1
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Duez Q, Tinnemans P, Elemans JAAW, Roithová J. Kinetics of ligand exchange in solution: a quantitative mass spectrometry approach. Chem Sci 2023; 14:9759-9769. [PMID: 37736645 PMCID: PMC10510763 DOI: 10.1039/d3sc03342b] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Accepted: 08/24/2023] [Indexed: 09/23/2023] Open
Abstract
Complex speciation and exchange kinetics of labile ligands are critical parameters for understanding the reactivity of metal complexes in solution. We present a novel approach to determine ligand exchange parameters based on electrospray ionization mass spectrometry (ESI-MS). The introduction of isotopically labelled ligands to a solution of metal host and unlabelled ligands allows the quantitative investigation of the solution-phase equilibria. Furthermore, ion mobility separation can target individual isomers, such as ligands bound at specific sites. As a proof of concept, we investigate the solution equilibria of labile pyridine ligands coordinated in the cavity of macrocyclic porphyrin cage complexes bearing diamagnetic or paramagnetic metal centres. The effects of solvent, porphyrin coordination sphere, transition metal, and counterion on ligand dissociation are discussed. Rate constants and activation parameters for ligand dissociation in the solution can be derived from our ESI-MS approach, thereby providing mechanistic insights that are not easily obtained from traditional solution-phase techniques.
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Affiliation(s)
- Quentin Duez
- Radboud University, Institute for Molecules and Materials Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Paul Tinnemans
- Radboud University, Institute for Molecules and Materials Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Johannes A A W Elemans
- Radboud University, Institute for Molecules and Materials Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
| | - Jana Roithová
- Radboud University, Institute for Molecules and Materials Heyendaalseweg 135 6525 AJ Nijmegen The Netherlands
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2
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Targeting emerging cancer hallmarks by transition metal complexes: Epigenetic reprogramming and epitherapies. Part II. Coord Chem Rev 2023. [DOI: 10.1016/j.ccr.2022.214899] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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3
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Modulation of Hedgehog Signaling for the Treatment of Basal Cell Carcinoma and the Development of Preclinical Models. Biomedicines 2022; 10:biomedicines10102376. [PMID: 36289637 PMCID: PMC9598418 DOI: 10.3390/biomedicines10102376] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2022] [Revised: 09/17/2022] [Accepted: 09/20/2022] [Indexed: 11/17/2022] Open
Abstract
Basal Cell Carcinoma (BCC) is the most commonly diagnosed cancer worldwide. While the survivability of BCC is high, many patients are excluded from clinically available treatments due to health risks or personal choice. Further, patients with advanced or metastatic disease have severely limited treatment options. The dysregulation of the Hedgehog (Hh) signaling cascade drives onset and progression of BCC. As such, the modulation of this pathway has driven advancements in BCC research. In this review, we focus firstly on inhibitors that target the Hh pathway as chemotherapeutics against BCC. Two therapies targeting Hh signaling have been made clinically available for BCC patients, but these treatments suffer from limited initial efficacy and a high rate of chemoresistant tumor recurrence. Herein, we describe more recent developments of chemical scaffolds that have been designed to hopefully improve upon the available therapeutics. We secondly discuss the history and recent efforts involving modulation of the Hh genome as a method of producing in vivo models of BCC for preclinical research. While there are many advancements left to be made towards improving patient outcomes with BCC, it is clear that targeting the Hh pathway will remain at the forefront of research efforts in designing more effective chemotherapeutics as well as relevant preclinical models.
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4
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Brue CR, Dukes MW, Masotti M, Holmgren R, Meade TJ. Functional Disruption of Gli1-DNA Recognition via a Cobalt(III) Complex. ChemMedChem 2022; 17:e202200025. [PMID: 35302712 PMCID: PMC10826845 DOI: 10.1002/cmdc.202200025] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Indexed: 12/29/2022]
Abstract
The aberrant activation of the Gli family of zinc finger transcription factors (ZFTFs) is associated with several types of human cancer, including medulloblastoma and basal cell carcinoma. We have reported the use of cobalt(III) Schiff-base complexes (Co(III)-sb) as potent inhibitors of ZFTFs in vivo. These complexes inhibit transcription by displacing the zinc finger domain's structural Zn(II) ion, destabilizing the alpha helix necessary for DNA recognition. Here, we describe the use of Co(III)-sb complexes for the selective inhibition of Gli1. Spectroscopic and computational studies of the Gli1 DNA binding domain found that Co(III)-sb displaced Zn(II) through direct coordination with the His residues of the Cys2 His2 Zn(II) binding site. As a result, there is a dose-dependent degradation of the alpha-helix content in the DNA binding domain of Gli1 and corresponding inhibition of consensus sequence recognition. We conclude that this strategy is well suited for the development of new and potent inhibitors of Gli1.
