Liquid crystals in biology I. Historical, biological and medical aspects

In our present state of knowledge, it is useful to assume that all matter, in the solar galaxy at least, is composed of atoms and subatomic particles which function independently or interact in accordance with the laws of physics to form molecules, coacervates or other aggregates. For practical purposes, these states of matter are recognizable in the three-dimensional terrestrial world as solids, liquids and gases. This differentiation suffices also for molecular studies but, to understand the properties of mobile organic and especially of living matter fundamentally, it is necessary to investigate and conceptualize how immaterial electromagnetic and electrostatic processes produce changes in state, phase and entropy compatible with self-replication, molecular memory and vitality This possibility exists in the properties of the liquid crystal (LC) as a mesophase in thermal and optical phase transitions, i.e. as an enantiomorphic intermediate form of matter which can form complex, self-replicating, ordered structures and macromolecules, easily recognizable in everyday TV visual displays, electronic communication devices and computers. It is suggested that, in prebiotic terrestrial situations, matter possessing these properties of the LC was a precursor in the evolution of living from inanimate matter and, in the lyotropic form, in the processes of life thereafter.     

Orientational processes in the yarns of high-molecular-mass cellulose acetate in vapors of nitromethane and its mixture with water

The phenomenon of spontaneous changes in the linear dimensions (elongation-contraction) is described for commercial and laboratory samples of acetate yarns processed by wet spinning from high- molecular -mass cellulose diacetate in vapors of a mesophas ogenic solvent (which is able to form a lyotropic LC phase with the polymer), nitromethane, and its mixtures with water. The thermodeformational, elastic- plastic, physicomechanical, and surface characteristics of the yarns at different stages of their spontaneous deformation are analyzed. When samples are treated with probe vapors, orientational processes in the polymer matrix are activated, and this observation makes it possible to prepare yarns with improved physicomechanical characteristics and with low linear density. A new phenomenon (to our knowledge) of cyclic three- stage deformation of acetate monofilaments in nitromethane vapors is discovered. This evidence is interpreted from the standpoint of phase (amorphous glassy-liquid crystalline state) and conformational transitions as well as by the mechanism of interaction between polymers and solvent vapors and related development of the LC phase.     

Liquid crystals in biology II. Origins and processes of life

Part II of this review elaborates a hypothesis presented in Part I (2003 Liq. Cryst. 30, 541) and earlier publications. This hypothesis proposes that specified naturally occurring substances in the aqueous lyotropic mesophase of the liquid crystalline state of matter possess the ability to replicate, polymerize spontaneously and engage in further transitions to form ordered two- and three-dimensional layered, cubic, helical and spherulitic structures resembling those described geochemically, and observed experimentally in elementary forms of living substance. This ability uses energy originating in the kinetics of particles showing Brownian movements, spin and tensions at liquid-liquid and solid-liquid interfaces. Energy is derived also from chemiosmosis, phosphorylation, negative entropy and bonding by covalent and electro-weak forces to build macromolecules in ordered sequences of lipids, peptides and nucleic acids. These can polymerize to form glyco- and lipo-proteins, polynucleotides, anabolic and catalytic enzymes, plausibly and causally associated with the morphogenesis, metabolism and replication of protista, plankton and other primitive forms of life observed in prebiotic pools and surfaces of the cooling litho-hydrosphere of planet earth.

Interactions in these ecological niches would undoubtedly promote biochemical evolution compatible with self-organization of diversified living processes. These phenomena reveal plausible, natural mechanisms for formation of bilayer membranes with ionic channels, and other ordered structures providing spaces in which oxidative reactions and syntheses may proceed. All of this can be linked causally to early steps in animation of matter in accordance with laws governing particle physics and chemistry, templates and the general logic of molecular memories expressed in polynucleotides and proteins. Phenomena indicative of transfer of information, cellular organization, metabolism and transmission of neural signals are identifiable additionally as mechanisms for diversification and evolution. There are, however, credibility gaps in trying to extend this reasoning to sexual reproduction, speciation, competitive survival and ontogeny in the higher plants and metazoa. Various probabilities are discussed in statistical and physico-chemical terms. It is suggested that these could justify the hypothesis in so far as natural processes are sufficient to engender conditions for emergence of primitive life and Darwinian evolution in eco-niches of terrestrial space and measurable time. But there are also, in the unique utilization of energy, exploitation of advantages and adaptive capabilities of organisms at all levels to changing environmental stresses, many indications of teleonomic forces operating in ways for which there is no explanation in accordance with the laws of physical or chemical processes. This might be because understanding of particle physics and wave mechanics is insufficiently deployed in molecular biology, or because the laws of physics are scientifically incomplete in this respect.     

