Marine epibiosis. III. Possible antifouling defense adaptations in Polysyncraton lacazei (Giard) (Didemnidae, Ascidiacea)

Polysyncraton lacazei (Giard), a colonial tunicate of the western Mediterranean, seems to be well-protected against epibiosis. Out of several thousand potential colonizers estimated, only one kamptozoan species, Loxocalyx sp., is found with some regularity (less-than-or-equal-to 21%) on the colonial surface. The results in this paper suggest the existence of overlapping mechanical, chemical and extrinsic adaptations with a good antifouling potential

Production of isoscalar pion pairs in the pd -> 3He pi pi reaction near threshold

The production near threshold of isoscalar pion pairs in the pd -> 3He(pi pi)^0 reaction is estimated in a two-step model which successfully describes the production of eta, omega and eta' mesons. A virtual pion beam, generated through an NN -> d pi reaction on one of the nucleons in the deuteron, produces a second pion via a pi N -> pi pi N reaction on the other nucleon. Using the same scale factor as for heavy meson production, the model reproduces the total pi^0 pi^0 production rate determined at an excess energy of 37 MeV. There are some indications in the data for a suppression of events with low pi pi masses, as in the pi^- p -> pi^0 pi^0 n reaction, and this is confirmed within the model. The model suggests that a significant fraction of the charged pion production in the p d -> 3He pi^+ pi^- reaction at Q=70 MeV might be associated with isoscalar pion pairs, though this does not explain the strong dependence observed on the pi^+ pi^- relative momentum angle.Comment: 13 pages including 4 eps figure

Eta-Helium Quasi-Bound States

The cross section and tensor analysing power t_20 of the d\vec{d}->eta 4He reaction have been measured at six c.m. momenta, 10 < p(eta) < 90 MeV/c. The threshold value of t_20 is consistent with 1/\sqrt{2}, which follows from parity conservation and Bose symmetry. The much slower momentum variation observed for the reaction amplitude, as compared to that for the analogous pd->eta 3He case, suggests strongly the existence of a quasi-bound state in the eta-4He system and optical model fits indicate that this probably also the case for eta-3He.Comment: LaTeX, uses elsart.sty, 10 pages, 3 Postscript figures, Submitted to Physics Letters

The role of the Roper resonance in n p --> d (pi pi)

In this work, a model for the n p --> d (pi pi) reaction is developed. It is shown that the structure of the deuteron momentum spectra for a neutron beam momentum of 1.46 GeV can be explained as a consequence of the interplay of two mechanisms involving the excitation of the N^*(1440) resonance and its subsequent decay into N (pi pi)^{T=0}_{S-wave} and Delta pi respectively. The relevance of the present analysis for the study of the Roper excitation and decay properties, as well as for the interpretation of other two-pion production experiments is discussed.Comment: 13 pages, 6 ps figure

Has charge symmetry breaking been observed in the d d -> alpha pi0 reaction?

Estimates are made of the d d -> alpha gamma gamma production cross sections in a model where each neutron-proton pair in the beam and target initiates an n p -> d gamma reaction. This approach, which successfully reproduces observables in two-pion production at intermediate energies, suggests that direct two-photon production could provide a very significant background to the measurement of the charge-symmetry-breaking (CSB) reaction d d -> alpha pi0. A non-vanishing CSB cross section has been reported which might be confused with such two-photon production under the given experimental conditions.Comment: 9 pages, ReVTEX, 2 figures, submitted to Phys. Rev. Let

Biological Activities of Cyclic and Acyclic B-Type Laxaphycins in SH-SY5Y Human Neuroblastoma Cells

