排序方式: 共有51条查询结果,搜索用时 15 毫秒
1.
The implementation of a hybrid QM-MM approach combining ab initio and density functional methods of TURBOMOLE with the molecular mechanics program package CHARMM is described. An interface has been created to allow data exchange between the two applications. With this method the efficient multiprocessor capabilities of TURBOMOLE can be utilized with CHARMM running as a single processor application. Therefore, features of nonparallel running code in CHARMM like the TRAVEL module for locating saddle points or VIBRAN for the calculation of second derivatives can be exploited by running the CPU intensive QM calculations in parallel. To test the methodology, several small systems are studied with both Hartree-Fock and density functional methods and varying QM-MM boundaries. Also, the computationally efficient RI-J method has been examined for use in QM-MM applications. A B(12) cofactor containing cobalt has been studied, to examine systems with a large QM region and transition metals. All tested methods perform satisfactory in comparison with pure quantum calculations. Additionally, algorithms for the characterization of saddle points have been tested for their potential use in QM-MM problems. The TRAVEL module of CHARMM has been applied to the Menshutkin reaction in the condensed phase, and a saddle point was located. This saddle point was verified by calculation of a steepest descent path connecting educt, transition state, and product, and by calculation of vibrational modes. 相似文献
2.
3.
Hui-Na Wang Qiu-An Xiang Hao-Hui Lin Jie-Ning Chen Wen-Jie Guo Wan-Meng Guo Xiang-Ning Yue Zhen-Fu Zhao Kunmei Ji Jia-Jie Chen 《Molecules (Basel, Switzerland)》2022,27(5)
Mast cells (MCs) are an important treatment target for high-affinity IgE Fc receptor (FcεRI)-mediated allergic diseases. The plant-derived molecule 4-methylumbelliferone (4-MU) has beneficial effects in animal models of inflammation and autoimmunity diseases. The aim of this study was to examine 4-MU effects on MC activation and probe the underlying molecular mechanism(s). We sensitized rat basophilic leukemia cells (RBLs) and mouse bone marrow-derived mast cells (BMMCs) with anti-dinitrophenol (DNP) immunoglobulin (Ig)E antibodies, stimulated them with exposure to DNP-human serum albumin (HSA), and then treated stimulated cells with 4-MU. Signaling-protein expression was determined by immunoblotting. In vivo allergic responses were examined in IgE-mediated passive cutaneous anaphylaxis (PCA) and ovalbumin (OVA)-induced active systemic anaphylaxis (ASA) mouse models. 4-MU inhibited β-hexosaminidase activity and histamine release dose-dependently in FcεRI-activated RBLs and BMMCs. Additionally, 4-MU reduced cytomorphological elongation and F-actin reorganization while down-regulating IgE/Ag-induced phosphorylation of SYK, NF-κB p65, ERK1/2, p38, and JNK. Moreover, 4-MU attenuated the PCA allergic reaction (i.e., less ear thickening and dye extravasation). Similarly, we found that 4-MU decreased body temperature, serum histamine, and IL4 secretion in OVA-challenged ASA model mice. In conclusion, 4-MU had a suppressing effect on MC activation both in vitro and in vivo and thus may represent a new strategy for treating IgE-mediated allergic conditions. 相似文献
4.
TD-SCDMA测试仪中Iub接口实现RLC层信令解码 总被引:1,自引:0,他引:1
为了更精确地完成TD-SCDMA测试仪中相关信令的解码测试工作,对TD-SCDMA系统的Uu接口RLC
层信令在Iub接口实现的解码进行了深入分析和研究,给出了RLC层的信令消息结构和流程,提出了”RLC解码的
一种算法,并且应用到TD-SCDMA测试仪中,经调试并实际测试后,得到了预期的良好效果。经过再改进,完全可
以满足市场需要。 相似文献
5.
保留指数是气相色谱中用于化合物结构鉴定的重要工具。本研究对基于正构烷烃和直链脂肪酸甲酯的线性保留指数进行线性拟合,发现在所设定的4种不同的升温条件下两种保留指数之间呈现较为固定的线性关系:在弱极性柱(固定液为5%苯基和95%的甲基聚硅氧烷)和极性柱(固定液为聚乙二醇)条件下,正构烷烃保留指数(y)与脂肪酸甲酯保留指数(x)之间的关系分别为y=1.005 1x+318.51(r2=1)和y=1.036 2x+562.519(r2=1)。采用文献保留指数对所建立的线性关系进行验证,发现通过公式换算得到的保留指数均在其对应文献值的均值加减方差范围内,说明换算公式真实有效。两种保留指数之间关系的建立对于化合物结构鉴定时扩大保留指数搜索范围、减少保留指数测定实验具有重要意义。 相似文献
6.
