229 results on '"Workentin, Mark S."'
Search Results
202. Controlling the Structure, Properties and Surface Reactivity of Clickable Azide-Functionalized Au 25 (SR) 18 Nanocluster Platforms Through Regioisomeric Ligand Modifications.
- Author
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Gunawardene PN, Martin J, Wong JM, Ding Z, Corrigan JF, and Workentin MS
- Abstract
To fine-tune structure-property correlations of thiolate-protected gold nanoclusters through post-assembly surface modifications, we report the synthesis of the o, m, and p regioisomeric forms of the anionic azide-functionalized [Au
25 (SCH2 CH2 -C6 H4 -N3 )18 ]1- platform. They can undergo cluster-surface strain-promoted alkyne-azide cycloaddition (CS-SPAAC) chemistry with complementary strained-alkynes. Although their optical properties are similar, the electrochemical properties appear to correlate with the position of the azido group. The ability to conduct CS-SPAAC chemistry without altering the parent nanocluster structure is different as the isomeric form of the surface ligand is changed, with the [Au25 (SCH2 CH2 -p-C6 H4 -N3 )18 ]1- isomer having the highest reaction rates, while the [Au25 (SCH2 CH2 -o-C6 H4 -N3 )18 ]1- isomer is not stable following CS-SPAAC. Single-crystal X-ray diffraction provide the molecular structure of the neutral forms of the three regioisomeric clusters, [Au25 (SCH2 CH2 -o/m/p-C6 H4 -N3 ]0 , which illustrates correlated structural features of the central core as the position of the azido moiety is changed., (© 2022 Wiley-VCH GmbH.)- Published
- 2022
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203. Anhydride Post-Synthetic Modification in a Hierarchical Metal-Organic Framework.
- Author
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Chen S, Song Z, Lyu J, Guo Y, Lucier BEG, Luo W, Workentin MS, Sun X, and Huang Y
- Abstract
Metal-organic frameworks (MOFs) are important porous materials. Post-synthetic modification (PSM) of MOFs via the pendant groups or secondary functional groups of organic linkers has been widely used to introduce new or enhance existing properties of MOFs for various practical applications. In this work, we have constructed, for the first time, a novel platform for PSM of MOFs by introducing an anhydride functional group into a hierarchically porous MOF (MIL-121) as an effective anchor. We have demonstrated that the combination of the high reactivity of anhydride and hierarchical porosity makes this protocol particularly novel and important, as it led to excellent opportunities of incorporating not only a wide variety of organic molecules with different sizes and chemical nature but also the noble metal complexes in MOFs. Specifically, we show that the anhydride group decorated in the MOF exhibits a high reactivity toward covalently binding 10 different guest molecules including alcohols, amines, thiols, and noble metal (Pt(II)/Pt(IV)) complexes, whereas the hierarchical pores created in the MOF allow the incorporation of guest species varying in size from methanol to larger molecules such as polyaromatic amines. This novel approach provides the community with a new avenue to prepare MOF-based materials for targeted applications. To illustrate this point, we furnish an example of using this new platform to prepare a Pt-based electrocatalyst which shows excellent catalytic activity toward the oxygen reduction reaction (ORR), a pivotal half-reaction in hydrogen-oxygen fuel cells and other energy storage and conversion devices.
- Published
- 2020
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204. Investigation of Au SAMs Photoclick Derivatization by PM-IRRAS.
- Author
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Luo W, Legge SM, Luo J, Lagugné-Labarthet F, and Workentin MS
- Abstract
In this work, we present a clean one-step process for modifying headgroups of self-assembled monolayers (SAMs) on gold using photo-enabled click chemistry. A thiolated, cyclopropenone-caged strained alkyne precursor was first functionalized onto a flat gold substrate through self-assembly. Exposure of the cyclopropenone SAM to UVA light initiated the efficient photochemical decarbonylation of the cyclopropenone moiety, revealing the strained alkyne capable of undergoing the interfacial strain-promoted alkyne-azide cycloaddition (SPAAC). Irradiated SAMs were derivatized with a series of model azides with varied hydrophobicity to demonstrate the generality of this chemical system for the modification and fine-tuning of the surface chemistry on gold substrates. SAMs were characterized at each step with polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) to confirm the successful functionalization and reactivity. Furthermore, to showcase the compatibility of this approach with biochemical applications, cyclopropenone SAMs were irradiated and modified with azide-bearing cell adhesion peptides to promote human fibroblast cell adhesion, and then imaged by live-cell fluorescence microscopy. Thus, the "photoclick" methodology reported here represents an improved, versatile, catalyst-free protocol that allows for a high degree of control over the modification of material surfaces, with applicability in materials science as well as biochemistry.
