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1.
《Electroanalysis》2005,17(4):327-333
Conducting polymers (CP) remain a promising material to construct stable potential all‐solid‐state ion‐selective potentiometric electrodes. The unique properties of poly(3,4‐ethylenedioxythiophene) doped with poly(4‐styrenesulfonate) ions, PEDOT‐PSS: high CP stability and affinity of doping anions towards Cu2+ ions, make it highly attractive for construction of all‐solid‐state copper(II)‐selective electrodes with outstanding selectivity. The additional benefits can arise from solution processability of commercially available PEDOT‐PSS system. This material was highly promising for a new sensor arrangement, i.e. to obtain disposable, planar and flexible all‐plastic Cu2+‐selective electrodes. These sensors can be obtained by casting a commercially available dispersion of PEDOT‐PSS (Baytron P) on a plastic, non‐conducting support material. The CP being both electrical lead and ion‐to‐electron transducer, was covered with plastic, solvent polymeric Cu2+ selective membrane. This extremely simple arrangement, after conditioning in dilute Cu2+ solution, was characterized with linear Nernstian responses within the activities range from: 0.1 to 10?4 M, followed by super‐Nernstian responses for lower activities. The latter result points to effective elimination of primary ions leakage from the plastic membrane / transducer phase and has resulted in significantly improved selectivities. Obtained log K values were equal to ?7.6 for Co2+, ?7.4 for Zn2+, ?7.2 for Ca2+ and ?6.8 for Na+, respectively.  相似文献   

2.
Acetonitrile and [FXeOXe‐ ‐ ‐FXeF][AsF6] react at ?60 °C in anhydrous HF (aHF) to form the CH3CN adduct of the previously unknown [XeOXe]2+ cation. The low‐temperature X‐ray structure of [CH3CN‐ ‐ ‐XeOXe‐ ‐ ‐NCCH3][AsF6]2 exhibits a well‐isolated adduct‐cation that has among the shortest Xe?N distances obtained for an sp‐hybridized nitrogen base adducted to xenon. The Raman spectrum was fully assigned by comparison with the calculated vibrational frequencies and with the aid of 18O‐enrichment studies. Natural bond orbital (NBO), atoms in molecules (AIM), electron localization function (ELF), and molecular electrostatic potential surface (MEPS) analyses show that the Xe?O bonds are semi‐ionic whereas the Xe?N bonds may be described as strong electrostatic (σ‐hole) interactions.  相似文献   

3.
Perinaphthenone (=1H‐phenalen‐1‐one), known for efficient population of its T1 (π,π*) state and suggested as a standard sensitizer for singlet oxygen (1Δg) formation, forms a single stereoisomer of a head‐to‐tail [2+2] photoadduct across its C(2)=C(3) bond with 2‐morpholinoprop‐2‐enenitrile in benzene by broad band UV excitation (λ≥280 nm). The reaction is advantageously run to low conversion of starting materials only. The structure of the adduct, especially the relative configuration at C(9), has been derived from 1H‐NMR data including NOE signal enhancement studies.  相似文献   

4.
An efficient CpxRhIII‐catalyzed enantioselective alkenyl C?H functionalization/[4+1] annulation of acryl amides and allenes is reported. The described transformation provides straightforward access to enantioenriched α,β‐unsaturated‐γ‐lactams bearing a quaternary stereocenter. The reaction operates under mild conditions, displays a broad functional‐group tolerance, and provides 2H‐pyrrol‐2‐ones with excellent selectivity of up to 97:3 er. Such scaffolds are frequently found in natural products and synthetic bioactive compounds and are of significant synthetic value. It is noteworthy that the allene serves as a one‐carbon unit in the [4+1]‐annulation.  相似文献   

5.
This study describes a new rhodium(III)‐catalyzed [3+2] annulation of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles with internal alkynes using a Cu(OAc)2 oxidant for building a spirocyclic ring system, which includes the functionalization of an aryl C(sp2)? H bond and addition/protonolysis of an alkene C?C bond. This method is applicable to a wide range of 5‐aryl‐2,3‐dihydro‐1H‐pyrroles and internal alkynes, and results in the assembly of the spiro[indene‐1,2′‐pyrrolidine] architectures in good yields with excellent regioselectivities.  相似文献   

