Hydrodynamic and molecular characteristics of graft copolymers of chitosan with acrylamide

The conformational properties of macromolecules of chitosan and its copolymers with acrylamide in a mixed solvent 0.33 M CH₃COOH + 0.3 M NaCl have been investigated by means of translation diffusion and viscometry. The copolymer macromolecules in a solvent suppressing polyelectrolyte effects possess a higher intracoil density (ρ_av = 0.010 g/cm³) than the chitosan macromolecules (ρ_av = 0.006 g/cm³), even though the hydrodynamic radius R _h of chitosan is smaller by a factor of ～1.5.     

Étude d'un modèle périodique de diffusion non linéaire en régime stationnaire pour une réaction réversible

For a partially inhibited solid electrode a periodic model of non-linear diffusion is defined, permitting the calculation of the attenuation factor, ?, of the diffusion current density as a function of the size and the closeness of active or inactive sites and of the diffusion layer thickness. Values of ? are compared with those obtained from the Landsberg's model [3]. In the case of a disk electrode rotating at N r.p.s., the influence of the characteristic parameters of the inhibiting coverage on the relationship between the diffusion current and N^1/2 is analysed in the experimentally accessible laminar flow domain.     

Bromination of phenols in bromoperoxidase-catalyzed oxidations

Phenol and ortho-substituted derivatives furnish products of selective para-bromination, if treated with sodium bromide, hydrogen peroxide, and the vanadate(V)-dependent bromoperoxidase I from the brown alga Ascophyllum nodosum. Relative rates of bromination in morpholine-4-ethane sulfonic acid (MES)-buffered aqueous tert-butanol (pH 6.2) increase by a factor 32, as the ortho-substituent in a phenol changes from F via Cl, OCH₃, C(CH₃)₃, and H to CH₃. The polar effect in phenol bromination by the enzymatic method, according to a Hammett-correlation (ρ=−3), compares to reactivity of molecular bromine under identical conditions (ρ=−2). Hypobromous acid is not able to electrophilically substitute bromine for hydrogen at pH 6.2 in aqueous tert-butanol. The tribromide anion behaves in MES-buffered aqueous tert-butanol as electrophile (ρ∼−3), showing a similar polar effect in phenol bromination as molecular bromine.     

A virial coefficient interrelation for temperatures from about 1.0 to 2.7 times the critical temperature

An interrelation among the virial coefficients for temperatures between about 1.0 and 2.7 times the critical temperature is derived from the experimentally observed linearity of the temperature, T, versus the density, ρ, at constant K = (Z − 1)/ρ, where Z is the compressibility factor. This relates higher virial coefficients at a given T to the temperature dependence of the previous coefficients at that T.The experimental linearity of the constant-K (ISOK) lines is confirmed for nitrogen, from which accurate values of B and C, the second and third virial coefficients, are derived. The new interrelation is then used to find the fourth virial coefficient, D, for nitrogen in this T range (120–340 K).It is also shown that the Lennard–Jones 6,12 intermolecular potential does not obey this interrelation because its ISOK lines are not linear, and therefore it cannot represent the PρT behavior of nitrogen or other common gases.     

Spin-lattice relaxations study of water mobility in natural natrolite

The mobility of water molecules in natural natrolite (Na₂Al₂Si₃O₁₀?2H₂O) is investigated by the ¹H NMR method. The spin-lattice relaxation times in the laboratory and rotating frames (T₁ and T_1ρ) are measured as a function of the temperature for a polycrystalline sample. From experimental T₁ data it follows that at T > 286 K the diffusion of water molecules along channels parallel to the c axis is observed. From experimental T_1ρ data it follows that at T > 250 K the diffusion of water molecules in transversal channels of natrolite is also observed. At a low temperature (T < 250 K) the dipolar interaction with paramagnetic impurities (presumably Fe³⁺ ions) becomes significant as a relaxation mechanism of ¹H nuclei.     

Evaluation of the parameters of the Bender equation of state for low acentric factor fluids and carbon dioxide

Volumetric properties of several low acentric factor fluids (Ar, CH₄, C₂H₆, Kr, N₂, Ne, O₂, Xe) as well as CO₂ are modeled using the Bender equation of state. This equation is a linear function of 19 adjustable parameters, which are evaluated from properties data, using a linear numerical procedure. The validity of the EOS is tested by calculating the Joule-Thomson inversion curve. A simple model is in particular used to correlate the inversion properties predicted by the Bender equation, expressed in term of reduced pressure as a function of reduced temperatures ranging from 0.8 to 6. The simple correlation reproduces accurately the used data. We employ data on state behaviour ρ(P,T) of homogeneous fluid phases, vapour-liquid equilibrium, second virial coefficient and the coordinates of the critical point.     

