Rod Molecules Research Articles

Liquid-Crystalline Complexes of Mesogenic Dimers Containing Oxyethylene Moieties with LiCF3SO3: Self-Organized Ion Conductive Materials

Mesomorphic dimeric compounds consisting of rigid mesogenic cores and flexible oxyethylene chains have been prepared as liquid-crystalline materials capable of complexing with ionic species. The incorporation of LiCF3SO3 into these materials results in the induction of smectic A phases and significant mesophase stabilization. The ion−dipole interactions between lithium ions and oxyethylene moieties have stabilized the mesomorphic layer structures. Ionic conductivities have been measured for the complexes forming homeotropically aligned molecular orientation of smectic phases. The highest value of conduction, which is observed for the direction parallel to the layer in the smectic A phase, is 5.5 × 10-4 S cm-1. These results suggest that the complexes of LiCF3SO3 with mesogenic rod−coil−rod molecules containing oxyethylene chains can function as self-organized ion conductive materials.

Establishing a degree of order: obtaining high-resolution NMR structures from molecular alignment

I would like to thank Eva de Alba for providing structural data as well as Ad Bax and James Baber for their critical comments.

Quaternary salt formation of optically active helical polymethacrylates having pyridyl group in the side chain

The reaction of diphenyl-3-pyridylmethyl and 1-(3-pyridyl)dibenzosuberyl methacrylates with CH 3I in CHCl 3 at 35°C for 24 h lead to quantitative quaternization of pyridyl group while the reaction using diphenyl-2-pyridylmethyl and 1-(2-pyridyl)dibenzosuberyl methacrylates gave only low degree of quaternization. Single-handed helical poly(diphenyl-3-pyridylmethyl) and poly[1-(3-pyridyl)dibenzosuberyl methacrylate] were also quantitatively quaternized with CH 3I under the above reaction conditions: the former polymer appeared to lose its helical conformation and the chiroptical properties through the reaction while the conformation of the latter polymer seems to survive the quaternization process. The latter polymer quantitatively reacted with decyl and octadecyl iodides in a CHCl 3–DMSO mixture at 55°C to give hairy rod molecules.

Assembly of thick filaments and myofibrils occurs in the absence of the myosin head

We investigated the importance of the myosin head in thick filament formation and myofibrillogenesis by generating transgenic Drosophila lines expressing either an embryonic or an adult isoform of the myosin rod in their indirect flight muscles. The headless myosin molecules retain the regulatory light-chain binding site, the alpha-helical rod and the C-terminal tailpiece. Both isoforms of headless myosin co-assemble with endogenous full-length myosin in wild-type muscle cells. However, rod polypeptides interfere with muscle function and cause a flightless phenotype. Electron microscopy demonstrates that this results from an antimorphic effect upon myofibril assembly. Thick filaments assemble when the myosin rod is expressed in mutant indirect flight muscles where no full-length myosin heavy chain is produced. These filaments show the characteristic hollow cross-section observed in wild type. The headless thick filaments can assemble with thin filaments into hexagonally packed arrays resembling normal myofibrils. However, thick filament length as well as sarcomere length and myofibril shape are abnormal. Therefore, thick filament assembly and many aspects of myofibrillogenesis are independent of the myosin head and these processes are regulated by the myosin rod and tailpiece. However, interaction of the myosin head with other myofibrillar components is necessary for defining filament length and myofibril dimensions.

Axisymmetric entry flow of semi-dilute xanthan gum solutions: prediction and experiment

Experimental observations of the flow patterns in axisymmetric entry for rigid rod molecules are presented. The features of the flow are a large secondary flow vortex whose size is relatively independent of the flowrate, a vortex which increases in size with the rigid rod polymer concentration, decreases in size as the solvent viscosity increases, and increases as the contraction ratio increases. The secondary flow vortex sizes predicted and observed for dilute and semi-dilute rigid fibre suspensions are similar to those observed for the semi-dilute rigid rod xanthan gum solutions. Also, rounding a corner in the contraction had no effect on the observed asymmetric entry flow of the rigid rod molecular solutions. Good agreement was observed between the dimensionless re-attachment length for a 0.04% w/w xanthan gum solution and the predicted secondary re-attachment length from Binding [J. Non-Newtonian Fluid Mech. 27 (1988) 173–189] which used the independently measured extensional viscosity in the prediction. The agreement between experiment and observation confirmed Binding's assertion that the fluid will show vortex enhancement if its steady shear viscosity undergoes shear thinning more rapidly than its extensional viscosity undergoes elongational thinning. Vortex enhancement for fluids with constant extensional viscosity and steady shear viscosity, as observed, agreed with predictions by Debbaut et al. [J. Non-Newtonian Fluid Mech. 29 (1988) 119–146] and Debbaut and Crochet [J. Non-Newtonian Fluid Mech. 30 (1988) 169–184]. From the data presented it would be fair to speculate that normal stresses impede vortex growth while elongational thickening increases vortex growth.

