SYNTHESIS AND ION BINDING PROPERTIES OF CYCLIC HOMOPEPTIDES

Synthesis and ion binding properties of cyclic homopeptides Starting from the isolation of the antibiotic Gramicidin S, the first biologically active cyclopeptide identified in 1944, cyclic peptides have attracted increasing interest due to their unique chemical and biological properties. In cyclic peptides the amino acidic chains are closed in the ring to give structures with reduced conformational freedom compared to linear precursors. As a consequence, cyclic peptides generally have greater resistance to in vivo enzymatic degradation, greater bioavailability and ultimately greater binding affinity and selectivity toward substrates. Synthesis of cyclic peptides, in particular head-to-tail cyclisation, represents a significant synthetic challenge and cyclization reaction requires particular conditions. For instance, high dilution is still the main route applicable to minimize unwanted intermolecular processes. The success or failure of macrocyclization relies on the ability of a linear precursor to conformationally pre-organize its reactive ends bringing them close to each other before ring closure. Many features have been found to favor cyclization such as introduction of cis-amide bond in the middle of the peptide chain, the presence of both D- and L- residues in the termini, introduction of N-methyl amino acids etc. In this thesis the synthesis of a series of linear homopeptides containing lysine, serine and aminoalanine were performed in solution following a classical orthogonal protection scheme. Macrocyclization reactions were carried out on completely protected peptide precursors under high dilution conditions in the presence of different salts (NaCl, LiCl, NaTPB and TEACl) to promote the head-to-tail condensation. Microcalorimetric titrations using linear tetra-, penta- and hexalysine containing peptides as ligands and NaClO4 and TEACl as salts indicated a very weak binding of the peptides with Na+ and a strong binding with Cl-. The binding constants for the complexation of chloride ions were evaluated to be Log K=1.51, Log K=1.47 and Log K=1.68, for tetra-, penta- and hexapeptide, respectively. These findings suggest that the mechanism commonly accepted for the metal-ion assisted cyclization has to be revised indicating that coordination of chloride ions (and not alkali metals) with amide groups along the chain is the factor that predominantly brings N- and C-termini closer, forcing them to react. Accordingly, the highest cyclization yields were obtained when TEACl was used as the salt. Moreover, MD simulations show the formation of stable complexes of linear peptides with Cl- while in complexes with sodium dissociation of the cation occurs. Binding properties of cyclic pentalysine toward different anions were investigated by means of microcalorimetric titrations in CH3CN. In complexation reactions with halides (Cl-, Br-, I-) as well as with NO3-, inflection was observed at a ratio n(A-)/n(L) 48 1 which indicates that the stoichiometry of the resulting complex is 1:1. In contrast, with H2PO4- we observed inflection at the ratio n(L)/n(A-) 48 2 i.e. two ligands are needed to coordinate one H2PO4- anion. Calorimetric titrations showed also that the most efficient binding of cyclopentalysine is with Cl- with the binding constant of Log K=5.72 while that of cyclohexalysine is with OAc- (Log K > 4, obtained by NMR titrations). In general, cyclic pentapeptide binds stronger all investigated anions than the corresponding cyclic hexapeptide. Complexation reactions of cyclic penta- and hexalysine were also investigated by 1H NMR and ESI-MS titrations. The results are in agreement with those obtained by microcalorimetric titrations. Linear H2N-(Leu)5-COOH and H2N-Phe-Leu-Leu-Phe-Leu-Leu-COOH were also prepared in order to confirm the role of chloride anion in assisting macrocyclization of peptides. With the ultimate goal to prepare a novel class of anion receptors, namely calixarene homo-cyclopeptide derivatives, work is in progress to set-up a simple and efficient method to directly conjugate the prepared homocyclopeptides to calixarenes by exploiting side chain functional groups

Synthesis of γ-glutamyl derivatives of sulfur-containing amino acids in a multigram scale via a two-step, one-pot procedure

\u3b3-Glutamyl derivatives of sulfur amino acids have been prepared in multigram scale starting from readily available starting materials. The synthesis comprises two one-pot operations, both consisting of two reactions. In the first operation, N-phtaloyl-l-glutamic acid anhydride is obtained from l-glutamic acid and phtalic anhydride. In the second one, N-phtaloyl-l-glutamic acid anhydride is used to acylate amino acids and the N-phtaloyl protecting group is removed. The described approach offers a viable entry to \u3b3-glutamyl derivatives of sulfur-containing amino acids with flavor-enhancer and nutraceutical properties

