Adsorption kinetics with time delay

A theory of adsorption kinetics of solutes onto a solid surface from the solution phase is proposed in which a time delay is introduced into the solute concentration on the surface. Equations governing the adsorption kinetics are similar to those for membrane transport with time delay (Ohshima and Kondo, Biophys. Chem. (1989) 33: 303). It is found that introduction of time delay causes, under certain conditions, overshoot or oscillation in the solute concentrations, both in the solution phase and on the surface. The criterion for oscillation depends on the scaled delay time , the ratio of the possible maximum amount of solutes adsorbed on the surface to the total solute amountR, and the scaled binding constantK. When the number of the binding sites is small, the criterion for oscillation is expressed as >exp(–1), where =(/K) exp().     

Transient photocapacitance study in 4-nitro-4′-aminodiphenyl layers

In 4-nitro-4-aminodiphenyl (NAD) layers the photocapacitance (PhC) transients were investigated. PhC spectral distribution as well as the temperature dependences of time constants (under/_on/or after/_off/illumination) have been measured. The photocapacitance spectral distribution possesses maxima at 350, 500, and 750 nm. It was shown that _on (T) is of exponential form while _off (T) is more complicated. The values of thermal activation energies (0.65±0.05) eV of both time constants coincide. The mechanism of photocapacitance process has been disclosed in NAD layers.     

Prediction of the non-Newtonian viscosity and shear stability of polymer solutions

The structure-property relationships derived here permit the prediction of both the zero-shear viscosity ₀, as well as the shear rate dependent viscosity . Using this molecular modeling it is now possible to predict over the whole concentration range, independently of the molecular weight, polymer concentration and imposed shear rate. However, the widely accepted concept: dilute — concentrated, is insufficient. Moreover it is necessary to take five distinct states of solution into account if the viscous behavior of polymeric liquids is to be described satisfactorily. For non-homogeneous, semi-dilute (moderately concentrated) solutions the slope in the linear region of the flow curve (= must be standardized against the overlap parameterc · []. As with the ₀-M-c-relationship, a-M -c- relationship can now be formulated for the complete range of concentration and molecular weight. Furthermore, it is possible to predict the onset of shear induced degradation of polymeric liquids subjected to a laminar velocity field on the basis of molecular modeling. These theoretically obtained results lead to the previously made ad hoc conclusion (Kulicke, Porter [32]) that, experimentally, it is not possible to detect the second Newtonian region.Roman and Italian symbols a exponent of the Mark-Houwink relationship - b exponent of the third term of the ₀-M -c relationship - c concentration /g · cm^–3 - E number of entanglements per molecule - F(r) connector tension - f function - G _i ^A shear modulus; A indicates that it /Pa has been evaluated by a transient shear flow experiment; i is the shear rate to whichG ^A refers to - G storage modulus /Pa - G _p plateau modulus /Pa - H() relaxation spectrum /Pa - h shift factor (₀/_r) - K _H Huggins constant - K _b third constant of the ₀-M -c relationship - K constant of the Mark-Houwink relationship - M molecular weight /g · mol^–1 - M _e molecular weight between two /g · mol^–1 entanglement couplings - N number of segments per molecule - n slope in the power-law region of the flow curve - p p-th mode of the relaxation time spectrum - R gas constant /8.314 J·K^–1·mol^–1 - r direction vector - T temperature /K Greek symbols ß reduced shear rate - shear rate /s^–1 - shear viscosity /Pa·s - _s solvent viscosity /Pa·s - _sp specific viscosity - ₀ zero-shear viscosity /Pa·s - apparent viscosity at shear rate - reduced viscosity - viscosity of polymeric liquid in /Pa·s the second Newtonian region - [] intrinsic viscosity/cm³·g^–1 - screening length/m - /g·cm ^–3 density - relaxation time/s - ₀ experimentally derived relaxation time/s - angular frequency of oscillation Indices conc concentrated - corr slope corrected - cr critical - deg degradation - e entanglement - exp experimental - mod moderately concentrated/semi-dilute - n number average - p polymer - R Rouse - rep reptation - s solvent - sp specific - theo theoretical - weight average - relaxation time - o experimental or steady state - * critical - ** transition moderately conc. — conc. - + transition dilute — moderately cone. Paper presented at the 2nd bilateral U.S.-West German Polymer Symposium, Yountville, the 7th–11th September 1987.     