6.
2H‐azirines can serve as three‐atom synthons by C?C bond cleavage, however, it involves a high energy barrier under thermal conditions (>50.0 kcal mol?1). Reported is a ruthenium‐catalyzed [3+2+2] cycloaddition reaction of 2H‐azirines with diynes, thus leading to the formation of fused azepine skeletons. This approach features an unprecedented metal‐catalyzed C?C bond cleavage of 2H‐azirines at room temperature, and the challenging construction of aza‐seven‐membered rings from diynes. The results of this study provide a new reaction pattern for constructing nitrogen‐containing seven‐membered rings and may find applications in the synthesis of other complex heterocycles.  相似文献   

7.
Ni0‐catalyzed chemo‐ and enantioselective [3+2] cycloaddition of cyclopropenones and α,β‐unsaturated ketones/imines is described. This reaction integrates C?C bond cleavage of cyclopropenones and enantioselective functionalization by carbonyl/imine group, offering a mild approach to γ‐alkenyl butenolides and lactams in excellent enantioselectivity (88–98 % ee) through intermolecular C?C activation.  相似文献   

8.
The reactions of alkyn‐1‐yl(vinyl)silanes R2Si[C?C‐Si(H)Me2]CH?CH2 [R = Me (1a), Ph (1b)], Me2Si[C?C‐Si(Br)Me2]CH?CH2 (2a), and of alkyn‐1‐yl(allyl)silanes R2Si[C?C‐Si(H)Me2]CH2CH?CH2 (R = Me (3a), R = Ph (3b)] with 9‐borabicyclo[3.3.1]nonane in a 1:1 ratio afford in high yield the 1‐silacyclopent‐2‐ene derivatives 4a, b and 5a, and the 1‐silacyclohex‐2‐ene derivatives 6a, b, respectively, all of which bear a functionally substituted silyl group in 2‐position and the boryl group in 3‐position. This is the result of selective intermolecular 1,2‐hydroboration of the vinyl or allyl group, followed by intramolecular 1,1‐organoboration of the alkynyl group. In the cases of 4a, b, potential electron‐deficient Si? H? B bridges are absent or extremely weak, whereas in 6a,b the existence of Si? H? B bridges is evident from the NMR spectroscopic data (1H, 11B, 13C and 29Si NMR). The molecular structure of 4b was determined by X‐ray analysis. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

9.
Quercetin 2,4‐dioxygenase (quercetinase) from Streptomyces uses nickel as the active‐site cofactor to catalyze oxidative cleavage of the flavonol quercetin. How this unusual active‐site metal supports catalysis and O2 activation is under debate. We present crystal structures of Ni‐quercetinase in three different states, thus providing direct insight into how quercetin and O2 are activated at the Ni2+ ion. The Ni2+ ion is coordinated by three histidine residues and a glutamate residue (E76) in all three states. Upon binding, quercetin replaces one water ligand at Ni and is stabilized by a short hydrogen bond through E76, the carboxylate group of which rotates by 90°. This conformational change weakens the interaction between Ni and the remaining water ligand, thereby preparing a coordination site at Ni to bind O2. O2 binds side‐on to the Ni2+ ion and is perpendicular to the C2?C3 and C3?C4 bonds of quercetin, which are cleaved in the following reaction steps.  相似文献   

