Organic nitrates form via the photodegradation of hydrocarbons in the troposphere in the presence of NO and NO2. This process competes with the chemical cycle leading to ozone production since it sequesters both nitrogen oxides and organic radicals. Hydroxy nitrates form via the atmospheric reactions of alkanes and alkenes and are thought to be an important nitrogen oxides reservoir. In this study, new synthetic methods to produce β-, γ-, and δ-hydroxy nitrates of atmospheric interest were developed. NMR and IR spectroscopies were used to characterize these compounds. Henry's law coefficients of C4 and C5 hydroxy nitrates at 291 ± 2 K were measured using a dynamic equilibrium system. The solubility decreases with the organic chain length and increases with increasing distance between the nitrooxy and hydroxy groups. Due to their large Henry's law coefficients these species will partition into droplets in the presence of clouds and fogs. Measurements of the OH reaction and photolysis rate coefficients are needed for an accurate assessment of the atmospheric lifetimes of these compounds.

Rate coefficients for the reaction of OH radical with eleven C 3 -C 6 hydroxyalkyl nitrates and with two C 4 hydroxy nitrates containing a double bond were determined at atmospheric pressure and 296 ( 2 K. The rate coefficients were measured in a photochemical reactor by the relative rate technique, employing solid-phase microextraction (SPME) coupled to gas chromatography (GC) for detection of the organic reactants. Hydroxyalkyl nitrates react faster than alkyl nitrates with the OH radical. The rate coefficients increase with increasing chain length and separation between the hydroxy and the nitrooxy groups. By including different loss processes such as photolysis, gas-phase reactions, and solubility, the tropospheric lifetime of C 3 -C 6 hydroxyalkyl nitrates is estimated to range between 0.5 and 4.5 days. Due to their higher reactivity and solubility, hydroxyalkyl nitrates have a shorter atmospheric lifetime than alkyl nitrates.

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Dedicated to Professor Jack D. Dunitz on the occasion of his 80th birthdayIn the chitons (Polyplacophora, Mollusca), the body is not entirely protected by the shell. Mineralized spicules or scales often, but not always, decorate the exposed part of the girdle. Here, we report a study on the composition and ultrastructural organization of these mineralized skeletal parts in four different chiton species. In all specimens, the mineral component (97 ± 98 wt-%) is aragonite, and the organic matrix (2 ± 3 wt-%) consists of highly glycosylated proteins. X-Ray diffraction and scanning electron microscopy show that the organic matrix fibers are aligned, morphologically and crystallographically, with the prismatic aragonite crystals. Matrix and mineral are thus clearly related. The matrix ± mineral composite bundles are, however, assembled in the various skeletal parts examined with widely different degrees of alignment and order. In the same organism, the crystals are aligned within a range of AE 158 in one type of spicule, while they are randomly oriented in another type. The wide heterogeneity in shape, density, and ultrastructure suggests that the girdle mineralized tissues do not fulfill a fundamental role necessary for the survival of the organism. This, together with the lack of chitin in the organic matrix, supports the hypothesis that they evolved separately from the other chiton mineralized tissues, namely the shell plates and teeth.Introduction. ± Calcium carbonate minerals are formed in vast amounts by many different organisms [1]. The crystals generally form in matrix frameworks, and their orientations, polymorph type, and morphologies are influenced by the matrix and by the environment in which they grow. They are, thus, the focus of much research in the field of biomineralization aimed at understanding the manner in which control is exerted over the biomineralization process.Calcium carbonate crystallizes in three anhydrous polymorphs; calcite, aragonite, and vaterite [2]. The most-common polymorphs formed by organisms are calcite and aragonite, and this is under strict genetic control. Calcite is the most stable form at ambient temperatures and pressures. Calcite formation at ambient temperature from pure water or from buffered solutions not containing Mg is both thermodynamically and kinetically favored. The formation of aragonite is, however, favored in the presence of Mg in high concentrations relative to Ca. Interestingly, the density of aragonite (2.93 g/cm 3 ) is higher than that of calcite (2.71 g/cm 3 ), such that aragonite is more stable than calcite at very low temperatures, close to absolute zero. Magnesium ions are not incorporated in the denser lattice of aragonite as a solid solution, in spite of Mg 2 being a smaller ion than Ca 2 . This occurs presumably because magnesium has a tightly bound hydration shell, and its removal during crystal growth is energetically unfavorable. In contrast to aragonite, Mg 2 ions may be incorporated inside the calcite lattice. The presence of Mg in the calcite ...

Rate coefficients for the gas-phase reactions of chlorine atoms with a series of C3−C6 hydroxyalkyl nitrates of atmospheric interest have been determined at 296 ± 2 K and atmospheric pressure. The experiments were conducted using the relative rate technique combined with solid-phase microextraction (SPME) sampling followed by gas chromatography (GC) analysis with an electron capture detector (ECD). The experiments were performed in a collapsible 100 L PVF-film (Tedlar) reaction chamber. It is shown that the presence of the hydroxy group enhances the reactivity of the hydroxyalkyl nitrates toward the Cl atom as compared to the corresponding alkyl nitrates and alkyl dinitrates. The Cl atom reactivity toward the hydroxyalkyl nitrates increases with the length of the alkyl chain and with increasing separation between the hydroxy and the nitrooxy groups. Tropospheric lifetimes are calculated using the determined rate coefficients and the atmospheric implications are briefly discussed.