Production of Hydronium Ion (H3O)+ and Protonated Water Clusters (H2O)nH+ after Energetic Ion Bombardment of Water Ice in Astrophysical Environments.

Water ice exists on many objects in space. The most abundant icy species, among them water, are present in the icy satellites of the outer Solar System giant planets. The nuclei of comets, which are mainly composed of water ice, give another example of its abundance. In the interstellar medium (ISM), ice mantles, formed by molecular species sticking on dust grains, consist mainly of water ice. All these objects are exposed to ionizing radiation like ions, UV photons, and electrons. Sputtering of atoms, molecules, ions, and radicals from icy surfaces may populate and maintain exospheres of icy objects in the Solar System. In other respects, ionized hydrides such as OH+, H2O+, and H3O+ have been detected in the gas phase in star-forming regions. Interactions with cosmic rays could be an additional explanation to the current models for the formation of those species. In fact, laboratory simulations showed that the main components of the sputtered ionic species from water ice are oxygen hydrides. In this work, water ice targets were irradiated at several temperatures (10-200 K) by 90 keV O6+ ions, yielding an electronic stopping power of about 12 eV/Å, when the nuclear stopping power is comparable to the electronic stopping power. Sputtering of secondary ions after bombardment of the ice target was analyzed by time-of-flight mass spectrometry (TOF-SIMS). Besides hydrogen ions (H+, H2+, H3+), also O+, O2+, OH+, (H2O)+, and clusters of (H2O)nH+ with n = 1-8 are emitted. Our results show a progressive yield decrease with increasing temperature of all of the detected species. This is related to the structure of the ice: the ionic sputtering yield for crystalline ice is much lower than for an amorphous ice. For instance, amorphous ice at 10 K exhibits a yield of the order of 2 × 10-6 secondary (H2O)nH+ hydride ions/projectile (with n = 1-8). As the temperature is increasing toward the phase transition to crystalline ice, the yields decrease by about one order of magnitude.

Thermal and energetic processing of ammonia and carbon dioxide bearing solid mixtures.

We present new experimental results on thermal and ion irradiation processing of frozen ammonia-carbon dioxide mixtures. Some mixtures were deposited at low temperatures (T ≈ 16 K). Upon warming up to 160 K, complex chemical reactions occur leading to the formation of new molecules and, in particular, of ammonium carbamate. We also show that the same species are produced when water is the dominant species in the ternary mixture with ammonia and carbon dioxide. The samples have been irradiated with 144 keV S(9+) ions at 16 K and 50 K. Also in this case, new chemical species are formed as e.g. ammonium formate, CO and OCN(-). The results are discussed in the light of their relevance to the chemical evolution of ices in the interstellar medium and in the solar system. In particular, we suggest searching for them among the gas phase species sublimating from grains around young stellar objects and from the cometary nuclei approaching the Sun.

Endogenous CO2 ice mixture on the surface of Europa and no detection of plume activity.

Jupiter's moon Europa has a subsurface ocean beneath an icy crust. Conditions within the ocean are unknown, and it is unclear whether it is connected to the surface. We observed Europa with the James Webb Space Telescope (JWST) to search for active release of material by probing its surface and atmosphere. A search for plumes yielded no detection of water, carbon monoxide, methanol, ethane, or methane fluorescence emissions. Four spectral features of carbon dioxide (CO2) ice were detected; their spectral shapes and distribution across Europa's surface indicate that the CO2 is mixed with other compounds and concentrated in Tara Regio. The 13CO2 absorption is consistent with an isotopic ratio of 12C/13C = 83 ± 19. We interpret these observations as indicating that carbon is sourced from within Europa.

The irradiation of ammonia ice studied by near edge x-ray absorption spectroscopy.

A vapor-deposited NH(3) ice film irradiated at 20 K with 150 eV photons has been studied with near-edge x-ray absorption fine structure (NEXAFS) spectroscopy at the nitrogen K-edge. Irradiation leads to the formation of high amounts (12%) of molecular nitrogen N(2), whose concentration as a function of the absorbed energy has been quantified to 0.13 molecule/eV. The stability of N(2) in solid NH(3) has been also studied, showing that N(2) continuously desorbs between 20 and 95 K from the irradiated ammonia ice film. Weak concentrations (<1%) of other photoproducts are also detected. Our NEXAFS simulations show that these features own to NH(2), N(2)H(2), and N(3)(-).

