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1.
The effect of N‐methylation on sequence scrambling in the fragmentation of b5 ions has been investigated by studying a variety of peptides containing sarcosine (N‐methylglycine). The product ion mass spectra for the b5 ions derived from Sar‐A‐A‐A‐Y‐A and Sar‐A‐A‐Y‐A‐A show only minor signals for non‐direct sequence ions the major fragmentation reactions occurring from the unrearranged structures. This is in contrast to the b5 ions where the Sar residue is replaced by Ala and sequence scrambling occurs. The b5 ion derived from Y‐Sar‐A‐A‐A‐A shows a product ion mass spectrum essentially identical to the spectrum of the b5 ion derived from Sar‐A‐A‐A‐Y‐A, indicating that in the former case macrocyclization has occurred but the macrocyclic form shows a strong preference to reopen to put the Sar residue in the N‐terminal position. Similar results were obtained in the comparison of b5 ions derived from A‐Sar‐A‐A‐Y‐A and Sar‐A‐A‐Y‐A‐A. The product ion mass spectra of the MH+ ions of Y‐Sar‐A‐A‐A‐A and A‐Sar‐A‐A‐Y‐A show substantial signals for non‐direct sequence ions indicating that fragmentation of the MH+ ions channels extensively through the respective b5 ions and further fragmentation of these species. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

2.
Adenosine receptors (ARs) are members of the superfamily of G protein-coupled receptors. The homology models of adenosine A1 and A2A receptors were constructed. The high-resolution X-ray structure of bovine rhodopsin and crystal structure of beta2-adrenergic receptor were used as templates. The binding sites of the A1 and A2A ARs were constructed by using data obtained from mutagenesis experiments as well as docking simulations of the respective AR antagonsists DPCPX and XAC. To compare rhodopsin- and beta2-adrenergic-based models, the binding mode of A1 (KW-3902, LUF-5437) and A2A (KW-6002, ZM-241385) ARs antagonists were also examined. The differences in the binding ability of both models were noted during the study. The beta2-adrenergic-based A2A AR model was much more capable to stabilize the ligand in the binding site cavity than the corresponding rhodopsin-based A2A AR model, however, such differences were not so clear in case of A1 AR models. It was suggested that for the A1 AR it is possible to use the crystal structure of rhodopsin as a template as well as beta2-adrenergic receptor, but for A2A AR, with the now available beta2-adrenergic receptor X-ray structure, docking studies should be avoided on the rhodopsin-based model. However, taking into account that the beta2AR shares about 31% of the residues with the AR in comparison to 21% in case of bRho, we suggest using beta2-adrenergic-based models for the A1 and A2A ARs for further in silico ligand screening also because of their generally better ability to stabilize ligands inside the binding pocket.  相似文献   

3.
A neutral polyfluorene derivative that contains 20 mol % 2,1,3‐benzothiadiazole (BT) is synthesized by Suzuki cross‐coupling polymerization. A cationic conjugated polymer A and an α‐mannose‐bearing polymer B are subsequently obtained through different post‐polymerization methods. As a result of the charged pendant groups or sugar‐bearing groups attached to the polymer side chains, both A and B show good water‐solubility. The titration of Concanavalin A (Con A) into polymer aqueous solution leads to different fluorescent responses for polymers A and B . Polymer A does not show any obvious fluorescence change upon interaction with Con A, whereas polymer B shows fluorescence increase in BT emission intensity when Con A is added. This is because of the specific interaction between α‐mannose and Con A, which induces polymer aggregation, and then facilitates energy transfer from the phenylene–fluorene segments to the BT units. A practical calibration curve ranging from 1 nM to 250 nM is obtained by correlating the changes in BT emission intensity with Con A concentration. The advantage of polymer B ‐based Con A macromolecular probe is that it shows signal increase upon Con A recognition, which is significantly different from other conjugated polymer‐based fluorescence quenching assays.  相似文献   

4.
We have examined the self-assembled membrane-bound aggregates of two annexin V (A5) dye conjugates and compared them to those from native A5. Native A5 and FITC-labeled A5 (A5-FITC) both formed discrete well-defined crystalline monolayer domains of p6 symmetry. However, A5-FITC also showed additional domains with a corrugated appearance not observed in native A5. In contrast, Cy3-labeled A5 (A5-Cy3) showed a mixture of crystalline monolayer and irregular multilayered domains, with the ratio of the two types varying significantly from sample to sample, and also required a much longer incubation time than native A5 and A5-FITC. When A5-FITC and A5-Cy3 were co-incubated on the same bilayer, well-defined crystalline monolayer domains containing both A5-FITC and A5-Cy3 were consistently observed at a much shorter incubation time than that of pure A5-Cy3 alone, indicating that A5-FITC facilitates the inclusion of A5-Cy3. These results suggest that dye labels can affect A5 2D self-assembly and crystal formation on membrane surfaces.  相似文献   

