Menthyl phospholide ester anions provide an operationally simple and high yielding entry to the first planar chiral enantiopure phospharuthenocene derivatives. 相似文献
As the complexity of microphotonic devices grows, the ability to precisely trim microring resonators becomes increasingly important. Photo-oxidation trimming uses UV irradiation to oxidize a cladding layer composed of polymerized hexamethyldisilane (6M2S) deposited with plasma-enhanced chemical vapor deposition (PECVD). PECVD 6M2S has optical properties that are compatible with microring devices, and its high cross linking renders it insoluble. Photo-oxidation decreases the refractive index of PECVD 6M2S by nearly 4%, permitting large resonance shifts that are not feasible with thermal trimming techniques. Resonance shifts from single-mode, 100 microm diameter Si3N4 (n =2.2) rings were as large as 12.8 nm for the TE mode and 23.5 nm for the TM mode. 相似文献
Although our pyrolytic studies of five alkyl nitrites (RONO) have shown that it is possible to determine precise, acceptable values for k1: we have been uncertain about the mechanism for the first order production of nitroxyl from primary and secondary nitrites. Nitroxyl could arise either from the direct elimination process (5) or from the disproportionation of the alkoxyl radical concerned and nitric oxide: Thus kexp = k5 or k1k6/[k2 + k6]. If the route is reaction (6), Eexp should be identical to E1, since the ratio k6/k2 is temperature independent. We preferred the elimination process because Eexp < E1 and Aexp was in agreement with transition-state calculations for such elimination processes. This study was concerned with the pyrolyses of ethyl and i-propyl nitrites in the presence of nitric oxide. The results show that nitroxyl is produced via the disproportionation of the alkoxyl radical and nitric oxide, as originally suggested by Levy. This is supported by the wealth of particularly photochemical data in the literature. Our and other previous spuriously low Arrhenius parameters are attributed to heterogeneous effects. 相似文献
The rate of decomposition of s-butyl nitrite (SBN) has been studied in the absence (130–160°C) and presence (160–200°C) of NO. Under the former conditions, for low concentrations of SBN (6 × 10?5 ? 10?4M) and small extents of reaction (~1.5%), the first-order homogeneous rates of acetaldehyde (AcH) formation are a direct measure of reaction (1) since k3c » k2(NO): . Unlike t-butyl nitrite (TBN), d(AcH)/dt is independent of added CF4 (~0.9 atm). Thus k3c is always » k2 (NO) over this pressure range. Large amounts of NO (~0.9 atm) (130–160°C) completely suppress AcH formation. k1 = 1016.2–40.9/θ sec?1. Since (E1 + RT) and ΔH°1 are identical, within experimental error, both may be equated with D(s-BuO-NO) = 41.5 ± 0.8 kcal/mol and E2 = 0 ± 0.8 kcal/mol. The thermochemistry leads to the result ΔH°f (s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document}) = ? 16.6 ± 0.8 kcal/mol. From ΔS°1 and A1, k2 is calculated to be 1010.4M?1 · sec?1, identical to that for TBN. From an independent observation that k6/k2 = 0.26 ± 0.01 independent of temperature, \documentclass{article}\pagestyle{empty}\begin{document}${\rm s - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}, we find E6 = 0 ± 1 kcal/mol and k6 = 109.8M?1 · sec?1. Under the conditions first cited, methyl ethyl ketone (MEK) is also a product of the reaction, the rate of which becomes measurable at extents of conversion >2%. However, this rate is ~0.1 that of AcH formation. Although MEK formation is affected by the ratio S/V for different reaction vessels, in a spherical reaction vessel, this MEK arises as the result of an essentially homogeneous first-order 4-centre elimination of HNO. \documentclass{article}\pagestyle{empty}\begin{document}${\rm SBN}\mathop \to \limits^{\rm 5} {\rm MEK} + {\rm HNO}$\end{document}; k5 = 1012.8–35.8/θ sec?1. Sec-butyl alcohol (SBA), formed at a rate comparable to MEK, is thought to arise via the hydrolysis of SBN, the water being formed from HNO. The rate of disappearance of SBN, that is, d(MEK + SBA + AcH)/dt, is given by kglobal = 1015.7–39.6/θ sec?1. In NO (~1 atm) the rate of formation of MEK was about twice that in the absence of NO, whereas the SBA was greatly reduced. This reaction was also affected by the ratio S/V of different reaction vessels. It was again concluded that in a spherical reaction vessel, the rate of MEK formation was essentially homogeneous and first order. This rate is given by kobs = 1012.9–35.4/θ sec?1, very similar to k5. However, although it is clear that the rate of formation of MEK is doubled in the presence of NO, the value for kobs makes it difficult to associate this extra MEK with the disproportionation of s-\documentclass{article}\pagestyle{empty}\begin{document}${\rm Bu}\mathop {\rm O}\limits^{\rm .}$\end{document} and NO: s-\documentclass{article}\pagestyle{empty}\begin{document}$s{\rm - Bu}\mathop {\rm O}\limits^{\rm .} + {\rm NO}\mathop \to \limits^{\rm 6} {\rm MEK} + {\rm HNO}$\end{document}. NO at temperatures of 130–160°C completely suppresses AcH formation. AcH reappears at higher temperatures (165–200°C), enabling k3c to be determined. Ignoring reaction (6), d(AcH)/dt = k1k3 (SBN )/[k3c + k2(NO)]; k3c = 1014.8–15.3/θ sec?1. Inclusion of reaction (6) into the mechanism makes very little difference to the result. Reaction (3c) is expected to be a pressure-dependent process. 相似文献
Bidentate and tridentate ligands for transition metals are accessible in one-pot reactions (yield 62–88%) by ring opening of cyclic diphos=phanes with organolithium compounds and subsequent reaction with electrophiles. 相似文献
Since the development of supramolecular chemical biology, self‐organised nano‐architectures have been widely explored in a variety of biomedical applications. Functionalized synthetic molecules with the ability of non‐covalent assembly in an aqueous environment are typically able to interact with biological systems and are therefore especially interesting for their use in theranostics. Nanostructures based on π‐conjugated oligomers are particularly promising as theranostic platforms as they bear outstanding photophysical properties as well as drug loading capabilities. This Feature Article provides an overview on the recent advances in the self‐assembly of intrinsically fluorescent nanoparticles from π‐conjugated small molecules such as fluorene or perylene based chromophores for biomedical applications.