The metal ion complexing properties of the ligand HQC (8-hydroxyquinoline-2-carboxylic acid) are reported. The structures of [Zn(HQCH)2] · 3H2O (1) and [Cd(HQCH)2] · 3H2O (2) were determined (HQCH = HQC with phenol protonated). Both 1 and 2 are triclinic, space group , with Z = 2. For 1 a = 7.152(3), b = 9.227(4), c = 15.629(7) Å, = 103.978(7)°, β = 94.896(7)°, γ = 108.033(8)°, R = 0.0499. For 2 a = 7.0897(5), b = 9.1674(7), c = 16.0672(11) Å, = 105.0240(10)°, β = 93.9910(10)°, γ = 107.1270(10)°, R = 0.0330. In 1 the Zn has a distorted octahedral coordination geometry, with Zn–N of 2.00 and 2.15 Å, and Zn–O to the protonated phenolic oxygens of 2.431 and 2.220 Å. The structure of 2 is similar, with Cd–N bonds of 2.220 and 2.228 Å, with Cd–O bonds to the protonated phenolate oxygens of 2.334 and 2.463 Å. The structures of 1 and 2, and isomorphous Ni(II) and Co(II) HQC complexes reported in the literature, show very interesting short (<2.5 Å) O–O distances in H-bonds involving the protons on the coordinated phenolates and lattice water molecules. These are discussed in relation to the possible role of short low-energy H-bonds in alcohol dehydrogenase in mediating the transfer of the hydroxyl proton of the alcohol to an adjacent serine oxygen.
The formation constants for HQC are determined by UV–Visible spectroscopy at 25 °C in 0.1 M NaClO4 with Mg(II), Ca(II), Sr(II), Ba(II), La(III), Gd(III), Zn(II), Cd(II), Ni(II), Cu(II), and Pb(II). These show greatest stabilization with metal ions with an ionic radius above 1.0 Å. This is as would be expected from the fact that HQC forms two five-membered chelate rings on complex-formation, which favors larger metal ions. The ligand design concept of using rigid aromatic backbones in ligands to achieve high levels of preorganization, and hence the high log K values (for a tridentate ligand) and strong metal ion selectivities observed for HQC, is discussed. 相似文献
We investigated the effect of suspended clay upon the phosphorus uptake rate exhibited by lotic periphyton communities. Suspended
inorganic clays and periphyton are common to aquatic environments, and both can strongly influence physical and chemical water
conditions. We used replicated artificial stream channels to test the prediction that suspended clay particles would affect
the uptake of soluble reactive phosphorus (SRP) by periphyton. Commercially available kaolinite and bentonite clays were characterized
for their aqueous suspension behavior and affinities for SRP. Periphyton was grown in a recirculating stream system and subjected
to simultaneous suspended clay and SRP additions. SRP removal from solution, both in the presence and absence of suspended
clays, was used to quantify SRP uptake parameters by periphyton. Clay type and concentrations of 20, 80, and 200 mg l−1 had no significant effect upon SRP uptake rate exhibited by periphyton during three 90-min experiments. Less than 1% of SRP
removal was attributable to the suspended clay load or artificial stream construction materials, based on clay isotherm data
and material sorption studies, indicating that 99% of SRP removal was attributable to biotic uptake. Removal of SRP (as KH2PO4) was described by a first-order equation with rate constants ranging between 0.02 and 0.14 min−1. Our results suggest that high turbidity conditions caused by suspended mineral clays have little immediate effect upon SRP
removal from the water column by periphyton.
