Infrared Spectroscopy of RNA Nucleosides in a Wide Range of Temperatures.

The RNA world hypothesis suggests that early cellular ancestors relied solely on RNA molecules for both genetic information storage and cellular functions. RNA, composed of four nucleosides-adenosine, guanosine, cytidine, and uridine-forms the basis of this theory. These nucleosides consist of purine nucleobases, adenine and guanine, and pyrimidine nucleobases, cytosine and uracil, bonded to ribose sugar. Notably, carbonaceous chondrite meteorites have revealed the presence of these bases and sugar, hinting at the potential existence of nucleosides in space. This study aims to present the infrared spectra of four RNA nucleosides commonly found in terrestrial biochemistry, facilitating their detection in space, especially in astrobiological and astrochemical contexts. Laboratory measurements involved obtaining mid- and far-IR spectra at three temperatures (-180 °C, room temperature, and +180 °C), followed by calculating molar extinction coefficients (ε) and integrated molar absorptivities (ψ) for corresponding bands. These spectral data, along with ε and ψ values, serve to provide quantitative insights into the presence and relative abundance of nucleosides in space and aid in their detection.

Thermochemistry of Sulfur-Based Vulcanization and of Devulcanized and Recycled Natural Rubber Compounds.

The vulcanization of rubber compounds is an exothermal process. A carbon black-filled and natural rubber-based (NR) formulation was mixed with different levels of sulfur (0.5, 1.0, 2.0, 4.0 and 6.0 phr) and studied with differential scanning calorimetry (DSC) for the determination of the vulcanization enthalpy. It was found that the vulcanization enthalpy is dependent on the amount of sulfur present in the compound and the vulcanization heat released was -18.4 kJ/mol S if referred to the entire rubber compound formulation or -46.0 kJ/mol S if the heat released is referred only to the NR present in the compound. The activation energy for the vulcanization of the rubber compounds was also determined by a DSC study at 49 kJ/mol and found to be quite independent from the sulfur content of the compounds under study. A simplified thermochemical model is proposed to explain the main reactions occurring during the vulcanization. The model correctly predicts that the vulcanization is an exothermal process although it gives an overestimation of the vulcanization enthalpy (which is larger for the EV vulcanization package and smaller for the conventional vulcanization system). If the devulcanization is conducted mechanochemically in order to break selectively the sulfur-based crosslinks, then the natural rubber compounds recovered from used tires can be re-vulcanized again and the exothermicity of such process can be measured satisfactorily with DSC analysis. This paper not only proposes a simplified mechanism of vulcanization and devulcanization but also proposes an analytical method to check the devulcanization status of the recycled rubber compound in order to distinguish truly devulcanized rubber from reclaimed rubber.

Integrated Molar Absorptivity of Mid- and Far-Infrared Spectra of Alanine and a Selection of Other Five Amino Acids of Astrobiological Relevance.

Alanine and other five proteinogeninc amino acids produced quite easily in exogenous and/or endogenous prebiotic processes, that is, valine, serine, proline, glutamic acid, and aspartic acid (Ala, Val, Ser, Pro, Glu, and Asp, respectively) were studied in the mid- and far-infrared spectral range. This work is an extension of the previous one where other proteinogenic amino acids glycine, isoleucine, phenylalanine, tyrosine, and tryptophan (Gly, Ile, Phe, Tyr, and Trp, respectively) were studied in the mid-infrared and in the far-infrared with the purpose to facilitate the search and identification of these astrobiological and astrochemical relevant molecules in space environments. The molar extinction coefficients (ɛ) of all mid- and far-infrared bands were determined as well as the integrated molar absorptivities (ψ). The mid-infrared spectra of Ala, Val, Ser, Pro, Glu, and Asp were recorded also at three different temperatures from -180°C to nearly ambient temperature and at 200°C. With the reported values of ɛ and ψ, it will be possible to estimate the relative abundance of these molecules in space environments.

