O_{2}

In CO_{2}-rich atmospheres that are always exposed to ionizing radiation (e.g., Venus and Mars), every fragmentation process can significantly impact the inventory of moieties present in these environments. Nevertheless, the production of O_{2}^{+} ions as a direct result of CO_{2} fragmentation has never been quantified so far. Since molecular oxygen is considered as a potential trace of living organisms, nonbiotic pathways for its production must be known. In this work, O_{2}^{+} coming from CO_{2} fragmentation by electron impact is unambiguously identified and measured in absolute scale.

Adolescents' perception of dietary behaviour in a public school in Chile: a focus groups study.

BACKGROUND: The objective of this study was to assess dietary behavior among sixth- to eighth-grade students to inform the delivery and content of nutrition education. METHODS: This was a qualitative study through focus groups. Subjects were 57 adolescents 10-14 years old, 30 males and 27 females distributed in six groups. To compare group responses, transcriptions were coded using the original question guide. The information was analyzed using the content analysis technique. RESULTS: The main findings showed that adolescents knew dietary guidelines, but they consumed non-healthy food. They liked to cook but preferred fast food preparations. They increased fast food consumption on weekends and with friends. In utilization of Information Communication Technologies (ICT), all students had access to technology through mobile phones, tablets and computers and were open to have an interactive program with personal information about diet and behavior. CONCLUSIONS: Adolescents dietary behavior is not healthy and can be changed with interactive programs considering participation, personal information and utilizing ICT.

Three-Body Fragmentation from Single Ionization of Water by Electron Impact: The Role of Satellite States.

Ionization of water with energy transfers close to the 2a1 inner valence orbital is accompanied by a fast electronic rearrangement driven by electron relaxation and electron-electron correlations. Quasi-degenerate single vacancy and satellites one-electron-two-vacancies excited states in outer shells are created and leave their fingerprints in the three-body fragmentation pattern. Single vacancy states have been associated with Auger decay and double ionization. Satellite excited states are here convincingly assigned to single ionization. We focus on the H0 + O+ + H0 fragmentation by electron impact taking advantage of the high sensitivity of the delayed extraction time-of-flight technique to uncover kinematic attributes of suprathermal O+ ions. It is found that the H0 ejections occur under a large angular rearrangement, in an approximate linear geometry, and leaving the O+ near at rest, with ∼50% of the O+ produced in water fragmentation by swift electrons presenting this feature.

A novel double-focusing time-of-flight mass spectrometer for absolute recoil ion cross sections measurements.

In this work, the inclusion of an Einzel-like lens inside the time-of-flight drift tube of a standard mass spectrometer coupled to a gas cell-to study ionization of atoms and molecules by electron impact-is described. Both this lens and a conical collimator are responsible for further focalization of the ions and charged molecular fragments inside the spectrometer, allowing a much better resolution at the time-of-flight spectra, leading to a separation of a single mass-to-charge unit up to 100 a.m.u. The procedure to obtain the overall absolute efficiency of the spectrometer and micro-channel plate detector is also discussed.

Síndrome general y dolores óseos en un paciente tratado con tenofovir / General and bone pain syndrome in a patient treated with tenofovir

El tenofovir (TDF), es el único inhibidor de la transcriptasa inversa análogo nucleótido para el tratamiento de la infección por virus de la inmunodeficiencia humana (VIH). Ocasionalmente, puede producir insuficiencia renal aguda y síndrome de Fanconi. Presentamos el caso de un varón de 64 años con infección por VIH conocida desde hace 22 años, en tratamiento con tenofovir. En las revisiones ambulatorias refería un cuadro progresivo de astenia y dolores óseos difusos. En varias determinaciones se había observado una elevación de la fosfatasa alcalina y la paratohormona (PTH). Durante el último mes empeoró su estado, por lo que fue ingresado en el hospital. Entre los datos analíticos destacaban: glucosuria marcada, hipofosfatemia, hiperfosfaturia e hipouricemia. Todas las alteraciones se resolvieron tras suspender el TDF, lo que ilustra la importancia de que los clínicos incluyan la posibilidad de tubulopatía proximal por TDF en pacientes con dolores óseos, síndrome general o alteraciones del metabolismo mineral (AU)

