We present a novel method for investigating the self-assembly process by following the average composition of the fragmentary species.

In a vortex generated by mechanical rotary stirring in an optical cell, DNA molecules in pure water temporarily align helically to the spiral flow, and dynamically display strong induced circular dichroism (CD) and linear dichroism (LD) responses. Although a sample solution without stirring provided the characteristic CD spectral pattern of DNA, an entirely different macroscopic CD spectral pattern with a much larger intensity and LD spectrum appeared upon mechanical rotary stirring of the sample solution. Clockwise (CW) and counterclockwise (CCW) stirring resulted in mirror-image CD spectral profiles and virtually the same LD profiles with different intensities. The CW stirring of the sample solution in LD spectroscopy always resulted in larger spectral intensities than CCW stirring, but the differences became negligible upon addition of NaCl or ethidium bromide. The observed CD and LD responses of the stirred sample solution decreased simultaneously as the double-stranded structure denatures with increasing temperatures. The results obtained in this study indicate that DNA, when it forms a double-stranded structure, can effectively align in the vortex flows, and show hydrodynamic preference to a right-handed vortex than to a left-handed vortex.Chiral hydrodynamic interactions between DNA and macroscopic torsional fluids attract considerable interest because of the involvement of microscopic and macroscopic chirality in biomolecular systems. DNA can hydrodynamically align and stretch in certain linear fluid flows, 15 where a worm-like chain model can reasonably account for the elastic behaviors and hydrodynamic interactions of DNA. 6 Here, as an innovative subject related to those studies, we noticed for the torsional flow dynamics of DNA, having a right-handed helical doublestranded structure, in chiral fluids such as a vortex that is recognized as one possible origin of chiral symmetry breaking in nature.710 Strick et al. reported the first single-molecule measurements of DNA topology using magnetic tweezers; they measured the extension and force of individual -phage DNA molecules and found that positively supercoiled DNA was more difficult to stretch than negatively supercoiled DNA. 11Other studies have also demonstrated experimentally the intrinsic chiral twist elasticity of DNA.1215 These studies raise an important question: What happens to DNA in a chiral macroscopic vortex generated by clockwise (CW) or counterclockwise (CCW) stirring? The present study reports a successful spectroscopic visualization of macroscopic helical alignments of DNA in a vortex. DNA, when it forms a doublestranded structure, can effectively align in the vortex flows, and it shows hydrodynamic preference to a right-handed vortex than to a left-handed vortex.It is known that certain achiral molecules form optically active assemblies in torsional fluids generated upon rotary stirring.9,10 Kaizu and co-workers 10a and Ribó and co-workers 10b10d have reported pioneering examples in which electrostatic J-aggregates of (4-sulfophenyl)p...

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