5.
Herein, bioinspired total syntheses of A201A, A201D, and A201E based on a previously reported biosynthetic pathway are presented. The challenging 1,2-cis-furanoside, a core structure of the A201 family, was obtained by remote 2-quinolinecarbonyl-assisted glycosylation. We accomplished the total synthesis of A201A and A201E based on the critical 1,2-cis-furanoside moiety through late-stage glycosylation without any interference from basic dimethyl adenosine. We also confirmed the absolute configuration of A201E by total synthesis. This modular synthesis strategy enables efficient preparation of A201 family antibiotics, allowing the study of their structure–activity relationships and mode of action. This study satisfies the increasing demand for developing novel antibiotics inspired by the A201 family.  相似文献   

6.
Herein, bioinspired total syntheses of A201A, A201D, and A201E based on a previously reported biosynthetic pathway are presented. The challenging 1,2-cis-furanoside, a core structure of the A201 family, was obtained by remote 2-quinolinecarbonyl-assisted glycosylation. We accomplished the total synthesis of A201A and A201E based on the critical 1,2-cis-furanoside moiety through late-stage glycosylation without any interference from basic dimethyl adenosine. We also confirmed the absolute configuration of A201E by total synthesis. This modular synthesis strategy enables efficient preparation of A201 family antibiotics, allowing the study of their structure–activity relationships and mode of action. This study satisfies the increasing demand for developing novel antibiotics inspired by the A201 family.  相似文献   

7.
In the present study, Indole-based-oxadiazole (1A-17A) compounds were successfully synthesized. The structures of all synthesized compounds were fully characterized by different sophisticated spectroscopic techniques such 1H NMR, 13C NMR, and HREI-MS. Further, the synthesized compounds were explored to investigate their broad-spectrum antibacterial and antibiofilm potential against multidrug resistant Pseudomonas aeruginosa (MDR-PA) and methicillin resistant Staphylococcus aureus (MRSA). The compounds possessed a broad spectrum of antibacterial activity having MIC values of values 1–8 mg/ml against the tested microorganisms. Compound A6 and A7 shows maximum antibacterial activity against MDR-PA, whereas A6, A7 and A11 shows highest activity against MRSA. Furthermore, antibiofilm assay shows that A6, A7 and A11 showed maximum inhibition of biofilm formation and it was found that at 4 mg/ml; A6, A7 and A11 inhibit MRSA biofilm formation by 81.1, 77.5 and 75.9%, respectively; whereas in case of P. aeruginosa; A6 and A7 showed maximum biofilm inhibition and inhibit biofilm formation by 81.5 and 73.7%, respectively. Molecular docking study showed that compounds A6, A7, A8, A10, and A11 had high binding affinity to bacterial peptidoglycan, indicating their potential inhibitory activity against tested bacteria, whereas A6 and A11 were found to be the most effective inhibitors of SARS CoV-2 main protease (3CLpro), with a binding affinity of ? 7.78 kcal/mol. Furthermore, SwissADME and pkCSM-pharmacokinetics online tools was applied to calculate the ADME/Tox profile of the synthesized compounds and the toxicity of these chemicals was found to be low. The Lipinski, Veber, Ghose, and Consensus LogP criteria were also used to predict drug-likeness levels of the compounds. Our findings imply that the synthesized compounds could be a useful for the preventing and treating biofilm-related microbial infection as well as SARS-CoV2 infections.  相似文献   

