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A variety of fatty acid functional derivatives were desorbed by fast atom bombardment and collisionally activated. Derivatives having a high proton affinity such as fatty amides, pyrrolidides and picolinyl esters fragment to give decompositions that originate remote from the charge site. In contrast, derivatives having a low proton affinity such as fatty acids and fatty esters fragment to give charge-initiated decompositions. Therefore, the choice of the fatty acid functional derivative is important in effecting charge-remote decompositions of the [M + H]+ ions. The collisional activation spectra of the [M + H]+ ions of fatty alcohols and fatty amines were also compared. Based on this comparison, the internal energy required in order for charge-remote fragmentations to occur is estimated to be between 1.4 and 2.9 eV. This work is a guide in designing functional derivatives of fatty acids that undergo charge-remote reactions. 相似文献
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Changfu Cheng Michael L. Gross 《Journal of the American Society for Mass Spectrometry》1998,9(6):620-627
Upon high-energy collisional activation, oxofatty-acid ions undergo fragmentations to produce a unique pattern of product ions by which the position of the ketone is revealed. The reactions occurring in the vicinity of the ketone, which are the subject of this article, produce a spectral pattern that is not symmetrical. Although cleavages of α, β, and γ C-C bonds occur on the side proximal to the charge site, giving α, β, and γ ions, respectively, there is only a γ′ ion formed on the side distal to the charge site. The resulting lack of symmetry seemingly contradicts the concept that the reactions are independent of the charge (i.e., that they are charge remote). To eliminate any interaction between the charge and the reaction site, oxofatty acids were linked to glycyrrhetic acid, a steroid with a rigid polycyclic system. The fragmentation pattern remains the same, indicating that the effect does not depend on charge but rather on the ketone. Isotopic labeling and MS/MS/MS studies confirm that the fragmentations of C-C bonds in the vicinity of the ketone are complex, charge-remote processes. Formation of [M-H-H2O]? and [M-H-CO2]? anions and the ion that is formed by homolytic cleavage of the β bond at the side distal to the charge, however, are charge directed. 相似文献
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The nature and location of a variety of modifications of fatty acids are determined by collisional activation (CA) of [M + 2Li ? H]+ ions. The sample molecules are cationized in situ on the probe tip, desorbed by fast atom bombardment and, upon CA, undergo charge-remote decompositions. This approach is a direct, totally instrumental method for structure elucidation. Advantages of CA of [M + 2Li ? H]+ ions are that fatty acids with substituents in close proximity to the carboxylate terminus and modified short-chain acids are readily determined: decompositions of carboxylate anions of these fatty acids result in collision-activated dissociation (CAD) spectra that give incomplete structural information. However, the CAD spectra of some [M ? H]? ions, such as those from epoxy acids, are simpler to interpret than those of the [M + 2Li ? H]+ ions. Thus, CA of fatty acid [M + 2Li ? H]+ ions is a complementary approach to CA of [M ? H]? ions for determining the fatty acid structures investigated here. The use of this approach for analyzing complex mixtures of modified fatty acids is also evaluated. 相似文献
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The fragmentations of a number of cinnamic acids substituted at the phenyl ring have been studied with the aid of 70 eV mass spectra and mass analysed ion kinetic energy spectra. Evidence is presented that the formation of [C9H7O2]+ ions occurs by intramolecular aromatic substitution reactions. A mechanism is proposed for the energetically favourable loss of the substituents from meta and para positions of the phenyl ring. The analytical use of intramolecular aromatic substitution reactions is briefly discussed. 相似文献