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Affiliation(s)
- Christopher R Brue
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL, 60208-3113, USA
| | - Meghan W Dukes
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL, 60208-3113, USA
| | - Meghan Masotti
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL, 60208-3113, USA
| | - Robert Holmgren
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL, 60208-3113, USA
| | - Thomas J Meade
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL, 60208-3113, USA
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5
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Giriraj K, Mohamed Kasim MS, Balasubramaniam K, Thangavel SK, Venkatesan J, Suresh S, Shanmugam P, Karri C. Various coordination modes of new coumarin Schiff bases toward Cobalt (III) ion: Synthesis, spectral characterization, in vitro cytotoxic activity, and investigation of apoptosis. Appl Organomet Chem 2021. [DOI: 10.1002/aoc.6536] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Kalaiarasi Giriraj
- Department of Chemistry Karpagam Academy of Higher Education (Deemed to be University) Coimbatore 641021 India
| | - Mohamed Subarkhan Mohamed Kasim
- The First Affiliated Hospital; Key Laboratory of Combined Multi Organ Transplantation, Ministry of Public Health, School of Medicine Zhejiang University Hangzhou PR China
| | - Keerthana Balasubramaniam
- Department of Microbiology Karpagam Academy of Higher Education (Deemed to be University) Coimbatore 641021 India
| | - Sathiya Kamatchi Thangavel
- Centre for Organometallic Chemistry, School of Chemistry Bharathidasan University Tiruchirappalli 620024 India
| | - Janani Venkatesan
- Department of Chemistry Karpagam Academy of Higher Education (Deemed to be University) Coimbatore 641021 India
| | - Sharmila Suresh
- Department of Chemistry Karpagam Academy of Higher Education (Deemed to be University) Coimbatore 641021 India
| | - Pritha Shanmugam
- Department of Chemistry Karpagam Academy of Higher Education (Deemed to be University) Coimbatore 641021 India
| | - Chiranjeevi Karri
- Department of Chemistry Karpagam Academy of Higher Education (Deemed to be University) Coimbatore 641021 India
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6
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Bowman EA, England BL, Patterson MA, Price NS, Stepler KE, Curnutte HA, Lease RE, Bradley CA, Craig PR. Pre-assembly required: Nickel(II) complexes containing a Schiff-base ligand derived from tris(2-aminoethyl)amine and acetylacetone, salicylaldehyde, or ortho-vanillin. Inorganica Chim Acta 2021. [DOI: 10.1016/j.ica.2021.120415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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7
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Frei A, King AP, Lowe GJ, Cain AK, Short FL, Dinh H, Elliott AG, Zuegg J, Wilson JJ, Blaskovich MAT. Nontoxic Cobalt(III) Schiff Base Complexes with Broad-Spectrum Antifungal Activity. Chemistry 2021; 27:2021-2029. [PMID: 33231906 PMCID: PMC7855930 DOI: 10.1002/chem.202003545] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 09/03/2020] [Indexed: 12/21/2022]
Abstract
Resistance to currently available antifungal drugs has quietly been on the rise but overshadowed by the alarming spread of antibacterial resistance. There is a striking lack of attention to the threat of drug-resistant fungal infections, with only a handful of new drugs currently in development. Given that metal complexes have proven to be useful new chemotypes in the fight against diseases such as cancer, malaria, and bacterial infections, it is reasonable to explore their possible utility in treating fungal infections. Herein we report a series of cobalt(III) Schiff base complexes with broad-spectrum antifungal activity. Some of these complexes show minimum inhibitory concentrations (MIC) in the low micro- to nanomolar range against a series of Candida and Cryptococcus yeasts. Additionally, we demonstrate that these compounds show no cytotoxicity against both bacterial and human cells. Finally, we report the first in vivo toxicity data on these compounds in Galleria mellonella, showing that doses as high as 266 mg kg-1 are tolerated without adverse effects, paving the way for further in vivo studies of these complexes.