Photolysis of Cometary Organic Dust Analogs on the EXPOSE-R2 Mission at the International Space Station.

We describe the results obtained on a set of organic samples that have been part of the experiment "Photochemistry on the Space Station (PSS)" on the EXPOSE-R2 mission conducted on the EXPOSE-R facility situated outside the International Space Station (ISS). The organic samples were prepared in the Catania laboratory by 200 keV He+ irradiation of N2:CH4:CO icy mixtures deposited at 17 K, on vacuum UV (VUV) transparent MgF2 windows. This organic material contains different chemical groups, including triple CN bonds, that are thought to be of interest for astrobiology. It is widely accepted that materials similar to that produced in the laboratory by ion irradiation of frozen ices could be present in some astrophysical environments such as comets. Once expelled from comets, these materials are exposed to solar radiation during their interplanetary journey. In the young Solar System, some of these processed materials could have reached early Earth and contributed to its chemical and prebiotic evolution. The samples were exposed for 16 months to the unshielded solar UV photons. It was found that, if an interplanetary dust particle (IDP) containing organic material (50% vol) is large enough (>20-30 µm), relevant chemical groups, such as those containing the CN triple bond, can survive for many years (>104 years) in the interplanetary medium.

Production of oxidants by ion irradiation of water/carbon dioxide frozen mixtures.

We present new experimental results on the formation of oxidants, such as hydrogen peroxide, ozone, and carbonic acid, under ion irradiation of icy mixtures of water/carbon dioxide at different ratios and temperatures (16 and 80 K). Pure water ice layers and mixtures with carbon dioxide were irradiated by 200 keV He+ ions. We found that the CO(2)/H(2)O ratio progressively decreased to a value of about 0.1, the H(2)O(2) production increased with increasing CO(2) abundance at both 16 and 80 K, and the CO and H(2)CO(3) production increased with increasing CO(2) abundance at 16 K. At 80 K, the synthesis of CO was less efficient because of the high volatility of the molecule that partially sublimed from the target. The production of carbonic acid was connected with the production of CO(3). O(3) was detected only after ion irradiation of CO(2)-rich mixtures. The experimental results are discussed with regard to the relevance they may have in the production of an energy source for a europan or a martian biosphere.

Cardiovascular effects of brain natriuretic peptide in essential hypertension.

We evaluated the cardiovascular effects of pathophysiological plasma levels of brain natriuretic peptide in seven patients with mild to moderate essential hypertension by performing equilibrium radionuclide angiocardiography at baseline and during brain natriuretic peptide infusion at increasing doses (4, 8, 10, and 12 pmol/kg per minute for 20 minutes each). Brain natriuretic peptide induced a progressive reduction of left ventricular end-diastolic volume (from 107.5 +/- 10.3 to 89.0 +/- 11.0 mL at the end of all infusion periods) and end-systolic volume, whereas stroke volume did not show any significant change (from 64.9 +/- 5.9 to 62.7 +/- 7.8 mL). Cardiac output, arterial pressure, and peripheral vascular resistance did not change significantly. The lack of effects on systemic hemodynamics was probably due to compensatory activation of the sympathetic nervous system, as indicated by the significant increase in plasma norepinephrine levels (from 1.75 +/- 0.18 to 2.19 +/- 0.21 nmol/L), heart rate (from 68 +/- 6 to 81 +/- 6 beats per minute), peak ejection rate, and peak filling rate. These results indicate that brain natriuretic peptide, at the pathophysiological plasma concentrations reached in this study, influences cardiovascular homeostasis mainly by reducing cardiac preload.

Acute effects of physiological increments of brain natriuretic peptide in humans.