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G. Petersson 《Journal of mass spectrometry : JMS》1972,6(5):565-576
Gas chromatography—mass spectrometry offers a convenient method for the separation and identification of hydroxy dicarboxylic acids as open-chain trimethylsilyl (TMS) derivatives. Mass spectra were studied of aldaric (tartronic, tartaric, pentaric and hexaric) acids and deoxyaldaric (malic, 2-deoxypentaric, 2-deoxyhexaric, 3-deoxypentaric and 3-deoxyhexaric) acids. The different structural types can be readily identified from their characteristic spectra. The most prominent fragmentations involving the rupture of one bond are the loss of a siliconlinked methyl group and the formation of α-cleavage ions by carbon chain cleavage. The further decay is characterized by a number of significant rearrangements specific of TMS derivatives. Several of these can be classified as involving migration of a TMS group to an oxygen atom or migration of an ester OTMS group to a silicon atom. Concomitant loss of a stable molecule often provides a driving force. Prominent odd-electron ions are formed by a McLafferty-type rearrangement of a TMS group. The decomposition of several even-electron ions can be regarded as analogous to that rearrangement. 相似文献
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Cui L Isbell MA Chawengsub Y Falck JR Campbell WB Nithipatikom K 《Journal of the American Society for Mass Spectrometry》2008,19(4):569-585
The fragmentation characteristics of monohydroxyeicosatetraenoic acids and dihydroxy- and trihydroxyeicosatrienoic acids were
investigated by electrospray ionization Fourier transform ion cyclotron resonance (FTICR) mass spectrometry using sustained
off-resonance irradiation collision-induced dissociation (SORI-CID) and infrared multiphoton dissociation (IRMPD). The fragmentation
patterns of these compounds were associated with the number and positions of the hydroxyl substituents. The fragmentation
is more complicated with increasing number of the hydroxyl groups of the compounds. In general, the major carbon-carbon cleavage
of [M−H]− ions occurred at the α-position to the hydroxyl group, and the carbon-carbon cleavage occurred when there was a double-bond at the β-position to the hydroxyl group. SORI-CID and IRMPD produced some common fragmentation patterns; however, each technique provided
some unique patterns that are useful for structural identification of these compounds. This study demonstrated the application
of FTICR via the identification of regioisomers of trihydroxyeicosatrienoic acids in rabbit aorta samples. 相似文献
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The first total syntheses of acetogenin 3 and its 4 S,8 R-isomer are described. The key step involves intermolecular metathesis of an alpha,beta-unsaturated ketone carrying a tetrahydropyranyl lactone with a tetrahydrofuran derivative. Compound 3 has spectroscopic and physical data consistent with those of natural montanacin D, suggesting that the absolute configuration of the natural product is as shown in 3. 相似文献
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Summary A TLC-densitometric method was introduced for the parallel determination of rosmarinic and caffeic acids. Experiments performed
to establish the optimal measurement parameters related to the excitation wave-length, colour stability, linearity of the
calibration curves, sensitivity and reproducibility. The application of TLC permits utilization of the fluorescence of both
phenols, often without the need for prior purification. This fluorescence measurement makes the detection extremely sensitive.