- Published
- 2020
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205. Nitrone-Modified Gold Nanoparticles: Synthesis, Characterization, and Their Potential as 18 F-Labeled Positron Emission Tomography Probes via I-SPANC.
- Author
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Ghiassian S, Yu L, Gobbo P, Nazemi A, Romagnoli T, Luo W, Luyt LG, and Workentin MS
- Abstract
A novel bioorthogonal gold nanoparticle (AuNP) template displaying interfacial nitrone functional groups for bioorthogonal interfacial strain-promoted alkyne-nitrone cycloaddition reactions has been synthesized. These nitrone-AuNPs were characterized in detail using
1 H nuclear magnetic resonance spectroscopy, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy, and a nanoparticle raw formula was calculated. The ability to control the conjugation of molecules of interest at the molecular level onto the nitrone-AuNP template allowed us to create a novel methodology for the synthesis of AuNP-based radiolabeled probes., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)- Published
- 2019
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206. Golden Opportunity: A Clickable Azide-Functionalized [Au 25 (SR) 18 ] - Nanocluster Platform for Interfacial Surface Modifications.
- Author
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Gunawardene PN, Corrigan JF, and Workentin MS
- Abstract
Ultrasmall atomically precise monolayer-protected gold thiolate nanoclusters are an intensely researched nanomaterial framework, but there is a lack of a system that can be directly synthesized and undergo interfacial surface chemistry. We report an [Au
25 (SCH2 CH2 - p -C6 H4 -N3 )18 ]- nanocluster platform with azide moieties appended onto each surface ligand. The structure of this surface reactive cluster has been confirmed by single-crystal X-ray crystallography, mass spectrometry and ultraviolet visible, infrared and nuclear magnetic resonance spectroscopies. We show that all surface azide moieties are amenable to cluster-surface strain-promoted alkyne-azide cycloaddition chemistry with a strained cyclooctyne, opening this as a new platform to allow functional, postassembly surface modifications to this very prominent nanocluster.- Published
- 2019
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207. Highly Electron-Deficient Pyridinium-Nitrones for Rapid and Tunable Inverse-Electron-Demand Strain-Promoted Alkyne-Nitrone Cycloaddition.
- Author
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Gunawardene PN, Luo W, Polgar AM, Corrigan JF, and Workentin MS
- Abstract
Highly accelerated inverse-electron-demand strain-promoted alkyne-nitrone cycloaddition (IED SPANC) between a stable cyclooctyne (bicyclo[6.1.0]nonyne (BCN)) and nitrones delocalized into a C
α -pyridinium functionality is reported, with the most electron-deficient "pyridinium-nitrone" displaying among the most rapid cycloadditions to BCN that is currently reported. Density functional theory (DFT) and X-ray crystallography are explored to rationalize the effects of N - and Cα -substituent modifications at the nitrone on IED SPANC reaction kinetics and the overall rapid reactivity of pyridinium-delocalized nitrones.- Published
- 2019
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208. Dual-Bioorthogonal Molecular Tool: "Click-to-Release" and "Double-Click" Reactivity on Small Molecules and Material Surfaces.
- Author
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Luo W, Luo J, Popik VV, and Workentin MS
- Subjects
- Alkynes chemistry, Azides chemistry, Cycloaddition Reaction, Gold chemistry, Ligands, Metal Nanoparticles chemistry, Proof of Concept Study, Surface Properties, Biocompatible Materials, Click Chemistry
- Abstract
The development of reactive moieties that enable molecular control of bond-forming and bond-breaking reactions within complex media is highly important in materials and biomaterials research as it provides opportunities to carefully manipulate small molecules and material surfaces in a reliable manner. Despite recent advances in the realization of new ligation strategies and "click-and-release" systems, there has been little development of multifunctional moieties that feature a broad range of chemical capabilities. To address this challenge, we designed a molecular tool that can utilize four well-defined bioorthogonal chemistries interchangeably for the attachment, replacement, and release of molecules within a system: the Staudinger-Bertozzi ligation (SBL), perfluoroaryl azide Staudinger reaction (PFAA-SR), strain-promoted alkyne-azide cycloaddition (SPAAC), and strain-promoted alkyne-nitrone cycloaddition (SPANC). We demonstrate "click-to-release" and "double-click" reactivity on small molecules and gold nanoparticles (AuNPs) as a model material substrate. As a proof of concept for material derivatization, we employed 5 nm AuNPs-functionalized with a Rhodamine B derivative and biotin through the double-click strategy-and showed their potential as a pretargeted delivery nanocarrier. This multifunctional molecular tool enables the design and production of molecular and material systems with unique, modular, and tunable dynamic properties that can be altered under mild and bioorthogonal conditions.