Polymer nanostructure development of fluorinated and aliphatic monoacrylates in smectic liquid crystals via photopolymerization

To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase.     

Polymer nanostructure development of fluorinated and aliphatic monoacrylates in smectic liquid crystals via photopolymerization

To develop viable polymer stabilized liquid crystal systems, it is crucial to understand the factors that affect polymer nanostructure evolution. This work examines the influence of the photopolymerization of aliphatic and fluorinated monoacrylate monomer within a room temperature smectic liquid crystal (LC). Additionally, the effect of LC order on polymerization kinetics, monomer and polymer organization, and the effect of the polymer on LC properties have been examined. Through this work, insight has been gained regarding the impact that the introduction of a fluorinated monoacrylate monomer has on polymerization kinetics, LC organization, and monomer/polymer segregation and organization within a polymer/LC system. Fluorinated moieties lower the surface energy of the monomer to enhance segregation between the smectic layers of the LC as compared with an analogous aliphatic monomer. Additionally, the enhanced segregation significantly increases the polymerization rate in the smectic phase and drives the continued segregation of the fluorinated polymer during and after polymerization. Fluorination also leads to the formation of an ordered polymer nanostructure if polymerized in ordered LC phases. This ordering is particularly evident when the fluorinated monomer is polymerized in the smectic phase in which the monomer is organized between the smectic layers of the LC. In addition, the ordered polymer structure found with the fluorinated monomer in the smectic phase leads to continued birefringence above the clearing point of the LC due to surface interactions between the LC and the ordered fluorinated polymer. The continued birefringence offers an exceptional opportunity to examine how factors such as polymer molecular mass and UV light intensity affect the overall polymer morphology of these polymer/LC systems. As the initiator concentration and UV light intensity are decreased, longer polymer chains form lattice-type morphologies; whereas, shorter polymer chains form smoother morphologies that more closely mirror the texture of the LC smectic phase.     

Electro‐optical switches based on polymer and dendrimer filled nematics

Two‐phase systems which can be switched electrically between a light scattering and a transparent state can be prepared based on either a dispersion of well‐defined sub‐micron sized crosslinked polymeric particles in a liquid crystal (LC) matrix (Polymer Filled Nematics, PFN's) or on a dispersion of palmitoyl‐functionalised poly(propylene imine) dendrimers in an LC (Dendrimer Filled Nematics). The present paper describes the preparation of both systems and their properties. The PFN's can be electrically switched between a scattering and a transparent state by an appropriate choice of materials and refractive indices. The preparation of the disperse polymeric phase is separated from the preparation of the polymer/LC blend, which enables control over the morphology of the system. Rather surprisingly, it is found that, due to the rheological properties of the PFN blends, stable films of the blends can be simply produced by conventional coating processes. The dendrimer‐stabilised nematics require extremely low switching voltages to switch from a scattering to a highly transparent state. Moreover, the switching process is totally reversible and hysteresis effects appear to be absent.     

Structural changes in discotic samples during transition from crystal to discotic mesophase as revealed by electron microscopy and diffraction

Classical methods of structural analysis cannot be applied to liquid crystals because higher order reflections disappear during the transition from crystal to liquid crystal due to the reduction in long range orientational and translational correlations. However, in order to relate physical properties to the molecular architecture, it is essential to have information about molecular positions and orientations in the crystalline state as well as in the liquid crystalline state. In this work, the transition from crystalline to liquid crystalline phase is carefully monitored and the relationship between the original lattice and the new molecular positions found using electron diffraction. In addition to this, a new high resolution electron-microscopic technique is described in which the positions of molecules in the crystalline and the quenched discotic phase are directly imaged and the defects observed in the crystalline and LC phase compared and quantitatively analysed.     

