====== CISS theory ======

The //Chirality-Induced Spin Selectivity// ( CISS ) effect was first discovered over two decades ago in the field of optical polarization. ([[https://www.science.org/doi/abs/10.1126/science.283.5403.814|ref.]])

It was found that a fundamental quantum property of electrons - known as 'spin' - is strongly influenced by the 'chirality' i.e. 'handedness' of molecules.

The 'spin' of an electron is crucial in determining whether or not it can occupy a particular electron 'shell' - or 'orbit' - around the atomic nucleus. The presence or absence of electrons in the shells very dramatically alters the chemical properties of an atom.

And, in laboratory settings, electron spin can now be manipulated with weak magnetic fields - leading to a a new area of study called 'Spin Chemistry'. ([[https://www.nature.com/articles/s41570-019-0087-1|ref.]])

Since most complex biological molecules are all 'handed' in the same way (see [[content:life_sciences:life_itself:homochirality]]) then, by implication, CISS effects might be highly important factors for bio-chemical reactions, Including vital processes such as [[content:life_sciences:life_itself:enzyme_catalysis]] and [[content:life_sciences:life_itself:protein_structuring]]. It's one of the research areas where it has recently become obvious that quantum effects can be highly important for biological systems.

Nonetheless, to date, the implications of CISS and the possible influence of magnetic fields for life systems have only been sketchily investigated.

In addition, CISS theory itself is poorly understood. Theoretical calculations for the strength of the effect differ very substantially from the results shown in practical experiments.

>Early theoretical efforts have indeed confirmed that SOC <sup>[ spin-orbit coupling ]</sup> may provide a qualitative explanation for some aspects of the experimental findings. Quantitatively, however, such calculations have consistently predicted effects that were smaller by up to several orders of magnitude than those observed experimentally. While additional theoretical research efforts, described in more detail below, have shed more light on CISS, a complete quantitative theory of the effect remains elusive and its microscopic origins are insufficiently understood.\\ [...]\\ At present, a unifying scheme that would allow one to interpret all experiments in terms of only a single microscopic effect – the “CISS effect” - has not yet been identified. While such a framework cannot be ruled out, chirality-induced spin selectivity may perhaps be thought of as a set of phenomena that have a unifying scheme only in the sense that they all derive from the interplay of spin-orbit interaction and chirality.\\ \\ Source : [[https://onlinelibrary.wiley.com/doi/10.1002/adma.202106629|Theory of Chirality Induced Spin Selectivity: Progress and Challenges]] //Advanced Materials//, Volume 34, Issue13{{:oa_padlock_red.png?16}}<sup> [ paywalled ] </sup>\\ A full copy of which may be accessed [[https://arxiv.org/pdf/2108.09998.pdf|here, at arXiv]]{{:oa_padlock_grn.png?16}}\\

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