Synthesis of μ2-Oxo-Bridged Iron(III) Tetraphenylporphyrin–Spacer–Nitroxide Dimers and their Structural and Dynamics Characterization by using EPR and MD Simulations

Iron(III) porphyrins have the propensity to form μ₂-oxo-dimers, the structures of which resemble two wheels on an axle. Whereas their crystal structure is known, their solution structure and internal dynamics is not. In the present work, the structure and dynamics of such dimers were studied by means of electron paramagnetic resonance (EPR) spectroscopy and quantum chemistry based molecular dynamics (MD) simulations by using the semiempirical tight-binding method (GFN-xTB). To enable EPR investigation of the dimers, a nitroxide was attached to each of the tetraphenylporphyrin cores through a linear and a bent linker. The inter-nitroxide distance distributions within the dimers were determined by continuous-wave (cw)-EPR and pulsed electron–electron double resonance (PELDOR or DEER) experiments and, with the help of MD, interpreted in terms of the rotation of the porphyrin planes with respect to each other around the Fe–O–Fe axis. It was found that such rotation is restricted to the four registers defined by the phenyl substituents. Within the registers, the rotation angle swings between 30° and 60° in the proximal and between 125° and 145° in the distal register. With EPR, all four angles were found to be equally populated, whereas the 30° and 145° angles are strongly favored to the expense of the 60° and 125° angles in the MD simulation. In either case, the internal dynamics of these dimers thus resemble the motion of a step motor.     

Synthesis and crystal structure of a pyrroline nitroxide radical, (N-2,2,5,5-tetramethyl-1-oxo-3-pyrroline-3-carbonyl) (N,N′-diisopropyl)urea

The title compound including a stable nitroxide radical was synthesized by a reaction of N,N-diisopropylcarbondiimide (DIC) with 2,2,5,5-tetramethyl-1-oxo-3-pyrroline-3-carboxylic acid (TPCO) in an EtOAc solution under nitrogen atmosphere. From 1:1 EtOAc/hexane the compound crystallizes in triclinic space group P with a = 11.078(2), b = 11.970(2), c = 15.746(3) Å, = 105.41(3), = 103.47(3), = 106.52(3)°, and Z = 4. In an asymmetric unit two molecules assemble with each other in similar bond distances and angles but show crystallographically independent conformation. A normal single C–N bond is observed in the title compound, other than the partial double C=N bond shown in the parent urea. A longer N–O distance of 1.26 Å implies the existence of a single electron bond between N and O atoms, which stabilizes the radical molecule.     

Synthesis, Crystal Structure and Magnetic Properties of a New Zn(II)-Nitronyl Nitroxide Complex

A new complex [Zn(NIT-1'-MeBzIm)Cl2(H2O)] (NIT-1'-MeBzIm = 2-{2'-[(l'- methyl)benzimidazolyl]}-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been prepared and structurally characterized by X-ray diffraction method. Crystal data: monoclinic, space group P21/n, Z = 4, C15H21Cl2N4O3Zn, Mr = 441.63, a = 7.2225(10), b = 30.849(4), c = 8.8758(13) , β = 103.904(2)°, V = 1919.6(5) 3, Dc = 1.528 g/cm3, μ(MoKα) = 1.579 mm1, F(000) = 908, R = 0.0436 and wR = 0.1029 for 2456 observed reflections with I > 2σ(I). X-ray analysis reveals that the Zn(II) ion is four-coordinated with a distorted tetrahedron. There also exist H-bonds, π-π piling interactions and weak intermolecular contacts between the NO groups which form a mutual stagger 3-D network configuration. Magnetic investigation reveals that there exists intermolecular antiferro- and ferromagnetic interactions in the title complex.     

A non‐volatile,bistable, and rewritable memory device fabricated with poly(nitroxide radical) and silver salt layers

A non‐volatile, bistable, and rewritable organic memory device was successfully fabricated with the layers of poly(2,2,6,6‐tetramethylpiperidine‐1‐oxyl methacrylate) (PTMA) and poly(methyl methacrylate) (PMMA) containing silver salt. The PTMA layer was employed as a p‐dopable material, while the silver salt‐dispersed PMMA layer acted as an n‐dopable material. The ON–OFF ratio between low‐conductivity and high‐conductivity states amounted to more than four orders of magnitude, and the retention time was longer than 10³ sec. The device was characterized by excellent rewritability. Copyright © 2007 John Wiley & Sons, Ltd.     

