Monoisotopic Mass?

The current IUPAC-recommended definition of the term "monoisotopic mass" of a chemical species is based on the most abundant isotopes of the constituent elements. It has even been proposed to constrain the definition to be based only on the atomic masses of the most abundant stable isotopes. Such an approach is flawed because in this way several elements and their compounds, in addition to isotopically enriched species, would not merit to be assigned a monoisotopic mass.

A Rapid Method for the Detection of Sarcosine Using SPIONs/Au/CS/SOX/NPs for Prostate Cancer Sensing.

Sarcosine is an amino acid that is formed by methylation of glycine and is present in trace amounts in the body. Increased sarcosine concentrations in blood plasma and urine are manifested in sarcosinemia and in some other diseases such as prostate cancer. For this purpose, sarcosine detection using the nanomedicine approach was proposed.

An HPLC-CAD/fluorescence lipidomics platform using fluorescent fatty acids as metabolic tracers.

Fluorescent lipids are important tools for live imaging in cell culture and animal models, yet their metabolism has not been well-characterized. Here we describe a novel combined HPLC and LC-MS/MS method developed to characterize both total lipid profiles and the products of fluorescently labeled lipids. Using this approach, we found that lipids labeled with the fluorescent tags, 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza--indacene (BODIPY FL), 4,4-difluoro-5-(2-thienyl)-4-bora-3a,4a-diaza--indacene [BODIPY(558/568)], and dipyrrometheneboron difluoride undecanoic acid (TopFluor) are all metabolized into varying arrays of polar and nonpolar fluorescent lipid products when they are fed to larval zebrafish.

Identification of trace levels of selenomethionine and related organic selenium species in high-ionic-strength waters.

A new anion-exchange chromatographic separation method was used for the simultaneous speciation analysis of selenoamino acids and the more ubiquitous inorganic selenium oxyanions, selenite and selenate. For quantification, this separation was coupled to inductively coupled plasma-mass spectrometry to achieve an instrumental detection limit of 5 ng Se L(-1) for all species. This chromatographic method was also coupled to electrospray tandem mass spectrometry to observe the negative ion mode fragmentation of selenomethionine and one of its oxidation products.

Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases.

All terrestrial organisms depend on nucleic acids (RNA and DNA), which use pyrimidine and purine nucleobases to encode genetic information. Carbon-rich meteorites may have been important sources of organic compounds required for the emergence of life on the early Earth; however, the origin and formation of nucleobases in meteorites has been debated for over 50 y. So far, the few nucleobases reported in meteorites are biologically common and lacked the structural diversity typical of other indigenous meteoritic organics.

Collision-induced dissociation mass spectra of positive ions derived from tetrahydropyranyl (THP) ethers of primary alcohols.

Peaks for [M + H](+) are not observed when electrospray ionization mass spectra of tetrahydropyranyl (THP) ethers are recorded under acidic conditions. However, gaseous [M + H](+) ions can be generated from ammonium adducts of THP ethers of primary alcohols by in-source fragmentation. The product ion spectra of these proton adducts show two significant peaks at m/z 85 and 103.

Collision-induced dissociation mass spectra of glucosinolate anions.

Collision-induced dissociation (CID) mass spectra of differently substituted glucosinolates were investigated under negative-ion mode. Data obtained from several glucosinolates and their isotopologues ((34)S and (2)H) revealed that many peaks observed are independent of the nature of the substituent group. For example, all investigated glucosinolate anions fragment to produce a product ion observed at m/z 195 for the thioglucose anion, which further dissociates via an ion/neutral complex to give two peaks at m/z 75 and 119.

Loss of benzene to generate an enolate anion by a site-specific double-hydrogen transfer during CID fragmentation of o-alkyl ethers of ortho-hydroxybenzoic acids.

Collision-induced dissociation of anions derived from ortho-alkyloxybenzoic acids provides a facile way of producing gaseous enolate anions. The alkyloxyphenyl anion produced after an initial loss of CO(2) undergoes elimination of a benzene molecule by a double-hydrogen transfer mechanism, unique to the ortho isomer, to form an enolate anion. Deuterium labeling studies confirmed that the two hydrogen atoms transferred in the benzene loss originate from positions 1 and 2 of the alkyl chain.

Low-energy collision-induced fragmentation of negative ions derived from ortho-, meta-, and para-hydroxyphenyl carbaldehydes, ketones, and related compounds.

Collision-induced dissociation (CID) mass spectra of anions derived from several hydroxyphenyl carbaldehydes and ketones were recorded and mechanistically rationalized. For example, the spectrum of m/z 121 ion of deprotonated ortho-hydroxybenzaldehyde shows an intense peak at m/z 93 for a loss of carbon monoxide attributable to an ortho-effect mediated by a charge-directed heterolytic fragmentation mechanism. In contrast, the m/z 121 ion derived from meta and para isomers undergoes a charge-remote homolytic cleavage to eliminate an *H and form a distonic anion radical, which eventually loses CO to produce a peak at m/z 92.

Surface Modification of Protein Nanocontainers and Their Self-Directing Character in Polymer Blends.

Tailoring the surfaces of a nanocontainer with polymer brushes that have different affinities to the components of a phase-separating polymer blend should impart self-directing properties to the nanocontainers. Such nanocontainers could then be used to deliver a variety of functional species in tunable amounts and in a site-specific manner to polymer systems. This paper describes the surface modification, subsequent characterization of nanocontainers derived from ferritin, and the effects of surface modification on their self-directing properties in a binary phase separating homopolymer blend.

An unprecedented rearrangement in collision-induced mass spectrometric fragmentation of protonated benzylamines.

The collision-induced dissociation (CID) mass spectra of several protonated benzylamines are described and mechanistically rationalized. Under collision-induced decomposition conditions, protonated dibenzylamine, for example, loses ammonia, thereby forming an ion of m/z 181. Deuterium labeling experiments confirmed that the additional proton transferred to the nitrogen atom during this loss of ammonia comes from the ortho positions of the phenyl rings and not from the benzylic methylene groups.

An unexpected ion-molecule adduct in negative-ion collision-induced decomposition ion-trap mass spectra of halogenated benzoic acids.

The ion observed at m/z 145 when product ion spectra of iodobenzoate anions are recorded using ion-trap mass spectrometers corresponds to the adduct ion [I(H(2)O)](-). The elements of water required for the formation of this adduct do not originate from the precursor ion but from traces of moisture present in the helium buffer gas. A collision-induced decomposition (CID) spectrum recorded from the [M-H](-) ion (m/z 251) derived from 3-iodo[2,4,5,6-(2)H(4)]benzoic acid also showed an ion at m/z 145.

Defensive chemicals of two species of Trachypachus Motschulski.

Analyses of pygidial gland contents of two species of a previously uninvestigated family of beetles (Trachypachidae) by Gas Chromatography-Mass Spectrometry (GC-MS) revealed that their chemistry is similar to that reported from many members of the family Carabidae. Nevertheless, the composition of defensive gland fluids of the two species Trachypachus slevini and T. gibbsii differs sufficiently to distinguish between the two species solely on the basis of their defensive chemistry.