Flow Birefringence Method Research Articles

DNA Integration with Silver and Gold Nanoparticles: Enhancement of DNA Optical Anisotropy.

DNA integration with silver and gold nanoparticles was carried out by the chemical reduction of silver and gold ions after the formation of their complexes with high molecular DNA in solution. It is shown that, for a good association of DNA with nanoparticles, the ions of silver and gold should be linked with DNA bases rather strongly. The proposed model of gold interaction with DNA is the coordination of gold to N7 guanine in a major groove followed by the transformation of the GC pair to Hoogsteen's type pairing, in which the gold atom is located between the bases and is bonded simultaneously to N7 guanine and N3 cytosine. For gold and silver nanoparticles associated with DNA, the peak of plasmon resonance shifts relative to that of free nanoparticles in solution. AFM (atomic force microscopy) images of both free and associated with DNA nanoparticles were obtained. Binding of high molecular DNA to gold and silver nanoparticles leads to a decrease in the size of its molecular coil in solution, but the bending rigidity of DNA helix (persistent length) does not change. The almost 3-fold increase in the optical anisotropy of DNA was observed when DNA was associated with gold nanoparticles. This result was obtained with the flow birefringence method using a light source with a wavelength of 550 nm, which is close to the peak of the plasmon resonance of gold nanoparticles. For DNA associated with silver nanoparticles, a similar result was obtained when using a light source with a wavelength of about 410 nm.

DNA Interaction with Head-to-Tail Associates of Cationic Surfactants Prevents Formation of Compact Particles.

Cationic azobenzene-containing surfactants are capable of condensing DNA in solution with formation of nanosized particles that can be employed in gene delivery. The ratio of surfactant/DNA concentration and solution ionic strength determines the result of DNA-surfactant interaction: Complexes with a micelle-like surfactant associates on DNA, which induces DNA shrinkage, DNA precipitation or DNA condensation with the emergence of nanosized particles. UV and fluorescence spectroscopy, low gradient viscometry and flow birefringence methods were employed to investigate DNA-surfactant and surfactant-surfactant interaction at different NaCl concentrations, [NaCl]. It was observed that [NaCl] (or the Debye screening radius) determines the surfactant-surfactant interaction in solutions without DNA. Monomers, micelles and non-micellar associates of azobenzene-containing surfactants with head-to-tail orientation of molecules were distinguished due to the features of their absorption spectra. The novel data enabled us to conclude that exactly the type of associates (together with the concentration of components) determines the result of DNA-surfactant interaction. Predomination of head-to-tail associates at 0.01 M < [NaCl] < 0.5 M induces DNA aggregation and in some cases DNA precipitation. High NaCl concentration (higher than 0.8 M) prevents electrostatic attraction of surfactants to DNA phosphates for complex formation. DAPI dye luminescence in solutions with DNA-surfactant complexes shows that surfactant tails overlap the DNA minor groove. The addition of di- and trivalent metal ions before and after the surfactant binding to DNA indicate that the bound surfactant molecules are located on DNA in islets.

Structural and dynamic characteristics of thermo- and pH-sensitive copolymers of 2-(diethylamino)ethyl methacrylate and 2-deoxy-2-methacrylamido-d-glucose

Polarized luminescence and flow birefringence methods were used in the studies of structural and dynamic characteristics of 2-(diethylamino)ethyl methacrylate and 2-deoxy-2-methacrylamido-d-glucose copolymers with varied content of cationic monomer units while changing temperature, pH and ionic strength of solutions. It was demonstrated that with increasing temperature, nanosecond relaxation times τIMM (which characterize intramolecular mobility of fragments of copolymer chain in solution) increase over a relatively narrow temperature range. Increase in relaxation times indicates strengthening intramolecular interactions and the formation of intramolecular hydrophobic domains. From the obtained flow birefringence data, it follows that in the vicinity of the lower critical solution temperature (LCST) we have molecular dispersed diluted copolymer solutions. The influence of temperature and ionic strength of solutions on the transition temperature were also studied. The observed changes in intramolecular interactions are accompanied by insignificant changes in root-mean-square dimensions of macromolecular coils; however, coils retain their asymmetry.

