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    The structure of plastocyanin tunes the midpoint potential by restricting axial ligation of the reduced copper ion
    (Springer Nature, 2023-08-23) Mammoser, Claire C.; LeMasters, Brynn E.; Edwards, Sydney G.; McRae, Emma M.; Mullins, M. Hunter; Wang, Yiqi; Garcia, Nicholas M.; Edmonds, Katherine A.; Giedroc, David P.; Thielges, Megan C.; Chemistry and Chemical Biology, School of Science
    Blue copper proteins are models for illustrating how proteins tune metal properties. Nevertheless, the mechanisms by which the protein controls the metal site remain to be fully elucidated. A hindrance is that the closed shell Cu(I) site is inaccessible to most spectroscopic analyses. Carbon deuterium (C-D) bonds used as vibrational probes afford nonperturbative, selective characterization of the key cysteine and methionine copper ligands in both redox states. The structural integrity of Nostoc plastocyanin was perturbed by disrupting potential hydrogen bonds between loops of the cupredoxin fold via mutagenesis (S9A, N33A, N34A), variably raising the midpoint potential. The C-D vibrations show little change to suggest substantial alteration to the Cu(II) coordination in the oxidized state or in the Cu(I) interaction with the cysteine ligand. They rather indicate, along with visible and NMR spectroscopy, that the methionine ligand distinctly interacts more strongly with the Cu(I) ion, in line with the increases in midpoint potential. Here we show that the protein structure determines the redox properties by restricting the interaction between the methionine ligand and Cu(I) in the reduced state.
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    Studies into exfoliation and coating of Egyptian blue in methanol for application to the detection of latent fingermarks
    (Elsevier, 2022-07) Shahbazi, Sorour; Goodpaster, John V.; Smith, Gregory D.; Becker, Thomas; Lewis, Simon W.; Chemistry and Chemical Biology, School of Science
    We have recently demonstrated that coated exfoliated Egyptian blue powder is effective for detecting latent fingermarks on a range of highly-patterned non-porous and semi-porous surfaces. In this extension of that work, we present our studies into an alternative approach to prepare exfoliated Egyptian blue coated with cetrimonium bromide and Tween® 20 using a simpler technique. The quality of the latent fingermarks developed with these exfoliated powders and the commercial powder were compared in a comprehensive study. Depletion series of natural fingermarks from a wide range of donors (12 males and females) deposited on non-porous (glass slides) and semi-porous (Australian banknotes) surfaces were used in this study. Enhancement in the performance of the coated exfoliated particles compared to the commercial powder was observed, particularly in the case of aged fingermarks and polymer banknotes as challenging substrates.
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    Methods to Detect Volatile Organic Compounds for Breath Biopsy Using Solid-Phase Microextraction and Gas Chromatography–Mass Spectrometry
    (MDPI, 2023-06-03) Schulz, Eray; Woollam, Mark; Grocki, Paul; Davis, Michael D.; Agarwal, Mangilal; Chemistry and Chemical Biology, School of Science
    Volatile organic compounds (VOCs) are byproducts from metabolic pathways that can be detected in exhaled breath and have been reported as biomarkers for different diseases. The gold standard for analysis is gas chromatography–mass spectrometry (GC–MS), which can be coupled with various sampling methods. The current study aims to develop and compare different methods for sampling and preconcentrating VOCs using solid-phase microextraction (SPME). An in-house sampling method, direct-breath SPME (DB–SPME), was developed to directly extract VOCs from breath using a SPME fiber. The method was optimized by exploring different SPME types, the overall exhalation volume, and breath fractionation. DB–SPME was quantitatively compared to two alternative methods involving the collection of breath in a Tedlar bag. In one method, VOCs were directly extracted from the Tedlar bag (Tedlar–SPME) and in the other, the VOCs were cryothermally transferred from the Tedlar bag to a headspace vial (cryotransfer). The methods were verified and quantitatively compared using breath samples (n = 15 for each method respectively) analyzed by GC–MS quadrupole time-of-flight (QTOF) for compounds including but not limited to acetone, isoprene, toluene, limonene, and pinene. The cryotransfer method was the most sensitive, demonstrating the strongest signal for the majority of the VOCs detected in the exhaled breath samples. However, VOCs with low molecular weights, including acetone and isoprene, were detected with the highest sensitivity using the Tedlar–SPME. On the other hand, the DB–SPME was less sensitive, although it was rapid and had the lowest background GC–MS signal. Overall, the three breath-sampling methods can detect a wide variety of VOCs in breath. The cryotransfer method may be optimal when collecting a large number of samples using Tedlar bags, as it allows the long-term storage of VOCs at low temperatures (−80 °C), while Tedlar–SPME may be more effective when targeting relatively small VOCs. The DB-SPME method may be the most efficient when more immediate analyses and results are required.
