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2014
Fully-drawn carbon-based chemical sensors on organic and inorganic surfaces.
Lab on a Chip,vol.14,p.4059-4066,2014Mech. abrasion is an extremely simple, rapid, and low-cost method for deposition of carbon-based materials onto a substrate. However, the method is limited in throughput, precision, and surface compatibility for drawing conductive pathways. Selective patterning of surfaces using laser-etching can facilitate substantial improvements to address these current limitations for the abrasive deposition of carbon-based materials. This study demonstrates the successful on-demand fabrication of fully-drawn chem. sensors on a wide variety of substrates (e.g., weighing paper, polymethyl methacrylate, silicon, and adhesive tape) using single-walled carbon nanotubes (SWCNTs) as sensing materials and graphite as electrodes. Mech. mixing of SWCNTs with solid or liq. selectors yields sensors that can detect and discriminate parts-per-million (ppm) quantities of various nitrogen-contg. vapors (pyridine, aniline, triethylamine). [on SciFinder(R)]
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2014Polycyclic aromatic hydrocarbons (PAHs) and fully-conjugated ladder polymers are leading candidates for organics electronics, as their inherent conformational rigidity encourages electron delocalization. Many of these systems consist of fused benzenoid or heterocyclic aromatic rings. Less frequently, however, PAHs are reported with character that alternates between the aromaticity of benzene fragments and the antiaromaticity of a nonbenzenoid moiety. This chapter will focus on recent work published on the theory, synthesis, and properties of two such systems: [N]phenylenes containing 4$π$-electron cyclobutadienoid character, and diaryl[a,e]pentalenes containing 8$π$-electron pentalenoid character.[on SciFinder (R)]
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2014We report a simple, rapid, and solvent-free methodol. for solid-state polymns. yielding poly(phenylene vinylenes) (PPVs) promoted by ball-milling. This solid-state Gilch polymn. method produces PPVs in as little as five minutes of milling. Detailed investigations of the parameter space governing the solid-state polymn., i.e., milling time, base strength, solid-state diln., milling frequency, and size of milling balls, revealed that polymn. by ball-milling is a rapid process achieving mol. no. av. wts. of up to 40 kDa in up to 70% yield. To explore the scope, a solid-state polymn. via the dithiocarbamate precursor route is explored. [on SciFinder(R)]
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2014
Fluorescence Sensing of Amine Vapors Using a Cationic Conjugated Polymer Combined with Various Anions.
Angewandte Chemie, International Edition,vol.53,p.9792–9796,2014A series of conjugated cationic polymers, differentiated only by their accompanying counter-anions, was prepd. and characterized. The choice of counter-anion (CA) was found to drastically impact the soly. of the polymers and their optical properties in soln. and in the solid state. Fluorescent polymer thin films were found to be instantaneously quenched by volatile amines in the gas phase at low ppm concns., and a mini-array with CAs as variable elements was found to be able to differentiate amines with good fidelity. [on SciFinder(R)] -
2014
Fluorofluorophores: Fluorescent Fluorous Chemical Tools Spanning the Visible Spectrum.
Journal of the American Chemical Society,vol.136,p.13574–13577,2014“Fluoro” refers to both fluorescent and fluorinated compds. Despite the shared prefix, there are very few fluorescent mols. that are sol. in perfluorinated solvents. This paucity is surprising, given that optical microscopy is a ubiquitous technique throughout the phys. sciences and the orthogonality of fluorous materials is a commonly exploited strategy in synthetic chem., materials science, and chem. biol. We have addressed this shortage by synthesizing a panel of “fluorofluorophores,” fluorescent mols. contg. high wt. percent fluorine with optical properties spanning the visible spectrum. We demonstrate the utility of these fluorofluorophores by prepg. fluorescent perfluorocarbon nanoemulsions. [on SciFinder(R)] -
2014A detector can detect an analyte including a carbon-carbon multiple bond moiety and capable of undergoing Diels-Alder reaction with a heteroarom. compd. having an extrudable group. The detector can detect, differentiate, and quantify ethylene. The detector can be a color based detector, a fluorescence based detector, or a resistivity based detector. [on SciFinder(R)]
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2014Embodiments described herein provide functionalized carbon nanostructures for use in various devices, including photovoltaic devices (e.g., solar cells). In some embodiments, carbon nanostructures substituted with at least one cyclobutyl and/or cyclobutenyl group are provided. Devices including such materials may exhibit increased efficiency, increased open circuit potential, high electron/hole mobility, and/or low elec. resistance. [on SciFinder(R)]
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2014Embodiments relating to the synthesis and processing of graphene mols. are provided. In some cases, methods for the electrochem. expansion and/or functionalization of graphene mols. are provided. In some embodiments, one or more species may be intercalated between adjacent graphene sheets. [on SciFinder(R)]
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2014
19F NMR fingerprints: identification of neutral organic compounds in a molecular container.
