyt. Further, the complexes were also evaluated for their DNA binding propensity through UV-vis absorption titration and fluorescence spectral studies. These results were consistent with BSA binding affinity and showed moderate binding affinity towards CT-DNA.
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http://dx.doi.org/10.1016/j.jinorgbio.2019.110786DOI Listing
October 2019

Geometric and electronic structure of a crystallographically characterized thiolate-ligated binuclear peroxo-bridged cobalt(III) complex.

J Biol Inorg Chem 2019 09 24;24(6):919-926. Epub 2019 Jul 24.

The Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA.

In order to shed light on metal-dependent mechanisms for O-O bond cleavage, and its microscopic reverse, we compare herein the electronic and geometric structures of O-derived binuclear Co(III)- and Mn(III)-peroxo compounds. Binuclear metal peroxo complexes are proposed to form as intermediates during Mn-promoted photosynthetic HO oxidation, and a Co-containing artificial leaf inspired by nature's photosynthetic HO oxidation catalyst. Crystallographic characterization of an extremely activated peroxo is made possible by working with substitution-inert, low-spin Co(III). Density functional theory (DFT) calculations show that the frontier orbitals of the Co(III)-peroxo compound differ noticeably from the analogous Mn(III)-peroxo compound. The highest occupied molecular orbital (HOMO) associated with the Co(III)-peroxo is more localized on the peroxo in an antibonding π*(O-O) orbital, whereas the HOMO of the structurally analogous Mn(III)-peroxo is delocalized over both the metal d-orbitals and peroxo π*(O-O) orbital. With low-spin d Co(III), filled t orbitals prevent π-back-donation from the doubly occupied antibonding π*(O-O) orbital onto the metal ion. This is not the case with high-spin d Mn(III), since these orbitals are half-filled. This weakens the peroxo O-O bond of the former relative to the latter.
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http://dx.doi.org/10.1007/s00775-019-01686-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6948190PMC
September 2019

Hydrogenolysis of Dinuclear PCN Ligated Pd μ-Hydroxides and Their Mononuclear Pd Hydroxide Analogues.

Chemistry 2019 Jul 3;25(42):9920-9929. Epub 2019 Jul 3.

Department of Chemistry, University of Washington, Box 351700, Seattle, Washington, 98195-1700, USA.

The hydrogenolysis of mono- and dinuclear Pd hydroxides was investigated both experimentally and computationally. It was found that the dinuclear μ-hydroxide complexes {[(PCN )Pd] (μ-OH)}(OTf) (PCN =1-[3-[(di-tert-butylphosphino)methyl]phenyl]-1H-pyrazole; PCN =1-[3-[(di-tert-butylphosphino)methyl]phenyl]-5-methyl-1H-pyrazole) react with H to form the analogous dinuclear hydride species {[(PCN )Pd] (μ-H)}(OTf). The dinuclear μ-hydride complexes were fully characterized, and are rare examples of structurally characterized unsupported singly bridged μ-H Pd dimers. The {[(PCN )Pd] (μ-OH)}(OTf) hydrogenolysis mechanism was investigated through experiments and computations. The hydrogenolysis of the mononuclear complex (PCN )Pd-OH resulted in a mixed ligand dinuclear species [(PCN )Pd](μ-H)[(PCC)Pd] (PCC=a dianionic version of PCN bound through phosphorus P, aryl C, and pyrazole C atoms) generated from initial ligand "rollover" C-H activation. Further exposure to H yields the bisphosphine Pd complex Pd[(H)PCN ] . When the ligand was protected at the pyrazole 5-position in the (PCN )Pd-OH complex, no hydride formed under the same conditions; the reaction proceeded directly to the bisphosphine Pd complex Pd[(H)PCN ] . Reaction mechanisms for the hydrogenolysis of the monomeric and dimeric hydroxides are proposed.
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http://dx.doi.org/10.1002/chem.201900507DOI Listing
July 2019

DANPY (dimethylaminonaphthylpyridinium): an economical and biocompatible fluorophore.

Org Biomol Chem 2019 04;17(15):3765-3780

Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195, USA.

