Rationale:In late October 2003, Southern California wildfires burned more than 3,000 km 2 . The wildfires produced heavy smoke that affected several communities participating in the University of Southern California Children's Health Study (CHS). Objectives: To study the acute effects of fire smoke on the health of CHS participants. Methods: A questionnaire was used to assess smoke exposure and occurrence of symptoms among CHS high-school students (n ϭ 873; age, 17-18 yr) and elementary-school children (n ϭ 5,551; age, 6-7 yr), in a total of 16 communities. Estimates of particulate matter (PM 10 ) concentrations during the 5 d with the highest fire activity were used to characterize community smoke level. Main Results: All symptoms (nose, eyes, and throat irritations; cough; bronchitis; cold; wheezing; asthma attacks), medication usage, and physician visits were associated with individually reported exposure differences within communities. Risks increased monotonically with the number of reported smoky days. For most outcomes, reporting rates between communities were also associated with the firerelated PM 10 levels. Associations tended to be strongest among those without asthma. Individuals with asthma were more likely to take preventive action, such as wearing masks or staying indoors during the fire. Conclusions: Exposure to wildfire smoke was associated with increased eye and respiratory symptoms, medication use, and physician visits.
Two polymorphic hydrogen peroxide solvates of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20; wurtzitane is an alternative name to iceane) were obtained using hydrated α-CL-20 as a guide. These novel H O solvates have high crystallographic densities (1.96 and 2.03 g cm , respectively), high predicted detonation velocities/pressures (with one solvate performing better than ϵ-CL-20), and a sensitivity similar to that of ϵ-CL-20. The use of hydrated materials as a guide will be important in the development of other energetic materials with hydrogen peroxide. These solvates represent an area of energetic materials that has yet to be explored.
A series of three energetic cocrystals containing 5,5′-dinitro-2H,2H′-3,3′-bi-1,2,4-triazole (DNBT) were obtained. These incorporate a class of energetic materials that has seen significant synthetic work, the azole family (tetrazoles, triazole, pyrazole, etc.), and yet have struggled to see broad application. A cocrystal was obtained with the triazole 5amino-3-nitro-1H-1,2,4-triazole (ANTA) in a stoichiometry of 2:1 (ANTA:DNBT). Two cocrystals were obtained with the pyrazoles 1H, 4H-3,6-dinitropyrazolo[4,3-c]pyrazole (DNPP) and 3,4-dinitropyrazole (3,4-DNP) in ratios of 1:1 (DNPP:DNBT) and 2:1 (3,4-DNP:DNBT). All three cocrystals, 2:1 ANTA/DNBT (1), 1:1 DNPP/DNBT (2), and 2:1 3,4-DNP/DNBT (3), have high densities (>1.800 g/ cm 3 ) and high predicted detonation velocities (>8000 m/s). In small-scale impact drop tests, cocrystals 1 and 2 were both found to be insensitive, whereas cocrystal 3 possesses sensitivity between that of its two pure components 3,4-DNP and DNBT. The hydrogen bonding motif of the three components with DNBT is preserved among all three cocrystals, and this observation suggests a generally useful motif to be employed in the development of other energetic−energetic cocrystals. These cocrystals represent an area of energetic materials that has yet to be explored for cocrystalline materials.
Conspectus In spite of the importance of energetic materials to a broad range of military (munitions, missiles) and civilian (mining, space exploration) technologies, the introduction of new chemical entities in the field occurs at a very slow pace. This situation is understandable considering the stringent requirements for cost and safety that must be met for new chemical entities to be fielded. If existing manufacturing infrastructure could be leveraged, then this would offer a fundamental shift in the discovery paradigm. Cocrystallization is an approach poised to realize this goal because it can use existing materials and make new chemical compositions through the assembly of multiple unique components in the solid state. This account describes early proof-of-principle studies with widely used energetics in the field, including 2,4,6-trinitrotoluene (TNT) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), forming cocrystals with nonenergetic coformers that alter key properties such as density, sensitivity, and morphology. The evolution of these studies to produce cocrystals between two energetic components is detailed, including those exploiting new intermolecular interaction motifs that drive assembly such as halogen bonding. Implications of cocrystallization for performance, sensitivity to external stimuli, and manufacturability are explored at each stage. The derivation of many of these cocrystals from energetic materials in common use satisfies the goal of using materials already demonstrated to be cost-effective at scale and with well-understood safety profiles. The account concludes with a discussion of cocrystallizing molecules having excess of oxidizing power with those that are oxygen-deficient to push the limits of explosive performance to unprecedented levels. The purposeful production of an arbitrary combination of two solid components into a cocrystal is far from certain, but the studies described motivate the continued exploration of novel materials and the development of predictive models for identifying crystallization partners. When such cocrystals form, many of their most important properties cannot be predicted, pointing to another challenge for the purposeful development of energetic materials based on cocrystallization.
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