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Affiliation(s)
- Angelo Frei
- Centre for Superbug SolutionsInstitute for Molecular BioscienceThe University of QueenslandSt. LuciaQLD4072Australia
| | - A. Paden King
- Department of Chemistry and Chemical BiologyCornell UniversityIthacaNY14853USA
| | - Gabrielle J. Lowe
- Centre for Superbug SolutionsInstitute for Molecular BioscienceThe University of QueenslandSt. LuciaQLD4072Australia
| | - Amy K. Cain
- Department of Molecular SciencesMacquarie UniversitySydneyNSW2109Australia
| | - Francesca L. Short
- Department of Molecular SciencesMacquarie UniversitySydneyNSW2109Australia
| | - Hue Dinh
- Department of Molecular SciencesMacquarie UniversitySydneyNSW2109Australia
- Department of Biological SciencesMacquarie UniversitySydneyNSW2109Australia
| | - Alysha G. Elliott
- Centre for Superbug SolutionsInstitute for Molecular BioscienceThe University of QueenslandSt. LuciaQLD4072Australia
| | - Johannes Zuegg
- Centre for Superbug SolutionsInstitute for Molecular BioscienceThe University of QueenslandSt. LuciaQLD4072Australia
| | - Justin J. Wilson
- Department of Chemistry and Chemical BiologyCornell UniversityIthacaNY14853USA
| | - Mark A. T. Blaskovich
- Centre for Superbug SolutionsInstitute for Molecular BioscienceThe University of QueenslandSt. LuciaQLD4072Australia
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8
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Roberts KF, Brue CR, Preston A, Baxter D, Herzog E, Varelas E, Meade TJ. Cobalt(III) Schiff base complexes stabilize non-fibrillar amyloid-β aggregates with reduced toxicity. J Inorg Biochem 2020; 213:111265. [PMID: 33059154 DOI: 10.1016/j.jinorgbio.2020.111265] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2020] [Revised: 09/18/2020] [Accepted: 09/24/2020] [Indexed: 12/12/2022]
Abstract
The aggregation of amyloid-β (Aβ) is believed to be foundational to the pathogenesis of Alzheimer's disease (AD). In vitro aggregation kinetics have been shown to correlate with rates of disease progression in both AD patients and animal models, thus proving to be a useful metric for testing Aβ-targeted therapeutics. Here we present evidence of cobalt(III) Schiff base complex ([Co(acetylacetonate)(NH3)2]Cl; Co(III)-sb) modulation of Aβ aggregation kinetics by a variety of complementary techniques. These include Thioflavin T (ThT) fluorescence, circular dichroism (CD) spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM). Our data was fitted to kinetic rate laws using a mathematical model developed by Knowles et al. in order to extract mechanistic information about the effect of Co(III)-sb on aggregation kinetics. Our analysis revealed that Co(III)-sb alters Aβ aggregation by decreasing the polymerization rate and increasing the nucleation rate, suggesting that Co(III)-sb causes Aβ to rapidly stabilize oligomeric species with reduced elongation into mature fibrils. This result was corroborated by TEM and AFM of Aβ aggregates in vitro. We also demonstrate that Aβ aggregate mixtures produced in the presence of Co(III)-sb exhibit decreased cytotoxicity compared to untreated samples.
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Affiliation(s)
- Kaleigh F Roberts
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States
| | - Christopher R Brue
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States
| | - Anna Preston
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States
| | - Damonick Baxter
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States
| | - Emma Herzog
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States
| | - Eleni Varelas
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States
| | - Thomas J Meade
- Departments of Chemistry, Molecular Biosciences, Neurobiology, and Radiology, Northwestern University, Evanston, IL 60208, United States.
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9
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Abbehausen C. Zinc finger domains as therapeutic targets for metal-based compounds - an update. Metallomics 2020; 11:15-28. [PMID: 30303505 DOI: 10.1039/c8mt00262b] [Citation(s) in RCA: 44] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Zinc finger proteins are one of the most abundant families of proteins and present a wide range of structures and functions. The structural zinc ion provides the correct conformation to specifically recognize DNA, RNA and protein sequences. Zinc fingers have essential functions in transcription, protein degradation, DNA repair, cell migration, and others. Recently, reports on the extensive participation of zinc fingers in disease have been published. On the other hand, much information remains to be unravelled as many genomes and proteomes are being reported. A variety of zinc fingers have been identified; however, their functions are still under investigation. Because zinc fingers have identified functions in several diseases, they are being increasingly recognized as drug targets. The replacement of Zn(ii) by another metal ion in zinc fingers is one of the most prominent methods of inhibition. From one side, zinc fingers play roles in the toxicity mechanisms of Ni(ii), Hg(ii), Cd(ii) and others. From the other side, gold, platinum, cobalt, and selenium complexes are amongst the compounds being developed as zinc finger inhibitors for therapy. The main challenge in the design of therapeutic zinc finger inhibitors is to achieve selectivity. Recently, the design of novel compounds and elucidation of the mechanisms of zinc substitution have renewed the possibilities of selective zinc finger inhibition by metal complexes. This review aims to update the status of novel strategies to selectively target zinc finger domains by metal complexes.
