Effects of molar mass, concentration and thermodynamic conditions on polymer-induced flow drag reduction

Drag reduction in Taylor flow of polystyrene solutions is investigated using a commercial rheometer equipped with a standard double-gap sample holder with axial symmetry. The dependence of drag reduction on various factors, including polymer molar mass, polymer concentration, and thermodynamic conditions is studied. Drag reduction induced by polystyrene in toluene is found to increase with increasing polymer concentration in the dilute concentration regime. It is also seen that molecules with high molar mass of the polymer promote drag reduction. In terms of hydrodynamic volume fraction normalisation, it is found that most of the drag reduction effect occurs at volume fractions below 0.2. It is observed that drag reduction is favoured by good thermodynamic conditions of the polymer-solvent system. Both the flow induced extension of the polymer chains and the hydrodynamic volume fraction occupied by the polymer molecules seem to play an important role for the drag reduction effect.     

MITOTIC INHIBITION BY PHENYLPORPHINES AND TETRASULFONATED ALUMINIUM PHTHALOCYANINE IN COMBINATION WITH LIGHT

This work relates to studies on modes of phototoxicity by tetrasulfonated aluminium phthalocyanine (AlPcS4), tetrahydroxy- and monosulfonated meso-tetraphenylporphines (3-THPP and TPPS1) on culture cells. Toxicity at moderate light exposures appears to be related to inhibition of microtubule function. Treatment of human cervix carcinoma cells of the line NHIK 3025 incubated for 18 h with the sensitizers and exposed to light inhibits multiplication for the first hours after light exposure, a significant fraction of the cells accumulating in mitosis. For the first hours after treatment, the mitotic cells were always mainly found in metaphase; generally seen as c-metaphases and three-group metaphases. During this time, anaphase and telophase cells were absent or greatly reduced in number. Indirect immunofluorescence staining of beta-tubulin showed that the spindle apparatus of mitotic cells was perturbed in all cases. The accumulation in mitosis was more extensive after treatment with AlPcS4 and light than after treatment with 3-THPP or TPPS1 and light. This may be related to the great difference in the lipophilic properties of these sensitizers; i.e. AlPcS4 being highly water soluble while TPPS1 and 3-THPP are lipophilic sensitizers. The lipophilicity of several sensitizers has been measured by two different methods, the partition between an aqueous and a lipophilic phase (Triton X-114) and the binding strength to a reverse phase column. The results show that the measured relative lipophilicity of the sensitizers may be influenced by the method of analysis.     

DETECTION OF UVR-INDUCED DNA DAMAGE IN MOUSE EPIDERMIS in vivo USING ALKALINE ELUTION

Abstract— Alkaline elution has been used to detect ultraviolet radiation (UVR)-induced DNA damage in the epidermis of C3H/Tif hr/hr mice. This technique detects DNA damage in the form of single-strand breaks and alkali-labile sites (SSB) formed directly by UVA (320–400 nm) or indirectly by UVB (280–320 nm). The latter induces DNA damage such as cyclobutane pyrimidine dimers and pyrimidine-pyrimidone (6–4)-photoproducts, which are then converted into transient SSB by cellular endonucleases, during nucleotide excision repair (NER). The irradiation system used had a spectral output similar in effect to solar UVR, with the UVB component inducing 94% of the edema response observed in mice. Consequently, the majority of SSB detected were those formed via NER of UVB-induced photoadducts. The number of SSB detected immediately after 8 kj/m² (2.7 minimum erythema doses determined at 48 h post-UVR [MED]) was low, indicating the formation of only small numbers of transient SSB. When DNA repair inhibitors hydroxyurea and 1 -β-D-arabinofuranosylcytosine were administered (intraperi-toneally) to mice 30 min before UVR, they prevented sealing of the DNA SSB formed during NER. A four-fold increase in the number of SSB detected resulted, which was found to be linearly related to the UVR dose. The SSB induced by 2 kj/m² (less than an MED) were readily detected, with the ear showing lower numbers of SSB than the dorsum. When repair inhibitors were added post-UVR, the rate of formation of SSB declined rapidly with time of administration, reflecting repair of DNA lesions. After a UVR dose of 6 kj/m² (2 MED), 50% of the initial repair-dependent SSB had been removed after approximately 2 h in the ear and 4 h in the dorsum; no more SSB appeared to be incised by 24 h post-UVR. The technique described is an efficient and highly sensitive one for the quantification of SSB induced in UV-irradiated skin samples in vivo.     

Characterization of cellulose by SEC-MALLS

Norway spruce (Picea abies) cellulose samplesdissolved in lithium chloride/N,N-dimethyl-acetamide(LiCl/DMAc) covering a wide range of average molecular weights were analyzed bysize exclusion chromatography (SEC) and multi-angle laser light detection(MALLS). The molecular weight distribution of the samples was compared to themolecular weight distribution of cotton linters cellulose samples. To obtaincomplete dissolution of high-molecular-weight wood cellulose, previouslypublished procedures for dissolving cellulose in LiCl/DMAc were modified. SECseparation was performed using macroporous monodisperse polymer particles ascolumn matrix. The refractive index increment (dn/dc) forcellulose in 0.5% LiCl/DMAc was found to be 0.104. The radius of gyration,R_G, of cellulose in 0.5% LiCl/DMAc depended on the molecular weight,M, according to the relation R_G M^0.55. Celluloseprepared from sprucewood by the sulfite cooking process had a broad molecularweight distribution compared to cotton linters cellulose.     

