Preparation of self-assembled zinc oxide nanoparticles multilayer films under ultrasonic irradiation

Zinc oxide nanoparticles were synthesized and self-assembled on the reactive surface of a glass slide functionalized with (3-mercaptopropyl)-trimethoxysilane under ultrasonic irradiation. The structure, morphology, and optical property of the zinc oxide nanoparticles were investigated by TEM, XRD, and UV-vis spectroscopy. The functionalized glass slide was soaked in an aqueous solution which dispersed zinc oxide nanoparticles under ultrasonic irradiation. Zinc oxide multilayer films grew up to several layers (up to 5 layers) depending on the immersion time. The self-assembled zinc oxide nanoparticles multilayer films were characterized using UV-vis spectroscopy and SEM. Ultrasonic irradiation was an efficient method to make multilayer films on the functionalized glass slide with zinc oxide nanoparticles.     

Preferential site of Gd in Gd-doped Fe3O4 nanopowder

Both structural refinement using X-ray powder diffraction data and energy calculation using quantum mechanics were used to determine the site preference and the amount of Gd in the host lattice of Gd doped Fe3O4 [Gd(x)Fe(3-x)O4 (x = 0.1)] nanopowder prepared by the sonochemical method. Among possible cation-disorder models, the model proposed by structural refinement, in which Gd ions might preferentially occupy the octahedral sites in Gd doped Fe3O4 having the inverse spinel structure, was confirmed by geometry energy calculation using a first-principle based on the density-functional theory. The final converged weighted R-factor, R(wp), and the goodness-of-fit indicator, S (= R(wp)/R(e)) were 6.73% and 1.22, respectively. The occupancy of Gd ions occupying octahedral sites was 0.04(2).     

Time-variable simulation of soil vapor intrusion into a building with a combined crawl space and basement

A time-variable one-dimensional model (called ViM for Vapor Intrusion Model)to predict indoor vapor concentrations in a dwelling with a combined basement and crawl space has been developed. ViM predicts vapor concentrations in each of the three compartments. Volatile chemicals that intrude into the dwelling are assumed to originate from soil, groundwater (where an attenuating plume is simulated), or ambient air. Processes included in the model are advection, diffusion, biodecay, and adsorption in the soil column; transport by diffusion and advection into individual crawl space and basement compartments; advection from each compartment into an overlying dwelling space; and exchange of ambient air and indoor air. The time-variable concentration fields are solved by first transforming the partial and ordinary differential equations into Laplace space, solving the resulting ordinary differential equations or algebraic equations, and numerically inverting those equations. This approach was an expedient way of handling the coupling between the subsurface and the dwelling. ViM was applied to a building (Building 20) located at the former Moffett Field Naval Air Station, in Mountain View, CA. The building is a former bachelor officer's quarters. The shallow groundwater beneath the building is contaminated with a number of volatile chemicals, including trichloroethene, cis-1,2-dichloroethene, and trans-1,2-dichloroethene, all of which were simulated. Using indoor air data collected in 2003-2004, and other field data collected prior to that time, the accuracy of the model's predictions was demonstrated. ViM's results were also compared against a version of the steady-state Johnson and Ettinger model (1) that was modified to accommodate a dwelling with a combined crawl space and basement (called the JEM model in this paper). The predictions from the JEM model were consistently higher than the predictions from ViM, but still near the upper range of the observed data.     

Natural occurrence of aflatoxin B1 in marketed foods and risk estimates of dietary exposure in Koreans

