Lucia C. S. Aguiar

Selectivity Studies Towards the Synthesis of Novel Biaryl Ureas by (Hetero)Nanocatalysis: Size Control and Support Effects

A series of novel biaryl ureas containing different structural patterns have been prepared in good yields in the presence of palladium nanoparticles (PdNPs) with narrow particle size distribution. In particular, α, β‐, and γ‐hydroxypropylated cyclodextrins were used as reductants/stabilizers under different Pd‐to‐cyclodextrin ratios to tune the particle size and exploit the surface/cavity effects in the Suzuki–Miyaura reaction. Catalyst recovery in this process was pursued as well. Owing to its excellent performance, ceria was explored as a support for these PdNPs. The heterogeneous catalyst was characterized and investigated in the reaction of N‐(4‐iodo‐aryl),N′‐alkyl urea and phenylboronic acid. Our preliminary results revealed a high activity of the catalyst at 0.5 mol % Pd0 during three consecutive cycles. It is suggested that the specific interface between Pd0 and the high‐surface‐area ceria has a role in the catalytic performance.

Efficient desymmetrization of 4,6-di-O-benzyl-myo-inositol by Lipozyme TL-IM

The enantioselective enzymatic desymmetrization of 4,6-di-O-benzyl-myo-inositol, a myo-inositol derivative, was effectively catalyzed by Thermomyces lanuginosus lipase (TL-IM). The product 1D-1-O-acetyl-4,6-di-O-benzyl-myo-inositol, a useful precursor to inositol phosphates, was obtained in excellent yield and enantiomeric excess. Through the investigation of the effects of solvent, biocatalyst load, and temperature, a more economical procedure resulted. The feasibility of biocatalyst reuse was also shown.

Hydrophilic cyclodextrin protected Pd nanoclusters: insights into their size control and host–guest behavior

The process of formation of narrow size spherical PdNPs covered by cyclodextrins with an average size of 5.1 nm ± 0.5 nm has been investigated in aqueous solution at room-temperature. Analyses by UV-Vis spectroscopy and dynamic light scattering (DLS) at the beginning of reaction indicated a fast exchange of chloride ions with water molecules within the palladium coordination sphere. This process is followed by reduction of Pd(II) species according to the α-HPCD concentration. The hydrodynamic radii observed from both PdNPs and α-HPCD aqueous solutions suggested that regular CDs assemblies in the order of a few nanometers may direct the homogeneous NPs growth towards uniform aggregates. These scattering measurements are corroborated by 1H DOSY NMR spectroscopy in solution and AFM (atomic force microscopy) analyses which provided evidence of stable hybrid assemblies. Interestingly, by changing the cavity size, structures with distinct hydrodynamic diameters are formed. Further evidence from ECD (electronic circular dichroism) spectra reveals that the primary face of cyclodextrin is most likely associated to the metal surface.