We report a route to the facile synthesis of Ag@Pd-Ag nanocubes by cotitrating Na2PdCl4 and AgNO3 into an aqueous suspension of Ag nanocubes at room temperature in the presence of ascorbic acid and poly(vinylpyrrolidone). With an increase in the total titration volume, we observed the codeposition of Pd and Ag atoms onto the edges, corners, and side faces of the Ag nanocubes in a site-by-site fashion. By maneuvering the Pd/Ag ratio, we could optimize the SERS and catalytic activities of the Ag@Pd-Ag nanocubes for in situ SERS monitoring of the Pd-catalyzed reduction of 4-nitrothiophenol by NaBH4.

Selective enrichment of phosphoproteins or phosphopeptides from complex mixtures is essential for MS-based phosphoproteomics, but still remains a challenge. In this article, we described an unprecedented approach to synthesize magnetic mesoporous Fe(3)O(4)@mTiO(2) microspheres with a well-defined core/shell structure, a pure and highly crystalline TiO(2) layer, high specific surface area (167.1 m(2)/g), large pore volume (0.45 cm(3)/g), appropriate and tunable pore size (8.6-16.4 nm), and high magnetic susceptibility. We investigated the applicability of Fe(3)O(4)@mTiO(2) microspheres in a study of the selective enrichment of phosphopeptides. The experiment results demonstrated that the Fe(3)O(4)@mTiO(2) possessed remarkable selectivity for phosphopeptides even at a very low molar ratio of phosphopeptides/non-phosphopeptides (1:1000), large enrichment capacity (as high as 225 mg/g, over 10 times as that of the Fe(3)O(4)@TiO(2) microspheres), extreme sensitivity (the detection limit was at the fmol level), excellent speed (the enrichment can be completed in less than 5 min), and high recovery of phosphopeptides (as high as 93%). In addition, the high magnetic susceptibility allowed convenient separation of the target peptides by magnetic separation. These outstanding features give the Fe(3)O(4)@mTiO(2) composite microspheres high benefit for mass spectrometric analysis of phosphopeptides.

A facile and effective approach to preparation of dual‐responsive magnetic core/shell composite microspheres is reported. The magnetite(Fe3O4)/poly(methacrylic acid) (PMAA) composite microspheres were synthesized through encapsulating γ‐methacryloxypropyltrimethoxysilane (MPS)‐modified magnetite colloid nanocrystal clusters (MCNCs) with crosslinked PMAA shell. First, the 200‐nm‐sized MCNCs were fabricated through solvothermal reaction, and then the MCNCs were modified with MPS to form active vinyl groups on the surface of MCNCs, and finally, a pH‐responsive shell of PMAA was coated onto the surface of MCNCs by distillation‐precipitation polymerization. The transmission electron microscopy (TEM) and vibrating sample magnetometer characterization showed that the obtained composite microspheres had well‐defined core/shell structure and high saturation magnetization value (35 emu/g). The experimental results indicated that the thickness and degree of crosslinking of PMAA shell could be well‐controlled. The pH‐induced change in size exhibited by the core/shell microspheres reflected the PMAA shell contained large amount of carboxyl groups. The carboxyl groups and high saturation magnetization make these microspheres have a great potential in biomolecule separation and drug carriers. Moreover, we also demonstrated that other magnetic polymeric microspheres, such as Fe3O4/PAA, Fe3O4/PAM, and Fe3O4/PNIPAM, could be synthesized by this approach. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

The critical value of soil Olsen-P is the point above which the probability of crop yield response to fertilizer P is small or nil. Determining this critical value is fundamental when making appropriate P fertilizer recommendations. In this study, the critical values were determined for continuous maize (Zea mays L.)-winter wheat (Triticum aestivum L.) cropping systems from a 15-year field experiment across three sites in China using linear-linear, linear-plateau and Mitscherlich models. The mean critical values for maize using the three models ranged from 12.1 to 17.3 mg P kg −1 (average 15.3 mg P kg −1 ) and for winter wheat from 12.5 to 19.0 mg P kg −1 (average 16.3 mg P kg −1 ) among study sites. The mean critical value for maize was approximately 7% lower than that for winter wheat across all sites based on the three models. Critical values identified by the Mitscherlich model were 1.4 to 2.1 times those from linear-linear and 1.3 to 1.9 times of those from linear-plateau and were crop and site dependent. There was a significant negative correlation (P<0.05) between the mean critical value from the three models and the observed P uptake by either maize or wheat. Our study shows that the critical values can vary with sites, crops and models used, and thus caution should be taken when selecting the most appropriate one when making P fertilizer recommendations for agronomic return and to minimize chances of negative environment impact from overfertilization.