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Excited-State Identification of a Nickel-Bipyridine Photocatalyst by Time-Resolved X-ray Absorption Spectroscopy. J Phys Chem Lett 2024; 15:4976-4982. [PMID: 38691639 PMCID: PMC11089568 DOI: 10.1021/acs.jpclett.4c00226] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 03/18/2024] [Accepted: 04/16/2024] [Indexed: 05/03/2024]
Abstract
Photoassisted catalysis using Ni complexes is an emerging field for cross-coupling reactions in organic synthesis. However, the mechanism by which light enables and enhances the reactivity of these complexes often remains elusive. Although optical techniques have been widely used to study the ground and excited states of photocatalysts, they lack the specificity to interrogate the electronic and structural changes at specific atoms. Herein, we report metal-specific studies using transient Ni L- and K-edge X-ray absorption spectroscopy of a prototypical Ni photocatalyst, (dtbbpy)Ni(o-tol)Cl (dtb = 4,4'-di-tert-butyl, bpy = bipyridine, o-tol = ortho-tolyl), in solution. We unambiguously confirm via direct experimental evidence that the long-lived (∼5 ns) excited state is a tetrahedral metal-centered triplet state. These results demonstrate the power of ultrafast X-ray spectroscopies to unambiguously elucidate the nature of excited states in important transition-metal-based photocatalytic systems.
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2
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Palladium K-edge X-ray Absorption Spectroscopy Studies on Controlled Ligand Systems. Inorg Chem 2023; 62:21128-21137. [PMID: 38039413 DOI: 10.1021/acs.inorgchem.3c03032] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2023]
Abstract
X-ray absorption spectroscopy (XAS) is widely used across the life and physical sciences to identify the electronic properties and structure surrounding a specific element. XAS is less often used for the characterization of organometallic compounds, especially for sensitive and highly reactive species. In this study, we used solid- and solution-phase XAS to compare a series of 25 palladium complexes in controlled ligand environments. The compounds include palladium centers in the formal I, II, III, and IV oxidation states, supported by tridentate and tetradentate macrocyclic ligands, with different halide and methyl ligand combinations. The Pd K-edge energies increased not only upon oxidizing the metal center but also upon increasing the denticity of the ligand framework, substituting sigma-donating methyl groups with chlorides, and increasing the charge of the overall metal complex by replacing charged ligands with neutral ligands. These trends were then applied to characterize compounds whose oxidation states were otherwise unconfirmed.
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3
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Coordination Chemistry of Sulfur-Containing Bifunctional Chelators: Toward in Vivo Stabilization of 64Cu PET Imaging Agents for Alzheimer's Disease. Inorg Chem 2023; 62:20820-20833. [PMID: 38060375 DOI: 10.1021/acs.inorgchem.3c02929] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
The broader utilization of 64Cu positron emission tomography (PET) imaging agents has been hindered by the unproductive demetalation induced by bioreductants. To advance the development of 64Cu-based PET imaging tracers for Alzheimer's Disease (AD), there is a need for novel ligand design strategies. In this study, we developed sulfur-containing dithiapyridinophane (N2S2) bifunctional chelators (BFCs) as well as all nitrogen-based diazapyridinophane (N4) BFCs to compare their abilities to chelate Cu and target Aβ aggregates. Through spectrophotometric titrations and electrochemical measurements, we have demonstrated that the N2S2-based BFCs exhibit >10 orders of magnitude higher binding affinity toward Cu(I) compared to their N4-based counterparts, while both types of BFCs exhibit high stability constants toward Cu(II). Notably, solid state structures for both Cu(II) and Cu(I) complexes supported by the two ligand frameworks were obtained, providing molecular insights into their copper chelating abilities. Aβ binding experiments were conducted to study the structure-affinity relationship, and fluorescence microscopy imaging studies confirmed the selective labeling of the BFCs and their copper complexes. Furthermore, we investigated the potential of these ligands for the 64Cu-based PET imaging of AD through radiolabeling and autoradiography studies. We believe our findings provide molecular insights into the design of bifunctional Cu chelators that can effectively stabilize both Cu(II) and Cu(I) and, thus, can have significant implications for the development of 64Cu PET imaging as a diagnostic tool for AD.
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4
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Amphiphilic Molecules Exhibiting Zwitterionic Excited-State Intramolecular Proton Transfer and Near-Infrared Emission for the Detection of Amyloid β Aggregates in Alzheimer's Disease. Chemistry 2023; 29:e202302408. [PMID: 37616059 PMCID: PMC10840928 DOI: 10.1002/chem.202302408] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2023] [Revised: 08/23/2023] [Accepted: 08/24/2023] [Indexed: 08/25/2023]
Abstract
Chromophores with zwitterionic excited-state intramolecular proton transfer (ESIPT) have been shown to have larger Stock shifts and red-shifted emission wavelengths compared to the conventional π-delocalized ESIPT molecules. However, there is still a dearth of design strategies to expand the current library of zwitterionic ESIPT compounds. Herein, a novel zwitterionic excited-state intramolecular proton transfer system is reported, enabled by addition of 1,4,7-triazacyclononane (TACN) fragments on a dicyanomethylene-4H-pyran (DCM) scaffold. The solvent-dependent steady-state photophysical studies, pKa measurements, and computational analysis strongly support that the ESIPT process is more efficient with two TACN groups attached to the DCM scaffold and not affected by polar protic solvents. Impressively, compound DCM-OH-2-DT exhibits a near-infrared (NIR) emission at 740 nm along with an uncommonly large Stokes shift. Moreover, DCM-OH-2-DT shows high affinity towards soluble amyloid β (Aβ) oligomers in vitro and in 5xFAD mouse brain sections, and we have successfully applied DCM-OH-2-DT for the in vivo imaging of Aβ aggregates and demonstrated its potential use as an early diagnostic agent for AD. Overall, this study can provide a general molecular design strategy for developing new zwitterionic ESIPT compounds with NIR emission in vivo imaging applications.
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5
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Insights into the Mechanism of CO 2 Electroreduction by Molecular Palladium-Pyridinophane Complexes. Inorg Chem 2023; 62:16801-16809. [PMID: 37787756 DOI: 10.1021/acs.inorgchem.3c02236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
Herein, we report the synthesis, characterization, and electrocatalytic CO2 reduction activity of a series of Pd(II) complexes supported by tetradentate pyridinophane ligands. In particular, we focus on the electrocatalytic CO2 reduction activity of a Pd(II) complex supported by the mixed hard--soft donor ligand 2,11-dithia[3.3](2,6)pyridinophane (N2S2). We also provide spectroscopic evidence of a CO-induced decomposition pathway for the same catalyst, which provides insights into catalyst poisoning for molecular Pd CO2 reduction electrocatalysts.
