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Nanoindentation performed with a conospherical tip on the (100) face of cytosine monohydrate (CM) revealed a highly anisotropic response over a range of loads. Post-indent atomic force microscopy images identified an asymmetric deformation response owing to the pro-chiral structure of the surface. Activation of low rugosity slip planes induces movement of π-stacks rather than their displacement along the 1-dimensional hydrogen bonded ribbon direction. Anisotropy arises because slip can only propagate to one side of the indent, as the tip itself imparts a barrier to slip on the preferred plane thereby forcing the activation of secondary slip systems and pileup. The anisotropic deformation is of interest in relation to previous work which proposed a ribbon–rotation model to account for the topotactic conversion between CM and the product of its dehydration. The asymmetry in the nanomechanical properties exhibited by CM provides further support for the rotational model put forth and also serves to underscore the inherent relationship between a hydrate's mechanical properties and its solid state dehydration mechanism. 

Data informatics approaches were applied to the Cambridge Structural Database (CSD) in an effort to discern fundamental trends related to the preparation, occurrence, and general properties of organic solvates. Foremost, the 50 most abundant solvate classes in the CSD were identified through SMILES string matching implemented through CSD Python API, and their relative occurrence rates were compared against data reported 20 years prior. These two sets of data suggest that solvate preparation methods have become less diverse over that time period with an increasing fraction derived from a smaller subset of solvents, though the relative abundance of hetero-solvates containing more than one type of solvent molecule simultaneously increased. A subsequent SMILES string matching facilitated the identification of ∼2700 pairs of solvate and solvent-free structures from the top 10 solvate classes. Data from the two related groups showed statistical differences in both the lattice symmetries and packing fractions. Solvates exhibited an inherent bias favoring triclinic lattice symmetry, which is likely related to the larger number of unique molecular components in the asymmetric unit. More surprising was the fact that solvates that do not exhibit disorder statistically had lower packing fractions than their solvent-free analogues. While solvate formation may in fact be a means to achieve phases with higher packing efficiency for some organic molecules, the data indicate this is not a general trend. 

Abstract Uricotelic species, such as squamate reptiles, birds and insects, effectively eliminate nitrogen as uric acid in a solid form commonly called urates. Observations made over a decade suggested that the voided urates produced by colubroids (modern snake species) exhibit remarkable differences from those of boids and pythons (ancient snake species). Here, we compare the urates generated by eight captive snake species fed the same diet. Although all fresh urates were wet at the time of excretion, those produced by modern snakes dried to a powdery solid, whereas those of ancient species dried to a rock-hard mass that was tightly adherent to surfaces. Powder X-ray diffraction and infrared spectroscopy analyses performed on voided urates produced by five modern and three ancient snakes confirmed their underlying chemical and structural differences. Urates excreted by ancient snakes were amorphous uric acid, whereas urates from modern snakes consisted primarily of ammonium acid urate, with some uric acid dihydrate. These compositional differences indicate that snakes have more than one mechanism to manage nitrogenous waste. Why different species use different nitrogen-handling pathways is not yet known, but the answer might be related to key differences in metabolism, physiology or, in the case of ancient snakes, the potential use of urates in social communication.