Damage processes in thermoviscoelastic materials with damage‐dependent thermal expansion coefficients

In this paper, we prove existence of global in time weak solutions for a highly nonlinear PDE system arising in the context of damage phenomena in thermoviscoelastic materials. The main novelty of the present contribution with respect to the ones already present in the literature consists in the possibility of taking into account a damage‐dependent thermal expansion coefficient. This term implies the presence of nonlinear coupling terms in the PDE system, which make the analysis more challenging. Copyright © 2015 John Wiley & Sons, Ltd.     

Synthesis,Magnetic Properties,and STM Spectroscopy of Cobalt(II) Cubanes [CoII4(Cl)4(HL)4]

Reaction of cobalt(II) chloride hexahydrate with N‐substituted diethanolamines H₂L^2–4 ( 3 ) in the presence of LiH in anhydrous THF leads under anaerobic conditions to the formation of three isostructural tetranuclear cobalt(II) complexes [Co^II₄(Cl)₄(HL^2–4)₄] ( 4 ) with a [Co₄(μ₃‐O)₄]⁴⁺ cubane core. According to X‐ray structural analyses, the complexes 4 a , c crystallize in the tetragonal space group I4₁/a, whereas for complex 4 b the tetragonal space group P$\bar 4$ was found. In the solid state the orientation of the cubane cores and the formation of a 3D framework were controlled by the ligand substituents of the cobalt(II) cubanes 4 . This also allowed detailed magnetic investigations on single crystals. The analysis of the SQUID magnetic susceptibility data for 4 a gave intramolecular ferromagnetic couplings of the cobalt(II) ions (J₁≈20.4 K, J₂≈7.6 K), resulting in an S=6 ground‐state multiplet. The anisotropy was found to be of the easy‐axis type (D=?1.55 K) with a resulting anisotropy barrier of Δ≈55.8 K. Two‐dimensional electron‐gas (2DEG) Hall magnetization measurements revealed that complex 4 a is a single‐molecule magnet and shows hysteretic magnetization characteristics with typical temperature and sweep‐rate dependencies below a blocking temperature of about 4.4 K. The hysteresis loops collapse at zero field owing to fast quantum tunneling of the magnetization (QTM). The structural and electronic properties of cobalt(II) cubane 4 a , deposited on a highly oriented pyrolytic graphite (HOPG) surface, were investigated by means of STM and current imaging tunneling spectroscopy (CITS) at RT and standard atmospheric pressure. In CITS measurements the rather large contrast found at the expected locations of the metal centers of the molecules indicated the presence of a strongly localized LUMO.     

A non-heme dinuclear iron(II) complex containing a single, unsupported hydroxo bridge

Complexation of the tetrapodal pentadentate NN4 ligand 2,6-C5H3N[CMe(CH2NH2)2]2 (I) with iron(II) perchlorate hydrate in methanol, in the presence of N-methylimidazole, produces a diferrous complex with a single, unsupported mu-OH ligand between two {(I)FeII} coordination modules.     

High-power single-polarization and single-transverse-mode fiber laser with an all-fiber cavity and fiber-grating stabilized spectrum

Conventionally, large-mode-area (LMA) fiber lasers use free-space polarizing components to achieve linear polarization output. External components, however, significantly limit laser robustness and power scalability. We demonstrate, to the best of our knowledge, the first high-power all-fiber cavity single-polarization single-transverse-mode LMA fiber laser, without the use of free-space polarizing components. This has been achieved by using tightly coiled high-birefringence 20 microm core LMA fiber. The lasing spectrum at 1085 nm has been stabilized by a fiber grating, spliced at one end of a LMA fiber. Up to 405 W of single-polarization output with a polarization extinction of >19 dB with a narrow spectrum (1.9 nm FWHM) and in a single-transverse mode (M2 < 1.1) has been demonstrated. The simplicity of a monolithic-cavity approach is highly beneficial for a number of applications, including the use of a fiber laser for nonlinear wavelength conversion and for coherent and spectral beam combining.     

