The calculation of equilibrium concentrations in large multimetal/multiligand systems

An algorithm for computing equilibrium concentrations by the “equilibrium constant” method is described. The main features of this algorithm are: (a) a damping procedure in conjunction with the Newton-Raphson technique that avoids divergence in dealing with very complicated (simultaneous presence of simple, mixed, protonated, polynuclear and hydroxypolynuclear species) and/or very large systems; (2) the use of devices to decrease core requirements, calculation time, and ill-conditioned problems; and (3) the calculation of errors in free and species concentrations from the uncertainties in analytical concentrations and in formation constants. Four systems are used for testing computer programs on calculation of equilibrium concentrations.     

A simplex search for conditions giving maximal and/or minimal concentrations of species in distribution plots

A new method is proposed for finding the conditions which maximize or minimize the concentration of a particular species in a multicomponent system. A Simplex procedure is combined with an iterative method for solving mass-balance equations from the total concentrations of the constituents of the system, its pH and the pertinent equilibrium constants. The following examples of application are given: (a) the optimum conditions for maximizing the concentration of mixed-ligand species in systems with more than one ligand; (b) the conditions for maximal or minimal formation of monomeric and dimeric species in the Cu(II)-triethanolamine system; (c) a search for local maximum/minimum in species distribution plots.     

Determination of complex reaction mechanisms. Analysis of chemical, biological and genetic networks

We present several methods of determining, not guessing, complex chemical reaction mechanisms and their functions. One method is based on the theory of correlation functions of measured time series of concentrations of chemical species; another is on measurements of temporal responses of concentrations to various perturbations of arbitrary magnitude; a third deals with the analysis of oscillatory systems; a fourth is on the use of genetic algorithms to determine functions of chemical reaction networks. All methods are applicable to chemical, biochemical, and biological reaction systems and to genetic networks and systems biology. The methods depend on the design of appropriate experiments on the whole system and corresponding theories for interpretation that lead to information on the causal chemical connectivity of species, on reaction pathways, on reaction mechanisms, on control centers in the system, and on functions of the system. The first three methods require no assumption of a model or hypothesis, nor extensive calculations, unlike the interpretation of measurements made on a gene network at only one time.     

循环伏安法用于化学振荡的研究

迄今为止,Belousov-Zhabotinskii(B-Z)振荡反应中Br~-浓度~CBr~-的变化主要用Br~-选择电极跟踪监测,取得了一定的成果。但是有一些研究表明,由于受到体系中KBrO_3等物种的干扰,Br~-选择电极的信号在定性和定量上都不一定是Br~-行为的真实反映。Noyes     

Trace analysis of acids and bases by conductometric titration with multiparametric non-linear regression

A chemometric method for analysis of conductometric titration data was introduced to extend its applicability to lower concentrations and more complex acid-base systems. Auxiliary pH measurements were made during the titration to assist the calculation of the distribution of protonable species on base of known or guessed equilibrium constants. Conductivity values of each ionized or ionizable species possibly present in the sample were introduced in a general equation where the only unknown parameters were the total concentrations of (conjugated) bases and of strong electrolytes not involved in acid-base equilibria. All these concentrations were adjusted by a multiparametric nonlinear regression (NLR) method, based on the Levenberg-Marquardt algorithm. This first conductometric titration method with NLR analysis (CT-NLR) was successfully applied to simulated conductometric titration data and to synthetic samples with multiple components at concentrations as low as those found in rainwater (∼10 μmol L⁻¹). It was possible to resolve and quantify mixtures containing a strong acid, formic acid, acetic acid, ammonium ion, bicarbonate and inert electrolyte with accuracy of 5% or better.     

