385176 Dispersed Microenvironments for Chemical Evolution
Biopolymers in current living organisms are usually synthesized with the help of enzymes and cell compartmentalization. Such mechanism was unlikely to exist in the prebiotic earth. Therefore, the first biopolymers for the evolution of early life forms should come from simpler systems with abiotic reaction mechanisms. Miller-Urey experiments have demonstrated the possibility of the formation of amino acids and hydroxy acids in the prebiotic world.1 Those materials can be used as building blocks for biopolymers. However, even though the source of monomers is understood, the formation of polymers in the prebiotic ocean still faces a number of challenges. The high water concentration in the ocean can hamper the polycondensation reaction by shifting the equilibrium to the reactant side. This enhances the difficulty of forming long chain polymers and shortens their life time.
In this work, an oil/water biphasic reaction media is designed to solve this problem. It has been shown that some water immiscible organic solvents can exist in the prebiotic world.2 Because of the lower water concentration in those oil solvents, they can facilitate the polymerization reaction by shifting the equilibrium to the product side and protect the synthesized polymers from hydrolysis by water. Also, the increased hydrophobicity of the growing polymer chain can further concentrate those polymers in the oil phase and speed up the evolutionary process. The oil phase can also be dispersed and stabilized by surfactants to form an emulsion. The dispersed oil phase has much higher interfacial area and can facilitate the absorption of building blocks from the prebiotic ocean.
The present work first focuses on the polymerization of lactic acid in the oil/water biphasic system. Polyesters have been proposed as one possible ancestor for polypeptides3 and lactic acid is a significant product from the Miller-Urey experiments. Also, polylactic acid (PLA) is a biodegradable polymer that has been well characterized and can be used in drug delivery applications.
Two different abiotic reaction pathways have been studied in this work. The first one is the polycondensation reaction of lactic acid with dicyclohexylcarbodiimide as condensing agent and 4-dimethylaminopyridine as catalyst. It has proved to be an efficient condensing agent for the polymerization of lactic acid when organic solvent is used alone.4 In our work, the interfacial reaction between the hydrophobic carbodiimide and hydrophilic lactic acid is able to produce long chain PLA. The second reaction pathway is starting from the ring-opening polymerization of lactide, the cyclic dimer of lactic acid. 5 Lactide has higher solubility in organic solvents than lactic acid. Therefore, the reaction can proceed directly in the oil phase. The ring-opening polymerization can be catalyzed by 4-dimethylaminopyridine which is a weak organic base and its distribution between oil and aqueous phase can be controlled by the pH of water. Polyester with high yield can be obtained and preserved in the oil phase under near neutral pH and room temperature.
The findings in this work provide another methodology to solve the mystery of the origin of life. The presence of oil phase successfully facilitates the polymerization and extends the life time of the synthesized polyester. The same biphasic reaction system can also be applied to the reaction and evolution of other biopolymers in the future.
1. Miller, S. L.; Urey, H. C., Organic compound synthesis on the primitive earth: Several questions about the origin of life have been answered, but much remains to be studied. Science 1959, 130 (3370), 245-251.
2. Lasaga, A. C.; Holland, H. D.; Dwyer, M. J., Primordial oil slick. Science 1971, 174 (4004), 53-55.
3. Orgel, L., Some consequences of the RNA world hypothesis. Origins Of Life And Evolution Of The Biosphere 2003, 33 (2), 211-218.
4. Akutsu, F., Inoki, M., Uei, H., Sueyoshi, H., Kasashima, Y., Naruchi, K., Yamaguchi Y., Sunahara, M., Synthesis of poly(lactic acid) by direct polycondensation of lactic acid using 1,1'-carbonyldiimidazole, N,N,N',N'-tetramethylchloroformamidinium chloride and N,N'-dicyclohexylcarbodiimide as condensing agents. Polym Journal 1998, 30, 421.
5. Coulembier, O., Dubois, P., 4-dimethylaminopyridine-based organoactivation: From simple esterification to lactide ring-opening "Living" polymerization. Journal of Polymer Science Part A: Polymer Chemistry 2012, 50 (9), 1672-1680.
