Moment theory for the analytical determination of rate constants for solute permeation at the interface of spherical molecular aggregates

Moment equations were developed on the basis of the Einstein equation for diffusion and the random walk model to analytically determine the rate constant for the interfacial solute permeation from a bulk solvent into molecular aggregates (k_in) and the inverse rate constant from the molecular aggregates to the bulk solvent (k_out). The moment equations were in good agreement with those derived in a different manner. To demonstrate their effectiveness in one concrete example, the moment equations were used to analytically determine the values of k_in and k_out of three electrically neutral solutes, i.e. resorcinol, phenol, and nitrobenzene, from the first absolute (μ_1A) and second central (μ_2C) moments of their elution peaks, as measured by electrokinetic chromatography (EKC), in which the sodium dodecyl sulfate (SDS) micelles were used as a pseudostationary phase. The values of k_in and k_out should be determined with no chemical modifications and no physical action with the molecular aggregates because they are dynamic systems formed through weak interactions between the components. The moment analysis of the elution peak profiles measured by EKC is effective to unambiguously determine k_in, k_out, and the partition equilibrium constant (k_in/k_out) under appropriate experimental conditions.     

Synthesis and Nonlinear Optical Properties of a New A-π-A Two-Photon Compound Utilizing Dibenzothiophene as Center

A new two‐photon material, 3E,6E‐bis(2‐pyrid‐4′‐ylvinyl)dibenzothiophene (BPVDBT), has been firstly synthesized by an efficient Pd‐catalyzed Heck coupling route. The single‐ and two‐photon fluorescence, quantum yields, lifetimes, solvent effects of the chromophore were studied in detail and the compound exhibited solvent‐sensitivity. The fluorescence intensity (I_out) and input excitation intensity (I_in) can fit in well with the quadratic parabolas, which indicates that the up‐converted fluorescence was induced by the two‐photon absorption (TPA). TPA cross‐section of BPVDBT has been measured using the two‐photon‐induced fluorescence method, whose value is 14.24×10^?50 cm⁴·s·photon^?1·molecule^?1 at 750 nm. The experimental results confirm that BPVDBT is a good two‐photon absorbing chromophore with an A‐π‐A type.     

Ethanol production in a bioreactor with an integrated membrane distillation module

Ethanol production in a bioreactor with integrated membrane distillation (MD) module has been investigated. A hydrophobic capillary polypropylene membrane (Accurel PP V8/2 HF), with an external/internal diameter ratio, d _out/d _in = 8.6 mm/5.5 mm and pore size 0.2 μm, was used in these studies. The products (mainly ethanol and acetic acid) formed during the fermentation of sugar with Saccharomyces cerevisiae inhibited the process. These products were selectively removed from the fermentation broth by the MD process, which increased the efficiency of the conversion of sugar to alcohol from 0.45 g to 0.5 g EtOH per g of fermented sucrose. The bioreactor efficiency also increased by almost 30 %. Separation of alcohol by the MD generates a higher yield of ethanol in the permeate than in the broth. The enrichment coefficient amounted to 4-8, and depended on the ethanol concentration in the broth. The separated solutions did not wet the membrane in use for 2500 h of the MD experiments and the retention of inorganic solutes was close to 100 %.     

Kinetic study on solute permeation at the interface of molecular aggregates by partial filling capillary electrophoresis

Moment analysis method using partial filling CE was developed for the kinetic study on solute permeation at the interface of spherical molecular aggregates. Moment equations for partial filling CE were developed by classifying CE systems into five categories according to the migration velocities of solute and molecular aggregate. The method was applied to the study on the dissolution of electrically neutral solutes into SDS micelles. Elution peaks were measured by partial filling CE while changing the concentration of SDS and the filling ratio of SDS micellar zone to the capillary (ϕ_M). Partition equilibrium constants (K_p) and rate constants of interfacial solute permeation of SDS micelles (k_in and k_out) were determined from the first absolute and second central moments of the elution peaks by using the moment equations. Their values were comparable irrespective of ϕ_M and were almost the same as those previously measured by complete filling CE. The positive correlation of K_p with the hydrophobicity of the solutes was explained in terms of the change in k_in and k_out. It was demonstrated that the moment analysis method using partial filling CE is effective for studying solute permeation kinetics at the interface of spherical molecular aggregates.     

