Curing of a rigid rod epoxy resin with an aliphatic diacid: an example of a lightly crosslinked liquid crystalline thermoset

By reacting a rigid rod epoxy terminated molecule (p-bis(2,3-epoxypropoxy)-α-methylstilbene) with an aliphatic carboxylic acid (decanedioic acid), a lightly crosslinked liquid crystalline network is obtained. This network exhibits a smectic-like phase. While the mesophasic structure resulted “frozen” by the crosslinks in the case of higly crosslinked liquid crystalline epoxy resins, in this case a reversible transition from the liquid crystalline to the isotropic phase is observed. Moreover, while curing the same rigid rod epoxy molecule with amines resulted in a thermoset with a nematic structure, in this case a more ordered mesophase can be obtained. Preliminary results show that it is possible to orient macroscopically the mesogenic chains by stretching thin films above the glass transition temperature (T_g) and then quickly cooling down to the glassy state. This makes this material very attractive in the field of optical applications.     

Conjugation of testosterone modifies the interaction of mono-functional cationic platinum(II) complexes with DNA, causing significant alterations to the DNA helix

Previously a range of androgen conjugates with non-conventional platinum(II) complexes have been synthesised with the aim of enhancing cellular delivery, and which have shown increased cytotoxic activity compared with non-steroidal compounds (M. J. Hannon et al., Dalton Trans., 2010, DOI: 10.1039/c0dt00838a). To further study this, the complexes have been assessed for their ability to bind to and alter the structure of DNA. All platinum(II) complexes studied herein bind to model nucleo-bases and DNA, but to our surprise, testosterone-based complexes caused the DNA helix to undergo significant unwinding and bending, whereas non-steroidal control complexes caused minimal structural alterations. These effects are similar to those cisplatin induces on DNA structure despite the fact that these compounds produce a monofunctional lesion. This ability attributed to interactions between the DNA helix and bulky steroidal skeleton of testosterone, coupled with the enhanced cellular delivery induced by the steroid make the steroid approach an exciting way to explore non-conventional platinum drug delivery.     

Stemmosides C and D, two novel unusual pregnane glycosides from Solenostemma argel: structural elucidation and configurational study by a combined NMR-quantum mechanical strategy

Stemmosides C and D, two novel pregnane glycosides characterized by an unusual C-17 side chain were isolated from the pericarps of Solenostemma argel. In addition, stemmoside D displays an uncommon 14β proton configuration, apparently being the first pregnane isolated from plants known to have a 15 keto, cis CD ring junction. Their structures have been established by ESIMS and NMR experiments. The relative configuration of the molecules was determined using a strategy based on the simulation of ¹H, ¹³C, and J coupling NMR parameters. DFT calculations of ¹H and ¹³C chemical shifts, and of the ¹H homonuclear spin–spin coupling constants were performed with the mPW1PW91 functional using the 6-31G(d,p) basis set on the fully optimized geometries of all the possible stereoisomers.     

The photoisomerization mechanism of azobenzene: a semiclassical simulation of nonadiabatic dynamics

We have simulated the photoisomerization dynamics of azobenzene, taking into account internal conversion and geometrical relaxation processes, by means of a semiclassical surface hopping approach. Both n-->pi* and pi-->pi* excitations and both cis-->trans and trans-->cis conversions have been considered. We show that in all cases the torsion around the N==N double bond is the preferred mechanism. The quantum yields measured are correctly reproduced and the observed differences are explained as a result of the competition between the inertia of the torsional motion and the premature deactivation of the excited state. Recent time-resolved spectroscopic experiments are interpreted in the light of the simulated dynamics.     

Binding models of reversible inhibitors to type-B monoamine oxidase

Interest in the inhibitors of type-B monoamine oxidase has grown in recent years, due to the evidence for multiple roles of one such agent (selegiline) in the pharmacological management of neurodegenerative disorders. A set of 130 reversible and selective inhibitors of MAO-B (including tetrazole, oxadiazolone, and oxadiazinone derivatives) were taken from the literature and subjected to a three-dimensional quantitative structure–activity relationship (3D-QSAR) study, using CoMFA and GOLPE procedures. The steric and lipophilic fields, alone and in combination, provided us with informative models and satisfactory predictions (q²=0.73). The validity of these models was checked against the 3D X-ray structure of human MAO-B. Flexible docking calculations, performed by using a new approach which took advantage from QXP and GRID computational tools, showed the diverse inhibitors to interact with MAO-B in a similar binding mode, irrespective of the heterocycle characterizing them. A significant trend of correlation was observed between estimated energies of the complexes and the experimental inhibition data.     

Gas chromatography-mass spectrometry characterization of the varnish and glue of an ancient 18th century double bass

A GC-MS investigation is conducted on the double bass "Panormus", property of Conservatorio di Musica "Vincenzo Bellini" in Palermo. The most important components of the varnish (fatty acids) and of the glue (proteinaceous amino acids), with which the musical instrument was treated in the past, are determined. The analyses are carried out by prior derivatization of fatty acids by acidic methanol and of amino acids by acidic methanol and trifluoroacetic anhydride (TFAA). Analytes identification is achieved by direct comparison with several reference materials and the use of a digitized library.