- Published
- 2019
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209. Dialkynylborane Complexes of Formazanate Ligands: Synthesis, Electronic Properties, and Reactivity.
- Author
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Van Belois A, Maar RR, Workentin MS, and Gilroy JB
- Abstract
Dialkynylborane complexes of N-donor ligands have received significant attention because of their application in biological imaging, as light-harvesting materials, and as the functional component of organic photovoltaics. Despite these advances, relatively few types of N-donor ligands have been explored in this context. To this end, we prepared a series of dialkynylborane complexes of formazanate ligands and explored their electronic properties and reactivity. In doing so, we demonstrated that (1) the nature of the alkynyl substituents has little influence over the UV-vis absorption properties of the title complexes, but does affect the potentials at which they are electrochemically oxidized and reduced, (2) dialkynylborane formazanate complexes can be converted to stable radical anions by chemical reduction with cobaltocene derivatives, and (3) copper-assisted alkyne-azide cycloaddition chemistry at the alkynyl substituents directly bound to boron can be used to elaborate structural diversity. These conclusions are likely to lead to the development of, and provide guiding principles for the design of, future examples of functional molecular materials based on boron complexes of N-donor ligands.
- Published
- 2019
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210. Loading across the Periodic Table: Introducing 14 Different Metal Ions To Enhance Metal-Organic Framework Performance.
- Author
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Chen S, Lucier BEG, Luo W, Xie X, Feng K, Chan H, Terskikh VV, Sun X, Sham TK, Workentin MS, and Huang Y
- Abstract
Loading metal guests within metal-organic frameworks (MOFs) via secondary functional groups is a promising route for introducing or enhancing MOF performance in various applications. In this work, 14 metal ions (Li
+ , Na+ , K+ , Mg2+ , Ca2+ , Ba2+ , Zn2+ , Co2+ , Mn2+ , Ag+ , Cd2+ , La3+ , In3+ , and Pb2+ ) have been successfully introduced within the MIL-121 MOF using a cost-efficient route involving free carboxylic groups on the linker. The local and long-range structure of the metal-loaded MOFs is characterized using multinuclear solid-state NMR and X-ray diffraction methods. Li/Mg/Ca-loaded MIL-121 and Ag nanoparticle-loaded MIL-121 exhibit enhanced H2 and CO2 adsorption; Ag nanoparticle-loaded MIL-121 also demonstrates remarkable catalytic activity in the reduction of 4-nitrophenol.- Published
- 2018
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211. NHC Ligated Group 11 Metal-Arylthiolates Containing an Azide Functionality Amenable to "Click" Reaction Chemistry.
- Author
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Somasundaram V, Gunawardene PN, Polgar AM, Workentin MS, and Corrigan JF
- Abstract
The reaction of N-heterocyclic carbene (NHC) Group 11 metal complexes, [(NHC)M-X] (X = chloride, acetate), with the new azide-modified arylthiol 1-HSCH
2 -2,5-Me2 -4-N3 CH2 -C6 H2 , 1 (for M = Au; X = Cl), or 1-Me3 SiSCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 , 2 (for M = Cu, X = Cl; M = Ag, X = OAc), affords the "clickable" NHC-metal thiolates [(i Pr2 -bimy)Au-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 5; [(IPr)Au-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 6; [(IPr)Ag-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 7; and [(IPr)Cu-(1-SCH2 -2,5-Me2 -4-N3 CH2 -C6 H2 )], 8 (i Pr2 -bimy = 1,3-di-isopropylbenzimidazol-2-ylidene, IPr = 1,3-bis(2,6-di-iso-propylphenyl)imidazol-2-ylidene). Single-crystal X-ray analysis of all metal complexes show that they are two-coordinate, nearly linear, with a terminally bonded thiolate ligand possessing an accessible azide (-N3 ) moiety. The strain-promoted alkyne-azide cycloaddition (SPAAC) reaction of complex 6 with bicyclo[6.1.0]non-4-yn-9-ylmethanol (BCN-OH) and dibenzocyclooctyne-amine (DBCO-NH2 ) illustrated the reactivity of the azide moiety toward strain-promoted cycloaddition. The rate of the SPAAC reaction between complex 6 and BCN-OH was determined via1 H NMR spectroscopy under second order conditions, and was compared to that of BCN-OH with PhCH2 N3 .- Published
- 2018
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212. Insights on the Application of the Retro Michael-Type Addition on Maleimide-Functionalized Gold Nanoparticles in Biology and Nanomedicine.
