A tetranuclear copper(II) cluster: bis(μ‐4‐chlorobenzoato‐κ2O:O′)(4‐chlorobenzoato‐κ2O,O′)(4‐chlorobenzoato‐κO)tetrakis(μ3‐2‐pyridylmethanolato‐κ4N,O:O:O)tetracopper(II)

The title compound, [Cu₄(C₇H₄ClO₂)₄(C₆H₆NO)₄], consists of isolated tetranuclear clusters, where the Cu²⁺ cations are five‐ and sixfold coordinated by O atoms from the 4‐chlorobenzoate anions and by pyridine N and methanolate O atoms from bidentate 2‐pyridylmethanolate ligands. While three Cu atoms are six‐coordinated by an NO₅ donor set forming distorted octahedra, the fourth Cu atom is five‐coordinated by an NO₄ donor set forming a distorted tetragonal–pyramidal coordination around the Cu atom. The nucleus is a deformed cubane‐like Cu₄O₄ structure, with Cu...Cu distances in the range 3.0266 (11)–3.5144 (13) Å.     

EPR Study of 5-Chlorosalicylate-Cu(II)-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Diethylnicotinamide Ternary Complex Systems in Frozen Water–Methanol Solutions

As a continuation of our previous study of Cu(II) ternary complexes, two new systems containing 5-chlorosalicylic acid (5-ClsalH) and different Cu(II) salts, with varying N,N-diethylnicotinamide (denia) concentrations, system III [CuSO₄(aq) + 2(5-ClsalH(solv)) + xdenia(l)] and system IV [Cu(ac)₂(aq) + 2(5-ClsalH(solv)) + xdenia(l)], where x = 0, 2, 4, 6 and 8, were prepared. The effects of Cu(II) salts containing anions of different basicity and N-donor ligand (denia) with varying ligand-to-metal ratio (x) on the formation of resulting complexes were studied by electron paramagnetic resonance (EPR) spectroscopy in frozen water–methanol solutions. Well-resolved ¹⁴N superhyperfine splitting lines (nonet) in the perpendicular region of the second-derivative axially symmetric Cu(II) EPR spectra indicated that for x > 4 in system III and for x ≥ 2 in system IV, four equivalent nitrogens could be coordinated to the central Cu(II) ions in the equatorial plane. Such information cannot be obtained by EPR spectroscopy of powder samples of the given Cu(II) complex systems. The differences between denia and ronicol containing Cu(II) complexes are discussed.     

Principal difference between stability and structural stability (robustness) as used in systems biology

The concepts stability and structural stability (robustness) are used often in systems biology. According to Kitano (2004) robustness is a fundamental property of evolvable complex biological systems. For that reason, the purpose of this review is to clarify: (a) how are strictly formulated concepts, such as stability and robustness of a dynamical system, used in computational systems biology; (b) what is meant by structural stability (robustness) in contemporary biology and how are stability and robustness distinguished from each other; and (c) why is it necessary to investigate whether a cell signal pathway is stable. We formulate the two concepts stability and structural stability (robustness) of a dynamical system with an arbitrary dimensionality, in the way they are known in mathematics and mechanics, and clarify the principal difference between them. We also consider how these two concepts are used in the analysis of a concrete biological system in systems biology. In the last section we formulate when, according to us, in biology (and in systems biology in particular), it should be said that a system (process) is stable, and when it is structurally stable.     

Determination of intermolecular copper–copper distances from the EPR half-field transitions and their comparison with distances from X-ray structures: applications to copper(II) complexes with biologically important ligands

An EPR method involving measurement of half-field transitions was applied to determine the intermolecular Cu–Cu distances in copper(II)-carboxylate complexes with biologically important ligands. The experimental powder EPR spectra are composed of allowed (ΔM _S  = ±1) transitions centered at ~3,200 Gauss and of weak intensity, nominally forbidden, half-field (ΔM _S  = ±2) peaks observable at ~1,600 Gauss. Values of the average interspin distance for each complex were determined from the ratios of integrated allowed and forbidden peak areas using each of several methods. The calculated interspin distances were correlated with the copper–copper distances experimentally obtained by X-ray crystallography. The distances determined from the EPR spectra agree well with the X-ray determined values when the crystallographic value for one member of a series is used to calibrate the series. Less satisfactory agreement is found when methods based on Cu-spin-label systems are used.     

How to use the Sun–Earth Lagrange points for fundamental physics and navigation

We illustrate the proposal, nicknamed LAGRANGE, to use spacecraft, located at the Sun–Earth Lagrange points, as a physical reference frame. Performing time of flight measurements of electromagnetic signals traveling on closed paths between the points, we show that it would be possible: (a) to refine gravitational time delay knowledge due both to the Sun and the Earth; (b) to detect the gravito-magnetic frame dragging of the Sun, so deducing information about the interior of the star; (c) to check the possible existence of a galactic gravitomagnetic field, which would imply a revision of the properties of a dark matter halo; (d) to set up a relativistic positioning and navigation system at the scale of the inner solar system. The paper presents estimated values for the relevant quantities and discusses the feasibility of the project analyzing the behavior of the space devices close to the Lagrange points.     

Effect of drying methods on the content of natural pigments and antioxidant capacity in extracts from medicinal plants: a spectroscopic study

Medicinal plants are a significant source of biological active and health protective compounds. Post-harvest treatments can affect, in different ways, the content and biological activity of such compounds. One of the most common post-harvesting methods is drying. In this study, we investigated the effect of drying method on the content of natural pigments (chlorophylls, carotenoids and anthocyanins) and on the antioxidant capacity of two traditionally used herbs, the Melissa officinalis (lemon balm) and the Urtica dioica (stinging nettle) both of them landraces collected from plants grown in Nitra region, West of Slovakia. The freeze-dried samples of both herbs exhibited the highest content of chlorophyll a (7.55 ± 0.13 mg/g dry mass for lemon balm and 9.41 ± 0.17 mg/g dry mass for stinging nettle), chlorophyll b (3.12 ± 0.28 mg/g dry mass for lemon balm and 3.34 ± 0.24 mg/g dry mass for stinging nettle) and carotenoids (2.11 ± 0.24 mg/g dry mass for lemon balm and 2.62 ± 0.06 mg/g dry mass for stinging nettle). The content of chlorophylls and carotenoids correlated with the DPPH antioxidant (radical scavenging) capacity. Higher antioxidant capacity of the lemon balm extracts compared to nettle samples was attributed to the higher content of polyphenol compounds anthocyanins. Despite the higher cost, the freeze drying (lyophilisation) was recommended as the most suitable drying method, mainly for reasons of preserving maximum pigment content and antioxidant capacity.     

Application of one-particle Green functions technique for calculation of vertical ionization potentials of closed-shell molecules described by CNDO/2 semiempirical Hamiltonian

A simple method of infinite summations of some dominant diagrams in the framework of the one-particle Green functions technique is suggested. This method for the calculation of the lowlying vertical ionization potentials of some simple closed-shell molecules described by CNDO/2 semiempirical Hamiltonian is applied. The obtained results are in quite-satisfactory agreement with the experimental values of the vertical ionization potentials measured by the photo-electron spectroscopy technique.