A series of water-soluble YVO 4 :Bi 3+ ,Eu 3+ nanocrystals, with surfaces functionalized by a branch polyethylenimine (BPEI) polymer, have been synthesized via a one-pot hydrothermal method. It was found that the particle size and crystal morphology could be efficiently controlled by different reaction temperatures, pH values and molecular weights of the BPEI polymer. The surface modification of the nanocrystals was characterized using Fourier transform infrared spectroscopy (FT-IR). The highly crystalline YVO 4 :Bi 3+ ,Eu 3+ nanoparticles, with an average diameter of 20 nm, can be dispersed in water due to the presence of amino ligands. When conjugated with biomolecules, the YVO 4 :Bi 3+ ,Eu 3+ nanocrystals retain their strong red emission, peaking at 619 nm under near-ultraviolet (n-UV) excitation. The results indicate that YVO 4 :Bi 3+ ,Eu 3+ nanocrystals can serve as a promising candidate for biological imaging, and immunoassay applications.

Aminoacylhistidine dipeptidases (PepD, EC 3.4.13.3) belong to the family of M20 metallopeptidases from the metallopeptidase H clan that catalyze a broad range of dipeptide and tripeptide substrates, including L-carnosine and L-homocarnosine. Homocarnosine has been suggested as a precursor for the neurotransmitter ␥-aminobutyric acid (GABA) and may mediate the antiseizure effects of GABAergic therapies. Here, we report the crystal structure of PepD from Vibrio alginolyticus and the results of mutational analysis of substrate-binding residues in the C-terminal as well as substrate specificity of the PepD catalytic domain-alone truncated protein PepD CAT . The structure of PepD was found to exist as a homodimer, in which each monomer comprises a catalytic domain containing two zinc ions at the active site center for its hydrolytic function and a lid domain utilizing hydrogen bonds between helices to form the dimer interface. Although the PepD is structurally similar to PepV, which exists as a monomer, putative substrate-binding residues reside in different topological regions of the polypeptide chain. In addition, the lid domain of the PepD contains an "extra" domain not observed in related M20 family metallopeptidases with a dimeric structure. Mutational assays confirmed both the putative di-zinc allocations and the architecture of substrate recognition. In addition, the catalytic domain-alone truncated PepD CAT exhibited substrate specificity to L-homocarnosine compared with that of the wild-type PepD, indicating a potential value in applications of PepD CAT for GABAergic therapies or neuroprotection.

In order to effectively improve erosion resistance and evaluate the effects of an oxy layer on AISI H13 tool steel after the oxynitriding process, this study used three different nitriding surface treatments, namely oxynitriding process 1 (using air), oxynitriding process 2 (using steam) and normal gas nitride. To evaluate the effects of microstructure and the erosion resistance of AISI H13 tool steel after different nitride processes, evaluated micro hardness, erosion tests and SEM microstructure inspections were conducted. Experimental results showed that the oxide layer can protect and improve the aluminum erosion for AISI H13 tool steel. Erosion tests of 2 and 4 h for oxynitriding process 1 could produce a thicker and complex oxide layer, which has higher hardness (HV 1021.9) and optimal weight loss (0.16 %). This procedure is proven to effectively reduce the ratio of Al-Fe-Si compounds during the A380 alloy erosion test.KEY WORDS: erosion resistance; AISI H13 tool steel; oxynitriding; A380 alloy. 421© 2009 ISIJ erosion test as shown in Fig. 1(b). The specimen was then dipped in aluminum alloy A380 for melting and maintained at 1 023 K. The rotational speed of the specimen was kept at 50 rpm. The dip time was 2 and 4 h for specimens to evaluate the erosion resistance and weight loss. After removing the aluminum, the specimens were cleaned with NaOH to remove oxide or other residues. The weight loss percentage of the erosion test was calculated as follows:IW is the initial weight and AW is the weight of after erosion test. In the experiment, three different kinds of surface treatments were: 1) normal gas nitriding: at temperature of 843 K for 1 h; 2) oxynitriding process 1: gas nitriding was carried out at temperature of 843 K for 1 h, and air oxidation at 823 K for 3 h; 3) oxynitriding process 2: gas nitriding was carried out at temperature of 803 K for 1 h, and steam oxidation at 798 K for 1 h. To evaluate the effects of erosion resistance on AISI H13 tool steel by nitriding process, erosion test, surface hardness and microstructure inspections were performed. Microhardness tests were measured by HV with loading of 200 g, which complied with the CNS 2115 Z8004 standard. Results and DiscussionThe microstructure of AISI H13 tool steel substrate obtained after quenching and tempering processes is shown in Fig. 2. This is the typical microstructure obtained through commercial heat treatment, which comprises the structure of tempered martensite and proeutectoid carbides. Figure 3 shows the microhardness test of AISI H13 tool steel after gas nitriding and different oxynitriding treatments. Gas nitriding was done with ammonia, decomposition NH 3 was used to dilute the ammonia so that it was not too aggressive. Normally, pure decomposition NH 3 is used to reduce the compound layer (white layer). Both carbon content and alloying additions raise surface hardness, thereby enhancing wear resistance. The actual hardness of the compound layer is usually substantially higher. However, a better thickness of the compound l...

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