Odd‐even effect during layer‐by‐layer assembly of polyelectrolytes inspired by marine mussel

Biomimetic polyelectrolyte of Dopa modified poly(acrylic acid) (PAADopa) was synthesized taking advantage of Dopa, the major unit of marine adhesive proteins. Zinc crosslinked PAADopa (PAADopa‐Zn) were formed at acidic pH for more compact structure and assembled with the positively charged polyethylenimine (PEI) to build robust polyelectrolyte multilayers at high salt concentration. Effects of pH, crosslinking degree, and salt concentration on polymer structure, film building process, and morphology were investigated, respectively. An “odd‐even” effect was observed by quartz crystal microbalance with dissipation and AFM in the presence of zinc ion, which becomes more obvious with an optimum crosslinking degree (Zn/Dopa = 2.0) under high salt concentration (0.6 M NaCl). It indicates the different swollen properties of PEI chain and PAADopa‐Zn complexes during the layer‐by‐layer building process under optimum crosslinking degree of PAADopa‐Zn at high salt concentration. Such odd‐even phenomenon of the biocompatible system is of critical importance for understanding the mechanism of layer formation and film structures. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 245–255     

Chiral ligand-exchange separation and resolution of extremely rigid glutamate analogs: 1-aminospiro[2.2]pentyl-1,4-dicarboxylic acids

Owing to their chelation ability, a series of fully constrained l-Glu analogs formed by the spiro-union of two cyclopropane rings (1-aminospiro[2.2]pentyl-1,4-dicarboxylic acids, ASPED A–D), was submitted to chiral ligand-exchange chromatographic (CLEC) analysis. As the initial step, two methodologically different chiral devices were evaluated. A chiral stationary phase (CSP) obtained by dynamic coating of C₁₈ chains with the S-trityl-(R)-cysteine ((R)-STC) was used first with this objective. The lack of separation of the enantiomers of ASPED C and D prompted us to utilize the chiral mobile phase (CMP) prepared from O-benzyl-(S)-serine ((S)-OBS). The latter afforded complete separation of the four pairs of enantiomers. For all the pairs, quantum mechanical investigations shed light on the main features responsible for the different enantiomer recognition mechanism with (S)-OBS. The validated analytical method was then fruitfully adopted for semi-preparative-scale isolation of the enantiomers of ASPED C.     

States of water,surface and rheological characterisation of a new biohydrogel as articular cartilage substitute

PVA based hydrogel was synthesised using, as crosslinking agent, trisodium trimetaphosphate (STMP) and its morphology was modified inducing a microporous structure to obtain potential substitutes for cartilage tissue. The hydrogel was characterised by Infrared Spectroscopy combined with Time of flight mass spectrometry (ToF‐SIMS) that confirmed the successful occurrence of crosslinking reaction, the hyphotised crosslinking arm and its homogeneous distribution. The mechanical spectra of the fully hydrated samples confirmed covalently crosslinked systems with a rheological behaviour similar to that of tibial cartilage. Further analysis in terms of water content measurements, thermal stability and cytotoxicity confirmed the applicability of such a hydrogel as cartilage substitute. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of hydrophilic isotactic polypropylenes promoted by metallocene catalysts

In this paper, the synthesis of isotactic polypropylenes (i‐PP) modified with ? OH groups in sides (iPP‐OH), by combination of polyinsertion ansa‐metallocene catalysis and ring opening of propene oxide (PO), is described. i‐PP sequences interrupted by isolated ethylene/p‐methylstyrene units forms the backbone. This enchainment is obtained by controlled copolymerization of propene with ethylene and p‐methylstyrene comonomers in the presence of rac‐ethylenebis(1‐indenyl)zirconiumdichloride/methylalumoxane system. The metallation reaction of the p‐methyl group with sec‐BuLi generates an anionic center that can be reacted with PO. The iPP‐OH is the result of the monoaddition reaction of PO followed by hydrolysis with acidified methanol. By changing experimental conditions in the backbone synthesis, a tuned number of the functionalizable sites as well as polypropylene sequence lengths can be obtained. As a consequence, iPP samples with a different number of ? OH groups for the backbone can be synthesized after the PO monoaddition reaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 7008–7013, 2006     

Improving the recovery of Ba from Sr Resin columns using chelating agents

Journal of Radioanalytical and Nuclear Chemistry - Age dating of Cs-137 sources requires the accurate and precise quantification of the isotope Ba-137. In previous efforts to determine the age of...     

Selective Array-Based Sensing of Anabolic Steroids in Aqueous Solution by Host–Guest Reporter Complexes

Arrayed complexes of a water-soluble deep cavitand and two fluorescent indicators show selective sensing of anabolic-androgenic steroids in aqueous environments. By combining the host–guest complexes with small amounts of heavy metal ions, discrimination between steroids that vary in structure by only a single π bond is possible. The sensing occurs through a triggered aggregation mechanism, which can be mediated by both the presence of metal ions and the steroids. The use of both “turn-on” and “turn-off” fluorophores is essential for good discrimination. As low as 10 μm steroid can be detected, and the discrimination is selective in steroid samples spiked into human urine.     

Layer‐by‐layer assembly of readily detachable chitosan and poly(acrylic acid) polyelectrolyte multilayer films

Free‐standing layer‐by‐layer (LbL) assembled thin films have recently found utility in a broad range of applications. Previously reported free‐standing LbL films have generally required covalent modifications to improve aqueous stability and render these films suitable for biomedical applications. Here, we engineered chitosan and poly(acrylic acid) containing polyelectrolyte multilayer films, which are readily detached from hydrophilic silicon in aqueous conditions. These films demonstrate remarkable stability over 28 days in simulated in vivo conditions (pH 7.4, phosphate buffered saline at 37 °C) without the incorporation of any covalent crosslinking modifications. These films exhibit moduli (27–420 kPa) resembling that of many biological tissues including tendon, show high visible light transmittance of greater than 50%, and prevent fibronectin adsorption. The properties of this new detachable LbL film architecture indicate its promise for use in a variety of applications, particularly in medicine and biotechnology. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 127–131     

Hydrocarbon Soluble Alkali-Metal-Aluminium Hydride Surrog[ATES]

A series of group 1 hydrocarbon-soluble donor free aluminates [AM(^tBuDHP)(TMP)Al(ⁱBu)₂] (AM=Li, Na, K, Rb) have been synthesised by combining an alkali metal dihydropyridyl unit [(2-^tBuC₅H₅N)AM)] containing a surrogate hydride (sp³ C−H) with [(ⁱBu)₂Al(TMP)]. These aluminates have been characterised by X-ray crystallography and NMR spectroscopy. While the lithium aluminate forms a monomer, the heavier alkali metal aluminates exist as polymeric chains propagated by non-covalent interactions between the alkali metal cations and the alkyldihydropyridyl units. Solvates [(THF)Li(^tBuDHP)(TMP)Al(ⁱBu)₂] and [(TMEDA)Na(^tBuDHP)(TMP)Al(ⁱBu)₂] have also been crystallographically characterised. Theoretical calculations show how the dispersion forces tend to increase on moving from Li to Rb, as opposed to the electrostatic forces of stabilization, which are orders of magnitude more significant. Having unique structural features, these bimetallic compounds can be considered as starting points for exploring unique reactivity trends as alkali-metal-aluminium hydride surrog[ATES].