Direct X‐Ray Scattering Evidence for Metal–Metal Interactions in Solution at the Molecular Level

The study of the aggregation of small molecules in solution induced by metallophilic interactions has been traditionally performed by spectroscopic methods through identification of chemical changes in the system. Herein we demonstrate the use of SAXS (small‐angle X‐ray scattering) to identify structures in solution, taking advantage of the excellent scattering intensity of heavy metals which have undergone association by metallophilic interactions. An analysis of the close relationship between solid‐state and solution arrangements of a dynamic [Ag₂(bisNHC)₂]²⁺ (NHC=N‐heterocyclic carbene) system, and how they are complementary to each other, is reported.     

A barium perchlorate complex with a lateral macrobicycle derived from 4,13‐diaza‐18‐crown‐6 containing a pyridine Schiff base spacer

In the crystal structure of (perchlorato‐κ²O,O′))(28,31,36,39tetraoxa‐1,9,17,25,42‐penta­aza­penta­cyclo­[23.8.5.1^11,15.0^3,8.0^18,23]­nonatriaconta‐3,5,7,9,11,13,15,16,18,20,22‐un­decaene‐κ⁸N¹,N⁹, N¹⁷,N⁴²,O²⁸,O³¹,O³⁶,O³⁹)­barium(II) perchlorate, [Ba(ClO₄)(C₃₃H₄₁N₅O₄)](ClO₄), the Ba^II cation is situated in the macrobicyclic cavity, bound to only eight of the nine available donor atoms of the Schiff base macrobicyclic receptor. The pivotal N5 atom does not belong to the coordination sphere of the Ba^II ion, in spite of its endo conformation with the lone pair directed towards the inside of the cavity. The Ba^II ion completes its coordination core with two O atoms of one bidentate perchlorate group.     

Statistical line-by-line model for atomic spectra in intermediate coupling

A statistical method to simulate detailed line accounting (DLA) calculations of complex spectra is proposed. The method is based on the recently developed partially resolved transition array model. Numerical examples show that spectrum calculations using the statistical approach are in good agreement with DLA results. In particular, the statistical method conserves systematic line coincidences across transition arrays differing only in the subshell occupation of excited spectator electrons important in opacity calculations. In addition, it is computationally efficient; hence, it can accelerate spectrum calculations without introducing significant uncertainties whenever the DLA method is considered impractical.     

The Lanczos method applied to quasi-static stark broadening of spectral lines

The quasi-static ion approximation of Stark broadened spectral lines involves an average of the field-dependent line shape over the microfield probability distribution. In the conventional approach, this can become computationally expensive since the calculation at each field point requires inverting a possibly large matrix. It is shown that these calculations are well suited to the “Padé Via Lanczos” approach, which allows for an efficient and accurate numerical integration over the quasi-static field. In turn, the integration forms the basis for determining convergence with Lanczos iterations. Simple examples are used to demonstrate improved performance over conventional methods.     

A Germanium Zeotype Containing Intratunnel Transition Metal Complexes

A new zeolite-type structure is adopted by (NH₄)⁺[M(NH₃)₂]⁺(Ge₉O₁₉)²⁻ (M=Cu, Ag; shown in the picture). These compounds are the first microporous germanates containing a transition metal complex inside their tunnels. The large separation between the metal centers and the unhindered access of reactants to these active sites through uniformly sized channels make these materials a good point of departure for designing new catalysts.     

Two- and three-dimensional laminar flows between disks co-rotating in a fixed cylindrical enclosure

