Superconducting isotope effect in ZrB12

The Zr isotope effect appears to be much stronger in ZrB12 than in elemental Zr (the B isotope effect in ZrB12 is known to be small). The superconductivity of ZrB12 is apparently caused by optical phonon modes associated with the internal motion of Zr atoms inside boron cages. © 1971.

Catalytic enantioselective arylations: boron to zinc exchange as a powerful tool for the generation of transferable aryl groups

The transmetalation between boron and zinc is of great importance for application in organic synthesis, since it allows the formation of new carbon-carbon bonds between organometallic units and electrophiles. The direct arylation of aldehydes or more scarcely ketones, in a catalytic, enantioselective manner using chiral catalysts has been described recently. The enantiomerically enriched diarylmethanols obtained in these reactions are valuable precursors for important bioactive molecules. This review provides a synopsis of this ever-growing field and highlights some of the challenges that still remain.

Synthesis of diaryl selenides using electrophilic selenium species and nucleophilic boron reagents in ionic liquids

We described herein the use of imidazolium ionic liquids [bmim]PF(6) and [bmim]BF(4) in the selective, metal and catalyst-free synthesis of unsymmetrical diaryl selenides by electrophilic substitution in arylboron reagents with arylselenium halides (Cl and Br) at room temperature. This is a general substitution reaction and it was performed with arylboronic acids or potassium aryltrifluoroborates bearing electron-withdrawing or electron-donating groups, affording the corresponding diaryl selenides in good to excellent yields. The ionic liquid [bmim][PF(6)] was easily recovered and utilized for further substitution reactions.

Merging Resource Availability with Isotope Mixing Models: The Role of Neutral Interaction Assumptions

Background: Bayesian mixing models have allowed for the inclusion of uncertainty and prior information in the analysis of trophic interactions using stable isotopes. Formulating prior distributions is relatively straightforward when incorporating dietary data. However, the use of data that are related, but not directly proportional, to diet (such as prey availability data) is often problematic because such information is not necessarily predictive of diet, and the information required to build a reliable prior distribution for all prey species is often unavailable. Omitting prey availability data impacts the estimation of a predator's diet and introduces the strong assumption of consumer ultrageneralism (where all prey are consumed in equal proportions), particularly when multiple prey have similar isotope values. Methodology: We develop a procedure to incorporate prey availability data into Bayesian mixing models conditional on the similarity of isotope values between two prey. If a pair of prey have similar isotope values (resulting in highly uncertain mixing model results), our model increases the weight of availability data in estimating the contribution of prey to a predator's diet. We test the utility of this method in an intertidal community against independently measured feeding rates. Conclusions: Our results indicate that our weighting procedure increases the accuracy by which consumer diets can be inferred in situations where multiple prey have similar isotope values. This suggests that the exchange of formalism for predictive power is merited, particularly when the relationship between prey availability and a predator's diet cannot be assumed for all species in a system.

Barrier-free substitutional doping of graphene sheets with boron atoms: Ab initio calculations

Using ab initio methods, we propose a simple and effective way to substitutionally dope graphene sheets with boron. The method consists of selectively exposing each side of the graphene sheet to different elements. We first expose one side of the membrane to boron while the other side is exposed to nitrogen. Proceeding this way, the B atoms will be spontaneously incorporated into the graphene membrane without any activation barrier. In a second step, the system should be exposed to a H-rich environment, which will remove the CN radical from the layer and form HCN, leading to a perfect substitutional doping.

Determination of the geographical origin of Brazilian wines by isotope and mineral analysis

In the present research, we studied wines from three different south Brazilian winemaking regions with the purpose of differentiating them by geographical origin of the grapes. Brazil`s wide territory and climate diversity allow grape cultivation and winemaking in many regions of different and unique characteristics. The wine grape cultivation for winemaking concentrates in the South Region, mainly in the Serra GaA(0)cha, the mountain area of the state of Rio Grande do Sul, which is responsible for 90% of the domestic wine production. However, in recent years, two new production regions have developed: the Campanha, the plains to the south and the Serra do Sudeste, the hills to the southeast of the state. Analysis of isotopic ratios of (18)O/(16)O of wine water, (13)C/(12)C of ethanol, and of minerals were used to characterize wines from different regions. The isotope analysis of delta(18)O of wine water and minerals Mg and Rb were the most efficient to differentiate the regions. By using isotope and mineral analysis, and discrimination analysis, it was possible to classify the wines from south Brazil.