Deformation of a Polymer Brush Immersed in a Binary Solvent

An analog of the Alexander‐De Gennes box model is used for the theoretical investigation of an external deformation of polymer brushes in a mixture of two solvents. The basic solvent A and the admixture B are assumed to be highly incompatible (Flory‐Huggins parameter χ_AB = 3.5). The thermodynamics of a polymer in the solvents A and B is described by parameters χ_A and χ_B, χ_A > χ_B. The brush behavior under deformation is investigated with regard to solvent composition and polymer‐solvent interactions. It is shown that in a pre‐binodal range of the solvent composition Φ_B < Φ_B⁰ in the bulk (here Φ_B⁰ is a binodal value) there is such a value of Φ_B = Φ _B* that deformation does not affect solvent composition inside the brush. This invariant quantity Φ _B*, being a function of only thermodynamic parameters, is independent of the brush characteristics, such as grafting density. It is shown that two types of the first‐order phase transitions can arise in the system considered: a compositional phase transition induced by a change in the solvent composition in the bulk, and a deformational phase transition caused by an external deformation of the brush. The value of Φ _B* defines a borderline concentration of the admixture in the bulk; the brush behavior in the ranges 00 ⪇ Φ_B ⪇ Φ _B* and Φ _B* ⪇ Φ_B < Φ_B⁰ are different. If no compositional phase transition occurs in the system, the deformational phase transition should arise under stretching at Φ _B* ⪇ Φ_B. If the compositional phase transition exists, it is realized in the range Φ_B < Φ _B* and causes the deformational phase transition in this concentration range, not only under stretching, but also under compression. Microphase segregation inside the brush is demonstrated for both phase transitions despite overestimation of the brush homogeneity in the box model.     

The effect of concentration,temperature, and molecular weight on the dynamics of rigid-rod molecules in semi-dilute solutions

The dynamics of rigid-rod-like molecules are studied using rheo-optical techniques. Measurements of flow birefringence as a function of shear rate are utilized to understand the scaling behavior of rotational diffusivity with respect to concentration and temperature. The concentration scaling exponent increases with increasing concentration and the scaling laws are valid in narrow concentration windows. The Doi-Edwards (DE) scaling law D_r ∼ c⁻², holds at very high concentrations (cL³ > 150). The concentration scaling exponent decreases dramatically with increasing temperature at concentrations, cL²d > 1. Scaling of rotational diffusivity, with respect to temperature and solvent viscosity in the semidilute regime, does not follow the predictions of DE theory (and related caging ideas). On the contrary, a model proposed by Fixman was found to explain both the temperature and concentration dependence of the rotational diffusivity. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 181–190, 1998     

Conformation of random polypeptide chains

The characteristic ratios C_of and C_∞ are calculated for infinitely long poly(L-amino acid) chains having a? CH₂? R′ substitution at the C^α atom, as functions of the valence angle τ at the C^α atom. The value of C_of is found to increase from 1.6 to 2.3 as τ varies from 105 to 115°. On the other hand, C_∞ decreases with increasing τ in the range 105–111°, passes through a minimum at 111°, and then increases slowly. Since, C_∞ is much less dependent on τ in the most commonly observed range (110–115°), any variation in τ in this range due to solvent would not appreciably affect C_∞. The calculated temperature coefficient of C_∞ is negative and increases significantly in absolute magnitude even for small deviations in τ from 110°.     

Solvation effect in the thermal decomposition of 2,2′‐azoisobutyronitrile in the three‐component system

The thermal decomposition rate constant (k_d ) of 2,2′‐azoisobutyronitrile in acrylonitrile (AN; monomer A)–methyl methacrylate (MM; monomer B) comonomer mixtures in N,N‐dimethylformamide (DMF) as a function of the comonomer mixture composition and its concentration in the solvent at 60 °C was studied. The dependences k_d = f(x_A ,C) [x_A (mole fraction of A in the comonomer mixture) = A/(A + B) = A/C, where C is the comonomer mixture concentration] have a different course as a function of C: from a curve k_d = f(x_A ) approaching the straight line (C = 2 mol · dm⁻³) to a convex curve possessing a maximum at a point x_A = 0.7 (C = 4 mol · dm⁻³) to a curve with a flattened wide maximum within the range of x_A = 0.2–0.8 (C = 7 mol · dm⁻³) to a curve with the shape of a lying s (C = 9 mol · dm⁻³). All the courses of the experimental dependences k_d = f(x_A ,C) can be explained with a hypothesis of initiator solvation by the comonomers AN and MM and the solvent DMF. The existing solvated forms, their relative stability constants, the thermal decomposition rate constants, and the relative contents in the system were determined. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2156–2166, 2000     

