Life is made of the intimate interaction of metabolism and genetics, both built around the chemistry of the most common elements of the Universe (hydrogen, oxygen, nitrogen, and carbon). The transmissible interaction of metabolic and genetic cycles results in the hypercycles of organization and de-organization of chemical information, of living and non-living. The origin-of-life quest has long been split into several attitudes exemplified by the aphorisms “genetics-first” or “metabolism-first”. Recently, the opposition between these approaches has been solved by more unitary theoretical and experimental frames taking into account energetic, evolutionary, proto-metabolic and environmental aspects. Nevertheless, a unitary and simple chemical frame is still needed that could afford both the precursors of the synthetic pathways eventually leading to RNA and to the key components of the central metabolic cycles, possibly connected with the synthesis of fatty acids. In order to approach the problem of the origin of life it is therefore reasonable to start from the assumption that both metabolism and genetics had a common origin, shared a common chemical frame, and were embedded under physical–chemical conditions favourable for the onset of both. The singleness of such a prebiotically productive chemical process would partake of Darwinian advantages over more complex fragmentary chemical systems. The prebiotic chemistry of formamide affords in a single and simple physical–chemical frame nucleic bases, acyclonucleosides, nucleotides, biogenic carboxylic acids, sugars, amino sugars, amino acids and condensing agents. Thus, we suggest the possibility that formamide could have jointly provided the main components for the onset of both (pre)genetic and (pre)metabolic processes. As a note of caution, we discuss the fact that these observations only indicate possible solutions at the level of organic substrates, not at the systemic chemical level.

Genetics first or metabolism first? The formamide clue

Artificial olfaction based on gas sensor arrays aims to substitute for, support, and surpass human olfaction. Like mammalian olfaction, a larger number of sensors and more signal processing are crucial for strengthening artificial olfaction. Due to rapid progress in computing capabilities and machine-learning algorithms, on-demand high-performance artificial olfaction that can eclipse human olfaction becomes inevitable once diverse and versatile gas sensing materials are provided. Here, rational strategies to design a myriad of different semiconductor-based chemiresistors and to grow gas sensing libraries enough to identify a wide range of odors and gases are reviewed, discussed, and suggested. Key approaches include the use of p-type oxide semiconductors, multinary perovskite and spinel oxides, carbon-based materials, metal chalcogenides, their heterostructures, as well as heterocomposites as distinctive sensing materials, the utilization of bilayer sensor design, the design of robust sensing materials, and the high-throughput screening of sensing materials. In addition, the state-of-the-art and key issues in the implementation of electronic noses are discussed. Finally, a perspective on chemiresistive sensing materials for next-generation artificial olfaction is provided.

Rational Design of Semiconductor-Based Chemiresistors and their Libraries for Next-Generation Artificial Olfaction.

In recent years, copper ferrite (CuFe2O4) nanoparticles (NPs) have attracted many researcher’s attention due to its potential application in water purification. CuFe2O4 NPs are low-cost magnetic material and stable under different conditions. Consequently, easily recovered from treated water using an external magnetic field and reused for several cycles. In this review, an emphasis was placed on understanding the impacts of certain factors such as synthesis method, calcination temperature, dopant type, pH and crystalline size on the magnetic properties of CuFe2O4 NPs and its nanocomposites (NCs). The application of CuFe2O4 NPs in water treatment and its ability to be combined with other nanomaterials for photocatalysis and adsorption were fully discussed. The possibility of recovery and reuse of CuFe2O4 NPs and its NCs were deliberated. Lastly, the gaps that are still open for research in the fine-tuning of the magnetic properties and other physical properties of CuFe2O4 NPs for its full utilisation in water purification were outlined. Hence, using CuFe2O4 NPs and its NCs at industrial scale for water purification can go a long way in lowering the costs of water, since it utilises visible light as an energy source and due to its ability to be reused several times.

Recent advances in copper ferrite nanoparticles and nanocomposites synthesis, magnetic properties and application in water treatment: Review