The densitometric quantification allows the routine analysis of many samples in a short time with reasonable accuracy. The
practical application of the elaborated method will be demonstrated on 5Salvia species. 相似文献
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Carboxylic acids, their chlorides, anhydrides, esters, lactones, amides, lactams and imides react with hydroxylamine to give hydroxamic acids which are then treated with iron(III). Other compounds or groups of compounds can also be determined after a prior conversion into hydroxylamine-reactive derivatives. The calorimetric applications of these reactions are reviewed. The effect of various factors is discussed. A selective procedure for determination of acid chlorides and anhydrides and an improved procedure for determination of carboxylic esters and lactones are presented. 相似文献
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Lintuluoto JM Nakayama K Setsune J 《Chemical communications (Cambridge, England)》2006,(33):3492-3494
Octaphyrin O1 has been found to be an effective sensor for the direct determination of absolute configuration of a variety of carboxylic acids at mM concentrations at room temperature based on CD exciton chirality method. 相似文献
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When mercury is quantified by ICP-MS under routine conditions (external calibration) in reference materials, which require mineralization with nitric acid, the experimental concentrations are almost always unacceptably low in comparison to certified values. Sorption of mercury on the Teflon surfaces of the digestion vessels, changes in the viscosity of the aspirated solutions, in the efficiency of the nebulization, in the aerosol transport, and memory effects cannot be responsible for the low results. The intensity of a mercury signal is strongly dependent on the concentration of nitric acid (and other mineral acids) in the measured solutions. Correct results for mercury in the SRM GBW-90101 (Chinese human hair; 2.16+/-0.21 mg Hg/kg certified) can only be obtained, when the solutions, with which the external calibration curves were established, have exactly the same nitric acid concentration as the aspirated digests (2.03+/-0.01 mg Hg/kg; n = 5), when mercury is determined by the standard addition method (2.10+/-0.01 mg Hg/kg; n = 5), or when the experimental mercury concentration obtained at a nitric acid concentration in the digest, different from the concentration in the external calibration solutions, is corrected mathematically based on a pre-established function [Hg2+] = f [HNO3]. The concentrations found by this mathematically based correction 2.04+/-0.01 mg Hg/kg (n = 5) is in good agreement with the values obtained by acid matched calibration or by the standard addition method. For practical work with large numbers of samples the mathematical correction appears to be the method of choice. For occasional mercury determinations, the standard addition method seems to be the most practicable. 相似文献
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Gübitz 《Journal of separation science》1979,2(11):669-670
A rapid method for the detection and quantltatlve determlnation of unsaturated fatty acids by TLC is presented. After separation on HPTLC-RP18-plates, reaction wlth p-hydroxybenzaldehyde is carried out by a dipping procedure. Nanogram amounts of unsaturated fatty acids can be determined with good reproducibility. 相似文献
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A novel titrimetric method for determination of aminobenzoic acids is based on their reaction with excess of bromine to form N-bromo-2,4,6-tribromoaniline, which liberates an equivalent amount of iodine when treated with iodide. The method is applicable to the aminobenzoic acids in the range 0.1-5.0 mg, with a recovery ranging from 96 to 99.7% and a coefficient of variation of 0.2-2.0%, depending on the concentration level. 相似文献
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Bakken V Helgaker T Uggerud E 《European journal of mass spectrometry (Chichester, England)》2004,10(5):625-638
Invoking a number of theoretical levels ranging from HF/STO-3G to CCSD(T)/aug-cc-pVQZ, we have made a detailed survey of six potential energy surfaces (NH4+, NH4*, [CH3CONHCH3]H+, [CH3CONHCH3]H*, [HCONHCH2CONH2]H+, [HCONHCH2CONH2]H*). In conjunction with this, ab inito direct dynamics calculations have been conducted, tracing out several hundred reaction trajectories to reveal details of the electron-capture dissociation mechanism. The model calculations suggest the possibility of a bimodal pattern where some of the radicals, formed upon recombination, dissociate almost directly within one picosecond, the remaining radicals being subject to complete energy redistribution with a subsequent dissociation occurring at the microsecond timescale. Both processes give rise to c and z backbone fragments, resulting from cleavage of N-Calpha bonds of the peptide chain. 相似文献
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Aqueous xenon trioxide in acidic or neutral solutions oxidises carboxylic acids quantitatively to carbon dioxide and water. Micro and semimicro amounts of carboxylic acids may be determined by the iodometric titration of the excess of xenon trioxide remaining in the reaction mixture. The optimum time and temperature for the reaction depend on the structure of the acid ; dicarboxylic and hydroxy-carboxylic acids react faster than corresponding monocarboxylic acids. Oxalic and polyhydroxy acids are oxidised within 20 min at room temperature while acetic, maleic, succinic, malonic acids require 2 hr at 40 degrees . Carboxylic acids in amounts less than 100 mug are determined with a coefficient of variation of 4%, which decreases to 1 % for amounts over 250 mug. 相似文献