Concentration Effects in Sec for Polymer/Polymer/Solvent Systems

Abstract

A model quantitatively describing the experimental shifts in elution volumes of polymeric solute A in the presence of another polymer B is developed. The concentration-dependent shrinkage of A coils has been evaluated from the intrinsic viscosity displayed by polymer A in the ternary solution formed by itself at c_A concentration + polymer B at c_B concentration + solvent. Resulting concentration effects depend on both polymer concentrations (c_A and c_B), on the intrinsic viscosities of both polymers in the solvent (|η|A and |η|B), on the Huggins' coefficients k_A and k_B, and on the quadratic concentration coefficients in the polynomial expansion of ηsp/c, namely k^′ _A and k^′ _B. Predicted elution volumes are compared with experimental ones for two different types of literature systems: those studying polymer A elution at diverse c_A concentrations in eluents consisting of mixtures of polymer B + solvent and those in which polymer A + polymer B mixtures are injected at once in the pure solvent used as eluent. In order to eliminate experimental uncertainties about k_i and k^′ _i (i=A, B) values, applied k^′ _i values were those obtained from the empirical correlation k^′ _i + 0.122 = k_i ² whereas k_i ones were obtained from Imai's equation.     

Optimation of PGNAA instrument design for cement raw materials using the MCNP code

A simulation study of a PGNAA measuring arrangement with a²⁵²Cf neutron source for the characterization of cement raw materials was carried out using the MCNP code to investigate the effect on the system response of varying the bulk density and the water contentv _w of samples of fixed dry composition. The source is placed at the centre of a lead cylinder of extemal radiusR _Pb. This cylinder is enclosed in a coaxial cylinder of polyethylene moderator of extermal radiusR _in. The sample material is confined to the space between an outer cylindrical surface of radiusR _out and the moderator cylinder. The first series of simulation runs was carried out for different sets of values ofR _in,R _out and , and constantv _w. The system specific responseS (count rate per wt%) shows a broad maximum aroundT _M=R _in-R _Pb=4 cm andT _S=R _out-R _in=8.5 cm and a dependence on that is almost linear in the region of the maximum. In a second series of runs the dependence ofS onv _w was studied for a geometry corresponding to a real experiment described elsewhere and for a geometry for which the density saturation effect is already apparent. It is shown that when the sensitivity of the system is optimized both andv _w must be used as calibration parameters while in the low-sensitivity design regionv _w can be used as the only calibration parameter.     

Separation of four flavonol glycosides from Solanum rostratum Dunal using aqueous two‐phase flotation followed by preparative high‐performance liquid chromatography

Aqueous two‐phase flotation followed by preparative high‐performance liquid chromatography was used to separate four flavonol glycosides from Solanum rostratum Dunal. In the aqueous two‐phase flotation section, the effects of sublation solvent, solution pH, (NH₄)₂SO₄ concentration in aqueous solution, cosolvent, N₂ flow rate, flotation time, and volumes of the polyethylene glycol phase on the recovery were investigated in detail, and the optimal conditions were selected: 50 wt% polyethylene glycol 1000 ethanol solvent as the flotation solvent, pH 4, 350 g/L of (NH₄)₂SO₄ concentration in aqueous phase, 40 mL/min of N₂ flow rate, 30 min of flotation time, 10.0 mL of flotation solvent volume, and two times. After aqueous two‐phase flotation concentration, the flotation products were purified by preparative high‐performance liquid chromatography. The purities of the final products A and B were 98.1 and 99.0%. Product B was the mixture of three compounds based on the analysis of high‐performance liquid chromatography at the temperature of 10°C, while product A was hyperoside after the identification by nuclear magnetic resonance. Astragalin, 3’‐O‐methylquercetin 3‐O‐β‐d ‐galactopyranoside, and 3’‐O‐methylquercetin 3‐O‐β‐d ‐glucopyranoside were obtained with the purity of 93.8, 97.1, and 99.2%, respectively, after the further separation of product B using preparative high‐performance liquid chromatography.     