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6
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Scrutinizing formally Ni IV centers through the lenses of core spectroscopy, molecular orbital theory, and valence bond theory. Chem Sci 2023; 14:6915-6929. [PMID: 37389249 PMCID: PMC10306094 DOI: 10.1039/d3sc02001k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2023] [Accepted: 05/30/2023] [Indexed: 07/01/2023] Open
Abstract
Nickel K- and L2,3-edge X-ray absorption spectra (XAS) are discussed for 16 complexes and complex ions with nickel centers spanning a range of formal oxidation states from II to IV. K-edge XAS alone is shown to be an ambiguous metric of physical oxidation state for these Ni complexes. Meanwhile, L2,3-edge XAS reveals that the physical d-counts of the formally NiIV compounds measured lie well above the d6 count implied by the oxidation state formalism. The generality of this phenomenon is explored computationally by scrutinizing 8 additional complexes. The extreme case of NiF62- is considered using high-level molecular orbital approaches as well as advanced valence bond methods. The emergent electronic structure picture reveals that even highly electronegative F-donors are incapable of supporting a physical d6 NiIV center. The reactivity of NiIV complexes is then discussed, highlighting the dominant role of the ligands in this chemistry over that of the metal centers.
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7
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Nickel-Carbon Bond Oxygenation with Green Oxidants via High-Valent Nickel Species. J Am Chem Soc 2023; 145:11161-11172. [PMID: 37183827 DOI: 10.1021/jacs.3c01012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Described herein is the synthesis of the NiII complex (tBuMe2tacn)NiII(cycloneophyl) (tBuMe2tacn = 1-tert-butyl-4,7-dimethyl-1,4,7-triazacyclononane, cycloneophyl = -CH2CMe2-o-C6H4-) and its reactivity with dioxygen and peroxides. The new tBuMe2tacn ligand is designed to enhance the oxidatively induced bond-forming reactivity of high-valent Ni intermediates. Tunable chemoselectivity for Csp2-O vs Csp2-Csp3 bond formation was achieved by selecting the appropriate solvent and reaction conditions. Importantly, the use of cumene hydroperoxide and meta-chloroperbenzoic acid suggests a heterolytic O-O bond cleavage upon reaction with (tBuMe2tacn)NiII(cycloneophyl). Mechanistic studies using isotopically labeled H2O2 support the generation of a high-valent Ni-oxygen species via an inner-sphere mechanism and subsequent reductive elimination to form the Csp2-O bond. Kinetic studies of the exceptionally fast Csp2-O bond-forming reaction reveal a first-order dependence on both (tBuMe2tacn)NiII(cycloneophyl) and H2O2, and thus an overall second-order reaction. Eyring analysis further suggests that the oxidation of the NiII complex by H2O2 is the rate-determining step, which can be modulated by the presence of coordinating solvents. Moreover, computational studies fully support the conclusions drawn from experimental results. Overall, this study reveals for the first time the ability to control the oxidatively induced C-C vs C-O bond formation reactions at a Ni center. Importantly, the described system merges the known organometallic reactivity of Ni with the biomimetic oxidative transformations resembling oxygenases and peroxidases, and involving high-valent metal-oxygen intermediates, which is a novel approach that should lead to unprecedented oxidative catalytic transformations.
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Simultaneous Fe 2+/Fe 3+ imaging shows Fe 3+ over Fe 2+ enrichment in Alzheimer's disease mouse brain. SCIENCE ADVANCES 2023; 9:eade7622. [PMID: 37075105 PMCID: PMC10115418 DOI: 10.1126/sciadv.ade7622] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Visualizing redox-active metal ions, such as Fe2+ and Fe3+ ions, are essential for understanding their roles in biological processes and human diseases. Despite the development of imaging probes and techniques, imaging both Fe2+ and Fe3+ simultaneously in living cells with high selectivity and sensitivity has not been reported. Here, we selected and developed DNAzyme-based fluorescent turn-on sensors that are selective for either Fe2+ or Fe3+, revealing a decreased Fe3+/Fe2+ ratio during ferroptosis and an increased Fe3+/Fe2+ ratio in Alzheimer's disease mouse brain. The elevated Fe3+/Fe2+ ratio was mainly observed in amyloid plaque regions, suggesting a correlation between amyloid plaques and the accumulation of Fe3+ and/or conversion of Fe2+ to Fe3+. Our sensors can provide deep insights into the biological roles of labile iron redox cycling.
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9
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C-H Bond Activation via Concerted Metalation-Deprotonation at a Palladium(III) Center. Chem Sci 2023; 14:3800-3808. [PMID: 37035706 PMCID: PMC10074423 DOI: 10.1039/d3sc00034f] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2023] [Accepted: 03/12/2023] [Indexed: 03/16/2023] Open
Abstract
Herein we report the direct observation of C-H bond activation at an isolated mononuclear Pd(III) center. The oxidation of the Pd(II) complex (MeN4)PdII(neophyl)Cl (neophyl = -CH2C(CH3)2Ph; MeN4 = N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) using...
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10
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Divalent 2-(4-Hydroxyphenyl)benzothiazole Bifunctional Chelators for 64Cu Positron Emission Tomography Imaging in Alzheimer's Disease. Inorg Chem 2022; 61:20326-20336. [PMID: 36463521 PMCID: PMC9887732 DOI: 10.1021/acs.inorgchem.2c02740] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/07/2022]
Abstract
Herein, we report a new series of divalent 2-(4-hydroxyphenyl)benzothiazole bifunctional chelators (BFCs) with high affinity for amyloid β aggregates and favorable lipophilicity for blood-brain barrier penetration. The addition of an alkyl carboxylate ester pendant arm offers high binding affinity toward Cu(II). The novel BFCs form stable 64Cu-radiolabeled complexes and exhibit promising partition coefficient (logD) values of 1.05-1.85. Among the five compounds tested, the 64Cu-YW-15 complex exhibits significant staining of amyloid β plaques in ex vivo autoradiography studies. In addition, biodistribution studies show that 64Cu-YW-15-Me exhibits moderate brain uptake (0.69 ± 0.08 %ID/g) in wild type mice.
