Nicola d'Alessandro

One-pot synthesis of lignin-stabilised platinum and palladium nanoparticles and their catalytic behaviour in oxidation and reduction reactions

A one-pot green method to synthesise Pt and Pd nanoparticles is reported. Two natural aromatic polymers, lignin and fulvic acid, were used as both reducing and stabilising agents at moderate temperature (80 °C) in water and under aerobic conditions. Full characterisation was performed using TEM, UV-vis, XRD, 195Pt and 1H NMR, FT-IR and GC-MS techniques. In the TEM images, we observed spherical nanoparticles of diameters in the range of 16 nm to 20 nm, in the case of Pd, and smaller ones of not so well defined shapes for Pt. GC-MS of the organic fractions formed during the preparation of the nanoparticles showed defined amounts of vanillin, a well known degradation product of these polymers. This finding indicates that the active participation of lignins and fulvic acids in the metal reduction step. The catalytic activity of the nanoparticles was tested for the NaBH4 reduction of 4-nitrophenol and for the aerobic oxidation of alcohols, reactions that are always conducted under green conditions. Both Pt and Pd nanoparticles show good catalytic activity in the reduction reaction, while in the aerobic oxidation reaction only the Pt nanoparticles were effective.

Solid-phase extraction and gas chromatographic analysis of phenolic compounds in virgin olive oil

Abstract A careful investigation on the potential application of solid phase extraction (SPE)-gas chromatography procedure in the analysis of phenol compounds in virgin olive oils was carried out. In doped refined olive oil samples a comparison between liquid/liquid and SPE extraction evidenced higher recovery when the C 18 sorbent phase was employed whereas, in the case of total suppression of residual sylanolic group (C 18 EC ), only contradictory data was obtained. The same procedures were carried out on 10 genuine samples of virgin olive oil. As observed with the standards, C 18 sorbent phase gave higher values compared to C 18 EC and the liquid/liquid extraction procedures. Satisfactory results were obtained in the detection of ligstroside aglycon but for the oleuropein aglycon the quantitative is not completely reliable for the overlap of some unknown no-phenol compounds.

Oxidation of dibenzothiophene by hydrogen peroxide or monopersulfate and metal–sulfophthalocyanine catalysts: an easy access to biphenylsultone or 2-(2′-hydroxybiphenyl)sulfonate under mild conditions

A catalytic system consisting of metal–sulfophthalocyanines (MPcS) and monopersulfate or hydrogen peroxide as oxidants was effective in the dibenzothiophene oxidative desulfurization with various yields and selectivities. Oxidations were conducted at room temperature in acetonitrile–water mixed solvent. The dibenzothiophene oxidation involved the step by step formation of dibenzothiophene dioxide and biphenylsultone (dibenzo-1,2-oxathiine 2,2-dioxide), followed by hydrolysis to 2(2′-hydroxybiphenyl)sulfonate and finally catalytic desulfurization to 2-hydroxybiphenyl (2-phenylphenol) and sulfuric acid; all the intermediate compounds were identified. Moreover, catalytic over-oxidation of 2-hydroxybiphenyl, with ring fission and formation of various oxidation products, among them carbon dioxide, oxalic and benzoic acid, was also observed. Among the various MPcS catalysts examined (M = Fe, Co and Ru), the ruthenium derivative exhibited the best performances with persulfate and iron derivative with hydrogen peroxide; in both cases the slow step of the process consisted in the oxidation of dibenzothiophene dioxide to biphenylsultone.

Deoxydehydration of glycerol to allyl alcohol catalyzed by rhenium derivatives

The deoxydehydration (DODH) of glycerol is effectively catalyzed by rhenium derivatives, either in neat glycerol or in the presence of solvents (in particular alcohols), in air or under hydrogen bubbling. Methyltrioxorhenium (MTO) and ReO3 were the only rhenium catalysts tested that can selectively catalyze the DODH reaction at very low temperatures (140 °C). The presence of oxygen is not necessary, although under nitrogen the reaction requires higher temperatures to occur. On the other hand, the presence of hydrogen often noticeably increased the selectivity versus allyl alcohol formation, reaching the considerable value of 90% in the case of reaction conducted in 2,4-dimethyl-3-pentanol with ReO3. The DODH reaction always exhibits a definite induction time that, in the case of MTO, corresponds more or less to the time required for its demethylation. Metal catalysts in both high – likely rhenium(VI) – and low oxidation states are involved. Re-addition of fresh glycerol at the end of the reaction indicates the feasibility of the reuse of the catalysts.

One-pot combination of enzyme and Pd nanoparticle catalysis for the synthesis of enantiomerically pure 1,2-amino alcohols

One-pot combinations of sequential catalytic reactions can offer practical and ecological advantages over classical multi-step synthesis schemes. In this context, the integration of enzymatic and chemo-catalytic transformations holds particular potential for efficient and selective reaction sequences that would not be 10 possible using either method alone. Here we report the one-pot combination of alcohol dehydrogenasecatalysed asymmetric reduction of 2-azido ketones and Pd nanoparticle-catalysed hydrogenation of the resulting azido alcohols, which gives access to both enantiomers of aromatic 1,2-amino alcohols in high yields and excellent optical purity (ee >99%). Furthermore, we demonstrate the incorporation of an upstream azidolysis and a downstream acylation step into the one-pot system, thus establishing a highly 15 integrated synthesis of the antiviral natural product (S)-tembamide in 73% yield (ee >99%) over 4 steps. Avoiding the purification and isolation of intermediates in this synthetic sequence leads to an unprecedentedly low ecological footprint, as quantified by E-factor and solvent demand.

