Heteropoly acids, their salts and polyoxometalates as heterogenous, efficient and eco-friendly catalysts in organic reactions: Some recent advances

In this review article, some recent advances of applying heteropoly acids and polyoxometalates as heterogeneous, reusable and eco-friendly catalysts in organic synthesis are discussed.     

An efficient and chemoselective method for protection of thiols catalyzed by aluminumdodecatungstophosphate (AlPW12O40), as a highly water tolerant Lewis acid catalyst

Protection of various thiols with diphenylmethanol was achieved in high yields at room temperature using catalytic amounts of AlPW₁₂O₄₀ in CH₂Cl₂. In the presence of this catalyst, protection of SH versus OH was achieved with high chemoselectivity and yields. The catalyst can be easily recovered and reused. Deprotection of DPM thioethers was also achieved using molecular iodine at reflux in CH₂Cl₂ in high yields.     

Improved Photodegradation of Organic Contaminants Using Nano‐TiO2 and TiO2–SiO2 Deposited on Portland Cement Concrete Blocks

The photocatalytic activity of TiO₂ nanoparticles (nano‐TiO₂) and its hybrid with SiO₂ (nano‐TiO₂–SiO₂) for degradation of some organic dyes on cementitious materials was studied in this work. Nanohybrid photocatalysts were prepared using an inorganic sol–gel precursor and then characterized using XRD, SEM and UV–Vis. The grain sizes were estimated by Scherrer's equation to be around 10 nm. Then, a thin layer was applied to Portland cement concrete (PCC) blocks by dipping them into nano‐TiO₂ and nano‐TiO₂–SiO₂ solution. The efficiency of coated PCC blocks for the photocatalytic decomposition of two dyes, Malachite Green oxalate (MG) and Methylene Blue (MB), was examined under UV and visible irradiation and then monitored by the chemical oxygen demand tests. The results showed that more than 80% and 92% of MG and MB were decomposed under UV–Vis irradiation using blocks coated with nano‐TiO₂–SiO₂. TiO₂/PCC and TiO₂–SiO₂/PCC blocks showed a significant ability to oxidize dyes under visible and UV lights and TiO₂–SiO₂/PCC blocks require less time for dye degradation. Based on these results, coated blocks have increased photocatalytic activity which can make them commercially accessible photocatalysts.     

Facile protection of carbonyl compounds as oxathiolanes and transoxathioacetalization of oxyacetals promoted by iron(III) trifluoroacetate or trifluoromethanesulfonate as chemoselective and recyclable catalysts

Oxathioacetalization of carbonyl compounds and transoxathioacetalization of O,O-acetals/ketals are reported under nearly neutral conditions promoted by iron(III) trifluoroacetate [Fe(CF₃CO₂)₃] or trifluoromethanesulfonate [Fe(CF₃SO₃)₃] as recyclable and highly efficient Lewis acid catalysts.     

Synthesis of new dyes containing double tetrazole groups for sensitization of TiO<Subscript>2</Subscript> nanoparticles in dye-sensitized solar cells

Di(1H-tetrazol-5-yl)methane is employed as a new electron acceptor group in the synthesis of two metal-free organic dyes containing triphenylamine donor group. Dye-sensitized nanocrystalline TiO₂ solar cell (DSSC) applying these novel dyes is constructed for consideration of their photovoltaic properties. The electronic properties of the dyes are also considered with the aid of theoretical calculations. The DSSC constructed from 4-(2,2-di(1H-tetrazol-5-yl)vinyl)-N,N-diphenylaniline (T1) shows a short-circuit photocurrent density of 13.38 mA cm^?2, an open circuit voltage of 578 mV, and a fill factor of 0.54, with a resulted solar energy-to-electricity conversion efficiency of 4.18% under simulated 1 sun irradiation (100 mW cm^?2). This result reveals that the dye with the di(1H-tetrazol-5-yl)methane anchoring group injects more electrons to the conduction band of TiO₂ in comparison with its analogs with single tetrazole ring in their anchoring group. It is found that in spite of a red-shift of the absorption spectrum resulted from the lengthening of the molecule, the dye with two di(1H-tetrazol-5-yl)methane groups gives lower performance than the dye with a single electron acceptor.     

