Light Scattering Photon Correlation Spectroscopy Research Articles

Biophysical and Transfection Studies of an Amine-Modified Poly(vinyl alcohol) for Gene Delivery

Novel, multifunctional polymers remain an attractive objective for drug delivery, especially for hydrophilic macromolecular drugs candidates such as peptides, proteins, RNA, and DNA. To facilitate intracellular delivery of DNA, new amine-modified poly(vinyl alcohol)s (PVAs) were synthesized by a two-step process using carbonyl diimidazole activated diamines to produce PVAs with different degrees of amine substitution. The resulting polymers were characterized using NMR, thermogravimetric analysis (TGA), and gelpermation chromatography (GPC). Atomic force microscopy (AFM), dynamic light scattering photon correlation spectroscopy (PCS), and zeta-potential were used to investigate polyplexes of DNA with PVA copolymers. These studies suggest an influence of the polycation structure on the morphology of condensed DNA in polyplexes. Significant differences were observed by changing both the degrees of amine substitution and the structure of the PVA backbone, demonstrating that both electrostatic and hydrophobic interactions affect DNA condensation. DNA condensation measured by an ethidium bromide intercalation assay showed a higher degree of condensation with pDNA with increasing degrees of amine substitution and more hydrophobic functional groups. These findings are in line with transfection experiments, in which a good uptake of these polymer DNA complexes was noted, unfortunately, with little endosomal escape. Co-administration of chloroquine resulted in increased endosomal escape and higher transfection efficiencies, due to disruption of the endosomal membrane. In this study, the structural requirements for DNA complexation and condensation were characterized to provide a basis for rational design of nonviral gene delivery systems.

Pressure and temperature dependence of structural relaxation in diglycidylether of bisphenol A

The structural (α-) relaxation in diglycidylether of bisphenol A (DGEBA) has been examined using three spectroscopic methods: dielectric spectroscopy (DS), dynamic light scattering–photon correlation spectroscopy (LS), and mechanical spectroscopy. The DS and LS measurements were carried out as a function of both temperature and pressure. Moreover, pressure-volumetemperature measurements were obtained for the DGEBA. These data allow an assessment of the relative contributions of thermal energy and free volume to structural relaxation in DGEBA. The results clearly show a substantial role for both thermal and free volume fluctuations in the dramatic slowing down of the dynamics. The combined temperature- and pressure-dependences of the dielectric and light scattering relaxation times were analyzed using the Avramov equation, implying that the fragility (normalized temperature dependence) is pressure independent over the studied range of pressures. The pressure dependence was the same as measured by the different spectroscopies. Conformance to the time-temperature-pressure superposition principle was also observed for all measurement techniques.

Time-resolved observation of ZrO2-colloid agglomeration

Abstract The agglomeration of ZrO2-nanoparticles is investigated in situ by a combination of light scattering photon correlation spectroscopy (PCS) and laser-induced breakdown detection (LIBD). Surface charge measurements suggest a point of zero charge (PZC) for ZrO2-colloids at pH 8.2 as confirmed with PCS by agglomeration rate measurements at higher concentrations (1011 particles cm−3). The agglomeration rate is investigated further at the PZC as a function of particle concentration. Utilizing the high sensitivity of LIBD the linear dependence of the agglomeration rate was confirmed for the first time at concentrations typical for natural systems, i.e. down to 2×106 particles cm−3. The results agree with the simple diffusion limited aggregation model of Smoluchowski (sticking factor 1) and no indication of an activation barrier are found. Zr(IV) is known for its similarity to Pu(IV) regarding colloid formation and hence the present investigations can serve as a model for the aggregation of Pu(IV)-colloids, the stability of which represents an important aspect in the safety assessment of nuclear waste repositories.

Dynamic light scattering studies of supercooled phenylphthalein–dimethylether dynamics under high pressure

The behavior of the α-relaxation process in phenylphthalein–dimethylether (PDE) under high pressure was studied by means of dynamic light scattering–photon correlation spectroscopy (DLS-PCS). The temperature dependence of the relaxation time of the α-process at ambient pressure was found to resemble that obtained from dielectric relaxation (DR) measurements. On the basis of the DLS measurements one can conclude that PDE satisfies the correlation between nonexponentiality and fragility established for low-molecular weight glass forming liquids and polymers. On the other hand, dielectric relaxation studies indicate that PDE is an exception from this correlation. These differences between the DLS and DR studies do not result from the overlap of the α- and β-processes in the DLS experiments but might be due to the different coupling of the probes seen in these experiments (optical anisotropy and dipole moment) to the dynamics of the entire PDE molecule. We also studied the effect of pressure on fragility and the glass transition temperature in PDE and we found that fragility is practically independent of pressure.

