Reactions of solid glycine induced by keV ion irradiation

Stability of carbonaceous dust analogues and glycine under UV irradiation and electron bombardment

The effect of UV photon (120–200 nm) and electron (2 keV) irradiation of analogues of interstellar carbonaceous dust and of glycine were investigated by means of IR spectroscopy. Films of hydrogenated amorphous carbon (HAC), taken as dust analogues, were found to be stable under UV photon and electron bombardment. High fluences of photons and electrons, of the order of 10¹⁹cm⁻², were needed for a film depletion of a few percent. UV photons were energetically more effective than electrons for depletion and led to a certain dehydrogenation of the HAC samples, whereas electrons led seemingly to a gradual erosion with no appreciable changes in the hydrocarbon structure. The rates of change observed may be relevant over the lifetime of a diffuse cloud, but cannot account for the rapid changes in hydrocarbon IR bands during the evolution of some proto-planetary nebulae. Glycine samples under the same photon and electron fluxes decay at a much faster rate, but tend usually to an equilibrium value different from zero, especially at low temperatures. Reversible reactions re-forming glycine, or the build-up of less transparent products, could explain this behavior. CO₂and methylamine were identified as UV photoproducts. Electron irradiation led to a gradual disappearance of the glycine layers, also with formation of CO₂. No other reaction products were clearly identified. The thicker glycine layers (a few hundred nm) were not wholly depleted, but a film of the order of the electron penetration depth (80 nm), was totally destroyed with an electron fluence of ∼1 × 10¹⁸cm⁻². A 60 nm ice layer on top of glycine provided only partial shielding from the 2 keV electrons. From an energetic point of view, 2 keV electrons are less efficient than UV photons and, according to literature data, much less efficient than MeV protons for the destruction of glycine. The use of keV electrons to simulate effects of cosmic rays on analogues of interstellar grains should be taken with care, due to the low penetration depths of electrons in many samples of interest.

Spectral studies on Ag8+ ions irradiated LAHCl·H2O and LAHBr·H2O single crystals

L-arginine hydrochloride monohydrate and L-arginine hydrobromide monohydrate single crystals are irradiated by 100 MeV Ag8+ swift heavy ions. The residual gases liberated from the irradiated samples are monitored as a function of ion fluence using quadrupole mass analyzer. The C2H3+, C2H2, N2, CO, HCl and CO2 are the dominant gases liberated. Fourier transform infrared spectra of irradiated crystals explain the breaking of bonds in a localized region of the crystals. The crystallinity of irradiated crystals is analyzed by powder X-ray diffractions.

A dose-survival model for low energy ion irradiation

PURPOSE

To explain the dose survival data for low energy ion irradiation in bioorganisms.

MATERIAL AND METHODS

Applying DNA target theory and considering physical processes of low energy ion radiation, a mathematical dose-survival model was derived to analyze the data of low energy ion irradiation of bioorganisms.

RESULTS

The survival fraction S of bioorganisms after a dose D of low energy ion irradiation was: The analysis showed that survival fraction of bioorganisms under low energy ion irradiation can be well fitted with this formula.

CONCLUSIONS

It was shown that the dose-survival effects of low energy ion irradiation in bioorganisms were related to the physical processes of low energy ion irradiation and repair effects that can be explained by momentum transfer processes occurring with low energy ion irradiation.

A novel approach for improving the productivity of ubiquinone-10 producing strain by low-energy ion beam irradiation

Agrobacterium tumefaciens ATCC4452 cells were irradiated by nitrogen ion beam, a new mutagen, with energy of 10 keV and fluence ranging from 2.6x10(14) ions/cm2 to 6.5x10(15) ions/cm2. A similar "saddle shape" survival curve due to ion beam irradiation appeared again in this study. Some mutants with high yield of ubiquinone-10 were induced by ion implantation. High mutation rate and wide mutation spectrum were also observed in the experiment. These results suggested that the mutagenic effect of such low-energy ion influx into bacterium cells could result from multiple processes involving direct collision of particles with cytoplasm, nucleolus, and cascade atomic and molecular reactions due to plentiful primary and secondary particles.

Survival of mammalian cells under high vacuum condition for ion bombardment

An ion beam has been used to irradiate various organisms and its effects have been studied. Because of the poor tolerance that mammalian cells have for vacuum, such studies have not been carried out on living mammalian cells until now. However, this work is important both for elucidating the mechanism of mutation in response to low-energy ions and in exploring possible new applications of ion beam technology. The current paper describes an investigation of the survival of mammalian cells (the A(L) cell line) in a high-vacuum chamber in preparation for ion bombardment studies. The ion beam facility is described and the actual vacuum profile that the cells endured in the target chamber is reported. Cells were damaged immediately following vacuum exposure; the injury was characterized by alteration of the membrane permeability, loss of firm adhesion to the dish, and increased fragility. Three cryoprotective agents were tested (glycerol, propylene glycol, and trehalose) and of these, glycerol showed the highest potency for protecting cells against vacuum stress. This was revealed by an increase in the cell survival level from <1 to >10% with a glycerol concentration of 15 and 20%. Two glycerol-based protocols were investigated (freezing-vacuum vs. non-freezing-vacuum), but there was no significant difference (P > 0.1) in their ability to improve cell survival, the values being 10.31 +/- 4.5 and 12.7 +/- 3.37%, respectively with 20% glycerol concentration. These cells had a normal growth capability, and also retained integrity of the cell surface antigen CD59. These initial experiments indicate that mammalian cells can withstand vacuum to the degree that is needed to study the effect of the ion beam. In addition to the improvements made in this study, other factors are discussed that may increase the survival of mammalian cells exposed to a vacuum in future studies.

Mutation of Gluconobacter oxydans and Bacillus megaterium in a two-step process of l-ascorbic acid manufacture by ion beam

AIM

To increase the transformation rate of l-sorbose to 2-keto-l-gulonic (2-KLG) acid in a two-step process of l-ascrobic acid manufacture by ion beam.

METHODS AND RESULTS

Gluconobacter oxydans (GO29) and Bacillus megaterium (BM80) were used in the present study. Ion implantation was carried out with the heavy ion implantation facility at the institute of Plasma Physics in China. 2-KLG in whole culture broth was determined by iodometry. Mutants were screened by single-colony isolation and 2-KLG accumulation in broth. GO29 and BM80 were implanted by either hydrogen ions (H(+)) or nitrogen ions (N(+)) with various doses, respectively. The average transformation rate of GM112-302 bred by ion beam in Gram-molecule was increased from 79.3 to 94.5% after eight passages in shaking flasks. Furthermore, in 180-ton fermentors in Jiangsu Jiangshan Pharmaceutical Co. Ltd, the transformation rate was stable at 92.0%, indicating a producer could get 0.99 kg of gulonic acid from 1.0 kg of sorbose.

CONCLUSION

Ion beam as a new mutation source had potential advantages in breeding. Comparing with original mixture GO29 and BM80, GM112-302 is more efficient in accumulating 2-KLG, especially at the later phase.

SIGNIFICANCE AND IMPACT OF THE STUDY

GM112-302 bred by ion beam implantation dramatically increased the transformation rate by 19.2%, which greatly increased efficiency and reduced the cost of l-ascorbic acid manufacture in a two-step process.