Nickel plasma produced by 532-nm and 1064-nm pulsed laser ablation

A comparison between laser ablation of nickel in vacuum by using 532-and 1064-nm Nd:YAG (Yttrium Aluminium Garnet) laser wavelengths, with an intensity of 5 × 10⁹ W/cm², is reported. Nanosecond pulsed ablation produces high nonisotropic emission of neutrals and ionic species. For 532-nm laser irradiation, mass quadrupole spectrometry, coupled to electrostatic ion deflection and time-of-flight measurements, allows estimation of the energy distributions of the emitted species from plasma. For 1064-nm laser ablation, a cylindrical electrostatic ion analyzer permits one to measure the yield and the charge state of the emitted ions and reconstruct the ion energy and charge state distributions. Neutrals show typical Boltzmann-like distributions, while ions show Coulomb-Boltzmann-shifted distributions depending on their charge state. Surface profiles of the ablated craters permitted study of the ablation threshold and yields of nickel in vacuum versus the laser fluence. The plasma temperature was evaluated using experimental data. Special regard is given to the ion acceleration process occurring inside the plasma due to the high electrical field generated at nonequilibrium plasma conditions and the angular distribution of the emitted species. Published in Russian in Fizika Plazmy, 2008, Vol. 34, No. 7, pp. 598–606. The text was submitted by the authors in English.     

In vitro laser ablation of laboratory developed biofilms using an Nd:YAG laser of 532 nm wavelength

We studied the laser ablation of laboratory-developed biofilm on titanium and glass surfaces. Specifically, Pseudoalteromonas carrageenovora, a marine biofilm forming bacterium was used to generate laboratory biofilm. Two fluences, 0.05 and 0.1 J/cm(2) and three durations of irradiation, 30 s, 5 min, and 10 min were tested using an Nd;YAG laser of 532 nm wavelength (in the green light area). Nonirradiated coupons with biofilm served as control. The biofilm removal efficiency increased with the increase in laser fluence and duration of irradiation. The maximum biofilm area cover on control coupons of glass and titanium was 62.5 and 76.0%, respectively. Upon irradiation with fluence 0.1 J/cm(2) for the very short duration of 30 s, this reduced to 5.6 and 12.4% and at 10 min to 2.17 and 0.7% on glass and titanium coupons, respectively, while the controls did not show any reductions (62.5 and 76.0% respectively, for glass and titanium coupons). The biofilm TRC (Total Resuscitated Cells) reduction during this period was even more prominent than the area cover, indicating that the remaining biofilm portions on coupons after irradiation were largely composed of dead bacterial cells. The TRC in the irradiation chamber medium for short durations of irradiation showed a significant increase, indicating that the laser irradiation removed live bacteria from the biofilm. The re-growth of the resuscitated cells showed they could grow like the control cells but with a significant lag. The laser's efficiency in the removal of biofilm was better seen on titanium coupons than on glass. Our results showed that a low-power pulsed laser irradiation could be used to remove biofilm formed on hard surfaces.     

Specificity of mutagenic effect of N-nitroso-N-methylurea and relation between its mutagenic activity and carbamoylating properties

Significance of carbamoylation for mutagenic effects of N-nitroso-N-methyl-urea (NMU) on the CHO-AT3-2 cell line of Chinese hamster was studied. True point mutations occurred, due to alkylation. Carbamoylation combined with alkylation, or carbamoylation after alkylation induced the increase in other types of gene mutations as well as micro- and macroaberrations. These effects may be explained by the synergistic effect of alkylation and carbamoylation. Possible mechanisms and levels of interaction between alkylation and carbamoylation are discussed.     

Measurement of hemoglobin oxygen saturation using Raman microspectroscopy and 532-nm excitation.

The resonant Raman enhancement of hemoglobin (Hb) in the Q band region allows simultaneous identification of oxy- and deoxy-Hb. The heme vibrational bands are well known at 532 nm, but the technique has never been used to determine microvascular Hb oxygen saturation (So(2)) in vivo. We implemented a system for in vivo noninvasive measurements of So(2). A laser light was focused onto areas of 15-30 microm in diameter. Using a microscope coupled to a spectrometer and a cooled detector, Raman spectra were obtained in backscattering geometry. Calibration was performed in vitro using blood at several Hb concentrations, equilibrated at various oxygen tensions. So(2) was estimated by measuring the intensity of Raman signals (peaks) in the 1,355- to 1,380-cm(-1) range (oxidation state marker band nu(4)), as well as from the nu(19) and nu(10) bands (1,500- to 1,650-cm(-1) range). In vivo observations were made in microvessels of anesthetized rats. Glass capillary path length and Hb concentration did not affect So(2) estimations from Raman spectra. The Hb Raman peaks observed in blood were consistent with earlier Raman studies using Hb solutions and isolated cells. The correlation between Raman-based So(2) estimations and So(2) measured by CO-oximetry was highly significant for nu(4), nu(10), and nu(19) bands. The method allowed So(2) determinations in all microvessel types, while diameter and erythrocyte velocity could be measured in the same vessels. Raman microspectroscopy has advantages over other techniques by providing noninvasive and reliable in vivo So(2) determinations in thin tissues, as well as in solid organs and tissues in which transillumination is not possible.     

