• Aluminum nanocomposites reinforced with monolayer polyaniline (C3N): assessing the mechanical and ballistic properties

      Eshkalak, Kasra Einalipour; Sadeghzadeh, Sadegh; Molaei, Fatemeh; Univ Arizona, Dept Min & Geol Engn (ROYAL SOC CHEMISTRY, 2020-05-25)
      This study unveils C3N, a new material that serves as an excellent reinforcement to enhance the mechanical properties of aluminum using a molecular dynamics simulation method. Results show that the C3N nanosheets greatly improve the mechanical properties of aluminum-based nanocomposites. With only 1.3 wt% C3N, the Young's modulus, fracture strength, and fracture strain increased by 27, 70, and 51 percent, respectively. A comparison between the reinforcement of graphene and C3N in an aluminum (Al) matrix shows that in terms of the mechanical properties, the graphene-aluminum composite is weaker than the C3N-aluminum composite in the tensile tests, but slightly stronger in the energy adsorption tests. Our findings show that the mechanical properties are highly dependent on the strain rate and temperature. The effects of various imperfections, such as the vacancy, crack, and void defects, on the mechanical properties were also studied. Results show that in the presence of void defects, the structure exhibited higher mechanical properties than when there were other defects. This phenomenon was found to be related to the decrease in the effective load transfer from aluminum to C3N. Furthermore, by increasing the weight percent of the nanosheets up to 5%, the energy absorption rate increased by 25% compared to the pure aluminum. When C3N was placed on top of the aluminum surface, the silicon nanoparticles were associated with a 35% energy adsorption by the nanocomposite. The results of this paper could be used to help understand and overcome some limitations in the fabrication of metallic nanocomposites with 2D material reinforcement.
    • Biophysical differentiation of susceptibility and chemical differences in Staphylococcus aureus

      Hilton, Shannon Huey; Crowther, Claire V; McLaren, Alex; Smithers, Jared P; Hayes, Mark A; Univ Arizona, Coll Med Phoenix, Dept Orthopaed (ROYAL SOC CHEMISTRY, 2020-02-19)
      Differentiating bacteria strains using biophysical forces has been the focus of recent studies using dielectrophoresis (DEP). The refinement of these studies has created high-resolution separations such that very subtle properties of the cells are enough to induce significant differences in measurable biophysical properties. These high-resolution capabilities build upon the advantages of DEP which include small sample sizes and fast analysis times. Studies focusing on differentiating antimicrobial resistant and susceptible bacteria potentially have significant impact on human health and medical care. A prime example is Staphylococcus aureus, which commonly colonizes adults without ill effects. However, the pathogen is an important cause of infections, including surgical site infections. Treatment of S. aureus infections is generally possible with antimicrobials, but antimicrobial resistance has emerged. Of special importance is resistance to methicillin, an antimicrobial created in response to resistance to penicillin. Here, dielectrophoresis is used to study methicillin-resistant (MRSA) and-susceptible S. aureus (MSSA) strains, both with and without the addition of a fluorescent label. The capture onset potential of fluorescently-labeled MRSA (865 +/- 71 V) and thus the ratio of electrokinetic to dielectrophoretic mobility, was found to be higher than that of fluorescently-labeled MSSA (685 +/- 61 V). This may be attributable to the PBP2a enzyme present in the MRSA strain and not in the MSSA bacteria. Further, unlabeled MRSA was found to have a capture onset potential of 732 +/- 44 V, while unlabeled MSSA was found to have a capture onset potential of 562 +/- 59 V. This shows that the fluorescently-labeled bacteria require a higher applied potential, and thus ratio of mobilities, to capture than the unlabeled bacteria.
    • Carbon monoxide attenuates the effects of snake venoms containing metalloproteinases with fibrinogenase or thrombin-like activity on plasmatic coagulation

