Search

NMR-Spectroscopic and s olid-s tate studies are conducted to gain insight into the dimeric structures in cometal-free asymmetric conjugate addition reactions of dialkylzinc reagents with aldehydes. X-ray structure determination of a zinc complex with a [2.2]paracyclophane ligand are supported by the DFT calculations for the structures of the zinc complexes of monomeric and dimeric species.

Abstract: Most plant‐based emissions of volatile organic compounds are considered mainly temperature dependent. However, certain oxygenated volatile organic compounds (OVOCs) have high water solubility; thus, also stomatal conductance could regulate their emissions from shoots. Due to their water solubility and sources in stem and roots, it has also been suggested that their emissions could be affected by transport in the xylem sap. Yet further understanding on the role of transport has been lacking until present. We used shoot‐scale long‐term dynamic flux data from Scots pines (Pinus sylvestris) to analyse the effects of transpiration and transport in xylem sap flow on emissions of 3 water‐soluble OVOCs: methanol, acetone, and acetaldehyde. We found a direct effect of transpiration on the shoot emissions of the 3 OVOCs. The emissions were best explained by a regression model that combined linear transpiration and exponential temperature effects. In addition, a structural equation model indicated that stomatal conductance affects emissions mainly indirectly, by regulating transpiration. A part of the temperature's effect is also indirect. The tight coupling of shoot emissions to transpiration clearly evidences that these OVOCs are transported in the xylem sap from their sources in roots and stem to leaves and to ambient air. [ABSTRACT FROM AUTHOR]

Two supramolecular tetrahedral cages based on a new electron-deficient trifluoromethyl-substituted pyridylimine ligand are synthesised by sub-component self-assembly. Their structures are characterised by NMR und UV-Vis spectroscopy, high-resolution mass spectrometry and single crystal X-ray diffraction. The iron(ii) complex shows host–guest chemistry, complex-to-complex transformations and novel electronic properties. [ABSTRACT FROM AUTHOR]

The synthesis and crystal structures with alkali halides of a ditopic benzo-15-crown-5 bis-urea receptor L have been presented. In addition, the anion binding properties of L and its alkali metal complexes in solution are presented. A comprehensive single-crystal X-ray crystallographic study of L, all together 13 crystal structures, including the ion pair complexes with NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbF, RbCl, and RbI, give a detailed view of how L behaves in the solid-state with different alkali halides depending on the size of the cation and anion. In the solid-state L forms a 1 : 1 complex with a sodium cation and the anion is complexed as a contact (NaCl) or a separate ion pair (NaBr, NaI). With larger potassium and rubidium cations L assembles into a 2 : 1 complex and forms a separated ion pair complex with the anion. Reflecting the crystal structures the L forms a 1 : 1 complex with Na+ in solution, and a 2 : 1 complex with K+, which were verified by Job's plot analysis in 4 : 1 CDCl3/dimethyl sulfoxide. The binding strength of the monomeric [L·Na]+ and the dimeric [2L·K]+ toward chloride, bromide and iodide anions was studied by 1H NMR titrations in 4 : 1 CDCl3/DMSO, and a clear turn-on effect of the cation complexation compared to the neutral receptor L alone (Ka with L for Cl−, Br− and I− being 832, 174 and 32 M−1, respectively) was observed. The monomeric [L·Na]+ binds chloride 9, bromide 8, and iodide 12 times stronger than L, while for the dimeric [2L·K]+ the corresponding increase in binding is 51 (Cl−), 84 (Br−), and 22 (I−) times with the same stoichiometric ratios as observed for the ion pair complexes in the solid-state. [ABSTRACT FROM AUTHOR]