To investigate the effects of physiological increases in plasma brain natriuretic peptide concentration in humans, we studied six healthy volunteers who received incremental infusions (0.25 pmol/kg per minute in the first hour and 0.50 pmol/kg per minute in the second) of synthetic human brain natriuretic peptide-32 in a placebo-controlled, crossover study. Peptide plasma levels were 1.69 +/- 0.39 pmol/L at baseline and rose 1.5- and 3-fold with the lower and higher doses, respectively. These values were within the normal range and also comparable to those reported in patients with mild essential hypertension. The urinary excretion rate of cGMP also increased during brain natriuretic peptide infusion, indicating stimulation of natriuretic peptide receptors. Peptide administration induced a significant 1.7-fold increase in urinary sodium excretion without affecting renal plasma flow (para-aminohippurate clearance), glomerular filtration rate (creatinine clearance), and urine flow rate. Fractional proximal sodium reabsorption (lithium clearance method) was unchanged, and fractional distal sodium reabsorption significantly decreased. Brain natriuretic peptide caused no changes in arterial pressure, heart rate, hematocrit, and serum proteins, but it exerted an inhibitory effect on the renin-aldosterone axis, as indicated by the significant 50% or more decrease of plasma renin activity and urinary excretion rate of aldosterone. These results suggest that brain natriuretic peptide may be involved in the overall regulation of body fluid and cardiovascular homeostasis in humans, mainly through its natriuretic and endocrine effects.

Effects of calcitonin on limb blood vessels in human obstructive arterial disease.

To check the possibility of a vasoactive effect of calcitonin in man, the authors treated ten hospitalized patients (seven males and three females, mean age 66.3 +/- 3.24), suffering from obstructive arterial disease in the lower extremities, with 100 units M.R.C. i.m. daily, for a period of 15 days. Five patients presented Raynaud's phenomenon. Treatment (B) led to an improvement of subjective symptomatology and to the disappearance of Raynaud's phenomenon in comparison with symptoms before treatment (A) and after a placebo period of 15 days (C). With respect to instrumental parameters, calcitonin induced: a) a slight increase of segmental plethysmography values (height/width ratio of curves) if compared with A (p less than 0.05) and more significantly if compared with C (p less than 0.01 and less than 0.0125, from right and left sides, respectively); b) a small change in venous-occlusion plethysmography values, if compared with A and C, both in basal conditions and after the "ischaemic test"; c) a significantly lesser reduction of digital photoelectric plethysmography values (height/width ratio of curves) after the "cold test" in comparison with A (p less than 0.01, both on the second and on the third fingers of the right hand), as well as with C (p less than 0.01 and p less than 0.025, on the second and on the third fingers, respectively). The present investigation points out the vasoactive influence of calcitonin in human obstructive disease. Results show the improvement in collateral limb circulation and, above all, in the amount of cutaneous flow. Little information is available on the mechanism of this effect, for which only hypotheses can at present be advanced.

Thyroxine-binding globulin in elderly patients with hepatocellular carcinoma.

In order to evaluate the possible relevance of the increased serum levels of thyroxine binding globulin (TBG) in elderly patients with cirrhosis and hepatocellular carcinoma (HCC), TBG and alpha-fetoprotein (AFP) levels were measured in 3 groups: (i) 14 healthy subjects (mean age: 74 +/- 2 years); (ii) 15 patients with cirrhosis of the liver (mean age: 70 +/- 1 years); (iii) 17 patients with cirrhosis and HCC (mean age: 71 +/- 1 years). Both TBG and AFP levels were significantly higher (p < 0.01) in the patients with HCC, as compared to the healthy subjects or to the cirrhotic ones without HCC. The increased plasma TBG levels in cirrhotic patients with HCC is probably due to a derepression of the TBG gene in hepatocytes undergoing neoplastic transformation. The results suggest that TBG together with AFP may be of diagnostic value for the presence of HCC in aging patients with liver cirrhosis.

Ion irradiation: its relevance to the evolution of complex organics in the outer solar system.

