That the rates and yields of reactions of organic radicals can be spin dependent is well known in the context of the radical pair mechanism (RPM). Less well known, but still well established, is the chiral-induced spin selectivity (CISS) effect in which chiral molecules act as spin filters that preferentially transmit electrons with spins polarized parallel or antiparallel to their direction of motion. Starting from the assumption that CISS can arise in electron transfer reactions of radical pairs, we propose a simple way to include CISS in conventional models of radical pair spin dynamics. We show that CISS can (a) increase the sensitivity of radical pairs to the direction of a weak external magnetic field, (b) change the dependence of the magnetic field effect on the reaction rate constants, and (c) destroy the field-inversion symmetry characteristic of the RPM. We argue that CISS polarization effects could be observable by EPR (electron paramagnetic resonance) of oriented samples either as differences in continuous wave, time-resolved spectra recorded with the spectrometer field parallel or perpendicular to the CISS quantization axis or as signals in the in-phase channel of an out-of-phase ESEEM (electron spin echo envelope modulation) experiment. Finally we assess whether CISS might be relevant to the hypothesis that the magnetic compass of migratory songbirds relies on photochemically-formed radical pairs in cryptochrome flavoproteins. Although CISS effects offer the possibility of evolving a more sensitive or precise compass, the associated lack of field-inversion symmetry has not hitherto been observed in behavioural experiments. In addition, it may no longer be safe to assume that the observation of a polar magnetic compass response in an animal can be used as evidence against a radical pair sensory mechanism.

在自由基对机制 (RPM) 的背景下，有机自由基的反应速率和产率可能与自旋有关，这是众所周知的。不太为人所知，但仍然很明确的是手性诱导的自旋选择性 (CISS) 效应，其中手性分子充当自旋过滤器，优先传输自旋极化平行或反平行于其运动方向的电子。从 CISS 可以出现在自由基对的电子转移反应中的假设出发，我们提出了一种简单的方法，将 CISS 包含在自由基对自旋动力学的传统模型中。我们表明CISS可以（a）增加自由基对对弱外部磁场方向的敏感性，（b）改变磁场效应对反应速率常数的依赖性，(c) 破坏 RPM 的场反转对称特性。我们认为，定向样品的 EPR（电子顺磁共振）可以观察到 CISS 极化效应，可以作为连续波的差异、用平行或垂直于 CISS 量化轴的光谱仪场记录的时间分辨光谱或作为输入信号异相 ESEEM（电子自旋回波包络调制）实验的相位通道。最后，我们评估了 CISS 是否可能与候鸟的磁罗盘依赖于隐花色素黄素蛋白中光化学形成的自由基对的假设有关。尽管 CISS 效应提供了发展更灵敏或更精确的罗盘的可能性，但迄今为止在行为实验中尚未观察到相关的场反转对称性缺乏。