Evaluation of a method for determining concentrations of isoeugenol, an AQUI-S residue, in fillet tissue from freshwater fish species

AQUI-S is a fish anesthetic/sedative that is approved for use in a number of countries throughout the world and has the potential for use in the United States. The active ingredient in AQUI-S is isoeugenol. A method for determining isoeugenol concentrations in edible fillet tissue is needed for regulatory purposes, including surveillance and potential use in studies fulfilling human food safety data requirements if U.S. Food and Drug Administration approval is pursued. A method was developed and evaluated for determining isoeugenol concentrations in fillet tissue using relatively common procedures and equipment. The method produced accurate and precise results with fillet tissue from 10 freshwater fish species. The percentage of isoeugenol recovered from samples fortified with isoeugenol at nominal concentrations of 1, 50, and 100 microg/g for all species was always >80 and <97%. Within-day precision for samples fortified at those same concentrations was < or =10%, and day-to-day precision was < or =4.0%. Method precision with fillet tissue containing biologically incurred isoeugenol was < or =8.1%. There were no or minimal chromatographic interferences in control fillet tissue extracts from 9 of the 10 species. The method detection limits for all but one species ranged from 0.004 to 0.014 microg/g, and the quantitation limits ranged from 0.012 to 0.048 microg/g.     

嵌入定理和BZ反应机理研究

The central object of this work is to explore a method, which can be used to get information of other dynamic variables from the dependent time behaviors of any one dynamic variable in complex systems. The embedding phase patterns of o-NH2C4COOHBZ reaction systems were made based on embedding theorem and the experimental data of concentration of bromine ion received by computer. A saturated embedding dimension m≥8 has been shown, and a related BZ reaction mechanics with 10 chemical species as dynamic variables was presented and resolved by Gear algorithm. The concentrations with time of Br-. Mn3+, HBrO2, HOBr and BrO2 were simulated.     

Nuclear magnetic resonance spectroscopic method for the estimation of competitive equilibrium constants

A nuclear magnetic resonance method is described which yields precise estimates of competitive equilibrium constants for systems in which two or more complexing agents compete for common species. Chemical-shift data under rapid exchange conditions are required, but neither analytical not equilibrium concentrations are needed. The method is demonstrated by estimating equilibria of proton exchange between aniline and pyridinium ion, proton exchange between triethylamine and diisopropylammonium ion, and cyclohexaamylose exchange between m- and p-hydroxybenzoic acids. The precisions of the equilibrium constants are similar to or better than those obtained from classical methods and are relatively free from interferences.     

Artificial neural networks applied for studying metallic complexes

Metallic complexes of multimetal and multiligand systems are complicated for calculating equilibrium concentrations in solutions. An artificial neural network has been developed for studying Al³⁺ and EDTA complexes in solution with an initial concentration of 0.01 mol L^?1 for these species. In this system there are 20 compounds and may exist 18 simultaneous reactions. The neural network has been trained and the simulated data of different concentrations as a function of pH are predicted with an accuracy of about 1% for all species simultaneously. A general analytical formula is presented, which directly relates all the concentrations as a function of pH. The analysis showed that predictions closer to the boundary of the input and output data are quantitative while out of these limits these are not even qualitative. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 1691–1701, 2001     

Relationship of two-dimensional predominance-zone diagrams with conditional constants for complexation equilibria

A method for the construction of two-dimensional predominance-zone diagrams for non-redox chemical species is proposed. The theory for systems containing the species L, ML and ML₂ and buffer X is developed. The chemical interactions of L, M, ML and ML₂ with X are considered through complexation coefficients dependent only on X, whereas the chemical interactions between the M/L species are treated with conditional constants which depend only on X. The method can be extended to systems which contain the species ML₃, ML₄, …, ML_n. This permits the construction of two-dimensional predominance-zone diagrams for non-redox chemical species, with interpretation and applications similar to those of Pourbaix diagrams.     

