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1.
The present study provides a comparison of two liquid chromatography–tandem mass spectrometry methods for ginsenosides analysis. The two methods have the same liquid chromatography separation procedure, and both use tandem mass spectrometry detection. However, one method uses multiple reaction monitoring transitions commonly recommended in the literature starting with [M + Na]+ as the molecular ions and with detection of specific fragment ions from the molecules M, while the other is an original method using [M + Cs]+ as molecular ions and Cs+ as fragment ion. The method using [M + Cs]+ as molecular ion has a very high sensitivity allowing the measurement of concentrations in the injecting solutions as low as 4 ng/ml with peaks at this concentration showing signal to noise ratio of 20 or higher. The procedures were utilized for the measurement of eight ginsenosides (Rb1, Rb2, Rc, Rd, Re, Rf (S), Rg1, and Rg2), although the method using [M + Cs]+ has the potential for measuring other ginsenosides. As an application, the ginsenosides were measured in several types of ginseng root, several dietary supplements containing ginseng extracts, four energy drinks, and a sample of ashwagandha.  相似文献   

2.
1,4‐Diazabicyclo[2.2.2]octane (dabco) and its derivatives have been extensively utilized as building units of excellent molecular ferroelectrics for decades. However, the homochiral dabco‐based ferroelectric remains a blank. Herein, by adding a methyl (Me) group accompanied by the introduction of homochirality to the [H2dabco]2+ in the non‐ferroelectric [H2dabco][TFSA]2 (TFSA=bis(trifluoromethylsulfonyl)ammonium), we successfully designed enantiomeric ferroelectrics [R and S‐2‐Me‐H2dabco][TFSA]2. The two enantiomers show two sequential phase transitions with transition temperature (Tc) as high as 405.8 K and 415.8 K, which is outstanding in both dabco‐based ferroelectrics and homochiral ferroelectrics. To our knowledge, [R and S‐2‐Me‐H2dabco][TFSA]2 are the first examples of dabco‐based homochiral ferroelectrics. This finding opens an avenue to construct dabco‐based homochiral ferroelectrics and will inspire the exploration of more eminent enantiomeric molecular ferroelectrics.  相似文献   

3.
The title complex, [Ag(C7H5O2)(C4H5N3)]n, is a polymer based on a mononuclear silver(I)‐centered fragment. The AgI atom is trigonally coordinated by two N atoms from two 2‐­amino­pyrimidine ligands and one O atom from one benzoate anion, giving zigzag polymeric chains with an [–Ag—N—C—N–]n backbone running along the a axis. It is proposed that intermolecular hydrogen bonding drives the formation of the chain polymer.  相似文献   

4.
Two novel chiral ruthenium(II) complexes, Δ‐[Ru(bpy)2(dmppd)]2+ and Λ‐[Ru(bpy)2(dmppd)]2+ (dmppd = 10,12‐dimethylpteridino[6,7‐f] [1,10]phenanthroline‐11,13(10H,12H)‐dione, bpy = 2,2′‐bipyridine), were synthesized and characterized by elemental analysis, 1H‐NMR and ES‐MS. The DNA‐binding behaviors of both complexes were studied by UV/VIS absorption titration, competitive binding experiments, viscosity measurements, thermal DNA denaturation, and circular‐dichroism spectra. The results indicate that both chiral complexes bind to calf‐thymus DNA in an intercalative mode, and the Δ enantiomer shows larger DNA affinity than the Λ enantiomer does. Theoretical‐calculation studies for the DNA‐binding behaviors of these complexes were carried out by the density‐functional‐theory method. The mechanism involved in the regulating and controlling of the DNA‐binding abilities of the complexes was further explored by the comparative studies of [Ru(bpy)2(dmppd)]2+ and of its parent complex [Ru(bpy)2(ppd)]2+ (ppd = pteridino[6,7‐f] [1,10]phenanthroline‐11,13 (10H,12H)‐dione).  相似文献   

