DNA cholesteric pitch as a function of density and ionic strength

The nature of chiral interactions among chiral biopolymers, such as DNA, protein alpha-helices, and rodlike virus particles, remains elusive. In particular, a satisfactory model connecting molecular chiral interactions and the pitch of the resulting chiral mesophases is lacking. We report the measurement of short-fragment (146-bp) DNA cholesteric spherulite pitch as a function of osmotic pressure, average DNA interaxial spacing, and salt concentration. We determined cholesteric pitch and interaxial spacing by polarizing optical microscopy and x-ray scattering, respectively, from which the twist-angle between DNA molecules can be calculated. Surprisingly, we found that decreasing ionic strength resulted in weaker chiral interactions between DNA chains, as evidenced by the decrease in the twist-angle, and consequent increase in the cholesteric pitch, for a fixed interaxial spacing. We propose that this behavior can be explained by increased smearing-out of the helical charge pattern along DNA as the Debye screening length is increased.     

Formation of the regular, optical isotropic phase of low molecular weight DNA molecules modified by cis-dichlorodiammineplatinum

It is shown that condensation of DNA molecules of low molecular mass (less than 1 X 10(6) in NaClO4-containing solution of poly(ethylene glycol) brings about formation of cholesteric liquid crystal phase; pattern of this phase is presented. It has been found by means of X-ray analysis and polarization microscopy that at certain level of modification with cis-dichlorodiammineplatinum (II) the DNA molecules instead of cholesteric structure form an ordered optically isotropic phase. The problem about the causes of the formation of such phase and about the pattern of spatial organisation of adjacent DNA molecules in it remains open.     

Synthesis and characterization of hydroxyethyl chitosan grafted by carboxyl ending DOVOB dendrimer: A novel liquid crystalline polymer

A novel chitosan derivative, hydroxyethyl chitosan grafted 3,4,5-tris[p-(n-dodecyloxy)-m-methoxybenzyloxy]benzoate (HECS-g-DOVOB) was prepared via grafting dendrimer 3,4,5-tris[p-(n-dodecyloxy)-m-methoxybenzyloxy]benzoic acid (DOVOB acid) onto hydroxyethyl chitosan (HECS). The structure of HECS-g-DOVOB was investigated by means of FTIR, ¹H NMR, UV and circular dichroism (CD). The degree of substitution was measured to be about 0.39 per glucose unit. The DOVOB acid was able to self-assemble into a thermotropic hexagonal columnar liquid crystalline phase showing fan-like texture, the aqueous HECS solution formed lyotropic cholesteric liquid crystal showing fingerprint texture. Whereas, HECS-g-DOVOB formed lyotropic cholesteric liquid crystal in concentrated DMSO solution with a planar texture, which was different to that of both DOVOB and HECS. The cholesteric pitch of HECS-g-DOVOB is much smaller than that of HECS. The fluorescence spectrum of HECS-g-DOVOB shows excimer fluorescence which is very similar to the dendrimer is a good indication for light-emitting polymeric material.     

DNA mesophases induced by spermidine: structural properties and biological implications.

Conditions of formation of DNA aggregates by the addition of spermidine were determined with 146 base pair DNA fragments as a function of spermidine and NaCl concentration. Two different phases of spermidine-DNA complexes are obtained: a cholesteric liquid crystalline phase with a large helical pitch, with interhelix distances ranging from 31.6 to 32.6 A, and a columnar hexagonal phase with a restricted fluidity in which DNA molecules are more closely packed (29.85 +/- 0.05 A). In both phases, the DNA molecule retains its B form. These phases are always observed in equilibrium with the dilute isotropic solution, and their phase diagram is defined for a DNA concentration of 1 mg/ml. DNA liquid crystalline phases induced by spermidine are compared with the DNA mesophases already described in concentrated solutions in the absence of spermidine. We propose that the liquid crystalline character of the spermidine DNA complexes is involved in the stimulation of the functional properties of the DNA reported in numerous experimental articles, and we discuss how the nature of the phase could regulate the degree of activity of the molecule.     

