Embedded silver ions-containing liposomes in polyelectrolyte multilayers: cargos films for antibacterial agents

A new antibacterial coating made of poly(L-lysine)/hyaluronic acid (PLL/HA) multilayer films and liposome aggregates loaded with silver ions was designed. Liposomes filled with an AgNO 3 solution were first aggregated by the addition of PLL in solution. The obtained micrometer-sized aggregates were then deposited on a PLL/HA multilayer film, playing the role of a spacer with the support. Finally, HA/PLL/HA capping layers were deposited on top of the architecture to form a composite AgNO 3 coating. Release of encapsulated AgNO 3 from this composite coating was followed and triggered upon temperature increase over the transition temperature of vesicles, found to be equal to 34 degrees C. After determination of the minimal inhibitory concentration (MIC) of AgNO 3 in solution, the antibacterial activity of the AgNO 3 coating was investigated against Escherichia coli. A 4-log reduction in the number of viable E. coli cells was observed after contact for 120 min with a 120 ng/cm (2) AgNO 3 coating. In comparison, no bactericidal activity was found for PLL/HA films previously dipped in an AgNO 3 solution and for PLL/HA films with liposome aggregates containing no AgNO 3 solution. The strong bactericidal effect could be linked to the diffusion of silver ions out of the AgNO 3 coating, leading to an important bactericidal concentration close to the membrane of the bacteria. A simple method to prepare antibacterial coatings loaded with a high and controlled amount of AgNO 3 is therefore proposed. This procedure is far superior to that soaking AgNO 3 or Ag nanoparticles into a coating. In principle, other small bactericidal chemicals like antibiotics could be encapsulated by this method. This study opens a new route to modify surfaces with small solutes that are not permeating phospholipid membranes below the phase transition temperature.     

Affinity of the highly preorganized ligand PDA (1,10-phenanthroline-2,9-dicarboxylic acid) for large metal ions of higher charge. A crystallographic and thermodynamic study of PDA complexes of thorium(IV) and the uranyl(VI) ion

The hydrothermal synthesis and structures of [UO2(PDA)] (1) and [Th(PDA)2(H2O)2].H2O (2) (PDA = 1,10-phenanthroline-2,9-dicarboxylic acid) are reported. 1 is orthorhombic, Pnma, a = 11.1318(7) A, b = 6.6926(4) A, c = 17.3114(12) A, V = 1289.71(14), Z = 4, R = 0.0313; 2 is triclinic, P1, a = 7.6190(15) A, b = 10.423(2) A, c = 17.367(4) A, alpha = 94.93(3) degrees , beta = 97.57(3) degrees , gamma = 109.26(3) degrees , V = 1278.3(4) A (3), Z = 2, R = 0.0654. The local geometry around the U in 1 is a pentagonal bipyramid with the two uranyl oxygens occupying the apical positions. The donor atoms in the plane comprise the four donor atoms from the PDA ligand (average U-N = 2.558 and U-O = 2.351 A) with the fifth site occupied by a bridging carboxylate oxygen from a neighboring UO2/PDA individual. The PDA ligand in 1 is exactly planar, with the U lying in the plane of the ligand. The latter planarity, as well as the near-ideal U-O and U-N bond lengths, and O-U-N and N-U-N bond angles within the chelate rings of 1 suggest that PDA binds to the uranyl cation in a low-strain manner. In 2, there are two PDA ligands bound to the Th (average Th-N = 2.694 and Th-O = 2.430 A) as well as two water molecules (Th-O = 2.473 and 2.532 A) to give the Th a coordination number of 10. The PDA ligands in 2 are bowed, with the Th lying out of the plane of the ligand. Molecular mechanics calculations suggest that the distortion of the PDA ligands in 2 arises because of steric crowding. UV spectroscopic studies of solutions containing 1:1 ratios of PDA and Th(4+) in 0.1 M NaClO4 at 25 degrees C indicate that log K1 for the Th(4+)/PDA complex is 25.7(9). The latter result confirms the previous prediction that complexes of PDA with metal ions of higher charge and an ionic radius of about 1.0 A such as Th(IV) would have remarkably high log K1 values with PDA. The origins of this very high stability are discussed in terms of a synergy between the pyridyl and the carboxylate donor groups of PDA. Metal ions of high charge normally bond poorly with pyridyl donors in aqueous solution because such metal ions require donor groups that are able to disperse charge to the solvent via hydrogen-bonding, which pyridyl groups are unable to do. In PDA, the carboxylates fulfill this need and so enable the high donor strength of the pyridyl groups of PDA to become apparent in the high log K1 for Th(IV) with PDA.     

Pentavalent uranium oxide via reduction of [UO2]2+ under hydrothermal reaction conditions

The synthesis, crystal structure, and spectroscopic characterization of [U(V)(H2O)2(U(VI)O2)2O4(OH)](H2O)4 (1), a mixed-valent U(V)/U(VI) oxide material, are reported. The hydrothermal reaction of UO2(2+) with Zn and hydrazine at 120 degrees C for three days yields 1 in the form of a dark red crystalline solid. Compound 1 has been characterized by a combination of single-crystal and powder X-ray diffraction (XRD), elemental analysis, thermogravimetric analysis, X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS). The structure consists of an extended sheet of edge and corner shared U(VI) pentagonal bipyramids that are further connected by edge sharing to square bipyramidal U(V) units. The overall topology is similar to the mineral ianthinite. The uranium L(III)-edge XAS revealed features consistent with those observed by single-crystal X-ray diffraction. High resolution XPS data analysis of the U4f region confirmed the oxidation states of U as originally assigned from XRD analysis and bond valence summations.     

