Browsing by Subject "chemistry, multidisciplinary"

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Acid/Base Controlled Size Modulation of Capsular Phosphates, Hydroxide Encapsulation, Quantitative and Clean Extraction of Sulfate with Carbonate Capsules of a Tripodal Urea Receptor
(2012-01) Akhuli, Bidyut; Ravikumar, I.; Ghosh, Pradyut; Ravikumar, I.
A simple tris-(2-aminoethyl) amine based pentafluorophenyl substituted tripodal urea receptor L has been extensively studied as a versatile receptor for various anions. Combined H-1-NMR, Isothermal Titration Calorimetry (ITC) and single crystal X-ray diffraction studies reveal that mononegative anions like F-, OH- and H2PO4- are encapsulated into the pseudocapsular dimeric assemblies of L with 1 : 1 stoichiometry whereas dinegative anions like CO32-, SO42- and HPO42- form tight capsular dimeric assemblies of L with 1 : 2 stoichiometries. Single crystal X-ray diffraction study clearly depicts that the size of the dimer of H2PO4- encapsulated pseudocapsule is 13.8 angstrom whereas the size of the tight HPO42- encapsulated capsular assembly is only 9.9 angstrom. The charge dependent anion encapsulated capsular size modulation of phosphates has been demonstrated by simple acid/base treatment via solution state P-31-NMR and single crystal X-ray diffraction studies. L is also capable of encapsulating hydroxide in its C-3v-symmetric cavity that is achieved upon treating a DMSO solution of L with tetrabutylammonium (TBA) cyanide and characterized by single crystal X-ray diffraction study. To the best of our knowledge this is the first report on the encapsulation of hydroxide in a neutral synthetic receptor. The excellent property of L to quantitatively capture aerial CO2 in the form of CO32- capsules [L-2(CO3)][N(n-Bu)(4)](2) in basic DMSO solution has been utilized to study the liquid-liquid extraction of SO42- from water via anion exchange. Almost quantitative and clean extraction of SO42- from water (99% from extracted pure mass and > 95% shown gravimetrically) has been unambiguously demonstrated by NMR, FT-IR, EDX, XRD and PXRD studies. Selective SO42- extraction is also demonstrated even in the presence of H2PO4- and NO3-. On the other hand the mixtures of L and TBACl (to solubilize L in CHCl3) results impure sulfate extraction even when 1 : 1 L/TBACl is used. Similar impure SO42- extraction is also observed when organic layers containing [L(Cl)][N(n-Bu)(4)] are used as the extractant, obtained upon precipitating SO42- from the extracted mass, [L-2(SO4)][N(n-Bu)(4)](2) in the carbonate capsules method using aqueous BaCl2 solution.
Application of a High-Throughput Enantiomeric Excess Optical Assay Involving a Dynamic Covalent Assembly: Parallel Asymmetric Allylation and ee Sensing of Homoallylic Alcohols
(2015-08) Jo, H. H.; Gao, X.; You, L.; Anslyn, E. V.; Krische, M. J.; Jo, H. H.; Gao, X.; Anslyn, E. V.; Krische, M. J.
Asymmetric Ir-catalyzed C-C coupling of primary alcohols with allyl-acetates, as described by Krische, to form chiral secondary homo-allylic alcohols were performed in parallel as a means to optimize the ee values thereof. Specifically, approximately 400 examples of this reaction were performed by varying the catalyst, added acids and bases, and starting reactants, to form 4-phenyl-1-butene-4-ol (1). The ee values for the transformations were determined in a high-throughput fashion using a 4-component assembly that creates a circular dichroism signal indicative of the extent of asymmetric induction. Further, a parallel and rapid quantitative TLC method measures the yield of each reaction, revealing which reactions give reliable ee values in the CD-based assay. Overall, the nearly 200 reactions whose ee values were determined could be quantitated in under two hours. Using a combination of the TLC method to measure yield with the CD-assay to measure ee values, several trends in reaction conditions were revealed. For example, it was found that the cyclometalated iridium catalyst modified by BINAP and m-nitro-p-cyano-benzoic acid delivered adduct 1 with the highest levels of enantiomeric enrichment (94%), whereas the corresponding SEGPHOS-modified catalyst gave a comparable yield but lower ee (91%). Most importantly, this study shows that supramolecular assemblies can report hundreds of ee values in a rapid and reliable fashion to analyze parallel synthesis routines.