Coniferous tree stems contain large amounts of oleoresin under positive pressure in the resin ducts. Studies in North-American pines indicated that the stem oleoresin exudation pressure (OEP) correlates negatively with transpiration rate and soil water content. However, it is not known how the OEP changes affect the emissions of volatile vapours from the trees. We measured the OEP, xylem diameter changes indicating changes in xylem water potential and monoterpene emissions under field conditions in mature Scots pine ( Pinus sylvestris L.) trees in southern Finland. Contrary to earlier reports, the diurnal OEP changes were positively correlated with temperature and transpiration rate. OEP was lowest at the top part of the stem, where water potentials were also more negative, and often closely linked to ambient temperature and stem monoterpene emissions. However, occasionally OEP was affected by sudden changes in vapour pressure deficit (VPD), indicating the importance of xylem water potential on OEP as well. We conclude that the oleoresin storage pools in tree stems are in a dynamic relationship with ambient temperature and xylem water potential, and that the canopy monoterpene emission rates may therefore be also regulated by whole tree processes and not only by the conditions prevailing in the upper canopy. [ABSTRACT FROM AUTHOR]

Anion–π interactions, intuitively repulsive forces, turned from controversial to a well-established non-covalent interaction over the past quarter of a century. Within this time frame the question “Anion–π interactions. Do they exist?” could be answered and even more importantly its functional relevance was proven. The present feature article summarizes the experimental findings of anion–π studies in the gas phase, solution and in the solid state and highlights the application of anion–π interactions in anion recognition, sensing and transport as well as in catalysis. Moreover, the biochemical relevance of this weak intermolecular force is comprehensively reviewed. [ABSTRACT FROM AUTHOR]

Crystal engineering provides tools to the rational design of materials with desired structures or properties. We have exploited the analogy between hydrogen bonds and halogen bonds to trap I2 in the channels of crystal structures, thus stabilizing the otherwise unfavourable tetrahalides via charge transfer interactions. [ABSTRACT FROM AUTHOR]

Enantiomerically pure cyclohexylhemicucurbit[8]uril (cycHC[8]), possessing a barrel-shaped cavity, has been prepared in high yield on a gram scale from either (R,R,N,N′)-cyclohex-1,2-diylurea and formaldehyde or cycHC[6]. In either case, a dynamic covalent library is first generated from which the desired cycHC can be amplified using a suitable anion template. [ABSTRACT FROM AUTHOR]

A detailed study of unexpectedly strong iodonium–sulfur halogen bonds in [I(2-imidazolidinethione)2]+ is presented. The interactions are characterized by single-crystal X-ray diffraction, charge density analysis based on QTAIM calculations, mass spectrometry, and NMR spectroscopy. The results, small RIS = 0.7 and high interaction energy of −60 kJ mol−1, support a coordinative nature of the halogen bond between the iodonium ion and the sp2 hybridized sulfur atoms. [ABSTRACT FROM AUTHOR]

The binding of different categories of alkyl ammonium (secondary and tertiary mono- and di-ammonium) salts with resorcinarenes and a pyrogallarene through weak interactions was analysed in all phases. 1H NMR spectroscopy and electrospray ionisation mass spectrometry were utilized in analysing the complexes in solution and in the gas phase, respectively. The 1H NMR titration studies in methanol-d4 reveal that the association constants for the 1 : 1 complexes vary according to the electronic properties of the hosts as well as the size, geometric orientation and charge concentration of the guest cations with binding constants of up to 950 M−1 in some cases. Mass spectrometry reveals 1 : 1 monomeric and 1 : 2 dimeric complexes in the gas phase. Six co-crystals, three of which are dimeric host–guest capsular assemblies, two open inclusion complexes and a pseudocapsular methanol solvate, were analysed in the solid state through single-crystal X-ray diffraction. The crystal structures confirm that the complexes are held together by multiple cation…π, CH…π and hydrogen bond interactions. [ABSTRACT FROM AUTHOR]

Acylhydrazone based extended dipyrrins L1-H and L2-H are introduced as complexometric ppb sensitive metal ion detectors. The binding of lanthanide, transition as well as post-transition metal ions is followed by UV-Vis measurements. The carbohydrate based ligand L2 is water soluble and thus can act as a metal ion sensor in this medium. [ABSTRACT FROM AUTHOR]

The syntheses and halogen bonded (XB) complexes of tetrahalogenated ethynyl cavitands are presented. These cavitands act as quite rigid 3D multivalent halogen bond donors and show strong XB with oxygen, nitrogen and bromide XB acceptors. [ABSTRACT FROM AUTHOR]