Dyes with nonlinear optical (NLO) properties enable new imaging techniques and photonic systems. We have developed a dye (DANPY-1) for photonics applications in biological substrates such as nucleic acids; however, the design specification also enables it to be used for visualizing biomolecules. It is a prototype dye demonstrating a water-soluble, NLO-active fluorophore with high photostability, a large Stokes shift, and a favorable toxicity profile. A practical and scalable synthetic route to DANPY salts has been optimized featuring: (1) convergent Pd-catalyzed Suzuki coupling with pyridine 4-boronic acid, (2) site-selective pyridyl N-methylation, and (3) direct recovery of crystalline intermediates without chromatography. We characterize the optical properties, biocompatibility, and biological staining behavior of DANPY-1. In addition to stability and solubility across a range of polar media, the DANPY-1 chromophore shows a first hyperpolarizability similar to common NLO dyes such as Disperse Red 1 and DAST, a large two-photon absorption cross section for its size, substantial affinity to nucleic acids in vitro, an ability to stain a variety of cellular components, and strong sensitivity of its fluorescence properties to its dielectric environment.
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http://dx.doi.org/10.1039/c8ob02536cDOI Listing
April 2019

Sodium-coupled electron transfer reactivity of metal-organic frameworks containing titanium clusters: the importance of cations in redox chemistry.

Chem Sci 2019 Feb 19;10(5):1322-1331. Epub 2018 Nov 19.

Department of Chemistry , University of Washington , Box 351700 , Seattle , Washington 98195-1700 , USA.

Stoichiometric reduction reactions of two metal-organic frameworks (MOFs) by the solution reagents (M = Cr, Co) are described. The two MOFs contain clusters with TiO rings: TiO(OH)(bdc); bdc = terephthalate (MIL-125) and TiO(OH)(bdc-NH); bdc-NH = 2-aminoterephthalate (NH-MIL-125). The stoichiometry of the redox reactions was probed using solution NMR methods. The extent of reduction is greatly enhanced by the presence of Na, which is incorporated into the bulk of the material. The roughly 1 : 1 stoichiometry of electrons and cations indicates that the storage of e in the MOF is tightly coupled to a cation within the architecture, for charge balance.
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http://dx.doi.org/10.1039/c8sc04138eDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6354900PMC
February 2019

Anionic Dinuclear Oxidovanadium(IV) Complexes with Azo Functionalized Tridentate Ligands and μ-Ethoxido Bridge Leading to an Unsymmetric Twisted Arrangement: Synthesis, X-ray Structure, Magnetic Properties, and Cytotoxicity.

Inorg Chem 2018 May 9;57(10):5767-5781. Epub 2018 May 9.

Department of Chemistry , University of Washington , Seattle , Washington 98195 , United States.

The synthesis of ethoxido-bridged dinuclear oxidovanadium(IV) complexes of the general formula (HNEt)[(VOL)(μ-OEt)] (1-3) with the azo dyes 2-(2'-carboxy-5'-X-phenylazo)-4-methylphenol (HL, X = H; HL, X = NO) and 2-(2'-carboxy-5'-Br-phenylazo)-2-naphthol (HL) as ligands is reported. The ligands differ in the substituents at the phenyl ring to probe their influence on the redox behavior, biological activity, and magnetochemistry of the complexes, for which the results are presented and discussed. All synthesized ligands and vanadium(IV) complexes have been characterized by various physicochemical techniques, namely, elemental analysis, electrospray ionization mass spectrometry, spectroscopic methods (UV/vis and IR), and cyclic voltammetry. X-ray crystallography of 1 and 3 revealed the presence of a twisted arrangement of the edged-shared bridging core unit. In agreement with the distorted nature of the twisted core, antiferromagnetic exchange interactions were observed between the vanadium(IV) centers of the dinuclear complexes with a superexchange mechanism operative. These results have been verified by DFT calculations. The complexes were also screened for their in vitro cytotoxicity against HeLa and HT-29 cancer cell lines. The results indicated that all the synthesized vanadium(IV) complexes (1-3) were cytotoxic in nature and were specific to a particular cell type. Complex 1 was found to be the most potent against HeLa cells (IC value 1.92 μM).
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http://dx.doi.org/10.1021/acs.inorgchem.8b00035DOI Listing
May 2018

How Do Ring Size and π-Donating Thiolate Ligands Affect Redox-Active, α-Imino-N-heterocycle Ligand Activation?

Inorg Chem 2018 Feb 7;57(4):1935-1949. Epub 2018 Feb 7.

The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.