In situ forming PLGA implant for 90 days controlled release of leuprolide acetate for treatment of prostate cancer

In prostate cancer, hormone therapy via leuprolide acetate drug (LUP) is used to lower the level of testosterone down to castration level to effectively control the development of prostate cancer. The objective of this study was to evaluate the effective parameters in degradation and controlled release of an injectable in situ formed polymeric implant, loaded with leuprolide acetate, in order to achieve an optimum formulation for sustained drug release for 90 days with minimum burst release. The main problem associating with such implants is their high burst release. Designing an injectable implant with sustained and minimum burst release has thus become an attractive challenge in drug delivery field. Effects of type of poly(lactic‐co‐glycolic acid) 75:25 copolymers (RG752, RG756) and addition of nano‐hydroxyapatite (HA) particles on degradation rates of the implants and release profiles were examined in vitro and in vivo in a rabbit animal model. Results showed that implants containing polymers with higher molecular weights had significantly lower weight loss and molecular weight reduction. Adding nanoparticles of hydroxyapatite into poly(lactic‐co‐glycolic acid) implants caused further reduction in degradation rates, leading to a more sustained drug release in vivo, with reduced burst release. Different conventional kinetic models were applied to drug release and degradation data. The degradation data fit well to the first‐order degradation model. Higuchi model was the best kinetic release model fitted to the experimental in vitro release data. This study led to an optimum formulation (RG756:RG752 3:1 + 5% HA) with sustained leuprolide release and testosterone suppression over a 90‐day period with significant decrease of burst release phase (50%, p < 0.001) compared with the conventional Eligard formulation. The histopathology test showed that the formulated implant had no effects of toxicity or tissue necrosis in organs of the animal model. Copyright © 2017 John Wiley & Sons, Ltd.     

ZnBr2 catalyzed domino Knoevenagel-hetero-Diels–Alder reaction: An efficient route to polycyclic thiopyranoindol annulated [3,4-c]quinolone derivatives

Various novel polycyclic thiopyranoindol annulated [3,4-c]quinolone derivatives were synthesized via domino Knoevenagel-hetero-Diels–Alder reactions of indoline-2-thions and novel N-acrylated anthranilaldehydes in refluxing ethanol as a solvent in the presence of 20 mol% ZnBr₂ as a Lewis acid catalyst. All reactions proceed with high yields with excellent regio- and stereoselectivity.     

Magnetic solid-phase extraction of warfarin and gemfibrozil in biological samples using polydopamine-coated magnetic nanoparticles via core-shell nanostructure

Herein, polydopamine-coated Fe₃O₄ spheres were synthesized using a very simple, easy, cost-effective, efficient, and fast method. First, magnetic nanoparticles (Fe₃O₄) were synthesized and were followed by accommodating polydopamine on the surface of the prepared Fe₃O₄. The prepared polydopamine-coated Fe₃O₄ spheres were utilized as a sorbent in magnetic solid phase extraction of gemfibrozil and warfarin (as the model analytes). The extracted model analytes were desorbed by a suitable organic solvent and were analyzed by high-performance liquid chromatography. Under optimized condition, the linearity of the method was in the range of 0.1–200.0 μg/L for the selected analytes in water. The limits of detection were calculated to be in the range of 0.026–0.055 μg/L for warfarin and gemfibrozil, respectively. The limits of quantification were calculated to be in the range of 0.089–0.185 μg/L. The inter-day and intra-day relative standard deviations were determined to be in the range of 1.4%–3.3% in three concentrations in order to calculate the method precision. Furthermore, the enrichment factors were found to be 78 and 81 for warfarin and gemfibrozil, respectively. Moreover, the calculated absolute recoveries were between 78% and 81%. The obtained recoveries indicated that the method was useful and applicable in complicated real samples.     

On monomial curves obtained by gluing

We study arithmetic properties of tangent cones associated to large families of monomial curves obtained by gluing. In particular, we characterize their Cohen-Macaulay and Gorenstein properties and prove that they have non-decreasing Hilbert functions. The results come from a careful analysis of some special Apéry sets of the numerical semigroups obtained by gluing under a condition that we call specific gluing. As a consequence, we complete and extend the results proved by Arslan et al. (in Proc. Am. Math. Soc. 137:2225–2232, 2009) about nice gluings by using different techniques. Our results also allow to prove that for a given numerical semigroup with a non-decreasing Hilbert function and an integer q>1, all extensions of it by q, except a finite number, have non-decreasing Hibert functions.