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11
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Novel Diagnostic
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Cu PET Imaging Agents for Alzheimer’s Disease. Alzheimers Dement 2022. [DOI: 10.1002/alz.069158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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12
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Amphiphilic stilbene derivatives attenuate the neurotoxicity of soluble Aβ 42 oligomers by controlling their interactions with cell membranes. Chem Sci 2022; 13:12818-12830. [PMID: 36519059 PMCID: PMC9645390 DOI: 10.1039/d2sc02654f] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 10/19/2022] [Indexed: 10/14/2023] Open
Abstract
The misfolded proteins or polypeptides commonly observed in neurodegenerative diseases, including Alzheimer's disease (AD), are promising drug targets for developing therapeutic agents. To target the amyloid-β (Aβ) peptide plaques and oligomers, the hallmarks of AD, we have developed twelve amphiphilic small molecules with different hydrophobic and hydrophilic fragments. In vitro fluorescence binding assays demonstrate that these amphiphilic compounds show high binding affinity to both Aβ plaques and oligomers, and six of them exhibit selective binding toward Aβ oligomers. These amphiphilic compounds can also label the Aβ species in the brain sections of transgenic AD mice, as shown by immunostaining with an Aβ antibody. Molecular docking studies were performed to obtain structure-affinity relationships. To our delight, four amphiphilic compounds can alleviate the Cu2+-Aβ induced toxicity in cell viability assays. In addition, confocal fluorescence imaging studies provide evidence that two compounds, ZY-15-MT and ZY-15-OMe, can disrupt the interactions between Aβ oligomers and human neuroblastoma SH-SY5Y cell membranes. Overall, these studies strongly suggest that developing compounds with amphiphilic properties that target Aβ oligomers and modulate the Aβ oligomer-cell membrane interactions can be an effective strategy for the development of small molecule AD therapeutics.
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13
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Isolation and Characterization of Heteroleptic Mononuclear Palladium(I) Complexes. J Am Chem Soc 2022; 144:20008-20015. [PMID: 36257056 DOI: 10.1021/jacs.2c08765] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Catalytic transformations involving Pd(0)/Pd(II) catalytic cycles are very well known, and processes involving high-valent Pd(III) and Pd(IV) and low-valent Pd(I) intermediates have also gained interest in recent years. Although low-valent Pd(I) intermediates are proposed in these catalytic cycles, isolated and characterized mononuclear Pd(I) species are very rare. Herein, we report the isolation of two heteroleptic mononuclear Pd(I) complexes stabilized by dithiapyridinophane ligands that were fully characterized by single-crystal X-ray diffraction; EPR, IR, UV-vis spectroscopies; and computational studies. Excitingly, one of these Pd(I) complexes shows Kumada Csp3-Csp2 cross-coupling competency, and initial studies of the other shows direct evidence for Csp3-H bond activation proposed to occur at the Pd(I) center.
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14
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Tracking the binding of multi-functional fluorescent tags for Alzheimer's disease using quantitative multiphoton microscopy. JOURNAL OF BIOPHOTONICS 2022; 15:e202200105. [PMID: 35686672 PMCID: PMC9728943 DOI: 10.1002/jbio.202200105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 06/08/2022] [Indexed: 06/15/2023]
Abstract
A recent theranostic approach to address Alzheimer's disease (AD) utilizes multifunctional targets that both tag and negate the toxicity of AD biomarkers. These compounds, which emit fluorescence with both an activation and a spectral shift in the presence of Aβ, were previously characterized with traditional fluorescence imaging for binary characterization. However, these multifunctional compounds have broad and dynamic emission spectra that are dependent on factors such as the local environment, presence of Aβ deposits, etc. Since quantitative multiphoton microscopy is sensitive to the binding dynamics of molecules, we characterized the performance of two such compounds, LS-4 and ZY-12-OMe, using Simultaneous Label-free Autofluorescence Multi-harmonic (SLAM) microscopy and Fast Optical Coherence, Autofluorescence Lifetime imaging and Second harmonic generation (FOCALS) microscopy. This study shows that the combination of quantitative multiphoton imaging with multifunctional tags for AD offers new insights into the interaction of these tags with AD biomarkers and the theranostic mechanisms.
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15
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Turn-on fluorescent sensors for Cu-rich amyloid β peptide aggregates. SENSORS & DIAGNOSTICS 2022; 1:709-713. [PMID: 35923774 PMCID: PMC9280444 DOI: 10.1039/d2sd00028h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/17/2022] [Accepted: 05/09/2022] [Indexed: 01/12/2023]
Abstract
Protein misfolding and metal dishomeostasis are two key pathological factors of Alzheimer's disease. Previous studies have shown that Cu-mediated amyloid β (Aβ) peptide aggregation leads to the formation of neurotoxic Aβ oligomers. Herein, we report a series of picolinic acid-based Cu-activatable sensors, which can be used for the fluorescence imaging of Cu-rich Aβ aggregates.
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16
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Allylic Amination of Pd(II)-Allyl Complexes via High-Valent Pd Intermediates. Organometallics 2022. [DOI: 10.1021/acs.organomet.2c00215] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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17
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Azo-Stilbene and Pyridine-Amine Hybrid Multifunctional Molecules to Target Metal-Mediated Neurotoxicity and Amyloid-β Aggregation in Alzheimer's Disease. Inorg Chem 2022; 61:10294-10309. [PMID: 35768324 DOI: 10.1021/acs.inorgchem.2c00502] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Neurodegenerative diseases such as Alzheimer's disease (AD) are associated with progressive neuronal cell death, and they are commonly correlated with aberrant protein misfolding and aggregation of Aβ peptides. Transition metal ions (Cu, Fe, and Zn) have been shown to promote aggregation and oxidative stress through formation of Aβ-metal complexes. In this context, integrating molecular scaffolds rationally is used here to generate multifunctional molecules as modulators for metal-induced abnormalities. This work encompasses two azo-stilbene (AS)-derived compounds (AS-HL1 and AS-HL2), the rationale behind the design, their synthesis, characterization, and metal chelation ability [Cu(II) and Zn(II)]. The molecular frameworks of the designed compounds consist of stilbene as an Aβ-interacting moiety, whereas N,N,O and N,N,N,O donor atoms are linked to generate the metal chelation moiety. Furthermore, we went on exploring their multifunctionality with respect to (w.r.t.) (i) their metal chelating capacities and (ii) their utility to modulate the aggregation pathways of both metal-free and metal-bound amyloid-β, (iii) scavenge free radicals, and (iv) inhibit the activity of acetylcholinesterase and (v) cytotoxicity. Moreover, the compounds were able to sequester Cu2+ from the Aβ-Cu complex as studied by the UV-visible spectroscopic assay. Molecular docking studies were also performed with Aβ and acetylcholinesterase enzyme. Overall, the studies presented here qualify these molecules as promising candidates for further investigation in the quest for finding a treatment for Alzheimer's disease.
