Synthesis of polymetallic macrocyclic terpene-derived hybrids

Terpene alkyne systems act as templates in the preparation of natural product hybrids and in macrocyclic structures having up to four terpene units and eight Co-atoms, which are built by using the Nicholas reaction.     

Introducing a Cell-Free Approach for the Identification of Brewing Yeast (<Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>) Strains Using MALDI-TOF MS

Matrix-assisted laser desorption ionization (MALDI) time-of-flight mass spectrometry (TOF MS) is now accepted as a quick, easy-to-use, cost-effective, and accurate technique for the identification of microorganisms. However, the successful identification of microorganisms is dependent upon careful attention to factors such as growth conditions, extraction methods, mass spectral data collection, and data analysis procedures. Currently, most microorganism identification has been limited to the species level, and only a limited number of publications have been successful in achieving strain-level identification. In this work, a “cell-free” approach is introduced where peptide analytes secreted by several Saccharomyces cerevisiae strains during their growth period are analyzed. The analysis of the cell supernatant generates mass spectral patterns that are specific to each strain. The patterns generated in combination with a robust data analysis workflow using the open-source programs MALDIquant and Mass-Up allows for strain-level identification of S. cerevisiae. The cell-free approach using the yeast supernatant to accurately identify yeast strains is presented here as a proof of concept.

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Botanical Characterization of Guiera senegalensis Leaves

Guiera senegalensis J. F. Gmel. (Combretaceae) is one of the most important West African medicinal plants, often used to treat a variety of microbial infections. The most frequently used plant part is the leaf, its medicinal use being corroborated by several in vitro antimicrobial activity studies. However, quality criteria for pharmaceutical use, including botanical identification, are not yet determined. Aiming the establishment of such criteria, the present work deepens today's knowledge on G. senegalensis leaf morphology and anatomy, the anatomical characters of both leaf transversal section and powdered leaves being hereby presented for the first time. The most useful characters for identification purposes are leaf isobilateral organization, with similar upper and lower surfaces and a palisade parenchyma on both surfaces; trichome insertion points on both epidermis, surrounded by polar arrangements of cells; tomentose indumentum on the upper epidermis consisting of compartmented and uniseriated trichomes with long, curved, or straight terminal cells; brown scales, isolated or inserted into the epidermis, formed by radially arranged cells surrounding a central cell, with a more or less circular form and a conspicuous base; calcium oxalate cluster crystals, isolated or inserted into the palisade parenchyma and absent in lateral veins.     

Osmotic coefficients of electrolyte solutions

In this paper, the osmotic coefficient, phi, of electrolyte solutions is considered. According to the Gibbs-Duhem equation, the calculation of phi follows from that of the mean activity coefficient, gamma, based on a pseudolattice approach recently proposed. For any given electrolyte, the whole range of concentrations providing gamma相似文献   

Rheological properties of microfibrillar suspension of TEMPO-oxidized pulp

The rheology of cellulose microfibril suspensions from TEMPO-oxidized pulp was investigated. The suspension showed a pseudo-plastic and thixotropic behavior, slowly evolving with time under a given shear rate. The viscosity was proportional to the concentration up to the critical concentration of 0.23%. Above it, the viscosity followed a power law with exponents from 2 to 6 depending on the shear rate, and the system showed shear thinning behavior and behaved gel-like. Below this concentration, the system was more Newtonian. Birefringence measurement of 0.44% and 0.78% suspension showed that microfibrils alignment saturated at a small shear rate with a Herman’s orientation parameter below 0.65 probably due to the interconnection of microfibrils.     

Grafting onto microfibrils of native cellulose

Attempts to modify the surface of oxidized cellulose microfibrils were made using amine terminated molecules. First, native cellulose was oxidized with catalytic amounts of 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO), sodium hypochlorite and sodium bromide in water. The primary alcohol moieties were selectively oxidized into carboxyl groups. Then, the oxidized cellulose was coupled with amines derivatives by a peptidic reaction by using carbodiimide and hydroxysuccimide as catalyst and amidation agent. The obtained coupled cellulose showed low polarity, with stability in non-polar solvents. The products were characterized by FTIR, ¹³C NMR, rheology and conductometric titration as well as transmission electron microscopy. Their hydrophobic character was evaluated by observing their behavior in polar and non-polar solvents.     