Considerable effort has been devoted to the development of first-row transition-metal catalysts containing redox-active imino-pyridine ligands that are capable of storing multiple reducing equivalents. This property allows abundant and inexpensive first-row transition metals, which favor sequential one-electron redox processes, to function as competent catalysts in the concerted two-electron reduction of substrates. Herein we report the syntheses and characterization of a series of iron complexes that contain both π-donating thiolate and π-accepting (α-imino)-N-heterocycle redox-active ligands, with progressively larger N-heterocycle rings (imidazole, pyridine, and quinoline). A cooperative interaction between these complementary redox-active ligands is shown to dictate the properties of these complexes. Unusually intense charge-transfer (CT) bands, and intraligand metrical parameters, reminiscent of a reduced (α-imino)-N-heterocycle ligand (L), initially suggested that the electron-donating thiolate had reduced the N-heterocycle. Sulfur K-edge X-ray absorption spectroscopic (XAS) data, however, provides evidence for direct communication, via backbonding, between the thiolate sulfur and the formally orthogonal (α-imino)-N-heterocycle ligand π*-orbitals. DFT calculations provide evidence for extensive delocalization of bonds over the sulfur, iron, and (α-imino)-N-heterocycle, and TD-DFT shows that the intense optical CT bands involve transitions between a mixed Fe/S donor, and (α-imino)-N-heterocycle π*-acceptor orbital. The energies and intensities of the optical and S K-edge pre-edge XAS transitions are shown to correlate with N-heterocycle ring size, as do the redox potentials. When the thiolate is replaced with a thioether, or when the low-spin S = 0 Fe(II) is replaced with a high-spin S = 3/2 Co(II), the N-heterocycle ligand metrical parameters and electronic structure do not change relative to the neutral L ligand. With respect to the development of future catalysts containing redox-active ligands, the energy cost of storing reducing equivalents is shown to be lowest when a quinoline, as opposed to imidazole or pyridine, is incorporated into the ligand backbone of the corresponding Fe complex.
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http://dx.doi.org/10.1021/acs.inorgchem.7b02748DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8312276PMC
February 2018

Catalytic Hydroalkylation of Allenes.

Angew Chem Int Ed Engl 2017 12 13;56(49):15703-15707. Epub 2017 Nov 13.

Department of Chemistry, University of Washington, Seattle, WA, 98195, USA.

We have developed a catalytic method for the hydroalkylation of allenes using alkyl triflates as electrophiles and silane as a hydride source. The reaction has an excellent substrate scope and is compatible with a wide range of functional groups, including esters, aryl halides, aryl boronic esters, sulfonamides, alkyl tosylates, and alkyl bromides. We found evidence for a reaction mechanism that involves unusual dinuclear copper ally complexes as catalytic intermediates. The unusual structure of these complexes provides a rationale for their unexpected reactivity.
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http://dx.doi.org/10.1002/anie.201709144DOI Listing
December 2017

Monomeric and Dimeric Oxidomolybdenum(V and VI) Complexes, Cytotoxicity, and DNA Interaction Studies: Molybdenum Assisted C═N Bond Cleavage of Salophen Ligands.

Inorg Chem 2017 Sep 31;56(18):11190-11210. Epub 2017 Aug 31.

Department of Chemistry, National Institute of Technology , Rourkela 769008, Odisha, India.

Four novel dimeric bis-μ-imido bridged metal-metal bonded oxidomolybdenum(V) complexes [MoOL'] (1-4) (where L' are rearranged ligands formed in situ from HL) and a new mononuclear dioxidomolybdenum(VI) complex [MoOL] (5) synthesized from salen type NO ligands are reported. This rare series of imido-bridged complexes (1-4) have been furnished from rearranged HL' ligands, containing an aromatic diimine (o-phenylenediamine) "linker", where Mo assisted hydrolysis followed by -C═N bond cleavage of one of the arms of the ligand HL took place. A monomeric molybdenum(V) intermediate species [MoO(HL')(OEt)] (I) was generated in situ. The concomitant deprotonation and dimerization of two molybdenum(V) intermediate species (I) ultimately resulted in the formation of a bis-μ-imido bridge between the two molybdenum centers of [MoOL'] (1-4). The mechanism of formation of 1-4 has been discussed, and one of the rare intermediate monomeric molybdenum(V) species I has been isolated in the solid state and characterized. The monomeric dioxidomolybdenum(VI) complex [MoOL] (5) was prepared from the ligand HL where the aromatic "linker" was replaced by an aliphatic diimine (1,2-diaminopropane). All the ligands and complexes have been characterized by elemental analysis, IR, UV-vis spectroscopy, NMR, ESI-MS, and cyclic voltammetry, and the structural features of 1, 2, 4, and 5 have been solved by X-ray crystallography. The DNA binding and cleavage activity of 1-5 have been explored. The complexes interact with CT-DNA by the groove binding mode, and the binding constants range between 10 and 10 M. Fairly good photoinduced cleavage of pUC19 supercoiled plasmid DNA was exhibited by all the complexes, with 4 showing the most promising photoinduced DNA cleavage activity of ∼93%. Moreover, in vitro cytotoxic activity of all the complexes was evaluated by MTT assay, which reveals that the complexes induce cell death in MCF-7 (human breast adenocarcinoma) and HCT-15 (colon cancer) cell lines.
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http://dx.doi.org/10.1021/acs.inorgchem.7b01578DOI Listing
September 2017

3D Systems' Technology Overview and New Applications in Manufacturing, Engineering, Science, and Education.

