Predicting the Relative Solubilities of Racemic and Enantiopure Crystals by Density‐Functional Theory

Isolation of chiral molecules as pure enantiomers remains a fundamental challenge in chemical research. Enantioselective enrichment through preferential crystallization is an efficient method to achieve enantiopure compounds, but its applicability depends on the relative stability of the enantiopure and racemic crystal forms. Using a simple thermodynamic model and first‐principles density‐functional calculations, it is possible to predict the difference in solubility between the enantiopure and racemic solid phases. This approach uses dispersion‐corrected density functionals and is capable of accurately predicting the solution‐phase entantiomeric excess to within about 10 % of experimental measurements on average. The accuracy of the exchange‐hole dipole moment (XDM) model of dispersion enables the viability of the proposed method.     

Understanding STEM‐focused elementary schools: Case study of Walter Bracken STEAM Academy

Increasingly, STEM focused high schools are used prepare students for college STEM majors and launch them into STEM careers. Yet a new focus on STEM education at the elementary levels suggests that the importance of STEM education is much broader than a preparation for workforce needs in high school or college. This paper describes a case study designed to articulate the mission and design of an effective and nationally recognized STEM‐focused elementary school. As described through the six most impactful components of STEM‐focused elementary school design at Walter Bracken STEAM Academy, the case study emphasizes the school's strong and inclusive school leadership, with staff organized into grade level groups empowered to innovate and honing their teaching practices. External partnerships are leveraged to broaden student learning opportunities. Students at Bracken engage in active learning opportunities and multidisciplinary lessons where STEM is used as a way of thinking and as a way to coherently combine content into active learning opportunities that are engaging for learners. By organizing the structural components of an exemplary STEM‐focused elementary school, we hope to deliver actionable reforms for elementary schools wanting to increase their STEM‐focused offerings.     

Peer‐coaching as a component of a professional development model for biology teachers

To increase the likelihood for continuous growth and improvement, professional development for high school biology teachers should include long‐term, targeted instruction with an accompanying peer‐coaching component. This study examined the views of biology teachers who were engaged in a two‐year professional development program, which included a strong peer‐coaching component. With an overall goal of enhancing the teachers’ instructional practices, the peer‐coaches and teachers collaborated to increase the amount of inquiry in the science classroom. Data were collected using focus groups and researcher notes. Emergent themes included the significance of relationships, importance of teacher commitment, and resulting change and growth in educators.     

Synthesis of 9-Bromo-2-fluoro-6,7-dihydro-5H-benzocycloheptene-8-carboxaldehyde

Cinnamaldehye is an antioxidant shown to induce apoptotic cell death in a number of human cancer cells. This article reports a synthesis of 9-bromo, 2-fluoro substituted, and Z-ring locked (by a trimethylene bridge at C-8 and C-11) crystalline fluorine-substituted derivative of cinnamaldehyde. The synthon, 8-fluoro-1-benzosuberone was treated with PBr₃, dimethylformamide (DMF), and CHCl₃ as a solvent to obtain 9-bromo-2-fluoro-6,7-dihydro-5H-benzocycloheptene-8-carboxaldehyde. The one-step trifunctionalization process converts a bicyclic ring–fused ketone into a β-bromo-α,β-unsaturated aldehyde in a chemoselective and regioselective manner. The process also creates a new carbon–carbon bond between C-8 and C-12. The structure of the previously unreported product has been obtained by x-ray crystallographic analysis. It has been characterized spectroscopically by infrared (IR), ¹H NMR, ¹³C NMR, gas chromatography–mass spectrometry (GC-MS), and elemental analysis. It is a structural element found in sterically hindered retinoids and is a useful advanced intermediate in the total synthesis of these naturally occuring bioactive polyenes.     

