Organothiol Monolayer Formation Directly on Muscovite Mica.

Organothiol monolayers on metal substrates (Au, Ag, Cu) and their use in a wide variety of applications have been extensively studied. Here, the growth of layers of organothiols directly onto muscovite mica is demonstrated using a simple procedure. Atomic force microscopy, surface X-ray diffraction, and vibrational sum-frequency generation IR spectroscopy studies revealed that organothiols with various functional endgroups could be self-assembled into (water) stable and adaptable ultra-flat organothiol monolayers over homogenous areas as large as 1 cm2 . The strength of the mica-organothiol interactions could be tuned by exchanging the potassium surface ions for copper ions. Several of these organothiol monolayers were subsequently used as a template for calcite growth.

Concentration-Dependent Adsorption of CsI at the Muscovite-Electrolyte Interface.

The interfacial structure of muscovite in contact with aqueous CsI solutions was measured using surface X-ray diffraction for several CsI concentrations (2-1000 mM). At CsI concentrations up to 200 mM, Cs+ adsorption is likely hindered by H3O+, as both cations compete for the adsorption site above the muscovite hexagonal cavity. Above this concentration, more Cs+ adsorbs than is required to compensate the negatively charged muscovite surface, which means that coadsorption of an anion takes place. The I- anion does not coadsorb in an ordered manner. Moreover, the hydration ring and water layers do not change significantly as a function of the CsI concentration.

The structure of PbCl2 on the {100} surface of NaCl and its consequences for crystal growth.

The role that additives play in the growth of sodium chloride is a topic which has been widely researched but not always fully understood at an atomic level. Lead chloride (PbCl2) is one such additive which has been reported to have growth inhibition effects on NaCl {100} and {111}; however, no definitive evidence has been reported which details the mechanism of this interaction. In this investigation, we used the technique of surface x-ray diffraction to determine the interaction between PbCl2 and NaCl {100} and the structure at the surface. We find that Pb2+ replaces a surface Na+ ion, while a Cl- ion is located on top of the Pb2+. This leads to a charge mismatch in the bulk crystal, which, as energetically unfavourable, leads to a growth blocking effect. While this is a similar mechanism as in the anticaking agent ferrocyanide, the effect of PbCl2 is much weaker, most likely due to the fact that the Pb2+ ion can more easily desorb. Moreover, PbCl2 has an even stronger effect on NaCl {111}.

Do solid-to-solid polymorphic transitions in DL-norleucine proceed through nucleation?

DL-Norleucine is a molecular crystal exhibiting two enantiotropic phase transitions. The high temperature α ↔ γ transition has been shown to proceed through nucleation and growth [Mnyukh et al., J. Phys. Chem. Solids, 1975, 36, 127]. We focus on the low temperature ß â†” α transition in a combined computational and experimental study. The temperature dependence of the structural and energetic properties of both polymorphic forms is nearly identical. Molecular dynamics simulations and nudged elastic band calculations of the transition process itself, suggest that the transition is governed by cooperative movements of bilayers over relatively large energy barriers.

Chemical, Biochemical, Cellular, and Physiological Characterization of Leucettinib-21, a Down Syndrome and Alzheimer's Disease Drug Candidate.

Leucettinibs are substituted 2-aminoimidazolin-4-ones (inspired by the marine sponge natural product Leucettamine B) developed as pharmacological inhibitors of DYRK1A (dual-specificity, tyrosine phosphorylation-regulated kinase 1A), a therapeutic target for indications such as Down syndrome and Alzheimer's disease. Leucettinib-21 was selected as a drug candidate following extensive structure/activity studies and multiparametric evaluations. We here report its physicochemical properties (X-ray powder diffraction, differential scanning calorimetry, stability, solubility, crystal structure) and drug-like profile. Leucettinib-21's selectivity (analyzed by radiometric, fluorescence, interaction, thermal shift, residence time assays) reveals DYRK1A as the first target but also some "off-targets" which may contribute to the drug's biological effects. Leucettinib-21 was cocrystallized with CLK1 and modeled in the DYRK1A structure. Leucettinib-21 inhibits DYRK1A in cells (demonstrated by direct catalytic activity and phosphorylation levels of Thr286-cyclin D1 or Thr212-Tau). Leucettinib-21 corrects memory disorders in the Down syndrome mouse model Ts65Dn and is now entering safety/tolerance phase 1 clinical trials.

