Identification and localization of the fatty acid modification in ghrelin by electron capture dissociation

Electron capture dissociation (ECD) has been demonstrated to be an effective fragmentation technique for characterizing the site and structure of the fatty acid modification in ghrelin, a 28-residue growth-hormone-releasing peptide that has an unusual ester-linked n-octanoyl (C8:0) modification at Ser-3. ECD cleaves 21 of 23 possible backbone amine bonds, with the product ions (c and z· ions) covering a greater amino acid sequence than those obtained by collisionally activated dissociation (CAD). Consistent with the ECD nonergodic mechanism, the ester-linked octanoyl group is retained on all backbone cleavage product ions, allowing for direct localization of this labile modification. In addition, ECD also induces the ester bond cleavage to cause the loss of octanoic acid from the ghrelin molecular ion; the elimination process is initiated by the capture of an electron at the protonated ester group, which is followed by the radical-site-initiated reaction known as -cleavage. The chemical composition of the attached fatty acid can be directly obtained from the accurate Fourier transform ion cyclotron resonance (FTICR) mass measurement of the ester bond cleavage product ions.     

LOW MOLECULAR WEIGHT O-CARBOXYMETHYLATED CHITOSANS DERIVED FROM IRRADIATED CHITOSAN AND THEIR ANTIBACTERIAL ACTIVITY

INTRODUCTIONChitin is the second most naturally abundant biopolymer and is found in a variety of organisms, including fungalcell walls, the exoskeleton of crustaceans, skeletal tissue of mollusks and the integument of insects.When treated with alkali, chitin can be deactylated and turned into chitosan, which is a linear binaryheteropolysaccharide composed of (1-4) linked 2-acetamido-2-deoxy-β-D-glucopyranose and 2-amino-2-deoxy-β-D-glucopyranose residues. Chitosan has a wide variety of …     

Detection and characterization of methionine oxidation in peptides by collision-induced dissociation and electron capture dissociation

Electron capture dissociation (ECD) and collision-induced dissociation (CID), the two complementary fragmentation techniques, are demonstrated to be effective in the detection and localization of the methionine sulfoxide [Met(O)] residues in peptides using Fourier transform ion cyclotron resonance (FTICR) mass spectrometry. The presence of Met(O) can be easily recognized in the low-energy CID spectrum showing the characteristic loss of methanesulfenic acid (CH(3)SOH, 64 Da) from the side chain of Met(O). The position of Met(O) can then be localized by ECD which is capable of providing extensive peptide backbone fragmentation without detaching the labile Met(O) side chain. We studied CID and ECD of several Met(O)-containing peptides that included the 44-residue human growth hormone-releasing factor (GRF) and the human atrial natriuretic peptide (ANP). The distinction and complementarity of the two fragmentation techniques were particularly remarkable in their effects on ANP, a disulfide bond-containing peptide. While the predominant fragmentation pathway in CID of ANP was the loss of CH(3)SOH (64 Da) from the molecular ion, ECD of ANP resulted in many sequence-informative products, including those from cleavages within the disulfide-bonded cyclic structure, to allow for the direct localization of Met(O) without the typical procedures for disulfide bond reduction followed by [bond]SH alkylation.     

Excitation spectra of one-dimensional spin-1/2 Fermi gas with an attraction

Using an exact Bethe ansatz solution, we rigorously study excitation spectra of the spin-1/2 Fermi gas (called Yang–Gaudin model) with an attractive interaction. Elementary excitations of this model involve particle-hole excitation, hole excitation and adding particles in the Fermi seas of pairs and unpaired fermions. The gapped magnon excitations in the spin sector show a ferromagnetic coupling to the Fermi sea of the single fermions. By numerically and analytically solving the Bethe ansatz equations and the thermodynamic Bethe ansatz equations of this model, we obtain excitation energies for various polarizations in the phase of the Fulde–Ferrell–Larkin–Ovchinnikov-like state. For a small momentum (long-wavelength limit) and in the strong interaction regime, we analytically obtained their linear dispersions with curvature corrections, effective masses as well as velocities in particle-hole excitations of pairs and unpaired fermions. Such a type of particle-hole excitations display a novel separation of collective motions of bosonic modes within paired and unpaired fermions. Finally, we also discuss magnon excitations in the spin sector and the application of Bragg spectroscopy for testing such separated charge excitation modes of pairs and single fermions.     

