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Abstract：
Low-concentration photochemically induced dynamic nuclear polarization (LC-photo-CIDNP) has recently emerged as an effective tool for the hyperpolarization of aromatic amino acids in solution, either in isolation or within proteins. One factor limiting the maximum achievable signal-to-noise ratio in LC-photo-CIDNP is the progressive degradation of the target molecule and photosensitizer upon long-term optical irradiation. Fortunately, this effect does not cause spectral distortions but leads to a progressively smaller signal buildup upon long-term data-collection (e.g. 500 nM tryptophan on a 600 MHz spectrometer after ca. 200 scans). Given that it is generally desirable to minimize the extent of photodamage, we report that low-μM amounts of the reductive radical quenchers vitamin C (VC, i.e., ascorbic acid) or 2-mercaptoethylamine (MEA) enable LC-photo-CIDNP data to be acquired for significantly longer time than ever possible before. This approach increases the sensitivity of LC-photo-CIDNP by more than 100%, with larger enhancement factors achieved in experiments involving more transients. Our results are consistent with VC and MEA acting primarily by reducing transient free radicals of the NMR molecule of interest, thus attenuating the extent of photodamage. The benefits of this reductive radical-quencher approach are highlighted by the ability to collect long-term high-resolution 2D 1H-13C LC-photo-CIDNP data on a dilute sample of the drkN SH3 protein (5 μM).
摘要：
低浓度光化学诱导的动态核极化（LC-photo-CIDNP）最近已成为溶液中芳香族氨基酸超极化的有效工具，无论是孤立的还是在蛋白质中。限制LC-光-CIDNP中最大可实现的信噪比的一个因素是目标分子和光敏剂在长期光学照射下的逐渐降解。幸运的是,这种效应不会引起光谱失真，但导致在长期数据收集后逐渐变小的信号积累（例如，在600MHz光谱仪上500nM色氨酸后，200次扫描)。鉴于通常希望最小化光损伤的程度，我们报道了低μM量的还原性自由基猝灭剂维生素C(VC，即，抗坏血酸）或2-巯基乙胺（MEA）使LC-photo-CIDNP数据能够比以前更长的时间获得。这种方法将LC-photo-CIDNP的灵敏度提高了100%以上，在涉及更多瞬态的实验中实现了更大的增强因子。我们的结果与VC和MEA的作用一致，主要是通过减少感兴趣的NMR分子的瞬时自由基，从而减弱光损伤的程度。这种还原性自由基猝灭剂方法的好处是能够在drkNSH3蛋白（5μM）的稀释样品上收集长期高分辨率2D1H-13CLC-photo-CIDNP数据。