8.
Various fragment sizes of the amyloid-β (Aβ) peptide have been utilized to mimic the properties of the full-length Aβ peptide in solution. Among these smaller fragments, Aβ16 and Aβ28 have been investigated extensively. In this work, we report the structural and thermodynamic properties of the Aβ16, Aβ28, and Aβ42 peptides in an aqueous solution environment. We performed replica exchange molecular dynamics simulations along with thermodynamic calculations for investigating the conformational free energies, secondary and tertiary structures of the Aβ16, Aβ28, and Aβ42 peptides. The results show that the thermodynamic properties vary from each other for these peptides. Furthermore, the secondary structures in the Asp1-Lys16 and Asp1-Lys28 regions of Aβ42 cannot be completely captured by the Aβ16 and Aβ28 fragments. For example, the β-sheet structures in the N-terminal region of Aβ16 and Aβ28 are either not present or the abundance is significantly decreased in Aβ42. The α-helix and β-sheet abundances in Aβ28 and Aβ42 show trends--to some extent--with the potential of mean forces but no such trend could be obtained for Aβ16. Interestingly, Arg5 forms salt bridges with large abundances in all three peptides. The formation of a salt bridge between Asp23-Lys28 is more preferred over the Glu22-Lys28 salt bridge in Aβ28 but this trend is vice versa for Aβ42. This study shows that the Asp1-Lys16 and Asp1-Lys28 regions of the full length Aβ42 peptide cannot be completely mimicked by studying the Aβ16 and Aβ28 peptides.  相似文献   

9.
小孔沸石微结构的CO_2吸附表征   总被引:2,自引:0,他引:2  
以3种已知结构的小孔沸石3A、4A和5A为研究对象,以N2和CO2为吸附质,通过吸附数据测定,研究了小孔沸石微孔结构的吸附表征方法.结果表明,N2吸附无法检测4A沸石的孔,而CO2吸附可以检测.对于4A和5A沸石,在35s内CO2吸附就可以达到平衡.HK(Horvath-Kawazoe)柱状模型不能表征4A和5A沸石的孔结构,但是HK球形模型可以,基于最大吸附量、D-A(Dubinin-Astakhov)方程和Langmuir-Freundlich模型计算了4A和5A沸石的微孔孔容,其中根据最大吸附容量和D-A方程计算的微孔孔容与文献值最接近.  相似文献   

10.
Epitaxial growth and electron doping of 12CaO·7Al2O3 (C12A7) and 12SrO·7Al2O3 (S12A7) are reported. The C12A7 films were prepared on Y3Al5O12 (YAG) single-crystal substrates by pulsed laser deposition at room temperature and subsequent thermal crystallization. X-ray diffraction patterns revealed the films were grown epitaxially with the orientation relationship of (001)[100] C12A7 || (001)[100] YAG. For S12A7, pseudo-homoepitaxial growth was attained on the C12A7 epitaxial layer. Upon electron doping, metallic conduction was achieved in the C12A7 film and the S12A7/C12A7 double-layered films. Analyses of optical absorption spectra for the S12A7/C12A7 films provided the densities of free electrons in each layer separately. Hall measurements exhibited larger electron mobility in the S12A7/C12A7 film than those in C12A7 and S12A7 films, suggesting free electrons may be accumulated at the S12A7/C12A7 interface due presumably to a discontinuity of the cage conduction bands.  相似文献   

11.
The amyloid cascade hypothesis proposes that amyloid-beta (Aβ) aggregation is the initial triggering event in Alzheimer's disease. Here, we utilize NMR spectroscopy and monitor the structural dynamics of two variants of Aβ, Aβ40 and Aβ42, as a function of temperature. Despite having identical amino acid sequence except for the two additional C-terminal residues, Aβ42 has higher aggregation propensity than Aβ40. As revealed by the NMR data on dynamics, including backbone chemical shifts, intra-methyl cross-correlated relaxation rates and glycine-based singlet-states, the C-terminal region of Aβ, especially the G33-L34-M35 segment, plays a particular role in the early steps of temperature-induced Aβ aggregation. In Aβ42, the distinct dynamical behaviour of C-terminal residues at higher temperatures is accompanied with marked changes in the backbone dynamics of residues V24-K28. The distinctive role of the C-terminal region of Aβ42 in the initiation of aggregation defines a target for the rational design of Aβ42 aggregation inhibitors.  相似文献   

12.
用多组分熔融接枝的方法将甲基丙烯酸缩水甘油酯( G M A) 和苯乙烯( St) 共同接枝于聚丙烯( P P) 上,制得多单体接枝聚丙烯 P P g ( G M A co St) .该接枝物具有高的 G M A 接枝率.本研究利用 F T I R、 S E M、 T E M、 D S C 和力学性能测试等分析方法,研究了多组分熔融接枝聚丙烯( P P g ( G M A co St)) 对尼龙6/ P P 共混物的形态结构, Tg 和力学性能的影响.结果表明, P P g ( G M A co St) 中的环氧基团与尼龙6( P A6) 末端的胺基发生化学反应,原位形成的 P P P A6 共聚物能有效的改善 P A6 与 P P 的相容性,可以使 P P 均匀的分散在 P A6 基体中,相区尺寸明显减小,提高了拉伸强度.由于两相的相容性较好,从而共混物的 Tg 有明显的变化.此外,通过透射电镜观察,发现 P A6/ P P g ( G M A co St)(70/30) 合金中存在着特殊的微相分离结构.  相似文献   