Au@Pt Dendrimer Encapsulated Nanoparticles As Model Electrocatalysts for Comparison of Experiment and Theory
(2012-01) Yancey, David F.; Zhang, Liang; Crooks, Richard M.; Henkelman, Graeme; Yancey, David F.; Zhang, Liang; Crooks, Richard M.; Henkelman, Graeme
In this paper we report the electrochemical synthesis of core@shell dendrimer-encapsulated nanoparticles (DENs) consisting of cores containing 147 Au atoms (Au-147) and Pt shells having similar to 54 or similar to 102 atoms (Au-147@Pt-n (n = 54 or 102)). The significance of this work arises from the correlation of the experimentally determined structural and electrocatalytic properties of these particles with density functional theory (DFT) calculations. Specifically, we describe an experimental and theoretical study of Pb underpotential deposition (UPD) on Au-147 DENs, the structure of both Au-147@Pb-n and Au-147@Pt-n DENs, and the activity of these DENs for the oxygen reduction reaction (ORR). DFT calculations show that Pb binding is stronger on the (100) facets of Au as compared to (111), and the calculated deposition and stripping potentials are consistent with those measured experimentally. Galvanic exchange is used to replace the surface Pb atoms with Pt, and a surface distortion is found for Au-147@Pt-n particles using molecular dynamics simulations in which the Pt-covered (100) facets shear into (111) diamond structures. DFT calculations of oxygen binding show that the distorted surfaces are the most active for the ORR, and that their activity is similar regardless of the Pt coverage. These calculations are consistent with rotating ring-disk voltammetry measurements.
A Benzocrown-6-Calix 4 Arene Methacrylate Copolymer: Selective Extraction of Caesium Ions from a Multi-Component System
(2010-09) Rambo, Brett M.; Kim, Sung Kuk; Kim, Jong Seung; Bielawski, Christopher W.; Sessler, Jonathan L.; Rambo, Brett M.; Kim, Sung Kuk; Bielawski, Christopher W.; Sessler, Jonathan L.
The synthesis and extraction properties of a copolymer comprised of a 10: 1 molar ratio of methyl methacrylate (MMA) and a methacrylate functionalized benzocrown-6-calix[ 4] arene are reported. Under aqueous-dichloromethane liquid-liquid extraction conditions, the copolymer displayed an enhanced selectivity for caesium over sodium and potassium (in the form of their picrate salts) as compared to an appropriate small molecule analogue. Further, the copolymer was capable of removing caesium nitrate from aqueous solution in the presence of various other anionic (e. g., F(-), Cl(-), and SO(4)(-)) and cationic species (e. g., K(+) and Na(+)). The ability of this polymeric system to extract inorganic caesium salts into dichloromethane from aqueous media scaled with the relative hydration energies (D(hyd)G degrees) of each anion studied (i.e., NO(3)(-) > Br(-) >> Cl(-) or F(-)).
Chemically Directing D-Block Heterometallics to Nanocrystal Surfaces as Molecular Beacons of Surface Structure
(2015-07) Rosen, Evelyn L.; Gilmore, Keith; Sawvel, A. M.; Hammack, April T.; Doris, Sean E.; Aloni, Shaul; Altoe, Virgina; Nordlund, Dennis; Weng, Tsu-Chien; Sokaras, Dimosthenis; Cohen, Bruce E.; Urban, Jeffrey J.; Ogletree, D. Frank; Milliron, Delia J.; Prendergasta, David; Helms, Bret A.; Milliron, Delia J.
Our understanding of structure and bonding in nanoscale materials is incomplete without knowledge of their surface structure. Needed are better surveying capabilities responsive not only to different atoms at the surface, but also their respective coordination environments. We report here that d-block organometallics, when placed at nanocrystal surfaces through heterometallic bonds, serve as molecular beacons broadcasting local surface structure in atomic detail. This unique ability stems from their elemental specificity and the sensitivity of their d-orbital level alignment to local coordination environment, which can be assessed spectroscopically. Re-surfacing cadmium and lead chalcogenide nanocrystals with iron- or ruthenium-based molecular beacons is readily accomplished with trimethylsilylated cyclopentadienyl metal carbonyls. For PbSe nanocrystals with iron-based beacons, we show how core-level X-ray spectroscopies and DFT calculations enrich our understanding of both charge and atomic reorganization at the surface when beacons are bound.
