Presence Of Perchlorate Salts Research Articles

Changes in membrane fatty acids of a halo-psychrophile exposed to magnesium perchlorate and low temperatures: Implications for Mars habitability

The presence of perchlorate salts in aqueous solutions bears two opposite effects on habitability. On the one hand, perchlorate salts trigger a decrease in the freezing point of the aqueous solutions, resulting in stable aqueous solutions at subzero temperatures, thereby widening the habitable conditions for potential microbial life. On the other hand, the presence of perchlorates in solution imposes a significant osmotic stress that compromises the integrity of microbial cell membranes, thereby restricting the habitable conditions in the same aqueous environment. Here we investigated the survivability and the changes in the composition of membrane fatty acids (FAs) of the bacterium Rhodococcus sp. JG-3 cells under warm (20°C), cold (4°C), and subzero temperatures (−10°C and −16°C), and in the presence (8 wt% and 16 wt%) and absence of magnesium perchlorate (Mg(ClO4)2). Bacterial cell survivability decreased with decreasing temperature and presence of magnesium perchlorate. However, Rhodococcus sp. JG-3 was able to tolerate up to 8 wt% Mg(ClO4)2 at −16°C. The presence of magnesium perchlorate in the medium decreased the concentration of total FAs, likely due to a destabilization of the molecules by the chaotropic effect of the perchlorate anion. At the maximum stress (both subzero temperatures and 16 wt% magnesium perchlorate), the composition of FAs changed, i.e., Rhodococcus sp. JG-3 cells increased the relative abundance of saturated FAs (SFAs) over the unsaturated (UFAs) or branched (BFAs). These changes in the proportion of FAs types may be a physiological response during cooling, aimed to improve lipid membrane stability. Interestingly, the composition and relative abundance of fatty acid types (i.e., SFAs, UFAs and BFAs) of Rhodococcus sp. JG-3 when simultaneously exposed to subzero temperatures and 16 wt% magnesium perchlorate was similar to that following freezing stress alone, suggesting that either both conditions triggered a similar response or that one response dominated over the other. Our findings contribute to understand the survivability and adaptation of extremophilic microorganisms under polyextreme conditions, such as those existing in the Martian subsurface today and/or in the past, which include the documented presence of magnesium perchlorate salts in ancient sediments and global cold temperatures.

Transport of cesium and potassium ions across bilayer lipid membranes — Cesium accumulation in biological cells according to the membrane potential

The transport of Cs+ across a bilayer lipid membrane between two aqueous phases containing chloride and perchlorate salts was readily observed when compared to using K+, because Cs+ is more hydrophobic than K+. After the Cs+ was distributed from the aqueous to the BLM with a counter anion, such as Cl− and ClO4−, the antiport of Cs+ and the counter anion across the bilayer lipid membrane was caused by applying the potential difference between the two aqueous phases. By comparing the permeability in the presence of chloride salts with that in the presence of perchlorate salts, it can be appreciated that the standard potential for the transport of Cs+ from the aqueous phase to the bilayer lipid membrane is about 60mV more negative than that of K+. According to the ion transport mechanism, the accumulation of Cs+ within living cells is assumed to be caused by the membrane potential, which is mainly generated by the transport of K+ across the cell membrane between the outside and inside. By use of a liquid membrane cell, it was verified that the membrane potential generated by the concentration ratio of K+ between two aqueous phases caused the accumulation of Cs+.

Detection of trace organics in Mars analog samples containing perchlorate by laser desorption/ionization mass spectrometry.

Evidence from recent Mars missions indicates the presence of perchlorate salts up to 1 wt % level in the near-surface materials. Mixed perchlorates and other oxychlorine species may complicate the detection of organic molecules in bulk martian samples when using pyrolysis techniques. To address this analytical challenge, we report here results of laboratory measurements with laser desorption mass spectrometry, including analyses performed on both commercial and Mars Organic Molecule Analyzer (MOMA) breadboard instruments. We demonstrate that the detection of nonvolatile organics in selected spiked mineral-matrix materials by laser desorption/ionization (LDI) mass spectrometry is not inhibited by the presence of up to 1 wt % perchlorate salt. The organics in the sample are not significantly degraded or combusted in the LDI process, and the parent molecular ion is retained in the mass spectrum. The LDI technique provides distinct potential benefits for the detection of organics in situ on the martian surface and has the potential to aid in the search for signs of life on Mars.