Journal of the American Chemical Society,vol.136,p.10683–10690,2014Improved methods for quickly identifying neutral org. compds. and differentiation of analytes with similar chem. structures are widely needed. We report a new approach to effectively “fingerprint” neutral org. mols. by using 19F NMR and mol. containers. The encapsulation of analytes induces characteristic up- or downfield shifts of 19F resonances that can be used as multidimensional parameters to fingerprint each analyte. The strategy can be achieved either with an array of fluorinated receptors or by incorporating multiple nonequivalent fluorine atoms in a single receptor. Spatial proximity of the analyte to the 19F is important to induce the most pronounced NMR shifts and is crucial in the differentiation of analytes with similar structures. This new scheme allows for the precise and simultaneous identification of multiple analytes in a complex mixt. [on SciFinder(R)] -
2014
Apparent roughness as indicator of (local) deoxygenation of graphene oxide.
Chemistry of Materials,vol.26,p.4849–4855,2014Detailed characterization of graphene oxide (GO) and its reduced forms continues to be a challenge. We have employed scanning tunneling microscopy (STM) to examine GO samples with varying degrees of deoxygenation via controlled chem. redn. Anal. of the roughness of the apparent height in STM topog. measurements, i.e. the äpparent roughness”, revealed a correlation between increasing deoxygenation and decreasing apparent roughness. This anal. can therefore be a useful supplement to the techniques currently available for the study of GO and related materials. The presence of a high elec. field underneath the STM tip can locally induce a reaction on the GO basal plane that leads to local deoxygenation, and the restoration of the sp2 hybridization of the carbons promotes increased planarity. These findings are in line with the apparent roughness values found for GO at varying levels of chem. redn. and illustrates the value of having a tool to gain structural/chem. insight on a local scale. This is the first example of employing an STM tip to locally reduce GO to reduced GO (rGO) and partially reduced GO (prGO) without locally destroying the graphene sample. Local manipulation on the nanoscale has utility for graphene nanoelectronics, and anal. employing the apparent roughness is an addnl. tool for the study of graphene oxide and related basal plane chem. [on SciFinder(R)] -
2014We report a simple, rapid, and solvent-free methodol. for solid-state polymns. yielding poly(phenylene vinylenes) (PPVs) promoted by ball-milling. This solid-state Gilch polymn. method produces PPVs in as little as five minutes of milling. Detailed investigations of the parameter space governing the solid-state polymn., i.e., milling time, base strength, solid-state diln., milling frequency, and size of milling balls, revealed that polymn. by ball-milling is a rapid process achieving mol. no. av. wts. of up to 40 kDa in up to 70% yield. To explore the scope, a solid-state polymn. via the dithiocarbamate precursor route is explored. [on SciFinder(R)]
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2014
Stereospecific Ring-Opening Metathesis Polymerization of Norbornadienes Employing Tungsten Oxo Alkylidene Initiators.
