Practical synthesis of (2'R)-2'-deoxy-2'-C-methyluridine by highly diastereoselective homogeneous hydrogenation

Diastereoselective hydrogenation of 2'-deoxy-2'-exo-methyleneuridine was carried out under homogeneous conditions using a low loading of a chiral Rh catalyst. This, coupled with improvements in the synthesis of the substrate, allowed the smooth pilot plant preparation of the title compound on >10 kg scale.     

Freezing Capture of Polymorphic Aggregates of Bolaamphiphilic L‐Valine‐Based Molecular Hydrogelators

Nanostructured xerogels have been prepared by the freeze‐drying of hydrogels and aggregates formed by bolaamphiphilic L ‐valine derivatives after aging under different environmental conditions. A wide variety of shapes and sizes has been achieved by a simple methodology. These nanostructures have been studied by SEM and WAXD and a dramatic influence of structural flexibility on the kinetics of aggregation has been observed. Such flexibility and a modulation of the hydrophobic effect have shown a profound influence in the packing of these compounds and revealed a high degree of polymorphism.     

The structure of germanosilicate glasses,studied by X-ray photoelectron spectroscopy

O1s photoelectron spectra of several alkali silicate, germanate and germanosilicate glasses are given. The concentration ratio of bridging and non-bridging oxygen atoms is determined from these spectra. In contrast to silicate glasses, in germanate glasses non-bridging oxygen atoms are only observed when the alkali oxide mole fraction exceeds 0.18. The introduction of SiO₂ in the germanate glasses drastically alters the ratio of fourfold coordinated to sixfold coordinated germanium atoms.     

Belief functions on real numbers

We generalize the TBM (transferable belief model) to the case where the frame of discernment is the extended set of real numbers , under the assumptions that ‘masses’ can only be given to intervals. Masses become densities, belief functions, plausibility functions and commonality functions become integrals of these densities and pignistic probabilities become pignistic densities. The mathematics of belief functions become essentially the mathematics of probability density functions on .     

Influence of rigid polymer matrices on the reversible photochemical reaction of α-p-dimethylaminophenyl-N-m-nitrophenylnitrone

The thermally reversible photocyclization of α-p-dimethylaminophenyl-N-m-nitrophenylnitrone (I) to the corresponding oxaziridine (II) was studied in solution and in rigid polymer matrices. Irradiation with light of wavelength above 380 nm causes a clean transformation of (I) to (II) in solution as well as in polymer matrices. The quantum yield of the photoreaction in solution is about 0.06, the value being almost independent of the nature of the solvent and the irradiation time. In poly-(methyl methacrylate) (PMMA) and in polystyrene (PSt) films, the photocyclization shows initial quantum yields of 0.1 and 0.23, respectively, which decrease with irradiation time. In solution in the dark, II reverted mainly to I with formation of side product(s) in a first-order reaction. The recovery of I during the dark reaction (60–90%) as well as the rate constant of the reaction are strongly affected by the solvent. The kinetics of the thermal return in the two polymer matrices does not follow the first-order rate law. The initial reaction rate as well as the extent of the recovery of I in PMMA film are greater than those in ethyl acetate.     

Photochemistry of nonconjugated bichromophoric systems: Photoreductive polyrecombination of diaryl ketones

The irradiation of nonconjugated bichromophoric systems, diaryl ketones, with ultraviolet light in the presence of hydrogen donors, such as isopropanol or bisbenzhydrol, yields high polymers. Two series of arylketones were investigated, namely bisbenzophenones and bisketotriazoles. The cage reaction, which arises from the cross combination between the acetone ketyl and bisbenzophenone ketyl radicals, was estimated to be very small but may constitute a chain termination reaction in the photopolymerization in isopropanol. The photopolymerization of bisdiketone–dihydrol systems was found to yield polymers with much higher molecular weights than those obtained from the photopolymerization of bisdiketone–isopropanol systems. The photolysis of some binary mixtures of aromatic diketones in the presence of isopropanol yielded statistical copolypinacols. In some favorable cases, the NMR spectrum of the copolymer obtained showed three distinct linkages and from the infrared spectrum intensities the copolymers composition and the number average length of the sequences may be determined.     

Tetrachlorobisphenol-A adipate polymers. III. Synthesis and crystalline properties of block copolymers of poly(tetrachlorobisphenol-A adipate) and polystyrene

Block copolymers having poly(tetrachlorobisphenol-A adipate) (PTBA) and polystyrene (PS) sequences were synthesized were synthesized by photodegradation of an oxime-containing polyester in the presence of styrene. Crystallinity, melting behavior, and spherulitic growth rates were studied as a function of block compositions and molecular weights. A model was proposed based on a complete phase separation between the two components. The influence of the polymer composition on the spherulitic growth rate is described by introducing a supplementary pre-exponential factor into the equation for the growth rate. This parameter is a measure of the tortuosity of the actual path that has to be covered owing to the presence of the noncrystallizable blocks.