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After pulsed excitation of close-packed colloidal quantum dots, the resulting excitons begin to migrate over individual nanoparticles due to the effect of Förster nonradiative energy transfer. Due to inhomogeneous broadening, this leads to a dependence of the peak position of the time-resolved fluorescence spectrum on time. In this work, a formula for the initial rate of this process has been derived. Furthermore, an estimate of the characteristic relaxation time for the hypothetical equilibrium Boltzmann distribution of excitons over the particles of the ensemble has been obtained. For typical inhomogeneous broadenings, this time was found to be so long that, in fact, equilibrium cannot be reached. The theoretical results obtained have been tested on colloidal nanoclusters and thin films of InP/ZnS nanoparticles. [ABSTRACT FROM AUTHOR]

Actual work devoted to the development of a novel homological approach for describing the kinetic properties of grossly nonstoichiometric oxides AB O 3- δ with perovskite structure. The approach consists in considering such oxides having different oxygen stoichiometry 3- δ as chemical homologues involved in the same oxygen exchange reaction and forming a continuous series in δ. The proposed approach is considered using the oxide with exceptional oxygen mobility Ba 0 · 5 Sr 0 · 5 Co 0 · 8 Fe 0 · 2 O 3- δ (BSCF). The kinetic properties of BSCF were studied by new method of the oxygen partial pressure relaxation. The equilibrium properties of BSCF were reported earlier and obtained by original technique of the quasi-equilibrium oxygen release. The power law dependence of the kinetic parameters on the equilibrium oxygen partial pressure is considered as the consequence of linear free energy relationship similar to the Brønsted-Evans-Polanyi relation. • Homological approach allows to describe the kinetic properties of grossly nonstoichiometric oxides. • Grossly nonstoichiometric perovskite BSCF is considered as a homologues series continuous in δ. • The power law dependence of the kinetic parameters is considered as the consequence of LFER. [ABSTRACT FROM AUTHOR]

A new mathematical formula was derived for near equilibrium relaxation processes of enzyme reactions including the conformational selection (CS) modes. CS is one of the most accepted molecular recognition mechanisms, in which protein conformers (CS conformers) are in an equilibrium with varying degrees of ligand binding affinity so that ligands select a particular conformer among them to bind. Using computer simulation techniques, our previous study (Egawa and Callender in Math Biosci 313: 61–70, 2019) predicted that the rate constant for the near equilibrium relaxation processes (kNER) and the concentration-sum of substrate and product (CLt) of enzyme reactions uniquely related to the presence of CS steps in a manner that 1/kNER versus CLt plot transformed from linear to quadratic as the elementary rate constants of inter-conversions among the CS conformers were becoming smaller relative to the rate constants at other steps of the enzymatic reaction system. Thus our previous work could provide a potential tool to detect the presence of CS steps in an enzyme reaction simply by assays using only trace amount of enzyme samples, although logical basis to have the quadratic deformation in the 1/kNER versus CLt plot in response to the presence of CS steps could not be clarified. Employing mathematical approaches that were alternative to those in our previous study, this study succeeded in deriving a theoretical equation that fully explained why and how the CS modes caused the quadratic characters in the 1/kNER versus CLt plot. [ABSTRACT FROM AUTHOR]

The results of studies of the optical and transport properties of epitaxial Pb0.74Sn0.26Te(In) films with a differently treated surface are presented. A comparative analysis of the results makes it possible to establish that the characteristic features of the photoconductivity spectra are defined by processes in the bulk while the surface states have practically no effect on the spectra. At the same time, the photoresponse kinetics and the rate of relaxation processes are heavily dependent on the state of the surface. The characteristic relaxation times of nonequilibrium charge carriers (about several milliseconds) are such that it is possible to use the methods of standard Fourier-transform spectroscopy to characterize optical transitions in the bulk. [ABSTRACT FROM AUTHOR]

