Calculation of electron interaction models in N2 and O2.

Cosmic rays have the potential to significantly affect the atmospheric composition by increasing the rate and changing the types of chemical reactions through ion production. The amount and states of ionization, and the spatial distribution of ions produced are still open questions for atmospheric models. To precisely estimate these quantities, it is necessary to simulate particle-molecule interactions, down to very low energies. Models enabling such simulations require interaction probabilities over a broad energy range and for all energetically allowed scattering processes. In this paper, we focus on electron interaction with the two most abundant molecules in the atmosphere, i.e., N2 and O2, as an initial step. A set of elastic and inelastic cross section models for electron transportation in oxygen and nitrogen molecules valid in the energy range 10 eV - 1 MeV, is presented. Comparison is made with available theoretical and experimental data and a reasonable good agreement is observed. Stopping power is calculated and compared with published data to assess the general consistency and reliability of our results. Good overall agreement is observed, with relative differences lower than 6% with the ESTAR database.

On the Formation of Interstellar CH- Anions: Exploring Mechanism and Rates for CH2 Reacting with H.

We present accurate ab initio calculations on the structural properties of a gas-phase reaction of possible interest for Saturn's outer atmosphere chemistry, in which the CH2 molecule has been detected. In the present study, that molecule is made to react with the H- anion to form the CH- species, one considered as a possible intermediate in ionic processes networks. The results indicate that this reaction is markedly exothermic and proceeds with the formation of an intermediate, which occurs via only a shallow barrier below the reagents and progresses directly to the product region. The corresponding rate coefficients of reactions are also computed by making use of the variational transition state theory modeling and found to efficiently lead to the formation of the final anion even at the lower temperatures of interstellar medium conditions.

Modeling Ionic Reactions at Interstellar Temperatures: The Case of NH2- + H2 ⇔ NH3 + H.

Structural features and enthalpy details are presented for the title reactions, both for the exothermic (forward) path to NH3 formation and for the endothermic (reverse) reaction to NH2- formation. Both pathways have relevance for the nitrogen chemistry in the interstellar medium (ISM). They are also helpful to document the possible role of H- in molecular clouds at temperatures well below room temperature. The structural calculations are carried out using different ab initio methods and are further employed to obtain the reaction rates down to the interstellar temperatures detected in earlier experiments. The reaction rates are obtained from the computed minimum energy path (MEP) using the variational transition-state theory (VTST) approach. The results indicate very good accord with experiment results at room temperature, while measured low temperature data down to 8 K are well described using an appropriately modified VTST approach. This is done by employing a temperature-dependent scaling, from room temperature conditions down to the lower ISM temperatures, which acknowledges the noncanonical behavior of the fast, barrierless exothermic reaction. The reasons for this behavior and the need for improving on the VTST method when used away from room temperatures are discussed.

Signature of surface periodicity in the electronic structure of Si(1 1 1)-(7 × 7).

The surface electronic structure of Si(1 1 1)-[Formula: see text] has been studied by angle-resolved photo electron spectroscopy. Replicas of the S 1 surface state are found in correspondence with several [Formula: see text] unit cells in the reciprocal space. This observation resolves in a direct way the long-standing dichotomy between the structural and electronic properties of the system previously discussed on the basis of the [Formula: see text] or [Formula: see text] R30° surface models.

A New Anisotropic Charge-Equilibration Method for Self-Assembly of Organics on Metal Surface: d-Alaninol on Cu(100).

The supramolecular chemistry at surfaces has been extensively studied by quantum and classical computational models in order to simulate and reproduce the correct energetics and structures of adsorbed molecules on surfaces at various coverages. We have developed a classical tool able to sample the configuration space overcoming the topological constraints of the standard classical molecular dynamics. Our model is based on the charge equilibration procedure combined with an anisotropic pairwise atomic interaction where an angular dependence, with respect to the metal surface, is explicitly taken into account. The d-alaninol molecule has been chosen as a prototype of a flexible and multifunctional chemical compound which can form manifold complex configurations upon absorption on a metal surface. A detailed analysis of molecular structures and energetics of partial and full coverage has been carried out. The experimental STM image of the monolayer is correctly reproduced by our calculations, indicating that this new approach represents a step forward in the efficient simulation of complex molecular self-assembly.

Formation of cyanopolyyne anions in the interstellar medium: the possible role of permanent dipoles.