13.
Chitosans with various degrees of deacetylation (D.D.), which were used as standard sample for FTIR determination, were prepared from completely deacetylated chitosan by homogeneous N-acetylation reaction. By combining four probable probe bands, i.e. 1655, 1560, 1380 and 1320 cm-1, eight probable reference bands, i.e. 3430, 2920, 2880, 1425, 1155, 1070, 1030 and 895 cm-1 and two baseline methods, the most suitable ratios Aprobe band/Aeterence band from IR spectra to determine the degree of acetylation of chitosan were evaluated from 48 combinations to be A1560/A2880, A1560/A2920 and A1655/A3430(A1560/A2880 is mostly recommended). The second baseline method, i.e. linking between adjacent two valleys, was better for measuring the absorbances of 1560 and 1655 cm-1 bands. The determination range of the D.D. (1%-100%) covered almost the whole range. The standard curves with A1560/A2880 and A1655/A3430 were also suitable for the determination of degree of substitution of other N-acylated chitosan, such as N-pr  相似文献   

14.
A following new interpretation of apparent induction period is proposed considering the experimental results obtained: octamethylcyclotetrasiloxane (D4) is activated by the reaction with acid to generate an activated derivative (A4). A4 reacts with D4 to generate A8, an active species containing eight dimethylsiloxane units. A8 backbites to generate mostly A4 and D4, which causes retardation in polymerization, but occasionally to form A3 and D5. A3 is highly reactive, and when the concentration of A3 exceeds a certain limit, much Ai where i is large enough is formed and promotes fast growth of chain at the interfacial area due to high concentration of D4. The interpretation assumes that A3 accelerates growth of chain faster than other species, and that A8 tends to backbite rather than grow. The interpretation is supported by the experimental results of polymerization conducted with D4 and D3, or D5 and D3 charged.  相似文献   

15.
Linear-dendritic copolymers containing hyperbranched poly(citric acid) and linear poly(ethylene glycol) blocks (PCA-PEG-PCA) were used as reducing and capping agents to synthesize and support gold nanoparticles (AuNPs). PCA-PEG-PCA copolymers with 1758, 1889 and 3446 molecular weights, called A1, A2 and A3 through this work, respectively, were synthesized using 2, 5, and 10 citric acid/PEG molar ratios. The diameter of A1, A2 and A3 in a fresh water solution was investigated using dynamic light scattering (DLS) and it was between 1.8 and 2.8 nm. AuNPs were simply synthesized and supported by addition a boiling aqueous solution of HAuCl4 to aqueous solutions of A1, A2 and A3. Supported AuNPs were stable in water for several months and agglomeration was not occurred. The loading capacity of A1, A2 and A3 and the size of synthesized AuNPs were investigated using UV spectroscopy and transmission electron microscopy (TEM). It was found that the loading capacity of PCA-PEG-PCA copolymers depend on the concentration of copolymers and the size of their poly(citric acid) parts directly. For example average loading capacities for 400 μM concentration of A1, A2 and A3 were 32.24, 37.4 and 41.52 μM, respectively, and average loading capacities for 400, 200 and 100 μM concentration of A1 were 32.24, 20.28 and 9.1 μM, respectively. Interestingly there was a reverse relation between the size of synthesized AuNPs and size of poly(citric acid) parts of PCA-PEG-PCA copolymers.  相似文献   

16.
李高  李艳梅 《化学进展》2020,32(1):14-22
β-淀粉样蛋白(Aβ)的聚集和沉积被认为是导致阿尔茨海默病的重要因素,早前的研究多集中在全长无修饰的Aβ1-40和Aβ1-42上。近些年研究发现,在AD患者大脑内存在着多种截短与修饰的Aβ蛋白,它们对AD的疾病进程有不可忽视的贡献。例如,焦谷氨酸Aβ、磷酸化Aβ被认为是AD患者出现症状的标志;截短的Aβ4-40/42在患者脑内的含量与Aβ1-40/42接近且具有类似的聚集性质和毒性;患者脑内氧化压力升高导致的酪氨酸硝基化、二聚化和甲硫氨酸氧化形式的Aβ也具有不同的性质。本文对这些截短与修饰的Aβ蛋白的产生、结构、毒性以及和AD的关联进行了综述。  相似文献   

