N-halogeno-compounds. Part 9 [1]. Azoxy- and azo-arenes derived from 4-(dichloroamino)tetrafluoropyridine; crystal structure of trans-2,3,5,6-tetrafluoro-4-(2,4,6-trimethylphenyl-onn-azoxy)pyridine

The nitrosoarenes ArNO (Ar = C₆H₅, 2-MeC₆H₄, 2,4,6- Me₃C₆H₂ and C₆F₅) have been condensed with 4-(dichloroamino)- tetrafluoropyridine to provide the azoxy-compounds py_FN$\text{N}\text{+}$($\text{N}\text{-}$)Ar (py_F = 2,3,5,6-tetrafluoro-4-pyridyl); de-oxygenation of the first three with triphenylphosphine or triethyl phosphite gave the corresponding azo-compounds, and the reverse reaction was achieved in the case of py_FNNC₆H₂Me₃-2,4,6 using peroxytrifluoroacetic acid. Thermolysis of 4-azidotetrafluoropyridine in the presence of pentafluoronitrosobenzene provided the perfluorinated azoxy-compound py_FN$\text{N}\text{+}$($\text{O}\text{-}$)C₆F₅. X-Ray methods have been used to determine the molecular geometry of py_FN$\text{N}\text{+}$($\text{O}\text{-}$)C₆H₂Me₃-2,4,6.     

Syntheses and polymerizations of some vinyl monomers containing nitro- or fluorophthalimides

4-Nitro-N-vinylphthalimide ( 4 ) was synthesized by two different procedures. Compound 4 was not polymerizable or copolymerizable by AIBN. Poly(N-vinylphthalimide) ( 17 ) was prepared and partially nitrated at 10–25°C. N,N′-(1,2-Ethanediyl)bis(4-nitrophthalimide) ( 15 ) and N,N′-(1,3-propanediyl)bis(4-nitrophthalimide) ( 16 ) were prepared by the condensation of the corresponding diamine with phthalic anhydride followed by nitration of the condensation products. 4-Nitrophthalic anhydride was prepared by the hydrolysis of 15 . Four styrene-substituted phthalimide monomers were synthesized. These include N-(4-vinylphenyl)phthalimide ( 25a ), N-(4-vinylphenyl)-3-fluorophthalimide ( 25b ), N-(4-vinylphenyl)-3-nitrophthalimide ( 25c ), and N-(4-vinylphenyl)-4-nitrophthalimide ( 25d ). Monomers 25a and 25b were polymerized by freeradical initiator (AIBN), whereas monomers 25c and 25d were not polymerizable or copolymerizable by AIBN due to a strong inhibitive effect exerted by the nitrophthalimide group. Monomers 25c and 25d were cationically polymerized (BF₃·OEt₂). Monomer 25b and styrene were copolymerized and their reactivity ratios were r₁ = 1.7 and r₂ = 0.55, respectively. The prepared polymers are useful as backbone polymers for grafting living anionic polymers.     

Metamaterial absorber based on circular ring structure with and without copper lines

This paper presents the analysis of circular ring metamaterial absorber with the existing of copper lines. The structure is designed using lossy FR4 substrate with thin copper layers. The circular ring shape with copper lines is printed on the top surface of FR4 substrate, while at the bottom surface is printed with full copper ground plane. Parametric study is done to investigate the effect of copper lines on the resonance frequency. From the simulation, the circular ring metamaterial absorber with vertical copper lines can resonates at lower frequency, but this structure is polarized sensitive. This drawback can be improved by adding horizontal copper lines together with the vertical copper lines. The circular ring structure with vertical and horizontal copper lines is not only polarization insensitive, but it can works at wide operating angle of incident waves.     

Modeling on an ecological food chain with recycling

We propose two nutrient-phytoplankton models with instantaneous and time delayed recycling, investigate the dynamics and examine the responses to model complexities. Instead of the familiar specific uptake rate and growth rate functions, we assume only that the nutrient uptake and phytoplankton growth rate functions are positive, increasing and bounded above. We use geometrical and analytical methods to find conditions for the existence of none, one, or at most two positive steady states and analyze the stability properties of each of these equilibria. With the variation of parameters, the system may lose its stability and bifurcation may occur. We study the occurrence of Hopf bifurcation and the possibility of stability switching. Numerical simulations illustrate the analytical results and provide further insight into the dynamics of the models, biological interpretations are given.     

Synthesis and design of polyurethane and its nanocomposites derived from canola-castor oil: Mechanical,thermal and shape memory properties

The recent global pandemic and its tremendous effect on the price fluctuations of crude oil illustrates the side effects of petroleum dependency more evident than ever. Over the past decades, both academic and industrial communities spared endless efforts in order to replace petroleum-based materials with bio-derived resources. In the current study, a series of shape memory polymer composites (SMPC's) was synthesized from epoxidized vegetable oils, namely canola oil and castor oil fatty acids (COFA's) as a 100% bio-based polyol and isophorone diisocyanate (IPDI) as an isocyanate using a solvent/catalyst-free method in order to eventuate polyurethanes (PU's). Thereafter, graphene oxide (GO) nanoplatelets were synthesized and embedded in the neat PU in order to overcome the thermomechanical drawbacks of the neat matrix. The chemical structure of the synthesized components, as well as the dispersion and distribution levels of the nanoparticles, was characterized. In the following, thermal and mechanical properties as well as shape memory behavior of the specimens were comprehensively investigated. Likewise, the thermal conductivity was determined. This study proves that synthesized PU's based on vegetable oil polyols, including graphene nanoparticles, exhibit proper thermal and mechanical properties, which make them stand as a potential candidate to compete with traditional petroleum-based SMPC's.     

Quaternary ammonium compounds in roots and leaves of Capparis spinosa L. from Saudi Arabia and Italy: investigation by HPLC-MS and 1H NMR

Capparis spinosa L. is a perennial plant typical of the Mediterranean flora and a multipurpose plant used for curing various human ailments. Quaternary ammonium compounds (QACs), as constituents of Capparaceae, play important roles in protecting against abiotic stress. Aim of this work was to determine QACs in root and leaves of caper from two proveniences. The presence of stachydrine, choline, glycine betaine and homo-stachydrine has been confirmed by high resolution MS, while ¹H NMR was applied to quantify the main QACs in the aqueous extracts. Stachydrine was quantified at 20.2 mg/g and 32.3 mg/g on dry leaves from South of Italy and Saudi Arabia, respectively, while a minor content was in dry roots (from 10.4 to 12.5 mg/g). Choline was considerably lower both in leaves and roots (from 0.3 to 1.2 mg/g). To our knowledge, this is the first report on the determination of QACs both in root and leaves of C. spinosa.