      Nielsen, Vance G.; Bazzell, Charles M.; Univ Arizona, Coll Med, Dept Anesthesiol (ROYAL SOC CHEMISTRY, 2016)
      Exposure of plasma to iron and carbon monoxide (CO) renders fibrinogen resistant to fibrinogenolytic or thrombin-like activity contained in pit viper venom. However, the direct effects of iron/CO on venom activity are unknown. Thus, we assessed if four different, metalloproteinase containing snake venoms exposed to iron/CO or CO alone could attenuate their fibrinogenolytic or thrombin-like activity. Venom (0-500 mu g ml(-1)) was exposed to 0-10 mu M FeCl3 and/or 0-100 mu M carbon monoxide releasing molecule-2 (CORM-2), or inactivated CORM-2 (iCORM-2) for 3 min at room temperature. Venom solution (0-8 mu g ml(-1) final concentration) was then placed in citrated human plasma containing tissue factor, followed by CaCl2 addition for commencement of coagulation. Data were determined with thrombelastography for 10-15 min at 37 degrees C. Iron had no effect on the first venom tested, so only CO was investigated subsequently. Exposure of venom to CO attenuated fibrinogenolytic or thrombin-like activity, and iCORM-2 did not affect the venom activities. Further investigation of the effect of CO exposure on similar venoms is justified.
    • Consensus structures of the Mo(v) sites of sulfite-oxidizing enzymes derived from variable frequency pulsed EPR spectroscopy, isotopic labelling and DFT calculations

      Enemark, John H; Univ Arizona, Dept Chem & Biochem (ROYAL SOC CHEMISTRY, 2017-10-21)
      Sulfite-oxidizing enzymes from eukaryotes and prokaryotes have five-coordinate distorted square-pyramidal coordination about the molybdenum atom. The paramagnetic Mo(v) state is easily generated, and over the years four distinct CW EPR spectra have been identified, depending upon enzyme source and the reaction conditions, namely high and low pH (hpH and lpH), phosphate inhibited (Pi) and sulfite (or blocked). Extensive studies of these paramagnetic forms of sulfite-oxidizing enzymes using variable frequency pulsed electron spin echo (ESE) spectroscopy, isotopic labeling and density functional theory (DFT) calculations have led to the consensus structures that are described here. Errors in some of the previously proposed structures are corrected.
    • The formation mechanism of gradient porous Si in a contactless electrochemical process

      Zhao, Mingrui; McCormack, Angelin; Keswani, Manish; Univ Arizona, Chem & Environm Engn; Univ Arizona, Mat Sci & Engn (ROYAL SOC CHEMISTRY, 2016)
      Recently, gradient porous silicon has been developed to meet the requirements of various applications due to its unique physical and chemical properties. In this paper, the formation mechanism and morphology of radially symmetric gradient porous silicon films fabricated using a contactless method and their dependence on different process parameters, such as HF concentration, solution pH, current density and wafer resistivity, have been investigated in detail. The design and geometry of the sample assembly allow decreasing current density radially inward on the silicon surface in contact with HF based etchant solution. In the presence of surfactants, an increase in the distribution range of porosity, pore diameter and depth was observed by increasing HF concentration or lowering pH of the etchant solution, as the formation of pores was considered to be limited by the etch rates of silicon dioxide. Gradient porous silicon was also found to be successfully formulated both at high (10 mA cm2 ) and low (3 mA cm2 ) current densities. Interestingly, the morphological gradient was not developed when dimethyl sulfoxide (instead of surfactants) was used in the etchant solution potentially due to limitations in the availability of oxidizing species at the silicon–etchant solution interface.
    • Gap controlled plasmon-dielectric coupling effects investigated with single nanoparticle-terminated atomic force microscope probes

