DELAYED-LIGHT STUDIES ON PHOTOSYNTHETIC ENERGY CONVERSION-III. EFFECT OF 3-(3,4-DICHLOROPHENYL)-1,1 -DIMETHYL UREA ON THE MILLISECOND EMISSION FROM CHLOROPLASTS PERFORMING PHOTOREDUCTION OF FERRICYANIDE*

Abstract— How does a plant convert electronic excitation of chlorophyll into stable chemical potential? The time scales of fluorescence (10^--⁹ sec) and steady-state enzymatic turnover (10–² sec) indicate that energy storage must be involved. Millisecond delayed singlet emission from chlorophyll allows measurement of metastable energy storage at Photoreaction II. Activation of noncyclic electron transport results in more rapid decay and in increase of emission at 10^--³ sec, both effects being inhibited by the poison DCMU. These results can be explained by at least three different models of the reaction center: the oxidized chlorophyll model, the chlorophyll triplet model, and the two-quantum electron-hole model.     

Voltammetric concentration measurements in diffusion-hindered media

In voltammetric analysis the signal—in most cases—depends on transport processes. When getting concentration values of analytes from voltammetric calibrating curves, it is expected that the mass transport characteristics in sample solutions and in calibrating standards are identical. Standard addition methods are used in analytical practice when making calibrating standard with transport properties matching that of the samples would be difficult. Voltammetric measurements can also be carried out in soil—in sediment—or in gel samples. The mass transport conditions in these media, however, can considerably differ from those existing in aqueous solutions. The application of standard addition technique, however, is not an option there. In this work, a glassy carbon electrode was applied with a built-in diffusion layer on its measuring surface and chronoamperometric measurements were carried out. The current–time transients taken in aqueous solution and in tortuous, diffusion-hindered media were compared. Ascorbic acid and iodine as analytes as well as silica sand sediments and green pepper pulps as tortuous matrices were used. It was proved that if the modified electrode is used for analysis, then short time chronoamperometric transients taken in tortuous media can be evaluated by calibration data taken in aqueous standard solutions.     

The dependence of electro-osmotic flow on current density and time

The dependence of the water transport number on current density is examined for three membranes whose characteristics cover a wide spectrum: poly(vinylbenzenesulfonate), porous Vycor glass and cellulose. Experiments and theory show that non-linear volume—time plots in electro-osmotic experiments arise from displacements of the membrane in the electric field, and that reliable water transport numbers can be obtained at a given current density. When the current density is varied, experiments show that the observed water transport number can: (a) increase at low current densities because of osmotic flow superimposed on water transport by the electric field; (b) decrease at higher current densities because of accumulation of salt in the membrane; (c) decrease more at current densities near and above the limiting value because of an increased contribution of hydrogen and hydroxide ions to transport. These phenomena arise from a combination of diffusion films at both membrane—solution interfaces and from the dependence of counteflon and water transport numbers on external salt concentration.     

An ab initio effective potential for two particles in the field of the core: a reduction of (N + 2)-electron problem to two-electron problem

We have used many-body Green function theory and the two-electron Bethe—Salpeter equation to derive an approximate two-electron position space hamiltonian eigenvalue equation for two electrons in the presence of a closed shell core. The resulting effective hamiltonian is nonlocal, energy independent, hermitian and nonadiabatic. It includes all the core—valence, valence—valence exchange effects, core screening effects and electron—electron correlation effects. If a closed form solution of the equation is difficult because of the need to construct the hamiltonian, a semi-empirical approach can be taken which expresses much of the hamiltonian in terms of known properties of the core. A semi-empirical analysis of this effective hamiltonian is shown to give well-known phenomenological effective hamiltonians and the connections to them. Thus this work can also be viewed as a theoretical justification and extension of the two-electron model potential or pseudopotential theories.     