• Pectin hydrogels were prepared by using zein nanoparticles as crosslinkers. • These gels were fluorescent and pH-responsive. • Interpolymer networks were formed primarily by hydrophobic forces. • Gels exhibited superior cytotoxicity towards HeLa cells via intracellular-antioxidative stress-apoptosis. • These gels were used for the direct release of the anticancer drug Doxorubicin inside cell nucleus. Herein, we report pH-responsive hydrogels of hierarchically self-assembled protein (zein, in the form of its nanoparticles of size 80–120 nm) and polysaccharide (pectin), where gelation occurred below pH 3 in the absence of crosslinkers, which we used for encapsulation and release of anticancer drug, Doxorubicin (DOX) in the cell nucleus. These nanoparticles, spherical in shape, in addition to helping in the formation of gel network also encapsulate the drug and pectin layer adsorbed on the surface of these nanoparticle allows for the drying, redispersion and enhanced swelling. A monovalent salt-dependent study performed in the concentration range of 1–100 mM clearly showed the associative interaction between the zein nanoparticles and pectin chains were hydrophobic in nature. FTIR results confirmed the loading of the drug inside the nanoparticles. Melting profile studies of these gels revealed that encapsulation of drug did not change the thermo-physical properties. Doxorubicin drug loaded hydrogels exhibited superior cytotoxicity towards cervical cancer cell lines by inducing intracellular-antioxidative stress-based apoptosis. Confocal microscopy revealed that the hydrogels required quite less time of 4 h to completely penetrate the cells assisted by the charge specific electrostatic interaction between the negatively charged HeLa cells and positively charged crosslinks. The data, further revealed that these pH specific hydrogels were suitable for release of the drug in cell nucleus is assisted by the acidic environment of cellular organelles, and hence have a potential in cancer therapy with minimal collateral damage to healthy cells. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism of the cis dihydroxylation of cis‐1,2‐dichloroethylene, trans‐1,2‐dichloroethylene, and trichloroethylene by osmium tetroxide was studied systematically in aqueous solution. The stoichiometry of the process was determined based on the principle of continuous variation of reactant ratios with spectrophotometric detection. The results always showed 1:1 stoichiometry, which is in agreement with dihydroxylation. All three reactions were found to proceed in two distinct steps. The first step occurred on a time scale of seconds and was associated with a minor change in absorbance and was identified as the formation of a 1:1 adduct between the two reagents, which is the osmium(VI) ester that plays a decisive role in catalytic applications. This species is formed in an equilibrium that is very much shifted toward the reactants, so the osmium(VI) complex is a short‐lived intermediate of the process, which is detected kinetically, but its concentration is never high enough for structural characterization. The second reaction is accompanied by major spectral changes; it involves the formation of the final products. Our results clearly show that it is possible to detect the intermediate of the process by careful kinetic studies. It is also possible that the same strategy might be successful in other OsO4‐dependent dihydroxylation processes. [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHA) are polyesters produced intracellularly by many bacterial species as energy storage materials, which are used in biomedical applications, including drug delivery systems, due to their biocompatibility and biodegradability. In this study, we evaluated the potential application of this nanomaterial as a basis of inhaled drug delivery systems. To that end, we assessed the possible interaction between PHA nanoparticles (NPs) and pulmonary surfactant using dynamic light scattering, Langmuir balances, and epifluorescence microscopy. Our results demonstrate that NPs deposited onto preformed monolayers of DPPC or DPPC/POPG bind these surfactant lipids. This interaction facilitated the translocation of the nanomaterial towards the aqueous subphase, with the subsequent loss of lipid from the interface. NPs that remained at the interface associated with liquid expanded (LE)/tilted condensed (TC) phase boundaries, decreasing the size of condensed domains and promoting the intermixing of TC and LE phases at submicroscopic scale. This provided the stability necessary for attaining high surface pressures upon compression, countering the destabilization induced by lipid loss. These effects were observed only for high NP loads, suggesting a limit for the use of these NPs in pulmonary drug delivery.

• Non-stoichiometric oxides ABO 3-δ are considered as continuous series of homologues. • A new relaxation methodology for the study of oxygen exchange in oxides is proposed. • Oxygen exchange in La 0.6 Sr 0.4 CoO 3-δ obeys the Brønsted-Evans-Polanyi relation. The study of the oxygen exchange of mixed ionic electronic conducting oxides with the gas phase, which determines the efficiency of devices planned to be used in distributed power generation and industrial chemistry is complicated by the strong dependence of their properties on widely varying oxygen nonstoichiometry δ. A new fruitful approach, in which non-stoichiometric oxides are considered as continuous δ -homologous series proposed for solving this problem, requires the development of a new methodology for the collection and analysis of the kinetic data. La 0.6 Sr 0.4 CoO 3- δ (LSC64) δ -homologues were used as examples to demonstrate the novel methodology for studying the kinetics of oxygen exchange by oxygen partial pressure relaxation technique. It includes analysis of the kinetic data in the isostoichiometric cross-section, a non-linear model of relaxation kinetics, a detailed consideration of the mass balance in the reactor, accounting for the particle size distribution in the sample and the response time of the experimental setup. For the continuous series of LSC64 δ -homologues, the Brønsted-Evans-Polanyi relationship is established: the linear correlation of the Gibbs activation energy with the chemical potential of the oxide, as well as the compensation effect between the activation parameters of the equilibrium oxygen exchange rate. [ABSTRACT FROM AUTHOR]

