Intermediate Chemical Species Research Articles

Spatial models of pattern formation during phagocytosis.

Phagocytosis, the biological process in which cells ingest large particles such as bacteria, is a key component of the innate immune response. Fcγ receptor (FcγR)-mediated phagocytosis is initiated when these receptors are activated after binding immunoglobulin G (IgG). Receptor activation initiates a signaling cascade that leads to the formation of the phagocytic cup and culminates with ingestion of the foreign particle. In the experimental system termed “frustrated phagocytosis”, cells attempt to internalize micropatterned disks of IgG. Cells that engage in frustrated phagocytosis form “rosettes” of actin-enriched structures called podosomes around the IgG disk. The mechanism that generates the rosette pattern is unknown. We present data that supports the involvement of Cdc42, a member of the Rho family of GTPases, in pattern formation. Cdc42 acts downstream of receptor activation, upstream of actin polymerization, and is known to play a role in polarity establishment. Reaction-diffusion models for GTPase spatiotemporal dynamics exist. We demonstrate how the addition of negative feedback and minor changes to these models can generate the experimentally observed rosette pattern of podosomes. We show that this pattern formation can occur through two general mechanisms. In the first mechanism, an intermediate species forms a ring of high activity around the IgG disk, which then promotes rosette organization. The second mechanism does not require initial ring formation but relies on spatial gradients of intermediate chemical species that are selectively activated over the IgG patch. Finally, we analyze the models to suggest experiments to test their validity.

Hamiltonian chemical kinetics for studying roaming in formaldehyde dissociation: Linear and nonlinear models

A recently developed theory for formulating chemical kinetics with a Hamiltonian theory similar to classical mechanics is applied to study linear and nonlinear kinetic models for the photodissociation of formaldehyde ( H 2 CO ) via roaming pathways. Chemical kinetic equations are proposed by mapping time invariant phase space structures, such as stationary points of the potential energy surface and periodic orbits, to relevant intermediate chemical species. Solving kinetic equations in the Hamiltonian framework, we calculate reaction paths to asymptotically stable equilibria for closed reactions and varying the initial concentration of H2CO at constant temperature and pressure. The reaction paths may be classified by defining a thermodynamic distance between initial and equilibrium states, as well as the entropy production. A brusselator-type nonlinear model is proposed as the phenomenological equivalent to the periodic orbit description of roaming mechanism given before. Treating the photodissociation of formaldehyde as an open system and properly selecting the rate coefficients of the reactions and the initial concentration of formaldehyde, a periodic orbit emanates as the result of a Hamiltonian Hopf bifurcation. This yields an oscillatory reaction between the two long-range metastable intermediates, { H…CHO } and { H…HCO }, which lead to radical and molecular products.

A scaling law for the required transition zone depth in hybrid LES-DNS

There is a substantial need to better understand multi-physics interactions in realistic laboratory experiments, yet it is currently unfeasible to perform direct numerical simulations (DNS) of most such problems. As a result, reduced-order models such as those used to represent unclosed subgrid-scale stresses in large-eddy simulations (LES) and advanced numerical techniques, including adaptive mesh refinement and nested grid structures, are required for the study of multi-physics interactions in practical situations. In particular, it is now possible to model many real-world flows with LES fidelity, and to selectively refine the computational mesh in a small region of the domain to resolve multi-physics interactions with DNS fidelity. However, rules and guidance for the valid implementation of this multi-fidelity ‘hybrid LES-DNS’ approach have yet to be fully formulated. Within the embedded DNS region, multi-physics interactions will be influenced by (i) macroscale features (e.g. large-scale shear gradients or body forces that produce turbulence), (ii) LES-regulated mesoscale features (e.g. advecting turbulent eddies), and (iii) microscale features that are subgrid-scale to the LES (e.g. layers of fast-reacting intermediate chemical species). In this study, we address the second of these effects, which poses particular challenges due to the transfer and overlapping nature of advecting mesoscale eddies between the purely LES (i.e. macroscale) and purely DNS (i.e. microscale) regions. By combining dimensional analysis and computational results, we formulate a scaling law for the required depth of the transition zone surrounding the embedded DNS region within hybrid LES-DNS computations of realistic turbulent flows.

