Chemiluminescence activation parameters

The rates of thermolysis (37) of the peroxyesters in argon-purged benzene can be followed conveniently by the direct, indirect, or activated chemiluminescence. In all of the cases reported peroxyesters in benzene solution show clean first-order reaction for low initial peroxide concentrations (10-5-10-3 M). The activation parameters for the peroxyester thermolyses reveal some important details of the reaction mechanism. The activation enthalpy obtained for peroxyester [28] is quite similar to that reported by Hiatt... 

Besides the isothermal kinetic methods mentioned above, by which activation parameters are determined by measuring the rate of dioxetane disappearance at several constant temperatures, a number of nonisothermal techniques have been developed. These include the temperature jump method, in which the kinetic run is initiated at a particular constant initial temperature (r,-), the temperature is suddenly raised or dropped by about 15°C, and is then held constant at the final temperature (7y), under conditions at which dioxetane consumption is negligible. Of course, for such nonisothermal kinetics only the chemiluminescence techniques are sufficiently sensitive to determine the rates. Since the intensities /, at 7 ,- and If at Tf correspond to the instantaneous rates at constant dioxetane concentration, the rate constants A ,- and kf are known directly. From the temperature dependence (Eq. 32), the activation energies are readily calculated. This convenient method has been modified to allow a step-function analysis at various temperatures and a continuous temperature variation.Finally, differential thermal analysis has been employed to assess the activation parameters in contrast to the above nonisothermal kinetic methods, in the latter the dioxetane is completely consumed and, thus, instead of initial rates, one measures total rates. 

The electrogenerated chemiluminescence (ECl) of five l-amino-3-anthryl-9-propane derivatives has been studied in tetrahydrofuran. Emission from intramolecular exciplexes in ECl spectra and weak emission from the locally excited anthracene moiety were observed. The influence of triplet state interaction in ECl emission is discussed. The chemiluminescent decomposition of three a-peroxy-lactones gives CO2 and the corresponding ketone in high yield. The chemiluminescent species produced has been investigated in some detail by measurements of lifetime, energy-transfer activation parameters, and photochemical reactions. 

A kinetics study has been performed on the aqueous iodine oxidation of the thiolactam (78). The rate of oxidation of (78) was found to be approximately 100 times that of a simple cyclic thioether, and this enhancement was ascribed to transannular anchimeric assistance provided by the nitrogen of the amide group <87JOC258i>. The thermal decomposition of the fused dioxetane (79) has been monitored by chemiluminescence decay, and this has been shown to follow first-order kinetics. The activation parameters have been calculated <83CL431>. Second-order rate constants for the quatemization of octahydro-lfl-azonine (9) and other azacycloalkanes with iodomethane in acetonitrile and methanol have been measured <68CCC1429>. The kinetics of the hydrogen-deuterium... 

An indirect method has been used to determine relative rate constants for the excitation step in peroxyoxalate CL from the imidazole (IM-H)-catalyzed reaction of bis(2,4,6-trichlorophenyl) oxalate (TCPO) with hydrogen peroxide in the presence of various ACTs18. In this case, the HEI is formed in slow reaction steps and its interaction with the ACT is not observed kinetically. However, application of the steady-state approximation to the reduced kinetic scheme for this transformation (Scheme 6) leads to a linear relationship of 1/S vs. 1/[ACT] (equation 5) and to the ratio of the chemiluminescence parameters /ic vrAi), which is a direct measure of the rate constant of the excitation step. Therefore, this method allows for the determination of relative rate constants for the excitation step in a complex reaction system, where this step cannot be observed directly by kinetic measurements18. The singlet quantum yield at infinite activator concentrations ( °), where all high-energy intermediates formed interact with the activator, is also obtained from this relationship (equation 5). 

Enzyme activities may also be measured in urine, cerebrospinal fluid, bone marrow cells or fluid, amniotic cells or fluid, red blood cells, leukocytes, and tissue cells. Cytochemical localization is possible in leukocytes and biopsy specimens (e.g., from liver and muscle). Under ideal conditions, both the concentration of the enzyme and its activity would be measured. Radioimmunoassay (RIA) and its alternative modes such as fluorescence immunoassay (FIA), fluorescence polarization immunoassay (FPIA), and chemiluminescence immunoassay (CLIA) (discussed later), can be used to measure enzyme concentration as well as other clinically important parameters. 

In vitro antioxidant activity was also evaluated in Piper regnellii, another plant from the Piperaceae family commonly used as it were P. umbellata. The activity of the extracts was evaluated in spontaneous lipid peroxidation of brain homogenates, and both TBARS and chemiluminescence were employed as parameters for lipid peroxidation evaluation. Although P. regnellii showed some antioxidant capacity, this was below that of P. umbellata, probably due to the absence of 4-nerolidylcatechol in the former. 

The process of lymphocyte activation can be investigated by determining whether or not a particular parameter of activation is prevented by inhibitors of ADPRT. Events that are not inhibited either occur before ADPRT is required or are independent of it. Such changes are the binding of mitogen to the cell surface, the early increase in phosphatidylinositol turnover in the plasma membrane [4], and the early increase in membrane chemiluminescence. Events that are inhibited presumably occur after ADPRT is required. These include the rejoining of DNA breaks (see below), subsequent protein and DNA synthesis [3, 4] and the increased expression of the c-myc gene [11] (Fig. 2). The later response of activated blasts to IL-2 does not appear to involve ADPRT [17]. 

Using chemiluminescence resulting from the reaction of NO and O3, Maurer and Fung (2000) characterised enzyme activity for purified murine macrophage NOS n. They also estimated the inhibitory parameters for a series of competitive antagonists and mechanism-based inactivators of NOS n. The estimated parameters were in agreement with those reported using other methods. 

Because the chemiluminescence method is a tool frequently used to qualify the stabilizing effect in polypropylene of various hindered amine, the analysis of CL kinetic parameters (oxidation induction time, oxidation rate, activation energy of oxidation, CL intensity) could provide reliable information related to the photodegradation state of polypropylene modified with different HALS compounds [76-78]. 

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