Peptides with regular enantiomeric sequences: a wide class of modular self-assembling architectures

Organic trans-annular assemblies constitute an expanding class of structures with promising applications for the design of nanotechnological devices. Among the strategies developed for the engineering of organic nanotubes, those characterized by regular alternating enantiomeric amino acid sequences have been proven particularly useful. In fact, cyclic peptides with an even number of regularly alternating D- and L-amino acids have the tendency to adopt local beta-conformation that are capable of forming trans-annular self-assembling architectures, hydrogen bond directed. The formation of such structures is the result of the conformational equivalence of the monomer units, a general principle that associates stereo-chemical to chemical equivalence in a polymer chain. For configurationally alternating sequences the conformational equivalence produces cyclic structures, where a monomer unit is related to the adjacent along the chain by a roto-reflection axis, Sn. A slight relaxation of the conformational equivalence can formally transform a cyclic structure into a conformationally quasi-equivalent helical structures characterized by the presence of polar inner channels, which allow the transient binding for an activated flow of specific ions. To prove our early predictions, we synthesized different alternating polypeptide and the corresponding linear and cyclic oligopeptides and investigated their conformations by NMR and CD spectroscopy as well as the formation of self-assembling structures by increasing the concentration in solution. Moreover, their predicted ability to behave as an ion-channel across bilayer membranes are investigated and experimental evidence of single molecule conducting events are reported. Finally, the possibility is suggested to obtain self-assembled trans-annular structures by chemically bridging the amino acid side chains stabilized using different strategies. A complex construct with good perspective for nano-technological applications is proposed in which cyclic DL-lysine side chains are bridged by the formation of salycilaldimmine metal chelates.     

Structure and optical properties of silica-supported Ag-Au nanoparticles

Bimetallic Ag-Au nanoparticles are synthesized by sequential deposition of Au and Ag on amorphous silica by Radio Frequency (RF)-sputtering under mild conditions. Specimens are thoroughly characterized by a multi-technique approach, aimed at investigating the system properties as a function of the Ag/Au content, as well as the evolution induced by ex-situ annealing under inert (N2) or reducing (4% H2/N2) atmospheres. The obtained results demonstrate the possibility to obtain Ag-Au alloyed nanoparticles with controllable size, shape, structure, and dispersion under mild conditions, so that the optical properties can be finely tuned as a function of the synthesis and thermal treatment conditions.     

Electronic coupling between azurin and gold at different protein/substrate orientations

By means of constrained classical molecular dynamics simulations, we have computed the structure of azurin deposited on a Au(111) surface at different possible orientations and the azimuthal forces acting on the protein at each sampled conformation. We have then evaluated the effect of the angular variation on the speed of electron tunneling between the protein redox site and the metal surface. We find that the azurin/gold electronic coupling has a strong dependence on the molecular orientation and is greatly enhanced by inclining the protein to lie as flat as possible on the surface. We discuss the implications of our results for scanning probe microscopy experiments in which tunneling currents are measured while the protein is subjected to mechanical forces exerted by the tip of the instrument.     

The resistance to detachment of dairy strains of Listeria monocytogenes from stainless steel by shear stress is related to the fluid dynamic characteristics of the location of isolation

Strains of Listeria monocytogenes isolated from artisanal Portuguese cheese-making dairies were divided into two categories on the basis of the locations from which they were isolated: strains from dynamic locations were those that were habitually exposed to flowing liquids during the process of cheese-making, whereas those from static locations were rarely, if ever, exposed to the shear stresses generated by liquid flows. The strength of attachment to stainless steel discs of all of these strains was obtained using a radial flow chamber. Initial attachment strengths to stainless steel (after a 0.5 h contact time) of L. monocytogenes strains were greater for the 5 isolates from surfaces exposed to flow (dynamic isolates) than for most (3 out of 4) of those that were not (static isolates). After a 24 h contact time, attachment strength of all isolates reached similar levels. These results suggest that strains having high initial attachment strength are more likely to persist on surfaces exposed to flow than strains having low initial attachment strength. The numerical values of shear forces obtained could prove useful in the rational design of cleaning and decontamination procedures in food processing facilities.     

