Rebound Process Research Articles

Dynamics of unsteady compressible cavitating flows associated with the cavity shedding

The main purpose of this work is to shed light on the physics involved in the two distinct cavity cloud shedding mechanisms in cloud cavitating flows, namely re-entrant jet mechanism (RJM) and shock wave propagation mechanism (SWM). A compressible cavitating flow solver, which considers the compressibility effects of both liquid and vapor, is used to account for the wave dynamics in cavitating flows. The compressible Navier-Stokes equations, coupling the mass, momentum energy equations, and phase fraction transport equation, along with the thermodynamic equations of state for both liquid and vapor, Saito cavitation model and the SST-SAS turbulence model, are solved. Numerical results are presented for the conditions of both the re-entrant jet mechanism and shock wave mechanism around a NACA66 (mod) hydrofoil (Leroux et al., 2005), respectively, with emphasis on the process of re-entrant jet development and shock wave formation and propagation. The results show that the re-entrant jet can cause the attached cavity sheet breakup for both the two cavity cloud shedding mechanisms in both high and low angle of attack, while the shock wave formation and propagation process only occurs under shock wave mechanism at low angles of attack. Pressure evolution illustrates that in the re-entrant jet mechanism, cavity cloud collapse will induce high pressure load, while no shock wave and thus the corresponding rebound phenomenon are observed. In shock wave mechanism, during the whole process of the shock wave dynamics, namely generation, propagation and rebound process, pressure fluctuations increase sharply along with the generation of the pressure peaks with large amplitude and short time interval. Further study on the compressible characteristics involved in the two cavity shedding mechanisms illustrates that vapor fraction and mass transfer have a significant effect in sonic speed and Mach number characteristics. The average and standard derivation of maximum Mach number (Mamax) in shock wave mechanism is lower than that in re-entrant jet mechanism. Cavitating flows are characterized by low sonic speed value in the cavitation region and high sonic speed value in the pure liquid region and a sonic speed boundary layer exists between the two regions, the thickness of which is about the size of the local attached cavity sheet on foil surface. In the process of shock wave generation and rebound, cavity volume and cavity volume rate experience large fluctuations, showing strong cavitation instabilities in shock wave mechanism.

Experimental study on the characteristics of the strong boiling induced by pressure relief at the top of vertical vessels

In this study, the strong boiling process of a superheated liquid induced by pressure relief at the top of a vertical vessel was experimentally investigated. Through monitoring the response of the pressure at the top of the vessel and the full field morphology of the two-phase flow, the correlations between the pressure rise and the two-phase flow as well as the trend of the characteristic pressure values under different discharge areas and filling rates were analyzed. The results indicated that the expansion of the mist-like two-phase flow, which was generated due to the strong boiling and bubble collapse, was the direct reason for the two pressure rebounds at the top of the vessel. And under the effect of the intermittent expansion of the two-phase flow, the pressure rising rate in the second rebound stage fluctuated. When the discharge area changed, the characteristic pressure values presented different relativeness under different filling rates. In addition, the average pressure rising rate during the second pressure rebound process presented an exponential growth with the increase of the discharge area, and the exponent coefficient decreased with the increase of the liquid filling rate.

A flexible nonlinear mixed effects model for HIV viral load rebound after treatment interruption.

Characterization of HIV viral rebound after the discontinuation of antiretroviral therapy is central to HIV cure research. We propose a parametric nonlinear mixed effects model for the viral rebound trajectory, which often has a rapid rise to a peak value followed by a decrease to a viral load set point. We choose a flexible functional form that captures the shapes of viral rebound trajectories and can also provide biological insights regarding the rebound process. Each parameter can incorporate a random effect to allow for variation in parameters across individuals. Key features of viral rebound trajectories such as viral set points are represented by the parameters in the model, which facilitates assessment of intervention effects and identification of important pretreatment interruption predictors for these features. We employ a stochastic expectation-maximization (StEM) algorithm to incorporate HIV-1 RNA values that are below the lower limit of assay quantification. We evaluate the performance of our model in simulation studies and apply the proposed model to longitudinal HIV-1 viral load data from five AIDS Clinical Trials Group treatment interruption studies.

