The combination of intense solar radiation and soil desiccation creates a short circuit in the biogeochemical carbon cycle, where soils release significant amounts of CO 2 and reactive nitrogen oxides by abiotic oxidation. Here we show that desert soils accumulate metal superoxides and peroxides at higher levels than non-desert soils. We also show the photogeneration of equimolar superoxide and hydroxyl radical in desiccated and aqueous soils, respectively, by a photo-induced electron transfer mechanism supported by their mineralogical composition. Reactivity of desert soils is further supported by the generation of hydroxyl radical via aqueous extracts in the dark. Our findings extend to desert soils the photogeneration of reactive oxygen species by certain mineral oxides and also explain previous studies on desert soil organic oxidant chemistry and microbiology. Similar processes driven by ultraviolet radiation may be operating in the surface soils on Mars.

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A new 2,4-dinitrophenylhydrazine (DNPH)-based photometric assay is developed for the quantification of carbonyls in protein samples from any biological source by protein carbonyl-DNPH hydrazone formation at acidic pH in the presence of denaturing urea, and subsequent hydrazone solubilization in the presence of SDS and stabilization from acid hydrolysis at pH 7.0. At this neutral (ntr) pH, interfering unreacted DNPH is uncharged and its thus increased hydrophobicity permits its 100% effective removal from the solubilizate with ethyl acetate/hexane wash. The ntrDNPH assay is more reliable and sensitive than the standard (std) DNPH photometric assay because it eliminates its main limitations: (i) interfering unreacted DNPH (pKa 1.55) that is nonspecifically bound to the TCA (pKa 0.7)-protein pellet is not effectively removed after wash with EtOH: ethyl acetate because it is positively charged, (ii) acid (TCA-induced) hydrolysis of the protein carbonyl-DNPH hydrazone, (iii) sample protein concentration re-determination, (iv) loss of sample acid (TCA)-soluble proteins, (v) DNA interference, and (vi) requires high protein quantity samples (≥ 1 mg). Considering ntrDNPH assay’s very low protein limit (1 µg), its cumulative and functional sensitivities are 2600- and 2000-fold higher than those of the stdDNPH assay, respectively. The present study elucidates the DNA interference mechanism on the stdDNPH assay, and also develops a standardized protocol for sample protein treatment and fractionation (into cytoplasmic/aqueous, membrane/lipid-bound, and histone/DNA-bound proteins; see Supplement section V) in order to ensure reproducible carbonyl determination on defined cell protein fractions, and to eliminate assay interference from protein samples containing (i) Cys sulfenic acid groups (via their neutralization with dithiothreitol), and (ii) DNA (via its removal by streptomycin sulfate precipitation). Lastly, the ntrDNPH assay determines carbonyl groups on cell wall polysaccharides, thus paving the way on studies to investigate cell walls acting as antioxidant defense in plants, fungi, bacteria and lichens.

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The aim of this study was to examine differences in intrinsic motivation and perceived academic competence as well as in their association between 5th-and 6th-grade students with learning disabilities (LD) (n = 40) and their typically achieving peers. Participants were 980 Greek elementary students from the metropolitan area of Athens. As predicted, students with LD showed lower intrinsic motivation and perceived academic competence than students without LD almost across all subscales. Exceptions were noticed in intrinsic motivation concerning curiosity/interest and history subscales as well as perceptions of academic competence in the subjects of history and science. Support was found that among typically achieving students intrinsic motivation was positively and significantly related at a moderate level to perceived academic competence across all subscales, as opposed to students with LD, for whom few correlations were found.

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The present study demonstrates that γ-radiolyzed perchlorate-containing Mars soil salt analogues (in a CO atmosphere) generate upon HO wetting the reactive oxygen species (ROS) superoxide radical (O), hydrogen peroxide (HO), and hydroxyl radicals (OH). This study also validates that analogue radiolysis forms oxychlorine species that, in turn, can UV-photolyze to OH upon UV photolysis. This investigation was made possible by the development of a new assay for inorganic-origin O and HO determination and by the modification of a previous assay for soil OH. Results show that radiolyzed Mg(ClO) generates HO and OH; and when included as part of a mixture analogous to the salt composition of samples analyzed at the Mars Phoenix site, the analogue generated O, HO, and OH, withOH levels 150-fold higher than in the radiolyzed Mg(ClO) samples. Radiolyzed Mars Phoenix site salt analogue that did not contain Mg(ClO) generated only OH also at 150-fold higher concentration than Mg(ClO) alone. Additionally, UV photolysis of the perchlorate γ radiolysis product chlorite (ClO) generated the oxychlorine products trihalide (Cl), chlorine dioxide (ClO), and hypochlorite (ClO), with the formation of OH by UV photolysis of ClO. While the generation of ROS may have contributed in part to CO production in the Viking Labeled Release (LR) experiment and O (g) release in the Viking Gas Exchange (GEx) experiment, our results indicate that they are not likely to be the major contributor to the LR and GEx results. However, due to their highly reactive nature, they are expected to play a significant role in the alteration of organics on Mars. Additionally, experiments with hypochlorite show that the thermal stability of NaClO is in the range of the thermal stability observed for thermally liable oxidant responsible for the Viking LR results. Key Words: Mars-Oxygen-Salts-Radiation-Habitability. Astrobiology 17, 319-336.