Phase transitions of concentrated DNA solutions in low concentrations of 1:1 supporting electrolyte

Transitions between isotropic and liquid crystalline phases of concentrated solutions of DNA with an average contour length (500 A) near the persistence length were examined in 0.01 M supporting 1:1 electrolyte (predominantly NaCl). A quantitative phase diagram describing the transitions occurring over a DNA concentration range from 100 to 290 mg/mL and temperatures from 20 to 60 degrees C was constructed from solid-state 31P-nmr data and examination of the morphologies of the mesophases by polarized light microscopy. Three anisotropic phases were observed in solutions with DNA concentrations of 160-290 mg/mL: an unidentified, weakly birefringent phase termed "precholesteric," a true cholesteric phase with pitch approximately 2 microns, and a third, presumably more highly ordered phase. Comparison with previous studies showed that the critical concentration for anisotropic phase formation and the nature of the phases formed by these DNA molecules are not strongly affected by decreasing the supporting electrolyte concentration from approximately 0.2 M to 10 mM. There are, however, profound effects of decreasing the supporting electrolyte concentration on the width of the transition from isotropic to totally anisotropic solutions, and the nature of the transitions between phases. Decreasing the supporting electrolyte concentration significantly increases the concentration range of persistence of the isotrophic phase, and results in the formation of triphasic solutions (isotropic and two liquid crystalline phases). Values of the critical DNA concentrations for anisotropic phase formation from the theory of A. Stroobants et al. [(1986) Macromolecules 19, 2232 to 2238] were found to be significantly lower than the observed values for any reasonable estimate of the effective radius, probably because of the relatively short lengths of DNA fragments examined in the present study. Comparison of the experimentally determined DNA concentrations required for anisotropic phase formation with the values predicted from Flory's lattice statistics theory, which explicitly considers the rod length, permitted estimation of the effective DNA radius. The estimated radius was inconsistent with effective radii calculated from Poisson-Boltzmann (P-B) theory based on a supporting electrolyte concentration of 10 mM, but was in fair agreement with P-B theory assuming that Na+ DNA contributes approximately 0.24 Na+ counterions/nucleotide to the effective free sodium ion concentration.     

Liquid crystal formation in supercoiled DNA solutions

The critical concentrations pertaining to the liquid crystal formation of pUC18 plasmid in saline solutions were obtained from (31)P nuclear magnetic resonance, polarized light microscopy, and phase equilibrium experiments. The transition is strongly first order with a broad gap between the isotropic and anisotropic phase. The critical boundaries are strongly and reversibly dependent on temperature and weakly dependent on ionic strength. With polarized light microscopy on magnetically oriented samples, the liquid crystalline phase is assigned cholesteric with a pitch on the order of 4 microm. Preliminary results show that at higher concentrations a true crystal is formed. The isotropic-cholesteric transition is interpreted with lyotropic liquid crystal theory including the effects of charge, orientation entropy, and excluded volume effects. It was found that the molecular free energy associated with the topology of the superhelix is of paramount importance in controlling the width of the phase gap. The theoretical results compare favorably with the critical boundary pertaining to the disappearance of the isotropic phase, but they fail to predict the low concentration at which the anisotropic phase first appears.     

Physical properties of cholesteryl esters

Cholesteryl esters, the intracellular storage form and intravascular transport form of cholesterol, can exist in crystal, liquid crystal and liquid states. The physical state of cholesteryl esters at physiologic temperatures may be a determinant of their pathogenicity. This review has surveyed saturated aliphatic cholesteryl esters of chain length 1 to 24 carbons and a series of medium-chained unsaturated cholesteryl esters from chain lengths 14 to 24 carbons. A systematic study of transition temperatures by polarizing microscopy and enthalpies by differential scanning calorimetry has provided unifying concepts concerning the phase behavior as a function of chain length and unsaturation. Neat cholesteryl esters show chain-length dependence of transition temperature and enthalpy of both the crystal and liquid crystal transitions. Double bond position along the fatty acyl chain affected stability of the liquid crystal phases; a smectic phase was not observed for any cholesteryl ester with a double bond more proximal than delta 9. 13C NMR spectroscopy in the isotropic liquid phase has provided evidence suggesting a balance of ring-ring vs. chain-chain interactions as a determinant for isotropic liquid----cholesteric vs. isotropic liquid----smectic transitions. Specifically, anisotropic molecular motions of the steroid ring are greater for cholesteryl esters forming a cholesteric phase than a smectic phase from the melt. Chain-chain interactions apparently predominate in smectic phase formation. The X-ray diffraction patterns of cholesteryl esters as a function of chain length reveal several isostructural series and known single crystal data are presented. A chain length depending on the periodicity of the smectic phase is observed which may be different for saturated vs. unsaturated esters. In summary, the phase behavior of cholesteryl ester molecules is complex and cannot be determined a priori from the phase behavior of component cholesterol and fatty acid. The data presented here should provide insight into the biological behavior of this lipid class.     