Iridium(III)‐Catalyzed Intermolecular C(sp3)−H Insertion Reaction of Quinoid Carbene: A Radical Mechanism

AbstractDescribed herein is an IrIII/porphyrin‐catalyzed intermolecular C(sp3)−H insertion reaction of a quinoid carbene (QC). The reaction was designed by harnessing the hydrogen‐atom transfer (HAT) reactivity of a metal‐QC species with aliphatic substrates followed by a radical rebound process to afford C−H arylation products. This methodology is efficient for the arylation of activated hydrocarbons such as 1,4‐cyclohexadienes (down to 40 min reaction time, up to 99 % yield, up to 1.0 g scale). It features unique regioselectivity, which is mainly governed by steric effects, as the insertion into primary C−H bonds is favored over secondary and/or tertiary C−H bonds in the substituted cyclohexene substrates. Mechanistic studies revealed a radical mechanism for the reaction.

Iridium(III)-Catalyzed Intermolecular C(sp3 )-H Insertion Reaction of Quinoid Carbene: A Radical Mechanism.

Described herein is an IrIII /porphyrin-catalyzed intermolecular C(sp3 )-H insertion reaction of a quinoid carbene (QC). The reaction was designed by harnessing the hydrogen-atom transfer (HAT) reactivity of a metal-QC species with aliphatic substrates followed by a radical rebound process to afford C-H arylation products. This methodology is efficient for the arylation of activated hydrocarbons such as 1,4-cyclohexadienes (down to 40 min reaction time, up to 99 % yield, up to 1.0 g scale). It features unique regioselectivity, which is mainly governed by steric effects, as the insertion into primary C-H bonds is favored over secondary and/or tertiary C-H bonds in the substituted cyclohexene substrates. Mechanistic studies revealed a radical mechanism for the reaction.

48‐4: Analysis of Fracture Mechanism in Sand Paper Drop Test for Cover Glass

Fracture mechanism of cover glasses on mobile devices in a drop event was investigated through high speed camera observation and conventional fracture surface analysis. Drop tests were performed for various chemically strengthened glasses with different mechanical properties and stress profiles. These were dropped on sandpapers with grit size of 180. Based on the observations, we confirmed that the fracture of cover glasses in the drop tests is caused by two consecutive steps. The first one is nucleation of a crack due to the contact with the protrusions of the sandpaper, which causes a strong tensile stress localized around the protrusions. The second one is the propagation of the crack due to a stress caused by bending of the smart phone during the rebound process after the first contact with the sandpaper. According to these investigations, we established a prediction formula for the “fracture drop height” for the sandpaper drop tests. It enables us to understand key parameters to improve the fracture drop height. For example, in addition to the stress induced by chemical strengthening, the mechanical properties of the cover glass and the body of the smartphone are key factors to improve the fracture drop height. We believe the knowledge in this study is important for improving the strength of the cover glasses in the future.

Reducing the rebound effect in micro-scale laser dynamic flexible forming through using plasticine as pressure-carrying medium

Abstract Micro-scale laser dynamic flexible forming (μLDFF) is a new kind of high velocity forming (HVF) process, which uses laser shock wave pressure to realize thin metal sheets micro-forming. Rebound effect usually occurs when forming deep complex micro-features, which has a significant effect on the forming precision. This work firstly investigates the impact and rebound behaviors of workpiece in μLDFF with rubber medium to probe the main affecting factors of rebound effect, then proposes a new μLDFF with plasticine medium to reduce the rebound effect. With the increase of laser energy, the average surface roughness of impact-affected zone (IAZ) reduces firstly by flattening behavior, and then increases afterward due to coining-like operation. The 3D deviation analyses between workpieces and micro-die are performed to characterize the fitability. When laser energy is 675 mJ, bottom region of workpiece fits well with the micro-die. When laser energy is increased to 1020 mJ, bottom region of workpiece separates from the micro-die due to rebound effect. A finite element model considering the machining marks on micro-die surface is built, and the predicted results are validated by experimental results. Coefficient of restitution (COR) and the rebound ratio (α) are used to investigate the impact and rebound process. The results show that rebound effect is dominated by laser energy, surface morphology of micro-die, and loading duration. To effectively reduce the rebound effect, the plasticine layer is first introduced as pressure-carrying medium in this work. The deformation behavior of plasticine medium is like a Reiner-Rivlin fluid. So the plasticine medium closely contacts with the sample during forming, this is equivalent to indirectly increasing the stiffness of sample and prolonging the loading duration. In addition, the plasticine layer can absorb impact-induced reflection wave. So plasticine medium can effectively improve the forming precision.

