An active atmospheric methane sink in high Arctic mineral cryosols

Methane (CH4) emission by carbon-rich cryosols at the high latitudes in Northern Hemisphere has been studied extensively. In contrast, data on the CH4 emission potential of carbon-poor cryosols is limited, despite their spatial predominance. This work employs CH4 flux measurements in the field and under laboratory conditions to show that the mineral cryosols at Axel Heiberg Island in the Canadian high Arctic consistently consume atmospheric CH4. Omics analyses present the first molecular evidence of active atmospheric CH4-oxidizing bacteria (atmMOB) in permafrost-affected cryosols, with the prevalent atmMOB genotype in our acidic mineral cryosols being closely related to Upland Soil Cluster α. The atmospheric (atm) CH4 uptake at the study site increases with ground temperature between 0 °C and 18 °C. Consequently, the atm CH4 sink strength is predicted to increase by a factor of 5-30 as the Arctic warms by 5-15 °C over a century. We demonstrate that acidic mineral cryosols are a previously unrecognized potential of CH4 sink that requires further investigation to determine its potential impact on larger scales. This study also calls attention to the poleward distribution of atmMOB, as well as to the potential influence of microbial atm CH4 oxidation, in the context of regional CH4 flux models and global warming.

Formation and characterization of iron-oligonucleotide complexes with matrix-assisted laser desorption/ionization fourier transform ion cyclotron resonance mass spectrometry

Iron-containing oligonucleotide negative ions can be generated by matrix-assisted laser desorption/ionization from a stainless steel target disk (by either defocusing the laser beam or by mixing iron salts such as FeCl3 with the matrix compound during the sample preparation). High resolution mass measurements reveal the presence of both Fe2+ (as M + Fe - 3H)- and Fe3+ (as M + Fe - 4H)- in the metal-oligonucleotide ions. The presence of Fe3+ is unexpected, and must involve replacement of protons from the nucleic bases or ribose groups as well as the phosphate groups of the oligonucleotides. Inspection of a range of small oligonucleotides and mononucleotides reveals that the presence of both Fe2+ and Fe3+ in the iron-biomolecule complexes is dependent on the number of acidic hydrogens that can be replaced in the oligonucleotide or nucleotide. Collisional dissociation of several metal-tetranucleotide ions revealed that the presence of the iron ion alters the fragmentation observed. The iron atom was observed to be present in all of the fragment ions, and, whenever possible, seemed to enhance the abundance of fragment ions containing both iron and a guanine nucleic base. These results suggest that iron may serve as a useful probe for characterizing phosphorylated biomolecules.

Investigation of oligonucleotide fragmentation with matrix-assisted laser desorption/ionization Fourier-transform mass spectrometry and sustained off-resonance irradiation

Matrix-assisted laser desorption/ionization (MALDI) can be combined with Fourier-transform ion cyclotron resonance mass spectrometry (FTMS) for the detailed structural examination of biomolecules such as peptides and oligonucleotides. We have been able to detect molecular ions for bovine heart cytochrome c (MW = 12,327) by MALDI-FTMS (355 nm laser desorption, 2,5-dihydroxybenzoic acid matrix). Although the mass resolution of these molecular ions is poor, the experiments verify that the MALDI-FTMS mass range for our 3-tesla instrument is in excess of m/z 12,000. Accurate mass measurements and selective dissociation experiments were used to examine the fragmentation pathways of small oligonucleotides in detail. Sustained off-resonance irradiation (SORI) was found to be superior to conventional on-resonance collisionally activated dissociation (CAD) for the efficient dissociation and detection of fragment ions for oligonucleotides. These experiments indicated that oligonucleotide fragmentation is a complex process and results not only from simple elimination of nucleic bases and cleavages of phosphate ester bonds, but also by rearrangement processes in which a terminal phosphate moiety can be transferred to an internal phosphate group.

Analysis of modified oligonucleotides by matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been applied to the structural characterization of modified oligodeoxyribonucleotide 4-, 6-, and 11-mers. Each oligonucleotide contained one modified base, either an O6-methyl-substituted guanine, an N6-(10R)-trans-opened benzo[a]pyrenediol epoxide adduct of adenine, or an N2-(R)-styrene oxide adduct of guanine. 3-Hydroxypicolinic acid was used as the MALDI matrix for molecular weight and purity determinations, while either 2,5-dihydroxybenzoic acid (DHBA) or an anthranilic/nicotinic acid (AA/NA) mixture was used to induce fragmentation for the production of structurally significant fragment ions. For the 4- and 6-mers, the oligonucleotide sequence could be obtained from the direct AA/NA or DHBA spectra. Sequence information was also obtained by inserting a time delay between the laser desorption event and ion detection to permit metastable decomposition. For the 11-mers, high-mass sequence ions were not detected. Although similar sequence ions were observed in both the positive and the negative ion mass spectra, more fragmentation was generally observed in the positive ion mode. In the positive ion mode, modified base fragment ions were observed when DHBA was used, and these fragments were examined using accurate mass measurements, collisionally induced dissociations, and ion-molecule reactions to characterize the modified base. MALDI-FTMS signals from one sample application can be used for the measurement of hundreds of spectra. The direct MALDI-FT mass spectra show matrix-dependent, structurally informative fragments, and CID experiments can be implemented using low-picomole sample quantities.

