Kua Jeremy, Loli Helen
Department of Chemistry and Biochemistry, University of San Diego , 5998 Alcala Park, San Diego, California 92110, United States.
J Phys Chem A. 2017 Oct 26;121(42):8154-8165. doi: 10.1021/acs.jpca.7b08685. Epub 2017 Oct 13.
We have investigated the nonoxidative stepwise co-oligomerization of formaldehyde and pyrrole to form porphinogen using density functional theory calculations that include free energy corrections. While the addition of formaldehyde to the pyrrole nitrogen is kinetically favored, thermodynamics suggest that this reaction is reversible in aqueous solution. The more thermodynamically favorable addition of formaldehyde to the ortho-carbon of pyrrole begins a stepwise process, forming dipyrromethane via an azafulvene intermediate. Subsequent additions of formaldehyde and pyrrole lead to bilanes (linear tetrapyrroles), which favorably cyclize to form porphinogen. Porphinogen is a precursor to porphin, the simplest unsubstituted porphyrin that could have played a role in primitive metabolism at the origin of life.
我们利用包含自由能校正的密度泛函理论计算，研究了甲醛和吡咯的非氧化逐步共低聚反应以形成卟吩原。虽然甲醛加成到吡咯氮上在动力学上是有利的，但热力学表明该反应在水溶液中是可逆的。甲醛加成到吡咯的邻位碳上在热力学上更有利，这开始了一个逐步过程，通过氮杂富烯中间体形成二吡咯甲烷。随后甲醛和吡咯的加成导致了连二吡咯（线性四吡咯），其有利地环化形成卟吩原。卟吩原是卟吩的前体，卟吩是最简单的未取代卟啉，可能在生命起源时的原始代谢中发挥了作用。