385176 Microenvironments Dispersed kwa ajili ya Chemical Evolution Biopolymers katika viumbe hai sasa ni kawaida synthesized kwa msaada wa enzymes na compartmentalization seli. Haikuwa vigumu kwa utaratibu huo kuwepo katika dunia iliyokuwa kabla ya uhai. Kwa hiyo, biopolymers ya kwanza kwa ajili ya mageuzi ya aina za maisha ya mapema inapaswa kuja kutoka kwa mifumo rahisi na taratibu za athari abiotic. Majaribio ya Miller-Urey yanaonyesha uwezekano wa kuunda amino asidi na asidi ya hydroxy katika ulimwengu wa prebiotic. Hata hivyo, ingawa chanzo cha monomeri kinaeleweka, kuundwa kwa polima katika bahari ya prebiotic bado inakabiliwa na changamoto kadhaa. Mzunguko wa juu wa maji katika bahari inaweza kuzuia athari polycondensation kwa kuhamisha usawa kwa upande reactant. Hii huongeza ugumu wa kuunda polima za mlolongo mrefu na kupunguza muda wao wa maisha. Katika kazi hii, mafuta / maji biphasic athari vyombo vya habari ni iliyoundwa kutatua tatizo hili. Kwa sababu ya viwango vya chini vya maji katika vimumunyifu vya mafuta, zinaweza kuwezesha athari ya polymerization kwa kuhamisha usawa kwa upande wa bidhaa na kulinda polima zilizotengenezwa kutoka kwa hydrolysis na maji. Pia, kuongezeka kwa hydrophobicity ya mlolongo wa polima unaokua kunaweza kuongeza polima hizo katika awamu ya mafuta na kuharakisha mchakato wa mageuzi. Awamu ya mafuta pia inaweza kutawanyika na kuimarishwa na surfactants kuunda emulsion. Awamu ya mafuta dispersed ina eneo la juu zaidi interfacial na inaweza kuwezesha kunyonya ya vitalu ya ujenzi kutoka bahari prebiotic. Kazi hii kwanza inazingatia polymerization ya asidi lactic katika mafuta-maji biphasic mfumo. Polyester ni moja ya asili ya polypeptides na asidi lactic ni moja ya bidhaa muhimu kutoka kwa majaribio ya Miller-Urey. Polylactic asidi (PLA) ni polima biodegradable ambayo imekuwa vizuri sifa na inaweza kutumika katika matumizi ya utoaji wa dawa. Njia mbili tofauti za athari za abiotic zimechunguzwa katika kazi hii. Mchakato wa polycondensation wa asidi ya lactic na dicyclocarbamide kama wakala wa condensing na 4-dimethylaminopyridine kama kichocheo. Ni moja ya viungo vya msingi vya polima ya asidi ya maziwa, ambayo hutumiwa kwa njia ya mfumuaji wa kikaboni, na kwa njia ya mfumuko wa polima ya asidi ya maziwa, ambayo hutumiwa kwa njia ya mfumuko wa polima ya asidi ya maziwa. Njia ya pili ya athari ni kuanzia kutoka kwa polymerization ya kufungua pete ya lactide, dimer ya mzunguko wa asidi ya maziwa. Lactide ina solubility ya juu katika solvents kikaboni kuliko asidi lactic. Kwa hiyo, athari inaweza kuendelea moja kwa moja katika awamu ya mafuta. Polymerization ya kufungua pete inaweza kuchochewa na 4-dimethylaminopyridine, ambayo ni msingi dhaifu wa kikaboni, na usambazaji wake kati ya mafuta na hatua ya maji inaweza kudhibitiwa na pH ya maji. Polyester na mavuno ya juu inaweza kupatikana na kuhifadhiwa katika awamu ya mafuta chini ya pH karibu na neutral na joto la chumba. Matokeo ya utafiti huo yanatusaidia kuelewa chanzo cha uhai. Uwepo wa awamu ya mafuta mafanikio kuwezesha polymerization na kupanua muda wa maisha ya polyester synthesized. Mfumo huo wa athari ya biphasic pia unaweza kutumika kwa athari na mageuzi ya biopolymers nyingine katika siku zijazo. 1. Uwe na mtazamo wa kweli Miller, S. L., Urey, H. C., Organic Compound Synthesis on the Primitive Earth: Maswali kadhaa kuhusu chanzo cha uhai yamejibiwa, lakini mengi bado yanahitaji kuchunguzwa. Sayansi, 1959, 130 (3370), 245-251. 2. Uwezekano wa kupata Lasaga, A. C.; Holland, H. D.; Dwyer, M. J., Mafuta ya Asili. Sayansi, 174 (400), 53-55. 3. Uwe na mtazamo wa kweli Orgel, L., Baadhi ya matokeo ya nadharia ya ulimwengu wa RNA. Asili ya Maisha na Mageuzi ya Biosphere, 2003 (picha ya chini) 4. Uwe na uhakika Akatsuki, F., Inoki, M., Uei, H., Suehashi, H., Kasumi, Y., Naruchi, K., Yamaguchi, Y., Sunahara, M., Synthesis of poly (lactic acid) by direct polycondensation of lactic acid using 1,1-carbonyldiimidazole, N, N, N, N, N, N'-tetramethyl chloroformyl chloride and N, N, N-dimethyl-methyl-carbodiamide as condensing agents. Polymaths, Jurnal ya Polymaths, 1999, p. 5. Uwe na mtazamo mzuri. Coulembier, O., Dubois, P., 4-dimethylaminopyridine-msingi organoactivation: Kutoka esterification rahisi kwa lactide pete-kufungua "kuishi" polymerization. Journal of Polymer Science, sehemu A: Kemikali ya Polymer 2012, 50 (9), 1672-1680