Specific energy cost for nitrogen fixation as NOx using DC glow discharge in air

We report on factors influencing the specific energy costs of producing NOx from pin-to-pin DC glow discharges in air at atmospheric pressure. Discharge current, gap distance, gas flowrate, exterior tube wall temperature and the presence and position of activated Al2O3 catalyst powder were examined. The presence of heated catalyst adjacent to the plasma zone improved energy efficiency by as much as 20% at low flows, but the most energy efficient conditions were found at the highest flowrates that allowed a stable discharge (about 10–15 l min−1). Under these conditions, the catalyst had no effect on efficiency in the present study. The lowest specific energy cost was observed to be between about 200–250 GJ/tN. The transport of active chemical species and energy are likely key factors controlling the specific energy costs of NOx production in the presence of a catalyst. Air plasma device design and operating conditions must ensure that plasma-generated active intermediate chemical species transport is optimally coupled with catalytically active surfaces.

Kinetics of neptunium sorption and desorption in the presence of aluminum (hydr)oxide minerals: Evidence for multi-step desorption at low pH

Kinetics analyses of sorption and desorption provide important insight into reaction mechanisms occurring at the mineral-water interface. They are also needed to determine when equilibrium is achieved, identify intermediate chemical species, and inform models describing neptunium mobility. Neptunium sorption to and desorption from four different aluminum (hydr)oxides - bayerite (α-Al(OH)3), gibbsite (γ-Al(OH)3), corundum (α-Al2O3), and γ-alumina (γ-Al2O3) - were investigated as a function of mineral concentration (5 – 170 m2 L−1), neptunium concentration (10−9 – 10−7 M), and pH (5.5 – 10.5). Neptunium sorption was characterized by a two-step reaction with an initial fast sorption step occurring within minutes followed by a slower equilibrium process, which was attributed to initial sorption of neptunium to a small number of strong sorption sites followed by sorption of neptunium to a larger number of weak sorption sites. The kinetics data were modeled using the linear and non-linear forms of the pseudo-first and pseudo-second order rate equations and the goodness of fit parameters were compared. Non-linear pseudo-second order rate constants described neptunium sorption to aluminum (hydr)oxides most accurately and were used to determine the reaction orders with respect to mineral concentration and [H+]. Neptunium desorption experiments demonstrated that the desorption mechanism changed as a function of pH and that the forward and reverse reactions were not equivalent. At pH ≥ 7.5, desorption reached steady-state within an hour and was accurately described by the non-linear pseudo-second order rate equations. A desorption plateau was observed at pH 5.5 that could not be described by either pseudo-first or –second order kinetics, suggesting the possibility of a multi-step desorption reaction. The comparatively slow desorption kinetics observed here suggests that sorbed neptunium could be slowly released back into the aqueous phase and act as a continuous source of contamination to the environment.

An experimental and kinetic modeling study of the oxidation of hexane isomers: Developing consistent reaction rate rules for alkanes