盘状液晶材料的研究进展

盘状液晶分子容易形成柱状堆积的超分子组装体, 由于分子在液晶态具有一定的流动性, 使得组装体具有良好的结构缺陷自修复功能. 因此具有特定芳香共轭结构的盘状液晶分子可以呈现较高的导电特性, 能够有效传输电荷, 具有制备光电器件的潜在应用价值. 本文主要介绍以苯环、苯并菲、六苯并蔻、苝和肽菁为中心核的盘状液晶材料, 其分子结构的化学修饰对液晶性能的影响, 液晶材料在有机发光二极管(OLED)、有机场效应晶体管(OFET)和太阳能电池器件中的应用, 以及盘状液晶材料相关的动力学研究进展.     

Clustering of nonpolar organic compounds in lipid media: evidence and implications

Semivolatile and nonpolar organic compounds, such as persistent organic pollutants, have a tendency to accumulate in organic matter phases from air and water. Once they enter living systems, they partition into lipids/waxes and can exert adverse toxicological effects. The current paradigm assumes that such chemicals are uniformly distributed in organic phases such as soil organic matter, plant waxes, and animal lipids and that partitioning and adsorption processes occur independently of intermolecular contaminant interactions. With use of a recently developed technique, two-photon excitation microscopy coupled with autofluorescence allowed us to directly visualize novel organic chemical behavior in living vegetation and other matrixes. Here, we show for the first time that polycyclic aromatic hydrocarbons, which were uniformly distributed in pure oils and waxes at the beginning of a study, form clusters over time. The number and diameter (typically 0.2-5 microm) of these clusters are dependent on the physical-chemical properties of the compound-media systems and time. This behavior is not accounted for in current models of phase partitioning of chemicals and may have important implications for understanding their environmental fate and their potential toxicological effects.     

Frustrated molecular packing in highly ordered smectic phase of side-chain liquid crystalline polymer with rigid polyacetylene backbone

Using poly(5-{[(4'-heptoxy-4-biphenylyl)carbonyl]oxy}-1-pentyne) as an example, we demonstrate the incorporative accommodation of the rigid polyacetylene backbones and the mesogenic pendants, which leads to a highly ordered smectic (Sm) phase with a frustrated structure. The polymer exhibits a recognizable sheetlike molecular shape due to its rigid backbone and relatively short spacer (three methylene units), and the building block of the liquid crystalline (LC) phase is the whole molecule. In the LC phase, five layers of the molecules stack as a smectic A (SmA) block, and adjacent SmA blocks glide halfway of the molecular width from one to another. In scanning tunneling microscopy (STM) experiments, the STM tip scrape is found to generate a regular nanopattern with periodic electron conductivity, of which the spacing is determined by the side-chain length.     

Structural evolution of liquid-crystalline solutions of hydroxypropyl cellulose and hydroxypropyl cellulose-based nanocomposites during flow

The phase state and orientation and dissipative characteristics of biphasic LC HPC-water solutions and filled systems formed on their basis during shear flow are studied by various methods. The concentration of solutions is selected on the basis of the corrected phase diagram constructed with the use of optical interferometry. Flow curves and concentration dependences of viscosity provide additional information about the phase state and structure of the samples and the role of fillers in the rheological properties of solutions. X-ray diffraction data are obtained with the use of a Couette cell consisting of two coaxial capillaries. In the case of a clay suspension in water, practically no orientation is attained. However, in the isotropic 30% solution, clay particles easily orient, a result that indicates an important role of the viscoelasticity of a medium in the orientation process. The development of orientation of HPC macromolecules and clay particles in relation to the shear rate is analyzed separately for systems with the biphasic matrix (LC + isotropic phase). In addition, the time decay of the orientation parameter during relaxation is investigated. It is shown that higher shear rates cause a more rapid relaxation of orientation, for which recovery of the cholesteric helix typical for LC solutions of cellulose derivatives in the equilibrium state plays an important role. Order parameters (separately for the two components) are calculated, and their evolution with the shear rate and total deformation is investigated for systems containing clay nanoparticles (also the structure-active component) in LC solutions. On the basis of these data, it is hypothesized that clay particles form the columnar mesophase, which, under certain conditions, may transform into the discotic mesophase. This transition is responsible for a certain decrease in the order parameter of HPC apparently due to the instability effect of the director. It is found that shearing substantially affects the structure of the system composed of two mesophase species; specifically, it either facilitates the reinforcement of one of them or provokes structural transitions.     