Ordered and Disordered Carboxylic Acid Monolayers on Calcite (104) and Muscovite (001) Surfaces.

The adsorption of carboxylic acid molecules at the calcite (104) and the muscovite (001) surface was investigated using surface X-ray diffraction. All four investigated carboxylic acid molecules, hexanoic acid, octanoic acid, lauric acid, and stearic acid, were found to adsorb at the calcite surface. Whereas the shortest two carboxylic acid molecules, hexanoic acid and octanoic acid, showed limited ordering and a flexible, disordered chain, the two longest carboxylic acid molecules form fully ordered monolayers, i.e., these form highly structured self-assembled monolayers. The latter molecules are oriented almost fully upright, with a tilt of up to 10°. The oxygen atoms of the organic molecules are found at similar positions to those of water molecules at the calcite-water interface. This suggests that in both cases, the oxygen atoms compensate for the broken bonds at the calcite surface. Under the same experimental conditions, stearic acid does not adsorb to K+ and Ca2+-functionalized muscovite mica because the neutral molecules do not engage in the ionic bonds typical for the mica interface. These differences in adsorption behavior are characteristic for the differences of the oil-solid interactions in carbonate and sandstone reservoirs.

Epitaxy of Rhodochrosite (MnCO3) on Muscovite Mica and Its Relation with Calcite (CaCO3).

The flatness of muscovite mica makes it a convenient substrate to study epitaxy. We have analyzed the growth of rhodochrosite (MnCO3) crystals in solution and on muscovite mica. Growth at high supersaturations occurs via the formation of amorphous MnCO3, which over time transforms into the crystalline form. In the presence of muscovite mica, epitaxial rhodochrosite crystals with a size of approximately 1 µm form. These crystals are kinetically roughened, because of the high supersaturation. The lattice match between MnCO3 and muscovite was found not to be the main reason for epitaxy. If the growth experiment is performed twice, the original epitaxial MnCO3 crystals are overgrown by many small crystallites. Similarly, spherical MnCO3 crystals with many overgrown facets can be formed on a muscovite surface that is exposed to humidity or by using a higher MnCO3 supersaturation. A comparison with calcite shows that epitaxy strongly depends on initial supersaturation for both carbonates. In contrast to previous studies, we find that at the right supersaturation, epitaxial calcite crystal growth is possible on freshly cleaved muscovite.

Monovalent - divalent cation competition at the muscovite mica surface: Experiment and theory.

HYPOTHESIS: Ion adsorption on mineral surfaces depends on several factors, such as the mineral surface structure and the valency, size and hydration of the ion. In order to understand competitive adsorption at mineral surfaces, experimental techniques are required that can probe multiple ionic species at the same time. By comparing adsorption of two different cations, it should be possible to derive the factors governing ion adsorption. Divalent cations are expected to bind stronger to the negatively-charged muscovite surface than monovalent cations. EXPERIMENTS: Here, the competition between the monovalent Cs+ and the divalent Ca2+ cation for adsorption at the muscovite mica basal plane was investigated using surface X-ray diffraction. Using an extended surface complexation model, we simultaneously fit the measured cation coverages and net surface charges reported in literature. FINDINGS: In order to reproduce those complementary data sets, both cation adsorption and anion coadsorption were included in the surface complexation model. Moreover, the intrinsic muscovite surface charge and the maximum of available adsorption sites had to be reduced compared to existing literature values. Competition experiments revealed that the affinity of Cs+ for the muscovite surface is larger than the affinity of Ca2+, showing that hydration forces are more important than electrostatics.

The crystal structures of four di-meth-oxy-benzaldehyde isomers.

The crystal structures of four di-meth-oxy-benzaldehyde (C9H10O3) isomers, namely the 2,3-, 2,4-, 2,5- and 3,5- isomers, are reported and compared to the previously reported crystal structures of 3,4-di-meth-oxy-benzaldehyde and 2,6-di-meth-oxy-benzaldehyde. All di-meth-oxy-benzaldehyde mol-ecules in the crystal structures are nearly planar. The largest deviation (1.2 Å) from the aromatic plane is found for one of the meth-oxy groups of 2,3-di-meth-oxy-benzaldehyde. Upon rapid cooling of 3,4-di-meth-oxy-benzaldehyde and 3,5-di-meth-oxy-benzaldehyde, a metastable polymorph is formed. The crystal studied for the 3,5- isomer was refined as a two-component twin.