5.
N‐Boc/Fmoc/Z‐N′‐formyl‐gem‐diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro‐inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion‐trap multi‐stage mass spectrometry (MSn). The MS2 collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N‐Fmoc/Z‐amino acids, dipeptide and tripeptide acids show the [M + Na‐NH2CHO]+ ion, arising from the loss of formamide, as the base peak. Differently, the MS2 CID spectra of [M + Na]+ ion of all the N‐Boc derivatives yield the abundant [M + Na‐C4H8]+ and [M + Na‐Boc + H]+ ions because of the loss of isobutylene and CO2 from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N‐protected dipeptidyl and tripeptidyl‐N′‐formamides is provided by MS2 and subsequent MSn experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M‐H]?, [M + HCOO]? and [M + Cl]? ions, the presence of in‐source CID fragment ions deriving from the involvement of the N‐protecting group. Furthermore, MSn spectra of [M + Cl]? ion of N‐protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C‐terminal gem‐diamino residue. The present paper represents an initial attempt to study the ESI‐MS behavior of these important intermediates and lays the groundwork for structural‐based studies on more complex partially modified retro‐inverso peptides. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

6.
Electron impact induced fragmentation of the title compounds obeys a route where the lactam moiety, OCNH, is cleaved first, with the accompanying formation of a cycloalkene ion. This can be verified by low-resolution, high-resolution, B/E and B2/E spectra as well as by collisional activation spectra of, for example, the ions m/z 82 and 67 from 7-azabicyclo[4.2.0]octan-8-one and from cyclohexene. The only, and fairly weak, fragment ions including O and N are [C3H3O]+, [CkH2k-2N]+ (k = 5–8) and [C3H6N]+. The ammonia chemical ionization spectra are also characteristic for all four lactams and show the same dominant ions in all cases, namely [M + 1]+, [M + 1 + NH3]+˙ and [2 M + 1]+˙.  相似文献   

7.
The two independent bis(3,5‐di­methyl­pyrazole)silver(I) cations in crystalline [Ag(C5H7N2)2]NO3 display N—Ag—N angles of 175.51 (14) and 174.44 (13)°, and an average Ag—N distance of 2.124 (5) Å. The nitrate anion is situated between [Ag(C5H7N2)2]+ units and interacts via hydrogen bonds with the NH groups. The two 3,5‐di­methyl­pyrazole ligands are trans about the silver center. Only a small deviation from linearity is observed in the coordination around silver.  相似文献   

8.
The title complex, [Ag2(C7H5O2)2(C18H18F2N2)]n, is a dinuclear silver(I) compound with one inversion centre between pairs of Ag atoms and another at the mid‐point of the central C—C bond in the butane‐1,4‐diamine moiety. Each of the smallest repeat units consists of two silver(I) cations, two benzoate anions and one N,N′‐bis(2‐fluorobenzyl­idene)­butane‐1,4‐di­amine Schiff base ligand. Each AgI ion is three‐coordinated in a trigonal configuration by two O atoms from two benzoate anions and one N atom from a Schiff base ligand. The di‐μ‐benzoato‐disilver(I) moieties are linked by the bridging Schiff base ligand, giving zigzag polymeric chains with an [–Ag⋯Ag—N—C—C—C—C—N–]n backbone running along the b axis.  相似文献   

9.
The title compound, {[CoLi2(C11H14N2O8)(H2O)3]·2H2O}n, constitutes the first example of a salt of the [MII(1,3‐pdta)]2− complex (1,3‐pdta is propane‐1,3‐diyldinitrilotetraacetate) with a monopositive cation as counter‐ion. Insertion of the Li+ cation could only be achieved through application of the ion‐exchange column technique which, however, appeared unsuccessful with other alkali metals and the ammonium cation. The structure contains two tetrahedrally coordinated Li+ cations, an octahedral [Co(1,3‐pdta)]2− anion and five water molecules, two of which are uncoordinated, and is built of two‐dimensional layers extending parallel to the (010) lattice plane, the constituents of which are connected by the coordinate bonds. O—Hwater...O hydrogen bonds operate both within and between these layers. The crystal investigated belongs to the enantiomeric space group P21 with only one (Λ) of two possible optical isomers of the [Co(1,3‐pdta)]2− complex. A possible cause of enantiomer separation during crystallization might be the rigidification and polarization of the [M(1,3‐pdta)]2− core, resulting from direct coordination of Li+ cations to three out of four carboxylate groups constituting the 1,3‐pdta ligand. The structure of (I) differs considerably from those of the other [MII(1,3‐pdta)]2− complexes, in which the charge compensation is realized by means of divalent hexaaqua complex cations. This finding demonstrates a significant structure‐determining role of the counter‐ions.  相似文献   