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Affiliation(s)
- C Abbehausen
- Institute of Chemistry, University of Campinas - UNICAMP, P.O. Box 6154, CEP 13083-970, Campinas, São Paulo, Brazil.
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10
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Iscen A, Brue CR, Roberts KF, Kim J, Schatz GC, Meade TJ. Inhibition of Amyloid-β Aggregation by Cobalt(III) Schiff Base Complexes: A Computational and Experimental Approach. J Am Chem Soc 2019; 141:16685-16695. [DOI: 10.1021/jacs.9b06388] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Aysenur Iscen
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Christopher R. Brue
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Kaleigh F. Roberts
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Joy Kim
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - George C. Schatz
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
| | - Thomas J. Meade
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Chemical and Biological Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, United States
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11
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Recent developments in penta-, hexa- and heptadentate Schiff base ligands and their metal complexes. Coord Chem Rev 2019. [DOI: 10.1016/j.ccr.2019.03.010] [Citation(s) in RCA: 189] [Impact Index Per Article: 37.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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12
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King AP, Gellineau HA, MacMillan SN, Wilson JJ. Physical properties, ligand substitution reactions, and biological activity of Co(iii)-Schiff base complexes. Dalton Trans 2019; 48:5987-6002. [PMID: 30672949 PMCID: PMC6504617 DOI: 10.1039/c8dt04606a] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Four cobalt(iii) complexes of the general formula [Co(Schiff base)(L)2]+, where L is ammonia (NH3) or 3-fluorobenzylamine (3F-BnNH2), were synthesized. The complexes were characterized by NMR spectroscopy, mass spectrometry, and X-ray crystallography. Their electrochemical properties, ligand substitution mechanisms, and ligand exchange rates in aqueous buffer were investigated. These physical properties were correlated to the cellular uptake and anticancer activities of the complexes. The complexes undergo sequential, dissociative ligand substitution, with the exchange rates depending heavily on the axial ligands. Eyring analyses revealed that the relative ligand exchange rates were largely impacted by differences in the entropy, rather than enthalpy, of activation for the complexes. Performing the substitution reactions in the presence of ascorbate led to a change in the reaction profile and kinetics, but no change in the final product. The cytotoxic activity of the complexes correlates with both the ligand exchange rate and reduction potential, with the more easily reduced and rapidly substituted complexes showing higher toxicity. These relationships may be valuable for the rational design of Co(iii) complexes as anticancer or antiviral prodrugs.
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Affiliation(s)
- A Paden King
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, USA.
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13
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Computational study of the [(CO)2(benzoate)MII/III(terephthalate)]0/1+ complexes with M = V, Cr, Mn, Fe and Co. COMPUT THEOR CHEM 2019. [DOI: 10.1016/j.comptc.2019.03.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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14
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Cobalt and copper complexes with formamidine ligands: Synthesis, crystal X-ray study, DFT calculations and cytotoxicity. Polyhedron 2019. [DOI: 10.1016/j.poly.2018.12.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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15
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Manojkumar Y, Ambika S, Arulkumar R, Gowdhami B, Balaji P, Vignesh G, Arunachalam S, Venuvanalingam P, Thirumurugan R, Akbarsha MA. Synthesis, DNA and BSA binding, in vitro anti-proliferative and in vivo anti-angiogenic properties of some cobalt(iii) Schiff base complexes. NEW J CHEM 2019. [DOI: 10.1039/c9nj01269a] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In the recent times metal complexes with dual mechanisms of action, anti-cancer and anti-angiogenic, have gained substantial interest in the field of medicinal chemistry.