Substituent effects on fluorene-based linear supramolecular polymerizsation

Two supramolecular systems were constructed based on fluorene-based π-conjugated monomers with or without spiro structures, respectively, and their self-assemble behaviour and optical properties were investigated. Concentration-dependent ¹H NMR and viscosity measurements indicated a transition from cyclic or oligomeric species at low concentrations to linear supramolecular polymers at high concentrations in the system without spiro structures. In contrast, the formation of cyclic species is minimised and not observed in the system with spiro structures.     

Dynamical Approach to Multi-Equilibria Problems Considering the Debye–Hückel Theory of Electrolyte Solutions: Concentration Quotients as a Function of Ionic Strength

We recently described a dynamical approach to the equilibrium problem that involves the formulation of the kinetic rate equations for each species. The equilibrium concentrations are determined by evolving the initial concentrations via this dynamical system to their steady state values. This dynamical approach is particularly attractive because it can be extended easily to very large multi-equilibria systems and the effects of ionic strength also are easily included. Here we describe mathematical methods for the determination of steady state concentrations of all species with the consideration of their activities using several approximations of Debye–Hückel theory of electrolyte solutions. We describe the equations for a system that consists of a triprotic acid H₃A and its conjugate bases. With these equations, two types of multi-equilibria systems were studied and compared to experimental data. The first system is exemplified by case studies of solutions of acetate-buffered acetic acid and the second system is exemplified by the hydroxide titration of citric acid. The discussion focuses on the effect of ionic strength on pH and on the amplification of acidity by ionic strength. Ionic strength effects are shown to cause significant deviations from the widely used Henderson–Hasselbalch equation.     

On-line monitoring of microg/L levels of haloacetic acids using ion chromatography with post-column nicotinamide reaction and fluorescence detection

A method for measuring the concentrations of the five regulated haloacetic acids (HAA5) in drinking water is reported. This method uses ion chromatography to separate HAA5 species, followed by post-column reaction with nicotinamide and detection of the fluorescent products. The result of method detection limit, accuracy, precision, linearity and interference studies are reported. The on-line monitoring method is compared directly to USEPA 552.3 in Memphis drinking water. Though not meant to replace the USEPA 552.3 for compliance monitoring, the proposed method does offer attractive alternatives considering the ease of automation and application of on-line monitoring directly from drinking water distribution systems.     

A Chemiluminescent Probe for HNO Quantification and Real‐Time Monitoring in Living Cells

Azanone (HNO) is a reactive nitrogen species with pronounced biological activity and high therapeutic potential for cardiovascular dysfunction. A critical barrier to understanding the biology of HNO and furthering clinical development is the quantification and real‐time monitoring of its delivery in living systems. Herein, we describe the design and synthesis of the first chemiluminescent probe for HNO, HNOCL‐1 , which can detect HNO generated from concentrations of Angeli's salt as low as 138 nm with high selectivity based on the reaction with a phosphine group to form a self‐cleavable azaylide intermediate. We have capitalized on this high sensitivity to develop a generalizable kinetics‐based approach, which provides real‐time quantitative measurements of HNO concentration at the picomolar level. HNOCL‐1 can monitor dynamics of HNO delivery in living cells and tissues, demonstrating the versatility of this method for tracking HNO in living systems.     

Speciation of halogenides and oxyhalogens by ion chromatography-inductively coupled plasma mass spectrometry

A speciation method utilizing ion chromatography coupled with inductively coupled plasma mass spectrometry is described for simultaneous analysis of eight halogenides and oxyhalogens: chloride, chlorite, chlorate, perchlorate, bromide, bromate, iodide and iodate. The method was applied for the analysis of drinking water samples collected from water treatment plants in areas in Finland, which are known to have high bromine concentrations in ground water. Water samples collected before and after disinfection were analyzed to get information about potential species conversion as a result of purification. Chloride and chlorate were the chlorine species found in these water samples, and iodine existed as both iodate and iodide. In the case of bromine, species conversion had taken place, since total bromine concentrations were increased during disinfection but bromide concentrations were decreased. No bromate was observed in the samples. The detection limits for all the chlorine species studied were 500 μg/l, for bromine species studied 10 μg/l, for iodide 0.1 μg/l and for iodate 0.2 μg/l.     

