1,721,119 research outputs found
Studies on the Reactivity of Cephalosporins. 6 Ozonolysis of A2-Cephem Derivatives as a New Entry to Highly Functionalized 2-Oxoazetidine and 2-Oxoazetidine-4-sulfenic Acid Derivatives.
No full textThe ozonolysis of Delta(2)-cephem derivatives 1, 2, and 3, to obtain highly functionalized 2-oxoazetidine and 2-oxoazetidine-4-sulfenic acid derivatives is described. An efficient and selective synthesis of the oxapenem derivative 16 is also reported
The path to life's origins. Remaining hurdles.
No full textRecent progress in abiotic syntheses, especially self-catalytic syntheses, as well as theoretical breakthroughs such as reconstruction of events of early molecular evolution and tracing repeat expansions in contemporary genomes, converge to a rather simple possible scenario of origin of life, notwithstanding the enormity of the problem. The scenario includes self-replicating RNA duplexes, supplemented by monomers and high-energy compounds that, as demonstrated or assumed, can all be synthesized abiotically. The self-replication would proceed with occasional mutational changes, propagated in later cycles. This audacious, as it may seem, walk toward the life origin already involves many laboratories, each exploring its own scenario. The one suggested in this outline seems to the authors well justified to engage in, while bypassing few steps to deal with later
Nano-Structured Lignin as Green Antioxidant and UV Shielding Ingredient for Sunscreen Applications
No full textGreen, biocompatible, and biodegradable antioxidants represent a milestone in cosmetic and cosmeceutical applications. Lignin is the most abundant polyphenol in nature, recovered as a low‐cost waste from the pulp and paper industry and biorefinery. This polymer is characterized by beneficial physical and chemical properties which are improved at the nanoscale level due to the emergence of antioxidant and UV shielding activities. Here we review the use of lignin nanoparti‐ cles in cosmetic and cosmeceutical applications, focusing on sunscreen and antiaging formulations. Advances in the technology for the preparation of lignin nanoparticles are described highlighting structure activity relationships
Recent advances in the chemistry of parainfluenza-1 (Sendai) virus inhibitors
No full textPurine and pyrimidine derivatives, antioxidants, fusion inhibitors, statins, prostaglandins, antibiotic nucleosides, inhibitors of Ca2+ homeostasis, carbohydrate derivatives, antisense polynucleotides and chimeras, are described as inhibitors of parainfluenza-1 (Sendai) viral infections. (C) 2003 Wiley Periodicals
Green and Scalable Preparation of Colloidal Suspension of Lignin Nanoparticles and Its Application in Eco-friendly Sunscreen Formulations
Full text linkLignin nanoparticles
(LNPs) are applied in several industrial applications.
The nanoprecipitation of LNPs is fast and inexpensive but currently
still limited to the use of hazardous organic solvents, making it
difficult to apply them on a large scale. Here, we report a scalable
nanoprecipitation procedure for the preparation of colloidal lignin
nanoparticles (cLNPs) by the use of the green solvents dimethylisosorbide
and isopropylidene glycerol. Irrespective of the experimental conditions,
cLNPs showed higher UV absorbing properties and radical scavenging
activity than parent LNPs and raw lignin. cLNPs were successively
used in the preparation of eco-friendly sunscreen formulations (SPF
15, 30, and 50+, as evaluated by the COLIPA assay), which showed high
UV-shielding activity even in the absence of synthetic boosters (microplastics)
and physical filters (TiO2 and ZnO). Biological assays
on human HaCaT keratinocytes and human skin equivalents demonstrated
the absence of cytotoxicity and genotoxicity, associated with an optimal
protection of the skin from UV-A damage
A biomimetic approach to lignin degradation: Metalloporphyrins catalyzed oxidation of lignin and lignin model compounds
