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Liquid Crystal Phases of DNA and Implications for The Origin of Life. Yang Yang, Xianfeng Song Advisor: Sima Setayeshgar Journal Club April 11 th , 2008. Outline. Part I: Introduction to liquid crystals Part II: Background on theories of origin of life
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Yang Yang, Xianfeng Song
Advisor: Sima Setayeshgar
April 11th, 2008
When the polarizers are arranged so that their planes of polarization are perpendicular to each other, the light is blocked. When the second filter (called the analyzer) is parallel to the first, all of the light passed by the first filter is also transmitted by the second.
When putting LC in between two polarizers, the polarization state is modified by LC. Now there will be light come through depends on the director’s direction, LC’s thickness, ray’s frequency.
From Nature 430, 413-414(22 July 2004)
The Schlieren texture, is characteristic of the nematic phase. The dark regions that represent alignment parallel or perpendicular to the director are called brushes.
A typical texture of chiral nematic liquid crystal with long pitch helix. Network-like defect lines are oily-streak lines.
The structure of chiral nematic liquid crystals
Texture of the smectic A phase
Picture of the smectic A phase
Picture of the smectic C phase
A class of liquid crystal phases in which molecules assemble into cylindrical structures
From Nature 406, 868-871, 2000
From Science 318, 1276 (2007)
100× of texture exhibited by the hexagonal columnar mesophase
Columnar phase formed by discotic molecules
Columnar phase formed by rod-like molecules
How the relatively simple organic building blocks polymerase and form more complex structures?
Franklin R, Gosling RG , Nature 171,1953
The paper gives us an idea how the small molecule s tend to self-organize themselves to larger molecule
Notes form Prof. Cherbas, Dept. of Biology,
[*]Onsager, Ann. N.Y. Acad. Sci. 51, 627 (1949); Bolhuis etc, J. Chem. Phys. 106, 666 (1997)
For N < 20, phase transitions from our data are marked by red open symbols (I-N, triangles; N-CU, circles; CU-C2, squares), and the range of each phase is indicated by colored columns (I, magenta; N, cyan, CU, yellow), at T = 20°C for 20 > N > 8 and T = 10°C for N = 6.
The phase diagram presents clear evidence that the origin of the LC phases in sDNA is the equilibrium end-to-end physical aggregation of short duplexes into extended duplex units that are long and rigid enough to order.
The observation of nematic and columnar LC phase provides clear evidence for end-to-end stacking of sDNA into rod-shaped aggregates.Discussion & Conclusion