Study of the conformation of polyelectrolytes in dilute solutions by elastic neutron scattering

Experiments using small angle neutron scattering have been performed on dilute solutions of polyelectrolytes without added salt; they allow to show that this method is very suitable for measuring the radius of gyration and determining the conformation of polyions in solution.     

Thermal decomposition kinetics of some aromatic azomonoethers

Thermal analysis of three azomonoether dyes, exhibiting liquid-crystalline properties, was performed in dynamic air atmosphere. Thermal stability studies and the evaluation of the kinetic parameters of each physical or chemical transformations are essential for a full characterization, before attempting accurate thin films’ depositions of such materials used in non-linear optical applications. New synthesized dyes with general formula: where R is a nematogenic group: CN, CF₃ or a highly polarizable group: NO₂ were investigated using TG, DTG, DTA and DSC techniques, under non-isothermal regime. The evolved gases were analyzed by FTIR spectroscopy. The activation energies of the first decomposition step were evaluated for each compound, the obtained results revealing complex mechanisms.     

Early induction of binucleated cells by ultraviolet A (UVA) radiation: a possible role of microfilaments.

The effects of UVA (365 nm) radiation on the cellular distribution of F-actin and formation of binucleated cells have been studied using 3T3 Swiss albino mouse fibroblasts and V79 Chinese hamster fibroblasts. Ultraviolet A at biologically relevant fluences was found to disintegrate the actin filaments in the cells shortly (5 min) after irradiation, concomitant with the formation of cells with two nuclei. In 76-100% of the bi- and multinucleated cells the distribution of F-actin was clearly altered. Cells in GI phase of the cell cycle were most probably involved in the formation of binucleated cells. The disintegration of F-actin was presumably not due to depolymerization of F-actin to G-actin, as the amount of F-actin in the cells was unaltered after UVA exposure but rather due to direct breakage of the actin filaments. Ultraviolet B (297/302 nm) had no effect on the cellular distribution of microfilaments, not even at highly lethal fluences.     

Rheological properties of concentrated latex suspensions of poly(styrene-butadiene)

Concentrated suspensions of charged latex particles of poly(styrene-butadiene) have been used as model systems to investigate the influence of surface charges on the rheology of colloidal suspensions. The suspensions were found to behave as elastic solids at small strains and to require a finite stress to flow. This was related to an ordered structure of the suspensions at rest, resulting from electrostatic and van der Waals forces. Important shear-thinning effects were observed as a consequence of structure rearrangements under shear. At a fixed shear rate, the steady-shear viscosity as a function of the ionic strength exhibits a minimum. Under oscillatory shear flow, the behavior of the concentrated suspensions was found to be non-linear above a very small strain amplitude. The non-linear output signal from dynamic experiments was analyzed using a fast Fourier transform algorithm. A maximum in the third harmonic intensity as a function of the strain amplitude was observed and the intensity of higher harmonics decreased with increasing ionic strength. The behavior of the suspensions could be adequately described using the structural model of Yziquel et al. (Yziquel F, Carreau PJ, Moan M, Tanguy PA (1999) Rheological modeling of concentrated colloidal suspensions. J Non-Newtonian Fluid Mech 86:133–155).     

Biological activity of 5-aminolevulinic acid and its methyl ester after storage under different conditions

5-Aminolevulinic acid (ALA) is a natural precursor of protoporphyrin IX (PpIX) and heme in cells. Photodynamic therapy (PDT) utilizes a metabolic imbalance in cancer cells, leading to increased PpIX generation from exogenous ALA. Due to chemical instability of ALA in therapeutic concentrations at pH values larger than 5.0 and at high temperatures, it looses its activity by spontaneous dimerization to 2,5-dicarboxyethyl-3,6-dihydropyrazine (DHPY). ALA esters are now supplementing ALA in PDT, but little is known about their stability. We have studied the stability of ALA and its methyl ester (MAL) stored under different conditions (temperatures, pH values) by measuring their ability to generate PpIX. 100mM solutions of both compounds were found to be stable at pH 4 and at 4 degrees C. However, at pH 5.5 they lost almost 10% of the initial activity during 5days of storage at 4 degrees C. The fastest decay of ALA and MAL was seen at pH 7.4 and at 37 degrees C, and followed first order kinetics. At pH 7.4 and at 4 degrees C MAL lost its PpIX producing ability more slowly than at 37 degrees C. Our work shows that solutions should be prepared immediately before use and stored at low temperatures. The pH of stock solutions should not exceed 5.