The electrochemical reduction of the purines guanine and adenine at platinum electrodes in several room temperature ionic liquids

The reduction of guanine was studied by microelectrode voltammetry in the room temperature ionic liquids (RTILs) N-hexyltriethylammonium bis (trifluoromethanesulfonyl) imide [N6,2,2,2][N(Tf)2], 1-butyl-3-methylimidazolium hexafluorosphosphate [C4mim][PF6], N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide [C4mpyrr][N(Tf)2], 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide [C4mim][N(Tf)2], N-butyl-N-methyl-pyrrolidinium dicyanamide [C4mpyrr][N(NC)2] and tris(P-hexyl)-tetradecylphosphonium trifluorotris(pentafluoroethyl)phosphate [P14,6,6,6][FAP] on a platinum microelectrode. In [N6,2,2,2][NTf2] and [P14,6,6,6][FAP], but not in the other ionic liquids studied, guanine reduction involves a one-electron, diffusion-controlled process at very negative potential to produce an unstable radical anion, which is thought to undergo a dimerization reaction, probably after proton abstraction from the cation of the ionic liquid. The rate of this subsequent reaction depends on the nature of the ionic liquid, and it is faster in the ionic liquid [P14,6,6,6][FAP], in which the formation of the resulting dimer can be voltammetrically monitored at less negative potentials than required for the reduction of the parent molecule. Adenine showed similar behaviour to guanine but the pyrimidines thymine and cytosine did not; thymine was not reduced at potentials less negative than required for solvent (RTIL) decomposition while only a poorly defined wave was seen for cytosine. The possibility for proton abstraction from the cation in [N6,2,2,2][NTf2] and [P14,6,6,6][FAP] is noted and this is thought to aid the electrochemical dimerization process. The resulting rapid reaction is thought to shift the reduction potentials for guanine and adenine to lower values than observed in RTILs where the scope for proton abstraction is not present. Such shifts are characteristic of so-called EC processes where reversible electron transfer is followed by a chemical reaction. © 2009 Elsevier B.V.

Laser-induced forward transfer of liquids: Study of the droplet ejection process

Laser-induced forward transfer (LIFT) is a laser direct-write technique that offers the possibility of printing patterns with a high spatial resolution from a wide range of materials in a solid or liquid state, such as conductors, dielectrics, and biomolecules in solution. This versatility has made LIFT a very promising alternative to lithography-based processes for the rapid prototyping of biomolecule microarrays. Here, we study the transfer process through the LIFT of droplets of a solution suitable for microarray preparation. The laser pulse energy and beam size were systematically varied, and the effect on the transferred droplets was evaluated. Controlled transfers in which the deposited droplets displayed optimal features could be obtained by varying these parameters. In addition, the transferred droplet volume displayed a linear dependence on the laser pulse energy. This dependence allowed determining a threshold energy density value, independent of the laser focusing conditions, which acted as necessary conditions for the transfer to occur. The corresponding sufficient condition was given by a different total energy threshold for each laser beam dimension. The threshold energy density was found to be the dimensional parameter that determined the amount of the transferred liquid per laser pulse, and there was no substantial loss of material due to liquid vaporization during the transfer.

Time-resolved imaging of the laser forward transfer of liquids

Time-resolved imaging is carried out to study the dynamics of the laser-induced forward transfer of an aqueous solution at different laser fluences. The transfer mechanisms are elucidated, and directly correlated with the material deposited at the analyzed irradiation conditions. It is found that there exists a fluence range in which regular and well-defined droplets are deposited. In this case, laser pulse energy absorption results in the formation of a plasma, which expansion originates a cavitation bubble in the liquid. After the further expansion and collapse of the bubble, a long and uniform jet is developed, which advances at a constant velocity until it reaches the receptor substrate. On the other hand, for lower fluences no material is deposited. In this case, although a jet can be also generated, it recoils before reaching the substrate. For higher fluences, splashing is observed on the receptor substrate due to the bursting of the cavitation bubble. Finally, a discussion of the possible mechanisms which lead to such singular dynamics is also provided.