- Author
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Weissman MR, Winger KT, Ghiassian S, Gobbo P, and Workentin MS
- Subjects
- Proton Magnetic Resonance Spectroscopy, Gold chemistry, Maleimides chemistry, Metal Nanoparticles, Nanomedicine
- Abstract
The glutathione-mediated retro Michael-type addition reaction is demonstrated to take place at the interface of small water-soluble maleimide-functionalized gold nanoparticles (Maleimide-AuNP). The retro Michael-type addition reaction can be blocked by hydrolyzing the Michael addition thioether adduct at the nanoparticle's interface under reaction conditions that do not cause AuNP decomposition. This procedure "locks" the molecule of interest onto the Maleimide-AuNP template for potential uses in medical imaging and bioconjugation, ensuring no loss of the molecular cargo from the nanocarrier. On the other hand, the glutathione-mediated retro Michael-type addition reaction can be exploited for delivering a molecular payload. As a proof of concept, a fluorogenic molecular cargo was incorporated onto a Maleimide-AuNP and delivered via the glutathione-mediated retro Michael-type addition reaction.
- Published
- 2016
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213. A nanoaggregate-on-mirror platform for molecular and biomolecular detection by surface-enhanced Raman spectroscopy.
- Author
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Wallace GQ, Tabatabaei M, Zuin MS, Workentin MS, and Lagugné-Labarthet F
- Subjects
- Gold chemistry, Humans, Phenols chemistry, Spectrum Analysis, Raman instrumentation, Sulfhydryl Compounds chemistry, Glucose analysis, Hydrogen Peroxide analysis, Metal Nanoparticles chemistry, Spectrum Analysis, Raman methods
- Abstract
A nanoaggregate-on-mirror (NAOM) structure has been developed for molecular and biomolecular detection using surface-enhanced Raman spectroscopy (SERS). The smooth surface of the gold mirror allows for simple and homogeneous functionalization, while the introduction of the nanoaggregates enhances the Raman signal of the molecule(s) in the vicinity of the aggregate-mirror junction. This is evidenced by functionalizing the gold mirror with 4-nitrothiophenol, and the further addition of gold nanoaggregates promotes local SERS activity only in the areas with the nanoaggregates. The application of the NAOM platform for biomolecular detection is highlighted using glucose and H2O2 as molecules of interest. In both cases, the gold mirror is functionalized with 4-mercaptophenylboronic acid (4-MPBA). Upon exposure to glucose, the boronic acid moiety of 4-MPBA forms a cyclic boronate ester. Once the nanoaggregates are added to the surface, detection of glucose is possible without the use of an enzyme. This method of indirect detection provides a limit of detection of 0.05 mM, along with a linear range of detection from 0.1 to 15 mM for glucose, encompassing the physiological range of blood glucose concentration. The detection of H2O2 is achieved with optical inspection and SERS. The H2O2 interferes with the coating of the gold mirror, enabling qualitative detection by visual inspection. Simultaneously, the H2O2 reacts with the boronic acid to form a phenol, a change that is detected by SERS.
- Published
- 2016
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214. Small gold nanoparticles for interfacial Staudinger-Bertozzi ligation.
- Author
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Gobbo P, Luo W, Cho SJ, Wang X, Biesinger MC, Hudson RH, and Workentin MS
- Subjects
- Azides chemistry, Methylation, Nanoparticles ultrastructure, Oligopeptides chemistry, Particle Size, Photoelectron Spectroscopy, Thermogravimetry, Benzoates chemistry, Gold chemistry, Nanoparticles chemistry, Phosphines chemistry
- Abstract
Small gold nanoparticles (AuNPs) that possess interfacial methyl-2-(diphenylphosphino)benzoate moieties have been successfully synthesized (Staudinger-AuNPs) and characterized by multi-nuclear MR spectroscopy, transmission electron microscopy (TEM), UV-Vis spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy (XPS). In particular, XPS was remarkably sensitive for characterization of the novel nanomaterial, and in furnishing proof of its interfacial reactivity. These Staudinger-AuNPs were found to be stable to the oxidation of the phosphine center. The reaction with benzyl azide in a Staudinger-Bertozzi ligation, as a model system, was investigated using (31)P NMR spectroscopy. This demonstrated that the interfacial reaction was clean and quantitative. To showcase the potential utility of these Staudinger-AuNPs in bioorganic chemistry, a AuNP bioconjugate was prepared by reacting the Staudinger-AuNPs with a novel azide-labeled CRGDK peptide. The CRGDK peptide could be covalently attached to the AuNP efficiently, chemoselectively, and with a high loading.
- Published
- 2015
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215. Thermodynamic and kinetic origins of Au25(0) nanocluster electrochemiluminescence.