3D Print Addit Manuf 2014 Sep;1(3):169-176

NASA Johnson Space Center, Houston, Texas.

Since the inception of 3D printing, an evolutionary process has taken place in which specific user and customer needs have crossed paths with the capabilities of a growing number of machines to create value-added businesses. Even today, over 30 years later, the growth of 3D printing and its utilization for the good of society is often limited by the various users' understanding of the technology for their specific needs. This article presents an overview of current 3D printing technologies and shows numerous examples from a multitude of fields from manufacturing to education.
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http://dx.doi.org/10.1089/3dp.2014.1502DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5363289PMC
September 2014

Sterically directed nitronate complexes of 2,6-di-tert-butyl-4-nitrophenoxide with Cu(ii) and Zn(ii) and their H-atom transfer reactivity.

Dalton Trans 2017 Feb;46(8):2551-2558

Department of Chemistry, University of Washington, Box 351700, Seattle, Washington 98195-1700, USA and Department of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520, USA.

The bulky 2,6-di-tert-butyl-4-nitrophenolate ligand forms complexes with [TpCu] and [TpZn] binding via the nitro group in an unusual nitronato-quinone resonance form (Tp = hydro-tris(3-tert-butyl-pyrazol-1-yl)borate). The Cu complex in the solid state has a five-coordinate κ-nitronate structure, while the Zn analogue has a four-coordinate κ-nitronate ligand. 4-Nitrophenol, without the 2,6-di-tert-butyl substituents, instead binds to [TpCu] through the phenolate oxygen. This difference in binding is very likely due to the steric difficulty in binding a 2,6-di-tert-butyl-phenolate ligand to the [TpM] unit. TpCu(κ-ONBuCHO) reacts with the hydroxylamine TEMPO-H (2,2,6,6-tetramethylpiperidin-1-ol) by abstracting a hydrogen atom. This system thus shows an unusual sterically enforced transition metal-ligand binding motif and a copper-phenolate interaction that differs from what is typically observed in biological and chemical catalysis.
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http://dx.doi.org/10.1039/c6dt04427aDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5385262PMC
February 2017

Metal-Assisted Oxo Atom Addition to an Fe(III) Thiolate.

J Am Chem Soc 2017 01 29;139(1):119-129. Epub 2016 Dec 29.

The Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States.

Cysteinate oxygenation is intimately tied to the function of both cysteine dioxygenases (CDOs) and nitrile hydratases (NHases), and yet the mechanisms by which sulfurs are oxidized by these enzymes are unknown, in part because intermediates have yet to be observed. Herein, we report a five-coordinate bis-thiolate ligated Fe(III) complex, [Fe(SN(Pr,Pr))] (2), that reacts with oxo atom donors (PhIO, IBX-ester, and HO) to afford a rare example of a singly oxygenated sulfenate, [Fe(η-SO)(S)N(Pr,Pr)] (5), resembling both a proposed intermediate in the CDO catalytic cycle and the essential NHase Fe-S(O) proposed to be intimately involved in nitrile hydrolysis. Comparison of the reactivity of 2 with that of a more electron-rich, crystallographically characterized derivative, [FeSNN(Pr,Pr)] (8), shows that oxo atom donor reactivity correlates with the metal ion's ability to bind exogenous ligands. Density functional theory calculations suggest that the mechanism of S-oxygenation does not proceed via direct attack at the thiolate sulfurs; the average spin-density on the thiolate sulfurs is approximately the same for 2 and 8, and Mulliken charges on the sulfurs of 8 are roughly twice those of 2, implying that 8 should be more susceptible to sulfur oxidation. Carboxamide-ligated 8 is shown to be unreactive towards oxo atom donors, in contrast to imine-ligated 2. Azide (N) is shown to inhibit sulfur oxidation with 2, and a green intermediate is observed, which then slowly converts to sulfenate-ligated 5. This suggests that the mechanism of sulfur oxidation involves initial coordination of the oxo atom donor to the metal ion. Whether the green intermediate is an oxo atom donor adduct, Fe-O═I-Ph, or an Fe(V)═O remains to be determined.
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http://dx.doi.org/10.1021/jacs.6b03512DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5262503PMC
January 2017

A Triazolopyrimidine-Based Dihydroorotate Dehydrogenase Inhibitor with Improved Drug-like Properties for Treatment and Prevention of Malaria.