Coherent Vector Meson Photoproduction with Nuclear Breakup in Relativistic Heavy Ion Collisions

Relativistic heavy ions are copious sources of virtual photons. The large photon flux gives rise to a substantial photonuclear interaction probability at impact parameters where no hadronic interactions can occur. Multiple photonuclear interactions in a single collision are possible. In this letter, we use mutual Coulomb excitation of both nuclei as a tag for moderate impact parameter collisions. We calculate the cross section for coherent vector meson production accompanied by mutual excitation, and show that the median impact parameter is much smaller than for untagged production. The vector meson rapidity and transverse momentum distribution are very different from untagged exclusive vector meson production.Comment: 14 pages, including 4 figure

Performance indicators for roadway bridges

Publicado em "Maintenance, monitoring, safety, risk and resilience of bridges and bridge networks". ISBN 978-1-138-02851-7The performance indicators should, by its definition, allow capturing the life-cycle degradation processes affecting maintenance plans or the remaining lifetime. The qualitative or quantitative performance indicators are obtained through visual inspections, non-destructive tests or monitoring systems. After their quantification and the comparison with the respective performance goals and thresholds, a Quality Control plan should be accomplished. The COST TU1406 Action aims to uniform the European performance indicators, systemize the knowledge on the Quality Control plans for bridges, establish quality specifications and finally to develop the guideline and recommendations for the assessment of performance indicators. This contribution focuses on the current work of the first Working Group, WG1, where the first step is a collection of the key performance indicators at a European level. First those key performance indicators which capture mechanical and technical properties and its degradation behavior are assessed, while the further consideration reflect on the natural aging, quality of the material, service life design methods, and sustainable, environmental, economic and social based indicators.COST (European Cooperation in Science and Technology)Project “LeCIE – Life-cycle assessment for railway construction – strategies and methods

Phenotypic and genetic analysis of carcass quality of different breeds’ fatlings

Dissection and quantitative-genetic analysis of carcass quality was performed on 318 fatlings of 5 different pig breeds: German, Dutch and Belgian Landrace, Yorkshire and Hampshire. Significant fixed effects (sex and genotype) and regression effects (age and body weight at slaughter) were fitted in the statistical model. Genetic parameters were estimated using the restricted maximum likelihood (REML) procedure based on an animal model with multivariate analyses. Heritability estimates for carcass traits were moderate to high except for back weight and neck weight. Among most of the carcass quality traits, the midrange strong and very strong positive genetic and phenotypic correlations were established. The traits that were analyzed showed sufficient genetic variation, indicating that their improvement is possible through genetic selection. Genetic variability was stable and expressed and justified further genetic changes in the desired direction

Inclusive meson production in peripheral collisions of ultrarelativistic heavy ions

There exist several proposals to use Weizs\"{a}cker-Williams photons generated by ultrarelativistic heavy ions to produce exotic particles in $\gamma\gamma$ fusion reactions. To estimate the background conditions for such reactions we analyze various mechanisms of meson production in very peripheral collisions of ultrarelativistic heavy ions at RHIC and LHC energies. Besides $\gamma\gamma$ fusion they include also electromagnetic $\gamma A$ interactions and strong nucleon-nucleon interactions in grazing $AA$ collisions. All these processes are characterised by low multiplicities of produced particles. $\gamma A$ and $AA$ events are simulated by corresponding Monte Carlo codes, RELDIS and FRITIOF. In each of these processes a certain fraction of pions is produced close to the mid-rapidity region that gives a background for the $\gamma\gamma$ events. The possibility of selecting mesons produced in $\gamma\gamma$ fusion events via different $p_t$ cut procedures is demonstrated.Comment: 27 pages with 4 eps-figures included, uses axodraw.sty Tab.2 and 3 correcte

Particle emission following Coulomb excitation in ultrarelativistic heavy-ion collisions