17.
研究了尼龙1010( P A1010) 与高抗冲聚苯乙烯( H I P S) 及马来酸酐官能化的 H I P S( H I P S g M A) 间的相互作用,利用 D S C, D M A, S E M 及拉伸测试等方法研究了不同组成比的共混物 P A1010/ H I P S 与 P A1010/ H I P S g M A 的结晶、玻璃化转变、形态及力学性能.结果表明 H I P S 与 P A1010 虽然结构相差甚远,但两者之间仍存在着一定的相互作用;而 H I P S g M A 可使 P A1010 的低温熔融峰变小,当 H I P S g M A 的含量≤50 % 时,随着其含量的增加,共混物中 P A1010 的结晶温度升高;当含量> 50 % 时, P A1010 发生分级结晶行为,其结晶温度由原来的178 ℃降至83 ℃,同时 H I P S g M A 与 P A1010 间的相互作用变大, D M A 谱上有明显的新的松驰峰. P A1010/ H I P S g M A 共混体系的拉伸性能要优于相同组成的 P A1010/ H I P S 体系.以上现象主要是由于 H I P S g M A 与 P A1010 中的端胺基发生了化学反应,产生了接枝共聚物 P A1010 g H I P  相似文献   

18.
Allyl‐telechelic polyisobutylene (A‐PIB‐A) produced by the bis‐benzocyclobutane dichloride (bBCB‐diCl) initiator contains the bis‐benzocyclobutane (bBCB) fragment at the center of the macromolecule (A‐PIB‐bBCB‐PIB‐A). Thermolysis of A‐PIB‐bBCB‐PIB‐A quantitatively converts the central bBCB fragment to a substituted conjugated tetraene (A‐PIB‐tetraene‐PIB‐A). The structure of A‐PIB‐tetraene‐PIB‐A was anticipated from small molecule models and identified/quantitated by 1H NMR spectroscopy. This is the first time a reactive functional group was introduced at the statistical center of a (telechelic) PIB. Subsequently, the A‐PIB‐tetraene‐PIB‐A was peroxidized to an epoxy derivative. Reaction of the A‐PIB‐tetraene‐PIB‐A with HSCH2CH2OH produced HOCH2‐telechelic PIB containing a central  CH2OH function, and hydrosilation with HSi(Me2)‐O‐Si(Me2)H produced SiH‐telechelic PIB with a central  SiH function. Reactions with maleic anhydride, tetracyanoethylene, butyl lithium, and potassium permanganate have also been examined. In sum, A‐PIB‐bBCB‐PIB‐A and A‐PIB‐tetraene‐PIB‐A are useful intermediates for the synthesis of novel PIB‐based materials for various end uses under investigation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1140–1145  相似文献   

19.
提出了成键原子的生物活性值(ai),并建立其连接性指数(mA).其中的0A、1A与取代芳烃对斜生栅列藻、日本长腿蛙蝌蚪、绿藻等三种生物的急性毒性关连,相关系数(R)依次为0.9516、0.9564、0.9335,优于相应文献的研究成果.证明mA与取代芳烃生物活性的相关性优于著名的Kier指数(mXv).  相似文献   

20.
Cytochrome P450 1A1 (CYP1A1), a heme-containing monooxygenase, is of particular importance for human health because of its vital roles in the metabolic activation of pro-carcinogenic compounds to the carcinogens. Deciphering the relevance of CYP1A1 to human diseases and screening of CYP1A1 modulators require reliable tool(s) for probing this key enzyme in complex biological matrices. Herein, a practical and ultrasensitive fluorescence-based assay for real-time sensing CYP1A1 activities in biological systems has been developed, via designing an isoform-specific fluorogenic sensor for CYP1A1 (CHPO). The newly developed fluorogenic substrate for CYP1A1 has been carefully investigated in terms of specificity, sensitivity, precision, quantitative linear range and the anti-interference ability. The excellent selectivity, strong anti-interference ability and fast response kinetics, making the practicability of CHPO-based CYP1A1 activity assay is better than that of most reported CYP1A1 activity assays. Furthermore, CHPO has been successfully used for imaging CYP1A1 activities in living cells and human tissues, as well as for high-throughput screening of CYP1A1 inhibitors using tissue preparations as enzyme sources. Collectively, this study provided a practical fluorogenic sensor for real-time sensing CYP1A1 in complex biological systems, which would strongly facilitate the investigations on the relevance of CYP1A1 to human diseases and promote high-throughput screening of CYP1A1 modulators for biomedical applications.  相似文献   

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