Thermolysis and Chemiluminescence of Monocyclic 1,2,4-Trioxan-5-ones

The 3,6-substituted 1,2,4-trioxan-5-ones 11 – 14 , on heating to 170–200°, underwent unimolecular thermolysis to generate electronically excited singlet ketones with an efficiency of ca. 0.2%. The chemiluminescence quantum yields (?oS_CL) depended on the nature of the 6-substitutents and increased linearly with temperature. The Arrhenius activation energies were obtained by measuring the rate of decay of luminescence and determined as 22.9, 30.4, 35.6, and 34.2 kcal/mol for 11 – 14 , respectively. Step analysis of the chemiluminescence of 14 afforded an average activation energy of 44.3 kcal/mol. This latter result is explicable in terms of two decomposition paths, higher and lower in energy, leading to excited and ‘dark’ products, respectively. The thermolysis of trioxanones 12 – 14 lacking a H-atom at the 6-position is interpreted as involving successive rupture of the peroxide bond, excision of ketone at the 3-substituted end, and loss of CO₂, to finally produce ketone originating from the 6-position (see Scheme 4).     

Structural and electrochemical studies of novel bis(mu-methoxo)diiron complexes: observation of Fe(III)Fe(IV) and Fe(IV)Fe(IV) states resonating with phenoxyl radicals

Novel diiron complexes with an Fe2(mu-OMe)2 core were studied as models of the active site of nonheme iron-containing enzymes. X-ray crystal structures of the complexes showed the existence of two types of ligand folding-parallel and twisted-both of which have four virtually equivalent phenolato groups sticking out from the Fe2O2 rhombic plane. Cyclic voltammetry measurements revealed two or more distinct redox waves in a region of relatively high potential, in addition to known Fe(II)/Fe(III) redox waves in a region of lower potential. These new peaks were assigned to the high-valence state of iron atoms, that is, Fe(III)Fe(IV) and Fe(IV)Fe(IV), resonating with the phenoxyl radical(s). The split width of the redox waves ranged from 0.14 to 0.20 eV, which may be a measure of the electronic interaction of the phenolate groups through the Fe2(mu-OMe)2 core.     

Effective interactions in the colloidal suspensions from hypernetted-chain theory

The hypernetted-chain (HNC) Ornstein-Zernike integral equations are used to determine the properties of simple models of colloidal solutions where the colloids and ions are immersed in a solvent considered as a dielectric continuum and have a size ratio equal to 80 and a charge ratio varying between 1 and 4000. At an infinite dilution of colloids, the effective interactions between colloids and ions are determined for ionic concentrations ranging from 0.001 to 0.1 mol/l and compared to those derived from the Poisson-Boltzmann theory. At finite concentrations, we discuss on the basis of the HNC results the possibility of an unambiguous definition of the effective interactions between the colloidal molecules.     

New fluorinated polysiloxanes containing an ester function in the spacer. I. Synthesis and characterization

Unsaturated perfluoroalkyl esters derived from undecylenic acid: CH₂?CH? (CH₂)₈? COO? CH₂? CH₂? R_F (with R_F?C₆F₁₃, 2a and R_F?C₈F₁₇, 2b ) and C₈F₁₇? (CH₂)₁₀? COO? CH₂? CH?CH₂, 2c were prepared with excellent yields. Their hydrosilylation by methylhydrodimethylsiloxane copolymers of various Si? H contents gives new fluorinated polysiloxanes which were examined by ¹H- and ¹³C-NMR, GPC, differential scanning calorimetry, and optical polarizing microscopy. Polymers derived from compounds 2a and 2b exhibit mesomorphic structures. © 1994 John Wiley & Sons, Inc.     

A general approach toward the synthesis of C-nucleoside pyrazolo[1,5-a]-1,3,5-triazines and their 3',5'-bisphosphate C-nucleotide analogues as the first reported in vivo stable P2Y(1)-receptor antagonists

In our effort to identify potent purinergic P2Y(1) receptor antagonists as potent platelet aggregation inhibitors with enhanced metabolic stability, we developed an efficient route for the large-scale preparation of 2'-deoxy-C-nucleosides of pyrazolo[1,5-a]-1,3,5-triazine. The key strategic elements of this novel synthetic approach involved the following: (i) the use of a novel activating group, the N-methyl-N-phenylamino group, which was easily generated in high yield by treatment of the pyrazolo[1,5-a]-1,3,5-triazin-4-one (5) with phosphorus oxychloride and dimethylaniline under high pressure, (ii) a regio- and stereospecific palladium-mediated coupling reaction of the readily available unprotected glycal 1,4-anhydro-2-deoxy-D-erythro-pent-1-enitol (4b) and the 8-iodo derivative (16), and (iii) the stereoselective reduction of the ketone group of the furanosyl ring followed by the subsequent displacement of the N-methyl-N-phenylamino group upon treatment with methylamine. The beta configuration at the anomeric C-1' position of the glycal moieties was perfectly retained throughout this conversion. This procedure afforded 8-(2'-deoxy-beta-D-ribofuranosyl)-2-methyl-4-(N-methylamino)pyrazolo[1,5-a]-1,3,5-triazine (21) and 8-(2'-deoxy-beta-D-xylofuranosyl)-2-methyl-4-(N-methylamino)pyrazolo[1,5-a]-1,3,5-triazine (24) with an overall yield of 50% and 39%, respectively. Finally, the conversion of nucleosides 21 and 24 to the pyrazolotriazine C-nucleotides 3',5'-bisphosphate 2 and 3',5'-cyclophosphate 26 is also described herein and represents the first reported nucleotide derivatives within the pyrazolo[1,5-a]-1,3,5-triazine series. Preliminary biological testing has shown that compound 2 strongly inhibits ADP-induced human platelet aggregation and shape change and possesses significant efficacies 30 min after injection in rat, highlighting a strong P2Y(1)-receptor antagonist activity in vitro combined with a prolonged duration of action in vivo.     

