Synthesis of new [[(3-substituted-5-isoxazolyl)-alkyliden]iminooxy]aminopropanol derivatives

The preparation of new [[(3-substituted-5-isoxazolyl)alkyliden]iminooxy]aminopropanol compounds is reported starting from the corresponding 1-isoxazolylalkanones. The ¹H- and ¹³C-nmr studies, carried out to establish the Z- and E-configuration of new derivatives, are also described.     

Statistical estimates and physics of close binary systems (CBS) of neutron stars

After some statistical considerations about the number of CBSs with one neutron star in our galaxy, we study the possible kinds of emission of CBSs with two neutron stars. Section 2 contains considerations on the dimension of such a system at the moment of its formation. From the comparison of different kinds of power emitted we deduce that the orbital gravitational emissionP _go dominates. The dynamical evolution of the orbital elementsa ande is determined byP _go and by tidal friction, which produce opposite effects. The quantitative comparison betweenP _goandP _tf (work made per unit time by tidal torque) says thatP _go>P _tf. Therefore we conclude that it isa<0 ande<0; that is the evolution of the systems is towards the collapse.     

A theory of the dielectric loss in the aligned nematic mesophase

A theory of dielectric absorption and dispersion in the nematic phase is developed which does not rely on the use of a nematic “director”. The major features of the spectrum are reproduced by using the fact that the autocorrelation functions 〈μ(0) · υ(t)〉 and 〈υ(t) · μ(0)〉 are no longer symmetry disallowed when the overall sample is anisotropic, as in the aligned nematic. Here μ is the dipole vector of the diffusing molecule and υ the centre of mass linear velocity.     

γ-Valerolactone (GVL) as a green and efficient dipolar aprotic reaction medium

The great challenge for modern research is to define the most efficient tools to make more sustainable the industrial production and manufacturing. Among the different aspects that require attention the replacement of toxic and/or non-renewable solvents it is certainly playing a crucial role. Dealing with widely used dipolar aprotic solvents, among the different alternatives proposed in the literature γ-valerolactone (GVL) plays a pivotal role covering different application area. In this contribution, the benefits derived from the use of GVL as a circular, safe, biomass-derived reaction medium are highlighted covering most recent publications (2021). The presentation has been divided into three major sections: (i) biomass valorization, (ii) materials synthesis, manufacturing and recycle and (iii) new synthetic methodologies.     

A quantum mechanical strategy to investigate the structure of liquids: the cases of acetonitrile, formamide, and their mixture

A computational strategy based on quantum mechanical (QM) calculations and continuum solvation models is used to investigate the structure of liquids (either neat liquids or mixtures). The strategy is based on the comparison of calculated and experimental spectroscopic properties (IR-Raman vibrational frequencies and Raman intensities). In particular, neat formamide, neat acetonitrile, and their equimolar mixture are studied comparing isolated and solvated clusters of different nature and size. In all cases, the study seems to indicate that liquids, even when strongly associated, can be effectively modeled in terms of a shell-like system in which clusters of strongly interacting molecules (the microenvironments) are solvated by a polarizable macroenvironment represented by the rest of the molecules. Only taking into proper account both these effects can a correct picture of the liquid structure be achieved.     

How to model solvent effects on molecular properties using quantum chemistry? Insights from polarizable discrete or continuum solvation models

We present a comparative study of solvent effects on the 15N NMR shielding constants and the lowest electronic excitation energy (n --> pi*) in the three diazines (pyrazine, pyrimidine, and pyridazine) in aqueous solution. This solvent is modeled using either a polarizable continuum model (PCM) or a discrete polarizable model (DPM). We analyze the results obtained with the two models in terms of differences/similarities in the reaction field produced at the solute. The PCM reaction field is found to be quite sensitive to the dimension of the cavity and so are the molecular properties. However, constructing the cavity so that the DPM and PCM reaction fields become similar in magnitude leads to quite similar results for the studied molecular properties modeling the solvent using either the PCM or the DPM. Compared to experimental data, the most accurate predicted results are obtained by describing the closest water molecules at the same level of sophistication as that of the solute, whereas the bulk solvent may be described using either PCM or MM. Finally, a comparison with geometry-optimized clusters seems to show that it is important to check potential deficiencies in the force field in order for this to treat hydrogen bonding in a consistent manner.     

Embedding effects on charge-transport parameters in molecular organic materials

We present a generalized version of the tight-binding approach to determine the electronic coupling parameter in charge (hole) transport phenomena in organic materials. The main novelty of this approach is that the "embedding effects" of the environment (either a solvent or a crystal packing) can be explicitly included in the calculation by considering an embedded dimer. One of the main features shown by the application of the method to both model systems and oligoacene crystals is that the routinely used "energy splitting in a dimer" approximation gives reasonable results even if the transfer units are not equivalent by symmetry but the embedding effects are properly taken into account.     

Towards a molecular scale interpretation of excitation energy transfer in solvated bichromophoric systems. II. The through-bond contribution

In this paper we present a quantum-mechanical investigation on the mechanisms which promote intramolecular EET coupling. This investigation is done by using a new computational strategy in which we combine a configuration-interaction and a linear response approach. The combined use of these two methods allows a direct identification and a quantification of both "direct" (coulomb and exchange) and through-bond (superexchange and charge-transfer) contributions. In addition, solvent effects are introduced using the polarizable continuum model. The method is applied to a family of naphthalene-bridge-naphthalene and naphthalene-bridge-anthracene systems, and the results obtained are compared with experiments. The results found suggest that the through-bond charge-transfer effects are not significant when the EET goes through permitted excitations on distant chromophores (see DN4 and DN6) while they become as important as (or even more important than) the covalent terms for EETs involving weakly allowed excitations (see A6N). By contrast, the presence of a very short bridge (in DN2) allows a very efficient delocalization of the excitation energy which is also largely modified by the presence of a solvent.