10.
The reaction of alkyn‐1‐yl(chloro)(methyl)vinyl‐ and alkyn‐1‐yl(chloro)(phenyl)‐vinylsilane with 9‐borabicyclo[3.3.1]nonane (9‐BBN) afforded selectively 1‐silacyclopent‐2‐ene derivatives containing a Si? Cl function, as a result of consecutive 1,2‐hydroboration and 1,1‐organoboration. Protodeborylation with acetic acid left the Si? Cl functions in various 1‐silacyclopent‐2‐enes untouched, whereas acetic acid in the presence of dipropylamine led to conversion of the Si? Cl into the Si? OAc function. New starting materials and all products were characterized in solution by multinuclear NMR spectroscopy (1H, 11B, 13C and 29Si NMR), and the molecular structures of two 1‐silacyclopent‐2‐ene derivatives were determined by X‐ray analysis. The gas phase geometries of 1‐silacyclopent‐2‐enes were optimized by DFT calculations [B3LYP/6‐311 + G(d,p) level of theory], found to be in reasonable agreement with the results of the crystal structure determination, and NMR parameters were calculated at the same level of theory. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

11.
A contractile dendritic motional device is reported where metal ions with biological importance—Ca2+ (the main regulatory and signaling species of the natural muscles), Mg2+, and Zn2+—initiate two kinds of motional functions. The first motional function is the metal‐ion‐induced contraction of a linear strand into a Z‐shaped dinuclear complex, and the second one is the change of the height of Z‐shaped complexes via transmetalation. By means of the pH‐dependent counterligand tren, the two motional features of the machine can depend on alternate additions of acid and base. An optical response is associated with the conversion of the linear form (which is yellow) into the metalated Z‐shaped one (which is red).  相似文献   

12.
The newly synthesized 2‐(alk‐3‐en‐1‐ynyl)cyclohex‐2‐enones 4 undergo photodimerization (chemo‐ and regio‐)selectively at the exocyclic C?C bond to give diastereoisomeric mixtures of 1,2‐dialkynyl‐1,2‐dimethylcyclobutanes. On irradiation of 4 in the presence of 2‐chloroacrylonitrile, cyclobutane formation occurs again (chemo‐ and regio‐)selectively at the exocyclic C?C bond to afford diastereoisomeric mixtures of 2‐alkynyl‐1‐chloro‐2‐methylcyclobutanecarbonitriles. Similarly, compounds 4 undergo photoaddition to 2,3‐dimethylbuta‐1,3‐diene exclusively at the exocyclic C?C bond to afford mixtures of [2+2] and [4+2] cycloadducts.  相似文献   

13.
RhII‐catalyzed intermolecular [3+2] cycloaddition of 2 H‐azirines with N‐sulfonyl‐1,2,3‐triazoles is disclosed, in which a series of fully functionalized pyrroles is produced via rhodium azavinyl carbene intermediates. A distinct feature of this reaction is that the azavinyl carbene serves as a [2 C] equivalent, instead of as [1 C] or aza‐[3 C] synthons, which have been reported previously in cyclopropanations and [3+n] cycloadditions. Moreover, this methodology has also been successfully applied in the total synthesis of URB447 as well as the formal synthesis of Atorvastatin (Lipitor).  相似文献   

14.
An electron‐deficient CpE rhodium(III) complex bearing a cyclopentadienyl ligand with two ethyl ester substituents catalyzes the tandem [2+2+2] annulation–lactamization of acetanilides with two alkynoates via cleavage of adjacent two C?H bonds to give densely substituted benzo[cd]indolones. The reactions of meta‐methoxy‐substituted acetanilides with two alkynoates also provided benzo[cd]indolones via cleavage of adjacent C?H/C?O bonds. Furthermore, 3,5‐dimethoxyacetanilides reacted with two alkynoates to give dearomatized spiro compounds.  相似文献   

15.
Although FeO42? (ferrate(IV)) is a very strong oxidant that readily oxidizes water in acidic medium, at pH 9–10 it is relatively stable (<2 % decomposition after 1 h at 298 K). However, FeO42? is readily activated by Ca2+ at pH 9–10 to generate O2. The reaction has the following rate law: d[O2]/dt=kCa[Ca2+][FeO42?]2. 18O‐labeling experiments show that both O atoms in O2 come from FeO42?. These results together with DFT calculations suggest that the function of Ca2+ is to facilitate O–O coupling between two FeO42‐ions by bridging them together. Similar activating effects are also observed with Mg2+ and Sr2+.  相似文献   