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Affiliation(s)
| | - Subramanian Ambika
- Department of Chemistry
- Bharathidasan University
- Tiruchirappalli-620024
- India
| | - Rasu Arulkumar
- Department of Chemistry
- Bharathidasan University
- Tiruchirappalli-620024
- India
| | - Balakrishnan Gowdhami
- National Center for Alternatives to Animal Experiments
- Bharathidasan University
- Tiruchirappalli-620024
- India
| | - Perumalsamy Balaji
- National Center for Alternatives to Animal Experiments
- Bharathidasan University
- Tiruchirappalli-620024
- India
| | - Gobalsamy Vignesh
- Department of Chemistry
- Einstein Art and Science College
- Tirunelveli-627012
- India
| | | | | | - Ramaswamy Thirumurugan
- National Center for Alternatives to Animal Experiments
- Bharathidasan University
- Tiruchirappalli-620024
- India
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16
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Zhang C, Sutherland M, Herasymchuk K, Clarke RM, Thompson JR, Chiang L, Walsby CJ, Storr T. Octahedral Co(III) salen complexes: the role of peripheral ligand electronics on axial ligand release upon reduction. CAN J CHEM 2018. [DOI: 10.1139/cjc-2017-0277] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
A series of octahedral CoIII salen complexes (where salen represents a N2O2 bis-Schiff-base bis-phenolate framework) were prepared with axial imidazole ligating groups. When using 1-methylimidazole (1-MeIm) axial ligands, the CoIII/CoII reduction potential could be altered by 220 mV via variation of the electron-donating ability of the para-ring substituents (R = H (1), OMe (2), tBu (3), Br (4), NO2 (5), and CF3 (6)). In addition, the irreversibility of the reduction process suggested substantial geometrical changes and axial ligand exchange upon reduction to the more labile CoII oxidation state. Installing an imidazole-coumarin conjugate as the axial ligands resulted in fluorescence quenching when bound to the CoIII centre (R = H (7), OMe (8), and CF3 (9)). The redox properties and fluorescence increase upon ligand release for 7–9 were studied under reducing conditions and in the presence of excess competing ligand (1-MeIm). It was determined that the Lewis acidity of the CoIII centre was the dominant factor in controlling axial ligand exchange for this series of complexes.
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Affiliation(s)
- Chen Zhang
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Mathew Sutherland
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Khrystyna Herasymchuk
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Ryan M. Clarke
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - John R. Thompson
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Linus Chiang
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Charles J. Walsby
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
| | - Tim Storr
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
- Department of Chemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC V5A 1S6, Canada
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17
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Seifikar Ghomi L, Behzad M, Tarahhomi A, Arab A. Crystal structures, DFT calculations, and Hirshfeld surface analyses of two new copper(II) and nickel(II) Schiff base complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine. J Mol Struct 2017. [DOI: 10.1016/j.molstruc.2017.08.089] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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18
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King AP, Gellineau HA, Ahn JE, MacMillan SN, Wilson JJ. Bis(thiosemicarbazone) Complexes of Cobalt(III). Synthesis, Characterization, and Anticancer Potential. Inorg Chem 2017; 56:6609-6623. [PMID: 28509538 PMCID: PMC8113979 DOI: 10.1021/acs.inorgchem.7b00710] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Nine bis(thiosemicarbazone) (BTSC) cobalt(III) complexes of the general formula [Co(BTSC)(L)2]NO3 were synthesized, where BTSC = diacetyl bis(thiosemicarbazone) (ATS), pyruvaldehyde bis(thiosemicarbazone) (PTS), or glyoxal bis(thiosemicarbazone) (GTS) and L = ammonia, imidazole (Im), or benzylamine (BnA). These compounds were characterized by multinuclear NMR spectroscopy, mass spectrometry, cyclic voltammetry, and X-ray crystallography. Their stability in phosphate-buffered saline was investigated and found to be highly dependent on the nature of the axial ligand, L. These studies revealed that complex stability is primarily dictated by the axial ligand following the sequence NH3 > Im > BnA. The cellular uptake and cytotoxicity in cancer cells were also determined. Both the cellular uptake and cytotoxicity were significantly affected by the nature of the equatorial BTSC. Complexes of ATS were taken up much more effectively than those of PTS and GTS. The cytotoxicity of the complexes was correlated to that of the free ligand. Cell uptake and cytotoxicity were also determined under hypoxic conditions. Only minor differences in the hypoxia activity and uptake were observed. Treatment of the cancer cells with the copper-depleting agent tetrathiomolybdate decreased the cytotoxic potency of the complexes, indicating that they may operate via a copper-dependent mechanism. These results provide a structure-activity relationship for this class of compounds, which may be applied for the rational design of new cobalt(III) anticancer agents.