Tenofovir (TDF), is the only nucleotide analogue reverse transcriptase inhibitor for treating human immunodeficiency virus (HIV). Occasionally, it may cause acute renal failure and Fanconi syndrome. We report the case of a 64-year-old male diagnosed with HIV infection 22 years previous and treated with tenofovir. In outpatient follow-up, the patient complained of progressive fatigue and diffuse aching bones. In several check-ups, increased alkaline phosphatase and parathyroid hormone (PTH) were observed. Over the past month, his condition worsened and he was admitted to hospital. Analytical data included marked glycosuria, hypophosphatemia, hyperphosphaturia and hypouricemia. All changes were resolved when TDF was discontinued.This illustrates the importance of clinical evaluations that include possible TDF-induced proximal tubulopathy in patients with general bone pain syndrome or mineral metabolism disturbances (AU)

Absolute cross sections for O2 dication production by electron impact.

Direct detection of homonuclear diatomic dications using mass spectrometry has the intrinsic inability to distinguish between fragments with the same mass-to-charge ratio, as is the case of the oxygen molecule. In this work, absolute cross sections for the double ionization of the homoisotopic (16)O2 molecule by electron impact, in the 30-400 eV energy range, is reported for the first time, and show significant discrepancies with previous results, obtained with the heteroisotopic (16)O(17)O. The measurements suggest that O2 (++) is mainly produced through post-collisional Auger-like deexcitation.

Ionization and fragmentation of methane induced by 40 eV to 480 eV synchrotron radiation: from valence to beyond core electron ionization.

Photoionization and fragmentation of gaseous methane induced by tunable synchrotron radiation were investigated in a wide energy range, from 40 eV up to 480 eV. We report electron-ion coincidence experiments by measuring the relative partial-ion yields and precursor-specific relative yields for individual fragment ions and for ion fragment pairs as a function of photon energy. The fragmentation patterns are discussed with emphasis on the transition behavior of the bond breaking reactions and of the hydrogen rearrangements from valence to core electron ionization. Below the C 1s threshold, a comparison between photon induced dissociation and electron impact data showed that the ionic fragments formation depends for both projectiles on the same final electronic state reached upon ionization.

Fragmentation and plasmid strand breaks in pure and gold-doped DNA irradiated by beams of fast hydrogen atoms.

The results of an investigation into the damage caused to dry plasmid DNA after irradiation by fast (keV) hydrogen atoms are presented. Agarose gel electrophoresis was used to assess single and double strand break yields as a function of dose in dry DNA samples deposited on a mica substrate. Damage levels were observed to increase with beam energy. Strand break yields demonstrated a considerable dependence on sample structure and the method of sample preparation. Additionally, the effect of high-Z nanoparticles on damage levels was investigated by irradiating DNA samples containing controlled amounts of gold nanoparticles. In contrast to previous (photonic) studies, no enhancement of strand break yields was observed with the particles showing a slight radioprotective effect. A model of DNA damage as a function of dose has been constructed in terms of the probability for the creation of single and double strand breaks, per unit ion flux. This model provides quantitative conclusions about the effects of both gold nanoparticles and the different buffers used in performing the assays and, in addition, infers the proportion of multiply damaged fragments.

Synthesis and analytical follow-up of the mineralization of a new fluorosurfactant prototype.

Fluorinated surfactants have become essential in numerous technical applications due to their unparalleled effectiveness and efficiency. The environmental persistence of the non-biodegradable perfluorinated alkyl moiety has become a matter of concern. Therefore, it was searched for new molecules with chemically stable fluorinated end groups which can be microbially transformed into labile fluorinated substances. One prototype substance, 10-(trifluoromethoxy)decane-1-sulfonate, has shown biomineralization. Monitoring the formation of metabolites over time elucidated the mechanism of biotransformation. Analysis was performed utilizing liquid chromatography-single quadrupole mass spectrometry (LC-MS) and quadrupole-time of flight tandem mass spectrometry (QqTOF-MS). It was possible to distinguish between two major degradation pathways of the fluorinated alkylsulfonate derivative: (i) a desulfonation and subsequent oxidation and degradation of the alkyl chain being predominant and (ii) an insertion of oxygen with a subsequent cleavage and degradation of the molecule. The utilized trifluoromethoxy-endgroup resulted in instable trifluoromethanol after degradation of the alkyl chain, which led to a high degree of mineralization of the molecule.