Effects of a flow field on amyloid fibrillogenesis in a β-lactoglobulin solution

The effects of a flow field on the amyloid fibrillogenesis of β-lactoglobulin (βLG) were investigated using a flow birefringence method and AFM imaging experiments. A 4wt% βLG aqueous solution was incubated at pH 2 and 80°C. A flow field was then applied by stirring at 250 and 474rpm. An incubation without stirring was used as a control sample. Flow birefringence measurements were taken at room temperature from the incubated sample solutions in which an elongational flow field was used. The birefringence pattern obtained indicated that the fibrils formed by the incubation were rigid rod-like molecules. Birefringence relaxation experiments revealed at least two relaxation processes, suggesting a double peaked distribution function for fibrils length. The length distribution of fibrils expected from the birefringence experiments was confirmed by the AFM images of amyloid fibrils. The order of the expected length of the resultant fibrils in both longer and shorter length distributions was those stirred at 250rpm≅474rpm>0rpm. The effects of the flow field applied during the incubation on amyloid fibrillogenesis was discussed on the basis of the rate process consideration. The present results demonstrated that the flow field should be considered as an important factor that regulates the fibrillogenesis of globular proteins.

Conformational and dynamic characteristics of copolymers of N,N-dimethylaminoethyl methacrylate and 2-deoxy-2-methacrylamido-D-glucose

The conformational and relaxation properties of N,N-dimethylaminoethyl methacrylate and 2-deoxy-2-methacrylamido-D-glucose copolymers in solutions are studied by the methods of molecular hydrodynamics (sedimentation, diffusion, viscometry), polarized luminescence, and flow birefringence. Kuhn-Mark-Houwink equations are obtained, and Kuhn statistical segment lengths at various degrees of protonation of amino groups are estimated. It is found that there is a correlation between the Kuhn statistical segment length and the intramolecular mobility of the copolymers.

Molecular, conformational, and optical characteristics of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate) in organic solvents

A number of samples of poly(dodecylammonium-2-acrylamido-2-methylpropanesulfonate)—a comb-like polymer with ionically bound side chains—are obtained by the polymerization of dodecylammonium-2-acrylamido-2-methylpropanesulfonate in an aqueous medium. The samples are obtained in a wide molecular-mass range. Molecular, hydrodynamic, and optical characteristics of the samples are determined by the methods of sedimentation-diffusion analysis, viscometry, and flow birefringence in dilute polymer solutions in chloroform and dimethyl sulfoxide containing small amounts of 0.1 M LiCl. It is shown that conformational and optical characteristics based on hydrodynamic and dynamo-optic investigations agree with the data available for acrylic and methacrylic polymers with the same lengths of side groups. In other words, the character of attachment (covalent or ionic) of long side chains to the backbone has no effect on the conformational and optical characteristics of macromolecules.

Hydrodynamic, conformational, and optical properties of cellulose tridecanoate molecules in solutions

Cellulose tridecanoates of various molecular weights were synthesized, and their characteristics in chloroform and tetrachloroethane solutions were studied by methods of translational diffusion, velocity sedimentation, flow birefringence (Maxwell’s method), and viscometry. The effects of solvent and temperature on the conformational characteristics of the macromolecules under consideration were examined. The anisotropy of the monomeric unit of cellulose tridecanoates was studied, and the contribution of pendant chains to the optical anisotropy of macromolecules of cellulose esters with aliphatic substituents was analyzed.

Optical, dynamic, and electro-optical properties of poly(N-acryloyl-11-aminoundecanoic acid) in solutions

The optical, electro-optical, and dynamic characteristics of poly(N-acryloyl-11-aminoundecanoic acid) in organic solvents and of the sodium salt of its monomer in water were studied via the methods of flow birefringence, equilibrium and nonequilibrium electric birefringence, and dynamic light scattering. It is shown that, in aqueous solutions, the monomer forms coarse particles of both symmetric and asymmetric shapes. The linear dimensions of these particles are estimated from the data of translational and rotational diffusion. Polymer macromolecules in organic solvents feature negative anisotropy of optical polarizability. Contributions of optical microform and macroform effects to the observed flow birefringence are analyzed in detail. The intrinsic optical anisotropy of the monomer unit of the polymer, which correlates well with the corresponding values for comb-shaped polymers of a similar structure, is estimated. It is shown that polymer molecules lack marked intrinsic permanent macromolecular dipoles and that electric birefringence in their solutions is associated with macroscopic induced dipole moments that appear during orientation of the dipole moments of polar groups in side chains of the polymer under application of an electric field.

