Aromatic Zipper Topology Dictates Water-Responsive Actuation in Phenylalanine-Based Crystals.

Water-responsive (WR) materials that reversibly deform in response to relative humidity (RH) changes are gaining increasing interest for their potential in energy harvesting and soft robotics applications. Despite progress, there are significant gaps in the understanding of how supramolecular structure underpins the reconfiguration and performance of WR materials. Here, three crystals are compared based on the amino acid phenylalanine (F) that contain water channels and F packing domains that are either layered (F), continuously connected (phenylalanyl-phenylalanine, FF), or isolated (histidyl-tyrosyl-phenylalanine, HYF). Hydration-induced reconfiguration is analyzed through changes in hydrogen-bond interactions and aromatic zipper topology. F crystals show the greatest WR deformation (WR energy density of 19.8 MJ m-3 ) followed by HYF (6.5 MJ m-3 ), while FF exhibits no observable response. The difference in water-responsiveness strongly correlates to the deformability of aromatic regions, with FF crystals being too stiff to deform, whereas HYF is too soft to efficiently transfer water tension to external loads.  These findings reveal aromatic topology design rules for WR crystals and provide insight into general mechanisms of high-performance WR actuation. Moreover, the best-performing crystal, F emerges as an efficient WR material for applications at scale and low cost.

Enhanced water-responsive actuation of porous Bombyx mori silk.

Bombyx mori silk with a nanoscale porous architecture significantly deforms in response to changes in relative humidity. Despite the increasing amount of water adsorption and water-responsive strain with increasing porosity of the silk, there is a range of porosities that result in silk's optimal water-responsive energy density at 3.1 MJ m-3. Our findings show the possibility of controlling water-responsive materials' swelling pressure by controlling their nanoporosities.

New Lamellar Silver Thiolate Coordination Polymers with Tunable Photoluminescence Energies by Metal Substitution.

The structures of two lamellar silver thiolate coordination polymers [Ag( p-SPhCO2H)] n (1) and [Ag( p-SPhCO2Me)] n (2) are described for the first time. Their inorganic part is composed of distorted Ag3S3 honeycomb networks separated by noninterpenetrated thiolate ligands. The main difference between the two compounds arises from dimeric hydrogen bonds present for the carboxylic acids. Indepth photophysical studies show that the silver thiolates exhibit multiemission properties, implying luminescence thermochromism. More interestingly, the synthesis of a heterometallic lamellar compound, [Ag0.85Cu0.15( p-SPhCO2H)] n (3), allows to obtain mixed metal thiolate coordination polymers and to tune the photophysical properties with the excitation wavelengths from a green vibronic luminescence to a single red emission band.

Structural Diversity of Coordination Polymers Based on a Heterotopic Ligand: Cu(II)-Carboxylate vs Cu(I)-Thiolate.

Two copper(II)-carboxylate disulfide coordination polymers [Cu2((O2CPhS)2)2(H2O)2] n (1, 2) and one copper(I)-thiolate coordination polymer [Cu( p-SPhCO2H)] n (3) have been synthesized using either the 4-mercaptobenzoic acid (HSPhCO2H) or the 4,4'-dithiodibenzoic acid ((SPhCO2H)2) as ligand. These three compounds were characterized by X-ray diffraction, IR, and thermogravimetric analyses. Compounds 1 and 2 are polymorphs with the presence, for both, of dinuclear paddle-wheel copper(II)-carboxylates. In 1, the adjacent dimeric Cu2 units are linked by two (O2CPhS)2 ligands generating a cyclic loop chain, and in 2, each pair of Cu (II) atoms is linked by four ligands to create 2D networks, that are 2-fold interpenetrated. Compound 3 presents a lamellar structure, with an exceptional thermal and chemical stability, and exhibits intrinsic multiple emission between 485 and 660 nm. The different intensities of these bands generate a cyclic luminescence thermochromism from yellow to green to yellow.

Water treatment by cavitation: Understanding it at a single bubble - bacterial cell level.

