title: 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.
authors.affiliation: Department of Chemistry, North Carolina State University , Raleigh, North Carolina 27695, USA.
authors.forename: Ana R M
authors.initials: AR
authors.lastname: Soares
authors.forename: Masahiko
authors.initials: M
authors.lastname: Taniguchi
authors.forename: Vanampally
authors.initials: V
authors.lastname: Chandrashaker
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey
mesh_terms: D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007700:Kinetics; D009821:Oils / Q000737:chemistry*; D010788:Photosynthesis; D011166:Porphyrins / Q000138:chemical synthesis; D012996:Solutions; D045725:Tetrapyrroles / Q000138:chemical synthesis*; D014867:Water / Q000737:chemistry
chemical_list: D009821:Oils; D011166:Porphyrins; D012996:Solutions; D045725:Tetrapyrroles; D014867:Water