Mapping Multivalency and Differential Affinities within Large Intrinsically Disordered Protein Complexes with Segmental Motion Analysis

Intrinsically disordered proteins (IDPs) can bind to multiple interaction partners. Numerous binding regions in the IDP that act in concert through complex cooperative effects facilitate such interactions, but complicate studying IDP complexes. To address this challenge we developed a combined fluorescence correlation and time‐resolved polarization spectroscopy approach to study the binding properties of the IDP nucleoporin153 (Nup153) to nuclear transport receptors (NTRs). The detection of segmental backbone mobility of Nup153 within the unperturbed complex provided a readout of local, region‐specific binding properties that are usually masked in measurements of the whole IDP. The binding affinities of functionally and structurally diverse NTRs to distinct regions of Nup153 can differ by orders of magnitudes—a result with implications for the diversity of transport routes in nucleocytoplasmic transport.     

Spatio-temporal organization in alloy electrodeposition: a morphochemical mathematical model and its experimental validation

This paper proposes a novel mathematical model for the formation of spatio-temporal patterns in electrodeposition. At variance with classical modelling approaches that are based on systems of reaction–diffusion equations just for chemical species, this model accounts for the coupling between surface morphology and surface composition as a means of understanding the formation of morphological patterns found in electroplating. The innovative version of the model described in this work contains an original, flexible and physically straightforward electrochemical source term, able to account for charge transfer and mass transport: adsorbate-induced effects on kinetic parameters are naturally incorporated in the adopted formalism. The relevant non-linear dynamics is investigated from both the analytical and numerical points of view. Mathematical modelling work is accompanied by an extensive, critical review of the literature on spatio-temporal pattern formation in alloy electrodeposition: published morphologies have been used as a benchmark for the validation of our model. Moreover, original experimental data are presented—and simulated with our model—on the formation of broken spiral patterns in Ni–P–W–Bi electrodeposition.     

Exciton transport at short times

Exciton transport at short times is studied for the model of Grover and Sibey. The transport is always wave-like, and is governed by the unrenormalized transfer integral appropriate to unclothed excitons. Comparison with the long-time transport confirms that clothing occurs within about 10 ps. The results are discussed in the light of recent work on the generalized exciton master equation. This gives initially wave-like transport whenever the initial exciton density matrix is diagonal, and its agreement with the present results supports the claim that it can treat short-time effects. Previous comparisons with the model of Grover and Sibey could be misleading because only the long-time behaviour was treated.     

Enantioselective adsorption of dipeptides on chiral stationary phases with grafted macrocyclic antibiotics using glycylaspartic acid as an example

The chromatographic behavior and adsorption of enantiomers of glycylaspartic acid on the Nautilus-E chiral stationary phase with grafted eremomycin antibiotic were studied. Acetate buf er mixtures with variable pH prepared in a water—methanol mixed solvent (volume ratio 60 : 40) were used as acetate buf ers. The retention of Gly—Asp was found to be enantioselective and depending on the ratio of various ionic forms of dipeptide in the mobile phase. The ratio is determined by the pH. A model of adsorption equilibrium assuming independent binding of diverse ionic forms with the stationary phase, which is characteristic of energy uniformity, was proposed. This model is well consistent with the experimental data. Features of application of the equilibrium dispersion and transport dispersion dynamic elution models for the determination of the adsorption isotherms by the inverse method are discussed.

     

Distal charge transport in peptides

Biological systems often transport charges and reactive processes over substantial distances. Traditional models of chemical kinetics generally do not describe such extreme distal processes. In this Review, an atomistic model for a distal transport of information, which was specifically developed for peptides, is considered. Chemical reactivity is taken as the result of distal effects based on two-step bifunctional kinetics involving unique, very rapid motional properties of peptides in the subpicosecond regime. The bifunctional model suggests highly efficient transport of charge and reactivity in an isolated peptide over a substantial distance; conversely, a very low efficiency in a water environment was found. The model suggests ultrafast transport of charge and reactivity over substantial molecular distances in a peptide environment. Many such domains can be active in a protein.     

(1D + 1D) approach mathematical modeling of two phase multicomponent transport flow in PEMFC

A quasi two dimensional (1D + 1D), multi-component model is developed in order to analyze the two-phase transport in polymer electrolyte fuel cell. Different operating parameters, including temperature and wettability are examined and their effects are discussed. The present simple and easy to implement model can be as accurate as a complete two dimensional model. Furthermore, it is seen that the simplification made in this model reduce the computational time.     

