Ultra-large-scale syntheses of monodisperse nanocrystals

The development of nanocrystals has been intensively pursued, not only for their fundamental scientific interest, but also for many technological applications. The synthesis of monodisperse nanocrystals (size variation <5%) is of key importance, because the properties of these nanocrystals depend strongly on their dimensions. For example, the colour sharpness of semiconductor nanocrystal-based optical devices is strongly dependent on the uniformity of the nanocrystals, and monodisperse magnetic nanocrystals are critical for the next-generation multi-terabit magnetic storage media. For these monodisperse nanocrystals to be used, an economical mass-production method needs to be developed. Unfortunately, however, in most syntheses reported so far, only sub-gram quantities of monodisperse nanocrystals were produced. Uniform-sized nanocrystals of CdSe (refs 10,11) and Au (refs 12,13) have been produced using colloidal chemical synthetic procedures. In addition, monodisperse magnetic nanocrystals such as Fe (refs 14,15), Co (refs 16-18), gamma-Fe(2)O(3) (refs 19,20), and Fe(3)O(4) (refs 21,22) have been synthesized by using various synthetic methods. Here, we report on the ultra-large-scale synthesis of monodisperse nanocrystals using inexpensive and non-toxic metal salts as reactants. We were able to synthesize as much as 40 g of monodisperse nanocrystals in a single reaction, without a size-sorting process. Moreover, the particle size could be controlled simply by varying the experimental conditions. The current synthetic procedure is very general and nanocrystals of many transition metal oxides were successfully synthesized using a very similar procedure.     

Fabrication of a depletion mode GaAs MOSFET using Al2O3 as a gate insulator through the selective wet oxidation of AlAs

A 1 μm thick undoped GaAs buffer layer, a 1500 Å thick n-type GaAs layer, an undoped 500 Å thick AlAs layer and a 50 Å thick GaAs cap layer were consecutively grown by molecular beam epitaxy (MBE) on a [100] oriented semi-insulating GaAs substrate. The AlAs layer was oxidized in a N₂ bubbled H₂O vapor ambient at 400°C for 3 h and fully converted to Al₂O₃ for use as a gate insulator. The I–V characteristics, having a maximum drain current of 10.6 mA, a current cut-off voltage of −4.5 V and a maximum transconductance value of 11.25 mS/mm, indicate that the selective wet thermal oxidation of AlAs/GaAs was successful in producing a depletion mode GaAs MOSFET.     

Effect of a global regulatory gene, afsR2, from Streptomyces lividans on avermectin production in Streptomyces avermitilis

The global regulatory gene, afsR2, from Streptomyces lividans was previously reported to highly stimulate two structurally unrelated antibiotics, actinorhodin and undecylprodigiosin, in both S. lividans and its close relative S. coelicolor. Production of eight avermectin components was also improved in S. avermitilis: the use of wild-type S. avermitilis and its high-producing mutant, transformed by introduction of multiple copies of afsR2, increased the total avermectin productions by 2.3-fold and 1.5-fold, respectively.     

Fermented sea tangle attenuates oxidative stress in individuals with a high level of γ-glutamyltransferase: A randomized,double-blind,and placebo-controlled clinical study

A randomized, double-blind, placebo-controlled study of fermented sea tangle (FST) was conducted using 48 healthy volunteers with high levels of γ-glutamyltransferase (GGT). Participants (n=48) were divided into a placebo group and a FST group, which consumed FST (1.5 g/day) for 4 weeks. Serum GGT, aspartate aminotransferase (AST), alanine aminotransferase (ALT), and lactate dehydrogenase (LDH) levels were determined. Plasma 8-isoprostane, 8-hydroxydeoxyguanosine (8-OHdG), and protein carbonyl contents, which indicate lipid peroxidation, DNA damage, and oxidation of protein, were determined. Decreased serum GGT was found in FST consumption group, compared to the placebo group [mean values (IU/L): 78.71±19.14 and 116.75±38.55, respectively, p<0.001]. Administration of FST significantly (p<0.05) decreased levels of serum AST [mean values (IU/L): 31.08±7.25 and 26.79±6.53 respectively, p<0.001] and ALT [mean values (IU/L): 42.63±18.99 and 31.83±14.21, respectively, p=0.001], compared to the placebo group, and significantly (p<0.05) decreased concentrations of plasma 8-isoprostane, 8-OHdG, and protein carbonyl levels.     

Influence of copper morphology in forming nucleation seeds for graphene growth

We report that highly crystalline graphene can be obtained from well-controlled surface morphology of the copper substrate. Flat copper surface was prepared by using a chemical mechanical polishing method. At early growth stage, the density of graphene nucleation seeds from polished Cu film was much lower and the domain sizes of graphene flakes were larger than those from unpolished Cu film. At later growth stage, these domains were stitched together to form monolayer graphene, where the orientation of each domain crystal was unexpectedly not much different from each other. We also found that grain boundaries and intentionally formed scratched area play an important role for nucleation seeds. Although the best monolayer graphene was grown from polished Cu with a low sheet resistance of 260 Ω/sq, a small portion of multilayers were also formed near the impurity particles or locally protruded parts.     

