4,4 '-Dipyridyl-N,N '-dioxide complexes of metal-thiocyanate/selenocyanate: pi-stacked molecular rods as three-dimensional support for two-dimensional polymeric sheets and intra/interchain S center dot center dot center dot S interaction dependent architecture of the R-2(2)(8) synthon driven assembly of one-dimensional polymeric chains

Three supramolecular complexes of Co(II) using SCN-/SeCN- in combination with 4,4'-dipyridyl-N,N'-dioxide (dpyo), i.e., {[Co(SCN)(2)(dpyo)(2)].(dpyo)}(n) ( 1), {[Co(SCN)(2)(dpyo)(H2O)(2)].(H2O)}(n) ( 2), {[Co(SeCN)(2)(dpyo)(H2O)(2)]center dot(H2O)}(n) ( 3), have been synthesized and characterized by single-crystal X-ray analysis. Complex 1 is a rare example of a dpyo bridged two-dimensional (2D) coordination polymer, and pi-stacked dpyo supramolecular rods are generated by the lattice dpyo, passing through the rhombic grid of stacked layers, resulting in a three-dimensional (3D) superstructure. Complexes 2 and 3 are isomorphous one-dimensional (1D) coordination polymers [-Co-dpyo-Co-] that undergo self-assembly leading to a bilayer architecture derived through an R-2(2)(8) H-bonding synthon between coordinated water and dpyo oxygen. A reinvestigation of coordination polymers [Mn(SCN)(2)(dpyo)( H2O)(MeOH)](n) ( 4) and {[Fe(SCN)(2)(dpyo)(H2O)(2)]center dot(H2O)}(n) ( 5) reported recently by our group [ Manna et al. Indian J. Chem. 2006, 45A, 1813] reveals brick wall topology rather than bilayer architecture is due to the decisive role of S center dot center dot center dot S/Se center dot center dot center dot Se interactions in determining the helical nature in 4 and 5 as compared to zigzag polymeric chains in 2 and 3, although the same R-2(2)(8) synthon is responsible for supramolecular assembly in these complexes.

The synthesis and characterisation of two new iron thioantimonates: [Fe(en)(3)](2)Sb2S5 center dot 0.55H(2)O and [Fe(en)(3)](2)Sb4S8

Two new iron thioantimonates, [Fe(en)(3)](2)Sb2S5 (.) 0.55H(2)O (1) and [Fe(en)(3)](2)Sb4S8 (2). were synthesised under solvothermal conditions from the reactions of Sb2S3, FeCl2 and S in the presence of ethylenediamine at 413 and 438 K, respectively. The products were characterised by single-crystal X-ray diffraction, elemental analysis and SQUID magnetometry. Compound 1 is unusual in containing isolated Sb2S54- anions formed from two corner-sharing SbS33- trigonal pyramids. These units are arranged in rippled layers, 4 A apart, parallel to the bc-plane. Octahedrally coordinated [Fe(en)(3)](2+) cations lie in depressions within these anionic layers. In compound (2), repeated corner linking of SbS33- trigonal pyramids generates SbS2- chains, which may be considered as a polymerised form of the Sb2S54- anions in 1. The SbS2- chains are separated by [Fe(en)(3)](2+) cations. In both compounds, there is an extensive network of hydrogen bonds between the nitrogen atoms of the ethylenediamine ligands and the sulfur atoms of the anions and, in the case of 1, the uncoordinated water molecule. (c) 2005 Elsevier Ltd. All rights reserved.

Synthesis, crystal structure, magnetic behavior and thermal property of three polynuclear complexes: [M(dca)(2)(H2O)2](n)center dot(hmt)(n) [M = Mn(II), Co(II)] and [Co(dca)(2)(bpds)](n) [dca, dicyanamide; hint, hexamethylenetetramine; bpds, 4,4 '-bipyridyl disulfide]

Three mu(1.5)-dicyanamide bridged Mn(II) and Co(II) complexes having molecular formula [Mn(dca)(2)(H2O)(2)](n)center dot(hmt)(n) (1), [Co(dca)(2) (H2O)(2)](n)center dot(hmt)(n) (2) and [Co(dca)(2)(bpds)](n) (3) [dca = dicyanamide; hmt = hexamethylenetetramine; bpds = 4,4'-bipyridyl disulfide] have been synthesized and characterized by single crystal X-ray diffraction study, low temperature (300-2 K) magnetic measurement and thermal behavior. The X-ray diffraction analysis of 1 and 2 reveals that they are isostructural, comprising of 1D coordination polymers [M(dca)(2)(H2O)(2)](n) [M = Mn(II), Co(II) for 1 and 2. respectively] with uncoordinated hmt molecules located among the chains. The [M(dca)(2)(H2O)(2)](n) chains and the lattice hint molecules are connected through H-bonds resulting in a 3D supramolecular architecture. The octahedral N4O2 chromophore surrounding the metal ion forms via two trans located water oxygens and four nitrogens from four nitrile dca. Complex 3 is a 1D chain formed by two mu(1.5)-dca and one bridging bpds. The octahedral N-6 coordination sphere surrounding the cobalt ions comprises four nitrogens from dca and two from bpds. Low temperature magnetic study indicates small antiferromagnetic coupling for all the complexes. Best fit parameters for 1: J = -0.17 cm(-1), g = -2.03 with R = 6.1 x 10(-4), for 2, J = -0.50 cm(-1), and for 3, J = -0.95 cm(-1). (c) 2005 Elsevier B.V. All rights reserved.

