Cholesteric Liquid Crystalline Phase Research Articles

Supramolecular ordering of DNA in the cholesteric liquid crystalline phase: an ultrastructural study

Aqueous solutions of 146-base pair DNA fragments form a cholesteric liquid crystalline phase in the range of about 160-290 mg/ml. We present a structural analysis of this phase by comparing the data obtained from polarizing and electron microscopy. This phase shows multiple aspects or "textures" which are presented and interpreted. They mainly depend on the orientation of the structure relative to the observation plane and on the nature, distribution, and amount of defects present in the phase. These defects are then analyzed with the two methods, and the molecular orientations can be defined precisely in their core. The biological interest of such structural analyses is discussed in relation with the understanding of chromatin structure and function.

Organic reactions in liquid-crystalline solvents. Regiochemical control of bimolecular pericyclic reactions by cholesteric and smectic liquid-crystalline solvents

The addition reactions of N-phenyl,N-para-biphenyl, and N-para,para'-terphenyl-maleimide with 7-dehydrocholesteryl acetate have been carried out in the isotropic and cholesteric liquid crystalline phases of a series of steroidal mesogens, and in the isotropic, smectic A, and smectic B phases of 4,4'-dialkylbiphenyl mesogens at temperatures between 180 and 240°C. In isotropic solvents, mixtures of four adducts are obtained, in relative yields that are essentially independent of the maleimide substituent. The tree major products (two ene-adducts and one Diels-Alder adduct) are formed via transition states in which the long molecular axes of the reactants are oriented perpendicular to one another, while the fourth (minor) product is an ene-adduct formed via a transition state with a parallel relative orientation of the reactants' long molecular axes

Liquid crystalline phase‐formation behavior of cellulose cinnamate

AbstractCellulose cinnamates with degrees of substitution (DS) of up to 2.3 were prepared by a reaction of cellulose with cinnamoyl chloride in pyridine. The cellulose cinnamate was found to form a cholesteric liquid crystalline phase at the concentrations higher than a critical concentration in some organic solvents. The critical concentration showed tendencies to be higher for the cellulose cinnamate with higher DS and with higher degree of polymerization (DP). Influences of formation of liquid crystalline phase and of irradiation with UV light on the physical strength of the cellulose cinnamate film were investigated and both were found to make the breaking strength and modulus of elastisity of the film higher.

Second-Harmonic Generation in Noncentrosymmetric p-Nitroaniline Spontaneously Crystallized by Quenching from Lyotropic Liquid Crystalline Poly(γ-benzyl-L-glutamate)

We have found a new crystal structure of p-nitroaniline (pNA) formed by quenching a mixture of poly(γ-benzyl-L-glutamate) (PBLG) and pNA in its lyotropic cholesteric liquid crystalline phase. Strong second-harmonic generation (SHG) has been observed in this quenched material, indicating the formation of a noncentrosymmetric structure of pNA. The maximum SH light intensity observed in PBLG/pNA=3:2 is as large as 3.6 times that of 2-methyl-4-nitroaniline (MNA) powder. We have confirmed, on the basis of X-ray and differential scanning calorimetry (DSC) measurements, that the SHG-active crystal of pNA is segregatedly formed from the crystal domain consisting of α-helical PBLG.

Overview of partial orientational and positional ordering in concentrated systems

This paper provides an overview of the static behavior of systems with partial orientational and positional ordering of the species. The understanding of the static behavior provides the foundation needed to understand the dynamic properties of such systems, which are described in more detail in other papers in this issue. More specifically, this paper provides an overview of the fact that species of different dimensions exhibit similar types of partial ordering of the species. This paper further provides an overview of liquid crystalline (LC) phases and molecules, including discussions of types of chemical structures (both rigid and semiflexible) in LC molecules (both nonpolymeric and polymeric); thermotropic and lyotropic LCs; nematic and multiple smectic LC phases; reentrant nematic LC phases; cholesteric LC phases and blue phases; smectic crystal phases; columnar phases; micelles and lamellar LC structures; LC phase transitions; LC glasses; viscosities of LC phases; and dynamic textures and patterns in LC phases.