Polyamine structural effects on the induction and stabilization of liquid crystalline DNA: potential applications to DNA packaging,gene therapy and polyamine therapeutics

DNA undergoes condensation, conformational transitions, aggregation and resolubilization in the presence of polyamines, positively charged organic molecules present in all cells. Under carefully controlled environmental conditions, DNA can also transform to a liquid crystalline state in vitro. We undertook the present work to examine the ability of spermidine, N⁴-methylspermidine, spermine, N¹-acetylspermine and a group of tetramine, pentamine and hexamine analogs of spermine to induce and stabilize liquid crystalline DNA. Liquid crystalline textures were identified under a polarizing microscope. In the absence of polyamines, calf thymus DNA assumed a diffused, planar cholesteric phase with entrapped bubbles when incubated on a glass slide at 37°C. In the presence of spermidine and spermine, the characteristic fingerprint textures of the cholesteric phase, adopting a hexagonal order, were obtained. The helical pitch was 2.5 µm. The final structures were dendrimeric and crystalline when DNA was treated with spermine homologs and bis(ethyl) derivatives. A cholesteric structure was observed when DNA was treated with a hexamine at 37°C. This structure changed to a hexagonal dendrimer with fluidity on prolonged incubation. These data show a structural specificity effect of polyamines on liquid crystalline phase transitions of DNA and suggest a possible physiological function of natural polyamines.     

A 2H-NMR study of the DNA hydration water in solid Li-DNA assembles

High-resolution ²H-nmr is employed to monitor the D₂O in hydrated solids of Li-DNA prepared from solution by three different methods: lyophilization, slow evaporation of the water, and wet spinning in alcohol. From the spectral shapes and spin–spin relaxation measurements, the DNA in the lyophilized samples is found to be locally ordered with a domain size of ～ 0.4 μm. Much longer range macrosopic ordering is found in samples prepared by slow evaporation of the water. Here the DNA spontaneously assembles into a structure that is probably cholesteric, in which the pitch axis is perpendicular to the plane on which the DNA dried. The wet-spinning method produces macroscopically, uniaxially oriented DNA molecules with a maximum helix axis disorder of 12°. To aid in the comparison between calculated and experimental line shapes, a two-dimensional technique is employed to separate the contributions to the line width arising from DNA static disorder, magnetic inhomogeneities, and spin–spin relaxation.     

Binding of Mg2+, Cd2+, and Ni2+ to liquid crystalline NaDNA: polarized light microscopy and NMR investigations

The interaction of the divalent metal ions Mg(2+), Cd(2+), and Ni(2+) with liquid crystalline NaDNA solutions (molar ratios Me(2+)/DNA-phosphate 相似文献   

Liquid crystal phases of DNA: evaluation of DNA organization by two-photon fluorescence microscopy and polarization analysis

We report on the investigation of the structure of DNA liquid crystal (LC) phases by means of polarization sensitive two-photon microscopy (PSTPM). DNA was stained with fluorescent dyes, an intercalator propidium iodide, or a groove binder Hoechst 3342, and the angular dependence of the intensity of two-photon excited fluorescence emitted by the dye was collected. The local orientation of DNA molecules in cholesteric and columnar LC phases was established on the basis of the relative angle between the transition dipole of the dye and the long axis of DNA helix. Three-dimensional images of the cholesteric phase were obtained making use of the intrinsic 3D resolving ability of two-photon microscopy. We also discuss the influence of dyes on the parameters of DNA LC phases and comment on advantages and limitations of the PSTPM technique in comparison with other LC characterization techniques.     