Ion irradiation of carbon containing ices produces several effects among which the formation of complex molecules and even refractory organic materials whose spectral color and molecular complexity both depend on the amount of deposited energy. Here results from laboratory experiments are summarized. Their relevance for the formation and evolution of simple molecules and complex organic materials on planetary bodies in the external Solar System is outlined.

Organics produced by ion irradiation of ices: some recent results.

Some results, recently obtained from laboratory experiments of ion irradiation of ice mixtures containing H, C, N, and O, are here summarized. They are relevant to the formation and evolution of complex organics on interstellar dust, comets and other small bodies in the external Solar System. In particular the formation of CN-bearing species is discussed. Interstellar dust incorporated into primitive Solar System bodies and subsequently delivered to the early Earth, may have contributed to the origin of life. The delivery of CN-bearing species seems to have been necessary because molecules containing the cyanogen bond are difficult to be produced in an environment that is not strongly reducing as that of the early Earth probably was. Moreover we report on an ongoing research program concerning the interaction between refractory materials produced by ion irradiation of simple ices and biological materials (amino acids, proteins, cells).

Production and evolution of carbonaceous material by ion irradiation in space.

We review recent experimental studies concerning the evolution, driven by ion irradiation, of carbonaceous material from frozen gas to a refractory molecular solid. Under further irradiation the latter changes to a polymer-like material and ultimately to amorphous carbon. Most of the results have been obtained by "in situ" and remote IR and Raman spectroscopy. The results have been applied to demonstrate that molecular solids may be easily formed by irradiation of frozen mantles in dense interstellar clouds. Polymer-like material and amorphous carbons may result by further irradiation of organic mantles on grains in the diffuse interstellar medium. Those grains, during the aggregation to form extended bodies like comets (T-Tau phase of the Sun), are further modified. These latter are also irradiated, after the comet formation, during their long stay in the Oort cloud. In particular it has been suggested that comet may develop an ion-produced cometary organic crust that laboratory evidences show to be stable against temperature increases experienced during passages near the Sun. The comparison between the Raman spectra of some IDP (Interplanetary Dust Particles) and the Raman spectra of some ion-produced amorphous carbons, is also discussed.

[Reactivation of the allogenous component of experimental skin inflammation after exposure to ultraviolet rays]. / Riattivazione della componente algogena della flogosi cutanea sperimentale dopo esposizione a raggi ultravioletti.

The effects of U.V. radiation induced cutaneous erythema on an experimental inflammation focus in another part of the body have been studied. The skin inflammation caused by carbon dioxide snow was used as a model. The onset of erythema is followed by reactivation of the diminishing inflammation process. It is therefore deduced that such effects are transmitted humorally and that reactivation is caused by histamine circulation. Histamine is released locally from the U.V. induced erythema and, entering into the circulation, increased the permeability of the microvessels in the inflamed area. This sends inactive chemical mediators to the interstitial sector where the appropriate conditions for their activation exist.

[Reactivation of the algogenic component in experimental inflammation induced by histamine administration]. / Riattivazione della componente algogena nella flogosi sperimentalmente indotta dopo somministrazione di istamina.

The action of i.v. histamine on human skin inflammation experimentally induced with carbon dioxide snow in man is described. Histamine was injected when the skin reaction was on the wane to determine its possible reactivation of inflammation. Complete recrudescence of erythralgia was noted (reappearance of pain and of erythralgic halo, with a fresh spread of secondary hyperalgesia). It is felt that histamine was responsible. Its arrival to the reaction site through microvessels in a state of increased permeability during the remission of inflammation may be assumed to promote the passage of chemical mediators in the preactive stage from the vascular to the interstitial sector, and thus to pave the way for their activation.

Radiation chemistry of ices of planetological interest at low temperature.

We present the results of recent experiments on some physico-chemical effects induced by fast ion colliding with solids of relevance for the physics of planetary objects. The production of molecular solids, polymer-like materials and amorphous carbon by irradiation of frozen hydrocarbons and pentacene is discussed. We also report on a set of experimental results obtained irradiating methanol and water-methanol mixtures. Because of bombardment different species form. The techniques used for the analysis are "in situ" infrared (IR) and Raman spectroscopy. The experimental results are finally discussed in the light of their relevance for planetary physics.