Immunological Detection of Small Organic Molecules in the Presence of Perchlorates: Relevance to the Life Marker Chip and Life Detection on Mars

The proposed ExoMars mission, due to launch in 2018, aims to look for evidence of extant and extinct life in martian rocks and regolith. Previous attempts to detect organic molecules of biological or abiotic origin on Mars have been unsuccessful, which may be attributable to destruction of these molecules by perchlorate salts during pyrolysis sample extraction techniques. Organic molecules can also be extracted and measured with solvent-based systems. The ExoMars payload includes the Life Marker Chip (LMC) instrument, capable of detecting biomarker molecules of extant and extinct Earth-like life in liquid extracts of martian samples with an antibody microarray assay. The aim of the work reported here was to investigate whether the presence of perchlorate salts, at levels similar to those at the NASA Phoenix landing site, would compromise the LMC extraction and detection method. To test this, we implemented an LMC-representative sample extraction process with an LMC-representative antibody assay and used these to extract and analyze a model sample that consisted of a Mars analog sample matrix (JSC Mars-1) spiked with a representative organic molecular target (pyrene, an example of abiotic meteoritic infall targets) in the presence of perchlorate salts. We found no significant change in immunoassay function when using pyrene standards with added perchlorate salts. When model samples spiked with perchlorate salts were subjected to an LMC-representative liquid extraction, immunoassays functioned in a liquid extract and detected extracted pyrene. For the same model sample matrix without perchlorate salts, we observed anomalous assay signals that coincided with yellow coloration of the extracts. This unexpected observation is being studied further. This initial study indicates that the presence of perchlorate salts, at levels similar to those detected at the NASA Phoenix landing site, is unlikely to prevent the LMC from extracting and detecting organic molecules from martian samples.

The influence of perchlorates on the fluorescence quenching of 9,10-dichloroanthracene by bromide salts in acetone

Fluorescence quenching of 9,10-dichloroanthracene by lithium bromide and tetra- n-butylammonium bromide in acetone has been investigated in the presence of perchlorate salts. In the presence of LiBr, the Stern–Volmer (S–V) plots exhibit downward curvatures indicating that two species are responsible for the quenching process, namely free bromide anions and lithium bromide ion pairs. The addition of a perchlorate salt modifies the S–V dependencies due to the influence of perchlorates on the degree of lithium bromide dissociation. The association constant of lithium bromide has been determined by conductivity measurements and it agrees well with the estimates made from the fluorescence quenching measurements. The mechanism of fluorescence quenching by lithium bromide is discussed on the basis of electron transfer and the heavy-atom effect.

Grafting of polytetrahydrofuran from neoprene W in the presence of perchlorate salts

AbstractSilver, mercury, and lead perchlorates can be used to prepare graft copolymers of polytetrahydrofuran from neoprene. Iron and aluminum perchlorates lead to graft copolymers but the conversion is low. The most efficient graft copolymerizations are obtained at high salt‐to‐neoprene ratios, long reaction times, and low monomer‐to‐neoprene concentration ratios. Very surprisingly, high initial monomer‐to‐neoprene concentration ratios lead to low graft copolymerization efficiencies.

Stopped‐flow studies of cationic polymerizations

AbstractThis paper summarizes results and conclusions from an extensive study by stopped‐flow methods of the rapid nonstationary phase of the polymerization by HClO4 in CH2Cl2 of styrene and some styrene derivatives. With styrene, this precursor reaction is detectable but unimportant at 0°C, becomes longer‐lasting as the reaction temperature falls, and at –97°C is the only contributor to the polymerization.Detailed studies at −60 and −80°C, identifying a transient absorption (λmax‐340 nm) as that of the (poly)styryl carbenium ion, lead to the conclusion that the reaction is a composite, with nonionic as well as ionic components. The rates of the polymerization by the two mechanisms can be distinguished only in favorable circumstances (presence of perchlorate salts) but can be interpreted to yield approximate rate constants for propagation by polystyryl carbenium ion‐perchlorate ion‐pairs, viz., kp± ∼ 2000 M−1S−1 at −80°C; 4000–5000 at −60°C. The rate constants of propagation by free ions are estimated as 10–20 times greater.

Electrophilic cleavage of the sulphur–sulphur bond. Kinetics of the isotopic exchange between p-chlorophenylsulphenyl chloride and pp′-dichlorodiphenyl disulphide in the dark

Kinetics of the isotopic exchange between p-chlorophenylsulphenyl chloride and the corresponding [35S2]disulphide in benzene in the dark are of the second order, first order with respect to each compound. Change to chlorobenzene as solvent results in a four-fold increase of the exchange rate. Moreover, addition of tetra-alkylammonium perchlorates in benzene dramatically accelerates the exchange which, however, remains of the first order with respect to the disulphide. Also, addition of tetra-n-butylammonium chloride does not depress the exchange rate in the presence of perchlorate salts. These results suggest a polar mechanism for the exchange in the dark which cannot involve a sulphenium ion in a kinetically important step. Rather, the sulphenyl chloride must be the electrophilic species involved in the sulphur–sulphur bond breaking.