Poster
# 55
Poster |
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6th Internet World Congress for Biomedical Sciences |
Bartolomé Quintero(1), María del Carmen Cabeza(2)
(1)(2)Dpt. Physical Chemistry. Faculty of Pharmacy. University of Granada - Granada. Spain
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[Biophysics] |
[Cell Biology & Cytology] |
The absorption spectra registered with aliquots taken from samples of acid aqueous solutions of 10 mM PDQ (37 ºC, acetate buffer pH5) kept in darkness in the presence of oxygen, did not show significant changes. On the contrary, the spectra from neutral aqueous solution of PDQ (37 ºC, phosphate buffer pH7) showed a noticeable decrease in the absorption band located at 348 nm 24 h after preparing the solution.
Degradation of aerated PDQ solutions (aerobic conditions) involves the appearance of of hydroquinone and quinone. So, the fluorescent emission from hydroquinone (lexc = 280 nm; lem = 327 nm) is observed with 10 mM PDQ solutions (37 ºC, phosphate buffer pH7) kept for 24 h in darkness. Moreover, HPLC analysis of PDQ in an aqueous solution (phosphate buffer, pH7), kept for 24 hours in darkness at 25ºC under aerobic conditions, reveals the appearance of signals belonging to hydroquinone (10.8 min) and quinone (30.1 min). The chromatogram of the sample kept under similar conditions but previously purged with argon (anaerobic conditions) shows no signal for either hydroquinone or quinone.
The ESR spectra registered using 80 mM PDQ solutions in phosphate buffer pH7 in the presence of the spin-trap DMPO (110 mM) either in aerobic or in anaerobic conditions, gave only one stable adduct which can be put down to a p-hydroxyphenyl radical (aH = 24.5 G; aN = 15.9 G). This result can be also obtained using as spin trap PBN (aH = 4.1 G; aN = 15.9 G) o 4-POBN (aH = 3.2 G; aN = 15.6 G) [conc = 50 mM] even in the presence of hydroxyl radical scavengers such as DMSO (1.4 M) or ethanol (2.0 M).
DTPA does not change the features of the PDQ absorption spectrum (Fig. 1) but decreases the intensity of the signals registered in RSE as well as the PDQ degradation rate. Figure 2 shows the variation as a function of the time of the absorbance measured at 348 nm with aerated 0.01 mM PDQ solutions (37º C, phosphate buffer pH7) kept in darkness. As it can be observed by adding DTPA (1.5 mM) practically the reaction is stopped in the time interval studied. In addition, the degradation rate does not change as the Fe2+ is present in concentration 1 mM or 10 mM
The oxygen consumption measured in the first step of the dediazoniation process (up to 180 min) indicates (Fig. 3) that the consumption decreases in the presence of DTPA (0.5 mM)
The absorption spectrum of 0.44 mM hydroquinone (H2Q) solution in phosphate buffer pH7 changes 24 h after preparing the solution. The band located at 288 nm decreases and a new band appears centered at 245 nm. In the presence of DTPA (2.8 mM) there is no lowering in the band at 288 nm and the band at 245 nm is significantly less intense (Fig.4)
In basic medium (borate buffer pH9) the hydroquinone degradation rate increases. The spectra shown in Figure 5 were obtained just after preparing the solution. It can be seen that the spectrum registered with the 0.35 mM H2Q presents an absorbance at 288 nm lower than that measured with a solution containing the same concentration of H2Q added with DTPA (2.8 mM). Likewise, it can be checked that the absorption about 311 nm is higher in the case of the solution containing only H2Q
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[Biophysics] |
[Cell Biology & Cytology] |