Integrated Molar Absorptivity of Mid- and Far-Infrared Spectra of Glycine and Other Selected Amino Acids.

A selection of five proteinogenic amino acids-glycine, isoleucine, phenylalanine, tyrosine, and tryptophan-were studied in the mid-infrared and in the far-infrared with the purpose to facilitate the search and identification of these astrobiologically and astrochemically relevant molecules in space environments. The molar extinction coefficients (ɛ) of all mid- and far-infrared bands were determined as well as the integrated molar absorptivities (ψ). The mid-infrared spectra of the five selected amino acids were recorded also at three different temperatures from -180°C to ambient temperature to +200°C. We measured the wavelength shift of the infrared bands caused by temperature; and for the most relevant or temperature-sensitive infrared bands, a series of linear equations were determined relating wavelength position with temperature. Such equations may provide estimates of the temperature of these molecules once detected in astrophysical objects; and with the reported values of ɛ and ψ, it will be possible to estimate the relative abundance of these molecules in space environments.

On the Optical Activity of Poly(L-Lactic Acid) (PLLA) Oligomers and Polymer: Detection of Multiple Cotton Effect on Thin PLLA Solid Film Loaded with Two Dyes.

Optical rotatory dispersion (ORD) is a beautiful analytical technique for the study of chiral molecules and polymers. In this study, ORD was applied successfully to follow the degree of polycondensation of l-(+)-lactic acid toward the formation of poly(lactic acid) oligomers (PLAO) and high molecular weight poly(L-lactic acid) (PLLA) in a simple esterification reaction equipment. PLLA is a biodegradable polymer obtainable from renewable raw materials. The racemization of the intrinsically isotactic PLLA through thermal treatment can be easily followed through the use of ORD spectroscopy. Organic or molecular electronics is a hot topic dealing with the combination of π-conjugated organic compounds and polymers with specific properties (e.g., chirality) which can be exploited to construct optoelectronic devices, such as organic light-emitting diodes (OLEDs), organic photovoltaic (OPV) high efficiency cells, switchable chirality devices, organic field-effect transistors (OFETs), and so on. ORD spectroscopy was applied to study either the gigantic optical rotation of PLLA films, as well as to detect successfully the excitonic coupling, occurring in thin solid PLLA green film loaded with a combination of two dyes: SY96 (a pyrazolone dye) and PB16 (the metal-free phthalocyanine pigment). The latter compound PLLA loaded with SY96 and PB16 shows a really gigantic optical activity in addition to typical ORD signal due to exciton coupling and may be considered as a simple and easily accessible model composite of a chiral polymer matrix combined with π-conjugated dyes for molecular electronics studies.

Fullerene Radiolysis in Astrophysical Ice Analogs: A Mass Spectrometric Study of the Products.

The γ-radiolysis of fullerenes (C60 and C70) was performed to investigate the role of fullerenes as a carbon source in building organic molecules in astrophysical ice analog media. Mass spectrometric analyses and the sequential collision-induced dissociation processes enabled us to determine the plausible chemical structure of new products originated during γ-irradiation of fullerenes. The radiolytic products are grouped into six principal compound families. We assessed the relative yield, as percentage, for each new radiolytic compound, and designed the reaction schemes that lead to γ-irradiation products. The reactions start with the formation of primary radicals due to the radiolysis of solvents that react with the fullerenes' structures, forming fullerene radical adducts. The fate of these fullerene radical adducts depends on two factors: (i) the nature of radicals formed by irradiation of solvents and consequently by their ability to give secondary reactions, (ii) whether the onset of thermalization energy processes occurs or does not occur. Here, we present the results regarding the fragmentation processes that lead to functionalized carbonaceous chains characterized by lower molecular weight. We identify the chemical nature of functionalized chain products, propose the reaction schemes, and quantify their relative yields.

Raman spectroscopy as a tool to investigate the structure and electronic properties of carbon-atom wires.