无机-有机纳米复合材料：有机氮氧自由基/MnPS3夹层物的合成与磁性

合成了一个无机,有机纳米复合物(MPYNN)0.14Mn0.93PS3,即有机氮氧自由基MPYNN(N-甲基吡啶阳离子自由基)的MnPS3夹层化合物.通过X-射线粉末衍射和红外光谱等对其结构进行了表征,根据其0.56 nm的层间距扩大值推测夹层化合物中的客体分子在层间采取了分子平面近乎垂直于主体层的排列方式.通过SQUID测试了所得到的夹层化合物的磁性,结果表明夹层化合物(MPYNN)0.14Mn0.93PS3在10 K以上具有顺磁特性,而在7 K时出现了一个明显的磁相变,表现出自发磁化.     

Syntheses,crystal structures,magnetic and luminescent properties of lanthanide complexes with nitronyl nitroxide radical as ligand

Four lanthanide-nitronyl nitroxide radical complexes, [Ln(hfac)₃(NIT-3Methien)₂] (Ln = Pr (1), Tb (2), Dy (3), Ho (4); hfac = hexafluoroacetylacetonate; NIT-3Methien = 2-(3-methylthiophene)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide), have been synthesized, and structurally and magnetically characterized. Single-crystal X-ray diffraction shows that 1–4 have similar mononuclear tri-spin structures in which central Ln(III) ions are eight coordinate by two NIT-3Methien radicals and three hfac coligands. The magnetic studies indicate that there are antiferromagnetic interactions between Ln(III) ions and radicals in 1, 2, and 4, while ferromagnetic interactions are present in 3. The luminescence properties of 2 and 3 were studied.     

Copolymerization of 2,3,4,5,6‐Pentafluorostyrene and Methacrylic Acid by Nitroxide‐Mediated Polymerization: The Importance of Reactivity Ratios

Amphiphilic block copolymers of 2,3,4,5,6‐pentafluorostyrene (PFS) and methacrylic acid (MAA) are synthesized via nitroxide‐mediated polymerization (NMP). It is established that to obtain a controlled copolymerization a minimum of 40 mol% of PFS is required, which is significantly greater than other copolymerization systems such as using 4.5–8 mol% styrene or 1 mol% of 9‐(4‐vinylbenzyl)‐9H‐carbazole to control the copolymerization of methacrylates. It is surmised that this lack of control is due to the reactivity ratios that favor the addition of MAA rather than PFS (r_PFS = 0.14, r_MAA = 6.97). However this reactivity ratio pair suggests that a one‐shot delayed injection approach can be utilized to synthesize almost pure block copolymers in one pot. Therefore, poly(PFS)‐b‐(PFS‐ran‐MAA) block copolymers are synthesized by a one‐shot delayed addition of MAA. While the concentration of irreversibly terminated chains is evident these results suggest a promising route to the synthesis of fluorinated amphiphilic block copolymers by NMP.

     

氮氧自由基中的多光子化学反应(Ⅰ)

在不同光源照射下,作者利用乙基亚硝基有机化合物在乙醇溶剂下,产生双光子的化学反应,用电子自旋共振吸收谐振腔为反应器.在不同的流速下,生成3种同分异构自由基.其结构由电子自旋共振光谱确定、微观的氢键跳动频率由不同波形的氮核超精细偶合常数的变化而确定、利用Charm软件计算,确定β-氢超精细偶合常数的意义及其几何形状.     

A Simple Method of Synthesis of 3-Carboxy-2,2,5,5-Tetraethylpyrrolidine-1-oxyl and Preparation of Reduction-Resistant Spin Labels and Probes of Pyrrolidine Series

Stable free radicals are widely used as molecular probes and labels in various biophysical and biomedical research applications of magnetic resonance spectroscopy and imaging. Among these radicals, sterically shielded nitroxides of pyrrolidine series demonstrate the highest stability in biological systems. Here, we suggest new convenient procedure for preparation of 3-carboxy-2,2,5,5-tetraethylpyrrolidine-1-oxyl, a reduction-resistant analog of widely used carboxy-Proxyl, from cheap commercially available reagents with the yield exceeding the most optimistic literature data. Several new spin labels and probes of 2,2,5,5-tetraethylpyrrolidine-1-oxyl series were prepared and reduction of these radicals in ascorbate solutions, mice blood and tissue homogenates was studied.     

Synthesis of C_(60) Nitroxide Derivatives

MagginiIfirstreportedthesynthesisoffulleropyrrolidinederivativesbyl,3dipolarcycloaddition,whichprovedtobeoneofthemosteffectivemethodtoobtainfullerenemonoadductderivatives.In1995,Corvaja'reportedthesynthesisofC,,derivativecovalentlylinkedwitha11itroxideradical2,2,6,6-tetramethylpiperidine-l-oxylbyl,3dipolarcycloadditionusingC,,,TOACandparaformaldehydeasthereactants.ThiscompoundisuniqueinthestudyoftheintramolecularinteractionofaradicalspecieswiththeC,.>core.Herewereportanothermethodtosynthes…