Donor-Acceptor Complexes in Copolymerization. IV. Alternating Tendency in Free Radical Copolymerization. NMR Analyses of Alternating and Random Copolymers

An NMR investigation was carried out on variable composition, random and equimolar, alternating copolymers of acrylonitrile (A) with styrene (S), isoprene (I), and butadiene (B). The NMR spectra of the SA copolymers contained peaks at 3 τ (aromatic ring protons), 7.2-7.5 τ (CH protons of A), and 8.1 -8.5 τ (CH and CH₂ protons of S and CH₂ protons of A). All NM R peaks of the alternating SA copolymer were shifted to the higher field due to the shielding effect of S. The NMR spectra of the IA copolymers contained peaks at 4.72-4.91 τ (?CH protons of I), 7.27-7.4 τ (CH protons of A), 7.71-7.93 τ (CH₂ protons of I), and 8.35 τ (CH₃ protons of I and CH₂ protons of A). The peaks at 4.72 τ (?CH) and 7.72 τ (CH₂) were assigned to I in the I-A diad and the peaks at 4.91 τ (?CH) and 7.93 τ (CH₂) were assigned to I in the I-I diad. The NMR spectra of the BA copolymers contained peaks at 4.4-4.6 τ (?CH protons of B), 7.2-7.5 τ (CH protons of A), 7.71-7.97 T (CH₂ protons of B), and 8.0-8.4 τ (CH₂ protons of A). The peaks at 4.42 τ (?CH) and 7.71 τ (CH₂) were assigned to B in the B-A diad and the peaks at 4.6 τ (?CH) and 7.9 τ(CH₂) were assigned to B in the B-B diad. The alternating structure of the copolymers prepared through metal halide-activated complexes was confirmed by NMR analysis. The random copolymers prepared by free radical initiation contain a high concentration of alternating sequences, as anticipated from the values of r₁ and r₂ where r₁(S, I, and B) is 6-10 times higher than r₂ (A).     

Solvation Dynamics of a Radical Ion Pair in Micro‐Heterogeneous Binary Solvents: A Semi‐Quantitative Study Utilizing MARY Line‐Broadening Experiments

This work aims at elucidating the mechanism of solvation of a radical ion pair (RIP) in a micro‐heterogeneous binary solvent mixture using magnetically affected reaction yield (MARY) spectroscopy. For the exciplex‐forming 9,10‐dimethylanthracene/N,N‐dimethylaniline system a comparative, composition‐dependent MARY line‐broadening study is undertaken in a heterogeneous (toluene/dimethylsulfoxide) and a quasi‐homogenous (propyl acetate/butyronitrile) solvent mixture. The half‐saturation field extrapolated to zero‐quencher concentration, B_1/2, and the self‐exchange rate constants are analyzed in the light of solvent dynamical properties of the mixtures and a dielectric continuum solvation model. The dependence of B_1/2 on the solvent composition is explained by cluster formation giving rise to shortened RIP lifetimes. The results are in qualitative agreement with the continuum solvation model suggesting that it could serve as a theoretical basis for quantitative modeling.     

Radical copolymerization of N-alkylmaleimides with isobutene and the properties of the resulting alternating copolymers

Radical copolymerization of N-methylmaleimide (MeMI) as well as other N-alkylmaleimides (RMI) and isobutene (IB) was carried out with 2,2′-azobis(isobutyronitrile) as an initiator at 60°C. The initial rate of the copolymerization (R_p) was dependent on the monomer composition and was maximum at the 40 mol % of MeMI in the feed. A solvent effect on the R_p and the monomer reactivity ratio was observed in this copolymerization system, i.e., copolymerization in chloroform produced a higher R_p and an alternating tendency compared with those in dioxane (r_MeMI = 0.14, r_1B = 0 in chloroform and r_MeMI = 0.47, r_1B = 0 in dioxane). The alternating copolymer of RMI and IB shows a high glass transition temperature (T_g) and excellent thermal stability, e.g., the T_g and the thermal decomposition temperature (T_d) were 152 and 363°C, respectively, for the alternating copolymer of MeMI and IB. Both the T_g and T_d increased as the concentration of the MeMI unit in the copolymers increased. Colorless transparent sheets were obtained from press molding the alternating copolymers. They showed excellent mechanical and optical properties. © 1996 John Wiley & Sons, Inc.     