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Hesari M, Workentin MS, and Ding Z
- Abstract
Au clusters with protecting organothiolate ligands and core diameters less than 2 nm are molecule-like structures, suitable for catalysis, optoelectronics and biology applications. The spectroscopy and electrochemistry of Au25(0) (Au25[(SCH2CH2Ph)18], SCH2CH2Ph = 2-phenylethanethiol) allowed us to construct a Latimer-type diagram for the first time, which revealed a rich photoelectrochemistry of the cluster and the unique relationship to its various oxidation states and corresponding excited states. The occurrence of cluster electrochemiluminescence (ECL) was examined in the presence of tri-n-propylamine (TPrA) as a co-reactant and was discovered to be in the near-infrared (NIR) region with peak wavelengths of 860, 865, and 960 nm, emitted by Au25(+*), Au25(0*), and Au25(-*), respectively. The light emissions, with an efficiency up to 103% relative to that of the efficient Ru(bpy)3(2+)/TPrA system, depended on the kinetics of the reactions between the electrogenerated TPrA radical and Au25(z) (z = 2+, 1+, 1-, and 2-) in the vicinity of the electrode or the bulk Au25(0). These thermodynamic and kinetic origins were further explored by means of spooling ECL and photoluminescence spectroscopy during a sweep of the potential or at a constant potential applied to the working electrode. NIR-ECL emissions of the cluster can be tuned in wavelength and intensity by adjusting the applied potential and TPrA concentration based on the above discoveries., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)
- Published
- 2014
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216. Tessellated gold nanostructures from Au144(SCH2CH2Ph)60 molecular precursors and their use in organic solar cell enhancement.
- Author
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Bauld R, Hesari M, Workentin MS, and Fanchini G
- Abstract
We report for the first time the fabrication of nanocomposite hole-blocking layers consisting of poly-3,4-ethylene-dioxythiophene:poly-styrene-sulfonate (PEDOT:PSS) thin films incorporating networks of gold nanoparticles assembled from Au144(SCH2CH2Ph)60, a molecular gold precursor. These thin films can be prepared reproducibly on indium tin oxide by spinning on it Au144(SCH2CH2Ph)60 solutions in chlorobenzene, annealing the resulting thin film at 400 °C, and subsequently spinning PEDOT:PSS on top. The use of our nanocomposite hole-blocking layers for enhancing the photoconversion efficiency of bulk heterojunction organic solar cells is demonstrated. By varying the concentration of Au144(SCH2CH2Ph)60 in the starting solution and the annealing time, different gold nanostructures were obtained ranging from individual gold nanoparticles (AuNPs) to tessellated networks of gold nanostructures (Tess-AuNPs). Improvement in organic solar cell efficiencies up to 10% relative to a reference cell is demonstrated with Tess-AuNPs embedded in PEDOT:PSS.
- Published
- 2014
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217. Versatile strained alkyne modified water-soluble AuNPs for interfacial strain promoted azide-alkyne cycloaddition (I-SPAAC).
- Author
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Gobbo P, Mossman Z, Nazemi A, Niaux A, Biesinger MC, Gillies ER, and Workentin MS
- Abstract
Versatile water- and organic solvent-soluble AuNPs that incorporate an interfacial strained alkyne capable of efficient pour and mix strain promoted interfacial cycloadditions with azide partners have been synthesized and carefully characterized for the first time. The use of XPS to quantitate the loading of the strained alkyne on the AuNPs is noteworthy. The reactivity towards the interfacial strain promoted azide-alkyne cycloaddition reaction was demonstrated by using azide-decorated polymersomes as bioorthogonal reaction partners.
- Published
- 2014
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218. Arresting the time-dependent H 2 O 2 mediated synthesis of gold nanoparticles for analytical detection and preparative chemistry.
- Author
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Gobbo P, Biondi MJ, Feld JJ, and Workentin MS
- Abstract
The time-dependent progression from gold nanosponges (AuNS) to discrete small gold nanoparticles (AuNPs) mediated by H
2 O2 in MES buffer is blocked by the addition of a thiol, glutathione. This represents an important improvement for the plasmonic ELISA, and also leads to a time-dependent approach for the synthesis of AuNS and AuNPs in water with precise control over nanostructure size.- Published
- 2013
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219. Michael addition reactions for the modification of gold nanoparticles facilitated by hyperbaric conditions.
