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Excitonic Coupling in Fluorene-Based Bichromophoric Systems: Vibrational Quenching and the Transition from Weak to Intermediate Coupling. J Phys Chem A 2023; 127:7198-7204. [PMID: 37594308 DOI: 10.1021/acs.jpca.3c03511] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/19/2023]
Abstract
Excimeric systems (i.e., excited dimers) have well served as model compounds for the study of the delocalization of electronic energy over weakly interacting chromophores. However, there remain relatively few isolated systems in which such interactions can be studied experimentally at a level to afford detailed comparisons with theory. In this Article, we examine a series of covalently and noncovalently linked dimers of fluorene, as a model aromatic chromophore, where the formation of excimers requires a π-stacked, cofacial orientation at van der Waals contact. Building upon a series of seminal prior studies that examined vibronic quenching of the excitation interaction in van der Waals dimers, the key question that we sought to address here is whether a single quenching factor could reproduce experimental excitonic splittings across a series of covalently and noncovalently linked bichromophoric systems built from the same chromophore. In comparing experimentally measured excitonic splittings with calculated static splittings using time-dependent density functional methods, we find that all systems save one fall on a line with a slope of 0.080(8), reflecting a vibrational quenching of roughly 1 order of magnitude. The outlier, which shows a significantly reduced quenching factor, represents a cyclophane-linked system where the fluorene moieties are constrained in a cofacial arrangement. We argue that this system evidences the transition from the weak to intermediate coupling regime.
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Design and Synthesis of Cofacially-Arrayed Polyfluorene Wires for Electron and Energy Transfer Studies. Molecules 2023; 28:molecules28093717. [PMID: 37175127 PMCID: PMC10180040 DOI: 10.3390/molecules28093717] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 04/17/2023] [Accepted: 04/18/2023] [Indexed: 05/15/2023] Open
Abstract
A study of cofacially arrayed π-systems is of particular importance for the design of functional materials for efficient long-range intra-chain charge transfer through the bulk semiconducting materials in the layers of photovoltaic devices. The effect of π-stacking between a pair of aromatic rings has been mainly studied in the form of cyclophanes, where aromatic rings are forced into a sandwich-like geometry, which extensively deforms the aromatic rings from planarity. The synthetic difficulties associated with the preparation of cyclophane-like structures has prevented the synthesis of many examples of their multi-layered analogues. Moreover, the few available multi-layered cyclophanes are not readily amenable to the structural modification required for the construction of D-spacer-A triads needed to explore mechanisms of electron and energy transfer. In this review, we recount how a detailed experimental and computational analysis of 1,3-diarylalkanes led to the design of a new class of cofacially arrayed polyfluorenes that retain their π-stacked structure. Thus, efficient synthetic strategies have been established for the ready preparation of monodisperse polyfluorenes with up to six π-stacked fluorenes, which afford ready access to D-spacer-A triads by linking donor and acceptor groups to the polyfluorene spacers via single methylenes. Detailed 1H NMR spectroscopy, X-ray crystallography, electrochemistry, and He(I) photoelectron spectroscopy of F2-F6 have confirmed the rigid cofacial stacking of multiple fluorenes in F2-F6, despite the presence of rotatable C-C bonds. These polyfluorenes (F2-F6) form stable cation radicals in which a single hole is delocalized amongst the stacked fluorenes, as judged by the presence of intense charge-resonance transition in their optical spectra. Interestingly, these studies also discern that delocalization of a single cationic charge could occur over multiple fluorene rings in F2-F6, while the exciton is likely localized only onto two fluorenes in F2-F6. Facile synthesis of the D-spacer-A triads allowed us to demonstrate that efficient triplet energy transfer can occur through π-stacked polyfluorenes; the mechanism of energy transfer crosses over from tunneling to hopping with increasing number of fluorenes in the polyfluorene spacer. We suggest that the development of rigidly held π-stacked polyfluorenes, described herein, with well-defined redox and optoelectronic properties provides an ideal scaffold for the study of electron and energy transfer in D-spacer-A triads, where the Fn spacers serve as models for cofacially stacked π-systems.
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Abstract
We employed the density functionaly theory (DFT)-predicted regioselectivity of the intramolecular Scholl reaction in phenanthrene and dibenzo[g,p]chrysene frameworks to obtain π-extended mono and double [7]helicenes, respectively. The formation of these helical structures occurs despite the buildup of a large strain energy up to 30 kcal/mol compared with their most stable isomers. The twisted and strained structures were characterized and analyzed by experimental (NMR, UV-vis, emission, electrochemistry, and single-crystal X-ray diffraction) techniques and were further supported by DFT calculations.
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4
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Risk factors for chronic pulmonary aspergillosis in post-TB patients. Int J Tuberc Lung Dis 2021; 25:324-326. [PMID: 33762078 DOI: 10.5588/ijtld.20.0735] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
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5
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Abstract
Two different series of π-extended dibenzo[g,p]chrysenes are synthesized. The experimental and DFT data showed the significant effects of both position and substituent on the optoelectronic and charge delocalization behavior.
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Electron-Transfer-Induced Self-Assembly of a Molecular Tweezer Platform. Chemistry 2020; 26:14085-14089. [PMID: 32608146 DOI: 10.1002/chem.202001919] [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: 04/20/2020] [Indexed: 12/31/2022]
Abstract
The design and synthesis of a new molecular tweezer (T-tmp) with electron-rich pincers are reported. The stable monocationic radicals and self-assembled dimeric radicals of this molecular tweezer platform were prepared by chemical oxidative titration. With the aid of DFT calculations, it was found that the dimeric radicals with syn-syn-syn conformer has the most stable structure, with the hole primarily delocalized between parallel stacked pyrenyl groups.
