216 research outputs found
Condensation of Fivefold-Symmetric Molecules in Two Dimensions
We report the formation of a two-dimensional glass by solidification of a two-dimensional gas of fivefold-symmetric molecules on a copper surface upon cooling. Direct observation with scanning tunneling microscopy allows a detailed insight into the implications of a symmetry mismatch
between molecular geometry and crystal lattice
Stereospecific on-Surface Cyclodehydrogenation of Bishelicenes: Preservation of Handedness from Helical to Planar Chirality
Flattening helices while keeping the handedness: On-surface cyclodehydrogenation of bishelicene enantiomers leads stereospecifically to (M,M) and (P,P) chiral planar polyaromatic hydrocarbons. This is followed by their homochiral aggregation into a 2D conglomerate. Thermally induced cyclodehydrogenation proceeds stereospecifically to chiral, planar coronocoronene. Such a reaction is a special example of topochemistry in which enantiospecific conversion is supported by the alignment of the reactant by the surface
Scattering of rare-gas atoms at a metal surface: evidence of anticorrugation of the helium-atom potential-energy surface and the surface electron density
Recent measurements of the scattering of He and Ne atoms at Rh(110) suggest
that these two rare-gas atoms measure a qualitatively different surface
corrugation: While Ne atom scattering seemingly reflects the electron-density
undulation of the substrate surface, the scattering potential of He atoms
appears to be anticorrugated. An understanding of this perplexing result is
lacking. In this paper we present density functional theory calculations of the
interaction potentials of He and Ne with Rh(110). We find that, and explain
why, the nature of the interaction of the two probe particles is qualitatively
different, which implies that the topographies of their scattering potentials
are indeed anticorrugated.Comment: RevTeX, 4 pages, 10 figure
The influence of motivation and attentional style on affective, cognitive, and behavioral outcomes of an exercise class
Exercise classes are a popular form of physical activity. A greater understanding of the individual difference factors that might influence the outcomes of such classes could help to minimize the high dropout rates associated with exercise. The study explored the effects of dominant attentional style and degree of self-determination on affective, cognitive, and behavioral outcomes following structured exercise classes. Data from 417 female participants revealed that those with a dominant attentional style for association (Associators) reported significantly (P < 0.05) more positive affective, cognitive, and behavioral outcomes than did Dissociators, and were more self-determined. Highly self-determined individuals reported the most positive outcomes. Almost 29% of the variance in participantsâ affective valence could be explained by Dissociatorsâ behavioral regulations. Results lend support to the notion that attentional style is associated with motivation. The combination of attentional style and degree of self-determination appear to be noteworthy individual difference factors that influence responses to exercise classes and could thus have a bearing on long-term exercise adherence
First enantioseparation and circular dichroism spectra of Au38 clusters protected by achiral ligands
Bestowing chirality to metals is central in fields such as heterogeneous catalysis and modern optics. Although the bulk phase of metals is symmetric, their surfaces can become chiral through adsorption of molecules. Interestingly, even achiral molecules can lead to locally chiral, though globally racemic, surfaces. A similar situation can be obtained for metal particles or clusters. Here we report the first separation of the enantiomers of a gold cluster protected by achiral thiolates, Au38(SCH2CH2Ph)24, achieved by chiral high-performance liquid chromatography. The chirality of the nanocluster arises from the chiral arrangement of the thiolates on its surface, forming 'staple motifs'. The enantiomers show mirror-image circular dichroism responses and large anisotropy factors of up to 4Ă10â3. Comparison with reported circular dichroism spectra of other Au38 clusters reveals that the influence of the ligand on the chiroptical properties is minor
Homochirality in biomineral suprastructures induced by assembly of single-enantiomer amino acids from a nonracemic mixture
© 2019, The Author(s). Since Pasteur first successfully separated right-handed and left-handed tartrate crystals in 1848, the understanding of how homochirality is achieved from enantiomeric mixtures has long been incomplete. Here, we report on a chirality dominance effect where organized, three-dimensional homochiral suprastructures of the biomineral calcium carbonate (vaterite) can be induced from a mixed nonracemic amino acid system. Right-handed (counterclockwise) homochiral vaterite helicoids are induced when the amino acid l-Asp is in the majority, whereas left-handed (clockwise) homochiral morphology is induced when d-Asp is in the majority. Unexpectedly, the Asp that incorporates into the homochiral vaterite helicoids maintains the same enantiomer ratio as that of the initial growth solution, thus showing chirality transfer without chirality amplification. Changes in the degree of chirality of the vaterite helicoids are postulated to result from the extent of majority enantiomer assembly on the mineral surface. These mechanistic insights potentially have major implications for high-level advanced materials synthesis
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