Wet-Dry Cycling Delays the Gelation of Hyperbranched Polyesters: Implications to the Origin of Life.

Irena Mamajanov

doi:10.3390/life9030056

Abstract

In extant biology, biopolymers perform multiple crucial functions. The biopolymers are synthesized by enzyme-controlled biosystems that would not have been available at the earliest stages of chemical evolution and consist of correctly sequenced and/or linked monomers. Some of the abiotic “messy” polymers approximate some functions of biopolymers. Condensation polymers are an attractive search target for abiotic functional polymers since principal polymers of life are produced by condensation and since condensation allows for the accurate construction of high polymers. Herein the formation of hyperbranched polyesters that have been previously used in the construction of enzyme-like catalytic complexes is explored. The experimental setup compares between the branched polyesters prepared under mild continuous heating and the wet-dry cycling associated with environmental conditions, such as dew formation or tidal activities. The results reveal that periodic wetting during which partial hydrolysis of the polyester occurs, helps to control the chain growth and delays the gel transition, a mechanism contributing to the tar formation. Moreover, the NMR and mass spec analyses indicate that continuously dried samples contain higher quantities of crosslinked and macrocyclic products, whereas cycled systems are enriched in branched structures. Ostensibly, environmental conditions have the ability to exert a rudimentary pressure to selectively enrich the polyesterification products in polymers of different structures and properties. At the early stages of chemical evolution, in the absence of biological machinery, this example of environmental control could have been for selectivity in chemical systems. As expected in marginally controlled systems, the identification of each component of the heterogeneous system has proved challenging, but it is not crucial for drawing the conclusions.

Highlights

In modern biological systems, biopolymers perform a multitude of functions
We have previously demonstrated that straightforwardly synthesized mixture of amine-bearing hyperbranched polyesters (HBPEs) is capable of catalyzing the Kemp elimination process by modulating the polarity of the environments in
The results presented here indicate that wet-dry cycles associated with day-night, tidal, or seasonal environmental changes promote the formation of soluble lower molecular weight HBPE whereas continuous drying is conducive to the formation of insoluble polymers

Summary

Introduction

The major biopolymers (i.e., polypeptides, nucleic acids, polysaccharides) are characterized by a specific monomer sequencing and folding to achieve the necessary functions. The synthesis of biopolymers is accomplished through intricate enzyme-controlled processes [1], that would not have been available at the earliest stages of chemical evolution. The abiotic synthesis of biopolymers is an active area of research. It has long been recognized that abiotic reactions can produce many monomers of biopolymers. The Miller−Urey experiment showed that some of the simpler amino acids (e.g., glycine and alanine) are readily formed in a model prebiotic atmosphere [2,3]. Different biopolymer blocks, including sugars and nucleobases, are formed in a variety

Methods

Findings

Discussion

Conclusion