Search

Aminomalononitrile (AMN), the HCN formal trimer, is a molecule of interest in prebiotic chemistry, in fine organic synthesis, and, currently, in materials science, mainly for bio-applications. Herein, differential scanning calorimetry (DSC) measurements by means of non-isothermal experiments of the stable AMN p-toluenesulfonate salt (AMNS) showed successful bulk AMN polymerization. The results indicated that this thermally stimulated polymerization is initiated at relatively low temperatures, and an autocatalytic kinetic model can be used to appropriately describe, determining the kinetic triplet, including the activation energy, the pre-exponential factor, and the mechanism function (Eα, A and f(α)). A preliminary structural characterization, by means of Fourier transform infrared (FTIR) spectroscopy, supported the effective generation of HCN-derived polymers prepared from AMNS. This study demonstrated the autocatalytic, highly efficient, and straightforward character of AMN polymerization, and to the best of our knowledge, it describes, for the first time, a systematic and extended kinetic analysis for gaining mechanistic insights into this process. The latter was accomplished through the help of simultaneous thermogravimetry (TG)-DSC and the in situ mass spectrometry (MS) technique for investigating the gas products generated during these polymerizations. These analyses revealed that dehydrocyanation and deamination processes must be important elimination reactions involved in the complex AMN polymerization mechanism. [ABSTRACT FROM AUTHOR]

For the first time, chemometrics was applied to the recently reported microwave-driven cyanide polymerization. Fast, easy, robust, low-cost, and green-solvent processes are characteristic of these types of reactions. These economic and environmental benefits, originally inspired by the constraints imposed by plausible prebiotic synthetic conditions, have taken advantage of the development of a new generation of HCN-derived multifunctional materials. HCN-derived polymers present tunable properties by temperature and reaction time. However, the apparently random behavior observed in the evolution of cyanide polymerizations, assisted by microwave radiation over time at different temperatures, leads us to study this highly complex system using multivariate analytical tools to have a proper view of the system. Two components are sufficient to explain between 84 and 98% of the total variance in the data in all principal component analyses. In addition, two components explain more than 91% of the total variance in the data in the case of principal component analysis for categorical data. These consistent statistical results indicate that microwave-driven polymerization is a more robust process than conventional thermal syntheses but also that plausible prebiotic chemistry in alkaline subaerial environments could be more complex than in the aerial part of these systems, presenting a clear example of the "messy chemistry" approach of interest in the research about the origins of life. In addition, the methodology discussed herein could be useful for the data analysis of extraterrestrial samples and for the design of soft materials, in a feedback view between prebiotic chemistry and materials science. [ABSTRACT FROM AUTHOR]

Herein, the potential of alkaline hydrothermal environments for the synthesis of possible ancestral pre-RNA nucleobases using cyanide as a primary source of carbon and nitrogen is described. Water cyanide polymerizations were assisted by microwave radiation to obtain high temperature and a relatively high pressure (MWR, 180 °C, 15 bar) and were also carried out using a conventional thermal system (CTS, 80 °C, 1 bar) to simulate subaerial and aerial hydrothermal conditions, respectively, on the early Earth. For these syntheses, the initial concentration of cyanide and the diffusion effects were studied. In addition, it is well known that hydrolysis conditions are directly related to the amount and diversity of organic molecules released from cyanide polymers. Thus, as a first step, we studied the effect of several hydrolysis procedures, generally used in prebiotic chemistry, on some of the potential pre-RNA nucleobases of interest, together with some of their isomers and/or deamination products, also presumably formed in these complex reactions. The results show that the alkaline hydrothermal scenarios with a relatively constant pH are good geological scenarios for the generation of noncanonical nucleobases using cyanide as a prebiotic precursor. [ABSTRACT FROM AUTHOR]