Effect of electrostatic interactions on the structure and dynamics of a model polyelectrolyte. I. Diffusion

The dynamics of a 20 base pair oligonucleotide is studied by dynamic light scattering-photon correlation spectroscopy and depolarized Fabry–Perot interferometry. The 20 base pair oligonucleotide is a well-defined, albeit short, rigid rod molecule that serves as a model for polyelectrolyte solution dynamics. The effects of added salt on the solution rotational and translational dynamics are examined in detail as functions of the 20-mer concentration. Coupled mode theory together with counterion condensation theory gives good predictions for the effects of salt on the translational diffusion of the 20-mer at the relatively low oligonucleotide concentrations studied. Comparison of the experimental results with these theories shows that the effective charge density of the polyion in solution is approximately equal to the reciprocal of the product of the Bjerrum length and the counterion charge, νeff≅1/NλB. Calculation shows that the numerical solution of the coupled mode theory matrix gives a better fit of our measured polyion diffusion coefficients than the approximate equation derived by Lin, Lee, and Schurr. Simple approximations for the effective rod length, Leff=L+κ−1, and effective rod diameter, deff=d+κ−1, are used to model the thermodynamic-hydrodynamic interactions for charged rodlike molecules and to make predictions for the diffusion second virial coefficient as a function of added salt concentration. This alternative to the coupled mode theory also gives good agreement with experiment. The rotational diffusion constants of the oligonucleotide measured by depolarized Fabry–Perot interferometry show a slowing down of the rotation at low added salt concentrations as the oligonucleotide concentration is increased.

Structural aspects of the nematic-isotropic transition in liquid crystals: an investigation using a development of the Lebwohl-Lasher lattice model

This paper explores further the predictions of the Lebwohl-Lasher model [1] for the description of order in a liquid crystalline system, especially in the region of the nematic- isotropic transition. The model is based on a lattice, each cell of which contains a director representing the long axis of a rod molecule. The energy of each director is determined by the relative orientations of its six nearest neighbours, and the probability of a director orientation being moved to another chosen at random depends on the Boltzmann function of the difference between the old and the new energies in accord with the normal Monte Carlo procedure. The validity of this model to describe this transition has been demonstrated in several previous studies [2–16] and its simplicity permits calculations over a statistically significant number of molecules. Preliminary studies of the model behaviour have been made below the transition temperature in order to investigate the influence of boundary conditions. The simulated P2 and P2/P4quantities are compared both with experimental data and with the theory of Maier and Saupe [17]. The predictions of the model are analysed in the normal way using the Ornstein-Zernike expression for pairwise correlation functions, while this expression is modified in order to describe the short-range order which is superimposed on the background level of long-range order present in the nematic phase. The model's predictions of enthalpy changes across the transition are compared with calorimetric data from the literature [18]. The opportunity of working with a large model is taken to extend the Zhang plot to test for the presence of first order character within the transition. A structural description of the transition is proposed, based on the molecular director maps, and the identification of more ordered and less ordered regions achieved by the analysis of the distribution of local energies into two sub-distributions with widths in accord with the mean values of their energies. As the transition is approached from above, the isotropic melt structure is seen to contain nematic nuclei which increase in volume fraction with decreasing temperature. At the transition these nuclei appear to join to give a percolating phase having a single orientation across the model. With decreasing temperature within the nematic region, isolated regions of disorder become continually smaller with a corresponding increase in the overall order parameter (P2). This paper focuses particularly on the structural implications of the predicted nematicisotropic transition. It is recognized that aspects characterizing the physics of the transition can be obtained through averaging energy parameters over very large numbers of cycles, and using models as large as possible. While the 503 model presented here is particularly large by current standards, it is designed in this way to show a representative picture of the structure in the transition region. The aspect of the work reported, despite the availability of a large model, does not seek to generate better averages than previously reported, and the calculation of some such parameters in the earlier sections is to check that the model is behaving properly and in accord with results reported previously.