Water fragmentation and energy loss by carbon ions at the distal region of the Bragg peak.

Time-of-flight mass spectrometry was used to investigate fragmentation and energy transfer processes in water by C ions at the distal part of the Bragg peak. Measurements of the positive ion fragments from ionization, electron capture, electron loss, transfer-loss and loss-ionization channels have allowed us for the first time (a) to obtain a quantitative determination of the energy lost by C ions in water and (b) to show that total water fragment ion production has a much flatter profile with projectile energy than would be expected if the water radical formation was assumed to follow the energy-loss profile obtained from available stopping power models.

Fragmentation of water by heavy ions.

Absolute cross sections for fragmentation of water molecules by C3+ and O5+ ions over an energy region where the Bragg peak maximizes were measured for ionization, electron capture, and electron loss channels. A collision regime where sigmaSigmaOq+> or =sigmaH2O+ was reached for the first time, producing large abundances of H+ and O+ fragments in comparison to proton impact. Our findings have straightforward implications in the subsequent fast chemistry at the ionization site and on the O production in the first stages of water radiolysis. An unexpected channel-independent relationship between the cross sections for the fragmentation products, which is also approximately independent of the particle type, energy, and charge state, is found. A model is presented to explain such behavior allowing the cross sections of all fragmentation products to be obtained from single and double electron removal cross sections.

Effective strength of the electron-electron interaction in simultaneous projectile and target ionization.

The determination of the right balance between the strong-field interaction of the screened target nucleus and the two-center electron-electron interaction has been controversial since the early attempts to describe the stripping of light, swift ions, by heavy targets. In this work, we find a region of influence for the electron-electron contribution which clearly indicates that this interaction is an essential contribution to the stripping process for both light and heavy targets.

Changes in Saccharomyces cerevisiae development induced by magnetic fields.

Saccharomyces cerevisiae cultures exposed to 110 mT and 220 mT steady magnetic fields (SMF) were studied to observe eventual induced growth alterations and changes in metabolic activity. Cell mass (biomass) growth was evaluated by light spectrometry, and metabolic alterations were estimated on the basis of the CO2 pressure produced and by the culture media pH changes, measured at the beginning and the end of the observation. The yeast strain DAUFPE-1012, cultivated in a nonaerated liquid agar Sabouraud glucose medium, was exposed to SMF generated by NdFeBr magnets. Results showed alterations induced by 220 mT SMF as an increment in cell proliferation (1.84%) and an increased CO2 production (36.1%) as compared to control groups. Furthermore, the initial-to-final pH difference in 220 mT SMF exposed cultures was higher than the 110 mT SMF and the control values. The whole acidification and the rise in CO2 production observed after 220 mT SMF exposure did not correspond to the biomass growth values, as compared to the other cultures, and was apparently provoked by a enhancement in the cellular metabolic rate. This technique becomes very promising for future biotechnological applications in fermentative processes.

Asymmetric Pauson-Khand reactions using camphor-derived chelating thiols as chiral controllers.

A convenient procedure for the preparation of enantiopure 10-(R-thio)-2-exo-bornanethiols from (1S)-camphor-10-thiol has been developed. The ethynyl derivatives of these thiols gave excellent diastereoselectivities (up to 98:2) in Pauson-Khand reactions with norbornene and norbornadiene through the intermediacy of a chelated dicobalt pentacarbonyl complex. Thermal reaction conditions starting from the preformed chelated complex gave better results than N-oxide-promoted runs with in situ generation of the chelated intermediate. The corresponding adducts have been elaborated through a protocol consisting of conjugate addition, samarium iodide-promoted cleavage of the chiral auxiliary, and retro-Diels-Alder reaction to afford 4-substituted 2-cyclopentenones in high enantiomeric purity.

Mutants blocked in penicillin biosynthesis show a deletion of the entire penicillin gene cluster at a specific site within a conserved hexanucleotide sequence.