SCARABAEID BEETLE EXOCUTICLE AS AN OPTICAL ANALOGUE OF CHOLESTERIC LIQUID CRYSTALS

1. A review is given of the optical and architectural analogies between cholesteric liquid crystals and certain insect cuticles (Coleoptera: Scarabaeidae). Earlier observations on the optical properties (reflexion of circularly polarized light and high form optical rotation) are confirmed and extended. Both cholesteric liquid crystals and lamellate cuticle have helicoidal structure (Fig. i). Even though their chemistry and physical states are very different, we are justified in making the analogy, since their optical properties depend primarily on the pitch of their helicoidal architecture. 2. The unusual optical properties were located for the first time in the outer 5 to 20 μ of the exocuticle. This layer is transparent and has regular spacings in the range required for interference colours according to Bragg's law. Among Scarabaeid beetles which show interference colours, we distinguish two types of outer exocuticle. (i) Optically active cuticles which reflect circularly polarized interference colours; show high angles of form optical rotation in transmitted light; and anomalous form birefringence perpendicular to the cuticle surface (reversible by deproteinization). (2) Optically inactive cuticles which show none of the above properties and in which the form birefringence is parallel to the cuticle surface. In the electron microscope the ultrastructure of these two types of outer exocuticle is clearly different. 3. All of the optically active species reflect left hand circularly polarized light, irrespective of the wavelength of the reflected colour. They therefore appear dark when viewed through a right hand circular analyser. The sense of reflected circularly polarized light does not reverse at higher wavelengths as recorded by previous workers. (A simple treatment is given for combinations of various wavelengths with retardation plates of varying values, as used in circular analysers.) We confirm earlier reports that the sense of reflected circularly polarized light is of the opposite sense to the transmitted light. 4. Using monochromatic light we have measured the anomalous dispersion with wavelength of the magnitude of optical rotation for various optically active cuticles. The dispersion curves change from negative values at lower wavelengths to positive values at higher wavelengths, and cross the zero optical rotation axis at a wavelength (AQ) corresponding to the interference colour of each sample. There is reasonable agreement between A₀ and the interference colour calculated from ultrastructural evidence and by comparison with interference filters of known wavelength. A dispersion curve measured for a combined sample of two cuticles with different dispersion curves showed that the resultant is an algebraic summation of the two component curves. 5. We present the first experimental verification of existing mathematical treatments of anomalous form optical rotatory dispersion curves. Although these treatments were derived for cholesteric liquid crystals, they give a reasonable fit to our measured curves for cuticle. We have confirmed from our cuticle dispersion curves that a second zero value for optical rotation occurs at a wavelength higher than A₀, as predicted by the theory of Chandrasekhar and Rao (1968). This has not yet been observed in any cholesteric liquid crystal system. 6. Our evidence shows that in optically active cuticle, interference colour is determined by helicoid pitch. In Lomaptera interference coloration follows the bilateral symmetry of the insect. Hence helicoidal pitch is controlled in a bilaterally symmetrical manner. However, the sense of helicoid rotation is the same all over the beetle and is therefore bilaterally asymmetrical. This supports the view that helicoid pitch is under the local control of the epidermal cells which secrete the cuticle, whereas its sense of rotation may be determined by an extracellular self-assembly process. In view of the self-assembling properties of cholesteric liquid crystals, it is tempting to suggest that helicoidal cuticle could be formed by the stabilization of a liquid crystal. 7. We discuss in detail the differences between optically active and inactive cuticles. The constructive interference colours arising from both types are then briefly compared with other multiple layer reflecting systems in other animals. 8. A detailed comparison is made between the optics of cuticle and cholesteric liquid crystals. The optical analogy provides a two-way contact between cuticle biophysicists and liquid crystal physical chemists.     

The effect of ethidium bromide on the liquid crystalline phases of aqueous DNA.

The influence of the intercalation of ethidium bromide (EB) on the characteristics of the DNA cholesteric and hexagonal mesophases is studied by optical microscopy, circular dichroism, and X-ray diffraction. The distance between DNA rods in the hexagonal phase is not modified by the presence of EB whereas the pitch of the cholesteric mesophase is considerably shortened by the dye. This seems to be related to the stereochemical effect of the intercalation rather than to the presence of a random distribution of the positive charge of the dye.     

