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We synthesized the liquid crystal dimer and trimer members of a series of flexible linear oligomers and characterized their microscopic and nanoscopic properties using resonant soft X-ray scattering and a number of other experimental techniques. On the microscopic scale, the twist–bend phases of the dimer and trimer appear essentially identical. However, while the liquid crystal dimer exhibits a temperature-dependent variation of its twist–bend helical pitch varying from 100 to 170 Å on heating, the trimer exhibits an essentially temperature-independent pitch of 66 Å, significantly shorter than those reported for other twist–bend forming materials in the literature. We attribute this to a specific combination of intrinsic conformational bend of the trimer molecules and a sterically favorable intercalation of the trimers over a commensurate fraction (two-thirds) of the molecular length. We develop a geometric model of the twist–bend phase for these materials with the molecules arranging into helical chain structures, and we fully determine their respective geometric parameters.

Smectic ordering in aqueous solutions of monodisperse stiff double-stranded DNA fragments is known not to occur, despite the fact that these systems exhibit both chiral nematic and columnar mesophases. Here, we show, unambiguously, that a smectic-A type of phase is formed by increasing the DNA’s flexibility through the introduction of an unpaired single-stranded DNA spacer in the middle of each duplex. This is unusual for a lyotropic system, where flexibility typically destabilizes the smectic phase. We also report on simulations suggesting that the gapped duplexes (resembling chain-sticks) attain a folded conformation in the smectic layers, and argue that this layer structure, which we designate as smectic-fA phase, is thermodynamically stabilized by both entropic and energetic contributions to the system’s free energy. Our results demonstrate that DNA as a building block offers an exquisitely tunable means to engineer a potentially rich assortment of lyotropic liquid crystals. DNA can be used as a tunable building block to create a variety of self-assembly-driven liquid crystals. Here, the authors report the stabilization of a smectic-A liquid crystal phase, where constituent molecules—two rigid dsDNA segments linked by a flexible ssDNA spacer—attain a folded configuration.

Among the recently developed ferroelectric nematic liquid crystals, FNLC-919, synthesized by Merck Electronics KGaA, stands out for its stable, room-temperature, ferroelectric nematic (NF) phase. This renders it a promising candidate for both fundamental research and device-level applications. In this study, we present a comprehensive experimental investigation of FNLC-919, focusing on its structural, optical, dielectric, and elastic properties in the paraelectric nematic (N) and the intermediate antiferroelectric phase (dubbed NX) that occur in a temperature range between the N and NF phases. Key material parameters such as ferroelectric polarization, viscosity, and nanostructure are characterized as functions of temperature in all mesophases, while the orientational elastic constants are determined only in the N and NX phases. Our findings are compared with prior results concerning the benchmark compound DIO that also exhibits the phase sequence N-NX-NF and reveals a smectic-like mass density wave coinciding with antiferroelectric ordering in the NX phase.

Although its mesomorphic properties have been studied for many years, only recently has the molecule of life begun to reveal the true range of its rich liquid crystalline behavior. End-to-end interactions between concentrated, ultrashort DNA duplexes—driving the self-assembly of aggregates that organize into liquid crystal phases—and the incorporation of flexible single-stranded “gaps” in otherwise fully paired duplexes—producing clear evidence of an elementary lamellar (smectic-A) phase in DNA solutions—are two exciting developments that have opened avenues for discovery. Here, we report on a wider investigation of the nature and temperature dependence of smectic ordering in concentrated solutions of various “gapped” DNA (GDNA) constructs. We examine symmetric GDNA constructs consisting of two 48-base pair duplex segments bridged by a single-stranded sequence of 2 to 20 thymine bases. Two distinct smectic layer structures are observed for DNA concentration in the range ∼230 to ∼280 mg/mL. One exhibits an interlayer periodicity comparable with two-duplex lengths (“bilayer” structure), and the other has a period similar to a single-duplex length (“monolayer” structure). The bilayer structure is observed for gap length ≳10 bases and melts into the cholesteric phase at a temperature between 30 °C and 35 °C. The monolayer structure predominates for gap length ≲10 bases and persists to >40 °C. We discuss models for the two layer structures and mechanisms for their stability. We also report results for asymmetric gapped constructs and for constructs with terminal overhangs, which further support the model layer structures.

Although its mesomorphic properties have been studied for many years, only recently has the molecule of life begun to reveal the true range of its rich liquid crystalline behavior. End-to-end interactions between concentrated, ultrashort DNA duplexes—driving the self-assembly of aggregates that organize into liquid crystal phases—and the incorporation of flexible single-stranded “gaps” in otherwise fully paired duplexes—producing clear evidence of an elementary lamellar (smectic-A) phase in DNA solutions—are two exciting developments that have opened avenues for discovery. Here, we report on a wider investigation of the nature and temperature dependence of smectic ordering in concentrated solutions of various “gapped” DNA (GDNA) constructs. We examine symmetric GDNA constructs consisting of two 48-base pair duplex segments bridged by a single-stranded sequence of 2 to 20 thymine bases. Two distinct smectic layer structures are observed for DNA concentration in the range ∼ 230 to ∼ 280 mg/mL. One exhibits an interlayer periodicity comparable with two-duplex lengths (“bilayer” structure), and the other has a period similar to a single-duplex length (“monolayer” structure). The bilayer structure is observed for gap length ≳10 bases and melts into the cholesteric phase at a temperature between 30 °C and 35 °C. The monolayer structure predominates for gap length ≲10 bases and persists to > 40 ° C. We discuss models for the two layer structures and mechanisms for their stability. We also report results for asymmetric gapped constructs and for constructs with terminal overhangs, which further support the model layer structures.