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    Two distinct rotations of bithiazole DNA intercalation revealed by direct comparison of crystal structures of Co(III)•bleomycin A2 and B2 bound to duplex 5’-TAGTT sites
    (Elsevier, 2023-01-01) Goodwin, Kristie D.; Lewis, Mark A.; Long, Eric C.; Georgiadis, Millie M.; Chemistry and Chemical Biology, School of Science
    Bleomycins constitute a family of anticancer natural products that bind DNA through intercalation of a C-terminal tail/bithiazole moiety and hydrogen-bonding interactions between the remainder of the drug and the minor groove. The clinical utility of the bleomycins is believed to result from single- and double-strand DNA cleavage mediated by the HOO-Fe(III) form of the drug. The bleomycins also serve as a model system to understand the nature of complex drug-DNA interactions that may guide future DNA-targeted drug discovery. In this study, the impact of the C-terminal tail on bleomycin-DNA interactions was investigated. Toward this goal, we determined two crystal structures of HOO-Co(III)•BLMA2 “green” (a stable structural analogue of the active HOO-Fe(III) drug) bound to duplex DNA containing 5′-TAGTT, one in which the entire drug is bound (fully bound) and a second with only the C-terminal tail/bithiazole bound (partially bound). The structures reported here were captured by soaking HOO-Co(III)•BLMA2 into preformed host–guest crystals including a preferred DNA-binding site. While the overall structure of DNA-bound BLMA2 was found to be similar to those reported earlier at the same DNA site for BLMB2, the intercalated bithiazole of BLMB2 is “flipped” 180˚ relative to DNA-bound BLMA2. This finding highlights an unidentified role for the C-terminal tail in directing the intercalation of the bithiazole. In addition, these analyses identified specific bond rotations within the C-terminal domain of the drug that may be relevant for its reorganization and ability to carry out a double-strand DNA cleavage event.
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    Metal-free visible-light-promoted C(sp3)-H functionalization of aliphatic cyclic ethers using trace O2
    (Royal Society of Chemistry, 2021) Niu, Ben; Blackburn, Bryan G.; Sachidanandan, Krishnakumar; Cooke, Maria Victoria; Laulhé, Sébastien; Chemistry and Chemical Biology, School of Science
    Presented is a light-promoted C-C bond forming reaction yielding sulfone and phosphate derivatives at room temperature in the absence of metals or photoredox catalyst. This transformation proceeds in neat conditions through an auto-oxidation mechanism which is maintained through the leaching of trace amounts of O2 as sole green oxidant.
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    Synthesis of Imide and Amine Derivatives via Deoxyamination of Alcohols Using N-Haloimides and Triphenylphosphine
    (Wiley, 2021) Irving, Charles D.; Floreancig, Jack T.; Gasonoo, Makafui; Kelley, Alexandra S.; Laulhé, Sébastien; Chemistry and Chemical Biology, School of Science
    A deoxyamination methodology of activated and unactivated alcohols is presented. The reaction is mediated by phosphonium intermediates generated in situ from N-haloimides and triphenylphosphine. The protocol allows for the synthesis of phthalimide and amine derivatives in moderate to good yields at room temperature. A series of NMR experiments have provided insight into the reactive intermediates involved and the mechanism of this deoxyamination reaction.
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    Transition-Metal-Free Photoredox Phosphonation of Aryl C–N and C–X Bonds in Aqueous Solvent Mixtures
    (American Chemical Society, 2022) Pan, Lei; Kelley, Alexandra S.; Cooke, Maria Victoria; Deckert, Macy M.; Laulhé, Sébastien; Chemistry and Chemical Biology, School of Science
    Herein, we present an efficient and mild methodology for the synthesis of aromatic phosphonate esters in good to excellent yields using 10H-phenothiazine, an inexpensive commodity chemical, as a photoredox catalyst. The reaction exhibits wide functional group compatibility enabling the transformation in the presence of ketone, amide, ester, amine, and alcohol moieties. Importantly, the reaction proceeds using a green solvent mixture primarily composed of water, thus lowering the environmental footprint of this transformation compared to current methods. The transformation also proceeds under atmospheric conditions, which further differentiates it from current methods that require inert atmosphere. Mechanistic work using fluorescence quenching experiments and radical trapping approaches support the proposed mechanism.