Laxaphycins are a family of non-ribosomal lipopeptides that have been isolated from several cyanobacteria. Some of these compounds have presented cytotoxic activities, but their mechanism of action is poorly understood. In this work, the already described laxaphycins B and B3, and acyclolaxaphycins B and B3 were isolated from the marine cyanobacteria Anabaena torulosa. Moreover, two new acyclic compounds, [des-(Ala4-Hle5)] acyclolaxaphycins B and B3, were purified from the herviborous gastropod Stylocheilus striatus, with this being the first description of biotransformed laxaphycins. The structure of these new compounds was elucidated, together with the absolute configuration of acyclolaxaphycins B and B3. The bioactivities of the six peptides were determined in SH-SY5Y human neuroblastoma cells. Laxaphycins B and B3 were cytotoxic (IC50: 1.8 and 0.8 µM, respectively) through the induction of apoptosis. In comparison, acyclic laxaphycins did not show cytotoxicity but affected mitochondrial functioning, so their effect on autophagy-related protein expression was analyzed, finding that acyclic peptides affected this process by increasing AMPK phosphorylation and inhibiting mTOR. This work confirms the pro-apoptotic properties of cyclic laxaphycins B and is the first report indicating the effects on autophagy of their acyclic analogs. Moreover, gastropod-derived compounds presented ring opening and amino-acids deletion, a biotransformation that had not been previously describedThe research leading to these results has received funding from the following FEDER cofunded-grants. From Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia, 2017 GRC GI-1682 (ED431C 2017/01). From CDTI and Technological Funds, supported by Ministerio de Economía, Industria y Competitividad, AGL2016-78728-R (AEI/FEDER, UE), ISCIII/PI16/01830 and RTC-2016-5507-2, ITC-20161072. From European Union POCTEP 0161-Nanoeaters -1-E-1, Interreg AlertoxNet EAPA-317-2016, Interreg Agritox EAPA-998-2018, and H2020 778069-EMERTOXS

Didemnin B: Comparative study and conformational approach in solution

A comparative study of isodideimnine-1 and didemnin B is presented using spcctroecopic methods, partial degradation and partial synthesis. This leads to the conclusion of the presence of a single depsipeptide, namely didemnin B, with (3S,4R,5S) isostatine instead of the previous statine residue. An attempt to determine the whole conformation in solution of didemnin B by using 2D-NMR is also described

Backward pion-nucleon scattering

A global analysis of the world data on differential cross sections and polarization asymmetries of backward pion-nucleon scattering for invariant collision energies above 3 GeV is performed in a Regge model. Including the $N_\alpha$, $N_\gamma$, $\Delta_\delta$ and $\Delta_\beta$ trajectories, we reproduce both angular distributions and polarization data for small values of the Mandelstam variable $u$, in contrast to previous analyses. The model amplitude is used to obtain evidence for baryon resonances with mass below 3 GeV. Our analysis suggests a $G_{39}$ resonance with a mass of 2.83 GeV as member of the $\Delta_{\beta}$ trajectory from the corresponding Chew-Frautschi plot.Comment: 12 pages, 16 figure

Near-Threshold Production of omega Mesons in the pp -> pp omega Reaction

The total cross section for omega production in the pp -> pp omega reaction has been measured at five c.m. excess energies from 3.8 to 30 MeV. The energy dependence is easily understood in terms of a strong proton-proton final state interaction combined with a smearing over the width of the state. The ratio of near-threshold phi and omega production is consistent with the predictions of a one-pion-exchange model and the degree of violation of the OZI rule is similar to that found in the pi-p -> n omega/phi reactions.Comment: Report in LaTeX2e. 12 pages with 2 eps figure

Measurement of the tensor Ayy and vector Ay analyzing powers of the deuteron inelastic scattering off berillium at 5.0 GeV/c and 178 mr

Tensor Ayy and vector Ay analyzing powers in the inelastic scattering of deuterons with the momentum of 5.0 GeV/c on beryllium at an angle of 178 mr in the vicinity of the excitation of baryonic resonances with masses up to 1.8 GeV/c^2 have been measured. The Ayy data are in a good agreement with the previous data obtained at 4.5 and 5.5 GeV/c. The results of the experiment are compared with the predictions of the plane wave impulse approximation and \omega-meson exchange models.Comment: 18 pages, 9 figure