Graphene, nanotubes and other carbon nanostructures have shown potential as candidates for advanced technological applications due to the different coordination of carbon atoms and to the possibility of π-conjugation. In this context, atomic-scale wires comprised of sp-hybridized carbon atoms represent ideal 1D systems to potentially downscale devices to the atomic level. Carbon-atom wires (CAWs) can be arranged in two possible structures: a sequence of double bonds (cumulenes), resulting in a 1D metal, or an alternating sequence of single-triple bonds (polyynes), expected to show semiconducting properties. The electronic and optical properties of CAWs can be finely tuned by controlling the wire length (i.e., the number of carbon atoms) and the type of termination (e.g., atom, molecular group or nanostructure). Although linear, sp-hybridized carbon systems are still considered elusive and unstable materials, a number of nanostructures consisting of sp-carbon wires have been produced and characterized to date. In this short review, we present the main CAW synthesis techniques and stabilization strategies and we discuss the current status of the understanding of their structural, electronic and vibrational properties with particular attention to how these properties are related to one another. We focus on the use of vibrational spectroscopy to provide information on the structural and electronic properties of the system (e.g., determination of wire length). Moreover, by employing Raman spectroscopy and surface enhanced Raman scattering in combination with the support of first principles calculations, we show that a detailed understanding of the charge transfer between CAWs and metal nanoparticles may open the possibility to tune the electronic structure from alternating to equalized bonds.

Chemical and thermochemical aspects of the ozonolysis of ethyl oleate: decomposition enthalpy of ethyl oleate ozonide.

Neat ethyl oleate was ozonized in a bubble reactor and the progress of the ozonolysis was followed by infrared (FT-IR) spectroscopy and by the differential scanning calorimetry (DSC). The ozonolysis was conducted till a molar ratio O3/C=C≈1 when the exothermal reaction spontaneously went to completion. A specific thermochemical calculation on ethyl oleate ozonation has been made to determine the theoretical heat of the ozonization reaction using the group increment approach. A linear relationship was found both in the integrated absorptivity of the ozonide infrared band at 1110 cm(-1) and the ozonolysis time as well as the thermal decomposition enthalpy of the ozonides and peroxides formed as a result of the ozonation. The DSC decomposition temperature of ozonated ethyl oleate occurs with an exothermal peak at about 150-155 °C with a decomposition enthalpy of 243.0 kJ/mol at molar ratio O3/C=C≈1. It is shown that the decomposition enthalpy of ozonized ethyl oleate is a constant value (≈243 kJ/mol) at any stage of the O3/C=C once an adequate normalization of the decomposition enthalpy for the amount of the adsorbed ozone is taken into consideration. The decomposition enthalpy of ozonized ethyl oleate was also calculated using a simplified thermochemical model, obtaining a result in reasonable agreement with the experimental value.

Far infrared (terahertz) spectroscopy of a series of polycyclic aromatic hydrocarbons and application to structure interpretation of asphaltenes and related compounds.

A series of 33 different polycyclic aromatic hydrocarbons (PAHs) were studied by far infrared spectroscopy (terahertz spectroscopy) in the spectral range comprised between 600 and 50 cm(-1). In addition to common PAHs like naphthalene, anthracene, phenanthrene, fluoranthene, picene, pyrene, benzo[α]pyrene, and perylene, also quite unusual PAHs were studied like tetracene, pentacene, acenaphtene, acenaphtylene, triphenylene, and decacyclene. A series of alkylated naphthalenes and anthracenes were studied as well as methypyrene. Partially or totally hydrogenated PAHs were also object of the present investigation, ranging from tetrahydronaphthalene (tetralin) to decahydronaphthalene (decalin), 9,10-dihydroanthracene, 9,10-dihydrophenanthrene, hexahydropyrene, and dodecahydrotriphenylene. Finally, the large and quite rare PAHs coronene, quaterrylene, hexabenzocoronene, and dicoronylene were studied by far infrared spectroscopy. The resulting reference spectra were used in the interpretation of the chemical structure of asphaltenes (as extracted from a heavy petroleum fraction and from bitumen), the chemical structures of other petroleum fractions known as DAE (distillate aromatic extract) and RAE (residual aromatic extract), and a possible interpretation of components of the chemical structure of anthracite coal. Asphaltenes, heavy petroleum fractions, and coal were proposed as model compounds for the interpretation of the emission spectra of certain proto-planetary nebulae (PPNe) with a good matching in the mid infrared between the band pattern of the PPNe emission spectra and the spectra of these oil fractions or coal. Although this study was finalized in an astrochemical context, it may find application also in the petroleum and coal chemistry.

