Molecular dynamics of a dendrimer-dye guest-host system

We use molecular dynamics to investigate the instantaneous structure of a fourth generation (dansyl terminated) dendrimer of propylene amine dissolved in CH(2)Cl(2), and of the same system upon the subsequent encapsulation of several eosin Y dyes. Calculations, in a cubic box with up to approximately 3500 solvent molecules and a maximum of 12 eosins, show that one of the effects of the presence of the guest molecules is to "close" the structure of the box where they are contained. Multiple entrances-exits of the guest molecules in the dendrimer are observed in less than a nanosecond, until the excess eosins are irreversibly expelled and their number is finally brought down to the experimental limit of 6. The guest molecules are distributed at two main distances from the center of the dendrimer and their surroundings are far from static. Eosins move inside the hyperbranched molecule in a way similar to what the solvent molecules do and sometimes aggregate.     

Frequency measurements of 3 to 11 THz laser lines of CH3OH

We measured the frequencies of 12 far-infrared laser lines generated in a high- frequency Fabry-Perot laser cavity containing methanol, pumped by a CO₂ laser. The frequencies are in the range 2.8 to 11.4 THz (105.4 to 26.2 µm). Ten of the measured frequencies are higher than 7 THz, and help to fill the laser frequency gaps in this region. Five of the measured lines are new. The 11.4 THz line has the highest frequency of an optically pumped laser ever measured with the CO₂ laser heterodyne technique.This work has been financed by the Brazilian Government - Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), and by the United States Government - NASA Grant W-18, 623.Contribution of NIST, not subject to U.S. Copyright.     

Modeling of cw-EPR spectra of propagating radicals in methacrylic polymerization at different temperatures

The temperature dependence of the cw-EPR spectra corresponding to the propagating radical responsible for the polymerization of methacrylic monomers has been simulated by an integrated computational approach that determines the structural and magnetic parameters (via quantum mechanical calculations) and diffusive properties (via hydrodynamic based methods), which represent the overall input of the stochastic Liouville equation that yields the spectrum. The system has been modeled as a rotator with only one relaxation process, the rotation around the C alpha-C beta bond. The simulations clearly indicate that the change of the spectral shape with the temperature is essentially related to the internal flexibility of the radical end.     

Role of the intracellular cavity in potassium channel conductivity

The role of several fragments of the potassium channel KcsA has been examined by the Poisson-Nernst-Planck (PNP) theory. The efficiency of the computational method allowed comparing a large number of channel models, with different intracellular gate openings, partial atomic charges, and amino acid sequences. Perhaps counter-intuitively, the calculated ion current decreases when the mean radius of the entrance cavity increases. Widening of the vestibule, in fact, increases the volume accessible to water, which is the volume with a high dielectric constant. In turn, water screens the attractive charges of the P-loop backbone. The backbone charges of the M2 helixes instead oppose the entrance of potassium ions through a complicated mechanism that can be separated in the activity of two interfering dipoles. The conductance of the KcsA models increased when two neutral residues in M2 were mutated to glutamic acid, in agreement with experimental results (Brelidze, T. I.; Niu, X.; Magleby, K. L. PNAS 2003, 100, 9017-9022). As a general conclusion, a relation between channel conductance and potassium concentration in the intracellular cavity emerged. Although the ion transport is the result of the fine balance of a number of different effects, the experimental results can be reproduced quantitatively only on the basis of electrostatic forces, which are the only driving forces modeled by the PNP theory.     

Singling out the electrochemistry of individual single-walled carbon nanotubes in solution

Bandgap fluorescence spectroscopy of aqueous, micelle-like suspensions of SWNTs has given access to the electronic energies of individual semiconducting SWNTs, while substantially lower is the success achieved in the determination of the redox properties of SWNTs as individual entities. Here we report an extensive voltammetric and vis-NIR spectroelectrochemical investigation of true solutions of unfunctionalized SWNTs and determine the standard electrochemical potentials of reduction and oxidation as a function of the tube diameter of a large number of semiconducting SWNTs. We also establish the Fermi energy and the exciton binding energy for individual tubes in solution. The linear correlation found between the potentials and the optical transition energies is quantified in two simple equations that allow one to calculate the redox potentials of SWNTs that are insufficiently abundant or absent in the samples.     

