首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
The specific cleavage of N-Cα bonds on the peptide backbone to form the so-called ‘c’ and ‘z + 2’ products, which can be used for the rapid determination of protein amino-acid sequences, has been examined to clarify the mechanism(s) that occur during hydrogen abstraction induced by bombardment with 337-nm laser photons in matrix-assisted laser desorption/ionization (MALDI) method. Intramolecular hydrogen abstraction, which results from the hydrogen(s) on the Cα or Cβ carbon, did not occur with a deuterium-labeled dodecapeptide. To confirm a proposition that intermolecular hydrogen abstraction occurs between the peptide and the MALDI matrix, a deuterium dodecapeptide embedded in a deuterium 2,5-dihydroxybenzoic acid matrix at a molar ratio of 1:7000 was analyzed. The resulting deuterium c product ions suggested that c ions form via intermolecular hydrogen abstraction, although the results obtained did not deny any other possibilities such as intramolecular transfer of labile hydrogen. A mechanism for the N-Cα bond cleavage has been proposed that the formation of hypervalent radical species and subsequent prompt bond cleavages occur. The proposed mechanism successfully rationalizes the formation of both the z + 2 and the c product ions.  相似文献   

2.
Actinomycin D (AMD) is an anticancer antibiotic that can bind selectively to both double-stranded and single-stranded DNA, and this binding greatly enhances DNA photosensitization. Using electron paramagnetic resonance (EPR) in combination with spin trapping techniques, a systematic study was carried out on the reactive oxygen species generated in the photosensitization process of AMD. It was found that 1O2 and O2- are important reactive intermediates either insolution or in DNA complexes, and the generation of these species is in competition. This finding suggests that the photodynamic action of AMD proceeds via two pathways: energy transfer (type Ⅰ mechanism) and electron transfer (type Ⅱ mechanism). 1O2 is the main product formed via energy transfer reaction in solution while electron transfer between the excited states of AMD and DNA becomes the predominant pathway in DNA complexes.  相似文献   

3.
Copper supported on magnetite nanoparticles modified with environmentally friendly ligand tricine was devised for synthesis of acetamides via C–C oxidative cleavage of ketones with amines. The catalyst was characterized using different techniques, including Fourier transform infrared, X-ray diffraction, scannin electron microscopy, vibrating sample magnetometry, thermogravimetric analysis, and energy dispersive x-ray spectroscopy. The protocol showed relatively high yields of acetamide products. Furthermore, the magnetic recovery of the catalyst rendered the overall process fast and efficient. It was used in the reaction for six consecutive cycles with negligible loss of catalytic activity. This research is the first report of application of magnetic nanocatalysts for synthesis of acetamides from ketones of low activity through a C–C bond cleavage strategy.  相似文献   

4.
Using potassium iodide as a catalyst and m-chloroperbenzoic acid as an oxidant, an efficient catalytic procedure has been developed for the azidoselenenylation of alkenes with sodium azide and diselenides, and a series of corresponding β-azidoselenides, most of which are new compounds, have been prepared in moderate to good yields under mild reaction conditions. This in situ generation of the electrophilic selenenylating reagents with addition to alkenes is a stereospecific anti addition, which occurs with a Markovnikov orientation.  相似文献   

5.
We report the synthesis of biaryl ketones via an unprecedented copper/silver catalyzed acylative cross-coupling of thiol esters with either an arylboronic acid or a potassium aryltrifluoroborate. This new method proceeds without a requisite Pd-catalyst and Cu(I)TC mediator, and is efficient, versatile, operationally simple, and accommodating functionally diverse thiol esters, arylboronic acids, and potassium aryltrifluoroborates.  相似文献   

6.
Yang Y  Chen L  Zhang Z  Zhang Y 《Organic letters》2011,13(6):1342-1345
A novel palladium-catalyzed C-3 acylation of indolizines with α,β-unsaturated carboxylic acids via C-H bond and C═C double bond cleavage under oxidative conditions is described. The regioselectivity is assisted by the carboxylic group, and the selection of the oxidant is crucial to the reaction.  相似文献   

7.
8.
9.
Fluorescent dyes are heavily sought for their potentials applications in bioimaging, sensing, theranostic,and optoelectronic materials. Among them, BODIPY dyes are privileged fluorophores that are now widely used in highly diverse research fields. The increasing success of BODIPY dyes is closely associated with their excellent and tunable photophysical properties due to their rich functionalization chemistry.Recently, growing research efforts have been devoted to the direct functionalization of the BODIPY core,because it allows the facile installation of desired functional groups in a single atom economical step. The challenges of this direct C–H derivation come from the difficulties in finding suitable functionalization agents and proper control of the regioselectivity of the functionalization. The aim of this work is to provide an overview of BODIPY dyes and a summarization of the different synthetic methodologies reported for direct C–H functionalization of the BODIPY framework.  相似文献   