      Huang, Qian; Teran Arce, Fernando; Lee, Joon; Yoon, Ilsun; Villanueva, Joshua; Lal, Ratnesh; Sirbuly, Donald J.; Univ Arizona, Dept Biomed Engn, Dept Med, Div Translat & Regenerat Med (ROYAL SOC CHEMISTRY, 2016-09-13)
      Precise positioning of a plasmonic nanoparticle (NP) near a small dielectric surface is not only necessary for understanding gap-dependent interactions between a metal and dielectric but it is also a critical component in building ultrasensitive molecular rulers and force sensing devices. In this study we investigate the gap-dependent scattering of gold and silver NPs by controllably depositing them on an atomic force microscope (AFM) tip and monitoring their scattering within the evanescent field of a tin dioxide nanofiber waveguide. The enhanced distance-dependent scattering profiles due to plasmon-dielectric coupling effects show similar decays for both gold and silver NPs given the strong dependence of the coupling on the decaying power in the near-field. Experiments and simulations also demonstrate that the NPs attached to the AFM tips act as free NPs, eliminating optical interference typically observed from secondary dielectric substrates. With the ability to reproducibly place individual plasmonic NPs on an AFM tip, and optically monitor near-field plasmon-dielectric coupling effects, this approach allows a wide-variety of light-matter interactions studies to be carried out on other low-dimensional nanomaterials.
    • HMGB1 binds to the KRAS promoter G-quadruplex: a new player in oncogene transcriptional regulation?

      Amato, Jussara; Madanayake, Thushara W.; Iaccarino, Nunzia; Novellino, Ettore; Randazzo, Antonio; Hurley, Laurence H.; Pagano, Bruno; Univ Arizona, Coll Pharm (ROYAL SOC CHEMISTRY, 2018-09-04)
      This communication reports on a possible distinct role of HMGB1 protein. Biophysical studies revealed that HMGB1 binds and stabilizes the G-quadruplex of the KRAS promoter element that is responsible for most of the transcriptional activity. Biological data showed that inhibition of HMGB1 increases KRAS expression. These results suggest that HMGB1 could play a role in the gene transcriptional regulation via the functional recognition of the G-quadruplex.
    • The influence of electrically conductive and non-conductive nanocomposite scaffolds on the maturation and excitability of engineered cardiac tissues

      Navaei, Ali; Rahmani Eliato, Kiarash; Ros, Robert; Migrino, Raymond Q; Willis, Brigham C; Nikkhah, Mehdi; Univ Arizona, Coll Med (ROYAL SOC CHEMISTRY, 2019-01-29)
      Utilization of electrically conductive nanomaterials for developing nanocomposite scaffolds has been at the center of attention for engineering functional cardiac tissues. The primary motive in the use of conductive nanomaterials has been to develop biomimetic scaffolds to recapitulate the extracellular matrix (ECM) of the native heart and to promote cardiac tissue maturity, excitability and electrical signal propagation. Alternatively, it is well accepted that the inclusion of nanomaterials also alters the stiffness and nano-scale topography of the scaffolds. However, what is missing in the literature is that to what extent the sole presence of nanomaterials within a scaffold, regardless of their conductivity, influences the maturation and excitability of engineered cardiac tissues. To address this knowledge gap, we developed four different classes of gelatin methacrylate (GelMA) hydrogels, with varied concentrations, embedded electrically conductive gold nanorods (GNRs) and non-conductive silica nanomaterials (SNPs), to assess the influence of matrix stiffness and the presence of nanomaterials on cardiac cell adhesion, protein expression (i.e. maturation), and tissue-level excitability. Our results demonstrated that either embedding nanomaterials (i.e. GNRs and SNPs) or increasing the matrix stiffness significantly promoted cellular retention and the expression of cardiac-specific markers, including sarcomeric α-actinin (SAC), cardiac troponin I (cTnI) and connexin43 (Cx43) gap junctions. Notably, excitation voltage thresholds at a high frequency (i.e. 2 Hz and higher), in both coupled and uncoupled gap junctions induced by heptanol, were lower for scaffolds embedded conductive GNRs or non-conductive SNPs, independent of matrix stiffness. Overall, our findings demonstrated that the sole presence of nanomaterials within the scaffolding matrix had a more pronounced influence as compared to the scaffold stiffness on the cell-cell coupling, maturation and excitability of engineered cardiac tissues.
    • Investigating the effect of teacher mediation on student expressed reasoning