Main‐chain,thermotropic, liquid‐crystalline,hydrogen‐bonded polymers of 4,4′‐bipyridyl with aliphatic dicarboxylic acids

A series of main‐chain, thermotropic, liquid‐crystalline (LC), hydrogen‐bonded polymers or self‐assembled structures based on 4,4′‐bipyridyl as a hydrogen‐bond acceptor and aliphatic dicarboxylic acids, such as adipic and sebacic acids, as hydrogen‐bond donors were prepared by a slow evaporation technique from a pyridine solution and were characterized for their thermotropic, LC properties with a number of experimental techniques. The homopolymer of 4,4′‐bipyridyl with adipic acid exhibited high‐order and low‐order smectic phases, and that with sebacic acid exhibited only a high‐order smectic phase. Like the homopolymer with adipic acid, the two copolymers of 4,4′‐bipyridyl with adipic and sebacic acids (75/25 and 25/75) also exhibited two types of smectic phases. In contrast, the copolymer of 4,4′‐bipyridyl with adipic and sebacic acids (50/50), like the homopolymer with sebacic acid, exhibited only one high‐order smectic phase. Each of them, including the copolymers, had a broad temperature range of LC phases (36–51 °C). The effect of copolymerization for these hydrogen‐bonded polymers on the thermotropic properties was examined. Generally, copolymerization increased the temperature range of LC phases for these polymers, as expected, with a larger decrease in the crystal‐to‐LC transition than in the LC‐to‐isotropic transition. Additionally, it neither suppressed the formation of smectic phases nor promoted the formation of a nematic phase in these hydrogen‐bonded polymers, as usually observed in many thermotropic LC polymers. The thermal transitions for all of them, measured by differential scanning calorimetry, were well below their decomposition temperatures, as measured by thermogravimetric analysis, which were in the temperature range of 193–210 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1282–1295, 2003     

Theoretical Definition of a Functional Group and the Molecular Orbital Paradigm

It is the purpose of this review to demonstrate that the empirical classification of the observations of chemistry in terms of the properties assigned to functional groups is a consequence of and is predicted by physics. This is accomplished by showing that the atoms and functional groups of chemistry can be identified with bounded space-filling objects whose properties are defined by quantum mechanics. The quantum mechanical definition of a group is combined with a new pictorial representation of its form to obtain a unified picture which should make it eminently recognizable to chemists. This picture, when combined with the demonstrated ability of these groups to recover the measured properties of atoms in molecules, is offered as one which meets the expectations a chemist associates with the concept of a functional group. The manner in which this physical definition of a group differs fundamentally from models of functional groups based upon molecular orbital theory is discussed.     

Rheological properties and phase behavior of a hydroxypropyl cellulose-poly(ethylene glycol) system

The relaxation and phase behavior of solutions of hydroxypropyl cellulose in poly(ethylene glycols) of various molecular masses has been studied by dynamic mechanical analysis. The dynamic mechanical data are compared with the results of microinterferometry and polarization-microscopy measurements. The combination of optical and mechanical characteristics makes it possible to construct generalized phase- relaxation diagrams for the binary systems under study. Solutions based on lowmolecular-mass poly(ethylene glycol) are characterized by LC equilibrium. With an increase in the molecular mass of poly(ethylene glycol) in a certain temperature-concentration region, amorphous phase separation takes place and the phase diagram is the superposition of LC and amorphous equilibria. The relaxation properties of the systems are sensitive to the phase state and its transformation.     

Induction of Columnar and Smectic Phases for Spiropyran Derivatives: Effects of Acidichromism and Photochromism

Liquid‐crystalline (LC) properties have been induced in a number of spiropyran derivatives by the addition of methanesulfonic acid. Spiropyran derivatives containing one or two gallic acid moieties with one, two, or three long alkyl chains were prepared. Acid‐induced spiro–protonated‐merocyanine isomerization induced mesomorphism for these materials. Equimolar mixtures of methanesulfonic acid and the spiropyran derivatives with one or two dodecyloxy chains exhibited smectic A phases, whereas the spiropyran derivatives containing the gallic acid moiety with three dodecyloxy chains showed hexagonal columnar phases. On the contrary, photoirradiation of the spiropyran compounds in the bulk liquid state did not lead to the induction of mesomorphism, although the merocyanine form was induced. These results suggest that these merocyanine derivatives with ionic and nonionic moieties cannot simply form nanosegregated LC structures. Complex formation of the merocyanine form with methanesulfonic acid may play a key role in the formation of LC molecular assemblies.     

