Chemistry, Department of

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Synthesis of Heterobenzylic Fluorides

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2018-01-17
Abstract: 

Fluorination at heterobenzylic positions can have a significant impact on basicity, lipophilicity, and metabolism of drug leads. As a consequence, the development of new methods to access heterobenzylic fluorides has particular relevance to medicinal chemistry. This Short Review provides a survey of common methods used to synthesize heterobenzylic fluorides and includes fluoride displacement reactions of previously functionalized molecules (e.g., deoxyfluorination and halide exchange) and electrophilic fluorination of resonance stabilized heterobenzylic anions. In addition, recent advances in the direct fluorination of heterobenzylic C(sp3)-H bonds and monofluoromethylation of heterocyclic C(sp2)-H bonds are presented.

Document type: 
Article

Tuning Electronic Structure To Control Manganese Nitride Activation

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-11-18
Abstract: 

Investigation of a series of oxidized nitridomanganese(V) salen complexes with different para ring substituents (R = CF3, tBu, and NMe2) demonstrates that nitride activation is dictated by remote ligand electronics. For R = CF3 and tBu, oxidation affords a Mn(VI) species and nitride activation, with dinitrogen homocoupling accelerated by the more electron-withdrawing CF3 substituent. Employing an electron-donating substituent (R = NMe2) results in a localized ligand radical species that is resistant to N coupling of the nitrides and is stable in solution at both 195 and 298 K.

Document type: 
Article
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Digitized Molecular Detection on Off-the-shelf Blu-ray Discs: Upgraded Resolution and Enhanced Sensitivity

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-03-22
Abstract: 

Beyond the intrinsic capability of storing and archiving high-definition movies and games, off-the-shelf Blu-ray discs have been adopted for the preparation of molecular binding assays, which are subsequently read and quantitated with a standard computer drive in conjunction with the disc-quality check program. The performance of this digitized molecular detection system has been examined first with an artificial “ink assay” (an array of microsize ink dots) to define the quantitation capability and the lateral resolution; the conventional biotin-streptavidin binding assay was then tested with the Blu-ray detection platform, and the results compared with that obtained on a DVD. The upgraded lateral resolution (<100 μm) and enhanced assay performance (linear response up to 0.4 μg/mL and LOD estimated to be >< 0.1 μg/mL for the trial biotin-streptavidin system augments its potential to be adapted as a cost-effective and quantitative diagnostic tool for on-site analysis and point-of-care medical diagnosis at trace amounts.

Document type: 
Article

Host-guest Interaction at Molecular Interfaces: Binding of Cucurbit[7]uril on Ferrocenyl Self-assembled Monolayers on Gold

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-03-22
Abstract: 

Ferrocene (Fc) encapsulated cucurbit[7]uril (CB[7]) supramolecular host-guest complex  (Fc@CB[7]) as a synthetic recognition pair has been widely adapted for coupling biomolecules and nanomaterials due to its ultra-high binding affinity. In this paper, we have explored the binding of CB[7] on binary ferrocenylundecanethiolate/octanethiolate self-assembled monolayer on gold  (FcC11S-/C8S-Au), a model system to deepen our understanding of host-guest chemistry at molecular interfaces. It has been shown that upon incubation with CB[7] solution, the redox behavior FcC11S-/C8S-Au changes remarkably, i.e., a new pair of peaks appeared at more positive potential with narrowed widths. The ease of quantitation of surface bound-redox species (Fc+/Fc and  Fc+@CB[7]/ Fc@CB[7]) enabled us to determine the thermodynamic formation constant of  Fc@CB[7] at FcC11S-/C8S-Au (7.3±1.8 × 104 M-1). With time-dependent redox responses, we were able to, for the first time, deduce both the binding and dissociation rate constants, 2.8±0.3 × 103  M-1s-1 and 0.08±0.01 s-1, respectively. These results showed substantial differences both thermodynamically and kinetically for the formation of host-guest inclusion complex at molecular interfaces with respect to solution-diffused, homogenous environments.

