Biomedical subjects
Publications and source records attributed to P Papadopoulos.
A case with multiple congenital coronary arteriovenous fistulae is reported. The right coronary artery was communicating with the right ventricle. The left coronary artery was entering directly into the pulmonary trunk and two terminal branches of the anterior descending into the left ventricle. The direct communication of the left coronary artery without interposition of an accessory artery or a circoid plexus is met for the first time.
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The structure and the associated dynamics have been investigated in a series of oligopeptides of gamma-benzyl-l-glutamate using DSC, WAXS, FTIR, NMR and dielectric spectroscopy, and rheology, respectively. The peptides with degrees of polymerization below 18 are mixtures of a lamellar assembly of beta sheets and of columnar hexagonal arrangement of alpha helices, whereas for longer chains, the intramolecular hydrogen bonds stabilize only the alpha-helical conformations. Multiple dielectrically active processes were found. Starting from low temperatures, the two Arrhenius processes (gamma and beta), with apparent activation energies of 20.6 and 50.2 kJ/mol, respectively, associate with the local relaxation of the side-chain methylene units (gamma process) and with more cooperative motions of the side chain dipoles sensitive to the 7/2 helical packing (beta process). The glass transition is manifested in the thermal properties with a step in the heat capacity and with an intense dielectric process bearing characteristics (molecular weight dependence, temperature dependence of relaxation times) known from amorphous polymers. Based on these findings, the alpha process is attributed to the relaxation of amorphous segments located between and at the end of helically ordered segments. Two slower processes were identified with opposite molecular weight dependence. The weak intermediate mode with an M2 molecular weight dependence of the characteristic relaxation times suggests amorphous-like chains, whereas the strong slower process originates from the loss of dipole orientational capacity caused by structural defects and reflects the migration of helical sequences along the chains. This identifies the helices as structures extending over rather short fragments of chains (i.e., of low persistence length). The viscoelastic response indicated that the structural defects arise from locally aggregated chains that inhibit the flow of oligopeptides.
We report on the self-assembly mechanism and dynamics in a series of poly(gamma-benzyl-l-glutamate)-b-poly(glycine) (PBLG-b-PGly) diblock copolymers within the composition range 0.67 < or = f(PBLG) < or = 0.97 and the temperature (T) range 303 < T < 433 K. Small- and wide-angle X-ray scattering, (13)C NMR, and differential scanning calorimetry are used for the structure investigation coupled with dielectric spectroscopy for both the peptide secondary structure and the associated dynamics. These techniques provide not only the nanophase morphology but also the type and persistence of peptide secondary structures. The thermodynamic confinement of the blocks within the nanodomains and the disparity in their packing efficiency results in multiple chain folding of the PGly secondary structure that effectively stabilize a lamellar morphology for high f(PBLG). Nanoscale confinement proves to be important in controlling the persistence length of secondary peptide motifs.