Co-operative mutagenic actions of bisulfite and nitrogen nucleophiles.

The combined effect of bisulfite and a nitrogen nucleophile, i.e. semicarbazide, methoxyamine or hydroxylamine, to chemically modify cytosine and to cause mutation and inactivation of bacteriophage lambda was investigated. A rapid transamination of cytidine with each of the amines took place in the presence of bisulfite, and the reaction product was solely the N(4)-transaminated 5,6-dihydrocytidine-6-sulfonate. Modifications of cytidine with bisulfite alone and with the nitrogen nucleophile alone were much slower reactions than those using a combination of bisulfite and the nucleophile. Whereas the product of the modification with the bisulfite/semicarbazide, 5,6-dihydro-4-semicarbazido-2-ketopyrimidine ribofuranoside-6-sulfonate, is convertible to 4-semicarbazido-2-ketopyrimidine ribofuranoside by treatment with a phosphate buffer, the products of the modification with the bisulfite/methoxyamine and with the bisulfite/hydroxylamine, i.e. 4-methoxy-5,6-dihydrocytidine-6-sulfonate and 4-hydroxy-5,6-dihydrocytidine-6-sulfonate, were stable in phosphate buffer.Inactivation and the “clear” mutation of bacteriophage lambda were observed when the phage was treated with sodium bisulfite in the presence of semicarbazide, methoxyamine or hydroxylamine. Under the conditions used, only very small increases in the mutation frequency were obtained by treatment of the phage with bisulfite alone or with the base alone. It was concluded that the residues, 5,6-dihydro-4-semicarbazido-2-ketopyrimidine-6-sulfonate, 4-methoxy-5, 6-dihydrocytosine-6-sulfonate and 4-hydroxy-5,6-dihydrocytosine-6-sulfonate in DNA are the causes of the mutation.When phage that had been inactivated by the semicarbazide/bisulfite reagent was subsequently treated with a phosphate buffer, a reactivation took place. The rate of the reactivation increased as the concentration of phosphate in the buffer increased. This reactivation was not accompanied by change in the mutation frequency. No reactivation was observed after a similar incubation when the prior inactivation had been induced by either methoxyamine/bisulfite or hydroxylamine/bisulfite. These results indicate that the 4-semicarbazido-2-ketopyrimidine residue is also mutagenic but is less lethal than the corresponding 5,6-dihydro-6-sulfonate structure.These results offer the first clear example of the co-operative mutagenic action of two different reagents.     

Dominant lethal test in the mouse for mutagenic effects of saccharine

Summary Twenty male NMRI mice received 5 g saccharine per kilogram body weight by the oral route daily for 5 successive days. After the last dose each male was mated with 3 untreated females. For fractionated examination with regard to successive germ cell stages, each week 3 other untreated females were placed with each male for mating. The whole mating period was 8 weeks. The uteri of the females were inspected on the 14th day of gestation and pre-implantative and post-implantative loss determined from the numbers of corpora lutea, implantations, live and dead implants.The treatment did not damage the males and did not impair their mating capacity or their fertility.Post-implantative loss remained unaffected by the saccharine treatment compared with parallel controls.Pre-implantative loss persisted in the saccharine-treated group throughout the 8 weeks in the normal range of the strain. A statistically significant difference between saccharine group and control group in the 3rd week of mating after treatment was without biological relevance.Our investigations revealed no indication of a mutagenic action of saccharine in terms of an induction of dominant lethal mutations.This is in keeping with cytogenetic in vitro findings of other authors on human leukocytes.

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Zusammenfassung 20 männliche NMRI-Mäuse erhielten täglich je 5 g Saccharin per os pro Kilogramm Körpergewicht an 5 aufeinanderfolgenden Tagen. Nach der letzten Applikation wurde jedes Männchen mit 3 unbehandelten Weibchen gepaart. Zur fraktionierten Untersuchung der aufeinanderfolgenden Keimzellstadien der Männchen wurden jede Woche 3 neue, unbehandelte Weibchen zu jedem Bock gesetzt und besamen lassen, insgesamt über 8 Wochen.Die Uteri der Weibchen wurden am 14. Tag der Trächtigkeit untersucht, und der präimplantative under postimplantative Verlust wurden an Hand der Corpora lutea, der Implantationen und der lebenden und toten Keimlinge ermittelt.Die Behandlung schädigte die Männchen nicht und beeinträchtigte nicht ihre Deckfreudigkeit und Fertilität.Der postimplantative Verlust blieb im Vergleich zu der parallel durchgeführten Kontrolle unbeeinflußt durch die Behandlung mit Saccharin.Der präimplantative Verlust der mit Saccharin behandelten Gruppe lag während aller 8 Versuchswochen im Bereich der Norm des Stammes. Eine in der 3. Paarungswoche nach den Applikationen aufgetretene statistische Signifikanz zwischen den Verlusten der Saccharin-Gruppe und der Kontroll-Gruppe war ohne biologische Relevanz.Unsere Untersuchungen erbrachten keinen Hinweis für eine mutagene Wirkung von Saccharin im Sinne der Induktion dominanter Letalmutationen.Dies steht im Einklang mit cytogenetischen in vitro-Befunden anderer Autoren an menschlichen Leukocyten.

