Spectral-kinetic method

The spectral-kinetic method has been proposed for studying ligand exchange rates [130], Consider the case of Eu(III) and the spectroscopic excited state is 5Do and this state is selectively excited by a pulsed dye laser. Let us consider the equilibrium... 

Ermolaev VL, Gruzdev VP (1984) Novel spectral-kinetic method for investigation of ligand exchange in labile metal complexes in solutions. Inorg Chim Acta 95 179-185... 

A major treatise devoted to experimental methods of chemistry is Techniques of Chemistry , edited first by Weissberger, and then by Saunders, Wiley, New York. This publication, which began in 1970, so far consists of 21 volumes, most of them in several parts, covering such topics as electrochemical and spectral methods, kinetic methods, photochronusm, and organic solvents. Techniques of Chemistry is a successor to an earlier series, called Techniques of Organic Chemistry , which appeared in 14 volumes, some of them in more than one edition, from 1945 to 1969. 

The PDM-ECD kinetic method demonstrated above is expected to be applicable to any IM reaction where (1) the reactant ion can be generated by a thermal electron capture reaction, (2) the neutral reactant does not react significantly with thermal electrons, and (3) either the reactant or the product negative ion possess a uniquely high PD cross section in some region of the UVA is/near-IR spectral range between 250 and 1200 nm. ... 

A kinetic method for pK determination in aqueous DMSO has recently been developed (Earls et al., 1974 Cockerill et al., 1974). This is based on rates of isotopic exchange and is applicable to the p a range ca. 15-25. The method has the advantage that it does not depend on spectral changes occurring on ionization. However, the majority of p/sfa values of weak acids have been obtained by the equilibrium technique, using acidity functions (AF) (Hammett, 1940 Bowden, 1966 Rochester, 1970). 

Two different types of pulsed EPR experiments are possible a spectrum can be measured at a fixed time after the pulse by variation of the field strength B (Eq. 72), or the time profile of a particular spectral line can be measured at constant B to give kinetic information. One vziriation of this kinetic method is to detect the recombination of singlet-state radical ion pairs in liquid hydrocarbons by the fluorescence of the product excited state [142]. This technique is known as fluorescence-detected magnetic resonance (FDMR) and provides information on the spin dynamics of the radical ion pair as well as the chemical kinetics. 

These processes that bring about averaging of spectral features occur reversibly, whether by acid-catalyzed intermolecular exchange or by unimolecular reorganization. NMR is one of the few methods for examining the effects of reaction rates when a system is at equilibrium. Most other kinetic methods require that one substance be transformed irreversibly into another. The dynamic effects of the averaging of chemical shifts or coupling constants provide a nearly unique window into processes that occur on the order of a few times per second. (The subject is examined further in Section 5-2.)... 

Most uses of flow techniques involve the quantitative determination of some target species. This chapter describes various ways of using flow techniques with quantitative purposes, such as calibration curves, based on peak height or peak area, and titrations, based on distance between equivalence points or single-point method. Stopped-flow technique can be used for both, quantitative approach, for example in kinetic methods, or for qualitative determinations inasmuch as it allows spectral and potential scans to be performed. Multiparameter analysis is presented in two forms to be carried out, by multivariate chemometric techniques or by applying sandwich technique. Finally, smart systems are presented as a step forward in automation, commonly used in multiparameter analysis. 

Molten salt investigation methods can be divided into two classes thermodynamic and kinetic. In some cases, the analysis of melting diagrams and isotherms of physical-chemical properties such as density, surface tension, viscosity and electroconductivity enables the determination of the ionic composition of the melt. Direct investigation of the complex structure is performed using spectral methods [294]. 

The structure of HRP-I has been identified as an Fe(IV) porphyrin -ir-cation radical by a variety of spectroscopic methods (71-74). The oxidized forms of HRP present differences in their visible absorption spectra (75-77). These distinct spectral characteristics of HRP have made this a very useful redox protein for studying one-electron transfers in alkaloid reactions. An example is illustrated in Fig. 2 where the one-electron oxidation of vindoline is followed by observing the oxidation of native HRP (curve A) with equimolar H202 to HRP-compound I (curve B). Addition of vindoline to the reaction mixture yields the absorption spectrum of HRP-compound II (curve C) (78). This methodology can yield useful information on the stoichiometry and kinetics of electron transfer from an alkaloid substrate to HRP. Several excellent reviews on the properties, mechanism, and oxidation states of peroxidases have been published (79-81). 

Electronic polarization of the environment. This effect is related to the square of the refractive index, n1 2 (dielectric constant at the frequency of light). Here the spectral shift occurs instantly (10 15 s), and its evolution with time is not observed by the kinetic spectroscopic methods. The protein molecule is a medium with a relatively high electronic polarization (n= 1.5 -s-1.6). 

Nearly all the spectral region has been used in one kinetic study or another to follow the progress of a chemical reaction. In toto it represents by far the most powerful and utilized method of monitoring. 

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