Evaluation of correlated studies using liquid cell and cryo-transmission electron microscopy: Hydration of calcium sulphate and the phase transformation pathways of bassanite to gypsum.

Insight into the nucleation, growth and phase transformations of calcium sulphate could improve the performance of construction materials, reduce scaling in industrial processes and aid understanding of its formation in the natural environment. Recent studies have suggested that the calcium sulphate pseudo polymorph, gypsum (CaSO4 ·2H2 O) can form in aqueous solution via a bassanite (CaSO4 ·0.5H2 O) intermediate. Some in situ experimental work has also suggested that the transformation of bassanite to gypsum can occur through an oriented assembly mechanism. In this work, we have exploited liquid cell transmission electron microscopy (LCTEM) to study the transformation of bassanite to gypsum in an undersaturated aqueous solution of calcium sulphate. This was benchmarked against cryogenic TEM (cryo-TEM) studies to validate internally the data obtained from the two microscopy techniques. When coupled with Raman spectroscopy, the real-time data generated by LCTEM, and structural data obtained from cryo-TEM show that bassanite can transform to gypsum via more than one pathway, the predominant one being dissolution/reprecipitation. Comparisons between LCTEM and cryo-TEM also show that the transformation is slower within the confined region of the liquid cell as compared to a bulk solution. This work highlights the important role of a correlated microscopy approach for the study of dynamic processes such as crystallisation from solution if we are to extract true mechanistic understanding.

Correction: A new potential for methylammonium lead iodide.

Correction for 'A new potential for methylammonium lead iodide' by C. M. Handley et al., Phys. Chem. Chem. Phys., 2017, 19, 2313-2321.

A new potential for methylammonium lead iodide.

We present a new set of interatomic potentials for modelling methylammonium lead iodide. The potential model uses existing potentials for lead iodide and methylammonium, and new functions are fitted to enable these pre-existing potentials to be used together, while still being capable of modelling lead iodide and methylammonium iodide as separate materials. Fitting was performed using a combination of ab initio and experimental reference data. Our simulations are in agreement with experiment and reveal the short and long range ordering of the molecular cations and lead iodide octahedra.

Sampling the structure of calcium carbonate nanoparticles with metadynamics.

Metadynamics is employed to sample the configurations available to calcium carbonate nanoparticles in water, and to map an approximate free energy as a function of crystalline order. These data are used to investigate the validity of bulk and ideal surface energies in predicting structure at the nanoscale. Results indicate that such predictions can determine the structure and morphology of particles as small as 3-4 nm in diameter. Comparisons are made to earlier results on 2 nm particles under constant volume conditions which support nanoconfinement as a mechanism for enhancing the stability of amorphous calcium carbonate. Our results indicate that crystalline calcitelike structure is thermodynamically preferred for nanoparticles as small as 2 nm in the absence of nanoconfinement.

Metadynamics simulations of calcite crystallization on self-assembled monolayers.

We show that recent developments in the application of metadynamics methods to direct simulations of crystallization make it possible to predict the orientation of crystals grown on self-assembled monolayers. In contrast to previous studies, the method allows for dynamic treatment of the organic component and the inclusion of explicit surface water without the need for computationally intensive interfacial energy calculations or prior knowledge of the interfacial structure. The method is applied to calcite crystallization on carboxylate terminated alkanethiols arrayed on Au (111). We demonstrate that a dynamic treatment of the monolayer is sufficient to reproduce the experimental results without the need to impose epitaxial constraints on the system. We also observe an odd-even effect in the variation of selectivity with organic chain length, reproducing experimentally observed orientations in both cases. Analysis of the ordering process in our simulations suggests a cycle of mutual control in which both the organic and mineral components induce complementary local order across the interface, leading to the formation of a critical crystalline region. The influence of pH, together with some factors that might affect the range of applicability of our method, is discussed.

Molluscum contagiosum presenting as cellulitis in an AIDS patient: cytologic and ultrastructural features.

This report describes the cytologic features of molluscum contagiosum presenting clinically as a left thigh abscess in a 29-yr-old male with AIDS. The fine-needle aspiration findings are correlated with the histologic and ultrastructural findings. Molluscum contagiosum's clinical presentation, natural course, and induction of host immune responses in immunocompetent and immunosuppressed individuals as identified by light microscopy, immunocytochemically and ultrastructurally are reviewed. Molluscum contagiosum presenting clinically and cytologically as an abscess is unusual. In this report, we emphasize the inclusion of molluscum contagiosum in a differential diagnosis of an abscess, particularly in immunosuppressed patients, and discuss the cytologic differential diagnoses.

Body size estimation in bulimia.

Body size estimation was studied in 22 patients with bulimia and 20 normal controls. Two methods of body size estimation were used, a distorting television image method (DTIM) and the image marking method (IMM). The subjects estimated body size of a dummy as well as their own body on the DTIM. When estimating body size on the DTIM the bulimics overestimated and the controls underestimated, there being a significant difference between the two groups. There was no difference between the groups when estimating the size of the dummy. On the IMM a significant difference was found between the bulimic and control groups, the bulimics overestimating body size and the controls being more accurate. Marked directional effects were found with the DTIM. The two methods of body size estimation are compared.