Journal of the American Chemical Society,vol.136,p.10910–10913,2014We report here the polymn. of several 7-isopropylidene-2,3-disubstituted norbornadienes, 7-oxa-2,3-dicarboalkoxynorbornadienes, and 11-oxa-benzonorbornadienes with a single tungsten oxo alkylidene catalyst, W(O)(CH-t-Bu)(OHMT)(Me2Pyr) (OHMT = 2,6-dimesitylphenoxide; Me2Pyr = 2,5-dimethylpyrrolide) to give cis, stereoregular polymers. The tacticities of the menthyl ester derivs. of two polymers were detd. for two types. For poly(7-isopropylidene-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis, isotactic, while for poly(7-oxa-2,3-dicarbomenthoxynorbornadiene) the structure was shown to be cis, syndiotactic. A bis-trifluoromethyl-7-isopropylidene norbornadiene was not polymd. stereoregularly with W(O)(CHCMe2Ph)(Me2Pyr)(OHMT) alone, but a cis, stereoregular polymer was formed in the presence of 1 equiv of B(C6F5)3. [on SciFinder(R)] -
2014
Clostridium difficile as a cause of healthcare-associated diarrhoea among children in Auckland, New Zealand: clinical and molecular epidemiology
European journal of clinical microbiology & infectious diseases : official publication of the European Society of Clinical Microbiology,vol.33,p.1741–1747,2014We aimed to determine the incidence of Clostridium difficile infection (CDI), the molecular epidemiology of circulating C. difficile strains and risk factors for CDI among hospitalised children in the Auckland region. A cross-sectional study was undertaken of hospitalised children <15 years of age in two hospitals investigated for healthcare-associated diarrhoea between November 2011 and June 2012. Stool specimens were analysed for the presence of C. difficile using a two-step testing algorithm including polymerase chain reaction (PCR). C. difficile was cultured and PCR ribotyping performed. Demographic data, illness characteristics and risk factors were compared between children with and without CDI. Non-duplicate stool specimens were collected from 320 children with a median age of 1.2 years (range 3 days to 15 years). Forty-six patients (14 %) tested met the definition for CDI. The overall incidence of CDI was 2.0 per 10,000 bed days. The percentage of positive tests among neonates was only 2.6 %. PCR ribotyping showed a range of strains, with ribotype 014 being the most common. Significant risk factors for CDI were treatment with proton pump inhibitors [risk ratio (RR) 1.74, 95 % confidence interval (CI) 1.09-5.59; p = 0.002], presence of underlying malignancy (RR 2.71, 95 % CI 1.65-4.62; p = 0.001), receiving chemotherapy (RR 2.70, 95 % CI 1.41-4.83; p = 0.003) and exposure to antibiotics (RR 1.17, 95 % CI 0.99-1.17; p = 0.03). C. difficile is an important cause of healthcare-associated diarrhoea in this paediatric population. The notion that neonatal populations will always have high rates of colonisation with C. difficile may not be correct. Several risk factors associated with CDI among adults were also found to be significant.[on SciFinder (R)] -
2014
Fluorofluorophores: Fluorescent Fluorous Chemical Tools Spanning the Visible Spectrum.
Journal of the American Chemical Society,vol.136,p.13574–13577,2014“Fluoro” refers to both fluorescent and fluorinated compds. Despite the shared prefix, there are very few fluorescent mols. that are sol. in perfluorinated solvents. This paucity is surprising, given that optical microscopy is a ubiquitous technique throughout the phys. sciences and the orthogonality of fluorous materials is a commonly exploited strategy in synthetic chem., materials science, and chem. biol. We have addressed this shortage by synthesizing a panel of “fluorofluorophores,” fluorescent mols. contg. high wt. percent fluorine with optical properties spanning the visible spectrum. We demonstrate the utility of these fluorofluorophores by prepg. fluorescent perfluorocarbon nanoemulsions. [on SciFinder(R)] -
2014We report magic angle spinning, dynamic nuclear polarization (DNP) experiments at magnetic fields of 9.4 T, 14.1 T, and 18.8 T using the narrow line polarizing agents 1,3-bisdiphenylene-2-phenylallyl (BDPA) dispersed in polystyrene, and sulfonated-BDPA (SA-BDPA) and trityl OX063 in glassy glycerol/water matrices. The (1)H DNP enhancement field profiles of the BDPA radicals exhibit a significant DNP Overhauser effect (OE) as well as a solid effect (SE) despite the fact that these samples are insulating solids. In contrast, trityl exhibits only a SE enhancement. Data suggest that the appearance of the OE is due to rather strong electron-nuclear hyperfine couplings present in BDPA and SA-BDPA, which are absent in trityl and perdeuterated BDPA (d21-BDPA). In