- Author
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Hartlen KD, Ismaili H, Zhu J, and Workentin MS
- Subjects
- Magnetic Resonance Spectroscopy, Microscopy, Electron, Transmission, Gold chemistry, Metal Nanoparticles chemistry, Oxygen chemistry
- Abstract
The chemical interfacial modification of organic solvent soluble 2.4 ± 0.5 nm maleimide-modified monolayer protected gold nanoparticles (2-C(12)AuNPs) with primary or secondary amines via Michael addition reactions is demonstrated. Michael addition reactions between 2-C(12)AuNPs and primary or secondary amines at ambient temperature and pressure and under the conditions where the AuNP is soluble and stable are possible albeit sluggish, often taking days to weeks to go to completion. The rates and efficacies of the these same reactions are drastically increased at hyperbaric pressure conditions (11 000 atm) with no observed adverse effect to the gold nanoparticle stability. The resulting Michael addition adducts (3-C(12)AuNPs) formed from 2-C(12)AuNPs and the corresponding amines were characterized by TEM and by comparison of the (1)H NMR spectra of the 3-C(12)AuNPs with those of model reactions of the same amines with N-dodecylmaleimide, 2. The Michael addition reactions occur more readily with 2 rather than 2-C(12)AuNPs, consistent with the local environment of the latter imposing additional steric or other barriers to the reaction. The use of hyperbaric conditions makes the reaction of the organic solvent soluble 2-C(12)AuNP via Michael addition a viable interfacial modification process that is otherwise impractical. The results also suggest that it is a useful protocol for facilitating Michael addition reactions generally in solution at low temperatures.
- Published
- 2012
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220. Maleimide-modified phosphonium ionic liquids: a template towards (multi)task-specific ionic liquids.
- Author
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Tindale JJ, Hartlen KD, Alizadeh A, Workentin MS, and Ragogna PJ
- Abstract
The synthesis and characterization of several compounds representing a new class of multitask-specific phosphonium ionic liquids that contain a maleimide functionality is reported. The maleimide moiety of the ionic liquid (IL) is shown to undergo Michael-type additions with substrates containing either a thiol or amine moiety, thus, serving as a template to introduce wide structural diversity into the IL. Multitask-specific ILs are accessible by reaction of the maleimide with Michael donors that are capable of serving some function. As a model example to illustrate this concept, a redox active ferrocenyl thiol was incorporated and examined by cyclic voltammetry. Because the maleimide moiety is highly reactive to additions, the task-specific ionic liquids (TSILs) are prepared as the furan-protected Diels-Alder maleimide. The maleimide moiety can then be liberated when required by simple heating.
- Published
- 2010
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221. A nanoscopic 3D polyferrocenyl assembly: the triacontakaihexa(ferrocenylmethylthiolate) [Ag48(mu4-S)6(mu(2/3)-SCH2Fc)36].
- Author
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Ahmar S, MacDonald DG, Vijayaratnam N, Battista TL, Workentin MS, and Corrigan JF
- Published
- 2010
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222. Efficient homogeneous radical-anion chain reactions initiated by dissociative electron transfer to 3,3,6,6-tetraaryl-1,2-dioxanes.
- Author
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Stringle DL, Magri DC, and Workentin MS
- Subjects
- Electron Transport, Molecular Structure, Oxidation-Reduction, Anions chemistry, Dioxanes chemistry
- Abstract
A series of 3,3,6,6-tetraaryl-1,2-dioxanes (TADs) have been investigated at an inert electrode by using cyclic voltammetry, constant potential electrolysis and digital simulations. The series consists of the phenyl-substituted TAD (1 a), p-methoxy-aryl TADs (1 b, 1 c) and the p-methoxy/nitro-bearing TAD (1 d). The heterogeneous electron-transfer (ET) reduction is dissociative, causing rupture of the oxygen-oxygen bond, which generates a distonic radical-anion that reacts competitively either by beta-scission fragmentation or ET. Fragmentation of the distonic radical anion yields an alkene, a substituted benzophenone, and a benzophenone radical anion. The benzophenone radical-anion propagates an efficient homogeneous ET-fragmentation chain reaction that accounts for the potential dependence of the product ratios and the low charge consumption observed in the controlled potential electrolysis experiments. Digital simulation of the experimental cyclic voltammograms allowed for estimates of the rate constants of the heterogeneous ET to the O--O bond, and for the rate constants for the beta-scission fragmentation of the distonic radical-anions. Density functional theory calculations corroborate the differences in the heterogeneous kinetics of the initial dissociative ET. The endoperoxides 1 a-1 c react predominantly by a concerted dissociative ET mechanism, although the data suggests a stepwise dissociative pathway is also competitive. Bearing a nitro-aryl substituent, 1 d provides a rare example of an endoperoxide that proceeds by a stepwise dissociative ET mechanism. Irrespective of the initial mechanistic details, we find a propagating radical-anion cycle is a general mechanistic feature.