Stability toward High Energy Radiation of Non-Proteinogenic Amino Acids: Implications for the Origins of Life.

A series of non-proteinogenic amino acids, most of them found quite commonly in the meteorites known as carbonaceous chondrites, were subjected to solid state radiolysis in vacuum to a total radiation dose of 3.2 MGy corresponding to 23% of the total dose expected to be taken by organic molecules buried in asteroids and meteorites since the beginning of the solar system 4.6 × 109 years ago. The radiolyzed amino acids were studied by FT-IR spectroscopy, Differential Scanning Calorimetry (DSC) and by polarimety and Optical Rotatory Dispersion (ORD). It is shown that an important fraction of each amino acid is able to "survive" the massive dose of radiation, while the enantiomeric excess is partially preserved. Based on the results obtained, it is concluded that it is unsurprising to find amino acids even in enantiomeric excess in carbonaceous chondrites.

Topological anisotropy of stone-wales waves in graphenic fragments.

Stone-Wales operators interchange four adjacent hexagons with two pentagon-heptagon 5|7 pairs that, graphically, may be iteratively propagated in the graphene layer, originating a new interesting structural defect called here Stone-Wales wave. By minimization, the Wiener index topological invariant evidences a marked anisotropy of the Stone-Wales defects that, topologically, are in fact preferably generated and propagated along the diagonal of the graphenic fragments, including carbon nanotubes and graphene nanoribbons. This peculiar edge-effect is shown in this paper having a predominant topological origin, leaving to future experimental investigations the task of verifying the occurrence in nature of wave-like defects similar to the ones proposed here. Graph-theoretical tools used in this paper for the generation and the propagation of the Stone-Wales defects waves are applicable to investigate isomeric modifications of chemical structures with various dimensionality like fullerenes, nanotubes, graphenic layers, schwarzites, zeolites.

Vibrational characterization of dinaphthylpolyynes: a model system for the study of end-capped sp carbon chains.

We perform a systematic investigation of the resonance and vibrational properties of naphthyl-terminated sp carbon chains (dinaphthylpolyynes) by combined multi-wavelength resonant Raman (MWRR) spectroscopy, ultraviolet-visible spectroscopy, and Fourier-transform infrared (FT-IR) spectroscopy, plus ab initio density functional theory (DFT) calculations. We show that the MWWR and FT-IR spectroscopies are particularly suited to identify chains of different lengths and different terminations, respectively. By DFT calculations, we further extend those findings to sp carbon chains end-capped by other organic structures. The present analysis shows that combined MWRR and FT-IR provide a powerful tool to draw a complete picture of chemically stabilized sp carbon chains.

Synthesis, characterization, and modeling of naphthyl-terminated sp carbon chains: dinaphthylpolyynes.

