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A detailed quantum chemical investigation of a new reaction mechanism possibly leading to the formation of cyanoketene (NC–CH═C═O) in the interstellar medium (ISM) was carried out. Different reaction channels have been found by the AutoMeKin program, and the structures and harmonic force fields of the key stationary points have been characterized at the density functional theory level employing last-generation double-hybrid functionals. Finally, single-point computations at those geometries by state-of-the-art composite wave function methods provided accurate energies for the evaluation of thermochemical and kinetic parameters in the framework of an Ab Initio Transition State Theory based Master Equation (AITSTME) strategy. Our results indicate that the barrier-less association reaction of the formyl radical (HCO•) to the cyanocarbene radical (HCCN) can lead to the formation of cyanoketene under the harsh conditions of the ISM. Canonical rate constants computed for temperatures up to 600 K show that the most abundant product is indeed cyanoketene. The formation of other, even more stable, species involves higher activation energies and/or less favorable multi-step processes. Furthermore, to aid the search of cyanoketene, still undetected in the ISM, its rotational spectrum was recorded up to 530 GHz. The refined set of spectroscopic constants obtained in this way allows for spectral predictions from the microwave to the terahertz region, particularly for the bright b-type transitions, which can be targeted for the identification of cyanoketene in spectral line surveys. Despite cyanoketene was already sought without success in a variety of astronomical sources, we suggest to look for it in those sources where HCO or HCCN have already been detected, namely, W3, NGC2024, W51, K3-50, IRC + 2016, and TMC-1.

The scaled roto-diffusion tensor that includes dissipative and energetic properties of a molecule introduced here describes molecular local and global flexibility allowing a rigorous hierarchical selection of the relevant dynamics.

Cyanoacetaldehyde (NC-CH2CH=O) is considered, together with guanidine and urea, as a precursor of the pyrimidine bases cytosine and uracil. Although it has not yet been detected in the interstellar medium (ISM), several hypotheses have been put forward about its synthesis in solution and in the gas phase. In this paper, we present a gas-phase model of the barrierless reaction between formyl (HCO) and cyanomethyl (CH2CN) radicals leading to cyanoacetaldehyde and focus on its evolution through isomerization and dissociation pathways. The potential-energy surface for all reactions has been explored by DFT calculations employing double-hybrid functionals and further refined through the "Cheap" composite scheme. Our results indicate that the direct association of the two reacting radicals (HCO and CH2CN) is strongly exothermic and thus thermodynamically favored under the harsh conditions of the ISM. Microcanonical rate constants computed with the help of the StarRate program for energies up to 6 kJ mol(-)(1) above the dissociation limit show that the most abundant products are the two conformers of cyanoacetaldehyde (nitrile and carbonyl groups in a cis or trans configuration) which, despite having comparable stability, are obtained with a cis/trans ratio of 0.35:0.65. The formation of other products with relative abundances not exceeding 10% is also discussed.

THE ''LIfe in Space'' project was funded in the wake of the Italian Space Agency's proposal for the development of a network of institutions and laboratories conceived to implement Italian participation in space astrobiology experiments. Of primary concern for this project is the study of the origin of life in the Universe, a focus that will promote investigation into prebiotic chemistry in various possible scenarios, whether in polar or nonpolar solvents (e.g., Titan's environment). Such results will link with study of the effects of simulated space conditions on possible chemical bio- signatures. The limits of life as we know it will be investigated in ground-based experiments with microorganisms that have already demonstrated their resistance to extreme environments on Earth and to real or simulated space conditions. The potential survival of microorganisms will also be examined with up-to-date molecular methods. The ability of some microorganisms to produce atmospheric and surface biosignatures when exposed to simulated conditions will be tested and compared with the possible existence of bio- signatures on potentially habitable exoplanets. Furthermore, the search for potentially habitable exoplanets, with space- based observational methods, will be optimized by way of dedicated climate models with the capacity to predict the detectability of atmospheric biosignatures for a broad range of planetary conditions. The project embraces the four most important topics in astrobiological research, as listed below, along with relevant contributions from the participating Italian institutions. Origins and evolution of organic compounds of biological significance in space (comets, asteroids, rocky planets, and moons); Prebiotic syntheses, origin of life, and early life; The limits of life and biological habitability: origin, evolution and adaptation of life in extreme environments on Earth and in space; Biomarkers for life detection in the Solar System and on exoplanets.

A framework for the stochastic description of relaxation processes in flexible macromolecules including dissipative effects has been recently introduced, starting from an atomistic view, describing the joint relaxation of internal coordinates and global degrees of freedom, and depending on parameters recoverable from classic force fields (energetics) and medium modelling at the continuum level (friction tensors). The new approach provides a rational context for the interpretation of magnetic resonance relaxation experiments. In its simplest formulation, the semi-flexible Brownian (SFB) model has been until now shown to reproduce correctly correlation functions and spectral densities related to orientational properties obtained by direct molecular dynamics simulations of peptides. Here, for the first time, we applied directly the SFB approach to the practical evaluation of high-quality 13C nuclear magnetic resonance relaxation parameters, T1 and T2, and the heteronuclear NOE of several oligosaccharides, which were previously interpreted on the basis of refined ad hoc modelling. The calculated NMR relaxation parameters were in agreement with the experimental data, showing that this general approach can be applied to diverse classes of molecular systems, with the minimal usage of adjustable parameters.

