L. Zhang, Y. Qu, J. Gu et al.
Journal of Molecular Liquids 337 (2021) 116480
Fig. 1. The fabrication of DNA melts by electrostatic complexation of DNA and ammonium bromides.
the research of Ishiba et al., the results do give us some hints on the
impact of different counterions of ammonium surfactants on the
phase transition processes of DNA-surfactants materials.
ature. The filtrate was concentrated in vacuo to remove all the sol-
vent. The residue was dried by lyophilization over 24 h to afford
DDA+Iꢀ as white solid. Elemental Analysis (%) Calcd for C26H56NI:
C, 61.28; H, 11.08; N, 2.75. Found: C, 61.54; H, 11.12; N, 2.76.
DDA+[BF4]ꢀ [30]: To a solution of DDA+Brꢀ (0.30 g, 0.65 mmol)
in acetone (10 mL) was added NaBF4 (71.3 mg, 0.65 mmol, 1 eq).
The mixture was filtered after being stirred over 24 h at room tem-
perature. The filtrate was concentrated in vacuo to remove all the
solvent. The residue was dried by lyophilization over 24 h to afford
Among the reported DNA-surfactants complexes, DNA-DDA(Br)
gave Cr ꢀ LC ꢀ IL phase transitions at temperatures above room
temperature but lower than 100 °C [12], which makes it ideal as
the target DNA melt in our research, based on the consideration
of easy measurements on the phase transition temperatures. In
this work, employing various anionic counterions, different ammo-
nium surfactants DDA+Xꢀ were prepared, which then were used for
the fabrication of DNA-DDA(X) complexes under room tempera-
ture (Fig. 2a). According to the studies on the phase transitions of
DNA-surfactants complexes, the influences of counterions of
ammonium surfactants on the thermodynamic stability of LC
states would be revealed, which gives a different perspective on
the impacting factors for maintaining the LC thermal stability from
that of previously reported works [12,13] (Fig. 2b). These results
would afford a new strategy on the tunability of physical proper-
ties of solvent-free soft materials based on biomolecules, including
nucleic acids [11,12,14,19,22], polypeptides [23–26], proteins [27]
and viruses [11].
DDA+[BF4]ꢀ as white solid. Elemental Analysis (%) Calcd for C26H56
-
NBF4: C, 66.51; H, 12.02; N, 2.98. Found: C, 66.56; H, 12.03; N, 2.98.
General synthetic procedure for DDA+[MnCl2Br]ꢀ, DDA+[-
FeCl3Br]ꢀ, DDA+[CoCl2Br]ꢀ DDA+[NiCl2Br]ꢀ, DDA+[CuCl2Br]ꢀ
[19]: To a solution of DDA+Brꢀ (0.30 g, 0.65 mmol) in methanol
(15 mL) was added metal halides (0.65 mmol, 1 eq), including
MnCl2, FeCl3, CoCl2, NiCl2, CuCl2. The mixture was stirred overnight
at room temperature and concentrated in vacuo to remove metha-
nol. The residue was dried by lyophilization overnight to afford
DDA+[MnCl2Br]ꢀ as yellow-green solid. During the preparation,
no other elements were introduced and all the used compounds
were collected as the final product, thus no further elemental anal-
ysis was carried out.
DDA+[TsO]ꢀ: To a solution of DDA+Brꢀ (0.30 g, 0.65 mmol) in
acyl acetate (20 mL) was added TsOH (112 mg, 0.65 mmol, 1 eq).
The mixture was stirred over 8 h at 50 °C and concentrated in
vacuo to remove solvent over 3 h at 60 °C. The residue was dried
in vacuo at 70 °C to afford DDA+[TsO]ꢀ as red oil. 1H NMR showed
there is no impurities in the as-prepared DDA+[TsO]ꢀ. 1H NMR
(400 MHz, CDCl3): d 7.74 (d, J = 8.4 Hz, 2H), 7.17 (d, J = 8.0 Hz,
2H), 4.13 (s, 6H), 3.37 (br s, 4 H), 2.35 (s, 3 H), 1.66 (br s, 4 H),
1.32–1.25 (m, 36H), 0.88 (t, J = 6.8 Hz, 6 H).
2. Experimental
2.1. Synthesis of ammonium surfactants
DDA+Fꢀ [28]: To a solution of DDA+Clꢀ (0.339 g, 0.81 mmol) in
methanol (10 mL) was added KF (47 mg, 0.81 mmol, 1 eq). The
resulted mixture was filtered after being stirred over 15 min at
room temperature. The filtrate was concentrated to remove 25%
of methanol, and the precipitated solid was filtered off. Repeated
this process three more times to remove all methanol. The residue
was dried over 24 h to afford DDA+Fꢀ as white solid. Elemental
Analysis (%) Calcd for C26H56NF: C, 77.73; H, 14.05; N, 3.49. Found:
C, 77.08; H, 13.91; N, 3.44.
2.2. Synthesis of DNA materials
General synthetic procedure for DNA-DDA(X): the aqueous
solutions of DDA+Xꢀ (3.3 ꢁ 10ꢀ3 mmol) was added into the aque-
ous DNA (50-CCTCGCTCTGCTAATCCTGTTA-30) solution (1.5 mM,
DDA+Clꢀ [29]: To a solution of DDA+Brꢀ (0.926 g, 2 mmol) in
ethanol (20 mL) was added NaOH (80 mg, 2 mmol, 1 eq). The mix-
ture was filtered after being stirred over 15 min at room tempera-
ture. The filtrate was concentrated in vacuo to remove all the
solvent. The residue was dried over 24 h to afford DDA+OH–. To a
HCl aqueous solution (1 M, 1 mL) was added DDA+OH–(0.40 g
1 mmol, 1 eq) under Ar2, and the mixture was stirred over 24 h.
Finally, the resulted mixture afforded DDA+Clꢀ as white solid after
lyophilization. Elemental Analysis (%) Calcd for C26H56NCl: C,
74.68; H, 13.50; N, 3.35. Found: C, 74.19; H, 13.43; N, 3.32.
DDA+Iꢀ [30]: To a solution of DDA+Brꢀ (0.30 g, 0.65 mmol) in
acetone (10 mL) was added NaI (97.2 mg, 0.65 mmol, 1 eq). The
mixture was filtered after being stirred over 24 h at room temper-
20
lL) using a pipette, which led to the precipitate of DNA-DDA
(X) complex. The precipitate was purified by centrifugation over
three times and lyophilization to afford the needed DNA materials.
3. Results and discussion
3.1. Ammonium surfactants with different counterions
Ammonium surfactants DDA+Xꢀ, including DDA+Fꢀ [28], DDA+-
Clꢀ [29], DDA+Iꢀ, DDA+[BF4]ꢀ [30], DDA+[MnCl2Br]ꢀ, DDA+[FeCl3-
Br]ꢀ, DDA+[CoCl2Br]ꢀ, DDA+[NiCl2Br]ꢀ and DDA+[CuCl2Br]ꢀ [19],
2