10.
The complexes [Ag(η2‐N∧S)2](PF6), N∧S = 1‐methyl‐2‐(methylthiomethyl)‐1H‐benzimidazole, mmb (complex 1 ) or 1‐methyl‐2‐(tert‐butylthiomethyl)‐1H‐benzimidazole, mtb (complex 2 ), and [Ag(μ,η2‐mmb)(μ,η2‐O2PF2)] (complex 3 ) were synthesized and characterized by X‐ray crystallography. Long Ag–S (ca. 2.70 Å) and shorter Ag–N bonds (ca. 2.23 Å) are part of characteristically distorted tetrahedral coordination arrangements at the silver(I) ions in 1 and 2 . Unexpectedly, the comparison with the copper analogue [Cu(η2‐mmb)2](PF6) reveals a more tetrahedral and less linear coordination arrangement for the corresponding silver species. Compound 3 as obtained by hydrolysis of the PF6 ion or by the use of AgPO2F2 exhibits bridging mmb and η2‐difluorophosphate ligands in a chain‐type structure.  相似文献   

11.
电喷雾质谱被应用于分辨2-氨基-1,3-恶嗪及六氢化-4-苯基-吡喃[2,3-d]嘧啶-2-酮的杂环结构。两类化合物均为三组份反应的产物,且其杂环的结构很难用NMR判断。实验首次系统研究了两类化合物的质谱学行为(包括氘代实验和高分辨质谱研究),发现前者在CID实验中丢失CH2N2和HCNO,而后者为直接丢失尿素。这些特征丢失为该类衍生物的结构判断,尤其是高通量的合成产物分析提供了重要的依据。  相似文献   

12.
Chemical ionization mass spectra of several ethers obtained with He/(CH3)4Si mixtures as the reagent gases contain abundant [M + 73]+ adduct ions which identify the relative molecular mass. For the di-n-alkyl ethers, these [M + 73]+ ions are formed by sample ion/sample molecule reactions of the fragment ions, [M + 73 ? CnH2n]+ and [M + 73 ? 2CnH2n]+. Small amounts of [M + H]+ ions are also formed, predominantly by proton transfer reactions of the [M + 73 ? 2CnH2n]+ or [(CH3)3SiOH2]+ ions with the ethers. The di-s-alkyl ethers give no [M + 73] + ions, but do give [M + H]+ ions, which allow the determination of the relative molecular mass. These [M + H]+ ions result primarily from proton transfer reactions from the dominant fragment ion, [(CH3)3SiOH2]+ with the ether. Methyl phenyl ether gives only [M + 73]+ adduct ions, by a bimolecular addition of the trimethylsilyl ion to the ether, not by the two-step process found for the di-n-alkyl ethers. Ethyl phenyl ether gives [M + 73]+ by both the two-step process and the bimolecular addition. Although the mass spectra of the alkyl etherr are temperature-dependent, the sensitivities of the di-alkyl ethers and ethyl phenyl ether are independent of temperature. However, the sensitivity for methyl phenyl ether decreases significantly with increasing temperature.  相似文献   

13.
Experimental and theoretical studies on the oxidation of saturated hydrocarbons (n‐hexane, cyclohexane, n‐heptane, n‐octane and isooctane) and ethanol in 28 Torr O2 or air plasma generated by a hollow cathode discharge ion source were made. Ions corresponding to [M + 15]+ and [M + 13]+ in addition to [M ? H]+ and [M ? 3H]+ were detected as major ions where M is the sample molecule. The ions [M + 15]+ and [M + 13]+ were assigned as oxidation products, [M ? H + O]+ and [M ? 3H + O]+, respectively. By the tandem mass spectrometry analysis of [M ? H + O]+ and [M ? 3H + O]+, H2O, olefins (and/or cycloalkanes) and oxygen‐containing compounds were eliminated from these ions. Ozone as one of the terminal products in the O2 plasma was postulated as the oxidizing reagent. As an example, the reactions of C6H14+? with O2 and of C6H13+ (CH3CH2CH+CH2CH2CH3) with ozone were examined by density functional theory calculations. Nucleophilic interaction of ozone with C6H13+ leads to the formation of protonated ketone, CH3CH2C(=OH+)CH2CH2CH3. In air plasma, [M ? H + O]+ became predominant over carbocations, [M ? H]+ and [M ? 3H]+. For ethanol, the protonated acetic acid CH3C(OH)2+ (m/z 61.03) was formed as the oxidation product. The peaks at m/z 75.04 and 75.08 are assigned as protonated ethyl formate and protonated diethyl ether, respectively, and that at m/z 89.06 as protonated ethyl acetate. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

