Synthesis, structure, and magnetic properties of (6-9)-nuclear Ni(II) trimethylacetates and their heterospin complexes with nitroxides

New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)] x 0.5 C6H14 x 0.5 H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4] x C5H10O2 x 3 H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 6-9 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L(1)-L(3)), methyl (L(4)), or imidazole (L(5)) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(1))2(H2O)] x 0.5 C6H14 x H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)] x H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L(3))2(H2O)] x H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L(4))] x 1.5 C6H14 (6'), and [Ni4OH)3(C5H9O2)5(C5H10O2)4(L(5))] x 1.5 C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni6(mu4-OH)2(mu3-OH)2(mu2-C5H9O2-O,O')6(mu2-C5H9O2-O,O)(mu4-C5H9O2-O,O,O',O')(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1a-c) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6') with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane.     

Electron paramagnetic resonance of three-spin nitroxide-copper(II)-nitroxide clusters coupled by a strong exchange interaction

The complex of Cu(2+) hexafluoroacetylacetonate with two pyrazol-substituted nitronyl nitroxides represents an unusual exchange-coupled three-spin system. The antiferromagnetic exchange coupling, which already atT < 150 K is larger than the thermal energy kT, induces the transition from a total spin state S = (3)/(2) to a state S = (1)/(2) and produces static spin polarization. Anomalous electron paramagnetic resonance (EPR) spectra of an S = (1)/(2) state were detected experimentally and described theoretically. The effective g factor of the three-spin system is smaller than 2, despite the fact that all the individual components have g > 2. The observed signals with g < 2 are highly informative and can be employed for determination of the sign and value of the exchange interaction in three-spin nitroxide-copper-nitroxide clusters.     

2-iodylphenol ethers: preparation, X-ray crystal structure, and reactivity of new hypervalent iodine(V) oxidizing reagents

2-Iodylphenol ethers were prepared by the dimethyldioxirane oxidation of the corresponding 2-iodophenol ethers and isolated as chemically stable, microcrystalline products. Single-crystal X-ray diffraction analysis of 1-iodyl-2-isopropoxybenzene 8c and 1-iodyl-2-butoxybenzene 8d revealed pseudopolymeric arrangements in the solid state formed by intermolecular interactions between IO2 groups of different molecules. 2-Iodylphenol ethers can selectively oxidize sulfides to sulfoxides and alcohols to the respective aldehydes or ketones.     

Better understanding of the ring-cleavage process of cyanocyclopropyl anionic derivatives. A theoretical study based on the electron localization function

[reaction: see text] Theoretical calculations at the B3LYP/6-31+G(d), MP2/6-31+G(d), and G3(MP2) levels have been carried out to understand the alternative reaction pathways (the cyclopropyl ring cleavage (RC) and the retrocycloaddition reaction (rCA)) of a constrained tricyanocyclopropyl anionic derivative. The more energetically favorable path is found to be the RC process, a formally "forbidden" rearrangement (Leiviers, M.; Tam, I.; Groves, K.; Leung, D.; Xie, Y.; Breslow, R. Org. Lett. 2003, 5, 19, 3407) yielding an allylic anion system via a concerted transition structure, in agreement with experimental outcomes. rCA is more energetically favorable along a two-stage mechanism, via an intermediate, than a synchronous concerted process. By using isodesmic reactions, we have found that B3LYP presents limitations when it calculates carbon-carbon bond-breaking processes along the present rCA reaction. A detailed analysis of the nature of the topology of the reactive potential energy surface for the RC process points out the presence of a valley-ridge inflection point in the uphill part. An explanation for the low-energy barrier associated with RC is furnished on the analysis of the evolution of the twisting (dis-/conrotatory) motions of cyano substituents in the cyclopropyl ring as well as on the number and type of electron pairs provided by the electron localization function (ELF).     

Separation performance of single-stranded DNA electrophoresis in photopolymerized cross-linked polyacrylamide gels

Considerable effort has been directed toward optimizing performance and maximizing throughput in ssDNA electrophoresis because it is a critical analytical step in a variety of genomic assays. Ultimately, it would be desirable to quantitatively determine the achievable level of separation resolution directly from measurements of fundamental physical properties associated with the gel matrix rather than by the trial and error process often employed. Unfortunately, this predictive capability is currently lacking, due in large part to the need for a more detailed understanding of the fundamental parameters governing separation performance (mobility, diffusion, and dispersion). We seek to address this issue by systematically characterizing electrophoretic mobility, diffusion, and dispersion behavior of ssDNA fragments in the 70-1,000 base range in a photopolymerized cross-linked polyacrylamide matrix using a slab gel DNA sequencer. Data are collected for gel concentrations of 6, 9, and 12%T at electric fields ranging from 15 to 40 V/cm, and resolution predictions are compared with corresponding experimentally measured values. The data exhibit a transition from behavior consistent with the Ogston model for small fragments to behavior in agreement with the biased reptation model at larger fragment sizes. Mobility data are also used to estimate the mean gel pore size and compare the predictions of several models.     