- Published
- 2010
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223. A radical-anion chain mechanism initiated by dissociative electron transfer to a bicyclic endoperoxide: insight into the fragmentation chemistry of neutral biradicals and distonic radical anions.
- Author
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Magri DC and Workentin MS
- Subjects
- Anions, Electron Transport, Kinetics, Peroxides chemistry
- Abstract
The electron-transfer (ET) reduction of two diphenyl-substituted bicyclic endoperoxides was studied in N,N-dimethylformamide by heterogeneous electrochemical techniques. The study provides insight into the structural parameters that affect the reduction mechanism of the O-O bond and dictate the reactivity of distonic radical anions, in addition to evaluating previously unknown thermochemical parameters. Notably, the standard reduction potentials and the bond dissociation energies (BDEs) were evaluated to be -0.55+/-0.15 V and 20+/-3 kcal mol(-1), respectively, the last representing some of the lowest BDEs ever reported. The endoperoxides react by concerted dissociative electron transfer (DET) reduction of the O-O bond yielding a distonic radical-anion intermediate. The reduction of 1,4-diphenyl-2,3-dioxabicyclo[2.2.2]oct-5-ene (1) results in the quantitative formation of 1,4-diphenylcyclohex-2-ene-cis-1,4-diol by an overall two-electron mechanism. In contrast, ET to 1,4-diphenyl-2,3-dioxabicyclo[2.2.2]octane (2) yields 1,4-diphenylcyclohexane-cis-1,4-diol as the major product; however, in competition with the second ET from the electrode, the distonic radical anion undergoes a beta-scission fragmentation yielding 1,4-diphenyl-1,4-butanedione radical anion and ethylene in a mechanism involving less than one electron. These observations are rationalized by an unprecedented catalytic radical-anion chain mechanism, the first ever reported for a bicyclic endoperoxide. The product ratios and the efficiency of the catalytic mechanism are dependent on the electrode potential and the concentration of weak non-nucleophilic acid. A thermochemical cycle for calculating the driving force for beta-scission fragmentation is presented, and provides insight into why the fragmentation chemistry of distonic radical anions is different from analogous neutral biradicals.
- Published
- 2008
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224. Electrochemical reduction of G3-factor endoperoxide and its methyl ether: evidence for a competition between concerted and stepwise dissociative electron transfer.
- Author
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Najjar F, André-Barrès C, Baltas M, Lacaze-Dufaure C, Magri DC, Workentin MS, and Tzédakis T
- Abstract
The reduction of the bicyclic G-factor endoperoxides G3 and G3Me was studied in N,N-dimethylformamide using cyclic voltammetry and convolution analysis. Electron transfer leads to irreversible cleavage of the O--O bond. Detailed analysis of the voltammetry curves reveals a non-linear dependence on the transfer coefficient indicating a mechanistic transition from a stepwise mechanism to one with more concerted character with increasing potential. By using quantum calculations to estimate the O--O bond dissociation energies, the experimental data was used to evaluate the standard reduction potentials and other pertinent thermochemical information.
- Published
- 2007
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225. Electron transfer to sulfides and disulfides: intrinsic barriers and relationship between heterogeneous and homogeneous electron-transfer kinetics.
- Author
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Meneses AB, Antonello S, Arévalo MC, González CC, Sharma J, Wallette AN, Workentin MS, and Maran F
- Subjects
- Electron Transport, Kinetics, Disulfides chemistry, Sulfides chemistry, Thermodynamics
- Abstract
The electron-acceptor properties of series of related sulfides and disulfides were investigated in N,N-dimethylformamide with homogeneous (redox catalysis) and/or heterogeneous (cyclic voltammetry and convolution analysis) electrochemical techniques. The electron-transfer rate constants were determined as a function of the reaction free energy and the corresponding intrinsic barriers were determined. The dependence of relevant thermodynamic and kinetic parameters on substituents was assessed. The kinetic data were also analyzed in relation to corresponding data pertaining to reduction of diaryl disulfides. All investigated reductions take place by stepwise dissociative electron transfer (DET) which causes cleavage of the C(alkyl)--S or S--S bond. A generalized picture of how the intrinsic electron-transfer barrier depends on molecular features, ring substituents, and the presence of spacers between the frangible bond and aromatic groups was established. The reduction mechanism was found to undergo a progressive (and now predictable) transition between common stepwise DET and DET proceeding through formation of loose radical anions. The intrinsic barriers were compared with available results for ET to several classes of dissociative- and nondissociative-type acceptors, and this led to verification that the heterogeneous and the homogeneous data correlate as predicted by the Hush theory.