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Angular ladder-type meta-phenylenes: synthesis and electronic structural analysis. Org Chem Front 2020; 7:3215-3222. [PMID: 33796320 PMCID: PMC8009403 DOI: 10.1039/d0qo00924e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Herein, we report the synthesis of two new series of angular (all-syn) ladder-type meta-[n]phenylenes (LMP, n = 3-8). One series contains keto groups at the termini bridges, denoted angular keto (AKn), the second contains alkyl groups at all bridge sp3 carbons, denoted angular alkyl (AAn). Their electronic and structural properties were delineated by a combination of electrochemistry and spectroscopic (UV-Vis and emission) methods and further supported by DFT calculations. Interestingly, experimental and DFT data show that changing the bridging group at the termini from alkyl (AAn) to keto (AKn) gives an increase in the first reduction potentials and LUMO energies, as the π-system is extended. Also, the charge (de)localization behavior is different for these two species; while the AAn compounds stablize charge with Robin-Day class III, the AKn compounds show a clear switch from class III to class II. In comparison with the linear analogues (LKn and LAn), DFT results reveal a shape independency of the charge (de)localization mechanism in acceptor-π-acceptor series (AKn/LKn).
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Redox-Induced Molecular Actuators: The Case of Oxy-Alternate Bridged Cyclotetraveratrylene. Org Lett 2019; 21:7987-7991. [PMID: 31553195 DOI: 10.1021/acs.orglett.9b02971] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report a practical two-step approach for the synthesis of hybrid-bridge macrocyclic molecules that has been used to synthesize two novel oxy-alternate-bridged macrocyclic molecules, oxy-alternate cyclotetraveratrylene (O-altCTTV) and oxy-alternate cyclohexaveratrylene (O-altCHV). Electrochemistry, absorption spectroscopy, X-ray crystallography, and DFT calculations demonstrate that O-altCTTV acts as a redox-induced molecular actuator, as its switches from the open conformation in the neutral state to the closed conformation in the cation-radical state.
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Non- planar dodecaalkoxy-hexa-peri-hexabenzocoronene with six reversible oxidation States. J Photochem Photobiol A Chem 2019. [DOI: 10.1016/j.jphotochem.2019.111881] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Highly robust cation radical salts: Aromatic oxidants from cycloannulated aromatic donors. J Photochem Photobiol A Chem 2019. [DOI: 10.1016/j.jphotochem.2019.111882] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Role of Conserved Histidine and Serine in the HCXXXXXRS Motif of Human Dual-Specificity Phosphatase 5. J Chem Inf Model 2019; 59:1563-1574. [PMID: 30835471 DOI: 10.1021/acs.jcim.8b00919] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
BACKGROUND The mitogen-activated protein kinase (MAPK) pathway is functionally generic and critical in maintaining physiological homeostasis and normal tissue development. This pathway is under tight regulation, which is in part mediated by dual-specific phosphatases (DUSPs), which dephosphorylate serine, threonine, and tyrosine residues of the ERK family of proteins. DUSP5 is of high clinical interest because of mutations we identified in this protein in patients with vascular anomalies. Unlike other DUSPs, DUSP5 has unique specificity toward substrate pERK1/2. Using molecular docking and simulation strategies, we previously showed that DUSP5 has two pockets, which are utilized in a specific fashion to facilitate specificity toward catalysis of its substrate pERK1/2. Remarkably, most DUSPs share high similarity in their catalytic sites. Studying the catalytic domain of DUSP5 and identifying amino acid residues that are important for dephosphorylating pERK1/2 could be critical in developing small molecules for therapies targeting DUSP5. RESULTS In this study, we utilized computational modeling to identify and predict the importance of two conserved amino acid residues, H262 and S270, in the DUSP5 catalytic site. Modeling studies predicted that catalytic activity of DUSP5 would be altered if these critical conserved residues were mutated. We next generated independent Glutathione-S-Transferase (GST)-tagged full-length DUSP5 mutant proteins carrying specific mutations H262F and S270A in the phosphatase domain. Biochemical analysis was performed on these purified proteins, and consistent with our computational prediction, we observed altered enzyme activity kinetic profiles for both mutants with a synthetic small molecule substrate (pNPP) and the physiological relevant substrate (pERK) when compared to wild type GST-DUSP5 protein. CONCLUSION Our molecular modeling and biochemical studies combined demonstrate that enzymatic activity of phosphatases can be manipulated by mutating specific conserved amino acid residues in the catalytic site (phosphatase domain). This strategy could facilitate generation of small molecules that will serve as agonists/antagonists of DUSP5 activity.
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Discovery and Characterization of Halogenated Xanthene Inhibitors of DUSP5 as Potential Photodynamic Therapeutics. J Photochem Photobiol A Chem 2019; 375:114-131. [PMID: 31839699 PMCID: PMC6910256 DOI: 10.1016/j.jphotochem.2019.01.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Dual specific phosphatases (DUSPs) are an important class of mitogen-activated protein kinase (MAPK) regulators, and are drug targets for treating vascular diseases. Previously we had shown that DUSP5 plays a role in embryonic vertebrate vascular patterning. Herein, we screened a library of FDA-approved drugs and related compounds, using a para-nitrophenylphosphate substrate (pNPP)-based assay. This assay identified merbromin (also known as mercurochrome) as targeting DUSP5; and, we subsequently identified xanthene-ring based merbromin analogs eosin Y, erythrosin B, and rose bengal, all of which inhibit DUSP5 in vitro. Inhibition was time-dependent for merbromin, eosin Y, 2',7'-dibromofluorescein, and 2',7'-dichlorofluorescein, with enzyme inhibition increasing over time. Reaction progress curve data fit best to a slow-binding model of irreversible enzyme inactivation. Potency of the time-dependent compounds, except for 2',7'-dichlorofluorescein, was diminished when dithiothreitol (DTT) was present, suggesting thiol reactivity. Two additional merbromin analogs, erythrosin B and rose bengal also inhibit DUSP5, but have the therapeutic advantage of being less sensitive to DTT and exhibiting little time dependence for inhibition. Inhibition potency is correlated with the xanthene dye's LUMO energy, which affects ability to form light-activated radical anions, a likely active inhibitor form. Consistent with this hypothesis, rose bengal inhibition is light-dependent and demonstrates the expected red shifted spectrum upon binding to DUSP5, with a Kd of 690 nM. These studies provide a mechanistic foundation for further development of xanthene dyes for treating vascular diseases that respond to DUSP5 inhibition, with the following relative potencies: rose bengal > merbromin > erythrosin B > eosin Y.