Alkanes are key components in gasoline, jet and diesel fuels and considerably influence the combustion behavior of these fuels because of their wide range of reactivity. An improved understanding of their combustion behavior and the development of chemical kinetic models that can accurately simulate their combustion behavior are important for the development of next-generation internal-combustion and gas-turbine engines. The current work provides improved insight into oxidation mechanisms of a representative family of hydrocarbon fuels, specifically the hexane isomers: n-hexane, 2-methylpentane, 3-methylpentane, 2,2-dimethylbutane and 2,3-dimethylbutane. These isomers provide carbon “skeletons” ranging from straight-chained to highly-branched and provide a framework for the subsequent development of kinetic mechanisms for larger alkanes. New ignition delay times for the four branched hexane isomers were measured in a high-pressure shock tube and in a rapid compression machine, both at stoichiometric conditions (φ = 1), p = 15 bar and XO2 = 21% over temperatures from 600 to1300 K. These data were combined with previously published measurements under the same conditions for the remaining n-hexane isomer to provide a complete body of experimental data for kinetic modeling analysis. In addition, very recent experimental measurements of individual intermediate chemical species concentrations from all five hexane isomers in a jet-stirred reactor are also included and provide another family of data for further assessment of hexane isomer reactivity. Different reactivities were observed for each hexane isomer in each experimental facility, resulting from differences in their molecular structures. Consistent reaction rate rules have been applied to develop a combined detailed chemical kinetic model for all five hexane isomers. Kinetic model validation studies are reported to show that the current model reproduces well the ignition delay times of all five alkane isomers, as well as their variations in reactivity over a wide range of temperatures and other operating conditions. Equally important, these results show that it is not necessary to have a separate, different kinetic model for each isomer of a family of alkane fuels and that a single, coherent, integrated set of reaction rate classes and rules is sufficient to accurately describe combustion rates of combustion of straight-chain n-alkanes and branched-chain alkane fuels. This suggests strongly that a single set of reaction classes and rate rules should be sufficient to describe combustion kinetics of alkane fuels of any size and degree of branching.

Ostwald ripening of confined nanoparticles: chemomechanical coupling in nanopores.

Ostwald ripening is a major source of deactivation of functional nanomaterials. It consists in the growth of large nanoparticles at the expense of smaller ones via the formation and decomposition of intermediate chemical species. In most materials of practical interest nanoparticles are dispersed in porous supports with which they interact mechanically. We analyze the consequences of this chemo-mechanical coupling on both kinetic and equilibrium aspects of Ostwald ripening. We show that the long-term stability of a collection of confined nanoparticles depends on nucleation-like events, whereby few particles break through the pore walls early in the process and later grow at the expense of all other particles. This notably explains why the stability of confined nanoparticles depends critically on their initial size distribution; it also provides an explanation for the occasional observation of bimodal particle size distributions in aged materials.

Flame Propagation Enhancement by Dielectric Barrier Discharge-Generated Intermediate Species

ABSTRACT The interaction between nonthermal plasma (NTP) and fuel-air mixtures was studied both experimentally and by means of simulations, to elucidate their promotional effect on flame propagation. A promotional effect on flame propagation velocity was experimentally observed by generating a dielectric barrier discharge (DBD), prior to spark plug ignition of an n-heptane mixture in a high-pressure and -temperature environment, using a rapid compression and expansion machine (RCEM). A novel method of concentration calibration for mass-spectral analysis was conducted, to determine the intermediate species in the fuel-air mixtures passing through the DBD plasma. The effect of the intermediate chemical species on flame propagation was examined numerically using the PREMIX code, with the observed species being considered as initial additives in the calculations. The promotional effect was reproduced numerically with the addition of alkyl hydroperoxide to an n-heptane/air mixture; and the higher the temperature and leaner the mixture in the parameter region, the more pronounced was the effect. The promotional behavior was examined using reaction path analysis, on the basis of which enhanced low-temperature oxidation reactions, due to the dissociation of the alkyl hydroperoxide, were determined in pre-flame region.

Modeling Framework for Biogenic Methane Formation from Coal

In situ biodegradation of coal to methane offers an innovative and attractive alternative to the prevailing methods of harnessing the energy potential of coal. This alternative approach employs a community of microorganisms to biologically generate methane from unmined coal and has the promise of causing less pollution, reducing the environmental impact of mining, and being potentially less expensive.(9,10,15−18) The goal of our work is to develop a novel, comprehensive, and quantitative mathematical modeling framework to better understand the process of biogenic methane formation from coal. Intermediate chemical species and metabolic pathways are identified using existing literature information and are incorporated into a lumped kinetic model, referred to as the Coal to Methane (C2M) Kinetic Model. Several intermediate compounds have been lumped into polyaromatics (PACs), long chain fatty acids (LCFAs), and mid chain fatty acids (MCFAs), etc. The simulations of the model and sensitivity analysis along wi...

