Phase separation and liquid crystallization of complementary sequences in mixtures of nanoDNA oligomers

1. 

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   Fig. 1.

   Phase diagram of aqueous solution of a 1:1 mixture of nDNA-A and nDNA-B. Upon increasing the total DNA concentration c, a chiral nematic (N*), a columnar (C), and a crystalline phase (X) appear whose textures from DTLM are shown. Upon increasing the temperature T, phases melt into an isotropic phase of SSs (Iso-SS). When c < 600 mg/ml and at T below the nDNA duplex unbinding temperature, an isotropic phase of DSs is found (Iso-DS).

   
   
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   Fig. 2.

   Depolarized transmitted optical microscopy images of LC domains in unbalanced mixtures of nDNA-A and nDNA-B (a) and of nDNA-SC in a solution containing a mixture of SS nDNA sequences (b). The molar ratios are [B]/[A] = 3 and [MIX]/[SC] = 4. (Scale bar: 20 μm.)

   
   
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   Fig. 3.

   Depolarized transmitted optical microscopy (a) and fluorescence (b) images of the same columnar domains in an unbalanced A–B mixture ([B]/[A] = 10) in which a small fraction (1/40) of A sequences was labeled with fluorescein bound externally to the double helix. (Scale bar: 50 μm.) (a) Duplex-rich LC domains appear brighter on the coil-rich background because of the LC birefringence. The developable domain textures are consistent with the columnar phase constraint of constant column spacing. The sketch shows the cross-section of the shield-like domains, where the black lines represent the local columnar axis.

   
   
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   Fig. 4.

   Volume fraction of LC domains, φ_LC, as a function of φ_DS, the ratio between the total volumes of duplexes and the total volume of nDNA, as computed on the basis of the sample prepartion. Circles and squares represent A-B and SC-MIX mixtures, respectively. Lines represent φ_LC = φ_DS (dashed) and φ_LC = 0.8 φ_DS (solid). Error bars are evaluated as described in the text.

   
   
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   Fig. 5.

   Time dependence of number and radius of LC nuclei for an A–B mixture. The number of LC nuclei N _N measured after the hot stage reaches T = 35°C (diamond) and calculated from a nucleation rate of 0.8 nuclei per second (line) are reported in a. The radius of the largest (early nucleated) LC domains r _N,MAX (circles), the mean nuclei radius 〈r _N〉 (squares), and the best fits of the Von Smoluchowski model to the data (lines) are shown in b. The noise in the fitting curve for 〈r _N〉 is attributable to the convolution of the model with the derivative of N _N, performed to take into account the time distribution in the first appearance of the nuclei.

   
   
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   Fig. 6.

   Depolarized transmitted optical microscopy (a and c) and fluorescence (b and d) images of droplets of a SC nDNA mixed with PEG (molecular mass 8,000 Da). Birefringent domains are visible at room temperature under crossed polarizers (a), and the segregation of DNA helices is manifested through the fluorescent dye ethidium bromide (b). Sample held for hours at high temperature (75°C), at which LC domains melt, still show DS-rich domains, visible both under slightly decrossed polarizers (c) and in fluorescence image (d). (Scale bar: 50 μm.)