[Display omitted] • A change in the exponent n may indicate a change in the RDS mechanism. • The phase transition affects the kinetics of surface oxygen exchange. • The phase transition does not affect the mechanism of bulk vacancy mobility. Oxygen partial pressure relaxation technique was used to study transient kinetics of re-equilibration in the reaction of nonstoichiometric oxide Ba 0.5 Sr 0.5 Co 0.75 Fe 0.2 Mo 0.05 O 3- δ with oxygen within a region of 3- δ stoichiometry close to the nominal oxidation state 3+ for cobalt where an isosymmetric phase transition cubic perovskite P1 – cubic perovskite P2 is observed. The relaxation data were analyzed using a macrokinetic model that explicitly takes into account the power-law dependence of the surface reaction rate on the oxygen partial pressure. A twofold decrease in the power-law exponent (n = 0.7 to n = 0.3) was found at the point of the P1-P2 phase transition, which indicates a change in the mechanism of the rate-determining step of the reaction caused by the transition. At the same time, the functional dependence of the diffusion mobility of oxygen vacancies on the equilibrium oxygen pressure does not change at the transition point, which means that the transition does not affect the mechanism of bulk vacancy mobility. [ABSTRACT FROM AUTHOR]

In this study, the stress relaxation of amorphous Fe 0.7 Nb 0.1 Ti 0.1 Zr 0.1 alloy was investigated by differential thermal analysis (DTA) to enhance the soft magnetic properties. Amorphous Fe 0.7 Nb 0.1 Zr 0.1 T 0.1 alloy was produced by mechanical alloying technique using the mixture of pure elements and without adding metalloids. It was found that the stress relaxation process follows the Johnson-Mehl-Avrami model and the mechanism was volume diffusion control with three dimensional growth of the nuclei. The relation of stress relaxation progress (α), with time was proposed as: dα dt = β dα dT = 3.04 exp − 4312 RT 1 − α − ln 1 − α 0.37 . The final achieved microstructure leads to higher saturation magnetization and lower coercivity that are favorable for soft magnetic applications. [ABSTRACT FROM AUTHOR]

Structural relaxation during isothermal annealing, quantified by enthalpy recovery of Zr 44 Ti 11 Cu 10 Ni 10 Be 25 towards its metastable equilibrium and correlation to embrittlement, quantified through fracture toughness, K Q , is studied. Enthalpy relaxation over time obeys the Kohlrausch-William-Watts (KWW) stretch exponent with β = 0.74 and τ = 11,000 s. Such β and τ are used to fit experimental K Q ( t ) with KWW, resulting in R 2 = 0.79. This finding combined with a controlled characterization of the glasses' K Q versus temperature, fictive temperature, and their combination, revealed that embrittlement in metallic glasses is predominantly controlled by structural rearrangements, whereas volume changes from thermal expansion have negligible influence. [ABSTRACT FROM AUTHOR]

The paper reports the study of the photoinduced high spin (HS) state lifetime in a multistep spin crossover compound. Despite the pronounced three‐step transition of the [Fe(dpsme)Pt(CN)4]·2/3dpsme·xEtOH·yH2O {dpsme = 4,4′‐di(pyridylthio)methane; EtOH = ethanol} 3D compound, neither the T(LIESST) nor the relaxation kinetics exhibits stepwise features. From the detailed investigation (experiments and simulations) of these relaxations and the observation of the light‐induced thermal hysteresis, a phase transition around 58 K is suspected. [ABSTRACT FROM AUTHOR]

• Mo-doped BSCF oxide is studied using methods of relaxation and oxygen permeability. • Common quasi-linear kinetic model of the surface reaction is suggested for the two methods. • Quantitative agreement between relaxation and permeation is shown for the surface reaction rate. The kinetic parameters of the reaction of nonstoichiometric oxide Ba 0.5 Sr 0.5 Co 0.75 Fe 0.2 Mo 0.05 O 3-δ with molecular oxygen were determined by two independent methods: the steady-state oxygen permeability of the hollow fiber membrane and the transient kinetics of re-equilibration. To analyze the results, we used mathematical models that take into account the inhomogeneity of conditions in the relaxation reactor and gas flows in the tubular membrane. For a correct comparison of the two methods, the same formulation of the surface reaction rate was used in both models, taking into account the dependence of the reaction rate constant on oxide stoichiometry. As a result, a quantitative agreement was obtained between the values of the equilibrium exchange rate R 0 , including its activation energy, and the dependence on the oxygen partial pressure. [ABSTRACT FROM AUTHOR]