Temperature-induced changes of the packing of double-stranded linear DNA molecules in particles of liquid-crystalline dispersions

The circular dichroism spectra of liquid-crystalline dispersions obtained by phase exclusion of linear double-stranded DNA molecules from aqueous saline solutions of polyethylene glycol (120 ≤ C_PEG ≤ 300 mg/mL) have been investigated. The formation of liquid-crystalline dispersions at polyethylene glycol concentrations ranging from 120 to 200 mg/mL was accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism; this is indicative of cholesteric packing of the double stranded DNA molecules in the particles of the dispersion. Liquid-crystalline dispersions formed at PEG concentrations higher than 220 mg/mL and room temperature did not show any abnormal bands in the circular dichroism spectra; this is indicative of hexagonal packing of double-stranded DNA molecules in the particles of the dispersions. Heating of optically inactive liquid crystal dispersions induced a transition of the dispersions into a different state accompanied by the emergence of an abnormal negative band in the spectrum of circular dichroism. This transition is considered within the concept of the transformation of a hexagonal packing of DNA molecules into a cholesteric packing. A qualitative mechanism of such a transition is proposed that is formulated in the terms of the “quasinematic” layers of double-stranded DNA molecules that change their spatial orientation under the competing influences of the osmotic pressure of the solvent, orientational elasticity of the cholesteric packing, and thermal fluctuations.     

A liquid crystalline phase in spermidine-condensed DNA.

Over a large range of salt and spermidine concentrations, short DNA fragments precipitated by spermidine (a polyamine) sediment in a pellet from a dilute isotropic supernatant. We report here that the DNA-condensed phase consists of a cholesteric liquid crystal in equilibrium with a more concentrated phase. These results are discussed according to Flory's theory for the ordering of rigid polymers. The liquid crystal described here corresponds to an ordering in the presence of attractive interactions, in contrast with classical liquid crystalline DNA. Polyamines are often used in vitro to study the functional properties of DNA. We suggest that the existence of a liquid crystalline state in spermidine-condensed DNA is relevant to these studies.     

Formation of liquid-crystalline dispersions of double-stranded DNA-chitosan complexes

Right-handed helical double-stranded DNA molecules were shown to interact with chitosans to form under certain conditions (chitosan molecular weight, content of amino groups, distance between amino groups, ionic strength and pH of solution) cholesteric liquid-crystalline dispersions characterized by abnormal positive band in CD spectrum in the absorption region of DNA nitrogen bases. Conditions were found for the appearance of intense negative band in CD spectrum upon dispersion formation. In some cases, no intense band appeared in CD spectrum in spite of dispersion formation. These results indicate not only the multiple forms of liquid-crystalline dispersions of DNA-chitosan complexes but also a possibility to control the spatial properties of these complexes. The multiplicity of liquid-crystalline forms of DNA-chitosan complexes was attempted to explain by the effect of character of dipoles distribution over the surface of DNA molecules on the sense of spatial twist of cholesteric liquid crystals resulting from molecules of the complexes.     

A 23Na-NMR study of sodium-DNA interactions in concentrated DNA solutions at low-supporting electrolyte concentration