Does fragility depend on pressure? A dynamic light scattering study of a fragile glass-former

Relaxation times of the α-process in the fragile glass-forming liquid diglycidyl ether of bisphenol-A (EPON 828) were measured in a broad pressure (1–1500 bar) and temperature (264–293 K) ranges by means of the depolarized dynamic light scattering—photon correlation spectroscopy. Based on this experimental data the fragility of the supercooled liquid was calculated in two ways: as a steepness index m of the “Angell plot” and as the DT-parameter from the Vogel–Fulcher–Tammann Law, and was studied as a function of pressure. It was found, that while the steepness index depends on pressure, the DT parameter is pressure independent. The pressure dependence of the glass transition temperature Tg in EPON 828 was found to be nonlinear. Additionally, we established a relationship between the steepness index mT, the activation volume ΔV#, and the coefficient ∂Tg/∂Pg. In this pressure dependent study we found that also for EPON 828 the nonexponentiality of the correlation function of the α-process correlates well with the non-Arrhenius behavior (steepness index) of the relaxation times. An equation of state describing the temperature and pressure dependence of the structural relaxation time was proposed and verified using experimental data.

Colloid particle sizes in the Mississippi River and some of its tributaries, from Minneapolis to below New Orleans

An on-board technique was developed that combined discharge-weighted pumping to a high-speed continuous-flow centrifuge for isolation of the particulate-sized material with ultrafiltration for isolation of colloid-sized material. In order to address whether these processes changed the particle sizes during isolation, samples of particles in suspension were collected at various steps in the isolation process to evaluate changes in particle size. Particle sizes were determined using laser light-scattering photon correlation spectroscopy and indicated no change in size during the colloid isolation process. Mississippi River colloid particle sizes from twelve sites from Minneapolis to below New Orleans were compared with sizes from four tributaries and three seasons, and from predominantly autochthonous sources upstream to more allochthonous sources downstream. © 1998 John Wiley & Sons, Ltd.

Stabilization of block copolymer micelles by UV and fast electron radiation

AbstractMicelles of a block copoymer poly(styrene/butadiene/styrene) with cores consisting of polybutadiene blocks were stabilized in dilute solutions by UV radiation in the presence of a photo‐initiator and also by fast electrons, and micelles of a block copolymer poly(styrene/ethene‐co‐1‐butene/styrene) with cores formed by the aliphatic blocks were stabilized by fast electrons, in dilute solutions. Stabilization of micelles, i. e., crosslinking of the chains in micellar cores as well as the properties of stabilized micelles were studied by conventional light scattering, by light scattering photon correlation spectroscopy and by gel permeation chromatography.

Characterization of poly(styrene‐co‐divinylbenzene) microgels

AbstractTightly cross‐linked poly(styrene‐co‐divinylbenzene) microgels with molecular weights in the range 107 to 108 g mole−1 were studied in solution in dimethylformamide containing 7 g dm−3 LiBr. Laser light scattering photon correlation spectroscopy (PCS) was used to measure z‐average translational diffusion coefficients D̄z and dilute solution viscometry to measure intrinsic viscosities [η]; values of the equivalent hydrodynamic radii 〈R〉 and 〈RD−1〉 were derived. Weight‐average molecular weights M̄w and z‐average mean‐square radii of gyration 〈S2〉z were determined by conventional light scattering. The microgels were investigated by gel permeation chromatography, and molecular weight data obtained using the [η]M calibration procedure were in satisfactory agreement with results obtained by electron microsocopy and conventional light scattering.

Ultramicroscopy of association colloids formed from block copolymers

Ultramicroscopy studies have been made of micelle formation by two poly(styrene)-poly(isoprene) block copolymers in organic solvents (N,N-dimethylacetamide and n-decane respectively) and a poly( l-glutamic acid)-poly( l-leucine) block copolymer in an aqueous solution of 0.2M NaCl at pH = 4.0. The technique provides a method of determining the number-average translational diffusion coefficient) D ̄ n , of association colloids and leads, via the Stokes-Einstein relation, to a measure of the number-average of the reciprocal hydrodynamic radius (R D ̄ 1) n for spherical particles. Particles having a radius less than approximately 30 nm were too small to be detected by the technique. The ultramicroscopy results were compared with data obtained by laser light scattering photon correlation spectroscopy which provides a measure of the z-average translational diffusion coefficient. D ̄ z . An additional comparison was made by carrying out measurements on two well-characterized poly(styrene/divinyl benzene) latices.