Supramolecular metathesis: co-former exchange in co-crystals of pyrazine with (R, R)-,(S, S)-,(R, S)-and (S, S/R, R)-tartaric acid

Co-crystals of dextro-(R,R), levo-(S,S), meso-(R,S) and racemic (R,R–S,S)-tartaric acid with pyrazine were obtained by manual kneading and slurry experiments; subsequent reactions in the solid state between these co-crystals and the various forms of tartaric acid in the solid state and via slurry show that co-former exchange takes place according to the sequence of stability [(R,S)-ta]2·py > (S,S/R,R)-ta·py > (R,R)-ta·py or (S,S)-ta·py

Mechanochemical preparation of adducts (co-crystals and molecular salts) of 1, 4-diazabicyclo-2.2. 2-octane with aromatic polycarboxylic acids

Solid-state adducts (co-crystals and molecular salts) of 1,4-diazabicyclo-[2.2.2]-octane (DABCO) with aromatic polycarboxylic acids (isophthalic acid, isoH2, dinicotinic acid, dinH2 and dipicolinic acid, dipH2) were prepared in the solid state by grinding and kneading techniques, and fully characterized via X-ray diffraction. The polycarboxylic acids differ for the presence/absence and position of a nitrogen atom in the aromatic ring; the extent of proton transfer, from the carboxylic groups on the acids to the nitrogen atoms on DABCO, reflects the trend of solution acidity of the three polycarboxylic acids

Direct observation of intermediates in a thermodynamically controlled solid-state dynamic covalent reaction.

We present the first polymorph interconversion study that uses solid-state dynamic covalent chemistry (DCC). This system exhibits unexpected and rich behavior, including the observation that under appropriate conditions the polymorph interconversion of a heterodimer proceeds through reversible covalent chemistry intermediates, and this route is facilitated by one of the two disulfide homodimers involved in the reaction. Furthermore, we demonstrate experimentally that in all cases a dynamic equilibrium is reached, meaning that changing the milling conditions affects the free energy difference between the two polymorphs and thus their relative stability. We suggest that this effect is due to the surface solvation energy combined with the high surface to volume ratio of the nanocrystalline powder.We are grateful to the EPSRC (AMB, JKMS and DJW) and ERC(DJW) for financial support.This is the accepted manuscript. The final version is available from ACS at http://pubs.acs.org/doi/abs/10.1021/ja500707z

The effect of fission-energy Xe ion irradiation on the structural integrity and dissolution of the CeO2_2 matrix

© 2016 The Authors.This work considers the effect of fission fragment damage on the structural integrity and dissolution of the CeO₂ matrix in water, as a simulant for the UO₂ matrix of spent nuclear fuel. For this purpose, thin films of CeO₂ on Si substrates were produced and irradiated by 92 MeV 129Xe23+ ions to a fluence of 4.8 × 1015 ions/cm2 to simulate fission damage that occurs within nuclear fuels along with bulk CeO₂ samples. The irradiated and unirradiated samples were characterised and a static batch dissolution experiment was conducted to study the effect of the induced irradiation damage on dissolution of the CeO₂ matrix. Complex restructuring took place in the irradiated films and the irradiated samples showed an increase in the amount of dissolved cerium, as compared to the corresponding unirradiated samples. Secondary phases were also observed on the surface of the irradiated CeO₂ films after the dissolution experiment.The irradiation experiment was performed at the Grand Accélérateur National d’Ions Lourds (GANIL) Caen, France, and supported by the French Network EMIR. The support in planning and execution of the experiment by the CIMAP-CIRIL and the GANIL staff, especially, I. Monnet, C. Grygiel, T. Madi and F. Durantel is much appreciated. Thanks are given to I. Buisman and M. Walker from the Department of Earth Sciences, University of Cambridge for help in conducting electron probe microanalysis and polishing the samples, respectively. A.J. Popel acknowledges funding from the UK EPSRC (grant EP/I036400/1 and EP/L018616/1) and Radioactive Waste Management Ltd (formerly the Radioactive Waste Management Directorate of the UK Nuclear Decommissioning Authority, contract NPO004411A-EPS02)

Discovery of a maximum damage structure for Xe-irradiated borosilicate glass ceramics containing powellite

