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Creating next-generation pyrotechnic emitters capable of dynamically controllable light output requires a paradigm shift away from emission control via formulation. This work demonstrates the ability to modulate light emission intensity of a pyrotechnic flame with 2.46 GHz microwave energy within a multimodal cavity. Stoichiometric mixtures of three pyrotechnic systems are investigated: magnesium fuel with oxidizers of NaNO3, KNO3, or CsNO3. Using time-resolved visible and infrared emission spectroscopy and high-speed color videography, microwave illumination of flames is found to produce enhanced atomic photo emission from the alkali species. Emission increases of up to ~120% are demonstrated, which are predominantly in the visible and near-infrared wavelengths and have little effect on flame emission chromaticity. At near- and mid-IR wavelengths, gray body continuum enhancement is observed with moderate enhanced emission from CO2 and H2O bands. Sustained light emission from microwave illumination of combustion products long after pyrotechnic extinguishment was also demonstrated. A simplified model of microwave-enhanced visible and near-IR emission is presented and shown to be consistent with the observed trend of elevated emission enhancement for lower wavelength alkali transitions. Sensitivity analysis is performed which suggests a lower equilibrium population of electronically excited alkali atoms is primarily responsible for maximizing the degree of light emission enhancement of applied microwave fields, especially in extinguished low-temperature pyrotechnic plumes. These findings suggest microwave illumination of alkali-containing pyrotechnic flames may be a useful strategy to achieve dynamic control of light emission intensity.

A method to empirically determine the gaseous emissions produced from a pyrotechnic flare composition through the combination of gas chromatography and mass spectrometry is described. In this approach, milligram quantities of a model yellow signal flare composition and its individual polymeric constituents were subjected to pyrolysis at conditions that were guided via thermal analysis. Many volatile organic compounds and polycyclic aromatic hydrocarbons were identified as emission products even though thermochemical calculations fail to anticipate such products. Thus, these data may complement characterization of emission products predicted in silico. Pyrolysis of this pyrotechnic composition also demonstrated unique products formed via donation of nitrogen to aromatic fragments originating from resinous portions of the formulation. These products included EPA priority pollutants that were not formed by decomposition from staple ingredients. This work demonstrates that a variety of EPA priority pollutants...

“Green” pyrotechnics seek to remove known environmental pollutants and health hazards from their formulations. This chemical engineering approach often focuses on maintaining performance effects upon replacement of objectionable ingredients, yet neglects the chemical products formed by the exothermic reaction. In this work, milligram quantities of a lab-scale pyrotechnic red smoke composition were functioned within a thermal probe for product identification by pyrolysis-gas chromatography-mass spectrometry. Thermally decomposed ingredients and new side product derivatives were identified at lower relative abundances to the intact organic dye (as the engineered sublimation product). Side products included chlorination of the organic dye donated by the chlorate oxidizer. Machine learning quantitative structure-activity relationship models computed impacts to health and environmental hazards. High to very high toxicities were predicted for inhalation, mutagenicity, developmental, and endocrine disruption for common military pyrotechnic dyes and their analogous chlorinated side products. These results underscore the need to revise objectives of “green” pyrotechnic engineering.

Ubiquitin confined within nanodroplets was irradiated with a variable-power CO(2) laser. Mass spectrometry analysis shows evidence for a protein “melting”-like transition within droplets prior to solvent evaporation and ion formation. Ion mobility spectrometry reveals that structures associated with early steps of denaturation are trapped because of short droplet lifetimes.

Novel yellow-light emitting pyrotechnic compositions absent perchlorate oxidizers were investigated for use in the Mk 144 marine smoke and illumination signal. In laboratory-scale testing, three candidate formulations met or surpassed performance metrics of luminous intensity, dominant wavelength, color purity, and burn time when compared to a mock Mk 144 formulation which currently utilizes the environmentally hazardous potassium perchlorate. Also, one identified formulation does not utilize any barium compounds which may be the focus of future regulations. Furthermore, these candidate systems exhibited similar insensitivity to electrostatic, friction, and impact ignition stimuli in comparison to the mock Mk 144 formulation. Therefore, replacement formulations for the Mk 144 marine smoke and illumination signal have been identified with increased performance, environmental sustainability, and acceptable safety characteristics.

The cooperativity of ligand binding is central to biological regulation and new approaches are needed to quantify these allosteric relationships. Herein, we exploit a suite of mass spectrometry (MS) experiments to provide novel insights into homotropic Cu-binding cooperativity, gas- phase stabilities and conformational ensembles of the D2- symmetric, homotetrameric copper-sensitive operon repressor (CsoR) as a function of Cu I ligation state. Cu I binding is overall positively cooperative, but is characterized by distinct ligation state-specific cooperativities. Structural transitions occur upon binding the first and fourth Cu I , with the latter occurring with significantly higher cooperativity than previous steps; this results in the formation of a holo-tetramer that is markedly more resistant than apo-, and partially ligated CsoR tetramers toward surface-induced dissociation (SID). The structural, dynamic and thermodynamic origins of cooperativity of ligand binding (allostery) is a subject of considerable interest, motivated by the central role this process plays in the regulation of biological activity. (1) Cooperativity can be positive or negative and involve the binding of the same (homotropic) or different (heterotropic) ligands, often to an homooligomeric protein. (2, 3) Bacterial repressors that function to control transition metal bioavail- ability in cells are typically homodimeric or homotetrameric and minimally bind two "ligands": a DNA operator found upstream of metal-regulated genes and a specific (cognate) transition metal ion(s). (4) Although a robust thermodynamic framework capable of quantifying both homo- and hetero- tropic cooperativity in these systems is available, (5) these ensemble-based methods suffer from the limitation that a specific, partially ligated state can not be studied independ- ently of other states. Such step-wise insights are required to understand allosteric coupling beyond a generally phenom- enological description. (1)

A new method for enhancing peptide ion identification in proteomics analyses using ion mobility data is presented. Ideally, direct comparisons of experimental drift times (tD) with a standard mobility database could be used to rank candidate peptide sequence assignments. Such a database would represent only a fraction of sequences in protein databases and significant difficulties associated with the verification of data for constituent peptide ions would exist. A method that employs intrinsic amino acid size parameters to obtain ion mobility predictions that can be used to rank candidate peptide ion assignments is proposed. Intrinsic amino acid size parameters have been determined for doubly-charged peptide ions from an annotated yeast proteome. Predictions of ion mobilities using the intrinsic size parameters are more accurate than those obtained from a polynomial fit to tD versus molecular weight data. More than a two-fold improvement in prediction accuracy has been observed for a group of arginine-terminated peptide ions twelve residues in length. The use of this predictive enhancement as a means to aid peptide ion identification is discussed and a simple peptide ion scoring scheme is presented.

Isomerizations of the retinal chromophore were investigated using the IMS-IMS technique. Four different structural features of the chromophore were observed, isolated, excited collisionally, and the resulting isomer and fragment distributions were measured. By establishing the threshold activation voltages for isomerization for each of the reaction pathways, and by measuring the threshold activation voltage for fragmentation, the relative energies of the isomers as well as the energy barriers for isomerization were determined. The energy barrier for a single cis–trans isomerization is (0.64±0.05) eV, which is significantly lower than that observed for the reaction within opsin proteins.

A polyalanine-based peptide which forms a stable, negatively-charged α-helix in the gas phase is reported. Addition of an N-terminal acidic residue forms a stabilizing hydrogen bond network and an electrostatic interaction with the helical dipole. Formation of this secondary structure was demonstrated using ion mobility-mass spectrometry and molecular modelling techniques.