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    Design of Anisotropically Shaped Plasmonic Nanocrystals from Ultrasmall Sn-Decorated In2O3 Nanoclusters Used as Seed Materials
    (American Chemical Society, 2022-12-07) Davis, Gregory A., Jr.; Prusty, Gyanaranjan; Hati, Sumon; Lee, Jacob T.; Langlais, Sarah R.; Zhan , Xun; Sardar, Rajesh; Chemistry and Chemical Biology, School of Science
    Ultrasmall inorganic nanoclusters (<2.0 nm in diameter) bridge the gap between individual molecules and large nanocrystals (NCs) and provide the critical foundation to design and prepare new solid-state nanomaterials with previously unknown properties and functions. Herein, for the first time, we report the monodispersed colloidal synthesis and successful isolation of metastable, rhombohedral-phase, <2.0 nm indium oxide (In2O3) nanoclusters. Ultrasmall nanocluster formation is controlled by a kinetically driven growth process, as evaluated through the variation of metal-to-passivating ligand concentrations. Although <2.0 nm-diameter In2O3 nanoclusters are synthesized in the presence of tin (Sn) precursors, they do not display typical localized surface plasmon resonance (LSPR) properties, which are commonly observed in Sn-doped In2O3 (Sn:In2O3) NCs. Our Raman and X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy (HRTEM) analyses support the existence of Sn-decorated In2O3 nanoclusters, where Sn complexes reside on the surface of the nanocluster as Z-type ligands, as opposed to the formation of Sn:In2O3 nanoclusters, which behave as wide band gap (∼5.5 eV) nanomaterials. The experimentally determined band gap is in good agreement with the theoretical effective mass calculations. The newly synthesized Sn-decorated, 1.7 nm-diameter In2O3 nanoclusters are further used as reactive monomers for the seeded growth synthesis of bcc-phase, plasmonic Sn:In2O3 NCs via ex situ injection of In precursors without the addition of any Sn precursors. The LSPR peak of Sn:In2O3 NCs, which appear to form nanoflower assemblies, is tunable in the 1800–4000 nm region and possibly even the deep-IR region. In addition to altering the size and assembly of the spherical Sn:In2O3 NCs by introducing different amounts of indium acetylacetonate, injection of indium chloride precursors in the reaction mixture results in the formation of rod-shaped NCs. Surprisingly, Sn-decorated, <1.5 nm-diameter In2O3 nanoclusters do not grow into large plasmonic Sn:In2O3 NCs. Taken together, the results presented here contribute to the fundamental understanding of the surface free energy of ultrasmall metal oxide nanoclusters and further advance the knowledge on the phase transformation and growth of plasmonic NCs.
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    Inorganic–Organic Interfacial Electronic Effects in Ligand-Passivated WO3–x Nanoplatelets Induce Tunable Plasmonic Properties for Smart Windows
    (ACS, 2022-07-06) Lee, Jacob T.; Das, Debabrata; Davis, Gregory A., Jr.; Hati, Sumon; Ramana, C. V.; Sardar, Rajesh; Chemistry and Chemical Biology, School of Science
    Transition-metal oxide (TMO) nanocrystals (NCs), displaying localized surface plasmon resonance (LSPR) properties, are an emerging class of nanomaterials due to their high stability, high earth abundance, and wide range of spectral responses covering the near-to-far infrared region of the solar spectrum. Although surface passivating ligands are ubiquitous to colloidal NC-based research, the role of ligands, specifically the impact of their chemical structure on the dielectric and LSPR properties of TMO NC films, has not been investigated in detail. Here, we report for the first time the chemical effects at the metal–ligand (inorganic–organic) interfaces influencing the optical constants and LSPR properties of thin films comprising highly oxygen-deficient, sub-stoichiometric, LSPR-active tungsten oxide (WO3–x) nanoplatelets (NPLs). We studied ligands with two different types of binding head groups, aromatic conjugation, and short and long hydrocarbon chains. Using density functional theory calculations, we determine that the changes in the interfacial dipole moments and polarizability control the permittivity at the interface, resulting in the alteration of dielectric and LSPR properties of ligand-passivated NPL in thin nanocrystalline films. The photochromic properties of WO3–x NPL passivated with different ligands in thin films have also been investigated to highlight the impact of interfacial permittivity caused by the chemical structures of passivating ligands. Taken together, this study provides a fundamental understanding of emerging properties at the metal–ligand interface that could be further optimized for energy efficiency in smart windows.
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    An Overview of α-Aminoalkyl Radical Mediated Halogen-Atom Transfer
    (Wiley, 2023-11-08) Sachidanandan, Krishnakumar; Niu, Ben; Laulhé, Sébastien; Chemistry and Chemical Biology, School of Science
    The merging of photocatalysis with halogen-atom transfer (XAT) processes has proven to be a versatile tool for the generation of carbon-centered radicals in organic synthesis. XAT processes are unique in that they generate radicals without requiring the use of strong reductants necessary for the traditional single electron transfer (SET) activation of halides. Pathways to achieve XAT in synthetic applications can be categorized into three major sections: i) heteroatom-based activators, ii) metal-based activators, and iii) carbon-based activators among which α-aminoalkyl radicals have taken the center stage. Access to these α-aminoalkyl radicals as XAT reagents has gained significant attention in the past few years due to the robustness of the reactions, the simplicity of the reagents required, and the broadness of their applications. Generation of these α-aminoalkyl radicals is simply achieved through the single electron oxidation of tertiary amines, which after deprotonation at the α-position generates the α-aminoalkyl radicals. Due to the wide scope of tertiary amines available and the tunable nucleophilicity of α-aminoalkyl radical formed, this strategy has become an attractive alternative to heteroatom/metal-based radicals for XAT. In this minireview, we focus our attention on recent (2020–2023) developments and uses of this robust technology to mediate XAT processes.