Photodegradation of antibiotic 5-sulfaminouracil in the presence of vitamin B2: A kinetic study

Figures & data

Figure 1. SFU structure.

Figure 2. Spectral changes of SFU (0.3 mM) vs. Rf (0.02 mM) in MeOH–H₂O 1:1 (v/v) solutions upon irradiation under aerobic conditions. (A) Absorption spectra of Rf and SFU vs. MeOH:H₂O. (B) Spectral changes of SFU (0.3 mM) + Rf (0.02 mM) in MeOH–H₂O (1:1, v/v) solutions upon irradiation under aerobic conditions. Numbers above the spectrum indicate irradiation time in minutes.

Figure 3. Consumed oxygen vs. irradiation time in MeOH–H₂O (1:1, v/v) solution. Solutions were irradiated with visible light (>400 nm) under air-saturated conditions in the presence of 0.04 mM Rf: (a) with SFU 0.4 mM and (b) with SFU 0.4 mM plus 14 µg/ml SOD.

Table 1. Rate constants for the quenching of ¹Rf*, k_Q(1) (M⁻¹ s⁻¹) and ³Rf*, k_Q(3) (M⁻¹ s⁻¹) by SFU in MeOH–H₂O 1:1 (v/v) and relative rates of oxygen consumption by SFU upon Rf sensitization of solutions in the absence [V_ox(Rf)] and in the presence of SOD 14 µg/ml [V_ox(Rf + SOD)]

Medium	kQ(1) × 10^9	kQ(3) × 10^9	Vox(Rf)	Vox(Rf + SOD)
MeOH–H2O 1:1	7.40 ± 0.10	2.06 ± 0.11	1	0.51

Figure 4. Evolution of the 445 nm band of Rf in MeOH–H₂O (1:1, v/v) (deareated) upon irradiation with visible light. (a) Rf (0.02 mM) not irradiated, (b) Rf (0.2 mM) + SFU (0.05 mM) irradiated for 6 minutes, (c) Rf (0.02 mM) irradiated for 6 minutes. Inset: Sterrn–Volmer plot for the quenching of Rf triplet state by SFU in argon-saturated solutions of MeOH–H₂O 1:1 (v/v).

Figure 5. Stern–Volmer plot for the static fluorescence quenching of Rf (0.01 mM) by SFU in MeOH:H₂O (1:1, v/v) solution.

Scheme 1. (A) Ionization equilibrium in SFU; (B) ionization equilibrium in uracil.

Figure 6. Time evolution of the absorption spectrum of SFU 0.5 mM upon PN-sensitized irradiation vs. PN in H₂O (pH 12).

Figure 7. (A) Stern–Volmer plots for the quenching of O₂(¹Δ_g) phosphorescence by SFU in D₂O at (a) pD 7 and (b) pD 12. PN (Abs₃₅₅ = 0.40) as a sensitizer. (B) First-order plot for the concentration changes of SFU 0.4 mM or Trp 0.4 mM, under irradiation with visible light (cutoff > 400 nm) in the presence of PN (Abs₃₅₅ = 0.5).

Table 2. Rate constants for the reactive (k_r, M⁻¹ s⁻¹) and overall quenching (k_t, M⁻¹ s⁻¹) of O₂(¹Δ_g) by SFU, ratio k_r/k_t and relative rates of oxygen consumption (V_ox) upon PN-sensitized irradiation of SFU

Medium	kt × 10^8	kr × 10^8	kr/kt	VoxPN
H2O pH/pD 7	0.79 ± 0.01 (0.005)	0.60 ± 0.01 (NR*)	0.75	0.77
H2O pH/pD 12	3.09 ± 0.05 (0.14**)	2.97 ± 0.01 (0.15**)	∼1	1
			∼1

Parentheses indicate bibliographic data for uracil, included for comparative purposes.

*No reaction was observed.

**Determined at pH/pD 11.

Portalone G, Bencivenni L, Colapietro M, Pieretti A, Ramondo F. The effect of hydrogen bonding on the structures of uracil and some methyl derivatives studied by experiment and theory. Acta Chem Scand 1999;53:57–68.

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