      Moreira, Patricia; Marzabal, Ainoa; Talanquer, Vicente; Univ Arizona, Dept Chem & Biochem (ROYAL SOC CHEMISTRY, 2019-07-01)
      Understanding how chemistry teachers' interventions shape the reasoning that students express after a lesson is critical to support prospective and in-service teachers as they work with students' ideas in the classroom. In this qualitative research study, we analysed changes in the reasoning expressed by 10th grade students in a Chilean school in their written explanations about freezing point depression before and after a lesson on the topic. We also investigated how the teacher's interventions shaped the type of reasoning expressed by participating students. Our findings revealed significant shifts in the types of explanations generated after the lesson. A significant number of students transitioned from relational to simple causal reasoning in their pre- and post-lesson explanations. After the lesson most of the explanations were based on the activities of one or more of the system's entities. Analysis of teacher-student interactions during the observed lesson suggests that the teacher's mediation played a central role in the shift towards simple causal reasoning with centralized causality that was observed. The teacher in our study was more skilled at eliciting students' ideas than at helping students develop them with proper scaffolding. Thus, the observed classroom talk could not be considered as accountable talk, as most of the key ideas were introduced, selected, or reshaped by the teacher.
    • Investigating the effects of adding hybrid nanoparticles, graphene and boron nitride nanosheets, to octadecane on its thermal properties

      Tafrishi, Hossein; Sadeghzadeh, Sadegh; Molaei, Fatemeh; Siavoshi, Hossein; Univ Arizona, Min & Geol Engn Dept (ROYAL SOC CHEMISTRY, 2020-04-14)
      Octadecane is an alkane that is used to store thermal energy at ambient temperature as a phase change material. A molecular dynamics study was conducted to investigate the effects of adding graphene and a boron nitride nanosheet on the thermal and structural properties of octadecane paraffin. The PCFF force field for paraffin, AIREBO potential for graphene, Tersoff potential for the boron nitride nanosheet, and Lennard-Jones potential for the van der Waals interaction between the nanoparticles and n-alkanes were used. Equilibrium and nonequilibrium molecular dynamics simulations were used to study the nano-enhanced phase change material properties. Results showed that the nanocomposite had a lower density change, more heat capacity (except at 300 K), more thermal conductivity, and a lower diffusion coefficient in comparison with pure paraffin. Additionally, the nanocomposite had a higher melting point, higher phonon density of state and radial distribution function peaks.
    • Ion diffusion coefficients in poly(3-alkylthiophenes) for energy conversion and biosensing: role of side-chain length and microstructure

      Harris, Jonathan K.; Ratcliff, Erin L.; Univ Arizona, Dept Chem Engn; Univ Arizona, Dept Mat Sci & Engn; Univ Arizona, Dept Chem & Biochem (ROYAL SOC CHEMISTRY, 2020-09-15)
      Conductive polymers are promising materials as active elements for energy storage and conversion devices due to mixed ion-electron conduction. The ion diffusion coefficient is a relative measure of the efficacy of ion transport, allowing for comparison between materials and electrochemical conditions. In this work, diffusion coefficients of hexafluorophosphate (PF6-) counterions in poly(3-alkylthiophene) (P3AT) materials are measured as a function of both side-chain length and microstructure using electrochemical impedance spectroscopy (EIS). For semi-crystalline films, the diffusion coefficient is found to be anomalous and nearly independent of applied electrochemical potential. The anomalous behavior of diffusion indicates that spin casting yields compact films with an enthalpic barrier to ion transport, attributed to ionic trapping. Diffusion coefficient values similar to 10(-11)cm(2)s(-1)were measured for all films, indicating interchain spacing, in the absence of strong intermolecular interactions with the electrolyte, is not a viable design strategy to control ion transport. For the prototypical system of poly(3-hexylthiophene), we observe almost no potential dependence in ion transport for regioregular and regiorandom films of comparable molecular weight, with both exhibiting anomalous diffusion. Alternatively, changing the microstructure of poly(3-hexylthiophene) to a mostly amorphous, ion-imprinted structure yields similar to 500x increase in the diffusion coefficient to similar to 2 x 10(-8)cm(2)s(-1)at 0.8 Vvs.Ag/Ag(+)with behavior closer to ordinary diffusion. Collectively, these results indicate new insight into ion transport in conductive polymers, where ionic trapping effects can be mitigated through electrodeposition protocols over post-synthesis processing (i.e.spin coating).
    • Liquid amphiphilic polymer for effective airborne dust suppression

