Function from configurational degeneracy in disordered framework materials.

The existence of correlated disorder in molecular frameworks is an obvious mechanism by which unusual cooperative phenomena might be realised. We show that the use of local-symmetry lowering approaches can allow ostensibly high-symmetry framework structures to harbour exotic disordered states often studied in the context of spin lattice models. These states exhibit strongly cooperative behaviour that might be exploited in anomalous mechanical, host/guest, and information storage behaviour. Our contribution focuses in particular on the concepts of (i) combinatorial mechanics, (ii) adaptive flexibility, and (iii) error-correcting data storage in framework materials.

HPLC Analysis of Phenolic Compounds and Flavonoids with Overlapping Peaks.

The identification and quantification of phenolic compounds and flavonoids in various natural food products is typically conducted using HPLC analysis. Their analysis is particularly complex since most natural food products contain a large number of different phenolic compounds, many of which have similar chemical characteristics such as polarity, which makes complete separation of all eluents extremely difficult. In this work we present and validate a method for the quantitative determination of the concentration of two compounds with similar retention times, i.e. they show overlapping peaks in a mixed solution. Two pairs of phenolic compounds were investigated: caffeic and vanillic acids and ferulic and p-coumaric acids. This technique takes advantage of the different absorbances of the two phenolic compounds in the eluent at various wavelengths and can be used for the quantitative determination of the concentration of these compounds even if they are not separated in the HPLC column. The presented method could be used to interpret the results of HPLC analysis of food products which possess a vast spectrum of phenolic compounds and flavonoids.

Quantitative assessment of tolerance response to stress after exposure to oregano and rosemary essential oils, carvacrol and 1,8-cineole in Salmonella Enteritidis 86 and its isogenic deletion mutants ∆dps, ∆rpoS and ∆ompR.

This study assessed the influence of rpoS, dps and ompR genes on the tolerance response of Salmonella Enteritidis 86 (SE86) to homologous and heterologous stressing agents after exposure to essential oils (EOs) from Origanum vulgare L. (oregano; OVEO) and Rosmarinus officinalis L. (rosemary; ROEO) and their major constituents (ICs), carvacrol (CAR) and 1,8-cineole (CIN), respectively, by modelling the log reduction over time. Minimum inhibitory concentration values of OVEO (1.25 µL/mL), CAR (0.62 µL/mL), ROEO (20 µL/mL) and CIN (10 µL/mL) against SE86 were always one-fold higher than those against ∆dps, ∆rpoS and ∆ompR mutants. Exposure to the same concentration of OVEO, CAR, ROEO or CIN caused higher reductions (up to 2.5 log CFU/mL) in ∆dps, ∆rpoS and ∆ompR mutants than in SE86 in chicken broth. In assays with homologous stressing agents, ompR, dps and rpoS influenced the tolerance to OEs or ICs. After adaptation to OVEO, CAR, ROEO and CIN, osmotolerance and acid tolerance of SE86 were influenced by rpoS gene, while thermotolerance of SE86 was influenced by ompR. Tolerance of SE86 to sodium hypochlorite after adaptation to OEs or ICs was influenced by rpoS and dps. These findings quantitatively describe for the first time the influence of rpoS, dps and ompR genes on the tolerance of Salmonella Enteritidis to OVEO, CAR, ROEO and CIN.

On the dynamics and control of mechanical properties of hierarchical rotating rigid unit auxetics.

In this work, we investigate the deformation mechanism of auxetic hierarchical rotating square systems through a dynamics approach. We show how their deformation behaviour, hence their mechanical properties and final configuration for a given applied load, can be manipulated solely by altering the resistance to rotational motion of the hinges within the system. This provides enhanced tunability without necessarily changing the geometry of the system, a phenomenon which is not typically observed in other non-hierarchical unimode auxetic systems. This gives this hierarchical system increased versatility and tunability thus making it more amenable to be employed in practical application which may range from smart filtration to smart dressings.

Auxetic Perforated Mechanical Metamaterials with Randomly Oriented Cuts.

Perforated systems with quasi-disordered arrays of slits are found to exhibit auxetic characteristics almost as much as their traditional ordered "rotating-squares" counterparts. This provides a highly robust methodology for constructing auxetics that may be used for various practical applications such as skin grafting, where a high degree of precision may not always be achievable.

Hierarchical auxetic mechanical metamaterials.

Auxetic mechanical metamaterials are engineered systems that exhibit the unusual macroscopic property of a negative Poisson's ratio due to sub-unit structure rather than chemical composition. Although their unique behaviour makes them superior to conventional materials in many practical applications, they are limited in availability. Here, we propose a new class of hierarchical auxetics based on the rotating rigid units mechanism. These systems retain the enhanced properties from having a negative Poisson's ratio with the added benefits of being a hierarchical system. Using simulations on typical hierarchical multi-level rotating squares, we show that, through design, one can control the extent of auxeticity, degree of aperture and size of the different pores in the system. This makes the system more versatile than similar non-hierarchical ones, making them promising candidates for industrial and biomedical applications, such as stents and skin grafts.

Tailoring graphene to achieve negative Poisson's ratio properties.

Graphene can be made auxetic through the introduction of vacancy defects. This results in the thinnest negative Poisson's ratio material at ambient conditions known so far, an effect achieved via a nanoscale de-wrinkling mechanism that mimics the behavior at the macroscale exhibited by a crumpled sheet of paper when stretched.