Measurements of the(p,ρ,T) relation of methane and carbon dioxide in the temperature range 240 K to 520 K at pressures up to 30 MPa using a new accurate single-sinker densimeter

Comprehensive (p, ρ, T) measurements on pure methane (159 values) and pure carbon dioxide (118 values) have been carried out in the temperature range 240 K to 520 K at pressures up to 30 MPa. The measurements were performed by means of a single-sinker densimeter that is based on Archimedes’ buoyancy principle. The total relative uncertainty of the measurements in the density ρ was estimated to be⩽ |(1.5 to 2) · 10 ^− 4·ρ | for methane and⩽ |(2 to 3) · 10 ^− 4·ρ | for carbon dioxide. The measurements are compared with previous results of other experimentalists and with values calculated from current equations of state. Moreover, previously unpublished results of (p, ρ, T) measurements on carbon dioxide (29 values) and methane (53 values) are listed in the appendix.     

The effect of element substitution on high-temperature thermoelectric properties of Ca3Co2O6 compounds

Polycrystalline Ca₃Co_1.8M_0.2O₆ (M=Mn, Fe, Co, Ni, Cu) and Ca_2.7Na_0.3Co₂O₆ were synthesized by solid-state reaction to evaluate the effect of substitution on the thermoelectric properties of Ca₃Co₂O₆. Substitution by Mn, Cu and Na appears to increase carrier density, given that electrical resistivity (ρ) and the Seebeck coefficient (S) were simultaneously reduced. Conversely, Fe substitution seems to reduce carrier density, resulting in a simultaneous increase in S and ρ. Cu and Na substitution resulted in a significant decrease in ρ due to enhancement of grain size and grain boundary connectivity, which could have a strong impact on ρ. Not only the intrinsic substitution effect on the electronic state but also this modification of the microstructure plays an important role in improvement of the thermoelectric power factor, particularly in the case of the Na-substituted sample.     

On the electronic and structural properties of aluminum diboride Al0.9B2

Single crystals of aluminum diboride (space group P6/mmm, No. 191) a=3.0050(1) Å, c=3.2537 (8)  Å; Z=1) were prepared by the aluminum flux method. Crystal structure refinement shows defects at the aluminum site and resulted in composition Al_0.894(9)B₂≈Al_0.9B₂. The defect structure model is confirmed by the measured mass density ρ_exp=2.9(1) g/cm³ in comparison with a calculated value ρ_x=3.17 g/cm³ for full occupancy of the aluminum position. The results of ¹¹B NMR measurements support the defect model and are in agreement with the structure obtained by X-ray diffraction methods. Electrical resistivity measured on a single crystal parallel to its hexagonal basal plane with ρ(300 K)−ρ(2 K)=2.35 μΩ cm shows temperature dependence like a typical metal. Charge is dominantly carried by holes (Hall-coefficient R=+2×10⁻¹¹ m/C). Respective, p-type conductivity is confirmed by theoretical calculations. Chemical bonding in aluminum diboride is discussed using the electron localization function.     

Lamellar thickness of crystallizable ethene runs in ethene-propene copolymers by solid state NMR

Crystallizable runs of ethene in ethene-propene copolymers can be identified in ¹³C CPMAS NMR spectra as a resonance at 33 ppm. In the absence of spin diffusion, the variation in intensity of this resonance with a ¹H spin lock will reflect the intrinsic T^H_1ρ. Spin diffusion leads to a more complex relaxation decay, which reflects the local polymer morphology. Simulations of the spin diffusion process have been carried out for a simplified two-phase model for the morphology with the aim of determining whether the lamellar thickness of the crystalline and amorphous regions can be found from the T^H_1ρ observed via the ¹³C NMR spectrum. Calculations covering the expected range of the input parameters, namely the spin diffusion coefficients, domain lengths, and intrinsic relaxation times, show that, providing the intrinsic relaxation time in the amorphous phase is known, an accurate estimate of the crystalline and amorphous lamellar thicknesses can be made. Analysis of simulated T^H_1ρ decays indicate that, in general, the time constant of the fastest decaying component can be identified with the intrinsic relaxation time of the amorphous phase. © 1994 John Wiley & Sons, Inc.     