A new diamantane functionalized tris(aryloxide) ligand system for small molecule activation chemistry at reactive uranium complexes

The diamantane functionalized triazacyclononane ligand (^DiaArOH)₃tacn (L₃) has been synthesized and the reactivity of its U(III) metallated product [((^DiaArO)₃tacn)U] (1) has been explored. Complex 1 promotes dichloromethane and azidotrimethylsilane activation to generate U(IV) complex [((^DiaArO)₃tacn)U(Cl)] (2) and U(V) complex [((^DiaArO)₃tacn)U(NTMS)] (3), respectively. Spectroscopic investigations of complexes 1, 2, and 3 will be discussed, along with molecular structures where possible.     

Solvent dependent reactivity: solvent activation vs. solvent coordination in alkylphosphane iron complexes

The pyridine-derived tetrapodal tetraphosphane C5H3N[CMe(CH2PMe2)2]2 is susceptible to selective protonolysis of a phosphorus-carbon bond in the presence of iron(II) salts. Water produces dimethylphosphinic acid, Me2POH, and protonates the anionic remainder of the tetraphosphane. The resulting iron(II) complexes and (tetrafluoroborate and perchlorate salts, respectively) contain the residual chelate ligand in which a methyl group, derived from the ligand skeleton, is in agostic interaction with the metal centre, and in which Me2POH, unavailable in the free state owing to rapid tautomerisation, is metal-coordinated and thus stabilised. Full NMR details are presented, including 31P simulations. The reactivity towards alcohols is similar (compounds), and has been studied using deuterium labels (NMR). P-C bond cleavage may be suppressed only if all protic agents are rigorously excluded, as in the reaction of with Fe(SO3CF3)2.2CH3CN in acetonitrile solution, which produces the complex [Fe(NCMe)](SO3CF3)2. In it, the ligand acts as an NP4 coordination cap but is severely distorted from square-pyramidal geometry. The reaction of with anhydrous ferrous bromide, FeBr2, in methanol again produces a dimethylphosphinic acid ester ligand, but the complex now contains ferric iron coordinated by a carbanionic residual chelate ligand, implicating H+ as the oxidising agent under these conditions. Full spectroscopic and X-ray structural details are presented for all compounds.     

The [Fe(III)[Fe(III)(L1)2]3] star-type single-molecule magnet

Star-shaped complex [Fe(III)[Fe(III)(L1)2]3] (3) was synthesized starting from N-methyldiethanolamine H2L1 (1) and ferric chloride in the presence of sodium hydride. For 3, two different high-spin iron(III) ion sites were confirmed by M?ssbauer spectroscopy at 77 K. Single-crystal X-ray structure determination revealed that 3 crystallizes with four molecules of chloroform, but, with only three molecules of dichloromethane. The unit cell of 3.4CHCl3 contains the enantiomers (delta)-[(S,S)(R,R)(R,R)] and (lambda)-[(R,R)(S,S)(S,S)], whereas in case of 3.3CH2Cl2 four independent molecules, forming pairs of the enantiomers [lambda-(R,R)(R,R)(R,R)]-3 and [lambda-(S,S)(S,S)(S,S)]-3, were observed in the unit cell. According to SQUID measurements, the antiferromagnetic intramolecular coupling of the iron(III) ions in 3 results in a S = 10/2 ground state multiplet. The anisotropy is of the easy-axis type. EPR measurements enabled an accurate determination of the ligand-field splitting parameters. The ferric star 3 is a single-molecule magnet (SMM) and shows hysteretic magnetization characteristics below a blocking temperature of about 1.2 K. However, weak intermolecular couplings, mediated in a chainlike fashion via solvent molecules, have a strong influence on the magnetic properties. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) were used to determine the structural and electronic properties of star-type tetranuclear iron(III) complex 3. The molecules were deposited onto highly ordered pyrolytic graphite (HOPG). Small, regular molecule clusters, two-dimensional monolayers as well as separated single molecules were observed. In our STS measurements we found a rather large contrast at the expected locations of the metal centers of the molecules. This direct addressing of the metal centers was confirmed by DFT calculations.     