16.
The search for more biocompatible alternatives to Gd3+‐based MRI agents, and the interest in 52Mn for PET imaging call for ligands that form inert Mn2+ chelates. Given the labile nature of Mn2+, high inertness is challenging to achieve. The strongly preorganized structure of the 2,4‐pyridyl‐disubstituted bispidol ligand L1 endows its Mn2+ complex with exceptional kinetic inertness. Indeed, MnL1 did not show any dissociation for 140 days in the presence of 50 equiv. of Zn2+ (37 °C, pH 6), while recently reported potential MRI agents MnPyC3A and MnPC2A‐EA have dissociation half‐lives of 0.285 h and 54.4 h under similar conditions. In addition, the relaxivity of MnL1 (4.28 mm ?1 s?1 at 25 °C, 20 MHz) is remarkable for a monohydrated, small Mn2+ chelate. In vivo MRI experiments in mice and determination of the tissue Mn content evidence rapid renal clearance of MnL1. Additionally, L1 could be radiolabeled with 52Mn and the complex revealed good stability in biological media.  相似文献   

17.
An effective and pragmatic strategy for the synthesis of structurally diverse indolo[2,3‐c]isoquinolin‐5‐ones has been developed via a Rh(III)‐catalyzed C?H activation and [4+2] annulation reaction of N‐methoxybenzamides and 3‐diazoindolin‐2‐imines. The reaction involves the efficient formation of two new (one C?C and one C?N) bonds under operationally simple conditions and has the benefits of a broad substrate scope.  相似文献   

18.
The phenylimidorhenium(V) complexes [Re(NPh)X3(PPh3)2] (X = Cl, Br) react with the N‐heterocyclic carbene (NHC) 1,3‐diethyl‐4,5‐dimethylimidazole‐2‐ylidene (LEt) under formation of the stable rhenium(V) complex cations [Re(NPh)X(LEt)4]2+ (X = Cl, Br), which can be isolated as their chloride or [PF6]? salts. The compounds are remarkably stable against air, moisture and ligand exchange. The hydroxo species [Re(NPh)(OH)(LEt)4]2+ is formed when moist solvents are used during the synthesis. The rhenium atoms in all three complexes are coordinated in a distorted octahedral fashion with the four NHC ligands in equatorial planes of the molecules. The Re–C(carbene) bond lengths between 2.171(8) and 2.221(3) Å indicate mainly σ‐bonding between the NHC ligand and the electron deficient d2 metal atoms. Attempts to prepare analogous phenylimido complexes from [Re(NPh)Cl3(PPh3)2] and 1,3‐diisopropyl‐4,5‐dimethylimidazole‐2‐ylidene (Li?Pr) led to a cleavage of the rhenium‐nitrogen multiple bond and the formation of the dioxo complex [ReO2(Li?Pr)4]+.  相似文献   

19.
The substituent‐induced chemical shifts (SCS) of C2 and C3 on the 13C NMR spectra of 1‐aryl‐3,3‐difluoro‐2‐halocyclopropenes were studied. The correlation between SCS and Hammett constants shows that the tendency of effect by the substituents on the phenyl ring is BrC2(ρ = 4.66) > ClC2(ρ = 4.50) and ClC3(ρ = ?1.63) > BrC3(ρ = ?1.41). The DSP treatment further confirms the SCS of C2 and C3 are the main contribution of the resonance effect and field effect, respectively. Those results of the incremental shifts reveals that the gem‐difluorocyclopropenyl bearing the phenyl group possesses a triple bond character, which is also observed in IR spectra with high n?C=C (1768–1945 cm?1).  相似文献   

20.
A rhodium(III)‐catalyzed [3+2]/[5+2] annulation of 4‐aryl 1‐tosyl‐1,2,3‐triazoles with internal alkynes is presented. This transformation provides straightforward access to indeno[1,7‐cd]azepine architectures through a sequence involving the formation of a rhodium(III) azavinyl carbene, dual C(sp2)? H functionalization, and [3+2]/[5+2] annulation.  相似文献   

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