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Affiliation(s)
- A. Paden King
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
| | - Hendryck A. Gellineau
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
| | - Jung-Eun Ahn
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
| | - Samantha N. MacMillan
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
| | - Justin J. Wilson
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States
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19
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Masoudi M, Behzad M, Arab A, Tarahhomi A, Rudbari HA, Bruno G. Crystal structures, DFT calculations and Hirshfeld surface analyses of three new cobalt(III) Schiff base complexes derived from meso-1,2-diphenyl-1,2-ethylenediamine. J Mol Struct 2016. [DOI: 10.1016/j.molstruc.2016.05.092] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
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20
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Heffern MC, Reichova V, Coomes JL, Harney AS, Bajema EA, Meade TJ. Tuning cobalt(III) Schiff base complexes as activated protein inhibitors. Inorg Chem 2015; 54:9066-74. [PMID: 26331337 PMCID: PMC4638226 DOI: 10.1021/acs.inorgchem.5b01415] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Cobalt(III) Schiff base complexes ([Co(acacen)(L)2](+), where L = NH3) inhibit histidine-containing proteins through dissociative exchange of the labile axial ligands (L). This work investigates axial ligand exchange dynamics of [Co(acacen)(L)2](+) complexes toward the development of protein inhibitors that are activated by external triggers such as light irradiation. We sought to investigate ligand exchange dynamics to design a Co(III) complex that is substitutionally inert under normal physiological conditions for selective activation. Fluorescent imidazoles (C3Im) were prepared as axial ligands in [Co(acacen)(L)2](+) to produce complexes (CoC3Im) that could report on ligand exchange and, thus, complex stability. These fluorescent imidazole reporters guided the design of a new dinuclear Co(III) Schiff base complex containing bridging diimidazole ligands, which exhibits enhanced stability to ligand exchange with competing imidazoles and to hydrolysis within a biologically relevant pH range. These studies inform the design of biocompatible Co(III) Schiff base complexes that can be selectively activated for protein inhibition with spatial and temporal specificity.
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Affiliation(s)
| | | | - Joseph L. Coomes
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Allison S. Harney
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Elizabeth A. Bajema
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113, United States
| | - Thomas J. Meade
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113, United States
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21
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Vistain LF, Yamamoto N, Rathore R, Cha P, Meade TJ. Targeted Inhibition of Snail Activity in Breast Cancer Cells by Using a Co(III) -Ebox Conjugate. Chembiochem 2015; 16:2065-72. [PMID: 26305708 DOI: 10.1002/cbic.201500289] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2015] [Indexed: 12/29/2022]
Abstract
The transition from a non-invasive to an invasive phenotype is an essential step in tumor metastasis. The Snail family of transcription factors (TFs) is known to play a significant role in this transition. These TFs are zinc fingers that bind to the CAGGTG Ebox consensus sequence. Co(III) -Ebox is a cobalt(III) complex attached to an Ebox oligonucleotide that confers specificity towards Snail TFs. Co(III) -Ebox has been shown to inhibit Snail-mediated embryonic neural crest development in Xenopus laevis, but its efficacy in inhibiting Snail-induced cancer cell invasiveness has not been explored. Here, we describe the efficacy of Co(III) -Ebox in inhibiting the invasive aspects of heregulin-β1(HRG)-treated breast cancer cells. Co(III) -Ebox was found to inhibit the capacity of Snail to repress target genes after HRG induction. Snail inhibition by Co(III) -Ebox reduced the invasive propensity of cells in 2D and 3D, thereby demonstrating promise in inhibiting metastasis.
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Affiliation(s)
- Luke F Vistain
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, Radiology, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA
| | - Natsuho Yamamoto
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, Radiology, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA
| | - Richa Rathore
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, Radiology, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA
| | - Peter Cha
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, Radiology, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA
| | - Thomas J Meade
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, Radiology, Northwestern University, 2145 Sheridan Road, Evanston, IL, 60208-3113, USA.
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22
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Holbrook RJ, Weinberg DJ, Peterson MD, Weiss EA, Meade TJ. Light-activated protein inhibition through photoinduced electron transfer of a ruthenium(II)-cobalt(III) bimetallic complex. J Am Chem Soc 2015; 137:3379-85. [PMID: 25671465 DOI: 10.1021/jacs.5b00342] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
We describe a mechanism of light activation that initiates protein inhibitory action of a biologically inert Co(III) Schiff base (Co(III)-sb) complex. Photoinduced electron transfer (PET) occurs from a Ru(II) bipyridal complex to a covalently attached Co(III) complex and is gated by conformational changes that occur in tens of nanoseconds. Reduction of the Co(III)-sb by PET initiates displacement of the inert axial imidazole ligands, promoting coordination to active site histidines of α-thrombin. Upon exposure to 455 nm light, the rate of ligand exchange with 4-methylimidazole, a histidine mimic, increases by approximately 5-fold, as observed by NMR spectroscopy. Similarly, the rate of α-thrombin inhibition increases over 5-fold upon irradiation. These results convey a strategy for light activation of inorganic therapeutic agents through PET utilizing redox-active metal centers.