Optical response of the Cu2S2 diamond core in (NGuaS)2Cl2

Density functional theory (DFT) and time‐dependent DFT calculations are presented for the dicopper thiolate complex Cu₂(NGuaS)₂Cl₂ [NGuaS=2‐(1,1,3,3‐tetramethylguanidino) benzenethiolate] with a special focus on the bonding mechanism of the Cu₂S₂Cl₂ core and the spectroscopic response. This complex is relevant for the understanding of dicopper redox centers, for example, the Cu_A center. Its UV/Vis absorption is theoretically studied and found to be similar to other structural Cu_A models. The spectrum can be roughly divided in the known regions of metal d‐d absorptions and metal to ligand charge transfer regions. Nevertheless the chloride ions play an important role as electron donors, with the thiolate groups as electron acceptors. The bonding mechanism is dissected by means of charge decomposition analysis which reveals the large covalency of the Cu₂S₂ diamond core mediated between Cu and S‐S π and π* orbitals forming Cu‐S σ bonds. Measured resonant Raman spectra are shown for 360‐ and 720‐nm excitation wavelength and interpreted using the calculated vibrational eigenmodes and frequencies. The calculations help to rationalize the varying resonant behavior at different optical excitations. Especially the phenylene rings are only resonant for 720 nm. © 2016 Wiley Periodicals, Inc.     

Assessment of the efficiency of long-range corrected functionals for some properties of large compounds

Using the long-range correction (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated a series of properties that are known to be poorly reproduced by standard functionals: Bond length alternation of pi-conjugated polymers, polarizabilities of delocalized chains, and electronic spectra of extended dyes. For each of these properties, we present cases in which traditional hybrid functionals do provide accurate results and cases in which they fail to reproduce the correct trends. The quality of the results is assessed with regard to experimental values and/or data arising from electron-correlated wave function approaches. It turns out that (i) both LC-DFT and CAM-B3LYP provide an accurate bond length alternation for polyacetylene and polymethineimine, although for the latter they decrease slightly too rapidly with chain length. (ii) The LC generalized gradient approximation and MP2 polarizabilities of long polyphosphazene and polymethineimine oligomers agree almost perfectly. In the same way, CAM-B3LYP corrects the major part of the B3LYP faults. (iii) LC and CAM techniques do not help in correcting the nonrealistic evolution with chain length of the absorption wavelengths of cyanine derivatives. In addition, though both schemes significantly overestimate the ground to excited state transition energy of substituted anthraquinone dyes, they provide a more consistent picture once a statistical treatment is performed than do traditional hybrid functionals.     

First hyperpolarizability of polymethineimine with long-range corrected functionals

Using the long-range corrected (LC) density functional theory (DFT) scheme introduced by Iikura et al. [J. Chem. Phys. 115, 3540 (2001)] and the Coulomb-attenuating model (CAM-B3LYP) of Yanai et al. [Chem. Phys. Lett. 393, 51 (2004)], we have calculated the longitudinal dipole moments and static electronic first hyperpolarizabilities of increasingly long polymehtineimine oligomers. For comparison purposes Hartree-Fock (HF), Moller-Plesset perturbation theory (MP2), and conventional pure and hybrid functionals have been considered as well. HF, generalized gradient approximation (GGA), and conventional hybrids provide too large dipole moments for long oligomers, while LC-DFT allows to reduce the discrepancy with respect to MP2 by a factor of 3. For the first hyperpolarizability, the incorrect evolution with the chain length predicted by HF is strongly worsened by BLYP, Perdew-Burke-Ernzerhof (PBE), and also by B3LYP and PBE0. On the reverse, LC-BLYP and LC-PBE hyperpolarizabilities are correctly predicted to be positive (but for the two smallest chains). Indeed, for medium and long oligomers LC hyperpolarizabilities are slightly smaller than MP2 hyperpolarizabilities, as it should be. CAM-B3LYP also strongly improves the B3LYP results, though a bit less impressively for small chain lengths. The present study demonstrates the efficiency of long-range DFT, even in very pathological cases.     

Molecular Fluids at High Dimensionality

We extend the analysis of orientational first-order phase transitions in anisotropic molecular fluids at high spatial dimensionality to hard-disk fluids, and then to mixture of hard disks and hard spheres. The effect of hard-sphere admixture depends sensitively on the relative sizes of the two geometrical objects, and large spheres completely quench the disk transition. An introductory study is made of spatially ordered states.     

Effect of the carbon filler on the curing kinetics of epoxycyanate cooligomer

The influence of carbon fibre on the curing kinetics of the prepolymer based on bisphenol A cyanurate and epoxy resin has been studied using infra‐red spectroscopy. It was found that curing process of prepolymer is very complicated. It is shown that in curing the prepolymer a number of the sequential transformations of ones cycle structure into others occurs. An introduction of the carbon fiber (CF) of two types, original CF and modified CF (MCF) containing phosphate groups, affect strongly the prepolymer curing. Both CF and MCF accelerate the conversion rate of epoxy groups. In the case of cyanate groups, the former does not practically affect their conversion whereas the latter decelerates strongly this process. In the paper the influence mechanism of CF is considered.     

Thermal Expansion of HMX

Abstract  

Thermal expansion of the β-phase of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (β-HMX, C₄H₈N₈O₈) was studied in the temperature range of −150 to 30 °C. β-HMX is monoclinic (a = 6.5255(10) ?, b = 11.0369(18) ?, c = 7.3640(12) ?, and β = 102.67(1)°), space group P2₁/n. On cooling from room temperature to −150 °C the crystal under goes an anisotropic contraction with the a-axis virtually unchanged while the b and c axes contract by approximately 1.8 and 0.6% respectively. The disproportionate change in the a and c axes results in approximately a 0.4% change in the β angle. Despite the large differences in expansion along the different axes no phase change was observed.