Simultaneous quantitation of seven pyrethroid metabolites in human urine by capillary gas chromatography–mass spectrometry

Pyrethroid insecticides are applied in the residential environment, as well as in agricultural crops, for insect control purpose. We developed and validated an accurate, sensitive, and reproducible analytical method to simultaneously detect seven pyrethroid metabolites, namely, 3‐(2,2‐dichlorovinyl)‐2,2‐dimethyl‐(1‐cyclopropane) carboxylic acid, 3‐(2,2‐dibromovinyl)‐2,2‐dimethyl‐(1‐cyclopropane) carboxylic acid, 3‐phenoxybenzoic acid, 4‐fluoro‐3‐phenoxybenzoic acid, 2‐methyl‐3‐phenylbenzoic acid, 4‐chloro‐α‐isoproply benzeneacetic acid, and 3‐(2‐chloro‐3,3,3‐trifluoroprop‐1‐enyl)‐2,2‐dimethylcyclopropanecarboxylic acid, in human urine. This method employs deconjugation with enzyme, SPE using Agilent C18 cartridges on a RapidTrace SPE workstation, derivatization using hexafluoro isopropanol and N,N′‐diisopropylcarbodiimide, and compounds separation and identification on GC–MS. The detection limits of seven metabolites were 0.02–0.08 ng/mL in urine. The recoveries of seven metabolites were 81–104%, 85–99%, and 83–99% in urine specimens fortified at 0.1, 0.4, and 3.2 ng/mL concentrations, respectively. The overall coefficient of variation was 4.3–10.8% in two quality control specimens which were repeatedly measured during a period of 2 months. This method was applied to urine samples collected from children living in Boston, MA. The median concentrations of six detected pyrethroid metabolites ranged from 0.06 to 0.86 ng/mL in urine.     

Liquid crystal effects on bacterial viability

The primary objective of this research was to test the hypothesis that lyotropic chromonic liquid crystals (neutral grey, red 14, blue 27, cromolyn) are not toxic to bacteria as compared with surfactant‐based lyotropic (CPCl and CsPFO) or thermotropic (5CB and E7) liquid crystals. Biocompatibility of most liquid crystals is currently unknown and is required for the development of systems interfacing liquid crystals and biological systems. Potential liquid crystal toxicity was evaluated by two methods. The first examined bacterial survival measured by bacterial growth over 24 hours, after exposure to various liquid crystals. The second toxicity method evaluated liquid crystal effects on bacterial membrane permeability using two fluorescent dyes. Three different types of bacteria were evaluated to assess bacterial structure differences with respect to liquid crystal toxicity. The results of this study indicate that lyotropic chromonic liquid crystals are not toxic to bacteria, whereas thermotropic and surfactant‐based lyotropic liquid crystals are toxic to one or more forms of bacteria. We conclude that lyotropic chromonic liquid crystals may be the preferred material in designing liquid crystal‐based systems that interact with biological systems, especially in the use of liquid crystal‐based biosensors.     

Breath biosensing: using electrochemical enzymatic sensors for detection of biomarkers in human breath

Detection of biomarkers for disease by noninvasive methods is critical for the early diagnosis and screening of disease, enabling prompt treatment. Breath biosensors are a viable option as the exhaled breath contains several biomarkers linked to lung cancer, oxidative stress, diabetes, and other diseases. Breath analysis has been achieved by advanced analytical techniques such as gas chromatography and infrared spectroscopy. However, electrochemical enzymatic breath biosensors offer a cost-effective, sensitive platform for biomarker detection without complex analysis and interpretation by trained laboratory personnel. This review aims to summarize recent advances in the field of electrochemical enzymatic breath biosensors and offer future opportunities from other applications of nonelectrochemical enzymatic breath biosensors.     

