Chemiluminescence reaction rates

Mashiko, S., et al. (1991). Chemiluminescence reaction rates of Cypridina luciferin analog with superoxide. In Stanley, P. E., and Kricka, L. J. (eds.), Biolumin. Chemilumin. Proc. Int. Symp., 6th, 1990, pp. 475-478. Wiley, Chichester, UK. 

The first detailed investigation of the reaction kinetics was reported in 1984 (68). The reaction of bis(pentachlorophenyl) oxalate [1173-75-7] (PCPO) and hydrogen peroxide cataly2ed by sodium saUcylate in chlorobenzene produced chemiluminescence from diphenylamine (DPA) as a simple time—intensity profile from which a chemiluminescence decay rate constant could be determined. These studies demonstrated a first-order dependence for both PCPO and hydrogen peroxide and a zero-order dependence on the fluorescer in accord with an earher study (9). Furthermore, the chemiluminescence quantum efficiencies Qc) are dependent on the ease of oxidation of the fluorescer, an unstable, short-hved intermediate (r = 0.5 /is) serves as the chemical activator, and such a short-hved species "is not consistent with attempts to identify a relatively stable dioxetane as the intermediate" (68). 

Most peroxyoxalate chemiluminescent reactions are catalyzed by bases and the reaction rate, chemiluminescent intensity, and chemiluminescent lifetime can be varied by selection of the base and its concentration. Weak bases such as sodium saUcylate or imidazole are generally preferred (94). 

The rate of protonation may vary according to the structure of the light-emitter and the environment around the light emitter. In the case of chemiluminescence reactions in solutions, the hydrophobicity, permittivity (dielectric constant) and protogenic nature of the solvent are important environmental factors. In the case of bioluminescence involving a luciferase or photoprotein, the protein environment surrounding the light-emitter will be a crucial factor. 

Suzuki, N., etal. (1991). Reaction rates for the chemiluminescence of Cypridina luciferin analogs with superoxide a quenching experiment with superoxide dismutase. Agric. Biol. Chem. 55 157-160. 

Figure 13, indicates that the first mole of phenol is released in <30 s, the same elapsed time for the chemiluminescence to reach a maximum intensity. In fact, the measured rate constant r, for the rise in the chemiluminescence emission, is identical to the rate of the first phenol s release from the oxalate ester. Furthermore, the slower rate of release of the second phenol ligand has a rate constant that is identical to the chemiluminescence decay rate f. Thus, the model allows a quantitative analysis of the reaction mechanism, heretofore not available to us. We intend to continue this avenue of investigation in order to optimize the chemiluminescence efficiencies under HPLC conditions and to delineate further the mechanism for peroxy-oxalate chemiluminescence. 

Another approach to the determination of surface kinetics in these systems has been to combine molecular beams in the 10 2-10 1 mbar pressure range with the use of the infrared chemiluminescence of the C02 formed during steady-state NO + CO reactions. This methodology has been used to follow the kinetics of the reaction over Pd(110) and Pd(l 11) surfaces [49], The activity of the NO + CO reaction on Pd(l 10) was determined to be much higher than on Pd(lll), as expected based on the UHV work discussed in previous sections but in contrast with result from experiments under higher pressures. On the basis of the experimental data on the dependence of the reaction rate on CO and NO pressures, the coverages of NO, CO, N, and O were calculated under various flux conditions. Note that this approach relied on the detection of the evolution of gas-phase... 

Chemiluminescent reactions must proceed at a sufficiently fast rate to provide the minimum number of quanta per time unit, as determined by the sensitivity of the detector used. According to Hercules 4> a chemiluminescence reaction with 100% efficiency emitting only one photon per fortnight would not be detected . 

Chemiluminescent techniques have been used to determine nanomolar quantities of nitrate and nitrite in seawater [124,125]. This method depends on the selective reduction of these species to nitric oxide, which is then determined by its chemiluminescent reaction with ozone, using a commercial nitrogen oxides analyser. The necessary equipment is compact and sufficiently sturdy to allow shipboard use. A precision of 2nmol/l is claimed, and an analytical range of 2nmol/l with analysis rates of 10-12 samples hourly. 

