Showing papers by "Sean Parkin published in 2014"
TL;DR: The synthesis and characterization of "bistetracene", an unconventional, linearly extended conjugated core with eight fused rings, provides valuable insight into the design of unconventional semiconductor compounds based on higher PAHs for use in high-performance devices.
Abstract: We report the synthesis and characterization of “bistetracene”, an unconventional, linearly extended conjugated core with eight fused rings. The annellation mode of the system allows for increased stability of the conjugated system relative to linear analogues due to the increased number of Clar aromatic sextets. By attaching the appropriate solubilizing substituents, efficient molecular packing with large transfer integrals can be obtained. The electronic structure calculations suggest these large polycyclic aromatic hydrocarbons (PAHs) exhibit excellent intrinsic charge transport properties. Charge carrier mobilities as large as 6.1 cm2 V–1 s–1 and current on/off ratios of 107 were determined experimentally for one of our compounds. Our study provides valuable insight into the design of unconventional semiconductor compounds based on higher PAHs for use in high-performance devices.
150 citations
TL;DR: The best compound exhibited a 1880-fold increase in cytotoxicity in human cancer cells upon light-activation and was 19-fold more potent than the well-known chemotherapeutic, cisplatin.
Abstract: Two novel strained ruthenium(II) polypyridyl complexes containing a 2,3-dihydro-1,4-dioxino[2,3-f]-1,10-phenanthroline (dop) ligand selectively ejected a methylated ligand when irradiated with >400 nm light. The best compound exhibited a 1880-fold increase in cytotoxicity in human cancer cells upon light-activation and was 19-fold more potent than the well-known chemotherapeutic, cisplatin.
69 citations
TL;DR: Ru(bpy)2dppz, a well studied "light-switch" metal complex, transforms into a photochemical " light- switch" and DNA damaging agent by incorporating structural strain.
60 citations
TL;DR: In this article, the stability of the radical cation forms of a series of redox shuttle additives was studied to determine if there is a correlation between radicalcation stability and the number of cycles of overcharge protection.
Abstract: A variety of mechanisms lead to the failure of lithium-ion batteries. One is overcharge, a condition in which a battery's voltage rises above its designed end-of-charge potential. Electrolyte additives called redox shuttles limit cell potential by preferentially oxidizing, and cycling between the cathode and anode in their radical cation and neutral forms. Currently, testing requires coin cell assembly and repeated cycling, which can be an expensive and time consuming process. It is commonly accepted that degradation of the radical cation form of a redox shuttle leads to overcharge protection failure. We thus studied the stability of the radical cation forms of a series of redox shuttle additives to determine if there is a correlation between radical cation stability and the number of cycles of overcharge protection. While the reversibility of oxidations in cyclic voltammetry did not correlate to trends in overcharge performance, results from both UV-vis and electron paramagnetic resonance spectroscopy showed a correlation between stability and overcharge protection. Our results reveal trends within a few hours for what otherwise takes months of battery cycling to determine, providing a fast and relatively inexpensive method for predicting redox shuttle performance.
46 citations
TL;DR: 3,7-Disubstituted N-ethylphenothiazine derivatives were synthesized as redox shuttle candidates for lithium-ion batteries and battery cycling results show that three derivatives prevent overcharge.
43 citations
TL;DR: In this article, the authors synthesized diarylamines with varied structures, including fused heteroaromatic ring systems and electron-withdrawing substituents, and found that trends in oxidation potentials correlated with those in calculated ionization potentials.
Abstract: Overcharge, a condition in which cell voltage rises to undesirably high potentials, can be prevented in lithium-ion batteries by incorporating redox shuttles into the battery electrolyte. Although extensive overcharge protection has been demonstrated in batteries with LiFePO4 cathodes, the redox shuttles that work in these batteries are incompatible with higher voltage cathodes. Designing stable additives with higher oxidation potentials is necessary to protect high voltage batteries from overcharge. Toward that goal, we synthesized diarylamines with varied structures, including fused heteroaromatic ring systems and electron-withdrawing substituents. We found that trends in oxidation potentials correlated with those in calculated adiabatic ionization potentials. Some diarylamine derivatives protected batteries from overcharge with varying degrees of success.
32 citations
TL;DR: In this paper, homogeneous catalysts that are soluble and stable in primary amine-based CO2 capture solvents were reported, which contain electron-donating multi-dentate anionic ligands and perform catalytic CO2 hydration at unparalleled observed rates under conditions conducive to industrial post-combustion carbon capture processes.