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Affiliation(s)
- Robert J Holbrook
- Department of Chemistry, Northwestern University , Evanston, Illinois 60208, United States
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23
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Nguyen DT, Cavazos RJ, Harris AN, Petros RA. Werner Complexes Viewed Anew: Utilizing Cobalt Coordination Chemistry for ‘Traceless’ Stimuli-Responsive Bioconjugation Involving Therapeutic Nanoparticles, Protein PEGylation, and Drug-(Bio)polymer Conjugates. COMMENT INORG CHEM 2014. [DOI: 10.1080/02603594.2014.940103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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24
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Heffern MC, Velasco PT, Matosziuk LM, Coomes JL, Karras C, Ratner MA, Klein WB, Eckermann AL, Meade TJ. Modulation of amyloid-β aggregation by histidine-coordinating Cobalt(III) Schiff base complexes. Chembiochem 2014; 15:1584-9. [PMID: 24961930 PMCID: PMC4166533 DOI: 10.1002/cbic.201402201] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Indexed: 01/14/2023]
Abstract
Oligomers of the Aβ42 peptide are significant neurotoxins linked to Alzheimer's disease (AD). Histidine (His) residues present at the N terminus of Aβ42 are believed to influence toxicity by either serving as metal-ion binding sites (which promote oligomerization and oxidative damage) or facilitating synaptic binding. Transition metal complexes that bind to these residues and modulate Aβ toxicity have emerged as therapeutic candidates. Cobalt(III) Schiff base complexes (Co-sb) were evaluated for their ability to interact with Aβ peptides. HPLC-MS, NMR, fluorescence, and DFT studies demonstrated that Co-sb complexes could interact with the His residues in a truncated Aβ16 peptide representing the Aβ42 N terminus. Coordination of Co-sb complexes altered the structure of Aβ42 peptides and promoted the formation of large soluble oligomers. Interestingly, this structural perturbation of Aβ correlated to reduced synaptic binding to hippocampal neurons. These results demonstrate the promise of Co-sb complexes in anti-AD therapeutic approaches.
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Affiliation(s)
- Marie C. Heffern
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Pauline T. Velasco
- Department of Neurobiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Lauren M. Matosziuk
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Joseph L. Coomes
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Constantine Karras
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Mark A. Ratner
- Department of Chemistry, Northwestern University, Evanston, IL 60208-3113, USA
| | - William B. Klein
- Department of Neurobiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Amanda L. Eckermann
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, IL 60208-3113, USA
| | - Thomas J. Meade
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, IL 60208-3113, USA
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25
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Okuhata M, Mochida T. Ionic liquids from the cationic cobalt(III) Schiff base complex, [Co(acacen)L2][Tf2N] (acacen = N,N′-bis(acetylacetone)ethylenediamine, Tf2N = bis(trifluoromethanesulfonyl)amide). J COORD CHEM 2014. [DOI: 10.1080/00958972.2014.917295] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Affiliation(s)
- Megumi Okuhata
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
| | - Tomoyuki Mochida
- Department of Chemistry, Graduate School of Science, Kobe University, Kobe, Japan
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26
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Heffern MC, Kurutz JW, Meade TJ. Spectroscopic elucidation of the inhibitory mechanism of Cys2His2 zinc finger transcription factors by cobalt(III) Schiff base complexes. Chemistry 2013; 19:17043-53. [PMID: 24203451 DOI: 10.1002/chem.201301659] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 10/05/2013] [Indexed: 01/22/2023]
Abstract
Transcription factors are key regulators in both normal and pathological cell processes. Affecting the activity of these proteins is a promising strategy for understanding gene regulation and developing effective therapeutics. Co(III) Schiff base complexes ([Co(acacen)(L)2](+) where L=labile axial ligands) have been shown to be potent inhibitors of a number of zinc metalloproteins including Cys2His2 zinc finger transcription factors. Inhibition by [Co(acacen)(L)2](+) of the target protein is believed to occur through a dissociative exchange of the labile axial ligands for histidine (His) residues essential for function. Here, we report a series of spectroscopic investigations with model peptides of zinc fingers that elucidate the interaction between [Co(acacen)(L)2](+) complexes and zinc finger transcription factors. Observed changes in NMR chemical shifts and 2D (1)H-(1)H NOESY NMR spectra demonstrate the preference of [Co(acacen)(L)2](+) complexes to coordinate His residues over other amino acids. The conformation of [Co(acacen)(L)2](+) upon His coordination was characterized by (1)H NMR spectroscopy, near-UV CD, and electronic absorption. These studies reveal that the resulting His-coordinated [Co(acacen)(L)2](+) complex possesses an octahedral structure. The effects of [Co(acacen)(L)2](+) complexes on the zinc-finger structure were assessed by the degree of hydrogen bonding (probed by 2D NMR spectroscopy) and secondary-structure profiles measured by far-UV CD. These structural studies demonstrate the ability of [Co(acacen)(L)2](+) complexes to disrupt the ββα structure of zinc fingers, resulting in primarily random-coil conformations. A mechanism is described wherein [Co(acacen)(L)2](+) complexes inhibit zinc finger transcription factor activity through selectively coordinating His residues in the zinc finger by dissociative ligand exchange and disrupting the ββα structural motif required for gene regulation.
