Multiple liquid crystal phases of DNA at high concentrations

Abstract

Fig. 1 Dependence of solid state31 P NMR linewidth on DNA concentration suggesting multiple phase transitions. DNA fragments of average length 146 base pairs (~500 Å) and with a narrow distribution about this length were prepared by digestion with micrococcal nuclease of calf-thymus chromatin previously depleted of histone H1, and by subsequent deproteinization 16 . Short DNA molecules are studied as a preliminary step to understanding the natural behavior of DNA at in vivo concentrations. Such defined samples are useful because effects of relative molecular mass heterogeneity are minimized and phase transitions are sharp and kinetically rapid. Using DNA fragments of this size is appropriate because the driving forces are the same for ordering of high axial ratio, rod-like molecules and long semi-flexible polymers of identical composition 5,6 . Open circles: data taken at 30ºC; filled circles: data taken at 50ºC. Spectra were obtained on non-spinning samples at a phosphorus frequency of 61.3 MHz on the 'Seminole', an in-house constructed multinuclear Fourier transform (FT) spectrometer equipped with wide-bore superconducting solenoid and quadrature detection, modified for solid-state applications. Sweep width was ±25 kHz, pulse repetition times were 3 s, and 600 scans were added for each spectrum. Gated proton decoupling was applied during data acquisition.

Thermotropic liquid crystals from biomacromolecules

“…Thus, it is not surprising that the study of LCs emerged as a scientific discipline in part from biology and from the study of myelin figures, lipids, and cell membranes (4). These and the LC phases formed from many other biomolecules, including nucleic acids (5,6), proteins (7,8), and viruses (9,10), are classified as lyotropic, the general term applied to LC structures formed in water and stabilized by the distinctly biological theme of amphiphilic partitioning of hydrophilic and hydrophobic molecular components into separate domains. However, the principal thrust and achievement of the study of LCs has been in the science and application of thermotropic materials, structures, and phases in which molecules that are only weakly amphiphilic exhibit LC ordering by virtue of their steric molecular shape, flexibility, and/or weak intermolecular interactions [e.g., van der Waals and dipolar forces (11)].…”

Semiconductor Nanorod Liquid Crystals

“…One important characteristic of organic macromolecules is their propensity to form liquid crystalline phases when they possess a rod-like shape (10,11).…”

Phase Transitions in Finite Systems using Information Theory

“…In fact the characteristic of phase transitions in finite systems, and in particular the occurrence of a negative heat capacity, have first been discussed in the astrophysical context [2,31,26,69,70,71,72,73]. Since these pioneering works in astrophysics, an abundant literature is focused on the understanding of phase transition in small systems from a general point of view [15,30,36,74,75,76,77,78,79] or in the mean-field context [4,80] or for some specific systems such as metallic clusters [48,68] or nuclei [81] and even DNA [82].…”