A small library of triazolylidene‐boranes that differ only in the nature of the aryl group on the external nitrogen atom was prepared. Their reactivity as hydrogen‐atom donors, as well as that of the corresponding N‐heterocyclic carbene (NHC)‐boryl radicals toward methyl acrylate and oxygen, was investigated by laser flash photolysis, molecular orbital calculations, and ESR spin‐trapping experiments, and benchmarked relative to the already known dimethyltriazolylidene‐borane. The new NHC‐boranes were also used as co‐initiators for the Type I photopolymerization of acrylates. This allowed a structure–reactivity relationship with regard to the substitution pattern of the NHC to be established and the role of electronic effects in the reactivity of NHC‐boryl radicals to be probed. Although their rate of addition to methyl acrylate depends on their electronegativity, the radicals are all nucleophilic and good initiators for photopolymerization reactions. 相似文献
We consider as in Part I a family of linearly elastic shells of thickness 2?, all having the same middle surfaceS=?(?)?R3, whereω?R2 is a bounded and connected open set with a Lipschitz-continuous boundary, and?∈l3 (?;R3). The shells are clamped on a portion of their lateral face, whose middle line is?(γ0), whereγ0 is any portion of?ω withlength γ0>0. We make an essential geometrical assumption on the middle surfaceS and on the setγ0, which states that the space of inextensional displacements $$\begin{gathered} V_F (\omega ) = \{ \eta = (\eta _i ) \in H^1 (\omega ) \times H^1 (\omega ) \times H^2 (\omega ); \hfill \\ \eta _i = \partial _v \eta _3 = 0 on \gamma _0 ,\gamma _{\alpha \beta } (\eta ) = 0 in \omega \} , \hfill \\ \end{gathered}$$ where $\gamma _{\alpha \beta }$ (η) are the components of the linearized change is metric tensor ofS, contains non-zero functions. This assumption is satisfied in particular ifS is a portion of cylinder and?(γ0) is contained in a generatrix ofS. We show that, if the applied body force density isO(?2) with respect to?, the fieldu(?)=(ui(?)), whereui(?) denote the three covariant components of the displacement of the points of the shell given by the equations of three-dimensional elasticity, once “scaled” so as to be defined over the fixed domain Ω=ω×]?1, 1[, converges as?→0 inH1(Ω) to a limitu, which is independent of the transverse variable. Furthermore, the averageζ=1/2ts?11udx3, which belongs to the spaceVF(ω), satisfies the (scaled) two-dimensional equations of a “flexural shell”, viz., $$\frac{1}{3}\mathop \smallint \limits_\omega a^{\alpha \beta \sigma \tau } \rho _{\sigma \tau } (\zeta )\rho _{\alpha \beta } (\eta )\sqrt {a } dy = \mathop \smallint \limits_\omega \left\{ {\mathop \smallint \limits_{ - 1}^1 f^i dx_3 } \right\} \eta _i \sqrt {a } dy$$ for allη=(ηi) ∈VF(ω), where $a^{\alpha \beta \sigma \tau }$ are the components of the two-dimensional elasticity tensor of the surfaceS, $$\begin{gathered} \rho _{\alpha \beta } (\eta ) = \partial _{\alpha \beta } \eta _3 - \Gamma _{\alpha \beta }^\sigma \partial _\sigma \eta _3 + b_\beta ^\sigma \left( {\partial _\alpha \eta _\sigma - \Gamma _{\alpha \sigma }^\tau \eta _\tau } \right) \hfill \\ + b_\alpha ^\sigma \left( {\partial _\beta \eta _\sigma - \Gamma _{\beta \sigma }^\tau \eta _\tau } \right) + b_\alpha ^\sigma {\text{|}}_\beta \eta _\sigma - c_{\alpha \beta } \eta _3 \hfill \\ \end{gathered} $$ are the components of the linearized change of curvature tensor ofS, $\Gamma _{\alpha \beta }^\sigma$ are the Christoffel symbols ofS, $b_\alpha ^\beta$ are the mixed components of the curvature tensor ofS, andfi are the scaled components of the applied body force. Under the above assumptions, the two-dimensional equations of a “flexural shell” are therefore justified. 相似文献
Nine different perylene derivatives are prepared and their ability to initiate, when combined with an iodonium salt (and optionally N‐vinylcarbazole), a ring‐opening cationic photopolymerization of epoxides under very soft halogen lamp irradiation is investigated. One of them is particularly efficient under a red laser diode exposure at 635 nm and belongs now to the very few systems available at this wavelength. The photochemical mechanisms are studied by steady‐state photolysis, electron spin resonance spin trapping, fluorescence, cyclic voltammetry, and laser flash photolysis techniques.
