基于随机共振和微纳传感器阵列的六氟化硫检测方法研究

建立了一种基于随机共振和微纳传感器阵列的六氟化硫气体检测方法.使用两个360 μm极间距离的微纳传感器构成的阵列结合随机共振算法,在室温常压,相对湿度70%的条件下检测3.0～24 g/m3 SF6气体及纯SF6气体,以信噪比极大值实现各浓度SF6气体的区分.传感器工作于微电离平衡状态,检测过程中无有害气体产生,安全性较高.为检验该方法的实用性,依据国家标准在温度20 ℃、相对湿度70%和常压条件下模拟现场检测3.0～12 g/m3SF6气体,结果表明: 本方法具有较好的重复性和实用性.     

Precise and global identification of phospholipid molecular species by an Orbitrap mass spectrometer and automated search engine Lipid Search

In the present research, we have established a new lipidomics approach for the comprehensive and precise identification of molecular species in a crude lipid mixture using a LTQ Orbitrap mass spectrometer (MS) and reverse-phase liquid chromatography (RPLC) combination with our newly developed lipid search engine “Lipid Search”. LTQ Orbitrap provides high mass accuracy MS spectra by Fourier-transform (FT) mass spectrometer mode and can perform rapid MSⁿ by ion trap (IT) mass spectrometer mode. In this study, the negative ion mode was selected to detect fragment ions from phospholipids, such as fatty acid anions, by MS2 or MS3. We selected the specific detection approach by neutral loss survey-dependent MS3, for the identification of molecular species of phosphatidylcholine, sphingomyelin and phosphatidylserine. Identification of molecular species was performed by using both the high mass accuracy of the mass spectrometric data obtained from FT mode and structural data obtained from fragments in IT mode. Some alkylacyl and alkenylacyl species have the same m/z value as molecular-related ions and fragment ions, thus, direct acid hydrolysis analysis was performed to identify alkylacyl and alkenylacyl species, and then the RPLC–LTQ Orbitrap method was applied. As a result, 290 species from mouse liver and 248 species from mouse brain were identified within six different classes of phospholipid, only those in manually detected and confirmed. Most of all manually detected mass peaks were also automatically detected by “Lipid Search”. Adding to differences in molecular species in different classes of phospholipids, many characteristic differences in molecular species were detected in mouse liver and brain. More variable number of saturated and monounsaturated fatty acid-containing molecular species were detected in mouse brain than liver.     

Conformational analysis of methylphenidate: comparison of molecular orbital and molecular mechanics methods

Summary Methylphenidate (MP) binds to the cocaine binding site on the dopamine transporter and inhibits reuptake of dopamine, but does not appear to have the same abuse potential as cocaine. This study, part of a comprehensive effort to identify a drug treatment for cocaine abuse, investigates the effect of choice of calculation technique and of solvent model on the conformational potential energy surface (PES) of MP and a rigid methylphenidate (RMP) analogue which exhibits the same dopamine transporter binding affinity as MP. Conformational analysis was carried out by the AM1 and AM1/SM5.4 semiempirical molecular orbital methods, a molecular mechanics method (Tripos force field with the dielectric set equal to that of vacuum or water) and the HF/6-31G* molecular orbital method in vacuum phase. Although all three methods differ somewhat in the local details of the PES, the general trends are the same for neutral and protonated MP. In vacuum phase, protonation has a distinctive effect in decreasing the regions of space available to the local conformational minima. Solvent has little effect on the PES of the neutral molecule and tends to stabilize the protonated species. The random search (RS) conformational analysis technique using the Tripos force field was found to be capable of locating the minima found by the molecular orbital methods using systematic grid search. This suggests that the RS/Tripos force field/vacuum phase protocol is a reasonable choice for locating the local minima of MP. However, the Tripos force field gave significantly larger phenyl ring rotational barriers than the molecular orbital methods for MP and RMP. For both the neutral and protonated cases, all three methods found the phenyl ring rotational barriers for the RMP conformers/invertamers (denoted as cte, tte, and cta) to be: cte, tte> MP > cta. Solvation has negligible effect on the phenyl ring rotational barrier of RMP. The B3LYP/6-31G* density functional method was used to calculate the phenyl ring rotational barrier for neutral MP and gave results very similar to those of the HF/6-31G* method.     

Testing an alternative search algorithm for compound identification with the ‘Wiley Registry of Tandem Mass Spectral Data,MSforID’

A tandem mass spectral database system consists of a library of reference spectra and a search program. State‐of‐the‐art search programs show a high tolerance for variability in compound‐specific fragmentation patterns produced by collision‐induced decomposition and enable sensitive and specific ‘identity search’. In this communication, performance characteristics of two search algorithms combined with the ‘Wiley Registry of Tandem Mass Spectral Data, MSforID’ (Wiley Registry MSMS, John Wiley and Sons, Hoboken, NJ, USA) were evaluated. The search algorithms tested were the MSMS search algorithm implemented in the NIST MS Search program 2.0g (NIST, Gaithersburg, MD, USA) and the MSforID algorithm (John Wiley and Sons, Hoboken, NJ, USA). Sample spectra were acquired on different instruments and, thus, covered a broad range of possible experimental conditions or were generated in silico. For each algorithm, more than 30 000 matches were performed. Statistical evaluation of the library search results revealed that principally both search algorithms can be combined with the Wiley Registry MSMS to create a reliable identification tool. It appears, however, that a higher degree of spectral similarity is necessary to obtain a correct match with the NIST MS Search program. This characteristic of the NIST MS Search program has a positive effect on specificity as it helps to avoid false positive matches (type I errors), but reduces sensitivity. Thus, particularly with sample spectra acquired on instruments differing in their setup from tandem‐in‐space type fragmentation, a comparably higher number of false negative matches (type II errors) were observed by searching the Wiley Registry MSMS. Copyright © 2013 John Wiley & Sons, Ltd.     

