Artificial metalloenzymes for olefin metathesis based on the biotin-(strept)avidin technology

Incorporation of a biotinylated Hoveyda-Grubbs catalyst within (strept)avidin affords artificial metalloenzymes for the ring-closing metathesis of N-tosyl diallylamine in aqueous solution. Optimization of the performance can be achieved either by chemical or genetic means.     

Stereoselective synthesis of trisubstituted olefins by a directed allylic substitution strategy

New methodology for the stereoselective synthesis of trisubstituted olefins is presented. The use of ortho-diphenylphosphanyl benzoate (o-DPPB) as a directing leaving group for copper-mediated allylic substitution with Grignard reagents allowed for the stereoselective construction of a wide range of E olefins, without the need for an adjacent electron-withdrawing group. Our modular three-step approach toward trisubstituted alkenes commenced with geminal α-methylene aldehydes. Addition of an organometallic reagent and introduction of the o-DPPB group by esterification was followed by the o-DPPB-directed copper-mediated allylic substitution with a Grignard reagent to furnish stereodefined trisubstituted olefins. Additionally, incorporation of a stereocenter from the chiral pool allowed the preparation of an enantiomerically pure olefin that bore three alkyl substituents in high E/Z selectivity.     

Photoageing of Baltic amber – Influence of daylight radiation behind window glass on surface colour and chemistry

The aim of this study was to provide evidence about the interaction between Baltic amber and daylight behind window glass, essential to understanding the mechanisms by which the material degrades in museum environments and to propose techniques for preventive conservation based on the control of environmental parameters where amber objects are stored or displayed. To investigate the photodegradation of Baltic amber, the methodology consisted of artificial ageing, in order to initiate degradation of model amber samples, and non-destructive analytical techniques, in order to identify and quantify changes in colour and chemical properties. Prism-shaped samples, obtained from a large amber piece, were exposed to different microclimatic conditions, subjected to accelerated photoageing and analysed by spectrocolorimetry, infrared spectroscopy and Raman spectroscopy. The experiments provided results about surface discolouration, oxidation of the molecular structure and breakdown of unsaturated carbon-carbon bonds in various environmental conditions, confirming the degrading role of daylight behind window glass. The conclusions of this study can be applied to the development of techniques for preventive conservation of museum collections containing amber objects.     

Evaporation‐Driven Self‐Assembly of Colloidal Silica Dispersion: New Insights on Janus Particles

The evaporation driven self‐assembly of novel colloidal silica Janus particles was evaluated by scanning electron microscopy in comparison to unfunctionalized silica particles. The cyclodextrin‐ and azobenzene‐modified compound was obtained utilizing Pickering emulsion approach, in which the particles were immobilized on solidified wax droplets and subsequently functionalized. Silica particles were modified with 3‐aminopropyl trimethoxysilane and afterward reacted with tosyl‐β‐CD or phenylazo(benzoic acid), respectively. Mesoscopic structures of the colloidal dispersions, as dried films from aqueous solution, have been investigated by scanning electron microscopy and dynamic light scattering. Interestingly, it has been observed that the Janus particles show a significantly different evaporation‐induced assembly than the unmodified particles.