Molecular Dynamics of "Hairy Rod" Molecules in the Solid State: Poly(.gamma.-methyl L-glutamate)-co-(.gamma.-n-octadecyl L-glutamate) in Solution-Cast Films

We present the thermal, structural, and dynamic properties of poly(γ-methyl L-glutamate)-co-(y-octadecyl L-glutamate) with 30% octadecyl chains in solution-cast films. This substance is an example of a so-called hairy rod molecule. The peptide backbones form stiff rods which are surrounded by the side chains. The structure of the solution-cast film was measured by WAXS and SAXS. We found amorphous and crystalline side chain parts. The melting point of the crystalline side chains is ca. 293 K. The thermal properties of these hairy rods are investigated with differential scanning calorimetry, and the dynamic properties are measured between 110 and 370 K with broad-band dielectric spectroscopy (10 -2 -10 9 Hz) and variable-temperature 13 C-CP/MAS solid-state NMR. Three dielectric-active relaxation processes are observed : Two processes have a temperature dependence according to the Williams-Landel-Ferry (WLF) equation. They approach each other with decreasing temperature and merge at about 238 K, i.e., the calorimetric glass transition temperature. These two processes are discussed as fluctuations of the main chain and the surrounding side chain groups. The third relaxation process has an Arrhenius-type temperature dependence with an activation energy of 43 kJ/mol. It is assigned to fluctuations of the carboxyl groups in the side chains. The variable-temperature NMR results confirm that one of the WLF-type relaxations is caused by the side chains. These NMR experiments also show that the main chains undergo no local relaxation in the investigated temperature and frequency region and stay in the α-helix conformation.

In situ thermoset molecular composites

AbstractThe polymerization of rigid rod polymer precursors in a reactive matrix precursor, which is later cured in the mold, constitutes the in situ process. A poly‐azomethine (PAM) was used as the rigid rod molecule. The resin used was an epoxy. We discuss the prediction of mechanical properties using micromechanics equations for chopped fiber composites. The chemistry used to synthesize the rigid rod polymer PAM in the epoxy precursor is reviewed. Approaches to better control the cure of these epoxy systems through cure kinetics and cure rheology studies completes the thermoset in situ molecular composite process. There was a 71% increase in tensile modulus in comparison to that of the neat epoxy resin. Molecular modeling simulations and continuum mechanics are used to help understand these findings. PAM/epoxy systems were used as a matrix material in the fabrication of unidirectional glass fiber/(PAM/epoxy) structural composites. © 1994 John Wiley & Sons, Inc.

Orientation fluctuations in concentrated solutions of hairy-rod polymers

Photon correlation spectroscopy in the depolarized geometry was employed to measure the orientation relaxation correlation functionC(q,t) in poly(p-2,5-dodecyl-1,4-phenylene)/toluene solutions at different scattering wavevectorsq. The large optical anisotropy of this hairy rod molecule with an average lengthL=117 nm allowed a detailed analysis of both amplitude and shape ofC(q,t) that revealed two mechanisms for relaxing the orientation fluctuations in the concentrated regime (10<cL3<230). The comparison of the rotational diffusivity and the anisotropic scattering intensity with theoretical, simulation and experimental results of rigid rods indicated quantitatively different behavior for the present stiff-chain bearing two long side groups per repeating unit.

Pressure effects and thermal stability of myosin rods and rod minifilaments: fluorescence and circular dichroism studies.