Geometrical isomers of [TEAH][Co(L-Se)(2)]center dot xH(2)O: synthesis, structural, spectroscopic and computational studies

Trans-1, [HNEt3][Co-III(L-Se)(2)]center dot H2O and cis-1, [HNEt3][Co-III(L-Se)(2)]center dot 3H(2)O have been synthesized and characterized by single-crystal X-ray studies. The counter ion Et3NH+ plays a crucial role in the crystal packing leading to the formation of two distinctly different supramolecular assemblies in the two complexes. In trans-1, Co-bisphenolate units and triethylamine molecules are arranged in a linear fashion leading to a supramolecular columnar assembly along the crystallographic a-axis. In this assembly, triethylammonium ions are sandwiched between successive Co-bisphenolate units and act as gluing agents joining Co-bisphenolate units on either side through C-H center dot center dot center dot pi interactions. In sharp contrast to trans-1, Co-bisphenolate units and triethylammonium ions in cis-1 are arranged in a helical supramolecular assembly through similar C-H center dot center dot center dot pi interactions along the crystallographic b-axis. The Se center dot center dot center dot Se van der Waals interactions may be responsible for the predominant occurrence of the cis-isomer. The cyclic voltammetric studies showed quasi-reversible waves for the cobalt(III) -> cobalt(II) reductions with E-1/2 = 0.635 and 0.628 V vs. Ag/AgCl for cis-1 (at similar to 5 degrees C) and trans-1 (at similar to 25 degrees C), respectively. DFT calculations show that the trans-form is the thermodynamic product with higher stability than the cis-one, which is consistent with the variable temperature H-1 NMR studies

Synthesis and crystal structure of [(BU4N)-B-n][Er(pic)(4)] center dot 5.5H(2)O: a new infrared emitter

The new erbium(III) complex of picolinic acid (Hpic), ["Bu4N][Er(pic)(4)].5.5H(2)O, was synthesized and the crystal structure determined by single-crystal X-ray diffraction. The compound was further characterized using IR, Raman, H-1 NMR and elemental analysis. The picolinate ligands (pic(-)) are coordinated through N,O-chelation to the erbium cations, as shown by X-ray diffraction and spectroscopic results, leading to an eight coordinate complex. Photoluminescence measurements were performed for this compound which exhibits infrared emission. (C) 2003 Elsevier B.V. All rights reserved.

Lanthanide complexes of 2-hydroxynicotinic acid: synthesis, luminescence properties and the crystal structures of [Ln(HnicO)(2)(mu-HnicO)(H2O)] center dot nH(2)O (Ln = Tb, Eu)

New lanthanide complexes of 2-hydroxynicotinic acid (H(2)nicO) [Ln(HnicO)(2)(mu-HnicO)(H2O)] (.) nH(2)O (Ln = Eu, Gd, Tb, Er, Tm) were prepared. The crystal structures of the [Tb(HnicO)(2)(g-HnicO)(H2O)] (.) 1.75H(2)O(1) and [Eu(HniCO)(2)(mu-HnicO)(H2O)] (.) 1.25H(2)O (2) complexes were determined by X-ray diffraction. The 2-hydroxynicotinate ligand coordinates through O,O-chelation to the lanthanide(III) ions as shown by X-ray diffraction and the infrared, Raman and NMR spectroscopy results. Photoluminescence measurements were performed for the Eu(III) and Tb(III) complexes. Lifetimes of 0.592 +/- 0.007 and 0.113 +/- 0.002 ms were determined for the Eu3+ and Tb3+ emitting states D-5(0) and D-5(4), respectively. A value around 30% was found for the D-5(0) quantum efficiency. The energy transfer mechanisms between the lanthanide ions and the ligands are discussed and compared with those observed in similar complexes involving the 3-hydroxypicolinate ligand based on the luminescence of the respective Gd3+-based complexes. (C) 2003 Published by Elsevier Ltd.