Simulation of phase transition process in reconstructed porous medium based on lattice Boltzmann method

At the pore scale level, 2-D porous medium structures of porous media with different porosities (isotropic) and the same porosities (anisotropic) were constructed using quartet structure generation set. A random porous cavity was selected and combined with the lattice Boltzmann model to describe the gas-liquid phase transition process. Bubble generation, growth, mutual fusion, and collision as well as rebound process in porous media framework were investigated by simulating the phase transition phenomenon in porous media. Calculation results show that in three different heat loads, the maximum relative errors between the qualities of gas phase and liquid phase and theoretical solution of gas phase were 0.09%, 0.19%, and 0.32%, respectively, whereas the values for liquid phase were 0.11%, 0.38%, and 1.49%, respectively. Simulation results coincide with the theoretical solution perfectly, verifying the accuracy and feasibility of the model for random porous structures.

Impact characterization of agricultural products by fall trajectory simulation and measurement

Since 40 years, artificial fruits or dummies are built similar to real agricultural produce in order to measure mechanical load caused due to harvest and post-harvest handling systems. As shown by Praeger et al., 2013 the evaluation of how close these electronic fruits reflect real products impact behavior has been largely neglected during their design.The paper dealt with development of a test method for comparison of elastic characteristics of real potato tubers and of dummy materials (built based on 2 component polyurethane elastomers) falling on metal or plastic materials. Therefore, the trajectory of the produce center of the whole drop process was simulated based on measurements with a miniaturised 3-axis accelerometer inside the samples, force measurements at the impact position and videos made with a high speed camera of the fall and rebound process. A simulation model of the impact was developed and impacts were characterised by forces, coefficients of restitutions, accumulated energy and deformation features obtained by quasi- rigid body impact simulations. Exemplary impact characteristics are presented for real potatoes of different water status and artificial tuber dummies using force-deformation courses and coefficients of restitution. The testing procedure showed to be useful for the systematic design of optimised dummy materials, for instance based on polyurethane elastomers, for a highly realistic replication of impact performance of real fruit and to improve the applicability and accuracy of dummies in field measurements. The drop tests and simulations for tuber dummies and real potatoes showed a wide range of impact characteristics when falling onto steel. In general, impact forces of the currently used dummies were higher and deformations were reduced compared to those of potato tubers. One dummy tested in this study showed impact characteristics widely similar to potato tuber material.

Stereoselective Metabolism of Omeprazole by Cytochrome P450 2C19 and 3A4: Mechanistic Insights from DFT Study.

The efficacy of S-omeprazole as a proton pump inhibitor compared with that of its enantiomer R-omeprazole is studied using density functional theoretical calculations. The pharmacokinetic studies suggest that the efficacy of S-omeprazole presumably depends on metabolic pathway and excretion from the human body. The density functional theory calculations at SMDwater-B3LYP-D3/6-311+G(d,p)/LANL2DZ//B3LYP/6-31G(d)/LANL2DZ with triradicaloid model active species, [Por•+FeIV(SH)O], of CYP2C19 enzyme with high-spin quartet and low-spin doublet states demonstrate C-H bond activation mechanism through a two-state rebound process for the hydroxylation of R-omeprazole and S-omeprazole. The calculated activation free energy barriers for the hydrogen abstraction are 15.7 and 17.5 kcal/mol for R-omeprazole and S-omeprazole, respectively. The hydroxylation of R-omeprazole and S-omeprazole is thermodynamically favored; however, the hydroxylated intermediate of S-omeprazole further disintegrates to metabolite 5- O-desmethylomeprazole with a higher kinetic barrier. We have examined the sulfoxidation of S-omeprazole to omeprazole sulfone metabolite by CYP3A4, and the observed activation free energy barrier is 9.9 kcal/mol. The computational results reveal that CYP2C19 exclusively metabolizes R-omeprazole to hydroxyomeprazole, which is hydrophilic and can easily excrete, whereas CYP3A4 metabolizes S-omeprazole to lipophilic sulfone; hence, the excretion of this metabolite would be relatively slower from the body. The spin density analysis and molecular orbital analysis performed using biorthogonalization calculations indicate that R-omeprazole favors high-spin pathway for metabolism process whereas S-omeprazole prefers the low-spin pathway.