Turbulent flame propagation enhancement by application of dielectric barrier discharge to fuel-air mixtures

The promotional effect of non-thermal plasma (NTP) on lean flame propagation in turbulent fuel-air mixtures in a reciprocating engine-like high-temperature and -pressure environment was investigated. A turbulent flow was created by installing a perforated plate with oblique holes in the combustion chamber of a rapid compression and expansion machine (RCEM). Ignition was conducted by conventional spark plug. The NTP was generated by a dielectric-barrier discharge (DBD) device installed in the combustion chamber near the spark plug. A portion of the lean fuel-air mixture (ϕ = 0.5) in the chamber passed through the NTP and diffused throughout the chamber before spark ignition. To elucidate whether the effect persisted even when the plasma-affected volume was diffused by the flow, two types of experiments with temporal delay were conducted. The fuels evaluated were n-heptane as a representative fuel with a strong low-temperature oxidation reaction, i-octane as a representative fuel with a weak low-temperature reaction, and a primary reference fuel consisting of a mixture of these two fuels. Temporal growth of the flame was observed using a high-speed camera with an image intensifier. The evolution of in-cylinder pressure was also monitored and the characteristic time of the mass fraction burned was evaluated accordingly. It was found that flame propagation was promoted by DBD for n-heptane-containing mixtures at a certain initial temperature while the i-octane-air mixture did not exhibit such enhancement. The results obtained suggest that long-lived intermediate chemical species formed by the plasma diffuse into the cylinder, affecting flame propagation through promotion of a low-temperature oxidation reaction. In addition to these findings, the effect of NTP on burning periods were evaluated.

On the quantification of spatial resolution for three-dimensional computed tomography of chemiluminescence: erratum.

This erratum clarifies an accidental omission of a citation.

On the quantification of spatial resolution for three-dimensional computed tomography of chemiluminescence.

Three-dimensional computed tomography of chemiluminescence (CTC) for combustion diagnostics is attracting a surged research interest due to recent progress in sensor technologies and reduced costs of high-speed cameras. For example, it has been applied to recover the 3D distributions of intermediate chemical species such as CH* and OH*, heat release rate, and flame topology. Although these applications were demonstrated to be successful, there are still a few drawbacks of this technique that have not be cured. For example, to the best of the authors' knowledge, all the imaging models that have been developed so far ignore the imperfections of cameras such as lens distortion and skewness. However, this will unavoidably introduce errors into the weight matrix. In addition, spatial resolution of a CTC system is a critical performance parameter. However, it has only been studied qualitatively and no quantitative quantification method is reported so far. This work aims to solve these problems by improving the imaging model and developing a method based on edge spread function for the quantification of spatial resolution. Although this work is conducted under the context of CTC for combustion diagnostics, it also provides useful insights for other tomographic modalities such as volumetric laser-induced fluorescence and tomographic laser-induced incandescence.

Importance of detailed chemical kinetics on combustion and soot modelling of ventilated and under-ventilated fires in compartment

A novel in-house computation code based on large eddy simulations (LES) incorporating fully coupled subgrid-scale (SGS) turbulence, combustion, soot and radiation models for turbulent reacting flows in compartment fires has been developed. It uniquely embraces the detailed reaction mechanisms for the chemical processes involved during combustion, which provides a comprehensive description of the fuel oxidation processes. Furthermore, it gives a more complete representation of the generation of intermediate chemical by-products including toxic gases such as carbon monoxide and irritant gases such as soot. Since the modelling of hydrocarbons by-products are enabled when considering the full chemical profile, the formation of soot particles is correlated to the concentration of main soot incipient acetylene, which provides an appropriate representation of nucleation, surface growth processes. The LES code has been validated with experimental fire tests results for both ventilated and under-ventilated fires in compartment for confirmation of its robustness. The importance of incorporating the detailed reaction mechanisms in compartment fire simulations has been confirmed by comparing with experiments. For under-ventilated fires in compartment, the chemical kinetics become increasingly important since the combustion efficiency drops significantly involving generation of intermediate chemical species. It is discovered that species concentrations especially CO2 and CO are more accurately predicted by the detailed scheme comparing to the multi-step scheme, since the formation of hydrocarbons and nitrogen oxides are considered. In general, the simulation incorporating detailed kinetics showed an averaged improvement of 9.2% and 81.7% in the prediction of CO2/CO ratio and volume fraction of soot respectively. This also improves the replication of the flame structure as the fire is chemically-driven within the combustion zone.

