Effect of herbage density, height and age on nutrient and invertebrate generalist predator abundance in permanent and temporary pastures

© 2020 by the authors. The aim of this research was to assess differences in the quantity and quality of herbage and invertebrate generalist predator abundance among permanent and temporary pastures. Two permanent pastures and four temporary ley pastures (either one year or two years since being sown) were monitored weekly for 10 weeks in the spring. Permanent pastures included a diverse range of native UK grass species, and temporary ley pastures were predominantly perennial ryegrass (Lolium perenne) with or without white clover (Trifolium repens). Weekly measurements of herbage height (in centimeters), herbage cover (fresh and dry matter in kg per hectare) and herbage density (fresh and dry matter in kg per hectare per centimeter) were obtained for each field, along with lycosid spider and carabid beetle abundance. Weekly pasture samples were used to obtain nutrient concentrations of dry matter, crude protein, neutral detergent fibre (NDF), acid detergent fibre (ADF), ash, oil, sugars, digestible organic matter in the dry matter (DOMD) and metabolisable energy (ME) in the herbage as a measure of forage quality for grazing or harvesting. A linear mixed model was used to assess the effect of sward age, herbage density and height on herbage production, nutrient concentrations and invertebrate abundance. Although this study showed that permanent pastures were associated with lower nutrient concentrations of crude protein, ash, oil and ME compared to younger and predominantly perennial ryegrass pastures, the older pastures were associated with higher carabid numbers. Furthermore, permanent pastures had a higher density of dry matter herbage compared to younger pastures, and more dense and taller swards were associated with higher lycosid numbers. The study suggests that within pastures of 3 to 20 cm height, increasing the height and density of swards increases both ME and oil concentrations in herbage, therefore enhancing forage nutrient quality. Older and more permanent pastures can be beneficial for plant and invertebrate generalist predator populations, and still provide a useful source of nutrients for forage production

Acid/base-triggered switching of circularly polarized luminescence and electronic circular dichroism in organic and organometallic helicenes.

Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene-bipyridine proligand 1 a and in its “rollover” cycloplatinated derivative 2 a. Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum-chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene-bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge-transfer-type transition rather than a π–π* transition) as well as an increase in the HOMO–LUMO character of the transition and stabilization of the LUMO level upon protonation

Acid/base-triggered switching of circularly polarized luminescence and electronic circular dichroism in organic and organometallic helicenes

Electronic circular dichroism and circularly polarized luminescence acid/base switching activity has been demonstrated in helicene-bipyridine proligand 1 a and in its “rollover” cycloplatinated derivative 2 a. Whereas proligand 1 a displays a strong bathochromic shift (>160 nm) of the nonpolarized and circularly polarized luminescence upon protonation, complex 2 a displays slightly stronger emission. This strikingly different behavior between singlet emission in the organic helicene and triplet emission in the organometallic derivative has been rationalized by using quantum-chemical calculations. The very large bathochromic shift of the emission observed upon protonation of azahelicene-bipyridine 1 a has been attributed to the decrease in aromaticity (promoting a charge-transfer-type transition rather than a π–π* transition) as well as an increase in the HOMO–LUMO character of the transition and stabilization of the LUMO level upon protonation

Group 4 Metal Complexes of Nitrogen-Bridged Dialkoxide Ligands: Synthesis, Structure, and Polymerization Activity Studies

Neutral soluble titanium(IV) and zirconium(IV) complexes of new amino-dialkoxide ligands {OCR2CH2N(CH2Ph)CH2CR2O}2- ({ONOR}2-) have been prepared. Alcohol and alkane elimination reactions from {ONOR}H2 (R = Me, 1; p-tol, 2) and salt metathesis routes from Li2{ONOMe} in situ-generated afford {ONOMe}Ti(OiPr)2 (3), {ONOR}2M (R = Me, M = Ti, 5; Zr, 6; R = p-tol, M = Zr, 7), {ONOMe}Zr(CH2Ph)2 (8), {ONOMe}ZrCl2(THF)n (n = 0, 9; n = 1, 10), {ONOMe}Zr(NMe2)2 (11), and {ONOR}TiCl2 (R = Me, 13; R = p-tol, 14) in good yields. X-ray crystallographic studies showed that 3, 8, 13, and 14 adopt in the solid state mononuclear structures, with coordination of the nitrogen atom to the metal center. Dinuclear structures with bridging alkoxide and amido ligands were observed for 6 and a mixed amido-{ONOMe}Zr complex (12) isolated in the preparation of 11. NMR data are consistent with the existence of a single monomeric species in toluene solution for all complexes, except 11 and dichlorozirconium complexes 9 and 10, for which mixtures of monomeric and possibly aggregated species are observed in toluene and THF. The dynamic behavior of monomeric species 3, 8, 13, and 14 in toluene was investigated by variable-temperature NMR spectroscopy. The activation parameters determined by line-shape analysis, in particular for 8 (ΔH⧧ = 20.0 ± 1 kcal·mol-1; ΔS⧧ = 13.1 ± 2 cal·mol-1·K-1) and 13 (ΔH⧧ = 17.4 ± 1 kcal·mol-1; ΔS⧧ = 11.4 ± 2 cal·mol-1·K-1), suggest a process involving dissociation of nitrogen, inversion of configuration at nitrogen, and amine re-coordination. The bulkiness of the R substituents affects the fluxional behavior of {ONOR}TiCl2 (R = Me, 13; R = p-tol, 14). The THF-free dichlorozirconium complex 9 in combination with MAO generates highly active but very unstable ethylene polymerization catalyst systems

Synthesis, structure and reactivity of new yttrium bis(dimethylsilyl)amido and bis(trimethylsilyl)methyl complexes of a tetradentate bis(phenoxide) ligand

The reactions of a bulky amino-methoxy bis(phenolate) ligand H2L with Y(CH2SiMe3)3(THF)2 and Y[N(SiHMe2)2]3(THF)2 under mild condition leads to the selective formation of the thermally stable complexes [L]Y(CH2SiMe3)(THF) (1) and [L]Y[N(SiHMe2)2](THF) (2). The X-ray structures revealed very similar binding of the [ONOO] ligand core to the metal for both complexes, which feature an octahedral geometry involving coordination of the methoxy side-arm of the ligand and of a remaining THF molecule. 1H-NMR spectroscopy indicates that the solid state structure of 1 and 2 is retained in hydrocarbon solutions with THF coordinated to yttrium. Alkyl complex 1 showed no activity in ethylene polymerization, presumably due to the presence of coordinated THF. The amido complex 2 catalyzed sluggishly the polymerization of methyl methacrylate to give isotactic-rich PMMA but is very active for the ring-opening polymerization of ε-caprolactone. New alkyl and amido yttrium complexes of a tetradentate bis(phenolate) ligand have been prepared, structurally characterized and investigated as polymerization catalysts