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Aromatic Carotenoids

Aromatic Carotenoids
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Aromatic carotenoids and maleimides

Aromatic carotenoids and maleimides as indicators for photic zone euxinia

Aromatic carotenoids are a special class of carotenoids, which are naturally occurring pigments found in various plants, bacteria, and algae. They are characterized by the presence of at least one aromatic ring within their molecular structure, unlike the typical aliphatic carotenoids that only contain carbon-carbon single bonds. This unique feature gives them distinct properties and functions compared to their aliphatic counterparts.

Here are some key characteristics of aromatic carotenoids:

  • Structure: As mentioned before, they have at least one aromatic ring, often benzene or naphthalene, incorporated into their structure. This aromatic ring introduces rigidity and planarity to the molecule, affecting its light absorption and interaction with other molecules.
  • Color: Due to their unique structure, aromatic carotenoids often exhibit vibrant colors like red, orange, yellow, and purple. These colors arise from the specific way they absorb and reflect different wavelengths of light.
  • Functions: They play various roles in their host organisms, including:
    • Light-harvesting: In photosynthetic organisms, they can act as accessory pigments alongside chlorophyll, capturing light energy for photosynthesis.
    • Photoprotection: They can shield sensitive cellular components from harmful ultraviolet radiation by absorbing the damaging rays.
    • Signaling: In some cases, they might be involved in cell-to-cell communication or signaling within the organism.
    • Antioxidant activity: Some aromatic carotenoids possess antioxidant properties, helping to neutralize free radicals and protect cells from oxidative damage.

Examples of aromatic carotenoids:

Aromatic carotenoids

  • Lycopene: This bright red pigment, found in tomatoes, watermelon, and pink grapefruit, is a well-known example with potent antioxidant activity.
  • β-carotene: Although primarily classified as an aliphatic carotenoid, it does contain a single aromatic ring. It is known for its role in vitamin A conversion and its orange color in carrots, sweet potatoes, and mangoes.
  • Crocin: This carotenoid is responsible for the saffron spice’s intense yellow color and has various culinary and medicinal applications.
  • Astaxanthin: This red pigment is abundant in microalgae and some seafood and is known for its strong antioxidant properties and potential health benefits.

Interestingly, aromatic carotenoids have also been found in geological samples, such as fossils and ancient sediments. Their presence can provide valuable insights into past environmental conditions and the evolution of life on Earth.

Geological carotenoid Possible biological precursors Biological sources References
Okenane okenone Chromatiaceae Schaeffer et al., 19971
Chloroacetate chlorobactene, hydroxychlorobactene green pigmented Chlorobiaceae Grice et al., 1998c
Isorenieratane2 isorenieratene brown pigmented Chlorobiaceae Bosch et al., 1998, Grice et al., 1996b, Hartgers et al., 1993, Koopmans et al., 1996a, Pancost et al., 1998, Putschew et al., 1998, Simons and Kenig, 2001, Sinninghe Damst et al., 2001
b-isorenieratane3 b-isorenieratene, bcarotene4 brown pigmented Chlorobiaceae Grice et al., 1998c
Renieratane renieratene sponges or sponge symbionts? Chlorobiaceae? Hartgers et al., 1993, Schaefle et al., 1977
Renierapurpurane5 renierapurpurin sponges or sponge symbionts? Chlorobiaceae? Schaefle et al., 1977
Palaerenieratane6 unknown Chlorobiaceae? Hartgers et al., 1993, Koopmans et al., 1996a, Requejo et al., 1992
2,3,6-TMAs7 chlorobactene, hydroxychlorobactene, isorenieratene, b-isorenieratene, b-carotene 4 and similar structures mostly Chlorobiaceae3 Hartgers et al., 1993, Requejo et al., 1992, Summons and Powell, 1986, Summons and Powell, 1987, Summons and Powell, 1992
2,3,4-TMAs7 okenone, renieratene renierapurpurin Chromatiaceae Chlorobiaceae? Summons and Powell, 1987
3,4,5-TMAs7 precursor of palaerenieratane Chlorobiaceae? Hartgers et al., 1993, Requejo et al., 1992, Summons and Powell, 1987
Me i-Bu maleimide BChl c, d and e Chlorobiaceae, Chloroflexaceae Grice et al., 1996a, Grice et al., 1997, Pancost et al., 2002

Biomarker classification