Thermotropic Luminescent Clustomesogen Showing a Nematic Phase: A Combination of Experimental and Molecular Simulation Studies

Octahedral Mo₆ nanoclusters are functionalized with two organic ligands containing cyanobiphenyl (CB) units, giving luminescent hybrid liquid crystals (LC). Although the mesogenic density around the bulky inorganic core is constant, the two hybrids show different LC properties. Interestingly, one of them shows a nematic phase, which is particularly rare for this kind of supermolecular system. This surprising result is explained by using large‐scale molecular dynamic simulations.     

Organization of four thermotropic liquid crystals of different polarities on model liquid and solid surfaces

The thermodynamic and surface properties of four structurally related thermotropic liquid crystals (LC) were investigated to understand their organization at gas-liquid and gas-solid interfaces. In this study, LC with a benzoyloxy azobenzene mesogenic core substituted with heptyloxy and/or dioxyethylene ether groups were used. The propensity of the LC to form self-assembled multilayers was demonstrated in the films spread at the air/aqueous interface using the Langmuir technique and Brewster angle microscopy and on the solid surfaces of Chromosorb WHP and silica, using differential scanning calorimetry. On the basis of the results obtained, a molecular recognition mechanism underlying separation processes using LC as selectors in gas chromatography is proposed.     

“Crystal memory” Affects the Properties of Peptide Hydrogels – The Case of the Cyclic Tyr-Tyr dipeptide

In this work a relationship between the crystal form and morphology and rheological properties of peptide-based hydrogels is examined. We show, that under favorable circumstances a correlation between a starting solid material and a self-assembly processes in solution can exist, leading to different properties of a resulting soft matter. This observation, together with an in-depth analysis of the influence of stereochemistry of self-assembled (ll ) and (dl ) Tyr-Tyr cyclic dipeptides (cYY) on the observed relationship between gelation and crystallization allowed us to gain a deeper understanding of the peptide hydrogelation processes at a molecular level, using liquid state NMR, rheological studies and scanning electron microscopy. In the course of our studies, several crystal forms of (ll )-cYY has been discovered and described in details using single crystal X-ray diffraction, as well as advanced solid state NMR, X-ray diffraction of powders, thermal analysis, FTIR, circular dichroism and crystal structure prediction (CSP) calculations. Subsequently, we found that while (ll )-cYY easily assembles into hydrogels with different properties depending on the starting solid form, (dl )-cYY always precipitated as one crystal form in the tested conditions. Molecular-level justification for this observation is given.     

Columnar liquid crystalline assembly of a U‐shaped molecular scaffold stabilized by covalent or noncovalent incorporation of aromatic molecules

We report on our serendipitous finding of the anomalous behavior of a novel liquid crystalline (LC) molecule U _H/H , containing a U‐shaped handle. While U _H/H itself shows a bicontinuous cubic (Cub_bi) phase, U _H/H in the presence of pyrene molecules as an external guest forms a hexagonal columnar (Col_h) phase without phase separation. Interestingly, even when the pyrene molecules were covalently attached to U _H/H ( U _Py/Py ), the molecule exhibited a Col_h phase, with a similar columnar geometry to that of U _H/H mixed with pyrene molecules (1–4 equiv.). This result means that no matter how the pyrene moieties are incorporated in the LC system, the resultant material exhibited a similar molecular assembly with a columnar geometry. This finding is interesting because U _H/H and pyrene molecules do not seem to have specific interactions or shape complementarity to form a columnar assembly, as in the case of U _Py/Py . © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 342–351     

Crack Formation and Propagation in Molecular Dynamics Simulations of Polymer Liquid Crystals

In recent papers we have used statistical mechanics to predict multiple phase formation in polymer liquid crystals (PLCs).^[1, 2] Now we have performed molecular dynamics simulations of PLC copolymers as materials consisting of LC islands in flexible matrices. A method for creating such materials on a computer is described. The overall concentration of the LC units, island size, and spatial distribution of the islands (random, in rows, and evenly distributed throughout the material) were varied. Crack formation and propagation as a function of these parameters were investigated. The local concentration of LC units in each chain has been defined. We found that the probability of a crack initiation site goes symbiotically with the local LC concentration. The first small crack is sometimes a part of the path through which the material breaks, however, although several small cracks may evolve at first, some of these never evolve into larger cracks since crack arrest occurs. The results can be used for creation of real materials with improved mechanical properties.