Kinetic studies of the chirality inversion of a series of mono- and bimetallic (p-cymene)(salicylaldiminato)RuII complexes with halo ligands (1and 2) in solution have been performed by means of the ...line-shape method, using 1H NMR spectroscopy to evaluate the signal exchange rates between diastereotopic protons in the p-cymene ligand. The activation parameters (DeltaHdouble dagger and DeltaSdouble dagger) associated with the flipping molecular mobility were determined from variable-temperature NMR analyses, and it was found that the neutral halo complexes 1 and 2 exhibit much lower enthalpies and entropies than the corresponding cationic pyridine analogues 3.
•Important subsets of chemical kinetics on reaction networks have interesting algebraic properties.•The results on the coincidence of the kinetic and stoichiometric subspaces of Feinberg and Horn ...(1977) and Feinberg (1987) are extended to complex factorizable systems with span surjective factor maps.•Initial results on noncomplex factorizable kinetics are derived through the study of their span surjective subset.•The branching type of a network determines which kinetics are available on the network.•Analysis of fifteen BST models of biological systems reveals novel network and kinetic properties little studied in CRNT so far.
This paper further develops the connection between Chemical Reaction Network Theory (CRNT) and Biochemical Systems Theory (BST) that we recently introduced 1. We first use algebraic properties of kinetic sets to study the set of complex factorizable kinetics CFK(N) on a CRN, which shares many characteristics with its subset of mass action kinetics. In particular, we extend the Theorem of Feinberg-Horn 9 on the coincidence of the kinetic and stoichiometric subsets of a mass action system to CF kinetics, using the concept of span surjectivity. We also introduce the branching type of a network, which determines the availability of kinetics on it and allows us to characterize the networks for which all kinetics are complex factorizable: A “Kinetics Landscape” provides an overview of kinetics sets, their algebraic properties and containment relationships. We then apply our results and those (of other CRNT researchers) reviewed in 1 to fifteen BST models of complex biological systems and discover novel network and kinetic properties that so far have not been widely studied in CRNT. In our view, these findings show an important benefit of connecting CRNT and BST modeling efforts.
ABSTRACT
The triazines 3‐(2‐pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PDT), 3‐(4‐phenyl‐2‐pyridyl)‐5,6‐diphenyl‐1,2,4‐triazine (PPDT), and 1,10‐phenanthroline (phen) were coordinated to the Fe2+ ion to ...form Fe ( PDT )2( phen )2+ (1), Fe ( PPDT )2( phen )2+ (2), Fe ( PDT )( phen )22+, (3) and Fe ( PPDT )( phen )22+ (4). The complexes were synthesized and characterized by mass spectroscopy and elemental analysis. The rate of substitution of these complexes by 2,2′‐bipyridine (bpy), 1,10‐phenanthroline (phen), and 2,2′,6,2″‐terpyridine (terpy) was studied in a sodium acetate–acetic acid buffers over the range 3.6–5.6 at 25, 35, and 45°C under pseudo–first‐order conditions. The reactions are first order with respect to the concentration of the complexes. The reaction rates increase with increasing bpy/phen/terpy and pH, whereas ionic strength has no influence on the rate of reaction. Plots of kobs versus bpy/phen/terpy and 1/H+ are linear with positive slopes and significant y‐intercepts. This indicates that the reactions proceed by both dissociative as well as associative pathways for which the associative pathway predominates the substitution kinetics. Observed temperature‐depended rate constants at the three temperatures at which substitution reactions were studied together with the protonation constants of the substituting ligands (phen, bpy, terpy) were used to evaluate the specific rate constants (k1 and k2) and thermodynamic parameters (Ea, ΔH#, ΔS#, and ΔG#). The reactivity order of the four complexes depends on the phenyl groups present on the triazine (PDT/PPDT) molecule. The π‐electrons on phenyl rings stabilizes the charge on the metal center by inductive donation of electrons toward the metal center resulting in a decrease in reactivity of the complex, and the order is 1 < 2 < 3 < 4. The rate of substitution is also influenced by the basicity of the incoming ligand (bpy/phen/terpy), and it decreased in the order: phen > terpy > bpy. Higher rate constants, low Ea values, and more negative entropy of activation (−ΔS#) values were observed for the associative path, revealing that substitution reactions at the octahedral iron(II) complexes by bpy, phen, and terpy occur predominantly by the associative mechanism. Density functional theory calculations support the interpretations.