Handling editor: D. Ryder 相似文献
Photolysis of FeL3, CoL3, NiL2, CuL2 and ZnL2, where L = S2CNEt2, in PVC matrices at ca. 90 K results in photooxidation of the metal complexes through irreversible metal to solvent charge transfer. DFT quantum mechanical studies of the S2CNMe2 anion and the Ni, Cu and Zn derivatives were carried out, providing a more nuanced understanding of the bonding of the dithiocarbamate ligand than suggested by classical resonance arguments. 相似文献
Four saccharinate complexes of divalent transition metals with 2,2′:6,2″-terpyridine (terpy) as a co-ligand have been synthesised, and characterised by elemental analysis and single crystal X-ray diffraction at low temperature. The complexes [M(terpy)(sac)(H2O)2] sac · H2O (1, M = Mn; 2, M = Co; 3, M = Ni) are isostructural, crystallising in space group Pbca. The metal ions have approximately octahedral coordination, with the two coordinated water molecules occupying cis-positions. These water molecules are hydrogen-bonded to the oxygen atom in the free water molecule. The copper(II) ion in the anhydrous complex [Cu(terpy)(sac)2] 4 is five-coordinate; the compound crystallises in the space group P2(1)/c. 相似文献
Possible non-target effects of the widely used, non-selective herbicide glyphosate were examined in six cyanobacterial strains, and the basis of their resistance was investigated. All cyanobacteria showed a remarkable tolerance to the herbicide up to millimolar levels. Two of them were found to possess an insensitive form of glyphosate target, the shikimate pathway enzyme 5-enol-pyruvyl-shikimate-3-phosphate synthase. Four strains were able to use the phosphonate as the only phosphorus source. Low uptake rates were measured only under phosphorus deprivation. Experimental evidence for glyphosate metabolism was also obtained in strains apparently unable to use the phosphonate. Results suggest that various mechanisms may concur in providing cyanobacterial strains with herbicide tolerance. The data also account for their widespread ability to metabolize the phosphonate. However, such a capability seems limited by low cell permeability to glyphosate, and is rapidly repressed when inorganic phosphate is available. 相似文献
The development of rice (Oryza sativa L.) cultivars with a higher Zn content in their grains has been suggested as a way to alleviate Zn malnutrition in human
populations subsisting on rice in their daily diets. This study was conducted to evaluate the effects of native soil Zn status
and fertilizer application on Zn concentrations in grains of five rice genotypes that had previously been identified as either
high or low in grain Zn. Genotypes were grown in field trials at four sites ranging in native soil-Zn status from severely
deficient to high in plant available Zn. At each site a −Zn plot was compared to a +Zn plot fertilized with 15 kg Zn ha−1. Results showed that native soil Zn status was the dominant factor to determine grain Zn concentrations followed by genotype
and fertilizer. Depending on soil-Zn status, grain Zn concentrations could range from 8 mg kg−1 to 47 mg kg−1 in a single genotype. This strong location effect will need to be considered in estimating potential benefits of Zn biofortification.
Our data furthermore showed that it was not possible to simply compensate for low soil Zn availability by fertilizer applications.
In all soils fertilizer Zn was taken up as seen by a 50–200% increase in total plant Zn content. However, in more Zn deficient
soils this additional Zn supply improved straw and grain yield and increased straw Zn concentrations by 43–95% but grain Zn
concentrations remained largely unchanged with a maximum increase of 6%. Even in soils with high Zn status fertilizer Zn was
predominantly stored in vegetative tissue. Genotypic differences in grain Zn concentrations were significant in all but the
severely Zn deficient soil, with genotypic means ranging from 11 to 24 mg kg−1 in a Zn deficient soil and from 34 to 46 mg kg−1 in a high Zn upland soil. Rankings of genotypes remained largely unchanged from Zn deficient to high Zn soils, which suggests
that developing high Zn cultivars through conventional breeding is feasible for a range of environments. However, it may be
a challenge to develop cultivars that respond to Zn fertilizer with higher grain yield and higher grain Zn concentrations
when grown in soils with low native Zn status. 相似文献
