On the origins of life’s homochirality: Inducing enantiomeric excess with spin-polarized electrons

Abstract

Life as we know it is homochiral, but the origins of biological homochirality on early Earth remain elusive. Shallow closed-basin lakes are a plausible prebiotic environment on early Earth, and most are expected to have significant sedimentary magnetite deposits. We hypothesize that ultraviolet (200- to 300-nm) irradiation of magnetite deposits could generate hydrated spin-polarized electrons sufficient to induce enantioselective prebiotic chemistry. Such electrons are potent reducing agents that drive reduction reactions where the spin polarization direction can enantioselectively alter the reaction kinetics. Our estimate of this chiral bias is based on the strong effective spin-orbit coupling observed in the chiral-induced spin selectivity (CISS) effect, as applied to energy differences in reduction reactions for different isomers. In the original CISS experiments, spin-selective electron transmission through a monolayer of double-strand DNA molecules is observed at room temperature—indicating a strong coupling between molecular chirality and electron spin. We propose that the chiral symmetry breaking due to the CISS effect, when applied to reduction chemistry, can induce enantioselective synthesis on the prebiotic Earth and thus facilitate the homochiral assembly of life’s building blocks.

The central dogma of biological homochirality: How does chiral information propagate in a prebiotic network?

“…In our initial work on enantioselective crystallization, we found that a magnetite surface magnetized by the north (south) pole of a magnet promotes the crystallization of D-RAO (L-RAO). To our delight, in our follow-up work, we observed that D-RAO (L-RAO) magnetizes the magnetite surface along the same direction as the north (south) pole of a magnet 2,35 . Therefore, the coupling between enantiomeric excess and net magnetization is mutually reinforcing, leading to the possibility of a cooperative feedback between chiral molecules and magnetic surfaces, as illustrated in Fig.…”

“…A natural question then is where to find a bias in the electron spin in a prebiotic setting. To address this question we recently proposed closed-basin evaporative lakes with sedimentary magnetite (Fe 3 O 4 ) deposits as plausible prebiotic environments that can accommodate spin-selective processes 35 . In these environments, authigenic magnetite forms as singledomain, superparamagnetic particles and gets magnetized under the geomagnetic field [36][37][38] .…”

Spin Chiral Anisotropy of Chiral Mesostructured Inorganic Materials with Different Intrinsic Magnetisms

“…In recent decades, chirality-dependent spin anisotropy, named spin chiral anisotropy (SChA), in materials endowed with chirality has been discovered. − In chemistry and biochemistry, chirality describes the geometric asymmetry of an object in which a chiral structure cannot be superimposed onto itself after an S n symmetry operation, including mirror plane (σ or S 1 ) and inversion ( I or S 2 ) symmetry. A pair of mirror-image chiral structures are designated as either left- or right-handedness. , In physics, chirality often refers to the locking between the projection of the intrinsic angular momentum and the motion of the particle. , For example, a moving electron has either a spin-up or spin-down state.…”

Reprogramming biocatalytic futile cycles through computational engineering of stereochemical promiscuity to create an amine racemase

“…L-amino acids for proteins and D-sugars for nucleic acids. 2,3 However, living organisms have also found a way to enrich metabolic and physiological diversity by allocating biochemical tasks to the non-preferred enantiomers that are readily available from the major chiral pool through stereoinversion. 4 For example, serine racemase supplies D-serine to mammalian brains as a signaling molecule.…”