Photochemical Reactions. 128th Communication. Isolation of a Thermally Labile 2,8-Dioxabicyclo[3.2.1]oct-3-ene Intermediate on Photolysis of 3,4: 5,6-Diepoxy-5,6-dihydro-β-ionone

Photolysis (λ = 254 mm, THF) of the diepoxyenone (E)- 1 at ?78° leads to the 2,8-dioxabicyclo[3.2.1]oct-3-ene intermediate 3 (51%). At ambient temperature 3 undergoes an unexpectedly rapid electrocyclic opening to the triketone 2 in quantitative yield. Compound 3 seems likely to be the intermediate in the acid-catalyzed rearrangement of (E)- 1 → 18 also.     

Reaction of 4,5-diamino-1,6-dihydropyrimidin-6-ones with two equivalents of chalcones

The reaction of 4,5-diamino-1,6-dihydropyrimidin-6-ones 1 with two equivalents of the chalcones 2 leads in an acidic medium to the formation of the 2,3,6,7-tetrahydro-1H-pyrimido[4,5-b][1,4]diazepin-6-one derivatives 3a-d . The structure elucidation of the products is based on nmr measurements and an X-ray diffraction.     

Application of Sputter-Assisted EPMA to Depth Profile Analysis

 A common problem in depth profile measurement is the calibration of the depth scale. The new technique of sputter assisted electron probe microanalysis offers the possibility of calculating the composition as well as the depth scale solely from the acquired X-ray intensity data without further information, e.g. sputter rates. To achieve a depth resolution that is smaller than the depth of information of the electron probe, i.e. 0.1–1 μm, special deconvolution algorithms must be applied to the acquired data. To assess the capabilities of this new technique it was applied to a Ti/Al/Ti multilayer on Si under different measurement conditions. Quantitative depth profiles were obtained by application of a deconvolution algorithm based on maximum entropy analysis. By comparison of these profiles with AES depth profiles and AFM roughness measurements, it was shown that the limiting factor to the achievable depth resolution is the occurrence of surface roughening induced by the sputtering process rather than the relatively large depth of information of the electron probe. We conclude that for certain applications sputter-assisted EPMA can be regarded as a valid depth profiling technique with a depth resolution in the nm range.     

C-Silylation de composes a fonction nitrile. Synthese de nitriles α-silicies

The direct silylation by Me₃SiCl/Li/THF of saturated nitriles having a hydrogen atom in the α position with respect to the function leads, according to a simple and rapid process, to the corresponding α-silylated nitriles in yields that are moderate but much higher than those given by the comparable previously known routes. α, β-Unsaturated nitriles give the derivatives resulting from the disilylation of the double bond. Allyl or benzyl cyanide and diphenyl acetonitrile first undergo the elimination of the nitrile group (which behaves as a halogen atom) whereas cyanamid affords bis(trimethylsilyl)carbodiimide giving after further silylation the unexpected tris(trimethylsilyl)amine.     

Glutathione peroxidase inhibitory assay for electrophilic pollutants in diesel exhaust and tobacco smoke

We developed a rapid kinetic bioassay demonstrating the inhibition of glutathione peroxidase 1 (GPx-1) by organic electrophilic pollutants, such as acrolein, crotonaldehyde, and p-benzoquinone, that are frequently found as components of tobacco smoke, diesel exhaust, and other combustion sources. In a complementary approach, we applied a high-resolution proton-transfer reaction time-of-flight mass spectrometer to monitor in real-time the generation of electrophilic volatile carbonyls in cigarette smoke. The new bioassay uses the important antioxidant selenoenzyme GPx-1, immobilized to 96-well microtiter plates, as a probe. The selenocysteine bearing subunits of the enzyme’s catalytic site are viewed as cysteine analogues and are vulnerable to electrophilic attack by compounds with conjugated carbonyl systems. The immobilization of GPx-1 to microtiter plate wells enabled facile removal of excess reactive inhibitory compounds after incubation with electrophilic chemicals or aqueous extracts of air samples derived from different sources. The inhibitory response of cigarette smoke and diesel exhaust particle extracts were compared with chemical standards of a group of electrophilic carbonyls and the arylating p-benzoquinone. GPx-1 activity was directly inactivated by millimolar concentrations of highly reactive electrophilic chemicals (including acrolein, glyoxal, methylglyoxal, and p-benzoquinone) and extracts of diesel and cigarette smoke. We conclude that the potential of air pollutant components to generate oxidative stress may be, in part, a result of electrophile-derived covalent modifications of enzymes involved in the cytosolic antioxidant defense.     

Photophysical Evidence of Charge‐Transfer‐Complex Pairs in Mixed‐Linker 5‐Amino/5‐Nitroisophthalate CAU‐10

The photochemistry of two isostructural metal–organic frameworks based on 5‐amino/5‐formamidoisophthalate (CAU‐10‐NH₂/NHCHO) or mixed‐linker 5‐amino/5‐formamido‐ and 5‐nitroisophthalate (CAU‐10‐NO₂/NH₂/NHCHO) has been studied using laser flash photolysis. 355 nm excitation of CAU‐10‐NH₂/NHCHO leads to a transient absorption spectrum characterized by a broad continuous absorption from 380 to 800 nm that was attributed to the presence of holes (440 nm) and electrons (600 nm) based on iPrOH and N₂O quenching, respectively. In contrast, no transients were observed for the isostructural mixed‐linker CAU‐10‐NO₂/NH₂/NHCHO, data that is compatible with the uniform distribution of linkers 5‐amino/5‐formamido/5‐nitroisophthalate as charge‐transfer complex pairs. The same effect of quenching of 5‐aminoisophthalate transients by 5‐nitroisophthalate was also observed in aqueous solution (pH 9) but with much lower strength. Using a simple Stern–Volmer formalism allowed the estimation of the interaction of 5‐aminoisophthalate with 5‐nitroisophthalate in MOF to be 5.2×10⁴ times stronger than in the aqueous phase.     

3-(2,5-Dioxopyrrolidin-1-yl), 3-(2,6-dioxopiperidin-1-yl), and 3-(1,3-dioxoisoindolin-2-yl)rhodanines. a novel type of rhodanine derivatives

3-Aminorhodanine 2 was reacted with cyclic anhydrides yielding 3-(2,5-dioxopyrrolidin-1-yl), 3-(2,6-dioxopiperidin-1-yl), and 3-(1,3-dioxoisoindolin-2-yl)rhodanine 6-8 , which in turn were condensated in 5 position with several aldehydes yielding the new rhodanine derivatives 9-11 .