Aflatoxin B1 (AFB1) is an unavoidable food contaminant. To evaluate the potential health risk of AFB1 to Koreans posed by food consumption, we determined the natural occurrence of AFB1 in food and estimated the excess risk for liver cancer through dietary exposure to AFB1. A total of 694 food samples collected from six different regions of South Korea were analyzed for their AFB, content. One hundred four of the 694 samples were found to give positive enzyme-linked immunosorbent assay (ELISA) readings for AFB1 and were further investigated with high-performance liquid chromatography. Thirty-two samples, including 2 maize samples, 3 soybean products, 20 peanut samples, nut samples, and their products, and 7 spices, were found to be contaminated with AFB1 (4.6% incidence), up to 48.6 microg kg(-1). The level of AFB1 contamination in 28 of the 32 food products was below 10 microg kg(-1), which is the legal tolerance limit in Korea. From data on daily food consumption, the exposure dose of AFB1 was estimated to be 6.42 x 10(-7) mg kg(-1) body weight (bw) day(-1). The major contributors to the dietary intake of AFB1 were soybean paste and soy sauce, which composed 91% of the total exposure to AFB1. The excess risk of liver cancer for those exposed to AFB1 through food intake was estimated to be 5.78 x 10(-6) for hepatitis B-negative individuals and 1.48 x 10(-4) for hepatitis B-positive individuals. These results suggest that special consideration is required to reduce the intake of AFB1 in hepatitis B-positive individuals.     

Characterization of a wheat heme oxygenase-1 gene and its responses to different abiotic stresses

In animals and recently in plants, heme oxygenase-1 (HO1) has been found to confer protection against a variety of oxidant-induced cell and tissue injuries. In this study, a wheat (Triticum aestivum) HO1 gene TaHO1 was cloned and sequenced. It encodes a polypeptide of 31.7 kD with a putative N-terminal plastid transit peptide. The amino acid sequence of TaHO1 was found to be 78% similar to that of maize HO1. Phylogenetic analysis revealed that TaHO1 clusters together with the HO1-like sequences in plants. The purified recombinant TaHO1 protein expressed in Escherichia coli was active in the conversion of heme to biliverdin IXa (BV), and showed that the V(max) was 8.8 U·mg(-1) protein with an apparent K(m) value for hemin of 3.04 μM. The optimum Tm and pH were 35 °C and 7.4, respectively. The result of subcellular localization of TaHO1 showed that the putative transit peptide was sufficient for green fluorescent protein (GFP) to localize in chloroplast and implied that TaHO1 gene product is at least localized in the chloroplast. Moreover, we found that TaHO1 mRNA could be differentially induced by the well-known nitric oxide (NO) donor sodium nitroprusside (SNP), gibberellin acid (GA), abscisic acid (ABA), hydrogen peroxide (H(2)O(2)) and NaCl treatments. Therefore, the results suggested that TaHO1 might play an important role in abiotic stress responses.     

超声处理对糙米淀粉的结构与理化特性的影响

以糙米淀粉为原料,探究不同超声时间处理对糙米淀粉的分子结构及理化特性的影响.结果 表明:与原淀粉相比,超声处理10 min的改性淀粉的官能团和化学键组成没有变化.超声处理10 min能够将糙米淀粉的粒径显著降低43.18％,崩解值从577 cP降低到388 cP,峰值黏度经过超声处理后降低,在30 min达到最低157...     

CdTe/CdS量子点荧光检测探针的制备及性能表征

优化建立简单的量子点制备方法,获得性能优良的量子点材料对于食品安全检测控制具有重要的促进意义。以巯基乙酸为稳定剂,通过水热法制备合成了核壳型CdTe/CdS量子点,采用荧光发射光谱及紫外可见光谱等对量子点的光学性能进行了评价,探究了量子点的稳定性。研究结果表明:在80℃回流,成核40 min,包壳40 min,pH=11,n(Cd~(2+)):n(Te~(2-)):n(TGA)=1:0.2:7的条件下,制备的量子点具有较优良的性能;改变上述实验条件,量子点粒径大小、尺寸分布范围以及荧光强度等都会发生不同程度的改变;稳定性研究结果表明制备的CdTe/CdS量子点随照射时间的延长,光致发光强度明显增强,量子产率也明显增加,从最初的7.80%增加到20.10%,并在第11 d达到最大。研究建立的量子点制备方法可以作为荧光探针在使用过程中根据需要调整合成条件以控制量子点大小,为食品中质量安全因子的检测提供了技术支撑,对于保障食品安全具有重要的作用。