      Lee, Taehee; Park, Junhyeok; Knoff, David S.; Kim, Kwangmin; Kim, Minkyu; Univ Arizona, Dept Min & Geol Engn; Univ Arizona, Dept Biomed Engn; Univ Arizona, BIO5 Inst (ROYAL SOC CHEMISTRY, 2019-12-02)
      Airborne dust is a byproduct of natural and artificial occurrences, including high winds in arid regions and human activities, and it affects most of the world's population. Watering is the most general practice for reducing airborne dust by wetting the surface of the dust source to agglomerate dust particles via the capillary effect, increasing the aerodynamic diameter of (ultra)fine particles and reducing dust emission. However, the short-term effectiveness due to fast water evaporation, requiring frequent watering, is a major disadvantage. Herein, we utilized biocompatible liquid polymers as additives in water to prolong moist conditions of dust sources due to their liquid state. After the water evaporated, the liquid polymers maintained moisture on the dust sources, resulting in significantly reduced (ultra)fine particle emissions and extended effectiveness compared to conventional water treatment. Interestingly, we observed greater dust suppressive effectiveness with liquid amphiphilic polymer than liquid hydrophilic polymer because of the synergistic effect of the liquid state and amphiphilic property of the polymer. Translating lab-scale experiments to pilot-scale field-testing confirmed the potential for utilizing biocompatible liquid amphiphilic polymers to advance airborne dust suppression technology.
    • A low-valent dinuclear ruthenium diazadiene complex catalyzes the oxidation of dihydrogen and reversible hydrogenation of quinones

      Yang, Xiuxiu; Gianetti, Thomas L.; Wörle, Michael D.; van Leest, Nicolaas P.; de Bruin, Bas; Grützmacher, Hansjörg; Univ Arizona, Dept Chem & Biochem (ROYAL SOC CHEMISTRY, 2019-01-28)
      The dinuclear ruthenium complex [Ru2H(mu-H)(Me(2)dad)(dbcot)(2)] contains a 1,4-dimethyl-diazabuta-1,3-diene (Me(2)dad) as a non-innocent bridging ligand between the metal centers to give a [Ru-2(Me(2)dad)] core. In addition, each ruthenium is bound to one dibenzo[a,e]cyclooctatetraene (dbcot) ligand. This Ru dimer converts H-2 to protons and electrons. It also catalyzes reversibly under mild conditions the selective hydrogenation of vitamins K-2 and K-3 to their corresponding hydroquinone equivalents without affecting the C=C double bonds. Mechanistic studies suggest that the [Ru-2(Me(2)dad)] moiety, like hydrogenases, reacts with H-2 and releases electrons and protons stepwise.
    • Low-valent homobimetallic Rh complexes: influence of ligands on the structure and the intramolecular reactivity of Rh–H intermediates

      Jurt, Pascal; Salnikov, Oleg G.; Gianetti, Thomas L.; Chukanov, Nikita V.; Baker, Matthew G.; Le Corre, Grégoire; Borger, Jaap E.; Verel, Rene; Gauthier, Sébastien; Fuhr, Olaf; et al. (ROYAL SOC CHEMISTRY, 2019-09-14)
      Supporting two metal binding sites by a tailored polydentate trop-based (trop = 5H-dibenzo[a,d]cyclohepten-5-yl) ligand yields highly unsymmetric homobimetallic rhodium(i) complexes. Their reaction with hydrogen rapidly forms Rh hydrides that undergo an intramolecular semihydrogenation of two C & xe002;C bonds of the trop ligand. This reaction is chemoselective and converts C & xe002;C bonds to a bridging carbene and an olefinic ligand in the first and the second semihydrogenation steps, respectively. Stabilization by a bridging diphosphine ligand allows characterization of a Rh hydride species by advanced NMR techniques and may provide insight into possible elementary steps of H-2 activation by interfacial sites of heterogeneous Rh/C catalysts.
    • Molecular doping in few-molecule polymer-dopant complexes shows reduced Coulomb binding

