Binding affinity and capacities for ytterbium(3+) and hafinum(4+) by chemical entities of plant tissue fragments.
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The binding affinity of ytterbium (Yb3+) and hafinum (Hf4+) to ligands of chemical entities of fragments of bermudagrass tissues and their resistance to exchanging Yb with other ligands and to displacement by protons were investigated. Chemical entities of acid resistant NDF (ARNDF), 0.1 N acid detergent fiber (0.1 N ADF), and permanganate cellulose (CELL) were prepared from fragments of bermudagrass hay (Cynodon dactylon [L.] Pers.) obtained by grinding to pass a 2-mm sieve. 175Ytterbium and Yb, as YbCl3, were initially bound to each preparation by soaking for 12 h in pH 5.5 borate buffer to obtain Yb bound onto ligands having affinity constants for Yb equal to or greater than that for the weakly stable borate ligand, Yb > or = borate. The fraction of Yb > or = borate was measured and fragments then sequentially exposed to acetate, citrate, nitrotriacetate (NTA), and EDTA ions to allow exchange of Yb from Yb > or = borate with ligands having affinity constants for Yb equal to or greater than acetate (Yb > or = acetate), citrate (Yb > or = citrate), NTA (Yb > or = NTA), and EDTA (Yb > or = EDTA) ions. Binding of Yb > or = borate indicated the existence of two species of ligands: strong ligands binding essentially 100% of added Yb at levels of 1 to 1,300 ppm (0.1 N ADF) and at 1 to 7,000 ppm (ARNDF); and weaker ligands binding 4 and 8% of the Yb, respectively, at levels of added Yb greater than 1,300 ppm and 7,000 ppm. Ytterbium > or = acetate of ARNDF, but not 0.1 N ADF, was as resistant to exchange as Yb > or = citrate. Ytterbium > or = borate was exchanged extensively (85% or greater) with soluble ligands having affinity constants > or = NTA. Ytterbium resistance to proton displacement at pH of 1.5 increased with Yb > or = EDTA > Yb > or = NTA > Yb > or = citrate > Yb > or = acetate. Very efficient binding of Yb to CELL suggested that such chemical preparations are not representative of native cellulose. Hafnium (4+) was strongly bound to plant tissues rendering both Hf and Hf-bound DM insoluble at a pH of 1.5 and insoluble in a modified NDF solvent without EDTA. It is concluded that Yb specifically applied as Yb > or = acetate and Hf4+ are indelible markers for estimating sojourn time of undigested plant tissues at the normal pH of the rumen. Because of its resistance to proton displacement, Hf4+ would be an indelible marker for estimating sojourn time in more acidic postgastric segments of the gastrointestinal tract. (+info)
Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics.
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It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 +/- 0.3) and the Moon (17.0 +/- 0.8) are below the chondritic ratio of 19.9 +/- 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago. (+info)
Catalytic ester-amide exchange using group (IV) metal alkoxide-activator complexes.
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A process for preparation of amides from unactivated esters and amines has been developed using a catalytic system comprised of group (IV) metal alkoxides in conjunction with additives including 1-hydroxy-7-azabenzotriazole (HOAt). In general, ester-amide exchange proceeds using a variety of structurally diverse esters and amines without azeotropic reflux to remove the alcohol byproduct. Initial mechanistic studies on the Zr(Ot-Bu)4-HOAt system revealed that the active catalyst is a novel, dimeric zirconium complex as determined by X-ray crystallography. (+info)
Reactive landing of gas-phase ions as a tool for the fabrication of metal oxide surfaces for in situ phosphopeptide enrichment.
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