Effect of bacterial lipopolysaccharide on gastric emptying of liquids in rats

The objectives of the present investigation were 1) to study the effect of bacterial lipopolysaccharide (LPS) on rat gastric emptying (GE) and 2) to investigate a possible involvement of the vagus nerve in the gastric action of LPS. Endotoxin from E. coli (strain 055:B5) was administered sc, ip or iv to male Wistar rats (220-280 g body weight) at a maximum dose of 50 µg/kg animal weight. Control animals received an equivalent volume of sterile saline solution. At a given time period after LPS administration, GE was evaluated by measuring gastric retention 10 min after the orogastric infusion of a test meal (2 ml/100 g animal weight), which consisted of 0.9% NaCl plus the marker phenol red (6 mg/dl). One group of animals was subjected to bilateral subdiaphragmatic vagotomy or sham operation 15 days before the test. A significant delay in GE of the test meal was observed 5 h after iv administration of the endotoxin at the dose of 50 µg/kg animal weight. The LPS-induced delay of GE was detected as early as 30 min and up to 8 h after endotoxin administration. The use of different doses of LPS ranging from 5 to 50 µg/kg animal weight showed that the alteration of GE was dose dependent. In addition, vagotomized animals receiving LPS displayed a GE that was not significantly different from that of the sham control group. However, a participation of the vagus nerve in LPS-induced delay in GE could not be clearly demonstrated by these experiments since vagotomy itself induced changes in this gastric parameter. The present study provides a suitable model for identifying the mechanisms underlying the effects of LPS on gastric emptying

Gastric emptying of liquids in rats dehydrated by water deprivation

The gastric emptying of liquids was investigated in male Wistar rats (8 to 10 weeks old, 210-300 g) dehydrated by water deprivation. In this model of dehydration, weight loss, hematocrit and plasma density were significantly higher in the dehydrated animals than in the control groups after 48 and 72 h of water deprivation (P<0.05). Three test meals (saline (N = 10), water (N = 10) and a WHO rehydrating solution containing in one liter 90 mEq sodium, 20 mEq potassium, 80 mEq chloride and 30 mEq citrate (N = 10)) were used to study gastric emptying following water deprivation for 24, 48 and 72 h. After 72 h, gastric emptying of the water (39.4% retention) and rehydrating solution (49.2% retention) test meals was significantly retarded compared to the corresponding control groups (P<0.05, Mann-Whitney test). The 72-h period of deprivation was used to study the recovery from dehydration, and water was supplied for 60 or 120 min after 67 h of deprivation. Body weight loss, hematocrit and plasma density tended to return to normal when water was offered for 120 min. In the animals supplied with water for 60 min, there was a recovery in the gastric emptying of water while the gastric emptying of the rehydrating solution was still retarded (53.1% retention; P<0.02, Kruskal-Wallis test). In the group supplied with water for 120 min, the gastric emptying of the rehydrating (51.7% retention) and gluco-saline (46.0% retention) solutions tended to be retarded (P = 0.04, Kruskal-Wallis test). In this model of dehydration caused by water deprivation, with little alteration in the body electrolyte content, gastric emptying of the rehydrating solution was retarded after rehydration with water. We conclude that the mechanisms whereby receptors in the duodenal mucosa can modify gastric motility are altered during dehydration caused by water deprivation

Residence of liquids in the infra-junctional portion of the proximal stomach in patients with gastroesophageal reflux disease

Patients with gastroesophageal reflux disease may have disturbances of gastric motility, which could play a role in the pathophysiology of the disease. Recent studies have suggested that the gastric region just below the gastroesophageal junction may have a distinct physiological behavior. We determined whether patients with gastroesophageal reflux disease have abnormal residence of food in the infra-junctional portion of the stomach after ingesting a liquid nutrient meal. Fasted adult patients with reflux disease (N = 11) and healthy volunteers (N = 10) ingested a liquid meal (320 ml; 437 kcal) labeled with 99m technetium-phytate and their total gastric emptying half-time and regional emptying from the stomach infra-junctional region were determined. In 8 patients, episodes of postprandial acidic reflux to the esophagus were measured for 2 h using pH monitoring. There were no differences between reflux patients and controls regarding total gastric emptying time (median: 68 min; range: 39-123 min vs 65 min and 60-99 min, respectively; P > 0.50). Food residence in the infra-junctional area was similar for patients and controls: 23% (range: 20-30) vs 27% (range: 19-30%; P = 0.28) and emptying from this area paralleled total gastric emptying (Rs = 0.79; P = 0.04). There was no correlation between residence of food in the infra-junctional area and episodes of gastroesophageal reflux (Rs = 0.06; P = 0.88). We conclude that it is unlikely that regional motor disturbances involving the infra-junctional region of the stomach play a relevant role in the pathogenesis of acidic gastroesophageal reflux.

Prompt electron emission and collisional ionization of ambient gas during pulsed laser ablation of silver

A silver target kept under partial vacuum conditions was irradiated with focused nanosecond pulses at 1:06 mm from a Nd:YAG laser. The electron emission monitored with a Langmuir probe shows a clear twin-peak distribution. The first peak which is very sharp has only a small delay and it indicates prompt electron emission with energy as much as 60 5 eV. Also the prompt electron emission shows a temporal profile with a width that is same as that for the laser pulse whereas the second peak is broader, covers several microseconds, and represents the low-energy electrons (2 0:5 eV) associated with the laser-induced silver plasma as revealed by time-of-flight measurements. It has been found that prompt electrons ejected from the target collisionally excite and ionize ambient gas molecules. Clearly resolved rotational structure is observed in the emission spectra of ambient nitrogen molecules. Combined with time-resolved spectroscopy, the prompt electrons can be used as excitation sources for various collisional excitation–relaxation experiments. The electron density corresponding to the first peak is estimated to be of the order of 1017 cm?--3 and it is found that the density increases as a function of distance away from the target. Dependence of probe current on laser intensity shows plasma shielding at high laser intensities.

