Ab Initio Prediction of the Stable Polymorphs of 4-amino-3,5-dinitrobenzamide (DOPLOL)

An ab initio crystal structure prediction study, starting from gas phase optimization of the molecule at the B3LYP level, with crystal structure generation using a global search algorithm, and lattice energy minimization within an exp-6 repulsion -dispersion potential, was carried out to generate the stable lattice energy minima of 4-amino-3,5-dinitrobenzamide (DOPLOL). The hypothetical structures with favorable packing and cell volume generated from the global search were reminimizedwith a distributed multipole model of the charge density of the molecule. The possible stable polymorphs of DOPLOL from the lower energy region of the generated energy landscape plot were analyzed. The hypothetical lattice energy minimized DOPLOL structures with packing motifs and intermolecular short contacts similar to known experimental DOPLOL crystal structures were analyzed in detail to authenticate the energy landscape. Thermodynamic stability of theoretically predicted structures of DOPLOL were verified from the second derivative mechanical properties evaluated from the hessian matrix and simulated PXRD patterns were generated. This work is licensed under a Creative Commons Attribution 4.0 International License

Microfluidic chemotaxis screening platform for quantification of bacterial viability

It is estimated that by 2050, over 10 million people globally will die each year as a direct result of antimicrobial resistance. This global health crisis has arisen from the use and often misuse of antibacterial drugs and poses a serious threat to all aspects of modern healthcare. The discovery of new antibacterial agents is, therefore, imperative. In this regard, novel surfaces with light activated antimicrobial agents and antimicrobial paints for use in healthcare environments are being developed and need rapid evaluation. To this end, we aim to utilise the natural phenomenon of bacterial chemotaxis (the ability of bacteria to move towards or away from environmental signals by flagella-mediated motility) to perform live-dead analysis on bacterial cells after exposure to antibacterial agents in a microfluidic device. One of the challenges of this approach is to quantify chemotactic motility independent of convective-diffusive forces, to distinguish between alive and dead cells. Operational parameters (e.g. flow rates) must be carefully chosen in order to avoid masking the chemotactic separation by lateral movement of bacteria due to diffusion in the direction of the chemotactic gradient. In this work, chemotaxis defined by Fick’s Law in a T-junction microfluidic chip was modelled by computational fluid dynamics (CFD), where chemotactic velocity was given as a function of the chemoattractant concentration and concentration gradient. The microchannels of the T-junction in the microfluidic device were 500 μm wide, 100 μm deep, and with a main channel length of 25 mm (Figure 1a). A range of flow rates was tested, and the spatial concentration of live bacteria estimated. The chip was fabricated by micro-milling channels on 1 mm thick polycarbonate. Pseudomonas aeruginosa PAO1 (mini-Tn7-GFP) was used as the model organism (in the mid-log phase to ensure maximum motility), as it causes serious infections in immunocompromised people and is frequently multidrug resistant (MDR). A chemoattractant, L-Threonine (4mM in 10 mM HEPES buffer) was tested on live bacterial culture. Bacteria and L-Thr were injected into the chip at three flow rates: 0.1 μl/min, 1 μl/min and 5 μl/min (each inlet). Fluorescence images were taken at the T-junction and 10 mm downstream of the channel to quantify the bacterial distribution across the channel width. Please click Additional Files below to see the full abstract

Flocculation on a chip: a novel screening approach to determine floc growth rates and select flocculating agents

