The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACT:We describe the synthesis and characterization of a family of materials, Zr 1-x Sn x Mo 2 O 8 (0 < x < 1) whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, α l , ranging from -7.9(2) × 10 -6 K -1 to +5.9(2) × 10 -6 K -1 (12 to 500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of "cubic" SnMo 2 O 8 , and use time-and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material.

Nanotechnology has been actively employed in the development of drug-delivery systems overcoming the limitations of conventional carriers. In nanomedicine, the ultimate goal is to design and develop a system for the prevention, diagnosis, control, and treatment of debilitating diseases. Nanoparticles can be designed and programmed to have unique physical properties, in order to protect the loaded drug against degradation and/or denaturation by natural processes inside the body, while selectively delivering it to target areas having the desired cells. This effectively minimizes the active pharmaceutical ingredient's (API's) systemic exposure and, consequently, the occurrence of adverse side effects. The enhanced control on the distribution and release of the entrapped drug molecules, through active targeting and controlledrelease technology, allows for their increased and accurate cellular uptake. In this review, we summarize the development of nanobased drug-delivery systems, with a focus on smart systems and the necessary characteristics required for the optimal drug nanocarrier. The recently developed class of crystalline porous polymers, covalent organic frameworks (COFs), possesses a unique combination of characteristics including permanent yet tunable discrete pores having high surface areas and large volumes, making them intrinsically designed to accommodate APIs as guest molecules in their highly ordered pores. The extensive synthetic and molecular design flexibility of COFs allows the structural control and tuning of their morphology, regularity, atomic connectivity, and porosity, for this specific application. Through an overview of the recent advancements in the novel application of metal− organic frameworks (MOFs) and COFs as drug nanocarriers, we demonstrate this promising alternative route to effectively increase the drug solubility and enhance the limited loading capacity and release control of nanoparticle systems. Since the first reported COF nanocarriers in 2011 as passive targeting drug-delivery systems, this application of COFs has been slowly gaining traction, with increasingly complex COF nanocarrier drug-delivery systems reported in the past year.

Polymorphism of crystalline drugs is a common phenomenon. However, the number of reported polymorphic cocrystals is very limited. In this work, the synthesis and solid state characterisation of a polymorphic cocrystal composed of sulfadimidine (SD) and 4-aminosalicylic acid (4-ASA) is reported for the first time. By liquid-assisted milling, the SD:4-ASA 1:1 form I cocrystal, the structure of which has been previously reported, was formed. By spray drying, a new polymorphic form (form II) of the SD:4-ASA 1:1 cocrystal was discovered which could also be obtained by solvent evaporation from ethanol and acetone. Structure determination of the form II cocrystal was calculated using high resolution X-ray powder diffraction. The solubility of the SD:4-ASA 1:1 cocrystal was dependent on the pH and predicted by a model established for a two amphoteric component cocrystal. The form I cocrystal was found to be thermodynamically more stable in aqueous solution than form II, which showed transformation to form I. Dissolution studies revealed that the dissolution rate of SD from both cocrystals was enhanced when compared to a physical equimolar mixture and pure SD.

A novel mechanism is identified leading to negative linear compressibility (NLC) in boron arsenate which is shown to arise from deformations in the framework tetrahedra rather than more conspicuous tetrahedral rotations. Instead, such rotations, which manifest as "rotating squares" when viewed down the c direction, are found to result in negative Poisson's ratio (NPR) in the (001) plane, which in turn augments the compressibility, a phenomenon that should be applicable to other auxetic materials. It is hypothesized that the generic NLC and NPR mechanisms identified here, as well as the augmented compressibility due to auxeticity should also feature in materials and metamaterials with similar characteristics. systems such as -cristobalite isostructural crystals with an I42d or I4 symmetry. Similarly, NLC is commonly associated with wine-rack motifs [37,39] or other mechanisms. [39] Negative compressibility and negative Poisson's ratio have also long been known in the vicinity of phase transformations. [39,47] The present work will study the effect of pressure, uniaxial loading, and shearing on boron arsenate, in an attempt to unearth the mechanisms which lead to NLC and NPR in this stable member of I4 space group, through the quantitative measurement of the molecular level deformations. This will help the understanding of the mechanisms leading to such anomalous "negative mechanical behavior" in crystals and in the process pave the way to the design of novel metamaterials inspired from it.

Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details.