ACS Infect Dis 2016 12 4;2(12):945-957. Epub 2016 Oct 4.

Medicines for Malaria Venture , 1215 Geneva, Switzerland.

The emergence of drug-resistant malaria parasites continues to hamper efforts to control this lethal disease. Dihydroorotate dehydrogenase has recently been validated as a new target for the treatment of malaria, and a selective inhibitor (DSM265) of the Plasmodium enzyme is currently in clinical development. With the goal of identifying a backup compound to DSM265, we explored replacement of the SF-aniline moiety of DSM265 with a series of CF-pyridinyls while maintaining the core triazolopyrimidine scaffold. This effort led to the identification of DSM421, which has improved solubility, lower intrinsic clearance, and increased plasma exposure after oral dosing compared to DSM265, while maintaining a long predicted human half-life. Its improved physical and chemical properties will allow it to be formulated more readily than DSM265. DSM421 showed excellent efficacy in the SCID mouse model of P. falciparum malaria that supports the prediction of a low human dose (<200 mg). Importantly DSM421 showed equal activity against both P. falciparum and P. vivax field isolates, while DSM265 was more active on P. falciparum. DSM421 has the potential to be developed as a single-dose cure or once-weekly chemopreventative for both P. falciparum and P. vivax malaria, leading to its advancement as a preclinical development candidate.
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http://dx.doi.org/10.1021/acsinfecdis.6b00144DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5148661PMC
December 2016

Synthesis, Radical Reactivity, and Thermochemistry of Monomeric Cu(II) Alkoxide Complexes Relevant to Cu/Radical Alcohol Oxidation Catalysis.

Inorg Chem 2016 Jun 12;55(11):5467-75. Epub 2016 May 12.

Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195, United States.

Two new monomeric Cu(II) alkoxide complexes were prepared and fully characterized as models for intermediates in copper/radical mediated alcohol oxidation catalysis: Tp(tBuR)Cu(II)OCH2CF3 with Tp(tBu) = hydro-tris(3-tert-butyl-pyrazol-1-yl)borate 1 or Tp(tBuMe) = hydro-tris(3-tert-butyl-5-methyl-pyrazol-1-yl)borate 2. These complexes were made as models for potential intermediates in enzymatic and synthetic catalytic cycles for alcohol oxidation. However, the alkoxide ligands are not readily oxidized by loss of H; instead, these complexes were found to be hydrogen atom acceptors. They oxidize the hydroxylamine TEMPOH, 2,4,6-tri-t-butylphenol, and 1,4-cyclohexadiene to the nitroxyl radical, phenoxyl radical, and benzene, with formation of HOCH2CF3 (TFE) and the Cu(I) complexes Tp(tBuR)Cu(I)-MeCN in dichloromethane/1% MeCN or 1/2 [Tp(tBuR)Cu(I)]2 in toluene. On the basis of thermodynamics and kinetics arguments, these reactions likely proceed through concerted proton-electron transfer mechanisms. Thermochemical analyses give lower limits for the "effective bond dissociation free energies (BDFE)" of the O-H bonds in 1/2[Tp(tBuR)Cu(I)]2 + TFE and upper limits for the free energies associated with alkoxide oxidations via hydrogen atom transfer (effective alkoxide α-C-H BDFEs). These values are summations of the free energies of multiple chemical steps, which include the energetically favorable formation of 1/2[Tp(tBuR)Cu(I)]2. The effective alkoxide α-C-H bonds are very weak, BDFE ≤ 38 ± 4 kcal mol(-1) for 1 and ≤44 ± 5 kcal mol(-1) for 2 (gas-phase estimates), because C-H homolysis is thermodynamically coupled to one electron transfer to Cu(II) as well as the favorable formation of the 1/2[Tp(tBuR)Cu(I)]2 dimer. Treating 1 with the H atom acceptor (t)Bu3ArO(•) did not result in the expected alkoxide oxidation to an aldehyde, but rather net 2,2,2-trifluoroethoxyl radical transfer occurred to generate an unusual 2-substituted dienone-ether product. Treating 2 with (t)Bu3ArO(•) gives no reaction, despite evidence that overall ligand oxidation and formation of 1/2[Tp(tBuMe)Cu(I)]2 is significantly exoergic. The origin of this lack of reactivity may be due to insufficient weakening of the alcohol α-C-H bond upon complexation to copper.
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http://dx.doi.org/10.1021/acs.inorgchem.6b00491DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4971887PMC
June 2016
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