Liquid crystalline (LC) phases formed by gapped DNA (GDNA) constructs, where two rigid duplexes are connected with a flexible single stranded linker, offer a versatile platform to investigate interactions between DNA molecules. Base pairs containing a locked nucleic acid (LNA-DNA or LNA-LNA pairs) are generally more stable compared to DNA-DNA pairs due to enhanced hydrogen bonding and/or attractive base stacking interactions. In concentrated solutions of GDNA constructs, the stability of terminal base pairs and the base stacking interactions between neighboring duplexes are critical for the formation of a bilayer smectic phase. By using temperature-resolved synchrotron small-angle X-ray scattering (SAXS) measurements, we quantified the impact of single LNA modification of terminal base pairs on the thermal stability of smectic LC phases. We observe that LNA-DNA terminal AT base pairing (A+T) increases the stability of the bilayer smectic phase by ∼9-18 °C relative to DNA-DNA pairing at the same duplex concentrations. While relatively large, this increase is still significantly less than the up to ∼30 °C increase observed when AT DNA-DNA pairs are replaced by GC pairs, suggesting the stacking interactions between A+T LNA-DNA base pairs are significantly weaker than those between unmodified GC base pairs. Our study illustrates the sensitivity of LC ordering in dense DNA solutions to a single nucleotide modification and demonstrates that LNA modifications can provide a new mechanism for tuning the stability of nucleic acid-based materials.

Chiral nematic liquid crystals are one-dimensional photonic band-gap materials whose reflection wavelength can be well tuned by temperature, but only limited and irreversible tuning can be achieved by electric fields. In contrast, oblique heliconical chiral nematic materials blueshift with <1kV/mm fields applied along the helix axis, whereas chiral ferroelectric nematic liquid crystals can be redshifted by <0.1kV/mm fields applied perpendicular to the helix axis. Here we demonstrate that in ferroelectric nematic liquid crystals, the reflection color can be reversibly tuned also by electric fields applied along the helix axis. In sandwich cells assembled with bare conducting indium tin oxide (ITO) substrates, the reflectivity peak wavelength increases by up to 200 nm under fields up to 0.4 kV/mm. When the ITO substrates are treated with an electrically insulating polymer layer, the reflectivity shift is suppressed. We propose a theoretical model assuming helical deformation of the helix axis under electric field. This model accounts for all observations and also yields an estimate of the splay elastic constant which is challenging to determine by other methods. Our findings expand understanding of ferroelectric nematic liquid crystals and suggest potential applications in both tunable reflectors and energy-efficient smart windows.

In-phase adenine-tracts (A-tracts) introduce intrinsic bending to double stranded DNA resulting in banana-shaped macromolecules. In this study, we investigate how such sequence-dependent bending influences DNA-based liquid crystalline (LC) phases formed by gapped DNA (GDNA) constructs. By incorporating three in-phase A-tracts into each duplex arm, we created a GDNA construct with bent duplexes and examined the LC phases they form using temperature-resolved synchrotron small-angle X-ray scattering and polarizing optical microscopy. Like the analogous constructs containing straight (rod-like) duplexes, the bent constructs exhibit a transition from bi-layer smectic-B phase to a monolayer smectic-A phase, although at ~30 °C lower temperatures. By comparing the monolayer spacing between the bent and straight constructs, we estimate a bending angle of ~11° per A-tract at room temperature and at physiologically relevant salt and cDNA. The bending angle decreases with increasing DNA concentration and temperature. Moreover, we demonstrate that divalent cations enhance the stability of the smectic-B phase up to ~30 mM Mg2+ but reduce it beyond that. The reduced thermal stabilities of the bilayer and in-layer ordering of bent duplexes imply reduced propensity for DNA condensation and heterochromatin formation under physiological conditions.

The polarization and density modulation associated with antiferroelectric ordering is studied experimentally as a function of temperature in two ferroelectric nematic liquid crystals, the prototypical single compound (DIO) and a commercial mixture (FNLC919). The modulation wavenumber qA is determined by small angle X-ray diffraction from the weak smectic-like density wave (wavenumber qS = 2qA) that accompanies the polarization modulation. Results for qS and the saturated value of the polarization are analyzed in terms of Landau theory previously developed to describe the para-/antiferro-/feroelectric sequence of phase transitions in solid ferroelectrics. The analysis indicates that the polarization modulation is reasonably well approximated by a simple sinusoid in the antiferroelectric phase of DIO, whereas in FNLC919 the modulation develops a strongly soliton-like profile (with sharply decreasing wavenumber) close to the antiferro- to ferrolectric transition.

We investigate the impact of poly-adenine (poly-A) sequences on the type and stability of liquid crystalline (LC) phases formed by concentrated solutions of gapped DNA (two duplex arms bridged by a flexible single strand) using synchrotron small angle X-ray scattering and polarizing optical microscopy. While samples with mixed sequence form layered (smectic) phases, poly-A samples demonstrate a columnar phase at lower temperatures (5-35 C), not previously observed in GDNA samples, and a smectic-B phase of exceptional stability at higher temperatures (35-65 C). We present a model that connects formation of these LC phases with the unique characteristics of poly-A sequences, which manifest in various biological contexts, including DNA condensation and nucleosome formation.Competing Interest StatementThe authors have declared no competing interest.