Photoresponsive materials feature properties that can be adjusted by light near-instantaneously, reversibly, and with high spatiotemporal precision. There is considerable interest in maximising the degree of photoswitching, and in measuring this degree during illumination in complex environments. We study the switching of photoresponsive lipid membranes that allow for precise and reversible manipulation of membrane shape, permeability, and fluidity. Though these macroscopic responses are clear, it is unclear how large the changes of trans/cis ratio are, and whether they can be improved. Here, we used small-angle X-ray scattering to measure the thickness of photoswitchable lipid membranes, and we correlate lipid bilayer thickness to trans/cis ratios. This reveals an unexpected dependency of photoswitching ratio upon aqueous phase composition. In buffer with ionic strength, we observe thickness variations twice as large as previously observed. Furthermore, soft X-rays can quantitatively isomerise photolipid membranes to the all-trans state; enabling X-ray-based membrane control. High energy X-rays do not influence the state of the photoswitches, presumably because they deposit less dose in the sample.

中文翻译：

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偶氮苯脂质囊泡的 SAXS 测量揭示了 X 射线的缓冲液依赖性光开关和定量 Z→E 异构化

光响应材料的特性可以通过光近乎瞬时、可逆地进行调节，并具有很高的时空精度。人们对最大化光开关的程度以及在复杂环境中的照明期间测量该程度有相当大的兴趣。我们研究了光响应脂质膜的转换，从而可以精确和可逆地操纵膜的形状、渗透性和流动性。虽然这些宏观反应很清楚，但不清楚变化有多大反式/顺式比例，以及是否可以提高。在这里，我们使用小角度 X 射线散射来测量光开关脂质膜的厚度，并将脂质双层厚度与反式/顺式比率。这揭示了光开关比对水相组成的出乎意料的依赖性。在具有离子强度的缓冲液中，我们观察到厚度变化是之前观察到的两倍。此外，软 X 射线可以将光脂膜定量异构化为反式状态; 启用基于 X 射线的膜控制。高能 X 射线不会影响光开关的状态，可能是因为它们在样品中沉积的剂量较少。