Capillary electrophoresis method for analysis of inorganic and organic anions related to habitability and the search for life

In situ missions of exploration require analytical methods that are capable of detecting a wide range of molecular targets in complex matrices without a priori assumptions of sample composition. Furthermore, these methods should minimize the number of reagents needed and any sample preparation steps. We have developed a method for the detection of metabolically relevant inorganic and organic anions that is suitable for implementation on in situ spaceflight missions. Using 55 mM acetic acid, 50 mM triethylamine, and 5% glycerol, more than 21 relevant anions are separated in less than 20 min. The method is robust to sample ionic strength, tolerating high concentrations of background salts (up to 900 mM NaCl and 300 mM MgSO₄). This is an important feature for future missions to ocean worlds. The method was validated using a culture of Escherichia coli and with high salinity natural samples collected from Mono Lake, California.     

Centrality dependence of charged-hadron transverse-momentum spectra in d+Au collisions at sqrt[s(NN)]=200 GeV

We have measured transverse momentum distributions of charged hadrons produced in d+Au collisions at sqrt[s(NN)]=200 GeV. The spectra were obtained for transverse momenta 0.25相似文献   

Peak Points for Pseudoconvex Domains: A Survey

This paper surveys results concerning peak points for pseudoconvex domains. It includes results of Laszlo that have not been published elsewhere.      

A hydrodynamic injection approach for capillary electrophoresis using rotor–stator valves

Sample injection is a critical step in a capillary electrophoresis (CE) analysis. Electrokinetic injection is the simplest approach and is often selected for implementation in portable CE instruments. However, in order to minimize the effect of sample matrix upon the results of a CE analysis, hydrodynamic injection is preferred. Although portable CE instruments with hydrodynamic injection have been reported, injection has always been performed at the grounded end of the capillary. This simplifies fluidic handling but limits coupling with electrochemical detectors and electrospray ionization–mass spectrometry (ESI–MS). We demonstrated previously that injection at the high-voltage (HV) end of the capillary could be performed using an HV-compatible rotary injection valve (fixed-volume injection). However, the mismatch between the bore sizes of the channels on the rotor–stator valve and the separation capillary caused peak tailing and undesired mixing, impairing analytical performance. In this work, we present an HV-compatible hydrodynamic injection approach that overcomes the issues associated with the fixed-volume injection approach reported previously. The performance of the CE instrument was demonstrated by analyzing a mixture of 13 amino acids by CE coupled to laser-induced fluorescence, which showed relative standard deviations for peak area and migration time below 5% and 1%, respectively, for triplicate analysis. Additionally, replicate measurements of a mixture of amino acids, peptides, nucleobases, and nucleosides by CE coupled to electrospray ionization–mass spectrometry (CE–ESI–MS) were performed to evaluate peak tailing, and results were similar to those obtained with a commercial CE–ESI–MS setup.     

A voltage trade study for the design of capillary electrophoresis instruments for spaceflight

Capillary electrophoresis (CE) systems have undergone extensive development for spaceflight applications. A flight-compatible high voltage power supply and the necessary voltage isolation for other energized components can be large contributors to both the volume and mass of a CE system, especially if typical high voltage levels of 25–30 kV are used. Here, we took advantage of our custom CE hardware to perform a trade study for simultaneous optimization of capillary length, high voltage level, and separation time, without sacrificing method performance. A capillary electrophoresis with capacitively coupled contactless conductivity detection (CE-C⁴D) method recently developed by our group to target inorganic cations and amino acids relevant to astrobiology was used as a test case. The results indicate that a 50 cm long capillary with 15 kV applied voltage (half of that used in the original method) can be used to achieve measurement goals while minimizing instrument size.     

Mechanisms of electron-stimulated desorption of protons from water: Gas,chemisorbed and ice phases

The stimulated desorption of ions from gas phase and condensed phase H₂O on Ni(111) has been examined theoretically and experimentally for the near threshold excitation region, 15 to 40 eV. The excited state potential energy curves have been calculated using configuration interaction for H₂O and a restricted Hartree-Fock (RHF) approach for a variety of small clusters including (H₂O)₅ and NiH₂O. Both proton yield and kinetic energy distributions have been measured for chemisorbed, ice phase, and gas phase water and are discussed in terms of specific electronic excitations corresponding to possible desorption pathways. For condensed phase water, the major proton desorption threshold occurs at 20–21 eV and is due to surface predissociation. The final state potential energy curves reached in this process are, in general, described by two electron excitations from the ground state and are thus not dipole allowed. At threshold, these potential energy curves correspond to the excited states of the neutral rather than the ionized molecule. Above 28–29 eV, predissociation or shake-up involving excitations from the O 2s orbital contributes to the ion yield and can give rise to protons of high (7–8 eV) kinetic energy.     

Effects of environmental lighting and dietary vitamin A on the vulnerability of the retina to light damage.

Abstract—The damaging effect of visible light on photoreceptors and pigment epithelium has been studied mainly in the albino rat with continuous or intermittent exposures to green light for up to several days. Similar damage as in the albino rat but with different doses of light and different times of exposures were observed in pigmented rats, hamster strains, mouse strains and in the nocturnal monkey. The damage is graded histologically mainly by the size of the area of the retina over which the photoreceptors have died. The damage is quantitatively assessed by the measurement of ERG and DNA content of the retina. The action spectrum for the irreversible damage agress with the absorption curve for rhodopsin. Threshold damage occurs with diffuse light that reduces acutely the rhodopsin of the whole retina by about 10%. Damage is a function of body and eye temperature during exposure. At a body temperature of 42°, 2–4 h of exposure produces the same damage as exposure for 30 h at normal temperature using 1500 lux. The damage is also very markedly dependent upon the light history of the animal prior to exposure. Cyclic environmental light of I to 10 ft-cd for several days or weeks reduces very significantly the damaging effect compared to animals reared simultaneously in continuous darkness. Cyclic light rearing is associated with a reduction in opsin and rhodopsin of the whole retina, an increase in the molar phospholipid/opsin ratio and a reduction in the length of the outer segment. Protection is also produced by Vitamin A deficiency but significantly only when rhodopsin content is decreased by maintenance in very weak cyclic light. Thus Vitamin A deficiency and environmental light seem to use the same mechanism. Results do not support the possibility that damage is caused by a cytotoxic effect of retinol.     

Pyrimidines. XVII. I-(Tetrahydro-2-pyranyl)cytosine, -uracil, -thymine and related compounds

In view of the reported biological activities of antibiotics Amicetin and Blasticidin S, 1-(tetrahydro-2-pyranyl)cytosine, -uracil, -thymine and related compounds were synthesized. These compounds were prepared by the Hilbert-Johnson method from 2-chloro-tetrahydropyran and corresponding 2,4-dimethoxypyrimidines.