A Chemistry and Material Perspective On Lithium Redox Flow Batteries Towards High-Density Electrical Energy Storage
(2015-11) Zhao, Yu; Ding, Yu; Li, Yutao; Peng, Lele; Byon, Hye Ryung; Goodenough, Jason B.; Yu, Guihua; Zhao, Yu; Ding, Yu; Li, Yutao; Peng, Lele|Goodenough, Jason B.; Yu, Guihua
Electrical energy storage system such as secondary batteries is the principle power source for portable electronics, electric vehicles and stationary energy storage. As an emerging battery technology, Li-redox flow batteries inherit the advantageous features of modular design of conventional redox flow batteries and high voltage and energy efficiency of Li-ion batteries, showing great promise as efficient electrical energy storage system in transportation, commercial, and residential applications. The chemistry of lithium redox flow batteries with aqueous or non-aqueous electrolyte enables widened electrochemical potential window thus may provide much greater energy density and efficiency than conventional redox flow batteries based on proton chemistry. This Review summarizes the design rationale, fundamentals and characterization of Li-redox flow batteries from a chemistry and material perspective, with particular emphasis on the new chemistries and materials. The latest advances and associated challenges/opportunities are comprehensively discussed.
Circular Dichroism of Multi-Component Assemblies for Chiral Amine Recognition and Rapid ee Determination
(2011-08) Metola, Pedro; Anslyn, Eric V.; James, Tony D.; Bull, Steven D.; Metola, Pedro; Anslyn, Eric V.
Upon mixing a chiral amine, enantiopure BINOL, and o-formyl phenyl boronic acid, the three components assemble efficiently and rapidly into chiral host-guest structures that produce distinct circular dichroism signals for each enantiomer of the amine. Employing BINOL and two derivatives to create an array of receptors, the CD signals resulting from several a-chiral primary amines were processed by principal component analysis and linear discriminant analysis to give satisfactory discrimination of the amines studied. Not only was the system able to differentiate the analytes chemoselectively and enantioselectively, but it also allowed for the rapid determination of chiral amine
Dendrimer-Encapsulated Nanoparticles: New Synthetic and Characterization Methods and Catalytic Applications
(2011-05) Myers, V. Sue; Weir, Michael G.; Carino, Emily V.; Yancey, David F.; Pande, Surojit; Crooks, Richard M.; Myers, V. Sue; Weir, Michael G.; Carino, Emily V.; Yancey, David F.; Pande, Surojit; Crooks, Richard M.
In this article we describe the synthesis, characterization, and applications of dendrimer-encapsulated nanoparticles (DENs). These materials are synthesized using a template approach in which metal ions are extracted into the interior of dendrimers and then subsequently reduced chemically to yield nearly size-monodisperse particles having diameters in the 1-2 nm range. Monometallic, bimetallic (alloy and core@shell), and semiconductor nanoparticles have been prepared by this route. The dendrimer component of these composites serves not only as a template for preparing the nanoparticle replica, but also as a stabilizer for the nanoparticle. In this perspective, we report on progress in the synthesis, characterization, and applications of these materials since our last review in 2005. Significant advances in the synthesis of core@shell DENs, characterization, and applications to homogeneous and heterogeneous catalysis (including electrocatalysis) are emphasized.
A Dicationic Calix 4 Pyrrole Derivative and Its Use for the Selective Recognition and Displacement-Based Sensing of Pyrophosphate
(2012-03) Sokkalingam, Punida; Kim, Dong Sub; Hwang, Hyonseok; Sessler, Jonathan L.; Lee, Cang-Hee; Kim, Dong Sub; Sessler, Jonathan L.
A new bis-pyridinium calix[4] pyrrole derivative is reported. This system forms a non-fluorescent complex upon exposure to the chromenolate anion. The resulting supramolecular ensemble binds the pyrophosphate anion with high affinity (K-a (2.55 +/- 0.12) x 10(7) M-1) in acetonitrile. It exhibits sensitive "turn-on" fluorescence when exposed to tetrabutylammonium pyrophosphate, and does so in preference to other anions, including the fluoride and phosphate anions.