Effect of the molecular architecture of side radicals on the optical properties of comb-shaped polymers

The optical properties of four comb-shaped polymers of the methacrylic series with different optically anisotropic groups in side chains are studied by the methods of flow birefringence and viscometry. The experimental values of the optical anisotropy are compared with theoretical estimates calculated in terms of the additivity principle of polarizabilities of valence bonds. It is shown the optical properties of comb-shaped polymers significantly depend on the position (even or odd) of optically anisotropic side groups relative to the main chain.

Self-organization and morphological characteristics of selenium-containing nanostructures based on rigid-chain polymers

Macroinitiators containing β-diketonate fragments were prepared by copolymerization of styrene with cobalt(II) 5-Formation and morphological characteristics of selenium-containing nanostructures formed by reduction of selenious acid with ascorbic acid in the presence of ionic or nonionic polymeric stabilizer in aqueous solutions were studied by methods of nonlinear optics and flow birefringence at widely varied selenium to polymer weight ratio in solution ν. The molecular weights, root-mean-square and hydrodynamic sizes, and mean density of the nanostructures were calculated, and the trends in variation of these quantities were compared.

Optical anisotropy of molecules of pyromellite-dianilic amido acid polyesters

The optical anisotropy of molecules of pyromellite-dianilic amido acid polyesters has been studied by the method of flow birefringence. Positive flow birefringence, which depends on the isomeric composition of the repeating unit, is detected. The thermodynamic rigidity of pyromellite-dianilic amido acid polyester molecules is calculated in terms of the valence-optical scheme. On passage from 100% para isomers of pyromellite-dianilic amido acid polyesters to macromolecules with a predominant content of meta isomers, optical anisotropy and equilibrium rigidity decrease by a factor of ∼2.

10.1007/s11498-008-2004-0

The linear dendritic polymers of the first and second generations have been investigated by the methods of flow birefringence and equilibrium and nonequilibrium electric birefringence. The side dendrons are attached to the polymer backbone through benzamide groups and contain long terminal hexyloxycarbonyl fragments. Optical, dynamic, dipolar, and conformational characteristics of the macromolecules in question have been analyzed in detail. It has been found that the macromolecules of dendritic polymers with dendrons based on L-aspartic acid possess permanent dipole moments and reorient in external electric and hydrodynamic fields according to the large-scale rotation mechanism. The introduction of rigid benzamide fragments substantially increases the equilibrium rigidity, optical anisotropy, and dipole moment of monomer units of dendritic macromolecules. The role of macro-and microform effects in the formation of optical features of the molecules under study is considered in detail.

The studies of molecular structure of Poly(1-trimethylsilyl-1-propyne) stereoisomers by the flow birefringence method

Optical properties of poly-1-trimethylsilyl-1-propyne (PTMSP) stereoisomers in solutions have been studied by means of flow birefringence method. Stereoisomers were chosen with various trans- and cis-configurations abundances of double C C bonds in monomeric units. The differences of main polarizabilities ( α 1 − α 2) or statistical segments have been determined. Significant growth of ( α 1 − α 2) values with increasing of the trans-isomer contents in chain molecule has been found. Optical anisotropy of monomeric segments, having cis- and trans-configurations, has been theoretically evaluated. It has been shown that observed significant increase of experimentally measured ( α 1 − α 2) values cannot be sufficiently explained by only specific chain polarizability growth due to higher trans-isomers contents. It has been demonstrated that high ( α 1 − α 2) value and it’s growth with increase of abundance of monomeric segments in trans-configuration has been caused by thermodynamical rigidity increase, i.e., higher number of monomeric units included into PTMSP statistical segment.

Optical and rheological properties of the dibutyl phthalate-decalin binary liquid system

The flow birefringence method, diffusometry, and viscosimetry were used to study optical and rheological properties of dibutyl phthalate-decalin liquid mixtures of various compositions. The molecular refraction was demonstrated to obey the additivity rule, while the Maxwell constant was observed to deviate slightly from this rule. The nonmonotonic dependence of the molecular mobility of the medium on its composition was revealed and examined. The effects observed were interpreted. According to the diffusiometry and viscosimetry data obtained, the mean size of the mobile units in the system attains its maximum value at a dibutyl phthalate mole fraction of 0.2.