It is well known that both semantic and syntactic information play a role in pronoun resolution in sentences. However, it
is unclear what the relative contribution of these sources of information is for the establishment of a coreferential relationship
between the pronoun and the antecedent in combination with a local structural case constraint on the pronoun (i.e. case assignment
of a pronoun under preposition governing). In a prepositional phrase in German and Dutch, it is the preposition that assigns
case to the pronoun. Furthermore, in these languages different overtly case-marked pronouns are used to refer to male and
female persons. Thus, one can manipulate biological/syntactic gender features separately from case marking features. 相似文献
1,3‐Dimethylimidazol‐2‐ylidene difluoroborane (NHC‐BF2H) was prepared in a one‐pot, two‐step reaction from the parent ligated borane (NHC‐BH3). The derived difluoroboryl radical (NHC‐BF2.) was generated by laser flash photolysis experiments and characterized by UV spectroscopy and rate‐constant measurements. It is transient and reacts quickly with O2. Unusually, it also reacts more rapidly with ethyl vinyl ether than with methyl acrylate. By this measure, it is the first electrophilic ligated boryl radical. Both NHC‐BH3 and NHC‐BF2H serve as co‐initiators in bulk photopolymerizations, converting both electron‐poor and electron‐rich monomers at roughly similar rates. However, the difluorinated coinitiator provides polymers with dramatically increased chain lengths from both monomers. 相似文献
Herein we detail a practical synthesis of bullvalene and a variety of mono‐ and disubstituted analogues through cobalt‐catalysed [6+2] cycloaddition of cyclooctatetraene to alkynes, followed by photochemical di‐π‐methane rearrangement. The application of isomer‐network analysis, coupled with quantum‐chemical calculations, provides a powerful automated tool for predicting the properties of bullvalene isomer networks. 相似文献
4‐Phenyl‐4‐thiazoline‐2‐thiol is an active pharmaceutical compound, one of whose activities is as a human indolenamine dioxygenase inhibitor. It has been shown recently that in both the solid state and the gas phase, the thiazolinethione tautomer should be preferred. As part of both research on this lead compound and a medicinal chemistry program, a series of substituted arylthiazolinethiones have been synthesized. The molecular conformations and tautomerism of 4‐(2‐methoxyphenyl)‐4‐thiazoline‐2‐thione and 4‐(4‐methoxyphenyl)‐4‐thiazoline‐2‐thione, both C10H9NOS2, are reported and compared with the geometry deduced from ab initio calculations [PBE/6‐311G(d,p)]. Both the crystal structure analyses and the calculations establish the thione tautomer for the two substituted arylthiazolinethiones. In the crystal structure of the 2‐methoxyphenyl regioisomer, the thiazolinethione unit was disordered over two conformations. Both isomers exhibit similar hydrogen‐bond patterns [R22(8) motif] and form dimers. The crystal packing is further reinforced by short S…S interactions in the 2‐methoxyphenyl isomer. The conformations of the two regioisomers correspond to stable geometries calculated from an ab initio energy‐relaxed scan. 相似文献
Advanced tools for cell imaging are of great interest for the detection, localization, and quantification of molecular biomarkers of cancer or infection. We describe a novel photopolymerization method to coat quantum dots (QDs) with polymer shells, in particular, molecularly imprinted polymers (MIPs), by using the visible light emitted from QDs excited by UV light. Fluorescent core–shell particles specifically recognizing glucuronic acid (GlcA) or N‐acetylneuraminic acid (NANA) were prepared. Simultaneous multiplexed labeling of human keratinocytes with green QDs conjugated with MIP‐GlcA and red QDs conjugated with MIP‐NANA was demonstrated by fluorescence imaging. The specificity of binding was verified with a non‐imprinted control polymer and by enzymatic cleavage of the terminal GlcA and NANA moieties. The coating strategy is potentially a generic method for the functionalization of QDs to address a much wider range of biocompatibility and biorecognition issues. 相似文献