Density functional calculation of the 2D potential surface and deuterium isotope effect on 13C chemical shifts in picolinic acid N-oxide. Comparison with experiment

2D free energy surfaces V = V(rOH, rO...O) for the intramolecular H-bond in the title compound were calculated by the DFT method and used in the calculation of primary and secondary chemical shifts of the compound dissolved in chloroform and acetonitrile. Solvent effects were accounted for by the SCRF/PCM method. The corresponding two-dimensional chemical shift surfaces with included solvent reaction field were obtained using the Continuous Set of Gauge Transformations approach at the B3LYP/6-311+G(2d,2p) level of theory. The chemical shifts were estimated as quantum averages along the two internal coordinates in the hydrogen bond and along several vibrational levels according to the Boltzmann distribution at room temperature. Fairly good agreement between the experimental and calculated isotope effects was obtained. 1D and 2D NMR spectra of solutions of picolinic acid N-oxide and its deuterated analogue were recorded and assigned.     

Influence of the Structure of Precursors on the Crystallization of PbTiO3 Thin Films

PbTiO₃ (PT) thin films and their respective sols derived from three lead sources have been studied in order to elucidate the role of the starting materials in the crystallization of the products. EXAFS analysis of sols revealed similar oligomeric Ti-units in PT precursors derived from lead oxide or lead 2-methoxyethoxide acetate and a significantly different local Ti neighborhood in those derived from lead acetate. Structural details of the perovskite phase in the thin films follow the same pattern of similarity.     

Mechanistic models for pool nucleate boiling heat transfer: input and validation

Correlations for nucleate boiling heat transfer should be improved, or in the long term possibly be replaced, by the development of mechanistic simulations that include the non-uniform spacing and variable characteristics of the nucleation sites and non-linear interactions between the sites. This paper discusses the interactions that should be included in simulations and some lessons from a first attempt to validate a particular simulation against experimental spatio-temporal data for wall temperature. Input data for nucleation site positions and characteristics are a particular problem and the prospects for obtaining this data from measurements that are independent of boiling are discussed.     

Extended Global Convergence Framework for Unconstrained Optimization

An extension of the global convergence framework for unconstrained derivative-free optimization methods is presented. The extension makes it possible for the framework to include optimization methods with varying cardinality of the ordered direction set. Grid-based search methods are shown to be a special case of the more general extended global convergence framework. Furthermore,the required properties of the sequence of ordered direction sets listed in the definition of grid-based methods are relaxed and simplified by removing the requirement of structural equivalence.     

Characterization of diabatic two-phase flows in microchannels: Flow parameter results for R-134a in a 0.5 mm channel

An optical measurement method for two-phase flow pattern characterization in microtubes has been utilized to determine the frequency of bubbles generated in a microevaporator, the coalescence rates of these bubbles and their length distribution as well as their mean velocity. The tests were run in a 0.5 mm glass channel using saturated R-134a at 30 °C (7.7 bar). The optical technique uses two laser diodes and photodiodes to measure these parameters and to also identify the flow regimes and their transitions. Four flow patterns (bubbly flow, slug flow, semi-annular flow and annular flow) with their transitions were detected and observed also by high speed video. It was also possible to characterize bubble coalescence rates, which were observed here to be an important phenomena controlling the flow pattern transition in microchannels. Two types of coalescence occurred depending on the presence of small bubbles or not. The two-phase flow pattern transitions observed did not compare well to a leading macroscale flow map for refrigerants nor to a microscale map for air–water flows. Time averaged cross-sectional void fractions were also calculated indirectly from the mean two-phase vapor velocities and compared reasonably well to homogeneous values.     

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.     

1-(2-Picolyl)-substituted 1,2,3-triazole as novel chelating ligand for the preparation of ruthenium complexes with potential anticancer activity

The 1,4-disubstituted 1,2,3-triazole ligand prepared by click chemistry 1-(2-picolyl)-4-phenyl-1H-1,2,3-triazole (ppt) was investigated as novel chelating ligand for Ru(II) complexes with potential antitumor activity. The preparation and structural characterization, mainly by NMR spectroscopy in solution and by X-ray crystallography in the solid state, of four new Ru(II) complexes is reported: two isomeric Ru-dmso compounds, trans,cis-[RuCl(2)(dmso-S)(2)(ppt)] (1) and cis,cis-[RuCl(2)(dmso-S)(2)(ppt)] (2), and two half-sandwich Ru-[9]aneS(3) coordination compounds, [Ru([9]aneS(3))(dmso-S)(ppt)][CF(3)SO(3)](2) (3) and [Ru([9]aneS(3))Cl(ppt)][CF(3)SO(3)] (4). In all compounds ppt firmly binds to ruthenium in a bidentate fashion through the pyridyl nitrogen atom and the triazole N2, thus forming a puckered six-membered ring. The chemical behavior in aqueous solution of the water-soluble complexes 3 and 4 was studied by UV-Vis and NMR spectroscopy and compared to that of the previously described organometallic analogue [Ru(η(6)-p-cymene)Cl(ppt)][Cl] (5) in view of their potential antitumor activity. Compounds 3-5 were tested also in vitro for cytotoxic activity against two human cancer cell lines, one sensitive and one resistant to cisplatin, in comparison with cisplatin. Compound 4, the one that aquates faster, was found to be more cytotoxic than cisplatin against human lung squamose carcinoma cell line (A-549).     

Factors that influence the antiproliferative activity of half sandwich Ru(II)-[9]aneS3 coordination compounds: activation kinetics and interaction with guanine derivatives

Half sandwich Ru(ii)-[9]aneS3 complexes ([9]aneS3 = 1,4,7-trithiacyclononane) are being studied for their antiproliferative activity. We investigated here the activation kinetics of three such complexes, namely [Ru([9]aneS3)(en)Cl](PF(6)) (1), [Ru([9]aneS3)(bpy)Cl](PF(6)) (2) and [Ru([9]aneS3)(pic)Cl] (3) (en = 1,2-diaminoethane, pic = picolinate), and their interaction with DNA model bases. The aim of the study was to assess how they are affected by the nature and charge of the chelating ligand. The model reactions of 1-3 with the guanine derivatives 9-methylguanine (9MeG), guanosine (Guo), and guanosine 5'-monophosphate (5'-GMP) were studied by NMR spectroscopy. All reactions lead, although with different rates and to different extents, to the formation of monofunctional adducts with the guanine derivatives N7-bonded to the Ru center. Two products, the complexes [Ru([9]aneS3)(en)(9MeG-N7)](PF(6))(2) (4) and [Ru([9]aneS3)(pic)(9MeG-N7)](PF(6)) (10), were structurally characterized also by X-ray crystallography. The structure of 4 is stabilized by strong intramolecular H-bonding between an NH of en and the carbonyl O6 of 9MeG. The kinetics of aquation and anation of complexes 2 and 3, as well as the kinetics and the mechanism of the reaction of complexes 1-3 with the biologically more relevant 5'-GMP ligand were studied by UV-Vis spectroscopy. The rate of the reaction of 1-3 with 5'-GMP depends on the nature of the chelating ligand rather than on the charge of the complex, decreasing in the order 3≈2 > 1. The measured enthalpies and entropies of activation (ΔH(≠) > 0, ΔS(≠) < 0) support an associative mechanism for the substitution process.