Mass spectral characterization of some nucleoside phosphates and phosphoramidates

Seven new synthetic nucleotide analogues have been characterized as their trimethylsilyl derivatives by recording their electron impact mass spectra. These spectra are consistent with their expected structures, most of which possess a cyclic phosphate or phosphoramidate group.     

Mass spectral study of meso-alkyl and meso-cycloalkyl calix(4)pyrroles under electron impact conditions

A series of meso-cycloalkyl calix(4)pyrroles (I) and meso-dialkyl calix(4)pyrroles (II) has been studied under electron ionization (EI) mass spectral conditions. All the calix(4)pyrroles showed prominent molecular ions. The cleavage of the C--C bond linked at position 2 of the pyrrole ring (beta-cleavage) is the foremost and dominant fragmentation process. The beta-cleavage process, either through ring opening or directly, results in the loss of an alkyl radical from the molecular ion. The collision-induced dissociation (CID) spectra of I showed specific sequential expulsion of pyrrole and/or cycloalkyl rings from the molecular ion with or without hydrogen migrations, revealing more information on the structure of individual compounds than was available from the EI spectra. The isomeric cycloalkyl calix(4)pyrroles showed distinguishable CID spectra, indicating structure specificity in initial ring opening whereas, in the case of II, the EI mass spectrum contains all the structure-indicative fragment ions. The CID spectra of II resulted in a dominant [M-R]+ ion, with other characteristic ions being less abundant.     

Mass spectral study on O,O-dialkyl N,N-dialkyl phosphoramidates under electron impact conditions

A series of O,O-dialkyl N,N-dialkyl phosphoramidates (1-25) were analyzed under GC-EIMS conditions. Clear-cut differences are found in the fragmentation of O,O-dialkyl N,N-dimethyl phosphoramidates (Series 1) and O,O-dimethyl N,N-dialkyl phosphoramidates (Series 2). The phosphoramidates comprising of mixed/crossed alkyl groups on nitrogen and oxygen (Series 3) showed mixed fragmentation pattern corresponding to both Series 1 and 2 depending on the nature of alkyl groups. All the possible isomers among the studied compounds showed distinguishable EI mass spectra. Although the major ions in the EI mass spectra for the isomers containing O-n-propyl or O-isopropyl and N,N-diethyl or N-isopropyl N-methyl are similar, the isomers could be distinguished by characteristic ions of low abundance at low mass region. The differences are prominent in the metastable ion spectra of characteristic ions.     

大黄酚和牛血清蛋白相互作用的电化学/光谱性质研究

在pH=4.0的Britton-Robinson(B-R)缓冲体系中,应用循环伏安法、示差脉冲伏安法和紫外光谱法对大黄酚与牛血清白蛋白(BSA)相互作用的电化学/光谱性质进行研究.结果表明,二者结合生成了一种非电活性的超分子化合物.BSA的存在导致大黄酚氧化还原峰电流降低,峰电位基本不变,峰电流的下降值同所加入的BSA浓度在一定范围内呈线性关系.线性范围为5.0×10-6~1.0×10-7mol/L,检出限为3×10-7mol/L.     

Ionization and dissociation of some perfluoroalkylene-linked silanes and cyclic siloxanes under electron-impact

The mass spectra of two silanes and two cyclic siloxanes of the general formulae HSi(CH₃)₂-C₆H₄? (CF₂)_n? C₆H₄(CH₃)₂SiH and (n = 2 and 3) are reported and discussed. Although some major differences are apparent between the spectra of the two silanes, the fragmentation patterns of the cyclic siloxanes are largely identical.     

A spectral study of the interaction between chelerythrine chloride and cytidine

To study the possible anticancer mechanisms of chelerythrine (CHE), and its interactions with cytidine were investigated by UV-vis spectrophotometric and spectrofluorimetric measurements and by thermodynamic calculations. The binding of CHE to cytidine could be characterized by the hypochromic and bathochromic effects in the absorption bands, and the quenching of fluorescence intensity. The spectral data were fit by linear analysis, yielding a binding constant of 2.49×104 L mol-1 at 25℃of CHE and cytidine, and a van't Hoff enthalpy of -20.02 kJ/mol for the exothermic interaction in the standard state. In addition, with     

Ab initio SCF study of the interaction between L-serine phosphate and ammonia

The possible conformational changes of L -serine phosphate due to the interaction with ammonia are investigated by means of ab initio MO-LCAO-SCF calculations, using a supermolecule approach and an STO -3G basis set. The most favorable conformation of a four-hydrated L -serine phosphate anion is found to be changed by the binding of an ammonium ion. Cointeraction of ammonia and NH suggests another conformational change through the displacement of the bridging water molecule of the polyhydrated L -serine phosphate anion.     