Rotationally resolved infrared spectroscopy of a jet-cooled phenyl radical in the gas phase

The first high-resolution IR spectra of a jet-cooled phenyl radical are reported, obtained via direct absorption laser spectroscopy in a slit-jet discharge supersonic expansion. The observed A-type band arises from fundamental excitation of the out-of-phase symmetric CH stretch mode (nu19) of b2 symmetry. Unambiguous spectral assignment of the rotational structure to the phenyl radical is facilitated by comparison with precision 2-line combination differences from Fourier transform microwave and direct absorption mm-wave measurements on the ground state [R. J. McMahon et al., Astrophys. J., 2003, 590, L61]. Least-squares fits to an asymmetric top Hamiltonian permit the upper-state rotational constants to be obtained. The corresponding gas-phase vibrational band origin at 3071.8904 (10) cm(-1) is in remarkably good agreement with previous matrix isolation studies [A. V. Friderichsen et al., J. Am. Chem. Soc., 2001, 123, 1977], and indicates only a relatively minor red shift (approximately 0.9 cm(-1)) between the gas and Ar matrix phase environment. Such studies offer considerable promise for further high resolution IR study of other aromatic radical species of particular relevance to combustion phenomena and interstellar chemistry.     

Simultaneous determination of residues in pollen and high-fructose corn syrup from eight neonicotinoid insecticides by liquid chromatography–tandem mass spectrometry

The neonicotinoids have recently been identified as a potential contributing factor to the sudden decline in adult honeybee population, commonly known as colony collapse disorder (CCD). To protect the health of honeybees and other pollinators, a new, simple, and sensitive liquid chromatography-electrospray ionization mass spectrometry method was developed and validated for simultaneous determination of eight neonicotinoids, including acetamiprid, clothianidin, dinotefuran, flonicamid, imidacloprid, nitenpyram, thiacloprid, and thiamethoxam, in pollen and high-fructose corn syrup (HFCS). In this method, eight neonicotinoids, along with their isotope-labeled internal standards, were extracted from 2 g of pollen or 5 g of HFCS using an optimized quick, easy, cheap, effective, rugged, and safe extraction procedure. The method limits of detection in pollen and HFCS matrices were 0.03 ng/g for acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam and ranged between 0.03 and 0.1 ng/g for nitenpyram and flonicamid. The precision and accuracy were well within the acceptable 20 % range. Selectivity, linearity, lower limit of quantitation, matrix effect, recovery, and stability in autosampler were also evaluated during validation. This validated method has been used successfully in analyzing a set of pollen and HFCS samples collected for evaluating potential honeybee exposure to neonicotinoids.     

PNA/dsDNA complexes: site specific binding and dsDNA biosensor applications

The ability of peptide nucleic acids (PNA) to form specific higher-order (i.e., three- and four-stranded) complexes with DNA makes it an ideal structural probe for designing strand-specific dsDNA biosensors. Higher-order complexes are formed between a dye-labeled charge-neutral PNA probe and complementary dsDNA. Addition of a light-harvesting cationic conjugated polymer (CCP) yields supramolecular structures held together by electrostatic forces that incorporate the CCP and the dye-labeled PNA/DNA complexes. Optimization of optical properties allows for excitation of the CCP and subsequent fluorescence resonance energy transfer (FRET) to the PNA-bound dye. In the case of noncomplementary dsDNA, complexation between the probe and target does not occur, and dye emission is weak. The binding between PNA and noncomplementary and complementary dsDNA was examined by several methods. Gel electrophoresis confirms specificity of binding and the formation of higher-order complexes. Nano-electrospray mass spectrometry gives insight into the stoichiometric composition, including PNA/DNA, PNA(2)/DNA, PNA/DNA(2), and PNA(2)/DNA(2) complexes. Finally, structural characteristics and binding-site specificity were examined using ion mobility mass spectrometry in conjunction with molecular dynamics. These results give possible conformations for each of the higher-order complexes formed and show exclusive binding of PNA to the complementary stretch of DNA for all PNA/DNA complexes. Overall, the capability and specificity of binding indicates that the CCP/PNA assay is a feasible detection method for dsDNA and eliminates the need for thermal denaturing steps typically required for DNA hybridization probe assays.