Solubility and Enhanced Tension of Solute in Solution

Abstract

In solution, solute molecules B are coupled by attractive forces between them and all other molecules present; and these other molecules enhance the tension in the coupling force between solute molecules an amount π_B, the osmotic pressure of the solution solute. Two equilibria determine the n ^o _B moles of pure solute which dissolve in n ¹⁰ _A moles of pure liquid solvent. If at T the solute is solid and in excess, then 1) the n _B ^lsat moles of B in the n^l _A moles of A in a solution saturated with B are in thermodynamic equilibrium with the solid solute at the same T and p and 2) the n _B ^lsat moles of B and n^l _A moles of A may also be in chemical equilibrium with the moles of new molecular or ionic species formed in the solution. Solute molecules dissolve until the chemical potential of the solution solute, p^l _B(T p, x_B ^lsat), equals the chemical potential of pure solid solute at the same T and p, μ _B ^so(T, p). When the solution is saturated with B and the mole fraction of B is x_B ^lsat = n _B ^lsat/σj n ¹ _j, then the vapor pressures of the solid solute at T and p, the solution solute at T and p, and the pure undercooled liquid solute at T and p-π _B ^lsat are identical. If at T the n _B ^lo moles of pure solute and the n^l _A moles of pure solvent are liquids, then if molecules of B are allowed to dissolve in A while molecules of A are dissolved in B, the resulting solutions may 1) contain only molecules of A and B or 2) contain A and B which also react to form other ionic and molecular species. The two solutions may be identical or they may differ. In all cases, however, the mole ratio of n^l _Bn^l _A in both solutions must be identical.     

Distribution of Pu(VI) from nitric acid to tri-n-butyl phosphate saturated with uranium(VI)

Solvent extraction of plutonium(VI) from nitric acid (1 to 5M) into 20% and 30% TBP in dodecane saturated with uranium(VI) (0% to 80%) has been studied. For a particular nitric acid concentration, the distribution coefficient (K _d ) is found to decrease with the increase in saturation of organic phase with uranium(VI). At a fixed organic phase the saturationK _d increased with increase in nitric acid concentration, however, the magnitude of this increase inK _d decreased with the increase in saturation.     

Cubic-grid Gaussian basis sets for electron scattering calculations IV

Summary An analytical formula has been derived for averaging the differential cross section for electron scattering with respect to isotropic target molecule orientation. It may be applied to any type ofT-matrix element k ^out|T|k ⁱⁿ in which the plane-wave functionsk ^out andk ⁱⁿ are expanded in a set ofs-type Gaussian functions. The formula for averaging was tested against results obtained by Monte-Carlo-type calculations and against experimental data for elastic electron scattering by the H₂ molecule.     

A revised equation for estimating the vapour pressure of low-volatility substances from isothermal TG data

Previous investigators have used the Langmuir vaporisation relation to estimate the vapour pressures of low-volatility compounds from thermogravimetric data. However, this equation is strictly valid for evaporation into a vacuum only. For measurements conducted at finite pressures, molecular diffusion must be taken into account. A revised equation is proposed: dm _A/dt8M _A P _A D _A B/T. It is also shown that the proportionality between vapour pressure and vaporisation rate is very general. It arises from the assumptions of ideal gas behaviour, Raoult's law and a negligible concentration of the sample compound far from the sample surface. This revised version was published online in August 2006 with corrections to the Cover Date.     

Batch and dynamic extraction of uranium(VI) from nitric acid medium by commercial phosphinic acid resin,Tulsion CH-96

Batch and dynamic extractions of uranium(VI) in 10⁻³–10⁻²M concentrations in 3–4M nitric acid medium have been investigated using a commercially available phosphinic acid resin (Tulsion CH-96). The extraction of uranium(VI) has been studied as a function of time, batch factor (V/m), concentrations of nitric acid and uranium(VI) ion. Dual extraction mechanism unique to phosphinic acid resin has been established for the extraction of uranium(VI). Distribution coefficient (K _d ) of uranium(VI) initially decreases with increasing concentration of nitric acid, reaches a minimum value at 1.3M, followed by increases in K _d . A maximum K _d value of ∼2000 ml/g was obtained at 5.0M nitric acid. Batch extraction data has been fitted into the linearized Langmuir adsorption isotherm. The performance of the resin under dynamic extraction conditions was assessed by following the breakthrough behavior of the system. Effect of flow rate, concentrations of nitric acid and uranium ion in the feed on the breakthrough behavior of the system was studied and the data was fitted using Thomas model.