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41.
Sanjib Das 《Inorganica chimica acta》2011,372(1):425-428
A new ligand with D-π-A symmetry has been synthesized in high yield by Knoevenagel condensation of 4-(dimethylamino)benzaldehyde with malononitrile. The ligand forms coordination polymers with Ag(I) salts at room temperature where the ultimate structure is dependent upon the counter anion. With AgNO3, a 2D tubular structure is formed where the nitrate anions bridge two Ag(I) centers. When AgBF4 is used, a 1D grid structure results but with AgOTf, a 1D zigzag structure is formed. Thus, anions control the structure of the coordination polymers formed. Each coordination polymer affords high TPA activity that can be correlated with the structure of the polymer. 相似文献
42.
Endostatin, a potent angiogenesis inhibitor, is an acid resistant protein with compact tertiary structure. Nuclear magnetic resonance, circular dichroism, and tryptophan emission fluorescence were used to monitor the structural changes of endostatin during acid-, heat-, and urea-induced unfolding processes. Results show that sulfate anions sensitize endostatin to acid, but specifically stabilize it against heat or urea. Moreover, the disappearance of the tertiary structure and the formation of the folding intermediate of endostatin at pH 3.0 are sulfate concentration dependent. These phenomena indicate that sulfate anions stabilize the folding intermediate more than the native structure of endostatin. In addition, heparin shows stronger effect than sodium sulfate on sensitizing endostatin against acid, and very limited stabilizing effect against urea. The loose structure of endostatin upon heparin binding may imply that the physiologically favorable structure for endostatin exerting its biological functions is not as compact as what was reported. 相似文献
43.
Streamwater chemistry was measured at 100-m intervals in all streams of the Hubbard Brook Valley, NH during ‘spring’ (May–July)
and during ‘fall’ (October–December) 2001. Overall, streamwater chemistry was very similar during these two periods, but fall
median concentrations were consistently higher than spring values, except for ANC, pH, NO3− and PO43−, which had lower values in fall. Median concentrations for NH4+ were approximately the same in spring and fall. Stream chemistry varied throughout the Hubbard Brook Valley by elevation,
channel length, drainage area and type of drainage, but most of the variability in stream chemistry was subtle and relatively
small. Overall, there were relatively large (two- to 10-fold) changes in chemistry with longitudinal distance of wetted channel,
elevation and/or size of drainage area in some streams and for some elements (e.g., H+, Aln+, DOC), but other chemical concentrations changed relatively little (e.g., Cl−, dissolved Si). The main Hubbard Brook, a fifth-order stream at the mouth of the Valley, was remarkably constant in chemistry
throughout its length, except where human disturbance near the mouth changed the chemistry. Differences in vegetation, geologic
substrates and wetland areas were related to changes in pattern of streamwater chemistry throughout the Valley. 相似文献
44.
45.
David B. Herbst 《Hydrobiologia》2001,466(1-3):209-219
The search for pattern in the geographic occurrence of salt lake flora and fauna often reveals strong associations of specific taxa with certain types of water chemistry. Solute composition, along with salinity and habitat stability, may provide a templet shaping the distribution of many organisms inhabiting saline lakes. A review of studies demonstrating habitat associations, specific solute tolerance, and ionic and osmotic adaptations provide evidence of fidelity to particular conditions of environmental chemistry across a wide taxonomic spectrum. Under low salinity conditions, some species show osmoregulatory adaptability to varied solute composition but the capacity for such flexibility is reduced with increased salinity and only certain taxa are found in hypersaline waters dominated by a particular solute. Anionic ratios of chloride, bicarbonate–carbonate, and sulfate appear to be especially important determinants of distribution. Specific solute tolerance presents an alternative explanation to disrupted hydrographic connections in describing how biogeographic distributions may be restricted to certain aquatic habitats in arid regions. Physiological adaptations to chemistry, exemplified in the brine fly genus Ephydra, may be an integral part of the evolution, ecology and diversification of saline water organisms. 相似文献
46.
M. J. Kropff 《Plant and Soil》1991,131(2):235-245
The impact of SO2 on the ionic balance of plants and its implications for intracellular pH regulation was studied to find explanations for long-term effects of SO2. When sulphur, taken up as SO2 by the shoots of plants, is not assimilated in organic compounds, but stored as sulphate, an equivalent amount of H+ is produced. These H+ ions are not buffered chemically, but removed by metabolic processes.On the basis of knowledge on metabolic buffering mechanisms a conceptual model is proposed for the removal of shoot-generated H+ by (i) OH- ions, produced in the leaves when sulphate and nitrate are assimilated in organic compounds and/or by (ii) OH- ions produced by decarboxylation of organic anions (a biochemical pH stat mechanism). The form in which nitrogen is supplied largely determines the potential of the plant to neutralize H+ in the leaves during SO2 uptake by the proposed mechanisms.In field experiments with N2 fixing Vicia faba L. crops, the increase of sulphate in the shoots of SO2-exposed plants was equivalent in charge to the decrease of organic anion content, calculated as the difference between inorganic cation content (C) and inorganic anion content (A), indicating that H+ ions produced in the leaves following SO2 uptake were partly removed by OH- from sulphate reduction and partly by decarboxylation of organic anions.The appearance of chronic SO2 injury (leaf damage) in the field experiment at the end of the growing period is discussed in relation to the impact of SO2 on the processes involved in regulation of intracellular pH. It is proposed that the metabolic buffering capacity of leaf cells is related to the rates of sulphate and nitrate reduction and the import rate of organic anions, rather than to the organic anion content in the vacuoles of the leaf cells. 相似文献
47.