The effect of Ag addition on electrical properties of the thermoelectric compound Ca3Co4O9

Ca₃Co₄O₉/Ag composites incorporating different amounts of Ag were synthesized by solid-state reaction. Scanning electron microscopy revealed Ag particles dispersed among and combined with Ca₃Co₄O₉ grains several times larger in size. The electrical resistivity (ρ) of the composites is favorably lower than that of Ca₃Co₄O₉ alone and decreases with increasing Ag content. It can thus be inferred that the highly conductive Ag particles between the oxide grains contribute to the reduction of ρ. Although minimal in smaller amounts, the addition of Ag also seems to have a negative impact on the Seebeck coefficient (S) of the composites due to its poor S. Since the reduction of ρ is more significant than the degradation of S, the power factor is found to be improved by the addition of 10 wt% Ag.     

Solubility of amphenicol bacteriostats in CO2

The solubilities of three veterinary amphenicol bacteriostats, chloramphenicol, florfenicol and thiamphenicol, were measured in supercritical carbon dioxide (SC-CO₂) by a re-circulating method at temperatures of 313.15 and 333.15 K and pressures ranging from 11.0 to 49.0 MPa. These compounds displayed very limited solubility in SC-CO₂ (10⁻⁵ to 10⁻⁷ mole fraction) over the range of experimental conditions. Chloramphenicol had the highest observed solubility of the three amphenicols, while the solubilities of florfenicol and thiamphenicol were almost an order of magnitude lower. The experimental solubility data were correlated with seven known density-based models. The density models (ln y versus ln ρ or ln ρ_r) gave better correlation than the semi-log scale of ln y versus ρ_r. Four models for ln E versus density correlations also gave better correlation than the semi-log scale of ln y versus ρ_r by introducing the enhancement factor E. The correlation accuracy of all the seven models mainly depends on the system investigated, measured density and temperature range.     

A Monte-Carlo simulation of diffusion and reaction in zeolites

Investigations of two-dimensional models to simulate diffusion and reaction in zeolites with a Monte-Carlo method are presented herein. New results of the simulation of single component diffusion and binary diffusion and a possible method to rescale the obtained diffusion coefficients in real units is presented. The estimation of an accurate activation energy was found to be the most important factor, the other parameters were estimated by simple assumptions.Complex reactions such as a consecutive reaction and xylene isomerisation were simulated with a new model. With this model the selective behaviour of the two reactions was investigated. A Type-III selectivity according to Wheeler was found for the consecutive reaction. For xylene isomerisation, reaction paths were simulated and compared with experimental reaction paths. The composition of the thermodynamic equilibrium was obtained for high transition probabilities and the relative rate constants from the literature could be confirmed. According to the results of the simulations one can conclude that a ratio of the diffusion coefficients of o-, m-, and p-xylene=1:1:1000 is too large to explain the experimentally observed distribution of the xylene isomers and a difference of only one order of magnitude was found.     

Selective deoxygenation of aryl selenoxides by triaryl phosphites. Evidence for a concerted transformation

Triaryl phosphites selectively reduce aryl selenoxides to selenides. The Hammett plot of the reactions of para-phenyl substituted triaryl phosphites with diphenyl selenoxide gave ρ=+2.3, whereas with bis(p-methoxyphenyl) selenoxide, ρ=−2.1. The results are consistent with a concerted mechanism for the oxygen transfer from Se to P.     

Oriented polymers from solution. III. NMR of polyethylene/polypropylene blends

T₁, T₂, and T_1ρ measurements are reported for a blended fiber of polyethylene and polypropylene prepared by the “surface growth” technique. The data support the view that the fiber contains mixed crystalline regions of each pure component that may weakly interact via spin diffusion. A tentative model is proposed for the blended fiber.     

Asymmetry of hydrogen lines in plasmas utilizing a statistical description of ion-quadruple interaction in Mozer-Baranger limit

Hydrogen line Stark profiles are calculated in the static ion approximation including the ion-quadrupole interaction and the quadratic Stark effect. The statistics of the ion-quadrupole interaction is evaluated in the Mozer-Baranger limit taking into account the screening and the ion correlations. The generalized functionB _ρ(β) exceeds several times the ordinary Chandrasekhar and von Neumann functionB(β)=B _ρ=0(β) (i.e.B _ρ(β) at ρ=0) and in the same proportion increases the importance of the ion-quadrupole interaction. Forn _e ranging from 10¹⁶ to 10¹⁸ cm^?3, calculated parameters of the asymmetry and shift ofH _β agree well with measurements by different authors.     