Document type: 
Article

Superhydrophobic Substrates from Off-The-Shelf Laboratory Filter Paper: Simplified Preparation, Patterning, and Assay Application

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-09-21
Abstract: 

Off-the-shelf laboratory filter paper of different pore-sizes and thicknesses can be modified with fluorine-free organosilanes to be superhydrophobic, patternable, and ready for quantitative assay applications. In particular, we have demonstrated that cellulose filter paper treated with a binary hexane solution of short (methyltrichlorosilane, MTS) and long (octadecyltrichlorosilane, OTS) organosilanes, exhibits remarkably high water contact angles (> 150 °) and low wetting hysteresis (~10 °). Beyond the optimized ratio between the two organosilanes, we have discovered that the thickness rather than the pore size dictates the resulting superhydrophobicity. Scanning electron microscope (SEM) images showed that silianization does not damage the cellulose microfibers; instead they are coated with uniform, particulate nanostructures, which should contribute to the observed surface properties. The modified filter paper is chemically stable and mechanically durable; it can be readily patterned with UV/ozone treatment to create hydrophilic regions to prepare chemical assays for colorimetric pH and nitrite detections.

Document type: 
Article

Revealing and Resolving the Restrained Enzymatic Cleavage of DNA Self-Assembled Monolayers on Gold: Electrochemical Quantitation and ESI-MS Confirmation

Peer reviewed: 
No, item is not peer reviewed.
Abstract: 

Herein we report a combined electrochemical and ESI-MS study of the enzymatic hydrolysis efficiency of DNA self-assembled monolayers (SAMs) on gold, platform systems for understanding nucleic acid surface chemistry and for constructing DNA-based biosensors. Our electrochemical approach is based on the comparison of the amounts of surface-tethered DNA nucleotides before and after Exonuclease I (Exo I) incubation using electrostatically bound [Ru(NH3)6]3+ as redox indicators. It is surprising to reveal that the hydrolysis efficiency of ssDNA SAMs does not depend on the packing density and base sequence, and that the cleavage ends with surface-bound shorter strands (9-13 mers). The ex-situ ESI-MS observations confirmed that the hydrolysis products for ssDNA SAMs (from 24 to 56 mers) are dominated with 10-15 mer fragments, in contrast to the complete digestion in solution. Such surface-restrained hydrolysis behavior is due to the steric hindrance of the underneath electrode to the Exo I/DNA binding, which is essential for the occurrence of Exo I-catalyzed processive cleavage. More importantly, we have shown that the hydrolysis efficiency of ssDNA SAMs can be remarkably improved by adopting long alkyl linkers (locating DNA strands further away from the substrates).

Document type: 
Article

Integrated Smartphone-App-Chip System for On-Site Ppb-Level Colorimetric Quantitation of Aflatoxins

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-07-18
Abstract: 

We demonstrate herein an integrated, smartphone-app-chip (SPAC) system for on-site quantitation of food toxins, as demonstrated with aflatoxin B1 (AFB1), at parts-per-billion (ppb) level in food products. The detection is based on an indirect competitive immunoassay fabricated on a transparent plastic chip with the assistance of a microfluidic channel plate. A 3D-printed optical accessory attached to a smartphone is adapted to align the assay chip and to provide uniform illumination for imaging, with which high-quality images of the assay chip are captured by the smartphone camera and directly processed using a custom-developed Android app. The performance of this smartphone-based detection system was tested using both spiked and moldy corn samples; consistent results with conventional ELISA kits were obtained. The achieved detection limit (3±1 μg/kg, equivalent to ppb) and dynamic response range (0.5−250 μg/kg) meet the requested testing standards set by authorities worldwide. We envision that the integrated SPAC system promises to be a simple and accurate method of food toxin quantitation, bringing much benefit for rapid on-site screening.