Intein-mediated synthesis of geranylgeranylated Rab7 protein in vitro

Production of recombinant proteins is an important prerequisite for biotechnology and life sciences in general. However, there is a paucity of methods for production of posttranslationally modified recombinant proteins or proteins with non-native functional groups, such as fluorophores, spin labels, and so forth. In this work we have used a combination of organic synthesis and in vitro protein ligation to construct monoprenylated Rab7 GTPase. The protein was prepared from a recombinant N-terminal portion and a peptide mimicking the C terminus of Rab7. For construction of a synthetic six-amino-acid-long fluorescent monoprenylated peptide, we used a block condensation strategy. Ligation was achieved with a yield of >70%. The resulting protein was purified from the unligated peptide by a combination of organic extraction and phase partitioning and refolding. The refolded monoprenylated semisynthetic Rab7 protein (Rab7GG) formed a stable complex with its natural chaperone REP-1 (Rab escort protein 1) and could serve as an acceptor of the second prenyl group in the enzymatic prenylation reaction. Using fluorescence spectroscopy, we characterized the interaction of the Rab7GG:REP-1 complex with Rab geranylgeranyl transferase and came to the conclusion that it functioned as a genuine intermediate of the prenylation reaction. Thus, we present the first example of the in vitro generation of a semisynthetic lipidated protein using the native chemical ligation method.     

Synthesis, reactivity, and structure of strictly homologous 18 and 19 valence electron iron nitrosyl complexes

The 18 and 19 valence electron (VE) nitrosyl complexes [Fe(NO)('pyS4')]BF4 ([1]BF4) and [Fe(NO)('pyS4')] (2) have been synthesized from [Fe('pyS4')]x ('pyS4'(2-) = 2,6-bis(2-mercaptophenylthiomethyl)pyridine(2-)) and either NOBF4 or NO gas. Complex [1]BF4 was also obtained from [Fe(CO)('pyS4')] and NOBF4. The cation [1]+ is reversibly reduced to give 2. Oxidation of 2 by [Cp2Fe]PF6 afforded [Fe(NO)('pyS4')]PF6 ([1]PF6). The molecular structures of [1]PF6 and 2 were determined by X-ray crystallography. They demonstrate that addition of one electron to [1]+ causes a significant elongation of the Fe-donor atom bonds and a bending of the FeNO angle. Density functional calculations show that the unpaired electron in 2 occupies an orbital, which is antibonding with respect to all Fe-ligand interactions. As expected from qualitative Molecular Orbital (MO) theory, it has a large contribution from a pi* type NO orbital. The nu(NO) frequency decreases from 1893 cm(-1) in [1]BF4 to 1648 cm(-1) in 2 (in KBr). The antibonding character of the unpaired electron explains the ready reaction of 2 with excess NO to give [Fe(NO)2('pyS4')] (3), the facile NO/CO exchange of 2 to afford [Fe(CO)('pyS4')], and the easy oxidation of 2 to [1]+.     

Reaction behaviour of dinuclear copper(I) complexes with m-xylyl-based ligands towards dioxygen

Intramolecular ligand hydroxylation was observed during the reactions of dioxygen with the dicopper(I) complexes of the ligands L(1)(L(1)=alpha,alpha'-bis[(2-pyridylethyl)amino]-m-xylene) and L(3)(L(3)=alpha, alpha'-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-m-xylene). The dinuclear copper(I) complex [Cu(2)L(3)](ClO(4))(2) and the dicopper(II) complex [Cu(2)(L(1)-O)(OH)(ClO(4))]ClO(4) were characterized by single-crystal X-ray structure analysis. Furthermore, phenolate-bridged complexes were synthesized with the ligand L(2)-OH (structurally characterized [Cu(2)(L(2)-O)Cl(3)] with L(2)=alpha, alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; synthesized from the reaction between [Cu(2)(L(2)-O)(OH)](ClO(4))(2) and Cl(-)) and Me-L(3)-OH: [Cu(2)(Me-L(3)-O)(mu-X)](ClO(4))(2)xnH(2)O (Me-L(3)-OH = 2,6-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-4-methylphenol and X = C(3)H(3)N(2)(-)(prz), MeCO(2)(-) and N(3)(-)). The magnetochemical characteristics of compounds were determined by temperature-dependent magnetic studies, revealing their antiferromagnetic behaviour [-2J(in cm(-1)) values: -92, -86 and -88; -374].