10.
11.
Electron capture by doubly charged peptide cations leads to neutral losses in addition to N-C(α) bond cleavages that give c and z fragments. In this work we discuss the influence of amino acid sequence on hydrogen versus ammonia loss and the propensity for subsequent partial side-chain cleavage after ammonia loss to give w fragment ions. Experiments were done on two series of doubly protonated dipeptides, [XK+2H](2+) and [XR+2H](2+), where X is one of the twenty common amino acid residues, excluding aspartic acid (D), and K and R are lysine and arginine, respectively. While it was previously established that NH(3) is lost exclusively from the N-terminal ammonium group and not from side-chain ammonium groups, we find here that ammonia can be lost from guanidinium radicals as well. The ratio between H loss and NH(3) loss reveals some information on internal ionic hydrogen bonds and peptide conformation since proton sharing between the N-terminal ammonium group and a basic side chain decreases the probability for NH(3) loss due to a lower recombination energy and as a result reduced capture probability. The abundance of w ions was found to correlate with the reaction energy for their formation; highest yield was found for CK and lowest for AK and HK. The survival rate of charge-reduced species was higher for XR than for XK, which is likely linked to the formation of long-lived C(α) radicals in the latter case. The probability for N-C(α) bond cleavage is smaller on average for XR than for XK which indicates that hydrogen transfer from the ε-ammonium radical to the amide group triggers some of the cleavages, or is a result of the different distances between the amide group and the charges in XR and XK. Finally, our data support the previous concept that charge partitioning between c and z fragments can be explained by competition between the two fragments for the proton.  相似文献   

12.
Reaction of meso-tetraphenylporpholactone with hydrazine converts the lactone moiety to an N-aminolactam. It also reduces the opposite pyrrolic moiety of both the starting material and the N-aminolactam, generating chlorin-like chlorolactone and N-aminochlorolactam, respectively. Reductive N-N cleavage of the N-aminoporpholactam generates the parent porpholactam.  相似文献   

13.
An efficient and broadly applicable alternative to the classical Pictet-Spengler synthesis of tetrahydro-β-carbolines is presented. The method relies on metal-catalyzed isomerization of allylic amines to form reactive iminium intermediates which can be trapped by a tethered indole nucleophile.  相似文献   

14.
A new palladium-catalyzed oxidative conversion of N-arylpropiolamides and H2O to various indoline-2,3-diones and acids through the C≡C triple bond cleavage and C(sp2)–H functionalization is described,which is promoted by a cooperative action of catalytic CuBr2,2,2,6,6-tetramethyl-1-piperidinyloxy(TEMPO)and O2.The method provides a practical tool for transformations of alkynes by means of a C–H functionalization strategy,which enables the formation of one C–C bond and multiple C–O bonds in a single reaction with high substrates compatibility and excellent functional group tolerance.  相似文献   

15.
16.
The DNA binding and cleavage activity of a synthetic polyamide containing dipeptide Ser-His has been investigated by spectroscopic techniques, such as electronic absorbance and circular dichroism (CD) spectropolarimetry, as well as gel electrophoresis. The results show that the molecule has a strong interaction with DNA and can improve DNA-cleavage ability about 100 fold as compared with single dipeptide Ser-His.  相似文献   

17.
18.
The cationic gadolinium metallocene [(C5Me5)2Gd][B(C6F5)4], when combined with an excess amount of Al(iBu)3, efficiently produces polyethylene at 80 °C under 0.8 MPa pressure of ethylene. After quenching, the resulting polyethylene has ethyl group at one end and isobutyl group at the other terminal. Because no Gd-alkyl species appears to be involved, a mechanism with conventional coordinative chain transfer polymerization (CCTP) is not feasible. Density functional theory (DFT) analyses indicate a novel mechanism in which the cationic Gd plays a crucial role by coordinating ethylene and assists the insertion of the coordinated ethylene into Al−C bond.  相似文献   

19.
Fluorescence spectroscopy is widely used as a tool for elucidating the structure and dynamics of the micellar medium. A prerequisite commonly encountered for quantitative approaches is that the fluorophore resides exclusively in the micellar phase. Providing the fluorophore with a long alkyl chain may appear advantageous with regard to fixing the probe into the micelle. The present work was aimed at determining which are the consequences of this process from a spectroscopic viewpoint. The nitrobenzoxadiazolyl (NBD) moiety, which leads to well known fluorescent probes, was directly grafted on three fatty amines, the chain length of which varied from 8 to 18 carbon atoms. The spectroscopic properties of these NBD derivatives were investigated in three different micellar media: SDS, CTAB and TX100. The dyes were incorporated into micelles, where they were located in the interfacial region, whatever the chain length. When the dyes were previously dissolved in ethanol, and subsequently placed in the presence of the surfactant solution, complete solubilization was obtained. However, when the surfactant solution was used to dissolve directly a thin film of dye, a certain amount of dye remained non-incorporated and formed microcrystals, whose quantity and size increased with chain length. These microcrystals were mainly detected by UV/Vis-absorption and fluorescence microscopy. They induced drastic errors in the determination of fluorescence quantum yields, although they hardly interfered with other steady-state measurements and with dynamical fluorescence measurements. In conclusion, it appeared that for a small, non-ionic fluorophore such as NBD, the presence of a long alkyl chain is not an advantage. It slows down the incorporation process, unless some alcohol is introduced in the medium. Short-chain probes are therefore best suited for the study of the micellar medium.  相似文献   

20.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号