Synthesis of lipids on the micelle/water interface using inorganic phosphate and an alkene oxide

Self-reproducing catalytic micelles as nanoscopic protocell precursors

Protocells at life's origin are often conceived as bilayer-enclosed precursors of life, whose self-reproduction rests on the early advent of replicating catalytic biopolymers. This Perspective describes an alternative scenario, wherein reproducing nanoscopic lipid micelles with catalytic capabilities were forerunners of biopolymer-containing protocells. This postulate gains considerable support from experiments describing micellar catalysis and autocatalytic proliferation, and, more recently, from reports on cross-catalysis in mixed micelles that lead to life-like steady-state dynamics. Such results, along with evidence for micellar prebiotic compatibility, synergize with predictions of our chemically stringent computer-simulated model, illustrating how mutually catalytic lipid networks may enable micellar compositional reproduction that could underlie primal selection and evolution. Finally, we highlight studies on how endogenously catalysed lipid modifications could guide further protocellular complexification, including micelle to vesicle transition and monomer to biopolymer progression. These portrayals substantiate the possibility that protocellular evolution could have been seeded by pre-RNA lipid assemblies.

The synthesis of mono-alkyl phosphates and their derivatives: an overview of their nature, preparation and use, including synthesis under plausible prebiotic conditions

Nucleic acids, phospholipids and other organic phosphates play central roles in biological pathways.

Prebiotic Lipidic Amphiphiles and Condensing Agents on the Early Earth

It is still uncertain how the first minimal cellular systems evolved to the complexity required for life to begin, but it is obvious that the role of amphiphilic compounds in the origin of life is one of huge relevance. Over the last four decades a number of studies have demonstrated how amphiphilic molecules can be synthesized under plausibly prebiotic conditions. The majority of these experiments also gave evidence for the ability of so formed amphiphiles to assemble in closed membranes of vesicles that, in principle, could have compartmented first biological processes on early Earth, including the emergence of self-replicating systems. For a competitive selection of the best performing molecular replicators to become operative, some kind of bounded units capable of harboring them are indispensable. Without the competition between dynamic populations of different compartments, life itself could not be distinguished from an otherwise disparate array or network of molecular interactions. In this review, we describe experiments that demonstrate how different prebiotically-available building blocks can become precursors of phospholipids that form vesicles. We discuss the experimental conditions that resemble plausibly those of the early Earth (or elsewhere) and consider the analytical methods that were used to characterize synthetic products. Two brief sections focus on phosphorylating agents, catalysts and coupling agents with particular attention given to their geochemical context. In Section 5, we describe how condensing agents such as cyanamide and urea can promote the abiotic synthesis of phospholipids. We conclude the review by reflecting on future studies of phospholipid compartments, particularly, on evolvable chemical systems that include giant vesicles composed of different lipidic amphiphiles.

Complementary amphiphilic ribonucleotides confined into nanostructured environments

This article focuses on the physico-chemical investigation of the time evolution of self-assembled structures composed by oppositely charged surfactant monomers. The cationic components were represented by the well known cetyl-trimethyl-ammonium-bromide (CTAB) while the anionic monomers consisted of amphiphilic ribonucleotide derivatives, also called nucleo-lipids (NL). The latter were generated in situ by direct reaction between a hydrophobic precursor, dodecyl epoxide (DE), and a pair of complementary ribonucleotide mono-phosphates: adenosine mono-phosphate (AMP) and uridine mono-phosphate (UMP). Analysis of reaction mixtures by liquid chromatography-electrospray ionization-single, tandem and sequential mass spectrometry (LC-ESI-MS, MS/MS and MS(3)) confirmed that the generated NL corresponded to ribonucleotides linked to one, two and even three hydroxy-dodecyl tails on their molecular structures and whose amounts had peculiar time dependences. In the solutions incubated with an equimolar mixture of both types of ribonucleotides, a remarkable positive feedback effect on the reaction products was ascribed to the contemporary presence of AMP and UMP. The variation of aggregate sizes, due to the incorporation process of NL monomers into starting CTAB micelles, was monitored through time-resolved measurements of both dynamic light-scattering (DLS) and electrophoretic mobilities, together with calculated zeta-(zeta)-potential. Finally, a kinetic model based on auto-catalytic mechanisms was outlined to analyze the process of the catanionic vesicles growth observed during the whole reaction time-course. The model was also in good agreement with MS data. The proposed colloidal system may be considered a simplified model whereby to study the potential role of complementary nucleic bases in triggering primitive chemical selections.