Correlation between the rotational mobility and the kinetics of the intramolecular exchange of the unpaired electron and bond in a tin-containing free radical with two pyrocatechol ligands

EPR spectroscopy was used to study the effect of the mobility of the medium on the dynamics of the interligand exchange of the unpaired electron and bond in the free radical formed upon the reaction of stannous bis-3,6-di-tert-butyl-o-semiquinolate with 3,6-di-tert-butyl-2-hydroxyphenoxyl in the presence of triphenylphosphine. A dependence exists between the characteristic exchange time _ex and the correlation time for the rotational mobility of the radical _c; _ex= _c. A temperature dependence was found for coefficient .Translated from Izvestiya Akademii Nauk SSSR. Seriya Khimicheskaya, No. 7, pp. 1663–1666, July, 1990.     

Generalized rheological characteristic of plastic disperse systems with polymeric and low-molecular dispersion media (matrices)

Analysis of literature data on the flow of polymeric and oligomeric compositions as well as on systems of low viscous dispersion media containing a high-disperse filler (carbon black, silica, high-disperse chalk) has been carried out. As the basic idea, a proposal is made that their viscosity anomaly is due not to the matrix viscosity anomaly, but to the gradual breakdown of the filler structural skeleton with increasing shear stress and shear rate . The viscosity anomaly of those compositions is determined by the zeroshear but not by the apparent matrix viscosity. A general relationship has been found to describe the flow of such systems depending on the zero-shear matrix viscosity values, ₀, their yield stress, _y , and filler volume concentration , whereK=4.9 andn=0.69 are constants.     

CPS GL 799

The effect of illumination on transport of sulfonated bisazo direct dyes, CI Direct Yellow 12, and CI Direct Yellow 4, into a cellulose membrane has been studied at various temperatures. Transport of CI Direct Yellow 12, which exhibits photoinduced reversible trans-cis isomerism in aqueous solution into a cellulose membrane, was influenced by illumination. It is likely that the transport was influenced by transisomerization of the photoisomeric dye and the diffusivity was controlled by surface diffusion rather than by pore diffusion under both light and dark conditions.Notations C Concentration of dye in the pores (mol/dm³) - C _E Concentration of electrolyte in the bulk solution (mol/dm³) - C _o Concentration of dye in the bulk solution (mol/dm³) - D _p Pore diffusivity (m²/s) - D _s Surface diffusivity (m²/s) - [M] Mean concentration of dye in membrane (mol/dm³) - [M] _L Local concentration of dye in membrane (=q+ _p C) (mol/dm³) - [M] Mean concentration of dye in membrane (mol/kg) - [M] _L Local concentration of dye in membrane (=q/V+ _p C) (mol/dm³) - F Fractional attainment of equilibrium - l Thickness of membrane (m) - q Concentration of dye adsorbed on pore wall (mol/dm³) - q _o Adsorbed concentration of dye in equilibrium withC _o (mol/dm³) - q Concentration of dye adsorbed on pore wall (mol/kg) - q _o Adsorbed concentration of dye in equilibrium withC _o (mol/kg) - t Time (s) - V Volume of membrane swollen with water per unit dry cellulose (dm³/kg) - x C/C _o - y q/q _o - z Distance that the dye diffused in the membrane (m) - q _o / _o C _o - D _s /D _p - Coefficient of the Freundlich isotherm - _p Pore void fraction - z/l - _p D _p t/l ² - _s D _s t/l ²     

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability ^c = – i is examined. Loss curves ( and tan ) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios (at maximum or tan )/ (at maximum or tan ) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.     

Correlation between solvent-reorganization dynamics and the kinetics of metallotropy in polar media

The kinetics of metallotropy of the 3,6-di-tert-butyl-2-(triphenylstannyl)oxyphenoxyl radical has been studied by ESR. The correlation between chemical exchange time _ex, solvent polarity, and longitudinal relaxation time of the solvent corresponds to the model of a process controlled by molecular dynamics. A linear relation between _ex and correlation time _c for reorientation movements of the radical is found: _ex = · _c. The coefficient depends on the dielectric properties of the solvent.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 410–413, March, 1994.This work was supported by the Russian Foundation for Basic Research, project No. 93-03-4372.     

Epithermal neutron flux characterization of the TRIGA MARK II reactor,Ljubljana, Yugoslavia,for use in NAA

The nonideality of the epithermal neutron flux distribution at a reactor site can be described by a 1/E¹⁺ spectrum representation, with parameter being a measure of the nonideality. -values were determined in 3 typical irradiation positions of the TRIGA MARK II reactor of the Jozef Stefan Institute, Ljubljana, Yugoslavia, using the Cd-ratio for multi-monitor method. The simpler Cd-ratio for dual monitor method (monitors:¹⁹⁷Au–⁹⁴Zr) also yielded reliable results. This characterisation is of use in the k₀-method of NAA, which is recently introduced at the Institute.     