In the present study hydrostatic pressure was applied upon both skeletal myosin rod molecules and rod minifilaments to learn more of the intra- and intermolecular interaction behavior of myosin. Applied pressure disassembled the rod minifilaments into individual rod molecules and dissociated each myosin rod molecule into two chains of alpha-helix. The dissociation and disassembly profiles of these systems were obtained by measuring their fluorescent anisotropy under pressure. The mid-disassembly pressure of rod minifilaments at 0.4 mg/mL concentration was 430-490 bar. However, dissociation of two helical strands of rod molecules occurred at a much higher pressure, with a mid-disassembly pressure of 1300 bar at this concentration. These results indicate that the intramolecular interactions occurring between two alpha-helical chains of a rod molecule are much more stable under pressure than the intermolecular interactions that occur among rod molecules in a minifilament. The regions in the rod molecules involved in filament assembly were investigated through usage of both the intrinsic fluorescence of tryptophan residues and the extrinsic fluorescence of 6-acryloyl-2-(dimethylamino)naphthalene (acrylodan) labeled cysteine residues. The blue spectral shifts upon minifilament formation suggest the participation of both light meromyosin (LMM) and subfragment-2 (S-2) regions of myosin rods in the filament formation. Profiles of thermal unfolding of myosin rod molecules and rod minifilaments were obtained by circular dichroism measurement. The multiple transitions exhibited upon unfolding profiles indicated the presence of more than one structural domain, each correlating with a cooperative transition. The domain transitional temperatures were found to be 1-4 degrees C higher for rods in minifilaments than those for rod molecules in a solution of similar ionic composition, indicating that all structural domains are involved in filament assembly. Furthermore, the domain transitional temperatures for rod molecules in a buffer containing 0.6 M NaCl were 6-8 degrees C higher than those for rod molecules in 5 mM sodium pyrophosphate buffer, suggesting that each structural domain of a rod molecule becomes stabilized at 0.6 M NaCl solution.

Molecular dynamics of rigid rod polymers

Molecular dynamics (MD) calculations have been used to study the behaviour of isolated rigid rod molecules of poly( p-phenylene), poly( p-phenylene benzobisthiazole) and poly( p-phenylene benzobisoxazole). The molecular mechanics force field was initially modified to improve agreement between minimized structural geometries and available X-ray data, as well as results from semiempirical molecular orbital calculations. The MD simulations show the molecules to be surprisingly flexible, with changes in end-to-end distances as large as 16%. An examination of the energies (calculated by various methods) associated with out-of-plane bending deformation, suggests that the rigid rod polymers may in fact be even more flexible than the simulations indicate. The results provide rationalizations for the relatively short persistence lengths measured in solution and for bending observed in high-resolution electron micrographs of these materials.

Curing kinetics of liquid-crystalline epoxy resins

Abstract By endcapping mesogenic rigid rod molecules with reactive epoxy groups a novel class of liquid-crystalline thermoset has been obtained. In fact is has been shown that the nematic molecular arrangement is sustained over the crosslinking reaction of liquid-crystalline epoxy resins when the curing reaction is carried out in the thermal stability range of the liquid-crystalline phase. Calorimetric analysis was used in characterizing the isothermal cure. An unsophisticated model is proposed for evaluating the activation energies of the crosslinking reaction. For liquid-crystalline epoxy resins lower activation energies result with respect to the cure reactions for non liquid-crystalline epoxy resins.

Dynamic melt rheology. II: Re‐examining the relationship of g′ in oscillatory rheometry to the melt elasticity

AbstractIn oscillatory rheometry, since the dynamic storage modulus (G′) represents the elastic component of the viscoelastic melt, it has been a rather common practice to associate it with the melt elasticity. Although this assumption might be valid in many instances, there can be exceptions as well. In the present study, we have chosen polypropylene/talc system to demonstrate an exception. For example, the melt elasticity decreases with increasing talc content as revealed by extrudate die swell, entrance pressure drop, and elastic compliance measurements; the opposite trend being reflected by G′. We can envision similar exceptions when stiffening agents are added to a polymer melt, e.g., rigid rod molecules. We are suggesting that G′ represents the elastic modulus or stiffness of the melt, which in certain situations might not reflect elasticity, i.e., the ability of a melt to recover from a deformation. The implication of the present manuscript is that caution be exercised when relating G′ to the melt elasticity of a polymer.