The distribution of Cs in reindeer tissues and organs was investigated in cases of high and low activity concentrations of Cs in the carcasses. The focus of the study was to find out whether the usually sampled neck part reliably represents the activity concentration of the carcass as a whole. In addition, the distribution patterns between different tissues and organs and the differences between adults and calves were investigated. According to the results, there are no noticeable differences between adults and calves or between different muscle tissues. Samples of neck muscle can be used as references for monitoring the radioactivity of reindeer meat. Some of the analyzed samples were taken after the Fukushima Nuclear Power Plant accident; their activity concentrations were low, showing that the accident in Japan did not endanger the radiation safety of Finnish reindeer meat. [ABSTRACT FROM AUTHOR]

The situation resulting from the Chernobyl fallout in 1987 was compared to that in 2000–2001 in Finland and NW Russia and that in 2003 in the Baltic countries. 786 humus (0–3 cm layer) samples were collected during 2000–2001 in the Barents Ecogeochemistry Project, and 177 samples in the Baltic countries in 2003. Nuclides emitting γ-radiation in the 0–3 cm humus layer were measured by the Radiation and Nuclear Safety Authority–STUK in Finland. In 1987 the project area was classified by the European Commission into four different fallout classes. 137Cs inventory Bg/m2 levels measured in 2000–2003 were compared to the EU''s class ranges. Fitting over the whole project area was implemented by generalizing the results for samples from the Baltic countries, for which Bq/m2 inventories could be calculated. A rough estimation was made by comparing the mass of organic matter and humus with 137Cs concentrations in these two areas. Changes in 137Cs concentration levels are illustrated in both thematic maps and tables. Radionuclide 137Cs concentrations (Bq/kg d.w.) were detected in the humus layer at all the 988 sampling sites. 134Cs was still present in 198 sites 15 years after the nuclear accident in Chernobyl. No other anthropogenic nuclides emitting γ-radiation were detected, but low levels of 60Co, 125Sb and 154Eu isotopes were found in 14 sites. Fifteen years after the Chernobyl accident, the radioactive nuclide 137Cs was and still is the most significant fallout radionuclide in the environment and in food chains. The results show that the fallout can still be detected in the uppermost humus layer in North East Europe. [Copyright &y& Elsevier]

Analyzes the distribution of endgroups within a urea-funtionalized poly(propyleneamine)-dendrimer of fourth generation by small-angle neutron scattering. Variation in the contrast between the solute and solvent in a systematic fashion; Partial scattering functions resulting from the analysis of the scattering intensity corrected for incoherent contributions.

• Drought effects on resin-based defences depends on the timescale considered. • Dry conditions increased carbon allocation on resin production at a long term, supporting resin pressure and flow. • At a seasonal time scale, drought reduced resin pressure but had no impact on resin flow. • Tree-to-tree variation of resin pressure and flow was related to the tree vitality and crown conditions. Droughts and other rapid changes in abiotic environmental conditions can predispose trees to damage by pest insects and pathogens. For survival of coniferous trees, functional resin-based defences are essential, and it is important to know how they react to changes in environmental conditions at various time scales. We studied the effects of differing water availabilities on resin-based defences in mature Scots pine (Pinus sylvestris) trees in a naturally drought-prone forest within a long-term irrigation experiment. Our objectives were to understand the effects of long-term drought on carbon allocation to resin production and to analyse its influence on resin flow and pressure in comparison to the shorter-term effects of seasonal drought. We tracked carbon allocation to resin after 13C-pulse labelling experiment in late summer 2017 and compared the observed resin dynamics between drought-exposed control trees and irrigated trees from June to August during the dry hot summer of 2018. Dry control trees showed higher allocation of labelled carbon to resin than irrigated trees. Resin pressure was higher in dry control than in irrigated trees with similar water potentials, and resin flow in June was higher in dry control than in irrigated trees with similar crown transparency. Yet, resin pressures of dry control trees in particular decreased with decreasing water availability from June to August. Resin flow was little affected by short-term changes in water availability and mostly associated with crown transparency. We suggest that because of differing timescales of direct drought effects and changes in allocation patterns, dry conditions may support resin-based defences in the long term, but a drought period decreases resin pressure in the short term. [ABSTRACT FROM AUTHOR]