     

Comparison of therapeutic effects between pulsed and continuous wave 810-nm wavelength laser irradiation for traumatic brain injury in mice

Background and Objective

Transcranial low-level laser therapy (LLLT) using near-infrared light can efficiently penetrate through the scalp and skull and could allow non-invasive treatment for traumatic brain injury (TBI). In the present study, we compared the therapeutic effect using 810-nm wavelength laser light in continuous and pulsed wave modes in a mouse model of TBI.

Study Design/Materials and Methods

TBI was induced by a controlled cortical-impact device and 4-hours post-TBI 1-group received a sham treatment and 3-groups received a single exposure to transcranial LLLT, either continuous wave or pulsed at 10-Hz or 100-Hz with a 50% duty cycle. An 810-nm Ga-Al-As diode laser delivered a spot with diameter of 1-cm onto the injured head with a power density of 50-mW/cm² for 12-minutes giving a fluence of 36-J/cm². Neurological severity score (NSS) and body weight were measured up to 4 weeks. Mice were sacrificed at 2, 15 and 28 days post-TBI and the lesion size was histologically analyzed. The quantity of ATP production in the brain tissue was determined immediately after laser irradiation. We examined the role of LLLT on the psychological state of the mice at 1 day and 4 weeks after TBI using tail suspension test and forced swim test.

Results

The 810-nm laser pulsed at 10-Hz was the most effective judged by improvement in NSS and body weight although the other laser regimens were also effective. The brain lesion volume of mice treated with 10-Hz pulsed-laser irradiation was significantly lower than control group at 15-days and 4-weeks post-TBI. Moreover, we found an antidepressant effect of LLLT at 4-weeks as shown by forced swim and tail suspension tests.

Conclusion

The therapeutic effect of LLLT for TBI with an 810-nm laser was more effective at 10-Hz pulse frequency than at CW and 100-Hz. This finding may provide a new insight into biological mechanisms of LLLT.     

Mechanism of the lethal and mutagenic effects of phenoxyacetic acids in Saccharomyces cerevisiae

MCPA and salicylic acid, two compounds with similar structures and almost the same dissociation pattern, were tested for lethal and mutagenic effects on, and uptake by, cells of Saccharomyces cerevisiae strain red18. The results obtained with the two compounds were similar, suggesting a common mechanism of action. It is proposed that they act by increasing the concentration of hydrogen ions within the cell, so that killing and mutation occur. Mutations were induced only when killing reached 95–99%. The compounds are considered weak mutagens for yeast cells. The methyl ester of MCPA also induced killing and reverse mutation, but only at concentrations about 100 times higher than for the undissociated acid. MCPA methyl ester did not increase the number of revertants in the Salmonella/liver microsome test. It is suggested that the effects of the methyl ester of MCPA depends on the ester being hydrolysed to the acid by yeast cells and the liver microsome preparation.     

Further studies on the lethal and mutagenic effects of 8-methoxypsoralen-induced lesions on plasmid DNA

Our previous results on the genotoxic effect of 8-methoxypsoralen-induced lesions on pBR322 suggested an important involvement of an inducible error-free repair pathway in the repair of plasmid lesions. We present herein further results obtained in order to explore that possibility, together with a more general report on the subject. pBR322 treated with increasing concentrations of 8-MOP plus fixed UVA light irradiation was used to transform several E. coli strains differing in their repair capacities, and plasmid survival and mutagenesis were determined. Survival results suggested that crosslinks were completely lethal in pBR322 whereas monoadducts were partially removed from plasmid DNA mainly through an error-free excision pathway. A mutagenic repair pathway did not show a significant contribution to the total repair process. Cell preirradiation stimulated plasmid recovery in recA+ strains, including the umuC strain, thus confirming our previous results indicating that an inducible error-free repair had occurred. Globally, our results showed a strong requirement on the excision pathway for the repair of psoralen-damaged plasmid DNA. In contrast, the recA dependent pathway was needed only for SOS induction. After a theoretical correction of the data for estimating the effect only due to 8-MOP adducts, a different pattern of repair mechanisms appeared to be involved.