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Development of probe-based real-time loop-mediated isothermal amplification for detection of Brucella. J Appl Microbiol 2019; 126:1332-1339. [PMID: 29851222 DOI: 10.1111/jam.13938] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2018] [Revised: 05/24/2018] [Accepted: 05/25/2018] [Indexed: 11/27/2022]
Abstract
AIM To develop a rapid, sensitive and specific diagnostic assay for the detection of Brucella. METHODS AND RESULTS The probe-based RT-LAMP was carried out by using a set of four or six primers and different LAMP chemicals to compare its results with real-time PCR. Detection of gene amplification is done within 40 min and can be seen by amplification curve, turbidity and addition of DNA-binding dye at the end of the reaction results in colour difference under normal day light and in UV. The sensitivity of probe-based real-time LAMP assay was found 10-fold higher than Taqman-based qPCR. The specificity of the developed assay was validated by the absence of any cross-reaction with other pathogenic bacteria. CONCLUSION The developed probe-based RT-LAMP assay is extremely rapid, cost effective, highly specific and sensitive, and has potential usefulness for rapid Brucella surveillance. SIGNIFICANCE AND IMPACT OF THE STUDY The developed probe-based RT-LAMP is a powerful gene amplification technique which is a specific, fast diagnostic tool for early detection and identification of Brucella.
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Calix[4]arene-Based Bis(Nitric Oxide) Complexes: Synthesis, Physical Properties, and Structural Characterization. Chem Asian J 2019; 14:542-546. [PMID: 30549456 DOI: 10.1002/asia.201801683] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Revised: 12/12/2018] [Indexed: 11/08/2022]
Abstract
Calix[4]arene-based molecules hold great promise as candidate sensors and storage materials for nitric oxide (NO), owing to their unprecedented binding affinity for NO. However, the structure of calix[4]arene is complicated by the availability of four possible conformers: 1,3-alternate, 1,2-alternate, cone, and partial cone (paco). Whilst complexes of NO with several of these conformers have previously been established, the 1,2-alternate conformer complex, that is, [1,2-alter⋅NO]+ , has not been previously reported. Herein, we determine the crystal structure of the NO complex with the 1,2-alternate conformer for the first time. In addition, we have also found that the 1,2-alternate and 1,3-alternate conformers can combine with two NO molecules to form stable bis(nitric oxide) complexes. These new complexes, which exhibit remarkable binding capacity for the construction of NO-storage molecules, were characterized by using X-ray crystallography and NMR, IR, and UV/Vis spectroscopy. These findings will extend our understanding of the interactions between nitric oxide and cofacially and non-cofacially arrayed aromatic rings, and we expect them to aid in the design and development of new supramolecular sensors and storage materials for NO with high capacity and efficacy.
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An Electron‐Rich Calix[4]arene‐Based Receptor with Unprecedented Binding Affinity for Nitric Oxide. Chemistry 2018; 24:17439-17443. [DOI: 10.1002/chem.201804245] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2018] [Indexed: 11/08/2022]
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Vertical vs. adiabatic ionization energies in solution and gas-phase: probing ionization-induced reorganization in conformationally-mobile bichromophoric actuators using photoelectron spectroscopy, electrochemistry and theory. Phys Chem Chem Phys 2018; 20:25615-25622. [PMID: 30283939 DOI: 10.1039/c8cp02936a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ionization-induced structural and conformational reorganization in various π-stacked dimers and covalently linked bichromophores is relevant to many processes in biological systems and functional materials. In this work, we examine the role of structural, conformational, and solvent reorganization in a set of conformationally mobile bichromophoric donors, using a combination of gas-phase photoelectron spectroscopy, solution-phase electrochemistry, and density functional theory (DFT) calculations. Photoelectron spectral analysis yields both adiabatic and vertical ionization energies (AIE/VIE), which are compared with measured (adiabatic) solution-phase oxidation potentials (Eox). Importantly, we find a strong correlation of Eox with AIE, but not VIE, reflecting variations in the attendant structural/conformational reorganization upon ionization. A careful comparison of the experimental data with the DFT calculations allowed us to probe the extent of charge stabilization in the gas phase and solution and to parse the reorganizational energy into its various components. This study highlights the importance of a synergistic approach of experiment and theory to study ionization-induced structural and conformational reorganization.
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π - π stacking vs. C-H/ π interaction: Excimer formation and charge resonance stabilization in van der Waals clusters of 9,9'-dimethylfluorene. J Chem Phys 2018; 149:134314. [PMID: 30292228 DOI: 10.1063/1.5044648] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Studies of exciton and hole stabilization in multichromophoric systems underpin our understanding of electron transfer and transport in materials and biomolecules. The simplest model systems are dimeric, and recently we compared the gas-phase spectroscopy and dynamics of van der Waals dimers of fluorene, 9-methylfluorene (MF), and 9,9'-dimethylfluorene (F1) to assess how sterically controlled facial encumbrance modulates the dynamics of excimer formation and charge resonance stabilization (CRS). Dimers of fluorene and MF show only excimer emission upon electronic excitation, and significant CRS as evidenced in a reduced ionization potential for the dimer relative the monomer. By contrast, the dimer of F1 shows no excimeric emission, rather structured emission from the locally excited state of a tilted (non π-stacked) dimer, evidencing the importance of C-H/π interactions and increased steric constraints that restrict a cofacial approach. In this work, we report our full results on van der Waals clusters of F1, using a combination of theory and experiments that include laser-induced fluorescence, mass-selected two-color resonant two-photon ionization spectroscopy, and two-color appearance potential measurements. We use the latter to derive the binding energies of the F1 dimer in ground, excited, and cation radical states. Our results are compared with van der Waals and covalently linked clusters of fluorene to assess both the relative strength of π-stacking and C-H/π interactions in polyaromatic assemblies and the role of π-stacking in excimer formation and CRS.