Alkylation of complementary ribonucleotides by 1,2-dodecyl-epoxide in a micellar environment: a liquid chromatography-electrospray ionization-sequential mass spectrometry investigation

Alkylation of a pair of complementary ribonucleotides, adenosine monophosphate (AMP) and uridine monophosphate (UMP), was accomplished by 1,2-dodecyl-epoxide (DE) in a oil-in-water microemulsion based on the cationic surfactant Cetyl-trimethyl-ammonium-bromide, providing a suitable catalytic interface for the reagents. Several, often isomeric, alkylation products, bearing one or two hydroxy-dodecyl moieties on their structures, were identified in the reaction mixtures by high-performance liquid chromatography coupled to electrospray ionization ion trap mass spectrometry. In particular, mass spectrometry (MS)/MS spectra, implemented by extracted ion chromatograms obtained for peculiar MS/MS product ions, indicated alkylation to occur on uracil and on uracil/phosphate OH groups in singly and doubly alkylated UMP, respectively. Adenine NH2 group and phosphate or ribose OH groups were found to be involved as such (single alkylation) or in combination, in the case of alkylated derivatives of AMP. The reaction of both endocyclic N and C=O groups (tautomerized to C-OH groups) of uracil and the predominance of nucleophilic attack to the more accessible carbon of the DE epoxydic bridge (the only exception being the reaction by the NH2 group of adenine) were inferred from MS3 spectra with the help of extracted ion chromatograms for specific fragment ions, after their structural characterization. Interestingly, alkylation on one of the uracil C=O groups and, partially, on the adenine NH2 group, both potentially involved in AMP/UMP base pairing in the micellar environment, were found to be hindered when both ribonucleotides were present in the reaction mixtures.

Reaction mixtures based on the CTAB-Dodecyl Epoxide-water microemulsion for the synthesis of novel Nucleo-Lipids

Nucleotide-functionalized amphiphiles can be generated in an aqueous microemulsion based on the cationic surfactant CetylTrimethylAmmonium Bromide (CTAB). The lipophilic precursor, Dodecyl Epoxide (DE), was able to hydrophobically modify several types of nucleotides (NMPs) giving rise to the production of novel anionic Nucleo-Lipids (NL), through a ring-opening reaction occurring at level of the CTAB micellar interface. The coexistence of both cationic (CTAB) and NL monomers triggered the spontaneous formation of aqueous suspensions of onion-like aggregates, as confirmed by optical microscopy and spectroturbidimetry. The solubilization process of DE into CTAB micellar phase in the presence of NMPs was first characterised through conductometry. DLS data showed a gradual micellar swelling resulting in a higher oil uptake upon addition of NMPs in the starting liquid L(1) phase. An important result achieved in this study was obtained through the inspection of long-aged suspensions incubated with each of four different types of NMPs, including their binary equimolar combinations. Samples made with the complementary pairs AU and CG showed up very stable vesicular systems, unlike the other random base paired mixtures, where we found a coexistence of liquid crystalline domains in equilibrium with either transparent liquid phases or dense isotropic gel phases. The potential role of the molecular recognition on the self-assembly properties of NL monomers has been discussed.

Primordial soup, fool's gold, and spontaneous generation: A brief introduction to the theory, history, and philosophy of the search for the origin of life

This study provides a concise background to the biochemical search for the origin of life, as grounded in the field of prebiotic chemistry. It is intended to provide a good summary of competing theories and place them in a broader context, raising questions about weaknesses in any particular theory. This material is relevant for science educators at all levels, and will stimulate interest in a wide variety of students.

Catanionic systems from conversion of nucleotides into nucleo-lipids

This article focuses on reactions performed in nanostructured environments where the pair of complementary nucleotides, 5'-AMP and 5'-UMP, are converted into their amphiphilic derivatives. The synthesis is carried out by using the hydrophobic reactant dodecyl epoxide (DE) dispersed in a micellar solution based on the cationic surfactant cetyltrimethylammoniumbromide (CTAB). Novel nucleo-lipids monomers and CTAB molecules give rise to the spontaneous self-assembly of catanionic supramolecular structures in water, showing typical Maltese crosses in optical microscopy. In the final colloidal suspensions, mono- and dichained derivatives have been identified in the system incubated with 5'-UMP through LC-QqTOF-MS analysis, whereas only mono-alkylated adducts are found in the analogue reaction with 5'-AMP. A new di-alkylated 5'-UMP adduct is obtained from the 1:1 mixture of both complementary nucleotides, in addition to the nucleo-lipids found in separate systems. Time-resolved DLS measurements reveal very different kinetic processes for aggregates' formation when 5'-UMP, 5'-AMP, or their equimolar combination are used in the reaction mixture. This system as a whole represents a potential experimental model where the effect of both intermolecular interactions and self-association processes can be investigated by tuning the type of nucleobases in the reaction mixtures.

Nucleotides and nucleolipids derivatives interaction effects during multi-lamellar vesicles formation

In this paper a micellar interface, constituted by the cationic surfactant CTAB, in presence of 1,2-epoxydodecane and nucleotides was used for catanionic multi-lamellar vesicles (MLVs) formation. The micellar solution of CTAB is able to disperse the 1,2 epoxydodecane in the micellar core promoting the reaction of this reagent with the nucleotide attracted by the positive surface charge of the micellar aggregates. The alkylation of AMP and UMP nucleotides leads to the synthesis of nucleolipids. The behaviour of the supramolecular structures formed depends on the starting reagents (AMP, UMP and AMP+UMP) and on the assembly capabilities of the products. In particular nucleotides and nucleotides derivatives interaction effects are evaluated during the multi-lamellar vesicles formation. NMR spectroscopy and UV-vis measurements performed on MLVs showed strong aryl interactions. Interestingly, NMR spectra revealed prevailing stacking interactions between complementary nucleolipids. The assembly of complementary nucleotides affects the course of the reaction during the MLVs formation. Moreover the MLVs supramolecular stability has been tested by means of turbidity and UV-vis measurements. In particular, an enhanced stability has been found in systems prepared with complementary nucleotides confirming that in these systems the self-assembly process is influenced by nucleolipids interactions. Furthermore by following the hypocromic effect during the micellar catalysis, we showed that even in the earlier stages of the reaction significant differences are detectable.