Carbon skeletal rearrangements in 2-phenylthiophene and 2,5-diphenylthiophene under conditions of electron-impact

The mass spectra of ¹³C-labelled 2-phenylthiophenes and 2,5-diphenylthiophenes were studied. The label distributions for the [HCS]⁺, [C₂H₂S]^+·, [C₈H₆]^+·, [C₉H₇]⁺ and [C₇H₅]S⁺ ions from 2-phenylthiophene and the [HCS]⁺, [C₉H₇]⁺, [C₇H₅S]^+·, and [C₁₅H₁₁]⁺ ions from 2,5-diphenylthiophene were interpreted in terms of both carbon skeletal rearrangements in the thiophene ring and migration of the phenyl substituent. The degree of carbon scrambling in the thiophene ring appeared to be almost independent of the electron beam energy. The formation of some of the fragment ions studied seems to be so fast that no carbon scrambling could be detected at all; in neither case was complete scrambling of the carbon atoms of the thiophene ring observed.     

The behaviour of arylsulfonylmethyl sulfonates under conditions of electron-impact. The loss of CH2O

The mass spectra of ten arylsulfonylmethyl arenesulfonates and two arylsolfonylmethyl trifluoromethanesulfonates are discussed. A notable fragmentation of these compounds is the loss of CH₂O from the molecular ions. A probable structure for the [M ? CH₂O]^?. ions, as based on the measurement of metastable rations, is given and a fragmentation mechanism leading to this structure is proposed.     

CO2 capture capacity of five- and six-membered cyclic amidines bearing silatranyl group under dry conditions

CO₂ capture and release behaviors of three amidines bearing silatranyl group in DMSO solution were evaluated under dry conditions containing a very small amount of water. A six-membered cyclic amidine with silatranyl group captured CO₂ at 25 °C under atmospheric pressure quantitatively, and the trapped CO₂ was released at 60 °C under Ar atmosphere. A five-membered cyclic amidine with silatranyl group also captured CO₂, but less efficiently, under the same conditions as above. In contrast, an acyclic amidine with silatranyl group did not capture CO₂ at all, as expected from the poor CO₂-capturing ability of the acyclic amidine moiety.     

A study of the fragmentation of caprolactam and its methyl derivatives under electron-impact

A study of the low and high-resolution mass spectra of caprolactam (I), 1-methylcaprolactam (II), 3-methylcaprolactam (III), 4-methylcaprolactam (IV), 5-methylcaprolactam (V), 6-methylcaprolactam (VI), 7-methylcaprolactam (VII) and deuterium labelled compounds has facilitated the proposal of some principal fragmentation mechanisms of ionized molecules of these compounds. The base peaks in the spectra of all compounds studied (except 3-methylcaprolactam) are the ions m/e 30 and m/e 44 respectively formed through the cleavage of the C6–C7 bond and the C2–N bond with simultaneous transfer of a hydrogen atom. It has been proved that the fragmentation of molecular ions leading to ions with the structure of cyclopentanone 2-methylcyclopentanone and 3-methylcyclopentanone respectively (according to the position of methyl group) is the general feature of the fragmentation of caprolactam and its methyl derivatives.     

Mass spectra of substituted thioglycollic acids and esters. Skeletal rearrangement upon electron-impact

The mass spectra of thioglycollic acids and esters are reported and discussed. The spectra of compounds of the type X·CH(Y)·S·CH₂·COOR(X > Y) contain skeletal rearrangement fragments with the composition R·Y·C₂H₃SO⁺. Ions produced by simple cleavage processes may be usefully correlated with structure.     

Ionization and dissociation of cyclic ethers and thioethers by electron-impact. A comparison between 1,4 dioxane, 1,4 dithiane and 1,4 oxathiane

The various modes of fragmentation of 1,4 dithiane and 1,4 oxathiane under electron-impact have been discussed using variation of their mass spectra with electrons energy, high resolution and AP of the main ions. It is shown that they are qualitatively very similar, but differ considerably from those of 1,4 dioxane.     