The possibility of attaching near-threshold electrons to N-terminated carbon chains, like those observed in the outer envelopes of carbon-rich stars, is examined via accurate quantum chemistry orbital structures evaluation and quantum scattering analysis of the corresponding extra-electron wavefunctions at meV energies. It is shown that the differences in the signs and sizes of the permanent dipole moments which exist for both the neutral and anionic species of the C(n)N series of molecules play a significant role in suggesting or excluding possible energy paths to permanent anion formations of cyanopolyynes, for which the cases with n from 1 to 7 are examined in more detail.

A study of selected fragmentation paths of the ethyne dication: theory and experiment.

The fragmentation of the C(2)H(2)(2+) dication, formed upon inner shell ionization and the subsequent Auger decay, has been studied by means of Auger electron-ion and Auger electron-ion-ion coincidence spectroscopy at four different kinetic energies of the Auger electron. The experimental investigation of three fragmentation paths leading to the C(2)H(+)/H(+), C(2)(+)/H(+) and C(+)/H(+) pairs has been complemented by theoretical calculations of the Potential Energy Surfaces (PES). It is found that when the amount of internal energy of the dication increases this is mainly transferred into the kinetic energy of the fragments of the second step of the dissociation.

Enantioselective HF loss promoted by resonant two-photon ionization of supersonically expanded (R)-1-phenyl-2,2,2-trifluoroethanol clusters.

(R)-1-phenyl-2,2,2-trifluoroethanol and its hydrogen bonded adducts with achiral (water, tetrahydrofuran) and chiral solvent molecules ((R)- and (S)-butan-2-ol, (R)- and (S)-3-hydroxy-tetrahydrofuran) have been ionized by resonant two-photon absorption. The presence of photofragments, attributable to the occurrence of a hydrogen fluoride loss reaction, has been interpreted with the aid of theoretical predictions at the DFT level of theory with the inclusion of dispersive terms. The HF elimination process takes place by a mechanism involving the preliminary C(alpha)-H hydrogen transfer to an hydroxyl oxygen assisted by the solvent molecule which is followed by extrusion of the HF molecule. The calculated energy barriers depend on the type of solvent as well as on its configuration and are consistent with the observed fragmentation ratios.

Modelling neurotransmitter functions: a laser spectroscopic study of (1S,2S)-N-methyl pseudoephedrine and its complexes with achiral and chiral molecules.

Wavelength and mass resolved resonance-enhanced two photon ionization (R2PI) excitation spectra of (1S,2S)-N-methyl pseudoephedrine (MPE) and its complexes with several achiral and chiral solvent molecules, including water (W), methyl (R)-lactate (L(R)), methyl (S)-lactate (L(S)), (R)-2-butanol (B(R)), and (S)-2-butanol (B(S)), have been recorded after a supersonic molecular beam expansion and examined in the light of ab initio calculations. The spectral patterns of the selected complexes have been interpreted in terms of the specific hydrogen-bond interactions operating in the diastereomeric complexes, whose nature in turn depends on the structure and the configuration of the solvent molecule. The obtained results confirm the view that a representative neurotransmitter molecule, like MPE, "communicates" with the enantiomers of a chiral substrate through different, specific interactions. These findings can be regarded as a further contribution to modelling neurotransmitter functions in biological systems.

Growth hormone in inflammatory bowel disease.

Crohn's disease and ulcerative colitis are inflammatory diseases of the gastrointestinal tract characterized by chronic relapsing inflammation and catabolism. Growth hormone/insulin-like growth factor-I axis is important in inflammatory bowel disease, because of the effects on epithelial cell kinetics, collagen deposition and immunomodulation. The potential of growth hormone as a therapeutic option in inflammatory bowel disease has been proven in various clinical settings. Acquired growth hormone resistance in inflammatory bowel disease seems to be mediated by a combination of undernutrition and active inflammation. In particular, proinflammatory cytokines, such as TNF-a and interleukin-6, have been implicated as potential mediators of growth hormone resistance. The introduction of anti-TNF-alpha monoclonal antibodies has proven very efficacious in patients with inflammatory bowel disease. By reducing cytokines levels in inflammatory cells of intestinal mucosa, infliximab could interfere with cytokine-induced growth hormone resistance. Recent in vivo data have shown that acquired growth hormone resistance in patients with inflammatory bowel disease may be reversed after the administration of anti-TNF-alpha therapy.

Chiral clusters in a supersonic beam: R2PI-TOF spectroscopy of diastereomeric carboxylic esters/(R)-(+)-1-phenyl-1-propanol complexes.

