Elemental profile of wheat in the las vegas market: Geographic origin discrimination and probabilistic health risk assessment.

This study investigates concentrations of toxic and potentially toxic elements (PTEs) in organic and conventional wheat flour and grains marketed in Las Vegas. Geographic origins of the samples were evaluated using Linear Discriminant Analysis (LDA). Monte Carlo Simulation technique was also employed to evaluate non-carcinogenic risk in four life stages. Concentrations of Al, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, Sr, and Zn were determined using inductively coupled plasma mass spectrometry (ICP-MS) following hot block-assisted digestion. Obtained results showed non-significant differences in contents of toxic and PTEs between conventional and organic wheat grains/flour. Using LDA, metal (loid)s were found to be indicative of geographical origin. The LDA produced a total correct classification rate of 95.8% and 100% for US and West Pacific Region samples, respectively. The results of the present study indicate that the estimated non-carcinogenic risk associated with toxic element intakes across the four life stages were far lower than the threshold value (Target Hazard Quotient (THQ) > 1). However, the probability of exceeding the threshold value for Mn is approximately 32% in children aged between 5 and 8 years. The findings of this study can aid in understanding dietary Mn exposure in children in Las Vegas.

Molecular dynamics simulations of the ionic liquid [EMIM+][TFMSI-] confined inside rutile (110) slit nanopores.

The structure and dynamics of the ionic liquid (IL) [EMIM(+)][TFMSI(-)] inside a rutile (110) slit nanopore of width H = 5.2 nm at T = 333 K are studied using classical molecular dynamics (MD) simulations. These results are compared against those obtained in our previous study (N. N. Rajput et al., J. Phys. Chem. C, 2012, 116, 5169-5181) for the same IL inside a slit graphitic nanopore of the same width. Electrostatic and dispersion interactions are present between the IL and the rutile walls, whereas only weaker van der Waals interactions are present between the IL and the graphitic walls. Our results suggest that the strength of the interactions between the pore walls and the IL can significantly affect the structure and dynamics of the confined IL. Layering effects were more pronounced for the IL inside a rutile pore as compared to inside a graphitic pore. The ions near the rutile pore walls had a liquid structure that was significantly different from that of the bulk IL; in contrast, the same ions near graphitic pore walls had a liquid structure that was similar to that of the bulk IL. Cations and anions adopted multiple orientations near the rutile walls, which contrast with the parallel orientations that were uniformly observed for the same ions near graphitic walls. The dynamics of [EMIM(+)][TFMSI(-)] inside a slit rutile pore are significantly slower than those observed inside a slit graphitic pore. Near the rutile walls, the dynamics of the ions were about an order of magnitude slower than those of ions near graphitic walls. The ions in the center of a rutile pore exhibit enhanced mobilities, but still about 2-4 times slower than those observed for ions in the center of a graphitic pore. The effects of variations in the amount of IL on the dynamics were very marked inside a rutile pore, with reductions of up to 4 times in the mobilities of the ions in the different regions of the pore; in contrast, pore loading seems to cause smaller variations in the dynamics of ILs inside a graphitic slit nanopore.

United States Grown and Imported Rice on Sale in Las Vegas: Metal(loid)s Composition and Geographic Origin Discrimination.