Where does the money go? Economic flow analysis of construction projects

A new approach is introduced for analysing the economic flows in a construction project that will complement the existing methods. The main focus of the new method is to trace the flow of costs in the project and identify their spatial characteristics as well as who are the final recipients. This type of analysis highlights the flow of costs of the specific project in the local economy. It can be used for decision-making purposes from the project-commissioning party. Costs were divided into six categories, namely: labour, materials, energy, office overheads, taxes and personnel, and into two levels: local and national. Three case studies of stone and reinforced concrete structures were selected and analysed to test the application of this method. The case studies showed that this method and the representation by a Sankey diagram can provide useful insights regarding both the spatialized distribution of the cost of a project and the economic flows going to direct labour versus overhead and taxes. For future projects, local authorities or developers can select the most economically suitable strategy maximizing the income of the local community.     

Effect of Grain Refinement and Cooling Rate on the Microstructure and Mechanical Properties of Secondary Al-Si-Cu Alloys

The effect of AlTi5B1 grain refinement and different solidification rates on metallurgical and mechanical properties of a secondary AlSi7Cu3Mg alloy is reported. While the Ti content ranges from 0.04 up to 0.225 wt.%, the cooling rate varies between 0.1 and 5.5 °C/s. Metallographic and thermal analysis techniques have been used to quantitatively examine the macro- and microstructural changes occurring with grain refiner addition at various cooling rates. The results indicate that a small AlTi5B1 addition produces the greatest refinement, while no significant reduction of grain size is obtained with a great amount of grain refiner. On increasing the cooling rate, a lower amount of AlTi5B1 master alloy is necessary to produce a uniform grain size throughout the casting. The combined addition of AlTi5B1 and Sr does not produce any reciprocal interaction or effect on primary α-Al and eutectic solidification. The grain refinement improves the plastic behavior of the alloy and increases the reliability of castings, as evidenced by the Weibull statistics.     

Biomass fueling of a SOFC by integrated gasifier: Study of the effect of operating conditions on system performance

Biomass gasification can be efficiently integrated with Solid Oxide Fuel Cells (SOFCs) to properly deploy the energy content of this renewable source and increasing the ratio of electric to thermal converted energy. The key objective of this work is to analyze in a systematic and wide process the integration of a biomass gasifier process with the SOFC operation. In particular the work aims at identifying the role of SOFC H₂ utilization as a basic parameter to maximize the system output and avoid gasifier bad operation issues such as tar production and carbon deposition. An efficient simulation framework is used to that purpose allowing for a detailed analysis of the influence of key driving parameters. The performance of the integrated system is thoroughly analyzed in the range of 1–2 kW electric power by also varying the input biomass characteristics in terms of Moisture Content (MC). Results show how a variation of the SOFC H₂ utilization, a parameter whose effects are also correlated with the gasifier air requirement, affects electrical power output also depending on the biomass Moisture Content.     

Numerical Assessment of the Mixing Performance of Different Serpentine Microchannels

The results of a comparative numerical study aimed at assessing the mixing performance of planar zig-zag, curvilinear, and square-wave microchannels of square cross-sections is presented in the paper. To evaluate the mixing enhancement characteristics of each geometry, suitable mixing indices are computed at different axial locations of a single repetitive module of each microchannel when fed with two equal streams of fluid having the same thermophysical properties but different solute concentrations. To separate the effects of the geometry from those of molecular diffusion, entrance flow, and channel length, the mixing in straight microchannels of the same length is also evaluated for comparison. Reynolds numbers in the range from 5 to 150 are considered. The study is performed both with reference to a fixed Péclet number, equal to 2500 and obtained by scaling the diffusion coefficient when varying the Reynolds number, and to a fixed diffusion coefficient, yielding a constant Schmidt number of 16.6. Pressure drops are also calculated. All numerical simulations are carried out using an in-house finite element code for the solution of all model equations.