      Dong, Chuan-ding; Schumacher, Stefan; Univ Arizona, James C Wyant Coll Opt Sci (ROYAL SOC CHEMISTRY, 2020-09)
      The mechanistic study of molecular doping of organic semiconductors (OSC) requires an improved understanding of the role and formation of integer charge transfer complexes (ICTC) on a microscopic level. In the present work we go one crucial step beyond the simplest scenario of an isolated bi-molecular ICTC and study ICTCs formed of up to two poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b,3,4-b '']dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDT-BT) oligomers and up to two CN6-CP molecules. We find that depending on geometric arrangement, complexes containing two conjugated oligomers and two dopant molecules can show p-type doping with double integer charge transfer, resulting in either two singly doped oligomers or one doubly doped oligomer. Interestingly, compared to an individual oligomer-dopant complex, the resulting in-gap states on the doped oligomers are significantly lowered in energy. Indicating that, already in the relatively small systems studied here, Coulomb binding of the doping-induced positive charge to the counter-ion is reduced which is an elemental step towards generating mobile charge carriers through molecular doping.
    • Polymer and magnetic nanoparticle composites with tunable magneto-optical activity: role of nanoparticle dispersion for high verdet constant materials

      Pavlopoulos, N. G.; Kang, K. S.; Holmen, L. N.; Lyons, N. P.; Akhoundi, F.; Carothers, K. J.; Jenkins, S. L.; Lee, T.; Kochenderfer, T. M.; Phan, A.; et al. (ROYAL SOC CHEMISTRY, 2020-03-10)
      We report on a new strategy for preparing polymer-nanoparticle composite Faraday rotators for use in magnetic sensing and optical isolation. While most applications of Faraday rotators make use of inorganic garnet crystals, these are generally limited by low magneto-optical activity (low Verdet constants), high cost, and/or limited processing options. This has led to an interest in new materials with improved activity and processing characteristics. We have developed a new type of magneto-optical material based on polymer-nanoparticle composites that can be completely prepared by solution processing methods with tunable Verdet constants and device sensitivity. By exchanging native surface ligands on magneto-optically active CoFe(2)O(4)nanocrystals with polymer compatible ligands, enhanced nanoparticle dispersion in processible polymer matrices was observed at up to 15 wt% inorganic loading. Employing a multilayer polymer film construct, functional Faraday rotator devices were prepared by simple sequential spin-coating of active nanocomposite and protective, barrier cellulose acetate layers. For these assemblies, magneto-optic activity and sensitivity are easily tuned through variation of nanoparticle feed and control of polymer film layers, respectively. These multilayered Faraday rotators show up to a 10-fold enhancement in Verdet constant compared to reference terbium gallium garnets at 1310 nm, opening new possibilities for the fabrication of "plastic garnets" as low cost alternatives to existing inorganic materials for use in the near-IR.
    • Progressions in reasoning about structure–property relationships

      Talanquer, Vicente; Univ Arizona, Dept Chem & Biochem (ROYAL SOC CHEMISTRY, 2017-10-13)
      In this essay, findings from research in science and chemistry education are used to describe and discuss progression in students' structure-property reasoning through schooling. This work provides insights into the challenges that students face to master this important component of chemical thinking. The analysis reveals that student reasoning is often guided by nonnormative implicit schemas that are little affected by traditional instruction. These schemas prioritize chemical composition over molecular structure, and centralized causality over emergence in the explanation and prediction of the properties of substances. The types of components that students invoke to make sense of properties and phenomena may change with schooling, but the underlying reasoning persists. In general, learners assume that observed properties and behaviors are directly related to the types of atoms present in a system and determined by these individual atoms' inherent characteristics.
    • Propentdyopent: the scaffold of a heme metabolite as an electron reservoir in transition metal complexes