Chemischer Transport fester Lösungen. 22 [1] Beschreibung des Chemischen Transports im System ZnS/ZnSe

Studies on the Chemical Vapor Transport in the System ZnS/ZnSe By means of chemical transport reactions homogeneous ionic mixed crystals with well defined compositions can be prepared in a simple way. This is shown at the example of ZnS/ZnSe‐mixed crystals. ZnS_1?xSe_x‐mixed crystals can be prepared by chemical vapour transport in the temperature gradient 1000 → 900 °C using iodine as transport agent. A thermodynamic model is presented to calculate the thermodynamic stability of ionic mixed phases and possible enrichment effects during the vapor transport. The results are compared with experimental fundings and well known transport models.     

Coupled transport membranes III: the rate-limiting step in uranium transport with a tertiary amine

This is the second paper describing the coupled transport of uranium ions through liquid membranes. The membranes consist of a microporous polymeric support with an organic solution of a tertiary amine complexing agent held within the pores by capillary forces. p]Both the composition of the organic solution and the structure of the microporous support have a marked effect on uranium flux. With increasing concentration of the agent in an inert diluent, both the amount of uranium that can be extracted into the membrane and the viscosity of the organic solution increase. These opposing effects result in a maximum flux at about 30 vol.% agent in the diluent. The size of the pores in the support also affects the flux; it appears that interaction with the pore walls in membranes with small pores hinders diffusion. p]Two types of interfacial effects have also been observed. The first of these is concentration polarization in the aqueous solution adjacent to the membrane surface. This effect can be reduced by increased stirring. Second, the transmembrane flux of uranium can be limited by the rate of formation (or dissociation) of the uranium complex at the membrane—solution interfaces.     

Phospholipids as Functional Constituents of Biomembranes

This article describes new methods for the synthesis of biologically active phospholipids. The physical properties of such compounds are directly related to their chemical structure, the position of the substituents esterified with glycerol not only influencing the physical properties but also the biological function of the phospholipids. Phase transitions can be induced by temperature changes and—in biological systems—by changes in the surface charge or the degree of protonation. In model studies, the properties of lipid phases differ sufficiently to influence and control biological membrane processes. Alkyl glycerides can modify the properties of biological membranes quickly and reversibly to increase the permeation of active compounds. An important example is the improved transport of cytostatic drugs across the blood-brain barrier. Knowledge about the substrate specificity of enzymes that metabolize phospholipids allows the synthesis of tailored cytotoxic phospholipids which selectively accumulate in malignant tissues. Thus, the interplay of chemical synthesis and investigations of physical structure lays a foundation for the understanding of simple membrane processes on a molecular level, and the experience gained with such model systems can, in turn, be used to influence natural membranes, such as those of the blood-brain barrier or of tumors, in a directed way.     

Activation of the hippocampal AC‐cAMP‐PKA‐CREB‐BDNF signaling pathway using WTKYR in depression model rats

Depression, also called “depression disorder,” is characterized by a significant and persistent low mood. It has become a major refractory disease in the 21st century. In recent years, Chinese medicine has shown some important clinical value in the treatment of depression. Among them, the Warming and “Tonifying” Kidney‐Yang Recipe (WTKYR) has been demonstrated to have obvious effects in the clinical treatments of depression; however, the mechanism remains unclear. This study is based on the adenylyl cyclase (AC)—cyclic adenosine monophosphate (cAMP)—protein kinase A (PKA)—cAMP response element‐binding protein (CREB)—brain derived neurotrophic factor (BDNF) signaling pathway, aiming to investigate the mechanism of WTKYR. The results showed that WTKYR can upregulate AC‐cAMP‐PKA‐CREB‐BDNF in the hippocampus of depression model rats and alleviate its depressive symptoms, which may be the mechanism of WTKYR.     

Chemischer Transport fester Lösungen. 10 [1] Zum Chemischen Transport von quaternären Cobalt(II)‐Zink‐ und Mangan(II)‐Zinkgermanaten

Chemical Vapor Transport of Solid Solutions 10 [1] The Chemical Vapor Transport of quarternary Cobalt(II)‐Zinc and Manganese(II)‐Zinc Germanates By means of chemical vapor transport methods using HCl or Cl₂ as transport agent the crystalline solid solutions (Zn_xCo_1—x)₂GeO₄ and (Mn_xZn_1—x)₂GeO₄ have been prepared (1050 → 900 °C, 850 → 700 °C, respectively). ZnGeO₃ — although unknown as a pure solid — can be stabilized as a mixed crystal (Mn_xZn_1—x)GeO₃ (x > 0, 5).     