The organization of the genes of the penicillin cluster has been studied in three different mutants of P. chrysogenum impaired in penicillin biosynthesis. The three blocked mutants (derived from the parental strain P. chrysogenum Bb-1) lacked the genes pcbAB, pcbC and penDE of the penicillin biosynthetic pathway and were unable to form isopenicillin N synthase and isopenicillin N acyltransferase. All strains were identified as P. chrysogenum derivatives by fingerprinting analysis with (GTG)n as a probe. The borders of the deleted region were cloned and sequenced, showing the same junction point in the three mutants. The deleted DNA region was found to be identical to that described in P. chrysogenum npe10. The frequent deletion of the pen gene cluster at this point may indicate that this cluster is located in an unstable genetic region, flanked by hot spots of recombination, that is easily lost by mutagen-induced recombination.

Molecular characterization of three loss-of-function mutations in the isopenicillin N-acyltransferase gene (penDE) of Penicillium chrysogenum.

Five mutants of Penicillium chrysogenum blocked in penicillin biosynthesis (npe) which are deficient in isopenicillin N-acyltransferase were isolated previously. Three of these mutants, npe6, npe7, and npe8, have been characterized at the molecular level and compared with npe10, a deletion mutant. Transcripts of normal size (1.15 kb) of the penDE genes, which encode isopenicillin N-acyltransferase, and also of the pcbAB (11.5 kb) and pcbC (1.1 kb) genes were observed in all mutants except for the npe10 mutant. Immunoblotting studies using antibodies against isopenicillin N-acyltransferase showed that all mutants (except npe10) formed the 40-kDa (unprocessed) protein and the 29-kDa subunit of the isopenicillin N-acyltransferase. The 11-kDa subunit could not be observed in the immunoblots. The mutant penDE genes of strains npe6, npe7, and npe8 were cloned and sequenced. These three strains showed a mutation in the penDE genes which results in a single amino acid change in each modified isopenicillin N-acyltransferase. The mutation in npe6 resulted in a change of Gly-150 to Val, whereas the mutation in both npe7 and npe8 introduced a change of Glu-258 to Lys. Replacement of the Val-150 and Lys-258 mutations by constructing hybrid isopenicillin N-acyltransferase molecules led to the recovery of the isopenicillin N-acyltransferase activity. The mutations in npe6, npe7, and npe8 do not affect the ability of the 40-kDa isopenicillin N-acyltransferase to be processed into the component subunits.

Catabolism of lysine in Penicillium chrysogenum leads to formation of 2-aminoadipic acid, a precursor of penicillin biosynthesis.

Penicillium chrysogenum L2, a lysine auxotroph blocked in the early steps of the lysine pathway before 2-aminoadipic acid, was able to synthesize penicillin when supplemented with lysine. The amount of penicillin produced increased as the level of lysine in the media was increased. The same results were observed in resting-cell systems. Catabolism of [U-14C]lysine by resting cells and batch cultures of P. chrysogenum L2 resulted in the formation of labeled saccharopine and 2-aminoadipic acid. Formation of [14C]saccharopine was also observed in vitro when cell extracts of P. chrysogenum L2 and Wis 54-1255 were used. Saccharopine dehydrogenase and saccharopine reductase activities were found in cell extracts of P. chrysogenum, which indicates that lysine catabolism may proceed by reversal of the two last steps of the lysine biosynthetic pathway. In addition, a high lysine:2-ketoglutarate-6-aminotransferase activity, which converts lysine into piperideine-6-carboxylic acid, was found in cell extracts of P. chrysogenum. These results suggest that lysine is catabolized to 2-aminoadipic acid in P. chrysogenum by two different pathways. The relative contribution of lysine catabolism in providing 2-aminoadipic acid for penicillin production is discussed.

The isopenicillin-N acyltransferase of Penicillium chrysogenum has isopenicillin-N amidohydrolase, 6-aminopenicillanic acid acyltransferase and penicillin amidase activities, all of which are encoded by the single penDE gene.