Conformational analysis of [Met5]-enkephalin: Solvation and ionization considerations

[Met5]-Enkephalin has the sequence Tyr-Gly-Gly-Phe-Met. Only the extended conformation of the peptide has been observed by X-ray crystallography. Nuclear magnetic resonance spectroscopy supports the presence of a turn at Gly 3 and Phe 4 in dimethyl sulfoxide. In this study, the peptide conformational states and thermodynamic properties are understood in terms of ionization state and solvent environment. In the calculation, final conformations obtained from multiple independent Monte Carlo simulated annealing conformational searches are starting points for molecular dynamics simulations. In an aqueous environment given by the use of solvation free energy and the zwitterionic state, dominant structural motifs computed are G-P Type II bend, G-G Type II bend, and G-G Type I bend motifs, in order of increasing free energy. In the calculation of the peptide with neutral N- and C-termini and solvation free energy, the extended conformer dominates (by at least a factor of 2.5), and the conformation of another low free energy conformer superimposes well on the pharmacophoric groups of morphine. Neutralization of charge and solvation induce and stabilize the extended conformation, respectively. A mechanism of inter-conversion between the extended conformer and three bent conformers is supported by /-scatter plots, and by the conformer relative free energies. An estimate of the entropy change of receptor unbinding is 8.3 cal K-1 mol-1, which gives rise to a -2.5 kcal/mol entropy contribution to the free energy of unbinding at 25 °C. The conformational analysis methodology described here should be useful in studies on short peptides and flexible protein surface loops that have important biological implications.     

Study on pyrolysis kinetics of walnut shell

Slow pyrolysis of walnut shell which is a cheap and abundantly available solid waste was carried out using thermogravimetric analysis. The effects of raw material heating rate on the pyrolysis properties and kinetic parameters were investigated. A two-step consecutive reaction model were used to simulate the pyrolysis process. The kinetic parameters were established by using the pattern search method. Comparison between experimental data and the model prediction indicated that the two-step consecutive reaction model can better describe the slow pyrolysis of walnut shell as the formation of an intermediate during the pyrolysis process was taken into account.     

A Comparison of Three Heuristic Algorithms for Molecular Docking

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A proposal for the molecular basis of μ and δ opiate receptor differentiation based on modeling of two types of cyclic enkephalins and a narcotic alkaloid

Summary The molecular basis underlying the divergent receptor selectivity of two cyclic opioid peptides Tyr-c[N -d-Orn²-Gly-Phe-Leu-] (c-ORN) and [d-Pen², l-Cys⁵]-enkephalinamide (c-PEN) was investigated using a molecular modeling approach. Ring closure and conformational searching procedures were used to determine low-energy cyclic backbone conformers. Following reinsertion of amino acid side chains, the narcotic alkaloid 7-[(1R)-1-methyl-1-hydroxy-3-phenylpropyl]-6,14-endoethenotetrahydro oripavine (PEO) was used as a flexible template for bimolecular superpositions with each of the determined peptide ring conformers using the coplanarity and cocentricity of the phenolic rings as the minimum constraint. A vector space of PEO, accounting for all possible orientations for the C₂₁-aromatic ring of PEO served as a geometrical locus for the aromatic ring of the Phe⁴ residue in the opioid peptides. Although a vast number of polypeptide conformations satisfied the criteria of the opiate pharmacophore, they could be grouped into three classes differing in magnitude and sign of the torsional angle values of the tyrosyl side chain. Only class III conformers for both c-ORN and c-PEN, having tyramine dihedral angles ₁ =–150° ± 30° and ₂=–155° ± 20°, had significant structural and conformational properties that were mutually compatible while respecting the PEO vector space. Comparison of these properties in the context of the divergent receptor selectivity of the studied opioid peptides suggests that the increased distortion of the peptide backbone in the closure region of c-PEN together with the pendant ,-dimethyl group, combine to generate a steric volume which is absent in c-ORN and that may be incompatible with a restrictive topography of the receptor. The nature and stereo-chemistry of substituents adjacent to the closure region of the peptides could also modulate receptor selection by interacting with a charged () or neutral () subsite.     

Weak approximation of the stochastic wave equation

We investigate the accuracy of approximation of E[φ(u(t))], where {u(t):t∈[0,∞)} is the solution of the stochastic wave equation driven by the space-time white noise and φ is an R-valued function defined on the Hilbert space L²(R). The approximation is done by the leap-frog scheme. We show that, under certain conditions on φ, the approximation by the leap-frog scheme is of order two.     

Log-concavity for Bernstein-type operators using stochastic orders

This paper aims to study the preservation of log-concavity for Bernstein-type operators. In particular, attention is focused on positive linear operators, defined on the positive semi-axis, admitting a probabilistic representation in terms of a process with independent increments. This class includes the classical Gamma, Szász, and Szász–Durrmeyer operators. With respect to the first and second operators, the results of this paper correct two erroneous counterexamples in [10]. As a main tool in our results we use stochastic order techniques. Our results include, as a particular case, the log-concavity of certain functions related to the incomplete Gamma function.