Measurements of the major cations Ca and Mg by the technique of diffusive gradients in thin films (DGTs) were systematically evaluated. The concentration in solution was calculated using Fick’s first law of diffusion from the directly measured flux to the DGT device. A selective cation exchange resin (Bio-Rad Chelex®100), which has been used extensively with DGT for trace metals, such as Cd2+, Cu2+ and Ni2+, was used for this work.
Elution of Ca and Mg from the resin with 1 M HNO3 was very reproducible. Measurements of Ca and Mg concentrations in synthetic solutions agreed well with the theoretical predictions. The negative response on uptake caused by lowered pH was investigated. Uptake was found to decline below pH 5. The capacity of the DGT device for Ca and Mg was also investigated to establish maximum deployment times for given concentrations.
Experiments with filtered and modified lake water show that DGT can be used to measure Ca and Mg when trace metals are present in the solution. An in situ deployment of DGT combined with an ultrafiltration study suggest that the Mg concentration measured by DGT is similar to the concentration found in the fraction <1 kDa. 相似文献
The 12-vertex closo-phosphaborane 1,7-P2B10Cl10 (1) has been prepared in low yield from the pyrolysis reaction of B2Cl4 with PCl3 at temperatures above 400 degrees C. A single-crystal X-ray structure determination of 1 (monoclinic space group P2(1)/n with a = 9.239(2) A, b = 16.786(3) A, c = 15.739(3) a, beta = 93.25(3) degrees, and Z = 4) confirmed that, consistent with its 26 skeletal electron count, the phosphaborane adopts a distorted icosahedral structure with the phosphorus atoms in the 1,7-positions. Crystals of 1 contain toluene in a 1:1 molar ratio embedded between each P atom of neighboring cluster molecules. Alteration of the pyrolytic conditions resulted in the formation of the phosphaboranes P4B8Cl6 (2) and P2B8Cl8 (3), which were characterized spectroscopically. Copyrolysis of B2Cl4 with a mixture of PCl3 and AsCl3 at 450 degrees C generated the six-vertex arsaphosphaborane AsPB4Cl4 (4) and traces of the icosahedral arsaphosphaborane AsPB10Cl10. These compounds are examples of heteroboranes which contain two different group-15 atoms within a single molecule. 相似文献
The reaction of the 4,4-dialkylated 2-cyclohexenones 1 or 2 with a twofold excess of a secondary amine 3 affords the 2-amino-1,3-cyclohexadienes 4 and 5 , respectively. Irradiation (λ ≧ 300 nm) of the morpholino derivative 4a yields a mixture of the isomeric 3-morpholino-6-methyl-1,3,5-heptatrienes 6 and 7 , while 5 gives only one corresponding product 8 . The reaction of enone 1 with an equimolar amount of pyrrolidine ( 3c ) affords the bis-enamine 9 which is converted to the unsaturated diketone 10 by oxidative hydrolysis. 相似文献
Here we report the first experimental detection of the C(s) symmetric nitroformyl radical, OCNO(X 2A') in a nitrogen-carbon dioxide matrix at 10 K using a Fourier transform infrared spectrometer (FTIR). The nu1 vibrational frequency was observed at 2113 cm(-1). This assignment was confirmed by follow-up experiments using isotopically labeled reactant molecules (15N, 18O, 13C). To synthesize this radical, we irradiated solid nitrogen-carbon dioxide ice mixtures with energetic electrons at 10 K. Suprathermal nitrogen atoms in their electronic ground and/or first electronically excited state were generated via the radiation induced degradation of molecular nitrogen; these atoms could then react with carbon dioxide to eventually yield the nitroformyl radical. We also investigated the kinetics of the formation of the nitroformyl radical and support the arguments with computations on the doublet and quartet OCNO potential energy surfaces (PESs). 相似文献
Whereas uranyl compounds at most show electron transfer satellites at 3 eV higher I in the U4f region, mixed oxides containing uranium(V) show a characteristic satellite at 7.9 eV higher I. Uranium-cerium blue and certain U(IV) compounds are also discussed. 相似文献
The enantio- and diastereoselective synthesis of allenyl aryl sulfides by asymmetric lithiation of 2-alkynyl (2-hetero)aryl sulfides is described. A dynamic thermodynamic resolution by selective crystallization of the intermediate lithium complexes derived from deprotonation, applying a bis(oxazoline) ligand, was achieved to give enantioselectivities up to 85% ee. Subsequent stereospecific nickel-catalyzed cross-coupling reactions with arylzinc reagents established a versatile access to threefold carbon-substituted allenes. 相似文献
While the basic fermented (sour) milk products, such as yogurt and kefir can be produced only in live flora version, the post
heat-treatment is preferred in their flavored variations to increase the storage time. Casein being in sour coagulum precipitates
during heat-treatment; therefore protective colloids surrounding the protein should be used to prevent it. Protective colloids
are plant extracts, the most known of them are pectin and amylopectin. Basic requirement of protective colloid effect is the
