MCD Reveals a Magnetic Field-Sensitive Pathway for Life’s Choice of α-Amino Acids

Amino acids serve as the fundamental building blocks of proteins and perform indispensable biological functions in living systems. During chemical evolution, α-amino acids played a crucial role as key structural modules in the assembly of primitive proteins and the formation of early metabolic networks. However, why life selected α-amino acids, rather than other structural types of amino acids, as the core components of protein backbones remains a fundamental question in origins-of-life research: Is this a result of life systems screening a pre-existing molecular library in the prebiotic environment, or does it stem from the unique physicochemical properties and reaction kinetics advantages of α-amino acids? Phosphorus, an essential element constituting nucleic acid backbones and participating in cellular energy metabolism, may have profoundly influenced this selection process through phosphorylation reactions driven under prebiotic chemical conditions.
This study utilized magnetic circular dichroism (MCD) spectroscopy to systematically compare the spectral behaviors of N-phosphorylated α-, β-, and γ-alanines in an aqueous environment. The results revealed that only the α-phosphorylated alanine exhibited a characteristic MCD signal under a magnetic field, which is attributed to a high-energy intermediate formed via an intramolecular five-membered ring transition state. Further experiments demonstrated that under a relatively strong external magnetic field, the rates of prebiotic reactions involving N-phosphorylalanine, such as hydrolysis and peptide bond formation, were significantly enhanced .
Based on these findings, we propose that magnetic fields can modulate the spatial orientation of functional groups within phosphorylated amino acid molecules, effectively stabilizing key reaction intermediates and reducing the reaction energy barrier. This mechanism provides important experimental evidence for understanding how life specifically selected the phosphorus metabolic pathway and α-amino acids in the early Earth environment. It also reveals, from a physicochemical perspective, that the selection of biochemical molecular structures may originate from their intrinsic properties and their reactivity adaptability within the Earth's magnetic field.