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18
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A five-coordinate Ni(I) complex supported by 1,4,7-triisopropyl-1,4,7-triazacyclononane. Chem Commun (Camb) 2022; 58:7360-7363. [PMID: 35708524 DOI: 10.1039/d2cc02516g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An isolated Ni(II)-nitrosyl complex supported by the bulky tridentate 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPr3TACN) ligand was obtained from the reaction of a Ni(II) dimethyl complex with NOPF6, suggesting the in situ formation of a Ni(I) species that reacts with the resulting NO product. Use of a π-acceptor ancillary isocyanide ligand led to the isolation and characterization of an uncommon 5-coordinate Ni(I) complex supported by the iPr3TACN ligand and tert-butylisocyanide.
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68Ga-Labeled Benzothiazole Derivatives for Imaging Aβ Plaques in Cerebral Amyloid Angiopathy. ACS OMEGA 2022; 7:20339-20346. [PMID: 35721913 PMCID: PMC9202065 DOI: 10.1021/acsomega.2c02369] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2022] [Accepted: 05/20/2022] [Indexed: 05/17/2023]
Abstract
Timely diagnostic imaging plays a crucial role in managing cerebral amyloid angiopathy (CAA)-the condition in which amyloid β is deposited on blood vessels. To selectively map these amyloid plaques, we have designed amyloid-targeting ligands that can effectively complex with 68Ga3+ while maintaining good affinity for amyloid β. In this study, we introduced novel 1,4,7-triazacyclononane-based bifunctional chelators (BFCs) that incorporate a benzothiazole moiety as the Aβ-binding fragment and form charged and neutral species with 68Ga3+. In vitro autoradiography using 5xFAD and WT mouse brain sections (11-month-old) suggested strong and specific binding of the 68Ga complexes to amyloid β. Biodistribution studies in CD-1 mice revealed a low brain uptake of 0.10-0.33% ID/g, thus suggesting 68Ga-labeled novel BFCs as promising candidates for detecting CAA.
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Neutral Ligands as Potential 64Cu Chelators for Positron Emission Tomography Imaging Applications in Alzheimer's Disease. Inorg Chem 2022; 61:4778-4787. [PMID: 35245023 DOI: 10.1021/acs.inorgchem.2c00621] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Positron emission tomography (PET), which uses positron-emitting radionuclides to visualize and measure processes in the human body, is a useful noninvasive diagnostic tool for Alzheimer's disease (AD). The development of longer-lived radiolabeled compounds is essential for further expansion of the use of PET imaging in healthcare, and diagnostic agents employing longer-lived radionuclides such as 64Cu (t1/2 = 12.7 h, β+ = 17%, β- = 39%, electron capture EC = 43%, and Emax = 0.656 MeV) can accomplish this task. One limitation of 64Cu PET agents for neuroimaging applications is their limited lipophilicity due to the presence of several anionic groups needed to ensure strong Cu chelation. Herein, we evaluate a series of neutral chelators containing the 1,4,7-triazacyclononane or 2,11-diaza[3.3](2,6)pyridinophane macrocycles that have pyridyl-containing arms incorporating Aβ-peptide-interacting fragments. The crystal structures of the corresponding Cu complexes confirm that the pyridyl N atoms are involved in binding to Cu. Radiolabeling and autoradiography studies show that the compounds efficiently chelate 64Cu, and the resulting complexes exhibit specific binding to the amyloid plaques in the AD mouse brain sections versus wild-type controls.
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21
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2-(4-Hydroxyphenyl)benzothiazole dicarboxylate ester TACN chelators for 64Cu PET imaging in Alzheimer's disease. Dalton Trans 2022; 51:1216-1224. [PMID: 34951428 PMCID: PMC8969080 DOI: 10.1039/d1dt02767k] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Herein we report a new series of bifunctional chelators (BFCs) with high affinity for amyloid β aggregates, strong binding affinity towards Cu(II), and favorable lipophilicity for potential blood-brain barrier (BBB) penetration. The alkyl carboxylate ester pendant arms show high binding affinity towards Cu(II). The BFCs form stable 64Cu-radiolabeled complexes and exhibit favorable partition coefficient (log D) values of 0.75-0.95. Among the five compounds tested, 64Cu-YW-1 and 64Cu-YW-13 complexes exhibit significant staining of amyloid plaques in ex vivo autoradiography studies.
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22
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Electrocatalytic H 2 evolution promoted by a bioinspired (N2S2)Ni(II) complex. Chem Commun (Camb) 2022; 58:1143-1146. [PMID: 34981080 DOI: 10.1039/d1cc05139c] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A bioinspired (N2S2)Ni(II) electrocatalyst is reported that produces H2 from CF3CO2H with a turnover frequency (TOF) of ∼1250 s-1 at low acid concentration (<0.043 M) in MeCN. A mechanism for the H2 production by this electrocatalyst is proposed and its activity is benchmarked against those of other reported molecular Ni H2 evolution electrocatalysts. The involvement of a hemilabile pyridyl group of the N2S2 ligand is proposed to mimic the role of a cysteine residue involved in the biological proton reduction performed by [NiFe] hydrogenases.
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23
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Organometallic Ni(II), Ni(III), and Ni(IV) Complexes Relevant to Carbon-Carbon and Carbon-Oxygen Bond Formation Reactions. Inorg Chem Front 2022. [DOI: 10.1039/d1qi01486b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The synthesis and spectroscopic and structural characterization of well-defined organometallic Ni(II) and Ni(III) complexes bearing the PyNMe3 ligand - a tetradentate N-based macrocyclic ligand which coordinates to the metal center...