Two Distinct Mechanisms for C-C Desaturation by Iron(II)- and 2-(Oxo)glutarate-Dependent Oxygenases: Importance of α-Heteroatom Assistance.

Hydroxylation of aliphatic carbons by nonheme Fe(IV)-oxo (ferryl) complexes proceeds by hydrogen-atom (H•) transfer (HAT) to the ferryl and subsequent coupling between the carbon radical and Fe(III)-coordinated oxygen (termed rebound). Enzymes that use H•-abstracting ferryl complexes for other transformations must either suppress rebound or further process hydroxylated intermediates. For olefin-installing C-C desaturations, it has been proposed that a second HAT to the Fe(III)-OH complex from the carbon α to the radical preempts rebound. Deuterium (2H) at the second site should slow this step, potentially making rebound competitive. Desaturations mediated by two related l-arginine-modifying iron(II)- and 2-(oxo)glutarate-dependent (Fe/2OG) oxygenases behave oppositely in this key test, implicating different mechanisms. NapI, the l-Arg 4,5-desaturase from the naphthyridinomycin biosynthetic pathway, abstracts H• first from C5 but hydroxylates this site (leading to guanidine release) to the same modest extent whether C4 harbors 1H or 2H. By contrast, an unexpected 3,4-desaturation of l-homoarginine (l-hArg) by VioC, the l-Arg 3-hydroxylase from the viomycin biosynthetic pathway, is markedly disfavored relative to C4 hydroxylation when C3 (the second hydrogen donor) harbors 2H. Anchimeric assistance by N6 permits removal of the C4-H as a proton in the NapI reaction, but, with no such assistance possible in the VioC desaturation, a second HAT step (from C3) is required. The close proximity (≤3.5 Å) of both l-hArg carbons to the oxygen ligand in an X-ray crystal structure of VioC harboring a vanadium-based ferryl mimic supports and rationalizes the sequential-HAT mechanism. The results suggest that, although the sequential-HAT mechanism is feasible, its geometric requirements may make competing hydroxylation unavoidable, thus explaining the presence of α-heteroatoms in nearly all native substrates for Fe/2OG desaturases.

Selective C-H halogenation over hydroxylation by non-heme iron(iv)-oxo.

Non-heme iron based halogenase enzymes promote selective halogenation of the sp3-C-H bond through iron(iv)-oxo-halide active species. During halogenation, competitive hydroxylation can be prevented completely in enzymatic systems. However, synthetic iron(iv)-oxo-halide intermediates often result in a mixture of halogenation and hydroxylation products. In this report, we have developed a new synthetic strategy by employing non-heme iron based complexes for selective sp3-C-H halogenation by overriding hydroxylation. A room temperature stable, iron(iv)-oxo complex, [Fe(2PyN2Q)(O)]2+ was directed for hydrogen atom abstraction (HAA) from aliphatic substrates and the iron(ii)-halide [FeII(2PyN2Q)(X)]+ (X, halogen) was exploited in conjunction to deliver the halogen atom to the ensuing carbon centered radical. Despite iron(iv)-oxo being an effective promoter of hydroxylation of aliphatic substrates, the perfect interplay of HAA and halogen atom transfer in this work leads to the halogenation product selectively by diverting the hydroxylation pathway. Experimental studies outline the mechanistic details of the iron(iv)-oxo mediated halogenation reactions. A kinetic isotope study between PhCH3 and C6D5CD3 showed a value of 13.5 that supports the initial HAA step as the RDS during halogenation. Successful implementation of this new strategy led to the establishment of a functional mimic of non-heme halogenase enzymes with an excellent selectivity for halogenation over hydroxylation. Detailed theoretical studies based on density functional methods reveal how the small difference in the ligand design leads to a large difference in the electronic structure of the [Fe(2PyN2Q)(O)]2+ species. Both experimental and computational studies suggest that the halide rebound process of the cage escaped radical with iron(iii)-halide is energetically favorable compared to iron(iii)-hydroxide and it brings in selective formation of halogenation products over hydroxylation.