14.
In the organometallic silver(I) supramolecular complex poly[[silver(I)‐μ3‐3‐[4‐(2‐thienyl)‐2H‐cyclopenta[d]pyridazin‐1‐yl]benzonitrile] perchlorate methanol solvate], {[Ag(C18H11N3S)](ClO4)·CH3OH}n, there is only one type of AgI center, which lies in an {AgN2Sπ} coordination environment. Two unsymmetric multidentate 3‐[4‐(2‐thienyl)‐2H‐cyclopenta[d]pyridazin‐1‐yl]benzonitrile (L) ligands link two AgI atoms through π–AgI interactions into an organometallic box‐like unit, from which two 3‐cyanobenzoyl arms stretch out in opposite directions and bind two AgI atoms from neighboring box‐like building blocks. This results in a novel two‐dimensional network extending in the crystallographic bc plane. These two‐dimensional sheets stack together along the crystallographic a axis to generate parallelogram‐like channels. The methanol solvent molecules and the perchlorate counter‐ions are located in the channels, where they are fixed by intermolecular hydrogen‐bonding interactions. This architecture may provide opportunities for host–guest chemistry, such as guest molecule loss and absorption or ion exchange. The new fulvene‐type multidentate ligand L is a good candidate for the preparation of Cp–AgI‐containing (Cp is cyclopentadienyl) organometallic coordination polymers or supramolecular complexes.  相似文献   

15.
The title complex, bis­[3,3′‐(pyridine‐4‐imino‐κN1)­di­propane­nitrile]silver(I) perchlorate, [Ag(CEAP)2]ClO4 {CEAP is 4‐[N,N‐bis(2‐cyano­ethyl)­amino]­pyridine, C11H12N4}, has been prepared and characterized. The unit cell consists of two crystallographically non‐equivalent mol­ecules. Cation cavities are constructed by [Ag(CEAP)2]+ cations through hydrogen bonds, and the ClO4 anions are incorporated into the cavities in μ4‐ and μ2‐ClO4 bridging modes through C—H⃛O hydrogen bonds.  相似文献   

16.
A good understanding of gas‐phase fragmentation chemistry of peptides is important for accurate protein identification. Additional product ions obtained by sodiated peptides can provide useful sequence information supplementary to protonated peptides and improve protein identification. In this work, we first demonstrate that the sodiated a3 ions are abundant in the tandem mass spectra of sodium‐cationized peptides although observations of a3 ions have rarely been reported in protonated peptides. Quantum chemical calculations combined with tandem mass spectrometry are used to investigate this phenomenon by using a model tetrapeptide GGAG. Our results reveal that the most stable [a3 + Na ? H]+ ion is present as a bidentate linear structure in which the sodium cation coordinates to the two backbone carbonyl oxygen atoms. Due to structural inflexibility, further fragmentation of the [a3 + Na ? H]+ ion needs to overcome several relatively high energetic barriers to form [b2 + Na ? H]+ ion with a diketopiperazine structure. As a result, low abundance of [b2 + Na ? H]+ ion is detected at relatively high collision energy. In addition, our computational data also indicate that the common oxazolone pathway to generate [b2 + Na ? H]+ from the [a3 + Na ? H]+ ion is unlikely. The present work provides a mechanistic insight into how a sodium ion affects the fragmentation behaviors of peptides. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

17.
The title compound, [Ag(C6H4N3O3)]n or [Ag(pyzca)]n (where pyzca is 3‐aminocarbonylpyrazine‐2‐carboxylate), (I), was obtained by silver‐catalysed partial hydrolysis of pyrazine‐2,3‐dicarbonitrile in aqueous solution. The compound has a distorted trigonal–planar coordination geometry around the AgI ion, with each ligand bridging three AgI ions to form a one‐dimensional strand of molecules parallel to the b axis. An extensive hydrogen‐bond pattern connects these strands to form a three‐dimensional network of mog topology.  相似文献   