Cavitation is a potentially useful phenomenon accompanied by extreme conditions, which is one of the reasons for its increased use in a variety of applications, such as surface cleaning, enhanced chemistry, and water treatment. Yet, we are still not able to answer many fundamental questions related to efficacy and effectiveness of cavitation treatment, such as: "Can single bubbles destroy contaminants?" and "What precisely is the mechanism behind bubble's cleaning power?". For these reasons, the present paper addresses cavitation as a tool for eradication and removal of wall-bound bacteria at a fundamental level of a single microbubble and a bacterial cell. We present a method to study bubble-bacteria interaction on a nano- to microscale resolution in both space and time. The method allows for accurate and fast positioning of a single microbubble above the individual wall-bound bacterial cell with optical tweezers and triggering of a violent microscale cavitation event, which either results in mechanical removal or destruction of the bacterial cell. Results on E. coli bacteria show that only cells in the immediate vicinity of the microbubble are affected, and that a very high likelihood of cell detachment and cell death exists for cells located directly under the center of a bubble. Further details behind near-wall microbubble dynamics are revealed by numerical simulations, which demonstrate that a water jet resulting from a near-wall bubble implosion is the primary mechanism of wall-bound cell damage. The results suggest that peak hydrodynamic forces as high as 0.8 µN and 1.2 µN are required to achieve consistent E. coli bacterial cell detachment or death with high frequency mechanical perturbations on a nano- to microsecond time scale. Understanding of the cavitation phenomenon at a fundamental level of a single bubble will enable further optimization of novel water treatment and surface cleaning technologies to provide more efficient and chemical-free processes.

Investigation of hydrodynamic cavitation induced reactive oxygen species production in microchannels via chemiluminescent luminol oxidation reactions.

Hydrodynamic cavitation was evaluated for its reactive oxygen species production in several convergent-divergent microchannel at the transition from micro to milli scale. Channel widths and heights were systematically varied to study the influence of geometrical parameters at the transitory scale. A photomultiplier tube was used for time-resolved photon detection and monitoring of the chemiluminescent luminol oxidation reactions, allowing for a contactless and in situ quantization of reactive oxygen species production in the channels. The radical production rates at various flow parameters were evaluated, showing an optimal yield per flow rate exists in the observed geometrical range. While cavitation cloud shedding was the prevailing regime in this type of channels, the photon arrival time analysis allowed for an investigation of the cavitation structure dynamics and their contribution to the chemical yield, revealing that radical production is not linked to the synchronous cavitation cloud collapse events. Instead, individual bubble collapses occurring throughout the cloud formation were recognized to be the source of the reactive oxygen species.

Localization and quantification of radical production in cavitating flows with luminol chemiluminescent reactions.

Hydrodynamic cavitation experiments in microfluidic systems have been performed with an aqueous solution of luminol as the working fluid. In order to identify where and how much reactive radical species are formed by the violent bubble collapse, the resulting chemiluminescent oxidation reaction of luminol was scrutinized downstream of a constriction in the microchannel. An original method was developed in order to map the intensity of chemiluminescence emitted from the micro-flow, allowing us to localize the region where radicals are produced. Time averaged void fraction measurements performed by laser induced fluorescence experiments were also used to determine the cavitation cloud position. The combination void fraction and chemiluminescence two-dimensional mapping demonstrated that the maximum chemiluminescent intensity area was found just downstream of the cavitation clouds. Furthermore, the radical yield can be obtained with our single photon counting technique. The maximum radical production rates of 1.2*107 OH/s and radical production per processed liquid volume of 2.15*1010 HO/l were observed. The proposed technique allows for two-dimensional characterisation of radical production in the microfluidic flow and could be a quick, non-intrusive way to optimise hydrodynamic cavitation reactor design and operating parameters, leading to enhancements in wastewater treatments and other process intensifications.

Intrinsic triple-emitting 2D copper thiolate coordination polymer as a ratiometric thermometer working over 400 K range.

A copper thiolate coordination polymer, [Cu(p-SPhCO2Me)]n, is described and exhibits, under UV, luminescence thermochromism, associated to a unique well-separated triple emission. This compound is the most promising candidate as a ratiometric temperature sensor, working in a wide temperature range, from 100 to 500 K, with a great sensitivity.

Shedding light on an ultra-bright photoluminescent lamellar gold thiolate coordination polymer [Au(p-SPhCO2Me)]n.

The first structure elucidation of a lamellar gold thiolate coordination polymer is described. [Au(p-SPhCO2Me)]n is obtained from the simultaneous esterification of mercaptobenzoic acid and reduction of the Au(iii) precursor. Despite the presence of aurophilic interactions, the intense phosphorescence (QY ∼ 70%) originates from intra-ligand and metal-to-ligand transitions.