In vitro and in vivo comparative analysis of antibacterial activity of green-synthesized silver nanoparticles.

This study aims to compare antibacterial effects of green-synthesized silver nanoparticles (AgNPs) with silver nitrate (AgNO3 ). AgNPs were successfully synthesized using Eucalyptus camaldulensis leaf extract as a reducing and stabilizing agent. Minimum inhibitory concentrations (MIC) of AgNPs and AgNO3 against Staphylococcus aureus and Pseudomonas aeruginosa ranged between 4.8 and 6.75 µg mL-1 . Growth curves demonstrated that inhibition of P. aeruginosa occurred right after AgNPs were added and throughout the period of the study (72 h). Antibacterial effects of both AgNPs and AgNO3 could be abrogated by cysteine and 2-mercaptoethanol, thiol-containing compounds. Galleria mellonella model revealed relatively low toxic effects of both AgNPs and AgNO3 . At 20MIC of AgNPs (≈137.8 mg kg-1 ), more than 80% survival of G. mellonella was observed. Unexpectedly, silver-containing agents could not rescue larvae after S. aureus infection. Further ex vivo experiments in the presence of coelomic larval fluid demonstrated the reduction of antibacterial activity of both AgNPs and AgNO3 . It was speculated that anionic molecules present in the coelomic fluid might neutralize the action of Ag ions. Binding of AgNPs or AgNO3 to albumin, a major protein in human blood which transport several endogenous compounds was not detected, indicating that the silver-containing agents could be applied as an antimicrobial agent.

Identifying overlapping and hierarchical thematic structures in networks of scholarly papers: a comparison of three approaches.

The aim of this paper is to introduce and assess three algorithms for the identification of overlapping thematic structures in networks of papers. We implemented three recently proposed approaches to the identification of overlapping and hierarchical substructures in graphs and applied the corresponding algorithms to a network of 492 information-science papers coupled via their cited sources. The thematic substructures obtained and overlaps produced by the three hierarchical cluster algorithms were compared to a content-based categorisation, which we based on the interpretation of titles, abstracts, and keywords. We defined sets of papers dealing with three topics located on different levels of aggregation: h-index, webometrics, and bibliometrics. We identified these topics with branches in the dendrograms produced by the three cluster algorithms and compared the overlapping topics they detected with one another and with the three predefined paper sets. We discuss the advantages and drawbacks of applying the three approaches to paper networks in research fields.

Refined crystal structure and idealized structure of mixed-valent Eu4F5(CN2)2: transition possible.

The new europium fluoride carbodiimide Eu(4)F(5)(CN(2))(2) was synthesized by solid state reaction from mixtures of EuF(3) and Li(2)(CN(2)) at 700 °C. The crystal structure as refined by single crystal X-ray diffraction (P ̅42(1)c, no. 114, a = 16.053(1) Å, c = 6.5150(6) Å, Z = 8) reveals three crystallographically distinct [N═C═N](2-) ions in the structure of mixed-valent Eu(4)F(5)(CN(2))(2). The presence of one Eu(3+) and three Eu(2+) per formula unit Eu(4)F(5)(CN(2))(2) is confirmed by magnetic measurements and (151)Eu-Mössbauer spectroscopy. The arrangement of Eu ions and gravity centers of [NCN](2-) ions in the structure of Eu(4)F(5)(CN(2))(2) follow the motif formed by atoms in the CuAl(2)-type structure. A possible high-symmetry structure of Eu(4)F(5)(CN(2))(2) is discussed on the basis of a group-subgroup scheme.

Synthesis and properties of tetracyanamidosilicates ARE[Si(CN2)4].

Tetracyanamidosilicates of the type ARE[Si(CN(2))(4)] with A = K, Rb, and Cs and RE = Y and La-Lu have been prepared by a solid-state metathesis reaction. The potassium compounds with RE = La-Gd crystallize orthorhombically in the space group P2(1)2(1)2. Rubidium as well as cesium compounds crystallize tetragonally in the space group I4. The luminescent properties of ARE[Si(CN(2))(4)]:Ln compounds with RE = Y, La, and Gd doped with 5 mol % Ln = Ce, Eu, or Tb were investigated. Temperature-dependent magnetic susceptibilities were measured for KGd[Si(CN(2))(4)]. The value of the magnetic moment is 7.3 mu(B)/Gd(3+) ion, which is in line with the expected value for the [Xe]4f(7) configuration of Gd(3+).

Compounds with the electron-rich [W6Cl18]2- cluster anion.

Cluster compounds of the general formula A(2)[W(6)Cl(18)] containing singly charged A cations (A = K, Rb, Ag, Tl, NH(4), N(C(2)H(5))(4), N(n-C(3)N(7))(4), N(n-C(4)H(9))(4)) and [W(6)Cl(18)](2-) anions have been synthesized. Compounds were obtained by W(6)Cl(18) reduction using methanol and the corresponding metal or (alkyl-)ammonium salts. The use of CoCp(2) as reducing agent in inert solvents such as tetrahydrofurane also leads to the ionic compound (Co(C(5)H(5))(2))(2)[W(6)Cl(18)]. All compounds described here evidence the existence of octahedral clusters of the M(6)X(12) type with 20 cluster electrons occupying metal centered states, thus exceeding the conventional number of 16 electrons for this cluster type. Electrospray ionization (ESI) mass spectra were recorded for the neutral compound W(6)Cl(18) and for the ionic salts K(2)[W(6)Cl(18)], Cs(2)[W(6)Cl(18)], and (Co(C(5)H(5))(2))(2)[W(6)Cl(18)], showing that the cluster W(6)Cl(18) unit in these compounds is preserved in solution. The base peak in the ESI spectra for all compounds corresponds to the [W(6)Cl(18)](2-) anion, so that neutral W(6)Cl(18) is prone to undergo a two electron reduction process. This result is confirmed by cyclic voltammetry experiments, which makes of W(6)Cl(18) a very clean mild oxidizing agent. The preparation of the complete series of ionic A(2)[W(6)Cl(18)] (A = K, Cs, CoCp(2)) clusters allows to systematically investigate their structural trends as function of the distinctive cations, which is the main focus of the present work.

Crystal structures, phase-transition, and photoluminescence of rare earth carbodiimides.

Rare earth carbodiimides with the general formula RE 2(CN 2) 3 crystallize with two modifications. A monoclinic( C2/m) modification is obtained for RE = Y, Ce-Tm and a rhombohedral ( R3 c) modification for RE = Tm-Lu. The space group R3 c is confirmed by single-crystal structure determination on Lu 2(CN 2) 3 and indexed powder patterns of RE = Tm, Yb and Lu. The use of diverse chemical syntheses conditions for Tm 2(CN 2) 3 revealed the dimorphic character of this compound. In addition, pressure experiments on Tm 2(CN 2) 3 have induced a phase-transition from rhombohedral to monoclinic. This transformation comprises an increase of the coordination number of Tm from 6 to 7, and a unit-cell volume reduction in the order of 20 %. The photoluminescence behavior of lanthanide doped Gd 2(CN 2) 3:Ln samples is presented with different activators (Ln = Ce, Tb) revealing a broad band emission of Gd 2(CN 2) 3:Ce, quite similar to that of the well-known YAG:Ce.