Erriah Bryan, Elliott Stuart J
School of Chemistry, University of Southampton Southampton SO17 1BJ UK
RSC Adv. 2019 Jul 29;9(40):23418-23424. doi: 10.1039/c9ra03748a. eCollection 2019 Jul 23.
Nuclear singlet lifetimes are often dependent on the quantity of paramagnetic oxygen species present in solution, although the extent to which quenching or removing molecular oxygen has on extending singlet lifetimes is typically an unknown factor. Here we investigate the behaviour of the singlet relaxation time constant as a function of the oxygen concentration in solution. An experimental demonstration is presented for a chemically inequivalent proton pair of the tripeptide alanine-glycine-glycine in solution. We introduce a simple methodology to ensure the solution is saturated with predetermined concentrations of oxygen gas prior to measurements of the singlet lifetime. Singlet lifetimes were measured by using the spin-lock induced crossing pulse sequence. We present a linear relationship between the amount of oxygen dissolved in solution and the singlet relaxation rate constant. Singlet relaxation was found to be ∼2.7 times less sensitive to relaxation induced by paramagnetic oxygen compared with longitudinal relaxation. The relaxation behaviour is described by using a model of correlated fluctuating fields. We additionally examine the extension of singlet lifetimes by doping solutions with the chelating agent sodium ascorbate, which scavenges oxygen radicals in solution.
核单重态寿命通常取决于溶液中顺磁性氧物种的数量，尽管淬灭或去除分子氧对延长单重态寿命的影响程度通常是一个未知因素。在此，我们研究单重态弛豫时间常数随溶液中氧浓度的变化行为。给出了溶液中三肽丙氨酸 - 甘氨酸 - 甘氨酸化学不等价质子对的实验演示。我们引入一种简单方法，以确保在测量单重态寿命之前，溶液用预定浓度的氧气饱和。通过使用自旋锁定诱导交叉脉冲序列测量单重态寿命。我们给出了溶液中溶解氧的量与单重态弛豫速率常数之间的线性关系。发现与纵向弛豫相比，单重态弛豫对顺磁性氧诱导的弛豫的敏感性约低2.7倍。通过使用相关涨落场模型描述弛豫行为。我们还通过用螯合剂抗坏血酸钠掺杂溶液来研究单重态寿命的延长，抗坏血酸钠可清除溶液中的氧自由基。