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Amphiphilic distyrylbenzene derivatives as potential therapeutic and imaging agents for the soluble amyloid‐β oligomers in Alzheimer’s disease. Alzheimers Dement 2021. [DOI: 10.1002/alz.056375] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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25
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Design of novel bifunctional chelators for diagnostic
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Cu PET imaging in Alzheimer’s disease. Alzheimers Dement 2021. [DOI: 10.1002/alz.056406] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Correction to “Synthesis and Reactivity of (N2P2)Ni Complexes Stabilized by a Diphosphonite Pyridinophane Ligand”. Organometallics 2021. [DOI: 10.1021/acs.organomet.1c00548] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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A General Approach to Convert Hemicyanine Dyes into Highly Optimized Photoacoustic Scaffolds for Analyte Sensing*. Angew Chem Int Ed Engl 2021; 60:18860-18866. [PMID: 34089556 PMCID: PMC8550804 DOI: 10.1002/anie.202105905] [Citation(s) in RCA: 48] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 05/26/2021] [Indexed: 12/19/2022]
Abstract
Most photoacoustic (PA) imaging agents are based on the repurposing of existing fluorescent dye platforms that exhibit non-optimal properties for PA applications. Herein, we introduce PA-HD, a new dye scaffold optimized for PA probe development that features a 4.8-fold increase in sensitivity and a red-shift of the λabs from 690 nm to 745 nm to enable ratiometric imaging. Computational modeling was used to elucidate the origin of these enhanced properties. To demonstrate the generalizability of our remodeling efforts, we developed three probes for β-galactosidase activity (PA-HD-Gal), nitroreductase activity (PA-HD-NTR), and H2 O2 (PA-HD-H2 O2 ). We generated two cancer models to evaluate PA-HD-Gal and PA-HD-NTR. We employed a murine model of Alzheimer's disease to test PA-HD-H2 O2 . There, we observed a PA signal increase at 735 nm of 1.79±0.20-fold relative to background, indicating the presence of oxidative stress. These results were confirmed via ratiometric calibration, which was not possible using the parent HD platform.
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Amyloid β-Binding Bifunctional Chelators with Favorable Lipophilicity for 64Cu Positron Emission Tomography Imaging in Alzheimer's Disease. Inorg Chem 2021; 60:12610-12620. [PMID: 34351146 DOI: 10.1021/acs.inorgchem.1c02079] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Herein, we report a new series of bifunctional chelators (BFCs) with a high affinity for amyloid aggregates, a strong binding affinity toward Cu(II), and favorable lipophilicity for potential blood-brain barrier penetration. The alkyl carboxylate ester pendant arms offer up to 3 orders of magnitude higher binding affinity toward Cu(II) and enable the BFCs to form stable 64Cu-radiolabeled complexes. Among the five compounds tested, the 64Cu-YW-7 and 64Cu-YW-10 complexes exhibit strong and specific staining of amyloid plaques in ex vivo autoradiography studies. Importantly, these BFCs have promising partition coefficient (log Doct) values of 0.91-1.26 and show some brain uptake in biodistribution studies using CD-1 mice. Overall, these BFCs could serve as lead compounds for the development of positron emission tomography imaging agents for AD diagnosis.
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Photoreductive chlorine elimination from a Ni(iii)Cl 2 complex supported by a tetradentate pyridinophane ligand. Chem Commun (Camb) 2021; 57:7264-7267. [PMID: 34195702 DOI: 10.1039/d1cc02114a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Herein we report the isolation, characterization, and photoreactivity of a stable NiIII dichloride complex supported by a tetradentate pyridinophane N-donor ligand. Upon irradiation, this complex undergoes an efficient photoreductive chlorine elimination reaction, both in solution and the solid-state. Subsequently, the NiIIICl2 species can be regenerated via a reaction with PhICl2.
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Synthesis and Reactivity of (N2P2)Ni Complexes Stabilized by a Diphosphonite Pyridinophane Ligand. Organometallics 2021. [DOI: 10.1021/acs.organomet.1c00003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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31
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Amphiphilic Distyrylbenzene Derivatives as Potential Therapeutic and Imaging Agents for Soluble and Insoluble Amyloid β Aggregates in Alzheimer's Disease. J Am Chem Soc 2021; 143:10462-10476. [PMID: 34213901 PMCID: PMC8762579 DOI: 10.1021/jacs.1c05470] [Citation(s) in RCA: 39] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Alzheimer's Disease (AD) is the most common neurodegenerative disease, and efficient therapeutic and early diagnostic agents for AD are still lacking. Herein, we report the development of a novel amphiphilic compound, LS-4, generated by linking a hydrophobic amyloid-binding distyrylbenzene fragment with a hydrophilic triazamacrocycle, which dramatically increases the binding affinity toward various amyloid β (Aβ) peptide aggregates, especially for soluble Aβ oligomers. Moreover, upon the administration of LS-4 to 5xFAD mice, fluorescence imaging of LS-4-treated brain sections reveals that LS-4 can penetrate the blood-brain barrier and bind to the Aβ oligomers in vivo. In addition, the treatment of 5xFAD mice with LS-4 reduces the amount of both amyloid plaques and associated phosphorylated tau aggregates vs the vehicle-treated 5xFAD mice, while microglia activation is also reduced. Molecular dynamics simulations corroborate the observation that introducing a hydrophilic moiety into the molecular structure of LS-4 can enhance the electrostatic interactions with the polar residues of the Aβ species. Finally, exploiting the Cu2+-chelating property of the triazamacrocycle, we performed a series of imaging and biodistribution studies that show the 64Cu-LS-4 complex binds to the amyloid plaques and can accumulate to a significantly larger extent in the 5xFAD mouse brains vs the wild-type controls. Overall, these results illustrate that the novel strategy, to employ an amphiphilic molecule containing a hydrophilic moiety attached to a hydrophobic amyloid-binding fragment, can increase the binding affinity for both soluble and insoluble Aβ aggregates and can thus be used to detect and regulate various Aβ species in AD.