Abstract. Red spruce ( Picea rubens Sarg.) seedlings were overwintered in two controlled environment chambers designed to simulate sub-zero winter conditions. One of the chambers was fumigated throughout the 5-month period with low concentrations of SO2 + NO2 . Extracts of extracellular fluid from trees in this treatment revealed accumulations of sulphite and nitrite, but not of sulphate or nitrate. Analysis of the chloroplast membrane lipid monogalactosyl diglyceride (MGDG) indicated a large increase in fatty acid saturation in both treatments during mid-winter, with a subsequent recovery to earlier levels. Although at the end of the experiment the MGDG of polluted trees contained significantly less linolenic acid, there was no overall treatment effect on fatty, acid content. In the following spring, there was some indication that flushing of leader buds began earlier and proceeded at a slower rate in polluted trees compared to controls, but no other growth parameters were affected by the winter treatment. The absorption of SO2 and NO2 and the accumulation of their products during dormancy is discussed as a potential mechanism for metabolic disruption, resulting in changes to seasonal responses which could be critical to the survival of the plant. 相似文献
48.
Simon A. Lewis A. Grant Butt M. Joanne Bowler John P. Leader Anthony D. C. Macknight 《The Journal of membrane biology》1985,83(1-2):119-137
Summary The effects of complete substitution of gluconate for mucosal and/or serosal medium Cl– on transepithelial Na+ transport have been studied using toad urinary bladder. With mucosal gluconate, transepithelial potential difference (V
T) decreased rapidly, transepithelial resistance (R
T) increased, and calculated short-circuit current (I
sc) decreased. CalculatedE
Na was unaffected, indicating that the inhibition of Na+ transport was a consequence of a decreased apical membrane Na+ conductance. This conclusion was supported by the finding that a higher amiloride concentration was required to inhibit the residual transport. With serosal gluconateV
T decreased,R
T increased andI
sc fell to a new steady-state value following an initial and variable transient increase in transport. Epithelial cells were shrunken markedly as judged histologically. CalculatedE
Na fell substantially (from 130 to 68 mV on average). Ba2+ (3mm) reduced calculatedE
Na in Cl– Ringer's but not in gluconate Ringer's. With replacement of serosal Cl– by acetate, transepithelial transport was stimulated, the decrease in cellular volume was prevented andE
Na did not fall. Replacement of serosal isosmotic Cl– medium by a hypo-osmotic gluconate medium (one-half normal) also prevented cell shrinkage and did not result in inhibition of Na+ transport. Thus the inhibition of Na+ transport can be correlated with changes in cell volume rather than with the change in Cl– per se. Nystatin virtually abolished the resistance of the apical plasma membrane as judged by measurement of tissue capacitance. With K+ gluconate mucosa, Na+ gluconate serosa, calculated basolateral membrane resistance was much greater, estimated basolateral emf was much lower, and the Na+/K+ basolateral permeability ratio was much higher than with acetate media. It is concluded the decrease in cellular volume associated with substitution of serosal gluconate for Cl– results in a loss of highly specific Ba2+-sensitive K+ conductance channels from the basolateral plasma membrane. It is possible that the number of Na+ pump sites in this membrane is also decreased. 相似文献
49.
In providing chemiluminescent probes that have high chemiluminescence intensity and high specificity to superoxide anions, novel chemiluminescent probes involving cyclodextrins covalently bound to 6-(4-methoxyphenyl)imidazo[1,2-alpha]pyrazin-3(7H)-one with fluorescein were synthesized and characterized. Using the hypoxanthine-xanthine oxidase system for the generation of the superoxide anions, these novel chemiluminescent probes showed higher superoxide-induced chemiluminescence intensity than that of 6-[4-[2-[N(')-(5-fluoresceinyl)thioureido]-ethoxy]phenyl]-2-methylimidazo[1,2-alpha]pyrazin-3(7H)-one (FCLA). When tested at a probe concentration of 1.0 microM, compound 6, in which 6-(4-methoxyphenyl)imidazo[1,2-alpha]pyrazin-3(7H)-one and fluorescein are covalently attached on the secondary and primary hydroxyl faces of gamma-cyclodextrin, respectively, showed green luminescence intensity that was 26 times that of FCLA, which was also the highest luminescence intensity in this present study. At probe concentrations of less than 1.0 microM, the ratio of the superoxide-dependent chemiluminescence intensity to the background chemiluminescence intensity for compound 6 was higher than that of FCLA. This high superoxide-induced chemiluminescence intensity and superoxide specificity in low probe concentrations indicates that 6 can be more effective than FCLA toward the measurement of superoxide anions. 相似文献
50.
We investigated regulation by extracellular ATP of channels important for volume regulation of rat hippocampal neurons. Cultures made from fetuses at the eighteenth gestational day were predominantly neuronal after 10-20 days in vitro, as indicated by immunostaining for neuron specific enolase. Neurons recorded with whole-cell patch clamp showed inward currents when membrane voltages were driven to values greater than -50 mV. Chloride conductance increased with 10 microM-100 microM extracellular ATP in a dose-dependent fashion. Similarly, an increase in taurine conductance was observed with 50 microM ATP. These currents were inhibited by the anion channel and purinergic receptor antagonists niflumic acid and suramin, respectively. The chloride conductance response to 10 microM ATP was increased over eight-fold in hypoosmotic medium (250 mOsm); however, chloride conductance in 0 mM ATP was not altered by this osmolality. Thus anion and osmolyte conducting channels activated via purinergic receptors may mediate volume regulation of hippocampal neurons. 相似文献