ACCUMULATION AND TRANSLOCATION OF SILICON IN RICE AND BEAN PLANTS USING THE 30SI STABLE ISOTOPE

The 30Si silicon isotope stable was used for assessing the accumulation and translocation of Si in rice and bean plants grown in labeled nutritive solution. The isotopic silicon composition in plant materials was determined by mass spectrometry (IRMS) using the method based on SiF4 formation. Considering the total-Si added into nutritive solutions, the quantity absorbed by plants was near to 51% for rice and 15% for bean plants. The accumulated amounts of Si per plant were about 150g in rice and 8.6g in bean. Approximately 70% of the total-Si accumulated was found in leaves. At presented experimental conditions, the results confirmed that once Si is accumulated in the old parts of rice and bean plant tissues it is not redistributed to new parts, even when Si is not supplied to plants from nutritive solution.

Spatial variation in the strength of mutualism between a jumping spider and a terrestrial bromeliad: Evidence from the stable isotope N-15

Psecas chapoda, a neotropical jumping spider strictly associated with the terrestrial bromeliad Bromelia balansae in cerrados and semi-deciduous forests in South America, effectively contributes to plant nutrition and growth. In this study, our goal was to investigate if spider density caused spatial variations in the strength of this spider-plant mutualism. We found a positive significant relationship between spider density and delta N-15 values for bromeliad leaves in different forest fragments. Open grassland Bromeliads were associated with spiders and had higher delta N-15 values compared to forest bromeliads. Although forest bromeliads had no association with spiders their total N concentrations were higher. These results suggest that bromeliad nutrition is likely more litter-based in forests and more spider-based in open grasslands. This study is one of the few to show nutrient provisioning and conditionality in a spider-plant system. (c) 2008 Elsevier Masson SAS. All rights reserved.

Frozen Chicken for Wild Fish: Nutritional Transition in the Brazilian Amazon Region Determined by Carbon and Nitrogen Stable Isotope Ratios in Fingernails

Objectives: Amazonian populations are experiencing dietary changes characteristic of the nutrition transition. However, the degree of change appears to vary between urban and rural settings. To investigate this process, we determined carbon and nitrogen stable isotope ratios in fingernails and dietary intake of Amazonian populations living along a rural to urban continuum along the Solimoes River in Brazil. Methods: Carbon and nitrogen stable isotope ratios were analyzed from the fingernails of 431 volunteer subjects living in different settings ranging from rural villages, small towns to urban centers along the Solimoes River. Data from 200 dietary intake surveys were also collected using food frequency questionnaires and 24-h recall interviews in an effort to determine qualitative aspects of diet composition. Results: Fingernail delta(13)C values (mean standard deviation) were -23.2 +/- 1.3, 20.2 +/- 1.5, and 17.4 +/- 1.3 parts per thousand and delta(15)N values were 11.8 +/- 0.6, 10.4 +/- 0.8, and 10.8 +/- 0.7 parts per thousand for those living in rural villages, small towns, and major cities, respectively. We found a gradual increase in the number of food items derived from C(4) plant types (meat and sugar) and the replacement of food items derived from C(3) plant types (fish and manioc flour) with increasing size of urban centers. Conclusion: Increasing urbanization in the Brazilian Amazon is associated with a significant change in food habits with processed and industrialized products playing an increasingly important role in the diet and contributing to the nutrition transition in the region. Am. J. Hum. Biol. 23:642-650, 2011. (C) 2011 Wiley-Liss, Inc.