Measurements of the isochoric heat capacity,the critical point (TC, ρC) and vapor–liquid coexistence curve (TS, ρS) of high-purity toluene near the critical point

Isochoric heat capacities (C_V, V, T), phase boundary properties (T_S, ρ_S) and the critical (T_C, ρ_C) parameters for high-purity (0.9999+ mole fraction) toluene have been measured with a high temperature, high pressure, nearly constant volume adiabatic calorimeter and quasi-static thermogram technique. Measurements were made at three selected liquid and vapor isochores 777.8, 555.25, and 214.64 kg m⁻³ in the temperature range from 379 to 591 K. For five near-critical isochores 268.68, 281.68, 296.62, 301.52, and 318.28 kg m⁻³, the measurements were made in the immediate vicinity of the coexistence curve in order to accurately determine the phase transition temperatures (T_S, ρ_S) (shape of the coexistence curve near the critical point) and the critical parameters (T_C, ρ_C). The total combined uncertainty of heat capacity, density, and temperature measurements were estimated to be less than 2%, 0.06%, and 15 mK, respectively. The uncertainties reported in this paper are expanded uncertainties at the 95% confidence level with a coverage factor of k = 2. The uncertainty of the phase transition and the critical temperature value was 0.02 K. The Krichevskii parameter for some toluene-containing binary mixtures was calculated. The derived values of the Krichevskii parameter were used to estimate the effect of dilute impurities on the critical parameters of toluene. The measured values of saturated density near the critical point were interpreted in terms of the “complete scaling” theory in order to study singularity behavior of the coexistence curve diameter. The measured isochoric heat capacities and saturated densities were compared with the data reported by other authors and values calculated from an equation of state and other correlations.     

Impact of the virulence-associated MAb3/1 epitope on the physicochemical surface properties of Legionella pneumophila sg1: An issue to explain infection potential?

The relationship between the presence/absence of the virulence-associated MAb3/1 epitope of sixteen Legionella pneumophila serogroup 1 strains and their respective surface physicochemical properties is evidenced from electrokinetic measurements (microelectrophoresis) performed as a function of KNO₃ electrolyte concentration (range 1–100 mM, pH ～ 6.5). Among the bacteria selected, nine original strains constitute the Dresden reference panel and differ according to the presence/absence of the virulence-associated monoclonal antibody MAb3/1 of the O-specific chain of the lipopolysaccharides (LPS). Five isogenic Lens strains, also investigated in the current study, present the epitope MAb3/1 of their LPS and were involved to some extent in the outbreak that stroke the Nord Pas-de-Calais region (France) in 2004. All bacteria exhibit the typical electrokinetic features of soft (permeable) particles. On the basis of Ohshima's model, analysis of the electrophoretic mobility data allows evaluating the intraparticular flow penetration length 1/λ₀ and the (negative) volume charge density ρ₀ that both reflect the structure and chemical composition of the soft bacterial component. Our results show that the virulent MAb3/1 positive strains are characterized on average by 1/λ₀ and ?ρ₀? values that are about 1.5 times larger and 5 times lower, respectively, than those derived for lesser virulent (MAb3/1 negative) strains. In other words, on average the soft surface layer of MAb3/1 positive strains is significantly less charged and more permeable than those of MAb3/1 negative strains. The intimate correlation between virulence-associated MAb3/1 epitope and charge density carried by the bacterial envelop was further confirmed by lower 1/λ₀ and greater ?ρ₀? values for lag-1 mutant CS332 strain, lacking the MAb3/1 epitope, compared to the parental strain AM511. A closer inspection of the dispersion in 1/λ₀ and ?ρ₀? data over the ensemble of analysed bacteria together with the reported number of Legionnaires’ disease cases they are responsible for, points out the charge density ?ρ₀? as the parameter that is most suitable for discriminating highly virulent (MAb3/1 positive) from less virulent (MAb3/1 negative) strains. Although short-range interaction determines infection process, our results suggest that the infection potential of Legionella pneumophila serogroup 1 may be also controlled significantly by non-specific long-range electrostatic repulsion the bacteria undergo when approaching negatively charged host cells to be infected.