Epitaxy of Rhodochrosite (MnCO) on Muscovite Mica and Its Relation with Calcite (CaCO).

The flatness of muscovite mica makes it a convenient substrate to study epitaxy. We have analyzed the growth of rhodochrosite (MnCO) crystals in solution and on muscovite mica. Growth at high supersaturations occurs via the formation of amorphous MnCO, which over time transforms into the crystalline form.

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 cm .

Epitaxial Crystallization of Insulin on an Ordered 2D Polymer Template.

Two-dimensional polymers (2DP) are a new class of materials that consist of a monolayer of ordered molecular building blocks, which have been covalently linked. One of these monomers was self-assembled on a flat muscovite mica scaffold and subsequently the organic layer was polymerized. The resulting flat and stable 2DP layer was used as a template for protein crystallization.

Epitaxy of Anthraquinone on (100) NaCl: A Quantitative Approach.

A growth cell suitable for microscopic in situ observation of well-controlled crystal growth from the vapor phase is used to study the heteroepitaxial growth of anthraquinone crystals on a (100) NaCl substrate. In this, the morphology, orientation, nucleation, and growth rate of the crystals is studied as a function of driving force, Δμ/. At the lowest Δμ/, the crystals are block-shaped and show no preferential orientation with respect to the substrate.

Additive Induced Formation of Ultrathin Sodium Chloride Needle Crystals.

A multitude of ultrathin crystal needles are formed during the evaporation of saturated aqueous NaCl solution droplets in the presence of amide containing additives. The needles are as small as 300 nm wide and 100-1000 μm in length. Heating experiments, X-ray diffraction, and energy dispersive X-ray spectroscopy showed that the needles are cubic sodium chloride crystals with the needle length direction pointing toward [100].

The structure of PbCl 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 (PbCl) 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 PbCl and NaCl {100} and the structure at the surface.

Surfaces with Controllable Topography and Chemistry Used as a Template for Protein Crystallization.

Surfaces with controllable topography and chemistry were prepared to act as substrates for protein crystallization, in order to investigate the influence of these surface properties on the protein crystallization outcome. Three different methods were investigated to deposit 1,3,5-tris(10-carboxydecyloxy)benzene (TCDB) on a muscovite mica substrate to find the best route for controlled topography. Of these three, sublimation worked best.

Additive Enhanced Creeping of Sodium Chloride Crystals.

This article investigates the mechanism behind the creeping of sodium chloride induced by additives. Here, an experimental approach is complemented with theoretical considerations to describe how creeping patterns of brine evolve and how the introduction of additives into the solution affects the morphology of the resultant crystals. We have found that these additives cause kinetic roughening and morphological instability mainly due to the reduction of surface free energy.

Structure and activity of the anticaking agent iron(III) meso-tartrate.

Iron(III) meso-tartrate, a metal-organic complex, is a new anticaking agent for sodium chloride. A molecular structure in solution is proposed, based on a combination of experimental and molecular modelling results. We show that the active complex is a binuclear iron(iii) complex with two bridging meso-tartrate ligands.

Versatile wedge-based system for the construction of unidirectional collagen scaffolds by directional freezing: practical and theoretical considerations.

Aligned unidirectional collagen scaffolds may aid regeneration of those tissues where alignment of cells and extracellular matrix is essential, as for instance in cartilage, nerve bundles, and skeletal muscle. Pores can be introduced by ice crystal formation followed by freeze-drying, the pore architecture reflecting the ice crystal morphology. In this study we developed a wedge-based system allowing the production of a wide range of collagen scaffolds with unidirectional pores by directional freezing.

Emergence of single-molecular chirality from achiral reactants.

The synthesis of enantiopure molecules from achiral precursors without the need for pre-existing chirality is a major challenge associated with the origin of life. We here show that an enantiopure product can be obtained from achiral starting materials in a single organic reaction. An essential characteristic of this reaction is that the chiral product precipitates from the solution, introducing a crystal-solution interface which functions as an asymmetric autocatalytic system that provides sufficient chiral amplification to reach an enantiopure end state.

Dibenzo crown ether layer formation on muscovite mica.

Stable layers of crown ethers were grown on muscovite mica using the potassium-crown ether interaction. The multilayers were grown from solution and from the vapor phase and were analyzed with atomic force microscopy (AFM), matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry, and surface X-ray diffraction (SXRD). The results show that the first molecular layer of the three investigated dibenzo crown ethers is more rigid than the second because of the strong interaction of the first molecular layer with the potassium ions on the surface of muscovite mica.