Educational value of different types of exhibits in an interactive science and technology center

This study analyzes the short-term consequences of visitors' use of different types of exhibits (i.e., "exemplars of phenomena" and "analogy based") together with the factors affecting visitors' understanding of and their evaluation of the use of such exhibits. One hundred and twenty five visitors (either alone or in groups) were observed during their interaction and interviewed immediately afterwards. Findings suggest that the type of exhibit constrains the nature of the understanding achieved. The use of analogical reasoning may lead to an intended causal explanation of an exhibit that is an exemplar of a phenomenon, but visitors often express misconceptions as a consequence of using this type of exhibit. Analogy-based exhibits are often not used as intended by the designer. This may be because visitors do not access the source domain intended; are unaware of the use of analogy per se (in particular, when the exhibit is of the subtype "only showing similarities between relationships"); only acquire fragmentary knowledge about the target; or fail to use analogical reasoning of which they were capable. Furthermore, exhibits related to everyday world situations are recognized to have an immediate educative value for visitors. Suggestions for enhancing the educative value of exhibits are proposed.

Isolation of culturable yeasts from market wines and evaluation of the 5 center dot 8S-ITS rDNA sequence analysis for identification purposes

Aims: To test the possibility that wines available in the marketplace may contain culturable yeasts and to evaluate the 5.8S-ITS rDNA sequence analysis as adequate means for the identification of isolates. Methods and Results: As a case study, typical Greek wines were surveyed. Sequence analysis of the 5.8S-ITS rDNA was tested for its robustness in species or strain identification. Sixteen isolates could be assigned into the species Brettanomyces bruxellensis, Saccharomyces cerevisiae and Rhodotorula pinicola, whereas four isolates could not be safely identified. B. bruxellensis was the dominant species present in house wines, while non-Saccharomyces sp. were viable in aged wines of high alcohol content. Conclusions: Yeast population depends on postfermentation procedures or storage conditions. Although 5.8S-ITS rDNA sequence analysis is generally a rapid method to identify wine yeast isolates at the species level, or even below that, it may not be sufficient for some genera. Significance and Impact of the Study: This is the first report to show that commercial wines may possess diverse and potentially harmful yeast populations. The knowledge of yeasts able to reside in this niche environment is essential towards integrated quality assurance programmes. For selected species, the 5.8S-ITS rDNA sequence analysis is a rapid and accurate means.

Genistein reverses changes of the proteome induced by oxidized-LDL in EA center dot hy 926 human endothelial cells

Endothelial cells are primary targets for pro-atherosclerotic stressors such as oxidized LDL (ox-LDL). The isoflavone genistein, on the other hand, is suggested to prevent a variety of processes underlying atherosclerosis and cardiovascular diseases. By analyzing the proteome of EA(.)hy 926 endothelial cells, here we show, that genistein reverses the ox-LDL-induced changes of the steady-state levels of several proteins involved in atherosclerosis. These alterations caused by genistein are functionally linked to the inhibition of ox-LDL induced apoptosis.

Crystal structures of [PhLi center dot(-)-sparteine](2), [PhOLi center dot(-)-sparteine](2), and the mixed aggregate [PhLi center dot PhOLi center dot 2(-)-sparteine]

Crystal structure determination of adducts of sparteine and PhLi, (-)-sparteine and PhOLi and of sparteine and PhLi/PhOLi reveal a four-membered ring with two lithium centers, each capped by a (-)-sparteine ligand, as central motif of all structure. Quantum-chemical calculations show that the mixed aggregate [PhLi center dot PhOLi center dot 2(-)-sparteine] is energetically more favorable than the model system {1/2[PhLi center dot(-)-sparteine](2) + 1/2[PhOLi center dot(-)-sparteine](2)}.

Computer simulations of structures, energetics and dynamics of myoglobin center dot center dot center dot ligand complexes

Myoglobin has been studied in considerable detail using different experimental and computational techniques over the past decades. Recent developments in time-resolved spectroscopy have provided experimental data amenable to detailed atomistic simulations. The main theme of the present review are results on the structures, energetics and dynamics of ligands ( CO, NO) interacting with myoglobin from computer simulations. Modern computational methods including free energy simulations, mixed quantum mechanics/molecular mechanics simulations, and reactive molecular dynamics simulations provide insight into the dynamics of ligand dynamics in confined spaces complementary to experiment. Application of these methods to calculate and understand experimental observations for myoglobin interacting with CO and NO are presented and discussed.

Using the Cayley-Hamilton theorem with N-partitioned matrices

A definition is given for the characteristic equation of anN-partitioned matrix. It is then proved that this matrix satisfies its own characteristic equation. This can then be regarded as a version of the Cayley-Hamilton theorem, of use withN-dimensional systems.

Euler's theorem under the microscope

In this article Geoff Tennant summarises the first half of Imre Lakatos's seminal 1976 book, "Proofs and refutations: the logic of mathematical discovery". Implications are drawn for the classroom treatment of proof.

Neural network basis function center selection using cluster analysis

This paper deals with the selection of centres for radial basis function (RBF) networks. A novel mean-tracking clustering algorithm is described as a way in which centers can be chosen based on a batch of collected data. A direct comparison is made between the mean-tracking algorithm and k-means clustering and it is shown how mean-tracking clustering is significantly better in terms of achieving an RBF network which performs accurate function modelling.