Influence of pH and salts on DMF-DMA derivatization for future Space Applications.

For gas chromatography - mass spectrometry (GC-MS) analyses performed in situ, pH and salts (e.g., chlorides, sulfates) may enhance or inhibit the detection of targeted molecules of interest for astrobiology (e.g. amino acids, fatty acids, nucleobases). Obviously, salts influence the ionic strength of the solutions, the pH value, and the salting effect. But the presence of salts may also produce complexes or mask ions in the sample (masking effect on hydroxide ion, ammonia, etc.). For future space missions, wet chemistry will be conducted before GC-MS analyses to detect the full organic content of a sample. The defined organic targets for space GC-MS instrument requirements are generally strongly polar or refractory organic compounds, such as amino acids playing a role in the protein production and metabolism regulations for life on Earth, nucleobases essential for DNA and RNA formation and mutation, and fatty acids that composed most of the eukaryote and prokaryote membranes on Earth and resist to environmental stress long enough to still be observed on Mars or ocean worlds in geological well-preserved records. The wet-chemistry chemical treatment consists of reacting an organic reagent with the sample to extract and volatilize polar or refractory organic molecules (i.e. dimethylformamide dimethyl acetal (DMF-DMA) in this study). DMF-DMA derivatizes functional groups with labile H in organics, without modifying their chiral conformation. The influence of pH and salt concentration of extraterrestrial materials on the DMF-DMA derivatization remains understudied. In this research, we studied the influence of different salts and pHs on the derivatization of organic molecules of astrobiological interest with DMF-DMA, such as amino acids, carboxylic acids, and nucleobases. Results show that salts and pH influence the derivatization yield, and that their effect depend on the nature of the organics and the salts studied. Second, monovalent salts lead to a higher or similar organic recovery compared to divalent salts regardless of pH below 8. However, a pH above 8 inhibits the DMF-DMA derivatization influencing the carboxylic acid function to become an anionic group without labile H. Overall, considering the negative effect of the salts on the detection of organic molecules, future space missions may have to consider a desalting step prior to derivatization and GC-MS analyses.

Fibrin glue inhibits migration of ocular surface epithelial cells.

PurposeFibrin glue has been used successfully in numerous ophthalmic surgical procedures. Recently, fibrin glue has been used in limbal stem cell transplantation to reduce both operative time and to negate the need for sutures. The aim of this study was to determine the effects of fibrin glue on epithelial cell migration in vitro.MethodsCorneoscleral rims were split to retain the epithelial layer, Bowman's layer, and anterior stroma. Rims were cut into eight equal-sized pieces and were placed directly on culture plates or affixed with fibrin glue. Rims were maintained in culture for 25 days and epithelial cell growth was monitored. Cells were photographed to measure area or growth and immunofluorescence staining of explants for fibrin was performed.ResultsExplants that were glued demonstrated significantly delayed epithelial cell growth and migration as compared with explants without glue. By day 16, all fibrin glue had dissolved and coincided with onset of cell growth from glued explants. Cell growth commenced between days 3 and 4 for control explants without glue and around days 14-16 for explants with fibrin glue.ConclusionsFibrin glue delays epithelial cell migration by acting as a physical barrier and can potentially interfere with explant-derived limbal epithelial cell migration on to the corneal surface. We propose that glue should be used to attach the conjunctival frill of the limbal explant but care should be taken to ensure that the glue does not wrap around the explant if used to secure the explant as well. Strategic use of glue, to attach the recessed conjunctiva, can be advantageous in delaying conjunctival cell migration and reducing the need for sequential sector conjunctival epitheliectomy.