Dynamic light scattering and cryogenic transmission electron microscopy investigations on metallo-supramolecular aqueous micelles: evidence of secondary aggregation

Metallo-supramolecular diblock copolymers consisting of a polystyrene (PS) block connected to a poly(ethylene oxide) (PEO) block by a bis(terpyridine)ruthenium complex (PS₂₀-[Ru]-PEO _y ) were used to prepare aqueous micelles. The length of the PS block was kept constant, while two PEOs of different molecular weight were used. The resulting hydrated micelles and aggregates were characterized by a combination of cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering measurements. The results were compared to those obtained for a covalent counterpart (PS₂₂-b-PEO₇₀). Cryogenic transmission electron microscopy allowed visualization of the PS core of the micelles. Moreover, the aggregates result from clustering of individual micelles.     

New Syntheses of Retinal and Its Acyclic Analog γ‐Retinal by an Extended Aldol Reaction with a C6 Building Block That Incorporates a C5 Unit after Decarboxylation. A Formal Route to Lycopene and β‐Carotene

Since the C₁₅ β‐end‐group aldehyde 10 ((β‐ionylidene)acetaldehyde), an excellent intermediate in the syntheses of retinoids, can be synthesized in many ways from β‐ionone, and since the corresponding acyclic C₁₅ ψ‐end‐group aldehyde 5 can easily be synthesized from citral ( 1 ) (Scheme 3), we applied the C₁₅+C₅ route to the syntheses of γ‐retinal ((all‐E)‐ 8 ) (Scheme 3) and retinal ((all‐E)‐ 13 ) (Scheme 4), and therefore, by coupling (2×C₂₀→C₄₀), to the preparation of lycopene ( 14 ) and β‐carotene ( 15 ) (Scheme 5). Our new syntheses of retinal ((all‐E)‐ 13 ) and γ‐retinal ((all‐E)‐ 8 use an extended aldol reaction with a C₆ building block that incorporates a C₅ unit after decarboxylation.     

A stabilized formulation of IBX (SIBX) for safe oxidation reactions including a new oxidative demethylation of phenolic methyl aryl ethers

[reaction: see text] SIBX is a nonexplosive formulation of IBX that can be used as a suspension in a variety of standard organic solvents such as refluxing EtOAc and THF to oxidize safely alcohols into aldehydes and ketones. The use of hot THF is limited to the oxidation of allylic and benzylic alcohols. Most yields are comparable to those obtained with IBX or DMP. SIBX can also be used to perform oxygenative demethylation of 2-methoxyarenols into orthoquinones and catechols.     

Ultrasound-assisted microencapsulation of jackfruit extract in eco-friendly powder particles: characterization and antiproliferative activity

The aim of the article was to develop stable and safe eco-friendly microcapsules and evaluate their physicochemical properties and their efficiency to protect a jackfruit extract. Eco-friendly microcapsules were produced by ultrasound and spray drying using only three safe ingredients: sucrose ester (SE), miglyol and maltodextrin (DE = 10). Some physicochemical properties, particle morphology, FT-IR, differential scanning calorimetry and antiproliferative activity were determined for microcapsules loaded or not with the jackfuit extract. The results revealed that the encapsulation process by spray drying produced stable microcapsules, with adequate physicochemical and fluid properties for a powder product. The cell viability on the proliferation of M12.C3.F6 cell line was not affected by powder microcapsules without jackfruit extract, indicating that capsules are not toxic for these cells. However, microcapsules with jackfruit extract (100 μg/ml) were able to inhibit significantly the proliferation of M12.C3.F6 cells. These microcapsules can be used for the protection of different compounds sensitive to light, oxygen and/or heat and displaying a very low aqueous solubility.     

Numerical methods for the simulation of a coalescence-driven droplet size distribution

The droplet size distribution in a turbulent flow field is considered and modeled by means of a population balance system. This paper studies different numerical methods for the 4D population balance equation and their impact on an output of interest, the time-space-averaged droplet size distribution at the outlet, which is known from experiments. These methods include different interpolations of the experimental data at the inlet, various discretizations in time and space, and different schemes for computing the coalescence integrals. It will be shown that noticeable changes in the output of interest might occur. In addition, the computational efficiency of the studied methods is discussed.