lower swelling temperature of hydrocolloid than the temperature of precipitation of sour coagulum. In this work we have examined
the precipitation of sour coagulum as a function of the type of lactic acid bacteria cultures applied during fermentation
as well as the swelling of heat protective plant hydrocolloids as a function of the composition (mainly of sugar content)
of medium. To investigate the precipitation of fermented coagulum skimmed milk was fermented with mesophilic butter culture,
thermophilic yogurt culture as well as with exopolysaccharide (EPS)-producing Prebiolact-2 culture. Precipitation was indicated
in the increase of great extent of viscosity. Amylopectin was dispersed into aqueous solution of pH 4.5, the saccharose concentration
of which was changed during the investigation of the swelling of heat protective hydrocolloids. A definite exothermic peak
was assigned to the swelling of hydrocolloids during the DSC experiments. We could conclude that the precipitation temperature
was increasing in the mesophilic-thermophilic-EPS producing microbes line, i.e. the heat stability and swelling temperature
of hydrocolloids depend on the saccharose content of aqueous medium and they increase with rising the concentration of saccharose. 相似文献
The effects of storage of size-exclusion column packing materials in methanolic or azide-water solutions on subsequent separations were tested. Three commercially available columns were used in these studies; the Toyo-Soda Bio-Sil TSK 125, Bio-Sil TSK 250 and the DuPont Bio-Series GF-250. Upon initial chromatography, all three columns bound up to 760 micrograms of cytochrome c tryptic peptides. Sample binding to packing material is probably a function of the positively charged basic groups on peptides or proteins interacting with silanol groups. The larger the peptide, the less the opportunity for silanol-charged group interaction, hence, less binding. Initial samples introduced to a new column occupy the binding sites. Equilibration with neat methanol removes the bound protein revealing sites which bind sample. After absorption of peptides to binding sites on the packing material, storage in neat methanol regenerates the binding sites. Storage in 10% methanol diminished the binding phenomenon, but storage in azide-water reduced binding to a range below detection at the microgram level. Our recommendation to users of size-exclusion chromatographic columns is that one satisfy the absorption capacity of a new column by injecting a sufficient quantity of a basic peptide standard or other convenient sample to reduce available binding sites before using the column for important separations. Store columns in azide-water or 10% methanol to prevent the regeneration of exposed silanol groups. 相似文献
The platelet component of shish-kebabs crystallizes after the core, during cooling or storage below the formation temperature of the core. Three basic platelet morphologies were previously identified which were mutually interconvertible, a process we have termed “hairdressing”. In this paper we show that these three categories are special cases of a continuous range of overgrowth spacings. Crystallization at high temperatures gives widely spaced overgrowths and, as the crystallization temperature is reduced, so the overgrowth spacing decreases gradually. In the extreme case (only obtainable by quenching) the overgrowths become so close as to overlap and appear continuous. We also report a variety of further effects which were caused by exposing the shish-kebabs, while in solvent, to temperatures above their initial formation temperature. A new theoretical approach is described which considers the depletion of material available to form new overgrowths during crystallization. Two versions of this theory are presented (one a computer simulation and one analytic); interpreting our results on the basis of this theory we show that shish-kebabs crystallize at high temperatures even when quenched (90°C and above except in a few exceptional circumstances) and we are able to explain all the features of shish-kebab crystallization that we have observed. 相似文献
The doubly deprotonated form of calix[6]arene, with two protonated triethylamines as counter-ions, crystallizes in the monoclinic system: space groupP21/n,a=8.465(4),b=17.822(8),c=15.182(6) Å,=90.18(4)°,V=2291(2) Å3,Z=2. Refinement led to a final conventionalR value of 0.063 for 1046 reflections. The macrocycle conformation is not apinched cone, usual for freeR-calix[6]arene, but a distorted 1,2,3-alternate cone, since the molecule lies on a symmetry center. Furthermore, one of the torsion angles defined by the methylene bridges is near to zero, which is unusual in calixarene structures.
Supplementary Data relating to this article (atomic coordinates for hydrogen atoms, anisotropic displacement parameters for oxygen and nitrogen atoms, and observed and calculated structure factors) are deposited with the British Library as Supplementary Publication No. SUP 82182 (7 pages). 相似文献