Characterization of radiation-induced products of thymidine 3'-monophosphate and thymidylyl (3'-->5') thymidine by high-performance liquid chromatography and laser-desorption Fourier-transform mass spectrometry

High-performance liquid chromatography (HPLC) and laser-desorption Fourier-transform mass spectrometry (LD FTMS) have been applied for direct measurements of radiation-induced products of nucleic acid constituents containing thymidine. Laser desorption FTMS could be used for the direct detection (neither hydrolyzed nor derivatized) of X ray-induced decomposition products of aqueous thymidine monophosphate. After these initial experiments, a variety of hydrogenated and hydroxylated thymine standards were acquired and examined by FTMS to assist in the identification of unknown radiation-induced decomposition products of thymine-containing nucleotides and dinucleotides. To extend these studies to dinucleotides, the radiation-induced products generated by the gamma radiolysis of thymidylyl (3'-->5') thymidine (TpT) were isolated by reverse-phase HPLC and identified by LD FTMS. Thymine and thymidine 3'-monophosphate were observed as the major products in this case. Several of the minor products of the HPLC profile were pooled in a single fraction and characterized simultaneously by LD FTMS. The resulting mass spectra indicated the presence of hydroxy-5,6-dihydrothymidine monophosphate, 5,6-dihydrothymidine monophosphate and thymidine monophosphate, thymine glycol, hydroxy-5,6-dihydrothymine, 5-hydroxy-methyluracil and 5,6-dihydrothymine. The combination of HPLC purification and LD FTMS structural characterization provides a useful tool for the direct measurement of radiation-induced products of nucleotides and dinucleotides.

Structural characterization of polycyclic aromatic hydrocarbon dihydrodiol epoxide DNA adducts using matrix-assisted laser desorption/ionization Fourier transform mass spectrometry

Matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been applied for the structural characterization of four polycyclic aromatic hydrocarbon dihydrodiol epoxide (PAHDE) adducts, including the 5,6-dimethylchrysene DE adduct of 2'-deoxyadenosine, the 5-methyl- and 5,6-dimethylchrysene DE adducts of 2'-deoxyguanosine, and the benzo[a]pyrene-DE adduct of 2'-deoxyguanosyl 3'-phosphate. Measurement of positive and negative ion mass spectra, accurate mass determinations, and CID experiments were carried out using 10-40 ng (20-70 pmol) of sample. An evaluation of five MALDI matrices showed that matrix selection can be used to control the degree of analyte fragmentation. Three MALDI matrices commonly used for the analysis of proteins (sinapinic acid, ferulic acid, 2,5-dihydroxybenzoic acid) gave positive ion adduct mass spectra showing protonated or sodiated molecular ions accompanied by abundant, structurally informative fragment ions. Fragmentation was significantly reduced when working with two matrices used for oligonucleotide analysis (an anthranilic-nicotinic acid mixture and 3-hydroxypicolinic acid). Using the CID capabilities of FTMS, isolation and activation of the MALDI-produced ions was used to provide additional structural information. While characteristic negative ions were not detected for the adenosyladduct, the guanosyl and guanosyl 3'-phosphate adducts gave [M-H]- ions when the anthranilic-nicotinic acid matrix mixture was used. The guanosyl adducts also showed [M-H-2H2O]- fragments. Compared with FAB or FAB-MS/MS for the analysis of underivatized PAH-DE adducts, MALDI-FTMS signals are long-lived, the direct MALDI-FT mass spectra show more structurally informative fragments, and accurate mass and CID experiments require lower sample quantities.

Synthesis and Characterization of Molybdenum Carbide Clusters Mo n C 4 n , ( n = 1 to 4)

Laser radiation (XeCl laser, 308-nanometer wavelength) focused into a cell containing Mo(CO)(6) vapor produced ultrafine particles in the extended waist of the laser beam. Negative ion mass spectrometry revealed molybdenum carbide cluster ions with a stoichiometry MonC4n (n = 1 to 4). The MonC4n(-) (n = 2 to 4) ions are completely unreactive with NH(3), H(2)O, and O(2), suggesting structures in which the molybdenum atoms are unavailable for coordination to additional ligands. Collision-induced dissociation studies of these anions show the loss of MoC(4) units as the main fragmentation pathway. This observation, together with the lack of addition reactions, provides a basis for structures in which a planar cluster of two, three, or four molybdenum atoms is surrounded by, and bonded to, carbon dimers.