Potentiometric, luminescence and NMR study of the interaction of Eu with glyceryl phosphates

Complexation of europium(III) with glyceryl-1- and -2-phosphates has been studied by metal ion luminescence, ¹H and ¹³C NMR spectroscopy and potentiometry. From the luminescence and NMR studies, the formation of a 1:1 inner-sphere complex, in which the glyceryl phosphate is directly bound to the metal, is confirmed. Similar apparent binding constants at pH 2 were obtained by the three methods. Values obtained by NMR at pH 2 are 53 M⁻¹ and 12 M⁻¹ for glyceryl-1- and -2-phosphate, respectively. By comparison with literature data on related systems it is suggested that the ligands bind through the phosphate group. To obtain structural information from the NMR data, complexation has also been studied with the lanthanide ions Dy(III), Er(III) and Gd(III) using both chemical shift and relaxation data. From this, metal-proton distance ratios have been calculated. Comparison of ¹H and ¹³C NMR spectral data in the presence of paramagnetic lanthanides suggests conformational equilibria in the solutions. From the potentiometric studies, global formation constants have been determined, and speciation diagrams obtained over the pH range 1.5pH7.0 for ligand/metal ratios of 1 and 30. Implications of these results on lanthanide induced fusion of phospholipid membranes are discussed.     

Ionization and dissociation of cyclic ethers and thioethers by electron-impact. A comparison between 1,3-dioxolane, 1,3-dithiolane and 1,3-oxathiolane

The various modes of fragmentation of 1,3-dithiolane and 1,3-oxathiolane under electron-impact have been discussed on the basis of the variation of their mass spectra with electron energy, the high resolution analysis and the AP's of the main ions. They are shown to be similar in both compounds, but considerably different from those of 1,3 dioxolane. From the AP of the [C₂H₅S]⁺ ion in 1,3-dithiolane, a heat of formation of 63 kcal/mol for the free radical CHS is obtained.     

Complexes of bidentate group VB chelates : XIX. Mass spectral studies on some methyl-substituted bidentate group VB donor ligands

The fragmentation patterns of seven bidentate and two tridentate Group VB donor ligands are reported. For these methyl-substituted ligands the initial fragmentation is essentially loss of methyl radicals. Phenyl, but not methyl, migration occurs for the bis(phenylmethylarsino)alkanes, but methyl migration is evident in the all aliphatic bidentate chelates. The tridentate ligands PhE(CH₂CH₂CH₂AsMe₂)2 (E = P, As) show similar fragmentation routes, but are more complex. The long chain diarsine, Me₂As(CH₂)₁₂AsMe₂, exhibits a tendency to cyclise and lose C₂H₄ fragments progressively.     

5种荧光染料探针与牛血清白蛋白相互作用研究

采用荧光光谱法研究了水溶液中四溴荧光素、四氯四溴荧光素、二碘荧光素、乙基罗丹明B、健那绿B等5种荧光染料探针与牛血清白蛋白(BSA)的相互作用.实验表明,这5种染料探针同牛血清白蛋白结合时,疏水作用力起决定性作用,静电力起次要作用,相比之下牛血清白蛋白(BSA)结合阴离子的能力最强,其次为中性分子,最后为阳离子.通过疏水作用力,5种染料均是以非极性苯基进入BSA疏水性腔体中同色氨酸残基发生作用,弱氢键的形成加强了这种作用力,且使得光谱间能量转移效率明显提高.5种染料探针的极性部位由于极性和空间效应的原因难以进入腔体内部,致使反应均按接近1∶1的方式进行.     

Radical-mediated reduction of the dithiocarbamate group under tin-free conditions

Reductive desulfurisation of dithiocarbamates is conveniently achieved using H(3)PO(2)-Et(3)N-ACCN in refluxing dioxane. Fused and spirocyclic β-lactams, prepared through 4-exo trig carbamoyl radical cyclisation-dithiocarbamate group transfer reactions, are reduced without fragmentation of the strained 4-membered ring. Diethyl tetraacetyl-d-glucopyranosyl dithiocarbamate is selectively reduced with or without acyloxy group migration depending on reaction conditions and choice of reductant. Deuterium incorporation from D(3)PO(2)-Et(3)N is observed for a system involving a nucleophilic radical intermediate, but not in the case of the electrophilic radical obtained through acyloxy group migration on a glucose derivative.