Synthesis,crystal structures and antimicrobial activity of azido and isocyanato Zn(II) complexes with the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent

Two Zn(II) complexes with the condensation product of 2-quinolinecarboxaldehyde and trimethylammonium acetohydrazide chloride (Girard’s T reagent) (HLCl) and monodentate pseudohalides (azide and cyanate) have been synthesized and characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. In both complexes, the coordination surroundings of the Zn(II) ions consist of a deprotonated hydrazone ligand coordinated through an NNO set of donor atoms and two monodentate pseudohalides (N₃^– or NCO^–) at the remaining coordination sites. The Zn(II) complexes showed low to moderate activity against laboratory control strains of pathogenic bacteria and fungi.     

Experimental electron density study of a complex between copper(II) and the antibacterial quinolone family member ciprofloxacin

An experimental charge density study of a 1 : 1 complex of Cu-cfx (cfx = ciprofloxacin), 1 [Cu(cfx)(H(2)O)(3)]SO4.2H(2)O, has been performed using single-crystal X-ray diffraction data collected at 100 K using conventional Mo Kalpha radiation. Metal-ligand (ML) bonds and hydrogen bonds (HBs) have been analysed using topological analysis of the electron density with the atoms in molecules (AIM) approach. The copper atom binds to two oxygen atoms in one end of the zwitterionic form of the cfx molecule, in addition to forming bonds with three water molecules, forming a square pyramidal coordination geometry. AIM decomposition of the experimental electron density establishes that the copper atom binds more strongly to the cfx molecule than to the water molecules, suggesting that the latter can be detached leaving behind a reactive, water-free Cu-cfx complex available for interaction with e.g. a macromolecular site. AIM analysis of the extensive hydrogen bond pattern reveals that the positively charged N-end of the zwitterionic cfx forms a relatively strong N-H-O hydrogen bond implying that this region of cfx may play an important role in the docking process in the active site. Visualisation and statistics of selected density derived properties on the molecular surface of the isolated cfx molecule vs its metal complexed counterpart points out regions of potential reactivity. The effect of the fluorine atom is to expand the negative region of the electrostatic potential, while the nitrogen end is heavily electropositive and willingly donates to--for molecular docking purposes--relatively strong hydrogen bonding. The Cu atom is highlighted as a potentially highly reactive site which is likely to interact strongly with any given negative ligand.     

A note on 3-Steiner intervals and betweenness

The geodesic and geodesic interval, namely the set of all vertices lying on geodesics between a pair of vertices in a connected graph, is a part of folklore in metric graph theory. It is also known that Steiner trees of a (multi) set with k (k>2) vertices, generalize geodesics. In Brešar et al. (2009) [1], the authors studied the k-Steiner intervals S(u₁,u₂,…,u_k) on connected graphs (k≥3) as the k-ary generalization of the geodesic intervals. The analogous betweenness axiom (b2) and the monotone axiom (m) were generalized from binary to k-ary functions as follows. For any u₁,…,u_k,x,x₁,…,x_k∈V(G) which are not necessarily distinct, The authors conjectured in Brešar et al. (2009) [1] that the 3-Steiner interval on a connected graph G satisfies the betweenness axiom (b2) if and only if each block of G is geodetic of diameter at most 2. In this paper we settle this conjecture. For this we show that there exists an isometric cycle of length 2k+1, k>2, in every geodetic block of diameter at least 3. We also introduce another axiom (b2(2)), which is meaningful only to 3-Steiner intervals and show that this axiom is equivalent to the monotone axiom.     

Numerical errors of the volume‐of‐fluid interface tracking algorithm

One of the important limitations of the interface tracking algorithms is that they can be used only as long as the local computational grid density allows surface tracking. In a dispersed flow, where the dimensions of the particular fluid parts are comparable or smaller than the grid spacing, several numerical and reconstruction errors become considerable. In this paper the analysis of the interface tracking errors is performed for the volume‐of‐fluid method with the least squares volume of fluid interface reconstruction algorithm. A few simple two‐fluid benchmarks are proposed for the investigation of the interface tracking grid dependence. The expression based on the gradient of the volume fraction variable is introduced for the estimation of the reconstruction correctness and can be used for the activation of an adaptive mesh refinement algorithm. Copyright © 2002 John Wiley & Sons, Ltd.     