Enantiopure isoindolinones through Viedma ripening.

Here we demonstrate that deracemization of isoindolinones using Viedma ripening is possible starting from a racemic mixture of conglomerate crystals. Crystals of the enantiopure isoindolinones lose their chiral identity upon dissolution even without the need for a catalyst. This enabled complete deracemization of the reported isoindolinones without a catalyst.

Polymorphism in porphyrin monolayers: the relation between adsorption configuration and molecular conformation.

Self-assembled monolayers of meso-5,10,15,20-tetrakis(undecyl)porphyrin copper(II) on a graphite/1-octanoic acid interface have been studied by Scanning Tunnelling Microscopy. Four distinct polymorphs were observed, varying in their unit cell size. Arrays of unit cells of the various polymorphs seamlessly connect to each other via shared unit cell vectors.

Little exchange at the liquid/solid interface: defect-mediated equilibration of physisorbed porphyrin monolayers.

The transition from low to high density 2D surface structures of copper porphyrins at a liquid/solid interface requires specific defects at which nearly all exchange of physisorbed molecules with those dissolved in the supernatant occurs.

Crystal structure transfer in core/shell nanowires.

Structure engineering is an emerging tool to control opto-electronic properties of semiconductors. Recently, control of crystal structure and the formation of a twinning superlattice have been shown for III-V nanowires. This level of control has not been obtained for Si nanowires, the most relevant material for the semiconductor industry.

The role of surface energies and chemical potential during nanowire growth.

We present an approach to quantitatively determine the magnitudes and the variation of the chemical potential in the droplet (Δμ), the solid-liquid (γ(SL)) and the liquid-vapor (γ(LV)) interface energies upon variation of the group III partial pressure during vapor-liquid-solid-growth of nanowires. For this study, we use GaP twinning superlattice nanowires. We show that γ(LV) is the quantity that is most sensitive to the Ga partial pressure (p(Ga)), its dependence on p(Ga) being three to four times as strong as that of γ(SL) or Δμ, and that as a consequence the surface energies are as important in determining the twin density as the chemical potential.

Formation of wurtzite InP nanowires explained by liquid-ordering.

We report an in situ surface X-ray diffraction study of liquid AuIn metal alloys in contact with zinc-blende InP (111)(B) substrates at elevated temperatures. We observe strong layering of the liquid metal alloy in the first three atomic layers in contact with the substrate. The first atomic layer of the alloy has a higher indium concentration than in bulk.

Complete chiral symmetry breaking of an amino acid derivative directed by circularly polarized light.

Circularly polarized light (CPL) emitted from star-forming regions is an attractive candidate as a cause of single chirality in nature. It has remained difficult, however, to translate the relatively small chemical effects observed on irradiation of molecular systems with CPL into high enantiomeric excesses. Here we demonstrate that irradiation of a racemic amino acid derivative with CPL leads to a small amount of chiral induction that can be amplified readily to give an enantiopure solid phase.

Paired twins and [112] morphology in GaP nanowires.

Formation of random as well as periodic planar defects can occur during vapor-liquid-solid growth of nanowires with the zinc-blende crystal structure. Here we investigate the formation of pairs of twin planes in GaP nanowires. In such pairs, the first twin plane is formed at a random position, rapidly followed by the formation of a second twin plane of which the position is directly related to that of the first one.

Self-assembly of porphyrins on a single crystalline organic substrate.

Layers of a free base porphyrin have been deposited from n-heptane solution onto single crystalline potassium acid phthalate substrates and the self-assembled structures have been characterized by atomic force microscopy and X-ray diffraction. Depending on the concentration of the porphyrin solution, different anisotropic structures are found that are epitaxially related to the substrate, with the length axis parallel to the [001] direction of the (010) substrate surface. For undersaturated solutions, islands, cellular structures, and a hole pattern of monolayers of approximately 2.

Fast attrition-enhanced deracemization of naproxen by a gradual in situ feed.

Grind and cure: Using the nonsteroidal anti-inflammatory drug naproxen, a novel concept is demonstrated to dramatically enhance the rate of the recently discovered process of deracemization using abrasive grinding. The process relies on a gradual feed of the racemic target material by an in situ conversion.

Complete chiral resolution using additive-induced crystal size bifurcation during grinding.

Grinding them down: By using a tailor-made additive, even in the absence of racemization in solution, abrasive grinding can yield an enantiopure solid state. This novel chiral resolution technique is based on an asymmetric bifurcation in the crystal size distribution as a result of stereoselective hampered crystal growth. R = o-tolyl.