Chemiluminescence of cereal products. II. Chemiluminescence spectra

Abstract

Spectra of ultraweak chemiluminescence (CL) accompanying auto-oxidation and hydration of cereal products have been measured using single photon counting and cut-off filters. The spectra cover the 380-880 nm spectral range with maxima centred around 600 nm. Analytically pure air-dried carbohydrates like agar, cellulose and nitrocellulose give emission too weak for spectral measurements. The emission from water pure carbohydrates is on average 4-12 times higher and emission spectra are similar to those from cereal products. The effect of free radical scavengers, SOD and O2* (1 delta g)-quenchers on CL spectra indicates a contribution of radical reactions with the participation of excited carbonyls, O2- and excited molecular oxygen dimoles. Moreover, possible mechanisms of chemi-excitation due to a cooperative H-bond formation during the hydration of carbohydrates and/or recombination of trapped radicals and electron-holes are discussed. It is also postulated that the excitation energy transfer to natural sensitizers occurring in cereal products may account for non-specific broad spectra and differences in the intensity of CL.

Chemiluminescence Energy Transfer Reaction for the On-Line Preparation of Peroxymonocarbonate and Eu(II)−Dipicolinate Complex

“…Such equilibrium had previously been observed by Richardson's group, 7 and HCO 4 -without metal ion was found to be a moderately reactive heterolytic oxidant that can be classified as an anionic peracid. 8 The effective equilibrium constant K 1 ) 27 ( 1 at 25°C was observed, and the observed equilibration rate constant was (2.4 ( 0.1) × 10 -3 s -1 .…”

“…Much research [1][2][3][4][5] has indicated that carbonate or bicarbonate acted not only as a buffer reagent but also as the CL enhancer. It has been confirmed that CO 3 2-was a luminous species when it coexisted with a strong oxidant in basic solution.…”

“…Recently, an interesting research work, the formation of a bicarbonate active species, peroxymonocarbonate (HCO 4 -), was reported. 6 It was discovered that the equilibrium of hydrogen peroxide and bicarbonate to form HCO 4 -occurred rapidly at 25°C near neutral pH in aqueous solution or ethanol/water mixtures (eq 1).…”

Carbonate-catalyzed chemiluminescence decomposition of peroxynitrite via (CO2)2∗ intermediate

“…Therefore, the effect of carbonate on the CL signal was obvious. It was well known that a number of CL analyses were carried out in the presence of carbonate solution [17,18], not only based on its buffer function but also its CL enhancement effect. To clarify the CL mechanism of the present system, the following experiments were carried out.…”

“…The results showed that DABCO and NaN 3 did not quench the CL intensity, which provided strong evidence that 1 O 2 did not contribute to the observed CL. A number of investigations [17,18] have demonstrated that carbonate was a luminous species when present with a strong oxidant in basic solution. In our previous work [23], the CL emission band at 436-446 nm was also recorded (as shown in Fig.…”