抗阿尔兹海默症藏药三味豆蔻汤的化学成分分析研究

三味豆蔻汤作为藏药的经典方剂,由药材豆蔻、香旱芹、荜茇和牦牛奶熬煮制成,其对阿尔兹海默症(Alzheimer's disease,AD)具有一定的治疗作用.该方剂化学成分复杂且极性、挥发性差异大,相关的物质基础研究较少.该研究分别采用气相色谱-质谱(GC-MS)、超高效液相色谱-高分辨串联质谱(UPLC-HRMS/MS...     

Gas-phase ion-molecule chemistry of borate and boronate esters

Borate esters B(OR)₃ and boronate esters RB(OR)₂ undergo ion-molecule reactions to yield both addition products (by an implied radiative emission mechanism), ligand exchange, and proton transfer products, in both positive and negative ion modes. Although an acidity for CH₃B(OR)₂ could not be determined, HOB(OR)₂ has an acidity between acetaldehyde and nitromethane. In light of the negligible polar electron acceptor properties of the -B(OR)₂ group, that functionality must therefore be one of the best resonance electron acceptor groups known, almost half again as effective as the nitro group.     

Gas-phase acidities of diols

The gas-phase acidities of several α, ω-alkanediols were measured with the equilibrium method in an ion cyclotron resonance spectrometer. The values obtained imply cyclization of the structures via an intramolecular hydrogen bond. The results are in quantitative disagreement with those obtained by the method of dissociation of the excited dimer species; care must be used in applying that method to ensure that all of the criteria for relating kinetics to equilibria are met.     

Conformational Analysis of 1,2-Dichlorobutane

Vibrational spectra have been published and normal coordinate calculations have been made for 1,2-dichlorobutane.^1,2 Those calculations were limited to the three conformers that had all four carbon atoms coplanar. Molecular mechanics calculations have now shown a conformer that was omitted to be the second most abundant conformer. Therefore, normal coordinate calculations have been made for this conformer and molecular mechanics calculations have been made for all possible conformers.     

Raman Spectrum of Chloromethyl Thiocyanate

Abstract

The liquid-state Raman spectrum was obtained for chloromethyl thiocyanate. The previously unobserved C-S-C bending band was observed at 188 cm^?1. The Raman spectrum supports the conclusion that only the C_S conformer is present.     

Conformational Analysis of 2, 3, 3-Trimethylhexane

Infrared and Raman spectra were obtained for 2, 3, 3-trimethylhexane and were interpreted with the aid of normal coordinate calculations. It was concluded that this compound exists in three molecular conformations, but a fourth conformer may exist. Vibrational assignments were made for the three conformers.     

Elusive structural changes of New Delhi metallo-β-lactamase revealed by ultraviolet photodissociation mass spectrometry

We use mass spectrometry (MS), under denaturing and non-denaturing solution conditions, along with ultraviolet photodissociation (UVPD) to characterize structural variations in New Delhi metallo-β-lactamase (NDM) upon perturbation by ligands or mutation. Mapping changes in the abundances and distributions of fragment ions enables sensitive detection of structural alterations throughout the protein. Binding of three covalent inhibitors was characterized: a pentafluorphenyl ester, an O-aryloxycarbonyl hydroxamate, and ebselen. The first two inhibitors modify Lys211 and maintain dizinc binding, although the pentafluorophenyl ester is not selective (Lys214 and Lys216 are also modified). Ebselen reacts with the sole Cys (Cys208) and ejects Zn2 from the active site. For each inhibitor, native UVPD-MS enabled simultaneous detection of the closing of a substrate-binding beta-hairpin loop, identification of covalently-modified residue(s), reporting of the metalation state of the enzyme, and in the case of ebselen, observation of the induction of partial disorder in the C-terminus of the protein. Owing to the ability of native UVPD-MS to track structural changes and metalation state with high sensitivity, we further used this method to evaluate the impact of mutations found in NDM clinical variants. Changes introduced by NDM-4 (M154L) and NDM-6 (A233V) are revealed to propagate through separate networks of interactions to direct zinc ligands, and the combination of these two mutations in NDM-15 (M154L, A233V) results in additive as well as additional structural changes. Insight from UVPD-MS helps to elucidate how distant mutations impact zinc affinity in the evolution of this antibiotic resistance determinant. UVPD-MS is a powerful tool capable of simultaneous reporting of ligand binding, conformational changes and metalation state of NDM, revealing structural aspects of ligand recognition and clinical variants that have proven difficult to probe.

We use mass spectrometry (MS) along with ultraviolet photodissociation (UVPD) to characterize structural variations in New Delhi metallo-β-lactamase (NDM) upon perturbation by ligands or mutation.     

Vibrational Analysis of 2,3-Dimethyl-1-Butene

Infrared and Raman spectra were obtained for 2,3-dimethyl-1-butene. The spectra showed the presence of two stable conformations. Vibrational assignments were made for both conformers with the aid of normal coordinate calculations. Values for the force constants that were obtained will be used in the future as the initial values for other substituted 1-alkenes, such as 2-isopropyl-3-methyl-1-butene.     

Rotational isomers of symmetrical difluoroacetone

Solid-state infrared spectra were obtained for symmetrical difluoroacetone that show different conformations present, depending on whether the solid state was obtained by cooling a liquid film or by deposition of the vapor onto a cooled plate. The spectra were used in conjunction with normal coordinate calculations that utilized a force field transferred from fluoroacetone to show that sym-difluoro-acetone exists in the gauche-gauche and cis-gauche conformations.