We propose a new approach to treat the kinetics of diffusion-influenced reversible bimolecular reactions and apply it first to the reactions of the type A + B ⇄ C + B. For this type of reactions with some provisions, Gopich et al. showed that the relaxation kinetics can be described exactly in the same way as the reactant decay in an 'equivalent' irreversible A + B → C + B reaction. In this article, we will show that the same relationship can be derived in a very elementary way by using a new approach based on the hierarchical kinetic equations governing the reduced distribution functions of reactant molecules. Because our analysis does not require the assumption that the reactants are interaction-free point particles, the effect of excluded volumes among the reactants can also be evaluated by utilizing the result derived for an irreversible reaction. [ABSTRACT FROM AUTHOR]

Some methods for direct (diffraction and scattering of radiations) and indirect (measurement of a residual resistance, computer simulation, approximated analytical calculations) study of statistical parameters of a correlation in a positional relationship of atoms, their ‘mixing’ energies, thermodynamic characteristics and structure of the short-range order, and also kinetics of its relaxation in substitutional (interstitial) solid solutions are reviewed. The properties of parameters of interaction and short-range order of atoms (long-range, anisotropic, and oscillating natures of their dependences on interatomic distance, and also nonanalyticity of parameters of the corresponding description in reciprocal space) for solutions of both types are illustrated. The state-of-the-art statistical-thermodynamic computational methods for equilibrium values of the short-range order parameters for such binary solutions are considered. With usage of the microscopical theory valid within the framework of the approximation corresponding to the decoupling of the three-particle correlation functions (three-site probabilities), the relationship of time evolution of the short-range order and diffuse scattering of radiations with diffusion of atoms on large intersite spacing interval in substitutional multicomponent solid solutions is analysed. The existing semiphenomenological models of relaxation of the specific residual resistance of substitutional (interstitial) solid solutions in application to the description of data of experimental measurements of its dependence on time are compared.

• SrFe 0.98 Mo 0.02 O 3-δ perovskite is considered as homologues series continuous in oxygen stoichiometry. • Oxygen exchange rate and diffusivity are analyzed in isobaric and isostoichiometric sections. • Brønsted-Evans-Polanyi relation is shown to be the reason of pn dependencies for kinetic constants. The properties of perovskite related oxides ABO 3- δ exhibiting mixed ionic-electronic conductivity (MIEC) are strongly dependent on oxygen stoichiometry 3- δ. The complexity of the theoretical interpretation of kinetic experiments is associated with the significant dependence of the kinetic properties of MIEC oxides on δ. It is proposed to consider such grossly nonstoichiometric oxides having different oxygen stoichiometry as chemical homologues participating in the oxygen exchange reaction and forming a series continuous in δ. The continuous homologous series approach is considered using the example of SrFe 0.98 Mo 0.02 O 3- δ. The equilibrium and kinetic properties of the oxide were studied by new methods of the oxygen partial pressure relaxation (OPPR) and quasi equilibrium oxygen release (QEOR). The power law dependence ∼ pn of the kinetic parameters on the equilibrium oxygen partial pressure is considered as the consequence of linear free energy relationship similar to the Brønsted-Evans-Polanyi relation. [ABSTRACT FROM AUTHOR]

Vascular plants are typically endohydric and are killed by drying beyond 30% relative water content. Bryophytes are ectohydric and are typically desiccation tolerant (DT). Mosses in open sun-exposed habitats show major electron flow to oxygen and high levels of non-photochemical quenching (NPQ) in chlorophyll fluorescence measurements. This has been regarded as a main source of photoprotection for these plants. The aim of the work described in this paper was to explore the rate and extent of relaxation of this quenching, and to seek evidence of its nature and consequences. Sequences of measurements were made during illumination at various intensities and a subsequent dark period. Light-response curves were constructed using dithiothreitol (DTT) as an inhibitor of violaxanthin de-epoxidase to provide additional evidence of the proportion of NPQ mediated by the xanthophyll cycle. The relaxation curves were fitted by exponential decay curves. A double-exponential fit to curves for the sun-adapted species gave a fast phase with a halflife of ca 6-16 seconds, and a slow phase with a halflife of ca 100-300 seconds. Shade species were best fitted by single-exponential curves. A persistent offset remained of ca 5-23% of the pre-darkening NPQ. Light-response curves for several species showed NPQ reduced in the presence of DTT to similar proportions of the control. Around 70-95% of NPQ in the bryophytes investigated relaxed with a halflife of ca 2-5 minutes. The fast phase of the double-exponential fit is consistent with likely rates of decay of the trans-thylakoid pH gradient and re-epoxidation of zeaxanthin. This leads to the same conclusion as the effect of DTT in depressing NPQ. The contrast in physiology between bryophytes and vascular plants reflects the different selection pressures facing leaf cells of poikilohydric plants and the mesophyll cells of vascular plants, and their divergent evolutionary histories since the mid-Palaeozoic. [ABSTRACT FROM AUTHOR]