18.
Spin‐labeled nitroxide derivatives of podophyllotoxin had better antitumor activity and less toxicity than that of the parent compounds. However, the 2‐H configurations of these spin‐labeled derivatives cannot be determined by nuclear magnetic resonance (NMR) methods. In the present paper, a high‐performance liquid chromatography‐diode array detection (HPLC‐DAD) and a high‐performance liquid chromatography‐electrospray ionization tandem mass spectrometry (HPLC‐ESI/MS/MS) method were developed and validated for the separation, identification of four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 position. In the HPLC‐ESI/MS spectra, each pair of diastereoisomers of the spin‐labeled derivatives in the mixture was directly confirmed and identified by [M+H]+ ions and ion ratios of relative abundance of [M‐ROH+H]+ (ion 397) to [M+H]+. When the [M‐ROH+H]+ ions (at m/z 397) were selected as the precursor ions to perform the MS/MS product ion scan. The product ions at m/z 313, 282, and 229 were the common diagnostic ions. The ion ratios of relative abundance of the [M‐ROH+H]+ (ion 397) to [M+H]+, [A+H]+ (ion 313) to [M‐ROH+H]+, [A+H‐OCH3]+ (ion 282) to [M‐ROH+H]+ and [M‐ROH‐ArH+H]+ (ion 229) to [M‐ROH+H]+ of each pair of diastereoisomers of the derivatives specifically exhibited a stereochemical effect. Thus, by using identical chromatographic conditions, the combination of DAD and MS/MS data permitted the separation and identification of the four pairs of diastereoisomers of spin‐labeled derivatives of podophyllotoxin at C‐2 in the mixture.  相似文献   

19.
A facile method based on electrospray mass spectrometry was established and validated for the differentiation of enantiomeric tadalafil isomers without using chiral chromatographic separation. The enantiomers were coupled with a chiral selector to form diastereomeric complex ions. Nickel–tadalafil complexes, [NiII(tadalafil)(l ‐Trp)‐H]+, produced a characteristic fragment ion at m /z 524 by loss of 1‐methyl‐1,6‐dihydropyrazine‐2,5‐dione via collision‐induced dissociation. The relative abundance of this fragment ion to the precursor contributed to differentiate tadalafil enantiomers, and energy‐resolved product‐ion spectra were applied to determine the molar composition of tadalafil in the mixture (R ,R and S ,S ) as well. In addition, the other two forms of stereomeric isomers of tadalafil (R ,S and S ,R ) could be also distinguished and analyzed by this method. The method was validated in different types of mass spectrometers (AB quadrupole time‐of‐flight and Bruker ion trap) and also verified by a chiral high‐performance liquid chromatography coupled with quadrupole time‐of‐flight. The chiral determination of tadalafil using MS method proved to be rapid (1‐min run time for each sample) and to have the same accuracy and precision comparable to chiral liquid chromatography mass spectrometry methods. This method provides an alternative to commonly used chromatographic technique for chiral determination and is particularly useful in rapid screening in enantioselective synthesis and enantiomeric impurity detection in pharmaceutical industry. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

20.
In catena‐poly­[[(di‐2‐pyridyl­amine‐κ2N,N′)silver(I)]‐μ‐nico­tinato‐κ2N:O], [Ag(C6H4NO2)(C10H9N3)]n, the AgI atom is tetracoordinated by two N atoms from the di‐2‐pyridyl­amine (BPA) ligand [Ag—N = 2.3785 (18) and 2.3298 (18) Å] and by one N atom and one carboxyl­ate O atom from nicotinate ligands [Ag—N = 2.2827 (15) Å and Ag—O = 2.3636 (14) Å]. Bridging by nicotinate N and O atoms generates a polymeric chain structure, which extends along [100]. The carboxyl O atom not bonded to the Ag atom takes part in an intrachain C—H⋯O hydrogen bond, further stabilizing the chain. Pairs of chains are linked by N—H⋯O hydrogen bonds to generate ribbons. There are no π–π interactions in this complex. In catena‐poly­[[(di‐2‐pyridyl­amine‐κ2N,N′)silver(I)]‐μ‐2,6‐di­hydroxy­benzoato‐κ2O1:O2], [Ag(C7H5O4)(C10H9N3)]n, the AgI atom has a distorted tetrahedral coordination, with three strong bonds to two pyridine N atoms from the BPA ligand [Ag—N = 2.286 (5) and 2.320 (5) Å] and to one carboxyl­ate O atom from the 2,6‐di­hydroxy­benzoate ligand [Ag—O = 2.222 (4) Å]; the fourth, weaker, Ag‐atom coordination is to one of the phenol O atoms [Ag⋯O = 2.703 (4) Å] of an adjacent moiety, and this interaction generates a polymeric chain along [100]. Pairs of chains are linked about inversion centers by N—H⋯O hydrogen bonds to form ribbons, within which there are π–π interactions. The ribbons are linked about inversion centers by pairs of C—H⋯O hydrogen bonds and additional π–π interactions between inversion‐related pairs of 2,6‐di­hydroxy­benzoate ligands to generate a three‐dimensional network.  相似文献   

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