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A General Approach to Convert Hemicyanine Dyes into Highly Optimized Photoacoustic Scaffolds for Analyte Sensing**. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202105905] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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33
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Electrocatalytic O 2 Reduction by an Organometallic Pd(III) Complex via a Binuclear Pd(III) Intermediate. ACS Catal 2021. [DOI: 10.1021/acscatal.0c05726] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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34
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A multifunctional chemical agent as an attenuator of amyloid and p‐tau burden and neuroinflammation in Alzheimer’s disease. Alzheimers Dement 2020. [DOI: 10.1002/alz.047006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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35
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Detection and Characterization of Mononuclear Pd(I) Complexes Supported by N2S2 and N4 Tetradentate Ligands. Inorg Chem 2020; 59:15659-15669. [PMID: 33058678 DOI: 10.1021/acs.inorgchem.0c01938] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Palladium is a versatile transition metal used to catalyze a large number of chemical transformations, largely due to its ability to access various oxidation states (0, I, II, III, and IV). Among these oxidation states, Pd(I) is arguably the least studied, and while dinuclear Pd(I) complexes are more common, mononuclear Pd(I) species are very rare. Reported herein are spectroscopic studies of a series of Pd(I) intermediates generated by the chemical reduction at low temperatures of Pd(II) precursors supported by the tetradentate ligands 2,11-dithia[3.3](2,6)pyridinophane (N2S2) and N,N'-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane (tBuN4): [(N2S2)PdII(MeCN)]2(OTf)4 (1), [(N2S2)PdIIMe]2(OTf)2 (2), [(N2S2)PdIICl](OTf) (3), [(N2S2)PdIIX](OTf)2 (X = tBuNC 4, PPh3 5), [(N2S2)PdIIMe(PPh3)](OTf) (6), and [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9). In addition, a stable Pd(I) dinuclear species, [(N2S2)PdI(μ-tBuNC)]2(ClO4)2 (7), was isolated upon the electrochemical reduction of 4 and structurally characterized. Moreover, the (tBuN4)PdI intermediates, formed from the chemical reduction of [(tBuN4)PdIIX2](OTf)2 (X = MeCN 8, tBuNC 9) complexes, were investigated by EPR spectroscopy, X-ray absorption spectroscopy (XAS), and DFT calculations and compared with the analogous (N2S2)PdI systems. Upon probing the stability of Pd(I) species under different ligand environments, it is apparent that the presence of soft ligands such as tBuNC and PPh3 significantly improves the stability of Pd(I) species, which should make the isolation of mononuclear Pd(I) species possible.
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Amentoflavone: A Bifunctional Metal Chelator that Controls the Formation of Neurotoxic Soluble Aβ 42 Oligomers. ACS Chem Neurosci 2020; 11:2741-2752. [PMID: 32786307 DOI: 10.1021/acschemneuro.0c00376] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Alzheimer's disease (AD) is the most common neurodegenerative disorder, yet the cause and progression of this disorder are not completely understood. While the main hallmark of AD is the deposition of amyloid plaques consisting of the β-amyloid (Aβ) peptide, transition metal ions are also known to play a significant role in disease pathology by expediting the formation of neurotoxic soluble β-amyloid (Aβ) oligomers, reactive oxygen species (ROS), and oxidative stress. Thus, bifunctional metal chelators that can control these deleterious properties are highly desirable. Herein, we show that amentoflavone (AMF), a natural biflavonoid compound, exhibits good metal-chelating properties, especially for chelating Cu2+ with very high affinity (pCu7.4 = 10.44). In addition, AMF binds to Aβ fibrils with a high affinity (Ki = 287 ± 20 nM), as revealed by a competition thioflavin T (ThT) assay, and specifically labels the amyloid plaques ex vivo in the brain sections of transgenic AD mice, as confirmed via immunostaining with an Aβ antibody. The effect of AMF on Aβ42 aggregation and disaggregation of Aβ42 fibrils was also investigated and revealed that AMF can control the formation of neurotoxic soluble Aβ42 oligomers, both in the absence and presence of metal ions, as confirmed via cell toxicity studies. Furthermore, an ascorbate consumption assay shows that AMF exhibits potent antioxidant properties and can chelate Cu2+ and significantly diminish the Cu2+-ascorbate redox cycling and reactive oxygen species (ROS) formation. Overall, these studies strongly suggest that AMF acts as a bifunctional chelator that can interact with various Aβ aggregates and reduce their neurotoxicity and can also bind Cu2+ and mediate its deleterious redox properties. Thus AMF has the potential to be a lead compound for further therapeutic agent development for AD.
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Improved Oxidative C-C Bond Formation Reactivity of High-Valent Pd Complexes Supported by a Pseudo-Tridentate Ligand. Inorg Chem 2020; 59:11782-11792. [PMID: 32799488 DOI: 10.1021/acs.inorgchem.0c01763] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
There is a large interest in developing oxidative transformations catalyzed by palladium complexes that employ environmentally friendly and economical oxidizing reagents such as dioxygen. Recently, we have reported the isolation and characterization of various mononuclear PdIII and PdIV complexes supported by the tetradentate ligands N,N'-dialkyl-2,11-diaza[3.3](2,6)pyridinophane (RN4, R = tBu, iPr, Me), and the aerobically induced C-C and C-heteroatom bond formation reactivity was investigated in detail. Given that the steric and electronic properties of the multidentate ligands were shown to tune the stability and reactivity of the corresponding high-valent Pd complexes, herein we report the use of an asymmetric N4 ligand, N-mehtyl-N'-tosyl-2,11-diaza[3.3](2,6)pyridinophane (TsMeN4), in which one amine N atom contains a tosyl group. The N-Ts donor atom exhibits a markedly reduced donating ability, which led to the formation of transiently stable PdIII and PdIV complexes, and consequently the corresponding O2 oxidation reactivity and the subsequent C-C bond formation were improved significantly.
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Metal-chelating benzothiazole multifunctional compounds for the modulation and 64Cu PET imaging of Aβ aggregation. Chem Sci 2020; 11:7789-7799. [PMID: 34094152 PMCID: PMC8163150 DOI: 10.1039/d0sc02641g] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2020] [Accepted: 07/07/2020] [Indexed: 12/14/2022] Open
Abstract
While Alzheimer's Disease (AD) is the most common neurodegenerative disease, there is still a dearth of efficient therapeutic and diagnostic agents for this disorder. Reported herein are a series of new multifunctional compounds (MFCs) with appreciable affinity for amyloid aggregates that can be potentially used for both the modulation of Aβ aggregation and its toxicity, as well as positron emission tomography (PET) imaging of Aβ aggregates. Firstly, among the six compounds tested HYR-16 is shown to be capable to reroute the toxic Cu-mediated Aβ oligomerization into the formation of less toxic amyloid fibrils. In addition, HYR-16 can also alleviate the formation of reactive oxygen species (ROS) caused by Cu2+ ions through Fenton-like reactions. Secondly, these MFCs can be easily converted to PET imaging agents by pre-chelation with the 64Cu radioisotope, and the Cu complexes of HYR-4 and HYR-17 exhibit good fluorescent staining and radiolabeling of amyloid plaques both in vitro and ex vivo. Importantly, the 64Cu-labeled HYR-17 is shown to have a significant brain uptake of up to 0.99 ± 0.04 %ID per g. Overall, by evaluating the various properties of these MFCs valuable structure-activity relationships were obtained that should aid the design of improved therapeutic and diagnostic agents for AD.