Phase diagram of the system dihexadecylphosphatidylcholine/dihexadecyl-phosphatidic acid/water/NaOH at pH=14

Differential-scanning-calorimetry, freeze-fracture electron microscopy, and³¹P-NMR spectroscopy were used to study the lyotropic and thermotropic properties of the system dihexadecylphosphatidylcholine/dihexadecylphosphatidic acid/water/ NaOH in dispersion with excess water at pH=14. The phase diagram showed that both phospholipids are demixed nearly completely in the gel phase. The coexistence of theP and theB -phase in the mixtures was pointed out in the freeze-fracture electron micrographs by the ripple structure (P -phase) and by the lamellar structure (B -phase).     

Orientation of the diphenylene propane unit in stretched polycarbonate from two-dimensional magic-angle-spinning NMR

Two-dimensional magic-angle-spinning (2D-MAS) NMR has been used to measure the orientation parameter, P₂, of the diphenylene propane unit in bisphenol-A polycarbonate oriented by stretching to various extension ratios,, atT=295K andT= 403 K.P ₂ is proportional to the birefringencen, with a maximum birefringencen ₀= 0.189. There is some evidence that the order parameterP ₂ of the DPP units with respect to the chain axis deviates from unity.n ₀ is therefore expected to be different from the birefringence,n ₀ , of perfectly aligned chains of polycarbonate. The experimental results obtained forP ₂() are compared to those predicted by the aggregate model.     

Influence of mobility of medium on dynamics of metallotropy in tin-containing 2-R-oxyphenoxyls

The rate of intramolecular migration of the triphenylstannyl group in 3,6-ditert-butyl-2(triphenylstannyl) oxyphenoxyl decreases with increasing viscosity of the medium. A linear relationship _ex=·_c is observed between the characteristic time of stannotropy _ex and the correlation time for reorientational motions of the radical _c within a range of temperature variation no greater than 30°C. The parameter depends on the medium; this is explained by the possibility of complexation of the radical with the solvent.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 781–786, April, 1990.     

Properties of double chlorides in the systems ACl/NdCl3 (ANa-Cs)

The pseudobinary systems ACl/NdCl₃ (A=Na-Cs) were reinvestigated by means of DTA. The following double chlorides were found primarily detected compounds are underlined):Na ₃Nd₅Cl₁₈; K₃NdCl₆, K₂NdCl₅,KNd ₂Cl₇;Rb ₃NdCl₆, Rb₂NdCl₅,RbNd ₂Cl₇; Cs₃NdCl₆,Cs ₂NdCl₅,CsNd ₂Cl₇.With a galvanic cell for solid electrolytes the thermodynamic functions of formation from ACl and NdCl₃ together with the free enthalpies of synproportionation from the compounds adjacent in the phase diagrams were measured. They revealed, that only the compounds A₂NdCl₅ are stable at ambient temperature. All other compounds are existing by a gain of entropy only at higher temperatures.The crystal structures of the compounds were determined by X-ray analysis on powders: the compounds are isotypic with the analogous double chlorides of La and Ce (A₃NdCl₆: high-temperature-modification = elpasolite-type; at room-temperature = metastable K₃MoCl₆-type; A₂NdCl₅=K₂PrCl₅-type; ANd₂Cl₇=-KEr₂F₇-type; Na₃Nd₅Cl₁₈=Na₃La₅Cl₁₈-type). Magnetic susceptibilities in the range from 80 to 300 K were measured with a Gouy-balance.