Effect of oil starvation on the isothermal impact problem

In this study, the effect of oil starvation on isothermal elastohydrodynamic lubrication of an impact motion is explored with the aid of numerical techniques. During the impact process, on comparison with the fully lubricated results, the pressure and film thickness are much lower and the entrapped film shape does not happen. The rebound is delayed by the oil starvation assumption. During the rebound process, a periphery entrapment is seen in the starved film thickness distribution. Under the starved condition, the maximum pressure gradient is higher. The central film thickness and minimum film thickness exhibit different variations compared with the results by fully flooded assumption.

Direct Observation of Oxygen Rebound with an Iron-Hydroxide Complex.

The rebound mechanism for alkane hydroxylation was invoked over 40 years ago to help explain reactivity patterns in cytochrome P450, and subsequently has been used to provide insight into a range of biological and synthetic systems. Efforts to model the rebound reaction in a synthetic system have been unsuccessful, in part because of the challenge in preparing a suitable metal-hydroxide complex at the correct oxidation level. Herein we report the synthesis of such a complex. The reaction of this species with a series of substituted radicals allows for the direct interrogation of the rebound process, providing insight into this uniformly invoked, but previously unobserved process.

Imparting Icephobicity with Substrate Flexibility.

Ice accumulation hinders the performance of, and poses safety threats for, infrastructure both on the ground and in the air. Previously, rationally designed superhydrophobic surfaces have demonstrated some potential as a passive means to mitigate ice accretion; however, further studies on material solutions that reduce impalement and the contact time for impacting supercooled droplets (high viscosity) and can also repel droplets that freeze during surface contact are urgently needed. Here we demonstrate the collaborative effect of substrate flexibility and surface micro/nanotexture on enhancing both icephobicity and the repellency of viscous droplets (typical of supercooled water). We first investigate the influence of increased viscosity (spanning from 0.9 to 1078 mPa·s using water-glycerol mixtures) on impalement resistance and the droplet-substrate contact time after impact. Then we examine the effect of droplet partial solidification on recoil and simulate more challenging icing conditions by impacting supercooled water droplets (down to -15 °C) onto flexible and rigid surfaces containing ice nucleation promoters (AgI). We demonstrate a passive mechanism for shedding partially solidified (recalescent) droplets-under conditions where partial solidification occurs much faster than the natural droplet oscillation-which does not rely on converting droplet surface energy into kinetic energy (classic recoil mechanism). Using an energy-based model (kinetic-elastic-capillary), we identify a previously unexplored mechanism whereby the substrate oscillation and velocity govern the rebound process, with low areal density and moderately stiff substrates acting to efficiently absorb the incoming droplet kinetic energy and rectify it back, allowing droplets to overcome adhesion and gravitational forces, and recoil. This mechanism applies for a range of droplet viscosities, spanning from low- to high-viscosity fluids and even ice slurries, which do not rebound from rigid superhydrophobic substrates. For a low-viscosity fluid, i.e., water, if the substrate oscillates faster than the droplet spreading and retraction, the action of the substrate is decoupled from the droplet oscillation, resulting in a reduction in the droplet-substrate contact time.