Kinetics of reactions catalyzed by enzymes in solutions of surfactants

The effect of surfactants, both in water-in-oil microemulsions (hydrated reverse micelles) and aqueous solutions upon enzymatic processes is reviewed, with special emphasis on the effect of the surfactant upon the kinetic parameters of the process. Differences and similarities between processes taking place in aqueous and organic solvents are highlighted, and the main models currently employed to interpret the results are briefly discussed.     

Bioassay directed identification of natural aryl hydrocarbon-receptor agonists in marmalade

Citrus fruit and citrus fruit products, like grapefruit, lemon and marmalade were shown to contain aryl hydrocarbon receptor (AhR) agonists, as detected with the DR CALUX bioassay. This is of interest regarding the role of the Ah-receptor pathway in the adverse effects of dioxins, PCBs and other aromatic hydrocarbons. So far it is unclear which compounds in citrus fruit are responsible for the AhR-mediated activity and whether regular exposure to these compounds can cause effects comparable to, e.g. dioxins. The present study aimed at developing a method for identifying unknown Ah-receptor agonists in citrus products based on bioassay directed analysis, using marmalade as a first target. Following extraction with hexane and purification on an aluminium oxide-column, the extract was fractionated by HPLC using a C-18 semi-preparative column. Fractions were extracted, solvent-exchanged into dimethylsulfoxide and subsequently tested with DR CALUX. Extracts were shown to contain primarily coumarins, furocoumarins (FCs) and polymethoxyflavones (PMFs). Identification of fractions most active in the bioassay via LC/MS revealed that bergapten (an FC) is the most important Ah-receptor agonist in marmalade. The approach and method developed resulted in the successful identification of the bioactive component. However, potential pitfalls of the procedure will be discussed.     

Metal-assisted in situ formation of a tridentate acetylacetone ligand for complexation of fac-Re(CO)3+ for radiopharmaceutical applications

Reaction of [NEt4]2[ReBr3(CO)3] with 2,4-pentanedione (acac) yields a complex of the type fac-Re(acac)(OH2)(CO)3 (1) under aqueous conditions. 1 was further reacted with a monodentate ligand (pyridine) to yield a fac-Re(acac)(pyridine)(CO)3 complex (2). Complex 1 was found to react with primary amines to generate a Schiff base (imine) in aqueous solutions. When a mixed-nitrogen donor bidentate ligand, 2-(2-aminoethyl)pyridine, that has different coordination affinities for fac-Re(acac)(OH2)(CO)3 was utilized, a unique tridentate ligand was formed in situ utilizing a metal-assisted Schiff base formation to yield a complex fac-Re(CO)3(3[(2-phenylethyl)imino]-2-pentanone) (3). Tridentate ligand formation was found to occur only with the Re-coordinated acac ligand. Reactions of acac with fac-Re(CO)3Br(2-(2-aminoethyl)pyridine) (4) or a mixture of [NEt4]2[ReBr3(CO)3], acac, and 2-(2-aminoethyl)pyridine did not yield the formation of complex 3 in water.     

The Revival of Enantioselective Perfluoroalkylation – Update of New Synthetic Approaches from 2015–2022

Over the last years, methods devoted to the synthesis of asymmetric molecules bearing a perfluoroalkylated chain have been limited in number. Among them, only a few can be used on a large variety of scaffolds. This microreview aims at summarizing these recent advances in enantioselective perfluoroalkylation (−CF₃, −CF₂H, −C_nF_2n+1) and highlights the need for new enantioselective methods to easily synthesize chiral fluorinated molecules which would be useful for the pharmaceutical and agrochemical industries. Some perspectives are also mentioned.