Characterization of N‐methylated amino acids by GC‐MS after ethyl chloroformate derivatization 下载免费PDF全文
B. Sudarshana Reddy V. Naresh Chary P. Pavankumar S. Prabhakar 《Journal of mass spectrometry : JMS》2016,51(8):638-650
Methylation is an essential metabolic process in the biological systems, and it is significant for several biological reactions in living organisms. Methylated compounds are known to be involved in most of the bodily functions, and some of them serve as biomarkers. Theoretically, all α‐amino acids can be methylated, and it is possible to encounter them in most animal/plant samples. But the analytical data, especially the mass spectral data, are available only for a few of the methylated amino acids. Thus, it is essential to generate mass spectral data and to develop mass spectrometry methods for the identification of all possible methylated amino acids for future metabolomic studies. In this study, all N‐methyl and N,N‐dimethyl amino acids were synthesized by the methylation of α‐amino acids and characterized by a GC‐MS method. The methylated amino acids were derivatized with ethyl chloroformate and analyzed by GC‐MS under EI and methane/CI conditions. The EI mass spectra of ethyl chloroformate derivatives of N‐methyl ( 1–18 ) and N,N‐dimethyl amino acids ( 19–35 ) showed abundant [M‐COOC2H5]+ ions. The fragment ions due to loss of C2H4, CO2, (CO2 + C2H4) from [M‐COOC2H5]+ were of structure indicative for 1–18 . The EI spectra of 19–35 showed less number of fragment ions when compared with those of 1–18 . The side chain group (R) caused specific fragment ions characteristic to its structure. The methane/CI spectra of the studied compounds showed [M + H]+ ions to substantiate their molecular weights. The detected EI fragment ions were characteristic of the structure that made easy identification of the studied compounds, including isomeric/isobaric compounds. Fragmentation patterns of the studied compounds ( 1–35 ) were confirmed by high‐resolution mass spectra data and further substantiated by the data obtained from 13C2‐labeled glycines and N‐ethoxycarbonyl methoxy esters. The method was applied to human plasma samples for the identification of amino acids and methylated amino acids. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
7.
Daisuke Nagae Koichiro Asahi Hisanori Miyoshi Kenzi Shimada Akihiro Yoshimi Hideki Ueno Jiro Murata Makoto Uchida Daisuke Kameda Go Kato Shoken Emori Go Kijima Sachiko Oshima Makoto Takemura Takemasa Arai Yoshio Kobayashi Tomohito Haseyama W.D. Schmidt-Ott 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):580
A device that produces a low-energy and largely spin polarized RI beam based on the atomic beam resonance method (RIABR) has been developed. We have performed measurements of stopping and drifting an incoming RI ion beam in a gas chamber, extraction of the ions into a vacuum region, and neutralization of the extracted low-energy ion beam. The drift efficiency of RI ions in a gas and the extraction efficiency at a Laval-type glass nozzle were found to be 0.72±0.04 and 0.033, respectively. The result of the experiment for the neutralization is also discussed. 相似文献
8.
Single nucleotide polymorphisms (SNPs) are the most common genetic polymorphisms and play a major role in many inherited diseases. Methylenetetrahydrofolate dehydrogenase 1 (MTHFD1) is one of the enzymes involved in folate metabolism. In the present study, the functional and structural consequences of nsSNPs of human MTHFD1 gene was analyzed using various computational tools like SIFT, PolyPhen2, PANTHER, PROVEAN, SNAP2, nsSNPAnalyzer, PhD-SNP, SNPs&GO, I-Mutant, MuPro, ConSurf, InterPro, NCBI Conserved Domain Search tool, ModPred, SPARKS-X, RAMPAGE, FT Site and PyMol. Out of 327 nsSNPs form human MTHFD1 gene, total 45 SNPs were predicted as functionally most significant SNPs, among which 17 were highly conserved and functional, 17 were highly conserved and structural residues. Among 45 most significant SNPs, 15 were predicted to be involved in post translational modifications. The p.Gly165Arg may interfere in homodimer interface formation. The p.Asn439Lys and p.Asp445Asn may interfere in binding interactions of MTHFD1 protein with cesium cation and potassium. The two SNPs (p.Asp562Gly and p.Gly637Cys) might interfere in interactions of MTHFD1 with ligand. 相似文献
9.
Pressure fluctuations and resulting refractive index changes, induced by the back pressure regulator (BPR) can be a significant source of UV detector noise in supercritical fluid chromatography (SFC). The refractive index (RI) of pure carbon dioxide (CO(2)) changes ≈0.2%/bar at the most commonly used conditions in supercritical fluid chromatography (SFC) (40 °C and 100 bar), compared to 0.0045%/bar for water (CO(2) IS 44× worse). Changes in RI cause changes in the focal length of the detector cell which results in changes in UV intensity entering the detector. The change in RI (ΔRI/bar) of CO(2) decreases 8-fold at 200 bar, compared to 100 bar. A new back pressure regulator (BPR) design representing an order of magnitude improvement in the state of the art is shown to produce peak to peak pressure noise (PN(p-p)) as low as 0.1 bar, at 200 bar, and 20Hz, compared to older equipment that attempted to maintain PN(p-p)<1bar, at <5Hz. With this lower PN(p-p), changes in baseline UV offsets could be measured as a function of very small changes in pressure. A pressure change of ±1 bar at 100 bar, common with some older BPR's, produced a UV baseline offset >0.5 mAU. A pressure change of ±0.5 bar representing the previous state-of-the-art, resulted in a UV offset of 0.3m AU. Baseline noise <0.05 is required to validate methods for trace analysis. The new BPR, with a PN(p-p) of 0.1 bar, demonstrated UV peak to peak noise (N(p-p))<0.02 mAU with a >0.03 min (10Hz) electronic filter under some conditions. This new low noise level makes it possible to validate SFC methods for the first time. 相似文献
10.
姚祖喜 《北京师范大学学报(自然科学版)》1999,(4)
研究多复变域RI(m,n)上Cauchy积分与Poisson-华积分,得到边界函数f∈LP,P>1时几乎处处收敛的结果. 相似文献