Dipicrylamine transport across an ultrathin phosphatidylethanolamine membrane

Admittance measurements at zero applied direct voltage are reported for solutions containing 10^?4 to 10^?7M dipicrylamine, in contact with a black phosphatidylethanolamine membrane. The experimental data can be interpreted quantitatively in terms of a model involving slow phase transfer and fast desorption—adsorption kinetics. The adsorption of dipicrylamine makes it possible to distinguish experimentally between ion transport across the membrane itself and that across the water/membrane interfaces.     

Elastic Moduli: a Tool for Understanding Chemical Bonding and Thermal Transport in Thermoelectric Materials

The elastic behavior of a material can be a powerful tool to decipher thermal transport. In thermoelectrics, measuring the elastic moduli—directly tied to sound velocity—is critical to understand trends in lattice thermal conductivity, as well as study bond anharmonicity and phase transitions, given the sensitivity of elastic moduli to the chemical bonding. In this review, we introduce the basics of elasticity and explain the origin of high-temperature lattice softening from a bonding perspective. We then review elasticity data throughout classes of thermoelectrics, and explore trends in sound velocity, anharmonicity, and thermal conductivity. We reveal how experimental sound velocities can improve the accuracy of common thermal conductivity models and present a critical discussion of Grüneisen parameter estimates from elastic moduli. Readers will be equipped with tools to leverage elasticity measurements or calculations to accurately interpret thermal transport trends.     

Optical sensitization of charge carrier transport in poly(N-vinyl carbazole)

Abstract— The photoconductivity of thin films of poly(N-vinyl carbazole), and poly(N-vinyl carbazole) sensitized with a thin layer of amorphous selenium, has been measured using a ‘xerographic’ condenser discharge technique and a conventional time of flight light pulse photo-response technique. Direct camer generation and hole mobility in the polymer was found to be strongly field dependent. There appears to be no evidence for deep trapping. Hole transport through the polymer was able to be sensitized by light absorbed in the selenium. The results indicate that the photosensitization mechanism can be thought of in terms of hole generation and transport in selenium, field-modulated injection across the selenium polymer interface and transport through the polymer.     

Model study of the effect of pore structure and condensation on multilayer adsorbate transport in porous media

A single-pore model approach to multilayer adsorbate transport in mesoporous media, previously shown to be capable of interpreting the observed behavior of relative vapor permeability PHs/PHL (or of the corresponding surface diffusion coefficient Ds), has been incorporated in a model pore network. The resulting more sophisticated model can simulate realistically the effect on PHs/PHL or Ds (i) of salient structural features of the porous medium (notably pore size dispersion and network connectivity) and (ii) of vapor condensation, which inevitably accompanies multilayer adsorbate transport in reality. An extensive generic parametric study of these effects has been performed on this basis. The results indicate that the aforementioned effects are ordinarily unlikely to induce substantial deviations of observed PHs/PHL behavior from the single-pore model benchmark. Thus, the utility of this simple model as a good basis for data analysis is confirmed, while the network model offers the possibility of exploiting external structural and other available information for a more refined interpretation of PHs/PHL behavior in particular mesoporous solid-vapor systems.     

Hexose transport regulation in cultured hamster cells

Hamster (nil) cells maintained overnight in culture medium containing cyclohemiximide and either glucose or fructose exhibit strikingly different rates of hexose transport and metabolism (i.e. uptake). Pretreatment of cultures with sulfhydryl reagents makes it possible to determine initial transport rates for a physiological sugar such as galactose which is a catabolite in hamster cells. Using galactose transport as a model, hexose uptake enhancements can now be shown to be due almost entirely to increases in the rate of the transport step. The transport regulation can best be accounted for by a model comprised of 2 antagonizing mechanism. This model involves turnover of transport carriers as well as inhibitory units ("regulators"). The experimental as well as the theoretical model may also apply to the well-known uptake enhancements observed in oncogenically transformed cells.