Surfactant assemblies and their various possible roles for the origin(s) of life

A large number of surfactants (surface active molecules) are chemically simple compounds that can be obtained by simple chemical reactions, in some cases even under presumably prebiotic conditions. Surfactant assemblies are self-organized polymolecular aggregates of surfactants, in the simplest case micelles, vesicles, hexagonal and cubic phases. It may be that these different types of surfactant assemblies have played various, so-far underestimated important roles in the processes that led to the formation of the first living systems. Although nucleic acids are key players in the formation of cells as we know them today (RNA world hypothesis), it is still unclear how RNA could have been formed under prebiotic conditions. Surfactants with their self-organizing properties may have assisted, controlled and compartimentalized some of the chemical reactions that eventually led to the formation of molecules like RNA. Therefore, surfactants were possibly very important in prebiotic times in the sense that they may have been involved in different physical and chemical processes that finally led to a transformation of non-living matter to the first cellular form(s) of life. This hypothesis is based on four main experimental observations: (i) Surfactant aggregation can lead to cell-like compartimentation (vesicles). (ii) Surfactant assemblies can provide local reaction conditions that are very different from the bulk medium, which may lead to a dramatic change in the rate of chemical reactions and to a change in reaction product distributions. (iii) The surface properties of surfactant assemblies that may be liquid- or solid-like, charged or neutral, and the elasticity and packing density of surfactant assemblies depend on the chemical structure of the surfactants, on the presence of other molecules, and on the overall environmental conditions (e. g. temperature). This wide range of surface characteristics of surfactant assemblies may allow a control of surface-bound chemical reactions not only by the charge or hydrophobicity of the surface but also by its "softness". (iv) Chiral polymolecular assemblies (helices) may form from chiral surfactants. There are many examples that illustrate the different roles and potential roles of surfactant assemblies in different research areas outside of the field of the origin(s) of life, most importantly in investigations of contemporary living systems, in nanotechnology applications, and in the development of drug delivery systems. Concepts and ideas behind many of these applications may have relevance also in connection to the different unsolved problems in understanding the origin(s) of life.

Did life begin on the beach?

Water is one of the prerequisites of life. Further requirements are the existence of a system of interacting organic molecules capable of capturing and converting the supply of external energy and elaborating the replicating function that is needed for propagation. None of this would be possible without the existence of some means of concentrating, selecting, and then containing these mutually interacting substances in proximity to one another, i.e., a primitive cell. Starting from this hypothesis we propose a model for the development of life on Earth. Our model embodies the following new features: (1) rapid cycles of catalysis and transport of material, (2) desegregation (separation by tidal action and degradation by catalysis) as well as segregation (by chromatography on tidal beaches), (3) cross-catalysis instead of auto-catalysis, as well as (4) compartmentalization, although the latter idea is of course not new. But our "lipid first" model, in contrast to earlier "peptide first" or "RNA first" models, provides for the compartments needed to act as a cradle for the subsequent development of information- rich molecules like peptides and RNA. If anything, the earliest information-rich molecules were probably membrane-spanning peptides/proteins.

Monolayer studies of single-chain polyprenyl phosphates

The monolayer properties of some single-chain polyprenyl phosphates (phytanyl, phytyl, and geranylgeranyl phosphates), which we regard as hypothetical primitive membrane lipids, were investigated at the air-water interface by surface pressure-area (pi-A) isotherm measurements. The molecular area/ pressure at various pH conditions dependence revealed the acid dissociation constants (pKa values) of the phosphate. The pKa values thus obtained at the air-water interface (pKa1 = 7.1 and pKa2 = 9.4 for phytanyl phosphate) were significantly shifted to higher pH than those observed in the bilayer state in water (pKa1 = 2.9 and pKa2 = 7.8). The difference in pKa values leads to a stability of the phosphate as both monolayer and bilayer states in a pH range of 2-6. In addition, the presence of ions such as sodium, magnesium, calcium, and lanthanum in the subphase significantly altered the stability of the polyprenyl phosphate monolayers, as shown by the determination of monolayer collapse and compression/expansion hysteresis. Although sodium ions in the subphase showed only a weak effect on the stabilization of the monolayer, addition of magnesium ions or of a small amount of calcium ions significantly suppressed the dissolution of the monolayer into the subphase and increased its mechanical stability against collapse. In contrast, the presence of larger amounts of calcium or of lanthanum ions induced collapse of the monolayers. Based on these experimental facts, a plausible scenario for the formation of primitive cell membrane by transformation of a monolayer to vesicle structures is proposed.