Saprygina Natalya N, Morozova Olga B, Abramova Tatyana V, Grampp Günter, Yurkovskaya Alexandra V
International Tomography Center, Institutskaya 3a, 630090 Novosibirsk, Russia.
J Phys Chem A. 2014 Jul 10;118(27):4966-74. doi: 10.1021/jp5044464. Epub 2014 Jun 25.
The photo-oxidation of purine nucleotides adenosine-5'-monophosphate (AMP) and guanosine-5'-monophosphate (GMP) by 3,3',4,4'-benzophenone tetracarboxylic acid (TCBP) has been investigated in aqueous solutions using nanosecond laser flash photolysis (LFP) and time-resolved chemically induced dynamic nuclear polarization (CIDNP). The pH dependences of quenching rate constants and of geminate polarization are measured within a wide range of pH values. As a result, the chemical reactivity of reacting species in different protonation states is determined. In acidic solution (pH < 4.9), the quenching rate constant is close to the diffusion-controlled limit: kq = 1.3 × 10(9) M(-1) s(-1) (GMP), and kq = 1.2 × 10(9) M(-1) s(-1) (AMP), whereas in neutral and basic solutions it is significantly lower: kq = 2.6 × 10(8) M(-1) s(-1) (GMP, 4.9 < pH < 9.4), kq = 3.5 × 10(7) M(-1) s(-1) (GMP, pH > 9.4), kq = 1.0 × 10(8) M(-1) s(-1) (AMP, pH > 6.5). Surprisingly, the strong influence of the protonation state of the phosphoric group on the oxidation of adenosine-5'-monophosphate is revealed: the deprotonation of the AMP phosphoric group (6.5) decreases the quenching rate constant from 5.0 × 10(8) M(-1) s(-1) (4.9 < pH < 6.5) to 1.0 × 10(8) M(-1) s(-1) (pH > 6.5).
利用纳秒激光闪光光解（LFP）和时间分辨化学诱导动态核极化（CIDNP）技术，研究了3,3',4,4'-二苯甲酮四羧酸（TCBP）在水溶液中对嘌呤核苷酸5'-单磷酸腺苷（AMP）和5'-单磷酸鸟苷（GMP）的光氧化作用。在较宽的pH值范围内测量了猝灭速率常数和双生极化的pH依赖性。结果，确定了不同质子化状态下反应物种的化学反应性。在酸性溶液（pH < 4.9）中，猝灭速率常数接近扩散控制极限：kq = 1.3×10⁹ M⁻¹ s⁻¹（GMP），kq = 1.2×10⁹ M⁻¹ s⁻¹（AMP），而在中性和碱性溶液中则显著较低：kq = 2.6×10⁸ M⁻¹ s⁻¹（GMP，4.9 < pH < 9.4），kq = 3.5×10⁷ M⁻¹ s⁻¹（GMP，pH > 9.4），kq = 1.0×10⁸ M⁻¹ s⁻¹（AMP，pH > 6.5）。令人惊讶的是，揭示了磷酸基团的质子化状态对5'-单磷酸腺苷氧化的强烈影响：AMP磷酸基团（6.5）的去质子化使猝灭速率常数从5.0×10⁸ M⁻¹ s⁻¹（4.9 < pH < 6.5）降至1.0×10⁸ M⁻¹ s⁻¹（pH > 6.5）。