27 citations
TL;DR: In this paper, a 1:1 molar ratio of carboxylic acid and pyridine functional groups was found for 2-[phenyl(propyl)amino]nicotinic acid with two polymorphs, one consisting of unique hydrogen-bonded tetramer units bearing both acid-acid and acid-pyridine hydrogen bonding motifs.
Abstract: Carboxylic acid–acid hydrogen-bonding dimer and acid–pyridine hydrogen-bonding motif are two competing supramolecular synthons that a molecule possessing both carboxylic acid and pyridine functional groups could form in the solid state. Their coexistence has been observed but for the molecules with the molar ratio of carboxylic acid and pyridine groups being greater than 1:1. In this crystal engineering study, 2-[phenyl(propyl)amino]nicotinic acid with a 1:1 molar ratio of these two functional groups was discovered to have two polymorphs, in which one consists of unique hydrogen-bonded tetramer units bearing both acid–acid and acid–pyridine hydrogen-bonding motifs, while the other is composed of acid–pyridine hydrogen-bonded chains. Quantum mechanical calculations were employed to unravel the essence of the coexistence of the two vying counterparts as well as the origins of the tetramer and chain structures.
20 citations
TL;DR: Significant differences in the force curve behaviour and salt and pH sensitivities suggest that different binding modes may be present in DNA condensed by dendrimers when compared to linear polycations.
Abstract: In recent years, dendriplexes, complexes of cationic dendrimers with DNA, have become attractive DNA delivery vehicles due to their well-defined chemistries. To better understand the nature of the forces condensing dendriplexes, we studied low generation poly(amidoamine) (PAMAM) dendrimer–DNA complexes and compared them to comparably charged linear arginine peptides. Using osmotic stress coupled with X-ray scattering, we have investigated the effect of molecular chain architecture on DNA–DNA intermolecular forces that determine the net attraction and equilibrium interhelical distance within these polycation condensed DNA arrays. In order to compact DNA, linear cations are believed to bind in DNA grooves and to interact with the phosphate backbone of apposing helices. We have previously shown a length dependent attraction resulting in higher packaging densities with increasing charge for linear cations. Hyperbranched polycations, such as polycationic dendrimers, presumably would not be able to bind to DNA and correlate their charges in the same manner as linear cations. We show that attractive and repulsive force amplitudes in PAMAM–DNA assemblies display significantly different trends than comparably charged linear arginines resulting in lower DNA packaging densities with increasing PAMAM generation. The salt and pH dependencies of packaging in PAMAM dendrimer–DNA and linear arginine–DNA complexes were also investigated. Significant differences in the force curve behaviour and salt and pH sensitivities suggest that different binding modes may be present in DNA condensed by dendrimers when compared to linear polycations.
18 citations
TL;DR: A new synthetic route to 5,11-disubstituted indeno[1,2-b]fluorene-6,12-diones that is amenable to larger scale reactions, allowing for the preparation of gram amounts of material.
Abstract: We report a new synthetic route to 5,11-disubstituted indeno[1,2-b]fluorene-6,12-diones that is amenable to larger scale reactions, allowing for the preparation of gram amounts of material. With this new methodology, we explored the effects on crystal packing morphology for the indeno[1,2-b]fluorene-6,12-diones by varying the substituents on the silylethynyl groups.
18 citations
TL;DR: In this article, the effect of pH on the packaging and forces in low-generation poly(amidoamine) dendriplexes was measured using small-angle X-ray scattering coupled with osmotic stress.
Abstract: Cationic polymers are capable of spontaneously condensing DNA into complexes suitable for nonviral gene therapy. The precisely defined molecular weights and highly symmetric surface chemistries of dendrimers, such as poly(amidoamine) (PAMAM), have made them attractive alternatives to conventional linear polymers for DNA delivery applications. In this paper, we use small-angle X-ray scattering (SAXS) coupled with osmotic stress to directly measure the effect of pH on the packaging and forces in low generation (G0 and G1) PAMAM–DNA complexes or dendriplexes. Because of the presence of both primary and tertiary amines with differing pKas, PAMAM changes its net charge with pH. We show that changing the pH at condensation results in large differences in the packaging and intermolecular forces in PAMAM dendriplexes. Both dendrimer/DNA systems show a large increase in attractions with decreasing pH scaling linearly with the inverse of the dendrimer charge, while repulsions in the system are nearly unaffected. pH...
TL;DR: The title compound, C19H17N3O3S (I), was prepared by a [3 + 2]cycloaddition azide condensation reaction using sodium azide and l-proline as a Lewis base catalyst as discussed by the authors.
