Primordial Oil Slick and the Formation of Hydrophobic Tetrapyrrole Macrocycles

Abstract

The functional end products of the extant biosynthesis of tetrapyrrole macrocycles in photosynthetic organisms are hydrophobic: chlorophylls and bacteriochlorophylls. A model for the possible prebiogenesis of hydrophobic analogues of nature's photosynthetic pigments was investigated by reaction of acyclic reactants in five media: aqueous solution (pH 7, 60°C, 24 h); aqueous solution containing 0.1 M decanoic acid (which forms a turbid suspension of vesicles); or aqueous solution accompanied by dodecane, mesitylene, or a five-component organic mixture (each of which forms a phase-separated organic layer). The organic mixture was composed of equimolar quantities of decanoic acid, dodecane, mesitylene, naphthalene, and pentyl acetate. The reaction of 1,5-dimethoxy-3-methylpentan-2,4-dione and 1-aminobutan-2-one to give etioporphyrinogens was enhanced in the presence of decanoic acid, affording (following chemical oxidation) etioporphyrins (tetraethyltetramethylporphyrins) in yields of 1.4-10.8% across the concentration range of 3.75-120 mM. The yield of etioporphyrins was greater in the presence of the five-component organic mixture (6.6% at 120 mM) versus that with dodecane or mesitylene (2.1% or 2.9%, respectively). The reaction in aqueous solution with no added oil-slick constituents resulted in phase separation-where the organic reactants themselves form an upper organic layer-and the yield of etioporphyrins was 0.5-2.6%. Analogous reactions leading to uroporphyrins (hydrophilic, eight carboxylic acids) or coproporphyrins (four carboxylic acids) were unaffected by the presence of decanoic acid or dodecane, and all yields were at most ∼2% or ∼8%, respectively. Taken together, the results indicate a facile means for the formation of highly hydrophobic constituents of potential value for prebiotic photosynthesis.

Aqueous–membrane partitioning of β-substituted porphyrins encompassing diverse polarity

“…The quantities of such porphyrins are small, but could have relevance to the accumulation of organic molecules by protocells. [9][10][11][12][13] Regardless, the observation of such multicomponent phenomena is inevitably precluded upon reliance on simple, serial, unianalyte laboratory studies.…”

“…The concentration of the P0 stock solution was also determined by absorption spectroscopy in THF using a molar absorption coefficient of 160 000 M À1 cm À1 at the peak of the Soret band (B400 nm), and found to be 1.54 mM, consistent with analysis above on the basis of absorption spectra in acid. 13,38 The absorption spectra of the six standard porphyrins (P8-P0) in 1 M HCl have been uploaded to the spectral database of PhotochemCAD. 39,40 In addition, the absorption and fluorescence emission spectra of selected porphyrins (uroporphyrin III, P4, P2, and P0) in 0.1 M potassium phosphate buffer (pH 7) or N,N-dimethylformamide, as well as absorption data for P0 in dimethylsulfoxide and 1-propanol, also have been made available in PhotochemCAD.…”

“…In studies concerning the origin of life, lipophilic or amphiphilic molecules from aqueous environments have been suggested to passively accumulate in the membranes of protocells. [9][10][11][12][13] Such heterotrophic enrichment could provide constituents and facilitate diverse chemistries for early living organisms.…”

Turbulent coherent structures and early life below the Kolmogorov scale

“…Many populations of biological organisms exist in an aqueous environment. As such, additional physical mechanisms governing population structure which are compatible with aqueous environments, such as active droplets, 5 slicks of fatty oils, 29 bubbles containing aerosols particles, 30 or surfactant micelles 31 have been considered as early mechanisms for group selection. Interestingly, while the chemical role and necessity of water itself for emergence and maintenance of life is well-appreciated, the potential role of its transport properties (in the absence of additional structures such as those described above) is relatively unexplored.…”

Paley's watchmaker analogy and prebiotic synthetic chemistry in surfactant assemblies. Formaldehyde scavenging by pyrroles leading to porphyrins as a case study

“…Our interests in chemical models for the origin of photosynthetic pigments [6][7][8][9][10] have led to examination of reactions in surfactant media, where hydrophobic reactants and products are expected to accumulate. Two recent reports bear on the studies reported herein.…”