Vibrational spectroscopy of ion-irradiated ices.

In the last 20 years we have studied some effects induced by fast ions (E approximately keV-MeV) impinging on solid materials (mainly ices) with a view to their astrophysical relevance. The main techniques used have been infrared and Raman spectroscopy. Here we review some of the results obtained so far concerning, in particular, the formation of new species not present in the original sample. When hydrocarbons are an important constituent of the target ion irradiation gives rise also to a refractory residue which is left over after warming up. In addition we present some preliminary results of a new study, still in progress, on the infrared properties of the organic residue formed after irradiation of an icy mixture with H-, C-, N- and O-bearing species. Furthermore we present the micro-Raman spectra of some fragments of Orgueil a carbonaceous chondrite meteorite. Some astrophysical applications of these laboratory results are also discussed.

[The effects of the acute administration of atrial natriuretic peptide on the mechanisms regulating diuresis and natriuresis in the essential hypertension patient]. / Effetti della somministrazione acuta di peptide atriale natriuretico su alcuni meccanismi di regolazione della diuresi e della natriuresi nell'iperteso essenziale.

The authors investigated the role of atrial natriuretic peptide (alpha-hANP 99-126) in essential hypertension by evaluating some hemodynamic and renal effects of acute peptide infusion (1 micrograms/kg for 1 min + 50 ng/kg for the following 20 min) in fourteen subjects: eight mild to moderate, untreated, essential hypertensives (EH) and six normotensive (N) controls, during 2 hour-clearance periods, the 1st after ANP infusion, the 2nd during placebo (PL) administration. The double-blind study was carried out after the patients had rested and fasted overnight. It showed no significant changes in heart rate (HR); instead, compared with placebo, mean blood pressure (MBP) decreased significantly in both groups, beginning from the 3rd min after ANP infusion was begun (N: PL = 87.04 +/- 1.7 mmHg, ANP = 80.9 +/- 3.7 mmHg, p less than 0.0001; EH: PL = 102.6 +/- 3.2 mmHg, ANP = 97.7 +/- 5.9 mmHg, p less than 0.01). Among the urinary parameters we considered, cyclic GMP (cGMP) increased after ANP infusion in all subjects (N: PL = 129.1 +/- 56.3 pmol/mL, ANP = 199.2 +/- 85.4 pmol/mL; EH: PL = 106.55 +/- 56.2 pmol/mL, ANP = 220.03 +/- 92.7 pmol/mL, p less than 0.05); diuresis showed a prompt and significant increase in EH (N: PL = 837 +/- 368 mL, ANP = 1066 +/- 340 mL; EH: PL = 713 +/- 286 mL, ANP = 1043 +/- 280 mL, p less than 0.005), and so did natriuresis (N: PL = 23 +/- 14.3 mEq/L, ANP = 33 +/- 14.6 mEq/L; EH: PL = 25.6 +/- 8.9 mEq/L, ANP = 41.9 +/- 13.8 mEq/L, p less than 0.01); urinary potassium excretion was significantly reduced in EH (N: PL = 18.7 +/- 12.9 mEq/L, ANP = 14.2 +/- 6.9 mEq/L; EH: PL = 16.5 +/- 7.9 mEq/L, ANP = 10.7 +/- 4.8 mEq/L, p less than 0.005), while no changes were noted in glomerular filtration rate (GFR), estimated as creatinine clearance, urinary magnesium, albumin and aldosterone excretion. To investigate other potential mechanisms involved in renal effects of ANP, the urinary excretion of both prostaglandins 6-cheto PGF1-alpha and thromboxane B2 (TXB2), and dopamine were studied. The results showed only a significant decrease of dopamine urinary excretion in EH after ANP administration (N: PL = 50.4 +/- 28.7 micrograms/L, ANP = 45.0 +/- 29.7 micrograms/L; EH: PL = 47.3 +/- 21.5 micrograms/L, ANP = 27.1 +/- 12.7 micrograms/mL, p less than 0.01).(ABSTRACT TRUNCATED AT 400 WORDS)