Extraction of Lantana camara essential oil by supercritical carbon dioxide: influence of the grinding and biological activity

The aim of this study was to produce Lantana camara essential oil by SFE and to study the effect of matrix grinding on the yield and/or composition of the extract. Experiments were carried out on grinding matrices (G) and on not grinding matrices (NG). The extracts were analyzed by GC-MS. A comparison with the oil obtained by hydrodistillation is also given. Finally, the antibacterial and antifungal activity of the various extracts has been assayed.     

Fluoride as a probe for H-bonding interactions in the active site of heme proteins: the case of Thermobifida fusca hemoglobin

The structural and functional properties of the active site of the bacterial hemoglobin from Thermobifida fusca are largely determined by three polar amino acids: TrpG8, TyrCD1, and TyrB10. We have exploited the availability of a combinatorial set of mutants, in each of which these three amino acids have been singly, doubly, or triply replaced by a Phe residue, to perform a detailed study on H-bonding interactions between the protein and heme-bound fluoride. By appropriate choice of the excitation conditions, ν(Fe-F) stretching bands have been detected in the resonance Raman spectra. In the wild-type protein and one of the mutants, two ν(Fe-F) bands have been observed and assigned to the presence of two protein conformers where fluoride is singly or doubly H-bonded. Furthermore, by plotting the CT1 charge-transfer transition energy vs the ν(Fe-F) wavenumbers, an empirical correlation has been found. The data are well fitted by a straight line with a positive slope. The position along the correlation line can be considered as a novel, general spectroscopic indicator of the extent of H-bonding in the active site of heme proteins. In agreement with the spectroscopic results, we have observed that the rate of ligand dissociation in stopped-flow kinetic measurements progressively increases upon substitution of the H-bonding amino acids. Molecular dynamics simulations have been performed on the fluoride complexes of native and mutated forms, indicating the prevalent interactions at the active site. All the techniques yield evidence that TrpG8 and TyrCD1 can form strong H bonds with fluoride, whereas TyrB10 plays only a minor role in the stabilization of the ligand.     

Rotamer libraries of spin labelled cysteines for protein studies

Studies of structure and dynamics of proteins using site-directed spin labelling rely on explicit modelling of spin label conformations. The large computational effort associated with such modelling with molecular dynamics (MD) simulations can be avoided by a rotamer library approach based on a coarse-grained representation of the conformational space of the spin label. We show here that libraries of about 200 rotamers, obtained by iterative projection of a long MD trajectory of the free spin label onto a set of canonical dihedral angles, provide a representation of the underlying trajectory adequate for EPR distance measurements. Rotamer analysis was performed on selected X-ray structures of spin labelled T4 lysozyme mutants to characterize the spin label rotamer ensemble on a single protein site. Furthermore, predictions based on the rotamer library approach are shown to be in nearly quantitative agreement with electron paramagnetic resonance (EPR) distance data on the Na(+)/H(+) antiporter NhaA and on the light-harvesting complex LHCII whose structures are known from independent cryo electron microscopy and X-ray studies, respectively. Suggestions for the selection of labelling sites in proteins are given, limitations of the approach discussed, and requirements for further development are outlined.     

A Noble‐Metal‐Free System for Photocatalytic Hydrogen Production from Water

A series of heteroleptic copper(I) complexes with bidentate $\widehat{PP}$ and $\widehat{NN}$ chelate ligands was prepared and successfully applied as photosensitizers in the light‐driven production of hydrogen, by using [Fe₃(CO)₁₂] as a water‐reduction catalyst (WRC). These systems efficiently reduces protons from water/THF/triethylamine mixtures, in which the amine serves as a sacrificial electron donor (SR). Turnover numbers (for H) up to 1330 were obtained with these fully noble‐metal‐free systems. The new complexes were electrochemically and photophysically characterized. They exhibited a correlation between the lifetimes of the MLCT excited state and their efficiency as photosensitizers in proton‐reduction systems. Within these experiments, considerably long excited‐state lifetimes of up to 54 μs were observed. Quenching studies with the SR, in the presence and absence of the WRC, showed that intramolecular deactivation was more efficient in the former case, thus suggesting the predominance of an oxidative quenching pathway.     

Development of new chromatographic tools based on A2A adenosine receptor subtype for ligand characterization and screening by FAC-MS

A liquid chromatographic stationary phase containing immobilized membranes from cells expressing A_2A adenosine receptor (A_2AAR) is firstly described. Cellular membranes from CHO cells stably transfected with human A_2AAR vector (A_2A(+)) and from the same cell line transfected with the corresponding empty vector (A_2A(?)) were entrapped on immobilized artificial membrane (IAM) support and packed into 6.6 mm I.D. glass columns to create A_2A(+)-IAM and A_2A(?)-IAM stationary phases. Frontal chromatography experiments on both A_2A(+)-IAM and A_2A(?)-IAM columns demonstrated the presence of a low specific interaction with the receptor. However, immobilized A_2A retained its ability to specifically bind known ligands as demonstrated by the agreement of the calculated K _d values with two different chromatographic protocols in comparison to previously reported data. In order to maximize the specific interaction, the same cellular membranes were immobilized on the inner surface of a silica capillary (40 cm?×?100 μm I.D.) by non-covalent interactions using the avidin–biotin coupling system to create two open tubular columns A_2A(+)-OT and A_2A(?)-OT. The open tubular system was characterized by ranking experiments for affinity studies in mixture useful for the selection of new potential candidates.

Ru(x)Pt(y)Sn(z) cluster-derived nanoparticle catalysts: spectroscopic investigation into the nature of active multinuclear single sites

Cluster-derived Ru(x)Pt(y)Sn(z) nanoparticles are active catalysts in the hydrogenation of nitrobenzene. The nature of the active sites has been elucidated by FTIR spectroscopy using CO and NO as probe molecules. A new metal carbonyl cluster precursor, Pt(2)Ru(2)(SnBu(t)(3))(2)(CO)(9)(μ-H)(2), has been synthesized to obtain a Ru(2)Pt(2)Sn(2)/SiO(2) catalyst, that displayed remarkably high levels of conversion and selectivities compared to other bi-and monometallic analogues. Spectroscopic comparisons with Ru(5)PtSn/SiO(2) indicate that both the nature and the stoichiometry of the metals play a key role in modulating the catalytic activities and selectivities. A multinuclear single-site containing Pt centers, which facilitate the hydrogen activation, coupled with a highly reactive Ru site, possibly involved in the nitrobenzene activation, can be hypothesized. The oxophilicity of tin helps with the anchoring of the nanoparticles, aids the dispersion of the other metals, and can play an important role in influencing the selectivity to aniline.     

Solvent-free, heterogeneous photooxygenation of hydrocarbons by hyflon membranes embedding a fluorous-tagged decatungstate

Hybrid fluoropolymeric membranes with 25% loading of the fluorous-tagged (RfN)4W10O32 effect the solvent-free photooxygenation of benzylic C-H bonds with up to 6100 TONs in 4 hours.