Concentrations of metal(loid)s, Ag, Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Se, Sr, V and Zn, were determined in rice on sale in Las Vegas. The rice samples were grown in five different countries, the USA, Thailand, India, Pakistan, and Bangladesh. The elemental concentrations in rice grain were determined using inductively coupled plasma mass spectrometry (ICP-MS) following hot block-assisted digestion. The accuracy of the laboratory procedure was verified by the analysis of rice flour standard reference material (NIST SRM 1568b). The mean metal(loid) contents in rice of various geographic origins were 3.18-5.91 mg kg-1 for Al, 0.05-0.12 mg kg-1 for As, 3.64-41 µg kg-1 for Cd, 5.11-12 µg kg-1 for Co, 0.12-0.14 mg kg-1 for Cr, 1.5-1.91 mg kg-1 for Cu, 3.04-4.98 mg kg-1 for Fe, 4.2-10.4 mg kg-1 for Mn, 0.21-0.41 mg kg-1 for Ni, 0.02-0.07 mg kg-1 for Se, 0.68-0.88 mg kg-1 for Sr, 3.64-5.26 µg kg-1 for V, and 16.6-19.9 mg kg-1 for Zn. respectively. The mean concentration of As in US rice was significantly higher than in Indian, Pakistani, and Bangladeshi rice. On the other hand, it was found a significantly low mean level of Cd in US-grown rice. It was also found that the concentrations of metal(loid)s in black and brown rice on sale in Las Vegas were statistically similar, except for Mn and Se. The geographic origin traceability of rice grain involved the use of ICP-MS analysis coupled with chemometrics that allowed their differentiation based on the rice metal(loid) profile, thus confirming their origins. Data were processed by linear discriminant analysis, and US and Thai rice samples were cross-validated with higher accuracy (100%). This authentication quickly discriminates US rice from the other regions and adds verifiable food safety measures for consumers.

Nontemplated approach to tuning the spectral properties of cyanine-based fluorescent nanoGUMBOS.

Template-free controlled aggregation and spectral properties in fluorescent organic nanoparticles (FONs) is highly desirable for various applications. Herein, we report a nontemplated method for controlling the aggregation in near-infrared (NIR) cyanine-based nanoparticles derived from a group of uniform materials based on organic salts (GUMBOS). Cationic heptamethine cyanine dye 1,1',3,3,3',3'-hexamethylindotricarbocyanine (HMT) was coupled with five different anions, viz., [NTf(2)(-)], [BETI(-)], [TFPB(-)], [AOT(-)], and [TFP4B(-)], by an ion-exchange method to obtain the respective GUMBOS. The nanoGUMBOS obtained via a reprecipitation method were primarily amorphous and spherical (30-100 nm) as suggested by selected area electron diffraction (SAED) and transmission electron microscopy (TEM). The formation of tunable self-assemblies within the nanoGUMBOS was characterized using absorption and fluorescence spectroscopy in conjunction with molecular dynamics simulations. Counterion-controlled spectral properties observed in the nanoGUMBOS were attributed to variations in J/H ratios with different anions. Association with the [AOT(-)] anion afforded predominant J aggregation enabling the highest fluorescence intensity, whereas [TFP4B(-)] disabled the fluorescence due to predominant H aggregation in the nanoparticles. Analyses of the stacking angle of the cations based on molecular dynamic simulation results in [HMT][NTf(2)], [HMT][BETI], and [HMT][AOT] dispersed in water and a visual analysis of the representative simulation snapshots also imply that the type of aggregation was controlled through the counterion associated with the dye cation.

Phenolic Polymer Solvation in Water and Ethylene Glycol, I: Molecular Dynamics Simulations.

Interactions between pre-cured phenolic polymer chains and a solvent have a significant impact on the structure and properties of the final postcured phenolic resin. Developing an understanding of the nature of these interactions is important and will aid in the selection of the proper solvent that will lead to the desired final product. Here, we investigate the role of the phenolic chain structure and the solvent type on the overall solvation performance of the system through molecular dynamics simulations. Two types of solvents are considered: ethylene glycol (EGL) and H2O. In addition, three phenolic chain structures are considered, including two novolac-type chains with either an ortho-ortho (OON) or an ortho-para (OPN) backbone network and a resole-type (RES) chain with an ortho-ortho network. Each system is characterized through a structural analysis of the solvation shell and the hydrogen-bonding environment as well as through a quantification of the solvation free energy along with partitioned interaction energies between specific molecular species. The combination of simulations and the analyses indicate that EGL provides a higher solvation free energy than H2O due to more energetically favorable hydrophilic interactions as well as favorable hydrophobic interactions between CH element groups. In addition, the phenolic chain structure significantly affects the solvation performance, with OON having limited intermolecular hydrogen-bond formations, while OPN and RES interact more favorably with the solvent molecules. The results suggest that a resole-type phenolic chain with an ortho-para network should have the best solvation performance in EGL, H2O, and other similar solvents.