Fluoropolymers were treated by an ambient air plasma at 18.7 watt of RF power, 1.0 torr of vacuum pressure, and 0.5-2.0 min of exposure time. The surface wettability and composition were characterized by contact angle measurements and X-ray photoelectron spectroscopy, respectively. The plasma-modified fluorinated surfaces exhibited two different relaxation kinetics based on contact angle ( θ) changes of water: i) an increase of cos θ for fully fluorinated (perfluorinated) polymers with nonpolarity, ii) a decay of cos θ for partially fluorinated polymers with polarity. A steady-state relaxation model was successfully applied to two different contact angle changes on the plasma-modified fluorinated surfaces. The initial polar fraction, f, was fitted as 0.03-0.2 for fully fluorinated polymers and 0.5-0.7 for partially fluorinated polymers, respectively. After the plasma treatment, the fully fluorinated polymers exhibited the relative increase of final polar fraction to initial one ( i.e., f/ f=1.2-2.4), but partially fluorinated polymers exhibited the relative decrease of final polar fraction to initial one ( i.e., f/ f=0.7-0.8). The continuous decrease of water contact angles on plasma-modified perfluorinated surfaces might be attributed to the further interactions of generated polar groups with atmospheric environment, while the increase of water contact angles on partially fluorinated surfaces are mainly attributed to the recovery of pristine surface by chain relaxation mechanism.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The dynamics of a neuronal marker, N-acetyl aspartate, in the motor cortex of human brain during hemodynamic response to millisecond auditory stimulus was studied by NMR spectroscopy and functional magnetic resonance imaging. The kinetic analysis of the data revealed the multi-substrate nature of responses to neural stimulation. Hypotheses about molecular mechanisms of processes were formulated. [ABSTRACT FROM AUTHOR]

Luminescence decay functions describe the time dependence of radiation emitted by a sample after excitation. An overview of the mathematical aspects and systematics of luminescence decays is presented. In particular, super-exponential (faster-than-exponential) decays are defined and the possibility of their observation in single species physicochemical systems discussed. It is shown that this type of behavior can be both spontaneous and induced (by acting upon the system in real time). Spontaneous super-exponentiality is identified for the first time in experimental decays, these being phosphorescence decays affected by triplet–triplet absorption. [ABSTRACT FROM AUTHOR]

Abstract: Two competing and mutually exclusive mechanisms of ligand recognition – conformational selection and induced fit – have dominated our interpretation of ligand binding in biological macromolecules for almost six decades. Conformational selection posits the pre-existence of multiple conformations of the macromolecule from which the ligand selects the optimal one. Induced fit, on the other hand, postulates the existence of conformational rearrangements of the original conformation into an optimal one that are induced by binding of the ligand. In the former case, conformational transitions precede the binding event; in the latter, conformational changes follow the binding step. Kineticists have used a facile criterion to distinguish between the two mechanisms based on the dependence of the rate of relaxation to equilibrium, k obs, on the ligand concentration, [L]. A value of k obs decreasing hyperbolically with [L] has been seen as diagnostic of conformational selection, while a value of k obs increasing hyperbolically with [L] has been considered diagnostic of induced fit. However, this simple conclusion is only valid under the rather unrealistic assumption of conformational transitions being much slower than binding and dissociation events. In general, induced fit only produces values of k obs that increase with [L] but conformational selection is more versatile and is associated with values of k obs that increase with, decrease with or are independent of [L]. The richer repertoire of kinetic properties of conformational selection applies to kinetic mechanisms with single or multiple saturable relaxations and explains the behavior of nearly all experimental systems reported in the literature thus far. Conformational selection is always sufficient and often necessary to account for the relaxation kinetics of ligand binding to a biological macromolecule and is therefore an essential component of any binding mechanism. On the other hand, induced fit is never necessary and only sufficient in a few cases. Therefore, the long assumed importance and preponderance of induced fit as a mechanism of ligand binding should be reconsidered. [Copyright &y& Elsevier]