Diene Hydroaminomethylation Via Ruthenium-Catalyzed C-C Bond forming Transfer Hydrogenation: Beyond Carbonylation
(2015-11) Oda, Susumu; Franke, Jana; Krische, Michael J.; Oda, Susumu; Franke, Jana; Krische, Michael J.
Under the conditions of ruthenium catalyzed transfer hydrogenation using 2-propanol as terminal reductant, 1,3-dienes engage in reductive C-C coupling with formaldimines obtained in situ from 1,3,5-tris( aryl)-hexahydro-1,3,5-triazines to form homoallylic amines. Deuterium labelling studies corroborate a mechanism involving reversible diene hydroruthenation to form an allylruthenium complex that engages in turn-over limiting imine addition. Protonolysis of the resulting amidoruthenium species releases product and delivers a ruthenium alkoxide, which upon beta-hydride elimination closes the catalytic cycle. These transformations, which include enantioselective variants, represent the first examples of diene hydroaminomethylation.
Direct Electrochemical Detection of Individual Collisions Between Magnetic Microbead/Silver Nanoparticle Conjugates and a Magnetized Ultramicroelectrode
(2015-07) Yoo, Jason J.; Kim, Joohoon; Crooks, Richard M.; Yoo, Jason J.; Kim, Joohoon; Crooks, Richard M.
Here, we report on the electrochemical detection of individual collisions between a conjugate consisting of silver nanoparticles (AgNPs) linked to conductive magnetic microbeads (cM mu Bs) via DNA hybridization and a magnetized electrode. The important result is that the presence of the magnetic field increases the flux of the conjugate to the electrode surface, and this in turn increases the collision frequency and improves the limit of detection (20 aM). In addition, the magnitude of the charge associated with the collisions is greatly enhanced in the presence of the magnetic field. The integration of DNA into the detection protocol potentially provides a means for using electrochemical collisions for applications in biological and chemical sensing.
Discrimination of Flavonoids and Red Wine Varietals by Arrays of Differential Peptidic Sensors
(2010-10) Umali, Alona P.; LeBoeuf, Sarah E.; Newberry, Robert W.; Kim, Siwon; Tran, Lee; Rome, Whitney A.; Tian, Tian A.; Taing, David; Hong, Jane; Kwan, Melissa; Heymann, Hildegarde; Anslyn, Eric V.; Umali, Alona P.; LeBoeuf, Sarah E.; Newberry, Robert W.; Kim, Siwon; Tran, Lee; Rome, Whitney A.; Tian, Tian A.; Taing, David; Hong, Jane; Kwan, Melissa; Anslyn, Eric V.
The chemical structures and concentrations of an organism's natural products are dependent upon its genome and environmental factors. Examples are the complex metabolite solutions resulting from plant and fermentation processes. Here, we describe sensor arrays composed of supramolecular ensembles that undergo indicator displacement and discriminate selected flavonoids and mixtures thereof: wine varietals. Changes in UV-vis absorbance upon indicator displacement in the array were analyzed using pattern recognition protocols. The flavonoids were differentiated in terms of structure and concentration, while red wines were generally classified by varietals, even from different vintners. The technique highlights the power of differential sensor arrays to classify mixtures by metabolite distribution, even when the natural products are not known.
A Dual-Fluorescent Composite of Graphene Oxide and Poly(3-Hexylthiophene) Enables the Ratiometric Detection of Amines
(2014-04) Meng, Dongli; Yang, Sshaojun; Sun, Dianming; Zeng, Yi; Sun, Jinhua; Li, Yi; Yan, Shouke; Huang, Yong; Bielawski, Christopher W.; Geng, Jianxin; Bielawski, Christopher W.
A composite prepared by grafting a conjugated polymer, poly(3-hexylthiophene) (P3HT), to the surface of graphene oxide was shown to result in a dual-fluorescent material with tunable photoluminescent properties. Capitalizing on these unique features, a new class of graphene-based sensors that enables the ratiometric fluorescence detection of amine-based pollutants was developed. Moreover, through a detailed spectroscopic study, the origin of the optical properties of the aforementioned composite was studied and was found to be due to electronic decoupling of the conjugated polymer from the GO. The methodology described herein effectively overcomes a long-standing challenge that has prevented graphene based composites from finding utility in sensing and related applications.