We study nuclear reactions induced by virtual photons associated with Lorentz-boosted Coulomb fields of ultrarelativistic heavy ions. Evaporation, fission and multifragmentation mechanisms are included in a new RELDIS code, which describes the deexcitation of residual nuclei formed after single and double photon absorption in peripheral heavy-ion collisions. Partial cross sections for different dissociation channels, including the multiple neutron emission ones, are calculated and compared with data when available. Rapidity and transverse momentum distributions of nucleons, nuclear fragments and pions, produced electromagnetically, are also calculated. These results provide important information for designing large-rapidity detectors and zero-degree calorimeters at RHIC and LHC. The electromagnetic dissociation of nuclei imposes some constrains on the investigation of exotic particle production in gamma-gamma fusion reactions.Comment: 26 LaTeX pages including 8 figures, uses epsf.st

Coulomb Effects on Electromagnetic Pair Production in Ultrarelativistic Heavy-Ion Collisions

We discuss the implications of the eikonal amplitude on the pair production probability in ultrarelativistic heavy-ion transits. In this context the Weizs\"acker-Williams method is shown to be exact in the ultrarelativistic limit, irrespective of the produced particles' mass. A new equivalent single-photon distribution is derived which correctly accounts for the Coulomb distortions. As an immediate application, consequences for unitarity violation in photo-dissociation processes in peripheral heavy-ion encounters are discussed.Comment: 13 pages, 4 .eps figure

Lymphocyte subsets and the role of Th1/Th2 balance in stressed chronic pain patients

Background: The complex regional pain syndrome (CRPS) and fibromyalgia (FM) are chronic pain syndromes occurring in highly stressed individuals. Despite the known connection between the nervous system and immune cells, information on distribution of lymphocyte subsets under stress and pain conditions is limited. Methods: We performed a comparative study in 15 patients with CRPS type I, 22 patients with FM and 37 age- and sex-matched healthy controls and investigated the influence of pain and stress on lymphocyte number, subpopulations and the Th1/Th2 cytokine ratio in T lymphocytes. Results: Lymphocyte numbers did not differ between groups. Quantitative analyses of lymphocyte subpopulations showed a significant reduction of cytotoxic CD8+ lymphocytes in both CRPS (p < 0.01) and FM (p < 0.05) patients as compared with healthy controls. Additionally, CRPS patients were characterized by a lower percentage of IL-2-producing T cell subpopulations reflecting a diminished Th1 response in contrast to no changes in the Th2 cytokine profile. Conclusions: Future studies are warranted to answer whether such immunological changes play a pathogenetic role in CRPS and FM or merely reflect the consequences of a pain-induced neurohumoral stress response, and whether they contribute to immunosuppression in stressed chronic pain patients. Copyright (c) 2008 S. Karger AG, Basel

Progression of liver fibrosis in HIV/HCV genotype 1 co-infected patients is related to the T allele of the rsI2979860 polymorphism of the IL28B gene

<p>Abstract</p> <p>Objective</p> <p>HIV/HCV co-infection is characterised by accelerated progression of liver disease. Recently, the rsl2979860 C/T polymorphism in the <it>IL28B </it>gene has been linked to progression towards cirrhosis in HCV mono-infected patients and to treatment response of HCV-infection in HIV/HCV co-infected patients. Our aim was to clarify by non-invasive techniques if this polymorphism affects fibrosis progression in HIV/HCV co-infection.</p> <p>Methods</p> <p>In a cross-sectional design, liver stiffness (transient elastography), surrogate markers of liver fibrosis (APRI and FIB-4 scores) and rsl2979860 genotypes were analysed in 84 HCV/H1V co-infected patients. <it>IL28B </it>genotypes were determined by real-time PCR using a light cycler. In 56 HIV/HCV co-infected patients we also studied progression of fibrosis in relation to rsl2979860 C/T genotypes over two years.</p> <p>Results</p> <p>82% of the patients were on HAART (74% without detectable HI viremia) and 67% were haemophiliacs, respectively. HCV genotype 1 was present in 62%. Cross-sectional median liver stiffness was 7.4 kPa and correlated with APRI and FIB-4 scores (r = 0.6 each, p < 0.001). Frequencies of <it>IL28B </it>genotypes were: CC 50%, CT 43% and TT 7%. In the cross-sectional analysis liver stiffness values were not different between the various <it>IL28B</it>-genotypes. Upon follow-up under HAART carriers of a C allele did not show further progression, while liver stiffness significantly increased in HIV/HCV co-infected patients with the T allele (p = 0.047).</p> <p>Conclusion</p> <p>Although progression of liver fibrosis was low under HAART in our cohort, progression was more pronounced in HIV/HCV genotype 1 co-infected patients with the T allele.</p