Reaction mechanism of sterol hydroxylation by steroid C25 dehydrogenase – Homology model, reactivity and isoenzymatic diversity

Steroid C25 dehydrogenase (S25DH) is a molybdenum-containing oxidoreductase isolated from the anaerobic Sterolibacterium denitrificans Chol-1S. S25DH is classified as ‘EBDH-like’ enzyme (EBDH, ethylbenzene dehydrogenase) and catalyzes the introduction of an OH group to the C25 atom of a sterol aliphatic side-chain. Due to its regioselectivity, S25DH is proposed as a catalyst in production of pharmaceuticals: calcifediol or 25-hydroxycholesterol. The aim of presented research was to obtain structural model of catalytic subunit α and investigate the reaction mechanism of the O2-independent tertiary carbon atom activation. Based on homology modeling and theoretical calculations, a S25DH α subunit model was for the first time characterized and compared to other S25DH-like isoforms. The molecular dynamics simulations of the enzyme-substrate complexes revealed two stable binding modes of a substrate, which are stabilized predominantly by van der Waals forces in the hydrophobic substrate channel. However, H-bond interactions involving polar residues with C3=O/C3-OH in the steroid ring appear to be responsible for positioning the substrate. These results may explain the experimental kinetic results which showed that 3-ketosterols are hydroxylated 5–10-fold faster than 3-hydroxysterols. The reaction mechanism was studied using QM:MM and QM-only cluster models. The postulated mechanism involves homolytic CH cleavage by the MoO ligand, giving rise to a radical intermediate with product obtained in an OH rebound process. The hypothesis was supported by kinetic isotopic effect (KIE) experiments involving 25,26,26,26-[2H]-cholesterol (4.5) and the theoretically predicted intrinsic KIE (7.0–7.2). Finally, we have demonstrated that the recombinant S25DH-like isoform catalyzes the same reaction as S25DH.

Induced liquid-solid contact via micro/nano multiscale texture on a surface and its effect on the Leidenfrost temperature

A significant increase in the Leidenfrost temperature (LFT) was observed on a micro/nano multiscale textured surface (MTS) compared with a polished surface (PS) and a micro rough surface (MRS). MTS was fabricated by anodic oxidation and has nano-scaled needles with micro roughness. It showed improved surface wetting characteristics (0° contact angle with liquid spreading). On the other hand, MRS was fabricated by mechanical polishing and it only has micro roughness. LFT on MTS and MRS increased by approximately 150°C and 30°C, respectively, compared with one for PS. The textures on each surface influenced the water droplet dynamics. The relationship between LFT and the dynamics of water droplet were studied by high-speed photography. The key phenomenon determining LFT was the rebound process of the droplet during a few milliseconds. On MRS and MTS, the rebound phenomenon of the droplet was disturbed by the surface-texture-induced liquid-solid contact even when the surface was initially at a high temperature over 300°C. The precursor wetting front, observed only on MTS and the capillary wicking phenomenon are likely the responsible mechanisms that significantly increased LFT on MTS.

Electron Transfer Mechanism in the Oxidation of Aryl 1-Methyl-1-phenylethyl Sulfides Promoted by Nonheme Iron(IV)–Oxo Complexes: The Rate of the Oxygen Rebound Process

The oxidation of aryl 1-methyl-1-phenylethyl sulfides promoted by the nonheme iron(IV)-oxo complexes [(N4Py)FeIV═O]2+ and [(Bn-TPEN)FeIV═O]2+ occurs by an electron transfer-oxygen rebound (ET-OT) mechanism leading to aryl 1-methyl-1-phenylethyl sulfoxides accompanied by products derived from Cα-S fragmentation of sulfide radical cations (2-phenyl-2-propanol and diaryl disulfides). For the first time, the rate constants for the oxygen rebound process (kOT), which are in the range of <0.8 × 104 to 3.5 × 104 s-1, were determined from the fragmentation rate constants of the radical cations (kf) and the S oxidation/fragmentation product ratios.

