Hybrid Scaffolds Built From PET and Collagen as a Model For Vascular Graft Architecture

A hybrid material with excellent mechanical and biological properties is produced by electrospinning a co‐solution of PET and collagen. The fibers are mapped using SEM, confocal Raman microscopy and collagenase digestion assays. Fibers of different compositions and morphologies are intermingled within the same membrane, resulting in a heterogeneous scaffold. The collagen distribution and exposure are found to depend on the PET/collagen ratio. The materials are chemically and mechanically characterized and biologically tested with fibroblasts (3T3‐L1) and a HUVEC culture in vitro. All of the hybrid scaffolds show better cell attachment and proliferation than PET. These materials are potential candidates to be used as vascular grafts.

     

Calix[4]arene-based metal-organic frameworks: towards hierarchically porous materials

An upper rim-functionalised calix[4]arene dicarboxylic acid (H(2)caldc) has been used to prepare four metal-organic frameworks, three of which have been structurally characterised and shown to form two- or three-dimensional network structures. Simulations suggest that such networks are likely to display interesting selectivity to guest molecules.     

Quantitative treatment of coarsely binned low-resolution recordings in molecular absorption spectroscopy

Optical multichannel detectors like photodiode arrays or CCD cameras combined with grating spectrometers are commonly used as detection systems in quantitative absorption spectroscopy. As a trade-off to broad spectral coverage, banded spectral features are sometimes recorded with insufficient spectral resolution and/or insufficiently fine detector binning. This renders the true physical spectrum of recorded intensities changed by instrumental and spectrum specific artefacts thus impeding comparability between results from different set-ups. In this work, it is demonstrated that in the case of a "well-behaved"--i.e. free of ro-vibronic structure--absorption band like the iodine monoxide IO(4<--0) transition, these effects can easily change the apparent peak absorption by up to 50%. Also deviations from the strict linearity (Beer-Lambert's law) between absorber concentration and apparent, i.e. pixelwise optical density occur. This can be critical in studies of chemical kinetics. It is shown that the observed non-linearity can cause errors of up to 50% in the determination of a second order rate coefficient for the IO self reaction. To overcome the problem, a consistent and rigorous integral approach for the treatment of intensity recordings is developed. Linearity between optical density and absorber concentration thereby is re-established. The method is validated using artificial test data as well as experimental data of the IO(4<--0) absorption transition, obtained in the context of I2/O3 photochemistry studies. The agreement is accurate to within +/-2% (test data) and +/-3% (experimental data) supporting the validity of the approach. Possible consequences for other spectroscopic work are indicated.     

Synthesis and characterization of new aromatic polyamides bearing crown ethers and acyclic ethylene oxide units in the pendant structure. III. Benzo‐18‐crown‐6 systems and their open‐chain counterparts

We report the synthesis and characterization of 10 novel polyamides containing the benzo‐18‐crown‐6 subunit and its dipodal counterpart, along with their properties, and a comparison with homologous polyamides bearing benzo‐12‐crown‐4, benzo‐15‐crown‐5, and the corresponding dipodal systems. The anomalous polymerization of some of the diacid monomers, that leads to insoluble gels under standard Yamazaki polymerization conditions, is described. The gel formation has been attributed to the threading of cyclic oligoamides with a growing polyamide chain to yield rotaxanes, polyrotaxanes, catenanes, or polycatenanes. Polyamide macrocycles have been characterized with matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. A route to avoid gel formation, consisting of a lower initial monomer concentration, is also described, along with the polymer properties of the polyamides obtained, including the chemical characterization, mechanical behavior, water sorption, morphology, diffusion data, and permeability of membranes prepared with these polymers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6252–6269, 2006     

Real-time full spectrum fitting of beam-based Doppler broadening data

A full spectrum fitting code, developed and used by the Bath positron group to compute the fractions of positrons annihilated from surface, defect and bulk states as a function of incident positron energy, is described. To date, the most useful application of the code has been in studies of ion-implanted silicon, being particularly useful in the observation of the formation of oxygen-divacancy complexes. The advantages and limitations of the code are discussed.     

The effect of terminal chain modifications on the mesomorphic properties of 4,4'-disubstituted diphenyldiacetylenes

A variety of terminal chain modifications (Y) were made on the diacetylenes in which X=C_nH_2n+1, C₁₂H₂₅O and F, and Y=CH₂CH(Me)C₂H₅, COCH₃, C≡CC₅H₁₁, C_nF_2n+1C_nH_2n+1 and CH=CHCO₂C₃H₇. Mesomorphic properties were determined by hot stage polarizing microscopy and DSC. These were compared with those for the dialkyl analogues (X=C_mH_2m+1, Y=C_nH_2n+1) and a series of 1- and 2-olefins (Y=CH=CHC_nH_2n+1 and CH₂CH=CHC_nH_2n+1). The 1-olefin series showed wider range nematics than the dialkyl compounds, whereas the above modifications showed either narrow range nematic phases, no mesophase or higher melting temperatures. New transition temperature and enthalpy data are provided for some of the dialkyl and F-alkyl compounds previously reported, for comparisons. Preliminary birefringence data are also included along with the results of some heat and UV stability studies.     

Reactivity of Bulged Bases in Duplex DNA with Redox-active Nickel and Cobalt Complexes

The square-planar, macrocyclic complex NiCR (CR=(2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2,11,13,15-pentaenato)) as well as CoCl 2 have been investigated as catalysts for the site-specific oxidation of bulged T, C, and A nucleotides in duplex DNA oligomers. Previous studies of NiCR using KHSO 5 as oxidant indicated that this combination of reagents successfully probes the accessibility of N7 of guanine residues in non-canonical DNA and folded RNA structures. In the present study, the order of reactivity of bulged bases in synthetic oligodeoxynucleotides with NiCR/KHSO 5 is shown to be G>C>T～A. Although the nickel complex generates a less-reactive oxidant than does cobalt, its selectivity for bulged bases is much greater, rendering it a useful probe of exposed Cs and Ts in addition to Gs in DNA and RNA structure.