We report a combined study on the synthesis, spectroscopic characterization, and theoretical modeling of a series of α,ω-dinaphthylpolyynes. We synthesized this family of naphthyl-terminated sp carbon chains by reacting diiodoacetylene and 1-ethynylnaphthalene under the Cadiot-Chodkiewicz reaction conditions. By means of liquid chromatography (HPLC), we separated the products and recorded their electronic absorption spectra, which enabled us to identify the complete series of dinaphthylpolyynes Ar-C(2n)-Ar (with Ar = naphthyl group and n = number of acetilenic units) with n ranging from 2 to 6. The longest wavelength transition (LWT) in the electronic spectra of the dinaphthylpolyynes red shifts linearly with n away from the LWT of the bare termination. This result is also supported by DFT-LDA simulations. Finally, we probed the stability of the dinaphthylpolyynes in a solid-state precipitate by Fourier-transform infrared spectroscopy and by differential scanning calorimetry (DSC).

Electronic absorption spectroscopy of polycyclic aromatic hydrocarbons (PAHs) radical cations generated in oleum: a superacid medium.

Oleum (fuming sulphuric acid), a well known superacid, was used as medium for the generation of the radical cation of a series of selected PAHs. The resulting radical cation spectra were studied by electronic absorption spectroscopy. Not only common PAHs like naphthalene, anthracene, tetracene, pentacene, perylene, pyrene, benzo[a]pyrene, phenanthrene and picene were studied but also the less common and very large PAHs relevant also for the astrochemical research, like coronene, hexabenzocoronene, quaterrylene, dicoronylene and a coronene oligomer. A correlation between the first ionization potential (IP1) of the PAHs studied and the energy to the so-called A-type band of the radical cations observed in oleum has led to the equation IP1=1.30EA+4.39 (in eV) which permits to estimate the energy of the PAHs radical cation transition (EA) in the VIS-NIR knowing the relative ionization potential or vice versa.

Interaction of C(60) fullerene with lipids.

Unsaturated lipids when exposed to air at room temperature undergo a slow autoxidation. When fullerene C(60) was dissolved in selected lipids (ethyl oleate, ethyl linoleate, linseed oil and castor oil) the spectrophotometric analysis shows that the oxidation is concentrated to C(60) which is converted to an epoxide C(60)O. Thus, fullerene C(60) displays antioxidant activity not only when dissolved in unsaturated lipids but also, more generally, when dissolved in unsaturated solvents subjected to autoxidation like, for example, in cyclohexene. The behaviour of C(60) in ethyl oleate has been compared with that of the known antioxidant TMPPD (N,N',N,N,'-tetramethyl-p-phenylenediamine) in ethyl oleate. The mechanism of the antioxidant action of C(60) in lipids has been proposed. The kinetics of C(60) oxidation in lipids was determined spectrophotometrically both at room temperature in the dark and under UV irradiation. The oxidized products derived from C(60) photo-oxidation in lipids have been identified.

Ozone reaction with carbon nanostructures. 2: The reaction of ozone with milled graphite and different carbon black grades.

Synthetic graphite particles 0.2 microns in diameter react with O3 at room temperature with evolution of CO2. Graphite is less reactive with ozone than carbon blacks having different surface area ranging from 120 to 8 m2/g, but graphite reactivity is comparable to that shown by powdered solid C60 and C70 fullerenes. The kinetic rate constant derived from the ozone consumption k appears in relation with the rate of CO2 evolution suggesting a very simple reaction stoichiometry at the early stages. The reaction between ozone and graphite or carbon blacks essentially involves two stages: the gasification of the surface to CO2 and its functionalization with oxygenated chemical groups, mainly as COOH but also other oxygenated chemical moieties. The pseudofirst order kinetics appears adequate to describe the heterogeneous reaction between ozone and the selected carbon materials. The discussion of the results is focused on the role played by fullerene-like carbon nanostructures, present in graphene sheets to explain the observed gasification rates and surface functionalization.

Ozone reaction with carbon nanostructures. 1: Reaction between solid C60 and C70 fullerenes and ozone.