Effect of photonic crystal structure on the nonlinear optical anisotropy of birefringent porous silicon

Anisotropic photonic crystal structures consisting of birefringent porous silicon layers with alternating porosity were fabricated. The in-plane birefringence formed as a result of anisotropic etching in Si(110) results in unique multilayered structures with two distinct photonic bandgaps for orthogonal light polarizations. Nonlinear optical studies based on the third-harmonic generation from these structures demonstrate variation in the symmetry of the nonlinear optical response.     

Toward Tailor‐Made Biocide Materials Based on Poly(propylene)/Copper Nanoparticles

A set of poly(propylene) composites containing different amounts of copper nanoparticles (CNP) were prepared by the melt mixed method and their antimicrobial behavior was quantitatively studied. The time needed to reduce the bacteria to 50% dropped to half with only 1 v/v % of CNP, compared to the polymer without CNP. After 4 h, this composite killed more than 99.9% of the bacteria. The biocide kinetics can be controlled by the nanofiller content; composites with CNP concentrations higher than 10 v/v % eliminated 99% of the bacteria in less than 2 h. X‐ray photoelectron spectroscopy did not detect CNP at the surface, therefore the biocide behavior was attributed to copper in the bulk of the composite.

     

Air-related mechanisms of noise generation by solid rubber tyres with cavities

There are four main air-related noise generation mechanisms at the tyre/road interface, which were all categorised more than 20 years ago. The first one is the so-called ‘air pumping’ mechanism. Two other air-related phenomena that occur when there are air movements near the contact patch of the tyre are ‘air resonant radiation’ and ‘pipe resonances’ which appear at the footprint of the tyre. In addition to these, there is a forth effect, which is mentioned in the literature, that is occurring due to turbulence effects of the air surrounding the spinning tyre. There has been less focus on the air-related mechanisms than on other types of tyre noise generation mechanisms. This paper attempts to add some detail to current understanding of the air-related noise generation at the tyre road interface and gives some further information on how to identify the differences due to these mechanisms. Specifically in the present paper, a solid rubber tyre running on a vehicle chassis dynamometer is used to study the first two mechanisms. This is done with emphasis on the time history of the recorded signal and not on the frequency spectrum, as is more commonly used. A comparison with existing theoretical models of these mechanisms reveals some of the strength and weaknesses of the current understanding of these phenomena.     

On the constitutive inequalities and acceleration waves in micropolar media

Acceleration waves in nonlinear thermoelastic micropolar media are considered. We establish the kinematic and dynamic compatibility relations for a singular surface of order 2 in the media. An analogy to the Fresnel–Hadamard–Duhem theorem and an expression for the acoustic tensor are derived. The condition for acceleration wave's propagation is formulated as an algebraic spectral problem. It is shown that the condition coincides with the strong ellipticity of equilibrium equations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Adsorption Reaction Dynamics of Systems Lysozyme and Nanodiamond/Nanosilica at pH=7-13

Adsorption reactions between surfaces of nanodiamond and nanosilica with diameter of 100 nm prepared as suspension solutions of 0.25 μg/μL and lysozyme molecule with different concentrations of 7 mmol/L PPBS at pH=7, 9, 11, and 13 have been investigated by fluores-cence spectroscopy. Adsorption reaction constants and coverages of lysozyme with different concentrations of 0-1000 nmol/L under the influences of different pH values have been ob-tained. Helicities and conformations of the adsorbed lysozyme molecules, free spaces of every adsorbed lysozyme molecule on the surfaces of nanoparticles at different concentrations and pH values have been deduced and discussed. The highest adsorption capabilities for both sys-tems and conformational efficiency of the adsorbed lysozyme molecule at pH=13 have been obtained. Lysozyme molecules can be prepared, adsorbed and carried with optimal activity and helicity, with 2 and 10 mg/m2 on unit nanosurface, 130 and 150 mg/g with respect to the weight of nanoparticle, within the linear regions of the coverages at around 150-250 nmol/L and four pH values for nanodiamond and nanosilica, respectively. They can be prepared inthe tightest packed form, with 20 and 55 mg/m2, 810-1680 and 580-1100 mg/g at threshold concentrations and four pH values for nanodiamond and nanosilica, respectively.