addition, and in contrast to other DNP mechanisms such as the solid effect or cross effect, the experimental data suggest that the OE in non-conducting solids scales favorably with magnetic field, increasing in magnitude in going from 5 T, to 9.4 T, to 14.1 T, and to 18.8 T. Simulations using a model two spin system consisting of an electron hyperfine coupled to a (1)H reproduce the essential features of the field profiles and indicate that the OE in these samples originates from the zero and double quantum cross relaxation induced by fluctuating hyperfine interactions between the intramolecular delocalized unpaired electrons and their neighboring nuclei, and that the size of these hyperfine couplings is crucial to the magnitude of the enhancements. Microwave power dependent studies show that the OE saturates at considerably lower power levels than the solid effect in the same samples. Our results provide new insights into the mechanism of the Overhauser effect, and also provide a new approach to perform DNP experiments in chemical, biophysical, and physical systems at high magnetic fields.[on SciFinder (R)]
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2014
A transferable model for singlet-fission kinetics [Erratum to document cited in CA160:710659].
Nature Chemistry,vol.6,p.649,2014On page 492, the 12th author’s name was incomplete; the cor. name is given and the online version has been cor. [on SciFinder(R)] -
2014Exciton fission is a process that occurs in certain org. materials whereby 1 singlet exciton splits into 2 independent triplets. In photovoltaic devices these 2 triplet excitons can each generate an electron, producing quantum yields per photon of >100% and potentially enabling single-junction power efficiencies >40%. Fission dynamics were measured using ultrafast photoinduced absorption and present a 1st-principles expression that successfully reproduces the fission rate in materials with vastly different structures. Fission is nonadiabatic and Marcus-like in weakly interacting systems, becoming adiabatic and coupling-independent at larger interaction strengths. In neat films, fission yields near unity were demonstrated even when monomers are sepd. by >5 AA. For efficient solar cells, fission must outcompete charge generation from the singlet exciton. This work lays the foundation for tailoring mol. properties like soly. and energy level alignment while maintaining the high fission yield required for photovoltaic applications. [on SciFinder(R)]
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2014Embodiments relating to the synthesis and processing of graphene mols. are provided. In some cases, methods for the electrochem. expansion and/or functionalization of graphene mols. are provided. In some embodiments, one or more species may be intercalated between adjacent graphene sheets. [on SciFinder(R)]
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2014
Dithiolodithiole as a building block for conjugated materials
Angewandte Chemie – International Edition,vol.53,p.5847–5851,2014The development of new conjugated organic materials for dyes, sensors, imaging, and flexible light emitting diodes, field-effect transistors, and photovoltaics has largely relied upon assembling $π$-conjugated molecules and polymers from a limited number of building blocks. The use of the dithiolodithiole heterocycle as a conjugated building block for organic materials is described. The resulting materials exhibit complimentary properties to widely used thiophene analogues, such as stronger donor characteristics, high crystallinity, and a decreased HOMO-LUMO gap. The dithiolodithiole (C4S4) motif is readily synthetically accessible using catalytic processes, and both the molecular and bulk properties of materials based on this building block can be tuned by judicious choice of substituents. -
2014
Wireless gas detection with a smartphone via rf communication
Proceedings of the National Academy of Sciences,vol.111,p.18162-18166,2014Chemical sensing is of critical importance to human health, safety, and security, yet it is not broadly implemented because existing sensors often require trained personnel, expensive and bulky equipment, and have large power requirements. This study reports the development of a smartphone-based sensing strategy that employs chemiresponsive nanomaterials integrated into the circuitry of commercial near-field communication tags to achieve non-line-of-sight, portable, and inexpensive detection and discrimination of gas-phase chemicals (e.g., ammonia, hydrogen peroxide, cyclohexanone, and water) at part-per-thousand and part-per-million concentrations.