Abstract: The synthesis of two molecules, B1 and B2, based on elements of norbadione A, the natural Cs+ chelator in mushrooms, associated, in the case of B2, with an 18-crown-6 ether is reported. Thermodynamic and kinetic analyses performed in water, ethanol and ethanol/water 9/1 v/v (M1) show in M1 and ethanol that B1 and B2 form stable complexes with Na+, K+ and Cs+. Affinity constants, measured spectrophotometrically in ethanol and M1, by the use of the Specfit program, are in the 105 and 106 range for B1 and B2, respectively. The second-order rate constants are in the 106–107 M−1 s−1 range and the first-order rate constants about unity. The ratios of the second-order/first-order rate constants confirm the thermodynamic results in EtOH. The kinetic processes become much too fast to allow runs in M1. Molecular simulations in EtOH imply the existence of two isomers for each of the Cs+/B1 and Cs+/B2 complexes. With B1, the more stable one is that in which the two enolates are parallel and mimic the alkali-metal inclusion cavity already envisaged for norbadione A. With B2, two similar structures are extracted, in both of which Cs+ is included in the crown ether and capped by the enolate. The affinity of B1 for Cs+ is comparable to that of norbadione A, whereas that of B2 is higher. These results are encouraging as they introduce a new series of alkali chelators which can lead to molecules capable of complexing 137Cs+ for radioactive decontamination. [Copyright &y& Elsevier]

Abstract: The synthesis and new optical features of four azophenylcarbazoles are described. All-optical poling of the azophenylcarbazoles with different donor groups was investigated. The highest optical poling efficiency was measured for relative larger molecules (branched). Parameters describing mobility of the azophenylcarbazoles (orientational diffusion coefficient vary from 2.2 × 10−5 s−1 to 8 × 10−5 s−1) were extracted using an adopted model. Photoinduced erasure while reading the poled media turned out to be more pronounced for less developed structures (less branched donor). Different polymer materials were investigated as the host matrix for the most interesting azophenylcarbazole molecule. [Copyright &y& Elsevier]

Abstract: The kinetics of sorption of micromolecular swelling agents by polymeric media often deviates from normal Fickian behavior in various ways, which have to be understood and interpreted, with the aid of appropriate models, in terms of the underlying physics. One difficulty which arises in this respect is that salient aspects of the observed kinetic behavior can be mimicked by extraneous effects, in the form of significant deviation from a boundary condition or of imperfect macroscopic homogeneity of the polymer film (modeled in both cases as a surface resistance to penetrant transport). Such effects have, in fact, been invoked (notably by Hansen (2010) ) to question the significance of conclusions drawn from modeling approaches based on the effect of intrinsic bulk polymer properties, leading to delayed (viscous) swelling and to build-up and decay of differential swelling stresses. We present here a brief critical account (following the mainstream modeling line initiated by Crank) of typical results concerning various salient aspects of observed non-Fickian sorption kinetics and of the comparative possibility of achieving satisfactory general interpretation thereof, in terms of approaches based on the aforementioned extraneous, versus intrinsic bulk property, effects. We find that the latter approach has been successful so far, both computationally and physically, by establishing a close physically significant analogy between non-Fickian sorption, and (both linear and non-linear) viscoelastic mechanical deformation, behavior. The former approach, on the other hand, proves weak on both counts. [Copyright &y& Elsevier]

Aim: Positive net work produced during cyclic contractions is partially limited by relaxation kinetics, which to date, have not been directly investigated. Therefore, the purpose of this investigation was to determine the influence of relaxation kinetics on cyclic work. Methods: Soleus muscles of four cats were isolated and subjected to a series of work loops (0.5, 1, 1.5 and 2 Hz cycle frequencies) during which stimulation terminated prior to the end of the shortening phase to allow for complete muscle relaxation and matched discrete sinusoidal shortening contractions during which stimulation remained on until the completion of the shortening phase. Muscle length changes during these protocols were centred on optimum length and were performed across muscle lengths that represented walking gait. Results: When muscle excursions were centred on Lo relaxation kinetics decreased muscular work by 2.8 ± 0.8%, 12.1 ± 4.1%, 27.9 ± 4.5% and 40.1 ± 5.9% for 0.5, 1, 1.5 and 2 Hz respectively. However, relaxation kinetics did not influence muscular work when muscle excursions represented walking gait. In addition, muscular work produced at muscle lengths associated with walking gait was less than the work produced across Lo (55.7 ± 20.0%, 53.5 ± 21.0%, and 50.1 ± 22.0% for 0.5, 1 and 1.5 Hz respectively). Conclusion: These results imply that relaxation kinetics are an important factor that limit the ability of muscle to produce work; however, the influence of relaxation kinetics on physiological function may depend on the relation between the optimum length and natural excursion of a muscle. [ABSTRACT FROM AUTHOR]

