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Mass Peaks (mass + peak)
Selected AbstractsInfluence of [2H]-labelled acetic acid as solvent in the synthesis of [2H]-labelled perhexilineJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 1 2010Søren Christian Schou Abstract Preparation of deuterium-labelled perhexiline from an unsaturated analogue was performed via reduction with deuterium gas and PtO2 in acetic acid. Low incorporation was observed when using acetic acid as solvent (most abundant mass peak was M), but when changing the solvent to deuterium-labelled acetic acid, e.g. acetic acid-OD or acetic acid- d4, a higher incorporation was observed (most abundant mass peak was M). Using hydrogen gas instead of deuterium gas with deuterium-labelled acetic acid, high levels of deuterium incorporation were observed (most abundant mass peak was M). An attempt to reduce a precursor with a fully deuterated pyridine to obtain perhexiline with a higher content of deuterium failed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Syntheses of cyclic polycarbonates by the direct phosgenation of bisphenol M,JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2005Hans R. Kricheldorf Abstract Bisphenol M was subjected to interfacial polycondensations in an NaOH/CH2Cl2 system with triethylamine as a catalyst. Regardless of the catalyst concentration, similar molecular weights were obtained, and matrix-assisted laser desorption/ionization time-of-flight mass spectra exclusively displayed mass peaks of cycles (detectable up to 15,000 Da). With triethyl benzyl ammonium chloride as a catalyst, linear chains became the main products, but the contents of the cycles and the molecular weights strongly increased with higher catalyst/bisphenol ratios. When the pseudo-high-dilution method was applied, both diphosgene and triphosgene yielded cyclic polycarbonates of low or moderate molecular weights. Size exclusion chromatography measurements, evaluated with the triple-detection method, yielded bimodal mass distribution curves with polydispersities of 5,12. Furthermore, a Mark,Houwink equation was elaborated, and it indicated that the hydrodynamic volume of poly(bisphenol M carbonate) was quite similar to that of poly(bisphenol A carbonate)s with similar concentrations of cyclic species. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1248,1254, 2005 [source] New Polymer Syntheses, 112MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 4 2003Hans R. Kricheldorf Abstract Bis(4-chlorophenyl)sebacate (BCPS) was polycondensed with 1,12-diamino-4,9-dioxadodecane or with its bistrimethylsilyl derivative in three different solvents with variation of time and temperature. The highest molecular weights were obtained in dimethylsulfoxide at 60,°C. The highest fraction of cyclic polyamides was detected by MALDI-TOF mass spectrometry in the samples with the highest molecular weights. Numerous polycondensations of BCPS and 1,13-diamino-4,7,10-trioxatridecane were performed with variation of solvent, time and temperature. Again the best results were obtained in dimethylsulfoxide at 60,°C. The fraction of cyclic polyamides increased with higher average molecular weights of the samples. The MALDI-TOF mass spectrum of the sample with the highest molar mass (Mn ca. 30,000 Da) exclusively displayed mass peaks of cycles (detected up to 13,000 Da). No side reactions were observed. MALDI-TOF mass spectrum (segment) of polyamide 1 prepared by polycondensation of DDD with BCPS in DMSO at 60,°C/48 h (no. 3, Table 1). [source] Methylene as a possible universal footprinting reagent that will include hydrophobic surface areas: Overview and feasibility: Properties of diazirine as a precursorPROTEIN SCIENCE, Issue 12 2000Frederic M. Richards Abstract Methylene is one of, if not the, most reactive organic chemical known. It has a very low specificity, which makes it essentially useless for synthesis, but suggests a possible role in protein footprinting with special importance in labeling solvent accessible nonpolar areas, identifying ligand binding sites, and outlining interaction areas on protomers that form homo or hetero oligomers in cellular assemblies. The singlet species is easily and conveniently formed by photolysis of diazirine. The reactions of interest are insertion into C-H bonds and addition to multiple bonds, both forming strong covalent bonds and stable compounds. Reaction with proteins and peptides is reported even in aqueous solutions where the vast majority of the reagent is used up in forming methanol. Species containing up to 5 to 10 extra : CH2 groups are easily detected by electrospray mass spectroscopy. In a mixture of a 14 Kd protein and a noninteracting 1.7 Kd peptide, the distribution of mass peaks in the electrospray spectra was close to that expected from random modification of the estimated solvent accessible area for the two molecules. For analysis at the single residue level, quantitation at labeling levels of one 13CH2 group per 10 to 20 kDa of protein appears to be possible with isotope ratio mass spectroscopy. In the absence of reactive solvents, photolysis of diazirine produces oily polymeric species that contain one or two nitrogen atoms, but not more, and are water soluble. [source] Using a triple-quadrupole mass spectrometer in accurate mass mode and an ion correlation program to identify compounds,RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2005Andrew H. Grange Atomic masses and isotopic abundances are independent and complementary properties for discriminating among ion compositions. The number of possible ion compositions is greatly reduced by accurately measuring exact masses of monoisotopic ions and the relative isotopic abundances (RIAs) of the ions greater in mass by +1,Da and +2,Da. When both properties are measured, a mass error limit of 6,10,mDa (<,31,ppm at 320,Da) and an RIA error limit of 10% are generally adequate for determining unique ion compositions for precursor and fragment ions produced from small molecules (less than 320,Da in this study). ,Inherent interferences', i.e., mass peaks seen in the product ion mass spectrum of the monoisotopic [M+H]+ ion of an analyte that are ,2, ,1, +1, or +2,Da different in mass from monoisotopic fragment ion masses, distort measured RIAs. This problem is overcome using an ion correlation program to compare the numbers of atoms of each element in a precursor ion to the sum of those in each fragment ion and its corresponding neutral loss. Synergy occurs when accurate measurement of only one pair of +1,Da and +2,Da RIAs for the precursor ion or a fragment ion rejects all but one possible ion composition for that ion, thereby indirectly rejecting all but one fragment ion-neutral loss combination for other exact masses. A triple-quadrupole mass spectrometer with accurate mass capability, using atmospheric pressure chemical ionization (APCI), was used to measure masses and RIAs of precursor and fragment ions. Nine chemicals were investigated as simulated unknowns. Mass accuracy and RIA accuracy were sufficient to determine unique compositions for all precursor ions and all but two of 40 fragment ions, and the two corresponding neutral losses. Interrogation of the chemical literature provided between one and three possible compounds for each of the nine analytes. This approach for identifying compounds compensates for the lack of commercial ESI and APCI mass spectral libraries, which precludes making tentative identifications based on spectral matches. Published in 2005 by John Wiley & Sons, Ltd. [source] Sex steroids, ANGELS and osteoporosisBIOESSAYS, Issue 3 2003Jonathan G. Moggs Osteoporosis is characterized by reduced bone density and strength. Bone mass peaks between age 30 and 40 and then declines. This can be accelerated by factors including menopause and insufficient dietary calcium. Hormone replacement therapy (HRT) is currently the standard treatment for osteoporosis. However, growing concern over potential side effects of HRT has driven a search for alternative therapies. A recent report1 reveals a potential alternative to HRT: a gender-neutral synthetic steroid that increases bone mass and strength without affecting reproductive organs. This compound acts via a novel extranuclear sex steroid receptor signaling mechanism that has important implications for nuclear receptor biology and human health. BioEssays 25:195,199, 2003. © 2003 Wiley Periodicals, Inc. [source] | |||||||||||||