Chirality-Induced Spin Selectivity (CISS)

Chirality is an extremely important property in physics and chemistry. It is appears in elementary particles like photons as well as in the basic building blocks of the body (such as amino acids, which make up proteins, and nucleic acids, which make up genetic material). Many other molecules are “chiral”, i.e. they can not be superimposed to their mirror image by translations and rotations. The two distinguishable variants (enantiomers) often occur in nature with one (strongly) preferred. A well known phenomenon arising for chiral molecules is optical activity, the rotation of the polarisation axis of light when passing through a solution of such molecules, e.g. sugar. An unexpected chirality effect has been first observed in transport measurements: if an electron subject to an electric bias travels through a chiral medium, transmission is favoured for a certain projection of the spin of the electron along the chiral axis and suppressed for the other. Which orientation is preferred depends on the chirality – handness of the medium – and on the direction of motion. Re- markably, no magnetic field is required and the CISS is very effective even at room temperature. Further experimental evidences have then emerged also in very different setups with no steady-state current and even in photo-induced electron transfer (PET) through a chiral bridge. The CISS phenomenon became recently a subject of intensive research.
In the seminar the basic concept of chirality in physics and chemistry will be discussed, followed by the initial observations of CISS, leading to present literature.