Asymmetric amplification in amino acid sublimation involving racemic compound to conglomerate conversion

A straightforward unprecedented sublimation protocol that reveals both conversion of a racemic compound into a racemic conglomerate and subsequent enantioenrichment has been developed for the proteinogenic amino acid valine. The phenomenon has been observed in closed and open systems, providing insight into asymmetric amplification mechanisms under presumably prebiotic condition

Complex Ordered Patterns in Mechanical Instability Induced Geometrically Frustrated Triangular Cellular Structures

Geometrical frustration arises when a local order cannot propagate throughout the space because of geometrical constraints. This phenomenon plays a major role in many systems leading to disordered ground-state configurations. Here, we report a theoretical and experimental study on the behavior of buckling-induced geometrically frustrated triangular cellular structures. To our surprise, we find that buckling induces complex ordered patterns which can be tuned by controlling the porosity of the structures. Our analysis reveals that the connected geometry of the cellular structure plays a crucial role in the generation of ordered states in this frustrated system.Engineering and Applied SciencesPhysic

Buckling-Induced Reversible Symmetry Breaking and Amplification of Chirality Using Supported Cellular Structures

Buckling‐induced reversible symmetry breaking and amplification of chirality using macro‐ and microscale supported cellular structures is described. Guided by extensive theoretical analysis, cellular structures are rationally designed, in which buckling induces a reversible switching between achiral and chiral configurations. Additionally, it is demonstrated that the proposed mechanism can be generalized over a wide range of length scales, geometries, materials, and stimuli.Chemistry and Chemical Biolog

Controlled growth and form of precipitating microsculptures

Controlled self-assembly of three-dimensional shapes holds great potential for fabrication of functional materials. Their practical realization requires a theoretical framework to quantify and guide the dynamic sculpting of the curved structures that often arise in accretive mineralization. Motivated by a variety of bioinspired coprecipitation patterns of carbonate and silica, we develop a geometrical theory for the kinetics of the growth front that leaves behind thin-walled complex structures. Our theory explains the range of previously observed experimental patterns and, in addition, predicts unexplored assembly pathways. This allows us to design a number of functional base shapes of optical microstructures, which we synthesize to demonstrate their light-guiding capabilities. Overall, our framework provides a way to understand and control the growth and form of functional precipitating microsculptures.Chemistry and Chemical Biolog

Explanation for the Emergence of a Single Chiral Solid State during Attrition-Enhanced Ostwald Ripening: Survival of the Fittest

The overabundant occurrence of single-handed chiral molecules in living systems has inspired scientists for well more than a century. A route to the evolution of a single chiral solid phase, using abrasive grinding of the crystals in contact with a saturated solution, has been demonstrated for the achiral compound NaClO3 crystallizing in a chiral space group and, recently, for an intrinsically chiral amino acid derivative. In order to obtain insight in the complex processes involved in these experiments, we developed a computer model that is based only on attrition and Ostwald ripening. We find that, besides the relative rates of attrition and Ostwald ripening, the racemization efficiency in the solution is an essential parameter in the deracemization process. For high efficiency the evolution to single chirality is stochastic, whereas for lower values the process becomes increasingly deterministic and the handedness of the single chiral solid end state is readily controllable. The results show excellent agreement with experimental data and allow a further optimization of this promising deracemization technique.

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/<i>kT</i>. At the lowest Δμ/<i>kT</i>, the crystals are block-shaped and show no preferential orientation with respect to the substrate. Increasing the driving force leads to the growth of oriented block- and needle-shaped crystals, which nucleate from macrosteps on the substrate. At the highest Δμ/<i>kT</i>, crystals nucleate on the flat surface areas or at monatomic steps on the substrate, resulting in a dramatic increase in epitaxial needle density. Growth rate measurements show an exponential behavior as a function of Δμ/<i>kT</i>. In all cases, the supply of growth units proceeds via surface diffusion over the NaCl substrate surface toward the anthraquinone crystals. At the lowest Δμ/<i>kT</i>, growth is partly limited by integration of the growth units at the crystal surfaces. At intermediate driving force, kinetic roughening sets in, leading to rounded needle tips. At the highest supersaturation, growth is completely governed by the supply of growth units via surface diffusion, leading to tip splitting as a consequence of morphological instability

Efficient Havinga–Kondepudi resolution of conglomerate amino acid derivatives by slow cooling and abrasive grinding

The complete resolution of the conglomerate racemates of two amino acid derivatives susceptible to racemization in solution was achieved by slow crystallization from a supersaturated solution accompanied by cooling and abrasive grinding.

Emergence of a Single Solid Chiral State from a Nearly Racemic Amino Acid Derivative

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

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