Chaos in the Belousov–Zhabotinsky reaction

The dynamics of reacting chemical systems is governed by typically polynomial differential equations that may contain nonlinear terms and/or embedded feedback loops. Thus the dynamics of such systems may exhibit features associated with nonlinear dynamical systems, including (among others): temporal oscillations, excitability, multistability, reaction-diffusion-driven formation of spatial patterns, and deterministic chaos. These behaviors are exhibited in the concentrations of intermediate chemical species. Bifurcations occur between particular dynamic behaviors as system parameters are varied. The governing differential equations of reacting chemical systems have as variables the concentrations of all chemical species involved, as well as controllable parameters, including temperature, the initial concentrations of all chemical species, and fixed reaction-rate constants. A discussion is presented of the kinetics of chemical reactions as well as some thermodynamic considerations important to the appearance of temporal oscillations and other nonlinear dynamic behaviors, e.g., deterministic chaos. The behavior, chemical details, and mechanism of the oscillatory Belousov–Zhabotinsky Reaction (BZR) are described. Furthermore, experimental and mathematical evidence is presented that the BZR does indeed exhibit deterministic chaos when run in a flow reactor. The origin of this chaos seems to be in toroidal dynamics in which flow-driven oscillations in the control species bromomalonic acid couple with the BZR limit cycle.

Application of CFD-chemical kinetics approach in detecting RCCI engine knocking fuelled with biodiesel/methanol

Abstract This study numerically investigated knocking phenomenal of a RCCI (Reactivity Controlled Compression Ignition) engine fuelled with biodiesel and methanol. A reduced biodiesel/methanol chemical reaction mechanism coupled with 3D-CFD model was developed and applied to capture local pressure and species concentrations at 10 different regions in the computational domain. A Butterworth band-pass filter was used to process local pressure traces and the maximum peak-to-peak of the filtered data was used to quantify the knocking intensity. Species concentrations analysis was applied to identify the engine knocking occurrence. Finally, knocking mitigations strategies using cooled EGR were assessed. In addition, based on numerical analysis, the effect of SOI (Start of Injection) and premixed methanol mass fraction on engine knocking were evaluated. The results showed that the filtered pressure signals and intermediate chemical species are favored methods to identify and predict engine knocking. Moreover, cooled EGR is an effective way to attenuate engine knocking. Retarded SOI and lower premixed methanol mass fraction could also suppress the engine knocking.

Hybrid Transported-Tabulated Strategy to Downsize Detailed Chemistry for Numerical Simulation of Premixed Flames

A strategy to introduce hydrocarbon combustion detailed chemistry into three-dimensional numerical simulation of flames is reported. Significant progress has been made recently in terms of accuracy and robustness in both chemical kinetics and flow computations. However, the highest resolution reached in simulation of practical burner does not yet ensure that the response of intermediate radical species is fully captured. In the method discussed, the full set of species and elementary reaction rates of the detailed mechanism are retained, but only species featuring non-zero concentration in fresh and burnt gases are transported with the flow. Intermediate chemical species, developing within thin flame layers, are expressed resorting to their self-similar properties observed in a series of canonical combustion problems, projected into an optimized progress variable defined from all transported species. The method is tested with success in various adiabatic and non-adiabatic laminar steady- and unsteady-strained premixed flames.