Phenolic Polymer Solvation in Water and Ethylene Glycol, II: Ab Initio Computations.

Ab initio techniques are used to study the interaction of ethylene glycol and water with a phenolic polymer. The water bonds more strongly with the phenolic OH than with the ring. The phenolic OH groups can form hydrogen bonds between themselves. For more than one water molecule, there is a competition between water-water and water-phenolic interactions. Ethylene glycol shows the same effects as those of water, but the potential energy surface is further complicated by CH2-phenolic interactions, different conformers of ethylene glycol, and two OH groups on each molecule. Thus, the ethylene glycol-phenolic potential is more complicated than the water-phenolic potential. The results of the ab initio calculations are compared to those obtained using a force field. These calibration studies show that the water system is easier to describe than the ethylene glycol system. The calibration studies confirm the reliability of force fields used in our companion molecular dynamics study of a phenolic polymer in water and ethylene solutions.

Computational and experimental investigation of Li-doped ionic liquid electrolytes: [pyr14][TFSI], [pyr13][FSI], and [EMIM][BF4].

We employ molecular dynamics (MD) simulation and experiment to investigate the structure, thermodynamics, and transport of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsufonyl)imide ([pyr14][TFSI]), N-methyl-N-propylpyrrolidinium bis(fluorosufonyl)imide ([pyr13][FSI]), and 1-ethyl-3-methylimidazolium boron tetrafluoride ([EMIM][BF4]), as a function of Li-salt mole fraction (0.05 ≤ xLi(+) ≤ 0.33) and temperature (298 K ≤ T ≤ 393 K). Structurally, Li(+) is shown to be solvated by three anion neighbors in [pyr14][TFSI] and four anion neighbors in both [pyr13][FSI] and [EMIM][BF4], and at all levels of xLi(+) we find the presence of lithium aggregates. Pulsed field gradient spin-echo NMR measurements of diffusion and electrochemical impedance spectroscopy measurements of ionic conductivity are made for the neat ionic liquids as well as 0.5 molal solutions of Li-salt in the ionic liquids. Bulk ionic liquid properties (density, diffusion, viscosity, and ionic conductivity) are obtained with MD simulations and show excellent agreement with experiment. While the diffusion exhibits a systematic decrease with increasing xLi(+), the contribution of Li(+) to ionic conductivity increases until reaching a saturation doping level of xLi(+) = 0.10. Comparatively, the Li(+) conductivity of [pyr14][TFSI] is an order of magnitude lower than that of the other liquids, which range between 0.1 and 0.3 mS/cm. Our transport results also demonstrate the necessity of long MD simulation runs (∼200 ns) to converge transport properties at room temperature. The differences in Li(+) transport are reflected in the residence times of Li(+) with the anions (τ(Li/-)), which are revealed to be much larger for [pyr14][TFSI] (up to 100 ns at the highest doping levels) than in either [EMIM][BF4] or [pyr13][FSI]. Finally, to comment on the relative kinetics of Li(+) transport in each liquid, we find that while the net motion of Li(+) with its solvation shell (vehicular) significantly contributes to net diffusion in all liquids, the importance of transport through anion exchange increases at high xLi(+) and in liquids with large anions.

Linear grain growth kinetics and rotation in nanocrystalline Ni.

We report three-dimensional atomistic molecular dynamics studies of grain growth kinetics in nanocrystalline Ni. The results show the grain size increasing linearly with time, contrary to the square root of the time kinetics observed in coarse-grained structures. The average grain boundary energy per unit area decreases simultaneously with the decrease in total grain boundary area associated with grain growth. The average mobility of the boundaries increases as the grain size increases. The results can be explained by a model that considers a size effect in the boundary mobility.