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Synthesis of Doubly Annulated m-Terphenyl-Based Molecular Tweezers and Their Charge-Transfer Complexes with DDQ as a Guest. Chemistry 2018; 24:13106-13109. [PMID: 30033629 DOI: 10.1002/chem.201803137] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 07/19/2018] [Indexed: 11/06/2022]
Abstract
The synthesis of a doubly-annulated m-terphenyl-based tweezer platform has been developed, which affords ready incorporation of various pincer units from monobenzenoid to polybenzenoid electron donors. The complexation study with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as guest has been carried out, and the crystal structure of T-Py∩DDQ reveals the sandwich-type binding mode in the solid state.
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Molecular Actuators in Action: Electron-Transfer-Induced Conformation Transformation in Cofacially Arrayed Polyfluorenes. J Phys Chem Lett 2018; 9:4233-4238. [PMID: 29985630 DOI: 10.1021/acs.jpclett.8b01918] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
There is much current interest in the design of molecular actuators, which undergo reversible, controlled motion in response to an external stimulus (light, heat, oxidation, etc.). Here we describe the design and synthesis of a series of cofacially arrayed polyfluorenes (MeF nH m) with varied end-capping groups, which undergo redox-controlled electromechanical actuation. Such cofacially arrayed polyfluorenes are a model molecular scaffold to investigate fundamental processes of charge and energy transfer across a π-stacked assembly, and we show with the aid of NMR and optical spectroscopies, X-ray crystallography and DFT calculations that in the neutral state the conformation of MeF nH1 and MeF nH2 is open rather than cofacial, with a conformational dependence that is highly influenced by the local environment. Upon (electro)chemical oxidation, these systems undergo a reversible transformation into a closed fully π-stacked conformation, driven by charge-resonance stabilization of the cationic charge. These findings are expected to aid the design of novel wire-like cofacially arrayed systems capable of undergo redox-controlled actuation.
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Game of Frontier Orbitals: A View on the Rational Design of Novel Charge-Transfer Materials. J Phys Chem Lett 2018; 9:3978-3986. [PMID: 29952570 DOI: 10.1021/acs.jpclett.8b01093] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Since the first application of frontier molecular orbitals (FMOs) to rationalize stereospecificity of pericyclic reactions, FMOs have remained at the forefront of chemical theory. Yet, the practical application of FMOs in the rational design and synthesis of novel charge transfer materials remains under-appreciated. In this Perspective, we demonstrate that molecular orbital theory is a powerful and universal tool capable of rationalizing the observed redox/optoelectronic properties of various aromatic hydrocarbons in the context of their application as charge-transfer materials. Importantly, the inspection of FMOs can provide instantaneous insight into the interchromophoric electronic coupling and polaron delocalization in polychromophoric assemblies, and therefore is invaluable for the rational design and synthesis of novel materials with tailored properties.
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Correction to “Critical Role of the Secondary Binding Pocket in Modulating the Enzymatic Activity of DUSP5 toward Phosphorylated ERKs”. Biochemistry 2018; 57:3987. [DOI: 10.1021/acs.biochem.8b00570] [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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The Role of Torsional Dynamics on Hole and Exciton Stabilization in π‐Stacked Assemblies: Design of Rigid Torsionomers of a Cofacial Bifluorene. Angew Chem Int Ed Engl 2018; 57:8189-8193. [DOI: 10.1002/anie.201804337] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Indexed: 11/12/2022]
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The Role of Torsional Dynamics on Hole and Exciton Stabilization in π‐Stacked Assemblies: Design of Rigid Torsionomers of a Cofacial Bifluorene. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201804337] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Strength of π-Stacking, from Neutral to Cation: Precision Measurement of Binding Energies in an Isolated π-Stacked Dimer. J Phys Chem Lett 2018; 9:2058-2061. [PMID: 29630843 DOI: 10.1021/acs.jpclett.8b00742] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
π-Stacking interactions are ubiquitious across chemistry and biochemistry, impacting areas from organic materials and photovoltaics to biochemistry and DNA. However, experimental data is lacking regarding the strength of π-stacking forces-an issue not settled even for the simplest model system, the isolated benzene dimer. Here, we use two-color appearance potential measurements to determine the binding energies of the isolated, π-stacked dimer of fluorene (C13H10) in ground, excited, and ionic states. Our measurements provide the first precise values for π-stacking interaction energies in these states, which are key benchmarks for theory. Indeed, theoretical predictions using ab initio and carefully benchmarked DFT methods are in excellent agreement with experiment.
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From Static to Dynamic: Electron Density of HOMO at Biaryl Linkage Controls the Mechanism of Hole Delocalization. J Am Chem Soc 2018; 140:4765-4769. [DOI: 10.1021/jacs.8b00466] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Isolation of a chiral anthracene cation radical: X-ray crystallography and computational interrogation of its racemization. Chem Commun (Camb) 2018; 53:2748-2751. [PMID: 28203653 DOI: 10.1039/c6cc10307c] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chiral cation-radical salts hold significant promise as charge-transfer materials, chiroptical switches, and electron-transfer catalysts for enantioselective synthesis. Herein we demonstrate that the readily-available chiral 9,10-diphenyleanthracene derivative (i.e.SANT) forms a robust cation radical, whose structure was elucidated by X-ray crystallography and DFT calculations. While SANT was observed to racemize on a timescale (t1/2) of 1.1 hours, a computational conformational search and kinetic analysis of the racemization pathway led us to identify a simple methyl substituted SANT derivative, which does not racemize (racemization t1/2 1013-1017 years).