The isopenicillin-N acyltransferase of Penicillium chrysogenum catalyzes the conversion of the biosynthetic intermediate isopenicillin N to the hydrophobic penicillins. The isopenicillin-N acyltransferase copurified with the acyl-CoA:6-aminopenicillanic acid (6-APA) acyltransferase activity which transfers an acyl residue from acyl-CoA derivatives (e.g. phenylacetyl-CoA, phenoxyacetyl-CoA) to 6-APA. Other thioesters of phenylacetic acid were also used as substrates. An amino acid sequence similar to that of the active site of thioesterases was found in the isopenicillin-N acyltransferase, suggesting that this site is involved in the transfer of phenylacetyl residues from phenylacetyl thioesters. Purified isopenicillin-N acyltransferase also showed isopenicillin-N amidohydrolase, penicillin transacylase and penicillin amidase activities. The isopenicillin-N amidohydrolase (releasing 6-APA) showed a much lower specific activity than the isopenicillin-N acyltransferase of the same enzyme preparation, suggesting that in the isopenicillin-N acyltransferase reaction the 6-APA is not released and is directly converted into benzylpenicillin. Penicillin transacylase exchanged side chains between two hydrophobic penicillin molecules; or between one penicillin molecule and 6-APA. The penicillin amidase activity is probably the reverse of the biosynthetic acyl-CoA:6-APA acyltransferase. Four P. chrysogenum mutants deficient in acyl-CoA:6-APA acyltransferase lacked the other four related activities. Transformation of these mutants with the penDE gene restored all five enzyme activities.

Resolution of chromosomes III and VI of Aspergillus nidulans by pulsed-field gel electrophoresis shows that the penicillin biosynthetic pathway genes pcbAB, pcbC, and penDE are clustered on chromosome VI (3.0 megabases).

An improved electrophoretic molecular karyotype of Aspergillus nidulans ATCC 28901 has been obtained by contour-clamped electric field gel electrophoresis, which separates seven chromosomal bands and allows resolution of chromosomes III and VI. The three genes of the penicillin biosynthetic pathway, pcbAB, pcbC, and penDE, encoding alpha-aminoadipyl-cysteinyl-valine synthetase, isopenicillin N synthase, and isopenicillin N acyltransferase, respectively, are clustered together on a chromosome of 3.0 Mg, corresponding to linkage group VI, whereas the argB gene was located on a chromosome of 3.4 Mb, corresponding to linkage group III. Three other strains of A. nidulans contained a modified chromosome III of about 3.1 Mb that overlaps with chromosome VI, forming a doublet. Resolution of chromosomes III and VI in strain ATCC 28901 allowed unequivocal mapping of the penicillin gene cluster on chromosome VI of A. nidulans.

Characterization of the Cephalosporium acremonium pcbAB gene encoding alpha-aminoadipyl-cysteinyl-valine synthetase, a large multidomain peptide synthetase: linkage to the pcbC gene as a cluster of early cephalosporin biosynthetic genes and evidence of multiple functional domains.

A 24-kb region of Cephalosporium acremonium C10 DNA was cloned by hybridization with the pcbAB and pcbC genes of Penicillium chrysogenum. A 3.2-kb BamHI fragment of this region complemented the mutation in the structural pcbC gene of the C. acremonium N2 mutant, resulting in cephalosporin production. A functional alpha-aminoadipyl-cysteinyl-valine (ACV) synthetase was encoded by a 15.6-kb EcoRI-BamHI DNA fragment, as shown by complementation of an ACV synthetase-deficient mutant of P. chrysogenum. Two transcripts of 1.15 and 11.4 kb were found by Northern (RNA blot) hybridization with probes internal to the pcbC and pcbAB genes, respectively. An open reading frame of 11,136 bp was located upstream of the pcbC gene that matched the 11.4-kb transcript initiation and termination regions. It encoded a protein of 3,712 amino acids with a deduced Mr of 414,791. The nucleotide sequence of the gene showed 62.9% similarity to the pcbAB gene encoding the ACV synthetase of P. chrysogenum; 54.9% of the amino acids were identical in both ACV synthetases. Three highly repetitive regions occur in the deduced amino acid sequence of C. acremonium ACV synthetase. Each is similar to the three repetitive domains in the deduced sequence of P. chrysogenum ACV synthetase and also to the amino acid sequence of gramicidin synthetase I and tyrocidine synthetase I of Bacillus brevis. These regions probably correspond to amino acid activating domains in the ACV synthetase protein. In addition, a thioesterase domain was present in the ACV synthetases of both fungi. A similarity has been found between the domains existing in multienzyme nonribosomal peptide synthetases and polyketide and fatty acid synthetases. The pcbAB gene is linked to the pcbC gene, forming a cluster of early cephalosporin-biosynthetic genes.