Optical And Magnetic Properties Of Rigid Rod Conjugated Molecules

ABSTRACTA series of new stable fiinctionalised aryl ethynyl compounds bearing nitronyl-nitroxy and galvinoxyl radicals were synthesised as potential organic magnets with optical properties. Our goal is to construct biradicals in linear or broken rod molecules with the aim of probing i) the efficiency of the conjugation for the intramolecular spin exchange, and / or ii) the inter-Molecular Magnetic interaction between the neighboring radicals in the solid state Materials.We focused our attention on the preparation of phenoxy, and galvinoxyl biradicals of the conjugated phenyl and thienyl diethynyl Moieties. The synthesis of these new components will be presented. Their optical and magnetic properties will be discussed both in solution and in the solid state.

Self-assembled monolayers of parent and derivatized [n]staffane-3,3(n-1)-dithiols on polycrystalline gold electrodes

Synthesis of the terminally disubstituted rigid rod molecules, [n]staffane-3,3 (n-1) -dithiols, n = 1-4, and their singly functionalized derivatives carrying and acetyl or a pentaammineruthenium(II), [Ru(NH 3 ) 5 ] 2+ , substituent is described. Self-assembled monolayers of the neat [n]staffane derivatives and of their mixtures with n-alkyl thiols were prepared on polycrystalline gold electrodes

The di-.pi.-methane rearrangement. 226. Molecular rods: synthesis and properties

Our earlier synthetic methodology affording bicyclo [2.2.2] octyl [1]-rod systems proved inadequate for [4]-rods. New synthetic approaches were developed, and [3]-and [4]-rod molecules were obtained. Sodium-potassium coupling was employed to afford the longer rod units. A radical anion approach gave lower yields. Hybrid rods with aromatic rings interposed were also synthesized

Study of the Lowest Electronic States in a Polythiophene Oligomer, α-Sexithienyl, by One and Two-Photon Spectroscopy

Abstract α-sexithienyl (T6) is a large rigid rod molecule with twelve conjugated double bonds. The electronic structure of T6 has been investigates by one-photon and two-photon spectroscopy as well as by photoconductivity. From the single crystal polarized spectra at 4.2K we observe that the lowest allowed π-π transition (λmax = 478 nm) is polarized parallel to the long molecular axis and a second intense transition at 370 nm is polarized parallel to the short in plane axis. The two-photon excitation spectra in polycristalline thin films have been investigated at 4.2 K in the spectral range between 910 and 1180 nm of the fundamental laser radiation. The intense two-photon absorption band at 544.9 nm is assigned to the 2lAg exciton band origin. The lowest “gerade” exciton level lies therefore at 898 cm−1 above the lowest one-photon allowed 11Bu exciton level. The photophysics of T6 is studied by photoconductivity and one-photon excitation spectroscopy. An efficient pathway for carrier generation open up at...

Electron microscopic observation of suprastructure constructed by inorganic rod molecule, imogolite.

Lyotropic liquid crystals formed by inorganic rigid rod molecules, imogolite, were observed directly by transmittion and scanning electron microscopies.

Three-dimensional structure of frozen-hydrated paracrystals of myosin rod

Myosin rod, the tail fragment of myosin, aggregates into various structures at physiological ionic strength. One form, the type II paracrystal, a thin, ribbon-like species, has recently been studied using conventional electron microscopy and was shown to possess two-dimensional order and, further, is likely to be useful in the investigation of the arrangement of myosin molecules in the backbone of the vertebrate muscle thick filament (Ward & Bennett, 1989). We have now examined this aggregate in the frozen-hydrated state by cryo-electron microscopy. Image analysis indicated that the projected structure has the same p12, plane group symmetry as seen after negative staining. A three-dimensional map, calculated from projections, indicated that the structure comprises a bilayer arrangement of strands of grouped rod molecules, with the strands parallel in each layer. The layers themselves are related by screw symmetry. Strands in adjacent layers have opposing polarity with their long axes at an angle of 32 degree to each other. Protein density measurements, carried out on unstained specimens using electron energy-loss spectroscopy, showed that the 44 X 13 X 13 nm unit cell is composed of 40% protein. The density measurements indicated that 9-12 rod molecules pass through each strand. Modelling rod molecules with 43 nm parallel overlaps in a body-centered tetragonal lattice produced a strand that compared favorably with the reconstructed strand. The size and content of these strands suggests that they are analogous to subfilaments observed in the vertebrate myosin thick filament.