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A Multifunctional Chemical Agent as an Attenuator of Amyloid Burden and Neuroinflammation in Alzheimer's Disease. ACS Chem Neurosci 2020; 11:1471-1481. [PMID: 32310630 PMCID: PMC7732605 DOI: 10.1021/acschemneuro.0c00114] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Alzheimer's disease (AD) is the most common neurodegenerative disease, and its main hallmark is the deposition of amyloid beta (Aβ) peptides. However, several clinical trials focusing on Aβ-targeting agents have failed recently, and thus new therapeutic leads are focusing on alternate targets such as tau protein pathology, Aβ-metal induced oxidative stress, and neuroinflammation. To address these different pathological aspects of AD, we have employed a multifunctional compound, L1 [4-(benzo[d]thiazol-2-yl)-2-((4,7-dimethyl-1,4,7-triazonan-1-yl)methyl)-6-methoxyphenol], that integrates Aβ-interacting and metal-binding fragments in a single molecular framework, exhibits significant antioxidant activity and metal chelating ability, and also rescues neuroblastoma N2A cells from Cu2+-induced Aβ neurotoxicity. Along with demonstrating in vivo Aβ-binding and favorable brain uptake properties, L1 treatment of transgenic 5xFAD mice significantly reduces the amount of both amyloid plaques and associated phosphorylated tau (p-tau) aggregates in the brain by 40-50% versus the vehicle-treated 5xFAD mice. Moreover, L1 mitigates the neuroinflammatory response of the activated microglia during the Aβ-induced inflammation process. Overall, these multifunctional properties of L1 to attenuate the formation of amyloid plaques and associated p-tau aggregates while also reducing the microglia-mediated neuroinflammatory response are quite uncommon among the previously reported amyloid-targeting chemical agents, and thus L1 could be envisioned as a lead compound for the development of novel AD therapeutics.
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Mononuclear Organometallic Pd(II), Pd(III), and Pd(IV) Complexes Stabilized by a Pyridinophane Ligand with a C-Donor Group. Organometallics 2019. [DOI: 10.1021/acs.organomet.9b00505] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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41
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Aerobic C-C and C-O bond formation reactions mediated by high-valent nickel species. Chem Sci 2019; 10:10366-10372. [PMID: 32110325 PMCID: PMC6984385 DOI: 10.1039/c9sc03758f] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Accepted: 09/17/2019] [Indexed: 11/21/2022] Open
Abstract
Nickel complexes have been widely employed as catalysts in C-C and C-heteroatom bond formation reactions. While Ni(0), Ni(i), and Ni(ii) intermediates are most relevant in these transformations, recently Ni(iii) and Ni(iv) species have also been proposed to play a role in catalysis. Reported herein is the synthesis, detailed characterization, and reactivity of a series of Ni(ii) and Ni(iii) metallacycle complexes stabilized by tetradentate pyridinophane ligands with various N-substituents. Interestingly, while the oxidation of the Ni(ii) complexes with various other oxidants led to exclusive C-C bond formation in very good yields, the use of O2 or H2O2 as oxidants led to formation of appreciable amounts of C-O bond formation products, especially for the Ni(ii) complex supported by an asymmetric pyridinophane ligand containing one tosyl N-substituent. Moreover, cryo-ESI-MS studies support the formation of several high-valent Ni species as key intermediates in this uncommon Ni-mediated oxygenase-type chemistry.
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42
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Electronic versus steric effects of pyridinophane ligands on Pd(iii) complexes. Dalton Trans 2018; 47:1151-1158. [PMID: 29271467 DOI: 10.1039/c7dt04366j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Several new PdII and PdIII complexes supported by electronically and sterically tuned tetradentate pyridinophane ligands MeN4OMe, MeN4, and tBuN4 were isolated and fully characterized (MeN4OMe: N,N'-dimethyl-2,11-diaza[3,3](2,6)-para-methoxypyridinophane; MeN4: N,N'-dimethyl-2,11-diaza[3,3](2,6)pyridinophane; tBuN4: N,N'-di-tert-butyl-2,11-diaza[3,3](2,6)pyridinophane). Cyclic voltammetry studies, UV-vis and EPR spectroscopy, and X-ray crystallography were employed to reveal that the steric properties of the N-substituents of the RN4 ligands have a pronounced effect on the electronic properties of the corresponding PdIII complexes, while the electronic tuning of the ligand pyridyl groups has a surprisingly minimal effect. An explanation for these observations was provided by DFT and TD-DFT calculations which suggest that the electronic properties of the PdIII complexes are mainly dictated by their frontier molecular orbitals that have major atomic contributions from the Pd center (mainly the Pd dz2 atomic orbital) and the axial N atom donors.
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Azo-dyes based small bifunctional molecules for metal chelation and controlling amyloid formation. Inorganica Chim Acta 2018; 471:419-429. [PMID: 30344337 PMCID: PMC6191838 DOI: 10.1016/j.ica.2017.11.029] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chemical tools are needed to discover new effective drugs for tackling multifaceted complex neurodegenerative diseases like Alzheimer's disease (AD). Multifunctional nature of two compounds, 5-((4-nitro-phenyl)diazenyl)quinolin-8-ol (HL1) and 4-((4-nitrophenyl)diazenyl)benzene-1,3-diol (HL2) is reported w.r.t. their ability to bind Cu2+ ions and amyloid aggregates related to AD. HL1 and HL2 have half congo-red type azo-stilbene structural framework incorporated with metal chelating groups, designed to chelate metal ions from metal-amyloid species. Metal binding studies of HL1 and HL2 are established by the methods of Job's Plot, UV-vis spectra with metal ions and stability constant determination. In addition, their metal complexes are isolated, purity checked by elemental analysis, spectroscopically characterized and their structural analyses were obtained from DFT based calculations including binding energy determination. Chicken egg white Lysozyme (CEWL) was used as a model peptide for fibrillation studies. HL1 is found as an excellent colorimetric sensor for amyloid fibrils. Inhibitory effect of HL1 and HL2 and their isolated metal complexes L1-Cu and L2-Cu on CEWL fibrillation was studied using ThT and ANS fluorescence assay along with TEM imaging. In addition, the cell toxicity studies on these compounds suggest that although azo dyes may be non-toxic but having a nitro-substitution lead to significant cell toxicity. Overall, these results suggest that this new class of multifunctional small molecules can interact with amyloids as well as metal ions and could be potential anti-aggregation metal chelating agents.
