Research ArticleASTROBIOLOGY

Membrane alternatives in worlds without oxygen: Creation of an azotosome

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Science Advances  27 Feb 2015:
Vol. 1, no. 1, e1400067
DOI: 10.1126/sciadv.1400067

Figures

  • Fig. 1 Liposomes and azotosomes.

    (A) Liposome in polar solvent. Polar heads are braced by nonpolar lipid tails. (B) Azotosome in nonpolar solvent. Nonpolar tails are braced by polar nitrogen–rich heads.

  • Fig. 2 Stretching a hexanenitrile azotosome and a hexane bilayer.

    The slope of the linear fit is proportional to the area modulus Ka.

  • Fig. 3 States of acrylonitrile.

    (A) Azotosome. Interlocking nitrogen and hydrogen atoms reinforce the structure. (B) Solid. Adjacent nitrogen atoms create some unfavorable repulsion. (C) Micelle. Adjacent nitrogen atoms make this highly unfavorable. (D) Azotosome vesicle of diameter 90 Å, the size of a small virus particle.

  • Fig. 4 Nitrogen head positions in selected azotosomes.

    (A) Initial grid. (B) Aminopentane (amorphous). (C) Pentanenitrile (hexagonal). (D) Acrylonitrile (close packed hexagonal).

  • Fig. 5 Umbrella sampling of the azotosome decomposition process.

    The test molecule is incrementally withdrawn from the membrane in the z direction.

  • Fig. 6 Stretching the azotosomes.

    The slope of the fit line is proportional to the area modulus Ka.

  • Fig. 7 Potential energy profile for the decomposition of acrylonitrile.

    The largest instantaneous energy barrier is the activation energy to decompose the azotosome.

Tables

  • Table 2 Error in OPLS-optimized structures.

    Average difference, for each species, between its OPLS structure and the structure obtained via ab initio optimization with Onsager’s self-consistent reaction field (SCRF) model of an implicit solvent.

    SpeciesΔ(bond
    length) (Å)
    Δ(bond
    angle) (°)
    Δ(dihedral)
    (°)
    Propanenitrile0.000.50.0
    Butanenitrile0.010.50.1
    Pentanenitrile0.010.40.1
    Hexanenitrile0.000.60.2
    Aminopropane0.010.70.7
    Aminobutane0.010.60.6
    Aminopentane0.010.60.4
    Aminohexane0.010.50.2
    Hexane0.010.30.0
    Methane0.021.50.0
    HCN0.010.00.0
    Acrylonitrile0.011.20.0
    Acetonitrile0.000.00.0
    Cyanoacetylene0.056.30.0
    Cyanoallene0.089.50.0
    2,4-Pentadiynenitrile0.0675.80.0
  • Table 3 Pairwise binding energies.

    OPLS and ab initio calculations produced similar results.

    SpeciesOPLS
    (kcal/mol)
    DFTvacuum
    (kcal/mol)
    DFTsolvent
    (kcal/mol)
    Propanenitrile−6.4−7.5−6.2
    Methane0.00.00.0
    HCN−4.1−3.0−2.3
    Acrylonitrile−5.6−6.0−4.9
    Acetonitrile−5.9−6.3−5.0
  • Table 4 Flexibility Ka of nitrile and amine azotosomes, and activation energy ΔE to remove a molecule from each azotosome.
    SpeciesKa (J/m2)ΔE (kcal/mol)
    Acrylonitrile0.2617.1
    Acetonitrile0.375.8
    Propanenitrile0.107.6
    Butanenitrile0.136.4
    Pentanenitrile0.558.4
    Hexanenitrile0.266.0
    Aminopropane0.225.2
    Aminobutane0.196.7
    Aminopentane0.287.7
    Aminohexane0.307.7
    Hexane bilayer2.20
  • Table 5 Gibbs free energy of decomposition.

    The net mechanical work required to remove a molecule from the membrane, within 20% uncertainty. These values are concentration-dependent.

    SpeciesΔG (kcal/mol)
    Acrylonitrile7.6
    Acetonitrile17.4
    Propanenitrile6.4
    Butanenitrile7.1
    Pentanenitrile13.4
    Hexanenitrile11.5
    Aminopropane5.9
    Aminobutane6.7
    Aminopentane9.6
    Aminohexane6.2

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