HCN polymers are a group of complex and heterogeneous substances that are widely known in the fields of astrobiology and prebiotic chemistry. In addition, they have recently received considerable attention as potential functional material coatings. However, the real nature and pathways of formation of HCN polymers remain open questions. It is well established that the tuning of macromolecular structures determines the properties and practical applications of a polymeric material. Herein, different synthetic conditions were explored for the production of HCN polymers from NH4CN or diaminomaleonitrile in aqueous media with different concentrations of the starting reactants and several reaction times. By using a systematic methodology, both series of polymers were shown to exhibit similar, but not identical, spectroscopic and thermal fingerprints, which resulted in a clear differentiation of their morphological and electrochemical properties. New macrostructures are proposed for HCN polymers, and promising insights are discussed for prebiotic chemistry and materials science on the basis of the experimental results. [ABSTRACT FROM AUTHOR]

The influence of the reaction conditions in the synthesis of HCN polymers in water at low temperature has been analyzed. The thermal stability of the HCN polymers obtained from aqueous solutions and under inert atmosphere was evaluated by thermogravimetry and differential scanning calorimetry (TG-DSC) techniques. In addition, in situ mass spectrometry (MS) was employed to investigate the characteristic functional groups of the decomposition residues at different temperatures. The structural complexity of this polymeric solid is reflected in the DTG curves, hence a peak deconvolution procedure was applied. The deconvolution revealed that the complex thermal decomposition of HCN samples occurs in multiple overlapping processes, not perceptible in the curves of weight loss, which were influenced by the differences in the polymerization conditions. In addition, the great molecular diversity found in this macromolecular system is also maintained in the DSC thermograms. The deconvolution of the DTG curves provided a strong fingerprint of the HCN polymers together with the DSC as a complementary mark. Although the full structures of the HCN polymers are not yet revealed, the deconvolution of the thermal curves provides an excellent signature for comparative purposes. The profile of the DTG and DSC curves can not only help design HCN polymers with specific properties but also help interpret remote-sensing observations of comets, meteorites and samples from different planetary environments. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a thermogravimetry (TG) study of hydrogen cyanide polymers, synthesized from the reaction of equimolar aqueous solutions of sodium cyanide and ammonium chloride. Differential thermal analysis (DTA) and differential scanning calorimetry (DSC) were also used to evaluate the thermal behaviour of these black polymers, which play an important role in prebiotic chemistry. A coupled TG–mass spectrometer (MS) system allowed us to analyze the principal volatile thermal decomposition and fragmentation products of the isolated HCN polymers under dynamic conditions and an inert atmosphere. After dehydration, a multi-step decomposition occurred in this particular polymeric system, due to the release of ammonia, hydrogen cyanide (depolymerization reaction), isocyanic acid (or cyanic acid) and formamide; these two latter species allow us identify bond connectivities. Finally, data collected from TG experiments in an oxidative atmosphere showed significant differences at higher temperatures, above 400 °C. According to these results, the different techniques of thermal analysis here applied have demonstrated to be an adequate methodology for the study and characterization of this complex macromolecular system, whose structure remains controversial even today. [Copyright &y& Elsevier]

[Display omitted] • Prebiotic chemistry inspires polymeric materials with advanced performances. • The electrochemistry characteristic of DAMN polymer has been explored. • These DAMN polymers may be potentially applied as non-enzymatic peroxide sensor. • Structural, thermal and morphological properties of DAMN polymers were analysed. • DSC-MS analysis during DAMN bulk polymerization revealed several elimination processes. HCN-derived polymers have recently attracted considerable attention due to their promising applications as multifunctional materials. This study, inspired by plausible early Earth geochemical conditions, describes a strategy to synthesize them from the self-initiated thermal bulk polymerization of the HCN tetramer, diaminomaleonitrile (DAMN), with outstanding sensing properties. These conjugated polymers were obtained through noncatalysed and simple isothermal reactions at 170 °C in the solid-state, and experiments at 190 °C permitted polymerization in the melt. Both processes are highly efficient, allowing quantitative yields of the end products. The conductivity properties of both polymers have been explored to show their high potential, especially DAMN polymers synthesized in melt, as nonenzymatic peroxide sensors. To better understand the differences found between the two series, structural characterisation was carried out using compositional data, Fourier transform infrared (FTIR), nuclear magnetic resonance (NMR) and X-ray photoelectron (XPS) spectroscopies, and X-ray diffraction (XRD) measurements. The interpretation of the structural data suggests that a two-dimensional (2-D) macrostructure based on N-heterocyclics is predominant regardless of the state of monomer aggregation during the course of polymerization, but preferably formed in the melt. The morphological and thermal stability properties of the polymers based on DAMN were also evaluated. Finally, the most likely mechanisms based on the dehydrocyanation and deamination reactions that take place during the polymerization reaction are proposed. This study demonstrates the robust and straightforward character of these thermally activated polymerizations, which are of interest to chemical evolution research and to current materials and surface science. [ABSTRACT FROM AUTHOR]

