The signal-to-noise ratio as the measure for the quantification of lysophospholipids by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

The subject of this report is the determination of lysophospholipids; lysophosphatidylcholine, lysophosphatidylethanolamine, lysophosphatidylserine and lysophosphatidic acid, by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS). The mean signal-to-noise ratio (S/N) was used for the first time as a measure of lysophospholipid concentration. Two different sample preparation procedures were applied, the 'standard' procedure and the 'premix' in order to check to what extent these methods influence the results of the lysophospholipid quantification. Results can be summarised as follows: (a) All classes of lysophospholipids can be easily and sensitively analysed by MALDI-TOF MS. The smallest detectable amount of lysophospholipids was 0.09 pmol on the sample plate. That is about two orders of magnitude lower than the amount detectable by standard chromatographic methods. (b) The mean S/N of all peaks detected in the positive ion mass spectra can be used as a measure of the lysophospholipid concentration. Whereas the S/N for neutral lysophospholipids correlated with the applied concentrations only when the samples were analysed as 'premix', the sample preparation and application procedure did not influence the quantification of acidic lysophospholipids. The standard deviations were not higher than 10% of the mean value. (c) All spectra were additionally analysed in the presence of CsCl. The addition of caesium ions makes the peak identification unambiguous in phospholipid mixtures, but the Cs adducts of lysophospholipids do not properly reflect their concentration and, therefore, they were not useful for quantification. (d) The applicability of the method was demonstrated on the organic extract of human neutrophils.     

Nitropyrazoles

The double Vilsmeier formylation of theC-methyl group in pyrazole derivatives has been shown to occur when a nitro-group is in the adjacent position of the ring. A method for the synthesis ofC-(diformylmethyl)nitropyrazoles based on this reaction has been developed.For the previous communication, see Ref. 1; for Part 2, see Ref.2 Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1273–1276, July, 1993.     

Electronic Structure and Photophysical Properties of Isoindole and its Benzo[f]- and Dibenzo[e,g]-Derivatives

The synthesis of N-methyl-benz[f]isoindole ( 2 ) and N-methyl-dibenz[e,g]isoindole ( 3 ) is reported. The NMR. spectra of N-methyl-isoindole ( 1 ) and of 2 have been analysed and the implications concerning the alternation of bond lengths are discussed. The photophysical properties of 1 to 3 have been investigated by the following methods: HeI photoelectron (PE.) spectroscopy, UV./VIS. absorption (polarization measurements by the stretched-foil technique) and emission spectroscopy (fluorescence spectra, lifetimes and quantum yields, phosphorescence spectra), and flash spectroscopy (triplet-triplet absorption spectra). The discussion of the results is based on HMO. and PPP SCF CI. calculations and points to the relationship between the heterocycles 1 to 3 and the corresponding benzenoid hydrocarbons obtained by replacement of the ? NMe? subunit by ? CH?CH? . Some comments concerning the ground state properties of isoindole and related compounds are derived from the analysis of their electronic structure.     

Para-ordered polybenzimidazole

A series of novel AB monomers such as 2-[p-carboxyphenyl]-5,6-diaminobenzimidazole hydrochloride have been synthesized. In addition, a new aromatic monomer, 1,3-diamino-4,6-bis(p-toluenesulfonamido)benzene has been prepared in high purity and substituted for 1,2,4,5-tetraaminobenzene in a polymerization with terephthalic acid. Homopolymerization of the AB monomers, and polycondensation of monomer with terephthalic acid in polyphosphoric acid, produced the rod-like para-oriented polymer, poly[1,7-dihydrobenzo(1,2-d: 4,5-d)diimidazole-2,6-diyl-1,4-phenylene]. The yellow polymer was completely soluble in methanesulfonic acid (MSA) and PPA, exhibiting intrinsic viscosities as high as 5 dl/g in MSA, and a blue opalescence in solution. Polymerization at temperatures above 225°C caused crystallization and subsequent precipitation to occur. Polymer thus obtained was completely insoluble in MSA and possessed a high degree of crystallinity as demonstrated by x-ray analysis.     

Electronic Structure and Photophysical Properties of Planar Conjugated Hydrocarbons with 4n-Membered Rings. I. Photoelectron Spectra of 1,5,9-Tridehydro[12]-annulene and Related Compounds

The HeI photoelectron spectra of the title compound 1 (1,5,9-cyclododecatriene-3,7,11-triyne), 1,5-didehydro[12]annulene (1,3,5,9-cyclododecatetraene-7, 11-diyne ( 2 )), sym-tri-benzotridehydro[12]annulene (tribenzo[a,e,i]-5,6,11,12,17,18-hexadehydrocyclododecene ( 3 )), and sym-dibenzodidehydro[8]annulene (dibenzo[a,e]-5,6,11,12-tetradehydrocyclooctene ( 4 )) have been recorded and analysed on the basis of various semi-empirical model calculations. Despite the distinct bond length alternation in the parent compounds and, apparently, in the radical cations, the first ionization occurs at low energies in these compounds (7.6 ± 0.2 eV). The spectra yield little information with regard to the transannular interactions of the triple bonds.     