A series of 72-hour growth inhibition tests with green alga Desmodesmus (Scenedesmus) subspicatus (ISO 8692) has been performed to test the delayed fluorescence (DF) parameters as possible endpoint measurements. Sensitivity to five toxicants with direct and indirect effects on photosynthesis was tested, and the median effective concentration (EC50) values derived from the cell concentration, absorbance and DF were compared. The sensitivity of DF intensity (DFI) was comparable with the two endpoints suggested in ISO 8692 for all five toxicants: potassium dichromate, 3,5-dichlorophenol (3,5-DCP), DCMU, copper and cadmium. In the case of potassium dichromate and copper, DFI was more sensitive than the other endpoints in this study. The analysis of DF relaxation kinetics showed a specific response to the herbicide DCMU. Additionally, a 24-hour test was performed with the same toxicant concentrations (except copper), where DFI was measured 30 minutes, one hour and 24 hours after the exposure. The influence of toxicants on DFI after a 24-hour exposure was comparable with the effects after 72 hours. Only 3,5-DCP influenced DFI after 30 minutes. DF proved to be a simple, reliable and rapid measurement to assess toxicity in algal tests, which can to some extent differentiate among various toxicants. [ABSTRACT FROM AUTHOR]

Abstract: Pressure-jump induced relaxation kinetics can be used to study both protein unfolding and refolding. These processes can be initiated by upward and downward pressure-jumps of amplitudes of a few 10 to 100 MPa, with a dead-time on the order of milliseconds. In many cases, the relaxation times can be easily determined when the pressure cell is connected to a spectroscopic detection device, such as a spectrofluorimeter. Adiabatic heating or cooling can be limited by small pressure-jump amplitudes and a special design of the sample cell. Here, we discuss the application of this method to four proteins: 33-kDa and 23-kDa proteins from photo-system II, a variant of the green fluorescent protein, and a fluorescent variant of ribonuclease A. The thermodynamically predicted equivalency of upward and downward pressure-jump induced protein relaxation kinetics for typical two-state folders was observed for the 33-kDa protein, only. In contrast, the three other proteins showed significantly different kinetics for pressure-jumps in opposite directions. These results cannot be explained by sequential reaction schemes. Instead, they are in line with a more complex free energy landscape involving multiple pathways. [Copyright &y& Elsevier]

Abstract: The interactions of Poly(A)·Poly(U) with the cis-platinum derivative of proflavine [{PtCl(tmen)}2{HNC13H7(NHCH2CH2)2}]+ (PRPt) and proflavine (PR) are investigated by spectrophotometry, spectrofluorimetry and T-jump relaxation at I =0.2M, pH 7.0, and T =25°C. Base–dye interactions prevail at high RNA/dye ratio and binding isotherms analysis reveals that both dyes bind to Poly(A)·Poly(U) according to the excluded site model (n =2). Only one relaxation effect is observed for the Poly(A)·Poly(U)/PRPt system, whereas two effects are observed with Poly(A)·Poly(U)/PR. The results agree with the sequence D+S⇆D, S⇆DSI ⇆DSII, where D,S is an external complex, DSI is a partially intercalated species, and DSII is the fully intercalated complex. Formation of DSII could be observed in the case of proflavine only. This result is interpreted by assuming that the platinum-containing residue of PRPt hinders the full intercalation of the acridine residue. [Copyright &y& Elsevier]

A new method for evaluating the rate constants of chemical reactions has been developed based on the differential photoconversion efficiencies of photochromic FRET acceptors incorporated into molecules on both sides of a chemical equilibrium. In the application of Photochromic Relaxation Kinetics (pcRelKin) to a bimolecular binding reaction, one of the two interacting molecules bears a FRET donor and the second a photochromic acceptor. The close proximity required for FRET is achieved only in the complex. After photoconversion, the system exists in a thermodynamically asymmetric state, which relaxes according to first order kinetics. PcRelKin offers unique advantages over classical relaxation kinetics. [ABSTRACT FROM AUTHOR]