Low-temperature speciation and chemical kinetic studies of n-heptane

Although there have been many ignition studies of n-heptane—a primary reference fuel—few studies have provided detailed insights into the low-temperature chemistry of n-heptane through direct measurements of intermediate species formed during ignition. Such measurements provide understanding of reaction pathways that form toxic air pollutants and greenhouse gas emissions while also providing key metrics essential to the development of chemical kinetic mechanisms. This paper presents new ignition and speciation data taken at high pressure (9atm), low temperatures (660–710K), and a dilution of inert gases-to-molecular oxygen of 5.64 (mole basis). The detailed time-histories of 17 species, including large alkenes, aldehydes, carbon monoxide, and n-heptane were quantified using gas chromatography. A detailed chemical kinetic mechanism developed previously for oxidation of n-heptane reproduced experimentally observed ignition delay times reasonably well, but predicted levels of some important intermediate chemical species that were significantly different from measured values. Results from recent theoretical studies of low temperature hydrocarbon oxidation reaction rates were used to upgrade the chemical kinetic mechanism for n-heptane, leading to much better agreement between experimental and computed intermediate species concentrations. The implications of these results to many other hydrocarbon fuel oxidation mechanisms in the literature are discussed.

“Analyte” is frequently used as synonym for “measurand”: is that correct?

In a measurement, a most basic concept is ‘‘measurand.’’When starting to draft a plan for a process called mea-surement, we must clearly specify the goal of the process.That goal must have been discussed with the end user(frequently called the customer) on beforehand. Agreeingon such a goal and respecting this agreement will ensurethat the result obtained at the end of the process as carriedout by the analyst, is fit for the intended use [1] of the resultby the end user. The product of a discussion between theend user of the result and the analyst is about what is thegoal of the process. Thereby the end user should not have toworry about how the analyst performs the process: that iswhat the end user pays the analyst for. Thus, the analystmust make sure that the measurement result (s)he obtains atthe end of the process is clearly related to the goal (s)he hasagreed with the end user. All intermediate steps that need tobe taken during the process, including whatever chemicaloperations such as weighings, dissolutions, separations,chemical transformations, preparation of samples suitablefor introduction into whatever type of spectrometer, mea-surements of other input quantities (see entry 2.50 in [2])into the measurement function (see entry 2.49 in [2]), etc.,deemed necessary by the analyst to reach the goal agreedwith the end user, ultimately are the analyst’s choice anddecision, not the end user’s. The analyst is in control ofassigning the value (with associated measurement uncer-tainty) to the measurement result [3]. The intermediatesteps, important as they may—or because sometimes theyare so important—pertain to the answer to the question howthe goal agreed with the end user, is attained by the analyst.This logic is the rationale for the fundamental change inthe definition of ‘‘measurand’’ in the 3rd edition of theInternational Vocabulary of Metrology—VIM [2].It is important to note that the ‘‘quantity subject tomeasurement,’’ the former definition of ‘‘measurand’’ inthe VIM, 2nd edition [4], was very different from the newdefinition in the 3rd edition of the VIM: ‘‘quantity intendedto be measured.’’ The definition in the 3rd edition is ofgreat help in chemistry, as chemistry-specific intermediatesteps now become part of the process of measurement,possibly including measurements performed on interme-diate chemical species showing up in the process (inclinical chemistry, such species is called component orchemical substance [6] and its meaning is considered to beoverlapping with the meaning of the term analyte). Thathas the consequence that all chemical preparation work ona sample in view of obtaining a measured value (withassociated uncertainty) for the intended measurement resultof an a priori specified quantity (the measurand) in theoriginal material as well as any desired transformation of achemical species and measurements of its properties,become an inherent part of the planned process. That alsohas the consequence that the uncertainty naturally associ-ated with each step in that chemical preparation work aswell as with any transformation process will have to beincluded in the uncertainty budget (see entry 2.33 in [2]) ofthe final measurement result for the measurand. That willincrease this final uncertainty, making it larger than just,for example, the measurement of electric current(s) in aninstrumental measuring system (see entry 3.2 in [2]). Butsuch a measurement uncertainty will correspond to a morerealistic measure of ‘‘doubt’’ [5] about the measurement

