Stereoselectivity and regioselectivity in the segment-coupling Prins cyclization

The scope of the segment-coupling Prins cyclization has been investigated. The method is outlined in Scheme 1 and involves esterification of a homoallylic alcohol (1), reductive acetylation to give the alpha-acetoxy ether (3), and cyclization on treatment with a Lewis acid to produce a tetrahydropyran (4). Alkene geometries dictate the product configurations, with E-alkenes leading to equatorial substituents and Z-alkenes leading to axial substituents (Table 1). Not unexpectedly, applying the method to allylic alcohols leads to fragmentation rather than a disfavored 5-endo-trig cyclization. Dienols in which one alkene is allylic and the other alkene is homoallylic cyclize efficiently and produce the tetrahydropyrans 49-54, Table 3. Dienols with two homoallylic alkenes cyclize with modest to high regioselectively, generating tetrahydropyrans 40-45, Table 2. The relative rates for cyclization decrease in the order of vinyl > Z-alkene > E-alkene > alkyne. The configurations of the products are consistent with cyclization via a chair conformation, Figure 1. The 2-oxonia Cope rearrangement may be a factor in the regioselectivity of diene cyclizations and in the erosion of stereoselectivity with Z-alkenes. This investigation establishes the stereoselectivity and regioselectivity for a number of synthetically useful segment-coupling Prins cyclizations.     

Dichloro-bis-(pyridine-2-yl-undecyl-amine)zinc(II), [ZnCl2(C16N2H26)2]: Synthesis,characterization and antimalarial activity

A nitrogen-based ligand (pyridine-2-yl-undecyl-amine) (1) was synthesized and used for the synthesis of a Zn(II) compound (dichloro-bis(pyridine-2-yl-undecyl-amine)zinc(II)) (2). Compound 2 was synthesized and characterized using IR, ¹H NMR, and ¹³C{¹H} NMR spectroscopy. The crystal structure of 2 was determined using single-crystal X-ray crystallography. The compound was tested for its anti-malarial activity using two methods, a semi-quantitative micro-assay and a previously self-developed quantitative in vitro method. Both methods were used to study the efficiency of 2 to inhibit the formation of the malaria pigment considered an important target of many anti-malarial drugs such as chloroquine and amodaquine. The efficiency of 2 to prevent the formation of β-hematin was 71.4%. The efficiency of amodiaquine as a standard drug was reported at 93.8%.     

Synthesis and structural studies of new Mannich base ligands and their metal complexes

The new Mannich bases bis(1,4-diphenylthiosemicarbazide methyl) phosphinic acid H₃L¹ and bis(1,4-diphenylsemicarbazide methyl) phosphinic acid H₃L² were synthesised from the condensation of phosphinic acid, formaldehyde with 1,4-diphenyl thiosemicarbazide and 1,4-diphenylsemicarbazide, respectively. Monomeric complexes of these ligands, of general formulae K₂[Cr^III(L ⁿ )Cl₂], K₃[Mn^II(L ⁿ )Cl₂] and K[M(L ⁿ )] (M = Co(II), Ni(II), Cu(II), Zn(II) or Hg(II); n = 1, 2), are reported. The mode of bonding and overall geometry of the complexes were determined through physico-chemical and spectroscopic methods. These studies revealed octahedral geometries for the Cr(III), Mn(II) complexes, square planar for Co(II), Ni(II) and Cu(II) complexes and tetrahedral for the Zn(II) and Hg(II) complexes.     

Synthesis and Characterization of Intramolecularly Stabilized Chiral Dimethylindium Alkoxides and their Use as Cross Coupling Reagents

The enantiomerically pure dimeric N, O‐5‐chelates [Me₂In(μ‐OCH₂CH(R)NMe₂)]₂ {R = Me (S) ( 2 ); R = ⁱPr (S) ( 3 ); R = ⁱBu (S) ( 4 ); R = Bz (S) ( 5 )}, and [Me₂In‐{μ‐(1R, 2S)‐OCH(Ph)CH(Me)NMe₂}]₂ ( 6 ), as well as the achiral dimeric N, O‐6‐chelate [Me₂In(μ‐O(CH₂)₃NMe₂)]₂ ( 7 ) have been synthesized from trimethylindium and equimolar amounts of the corresponding enantiomerically pure dimethylamino alcohols or of the achiral dimethylaminopropanol by elimination of methane. Their ¹H NMR, ¹³C NMR, and mass spectra as well as the X‐ray single crystal structure analyses of [Me₂In{μ‐O(CH₂)₂NMe₂}]₂ ( 1 ), 3, 5, 6 and 7 are described and discussed. The coordinative N→In bonds of the five‐coordinate indium complexes show dynamic dissociation/association processes. 1—6 were found to be useful reagents for the partial kinetic resolution of 2‐carbomethoxy‐1, 1′‐binaphthyl triflate.     