125 二次元対向流れにおける流動複屈折測定を用いた定常平面伸張粘度測定(S34-1 複雑流体の流れとその応用(1),S34 複雑流体の流れとその応用)

125 二次元対向流れにおける流動複屈折測定を用いた定常平面伸張粘度測定(S34-1 複雑流体の流れとその応用(1),S34 複雑流体の流れとその応用)

Elongational flow studies on the phase separation of hydroxypropylcellulose solution

The phase separation of hydroxypropylcellulose (HPC) in a mixed solvent of glycerol and water was investigated by an elongational flow birefringence method. In the one-phase region, the elongational flow birefringence had the characteristics of a typical coil-stretch transition-like pattern with a critical elongational strain rate \documentclass{article}\pagestyle{empty} \begin{document}$\dot \varepsilon_c.$\end{document} \documentclass{article}\pagestyle{empty} \begin{document}$\dot \varepsilon_c.$\end{document} increased monotonously with temperature, but in the vicinity of the phase-separation point, \documentclass{article}\pagestyle{empty} \begin{document}$\dot \varepsilon_c.$\end{document} began to decrease even in the one-phase region. In the two-phase region, the flow-induced birefringence pattern contained both a rigid rod-like response and the coil-stretch transition-like response of a flexible polymer. The appearance of the rod-like birefringence pattern indicates the association of HPC chains to form a precursor of the liquid-crystalline phase formation. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2984–2991, 2002

Determination of molecular weight and its distribution of flexible chain polymer by phase-modulated flow birefringence technique

The objective of this study is to develop a systematic method to determine molecular weight and its distribution of flexible chain polymer by birefringence experiments. Using the random walk model, birefringence δn and orientation angle ξ have been optically obtained as functions of molecular weights. To confirm the theory, polystyrene solutions with different molecular weights dissolved in polychlorinated biphenyl were experimented by the phase-modulated flow birefringence (PMFB) method. Birefringence of polystyrene solutions is proportional to (Σc i M i 1.6 )γ2, and cot(2χ) to (Σc i M i 1.6 /B1Σc i M i −0.2 )γ. The experimental results agreed well with the theoretical predictions proposed in this study.

Electrooptical Properties of Main-Chain Mesogenic Polymers in Nematic State and Dilute Solutions

Electrooptical and dielectric properties of two aromatic polyesters with hexaethyleneglycol spacers (as well as their low molecular weight structural analogues) were studied in dilute solutions and in nematic state using the methods of flow birefringence, equilibrium electric birefringence, and orientational elastic deformations in electric fields. It was shown that the macromolecules under investigation orientated in the electric field according to the small-scale mechanism, and the Kerr constant K values are in good agreement with the dipole structure of their molecules. The sign of dielectric anisotropy Δϵ for the polymer nematics under investigation coincides with the sign of K in dilute solutions. The values of Δϵ for polymer nematics are close to the same characteristics for their low molecular weight structural analogues. The comparative analysis of the data obtained for these polymers in dilute solutions and in the nematic state is carried out.

Rheological studies on the phase separation of hydroxypropylcellulose solution systems

AbstractPhase behavior of hydroxypropylcellulose (HPC) in a mixed solvent of glycerol and water was investigated by two different rheological methods: rheooptical birefringence measurement in an elongational flow field and viscometric measurement in a shear flow field. The association process of the HPC chain during phase separation observed by the elongational flow birefringence method was also investigated by the shear viscometric method. The temperature dependence of chain rigidity was determined by measuring the intrinsic viscosity, and change in the conformation was investigated by observing elongational flow birefringence over the temperature range from the one‐phase to inside a phase boundary. The results focus on the molecular process of phase separation. © 2001 John Wiley &amp; Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1976–1986, 2001

Equilibrium Rigidity of Polyorganophosphazene Molecules

The optical anisotropy and orientation angles of polyorganophosphazene (PPhPh) molecules with different lengths and side-chain structures have been investigated by flow birefringence and viscosimetry methods. Quantum-chemical calculations of the optical anisotropy per monomer unit within the polymer fragments with different conformations were carried out. It was shown that both short-range and long-range interactions (i. e. the structure of the polymer backbone and steric interactions between side chains) influenced the conformation of the PPhPh molecules and should be taken into account for the determination of the thermodynamic rigidity value A. The experimental value of A, (50 ± 5)·10–8 cm, obtained by different methods, adequately corresponds to the structure and observed physical parameters of the PPhPh molecules. Molecules of this class of polymers are not rigid chains in a common way (A > 150·10–8 cm), but alternating double bonds of their backbones bring about some increase in the equilibrium rigidity. It can be assumed that, for this class of polymers, the mesogeneity on a molecular level is defined by the strong interactions of fluorine-containing side chains rather than by the rigidity of their backbones.