Compounds N-(1H-benzimidazol-2-ylmethyl)aniline (L1), N-(1H-benzimidazol-2-ylmethyl)-2-bromoaniline (L2), and N-(1H-benzimidazol-2-ylmethyl)-2-aminothiophenol (L3) react with ZnII and CuII ...carboxylates to form complexes Zn2(L1)2(OBn)4 (1), Zn2(L2)2(OBn)4 (2), Zn2(L3)2(OBn)4 (3), Cu2(L2)2(OBn)4 (4), Zn(L1)2(OAc)2 (5), Zn(L2)2(OAc)2 (6) and Cu2(L1)2(OAc)4 (7). Structures of 2, 4 and 6 revealed that L1-L3 are monodentate, binding through the imidazolyl N-atom. The X-band EPR spectrum of 4 in the solid state is consistent with an antiferromagnetically-coupled (singlet) ground state and a low-lying EPR-active triplet excited state characterised by two main transitions. In dimethyl sulfoxide (DMSO) solution, a single resonance confirmed the retention of the dinuclear paddlewheel core. Complexes 1-7 formed active catalysts towards ring-opening polymerisation of -caprolactone. The polymerisation reactions follow first-order kinetics with respect to the monomer and occur through a coordination-insertion pathway. PUBLICATION ABSTRACT
•The kinetics of CO2 adsorption/desorption of a magnetite-based sorbent was studied.•Dynamic breakthrough experiments were performed in a lab-scale fixed bed reactor.•Pseudo-first order, ...pseudo-second order, and Avrami’s kinetic models were applied.•Film diffusion, intraparticle diffusion and surface reaction are the main diffusion mechanisms involved.•The dynamic CO2 adsorption behavior has been investigated with a deactivation model.
The CO2 adsorption and desorption kinetics of a magnetite-based sorbent, CB-FM, obtained coating a low-cost carbon black (CB) with magnetite fine particles (FM), has been systematically and thoroughly investigated for the first time under post-combustion capture operating conditions. Experimental data of CO2 uptake (18–150 °C) and extent of CO2 desorption (200–260 °C) have been fitted to different apparent kinetic models, namely pseudo-first-order, pseudo-second-order and Avrami’s fractional-order kinetic models. The mechanism of CO2 adsorption on CB-FM in terms of controlling mass transfer resistances, interparticle diffusion, intraparticle diffusion and Boyd’s film-diffusion models has been also investigated. Finally, a two-constants deactivation model has been adopted to simulate the dynamic breakthrough curves.
Phosphorus magnetic resonance spectroscopy ( super(31)P-MRS) enables the non-invasive evaluation of muscle metabolism. Resting Pi-to-ATP flux can be assessed through magnetization transfer (MT) ...techniques, and maximal oxidative flux (Q sub(max)) can be calculated by monitoring of phosphocreatine (PCr) recovery after exercise. In this study, the muscle metabolism parameters of 13 overweight-to-obese sedentary individuals were measured with both MT and dynamic PCr recovery measurements, and the interrelation between these measurements was investigated. In the dynamic experiments, knee extensions were performed at a workload of 30% of maximal voluntary capacity, and the consecutive PCr recovery was measured in a quadriceps muscle with a time resolution of 2 s with non-localized super(31)P-MRS at 3 T. Resting skeletal muscle metabolism was assessed through MT measurements of the same muscle group at 7 T. Significant linear correlations between the Q sub(max) and the MT parameters k sub(ATP) (r=0.77, P=0.002) and F sub(ATP) (r=0.62, P=0.023) were found in the study population. This would imply that the MT technique can possibly be used as an alternative method to assess muscle metabolism when necessary (e.g. in individuals after stroke or in uncooperative patients). Copyright copyright 2013 John Wiley & Sons, Ltd. We showed that mitochondrial capacity, determined by the maximal oxidative flux from PCr-recovery kinetics, correlates with the Pi-to-ATP flux at rest, as well as with the creatine-kinase flux at rest in overweight-to-obese sedentary subjects. This would suggest that magnetization transfer (MT) could provide a marker of skeletal muscle metabolism that correlates with exercise-recovery experiments. We also showed that the time constant of PCr recovery correlates with MT values only if there is low variability in end-exercise pH sub(i).