We have measured the uptake capacity of nitrogen (N) and potassium (K) from different soil depths by injecting 15N and caesium (Cs; as an analogue to K) at 5 and 50 cm soil depth and analysing the recovery of these markers in foliage and buds. The study was performed in monocultures of 40-year-old pedunculate oak (Quercus robur), European beech (Fagus sylvatica) and Norway spruce (Picea abies (L.) Karst.) located at an experimental site in Palsgård, Denmark. The markers were injected as a solution through plastic tubes around 20 trees of each species at either 5 or 50 cm soil depth in June 2003. After 65 days foliage and buds were harvested and the concentrations of 15N and Cs analysed. The recovery of 15N in the foliage and buds tended to be higher from 5 than 50 cm soil depth in oak whereas they where similar in spruce and beech after compensation for differences in immobilization of 15N in the soil. In oak more Cs was recovered from 5 than from 50 cm soil depth whereas in beech and spruce no difference could be detected. Out of the three investigated tree species, oak was found to have the lowest capacity to take up Cs at 50 cm soil depth compared to 5 cm soil depth also after compensating for differences in discrimination against Cs by the roots. The uptake capacity from 50 cm soil depth compared with 5 cm was higher than expected from the root distribution except for K in oak, which can probably be explained by a considerable overlap of the uptake zones around the roots and mycorrhizal hyphae in the topsoil. The study also shows that fine roots at different soil depths with different physiological properties can influence the nutrient uptake of trees. Estimates of fine root distribution alone may thus not reflect the nutrient uptake capacity of trees with sufficient accuracy. Our study shows that deep-rooted trees such as oak may have lower nutrient uptake capacity at deeper soil layers than more shallow-rooted trees such as spruce, as we found no evidence that deep-rooted trees obtained proportionally more nutrients from deeper soil layers. This has implications for models of nutrient cycling in forest ecosystems that use the distribution of roots as the sole criterion for predicting uptake of nutrients from different soil depths. 相似文献
We investigated the effects of removing near-stream Rhododendron and of the natural blowdown of canopy trees on nutrient export to streams in the southern Appalachians. Transects were instrumented
on adjacent hillslopes in a first-order watershed at the Coweeta Hydrologic Laboratory (35°03′N, 83°25′W). Dissolved organic
carbon (DOC), K+, Na+, Ca2+, Mg2+, NO3−-N, NH4+-N, PO43−-P, and SO42− were measured for 2 years prior to disturbance. In August 1995, riparian Rhododendron on one hillslope was cut, removing 30% of total woody biomass. In October 1995, Hurricane Opal uprooted nine canopy trees
on the other hillslope, downing 81% of the total woody biomass. Over the 3 years following the disturbance, soilwater concentrations
of NO3−-N tripled on the cut hillslope. There were also small changes in soilwater DOC, SO42−, Ca2+, and Mg2+. However, no significant changes occurred in groundwater nutrient concentrations following Rhododendron removal. In contrast, soilwater NO3−-N on the storm-affected hillslope showed persistent 500-fold increases, groundwater NO3−-N increased four fold, and streamwater NO3−-N doubled. Significant changes also occurred in soilwater pH, DOC, SO42−, Ca2+, and Mg2+. There were no significant changes in microbial immobilization of soil nutrients or water outflow on the storm-affected hillslope.
Our results suggest that Rhododendron thickets play a relatively minor role in controlling nutrient export to headwater streams. They further suggest that nutrient
uptake by canopy trees is a key control on NO3−-N export in upland riparian zones, and that disruption of the root–soil connection in canopy trees via uprooting promotes
significant nutrient loss to streams.
Received 30 January 2001; accepted 25 July 2002. 相似文献
Connexin hemichannels, that is, half gap junction channels (not connecting cells), have been implicated in the release of various messengers such as ATP and glutamate. We used connexin mimetic peptides, which are, small peptides mimicking a sequence on the connexin subunit, to investigate hemichannel functioning in endothelial cell lines. Short exposure (30 min) to synthetic peptides mimicking a sequence on the first or second extracellular loop of the connexin subunit strongly supressed ATP release and dye uptake triggered by either intracellular InsP3 elevation or exposure to zero extracellular calcium, while gap junctional coupling was not affected under these conditions. The effect was dependent on the expression of connexin-43 in the cells. Connexin mimetic peptides thus appear to be interesting tools to distinguish connexin hemichannel from gap junction channel functioning. In addition, they are well suited to further explore the role of connexins in cellular release or uptake processes, to investigate hemichannel gating and to reveal new unknown functions of the large conductance hemichannel pathway between the cell and its environment. Work performed up to now with these peptides should be re-interpreted in terms of these new findings. 相似文献