Dynamic 2D Manganese(II) Isonicotinate Framework with Reversible Crystal-To-Amorphous Transformation and Selective Guest Adsorption
(2014-04) Matoga, Dariusz; Gil, Barbara; Nitek, Wojciech; Todd, Alexander D.; Bielawski, Christopher W.; Todd, Alexander D.; Bielawski, Christopher W.
A 2D layered microporous isonicotinate-supported manganese(II) metal-organic framework was found to exhibit a reversible crystalto-amorphous transformation upon the removal and uptake of certain guest molecules. Unsaturated metal centers, generated in the dynamic framework upon activation, were found to facilitate the selective adsorption of CO2 versus N-2.
Dynamic Potential-Ph Diagrams Application to Electrocatalysts for Water Oxidation
(2011-07) Minguzzi, Alessandro; Fan, Fu-Ren F.; Vertova, Alberto; Rondinini, Sandra; Bard, Allen J.; Bard, Allen J.
The construction and use of "dynamic potential-pH diagrams" (DPPDs), that are intended to extend the usefulness of thermodynamic Pourbaix diagrams to include kinetic considerations is described. As an example, DPPDs are presented for the comparison of electrocatalysts for water oxidation, i.e., the oxygen evolution reaction (OER), an important electrochemical reaction because of its key role in energy conversion devices and biological systems (water electrolyses, photoelectrochemical water splitting, plant photosynthesis). The criteria for obtaining kinetic data are discussed and a 3-D diagram, which shows the heterogeneous electron transfer kinetics of an electrochemical system as a function of pH and applied potential is presented. DPPDs are given for four catalysts: IrO(2), Co(3)O(4), Co(3)O(4) electrodeposited in a phosphate medium (Co-Pi) and Pt, allowing a direct comparison of the activity of different electrode materials over a broad range of experimental conditions (pH, potential, current density). In addition, the experimental setup and the factors affecting the accurate collection and presentation of data (e. g., reference electrode system, correction of ohmic drops, bubble formation) are discussed.
Electrochemistry and Electrogenerated Chemiluminescence of Thiophene and Fluorene Oligomers. Benzoyl Peroxide as a Coreactant for Oligomerization of Thiophene Dimers
(2012-05) Nepomnyashchii, Alexander B.; Ono, Robert J.; Lyons, Dani M.; Bielawski, Christopher W.; Sessler, Jonathan L.; Bard, Allen J.; Nepomnyashchii, Alexander B.; Ono, Robert J.; Lyons, Dani M.; Bielawski, Christopher W.; Sessler, Jonathan L.; Bard, Allen J.
The electrochemical properties of oligomers of thiophene (with number of monomer units, n, from 2 to 12) and fluorene (n = 3 to 7) were investigated. Both sets of oligomers were characterized by the presence of two oxidation and two reduction waves as determined by cyclic voltammetry (CV), with the reversibility of the waves depending on the structural properties of the compounds. The addition or removal of a third electron was found to be difficult relative to the second, a finding shown for conjugated oligomers with chain lengths up to 7 in the case of the fluorenes and up to 12 for the thiophenes. The oligothiophenes showed a larger separation between the electrochemical waves for the same chain length, and also substantial electrogenerated chemiluminescence (ECL) signals, whose intensity increased with oligomer size. In contrast, the ECL intensity of the fluorene oligomers was essentially independent of chain length. The ECL spectra for the thiophene dodecamer were obtained with concentrations as low as 20 pM, a result that reflects a high ECL efficiency, close to that of the well-known ECL standard Ru(bpy)(3)(2+). Oligomers were also formed on electrochemical reduction of an appropriately functionalized dimer in the presence of benzoyl peroxide producing a longer wavelength emission (maximum at similar to 540 nm) as opposed to the spectrum of the dimer (lambda(em) = 390 nm).
Enhanced Phosphorescence in Dibenzophosphole Chalcogenide Mixed Crystal
(2011-06) Kabe, Ryota; Lynch, Vincent M.; Anzenbacher, Pavel; Lynch, Vincent M.
The single crystals of 9-phenyl-9-dibenzophosphole chalcogenides {oxide (1), sulfide (2) and selenide (3)} and a mixed crystal of 2 and 3 have been prepared and characterized by X-ray diffraction analysis. Several intermolecular interactions such as pi-pi and Se-H were observed in the mixed crystal of 2 and 3. The mixed crystal of 2 and 3 exhibited enhanced phosphorescence compared to the pure constituent crystal (2 or 3) at low temperature.