Conformation Diversity of a Fused‐Ring Pyrazine Derivative on Au(111) and Highly Ordered Pyrolytic Graphite

Heterocyclic aromatic compounds have attracted considerable attention because of their high carrier mobility that can be exploited in organic field‐effect transistors. This contribution presents a comparative study of the packing structure of 3,6‐didodecyl‐12‐(3,6‐didodecylphenanthro[9,10‐b]phenazin‐13‐yl)phenanthro[9,10‐b]phenazine (DP), an N‐heterocyclic aromatic compound, on Au(111) and highly ordered pyrolytic graphite (HOPG). High‐resolution scanning tunneling microscopy (STM) combined with atomistic simulations provide a picture of the interface of this organic semiconductor on an electrode that can have an impact on the field‐effect transistor (FET) performance. DP molecules adsorb with different conformational isomers (R/S: trans isomers; C: cis isomer) on HOPG and Au(111) substrates. All three isomers are found in the long‐range disordered lamella domains on Au(111). In contrast, only the R/S trans isomers self‐assemble into stable chiral domains on the HOPG surface. The substrate‐dependent adsorption configuration selectivity is supported by theoretical calculations. The van der Waals interaction between the molecules and the substrate dominates the adsorption binding energy of the DP molecules on the solid surface. The results provide molecular evidence of the interface structures of organic semiconductors on electrode surfaces.     

Gas Chromatography Combustion Isotope Ratio Mass Spectrometry to Detect Differences in Four Compartments of Simmental Cows Fed on C3 and C4 Diets

Fatty acids (FAs) metabolism in animals represents an important field of study since they influence the quality and the properties of the meat. The aim of this study is to assess the possibility to discriminate the diets of cows in different animal compartments and to study the fate of dietary FAs in the bovine organism, using carbon isotopic ratios. Five FAs, both essential (linoleic and linolenic) and non-essential (palmitic, stearic, and oleic) in four compartments (feed, rumen, liver, meat) of animals fed two different diets (based on either C3 or C4 plants) were considered. For all compartments, the carbon isotopic ratio (δ¹³C) of all FAs (with few exceptions) resulted significantly lower in cows fed on C3 than C4 plants, figuring as a powerful tool to discriminate between different diets. Moreover, chemical reactions taking place in each animal compartment result in fraction processes affecting the δ¹³C values. The δ¹³C_FAs tendentially increase from feed to meat in group C3. On the other hand, the δ¹³C_FAs generally increase from rumen to liver in group C4, while δ¹³C_FAs of rumen and meat are mostly not statistically different. Different trends in the δ¹³C_FAs of the two groups suggested different FAs fates depending on the diet.     

On the use of phase change materials applied on cork-coconut-cork panels

Journal of Thermal Analysis and Calorimetry - This work explores the potentialities of combining a multi-layer eco-friendly panel with a phase change material coating. Although the work is based on...     

Increasing flexibility and productivity in Industry 4.0 production networks with autonomous mobile robots and smart intralogistics

Manufacturing flexibility improves a firm’s ability to react in timely manner to customer demands and to increase production system productivity without incurring excessive costs and expending an excessive amount of resources. The emerging technologies in the Industry 4.0 era, such as cloud operations or industrial Artificial Intelligence, allow for new flexible production systems. We develop and test an analytical model for a throughput analysis and use it to reveal the conditions under which the autonomous mobile robots (AMR)-based flexible production networks are more advantageous as compared to the traditional production lines. Using a circular loop among workstations and inter-operational buffers, our model allows congestion to be avoided by utilizing multiple crosses and analyzing both the flow and the load/unload phases. The sensitivity analysis shows that the cost of the AMRs and the number of shifts are the key factors in improving flexibility and productivity. The outcomes of this research promote a deeper understanding of the role of AMRs in Industry 4.0-based production networks and can be utilized by production planners to determine optimal configurations and the associated performance impact of the AMR-based production networks in as compared to the traditionally balanced lines. This study supports the decision-makers in how the AMR in production systems in process industry can improve manufacturing performance in terms of productivity, flexibility, and costs.