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Zusammenfassung Die pseudobinären Systeme ACl/NdCl₃ (A=Na-Cs) wurden mittels DTA neu untersucht. Folgende Doppelchloride wurden gefunden (erstmalig beschriebene Verbindungen sind unterstrichen):Na ₃Nd₅Cl₁₈; K₃NdCl₆, K₂NdCl₅,KNd ₂Cl₇;Rb ₃NdCl₆, Rb₂NdCl₅,RbNd ₂Cl₇; Cs₃NdCl₆,Cs ₂NdCl₅,CsNd ₂Cl₇.Mit einer galvanischen Zelle für feste Elektrolyte wurden die thermodynamischen Funktionen für die Bildung aus ACl und NdCl₃ sowie die freien Enthalpien für die Synproportionierung aus den im Zustandsdiagramm benachbarten Verbindungen gemessen. Es zeigte sich, daß nur die Verbindungen A₂NdCl₅ bei Normaltemperaturen stabil sind. Alle anderen Verbindungen existieren aufgrund von Entropiegewinnen nur bei höheren Temperaturen. Anhand von Röntgen-Pulveraufnahmen wurden die Kristallstrukturen ermittelt. Die Verbindungen sind isotyp zu den entsprechenden Doppelchloriden des Lanthans und Cers (A₃NdCl₆: Hochtemperaturmodifikationen = Elpasolith-Typ; bei Normaltemperatur metastabil im K₃MoCl₆-Typ; A₂NdCl₅=K₂PrCl₅-Typ; ANd₂Cl₇=-KEr₂F₇-Typ; Na₃Nd₅Cl₁₈=Na₃La₅Cl₁₈-Typ). Mit einer Gouy-Waage wurden die magnetischen Suszeptibilitäten im Temperaturbereich 80–300 K gemessen.

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ACl/NdCl₃, =NaCs. , : Na₃Nd₅Cl₁₈, K₃NdCl₆, K₂NdCl₅, KNd₂Cl₇, Rb₃NdCl₆, Rb₂NdCl₅, RbNd₂Cl₇, Cs₃NdCl₆, Cs₂NdCl₅, CsNd₂Cl₇. , . , A₂NdCl₅. . . , . A₃NdCl₆ , — K₃l₆. A₂NdCl₅ — K₂rl₅, ANd₂Cl₇ — -KEr₂F₇, Na₃Nd₅Cl₁₈- Na₃La₅Cl₁₈. 80–300 .

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This work was supported by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.     

Catalase monolayers at the air/water interface I. Reversibilities and irreversibilities

/A-isotherms of catalase monolayers established at the air/water-interface are discussed quantitatively on the basis of molecular data: A relationship between a critical value of the surface pressure, the corresponding molecular area, and the molecular dimension of the molecules at the interface is proposed. It is shown that the unfolding of molecules at the water surface is pH-dependent. For each pH-value there is a distinct degree of unfolding; the molecules keep their globular state at neutral pH. Establishment at the surface of bulk solutions corresponding to globular and partly unfolded states, respectively, catalase molecules keep their original configuration on changing the pH-value of bulk-phase. The monolayers are confirmed to show reversibility with regard to lateral changes of state as well as irreversibility with respect to desorption of molecules.A model is proposed to explain the nature of the critical/A-value occurring in the/A-isotherms: on compression beyond _c, molecular segments are transferred from the surface into the bulkphase via a subsurface layer. From the experiments it is concluded that the surface pressure is determined, not only by the surface itself, but also by this subsurface layer.     

Characterization of polymer networks by measurements of the freezing point depression

Based on the phenomenon of freezing point depression of a solvent byT, experimental evidence is presented to show that the distance between the junction points can be calculated fromT. Direct measurements of the temperature-time-curve of the cooling network and the Differential Scanning Calorimetry offer the determination ofT. Except the mean distances ¯d _c in dependence on cross-linking density, swelling degree, and other network parameters, the distribution of the distance between the junction pointsH(d_c) can be determined, which allows conclusions on the course of cross-linking reaction. This paper attempts to give experimental evidence of influences of the breadth ofH(d_c) on application-relevant properties.     

Steroid compounds from the Pacific starfishesLuidia quinaria andDistolasterias elegans

One new and four previously known steroid compounds were identified from the Pacific starfishesLuidia quinaria andDistolasterias elegans. The structure of the new steroid was established from spectral data and chemical correlations with other steroids such as 5-cholestane-3,5,6,15,16,26-hexaol 3-sulfate (1). The previously known compounds were identified as 5-cholestane-3,5,6,15,26-pentaol 15-sulfate (2) fromLuidia quinaria and sodium (24S)-O-(-d-giucopyranosyll-5-cholestane-3,6,8,15,24-pentaol 6-sulfate (3), sodium (24S)-5-cholestane-3,6,8,15,24-pentaol 24-sulfate (4), and sodium tornasterol A sulfate (5).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 473–476, February, 1996.     