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From Intramolecular (Circular) in an Isolated Molecule to Intermolecular Hole Delocalization in a Two‐Dimensional Solid‐State Assembly: The Case of Pillarene. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201712159] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract P1-08-05: A phase I trial of chemotherapy followed by infusions of activated T cells armed with anti-CD3 and anti-HER2 bispecific antibody for stage III, Her2+ or Her2- breast cancer. Cancer Res 2018. [DOI: 10.1158/1538-7445.sabcs17-p1-08-05] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
Background: The balance in the immune system between immune surveillance and tolerance is known to be associated with the prognosis of breast cancer patients. The aim of this phase I study was to assess the safety of anti-CD3 x anti-HER2Bi bispecific antibody targeted (BAT) activated T cells (TC) in high risk breast cancer patients. The BAT T-cells exhibit anti-HER2 cytotoxicity, proliferate, and secrete immunokines upon tumor engagement.
Methods: High risk adjuvant breast cancer patients were recruited and completed standard adjuvant chemotherapy. BATs were produced by stimulating peripheral blood mononuclear cells (PBMC) obtained by leukapheresis; collected TC were then activated with anti-CD3 monoclonal antibody and expanded in IL-2 for 12-14 days. TC were armed with bispecific antibody and cryopreserved until used. Groups of 3 patients received 20, 40, 80 or 160 x 109 BATs per infusion twice a week for four weeks. All patients were treated at Roger Williams Medical Center.
Results: Nine patients were accrued and all had N3 disease. Eight of 9 patients were ER positive; 2 of 9 were HER2 overexpressing. The median OS has not reached as five of nine patients are still alive. OS range from 14.3 to 154.7 months (as December 11, 2016). Five out of the five patients who are alive have no evidence of disease and 1 patient had a secondary primary that has been successfully treated and she has no evidence of disease. It was feasible to grow up to 160 x 109 BATs and this dose level was tolerable without any cell-based dose limiting toxicities. BATs persisted in the blood for at least a week. BAT infusions induce cellular anti-tumor responses and cytokine responses.
Conclusion: Targeting HER2 positive and negative tumors induced cytotoxic anti-tumor responses, increases in Th1 cytokines and IL-12 serum levels. The prolonged survival in a high risk population suggests that BAT infusions provided a clinical benefit. These results are being confirmed in a phase II trial for metastatic breast cancer.
Citation Format: Dillon P, Rathore R, Thakur A, Colvin G, Kouttab N, Lum L. A phase I trial of chemotherapy followed by infusions of activated T cells armed with anti-CD3 and anti-HER2 bispecific antibody for stage III, Her2+ or Her2- breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P1-08-05.
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From Intramolecular (Circular) in an Isolated Molecule to Intermolecular Hole Delocalization in a Two-Dimensional Solid-State Assembly: The Case of Pillarene. Angew Chem Int Ed Engl 2018; 57:2144-2149. [PMID: 29327390 DOI: 10.1002/anie.201712159] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Indexed: 11/06/2022]
Abstract
To achieve long-range charge transport/separation and, in turn, bolster the efficiency of modern photovoltaic devices, new molecular scaffolds are needed that can self-assemble in two-dimensional (2D) arrays while maintaining both intra- and intermolecular electronic coupling. In an isolated molecule of pillarene, a single hole delocalizes intramolecularly via hopping amongst the circularly arrayed hydroquinone ether rings. The crystallization of pillarene cation radical produces a 2D self-assembly with three intermolecular dimeric (sandwich-like) contacts. Surprisingly, each pillarene in the crystal lattice bears a fractional formal charge of +1.5. This unusual stoichiometry of oxidized pillarene in crystals arises from effective charge distribution within the 2D array via an interplay of intra- and intermolecular electronic couplings. This important finding is expected to help advance the rational design of efficient solid-state materials for long-range charge transfer.
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Study of Förster Resonance Energy Transfer to Lipid Domain Markers Ascertains Partitioning of Semisynthetic Lipidated N-Ras in Lipid Raft Nanodomains. Biochemistry 2018; 57:872-881. [PMID: 29280621 DOI: 10.1021/acs.biochem.7b01181] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Cellular membranes are heterogeneous planar lipid bilayers displaying lateral phase separation with the nanometer-scale liquid-ordered phase (also known as "lipid rafts") surrounded by the liquid-disordered phase. Many membrane-associated proteins were found to permanently integrate into the lipid rafts, which is critical for their biological function. Isoforms H and N of Ras GTPase possess a unique ability to switch their lipid domain preference depending on the type of bound guanine nucleotide (GDP or GTP). This behavior, however, has never been demonstrated in vitro in model bilayers with recombinant proteins and therefore has been attributed to the action of binding of Ras to other proteins at the membrane surface. In this paper, we report the observation of the nucleotide-dependent switch of lipid domain preferences of the semisynthetic lipidated N-Ras in lipid raft vesicles in the absence of additional proteins. To detect segregation of Ras molecules in raft and disordered lipid domains, we measured Förster resonance energy transfer between the donor fluorophore, mant, attached to the protein-bound guanine nucleotides, and the acceptor, rhodamine-conjugated lipid, localized into the liquid-disordered domains. Herein, we established that N-Ras preferentially populated raft domains when bound to mant-GDP, while losing its preference for rafts when it was associated with a GTP mimic, mant-GppNHp. At the same time, the isolated lipidated C-terminal peptide of N-Ras was found to be localized outside of the liquid-ordered rafts, most likely in the bulk-disordered lipid. Substitution of the N-terminal G domain of N-Ras with a homologous G domain of H-Ras disrupted the nucleotide-dependent lipid domain switch.
