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991.
Chen TF Yoder JD Hruby DE 《European journal of mass spectrometry (Chichester, England)》2004,10(4):501-508
Myristoylpeptides were synthesized in order to determine if a neutral loss of 210 Da, C14H26O (the mass of the myristoyl moiety), was universal and observable by both liquid chromatography electrospray ionization quadrupole ion trap (LC-ESI-QIT) and matrix-assisted laser desorption/ionization time-of-flight time-of-flight (MALDI-ToF/ToF) mass spectrometry. Myristoylation was successfully introduced on the N-terminus, internally on the amino group of lysine and arginine. Larger peptides and the arginine compounds needed elevated temperatures for myristoylation. To our knowledge, this is the first report of a chemically-synthesized myristoylated arginine in a peptide. Collision energy studies for the LC-ESI-QIT instrument showed that modified peptides and a loss of 210 Da could be detected under commonly used conditions (energy level between 30 and 42%) with picomole amounts of sample. The loss of myristoyl moiety is observed on the MALDI-Tof/Tof mass spectrometer as well. Due to the hydrophobic properties of the myristoyl moiety, it is not surprising that the modified peptides all formed at least dimers, and in some cases trimers. We were also able to distinguish a mixture of two mono-myristoylated peptides. MS3 data from the LC-ESI-QIT instrument on a di-myristoylated peptide indicates the loss of 210 Da at either the N-terminus or lysine. We were also able to analyze a mixture of modified and unmodified peptides on the MALDI-ToF/ToF instrument. The data presented in this paper demonstrates the constant neutral loss of the 210 Da, C14H26O, from both N-terminally and internally myristoylated peptides can be identified unambiguously using LC-ESI-QIT or MALDI-ToF/ToF mass spectrometers. This will be a useful tool in determining the myristoylation status of candidate proteins after enzyme digestion, and in elucidating the modification sites of internal myristoyl proteins. 相似文献
992.
Bismuth (0–110 μg) is determined spectrophotometrically at 495 nm after its adsorptive extraction from dilute sulphuric acid as hexadecyltributylphosphonium tetraiodobismuthate(III) on microcystalline benzophenone and dissolution of the solid phase in carbon tetrachloride. The effects of acidity, diverse ions and masking studies are reported. The system is applied to the determination of bismuth in pharmaceutical samples. 相似文献
993.
The interaction of (Ph3P)2PtO2 (I) with the dicarboxylic acids HO2C(CH2)nCO2H (n = 1–3), phthalic acid and maleic acid gives the dicarboxylato complexes (Ph3P)2 (II) (n = 1–3), (Ph3P)2 (III) and cis-[(Ph3P)2Pt(O(O)CCHCHC(O)OH)2] (IV) in nearly quantitative yield. Thermal and photoinduced decarboxylation of III and IV yields the platina heterocycles (Ph3P)2 (V) and (Ph3P)2 (VI) with a carbon-platinum σ-bond. Complex VI has been characterized by an X-ray crystal structure determination. 相似文献
994.
S. K. Atkhamova R. K. Rakhmanberdyeva D. A. Rakhimov A. K. Karimdzhanov A. I. Ismailov K. Kh. Khodzhimatov T. T. Saidova 《Chemistry of Natural Compounds》1993,29(5):566-568
The polysaccharides of three cultivated varieties ofAlthea rosea have been investigated. The amounts of water-soluble polysaccharides and pectin substances in various organs of the plant have been determined. It has been shown that the maximum amount of water-soluble polysaccharides and pectin substances is present in the flowers. Their monosaccharide compositions have been studied. The physicochemical characteristics of the pectin substances are given. 相似文献
995.
A theoretical study is reported for nuclear spin echo in a two-spin system. It is assumed that the decay of the echo signals is due to translational diffusion of the molecules and to chemical exchange between magnetically distinct nuclei. The behavior of the spin system is described by McConnell's equations, as modified to include diffusion. The method of stationary Markov processes is applied to solve the equations of motion. Theoretical explanations are given for spin-echo observations. 相似文献
996.