      Gautam, R.; Chang, T. M.; Astashkin, A. V.; Lincoln, K. M.; Tomat, E.; Univ Arizona, Dept Chem & Biochem (ROYAL SOC CHEMISTRY, 2016)
      The dipyrrin-1,9-dione scaffold of heme metabolite propendyopent coordinates late transition metals (Co, Ni, Cu, and Zn) forming homoleptic, pseudo-tetrahedral complexes. Electrochemical and spectroscopic studies reveal that the monoanionic, bidentate ligands behave as electron reservoirs as the complexes reversibly host one or two ligand-based radicals.
    • The pure rotational spectrum of the T-shaped AlC2 radical ([X with combining tilde]2A1)

      Halfen, D. T.; Ziurys, L. M.; Univ Arizona, Dept Astron, Dept Chem & Biochem; Univ Arizona, Steward Observ (ROYAL SOC CHEMISTRY, 2018-04-28)
      The pure rotational spectrum of the AlC2 radical ((X) over tilde (2)A(1)) has been measured using Fourier transform microwave/millimeter-wave (FTMmmW) techniques in the frequency range 21-65 GHz. This study is the first high-resolution spectroscopic investigation of this molecule. AlC2 was created in a supersonic jet from the reaction of aluminum, generated by laser ablation, with a mixture of CH4 or HCCH, diluted in argon, in the presence of a DC discharge. Three transitions (N-Ka,N-Kc = 1(01) -> 0(00), 2(02) -> 1(01), and 3(03) -> 2(02)) were measured, each consisting of multiple fine/hyperfine components, resulting from the unpaired electron in the species and the aluminum-27 nuclear spin (I = 5/2). The data were analyzed using an asymmetric top Hamiltonian and rotational, fine structure, and hyperfine constants determined. These parameters agree well with those derived from previous theoretical calculations and optical spectra. An r(0) structure of AlC2 was determined with r(Al-C) = 1.924 angstrom, r(C-C) = 1.260 angstrom, and theta(C-Al-C) = 38.2 degrees. The Al-C bond was found to be significantly shorter than in other small, Al-bearing species. The Fermi contact term established in this work indicates that the unpaired electron in the valence orbital has considerable 3p(z)a(1) character, suggesting polarization towards the C-2 moiety. A high degree of ionic character in the molecule is also evident from the quadrupole coupling constant. These results are consistent with a T-shaped geometry and an Al+C2- bonding scheme. AlC2 is a possible interstellar molecule that may be present in the circumstellar envelopes of carbon-rich AGB stars.
    • Smartphone-based fluorescence detection of bisphenol A from water samples

      McCracken, Katherine E.; Tat, Trinny; Paz, Veronica; Yoon, Jeong-Yeol; Department of Agricultural & Biosystems Engineering, The University of Arizona; Department of Biomedical Engineering, The University of Arizona (ROYAL SOC CHEMISTRY, 2017)
      Bisphenol A (BPA), an emerging environmental contaminant and endocrine disrupting compound, has been observed globally in surface water and waste leachates at concentrations that are hazardous to aquatic life and potentially to humans. Limitations in field monitoring on account of the extensive laboratory infrastructure required for standard BPA detection warrants investigation into portable or handheld sensing platforms. In this work, we evaluated a standalone smartphone-based fluorescence sensing method for identifying BPA from water samples. Toward this goal, we demonstrated the novel application of 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS) as a fluorescent probe with suitable specificity to BPA compared to functionally and structurally similar hormone and endocrine disrupting compounds. Using this method, bisphenol A was quantifiable through both standard fluorescence spectroscopy and smartphone detection, with an empirical binding constant of K-SV = 2040 M-1 and a direct, unfiltered detection limit of 4.4 mu M from unprocessed samples, suitable for waste leachate and industrial samples. Implementation of further digital image processing and smartphone spectroscopy methods may help to lower this detection limit, bearing promise for future direct detection of bisphenol A from wastewater leachate and environmental samples via smartphones.