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Towards the rational design of novel charge-transfer materials: biaryls with a dihedral angle-independent hole delocalization mechanism. Chem Commun (Camb) 2018; 54:5851-5854. [DOI: 10.1039/c8cc02595a] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Herein, we demonstrate a rational design of novel materials using FMO analysis on the example of biaryls with dihedral angle independent mechanism of hole delocalization.
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An electron-transfer induced conformational transformation: from non-cofacial “sofa” to cofacial “boat” in cyclotetraveratrylene (CTTV) and formation of charge transfer complexes. Org Biomol Chem 2018; 16:5712-5717. [DOI: 10.1039/c8ob01118d] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Cyclotetraveratrylene (CTTV) undergoes oxidation-induced folding, consistent with interconversion from a non-cofacial “sofa” conformation to a cofacial “boat” conformer.
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FHBC, a Hexa‐
peri
‐hexabenzocoronene–Fluorene Hybrid: A Platform for Highly Soluble, Easily Functionalizable HBCs with an Expanded Graphitic Core. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201711739] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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FHBC, a Hexa‐
peri
‐hexabenzocoronene–Fluorene Hybrid: A Platform for Highly Soluble, Easily Functionalizable HBCs with an Expanded Graphitic Core. Angew Chem Int Ed Engl 2017; 57:790-794. [DOI: 10.1002/anie.201711739] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2017] [Indexed: 11/06/2022]
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Predictive Models in Differentiating Vertebral Lesions Using Multiparametric MRI. AJNR Am J Neuroradiol 2017; 38:2391-2398. [PMID: 29025721 DOI: 10.3174/ajnr.a5411] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Accepted: 07/22/2017] [Indexed: 11/07/2022]
Abstract
BACKGROUND AND PURPOSE Conventional MR imaging has high sensitivity but limited specificity in differentiating various vertebral lesions. We aimed to assess the ability of multiparametric MR imaging in differentiating spinal vertebral lesions and to develop statistical models for predicting the probability of malignant vertebral lesions. MATERIALS AND METHODS One hundred twenty-six consecutive patients underwent multiparametric MRI (conventional MR imaging, diffusion-weighted MR imaging, and in-phase/opposed-phase imaging) for vertebral lesions. Vertebral lesions were divided into 3 subgroups: infectious, noninfectious benign, and malignant. The cutoffs for apparent diffusion coefficient (expressed as 10-3 mm2/s) and signal intensity ratio values were calculated, and 3 predictive models were established for differentiating these subgroups. RESULTS Of the lesions of the 126 patients, 62 were infectious, 22 were noninfectious benign, and 42 were malignant. The mean ADC was 1.23 ± 0.16 for infectious, 1.41 ± 0.31 for noninfectious benign, and 1.01 ± 0.22 mm2/s for malignant lesions. The mean signal intensity ratio was 0.80 ± 0.13 for infectious, 0.75 ± 0.19 for noninfectious benign, and 0.98 ± 0.11 for the malignant group. The combination of ADC and signal intensity ratio showed strong discriminatory ability to differentiate lesion type. We found an area under the curve of 0.92 for the predictive model in differentiating infectious from malignant lesions and an area under the curve of 0.91 for the predictive model in differentiating noninfectious benign from malignant lesions. On the basis of the mean ADC and signal intensity ratio, we established automated statistical models that would be helpful in differentiating vertebral lesions. CONCLUSIONS Our study shows that multiparametric MRI differentiates various vertebral lesions, and we established prediction models for the same.
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Cofacially Arrayed Polyfluorenes: Spontaneous Formation of π-Stacked Assemblies in the Gas Phase. J Phys Chem Lett 2017; 8:5272-5276. [PMID: 29020769 DOI: 10.1021/acs.jpclett.7b02627] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Understanding geometrical and size dependencies of through-space charge delocalization in multichromophoric systems is critical to model electron transfer and transport in materials and biomolecules. In this work, we examine the size evolution of hole delocalization in van der Waals clusters of fluorene (i.e., (F)n), where a range of geometries are possible, reflecting both π-stacking and C-H/π interactions. Using mass-selected two-color resonant two-photon ionization spectroscopy (2CR2PI), we measure electronic spectra and vertical ionization potentials (IPs) in the gas phase. Results are compared with model covalently linked assemblies (denoted Fn), exhibiting a sterically enforced cofacial (i.e., π-stacked) orientation of chromophores. For both systems, an inverse size dependence (i.e., 1/n) of IP vs cluster size is found. Surprisingly, the values for the two sets fall on the same line! This trend is examined via theory, which emphasizes the important role of π-stacking, and its geometrical dependencies, in the process of hole delocalization in multichromophoric assemblies.
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Dual Specificity Phosphatase 5-Substrate Interaction: A Mechanistic Perspective. Compr Physiol 2017; 7:1449-1461. [PMID: 28915331 DOI: 10.1002/cphy.c170007] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The mammalian genome contains approximately 200 phosphatases that are responsible for catalytically removing phosphate groups from proteins. In this review, we discuss dual specificity phosphatase 5 (DUSP5). DUSP5 belongs to the dual specificity phosphatase (DUSP) family, so named after the family members' abilities to remove phosphate groups from serine/threonine and tyrosine residues. We provide a comparison of DUSP5's structure to other DUSPs and, using molecular modeling studies, provide an explanation for DUSP5's mechanistic interaction and specificity toward phospho-extracellular regulated kinase, its only known substrate. We also discuss new insights from molecular modeling studies that will influence our current thinking of mitogen-activated protein kinase signaling. Finally, we discuss the lessons learned from identifying small molecules that target DUSP5, which might benefit targeting efforts for other phosphatases. © 2017 American Physiological Society. Compr Physiol 7:1449-1461, 2017.