In order to increase the waste loading efficiency in nuclear waste glasses, alternate glass ceramic (GC) materials are sought that trap problematic molybdenum in a water-durable CaMoO4 phase within a borosilicate glass matrix. In order to test the radiation resistance of these candidate wasteforms, accelerated external radiation can be employed to replicate long-term damage. In this study, several glasses and GCs were synthesized with up to 10 mol% MoO3 and subjected to 92 MeV Xe ions with fluences ranging between 5 × 10^12 to 1.8 × 10^14 ions/cm2. The main mechanisms of modification following irradiation involve: (i) thermal and defect-assisted diffusion, (ii) relaxation from the ion's added energy, (iii) localized damage recovery from overlapping ion tracks, and (iv) the accumulation of point defects or the formation of voids that created significant strain and led to longer-range modifications. Most significantly, a saturation in alteration could be detected for fluences greater than 4 × 10^13 ions/cm2, which represents an average structure that is representative of the maximum damage state from these competing mechanisms. The results from this study can therefore be used for long-term structural projections in the development of more complex GCs for nuclear waste applications.EPSRC (Grant No. EP/K007882/1

Local strain heterogeneity and elastic relaxation dynamics associated with relaxor behavior in the single-crystal perovskite Pb(I n1/2 N b1/2) O3-PbZr O3-Pb(M g1/3 N b2/3) O3-PbTi O3

© 2017 American Physical Society. Recently, Pb(In1/2Nb1/2)O3-PbZrO3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PZ-PMN-PT) relaxor single crystals were demonstrated to possess improved temperature-insensitive properties, which would be desirable for high-power device applications. The relaxor character associated with the development of local random fields (RFs) and a high rhombohedral-tetragonal (R-T) ferroelectric transition temperature (TR-T > 120°C) would be critical for the excellent properties. A significant effect of the chemical substitution of In3+ and Zr4+ in PMN-PT to give PIN-PZ-PMN-PT is the development of local strain heterogeneity, which acts to suppress the development of macroscopic shear strains without suppressing the development of local ferroelectric moments and contribute substantially to the RFs in PIN-PZ-PMN-PT. Measurements of elastic and anelastic properties by resonant ultrasound spectroscopy show that PIN-PZ-PMN-PT crystal has a quite different form of elastic anomaly due to Vogel-Fulcher freezing, rather than the a discrete cubic-T transition seen in a single crystal of PMN-28PT. It also has high acoustic loss of the relaxor phase down to TR-T. Analysis of piezoresponse force microscopy phase images at different temperatures provides a quantitative insight into the extent to which the RFs influence the microdomain structure and the short-range order correlation length (ξ)

Synthesis and anticancer activity of Pt(0)-olefin complexes bearing 1,3,5-triaza-7-phosphaadamantane and N-heterocyclic carbene ligands

A series of Pt(0)-η2-olefin complexes bearing 1,3,5-triaza-7-phosphaadamantane (PTA) or N-heterocyclic carbenes are prepared following different synthetic strategies depending on the nature of coordinated alkene and spectator ligands. These new platinum(0) derivatives have been tested in vitro as anticancer agents toward three different tumor (human ovarian cancer A2780 and A2780cis and K562 myelogenous leukemia) and one non-tumor (Hacat keratinocytes) cell lines, proving to be in several cases highly and selectively cytotoxic against ovarian cancer cells. Furthermore, this antiproliferative effect is associated with the activation of an apoptosis process. In particular, complexes equipped with PTA as spectator ligand give comparable IC50 values on A2780 (cisplatin sensitive) and A2780cis (cisplatin resistant) cell lines, indirectly proving that these new Pt(0) substrates act with a mechanism of action conceivably different from cisplatin. This hypothesis is also confirmed by the fact that our compounds, in contrast to cisplatin, are not able to promote erythroid-differentiation activity on the K562 myelogenous leukemia cell line

Thermal Behavior of Iron Arsenides Under Non-Oxidizing Conditions.

Fe2As has been studied in situ by synchrotron powder X-ray diffraction (PXRD) over the range of temperatures 25-850 °C and under a neutral atmosphere to understand its thermal behavior, which is potentially important for gold extraction. For the first time, incongruent high-temperature reactions of Fe2As are observed as it breaks down and the existence of a previously undiscovered high-temperature FeAs phase with an NiAs-type structure has been determined experimentally. No evidence has been found for the existence of the high-temperature Fe3As2 phase. Hence, the previously published phase diagram for the Fe-As system has to be modified accordingly