Exploration of Plasticizer and Plastic Explosive Detection and Differentiation with Serum Albumin Cross-Reactive Arrays
(2012-03) Ivy, Michelle A.; Gallagher, Lauren T.; Ellington, Andrew D.; Anslyn, Eric V.; Ivy, Michelle A.; Gallagher, Lauren T.; Ellington, Andrew D.; Anslyn, Eric V.
Plastic explosives, such as Semtex and C4, are commonly used explosive mixtures. The differentiation and detection of the plasticizers within these mixtures could provide information for anti-terrorism and combat activities. In this study, we demonstrate a strategy of using cross-reactive serum albumin proteins to differentiate and detect the plasticizers found within these explosive mixtures. With our sensing ensemble, comprised of serum albumins, fluorescent indicators and an additive, we successfully classified the five plasticizers found within Semtex and C4 using linear discriminate analysis, and differentiated simulated Semtex and C4 mixtures based on surrogates of the explosive material(s) and the plasticizer composition in these samples. Finally, we have shown the utility of this type of cross-reactive array for real life use in a battlefield setting by examining these mixtures in the presence of soil contamination.
First Supramolecular Sensors for Phosphonate Anions
(2013-06) Esipenko, Nina A.; Koutnik, Petr; Minami, Tsuyoshi; Mosca, Lorenzo; Lynch, Vincent M.; Zyryanov, Grigory V.; Anzenbacher, Pavel; Lynch, Vincent M.
Fluorescent tripodal anion sensors with a 1,3,5-triethylbenzene core display a turn-on fluorescence response to phosphonate and phosphate anions and may be used as optical sensors. The properties of the receptors and sensors as well as their anion binding behavior were investigated both in solution and in solid state. The turn-on fluorescence response can be leveraged in sensing of phosphate anions and, most importantly, hydrolysis products of the nerve gas sarin, isopropyl methylphosphonate (IMP), and methylphosphonate (MP). The fluorescence signal amplification in the presence of anions allows for application of these molecules in a sensor microarray suitable for high-throughput screening.
From Monomers to Polymers: Steric and Supramolecular Effects on Dimensionality of Coordination Architectures of Heteroleptic Mercury(II) Halogenide-Tetradentate Schiff Base Complexes
(2015-03) Mahmoudi, Ghodrat.; Stilinovic, Vladimir; Gargari, Masoumeh Servati; Bauza, Antonio; Zaragoza, Guillermo; Kaminsky, Wwerner; Lynch, Vincent; Choquesillo-Lazarte, Duane; Sivakumar, K.; Khandar, Ali Akbar; Frontera, Antonio; Lynch, Vincent
In this study, neutral mercury(II) complexes of the composition [Hg(L1)(mu-Cl)(2)Hg3Cl6](n) (1), [Hg(L1)(mu-Br)(2)HgBr2] (2), [Hg(L3)Br-2] (2a), [Hg(L1)I-2] (3), [Hg(L2)Cl-2]center dot CH3OH (4) and [Hg(L2)(mu-Br)HgBr3](2) (5) (L1 = benzilbis((pyridin-2-yl)methylidenehydrazone); L2 = benzilbis((acetylpyridin-2-yl) methylidenehydrazone)) are described. Single-crystal X-ray crystallography showed that the molecular complexes can aggregate into larger entities depending upon the anion coordinated to the metal centre. Iodide gives discrete monomeric complexes, bromide generates a 1D coordination polymer formed through Hg-Br-Hg bridges and chloride gives rise to an inorganic-organic hybrid material. The significant differences in the reaction conditions indicate that the anions exert a substantial influence on the formation of the compounds - smaller anions show a larger potential for bridging metal ions and forming coordination polymers. A minute increase in the bulkiness of the ligand (two extra methyl substituents in L2) dramatically changes the coordination architectures, and leads to the formation of monomeric (chloride and iodide) and oligomeric (bromide) structures, rather than polymeric structures. The noncovalent C-H/pi and pi-hole interactions observed in the solid state architecture of some complexes have been rationalized by means of theoretical DFT calculations.