- Published
- 2007
- Full Text
- View/download PDF
226. A retro-Diels-Alder reaction to uncover maleimide-modified surfaces on monolayer-protected nanoparticles for reversible covalent assembly.
- Author
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Zhu J, Kell AJ, and Workentin MS
- Abstract
Maleimide-modified monolayer-protected gold nanoparticles (MPGN) are prepared from the protected furan-maleimide via the thermally reversible Diels-Adler reaction when required. These maleimide-MPGNs serve as a general platform allowing for a Diels-Alder reaction with furan-modified MPN to prepare larger 3D networks reversibly. [reaction: see text]
- Published
- 2006
- Full Text
- View/download PDF
227. Core size effects on the reactivity of organic substrates as monolayers on gold nanoparticles.
- Author
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Kell AJ, Donkers RL, and Workentin MS
- Abstract
Monolayer-protected nanoparticles (MPNs) with average core sizes of 1.7- (small), 2.2- (medium) and 4.5-nm (large) diameter have been prepared and functionalized with a variety of aryl ketone substrates, namely, 11-mercaptoundecaphenone (1), 1-(4-hexyl-phenyl)-11-mercaptoundecanone (2), 1-[4-(11-mercaptoundecyl)phenyl]hexanone (3), or 1-[4-(11-mercaptoundecyl)phenyl]undecanone (4). Upon irradiation in benzene solution, the aryl ketone-modified MPNs undergo the Norrish type II photoreaction and yield alkene- or acetophenone-modified MPNs exclusively, with no evidence for the generation of cyclobutanol. The extent of the photoreaction for the entire series of aryl ketones is dependent on the size of the MPN core. For 11-mercaptoundecaphenone, the reaction proceeds nearly to completion on the smallest MPN cores (99 +/- 1%) but occurs to a much lesser extent on medium (85 +/- 5%) and large cores (66 +/- 6%). The differences in the extents of reaction are rationalized by the decreased reactivity of substrates on terrace regions, which become increasingly larger with the core size. In lending support to this hypothesis, the edge and vertex sites of medium-sized MPNs were selectively populated with an aryl ketone probe and shown to react quantitatively, whereas selective population of the terrace sites on the same-sized MPNs results in a much lower extent of reaction. Together, these results indicate differences in reactivity of monolayer substrates on terrace versus edge/vertex sites of MPNs. The differences in reactivity with site will play a role in the design of modified MPNs for applications.
- Published
- 2005
- Full Text
- View/download PDF
228. Reductive electrochemical cyclization of a photochromic 1,2-dithienylcyclopentene dication.
- Author
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Gorodetsky B, Samachetty HD, Donkers RL, Workentin MS, and Branda NR
- Published
- 2004
- Full Text
- View/download PDF
229. Elucidation of the electron transfer reduction mechanism of anthracene endoperoxides.
- Author
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Donkers RL and Workentin MS
- Abstract
The homogeneous and heterogeneous reductions of the endoperoxides 9,10-diphenyl-9,10-epidioxyanthracene (DPA-O2) and 9,10-dimethyl-9,10-epidioxyanthracene (DMA-O2) were investigated, and they were found to undergo a dissociative electron-transfer reduction of the O-O bond to yield a distonic radical anion, with no evidence for C-O bond dissociation. A number of thermochemical parameters for each were determined using Savéant's model for dissociative electron transfer (ET), including E degrees, DeltaG(o)++, and bond dissociation energies. The products of the ET are dependent on the mode of reduction, namely heterogeneous or homogeneous, and on the electrode potential or standard potential of the homogeneous donor, respectively. The dissociative reduction of DMA-O2 under heterogeneous and homogeneous conditions yields the corresponding 9,10-dihydroxyanthracene DMA-(OH)2, quantitatively, in an overall two-electron process. In the case of DPA-O2, ET reduction also yields the corresponding 9,10-dihydroxyanthracene DPA-(OH)2 from reduction of the distonic radical anion, but in competition with this reduction, an O-neophyl-type rearrangement occurs that generates a carbon radical with a minimum rate constant of 5.9 x 10(10) s(-1). In the presence of a sufficiently reducing medium, the carbon-centered radical is reduced (E degrees = -0.85 V vs SCE) and ultimately yields 9-phenoxy-10-phenyl anthracene (PPA). The observation of this product is remarkable. In the heterogeneous ET, the yield of DPA-(OH)2/PPA is 97:3 and allows an estimate of the rate constant for ET to the distonic radical anion. In homogeneous reductions, the O-neophyl rearrangement is quantitative, but the yield of PPA depends on the redox properties of the donor. A unified mechanism of reduction of DPA-O2 is presented to account for these observations.
- Published
- 2004
- Full Text
- View/download PDF
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