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Improved synthesis of symmetrically & asymmetrically N-substituted pyridinophane derivatives. Org Biomol Chem 2018; 15:9923-9931. [PMID: 29164216 DOI: 10.1039/c7ob02508d] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The N,N'-di(toluenesulfonyl)-2,11-diaza[3,3](2,6)pyridinophane (TsN4) precursor was sought after as a starting point for the preparation of various symmetric and asymmetric pyridinophane-derived ligands. Various procedures to synthesize TsN4 had been published, but the crucial problem had been the purification of TsN4 from the larger 18- and 24-membered azamacrocycles. Most commonly, column chromatography or other laborious methods have been utilized for this separation, yet we have found an alternate selective dissolution method upon protonation which allows for multi-gram scale output of TsN4·HCl. This optimized synthesis of TsN4 also led to the development of symmetric RN4 derivatives as well as the asymmetric derivative N-(tosyl)-2,11-diaza[3,3](2,6)pyridinophane (TsHN4). Using this TsHN4 precursor, different N-substituents can be added to create a library of asymmetric RR'N4 macrocyclic ligands. These asymmetric RR'N4 derivatives expand the utility of the RN4 framework in coordination chemistry and the ability to study the electronic, steric, and denticity effects of these pyridinophane ligands on the metal center.
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Coordination Chemistry of Bifunctional Chemical Agents Designed for Applications in 64Cu PET Imaging for Alzheimer's Disease. Inorg Chem 2017; 56:13801-13814. [PMID: 29112419 PMCID: PMC5698879 DOI: 10.1021/acs.inorgchem.7b01883] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
Positron emission
tomography (PET) is emerging as one of the most important diagnostic
tools for brain imaging, yet the most commonly used radioisotopes
in PET imaging, 11C and 18F, have short half-lives,
and their usage is thus somewhat limited. By comparison, the 64Cu radionuclide has a half-life of 12.7 h, which is ideal
for administering and imaging purposes. In spite of appreciable research
efforts, high-affinity copper chelators suitable for brain imaging
applications are still lacking. Herein, we present the synthesis and
characterization of a series of bifunctional compounds (BFCs) based
on macrocyclic 1,4,7-triazacyclononane and 2,11-diaza[3.3](2,6)pyridinophane
ligand frameworks that exhibit a high affinity for Cu2+ ions. In addition, these BFCs contain a 2-phenylbenzothiazole fragment
that is known to interact tightly with amyloid β fibrillar aggregates.
Determination of the protonation constants (pKa values) and stability constants (log β values) of these
BFCs, as well as characterization of the isolated copper complexes
using X-ray crystallography, electron paramagnetic resonance spectroscopy,
and electrochemical studies, suggests that these BFCs exhibit desirable
properties for the development of novel 64Cu PET imaging
agents for Alzheimer’s disease. Novel bifunctional chelators
(BFCs) containing 1,4,7-triazacyclononane or pyridinophane macrocycles
and amyloid-binding 2-phenylbenzothiazole fragments have been synthesized,
and their copper coordination properties have been characterized in
detail. These BFCs are attractive candidates for the development of
novel 64Cu-labeled PET imaging agents for Alzheimer’s
disease.
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Evaluation of 64Cu-Based Radiopharmaceuticals that Target Aβ Peptide Aggregates as Diagnostic Tools for Alzheimer's Disease. J Am Chem Soc 2017; 139:12550-12558. [PMID: 28823165 PMCID: PMC5677763 DOI: 10.1021/jacs.7b05937] [Citation(s) in RCA: 43] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Indexed: 12/23/2022]
Abstract
Positron emission tomography (PET) imaging agents that detect amyloid plaques containing amyloid beta (Aβ) peptide aggregates in the brain of Alzheimer's disease (AD) patients have been successfully developed and recently approved by the FDA for clinical use. However, the short half-lives of the currently used radionuclides 11C (20.4 min) and 18F (109.8 min) may limit the widespread use of these imaging agents. Therefore, we have begun to evaluate novel AD diagnostic agents that can be radiolabeled with 64Cu, a radionuclide with a half-life of 12.7 h, ideal for PET imaging. Described herein are a series of bifunctional chelators (BFCs), L1-L5, that were designed to tightly bind 64Cu and shown to interact with Aβ aggregates both in vitro and in transgenic AD mouse brain sections. Importantly, biodistribution studies show that these compounds exhibit promising brain uptake and rapid clearance in wild-type mice, and initial microPET imaging studies of transgenic AD mice suggest that these compounds could serve as lead compounds for the development of improved diagnostic agents for AD.
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Mononuclear Rhodium(II) and Iridium(II) Complexes Supported by Tetradentate Pyridinophane Ligands. Inorg Chem 2017; 56:9404-9408. [DOI: 10.1021/acs.inorgchem.7b01619] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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49
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The small molecule JIB-04 disrupts O 2 binding in the Fe-dependent histone demethylase KDM4A/JMJD2A. Chem Commun (Camb) 2017; 53:2174-2177. [PMID: 28144654 PMCID: PMC5511625 DOI: 10.1039/c6cc09882g] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
JIB-04, a specific inhibitor of the O2-activating, Fe-dependent histone lysine demethylases, is revealed to disrupt the binding of O2 in KDM4A/JMJD2A through a continuous O2-consumption assay, X-ray crystal structure data, and molecular docking.
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Oxidative C-C Bond Formation Reactivity of Organometallic Ni(II), Ni(III), and Ni(IV) Complexes. J Am Chem Soc 2016; 139:35-38. [PMID: 27997181 DOI: 10.1021/jacs.6b10303] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The use of the tridentate ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn) and the cyclic alkyl/aryl C-donor ligand -CH2CMe2-o-C6H4- (cycloneophyl) allows for the synthesis of isolable organometallic NiII, NiIII, and NiIV complexes. Surprisingly, the five-coordinate NiIII complex is stable both in solution and the solid state, and exhibits limited C-C bond formation reactivity. Oxidation by one electron of this NiIII species generates a six-coordinate NiIV complex, with an acetonitrile molecule bound to Ni. Interestingly, illumination of the NiIV complex with blue LEDs results in rapid formation of the cyclic C-C product at room temperature. This reactivity has important implications for the recently developed dual Ni/photoredox catalytic systems proposed to involve high-valent organometallic Ni intermediates. Additional reactivity studies show the corresponding NiII species undergoes oxidative addition with alkyl halides, as well as rapid oxidation by O2, to generate detectable NiIII and/or NiIV intermediates and followed by C-C bond formation.
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