The design of heterogeneous catalysts relies on understanding the fundamental surface kinetics that controls catalyst performance, and microkinetic modeling is a tool that can help the researcher in ...streamlining the process of catalyst design. Microkinetic modeling is used to identify critical reaction intermediates and rate-determining elementary reactions, thereby providing vital information for designing an improved catalyst. In this review, we summarize general procedures for developing microkinetic models using reaction kinetics parameters obtained from experimental data, theoretical correlations, and quantum chemical calculations. We examine the methods required to ensure the thermodynamic consistency of the microkinetic model. We describe procedures required for parameter adjustments to account for the heterogeneity of the catalyst and the inherent errors in parameter estimation. We discuss the analysis of microkinetic models to determine the rate-determining reactions using the degree of rate control and reversibility of each elementary reaction. We introduce incorporation of Brønsted–Evans–Polanyi relations and scaling relations in microkinetic models and the effects of these relations on catalytic performance and formation of volcano curves are discussed. We review the analysis of reaction schemes in terms of the maximum rate of elementary reactions, and we outline a procedure to identify kinetically significant transition states and adsorbed intermediates. We explore the application of generalized rate expressions for the prediction of optimal binding energies of important surface intermediates and to estimate the extent of potential rate improvement. We also explore the application of microkinetic modeling in homogeneous catalysis, electro-catalysis, and transient reaction kinetics. We conclude by highlighting the challenges and opportunities in the application of microkinetic modeling for catalyst design.
In the food industry, it is necessary to know the shelf life of products to ensure end users that purchased food keeps all its properties in proper condition. In this work we studied the kinetics of ...deterioration of ham through accelerated testing, using the peroxide index as an indicator of impairment. The product was stored at 5, 15 and 30°C for 36h and peroxide was determined according to ISO 3960. The kinetics of the reaction was assumed to be zero order and kinetic constants found were 0.79, 0.90 and 1.08meqO^sub 2^/kg·h, in order of increasing temperature. The peroxide index increased in function of time in the ham studied; it exhibits kinetics of order zero, an activation energy of 8.4kJ·mol-1 relative to the storage temperature, and a Q^sub 10^ factor of 1.15.
Despite of being ubiquitous in proteins, NHbackbone···S hydrogen bonds linking the sulfur atom of methionine or cysteine to backbone NH groups remain poorly documented. Here, we report vibrationally ...resolved IR NH stretch spectra of two methionine-containing dipeptides (Ac-Phe-Met-NH2 and Ac-Met-Phe-NH2). The conformations observed for both molecules, assigned with the help of DFT-D quantum chemistry, provide spectroscopic evidence for the formation of NHbackbone···S H-bonds, surprisingly strong enough to challenge the classical intrabackbone NH···OC H-bonds. The methionine side chain is found to fold locally, forming a H-bond with the neighboring amide groups (NH(i) or NH(i+1)). Comparison with protein data bank structural information shows that such a local folding is also common in proteins where it concerns 24% of the methionine residues that have a sulfur atom linked to a backbone NH group. This convergence between the strength of these NH···S H-bonds and protein structural data illustrates their contribution to the stability of protein chains.
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