Synthesis and structure of Ca(18)Li(5)In(25.07): a novel intergrowth of Li-centered in(12) icosahedral clusters and electron-precise Zintl layers

A new ternary polar intermetallic, Ca(18)Li(5)In(25.07), was obtained from high-temperature reactions of the elements in welded Nb tubes. Its crystal structure, established by single-crystal X-ray diffraction, was found to crystallize in the orthorhombic space group Cmmm (No. 65). Unit cell parameters are a = 9.9151(6) A, b = 26.432(2) A, and c = 10.2116(6) A; Z = 2. The structure of Ca(18)Li(5)In(25.07) features two distinct types of indium anionic layers. An "electron-deficient" layer is made up of Li-centered In(12) icosahedra that are interconnected by bridging planar In(4) units and In atoms. A second In(3)(5-) layer is an electron-precise Zintl layer formed by fused four-, five-, and six-membered rings of three- and four-bonded indium atoms. The two distinct layers are alternately stacked and linked into a complex three-dimensional network. Vacancies are observed to occur only at the In(12) icosahedral and the bridging indium units within the "electron-deficient" layers. Magnetic property measurements indicate that Ca(18)Li(5)In(25.07) exhibits temperature-independent paramagnetism consistent with metallic behavior. Band structure calculations were performed to elucidate the role of defects and vacancies in the electronic structure of the electron-deficient "metallic" Zintl phase.     

Mass spectral fragmentation patterns of heterocycles. VI. Carbazole and 1,8-dideuteriocarbazole

The mass spectral fragmentation of carbazole was reinvestigated using metastable ion studies, exact mass measurements and 1,8-dideuteriocarbazole. 1,8-Dideuteriocarbazole was prepared by successive metalations and deuterations of carbazole. The ¹H- and ¹³C-nmr spectra of 1,8-dideuteriocarbazole confirmed earlier assignments for carbazole.     

Examination of phase eouilibrium of the Ca(NO3)2-H2O system with quasi-isothermal-quasi-isobaric thermogravimetry and DTA

By means of the quasi-isothermal-quasi-isobaric thermogravimetry (Q-TG) technique ideal experimental conditions can be realized. This provides a possibility to compare the measured data with data from other phase equilibrium (solubility, tension) examinations.On the example of the Ca(NO₃)₂-H₂O system it is demonstrated that the phase diagrams can be used to interpret thermoanalytical (especially Q-TG) curves, or conversely, the results of thermoanalytical (Q-TG, DTA) examinations can serve for the control of equilibrium data of phase diagrams or to supply missing data.

---

Zusammenfassung Mit Hilfe des quasi-isothermischen-quasi-isobaren thermogravimetrischen (Q-TG) Verfahrens können ideale Versuchsbedingungen realisiert werden. Das ermöglicht es, die gemessenen Daten mit von anderen Phasengleichgewicht-Untersuchungen (Lösbarkeit, Tension) stammenden Daten zu vergleichen.Durch das Beispiel des Ca(NO₃)₂-H₂O-Systems wurde es gezeigt, dass die Phasendiagramme zur Erklärung von thermoanalytischen (insbesondere Q-TG) Kurven können angewandt werden, oder umgekehrt, die Ergebnisse der thermoanalytischen (Q-TG, DTA) Untersuchungen als Kontrolle der Gleichgewichtsdaten der Phasendiagramme dienen können, oder die fehlenden Daten liefern können.

---

- (Q-) . ( , ). Ca(NO₃)₂-H₂O , ( Q-) , .

---

---

The authors are indebted to Prof. E. Pungor for valuable discussions, and thank Mrs. M. Kiss and Miss I. Fábián for their technical assistance.     

The Azo(Azoxy) Functionality as a π2 Component in Photo [2+2] cycloadditions ‘syn’- and ‘anti’-3,4-diazatricyclo[4.2.2.22,5]dodeca-3,7-diene,syntheses, photolyses,X-ray-structure analysis,and PE spectra

The propensity of the N?N bond to undergo photo [2 + 2] cycloadditions has been further explored. In the specifically designed 1,5-azo/enes 1–3 , no [2 + 2] cycloaddition has been observed upon either direct or sensitized excitation with light of various wave lengths at temperatures down to 77 K, in line with expectations based on X-ray ( 1 : d = 2.71 Å, ω = 129°) and PE measurements ( 1 : I₁ = 8.0₀, I₂ = 9.0₅ eV; 2 ; I₁ = 8.0₀, I₂ = 9.2₅eV). The steric/stereoelectronic demands for the participation of the N?N bond in pericyclic reactions are clearly more stringent than those for the C?C bond.     

Synthesis and structural characterisation of a novel tris-methylene bridged compound (NO) 4Fe2 Se(μ-CH2)3

The tris-methylene bridged compound (NO)₄Fe₂Se(μ-CH₂)₃ has been isolated. It has been characterised by IR and ¹H, ¹³C, and ⁷⁷Se NMR spectroscopy. Its structure has been determined by single-crystal X-ray diffraction methods. The structure consists of a heavy atom triangle consisting of one Se and two Fe atoms. The Fe-Fe and the two Fe-Se edges are bridged by methylene groups.