Isopren

Isopren er en meget vigtig byggesten, som danner grundlaget for biosyntesen af mange biologiske molekyler, f.eks. squalen (et intermediat i kolesterolbiosyntesen), terpener, gibberelliner, steroler, carotenoider, neophytadien gummi, fytolhalen på chlorofylmolekylet osv.

Biosyntesen af de forskellige molekyler, stoffer (terpener, gibberelliner, cholesterol osv.) sker ikke direkte ud fra isopren, men via en kompleks række af reaktioner.

Isopren i atmosfæren (kan) reagere med visse stoffer og bliver i så fald til aerosoler og de dannede aerosoler er hygroskopiske og er med til at danne skyer og tåge. Det viser sig at mange landplanter danner store mængder isopren og derfor er ophav til en stor del af bioaerosolerne. ^[1] ^[2]^[3]

"Isopren-vulkanen" i Ozark bjergskoven

The Ozarks Isoprene Experiment (OZIE) blev designet til at udforske egetræers udsendelse af isopren i Ozark bjergskoven i Missouri i USA. ^[4] ^[5] Det blev bekræftet, at egetræer er store isopren-udsendere med en middeludsendelse på 66 mgC g^-1 h^-1, men man opdagede også at isopren-udsendelsen er afhængig af bladenes temperaturer – jo højere; jo mere.

Isopren som biosignatur

I søgen af liv i universet er isopren foreslået som biosignatur.^[6]

Kilder/henvisninger

^ California Institute of Technology (2009, August 7). Organic Carbon Compounds Emitted By Trees Affect Air Quality. ScienceDaily Citat: "...In these studies, the research team focused on a chemical called isoprene, which is given off by many deciduous trees. "The king emitters are oaks," Wennberg says. "And the isoprene they emit is one of the reasons that the Smoky Mountains appear smoky."..."And isoprene only comes from plants. They make hundreds of millions of tons of this chemical...for reasons that we still do not fully understand."..."
^ Max Planck Society (2004, February 26). Astonishing Discovery Over The Amazonian Rain Forest. ScienceDaily Citat: "...natural aerosols from the Amazonian rain forest, and has found that they contained two previously unknown compounds, which are photooxidation products of isoprene. These compounds are hygroscopic and could impact cloud formation, rainfall and climate..."
^ Carnegie Mellon University. (2014, May 15). Emissions from forests influence very first stage of cloud formation. ScienceDaily Citat: "...This new study uncovers an indispensable ingredient to the long sought-after cloud formation recipe -- highly oxidized organic compounds..."It turns out that sulfuric acid and these oxidized organic compounds are unusually attracted to each other. This remarkably strong association may be a big part of why organics are really drawn to sulfuric acid under modern polluted conditions," Donahue said...The fine-tuned model not only predicted nucleation rates more accurately but also predicted the increases and decreases of nucleation observed in field experiments over the course of a year, especially for measurements near forests. This latter test is a strong confirmation of the fundamental role of emissions from forests in the very first stage of cloud formation, and that the new work may have succeeded in modeling that influence..."
^ agu.org: Wiedinmyer, C., et al. (2005), Ozarks Isoprene Experiment (OZIE): Measurements and modeling of the "isoprene volcano", J. Geophys. Res., 110, D18307, doi:10.1029/2005JD005800
^ worldwildlife.org: Ozark Mountain forests (NA0412)
^ Detecting This Specific Gas in an Alien World's Atmosphere May Be a Good Sign of Life. ScienceAlert 2021

Eksterne henvisninger

Rachel Pike: The science behind a climate headline Arkiveret 7. december 2009 hos Wayback Machine As a Ph.D candidate at Cambridge, Pike's research on isoprene, a major biofuel crop emission, and other molecules has taken her soaring over rainforest canopies in multi-ton labs-on-wings, into the cooled-down sub-levels of supercomputer grids, and into massive experimental atmospheric chambers. Her exhaustive work represents a major step toward a complete picture of how human activity affects the global ecosystem.

[1] California Institute of Technology (2009, August 7). Organic Carbon Compounds Emitted By Trees Affect Air Quality. ScienceDaily Citat: "...In these studies, the research team focused on a chemical called isoprene, which is given off by many deciduous trees. "The king emitters are oaks," Wennberg says. "And the isoprene they emit is one of the reasons that the Smoky Mountains appear smoky."..."And isoprene only comes from plants. They make hundreds of millions of tons of this chemical...for reasons that we still do not fully understand."..."

[2] Max Planck Society (2004, February 26). Astonishing Discovery Over The Amazonian Rain Forest. ScienceDaily Citat: "...natural aerosols from the Amazonian rain forest, and has found that they contained two previously unknown compounds, which are photooxidation products of isoprene. These compounds are hygroscopic and could impact cloud formation, rainfall and climate..."

[3] Carnegie Mellon University. (2014, May 15). Emissions from forests influence very first stage of cloud formation. ScienceDaily Citat: "...This new study uncovers an indispensable ingredient to the long sought-after cloud formation recipe -- highly oxidized organic compounds..."It turns out that sulfuric acid and these oxidized organic compounds are unusually attracted to each other. This remarkably strong association may be a big part of why organics are really drawn to sulfuric acid under modern polluted conditions," Donahue said...The fine-tuned model not only predicted nucleation rates more accurately but also predicted the increases and decreases of nucleation observed in field experiments over the course of a year, especially for measurements near forests. This latter test is a strong confirmation of the fundamental role of emissions from forests in the very first stage of cloud formation, and that the new work may have succeeded in modeling that influence..."

[4] u.org: Wiedinmyer, C., et al. (2005), Ozarks Isoprene Experiment (OZIE): Measurements and modeling of the "isoprene volcano", J. Geophys. Res., 110, D18307, doi:10.1029/2005JD005800

[5] worldwildlife.org: Ozark Mountain forests (NA0412)

[6] Detecting This Specific Gas in an Alien World's Atmosphere May Be a Good Sign of Life. ScienceAlert 2021

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