Matrix-assisted laser desorption/ionization Fourier-transform mass spectrometry of oligodeoxyribonucleotides

Conditions for the matrix-assisted laser desorption/ionization (MALDI) of oligodeoxyribonucleotides at 355 nm, developed using a 3-Tesla Fourier-transform ion cyclotron resonance mass spectrometer (FTMS), are reported. Efficient ion trapping and matrix selection are critical to the desorption and detection of oligonucleotides by FTMS. The achievable upper mass limit for the MALDI-FTMS of biomolecules on our 3-Tesla system has been extended from approximately 2 kDa to 6 kDa through the use of pulsed-trapping-plate ion deceleration techniques. By implementing the deceleration techniques, molecular ions for bovine insulin (MW = 5733.5), an oligodeoxythymidylic acid, pd[T]10 (MW = 3060.0), and a mixed-base 12-mer (MW = 3611.5) have been measured. For the analysis of oligonucleotides by FTMS, selection of an appropriate MALDI matrix is essential for the generation of [M-H]- ions. 3-Hydroxypicolinic acid provides a significant improvement over 2,5-dihydroxybenzoic acid for production of deprotonated molecules particularly for mixed-base oligomers. MALDI studies using FTMS have been duplicated using a newly constructed time-of-flight mass spectrometer (TOFMS) and oligonucleotide fragmentation on the TOFMS is reduced relative to that observed by FTMS. This may be a consequence of the longer times (milliseconds) required for FTMS detection.

Methyl guanine isomer distinction by hydrogen / deuterium exchange using a fourier transform mass spectrometer

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Differentiation of the seven isomers of methyl guanine has been accomplished by monitoring gas-phase hydrogen/deuterium (H/D) exchange reactions of the protonated molecular ions with deuterium oxide (D2O) in a Fourier transform mass spectrometer. In each case a distinctive reaction rate for the first H/D exchange was observed, and exchanges of up to three deuterium atoms occurred with characteristic ion abundances that could be used to differentiate the isomers. O(6)-Methyl guanine, for example, showed only one slow H/D exchange with D2O, whereas l-methyl guanine exchanged two hydrogen atoms at a significantly faster rate. On comparison of the possible resonance structures of each protonated isomer with the experimental information about the number and rate of H/D exchanges observed, a reaction mechanism involving a concerted proton abstraction-deuterium cation donation was proposed.

Applications of mass spectrometry to DNA sequencing

The ability of the mass spectrometer to analyze collectively the masses of DNA fragments that are produced in the Sanger procedure for sequencing may allow the gel electrophoresis step to be eliminated. On the other hand, if gel electrophoresis is required, the use of resonance ionization spectroscopy coupled to a mass spectrometer may enable much faster analysis of DNA bands labeled with stable isotopes. Other combinations of labeling of the DNA and its mass spectrometric analysis with or without gel electrophoresis are also considered. Recent advances in these areas of mass spectrometry are reviewed.

Investigation of UV matrix-assisted laser desorption fourier transform mass spectrometry for peptides

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Ultraviolet matrix-assisted laser desorption can be used to enhance formation of [M + H](+), [M + Na](+), and [M + K)(+) ions from small peptides for Fourier transform mass spectrometry (FTMS). In accord with laser desorption (LD) time-of-flight experiments, matrices such as nicotinic acid and 2-pyrazinecarboxylic acid exhibit strong enhancement effects (i.e., formation of abundant protonated and cationized molecules for the analyte with virtually no fragment ions) for 266 nm LD/FTMS, whereas pyrazinedicarboxylic acid provides no matrix enhancement at this wavelength. Both sinapinic acid and coumarin-120 provide strong matrix enhancement effects for the 355-nm LD of peptides. For the small peptides examined in this study, no significant differences in the abundance of fragment ions were observed between the 266- and 355-nm wavelengths. Matrix-assisted LD/FTMS is useful for the generation and characterization of ions corresponding to protonated and cationized molecules from virtually all biological compounds with molecular weights up to 2000. The lack of observation of biological ions with m/ z > 2500 may be related to inefficient trapping of these laser-desorbed ions or instrumental detection limitations of FTMS and is under further investigation.

Characterization of photo-induced pyrimidine cyclobutane dimers by laser desorption Fourier transform mass spectrometry

Laser desorption Fourier transform mass spectrometry was used to characterize the cis-syn cyclobutane photodimers of uracil-uracil, uracil-thymine and thymine-thymine. This soft ionization technique generated [M-H]- ions as well as some fragment ions. Investigation of the laser desorption process indicated that gas-phase dimerization reactions do not occur for pyrimidine monomers and dimers under these experimental conditions. Collisional dissociation of the [M-H]- ions provided structural information for the pyrimidine rings of the dimers. The fragment ions observed in the collisional dissociation spectra of these cyclobutane dimers suggested rearrangement of the [M-H]- parent ions to a macrocycle prior to dissociation.

The differentiation of methyl guanosine isomers by laser ionization Fourier transform mass spectrometry

Laser ionization of guanosines containing methyl substitutions in the 1-, N2-, 3'-O-, O6- and 7-positions generated two characteristic negative ions: loss of hydrogen to generate [M - H]- and elimination of the sugar ring to form the nucleic base ion. The ions generated by elimination of the sugar ring provided the information necessary to determine whether the methyl group was on the nucleic base or sugar ring. Fourier transform mass spectrometry was used to isolate and collisionally dissociate selected negative ions from these nucleosides. The collisional dissociation spectra indicated daughter ions which were sufficient to differentiate all the isomers with methyl substitution of the nucleic bases. In addition, accurate mass measurement and sequential collisional dissociation experiments were employed to investigate fragmentation mechanisms.