The exposure of powdered crystals of C60 and C70 fullerenes to ozone with an O3/O2 ratio of 9.7% w/w causes their immediate oxidation. The FT-IR spectroscopy shows the formation of CO2 and the accelerated disappearance of ozone. The infrared spectra of crystalline C60 and C70 powders that were exposed to ozone show absorption bands indicating that oxidation was accompanied by formation of alpha,beta-unsaturated carboxylic groups, aldehyde and other ketonic moieties. The spontaneous decay of O3 in the O3/O2 atmosphere monitored by FT-IR spectroscopy was found to follow a pseudofirst order kinetic law with k0 = 6.9 x 10(-5) s(-1). When powdered C60 is present in the system a k(C60)(1) = 2.0 x 10(-4) s(-1); k(C70)(1) = 1.4 x 10(-4) s(-1) for C70. The accelerated disappearance of O3 is due to its adsorption/reaction with the powdered fullerenes. After about approximately 1000 s the reaction enters in a second step wherein the disappearance of O3 slows down significantly due to the lack of further reaction sites on the powdered fullerene surfaces and due to accumulated CO2 in the gas phase which exerts an inhibitory effect in the ozone spontaneous decomposition.

On the action of ozone on gelatin.

Gelatin, the lower molecular weight derivative of collagen, was treated with ozone and the structural changes were studied with polarimetry, electronic absorption and FT-IR spectroscopy. The resulting ozonized gelatins were studied by thermal analysis (DSC and TGA) in comparison to a reference gelatin. It has been found that at relatively low ozone dose, for instance at ozone/gelatin molar ratios between 0.1 and 0.35 the structural damage introduced by ozone oxidation of gelatin is minimal to negligible and this may facilitate the industrial utilization of ozone in the cold sterilization of gelatin as well as in its bleaching processes required for certain applications. At higher O(3)/gelatin molar ratios the gelatine damage is evident both polarimetrically as suggested by the drop of its specific optical rotation and by spectrophotometrical analyses.

Polyynes and cyanopolyynes: their synthesis with the carbon arc gives the same abundances occurring in carbon-rich stars.

Carbon vapour generated from a carbon arc or by laser ablation of graphite is reactive with simple molecules and atoms producing end-capped polyyne chains. With these techniques both hydrogen-terminated polyynes as well as monocyano- and dicyanopolyynes have been produced. Experiments based on arcing graphite electrodes can reproduce the molecular distribution of polyynes existing around carbon-rich AGB stars. In fact, it has been found that the relative abundances of the polyynes produced in carbon arc in vacuum decreases by a factor between 3 and 5 as the chain length increases by a C(2) unit. An analogous trend has been observed both for polyynes and cyanopolyynes in the circumstellar environment around carbon-rich stars. This fact suggests that the mechanism of formation of the polyynes in the carbon arc may be similar to that occurring in the surroundings of the carbon-rich stars. Polyynes and cyanopolyynes represent authentic prebiotic molecules which appear quite ubiquitous in the cosmos and should have played a role in the early organic chemistry preceding the appearance of life.

Gamma-radiation induced polymerization of a chiral monomer: a new way to produce chiral amplification.

The treatment of the terpene beta(-)pinene with gamma radiation (at dose level: 150, 300 and 600 kGy) causes its polymerization into a resin and into a dimer. The yield of the resin and of the dimer appears to be linearly dependent to the radiation dose. The structure of the products was studied by FT-IR spectroscopy also in comparison to a reference beta(-)pinene resin prepared by cationic polymerization. A highly ordered structure was found in the case of the radiopolymer in comparison to the resin from cationic polymerization. Polarimetric measurements have shown astonishing enhancement in the optical activity of the radiopolymer and radiodimer in comparison to the starting optical activity of the beta(-)pinene monomer. Also DSC (differential scanning calorimetry) data supports the unexpected highly ordered structure for the beta(-)pinene radiopolymer in comparison to the resin prepared by cationic polymerization. The results have been discussed in terms of amplification of chirality caused by gamma radiation and the implications of this fact on the mechanism of chiral amplification on prebiotic molecules.