Zusammenfassung Die Infrarot-und Raman-Spektren folgender Hydroxylamin-Derivate wurden registriert und zugeordnet: (CH3)3SiONH2 (1), (CH3)3SiONHSi(CH3)3, (CH3)3SiON[Si(CH3)3]2 (3), CH3ONH2 (4), CH3ON[Si(CH3)3]2 (5), CH3NHOCH3, CH3N[Si(CH3)3]OCH3, (C2H5)2NOH und (C2H5)2NOSi(CH3)3. Eine Normalkoordinatenanalyse für NH2OH,1, 3, 4 und5 zeigt, daß sich die Spektren durch Übertragung gleichbleibender Kraftkonstanten der Molekülfragmente wiedergeben lassen. O-und N-Substituenten beeinflussen die NO-Kraftkonstante nicht; die SiO-und SiN-Valenzkraftkonstanten sind mit 3,3 mdyn/Å bemerkenswert niedrig.
Mit 4 Abbildungen 相似文献
Vibrational spectra and normal coordinate analysis of some methyl-and trimethylsilylhydroxylamines
The infrared and Raman spectra of the hydroxylamine derivatives quoted above were recorded and frequencies assigned. A normal coordinate treatment of NH2OH,1, 3, 4 and5 showed that the spectra can be explained by a single force field set up by transferring force constants from the different fragments of the molecules. The NO stretching force constant remains unaffected by different substituents. The SiO and SiN stretching force constants are remarkably small (c. 3.3 mdyn/Å).
Mit 4 Abbildungen 相似文献
997.
Y. Harima D.-H. Kim Y. Tsutitori X. Jiang R. Patil Y. Ooyama J. Ohshita A. Kunai 《Chemical physics letters》2006,420(4-6):387-390
Carrier mobilities in thin films of copolymers with repeat units consisting of oligothiophenes bridged by Si atoms are measured over a range of doping levels, where the numbers of thienylenes in the repeat unit are 7, 8, 10, 12, and 14. The mobilities for these polymer films increased with the increase in doping level and the mobility enhancement followed an increasing order of the π-conjugation length. The magnitude of the mobility increase for the Si polymer comprising 14 thiophene units reached ca. 104, implying that this π-conjugation length is almost sufficient to reproduce transport properties of polythiophenes. 相似文献
998.
Liposomes have been widely used as cellular and bioparticle mimics due to their lipid bilayer structure and relative ease of production and manipulation. Such biocolloids are frequently characterized by capillary electrophoresis (CE), which promises a wealth of information about such properties as surface charge, composition, and rigidity. The applicability of this information is somewhat limited, however, since it is interpreted with colloidal theories that do not account for the unique properties of biocolloids. In this work, the effects of deformability, mobile surface charges, intrinsic polarizability, and uneven surface charge distributions are incorporated into colloidal theories in order to better model the electrophoretic behaviors of liposomes. 相似文献
999.
Simone Gallarati Raimon Fabregat Rubn Laplaza Sinjini Bhattacharjee Matthew D. Wodrich Clemence Corminboeuf 《Chemical science》2021,12(20):6879
Hundreds of catalytic methods are developed each year to meet the demand for high-purity chiral compounds. The computational design of enantioselective organocatalysts remains a significant challenge, as catalysts are typically discovered through experimental screening. Recent advances in combining quantum chemical computations and machine learning (ML) hold great potential to propel the next leap forward in asymmetric catalysis. Within the context of quantum chemical machine learning (QML, or atomistic ML), the ML representations used to encode the three-dimensional structure of molecules and evaluate their similarity cannot easily capture the subtle energy differences that govern enantioselectivity. Here, we present a general strategy for improving molecular representations within an atomistic machine learning model to predict the DFT-computed enantiomeric excess of asymmetric propargylation organocatalysts solely from the structure of catalytic cycle intermediates. Mean absolute errors as low as 0.25 kcal mol−1 were achieved in predictions of the activation energy with respect to DFT computations. By virtue of its design, this strategy is generalisable to other ML models, to experimental data and to any catalytic asymmetric reaction, enabling the rapid screening of structurally diverse organocatalysts from available structural information.A machine learning model for enantioselectivity prediction using reaction-based molecular representations. 相似文献
1000.
S. K. Soh D. C. Sundberg 《Journal of polymer science. Part A, Polymer chemistry》1982,20(5):1299-1313
It is well known that the reaction rate and molecular weight of vinyl polymers can change markedly during the course of polymerization and that these changes are due to the influence of diffusion on the termination reaction. The chain length dependence of the termination rate constant has been considered in this work and has resulted in a general method of treating the polymerization kinetics and molecular weight distribution. This method is independent of the form of the chain length dependency and is capable of dealing with both disproportionation and recombination modes of termination. A specific model for the termination rate constant with chain length dependence is proposed and is based on free volume theory and entanglement coupling. Master curves for the characteristics of the reaction rate and molecular weight distribution are presented with the application of this model. 相似文献