Experimental study of embedding of attractors in concentration space

The embedding of attractors and their stable and unstable manifolds can be studied experimentally by controlled addition of chemical species to bring about a particular response. For stable small amplitude oscillations near a Hopf bifurcation from a steady state the embedding can be completely determined even in systems where two of the species are not observable. A quenching of the oscillations by dilution candetermine the steady state concentrations. A species that cannot quench the oscillations almost certainly cannot be an essential component of the oscillation. The method can be extended to a study of attractor associated with subharmonic and quasiperiodic bifurcations and of attractors corresponding to nonperiodic motion. We present preliminary results for a subharmonic bifurcation.     

Chemical shift imaging of molecular transport in colloidal systems: visualization and quantification of diffusion processes

Magnetic resonance imaging with chemical shift resolution is demonstrated to provide detailed information about molecular transport on the macroscopic scale in complex colloidal systems. The concentrations of species with distinct 1H resonance lines can be quantified from spatially resolved, high-resolution, 1H nuclear magnetic resonance spectra. The method is demonstrated by experiments on three systems with multiple simultaneous transport processes where the diffusion coefficients depend on position and/or on the concentration of other species: (1) release of poly(ethylene glycol) and imidazole from a hydrogel into an external reservoir of water, (2) migration of acetic acid and tetramethylammonium ions in a highly concentrated water-in-oil emulsion with initially non-uniform concentration of solutes, and (3) release of tetramethylammonium ions loaded into a hydrogel triggered by the diffusion of methyl green into the gel matrix.     

A two-dimensional (magnetic field and concentration) electron paramagnetic resonance method for analysis of multispecies complex equilibrium systems. information content of EPR spectra

A two-dimensional simulation method has been developed for the interpretation of electron paramagnetic resonance (EPR) spectra consisting of a multitude of strongly overlapping signal components. The set of EPR spectra for complex equilibrium systems is analyzed simultaneously as a function of metal and ligand concentrations and pH. The formation constants of the various species are adjusted together with the magnetic parameters of the component EPR spectra. At most 10 EPR-active and 5 EPR-silent species can be involved to simulate a maximum of 36 experimental spectra, while the number of adjusted parameters is at most 100. Statistical parameters are suggested to give the confidence intervals for parameter estimation and to distinguish alternative speciation models. The efficiency of the program is demonstrated for the copper(II)--L-asparagine system, in which 10 species, including 3 pairs of isomers, are characterized with magnetic parameters and formation constants. On the basis of the magnetic parameters, a structural assignment is made for the detected species. The two-dimensional approach can also supply the formation constant of the EPR-silent species, as demonstrated for the copper(II)--glycyl-L-serine system.     

Untersuchungen zur adsorptiven Anreicherung von Elementspuren an Adsorberharzen

Summary The adsorption behaviour of trace amounts of As(III), As(V), Fe(II), Hg(II), Pd(II), Pt(IV), Sb(V), Sn(II), Sn(IV) and Tl(III) from hydrochloric and hydrobromic acid solutions on Amberlite XAD-4 and XAD-7 resins by use of a chromatographic method was investigated. As expected, in certain acid concentrations, all of the elements are adsorbed partly or quantitatively. Furthermore, the adsorbability of 23 elements from sulphuric or hydrochloric acid solutions containing iodide or thiocyanate was examined. In accordance with analogous results for chloro- and bromocompounds it was found that the distribution behaviour of iodo- and thiocyanato-compounds is similar to that of corresponding solvent extraction systems. The adsorbed species of the trace compounds were estimated by comparison of the dependence of sorption rate on ligand concentration with the species distribution in the solution. The similarity of adsorbable and extractable species was discussed.

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Teil II: Fresenius Z Anal Chem (1988) 331:588