Flocculation is a key purification step in cell-based processes for the food and pharmaceutical industry where the removal of cells and cellular debris is aided by adding flocculating agents. However, finding the best suited flocculating agent and optimal conditions to achieve rapid and effective flocculation is a nontrivial task. In conventional analytical systems, turbulent mixing creates a dynamic equilibrium between floc growth and breakage, constraining the determination of floc formation rates. Furthermore, these systems typically rely on end-point measurements only. We have successfully developed for the first time a microfluidic system for the study of flocculation under well controlled conditions. In our microfluidic device (μFLOC), floc sizes and growth rates were monitored in real time using high-speed imaging and computational image analysis. The on-line and in situ detection allowed quantification of floc sizes and their growth kinetics. This eliminated the issues of sample handling, sample dispersion, and end-point measurements. We demonstrated the power of this approach by quantifying the growth rates of floc formation under forty different growth conditions by varying industrially relevant flocculating agents (pDADMAC, PEI, PEG), their concentration and dosage. Growth rates between 12.2 μm s−1 for a strongly cationic flocculant (pDADMAC) and 0.6 μm s−1 for a non-ionic flocculant (PEG) were observed, demonstrating the potential to rank flocculating conditions in a quantitative way. We have therefore created a screening tool to efficiently compare flocculating agents and rapidly find the best flocculating condition, which will significantly accelerate early bioprocess development

Estimation of semiconductor-like pigment concentrations in paint mixtures and their differentiation from paint layers using first-derivative reflectance spectra.

Identification of the techniques employed by artists, e.g. mixing and layering of paints, if used together with information about their colour palette and style, can help to attribute works of art with more confidence. In this study, we show how the pigment composition in binary paint mixtures can be quantified using optical-reflectance spectroscopy, by analysis of the peak features corresponding to colour-transition edges in the first-derivative spectra. This technique is found to be more robust than a number of other spectral-analysis methods, which can suffer due to shifts in the transition edges in mixed paints compared to those observed in spectra of pure ones. Our method also provides a means of distinguishing paint mixtures from layering in some cases. The spectroscopy also shows the presence of multiple electronic transitions, accessible within a narrow energy range, to be a common feature of many coloured pigments, which electronic-structure calculations attribute to shallow band edges. We also demonstrate the successful application of the reflectance-analysis technique to painted areas on a selection of medieval illuminated manuscripts.ARP is indebted to St. John’s College, Cambridge for providing a scholarship to fund this study, and to ASD Inc. (through the Alexander Goetz programme) and Analytik UK Ltd. for the loan of a Fieldspec 4 spectroradiometer for the completion of this work. JMS is indebted to Trinity College, Cambridge for provision of an Internal Graduate Studentship, and to the UK Engineering and Physical Sciences Research Council (EPSRC) for support under grant no. EP/K004956/1. The computational modelling was performed on the UK national HPC facility (Archer), accessed through the Materials Chemistry Consortium, which is funded through EPSRC grant no. EP/L000202.This is the final version of the article. It first appeared from Elsevier via https://doi.org/10.1016/j.talanta.2016.03.05

In situ non-invasive Raman spectroscopic characterisation of succinic acid polymorphism during segmented flow crystallisation

The kinetically regulated automated input crystalliser for Raman spectroscopy (KRAIC-R) combines highly controlled crystallisation environments, via tri segmented flow, with non-invasive confocal Raman spectroscopy. Taking advantage of the highly reproducible crystallisation environment within a segmented flow crystalliser and the non-invasive nature of confocal spectroscopy, we are able to shine light on the nucleation and growth of Raman active polymorphic materials without inducing unrepresentative crystallisation events through our analysis technique. Using the KRAIC-R we have probed the nucleation and subsequent growth of succinic acid. Succinic acid typically crystallises as β-SA from solution-based crystallisation although some examples of a small proportion of α-SA have been reported in the β-SA product. Here we show that α-SA and β-SA nucleate concomitantly but undergo Ostwald ripening to a predominantly β-SA product

Atomistic origin of the enhanced crystallization speed and n-type conductivity in Bi-doped Ge-Sb-Te phase-change materials

Phase-change alloys are the functional materials at the heart of an emerging digital-storage technology. The GeTe-Sb2Te3 pseudo-binary systems, in particular the composition Ge2Sb2Te5 (GST), are one of a handful of materials which meet the unique requirements of a stable amorphous phase, rapid amorphous-to-crystalline phase transition, and significant contrasts in optical and electrical properties between material states. The properties of GST can be optimized by doping with p-block elements, of which Bi has interesting effects on the crystallisation kinetics and electrical properties. We have carried out a comprehensive simulational study of Bi-doped GST, looking at trends in behavior and properties as a function of dopant concentration. Our results reveal how Bi integrates into the host matrix, and provide insight into its enhancement of the crystallisation speed. We propose a straightforward explanation for the reversal of the charge-carrier sign beyond a critical doping threshold. We also investigate how Bi affects the optical properties of GST. The microscopic insight from this study may assist in the future selection of dopants to optimize the phase-change properties of GST, and also of other PCMs, and the general methods employed in this work should be applicable to the study of related materials, e.g. doped chalcogenide glasses.This is the final published version. It's also available from Wiley at http://onlinelibrary.wiley.com/doi/10.1002/adfm.201401202/pdf