Twin peak distribution of electron emission profile and impact ionization of ambient molecules during laser ablation of silver target

Laser-induced plasma generated from a silver target under partial vacuum conditions using the fundamental output of nanosecond duration from a pulsed Nd:yttrium aluminum garnet laser is studied using a Langmuir probe. The time of flight measurements show a clear twin peak distribution in the temporal profile of electron emission. The first peak has almost the same duration as the laser pulse while the second lasts for several microseconds. The prompt electrons are energetic enough ('60 eV) to ionize the ambient gas molecules or atoms. The use of prompt electron pulses as sources for electron impact excitation is demonstrated by taking nitrogen, carbon dioxide, and argon as ambient gases.

Broadband coaxial cavity resonator for complex permittivity measurements of liquids

A novel cavity perturbation technique using coaxial cavity resonators for the measurement of complex permittivity of liquids is presented. The method employs two types of resonators (Resonator I and Resonator II). Resonator I operates in the frequency range 600 MHz-7 GHz and resonator II operates in the frequency range 4 GHz-14 GHz. The introduction of the capillary tube filled with the sample liquid into the coaxial resonator causes shifts in the resonance frequency and loaded Q-factor of the resonator. The shifts in the resonance frequency and loaded Q-factor are used to determine the real and imaginary parts of the complex permittivity of the sample liquid, respectively. Using this technique, the dielectric parameters of water and nitrobenzene are measured. The results are compared with those obtained using other standard methods. The sources of errors are analyzed.

Two-photon ionization of atomic inner-shells

Die Summation ueber des vollstaendige Spektrum des Atoms, die in der Stoehrungstheorie zweiter Ordnung vorkommt, wurde mit Hilfe der Greenschen Funktion Methode berechnet. Die Methode der Greenschen Funktion verlangt die Berechnung der unterschiedlichen Greenschen Funktionen: eine Coulomb-Greensche-Funktion im Fall von wasserstoffaehnlichen Ionen und eine Zentral-feld-Greensche-Funktion im Fall des Vielelektronen-Atoms. Die entwickelte Greensche Funktion erlaubte uns die folgenden atomaren Systeme in die Zweiphotonenionisierung der folgenden atomaren Systeme zu untersuchen: - wasserstoffaehnliche Ionen, um relativistische und Multipol-Effekte aufzudecken, - die aeussere Schale des Lithium; Helium und Helium-aehnliches Neon im Grundzustand, um taugliche Modelle des atomaren Feldes zu erhalten, - K- und L-Schalen des Argon, um die Vielelektronen-Effekte abzuschaetzen. Zusammenfassend, die relativistische Effekte ergeben sich in einer allgemeinen Reduzierung der Zweiphotonen Wirkungsquerschnitte. Zum Beispiel, betraegt das Verhaeltnis zwischen den nichtrelativistischen und relativistischen Wirkungsquerschnitten einen Faktor zwei fuer wasserstoffaehnliches Uran. Ausser dieser relativistischen Kontraktion, ist auch die relativistische Aufspaltung der Zwischenzustaende fuer mittelschwere Ionen sichtbar. Im Gegensatz zu den relativistischen Effekten, beeinflussen die Multipol-Effekte die totalen Wirkungsquerschnitte sehr wenig, so dass die Langwellennaeherung mit der exakten Naeherung fuer schwere Ionen sogar innerhalb von 5 Prozent uebereinstimmt. Die winkelaufgeloesten Wirkungsquerschnitte werden durch die relativistischen Effekte auf eine beeindruckende Weise beeinflusst: die Form der differentiellen Wirkungsquerschnitte aendert sich (qualitativ) abhaengig von der Photonenenergie. Ausserdem kann die Beruecksichtigung der hoeheren Multipole die elektronische Ausbeute um einen Faktor drei aendern. Die Vielelektronen-Effekte in der Zweiphotonenionisierung wurden am Beispiel der K- und L-Schalen des Argon analysiert. Hiermit wurden die totalen Wirkungsquerschnitte in einer Ein-aktives-Elektron-Naeherung (single-active-electron approximation) berechnet. Es hat sich herausgestellt, dass die Elektron--Elektron-Wechselwirkung sehr wichtig fuer die L-Schale und vernachlaessigbar fuer die K-Schale ist. Das bedeutet, dass man die totalen Wirkungsquerschnitte mit wasserstoffaehnlichen Modellen im Fall der K-Schale beschreiben kann, aber fuer die L-Schale fortgeschrittene Modelle erforderlich sind. Die Ergebnisse fuer Vielelektronen-Atome wurden mittels einer Dirac-Zentral-feld-Greenschen Funktion erlangt. Ein numerischer Algorithmus wurde urspruenglich von McGuire (1981) fuer der Schroedinger-Zentral-feld-Greensche Funktion eingefuehrt. Der Algorithmus wurde in dieser Arbeit zum ersten Mal fuer die Dirac-Gleichung angewandt. Unser Algorithmus benutzt die Kummer- und Tricomi-Funktionen, die mit Hilfe eines zuverlaessigen, aber noch immer langsamen Programmes berechnet wurden. Die Langsamkeit des Programms begrenzt den Bereich der Aufgaben, die effizient geloest werden koennen. Die Zentral-feld-Greensche Funktion konnte bei den folgenden Problemen benutzt werden: - Berechnung der Zweiphotonen-Zerfallsraten, - Berechnung der Zweiphotonenanregung und -ionisierungs-Wirkungsquerschnitte, - Berechnung die Multiphotonenanregung und -ionisierungs-Wirkungsquerschnitte, - Berechnung einer atomaren Vielelektronen-Green-Funktion. Von diesen Aufgaben koennen nur die ersten beiden in angemessener Zeit geloest werden. Fuer die letzten beiden Aufgaben ist unsere Implementierung zu langsam und muss weiter verbessert werden.