2-巯基-5-甲基苯并咪唑振动光谱的密度泛函理论研究

本文选用密度泛函理论中的B3LYP杂化泛函,在B3LYP/6-311++G(d, p)水平下,优化了2-巯基-5-甲基苯并咪唑分子(MMBI)的结构,优化结果表明,2-巯基-5-甲苯并咪唑分子是一个近平面结构.通过频率计算,获得了2-巯基-5-甲基苯并咪唑分子(MMBI)的拉曼光谱,并和实验获得的拉曼光谱图进行了对比,实验和理论计算获得的拉曼光谱图基本上是一致的,表明本文选取的DFT理论计算方法是可靠的.结合VEDA4软件对2-巯基-5-甲基苯并咪唑分子的拉曼谱带简正振动模式进行了指认.此外,分析并讨论了2-巯基-5-甲基苯并咪唑分子(MMBI)前线轨道,HOMO和LUMO轨道能级差为4.51 eV,电子有从HOMO跃迁到LUMO的趋势.采用含时密度泛函理论(time dependent density functional theory, TDDFT)对2-巯基-5-甲基苯并咪唑分子(MMBI)的激发态进行了计算分析,计算结果表明乙醇溶剂中2-巯基-5-甲基苯并咪唑分子(MMBI)理论计算的吸收波长为226 nm, 288 nm.对研究2-巯基-5-甲基苯并咪唑分子的性质,提供了理论...     

The ionic parachor and predicting properties of amino acid ionic liquid homologues of 1-alkyl-3-methylimidazolium glycine

The amino acid ionic liquids(AAILs) [C3mim][Gly](1-propyl-3-methylimidazolium glycine) and [C4mim][Gly](1-butyl-3methylimidazolium glycine) have been prepared by the neutralization method and characterized by 1 H NMR spectroscopy and differential scanning calorimetry(DSC).The values of their density,surface tension and refractive index were measured at(298.15 ± 0.05) K.Since the AAILs can form strong hydrogen bonds with water,small amounts of water are difficult to remove from the AAILs by common methods.In order to eliminate the effect of the impurity water,the standard addition method(SAM) was applied to these measurements.A new concept which is called the ionic parachor has been put forward.The [C n mim] + cations were treated as a group of reference ions and the individual values of their ionic parachor were evaluated in terms of an extrathermodynamic assumption.Then,using the values of the ionic parachor of reference ions,the parachor,surface tension γ and refractive index n D of the ionic liquids investigated in this work were estimated.The estimated values correlate quite well with the corresponding experimental values.     

Aqueous synthesis of CdSe and CdSe/CdS quantum dots with controllable introduction of Se and S sources

A new and convenient route is developed to synthesize CdSe and core-shell CdSe/CdS quantum dots(QDs) in aqueous solution.The gaseous precursors,H2Se and H2S,generated on-line by reducing SeO 3 2à with NaBH 4 and the reaction between Na 2 S and diluted H2SO 4,are used to form high-quality CdSe and CdSe/CdS QDs,respectively.The synthesized water-soluble CdSe and CdSe/CdS QDs possess high quantum yield(3% and 20%) and narrow full-width-at-half-maximum(43 nm and 38 nm).The synthesis process is easily reproducible with simple apparatus and low-toxic chemicals,and can be readily extended to the large-scale aqueous synthesis of QDs.     

Synthesis of pyridine-based poly(N-arylenebenzimidazole sulfone)

Poly（N-arylenebenzimidazole pyridine sulfone）（PNABIPS） has been prepared via the aromatic nucleophilic displacement reaction of 2,6-bis（2-benzimidazoly）pyridine（BBP） with bis（4-fluorophenyl） sulfone.BBP was synthesized by reaction of 2,6- pyridinedicarboxylic acid with 1,2-phenylenediamine in polyphosphoric acid.The chemical structure of BBP was confirmed by FTIR, HRMS,¹H NMR and ¹³C NMR.The characterization of the polymer was performed with FT-IR,¹H NMR,elemental analysis, GPC,XRD,DSC,TGA and solubility tests.The polymer was obtained in quantitative yield with M_n value 12,600 and M_w value 28,300,respectively.DSC and TGA measurements show that the glass transition temperature（T_g） is 312℃ and 5%weight loss temperature is 434℃ in nitrogen and 545℃ in air,respectively.In addition,the novel polymer exhibits good solubility,which can be dissolved in common organic solvent at room temperature.     

Unconventional chain-growth mode in the assembly of colloidal gold nanoparticles

One-dimensional assembly of gold nanoparticlesis achieved by a sphere-to-cylinder transformation of polymer shells. A large amount of monomers remains after the assembly, which is characteristic of the chain-growth "polymerization". Single-line chains can be converted to double-line chains, thus substantiating the unique role of the polymer shell.