Visualizing a Single-Crystal-to-Single-Crystal [2+2] Photodimerization through its Lattice Dynamics: An Experimental and Theoretical Investigation

In homogeneous solid-state reactions, the single-crystal nature of the starting material remains unchanged, and the system evolves seamlessly through a series of solid solutions of reactant and product. Among [2+2] photodimerizations of cinnamic acid derivatives in the solid state, those involving salts of the 4-aminocinnamic acid have been recognized to proceed homogeneously in a “single-crystal-to-single-crystal” fashion by X-ray diffraction techniques. Here the bromide salt of this compound class is taken as a model system in a Raman spectroscopy study at low wavelengths, to understand how such a mechanism defines the trend of the crystal lattice vibrations during the reaction. Vibrational mode calculations, based on dispersion corrected DFT simulations of the crystal lattices involved in the transformation, have assisted the interpretation of the experiments. Such an approach has allowed us to clarify the spectral signatures and to establish a correlation between the dynamics of the monomer and dimer systems in a process where chemical progress and crystal structural changes are demonstrated to occur simultaneously.     

Diastereoselective multicomponent synthesis and anti-HSV-1 evaluation of dihydrofuran-fused derivatives

Enolizable 6-membered cyclic 1,3-dicarbonyls undergo an efficient and diastereoselective domino condensation/addition/heterocyclization reaction with arylaldehydes and phenacyl chloride, producing highly substituted dihydrofuran-fused derivatives. Ring size of the cyclic 1,3-dicarbonyls and the presence of at least one keto group are crucial to the reaction's success. The new compounds were evaluated in vitro for antiviral activity against herpes simplex virus type-1 (HSV-1). Interestingly, some of them appeared able to interfere with HSV-1 replication, without detection of cytotoxic effects.     

Stable particles in anisotropic spin-1 chains

Motivated by field-theoretic predictions we investigate the stable excitations that exist in two characteristic gapped phases of a spin-1 model with Ising-like and single-ion anisotropies. The sine-Gordon theory indicates a region close to the phase boundary where a stable breather exists besides the stable particles, that form the Haldane triplet at the Heisenberg isotropic point. The numerical data, obtained by means of the Density Matrix Renormalization Group, confirm this picture in the so-called large-D phase for which we give also a quantitative analysis of the bound states using standard perturbation theory. However, the situation turns out to be considerably more intricate in the Haldane phase where, to the best of our data, we do not observe stable breathers contrarily to what could be expected from the sine-Gordon model, but rather only the three modes predicted by a novel anisotropic extension of the Non-Linear Sigma Model studied here by means of a saddle-point approximation.     

Vibrational dynamics of a glass forming liquid in nanoscopic confinement as probed by inelastic neutron scattering

In this article we present incoherent inelastic neutron scattering results, as a function of temperature, on the vibrational dynamics of a glass-forming liquid, namely propylene glycol, confined to the 26 Å pores of a controlled porous glass. The aim is to elucidate the effects induced by surface interactions (chemical traps) and geometrical restrictions (physical traps) on the fast microscopic dynamics of hydrogen-bonded liquids. The most prominent effect is the appearance of the ‘boson peak’ in the vibrational spectra. It is ascribed to an excess density of vibrational states due to quasilocalized collective atomic vibrations induced by confinement. A destructuring effect on the transient aggregates with the highest degree of connectivity, promoted by PG in the bulk phase, is hypothesized under confinement as a consequence of interactions, via hydrogen bond, between the hydroxyl groups (OH) of the PG molecule and the active silanol groups (Si–OH) on the surface of the porous glass.

Interfacial and/or finite-size effects are also found to give rise to a destructuring effect, under confinement, of the disordered Longitudinal Acoustic Mode, together with a broadening of the highest frequency torsional vibration and a stabilization, vs. T, of the internal CCO bending vibration.     

The effect of hydrogen bond on the vibrational dynamics of genistein free and complexed with β‐cyclodextrins

Inclusion, or host–guest, complexes are supramolecular assemblies in which two or more molecules hold together and organize by means of intermolecular noncovalent bonds. In the pharmaceutical field, inclusion complexation of drugs with unsubstituted and derivative β‐cyclodextrins (β‐CDs) has proven to be a successful method to improve the dissolution of water insoluble drugs. Genistein (Gen), an isoflavone constituent of Onodis spinosae radix, turned out to be a suitable guest molecule for the encapsulation into β‐CD, resulting in a significant improvement of its aqueous solubility. In the present study, the modifications of the vibrational spectrum of Gen caused by its inclusion into β‐CDs cavity have been characterized by means of Raman scattering experiments. These changes have been interpreted by comparing the experimental data with the vibrational wavenumbers and Raman intensities obtained by simulation for the free and complexed guest molecule. Following this strategy, we have obtained a deeper understanding of the host–guest interactions involved in the formation and stabilization of the complexes, with particular regard to the role played by the guest chemical groups, as well as to disentangle the effects directly related to the complexation process from those ascribed to other factors, such as formation of intra‐ and intermolecular hydrogen bonds. Copyright © 2009 John Wiley & Sons, Ltd.     

Comparison between classical and innovative class-modelling techniques for the characterisation of a PDO olive oil

An authentication study of the Italian PDO (protected designation of origin) olive oil Chianti Classico, based on near-infrared and UV–Visible spectroscopy, an artificial nose and an artificial tongue, with a set of samples representative of the whole Chianti Classico production and a considerable number of samples from a close production area (Maremma) was performed. The non-specific signals provided by the four fingerprinting analytical techniques, after a proper pre-processing, were used for building class models for Chianti Classico oils. The outcomes of classical class-modelling techniques like soft independent modelling of class analogy and quadratic discriminant analysis—unequal dispersed classes were compared with those of two techniques recently introduced into Chemometrics: multivariate range modelling and CAIMAN analogues modelling methods.     

Raman investigation of polymorphism in 1,1,4,4‐tetraphenyl‐butadiene

We present a Raman investigation of polymorphism in 1,1,4,4‐tetraphenyl‐butadiene (TPB), a well‐known blue luminescent molecule, which retains its emissive properties in the solid state. The use of low‐wavenumber (10–150 cm⁻¹) Raman microscopy, very sensitive to the crystal packing, allows us to single and pick up four different polymorphs. X‐ray analysis shows that the TPB molecules assume different conformations in the various polymorphs, a fact revealed also by the Raman spectra in the region of intra‐molecular vibrations. Lattice dynamics calculations yield a preliminary assignment of the low‐wavenumber Raman spectra and provide information of the relative stability of the phases. Copyright © 2013 John Wiley & Sons, Ltd.     

Weakly non-linear high frequency waves for a first order quasi-linear system involving source-like terms

Making use of the method of asymptotic expansion of multiple scales, a study of weakly non-linear, high frequency waves, through “homogeneous” media characterized by dissipative or dispersive hyperbolic systems of partial differential equations, is proposed. Within the present theoretical framework, asymptotic waves in a heat-conducting fluid are considered.     

Discontinuous Shock Structure in a Reacting Mixture Modelled by Grad 13 Moment Approximation

A preliminary analysis on the possible occurrence of sub-shocks into a gas mixture is carried out. The mixture, undergoing a reversible bimolecular reaction, is described by macroscopic equations obtained by Grad 13 moment approximation of the reactive Boltzmann equation.