On the simplification of kinetic reaction mechanisms of air–ethanol under high pressure conditions

In the last decade, the interest towards non-petroleum based fuels is strongly increased due to the current concerns about the impact of the transport system on atmospheric pollutions, mainly due to CO2 emissions. Ethanol, either blended with conventional fuels or in its pure form, is one of such fuels already in use in the automotive industries. As an example, the flex-fuel engines are designed to employ gasoline from 10% up to 85% of ethanol (E10,E85). In this work, the oxidation kinetics of ethanol with air has been considered and analyzed in an ambient at high pressure, ranging from 4 to 6MPa, by means of a Computational Singular Perturbation methodology. This study starts from a detailed kinetic reaction mechanism, which is extensively used in the literature and is made up by 235 reversible reactions among 46 chemical species. This mechanism has been used to get several families of simplified (skeletal) mechanisms by considering equivalence ratios in the range 0.2–2.0 and two sets of initial temperatures (900–1200K and 1200–1700K). The skeletal mechanisms have been validated by comparing the temperature and major chemical species profiles and the ignition delay time with those obtained by employing the detailed mechanism. Advantages and limitations of these mechanisms are highlighted. The accuracy of the skeletal mechanisms is very good in the range of equivalence ratio and temperature considered in the simplification procedure. Moreover, it is shown that a further simplification of the reaction mechanism is obtained by narrowing the range of equivalence ratio instead of the range of temperature. The most simplified skeletal mechanisms show an error in the prediction of temperature and fuel profiles lower than 3%, except for the case of low temperature and lean mixtures, where the maximum error increases up to 14%. Finally, the main reaction pathways are analyzed to show how the most important intermediate chemical species and products characterize the skeletal mechanisms for different values of equivalence ratio and temperature. The skeletal mechanisms are given as Supplementary data. The reader can refer to such data for the entire set of the retained reactions and species for each skeletal mechanism.

Formation dynamics of gold nanoparticles in poly(vinylpyrrolidone) and other protective agent solutions

Intermediate chemical species involved in the formation dynamics of gold nanoparticles triggered by photoreduction were detected on the temporal range from microseconds to seconds by the near-field heterodyne transient grating method. In the dynamic processes, it was found that not only the ionic species of gold (H[Au(I)Cl(2)], H[Au(III)Cl(4)]), but also the ionic species that formed complex species with the protective agent poly(vinylpyrrolidone) (PVP), (H[Au(I)Cl(2)]-PVP, H[Au(III)Cl(4)]-PVP), were involved. In addition, another chemical species was observed at PVP concentrations greater than 0.4 mM with the HAuCl(4) concentration of 10 mM; its diffusion coefficient was two orders smaller than those for the other ionic species. From the reaction mechanism and the hydrodynamic diameter for the component (3.5 nm) estimated by the Einstein-Stokes equation, we concluded that this component corresponds to gold nanoparticle nuclei. Since the dependence of the nuclei concentration on the PVP concentration showed a similar dependence as those for the H[Au(I)Cl(2)]-PVP and H[Au(III)Cl(4)]-PVP complex species, nucleation of gold nanoparticles occurred by way of the complex species. This reaction mechanism is true for the other four protecting agents (PVP K15, Triton X-100, Tween 20, Brij 58). Furthermore, we investigated the determining factor for the nucleation, and it was clarified that the determining factor for nuclei formation is the molecular ratio between HAuCl(4) and the protective agent, not the concentration of HAuCl(4) itself. Assuming a 2-step mechanism, this result suggests that the reaction is controlled by an initial reduction process aided by the protective agents, after which growth of the nuclei proceeds.