No full textAn overview of the state of the art for the use of synthetic metalloporphyrins in the catalytic oxidation of lignin and lignin model compounds is presented. The biomimetic oxidation of 5-5′ condensed and diphenylmethane lignin model compounds with several water soluble anionic and cationic iron and manganese porphyrins in the presence of hydrogen peroxide is described. Manganese porphyrins were found more effective in degrading lignin substructures than iron porphyrins. Among them the cationic manganese mesotetrakis(N-methyl-pyridinio) porphyrin pentaacetate [TPyMePMn(CH3COO)5], never used before in lignin oxidation, proved to be the best catalyst. The catalytic activity of porphyrins in hydrogen peroxide oxidation of residual kraft lignin was also investigated. TPyMePMn(CH3COO)5 was able to perform the most extensive degradation of the lignin structure, as demonstrated by the decrease of aliphatic hydroxyl groups and increase of carboxylic acids, as measured by quantitative 31P-NMR. No significant condensation reactions occurred during manganese porphyrin catalyzed oxidations of residual kraft lignin, while in the presence of iron porphyrins an increase of condensed moieties was detected
Carbon Nanotubes as Activating Tyrosinase Supports for the Selective Synthesis of Catechols
No full textA series of redox catalysts based on the immobilization of tyrosinase
on multiwalled carbon nanotubes has been prepared by applying the layer-by-layer
principle. The oxidized nanotubes (ox-MWCNTs) were treated with poly(diallyl
dimethylammonium chloride) (PDDA) and tyrosinase to yield ox-MWCNTs/
PDDA/tyrosinase I. Catalysts II and III have been prepared by increasing the
number of layers of PDDA and enzyme, while IV was obtained by co-immobilization
of tyrosinase with bovine serum albumin (ox-MWCNTs/PDDA/BSA-tyrosinase).
Attempts to covalently bind tyrosinase provided weakly active systems. The coating
of the enzyme based on the simple layer-by-layer principle has afforded catalysts I−
III, with a range of activity from 21 units/mg (multilayer, II) to 66 units/mg
(monolayer, I), the best system being catalyst IV (80 units/mg). The novel catalysts
were fully characterized by scanning electron microscopy and atomic force microscopy, showing increased activity with respect to
that of the native enzyme. These catalysts were used in the selective synthesis of catechols by oxidation of meta- and parasubstituted
phenols in an organic solvent (CH2Cl2) as the reaction medium. It is worth noting that immobilized tyrosinase was
able to catalyze the oxidation of very hindered phenol derivatives that are slightly reactive with the native enzyme. The increased
reactivity can be ascribed to a stabilization of the immobilized tyrosinase. The novel catalysts I and IV retained their activity for
five subsequent reactions, showing a higher stability in organic solvent than under traditional buffer conditions
A novel and efficient synthesis of DOPA and DOPA peptides by oxidation of tyrosine residues with IBX
No full textAn efficient route to 3,4-dihydroxylphenylalanine (DOPA) and DOPA peptides was described by oxidation of L-tyrosine and L-tyrosine derivatives with 2-iodoxybenzoic acid (IBX). DOPA was obtained after an situ reduction of the corresponding ortho-quinone with sodium dithionite. Oxidation reactions proceeded in good yields and high chemo- and regio-selectivity. The chirality of the DOPA residue was retained under the reaction conditions. The efficiency and the selectivity of the reaction were successfully tested using recyclable polymer-supported IBX
Advances in Nanotechnology Transition Metal Catalysts in Oxidative Desulfurization (ODS) Processes
No full textOrganosulfur compounds show a negative environmental impact because of SOx emissions by combustion of fuel oils. As a consequence, removal of sulfur is becoming a worldwide challenge. The hydrodesulfurization (HDS) process achieves limited performances in the case of refractory S-containing aromatic compounds, such as thiophene and substituted benzothiophenes (BTs), which require highly energy-demanding conditions (high temperature and pressure conditions). Oxidative desulfurization (ODS) is considered the most promising alternative to HDS. During ODS treatment, the organosulfur compounds are oxidized to corresponding sulfoxides and sulfones, which can be successively removed by extraction with polar solvents. Different stoichiometric oxidants have been used in the ODS processes with a different degree of efficacy and environmental impact. The design and development of catalytic procedures can increase the ODS energy efficiency as well as make it more economical and environmentally acceptable. Here we describe the advances in nanostructured organometallic catalysis and biotechology applied to ODS treatment
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