Interpretation of diffusion measurements in cholesterics

Abstract An interpretation of the pitch and time dependence of diffusion in the cholesteric liquid crystalline phase is proposed. Experimental results on nematics twisted by chiral dopands are discussed. The model predicts a decay of the translational diffusion coefficient D p in the helix direction with the observation time and a decrease of D p with shorter pitch length P o, in accord with experiment. From comparison with experimental data it is concluded that rotational diffusion in these samples is a collective phenomenon.

Texture of cholesteric cellulosic gels and films observed by electron microscopy

It is now well known that cellulose derivatives form cholesteric liquid crystalline phases in the bulk and in solution. The supramolecular arrangement of the cholesteric materials gives them unique optical properties. Light entering the cholesteric domain is partially reflected. Circularly-polarized light with the same handedness as the helicoidal structure and a wavelength corresponding to the cholesteric pitch will be reflected by the mesophase. Free-standing films displaying a cholesteric order are thus strongly desirable for many different applications.Even though transmission electron microscopy (TEM) seems to be the perfect technique to extend results obtained by optical microscopy, this approach has been used infrequently in the study of liquid crystals. Liquid crystals don't lend themselves to electron microscopy because of their fluidity. Lyotropic systems are destroyed by evaporation of the solvent under high vacuum. However, under specific conditions, solid cellulosic films can retain a helicoidal organization. Classical embedding and ultra-sectioning can thus be applied on such materials as long as they do not dissolve in water.

Evidence for random parallel and anti-parallel packing between neighbouring cholesteryl 4-(2-anthryloxy)butyrate (CAB) molecules in the cholesteric liquid-crystalline phase. Identification of the four photodimers fromCAB

Abstract The packing arrangements of cholesteryl 4-(2-anthryloxy)butyrate (CAB) have been investigated in its cholesteric liquid-crystalline, neat isotropic, and solution isotropic phases by analysing the distributions of photodimers obtained from each. The four photodimers of CAB have been identified unambiguously. Their distribution indicates that neighbouring pairs of CAB in the liquid-crystalline phase experience orientations that are parallel and anti-parallel with about equal probability.

Optical rotatory dispersion from liquid crystalline solutions and films of hydroxypropylcellulose

Abstract The chiroptical properties of (hydroxypropyl)cellulose (HPC) in methanol are measured by optical rotatory dispersion (ORD), both in isotropic solution and in the cholesteric liquid crystalline phase. The ORD spectra of HPC films cast from lyotropic solution are also examined. Isotropic solutions of HPC in methanol provide no ORD evidence for the presence of a helical conformation, or for concentration-induced changes in conformation. The ORD curve of HPC in methanol, when expressed as specific rotation, is independent of polymer concentration for isotropic solutions containing between 1 and 43 per cent polymer by weight. From the slope of Drude plots, the Cotton effect responsible for the observed ORD curve occurs at 175–180 nm. However a 45 per cent liquid crystal-line solution exhibits plain positive dispersion, and the magnitude of the specific rotation is also much greater than that found for solutions containing less than 43 per cent polymer. Results for more concentrated solutions confirm t...

Lines in liquid crystalline phases of biopolymers

DNA, PBLG and xanthan are three polymers which give cholesteric liquid crystalline phases in concentrated solution. We analyzed different structures encountered in these phases that we call « lines » because they all appear, in the polarizing microscope, as illuminated lines in a dark background. They correspond either to molecular discontinuities, or to surfaces separating two phases of different nature or to twist walls which are observed in homeotropic textures where the twist is prevented. The analysis of such structures gives information about the nature of the phase in which they are observed.

Freeze-Fractures in Cholesteric Mesophases of Polymers

Abstract Freeze-fracture techniques were used to study the cholesteric liquid crystalline phases of three polymer solutions (PBLG, Xanthan, HPC). All fracture surfaces showed a regular stratification corresponding to the half-helical pitch, P/2. Electron microscopy permits very small helical pitches (P/2 < 300 Å) to be observed and defects and textures previously analyzed in the polarizing microscope can be easily recognized: edge dislocations, +π and −π disclinations etc. Fractures oblique with respect to the cholesteric stratification present a regular distribution of parallel series of nested arcs whose nature is directly related to the cholesteric organization but the shape of the arcs can be modified by the presence of steps in the fracture surface. The position of these steps is related to the fracture direction with respect to the cholesteric stratification. Fractures through polygonal fields are very different from the classical patterns observed in the polarizing microscope since we are observing the distribution of molecular orientations in a plane instead of a projection of the whole structure. In such fields, cholesteric layers are distorted to form domes and basins and fractures normal to the axes of these deformations produce spiral and saddle-shaped patterns.