Abstract: The title compound, C19H17N3O3S (I), was prepared by a [3 + 2]cycloaddition azide condensation reaction using sodium azide and l-proline as a Lewis base catalyst. N-Methylation of compound (I) using CH3I gave compound (II), C20H19N3O3S. The benzothiophene ring systems in (I) and (II) are almost planar, with r.m.s deviations from the mean plane = 0.0205 (14) in (I) and 0.016 (2) A in (II). In (I) and (II), the triazole rings make dihedral angles of 32.68 (5) and 10.43 (8)°, respectively, with the mean planes of the benzothiophene ring systems. The trimethoxy phenyl rings make dihedral angles with the benzothiophene rings of 38.48 (4) in (I) and 60.43 (5)° in (II). In the crystal of (I), the molecules are linked into chains by N—H⋯O hydrogen bonds with R21(5) ring motifs. After the N-methylation of structure (I), no hydrogen-bonding interactions were observed for structure (II). The crystal structure of (II) has a minor component of disorder that corresponds to a 180° flip of the benzothiophene ring system [occupancy ratio 0.9363 (14):0.0637 (14)].
TL;DR: The title compound, C20H23N3O6·CH3OH, was synthesized by [3 + 2] cycloaddition of (Z)-2,3-bis(3,4,5-trimethoxyphenyl)acrylonitrile with sodium azide and ammonium chloride in DMF/water.
Abstract: The title compound, C20H23N3O6·CH3OH, was synthesized by [3 + 2] cycloaddition of (Z)-2,3-bis(3,4,5-trimethoxyphenyl)acrylonitrile with sodium azide and ammonium chloride in DMF/water. The central nitrogen of the triazole ring is protonated. The dihedral angles between the triazole ring and the 3,4,5-trimethoxyphenyl ring planes are 34.31 (4) and 45.03 (5)°, while that between the 3,4,5-trimethoxyphenyl rings is 51.87 (5)°. In the crystal, the molecules, along with two methanol solvent molecules are linked into an R44(10) centrosymmetric dimer by N—H⋯O and O—H⋯N hydrogen bonds.
TL;DR: The title monosuccinate derivative of melampomagnolide B [systematic name: 4-(((1aR,7aS,10a S,10bS,E)-1a-methyl-8-methylene-9-oxo-1a,2,3,6,7,7A,8,9,10 a,10 b-decahydrooxireno]cyclodeca[2′,3′:
Abstract: The title monosuccinate derivative of melampomagnolide B [systematic name: 4-(((1aR,7aS,10aS,10bS,E)-1a-methyl-8-methylene-9-oxo-1a,2,3,6,7,7a,8,9,10a,10b-decahydrooxireno[2′,3′:9,10]cyclodeca[1,2-b]furan-5-yl)methoxy)-4-oxobutanoic acid], C19H24O7, was obtained from the reaction of melampomagnolide B with succinic anhydride under nucleophilic addition reaction conditions. The molecule is built up from fused ten-, five- (lactone) and three-membered (epoxide) rings. The internal double bond in the ten-membered ring has the cis geometry (i.e. it is the E isomer). The lactone ring has an envelope-type conformation, with the (chiral) C atom opposite the lactone O atoms as the flap atom. In the crystal, O—H⋯O hydrogen bonds link the molecules into chains parallel to the b-axis direction.
TL;DR: The title compound, C12H14N6O, consists of three pyrazole rings bound via nitrogen to the distal ethane carbon of methoxy ethane, which was refined as a perfect ( 0.5:0.5) inversion twin.
Abstract: The title compound, C12H14N6O, consists of three pyrazole rings bound via nitrogen to the distal ethane carbon of methoxy ethane. The dihedral angles between the three pyrazole rings are 67.62 (14), 73.74 (14), and 78.92 (12)°. In the crystal, molecules are linked by bifurcated C—H,H⋯N hydrogen bonds, forming double-stranded chains along [001]. The chains are linked via C—H⋯O hydrogen bonds, forming a three-dimensional framework structure. The crystal was refined as a perfect (0.5:0.5) inversion twin.
TL;DR: The title compound, C33H35NO6, was prepared by the reaction of (Z)-3-(4-iodophenyl)-2-(3,4,5-trimethoxyphenyl)acrylonitrile with parthenolide under Heck reaction conditions.