Hydrogen cyanide, HCN, is considered a fundamental molecule in chemical evolution. The named HCN polymers have been suggested as precursors of important bioorganics. Some novel researches have focused on the role of mineral surfaces in the hydrolysis and/or polymerization of cyanide species, but until now, their role has been unclear. Understanding the role of minerals in chemical evolution processes is crucial because minerals undoubtedly interacted with the organic molecules formed on the early Earth by different process. Therefore, we simulated the probable interactions between HCN and a serpentinite-hosted alkaline hydrothermal system. We studied the effect of serpentinite during the thermolysis of HCN at basic conditions (i.e., HCN 0.15 M, 50 h, 100 °C, pH > 10). The HCN-derived thermal polymer and supernatant formed after treatment were analyzed by several complementary analytical techniques. The results obtained suggest that: (I) the mineral surfaces can act as mediators in the mechanisms of organic molecule production such as the polymerization of HCN; (II) the thermal and physicochemical properties of the HCN polymer produced are affected by the presence of the mineral surface; and (III) serpentinite seems to inhibit the formation of bioorganic molecules compared with the control (without mineral). [ABSTRACT FROM AUTHOR]

The solid-state polymerization (SSP) of organic molecules to form two-dimensional (2D) materials remains a challenge, especially when these reactions are performed in one pot using a single reagent. As will be shown, the SSP of the HCN tetramer diaminomaleonitrile (DAMN) may be an excellent example of these reactions. Dynamic experiments by differential scanning calorimetry (DSC) allow the analysis of the thermally initiated bulk polymerization of DAMN. Under nonisothermal measurements at low heating rates, a multiple-step polymerization reaction takes place. The SSP of DAMN is highly efficient, possibly due to the autocatalytic nature of its kinetics, which are consistent with the two-parameter Šesták-Berggren (SB) model and describe the three stages found in its complicated mechanism, confirmed also from an analysis of the variation in the apparent activation energy with the conversion degree. Relevant mechanistic aspects, such as the dehydrocyanation and deamination processes during SSP, are extracted by thermogravimetry-mass spectrometry (TG-MS). Moreover, some structural and morphological properties of these materials are characterized by Fourier-transform infrared (FTIR) spectroscopy and microscopy. All this information allows us to propose hypothetical pathways for the production of a complex conjugated system, predominantly constituted by a 2D macrostructure based on imidazole rings. This work opens up new possibilities for the synthesis of functional poly(heterocycle) systems, expanding our view of a plausible prebiotic chemical reaction space and providing the foundation for systematic studies of the structure-property relationships of novel HCN-derived polymers, which are currently of great interest in the fields of materials and surface science. [Display omitted] • Kinetic and the mechanism for the solid-state polymerization of DAMN was studied. • Šesták-Berggren model can describe these solid-state polymerizations monitoring by DSC. • Structural and morphological properties of DAMN polymers were analysed. • DAMN polymers may be potentially applied as multi-functional materials. [ABSTRACT FROM AUTHOR]