Aqueous solutions of DNA fragments with a contour length (500 A) near the persistence length at DNA concentrations ranging from 10 to 290 mg/mL solvent and a constant supporting electrolyte concentration of 0.01 M (predominantly NaCl) were examined by 23Na-nmr spectroscopy at temperatures of 20, 40, and 60 degrees C. Over the higher portion of this concentration range (greater than 100 mg/ml) the DNA solutions undergo a complex series of transitions between different anisotropic, liquid crystalline phases (T. E. Strzelecka and R. L. Rill, Biopolymers, in press). Counterions in solutions of strong polyelectrolytes are usually described in terms of a two-state model as free or "bound" (influenced by the electrostatic field of the polyanion). The longitudinal relaxation rate (R1 = 1/T1) at all DNA concentrations decreased with increasing temperature, demonstrating fast exchange between free and bound counterions. R1 increased nearly linearly with increasing DNA phosphate/sodium ratio in the isotropic domain until the onset of anisotropic phase formation, in agreement with similar nmr studies conducted at low DNA concentrations. The value of R1,b = 194 +/- 7 Hz obtained for the isotropic phase from 10 to 100 mg DNA/mL at 20 degrees C was in agreement with values reported previously. A nonlinear increase in R1 with DNA concentration was observed upon onset of anisotropic phase formation, indicating an increase in the product of the fraction of bond ions times their relaxation rate (r.R1,b). The spectral lineshape of all isotropic samples was Lorentzian. Spectra of anisotropic samples exhibited low magnitude quadrupole splitting of less than or equal to 400 Hz correlated with appearance of a cholesteric phase with pitch approximately 2 microns. The magnitude of the quadrupole splitting decreased with increasing DNA concentration at low temperatures and increased with concentration at high temperatures. At all concentrations the quadrupole splitting decreased then increased with temperature. These temperature- and concentration-dependent changes in quadrupole splitting are consistent with an angle between the DNA helix axis and the principal component (VZZ) of the local electric field gradient tensor near the "magic angle" of 54.7 degrees.     

Ordering of double-stranded DNA molecules in a cholesteric liquid-crystalline phase and in dispersion particles of this phase

The current notion of the organization of molecules in a cholesteric phase is fairly well substantiated in the case of low-molecular-weight compounds. However, this question is open to discussion in the case of double-stranded nucleic acids. In this work, an attempt to compare the well-known data on the structure of cholesteric phases formed by double-stranded DNA molecules and the results of experimental modeling obtained by the authors has been undertaken. The comparison brings leads to assumption regarding the high probability of the existence of both short-range (positional) and long-range (orientational) order in the arrangement of double-stranded DNA molecules in the liquid crystalline phase. The presence of the orientational order, i.e., the rotation of quasinematic layers of double-stranded DNA molecules through a small angle, determines the formation of a spatially twisted (cholesteric) structure with specific physical and chemical properties. In addition, these results prompt a suggestion on the mode of the ordering of dsDNA molecules in liquid-crystalline dispersion particles and allow these particles to be considered candidate biosensing units.     

Formation of Liquid-Crystalline Dispersions of Double-Stranded DNA–Chitosan Complexes

Right-handed helical double-stranded DNA molecules were shown to interact with chitosans to form under certain conditions (chitosan molecular weight, content of amino groups, distance between amino groups, ionic strength and pH of solution) cholesteric liquid-crystalline dispersions characterized by abnormal positive band in CD spectrum in the absorption region of DNA nitrogen bases. Conditions were found for the appearance of intense negative band in CD spectrum upon dispersion formation. In some cases, no intense band appeared in CD spectrum in spite of dispersion formation. These results indicate not only the multiple forms of liquid-crystalline dispersions of DNA–chitosan complexes but also a possibility to control the spatial properties of these complexes. The multiplicity of liquid-crystalline forms of DNA–chitosan complexes was attempted to explain by the effect of character of dipoles distribution over the surface of DNA molecules on the sense of spatial twist of cholesteric liquid crystals resulting from molecules of the complexes.     

Electrooptical behavior of aqueous (Hydroxypropyl)cellulose liquid crystals containing imidazolium salts

A dynamic control of the cholesteric coloration and optical clarity of aqueous (hydroxypropyl)cellulose (HPC) lyotropics is attainable under a weak electric field by employing a fluctuating ionic additive as P and T(c) shifter (P, cholesteric pitch; T(c), cloud point). The present Article demonstrates some examples of time-evolving gradation in reflection color and transparency for HPC liquid crystals containing various N-alkyl-substituted methylimidazolium salts ([CnMim][X]); this was perceivable when each anisotropic solution was sealed in a layer form between parallel slide glasses spaced by a pair of carbon electrodes and then electrified with a direct circuit. The electrooptical phenomenon was interpreted as being primarily due to generation of a disproportional dislocation of cation (CnMim(+))/anion (X(-)) constituents. Even after the electric supply was ceased, an appreciable potential difference remained in the color-gradated samples. It is suggested that the salt-containing liquid-crystalline system behaves like a quasi-capacitor as a viscous electrolytic medium of high resistance.