Document type: 
Article

Palladium-Catalyzed Allylation/Benzylation of H-Phosphinate Esters with Alcohols

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-09
Abstract: 

The Pd-catalyzed direct alkylation of H-phosphinic acids and hypophosphorous acid with allylic/benzylic alcohols has been described previously. Here, the extension of this methodology to H-phosphinate esters is presented. The new reaction appears general, although its scope is narrower than with the acids, and its mechanism is likely different. Various alcohols are examined in their reaction with phosphinylidene compounds R1R 2P(O)H.

Document type: 
Article
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Synthesis and Electronic Structure Determination of Uranium(VI) Ligand Radical Complexes

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2016-07
Abstract: 

 

 Pentagonal bipyramidal uranyl complexes of salen ligands, N,N’-bis(3-tert-butyl-(5R)-salicylidene)-1,2-phenylenediamine, in which R = tBu (1a), OMe (1b), and NMe2 (1c), were prepared and the electronic structure of the one-electron oxidized species [1a-c]+ were investigated in solution. The solid-state structures of 1a and 1b were solved by X-ray crystallography, and in the case of 1b an asymmetric UO22+ unit was found due to an intermolecular hydrogen bonding interaction. Electrochemical investigation of 1a-c by cyclic voltammetry showed that each complex exhibited at least one quasi-reversible redox process assigned to the oxidation of the phenolate moieties to phenoxyl radicals. The trend in redox potentials matches the electron-donating ability of the para-phenolate substituents. The electron paramagnetic resonance spectra of cations [1a-c]+ exhibited gav values of 1.997, 1.999, and 1.995, respectively, reflecting the ligand radical character of the oxidized forms, and in addition, spin-orbit coupling to the uranium centre. Chemical oxidation as monitored by ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy afforded the one-electron oxidized species. Weak low energy intra-ligand charge transfer (CT) transitions were observed for [1a-c]+ indicating localization of the ligand radical to form a phenolate / phenoxyl radical species. Further analysis using density functional theory (DFT) calculations predicted a localized phenoxyl radical for [1a-c]+ with a small but significant contribution of the phenylenediamine unit to the spin density. Time-dependent DFT (TD-DFT) calculations provided further insight into the nature of the low energy transitions, predicting both phenolate to phenoxyl intervalence charge transfer (IVCT) and phenylenediamine to phenoxyl CT character. Overall, [1a-c]+ are determined to be relatively localized ligand radical complexes, in which localization is enhanced as the electron donating ability of the para-phenolate substituents is increased (NMe2 > OMe > tBu).

Document type: 
Article
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Characterization of free radicals in clathrate hydrates of pyrrole, thiophene and isoxazole by muon spin spectroscopy

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2017-05-25
Abstract: 

Gas hydrates have long been of interest to the petrochemical industry but there has been growing interest in potential applications for carbon dioxide sequestration and hydrogen storage. This has prompted many fundamental studies of structure and host-guest interactions, but there has been relatively little investigation of chemical reactions of the guest molecules. In previous work we have shown that it is possible to use muon spin spectroscopy to characterize H-atom-like muonium and muoniated free radicals formed in clathrate hydrates. Muonium forms in clathrate hydrates of cyclopentane and tetrahydrofuran, whereas furan and its dihydro- derivatives form radicals. The current work extends studies to clathrates hydrates of other 5-membered heterocycles: thiophene, pyrrole and isoxazole. All form structure II hydrates. In addition to the clathrates, pure liquid samples of the heterocycles were studied to aid in the assignment of radical signals and for comparison with the enclathrated radicals. Similar to furan, two distinct radicals are formed when muonium reacts with thiophene and pyrrole. However, only one muoniated radical was detected from isoxazole. Muon, proton and nitrogen hyperfine constants were determined and compared with values predicted by DFT calculations to aid the structure assignments. The results show that Mu adds preferentially to the carbon adjacent to the heteroatom in thiophene and pyrrole, and to the carbon adjacent to O in isoxazole. The same radicals are formed in clathrates, but the spectra have broader signals, suggesting slower tumbling. Furthermore, additional signals in the avoided level-crossing spectra indicate anisotropy consistent with restricted motion of the radicals in the clathrate cages.

Document type: 
Article