Oxygen Barrier Properties of Waterborne Polyurethane/Silica Hybrids

The oxygen barrier properties of films obtained from waterborne polyurethane/silica hybrid dispersions were analyzed. Two different types of polyurethanes were used, based on poly(propylene glycol) and poly(1,4-butylene adipate). Three different strategies were followed in the preparation of the hybrid dispersions. In the first type of materials (series 1), the inorganic part came exclusively from the covalent incorporation of trifunctional silane groups into the polymeric chains. The other two series contained, in addition to the trifunctional silane groups, tetrafunctional silane groups either physically blended (series 2) or “in situ” generated (series 3). Materials of series 1 showed an increase of the oxygen permeability coefficient with the silane content. However, the other two types of materials presented just the opposite dependence. In this latter case, the systems containing “in situ” generated silica (series 3) presented higher permeability coefficient values, probably because of the steric hindrance imposed by the polyurethane that gave rise to silica networks containing silanol groups and free volume holes. Moreover, lower permeability coefficient values were obtained when larger size particles were added. This fact could mean that the polyurethane/silica interface effects were not totally hindered even when the organic/inorganic phases were covalently bonded.     

CONFORMATIONAL INVESTIGATION OF SOME SYMMETRICALLY SUBSTITUTED DIALKYL MONO-SULFIDES AND DISULFIDES BY IR SPECTROSCOPY

Abstract

Several infrared and Raman studies have been performed on compounds containing the disulfide group in the region of C-S and S-S stretching modes (1–4) in order to get a better insight of the correlations between molecular conformation and peculiar geometry parameters of the dihedral angle CS-SC.     

Electrospun Polyacrylic Acid Polymer Fibers Functionalized with Metallophthalocyanines for Photosensitizing and Gas Sensing Applications

The photophysical and photochemical properties of tetraaminophthalocyanine complexes of lutetium and zinc covalently linked to polyacrylic acid were studied alongside those of unsubstituted zinc phthalocyanine within the same polymeric fiber matrix. All three phthalocyanines within the solid fiber matrices showed photoactivity by the generation of singlet oxygen as was observed in solution. The fluorescence behaviors of the composite fibers equally parallel those in solution. For the unsubstituted zinc phthalocyanine composite, the fiber showed fluorescence quenching on interaction with gaseous nitrogen dioxide similar to that in DMF and, thus could be a promising nanofabric material in developing optoelectronic devices that are responsive to the gas.     

Photophysics of Silicon Phthalocyanines in Aqueous Media

Phthalocyanines have been used as photodynamic therapy (PDT) agents because of their uniquely favorable optical properties and high photostability. They have been shown to be highly successful for the treatment of cancer through efficient singlet‐oxygen (¹O₂) production. However, due to their hydrophobic properties, the considerations of solubility and cellular location have made understanding their photophysics in vitro and in vivo difficult. Indeed, many quantitative assessments of PDT reagents are undertaken in purely organic solvents, presenting challenges for interpreting observations during practical application in vivo. With steady‐state and time‐resolved laser spectroscopy, we show that for axial ligated silicon phthalocyanines in aqueous media, both the water:lipophile ratio and the pH have drastic effects on their photophysics, and ultimately dictate their functionality as PDT drugs. We suggest that considering the presented photophysics for PDT drugs in aqueous solutions leads to guidelines for a next generation of even more potent PDT agents.     

燃料电池铂钴锰合金催化剂的制备及性能

为提高PtCo/C合金催化剂的电化学性能,采用微波法合成铂钴锰催化剂前驱体,经高温热处理形成合金,最后通过酸处理得到铂钴锰合金催化剂(PtCoMn/C)。电化学测试结果表明:适量锰的添加可提升PtCo/C催化剂的活性和耐久性。PtCoMn/C催化剂在 0.9 V(vs RHE)电压下的质量比活性(MA)达到 0.666 A·mg_Pt^-1,是传统 Pt/C 的 2.66 倍,是 PtCo/C 催化剂的 1.30 倍。在30 000圈催化剂加速耐久性测试中,PtCoMn/C合金催化剂的电化学活性面积(ECSA)和质量比活性(MA)仅下降6.9%和27.1%,均远低于Pt/C催化剂。     

Acid-Promoted Oxygen-Atom Transfer from a Novel Dihydroisoquinoline-Derived Oxaziridine Substituted at Position 1

N-Alkyl-oxaziridines react in the presence of a nucleophile as an oxygenating agent; in the absence of a nucleophile, an isomerization reaction is observed. This study describes the synthesis of two new dihydroisoquinoline oxaziridines and their reactivity in an acid-promoted reaction in the presence and absence of sulfides.     

Simple Synthesis of Versatile Coumarin Scaffolds

We describe an approach using ring‐closing metathesis (RCM) to synthesize versatile coumarin derivatives that present appropriate substitutions both at the aromatic and at the α,β‐unsaturated lactone ring. The obtained compounds can be used as molecular scaffolds suitable for further diversifications through a combinatorial approach.