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Affiliation(s)
- Marie C Heffern
- Department of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113 (USA)
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27
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Peterson MD, Holbrook RJ, Meade TJ, Weiss EA. Photoinduced electron transfer from PbS quantum dots to cobalt(III) Schiff base complexes: light activation of a protein inhibitor. J Am Chem Soc 2013; 135:13162-7. [PMID: 23931454 DOI: 10.1021/ja4065393] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
This paper describes the activation of a biologically inert Co(III) Schiff base [Co(III)-SB] complex to its protein inhibitor form by photoinduced electron transfer (PET) from a colloidal PbS quantum dot (QD, radii of 1.5-1.7 nm) to the cobalt center, with a charge separation time constant of 125 ns. Reduction of the Co(III)-SB complex initiates release of the native axial ligands, promoting replacement with the histidine mimic 4-methylimidazole. The rate of ligand displacement increases by a factor of approximately 8 upon exposure of the PbS QD/Co(III)-SB mixture to light with an energy greater than the energy of the first excitonic state of the QDs, from which PET occurs. These results suggest an approach for the preparation of inorganic therapeutic agents that can be specifically coupled to a biologically active site by cooperative redox binding ligation.
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Affiliation(s)
- Mark D Peterson
- Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States
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28
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Fleck M, Layek M, Saha R, Bandyopadhyay D. Synthetic aspects, crystal structures and antibacterial activities of manganese(III) and cobalt(III) complexes containing a tetradentate Schiff base. TRANSIT METAL CHEM 2013. [DOI: 10.1007/s11243-013-9741-5] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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29
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Matosziuk LM, Holbrook RJ, Manus LM, Heffern MC, Ratner MA, Meade TJ. Rational design of [Co(acacen)L2]+ inhibitors of protein function. Dalton Trans 2013; 42:4002-12. [PMID: 23340849 PMCID: PMC3581327 DOI: 10.1039/c2dt32565a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Cobalt(III) Schiff base complexes, such as [Co(acacen)L(2)](+), inhibit the function of Zn(II)-dependent proteins through dissociative exchange of the axial ligands with key histidine residues of the target protein. Consequently the efficacy of these compounds depends strongly on the lability of the axial ligands. A series of [Co(acacen)L(2)](+) complexes with various axial ligands was investigated using DFT to determine the kinetics and thermodynamics of ligand exchange and hydrolysis. Results showed excellent agreement with experimental data, indicating that axial ligand lability is determined by several factors: pK(a) of the axial ligand, the kinetic barrier to ligand dissociation, and the relative thermodynamic stability of the complexes before and after exchange. Hammett plots were constructed to determine if the kinetics and thermodynamics of exchange can be modulated by the addition of an electron-withdrawing group (EWG) to either the axial ligand itself or to the equatorial acacen ligand. Results predict that addition of an EWG to the axial ligand will shift the kinetics and thermodynamics so as to promote axial ligand exchange, while addition of an EWG to acacen will decrease axial ligand lability. These investigations will aid in the design of the next generation of [Co(acacen)L(2)](2+), allowing researchers to develop new, more effective inhibitors.
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Affiliation(s)
- Lauren M. Matosziuk
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113
| | - Robert J. Holbrook
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113
| | - Lisa M. Manus
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113
| | - Marie C. Heffern
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113
| | - Mark A. Ratner
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113
| | - Thomas J. Meade
- Departments of Chemistry, Molecular Biosciences, Neurobiology, Biomedical Engineering, and Radiology, Northwestern University, Evanston, Illinois 60208-3113
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