Covalent versus Noncovalent Binding of Ruthenium η6-p-Cymene Complexes to Zinc-Finger Protein NCp7

Ruthenium–arene complexes are a unique class of organometallic compounds that have been shown to have prominent therapeutic potencies. Here, we have investigated the interactions of Ru-cymene complexes with a zinc-finger protein NCp7, aiming to understand the effects of various ligands on the reaction. Five different binding modes were observed on selected Ru-complexes. Ru-cymene complex can bind to proteins through either noncovalent binding alone or through a combination of covalent and noncovalent binding modes. Moreover, the noncovalent interaction can promote the coordination of Ru^II to NCp7, resulting synergistic effects of the different ligands. The binding of Ru(Cym) complexes leads to dysfunction of NCp7 through zinc-ejection and structural perturbation. These results indicate that the reactivity of Ru-complexes can be modulated by ligands through different approaches, which could be closely correlated to their different therapeutic effects.     

A characterization of planar partial cubes

Partial cubes as well as planar graphs have been extensively investigated. In this note we introduce an additional topological kind of condition to the Chepoi’s expansion procedure that characterizes planar partial cubes. As a consequence we obtain a characterization of some other planar subclasses of partial cubes.     

X‐ray Absorption Near‐Edge Structure and Nuclear Magnetic Resonance Study of the Lithium–Sulfur Battery and its Components

Understanding the mechanism(s) of polysulfide formation and knowledge about the interactions of sulfur and polysulfides with a host matrix and electrolyte are essential for the development of long‐cycle‐life lithium–sulfur (Li–S) batteries. To achieve this goal, new analytical tools need to be developed. Herein, sulfur K‐edge X‐ray absorption near‐edge structure (XANES) and ^6,7Li magic‐angle spinning (MAS) NMR studies on a Li–S battery and its sulfur components are reported. The characterization of different stoichiometric mixtures of sulfur and lithium compounds (polysulfides), synthesized through a chemical route with all‐sulfur‐based components in the Li–S battery (sulfur and electrolyte), enables the understanding of changes in the batteries measured in postmortem mode and in operando mode. A detailed XANES analysis is performed on different battery components (cathode composite and separator). The relative amounts of each sulfur compound in the cathode and separator are determined precisely, according to the linear combination fit of the XANES spectra, by using reference compounds. Complementary information about the lithium species within the cathode are obtained by using ⁷Li MAS NMR spectroscopy. The setup for the in operando XANES measurements can be viewed as a valuable analytical tool that can aid the understanding of the sulfur environment in Li–S batteries.     

Characterizing Flag Graphs and Induced Subgraphs of Cartesian Product Graphs

The vertices of the flag graph Φ(P) of a graded poset P are its maximal chains. Two vertices are adjacent whenever two maximal chains differ in exactly one element. In this paper we characterize induced subgraphs of Cartesian product graphs and flag graphs of graded posets. The latter class of graphs lies between isometric and induced subgraphs of Cartesian products in the embedding structure theory. Both characterization use certain edge-labelings of graphs.     

First ruthenium organometallic complex of antibacterial agent ofloxacin. Crystal structure and interactions with DNA

An organometallic ruthenium complex of quinolone antibacterial agent ofloxacin, [(η(6)-p-cymene)RuCl(O,O-oflo)]·2.8H(2)O (1·2.8H(2)O), was isolated, and its crystal structure was determined. In this "piano-stool" complex, quinolone is bidentately coordinated to the metal through the ring carbonyl and one of the carboxylic oxygen atoms. Interactions of the title complex with DNA were studied by spectroscopic methods [electronic, fluorescence, and circular dichroism (CD)] and atomic force microscopy (AFM). It was established that the electrostatic attraction between the ruthenium complex and DNA in a solution is important for binding because interactions were observed only in a solution with low ionic strengths. An induced-CD (ICD) signal was observed in a solution of DNA and the title complex, which proves interaction between ruthenium and macromolecules. Competitive binding between cisplatin and 1 to DNA revealed that cisplatin prevents binding of 1. Our experiments revealed that binding of the title complex to DNA occurs also if guanine N7 is protonated. AFM has shown that the title complex provokes DNA shrinkage. Preliminary biological tests have also been performed.