Multiple internal resonances in MEMS arch resonators

Micromachined shallow arch resonant beams have attracted significant attention thanks to their rich dynamical behavior, inherent nonlinearities, and the potential to excite various internal resonances. Currently, there is a lack of comprehensive experimental studies for the various types of internal resonances in arches and particularly at the micro and nano scales. Here, we aim to investigate and identify different types of internal resonances of an initially curved beam, electrothermally actuated and electrostatically driven, by electrical characterization techniques. Upon changing the electrothermal voltage of silicon micromachined arches, the second symmetric natural frequency of an arch is adjusted to near twice, three times, and four times the fundamental natural frequency, which gives rise to 2:1, 3:1, and 4:1 autoparametric resonances between the two modes. These resonances are demonstrated experimentally. We show various frequency-response curves of the total response around the excitation frequency and highlight the contribution of each mode before, during, and after the internal resonances. Allan-deviation results are also shown indicating enhanced frequency stabilization of the arch oscillation when experiencing internal resonances. These studies motivate further research in this direction to exploit internal resonances of micromachined resonators for practical applications, such as sensors and mechanical amplifier.     

Waste to wealth: conversion of nano‐magnetic eggshell (Fe3O4@Eggshell) to Fe3O4@Ca(HSO4)2: cheap,green and environment‐friendly solid acid catalyst

Eggshell is a hazardous waste by European Union regulations, so that discarded thousands of tons per year. To convert waste (eggshell) to wealth (catalyst), nano‐magnetic eggshell was prepared based on the nano‐Fe₃O₄, and then the eggshell was converted to Ca(HSO₄)₂ with organic acid, namely, chlorosulfonic acid. Based on the back titration, 5.18 mmol SO₄H group was loaded per gram of the nano‐structure. Using this method eggshell was converted to cheap, green and environment‐friendly solid acid catalyst. The prepared catalyst (nano‐ Fe₃O₄@Ca(HSO₄)₂) was characterized by Fourier transform infrared spectroscopy (FT‐IR), X‐ray diffraction (XRD), energy dispersive X‐ray spectroscopy (EDX), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM), and thermal gravimetric analysis (TGA). The activity of eggshell waste‐derived catalysts was successfully evaluated in the synthesis of value‐added products, namely indazolo[1,2‐b]‐phthalazinetrione derivatives as a benchmark multicomponent reaction. In addition, design of experiments shows that increase in amount of catalyst (and temperature), boost the reaction yield, especially with steeper slope at higher temperature.     

Investigation of a vortex tube using three different RANS-based turbulence models

Journal of Thermal Analysis and Calorimetry - The main objective of this study is to capture the function of temperature separation inside a vortex tube (VT), firstly, via testing it at different...     

Zwitterion-stabilized silica nanoparticles: toward nonstick nano

Using a short-chain zwitterionic organosiloxane, silica nanoparticles were stabilized against aggregation by high ionic strength and/or proteins. Turbidimetry and dynamic light scattering showed that "zwitterated" nanoparticles did not exhibit a significant increase in hydrodynamic radius. When challenged with 3 M NaCl or 50% fetal bovine serum, aggregation was inhibited for at least 24 h, longer with mild heat treatment, which produced nanoparticles with zero net surface charge. These findings suggest "zwitteration" of silica-capped nanoparticles provides excellent stability for in vivo circulation diagnostics and therapies.     

Coordination of carbonyl oxygen in the complexes of polymeric <Emphasis Type="Italic">N</Emphasis>-crotonyl-2-hydroxyphenylazomethine

The Schiff base N-crotonyl-2-hydroxyphenylazomethine HL, derived from the reaction of acrylamide and salicylaldehyde, was synthesised. Polymeric complexes were obtained from the reaction of polymeric HL with divalent metals. The mode of bonding and overall geometry of the complexes were determined through physico-chemical and spectroscopic methods and compared with that previously reported for the analogous monomeric ligand. These studies revealed tetrahedral geometries around the metal centres for Mn(II), Co(II), Zn(II), Cd(II) and Hg(II) complexes of general formula [M(L)Cl], octahedral for Ni(II) and Cu(II) complexes of general formula [M′(L)Cl(H₂O)₂], and square planar for Pd(II) complex of general formula [Pd(L)Cl].