In the present work, transition metal spinel ferrite (MFe2O4; M = Co, Ni, Zn) nanostructures synthesized by chemical co-precipitation method. XRD analysis confirms the formation of cubic spinel-type structure with space group Fd3m and the average crystallite size calculated by Scherrer's formula found to be in 9–14 nm range. Scanning electron microscopy was used to study surface morphology of the samples. Moreover, Raman and PL spectra also confirm the formation of the cubic structure. The Raman spectra measured on cobalt, nickel and zinc ferrite revealed a larger number of phonon bands than expected for the cubic spinel structure. The calculated optical energy band gaps, obtained by Tauc's relation from UV–Vis absorption spectra are found to be as 2.44, 3.54 and 3.25 eV for CoFe2O4, NiFe2O4&ZnFe2O, respectively. The analysis of the complex impedance spectra of all ferrites samples shows the presence of one semicircular arc at all selected temperatures, signifying a key role of the grain boundary contribution. The dielectric constants ( e ′ ) were measured in the frequency range from 10 Hz to 5 MHz at different temperatures and is found to be decreased suddenly with an increase in frequency and maintain a steady state or constant at higher frequencies for all the three samples. The AC conductivity is found to be increased with frequency and temperature of all the three samples which is explained on the basis of Koop's phenomenological theory.

Structural, optical and dielectric properties of transition metal (MFe2O4; M = Co, Ni and Zn) nanoferrites

Synthesis of ZnO nanopetals and its application as NO2 gas sensor

Synthesis, characterization and performance of zinc ferrite nanorods for room temperature sensing applications

Gas phase chemistry in the cold interstellar clouds is dominated by ion-molecule and radical-radical interactions, though some neutralneutral reactions are also barrier-free and efficient at cold temperatures. It has been suggested that it is impossible to synthesize detectable abundances of the pre-biotic HCN oligomer adenine (H5C5N5) in the interstellar medium via successive neutral-neutral reactions. We attempted therefore to use quantum chemical techniques to explore if adenine can possibly form in the interstellar space by radical-radical and radical-molecule interaction schemes, both in the gas phase and in the grains. We report results of ab initio calculations for the formation of adenine starting from some of the simple neutral molecules and radicals detected in the interstellar space. The reaction path is found to be totally exothermic and barrier free, which increases the probability of occurrence in the cold interstellar clouds (10−50 K). We also estimated the reaction rates.

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Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space

Nickel antimony oxide (NiSb2O6): A fascinating nanostructured material for gas sensing application

The highly porous spinel copper ferrite (CuFe2O4) hierarchical nanostructures have been prepared by the sol-gel method. The growth of the hollow CuFe2O4 hierarchicals has been characterized by scanning electron microscopic (SEM) images. The fabricated CuFe2O4 thin film displays a uniform surface morphology of porous hierarchicals having diameters in the range of 10–15 nm. The possible growth mechanism of its formation has been suggested. The liquefied petroleum gas (LPG) sensing capability of the fabricated nanostructure has been investigated at room temperature (25 °C). Sensing results show that the porous CuFe2O4 hierarchicals possess superb LPG sensing properties (in terms of sensor response, response and recovery times, reproducibility and stability) over other reported LPG sensors. The excellent response of CuFe2O4 towards LPG has been mainly ascribed to its porous structure and small size, which promotes the rapid diffusion of the LPG and increases the available active surface area of the film.

Fabrication of copper ferrite porous hierarchical nanostructures for an efficient liquefied petroleum gas sensor

In the present work, synthesis and characterization of thin films of nanostructured nickel ferrite (NiFe2O4), and its employment as liquefied petroleum gas (LPG) and carbon dioxide gas (CO2) sensors operable at room temperature (27 °C), have been reported. These thin films have been prepared using sol–gel spin coating technique. The structural and surface morphological properties of the fabricated films were studied by X-ray diffraction (XRD) and scanning electron microscopy, respectively. Single phase formation of inverse spinel structure (NiFe2O4) was confirmed by XRD data. The synthesized NiFe2O4 exhibits crystallite size ~23 nm, porosity ~38 % and specific surface area ~57 m2 g−1. In order to check the potential applicability of the fabricated films as gas sensor, the modulations in electrical behavior of the film had been recorded by exposure of LPG and CO2 respectively, in a controlled gas chamber. The mechanism of gas sensing of NiFe2O4 thin film has been explained on the basis of surface adsorbed oxygen on the surface of a sensor. The sensing results show that the fabricated sensor is challenging for the leakage detection of LPG as it possesses high sensitivity, stable behavior in long run and small response and recovery times towards LPG.

Ajendra Singh

Papers

Synthesis, characterization and performance of zinc ferrite nanorods for room temperature sensing applications

Quantum chemical study of a new reaction pathway for the adenine formation in the interstellar space

Nickel antimony oxide (NiSb2O6): A fascinating nanostructured material for gas sensing application

Fabrication of copper ferrite porous hierarchical nanostructures for an efficient liquefied petroleum gas sensor

Preparation and characterization of nanocrystalline nickel ferrite thin films for development of a gas sensor at room temperature