Liquid-crystalline solvents as mechanistic probes. 31. Identification of factors responsible for inhibition of .alpha.,.omega.-bis(1-pyrenyl)alkane intramolecular excimer formation in some cholesteric liquid-crystalline phases

Liquid-crystalline solvents as mechanistic probes. 31. Identification of factors responsible for inhibition of .alpha.,.omega.-bis(1-pyrenyl)alkane intramolecular excimer formation in some cholesteric liquid-crystalline phases

Thermotropic cellulose derivatives with flexible substituents

Three kinds of fully substituted cellulose derivatives, cellulose triheptanoate (CTH), tri-O-heptyl cellulose (THC) and tri-O-2-butoxyethyl cellulose (TBC) were prepared. These polymers, having a side chain of similar length but of differing chemical structure, were found to show significantly different therraotropic behavior: TBC forms a cholesteric liquid crystalline phase at temperatures between 50 °C and 165 °C, the cholesteric pitch covering the region of visible lights. THC also displays a cholestric structure at temperatures between 80 °C and 130 °C with pitches on the order of several micrometers. CTH appears to show liquid crystallinity only in a very limited temperature range around 100 °C.

Circular dichroism microscopy of compact forms of DNA and chromatin in vivo and in vitro: cholesteric liquid-crystalline phases of DNA and single dinoflagellate nuclei.

Two highly condensed structures of DNA have been analyzed in the circular dichroism (CD) microscope: the cholesteric liquid-crystalline phase of DNA and the nucleus of a dinoflagellate (Prorocentrum micans). In both cases, the DNA shows a helical cholesteric organization, but the helical pitch equals about 2500 nm in the first case and 250 nm in the second one. Since the absorption band of DNA is located at 260 nm, the reflection and absorption bands are well separated in the cholesteric phase of DNA and are overlapping in the dinoflagellate nucleus. However, both structures give a very strong negative CD signal at 265 nm. We show that this very strong signal cannot correspond to a Borrmann effect, i.e., to a superposition of the absorption and reflection bands, but is a differential absorption of left versus right circularly polarized light. This anomalous differential absorption is probably due to a significant scattering of light, inside of the structure, which produces a resonance phenomenon in the absorption band of the chromophore. Therefore, for any helical structure containing a chromophore, the apparent CD can be expressed as CD = [(epsilon L - epsilon R)cl] + (psi L - psi R) + (SL - SR) The first term is true absorption and is located in the absorption band of the chromophore, and the last term is true scattering and is observed at the wavelength corresponding to the helical pitch of the structure. The second term (psi L - psi R) corresponds to the anomalous differential absorption observed in dense superhelical structures of DNA. It superimposes to the first term in the absorption band of the chromophore. psi L - psi R is a measure of the perfection of the helical structure and of the density of chromophores in the material. Intercalative dyes [ethidium bromide and meso-tetrakis(4-N-methylpyridyl)porphine (H2TMpyP-4) and its nickel(II) derivative (NiIITMpyP-4)] were inserted in the dinoflagellate chromatin. The CD signal recorded in their absorption band mimics the signal observed in the absorption band of DNA. In both structures, the negative sign of the CD at 265 nm indicates that the twist occurring between DNA. In both structures, the negative sign of the CD at 265 nm indicates that the twist occurring between DNA molecules is left-handed, and we show that this situation is the most frequently encountered in vivo and vitro.

Formation of liquid-crystalline phases by two phenyl-alkanoyl esters of O-(hydroxypropyl)cellulose and the (3-chlorophenyl)urethane of cellulose

Thermotropic and lyotropic liquid-crystalline phases were produced from three newly synthesized cellulose derivatives, namely the phenylacetate and 3-phenylpropionate of O-(hydroxypropyl)cellulose, and the (3-chlorophenyl)-urethane of cellulose. The liquid-crystalline phases were characterized with regard to the shape of the molecular chains, helicoidal cholesteric structure (pitch and order parameter), refractive indices, optical behaviour, and textures in the polarizing microscope. The cellulosic-chain direction in thermotropic liquid crystals having banded textures was shown to lie perpendicular to the bands, and a positive birefringence was demonstrated for a cholesteric liquid-crystalline phase.