Wavelength and mass resolved resonance-enhanced two photon ionization (R2PI) excitation spectra of (R)-(+)-1-phenyl-1-propanol (P(R)) and its complexes with some chiral esters, i.e. methyl lactates (L(R) and L(S)), methyl 3-hydroxybutyrates (H(R) and H(S)), and methyl 2-chloropropionates (C(R) and C(S)), have been recorded after a supersonic molecular beam expansion and interpreted in the light of DFT calculations. The spectral features of the selected complexes were found to depend on the nature of hydrogen-bond interactions within the diasteromeric complexes, whose intensity in turn depends upon the structure and the configuration of the estereal moiety. The study further confirms resonant two-photon ionization spectroscopy, coupled with time-of-flight mass resolution (R2PI-TOF), as an excellent tool for gathering valuable information on the interactive forces in molecular clusters and for the enantiodiscrimination of chiral molecules in the gas phase.

Neuroendocrinology of mood disorders.

The neuroendocrine system, which plays an important role in regulation of mood, is dysfunctional in patients suffering from mood disorders. In order to improve the quality of life for patients, additional research is needed to define clinical implications of neuroendocrine dysfunction in mood disorders. It would be important to define which specific hormonal responses that are blunted in affective disorders contribute to mood symptoms and which medications that normalize neuroendocrine function are conditioning the impact of mood symptoms. Consideration and evaluation of endocrine status result important in psychiatric patients, both to ensure proper diagnosis and adequate treatment.

Laser plasma spectroscopy of Al-Cu-Fe quasicrystal an d alloy.

Electron number density and temperature were determined from laser-induced plasmas produced by irradiating Al-Cu-Fe targets of a quasicrystal and of an alloy of similar composition. The Al(I) atomic emission spectra of the two systems were measured as a function of the distance from the target and of the time delay after laser irradiation. Differences of plasma characteristics were observed for laser ablation of quasicrystal and alloy targets, and the results were interpreted on the basis of different plasma formation mechanisms for the two systems.

Different response of intracerebroventricular cadmium administration on blood pressure in normal and low urinary kallikrein rats.

Cadmium intracerebroventricular (i.c.v.) administration, at definite concentrations, induces a dose-dependent increase in the systemic blood pressure. Kallikreins are suggested to be important regulators of cardiovascular function. We evaluated the effects of 10 microg i.c.v. cadmium on mean blood pressure (MBP) and several urinary parameters such as 24h urine volume, sodium and potassium excretion and osmolality in a rat strain inbred for low urinary kallikrein and in normal-kallikrein Wistar rats. Low-kallikrein rats (LKR) showed an increase in MBP that, after an initial peak (27% from baseline), persisted higher than basal levels (10%) over 24h. In normal-kallikrein rats (NKR) a different reaction of blood pressure to cadmium was observed, causing a temporary increase (26% from baseline) of the systemic blood pressure, that returned to normal values within 2h. In addition, LKR showed a considerable reduction in the urinary volume (UV; 43.0+/-20 ml/24h versus 13.2+/-6 ml/24h, P<0.006), with an increase in the urinary osmolality (U(Osm); 500+/-210 mOsm/l versus 1391+/-245 mOsm/l, P<0.0002). Sodium (U(Na); 1761+/-432 microEq/24h versus 1156+/-522 microEq/24h, P<0.03) and potassium excretion (U(K); 2186+/-482 microEq/24h versus 936+/-299 microEq/24h, P<0.0006) were both significantly reduced. No changes in UV, U(Osm) and U(K) were observed in normal urinary kallikrein rats with the exception of U(Na) excretion that was significantly increased (667+/-274 microEq/24h versus 1725+/-300 microEq/24h, P<0.03). These results suggest that a genetically determined defect in urinary kallikrein excretion leads to a different hypertensive response to i.c.v. cadmium and to a different renal excretion of electrolytes. Perhaps the differences of blood pressure response could be due, at least in part, to a different sensitivity of LKR to cadmium: this implies a complex and articulate hypertensive effect of cadmium involving more systems than those supposed so far.

BRCA1 and BRCA2 germline mutations in Sardinian breast cancer families and their implications for genetic counseling.