A numerical investigation is performed for the constant property laminar flow of air in the space between a pair of disks clamped co-axially on a central hub and co-rotating in a stationary cylindrical enclosure. Both two- and three-dimensional flow conditions are examined in relation to the interdisk spacing, H, and the disk angular velocity, Ω. Two interdisk spacings are considered, corresponding to aspect ratios Γ = 0.186 and 0.279 (with Γ = H/(R₂+a−R), where R₂ is the disk radius, a is the disk rim–enclosure wall clearance, and R is the hub radius). A range of rotational speeds encompassing the transition from axisymmetric two-dimensional steady flow to non-axisymmetric three-dimensional unsteady flow are considered for various values of the Reynolds number, Re (with $ Re=\Omega R_2^2/v $, where v is the kinematic viscosity of air). Axisymmetric calculations are first performed for both aspect ratios in the range 3858≤Re≤23 150. Fully three-dimensional calculations are then performed for the configuration with Γ = 0.186 and Re = 23 150, and for the configuration with Γ = 0.279 and Re = 7715, 15 430 and 23 150. The axisymmetric calculations performed with Γ = 0.186 confirm many known features of the flow, including the transition from a steady flow to an oscillatory periodic regime. This occurs at ≈Re = 23 150 for a configuration with a/H = 0, and at ≈Re = 14 670 for one with a/H = 0.28 and a finite disk thickness (b/H = 0.2). Three-dimensional calculations performed for Γ = 0.186 with a/H = 0 and Re = 23 150 reveal a circumferentially periodic flow pattern with eight foci of intensified axial component of vorticity. The axisymmetric calculations performed with Γ = 0.279 and Re > 7715 yield a novel, non-unique steady solution for the velocity field that is asymmetric with respect to the interdisk mid-plane. No experimental verification of this finding exists to date, but similar situations are known to arise in the context of anomalous modes of the Taylor–Couette flow. Relaxing the axisymmetry constraint allows this flow to evolve to an oscillatory three-dimensional regime of increasing irregularity with increasing rotational speed. In this case, the number of foci of intensified axial vorticity varies with time, ranging from six at Re = 7715 to between six and eight at Re = 23 150. © 1998 John Wiley & Sons, Ltd.     

Generalized Structure Functions and Multifractal Detrended Fluctuation Analysis Applied to Vegetation Index Time Series: An Arid Rangeland Study

Estimates suggest that more than 70% of the world’s rangelands are degraded. The Normalized Difference Vegetation Index (NDVI) is commonly used by ecologists and agriculturalists to monitor vegetation and contribute to more sustainable rangeland management. This paper aims to explore the scaling character of NDVI and NDVI anomaly (NDVIa) time series by applying three fractal analyses: generalized structure function (GSF), multifractal detrended fluctuation analysis (MF-DFA), and Hurst index (HI). The study was conducted in four study areas in Southeastern Spain. Results suggest a multifractal character influenced by different land uses and spatial diversity. MF-DFA indicated an antipersistent character in study areas, while GSF and HI results indicated a persistent character. Different behaviors of generalized Hurst and scaling exponents were found between herbaceous and tree dominated areas. MF-DFA and surrogate and shuffle series allow us to study multifractal sources, reflecting the importance of long-range correlations in these areas. Two types of long-range correlation appear to be in place due to short-term memory reflecting seasonality and longer-term memory based on a time scale of a year or longer. The comparison of these series also provides us with a differentiating profile to distinguish among our four study areas that can improve land use and risk management in arid rangelands.     

Synthesis,spectroscopic/electrochemical characterization and DNA interaction study of novel ferrocenyl‐substituted porphyrins

We report the synthesis and characterization of two new meso‐ferrocenylporphyrins, with the ferrocenyl unit attached at the para position of a C₆F₄ group by a C? N bond with ? NH(CH₂)₂NH? ( 2a ) and ? NH(CH₂)₄NH? ( 2b ) spacers. Compounds 2a and 2b were characterized through elemental analyses, electrospray ionization high‐resolution mass spectrometry, ¹H NMR, UV–visible and fluorescence spectroscopies, electrochemistry and spectroelectrochemistry. The free base porphyrin 2 was included for comparison purposes. The binding ability of 2 and the porphyrin derivatives 2a and 2b with calf thymus DNA was determined using UV–visible and fluorescence spectroscopies. The results suggest that the interaction of these systems most probably occurs through π‐stacking by non‐classical modes involving the partial insertion of the C₆F₅ ring between adjacent base pairs on DNA and possible hydrogen interaction with the aliphatic ? NH(CH₂)_nNH? (n = 2 or 4) groups with calf thymus DNA. Moreover, we also demonstrate that porphyrins generate singlet oxygen species and show good photostability after irradiation.