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When Substituents Do Not Matter: Frontier Orbitals Explain the Unusually High and Invariant Oxidation Potential in Alkoxy-, Alkyl-, and H-Substituted Iptycenes. J Phys Chem Lett 2017; 8:4226-4230. [PMID: 28825830 DOI: 10.1021/acs.jpclett.7b01971] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Frontier molecular orbitals (FMOs) have played a critical role in predicting reactivity/selectivity of pericyclic reactions. Here we show that the structurally similar iptycene-based hydroquinone ether (HE), that is, MeOIpt and BOHE/BHHE, molecules have drastically different ordering of bisallylic and quinoidal FMOs. They are almost degenerate in BOHE/BHHE, while in MeOIpt, the bisallylic orbital lies far below the quinoidal HOMO. Oxidation of BOHE/BHHE induces coplanarization of the methoxy group and destabilizes the bisallylic HOMO, leading to a relatively low oxidation potential. In MeOIpt, considerable energy must be invested in coplanarization of the methoxy group to bring about orbital swapping, resulting in an oxidation potential higher than that in structurally similar BOHE/BHHE. As the quinoidal HOMO density does not extend to the substituent-bearing carbon in H-, alkyl-, and alkoxy-substituted iptycenes, their redox potentials remain invariant. This case study involving a simple visual inspection of the nodal arrangement as well as energetics of the FMOs and Walsh analysis could serve as a tool for the design of organic molecules with a desired redox potential.
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Comparative efficacy of oestrus synchronization protocols in buffalo (Bubalus bubalis). Trop Anim Health Prod 2017; 49:1377-1382. [DOI: 10.1007/s11250-017-1337-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2017] [Accepted: 06/22/2017] [Indexed: 11/29/2022]
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Unraveling the Coulombic Forces in Electronically Decoupled Bichromophoric Systems during Two Successive Electron Transfers. Chemistry 2017; 23:8834-8838. [DOI: 10.1002/chem.201702211] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2017] [Indexed: 11/06/2022]
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Serendipitous discovery of light-induced (In Situ) formation of an Azo-bridged dimeric sulfonated naphthol as a potent PTP1B inhibitor. BMC BIOCHEMISTRY 2017; 18:10. [PMID: 28569147 PMCID: PMC5452347 DOI: 10.1186/s12858-017-0083-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Accepted: 05/10/2017] [Indexed: 02/03/2023]
Abstract
Background Protein tyrosine phosphatases (PTPs) like dual specificity phosphatase 5 (DUSP5) and protein tyrosine phosphatase 1B (PTP1B) are drug targets for diseases that include cancer, diabetes, and vascular disorders such as hemangiomas. The PTPs are also known to be notoriously difficult targets for designing inihibitors that become viable drug leads. Therefore, the pipeline for approved drugs in this class is minimal. Furthermore, drug screening for targets like PTPs often produce false positive and false negative results. Results Studies presented herein provide important insights into: (a) how to detect such artifacts, (b) the importance of compound re-synthesis and verification, and (c) how in situ chemical reactivity of compounds, when diagnosed and characterized, can actually lead to serendipitous discovery of valuable new lead molecules. Initial docking of compounds from the National Cancer Institute (NCI), followed by experimental testing in enzyme inhibition assays, identified an inhibitor of DUSP5. Subsequent control experiments revealed that this compound demonstrated time-dependent inhibition, and also a time-dependent change in color of the inhibitor that correlated with potency of inhibition. In addition, the compound activity varied depending on vendor source. We hypothesized, and then confirmed by synthesis of the compound, that the actual inhibitor of DUSP5 was a dimeric form of the original inhibitor compound, formed upon exposure to light and oxygen. This compound has an IC50 of 36 μM for DUSP5, and is a competitive inhibitor. Testing against PTP1B, for selectivity, demonstrated the dimeric compound was actually a more potent inhibitor of PTP1B, with an IC50 of 2.1 μM. The compound, an azo-bridged dimer of sulfonated naphthol rings, resembles previously reported PTP inhibitors, but with 18-fold selectivity for PTP1B versus DUSP5. Conclusion We report the identification of a potent PTP1B inhibitor that was initially identified in a screen for DUSP5, implying common mechanism of inhibitory action for these scaffolds. Electronic supplementary material The online version of this article (doi:10.1186/s12858-017-0083-3) contains supplementary material, which is available to authorized users.
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Poly-p-hydroquinone Ethers: Isoenergetic Molecular Wires with Length-Invariant Oxidation Potentials and Cation Radical Excitation Energies. J Am Chem Soc 2017; 139:4334-4337. [DOI: 10.1021/jacs.7b01226] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Energy Gap between the Poly-p-phenylene Bridge and Donor Groups Controls the Hole Delocalization in Donor-Bridge-Donor Wires. J Am Chem Soc 2016; 138:16337-16344. [PMID: 27998092 DOI: 10.1021/jacs.6b09209] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Poly-p-phenylene wires are critically important as charge-transfer materials in photovoltaics. A comparative analysis of a series of poly-p-phenylene (RPPn) wires, capped with isoalkyl (iAPPn), alkoxy (ROPPn), and dialkylamino (R2NPPn) groups, shows unexpected evolution of oxidation potentials, i.e., decrease (-260 mV) for iAPPn, while increase for ROPPn (+100 mV) and R2NPPn (+350 mV) with increasing number of p-phenylenes. Moreover, redox/optical properties and DFT calculations of R2NPPn/R2NPPn+• further show that the symmetric bell-shaped hole distribution distorts and shifts toward one end of the molecule with only 4 p-phenylenes in R2NPPn+•, while shifting of the hole occurs with 6 and 8 p-phenylenes in ROPPn+• and iAPPn+•, respectively. Availability of accurate experimental data on highly electron-rich dialkylamino-capped R2NPPn together with ROPPn and iAPPn allowed us to demonstrate, using our recently developed Marcus-based multistate model (MSM), that an increase of oxidation potentials in R2NPPn arises due to an interplay between the electronic coupling (Hab) and energy difference between the end-capped groups and bridging phenylenes (Δε). A comparison of the three series of RPPn with varied Δε further demonstrates that decrease/increase/no change in oxidation energies of RPPn can be predicted based on the energy gap Δε and coupling Hab, i.e., decrease if Δε < Hab (i.e., iAPPn), increase if Δε > Hab (i.e., R2NPPn), and minimal change if Δε ≈ Hab (i.e., ROPPn). MSM also reproduces the switching of the nature of electronic transition in higher homologues of R2NPPn+• (n ≥ 4). These findings will aid in the development of improved models for charge-transfer dynamics in donor-bridge-acceptor systems.
