Theories based on competition for resources predict a monotonic negative relationship between population density and individual biomass in plant populations. They do not consider the role of facilitative interactions, which are known to be important in high stress environments. Using an individual-based 'zone-of-influence' model, we investigated the hypothesis that the balance between facilitative and competitive interactions determines biomass-density relationships. We tested model predictions with a field experiment on the clonal grass Elymus nutans in an alpine meadow. In the model, the relationship between mean individual biomass and density shifted from monotonic to humped as abiotic stress increased. The model results were supported by the field experiment, in which the greatest individual and population biomass were found at intermediate densities in a high-stress alpine habitat. Our results show that facilitation can affect biomass-density relationships.

We report the rare observation of an irreversible transformation from a chiral to an achiral crystal through the syntheses of two polymorphs of K[Co(HCOO)(3)], and their characterization using single and powder crystal X-ray diffractions, infrared spectroscopy, thermal analyses, and the study of their magnetic properties. The kinetic phase (1), obtained under a high concentration of reactants, has a chiral (4(9)·6(6)) framework and adopts the hexagonal space-group P 6(3)22. The thermodynamic phase (2), obtained from dilute solution, has an achiral (4(12)·6(3)) framework and adopts a monoclinic space group C 2/c. Once 1 has crystallized out from the concentrated solution, it dissolves slowly at the expense of the formation of 2. In the solid state 1 is irreversibly transformed to 2 very slowly at ambient conditions. The transformation is accompanied by an increase of the crystal density, a change of coordination mode of some formates from anti-anti to syn-anti and a change in the coordination number of K from 6 to 8. 1 is a spin-canted antiferromagnet (T(N) = 8.3 K) displaying two steps in the isothermal magnetization at 2 K, a spin-flop at 1.2 kOe and a flip to paramagnetic phase at 42.0 kOe. 2 is an antiferromagnet (T(N) = 2.0 K). Thermal properties and IR spectra of the two polymorphs have been studied, showing some differences.

The anion-interaction properties of a Ru(II) complex of [Ru(bpy)2(Htppip)](ClO4)2·H2O·DMF (RuL) {bpy =2,2'-bipyridine and Htppip =2-(4-(2,6-di(pyridin-2-yl)pyridin-4-yl)phenyl)-1H-imidazo[4,5-f][1,10]phenanthroline} were thoroughly investigated in CH3CN and CH3CN/H2O (50:1, v/v) solutions by UV-visible absorption, emission, and (1)H NMR spectra. These analyses revealed that RuL acts as an efficient "turn on" emission sensor for H2PO4(-), and a "turn off" sensor for F(-) and OAc(-); in addition, RuL exhibited slightly disturbed emission spectra in the presence of the other anions studied (Cl(-), Br(-), I(-), NO3(-), and ClO4(-)). The cation-sensing properties of RuL were also studied in both neat CH3CN and aqueous 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid buffer (pH = 7.2)/CH3CN (71/1, v/v) solutions. RuL was found to exhibit a colorimetric sensing ability that was highly selective for Fe(2+), as evidenced by an obvious color change from pale yellow to light red-purple to the naked eye over the other cations studied (Na(+), Mg(2+), Ba(2+), Mn(2+), Fe(3+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), and Ag(+)). To obtain insights into the possible binding modes and the sensing mechanisms, (1)H NMR spectral analysis, luminescence lifetime measurements, and density functional theoretical calculations were also performed.

The three Ru(II) complexes of [Ru(bpy)2(bipp)](ClO4)2 (1), [Ru(bpy)2(bopp)](ClO4)2 (2), and [Ru(bpy)2(btpp)](ClO4)2 (3) (where bpy = 2,2‘-bipyridine, bipp = 2-benzimidazoyl-pyrazino[2,3-f] [1,10]phenanthroline, bopp = 2-benzoxazolyl-pyrazino[2,3-f] [1,10]phenanthroline, and btpp = 2-benzthiazolyl-pyrazino[2,3-f] [1,10]phenanthroline) with variations in heteroatoms of NH (1), O(2), and S(3), have been synthesized and characterized. These complexes have been shown to act as promising calf thymus DNA intercalators and a new class of DNA light switches for the DNA, as evidenced by UV−visible and luminescence titrations, steady-state emission quenching by [Fe(CN)6]4-, DNA competitive binding with ethidium bromide, reverse salt titrations, viscosity measurements, and DNA melting experiments.