Radical scavenging activity of hetero-chitooligosaccharides

Nine hetero-chitooligosaccharides (hetero-COSs) consisting of relatively high molecular weights (90-, 75-, and 50-HMWCOS), medium molecular weights (90-,75-, and 50-MMWCOS), and low molecular weights (90-, 75-, and 50-LMWCOS) were prepared from partially deacetylated hetero-chitosans (90%, 75%, and 50% deacetylated chitosan), and their antioxidant activity based on their scavenging potency on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical was investigated. The results showed that the 90-MMWCOS, prepared from 90% deacetylated chitosan, showed the highest scavenging activity on the DPPH radical. Their scavenging pattern was dose- and time-dependent. Electron spin resonance (ESR) spectrum of DPPH treated with 90-MMWCOS decreased in a time-dependent manner and the reducing power of hetero-COSs increased in a dose-dependent manner. These results indicated that hetero-COSs have an antioxidant activity which is dependent on their degree of deacetylation and molecular weight.     

Antagonism of Helicobacter pylori by bacteriocins of lactic acid bacteria

Antimicrobial activity of seven bacteriocins produced by lactic acid bacteria against Helicobacter pylori strains (ATCC 43504, Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH [DSM] 4867, DSM 9691, and DSM 10242) was investigated in vitro using a broth microdilution assay. The bacteriocins chosen for the study were nisin A; lacticins A164, BH5, JW3, and NK24; pediocin PO2; and leucocin K. Antimicrobial activity of the bacteriocins varied among the H. pylori strains tested, of which strain ATCC 43504 was the most tolerant. Among the bacteriocins tested, lacticins A164 and BH5 produced by Lactococcus lactis subsp. lactis A164 and L. lactis BH5, respectively, showed the strongest antibacterial activity against H. pylori strains. MICs of the lacticins against H. pylori strains, when assessed by the critical dilution micromethod, ranged from 0.097 to 0.390 mg/liter (DSM strains) or from 12.5 to 25 mg/liter (ATCC 43504), supporting the strain-dependent sensitivity of the pathogen. Pediocin PO2 was less active than the lacticins against four strains of H. pylori, and leucocin K was the least active peptide, with no inhibition toward H. pylori ATCC 43504. Anti-Helicobacter activity of lacticin A164 was dependent on initial inoculum size as well as concentration of the bacteriocin added.     

LP-MOCVD grown (lnAs)m(GaAs)m short period superlattices on InP

(InAs)_m(GaAs)_m (1 ≤ m ≤ 12) short period superlattices (SPSs) have been grown on semi-insulated InP substrates with a 200 nm InP cap layer using low pressure metalorganic chemical vapor deposition (MOCVD). According to double crystal x-ray diffraction and transmission electron microscopy results, the critical layer thickness of (InAs)_m(GaAs)_m SPS was observed to be ～30Å (m = 5). For the SPS below the critical layer thickness, mirror-like surface morphology was found without defects, and strong intensity Fourier transformed photoluminescence (FT-PL) spectra were also obtained at room temperature. The SPS with m = 4 showed a drastic improvement in photoluminescence intensity of order of two compared to an InGaAs ternary layer. However, the SPS with a large value of m (m ≥ 6), rough surface was observed with defects, with broad and weak FT-PL spectra. The surface morphology of SPS was greatly affected by the substrate orientation. The SPS with m = 5 was grown on two degree tilted substrate from (100) direction and showed poor surface morphology as compared to the one grown on (100) exact substrate Moreover, the SPS grown on a (111)B substrate showed a rough triangular pattern with Nomarski optical microscopy. In-situ thermal annealed SPS with m = 4 showed a 18 meV increase in PL peak energy compared to the as-grown sample due to phase separation resulting from thermal interdiffusion.     

Antioxidant and antihypertensive protein hydrolysates produced from tuna liver by enzymatic hydrolysis

In order to better utilize a fish by-product, the enzymatic hydrolysis of tuna liver was performed using commercially available proteases such as Flavourzyme, Alcalase, Protamex, and Neutrase. The hydrolysates were prepared as both first step hydrolysates and second step hydrolysates. The molecular weight distribution of the hydrolysates was determined by size exclusion chromatography and matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, which analyzed a representative hydrolysate type with a weight range of 1000–3000 Da. The antioxidant activities of the tuna liver hydrolysates against 2,2-diphenyl-1-picrylhydrazyl (DPPH), hydroxyl radical, and hydrogen peroxide, along with a reducing power assay, showed that the second step hydrolysates had more potent antioxidant activity than the first step hydrolysates. However, the first step hydrolysates exhibited more effective chelating activity. Furthermore, the protection ability of the hydrolysates toward hydroxyl radical-induced oxidative DNA damage was evaluated by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular form. In addition, an angiotensin I-converting enzyme (ACE) inhibition assay revealed that all hydrolysates had similar ACE-inhibitory properties. These findings suggest that tuna liver hydrolysates may be a beneficial ingredient to use in functional foods.     

Resonance Properties of 3C-SiC Nanoelectromechanical Resonator in Room-Temperature Magnetomotive Transduction

We demonstrate the effect of nanoresonator geometry on the resonance property using a magnetomotive transduction technique for SiC nanoresonators in moderate conditions of pressure, temperature, and magnetic intensity. These trials were performed in conditions similar to those useful for practical applications to assist in the deployment of SiC-based nanoelectromechanical system prototype devices. This letter confirms that the resonant properties of a nanoscaled electromechanical resonator in moderate conditions are similar to those found during tests in ideal conditions. The resonance characteristics were analyzed based on the geometrical changes of the nanoresonator. The radio-frequency performance parameters such as the critical amplitude and dynamic range, which are crucial in the determination of linear operation range of nanoresonators, were maintained at a level comparable to those found under laboratory conditions. This letter brings this technology closer to practical applications in sensors, filters, and the oscillation of nanoscaled electromechanical devices.