Abstract: The title compound, C33H35NO6 [systematic name: (Z)-3-(4-{(E)-[(E)-1a,5-dimethyl-9-oxo-2,3,7,7a-tetrahydrooxireno[2′,3′:9,10]cyclodeca[1,2-b]furan-8(1aH,6H,9H,10aH,10bH)-ylidene]methyl}phenyl)-2-(3,4,5-trimethoxyphenyl)acrylonitrile methanol hemisolvate], C33H35NO6·0.5CH3OH, was prepared by the reaction of (Z)-3-(4-iodophenyl)-2-(3,4,5-trimethoxyphenyl)acrylonitrile with parthenolide [systematic name: (E)-1a,5-dimethyl-8-methylene-2,3,6,7,7a,8,10a,10b-octahydrooxireno[2′,3′:9,10]cyclodeca[1,2-b]furan-9(1aH)-one] under Heck reaction conditions. The molecule is built up from fused ten-, five- (lactone) and three-membered (epoxide) rings with a {4-[(Z)-2-cyano-2-(3,4,5-trimethoxyphenyl)ethenyl]phenyl}methylidene group as a substituent. The 4-[(Z)-2-cyano-2-(3,4,5-trimethoxyphenyl)ethenyl]phenyl group on the parthenolide exocyclic double bond is oriented in a trans position to the lactone ring to form the E isomer. The dihedral angle between the benzene ring of the phenyl moiety and the lactone ring mean plane is 21.93 (4)°.
TL;DR: The crystal structure of the title compound possesses mirror symmetry, with the halogen, N and C atoms all lying in the mirror plane, and the dihedral angle between the benzene ring and the nitro group is 90°.
Abstract: In the crystal structure of the title compound, C6H2Cl2INO2, there are weak C—H⋯Cl interactions and I⋯O [3.387 (4) A] close contacts. These interactions form sheets in the ac plane, with the closest contact between adjacent planes occurring between inversion-related nitro O atoms [3.025 (8) A]. The molecule possesses mirror symmetry, with the halogen, N and C atoms all lying in the mirror plane. Hence, the dihedral angle between the benzene ring and the nitro group is 90°.
TL;DR: In this paper, the reductive amination of 2,5-dimethylthiophene-3,4-dicarbaldehyde with various primary amines in a solution of sodium cyanoborohydride and methanol/acetic acid (80-88% yield) was accomplished by a general convenient route toward N-substituted 5,6-dihydro-4H-thieno[3, 4-c]-pyrroles.
TL;DR: In this paper, a tridentate coordination of pyridylmethylthiourea derivatives with [(en)2Co(OSO2CF3)2]- was studied, resulting in the formation of a hypodentate ethylenediamine ligand.
Abstract: Pyridylmethylthiourea derivatives coordinate with [(en)2Co(OSO2CF3)2]+ in a tridentate manner resulting in the formation of a hypodentate ethylenediamine ligand. Four ligands were studied: N-(R)phenyl-N′-2-pyridylmethylthiourea (R = H (1a), CH3 (1b), OCH3 (1c)) and N-benzyl-N′-2-pyridylmethylthiourea (2). These bind through the sulfur, a deprotonated exo nitrogen, and the pyridyl nitrogen atoms forming four and five-membered rings, respectively. The ligand also coordinates in a bidentate manner through the sulfur and deprotonated endo or exo nitrogen atoms, forming two additional coordination isomers. The solid state structure (X-ray) of one of the bidentate isomers of Co-1b2+ (endo isomer) shows that the coordinated thiourea sulfur induces a structural trans effect of 0.035 A on the trans Co–N bond while that of the tridentate isomer of Co-1a3+ confirms the coordination mode of the ligand and the presence of a protonated hypodentate ethylenediamine ligand as suggested by 1H and 13C NMR spectroscopy.
TL;DR: The title compound exhibits intramolecular O—H⋯O hydrogen bonding between the hydroxy group and the lactone ring O atom, forming a ring of graph-set motif S(6).
Abstract: The title compound, C21H23BrO3 [systematic name: (3E,3aS,6Z,9R,9aS,9bS)-3-(2-bromobenzylidene)-9-hydroxy-6,9-dimethyl-3,3a,4,5,7,8,9,9a-octahydroazuleno[4,5-b]furan-2(9bH)-one] was prepared by the reaction of 1-bromo-2-iodobenzene with micheliolide [systematic name: (3aS,R,9aS,9bS,Z)-9-hydroxy-6,9-dimethyl-3-methylene-3,3a,4,5,7,8,9,9a-octahydroazuleno[4,5-b]furan-2(9bH)-one] under Heck reaction conditions. The title compound exhibits intramolecular O—H⋯O hydrogen bonding between the hydroxy group and the lactone ring O atom, forming a ring of graph-set motif S(6). The 2-bromophenyl group is trans to the lactone ring, indicating that this is the E isomer (geometry of the exocyclic C=C bond). The dihedral angle between the benzene ring of the 2-bromophenyl moiety and the mean plane of the lactone ring is 51.68 (7)°.