Spatial organization of collagen in annelid cuticle: order and defects

The epidermis of Paralvinella grasslei (Polychaete, Annelida) is covered by an extracellular matrix, the cuticle, mainly composed as in other annelids of superimposed layers of non-striated collagen fibrils. The collagen fibrils of annelid cuticle are shown to be composed of parallel and sinuous microfibrils (thin sections and freeze-fracture replicas). The 3-dimensional organization of collagen is characterized by 2 different types of geometrical order: (a) Fibrils form a quasiorthogonal network, whose structure is comparable to that of a "plywood"; (b) Fibrils are helical, and goniometric studies show that microfibrils present a definite order within each fibril, which is termed "cylindrical twist". These 2 characteristics are those which have recently been evidenced in "blue phases", i.e., liquid crystals which are closely related to cholesteric liquid crystalline phases. Non-fluid analogues of cholesteric liquids are widespread among invertebrate cuticles and the presence of blue phase analogues suggests that a self-assembly mechanisms is involved in cuticle morpho-genesis, which is derived from that governing blue phase growth. The cuticular network presents local rearrangements of fibrils called "defects", despite the fact that they are elaborate structures which trigonal and pentagonal singularities. Branched fibrils are regularly observed. We discuss the involvement of these pattern disruptions in the cuticle growth process.

ChemInform Abstract: Solid‐State 31P NMR Studies of DNA Liquid Crystalline Phases. The Isotropic to Cholesteric Transition.

AbstractAqueous solutions of short DNA fragments with Na+ as counterion form a cholesteric liquid crystalline phase when the DNA concentration exceeds a critical value dependent on DNA length and solution ionic strength.

Determination of the order parameter in cholesteric liquid crystalline phase cellulose derivatives solutions by refractometry

The macroscopic order parameter S in the cholesteric liquid crystalline phase of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) solutions was calculated using refractive index data. Haller's extrapolation approach was used. The S calculated was compared with the S predicted from Doi's theory. The calculated values of S for HPC and EC solutions were in the range of 0.4–0.8 within our experimental range, and agreed with the predicted values of S obtained with Doi's theory. This result suggests that Haller's approach is valid for determining S for liquid crystalline solutions of HPC and EC, despite the scattering of the data at higher temperatures.

Cholesteric liquid crystalline phases given by three helical biological polymers : DNA, PBLG and xanthan. A comparative analysis of their textures

The cholesteric liquid crystalline phases of three polymers of biological interest have been investigated: PBLG (a polypeptide), DNA (a polynucleotide) and xanthan (a polysaccharide). The textures (and the defects which they contain) of these three mesophases are analysed and compared The main difference concerns focal lines which apparently do not occur in PBLG, are rare in DNA but occur frequently in xanthan. The frequency of occurrence of the different types of rotation and translation dislocations were measured : - π disclinations are always of the λ- type and + π disclinations are mainly λ +. Among polymers, differences exist in the distribution of translation dislocations but in these three cases, when only one layer is added, the defect may be either τ- λ+ or λ- τ + which distinguishes polymer mesophases from those of small molecules previously studied The main textures found in classical (small molecule) cholesteric phases were also obtained (i.e. planar textures, textures showing numerous disclinations and polygonal textures). However, they are more difficult to analyse especially for DNA and xanthan mesophases where the helicoidal pitches are small and may not be resolvable in an optical microscope.

Measurements of self-diffusion in the cholesteric liquid-crystalline phase by means of 13C NMR

We propose a new approach for the calculation of diffusion effects in NMR spectra of cholesteric liquid crystals (ChLC). 13C NMR spectra were recorded at 15.68 and 22.64 MHz for two ChLC mixtures with pitch lengths of 5.9 and 3.2 μm. The lineshape of the calculated spectra was fitted to the experimental with the diffusion constant D being the only fitting parameter. We obtained values of D ranging from 3 to 20 × 10 −12 m 2 s −1 for different temperatures. The activation energies in the order of 40 kJ/mol are comparable to the values in the nematic phase.