Chemical bonding in a set of six cuprous complexes with simple nitriles (CN-, HNC, HCN, CH3NC, and CH3CN) is investigated by means of a recently devised analysis scheme framed in density-functional theory and quantitatively singling out concurrent charge flows such as σ donation and π backdonation. The results of our analysis are comparatively assessed against qualitative models for charge redistribution based on the popular concepts of octet rule and resonance structures, and the relative importance of different charge-flow channels relating to σ donation, π back-donation, polarization, and hyperconjugation is discussed on a quantitative basis.

A gas-phase nitrogen-nitrogen noncovalent interaction has been unveiled in the nitroethane-trimethylamine complex in an environment free from solvent and matrix effects using rotational spectroscopy in supersonic expansion. Different quantum chemical models (NOCV/CD and NBO) agree in indicating that this interaction largely prevails over the C-H⋅⋅⋅O and C-H⋅⋅⋅N hydrogen bonds. Furthermore, a SAPT analysis shows that electrostatic and dispersion interactions play a comparable role in stabilizing the complex. The conformational landscape exploration and stationary points characterization have been performed using state-of-the-art quantum-chemical computations providing significant insights on structure determination.

Through an analysis of eighty tetrahedral and square-planar metal carbonyls of general formula [M(CO)(L0)(L)2] including newly synthesized chlorocarbonyl rhodium complexes with chelating atropoisomeric diphosphanes, we show how coordination geometry can switch the carbonyl stretching frequency into a selective probe of the r-donor and p-acceptor abilities of the ligands. We thus provide a framework whereby the r-donation and p-backdonation constituents of the Dewar–Chatt–Duncanson model can be quantitatively predicted through spectroscopic data on coordinated CO moieties and vice versa.

The virtual-reality framework AVATAR (Advanced Virtual Approach to Topological Analysis of Reactivity) for the immersive exploration of potential-energy landscapes is presented. AVATAR is based on modern consumer-grade virtual-reality technology and builds on two key concepts: (a) the reduction of the dimensionality of the potential-energy surface to two process-tailored, physically meaningful generalized coordinates, and (b) the analogy between the evolution of a chemical process and a pathway through valleys (potential wells) and mountain passes (saddle points) of the associated potential energy landscape. Examples including the discovery of competitive reaction paths in simple A + BC collisional systems and the interconversion between conformers in ring-puckering motions of flexible rings highlight the innovation potential that augmented and virtual reality convey for teaching, training, and supporting research in chemistry.

Chemical bonding in a set of six cuprous complexes with simple nitriles (CN−, HNC, HCN, CH3NC, and CH3CN) is investigated by means of a recently devised analysis scheme framed in density-functional theory and quantitatively singling out concurrent charge flows such as σ donation and π backdonation. The results of our analysis are comparatively assessed against qualitative models for charge redistribution based on the popular concepts of octet rule and resonance structures, and the relative importance of different charge-flow channels relating to σ donation, π back-donation, polarization, and hyperconjugation is discussed on a quantitative basis.

We present a four-component relativistic density functional theory study of the chemical bond and s–d hybridization in the group 11 cyanides M–CN (M = Cu, Ag, and Au). The analysis is carried out within the charge-displacement/natural orbital for chemical valence (CD-NOCV) scheme, which allows us to single out meaningful contributions to the total charge rearrangement that arises upon bond formation and to quantify the components of the Dewar–Chatt–Duncanson bonding model (the ligand-to-metal donation and metal-to-ligand back-donation). The M–CN bond is characterized by a large donation from the cyanide ion to the metal cation and by two small back-donation components from the metal toward the cyanide anion. The case of gold cyanide elucidates the peculiar role of the relativistic effects in determining the characteristics of the Au–C bond with respect to the copper and silver homologues. In AuCN, the donation and back-donation components are significantly enhanced, and the spin–orbit coupling, removing the degeneracy of the 5d atomic orbitals, induces a substantial split in the back-donation components. A simple spatial analysis of the NOCV-pair density, related to the ligand-to-metal donation component, allows us to quantify, with unprecedented accuracy, the charge rearrangement due to the s–d hybridization occurring at the metal site. The s–d hybridization plays a key role in determining the shape and size of the metal; it removes electron density from the bond axis and induces a significant flattening at the metal site in the position trans to the ligand. The s–d hybridization is present in all noble metal complexes, influencing the bond distances, and its effect is enhanced for Au, which is consistent with the preference of gold to form linear complexes. A comparative investigation of simple complexes [AuL]+/0of Au+with different ligands (L = F–,N-heterocyclic carbene, CO, and PH3) shows that the s–d hybridization mechanism is also influenced by the nature of the ligand.