Poly(vinylidene fluoride) (PVDF) and ethylene-chlorotrifluoroethylene (ECTFE) exhibited non-Fickian diffusion behaviors in the transient uptake of aromatic solvents. The diffusional exponents at the final stage of uptake exhibited asymptotic values ranging from 0.9–1.0 for the sigmoidal sorption of PVDF and 1.2–2.0 for the drastic accelerating sorption of ECTFE. The asymptotic diffusional exponent decreased with rising temperature. PVDF film exhibited a linear increase in both machine and transverse directions with fractional uptake, whereas ECTFE film increased linearly in the transverse direction and exponentially in the machine direction. A rate-type viscoelastic [Camera-Roda and Sarti, 1990] model was applied to reproduce the anomalous sorption of fluoropolymer-solvent systems. The fitted Deborah numbers ranged from 0.2–0.3 for PVDF, and 2–5 for ECTFE. The diffusivity ratio, D eq /D o ,of PVDF-solvent system was fitted as tenth order of magnitude lower than that of ECTFE-solvent system. The fraction of initial surface concentration, So, was fitted in the range of 0.6–0.8 for both ECTFE and PVDF. It is plausible to assume that diffusion coupled with comparable structural relaxation has the asymptotic diffusional exponents that are strongly dependent on accelerating curvature, and total sorption is contributed by relaxation-induced viscoelastic volume change along with concentration-driven Fickian diffusion. [ABSTRACT FROM AUTHOR]

Photo-illumination effects have been measured for [CoIII-LS(phen)(3,5-DBSQ)(3,5-DBCat)]·C6H5Cl, where LS, phen, 3,5-DBSQ and 3,5-DBCat denote low-spin, 1,10-phenanthroline, 3,5-di-tert-butyl-1,2-semiquinonate and 3,5-di-tert-butyl-1,2-catecholate, respectively. When the Co compound was illuminated at 5 K, the magnetization value, μeff increased from 1.7 to 2.7μB. The UV-Vis absorption spectra after illumination show that the absorption band at around 800 nm, characteristic of the [CoII-HS(phen)(3,5-DBSQ)2] state (HS denotes high-spin), increased and the charge transfer band from 3,5-DBCat to 3,5-DBSQ at 2500 nm was reduced. IR spectra show that the C&z.sbnd;O stretching peak at 1280 cm-1 is significantly decreased. These results confirm that a photo-induced intra-molecular electron transfer, [CoIII-LS(phen)(3,5-DBSQ)(3,5-DBCat)]·C6H5Cl↔[CoII-HS(phen)(3,5-DBSQ)2]·C6H5Cl, was induced by 532 or 830 nm light. The relaxation kinetics of valence tautomerism was studied. For T≥25 K, kVT0=0.205 s-1 and Ea=110.38 cm-1. Below 25 K, the rate constant for the valence tautomeric relaxation as T approaches the 0 K, which suggests that tunneling is the predominant mechanism for the relaxation. [Copyright &y& Elsevier]

Temperature-jump relaxation spectrometry has been used to study the unfolding properties of Ca2+-free Drosophila calmodulin from 278 to 336 K, monitored by absorption of Tyr-138. The T-jump amplitude data are well fitted throughout with a melting temperature Tm=315.7 K, ΔHom=140.5 kJ mol−1 and ΔCpo=3.28 kJ K−1 mol−1, giving ΔGo293=7.36 kJ mol−1 for the C-domain, in good agreement with other data. The relaxation rate observed (time range 1 μs–1 ms) obeys a simple two-state kinetic mechanism throughout. The activation energy for unfolding is nearly temperature-independent, in contrast to that for refolding, and hence the transition state is relatively compact, resembling the folded state, and the relaxation time, τ, shows complex temperature dependence. The domain unfolding is a two-state process occurring with τ of ∼100 μs at the Tm. At 296 K, when the C-domain is ∼6% unfolded, kunfolding≈305 s−1, krefolding≈4660 s−1 and τ≈200 μs. This closely resembles the rate and extent of a reported C-domain exchange process, inferred from NMR line-broadening at 296 K. The inherent instability of the apo-C-domain of calmodulin indicates that the unfolded form significantly contributes to the physical properties of apo-calmodulin at normal temperatures, and this instability is enhanced by low ionic strength conditions. [Copyright &y& Elsevier]

Through structural relaxation, the configuration of a viscous liquid changes to allow the Gibbs free energy to be minimum in response to temperature variations. In this review, the practical importance of relaxation in silicate melts is first illustrated by configurational heat capacity and entropy and their connection with viscosity via Adam-Gibbs theory. Relaxation effects on thermal expansion and compressibility are then examined, and the similarity of the kinetics of structural, enthalpy and volume relaxation is pointed out. Turning to microscopic mechanisms, we finally stress the importance of Si-O bond exchange and its decoupling with the motion of network-modifying elements near the glass transition. [ABSTRACT FROM AUTHOR]