The chemical behaviour of di(2-pyridyl)sulphide,dps. Crystal and molecular structure of μ-di(2-pyridyl)sulphidebis(trans-dichlorotriethylphosphine platinum(II)), [{Pt(PEt3)Cl2}2μ-dps] and its reactivity towards stannylated species

The coordinating ability of the ligand di(2-pyridyl)sulphide, dps, was studied in several situations. Dps behaved as a bidentate chelating agent with SnX4 (X=Cl or Br) and also with Pd and Pt (PdCl2 and K2PtCl4), whereas with [Pt2(PR3)2Cl4], (R = Et or Ph), it formed bridging complexes: [{Pt(PR3)Cl2}2-dps]. The crystal and molecular structure of [{Pt(PEt3)Cl2}2-dps] was determined. This complex, as well as [M(dps)Cl2], (M = Pd or Pt), underwent reactions with SnCl2, which inserts into the M–Cl bonds producing heterobimetallic products, which are important in catalysis.     

The effect of surface wettability on induction and growth of neurites from the PC-12 cell on a polymer surface

Surface properties of polymeric devices that are used to regenerate nervous damage are a point to be considered for axon regeneration in nerve system. In our previous studies, we prepared a wettability gradient on polyethylene (PE) surfaces using a corona discharge treatment from a knife-type electrode whose power increases gradually along the sample length. The PE surfaces were oxidized gradually with increasing power. The effect of surface wettability on the different types of cells has an important role for cell adhesion and proliferation. The purpose of this study is to investigate neurite formation on polymer surfaces with different wettability. Induction and growth of neurites from the rat pheochromocytoma (PC-12) cells attached on the polymer surfaces with different hydrophilicity were investigated using the wettability gradient PE surfaces prepared by a corona discharge treatment. Neurites were investigated for number and length of neurites in terms of surface wettability. It was observed that neurite formation of PC-12 cells was increased more onto the positions with moderate hydrophilicity of the wettability gradient surface than onto the more hydrophobic or hydrophilic positions. From those results, it could be assumed that initial adhesion of PC-12 cells was caused by more calf serum (CS) protein than nerve growth factor (NGF), whereas the neurite formation of PC-12 cells was caused by more NGF than CS protein. It follows from what has been said thus far that PC-12 cells are a differentiated neuronal phenotype with a long neurite at around the position 2.5 cm (water contact angle of about 55 deg). In conclusion, surface wettability plays an important role for neurite formation on the polymer surfaces for axon regeneration.     

Mean distance of closest approach of ions: Lithium salts in aqueous solutions

Numerical values for the mean distance of closest approach of ions, “a”, for lithium salts in aqueous solutions are presented and discussed. These values were obtained from both experimental activity and diffusion coefficients, and estimated by using different theoretical approaches.     

Fabrication and Evaluation of Gellan Gum/Hyaluronic Acid Hydrogel for Retinal Tissue Engineering Biomaterial and the Influence of Substrate Stress Relaxation on Retinal Pigment Epithelial Cells

Cell therapies for age-related macular degeneration (AMD) treatment have been developed by integrating hydrogel-based biomaterials. Until now, cell activity has been observed only in terms of the modulus of the hydrogel. In addition, cell behavior has only been observed in the 2D environment of the hydrogel and the 3D matrix. As time-dependent stress relaxation is considered a significant mechanical cue for the control of cellular activities, it is important to optimize hydrogels for retinal tissue engineering (TE) by applying this viewpoint. Herein, a gellan Gum (GG)/Hyaluronic acid (HA) hydrogel was fabricated using a facile physical crosslinking method. The physicochemical and mechanical properties were controlled by forming a different composition of GG and HA. The characterization was performed by conducting a mass swelling study, a sol fraction study, a weight loss test, a viscosity test, an injection force study, a compression test, and a stress relaxation analysis. The biological activity of the cells encapsulated in 3D constructs was evaluated by conducting a morphological study, a proliferation test, a live/dead analysis, histology, immunofluorescence staining, and a gene expression study to determine the most appropriate material for retinal TE biomaterial. Hydrogels with moderate amounts of HA showed improved physicochemical and mechanical properties suitable for injection into the retina. Moreover, the time-dependent stress relaxation property of the GG/HA hydrogel was enhanced when the appropriate amount of HA was loaded. In addition, the cellular compatibility of the GG/HA hydrogel in in vitro experiments was significantly improved in the fast-relaxing hydrogel. Overall, these results demonstrate the remarkable potential of GG/HA hydrogel as an injectable hydrogel for retinal TE and the importance of the stress relaxation property when designing retinal TE hydrogels. Therefore, we believe that GG/HA hydrogel is a prospective candidate for retinal TE biomaterial.     

Controlled preparation of poly(ethylene glycol) and poly(L‐lactide) block copolymers in the presence of a monomer activator

Polymerization of L ‐lactide (LA) was performed in the presence of trifluoromethanesulfonic acid (CF₃SO₃H) via an activated monomer mechanism to synthesize various block copolymers composed of polyethyleneglycol (PEG) and poly(L ‐lactide) (PLLA). The PLLAs obtained had molecular weights close to theoretical values calculated from LA/PEG molar ratios and exhibited monomodal GPC curves. A ¹H NMR spectroscopic study showed that the LA carbonyl carbon signal exhibited a change in chemical shift to lower field, caused by electron delocalization of the carbonyl carbon by CF₃SO₃H. We successfully prepared PEG and PLLA block copolymers using this activated monomer mechanism. We concluded that synthesis proceeded by LA ring‐opening polymerization caused by PEG in the presence of CF₃SO₃H to yield PEG and PLLA block copolymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5917–5922, 2009     

Vibrational spectroscopy at high pressure of the permanganate anion trapped in potassium bromide and potassium perchlorate matrices

The effect of high pressure on the resonance Raman spectra of the permanganate ion isolated in potassium bromide and potassium perchlorate matrices has been investigated at room temperature for pressures up to 50 kbar. The pressure dependences of the anharmonicity constants and harmonic frequencies have been determined from the overtones of the totally symmetric nu1(A1) mode of the permanganate ion. For both matrices, as the pressure increases, the anharmonicity constants decrease slightly, while the harmonic frequencies increase steadily. The effect of the potassium bromide phase transition from a face-centered to a body-centered structure was observed on the permanganate ion Raman spectrum at approximately 24 kbar. The perchlorate matrix does not exhibit any phase transition under the experimental conditions used in this study.     

Highly stereoselective one-pot procedure to prepare bis- and tris-chalcogenide alkenes via addition of disulfides and diselenides to terminal alkynes

We present here the reaction of diorganoyl dichalcogenides with terminal alkynes under catalyst-free conditions, by a one-pot procedure, to prepare bis- and tris-chalcogenide alkenes selectively, avoiding the previous preparation of chalcogen alkynes. The reaction proceeded cleanly under mild reaction conditions, and the addition of dichalcogenides to alkynes occurred stereoselectively to give exclusively the corresponding Z isomers. We observed that the selectivity control was governed by the effective participation of the hydroxyl group from propargyl alcohols. In addition, the bis-chalcogenide alkenes were exclusively obtained with propargyl alcohol having the acidic hydroxyl group proton. Conversely, the alkynes with no potentially acidic hydroxyl group proton, at propargyl positions, gave exclusively the tris-chalcogenide alkenes.