Intrinsic channel closing in strong-field single ionization of H2

Die Ionisation von H2 in intensiven Laserpulsen wird mit Hilfe der numerischen Integration der zeitabhängigen Schrödingergleichung für ein Einelektronenmodell untersucht, das die Vibrationsbewegung berücksichtigt. Die Spektren der kinetischen Elektronenenergie hängen stark von der Vibrationsquantenzahl des erzeugten H2+ Ions ab. Für bestimmte Vibrationszustände ist die Ausbeute der Elektronen in der Mitte des Plateaus stark erhöht. Der Effekt wird "channel closings" zugeschrieben, die in Atomen durch Variation der Laserintensität beobachtet wurden. The ionization of H2 in intense laser pulses is studied by numerical integration of the time-dependent Schrödinger equation for a single-active-electron model including the vibrational motion. The electron kinetic energy spectra in high-order above-threshold ionization are strongly dependent on the vibrational quantum number of the created H2+ ion. For certain vibrational states, the electron yield in the mid-plateau region is strongly enhanced. The effect is attributed to channel closings, which were previously observed in atoms by varying the laser intensity.

High laser field effects in multiphoton ionization of Na_2

Femtosecond pump/probe multiphoton ionization experiments on Na_2 molecules are performed. The dependence of the total Na^+_2 ion signal on the delay time and the intensity of the femtosecond laser pulses is studied in detail. It is observed that molecular vibrational wavepacket motion in different electronic states dominates the time dependence of the ion signal. For higher laser intensities the relative contributions from the A ^1 \summe^+_u and the 2 ^1 \produkt__g states change dramatically, indicating the increasing importance of a two-electron versus a one-electron process. For even stronger fields (10 ^12 W/ cm²) a vibrational wavepacket in the electronic ground state X ^1 \summe^+_g is formed and its dynamics is also observed in the transient Na^+_2 signal. Time-dependent quantum calculations are presented. The theoretical results agree well with the experiment.

Dissociative electron impact ionization of N2O5

Electron impact ionization of dinitrogen pentoxide for incident electron energies up to about 25 eV has been investigated by use of a crossed beams quadrupole mass spectrometer system. The experiments reported in this paper detected the fragmentation products NO2+, NO+, O+, N+, and NO3+. No stable N2O5+ ion was observed. The NO3+ fragment, for which we determine an appearance energy 13.25 +/- 0.30 ev, has not been observed previously. This appearance energy is close to the calculated threshold.

Photoassociative ionization of cold Na atoms: repulsive levels effects on the ion production rate

We have revisited photoassociative ionization (PAI) in a cold sample of Na atmos. A two-color experiment was performed ina magneto-optical trap through the addition of aprobe laser. The observation of a marked change in the PAI rate for a definite frequency range can be attributed to the influence of repuisive levels and a possible avoided crossing between long-range molecular levels. (c) 2009 by Astro Ltd. Published exclusively by WLLEY-VCH Verlag GmbH & Co. KGaA

The photothermal transparent transducer method applied to the spectroscopy of liquids

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)