CL emissions can be characterized by four parameters, including color, intensity, rate of production, and decay of intensity. The properties of several organic, chemiluminescent reactions known to produce emissions of light are shown in Table 1. 

Optimization strategies and a number of generalized limitations to the design of gas-phase chemiluminescence detectors have been described based on exact solutions of the governing equations for both exponential dilution and plug-flow models of the reaction chamber by Mehrabzadeh et al. [12, 13]. However, application of this approach requires a knowledge of the reaction mechanism and rate coefficients for the rate-determining steps of the chemiluminescent reaction considered. 

Chemiluminescence is believed to arise from the 2Bj and the 2B2 electronic states, as discussed above for the reaction of NO with ozone [17]. The primary emission is in a continuum in the range =400-1400 nm, with a maximum at =615 nm at 1 torr. This emission is significantly blue-shifted with respect to chemiluminescence in the NO + 03 reaction (Xmax = 1200 nm), as shown in Figure 2, owing to the greater exothermicity available to excite the N02 product [52], At pressures above approximately 1 torr of 02, the chemiluminescence reaction becomes independent of pressure with a second-order rate coefficient of 6.4 X 10 17 cm3 molec-1 s-1. At lower pressures, however, this rate constant decreases and then levels off at a minimum of 4.2 X 1(T18 cm3 molec-1 s-1 near 1 mtorr, and the emission maximum blue shifts to =560 nm [52], These results are consistent with the above mechanism in which the fractional contribution of (N02 ) to the emission spectrum increases as the pressure is decreased, therefore decreasing the rate at which (N02 ) is deactivated to form N02. Additionally, the radiative lifetime and emission spectrum of excited-state N02 vary with pressure, as discussed above for the NO + 03 reaction [19-22],... 

Rauhut and coworkers were the first to obtain rate constants from emission kinetic studies and to verify the dependence of kobsi and kobsi on the concentration of the base catalyst and on hydrogen peroxide, respectively. Schowen and coworkers , using TCPO, H2O2 and DPA, with triethylamine as catalyst, observed an oscillatory behavior in emission experiments and proposed a mechanism involving the formation of two HEIs (involved in parallel chemiluminescent reactions) to explain it. Other authors have also observed a similar oscillating behavior but have explained it as a complex... 

On the basis of the results discussed above, it is possible to propose a detailed mechanistic scheme for the occurrence of the chemiluminescent reaction of oxalic esters and hydrogen peroxide in the presence of imidazole as base and an ACT (Scheme 40). The oxalic ester (exemplified with TCPO) reacts in the rate-determining step with imidazole, catalyzed by... 

The peroxyoxalate system is the only intermolecular chemiluminescent reaction presumably involving the (71EEL sequence (Scheme 44), which shows high singlet excitation yields (4>s), as confirmed independently by several authors Moreover, Stevani and coworkers reported a correlation between the singlet quantum yields, extrapolated to infinite activator concentrations (4> ), and the free energy involved in back electron-transfer (AG bet), as well as between the catalytic electron-transfer/deactivation rate constants ratio, ln( cAx( i3), and E j2° (see Section V). A linear correlation of ln( cAx( i3) and E /2° was obtained for the peroxyoxalate reaction with TCPO and H2O2 catalyzed by imidazole and for the imidazole-catalyzed reaction of 57, both in the presence of five activators commonly used in CIEEL studies (anthracene, DPA, PPO, perylene and rubrene). A further confirmation of the validity of the CIEEL mechanism in the excitation step of... 

A relatively new analytical technique, chemiluminescence (CL), is an ultrasensitive technique, and it has been reported that reaction rates as low as 10 mole/year can be measured (1-5). Thus, it could monitor the aging reactions on a real-time basis while the resins are exposed to a simulated service environment. If the method can be shown to be sufficiently sensitive and reliable, the errors inherent in extrapolating accelerated aging data to the actual conditions encountered can be eliminated (6-8). 

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