Short Synthesis of Cytotoxic 4‐Arylcoumarins

A short synthesis of cytotoxic 4‐arylcoumarins via condensation of phenols with cinnamic acids in the presence of CF₃COOH, followed by dehydrogenation with DDQ, is described.     

Scaling analysis of the magnetocaloric effect in Gd5Si2Ge1.9X0.1 (X=Al, Cu, Ga, Mn, Fe, Co)

The field dependence of the magnetic entropy change has been studied for a series of doped Gd₅Si₂Ge₂ alloys, which possess a magnetic phase transition that is either entirely second order or a combination of primarily second-order mixed to a very minor degree with a first-order transition arising from a magneto-structural phase change. By analyzing the field scaling of the refrigerant capacity as well as of the reference temperatures used for constructing a universal scaling curve, a procedure for estimating the values of the critical exponents for the alloys was developed. For the cases where the transition is entirely second order, the results obtained from this procedure are comparable to the values obtained from the Kouvel–Fisher method. For the case of Fe-doped alloys which partially possess a first-order phase change, the Kouvel–Fisher method is inapplicable. However, their critical exponents determined by our developed procedure can be used to estimate the Curie temperature of the orthorhombic majority phase.     

High Pressure Fluorescence of 2,5-diphenyl-1,3,4-oxadiazole Crystals

The dependence of the fluorescence of 2,5-diphenyl-1,3,4-oxadiazole (DPO) crystals under compression up to 7 GPa was experimentally studied. The knowledge of the structural behavior at high pressure allows to relate the variation of the fluorescence to the diminution of the inter-molecular distance.     

Intensity distribution around the focal regions of real axicons

We present a theoretical and experimental study of the intensity distribution of a laser beam, after its propagation through a real axicon. We show that, while an ideal axicon generates Bessel-like radial intensity profile and smooth on-axis intensity around the focal region, in practice, the bluntness of the tip of the axicon causes significant deviations from these profiles. In particular, strong oscillations occur on the on-axis intensity. The input beam size also plays a strong role; for small beams the axicon acts more like a conventional lens, while for the large ones, it exhibits two focal regions. We also propose scheme for apodization. In all cases, the experiments match closely with the calculations. Our results show that axicons cannot be assumed to always generate smooth on-axis intensities and the structures coming from the real profiles should be taken into account for most applications.     

Tunable electronic coupling in iron-chromium mixed-valence ions of methylated Cp-indene ligands

A series of heterobimetallic η⁶-[(ferrocenyl)indene]-Cr(CO)₃ complexes differing for the position of the ferrocenyl group, 1-(ferrocenyl)indene and 2-(ferrocenyl)indene, and the degree of indene methylation (tetramethyl- and hexamethyl-) have been prepared and studied with the aim to stabilise the mono- and dications generated by chemical and electrochemical oxidation, and at same time to tune the metal-metal electronic coupling in the mixed-valence cations. The magnitude of electronic delocalisation and spin density in the cations have been monitored by means of optical techniques (UV-Vis, near-IR, mid-IR) and EPR spectroscopy. The results have been rationalised in the framework of Marcus-Hush theory and at quantum chemistry level by DFT and TD-DFT methods, establishing that a metal-to-metal electronic coupling occurs the magnitude of which depends on the degree of indene methylation.     

Influence of molecular weight and free NCO content on the rheological properties of lithium lubricating greases modified with NCO-terminated prepolymers

In this work, the use of reactive diisocyanate-terminated polymeric materials as rheology modifiers of lubricating greases has been studied. Particularly, the influences that free NCO content, molecular weight and functionality of the reactive prepolymers exert on the rheological response and microstructure of lubricating greases were analyzed. With this aim, NCO-terminated prepolymers were prepared from several di and trifunctional polyols and polymeric MDI. Afterwards, the reaction between terminal isocyanate groups and the hydroxy group located in the hydrocarbon chain of the 12-hydroxystearate lithium soap, used as thickener, was promoted during processing of lubricating greases. Polymeric materials used as additives and final lubricating greases were characterized by FTIR, DSC and GPC techniques. The effectiveness of these reactive additives was tested by performing small-amplitude oscillatory shear (SAOS), as well as standardized mechanical stability tests, on final greases. The rheological response was related to the microstructure of these greases, characterized by means of atomic force microscopy (AFM). From the experimental results obtained, it may be concluded that the effectiveness of these polymeric additives to modify the rheology of greases is due to the progress of the reaction between terminal isocyanate groups and the hydroxy group of lithium soap. However, a large dependence on both free NCO content and prepolymer molecular weight was found. Experimental results confirm that a balance between prepolymer molecular weight and NCO content is necessary to reach an optimal rheological modification of lithium greases. Moreover, this balance is a function of grease ageing, due to the progress of the reaction promoted.     

Thermal transitions of polylactide false-twist textured multifilaments determined by DSC and TMA

A partially oriented melt-extruded PLA multifilament was false-twist textured to stabilize its structure. Conventional DSC analysis showed a relaxation peak at the end of glass transition. Simultaneous consideration of the TMA curve enabled us to evaluate both the relaxation and the cold crystallisation produced during the DSC scan. The periodic load applied during TMA experiments also enabled us to examine the evolution of Young’s modulus along the glass transition, relaxation and cold crystallisation phenomena. Increases in Young’s modulus and in enthalpy are related because of crystallisation. Texturing increased crystallinity and decreased cold crystallisation of PLA during the DSC scan.     

Readily available (S)-proline-derived organocatalysts for the Lewis acid-mediated Lewis base-catalyzed stereoselective aldol reactions of activated thioesters

A set of enantiomerically pure Lewis bases containing different diphenyl phosphinyl oxide groups were easily synthesized in a straightforward procedure by reaction of readily available proline-based scaffolds and phosphinoyl chlorides. The newly synthesized derivatives were employed (0.1 mol equiv) as organocatalysts in the Lewis acid-mediated Lewis base-promoted direct stereoselective aldol reactions of activated thioesters with aromatic aldehydes, carried out in the presence of tetrachlorosilane and a tertiary amine. β-Hydroxy thioesters were obtained in moderate to high yields, with very high syn diastereoselectivities (dr up to >98:2), and fair enantioselectivities (ee up to 51%). Theoretical studies were performed in order to elucidate the origin of the stereoselection.