The role of combinatorial processes in the origin of life remains relatively unexplored. In a chemical model for the possible prebiogenesis of tetrapyrrole macrocycles reported previously, a tandem combinatorial reaction of two diones (substituents = methyl, acetic acid) and two aminoketones (substituents = ethyl, propanoic acid) afforded up to 538 porphyrins (upon oxidation of the corresponding porphyrinogens). The reaction was performed at a 1 : 1 ratio of hydrophobic and hydrophilic substituents in each pool of reactants, and the resulting porphyrins partitioned in ∼1 : 1 ratio between aqueous solution and phosphatidylcholine vesicle membranes. Here, a change in the ratio of hydrophobic and hydrophilic substituents of the [2 × 2] reaction gave corresponding changes in the polarity profile of the resulting porphyrins (3.5–9.0% yield). Reaction of four diones and four aminoketones (bearing hydrophilic or hydrophobic substituents) in the presence of lipid vesicles followed by photooxidation afforded porphyrins in 8.7% yield. The resulting porphyrins partitioned in ∼1 : 1 ratio between phosphatidylcholine vesicles and aqueous solution, as observed previously for the [2 × 2] reaction. Both the aqueous fraction and the vesicles fraction were photochemically active as evidenced by the fluorescence quantum yield (Φf ∼ 0.1). Software (PorphyrinViLiGe) for virtual library generation indicates that the [4 × 4] reaction affords up to 131 464 porphyrins. The relative insensitivity of physicochemical properties (partitioning, photoactivity) toward combinatorial expansion may be a valuable yet unappreciated attribute for prebiotic functionality.
组合过程在生命起源中的作用相对来说仍未得到探索。在之前报道的四
吡咯大环可能的前
生物起源
化学模型中,两个二元酸(取代基=甲基、
乙酸)和两个
氨基酮(取代基=乙基、
丙酸)的串联组合反应产生了多达 538 个
卟啉(在相应的
卟啉原氧化后)。反应以 1 :每个反应物池中疏
水和亲
水取代基的比例为 1 : 1,生成的
卟啉以 ∼1 :1 的比例在
水溶液和
磷脂酰
胆碱囊膜之间分配。在这里,改变[2 × 2]反应中疏
水和亲
水取代基的比例会相应地改变所得
卟啉的极性曲线(产率为 3.5-9.0%)。在有脂质囊泡存在的情况下,四种二元胺和四种
氨基酮(带有亲
水性或疏
水性取代基)发生反应,然后进行光氧化,得到
卟啉,产率为 8.7%。生成的
卟啉以 1 :
磷脂酰
胆碱囊泡和
水溶液之间的分配比例为 1:1,这与之前在[2 × 2]反应中观察到的情况相同。从荧光量子产率(Φf ∼ 0.1)可以看出,
水溶液部分和囊泡部分都具有光
化学活性。虚拟库生成软件(PorphyrinViLiGe)显示,[4 × 4]反应可生成多达 131 464 种
卟啉。理化性质(分配、光活性)对组合扩展的相对不敏感性可能是
生物前功能性的一个宝贵但未被重视的属性。