Thermogravimetrische Untersuchung an den Kristallhydraten der Acetate einiger Zweiwertiger Metalle

Journal of Thermal Analysis and Calorimetry - Die Acetate Mg(OCOCH3)2 · 4H2O, Ca(OCOCH3)2 · H2O, Mn(OCOCH3)2 · 4H2O, Co(OCOCH3)2 · 4H2O, Ni(OCOCH3)2 · 4H2O,...     

Mössbauer study of carbide phases in catalysts for ammonia synthesis

Samples of a catalyst CA-1 for ammonia synthesis were studied. After reduction the samples were treated with CO₂ or with a mixture of 1% O₂+2.4% H₂O+CO₂ at temperatures between 600 and 783 K. Mössbauer spectroscopy data indicate that above 600 K carbide phases and magnetite are formed. A probable mechanism for carbide formation is suggested.     

Metal ion distribution and solubility of Mn1−xCux(HCOO)2 · 2 H2O Mixed Crystals [1–5]

The metal ion distribution on the two metal sites of monoclinic Mn_1?xCu_x(HCOO)₂ · 2(H,D)₂O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm^?1 (v_OH), 2 875–2 990 cm^?1 (v_CH), 2 330–2 500 cm^?1 (v_OD of matrix isolated HDO molecules), 1 350–1 400 cm^?1 (symmetric CO₂ stretching modes), 570–950 cm^?1 (H₂O librations), and 490 cm^?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu²⁺ prefers the M(1) site, coordinated by HCOO^? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu²⁺. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5.     

Influence of the crystal field stabilization energy of metal(II) ions on the structural distortion of matrix-isolated SO4(2-) guest ions in selenate matrices

Infrared spectra of metal(II) selenate hydrates (MeSeO4.nH2O and Na2Me(SeO4)2.2H2O; n=6, 5, 4, 1; Me=Mg, Mn, Co, Ni, Cu, Zn, Cd) containing matrix-isolated SO42- guest ions are reported and discussed with respect to the S-O stretching modes 3 and 1. An adequate measure for the SO42- guest ion distortion is the site group splitting deltanuas (deltanuab and deltanuac in the case of a doublet and a triplet for 3, respectively; a, being the highest wavenumbered component of nu3) and deltanumax (the difference between the highest and the lowest wave numbered S-O stretching modes). It has been shown that the SO42- guest ion distortion depends on both the number of the sulfate oxygen atoms involved in coordinative bonds with the metal(II) ions and the electronic configuration of the metal(II) ions, i.e. their crystal field stabilization energy (CFSE) additionally to the site symmetry and the local potential at the lattice site of the host lattice. The SO42- guest ions matrix-isolated in MeSeO4.H2O (Me=Mn, Co, Zn) and in Na2Me(SeO4)2.2H2O (Me=Mn, Cu, Cd) exhibit three bands corresponding to the nu3 modes as deduced from the site group analysis and deltanuab approximately equal to deltanubc. When SO42- guest ions are incorporated in the triclinic Na2Me(SeO4)2.2H2O host lattices (Me=Co, Ni, Zn) the nu3 stretching region resembles a higher local symmetry of the SO42- guest ions (an approximate (A1 + E) splitting) than the crystallographic one (i.e. deltanuab>deltanubc instead of deltanuab approximately equal to deltanubc) and, hence, the ratio deltanuab/deltanubc has to be taken into account (the higher value of the ratio deltanuab/deltanubc, the weaker is the distortion of the SO42- guest ions). The SO42- guest ions incorporated in MeSeO4.nH2O (n=6, 5, 4) exhibit a higher local symmetry of the guest ions than that deduced from the site group analysis (D2d for the SO42- guest ions in MeSeO4.5H2O, MeSeO4.4H2O and in the monoclinic MeSeO4.6H2O host lattices and close to Td in the tetragonal MeSeO4.6H2O host lattices). The analysis of the infrared spectra of selenate host lattices containing SO42- guest ions reveals that the guest ions are stronger distorted when the adjacent metal(II) ions have CFSE not equal to 0. These ions are more resistant to angular deformations of the MeO6-octahedra (i.e. changes in the O-Me-O bond angles), thus facilitating the SO42- guest ion distortion as compared to those having CFSE=0 which allow stronger angular deformations of the respective metal octahedra. Infrared spectra of kieserite-type compounds MeSeO4.H2O (Me=Mn, Co, Zn) containing matrix-isolated SO42- guest ions and Me'2+ guest ions different from those of the host ions (i.e. Me'SO4.H2O in MeSeO4.H2O) are also presented and discussed (double matrix-spectroscopy).     

On Characters and Superdimensions of Some Infinite-Dimensional Irreducible Representations of osp(m|n)

Physics of Atomic Nuclei - Chiral spinors and self dual tensors of the Lie superalgebra osp(m|n) are infinite-dimensional representations belonging to the class of representations with Dynkin...     

