A Generalized Kinetic Model for Compartmentalization of Organometallic Catalysis

Compartmentalization is an attractive approach to enhance catalytic activity by retaining reactive intermediates and mitigating deactivating pathways. Such a concept has been well explored in biochemical and more recently, organometallic...

A Generalized Kinetic Model for Compartmentalization of Organometallic Catalysis

Compartmentalization is an attractive approach to enhance catalytic activity by retaining reactive intermediates and mitigating deactivating pathways. Such a concept has been well explored in biochemical and more recently, organometallic catalysis to ensure high reaction turnovers with minimal side reactions. However, a scarcity of theoretical framework towards confined organometallic chemistry impedes a broader utility for the implementation of compartmentalization. Herein, we report a general kinetic model and offer design guidance for a compartmentalized organometallic catalytic cycle. In comparison to a non-compartmentalized catalysis, compartmentalization is quantitatively shown to prevent the unwanted intermediate deactivation, boost the corresponding reaction efficiency (γ), and subsequently increase catalytic turnover frequency (TOF). The key parameter in the model is the volumetric diffusive conductance (F_V) that describes catalysts’ diffusion propensity across a compartment’s boundary. Optimal values of F_V for a specific organometallic chemistry are needed to achieve maximal values of γ and TOF. As illustrated in specific reaction examples, our model suggests that a tailored compartment design, including the use of nanomaterials, is needed to suit a specific organometallic catalytic cycle. This work provides justification and design principles for further exploration into compartmentalizing organometallics to enhance catalytic performance. The conclusions from this work are generally applicable to other catalytic systems that need proper design guidance in confinement and compartmentalization.

A Generalized Kinetic Model for Compartmentalization of Organometallic Catalysis

Compartmentalization is an attractive approach to enhance catalytic activity by retaining reactive intermediates and mitigating deactivating pathways. Such a concept has been well explored in biochemical and more recently, organometallic catalysis to ensure high reaction turnovers with minimal side reactions. However, a scarcity of theoretical framework towards confined organometallic chemistry impedes a broader utility for the implementation of compartmentalization. Herein, we report a general kinetic model and offer design guidance for a compartmentalized organometallic catalytic cycle. In comparison to a non-compartmentalized catalysis, compartmentalization is quantitatively shown to prevent the unwanted intermediate deactivation, boost the corresponding reaction efficiency (𝛾), and subsequently increase catalytic turnover frequency (𝑇𝑂𝐹). The key parameter in the model is the volumetric diffusive conductance (𝐹 ) that describes catalysts’ diffusion propensity across a compartment’s boundary. Optimal values of 𝐹 for a specific organometallic chemistry are needed to achieve maximal values of 𝛾 and 𝑇𝑂𝐹. Our model suggests a tailored compartment design, including the use of nanomaterials, is needed to suit a specific organometallic catalysis. This work provides justification and design principles for further exploration into compartmentalizing organometallics to enhance catalytic performance.

A generalized kinetic model of the advection-dispersion process in a sorbing medium

A new time-fractional derivative with Mittag-Leffler memory kernel, called the generalized Atangana-Baleanu time-fractional derivative is defined along with the associated integral operator. Some properties of the new operators are proved. The new operator is suitable to generate by particularization the known Atangana-Baleanu, Caputo-Fabrizio and Caputo time-fractional derivatives. A generalized mathematical model of the advection-dispersion process with kinetic adsorption is formulated by considering the constitutive equation of the diffusive flux with the new generalized time-fractional derivative. Analytical solutions of the generalized advection-dispersion equation with kinetic adsorption are determined using the Laplace transform method. The solution corresponding to the ordinary model is compared with solutions corresponding to the four models with fractional derivatives.

A generalized kinetic model describes ion-permeation mechanisms in various ion channels

Ion channels conduct various ions across biological membranes to maintain the membrane potential, to transmit the electrical signals, and to elicit the subsequent cellular responses by the signaling ions. Ion channels differ in their capabilities to select and conduct ions, which can be studied by the patch-clamp recording method that compares the current traces responding to the test voltage elicited at different conditions. In these experiments, the current-voltage curves are usually fitted by a sigmoidal function containing the Boltzmann factor. This equation is quite successful in fitting the experimental data in many cases, but it also fails in several others. Regretfully, some useful information may be lost in these data, which otherwise can reveal the ion-permeation mechanisms. Here we present a generalized kinetic model that captures the essential features of the current-voltage relations and describes the simple mechanism of the ion permeation through different ion channels. We demonstrate that this model is capable to fit various types of the patch-clamp data and explain their ion-permeation mechanisms.

GENERALIZED KINETIC MODEL OF GROWTH OF TWO- AND ZERO-DIMENSIONAL STRUCTURES OF SILICON AND GERMANIUM

In this work, a comprehensive consideration of the influence of the dependence of elastic stresses and surface energies on the thickness of the deposited material on the epitaxial formation of two-dimensional layers and quantum dots by the Stranski–Krastanow mechanism is carried out.

A Generalized Kinetic Model for Coupling between Stepping and ATP Hydrolysis of Kinesin Molecular Motors

A general kinetic model is presented for the chemomechanical coupling of dimeric kinesin molecular motors with and without extension of their neck linkers (NLs). A peculiar feature of the model is that the rate constants of ATPase activity of a kinesin head are independent of the strain on its NL, implying that the heads of the wild-type kinesin dimer and the mutant with extension of its NLs have the same force-independent rate constants of the ATPase activity. Based on the model, an analytical theory is presented on the force dependence of the dynamics of kinesin dimers with and without extension of their NLs at saturating ATP. With only a few adjustable parameters, diverse available single molecule data on the dynamics of various kinesin dimers, such as wild-type kinesin-1, kinesin-1 with mutated residues in the NLs, kinesin-1 with extension of the NLs and wild-type kinesin-2, under varying force and ATP concentration, can be reproduced very well. Additionally, we compare the power production among different kinesin dimers, showing that the mutation in the NLs reduces the power production and the extension of the NLs further reduces the power production.

Investigation of thermal oxidative degradation of carbon fiber-based material

To develop and carry out calculations of heat transfer in heat-shielding materials, it is necessary to study the mechanisms of material destruction. For a composite material, it is important to study the behavior of both the material as a whole and each of its components. The work is devoted to the study of thermal oxidative degradation of highly porous material based on chopped carbon fibers, which is the preform for making advanced carbon-ceramic composite materials. The study was conducted in an oxidizing air environment using simultaneous thermal analysis with varying the initial mass of the samples and at different heating rates (5, 10, 20 K/min). The dependences of thermal effects in the material and mass loss during destruction for each sample were obtained. The influence of variable parameters on the temperature of the beginning of material destruction and the steady removal speed was established. It is shown that the destruction of the material occurs in the surface layer of a certain thickness. According to the results of thermogravimetric studies with different heating rates, a generalized kinetic model of destruction was developed and the kinetic characteristics of destruction were determined.