Recent advances in acoustic diagnostics for electrochemical power systems

Over the last decade, acoustic methods, such as acoustic emission and ultrasonic testing, have been increasingly deployed for process diagnostics and health monitoring of electrochemical power devices including batteries, fuel cells, and water electrolysers. These acoustic are non-invasive, highly sensitive, and low cost, while also providing a high level of spatial and temporal resolution, and practicality. The application of these tools in electrochemical devices is based on identifying changes in acoustic signals due to physical, structural, and electrochemical properties change within the material which are then correlated to critical processes and the health status of the devices. This review discusses recent progress in the use of acoustic methods for process and health-monitoring of major electrochemical energy conversion and storage devices. First, the fundamental concepts and principles of acoustic emission and ultrasonic testing are introduced, followed by a discussion of the range of electrochemical energy conversion and storage systems, and how acoustic techniques are being used to study relevant materials and devices. Conclusions and future perspectives highlighting some of the unique challenges and potential commercial and academic applications of the devices are also discussed. It is expected that, with further developments, acoustic techniques will form a key part of the suite of diagnostic techniques routinely used to monitor electrochemical devices across various processes including fabrication, on-board maintenance, post-mortem examination and second life or recycle decision support to aid the deployment of these devices in increasingly demanding applications

A quantum crystallographic approach to short hydrogen bonds

In this work we use high-resolution synchrotron X-ray diffraction for electron density mapping, in conjunction with ab initio modelling, to study short O—H⋯O and O+—H⋯O− hydrogen bonds whose behaviour is known to be tuneable by temperature. The short hydrogen bonds have donor–acceptor distances in the region of 2.45 Å and are formed in substituted urea and organic acid molecular complexes of N,N′-dimethylurea oxalic acid 2 : 1 (1), N,N-dimethylurea 2,4-dinitrobenzoate 1 : 1 (2) and N,N-dimethylurea 3,5-dinitrobenzoic acid 2 : 2 (3). From the combined analyses, these complexes are found to fall within the salt-cocrystal continuum and exhibit short hydrogen bonds that can be characterised as both strong and electrostatic (1, 3) or very strong with a significant covalent contribution (2). An additional charge assisted component is found to be important in distinguishing the relatively uncommon O—H⋯O pseudo-covalent interaction from a typical strong hydrogen bond. The electron density is found to be sensitive to the extent of static proton transfer, presenting it as a useful parameter in the study of the salt–cocrystal continuum. From complementary calculated hydrogen atom potentials, we attribute changes in proton position to the molecular environment. Calculated potentials also show zero barrier to proton migration, forming an ‘energy slide’ between the donor and acceptor atoms. The better fundamental understanding of the short hydrogen bond in the ‘zone of fluctuation’ presented in a salt-cocrystal continuum, enabled by studies like this, provide greater insight into their related properties and can have implications in the regulation of pharmaceutical materials

Crystalline adducts of the Lawsone molecule (2-hydroxy-1,4-naphthaquinone): optical properties and computational modelling

Four new crystalline adducts of the Lawsone molecule (2-hydroxy-1,4-naphthaquinone) with 4,4'-bipyridine, 4-(2-pyridine-4-ethyl)pyridine, 1,3-di.4-pyridyl)propane and 2-hydroxy pyridine are reported. Adduct formation leads to colour shifts, which are characterised by UV/visible spectroscopy. Complementary quantum-chemical calculations are used to study the energetics of the adduct formation, and to gain insight into the origin of the observed colour changes