Seismic evidence of the rebound of the Adria foreland and the current geodynamics of the Central and Southern Apennines (Italy)

The sedimentary wedge of the Apennines foredeep in the Central Adriatic Sea provides evidence of westward tilting of the foreland during the Lower Pliocene. The wedge was covered by an Upper Pliocene-Lower Pleistocene sequence of parallel and horizontal strata that onlapped onto the pre-wedge sediments. The Southern Apennines contain younger foredeep growth strata because the chain front migrated until the Lower Pleistocene.Seismic profiles from the Central and Southern Apennines foredeep show a regional, apparently contrasting eastward-dipping set of post-growth parallel layers that are covered by a Middle/Upper Pleistocene Prograding Sedimentary Wedge (PSW), which is particularly thick in the Central Adriatic basin.In accordance with the “Law of Original Horizontality” and by excluding possible exceptions to this law (inclined depositions in several specific frameworks), the observed geometric setting can be explained as an effect of post-deposition inversion of the previous orogen-ward tilting. We infer that the driving mechanism of uplift was the regional isostatic rebound of the Adria foreland, which started in the Middle Pleistocene and is still active as indicated by the current uplift of Adria and by the passively raised chain. Under the same conditions, the greater the tilting of the foredeep during the chain migration, the greater the degree of isostatic rebound. The rheology of the foreland and sedimentary loading are also key elements of these crustal-scale vertical movements. Furthermore, normal faults and greater foredeep uplift of the foreland can play local roles in short-wavelength deformations.The current axis of the chain, which was affected by imbrication of the Apennine and Apulia units, is now subject to higher rates of rebound and erosion. We infer that inversion of some of the previous faults that originated the buried western margin of the Apulia carbonate platform (AP) triggered the extensional seismicity that is recorded along the chain.The rapid uplift of the foreland and of the overlying thrust belt since the Middle Pleistocene caused a change in the drainage network on the Adriatic side of the chain from a longitudinal pattern to a transverse pattern. In addition, erosion of the uplifted units contributed to the high rate of deposition of the PSW in the Adriatic foreland basin.The regional rebound process that is proposed in this work implies a primary role of the AP buoyancy and rejects the hypothesis of its current passive sinking, which is often regarded as the primary source of Apennines tectonics.

Computational Insight into the Mechanism of Alkane Hydroxylation by Non-heme Fe(PyTACN) Iron Complexes. Effects of the Substrate and Solvent

The reaction mechanisms for alkane hydroxylation catalyzed by non-heme Fe(V)O complexes presented in the literature vary from rebound stepwise to concerted highly asynchronous processes. The origin of these important differences is still not completely understood. Herein, in order to clarify this apparent inconsistency, the hydroxylation of a series of alkanes (methane and substrates bearing primary, secondary, and tertiary C-H bonds) through a Fe(V)O species, [Fe(V)(O)(OH)(PyTACN)](2+) (PyTACN = 1-(2'-pyridylmethyl)-4,7-dimethyl-1,4,7-triazacyclononane), has been computationally examined at the gas phase and in acetonitrile solution. The initial breaking of the C-H bond can occur via hydrogen atom transfer (HAT), leading to an intermediate where there is an interaction between the radical substrate and [Fe(IV)(OH)2(PyTACN)](2+), or through hydride transfer to form a cationic substrate interacting with the [Fe(III)(OH)2(PyTACN)](+) species. Our calculations show the following: (i) except for methane in the rest of the alkanes studied, the intermediate formed by R(+) and [Fe(III)(OH)2(PyTACN)](+) is more stable than that involving the alkyl radical and the [Fe(IV)(OH)2(PyTACN)](2+) complex; (ii) in spite of (i), the first step of the reaction mechanism for all substrates is a HAT instead of hydride abstraction; (iii) the HAT is the rate-determining step for all analyzed cases; and (iv) the barrier for the HAT decreases along methane → primary → secondary → tertiary carbon. The second part of the reaction mechanism corresponds to the rebound process. Therefore, the stereospecific hydroxylation of alkane C-H bonds by non-heme Fe(V)(O) species occurs through a rebound stepwise mechanism that resembles that taking place at heme analogues. Finally, our study also shows that, to properly describe alkane hydroxylation processes mediated by Fe(V)O species, it is essential to consider the solvent effects during geometry optimizations. The use of gas-phase geometries explains the variety of mechanisms for the hydroxylation of alkanes reported in the literature.