Synthesis and properties of stereoregular poly(ester amides) derived from carbohydrates

Two poly(ester amides) containing three methoxy groups stereoregularly attached to the main chain have been prepared by using naturally occurring L -arabinose and D -xylose as the starting materials. The polymers were prepared by the active ester polycondensation method and characterized by elemental analysis, IR, and ¹H- and ¹³C-NMR spectroscopies. Both viscosimetry and GPC were used to estimate the molecular weights. The polymers are hydrophilic, one of them being water soluble, and exhibited moderate optical activity. Thermal and X-ray diffraction studies revealed that they are slightly crystalline and stable up to 250°C under nitrogen. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 67–77, 1998     

Weighted and Ergodic Theorems for Series of Differences of Convolutions

We extend some results of C. Demeter about the boundedness of series of difference of convolutions to the setting of one-sided A _p weights. We need to use a different approach. To be precise, we prove that the kernel of the associated operator satisfies a generalized Hörmander condition. The weighted inequalities allow us to transfer the result to the ergodic case, when the operator is induced by a mean bounded, invertible, positive groups.     

Tunable DNA photocleavage by an acridine-imidazole conjugate

We report the synthesis and characterization of photonucleases N,N'-bis[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (7) and N-[2-[bis(1H-imidazol-4-ylmethyl)amino]ethyl]-3,6-acridinediamine (10), consisting of a central 3,6-acridinediamine chromophore attached to 4 and 2 metal-coordinating imidazole rings, respectively. In DNA reactions employing 16 metal salts, photocleavage of pUC19 plasmid is markedly enhanced when compound 7 is irradiated in the presence of either Hg(II), Fe(III), Cd(II), Zn(II), V(V), or Pb(II) (low-intensity visible light, pH 7.0, 22 degrees C, 8-50 microM 7). We also show that DNA photocleavage by 7 can be modulated by modifying buffer type and pH. Evidence of metal complex formation is provided by EDTA experiments and by NMR and electrospray ionization mass spectral data. Sodium azide, sodium benzoate, superoxide dismutase, and catalase indicate the involvement of type I and II photochemical processes in the metal-assisted DNA photocleavage reactions. Thermal melting studies show that compound 7 increases the Tm of calf thymus DNA by 10 +/- 1 degrees C at pH 7.0 and that the Tm is further increased upon the addition of either Hg(II), Cd(II), Zn(II), or Pb(II). In the case of Fe(III) and V(V), a colorimetric assay demonstrates that compound 7 sensitizes one electron photoreduction of these metals to Fe(II) and V(IV), likely accelerating the production of type I reactive oxygen species. Our data collectively indicate that buffer, pH, Hg(II), Fe(III), Cd(II), Zn(II), V(V), Pb(II), and light can be used to "tune" DNA cleavage by compound 7 under physiologically relevant conditions. The 3,6-acridinediamine acridine orange has demonstrated great promise for use as a photosensitizer in photodynamic therapy. In view of the distribution of iron in living cells, compound 7 and other metal-binding acridine-based photonucleases should be expected to demonstrate excellent photodynamic action in vivo.     

Cayley parametrization of semisimple lie groups and its application to physical laws in a (3+1)-dimensional cubic lattice

The assumption of a discrete space-time is expressed mathematically by restricting the space-time variables to the field of integer numbers, and by restricting to the field of rational numbers the functions describing the laws of motion. This rational character must be preserved under the transformations connecting different systems of reference. The Cayley parametrization of semisimple Lie groups, and in particular of the Lorentz group, satisfies this condition if we require these parameters to take only integer values. The rational points of the most frequently used transcendental functions are obtained with the help of the integer complex and hypercomplex numbers. Some applications are made concerning the laws of motion in special relativity defined over a (3+1)-dimensional cubic lattice.     

Symmetry selection rules for vibrationally inelastic tunneling

A combined experimental and theoretical study is presented for the C-D stretch mode excitation of acetylene isotopes, C2HD and C2D2, on Cu(100) via inelastic electron tunneling (IET) in a scanning tunneling microscope junction. The calculated IET images using density functional theory show that the measured signal from C2D2 derives from the antisymmetric stretch mode. Selection rules are derived and involve the constraint imposed by the IET image on the symmetry characters of the vibrational mode and the adsorbate-induced electron states at the Fermi level.     

Inelastic scattering and local heating in atomic gold wires

We present a method for including inelastic scattering in a first-principles density-functional computational scheme for molecular electronics. As an application, we study two geometries of four-atom gold wires corresponding to two different values of strain and present results for nonlinear differential conductance vs device bias. Our theory is in quantitative agreement with experimental results and explains the experimentally observed mode selectivity. We also identify the signatures of phonon heating.     

Measurement of strange-quark contributions to the nucleon's form factors at Q(2) = 0.230 (GeV/c)(2)

We report on a measurement of the parity-violating asymmetry in the scattering of longitudinally polarized electrons on unpolarized protons at a Q2 of 0.230 (GeV/c)(2) and a scattering angle of theta (e) = 30 degrees - 40 degrees. Using a large acceptance fast PbF2 calorimeter with a solid angle of delta omega = 0.62 sr, the A4 experiment is the first parity violation experiment to count individual scattering events. The measured asymmetry is A(phys)=(-5.44+/-0.54(stat)+/-0.26(sys))x10(-6). The standard model expectation assuming no strangeness contributions to the vector form factors is A(0) = (-6.30+/-0.43) x 10(-6). The difference is a direct measurement of the strangeness contribution to the vector form factors of the proton. The extracted value is G(s)(E) + 0.225G(s)(M) = 0.039+/-0.034 or F(s)(1) + 0.130F(s)(2) = 0.032+/-0.028.     

Synthesis and Characterization of Ethylene/Propylene Copolymers in the Whole Composition Range

Summary: The incorporation of comonomer molecules in the backbone of a homopolymer can influence the final properties of the material, decreasing its crystallinity and the melting and glass transition temperatures, and increasing its impact resistance and transparency. In the present work, ten ethylene/propylene copolymers have been synthesized using a supported metallocene catalytic system covering the whole composition range. Any desired composition was obtained by controlling the feed composition during the reaction. These synthesized copolymers have been characterized by different techniques in order to study the effect of the comonomer incorporation onto their final properties. When the comonomer content is low, the behaviour of the copolymer is similar to that of the corresponding homopolymer. Nevertheless, if the comonomer content increases, the copolymer becomes more amorphous (low crystallization temperature and soft XRD signals) and easily deformable, reaching a behaviour close to that corresponding to an elastomeric material. In order to corroborate these results the samples have been characterized by TREF and GPC-MALS. TREF analysis showed that copolymers containing less than 10% and more than 80% of ethylene are semicrystalline, with elution temperatures typical of this kind of polymers. Molecular weights are higher for homopolymers and they decrease as the comonomer concentration increases, whereas the polydispersity index keeps almost constant at the expected value for this kind of samples.