Right- and Left-Handed α-Helical Structures in Poly(L-alanyl-D-alanyl-L-alanyl-L -alanyl)

1973 ◽  
Vol 6 (3) ◽  
pp. 447-453 ◽  
Author(s):  
N. Lotan ◽  
F. Th. Hesselink ◽  
H. Benderly ◽  
J. F. Yan ◽  
I. Schechter ◽  
...  
Keyword(s):  
Helical Structures ◽  
Left Handed

Self-assembly of near-unity helical Ce1−xMxO2 (x = 0.1, M = Ni and Bi) solid solutions with tunable optical activity

2018 ◽  
Vol 42 (3) ◽  
pp. 1577-1580
Author(s):  
Jing Chen ◽  
Songmei Li ◽  
Juan Du ◽  
Jianhua Liu ◽  
Mei Yu ◽  
...  
Keyword(s):  
Optical Activity ◽  
Solid Solutions ◽  
Self Assembly ◽  
Visible Range ◽  
Helical Structures ◽  
Exciton Coupling ◽  
Left Handed ◽  
Uv Visible

Ce1−xMxO2 solid solutions show tunable optical activity throughout the whole UV–visible range ascribed to electronic exciton coupling between left-handed helical structures.

scholarly journals Liquid crystal phase of counter-rotating staircases – A case of antiferrochirality

2021 ◽  
Author(s):  
Ya-xin Li ◽  
Hong-fei Gao ◽  
Rui-bin Zhang ◽  
Kutlwano Gabana ◽  
Qing Chang ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Long Range ◽  
Short Range ◽  
Liquid Crystal Phase ◽  
Helical Structures ◽  
New Approach ◽  
Chiroptical Properties ◽  
Pi Conjugated ◽  
Left Handed ◽  
Straight Rod

Abstract Helical structures continue to inspire, and there is considerable temptation to attribute helicity to columnar liquid crystals (LC). While short isohelical sequences are undoubtedly present, and longer ones in chiral or chiral-doped compounds, the order is only short-range, equivalent to a paramagnet without or with field. However, here we report a confirmed example of a true LC phase of achiral compounds consisting of columns, each being a long-range homochiral helix. Long-range periodicity and isochirality are maintained by intercolumnar interaction. This orthorhombic LC, spacegroup Fddd, is discovered in compounds with either bent or straight rod-like pi-conjugated cores. There are 4 right and 4 left-handed ribbons or star-profiled columns per unit cell. The structure is equivalent to an antiferromagnet with twist replacing spins. A theory based on interacting quadrupoles confirms this structure as energetically favoured over alternatives. The findings open a new approach to homochirality in achiral compounds, with promising optical/chiroptical properties.

Helix-Sense-Selective Synthesis of Right- and Left-Handed Helical Luminescent Poly(diphenylacetylene)s with Memory of the Macromolecular Helicity and Their Helical Structures

2020 ◽  
Vol 142 (16) ◽  
pp. 7668-7682 ◽  
Author(s):  
Katsuhiro Maeda ◽  
Mai Nozaki ◽  
Kengo Hashimoto ◽  
Kouhei Shimomura ◽  
Daisuke Hirose ◽  
...  
Keyword(s):  
Selective Synthesis ◽  
Helical Structures ◽  
Left Handed ◽  
With Memory

scholarly journals Absolute instabilities in eccentric Taylor–Couette–Poiseuille flow

2014 ◽  
Vol 741 ◽  
pp. 543-566 ◽  
Author(s):  
Colin Leclercq ◽  
Benoît Pier ◽  
Julian F. Scott
Keyword(s):  
Vortex Flow ◽  
Energy Analysis ◽  
Outer Cylinder ◽  
Axial Flow ◽  
Helical Structures ◽  
Left Handed ◽  
Absolute Growth Rate ◽  
Absolute Growth ◽  
Taylor Couette ◽  
Annular Clearance

AbstractThe effect of eccentricity on absolute instabilities (AI) in the Taylor–Couette system with pressure-driven axial flow and fixed outer cylinder is investigated. Five modes of instability are considered, characterized by a pseudo-angular order $m$, with here $\vert m\vert \leq 2$. These modes correspond to toroidal ($m=0$) and helical structures ($m\neq 0$) deformed by the eccentricity. Throughout the parameter range, the mode with the largest absolute growth rate is always the Taylor-like vortex flow corresponding to $m=0$. Axial advection, characterized by a Reynolds number ${\mathit{Re}_z}$, carries perturbations downstream, and has a strong stabilizing effect on AI. On the other hand, the effect of the eccentricity $e$ is complex: increasing $e$ generally delays AI, except for a range of moderate eccentricites ${0.3\lesssim e \lesssim 0.6}$, where it favours AI for large enough ${\mathit{Re}_z}$. This striking behaviour is in contrast with temporal instability, always inhibited by eccentricity, and where left-handed helical modes of increasing $\vert m\vert $ dominate for larger ${\mathit{Re}_z}$. The instability mechanism of AI is clearly centrifugal, even for the larger values of ${\mathit{Re}_z}$ considered, as indicated by an energy analysis. For large enough ${\mathit{Re}_z}$, critical modes localize in the wide gap for low $e$, but their energy distribution is shifted towards the diverging section of the annulus for moderate $e$. For highly eccentric geometries, AI are controlled by the minimal annular clearance, and the critical modes are confined to the vicinity of the inner cylinder. Untangling the AI properties of each $m$ requires consideration of multiple pinch points.

scholarly journals Helical Surface Structures

2003 ◽  
Vol 210 ◽  
pp. 233-242 ◽  
Author(s):  
Axel Brandenburg ◽  
Eric G. Blackman
Keyword(s):  
Quantitative Measurement ◽  
Solar Surface ◽  
Mean Field ◽  
Helical Structures ◽  
The Past ◽  
Left Handed ◽  
Surface Field ◽  
The Mean ◽  
Helical Magnetic Field ◽  
Northern And Southern Hemispheres

Over the past few years there has been growing interest in helical magnetic field structures seen at the solar surface, in coronal mass ejections, as well as in the solar wind. Although there is a great deal of randomness in the data, on average the extended structures are mostly left-handed on the northern hemisphere and right-handed on the southern. Surface field structures are also classified as dextral (= right bearing) and sinistral (= left bearing) occurring preferentially in the northern and southern hemispheres respectively. Of particular interest here is a quantitative measurement of the associated emergence rates of helical structures, which translate to magnetic helicity fluxes. In this review, we give a brief survey of what has been found so far and what is expected based on models. Particular emphasis is put on the scale dependence of the associated fields and an attempt is made to estimate the helicity flux of the mean field vs. fluctuating field.

Diastereomeric Right- and Left-Handed Helical Structures with Fourteen (R)-Chiral Centers

2017 ◽  
Vol 23 (72) ◽  
pp. 18120-18124 ◽  
Author(s):  
Ryo Eto ◽  
Makoto Oba ◽  
Atsushi Ueda ◽  
Tsubasa Uku ◽  
Mitsunobu Doi ◽  
...  
Keyword(s):  
Helical Structures ◽  
Left Handed ◽  
Chiral Centers

scholarly journals Frontispiece: Diastereomeric Right- and Left-Handed Helical Structures with Fourteen (R )-Chiral Centers

2017 ◽  
Vol 23 (72) ◽  
Author(s):  
Ryo Eto ◽  
Makoto Oba ◽  
Atsushi Ueda ◽  
Tsubasa Uku ◽  
Mitsunobu Doi ◽  
...  
Keyword(s):  
Helical Structures ◽  
Left Handed ◽  
Chiral Centers
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