BACKGROUND: The Sardinian population is genetically homogeneous and could be useful in understanding better the genetics of a complex disease like breast cancer (BC). PATIENTS AND METHODS: Using a screening assay based on a combination of single-strand conformation polymorphism, denaturing high-performance liquid chromatography and sequence analysis, 47 Sardinian families with three or more BC cases were screened for germline mutations in BRCA1 and BRCA2 genes. RESULTS: Three BRCA1/2 germline sequence variants were identified. While BRCA2-Ile3412Val is a missense variant with unknown functional significance, BRCA2-8765delAG and BRCA1-Lys505ter are two deleterious mutations (due to their predicted effects on protein truncation), which were found in seven families (15%). BRCA2-8765delAG was found in six of eight (75%) BRCA1/2-positive families and seven of 501 (1.4%) unselected and consecutively collected BC patients. Prevalence of BRCA1/2 mutations in BC families was significantly correlated with the total number of female BCs (P <0.01) and increased by the presence of (i) at least one case of ovarian or male BC, or (ii) three generations affected, or (iii) bilateral BC. CONCLUSIONS: Identification of such features should address BC patients and their families to genetic counseling and BRCA1/2 mutational analysis. In addition, this is the first report of a detailed BRCA1/2 mutation screening in Sardinia, having immediate implications for the clinical management of BC families.

Chiral discrimination of 2,3-butanediols by laser spectroscopy.

The resonance enhanced two-photon ionization time-of-flight (R2PI-TOF) excitation spectra of supersonically expanded complexes of isomeric 2,3-butanediols with a suitable chromophore, i.e. R-(+)-1-phenyl-1-propanol, represent powerful means for structurally discriminating the diol moiety and for investigating the nature of the intra- and intermolecular interactions involved in the complexes.

Enantiodiscrimination of chiral alpha-aminophosphonic acids by mass spectrometry.

Diastereomeric clusters between first-group metal ions (M(+)) and chiral alpha-aminophosphonic acids (A and B) have been readily generated in the gas phase by electrospray ionization (ESI) and their fragmentation investigated by mass spectrometry. The complexes studied had the general formula [MA(S)B(2)](+) and [MA(R)B(2)](+), where M = H, Li, Na, or K, A(S) and A(R) are the two enantiomers of a given acid A, and B is a reference alpha-aminophosphonic acid of defined configuration. Collision-induced decomposition (CID) of [MA(S)B(2)](+) and [MA(R)B(2)](+) leads to fragmentation patterns characterized by [MAB](+)/[MB(2)] abundance ratios which depend on the configuration of ligand A. These different spectral features were correlated to the different stability of the diastereomeric [MA(S)B(2)](+) and [MA(R)B(2)](+) complexes in the gas phase. The results have been discussed in the light of MM2 Molecular Mechanics Force Field calculations.

R2PI Study of intermolecular hydrogen bond in solvent-free chiral complexes.

One- and two-color, mass selected R2PI spectra of the S(1)<--S(0) transitions in the bare (+)-(R)-1-phenyl-1-ethanol (E(R)) and its complexes with different solvent molecules (solv) (-)-(R)-2-butanol (B(R)) or (+)-(S)-2-butanol (B(S)) and (-)-(R)-2-butylamine (A(R)) or (+)-(S)-2-butylamine (A(S)), have been recorded after a supersonic molecular beam expansion. The one-color R2PI excitation spectra of the diastereomeric complexes are characterized by significant shifts of their band origin relative to that of bare E(R). The extent and the direction of these spectral shifts are found to depend on the structure and the configuration of solv and are attributed to different short-range interactions in the ground and excited states of the complexes. In analogy with other diastereomeric complexes, the phenomenological binding energy of the homochiral cluster is found to be greater than that of the heterochiral one.

Cholesterol and serotonin indices in depressed and suicidal patients.

BACKGROUND: Prolactin and cortisol responses to d-fenfluramine challenge of central serotonin are reduced in depressed and suicidal patients. Low serum cholesterol levels are also reported in suicidal behavior. Thus, we examined for a relationship between serum cholesterol and fenfluramine challenge responses in patients with depression and/or attempted suicide. METHODS: We studied 12 patients and six controls. Blood was drawn for baseline serum cholesterol and the d-fenfluramine challenge test performed. RESULTS: Serum cholesterol levels were significantly lower in suicidal patients than in either non-suicidal patients or controls. However, neither the prolactin nor cortisol responses to d-fenfluramine correlated significantly with serum cholesterol levels. CONCLUSION: No relationship was found between serum cholesterol and these peripheral indices of serotonergic function.