Catalytic aerobic oxidation of allylic alcohols to carbonyl compounds under mild conditions

A new catalytic aerobic oxidation of alcohols to aldehydes under green conditions was developed (room temperature and pressure, water solution, open vials). The water-soluble platinum(II) tetrasulfophthalocyanine (PtPcS) catalyst showed the best selectivity for carbonyl derivatives, and in particular for α,β-unsaturated alcohols; the reactions are slow.

Region-specific effects on brain metabolites of hypoxia and hyperoxia overlaid on cerebral ischemia in young and old rats: a quantitative proton magnetic resonance spectroscopy study

BackgroundBoth hypoxia and hyperoxia, deregulating the oxidative balance, may play a role in the pathology of neurodegenerative disorders underlain by cerebral ischemia. In the present study, quantitative proton magnetic resonance spectroscopy was used to evaluate regional metabolic alterations, following a 24-hour hypoxic or hyperoxic exposure on the background of ischemic brain insult, in two contrasting age-groups of rats: young - 3 months old and aged - 24 months old.MethodsCerebral ischemia was induced by ligation of the right common carotid artery. Concentrations of eight metabolites (alanine, choline-containing compounds, total creatine, γ-aminobutyric acid, glutamate, lactate, myo-inositol and N-acetylaspartate) were quantified from extracts in three different brain regions (fronto-parietal and occipital cortices and the hippocampus) from both hemispheres.ResultsIn the control normoxic condition, there were significant increases in lactate and myo-inositol concentrations in the hippocampus of the aged rats, compared with the respective values in the young ones. In the ischemia-hypoxia condition, the most prevalent changes in the brain metabolites were found in the hippocampal regions of both young and aged rats; but the effects were more evident in the aged animals. The ischemia-hyperoxia procedure caused less dedicated changes in the brain metabolites, which may reflect more limited tissue damage.ConclusionsWe conclude that the hippocampus turns out to be particularly susceptible to hypoxia overlaid on cerebral ischemia and that old age further increases this susceptibility.

Direct synthesis of adipic acid by mono-persulfate oxidation of cyclohexane, cyclohexanone or cyclohexanol catalyzed by water-soluble transition-metal complexes

A catalytic system consisting of water-soluble metal sulfophthalocyanines (MPcS) or various ruthenium complexes and mono-persulfate as the oxidant was effective in the oxidation of cyclohexanone, cyclohexanol and cyclohexane to adipic acid with different yields and selectivity. Oxidations were conducted at room temperature and under atmospheric pressure in aqueous media (or, in the case of cyclohexane, in a water–neat substrate double phase). The oxidation of cyclohexanol involved step-by-step formation of cyclohexanone, e-caprolactone and 6-hydroxyhexanoic acid, all of which have been identified in the reaction mixtures; in selected cases moderate over-oxidation of adipic acid to glutaric and succinic acid was also observed. Various MPcS catalysts were examined (M = Fe, Co, Ni, Cu and Ru), and the ruthenium derivative exhibited the best performances in terms of rate and selectivity. Mono-persulfate was found to be a more convenient oxidizing reagent than hydrogen peroxide; related patterns were observed when H2O2 was used, however extended dismutation of the oxidant limited the overall yields. Cyclohexane underwent slow oxidation when reacted with persulfate (water–substrate double phase) in the presence of the water-soluble metal catalysts; adipic acid was selectively produced (95%) in the presence of RuPcS catalyst with yields as high as 21% (48 h). The catalytic performance of simpler ruthenium derivatives, such as [RuCl2(DMSO)4] (RuDMS) and K5[Ru(H2O)P11O39] (RuPW), was also examined for comparison purposes. A kinetic scheme for cyclohexane oxidation is proposed.

The Photochemical Reaction between 1,4-Dicyanonaphthalene and benzyl ethers

Abstract Irradiation of 1,4-dicyanonaphthalene (DCN) and benzyl methyl ether gives the two diastereoisomeric 1-substituted 1,2-dihydronaphthalenes. A stereochemical assignment for these products, and related diastereoisomers pairs is proposed. The reaction occurs via the free radical ions and the low quantum efficiency is due to the slow deprotonation of the radical cation, with only moderate salt effect. In accordance with this scheme, the reaction with benzyl l-menthyl ether gives a low enantiomeric eccess.

Lignin coating to quench photocatalytic activity of titanium dioxide nanoparticles for potential skin care applications

Ultraviolet light can cause photodamage to the skin, such as sunburns and melanomas. TiO2 is introduced in sunscreen formulations to reflect and scatter UV radiation. However, it can also photocatalyze the production of reactive species like O2−˙ and OH˙. Here, we aimed to remove the photocatalytic activity of TiO2 (anatase and rutile), while preserving the UV filter property. Anatase and rutile were modified through two preparative protocols. The first used HCl lignin precipitation of ethylene glycol lignin solution in the presence of the cross-linker glutaraldehyde and anatase or rutile nanoparticles. The second protocol used HNO3 lignin precipitation of lignin aqueous solution in the presence of anatase or rutile nanoparticles. Both methodologies were performed at room temperature and ambient pressure in green media, with vigorous mixing followed by 20 kHz sonication. The composite materials obtained were fully characterized by SEM, XRD analysis and FT-IR spectroscopy, and their photostability, and photo and shielding activities were evaluated through reference reactions: oxidation of 2-propanol, an ene-reaction conducted on an α,β-unsaturated carboxylic derivative and photochemical transformation of o-nitrobenzaldehyde to o-nitrosobenzoic acid. Therefore, in the near future, industrial use of these new clusters can help to minimize TiO2 phototoxicity in sunscreen formulations, while preserving the sunscreen photoprotection activity.