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Liquid crystals (LCs) represent a challenging group of materials for direct transmission electron microscopy (TEM) studies due to the complications in specimen preparation and the severe radiation damage. In this paper, we summarize a series of specimen preparation methods, including thin film and cryo‐sectioning approaches, as a comprehensive toolset enabling high‐resolution direct cryo‐TEM observation of a broad range of LCs. We also present comparative analysis using cryo‐TEM and replica freeze‐fracture TEM on both thermotropic and lyotropic LCs. In addition to the revisits of previous practices, some new concepts are introduced, e.g., suspended thermotropic LC thin films, combined high‐pressure freezing and cryo‐sectioning of lyotropic LCs, and the complementary applications of direct TEM and indirect replica TEM techniques. The significance of subnanometer resolution cryo‐TEM observation is demonstrated in a few important issues in LC studies, including providing direct evidences for the existence of nanoscale smectic domains in nematic bent‐core thermotropic LCs, comprehensive understanding of the twist‐bend nematic phase, and probing the packing of columnar aggregates in lyotropic chromonic LCs. Direct TEM observation opens ways to a variety of TEM techniques, suggesting that TEM (replica, cryo, and in situ techniques), in general, may be a promising part of the solution to the lack of effective structural probe at the molecular scale in LC studies. Microsc. Res. Tech. 77:754–772, 2014. © 2014 Wiley Periodicals, Inc.

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b S Supporting Information ' INTRODUCTIONSmall molecule and polymeric liquid crystalline materials have applications in a multitude of areas, ranging from displays, optical/ electronic imaging, data storage, and stress/temperature sensing to chemical/fire resistance and artificial muscle actuation. 1 The design of typical molecular architectures that facilitate thermotropic liquid crystalline behavior is well documented. Molecules with structural anisotropy, i.e., a rigid moiety with high aspect ratio are frequently utilized to impart the order inherent in a liquid crystalline phase. Functionalization of these cores with flexible alkane chains of varying length then provides the structural complexity necessary to hinder crystallization while preserving liquid crystalline order. As such, thermotropic liquid crystals are inherently stimuli-responsive, as they can undergo a range of thermally induced transitions between glassy/crystalline, liquid crystalline, and isotropic states. Examples of thermotropic liquid crystalline small molecules or polymers that are also designed to respond to specific chemical stimuli are less prevalent. 2 One approach to designing a chemo-responsive liquid crystal involves incorporating a metal-binding ligand into the mesogenic core. In addition to introducing additional, nonthermal, stimuliresponsive behavior incorporation of metal ions into liquid crystalline materials offers the opportunity to impart a number of additional properties upon these systems. Chemical sensing, 3 catalysis, 4 and a host of biological applications 5 highlight the many practical properties of organic metal-coordinating species, while some specific lanthanide complexes also exhibit interesting luminescent and paramagnetic properties. 6 Additionally, the vast number of transition and lanthanide metal ions offers a multitude of potential geometries and binding motifs, which can be utilized to design the specific shapes necessary to retain, induce, or otherwise impact liquid crystallinity. This approach enhances the traditional thermotropic liquid crystal in two ways. First, ligands can be envisioned that, upon binding a metal ion, lose their original liquid crystalline order and thus offer a useful method of amplification for detection schemes and other applications. 7 Second, ligands that bind metal ions and retain, change, or acquire liquid crystalline order (metallomesogens) can also be envisaged. 8 The 2,6-bisbenzimidazolylpyridine (Bip) ligand offers a versatile scaffold from which highly functionalized derivatives can be accessed (e.g., 1 Et , Figure 1). 9,10 Piguet and co-workers have prepared a number of low molecular weight mesogenic Bip derivatives and investigated the effects of metal binding on their liquid crystalline properties. 11 Noting that the incorporation of a large metal center disrupts the organization of simpler Bip mesogens, 12 they decorated the Bip core with a highly alkylated liquid crystallinity-enhancing moiety in the 5 0 positions, which allowed access to a range of metallomeso...

Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155 ) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138 in the SmA and about 146 in the nematic phase). Dielectric and SHG measurements give evidence that in the SmA phase a polar structure can be induced by application of an electric field which disappears in the isotropic liquid phase. The electric field not only leads to a slight textural change even in the SmA phase but also polar-type electric current response (P S about 200 nC cm À2 ) is observed. This unusual electrooptical behaviour is discussed on the basis of the orientation of polar clusters formed by the bent molecules. In the paper we not only attempt to characterize the mesophases and to describe their physical properties, but we also show that these types of molecules represent the borderline between bent-shaped and calamitic liquid crystals.

The existence of the elusive biaxial phase has been the subject of much discussion since it was predicted by Freiser in 1970. More recently, there have been numerous attempts to find a thermotropic liquid crystal that exhibits a biaxial phase and with this, conflicting reports about whether such a phase has been positively identified in bent-core liquid crystals. One reason for the discrepancy is that there is currently no way to rule out surface effects or anchoring transitions, both of which may give a false positive identification of a uniaxial-biaxial nematic transition. We have developed a technique that uses a magnetic field to align the uniaxial director, thus widening its application to any bent-core nematic material.

Colorectal cancers (CRCs) exhibit differences in incidence, pathogenesis, molecular pathways and outcome depending on the location of the tumor. The transcriptomes of 27,927 single human CRC cells, from three left-sided and three right-sided CRC patients were profiled by scRNA-seq. Right-sided CRC harbors a significant proportion of exhausted CD8 T cells of a highly migratory nature. One cluster of cells from left-sided CRC exhibiting states preceding exhaustion and a high ratio of "pre-exhausted" to exhausted T cells were favorable prognostic markers. Notably, we identified a novel RBP4+ NTS+ subpopulation of cancer cells that exclusively expands in left-sided CRC. Tregs from left-sided CRC showed higher levels of immunotherapy-related genes than those from right-sided CRC, indicating that left-sided CRC may have increased responsiveness to immunotherapy. Antibody-dependent cellular phagocytosis (ADCP) and antibody-dependent cellular cytotoxicity (ADCC) induced by M2-like macrophages were more pronounced in left-sided CRC and correlated with a good prognosis in CRC.

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