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Toroidal delocalization of a single electron through circularly-arrayed benzophenone chromophores in hexakis(4-benzoylphenyl)benzene. J Photochem Photobiol A Chem 2016. [DOI: 10.1016/j.jphotochem.2016.05.002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Dihedral‐Angle‐Controlled Crossover from Static Hole Delocalization to Dynamic Hopping in Biaryl Cation Radicals. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201609695] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Dihedral-Angle-Controlled Crossover from Static Hole Delocalization to Dynamic Hopping in Biaryl Cation Radicals. Angew Chem Int Ed Engl 2016; 56:266-269. [DOI: 10.1002/anie.201609695] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Indexed: 11/10/2022]
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Critical Role of the Secondary Binding Pocket in Modulating the Enzymatic Activity of DUSP5 toward Phosphorylated ERKs. Biochemistry 2016; 55:6187-6195. [PMID: 27739308 DOI: 10.1021/acs.biochem.6b00498] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
DUSP5 is an inducible nuclear dual-specificity phosphatase that specifically interacts with and deactivates extracellular signal-regulated kinases ERK1 and ERK2, which are responsible for cell proliferation, differentiation, and survival. The phosphatase domain (PD) of DUSP5 has unique structural features absent from other nuclear DUSPs, such as the presence of a secondary anion-binding site in the proximity of the reaction center and a glutamic acid E264 positioned next to the catalytic cysteine C263, as well as a remote intramolecular disulfide linkage. The overall 400 ns molecular dynamics simulations indicate that the secondary binding site of DUSP5 PD acts as an allosteric regulator of the phosphatase activity of DUSP5. Our studies have identified E264 as a critical constituent of the dual binding pocket, which regulates the catalytic activity of DUSP5 by forming a salt bridge with arginine R269. Molecular dynamics studies showed that initial occupation of the secondary binding pocket leads to the breakage of the salt bridge, which then allows the occupation of the active site. Indeed, biochemical analysis using the pERK assay on mutant E264Q demonstrated that mutation of glutamic acid E264 leads to an increase in the DUSP5 catalytic activity. The role of the secondary binding site in assembling the DUSP5-pERK pre-reactive complex was further demonstrated by molecular dynamics simulations that showed that the remote C197-C219 disulfide linkage controls the structure of the secondary binding pocket based on its redox state (i.e., disulfide/dithiol) and, in turn, the enzymatic activity of DUSP5.
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First Experimental Evidence for the Diverse Requirements of Excimer vs Hole Stabilization in π-Stacked Assemblies. J Phys Chem Lett 2016; 7:3042-3045. [PMID: 27447947 DOI: 10.1021/acs.jpclett.6b01201] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Exciton formation and charge separation and transport are key dynamical events in a variety of functional polymeric materials and biological systems, including DNA. Beyond the necessary cofacial approach of a pair of aromatic molecules at van der Waals contact, the extent of overlap and necessary geometrical reorganization for optimal stabilization of an excimer vs dimer cation radical remain unresolved. Here, we compare experimentally the dynamics of excimer formation (via emission) and charge stabilization (via threshold ionization) of a novel covalently linked, cofacially stacked fluorene dimer (F2) with the unlinked van der Waals dimer of fluorene, that is, (F)2. Although the measured ionization potentials are identical, the excimeric state is stabilized by up to ∼30 kJ/mol in covalently linked F2. Supported by theory, this work demonstrates for the first time experimentally that optimal stabilization of an excimer requires a perfect sandwich-like geometry with maximal overlap, whereas hole stabilization in π-stacked aggregates is less geometrically restrictive.
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Two's Company, Three's a Crowd: Exciton Localization in Cofacially Arrayed Polyfluorenes. J Phys Chem Lett 2016; 7:2915-2920. [PMID: 27409718 DOI: 10.1021/acs.jpclett.6b01268] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Understanding the mechanisms of long-range energy transfer through polychromophoric assemblies is critically important in photovoltaics and biochemical systems. Using a set of cofacially arrayed polyfluorenes (Fn), we investigate the mechanism of (singlet) exciton delocalization in π-stacked polychromophoric assemblies. Calculations reveal that effective stabilization of an excimeric state requires an ideal sandwich-like arrangement; yet surprisingly, emission spectroscopy indicates that exciton delocalization is limited to only two fluorene units for all n. Herein, we show that delocalization is determined by the interplay between the energetic gain from delocalization, which quickly saturates beyond two units in larger Fn, and an energetic penalty associated with structural reorganization, which increases linearly with n. With these insights, we propose a hopping mechanism for exciton transfer, based upon the presence of multiple excimeric tautomers of similar energy in larger polyfluorenes (n ≥ 4) together with the anticipated low thermal barrier of their interconversion.
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