Hydrogen cyanide (HCN)-derived polymers have been recognized as sources of relevant organic molecules in prebiotic chemistry and material sciences. However, there are considerable gaps in the knowledge regarding the polymeric nature, the physicochemical properties, and the chemical pathways along polymer synthesis. HCN might have played an important role in prebiotic hydrothermal environments; however, only few experiments use cyanide species considering hydrothermal conditions. In this work, we synthesized an HCN-derived thermal polymer simulating an alkaline hydrothermal environment (i.e., HCN (l) 0.15 M, 50 h, 100 °C, pH approximately 10) and characterized its chemical structure, thermal behavior, and the hydrolysis effect. Elemental analysis and infrared spectroscopy suggest an important oxidation degree. The thermal behavior indicates that the polymer is more stable compared to other HCN-derived polymers. The mass spectrometric thermal analysis showed the gradual release of several volatile compounds along different thermal steps. The results suggest a complicate macrostructure formed by amide and hydroxyl groups, which are joined to the main reticular chain with conjugated bonds (C=O, N=O, –O–C=N). The hydrolysis treatment showed the pH conditions for the releasing of organics. The study of the synthesis of HCN-derived thermal polymers under feasible primitive hydrothermal conditions is relevant for considering hydrothermal vents as niches of chemical evolution on early Earth. [ABSTRACT FROM AUTHOR]

• Kinetic, structural characteristics and the mechanism for the formation of DAMN polymers was studied. • Šesták-Berggren model can successfully describe these melt polymerizations. • TG-DSC-MS analysis of DAMN revealed thermal processes during its bulk polymerization. • Prebiotic chemistry inspires polymeric materials with advanced performances. • These DAMN polymers may be potentially applied as multi-functional materials. HCN polymers are of great interest in research on the origin of life and, currently, in materials science because they have shown potential for the design of electrical devices, (photo)catalysts and biomedicine. Herein, calorimetric measurements have successfully described the bulk polymerization of HCN tetramer, diaminomaleonitrile (DAMN). Two series of nonisothermal experiments were carried out by differential scanning calorimetry (DSC), and low-heating rate (β) the thermograms (β ≤ 5 °C/min) indicated that the polymerization is initiated at temperatures lower than the DAMN melting point, ~180 °C; while higher heating rates results in a rapid polymerization reaction, which occurs entirely in the liquid phase. The DSC data were analysed using model-free linear iso-conversional methods to estimate kinetic parameters, such as activation energy, and a suitable kinetic model was proposed for these thermal polymerizations in the melt. A preliminary structural and morphological characterization by means of Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) was also completed. This study demonstrated the autocatalytic, highly efficient and straightforward character of this stimulated thermal polymerization of DAMN and, to the best of our knowledge, describes for the first time a systematic and extended kinetic analysis to gain mechanistic insights into this process. The latter was done through the help of simultaneous thermogravimetry (TG)-DSC and in situ mass spectrometry (MS) technique to investigate the gas products generated during these melt polymerizations. These analyses revealed that deamination and dehydrocyanation processes are two relevant reactions involved in DAMN polymerization mechanism. [ABSTRACT FROM AUTHOR]

• Temperature has a significant effect on the nature of NH 4 CN polymers. • Autocatalytic or n th order kinetic is conditioned by temperature for NH 4 CN polymerization. • The kinetic behaviour of the NH 4 CN polymerization presents diffusion limitations. • A reliable value for the activation energy of NH 4 CN polymerization has been obtained. Herein, a kinetic analysis for aqueous NH 4 CN polymerizations is presented, which is consistent with an autocatalytic model when polymerizations are performed at relatively high temperatures, 80–90 °C. Further experiments at lower polymerization temperatures, approximately 50 °C, have demonstrated that this relevant prebiotic reaction follows n th-order kinetics rather than an autocatalytic mechanism. In addition, the sol fractions of these precipitation polymerizations have been evaluated by UV–Vis measurements, which also show a mechanistic shift with the reaction temperature. This change in the kinetic behaviour led to the proposal of a simple empirical methodology to describe both chemical- and diffusion-controlled regions. Despite the simplicity of the approach based on the Hill equation, fundamental kinetic parameters, such as the activation energy, can be determined in the diffusion-free zone. These results motivated a systematic structural characterization study of the respective insoluble polymers by means of elemental analysis, FT-IR and NMR spectroscopies and XRD. All these kinetic and structural analyses confirmed that the temperature has a significant effect on the polymerization kinetic of the system, on the macrostructural features and properties of the HCN-based polymers, and presumably also on the polymerization pathways. These data increase our knowledge about the chemistry of this particular family of HCN polymers, which is currently of interest both in the field of materials science and in prebiotic chemistry and astrobiology. [ABSTRACT FROM AUTHOR]