Viscosity B coefficients of polyethyleneglycols in water

The viscosity B coefficients of polyethylene glycols (M=62–1000) are determined at 25 °C. The B coefficient increases non-linearly with the number of ethyleneoxide (EO) units. The increase of the B coefficient per EO(0.111 dm³/mole) is less than the B value for two methylene groups (0.160 dm³/mole). This is discussed in terms of changes in the configurations of polyethylene glycols with long EO chains.Molecular size is the major factor that contributes to B at shorter chains, but solvation (hydration) becomes dominant as the number of ethyleneoxide groups increases. The hydration parameter,(gH₂O/g ethyleneglycol), shows a linear dependence on B at low mass followed by a non-linear increase at high molecular mass and the viscosity C coefficient accounts for the solute-solute interactions.Symbols absolute viscosity - _d absolute viscosity of dispersion medium - _r relative viscosity - _sp specific viscosity - ¦ _o ¦ intrinsic viscosity at infinite dilution - ¦ _c ¦ intrinsic viscosity as a function of solute concentration - partial specific volume - volume fraction - hydration (weight of H₂O hydrating 1 g of polyethylene glycol) - _c hydration as a function of solute concentration - K shape function - K _c shape function as a function of solute concentration     

A simplified model of the ECD

A simplified model of the ECD is presented, which is based on the assumption that only a change in the concentration of electron is generating a signal. The model allows to determine four different time constants related to: the collection of electrons (₁), the loss of electrons in the capture process by the impurity molecules (₂), the loss of sample molecules by electron capture (_n) and the removing rate of molecules from the detector volume by the carrier gas (_v). The values of these time constants have been estimated to be in the range of s for ₁, ms for ₂, a part of a second for _n and a few seconds for _v. The electron capture efficiency coefficient (p) and the detection coefficient (S_d) have been defined. These coefficients serve in the model for the coulometric calculation of the mass of analyzed compounds, if the detector works using the conditions described.     

Vibrational isotope effect of linear and planar molecules: Deuterated bromoethenes

Linear (planar) molecules A and B which are identical except for isotopic substitutions at the atomic sites are considered. Stretching (bending, out-of-plane) frequencies _k and normal modes _k of the isotopically perturbed molecule B are expressed in terms of stretching (bending, out-of-plane) frequencies _i and the corresponding normal modes _i of the unperturbed molecule A. Complete specification of the unperturbed normal modes is not required. All that is needed are stretching (bending, out-of-plane) amplitudes | _i of the normal modes _i at those sites that are affected by isotopic substitution. The rule which interlaces frequencies _k of molecule A with frequencies _i of molecule B is derived. Given two isotopic molecules A and B that differ by a single isotopic substitution at site , the inversion relation is derived. This relation expresses unperturbed stretching (bending, out-of-plane) amplitudes at the site in terms of stretching (bending, out-of-plane) frequencies of molecules A and B . As an example, out-of-plane vibrations of deuterated bromoethene were considered. In the simplest method 12 out-of-plane frequencies of four polydeuterated bromoethenes were calculated from 12 out-of-plane frequencies of bromoethene and three monodeuterated bromoethenes. Standard deviation of thus calculated frequencies from experimental frequencies is =2.74 cm^–1. In another method, 15 out-of-plane frequencies of four polydeuterated bromoethenes and selected monodeuterated bromoethene are calculated from 9 out-of-plane frequencies of bromoethene and the remaining two monodeuterated bromoethenes. Depending on which monodeuterated bromoethene is selected (1-, cis- or trans-), standard deviation of thus obtained frequencies from experimental frequencies is 1=2.84 cm^–1, c=2.96 cm^–1 and t=2.72 cm^–1.     

A structural study of the naringin-β-cyclodextrin complex

The structure of the inclusion complex formed between naringin (naringenin-7-O--neohesperidoside) and-cyclodextrin (BCD) was studied in detail by UV and NMR spectroscopic techniques and potentiometry. A binding constant value of 1016±150M^–1 was arrived at from UV studies. Potentiometric studies showed that pK values of 4-OH and 5-OH were affected by and-cyclodextrins. One-dimensional difference NOE and spin-lattice relaxation time (T ₁) measurements indicated that the aglycone protion was affected more than the neohesperidoside portion. TheT ₁ values analysed for local motions indicated that _c values of complexed naringin was higher than that of free naringin. The internal rotation calculated for different groups showed _i values for the phenolic and dihydrobenzopyran portion decrease by a factor of 2. Also a value of 0.12–0.17 observed for the aglycone portion indicated that the coupling between guest and host is weak. All the studies have shown that the disposition in which the phenol group at 2 is inside the BCD cavity with 4-keto and 5-OH hydrogen bonded to the secondary hydroxyl groups at the rim of the wider end of the BCD cavity is the most probable one.