Functionalized electrospun mats from styrene-maleic anhydride copolymers for immobilization of acetylcholinesterase

A series of electrospun mats of styrene-maleic anhydride copolymers has been functionalized by modification with two types of spacers - a polymer with a flexible hydrophilic polyether chain (Jeffamine® ED) and a rigid low-molecular-weight spacer (р-phenylenediamine). The successful modification of the microfibrous mats with these bifunctional compounds has been proved by ATR-FTIR and X-ray photoelectron spectroscopy (XPS) analyses. In a further step, acetylcholinesterase (AChE) has been covalently immobilized onto the modified mats using glutaraldehyde as a binding agent. The amount of bound protein and the specific activity of the immobilized AChE have been determined. The highest activity has been displayed by AChE covalently bound to Jeffamine-modified microfibrous mats. Moreover, the immobilized AChE is characterized by enhanced thermal and storage stability as compared to the free enzyme.     

Electrospun Mats from Styrene/Maleic Anhydride Copolymers: Modification with Amines and Assessment of Antimicrobial Activity

New antimicrobial microfibrous electrospun mats from styrene/maleic anhydride copolymers were prepared. Two approaches were applied: (i) grafting of poly(propylene glycol) monoamine (Jeffamine® M‐600) on the mats followed by formation of complex with iodine; (ii) modification of the mats with amines of 8‐hydroxyquinoline or biguanide type with antimicrobial activity. Microbiological screening against S. aureus, E. coli and C. albicans revealed that both the formation of complex with iodine and the covalent attachment of 5‐amino‐8‐hydroxyquinoline or of chlorhexidine impart high antimicrobial activity to the mats. In addition, S. aureus bacteria did not adhere to modified mats.

     

Preparation,crystal structure and infrared spectroscopy of the new compound Rb4Be(SeO4)2(HSeO4)2·4H2O

A new compound, Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O, crystallizes in a comparatively wide concentration range from mixed beryllium rubidium selenate solutions (from solutions containing 29.06 mass% beryllium selenate and 25.75 mass% rubidium selenate up to solutions containing 12.53 mass% beryllium selenate and 55.32 mass% rubidium selenate).Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O crystallizes in the acentric orthorhombic space group Pmn2₁ (a = 32.607(4), b = 10.676(2), c = 6.069(1) Å, V = 2112.8 ų, Z = 4, R1 = 0.047 for 4059 F_o > 4σ(F_o) and 311 variables). The crystal structure is composed of Be(H₂O)₄ tetrahedra arranged in layers at x = 0 and x = ½, alternating with broad layers built up from SeO₄ and HSeO₄ selenate tetrahedra and Rb cations. The beryllium–water layers are linked to the rest of the structure via hydrogen bonds only. The H₂O molecules as well as the OH molecules of the acid HSeO₄ groups form strong to very strong hydrogen bonds with donor–acceptor distances between 2.58 and 2.74 Å.Vibrational spectra (infrared and Raman) of Rb₄Be(SeO₄)₂(HSeO₄)₂·4H₂O are presented and discussed in the region of the fundamentals of both the selenate and the beryllium tetrahedra (skeleton motions) as well as in the region of the OH vibrations at ambient and liquid nitrogen temperature (LNT). The appearance of four Raman bands corresponding to ν₁ of the selenate ions reflects the existence of four crystallographically different selenate tetrahedra in the structure. The spectroscopic experiments reveal that the ν₁ modes of the selenate ions appear at higher frequencies than some components of ν₃. Bands of an AB doublet structure (2950, 2390 cm^?1) arising from the OH stretching modes of the HSeO₄^- ions are recognized in the infrared spectra. The appearance of two infrared bands (1308, 1250 cm^?1) corresponding to δ(OH) (in-plane bending modes of the OH groups) confirms the structural data regarding the existence of two crystallographically different OH groups. The water librations are also briefly commented. The appearance of a band at a comparatively large wavenumber (1013 cm^?1) corresponding to rocking librations of the water molecules indicate that strong hydrogen bonds are formed in the title compound.     

Experimental and theoretical study on the absorption and fluorescence properties of substituted aryl hydrazones of 1,8-naphthalimide

Absorption and fluorescence spectra in acetonitrile for a series of substituted aryl hydrazones of N-hexyl-1,8-naphthalimide are studied with the aim of potential application of the compounds for enzyme activity localization. The influence of the substituents on the spectral characteristics has been evaluated. The absorption and fluorescence energies of substituted aryl-1,8-naphthalimide hydrazones have been calculated with the PCM TDDFT formalism. The M06 and PBE0 functionals, combined with the 6-31+G(d) atomic basis set, have been found to accurately model the excited state properties of the present set of solvated fluorophores. Absorption and fluorescence spectral characteristics have been rationalized in terms of experimental and theoretical electronic indices in order to assess their predictive abilities for application in designing analogues with good emitting properties. An excellent linear dependence is established between the experimental fluorescence and Hammett σ(p)(+) substituent constants and on the other hand σ(p)(+) constants correlate with the theoretically calculated values for the electrostatic potential at nuclei (EPN). A model for predicting the fluorescence properties of substituted hydrazones by means of EPN is drawn, including the polysubstituted derivatives, where Hammett constants are not applicable.