Positive Ion ESI Mass Research Articles

Rapid sample classification using an open port sampling interface coupled with liquid introduction atmospheric pressure ionization mass spectrometry.

An "Open Access"-like mass spectrometric platform to fully utilize the simplicity of the manual open port sampling interface for rapid characterization of unprocessed samples by liquid introduction atmospheric pressure ionization mass spectrometry has been lacking. The in-house developed integrated software with a simple, small and relatively low-cost mass spectrometry system introduced here fills this void. Software was developed to operate the mass spectrometer, to collect and process mass spectrometric data files, to build a database and to classify samples using such a database. These tasks were accomplished via the vendor-provided software libraries. Sample classification based on spectral comparison utilized the spectral contrast angle method. Using the developed software platform near real-time sample classification is exemplified using a series of commercially available blue ink rollerball pens and vegetable oils. In the case of the inks, full scan positive and negative ion ESI mass spectra were both used for database generation and sample classification. For the vegetable oils, full scan positive ion mode APCI mass spectra were recorded. The overall accuracy of the employed spectral contrast angle statistical model was 95.3% and 98% in case of the inks and oils, respectively, using leave-one-out cross-validation. This work illustrates that an open port sampling interface/mass spectrometer combination, with appropriate instrument control and data processing software, is a viable direct liquid extraction sampling and analysis system suitable for the non-expert user and near real-time sample classification via database matching. Published in 2016. This article is a U.S. Government work and is in the public domain in the USA.

Anti-Inflammatory, Anti-Osteoclastogenic and Antioxidant Effects of Malva sylvestris Extract and Fractions: In Vitro and In Vivo Studies.

Given their medical importance, natural products represent a tremendous source of drug discovery. The aim of this study was to investigate Malva sylvestris L. extract and fractions and their pharmacological activities followed by chemical identification. The aqueous fraction (AF) was identified as the bioactive fraction in the in vitro and in vivo assays. The AF controlled the neutrophil migration to the peritoneal cavity by 66%, inhibited the antiedematogenic activity by 58.8%, and controlled IL-1β cytokine expression by 54%. The in vitro viability tests showed a concentration-dependent effect, where the MSE and fractions at concentrations under 10 μg/mL were non-toxic to cells. Transcriptional factors of carbonic anhydrase II (CAII), cathepsin K (Ctsk) and tartrate-resistant acid phosphatase (TRAP) were analyzed by qPCR in RAW 264.7 cell lines. The gene expression analysis showed that the AF was the only treatment that could downregulate all the study genes: CAII, Ctsk and TRAP (p<0.05). TRAP staining was used to evaluate osteoclast formation. AF treatments reduced the number of osteoclastogenesis 2.6-fold compared to the vehicle control group. Matrix metalloproteinase 9 (MMP-9) activity decreased 75% with the AF treatment. Moreover, the bioactive fraction had the ability to regulate the oxidation pathway in the ABTS (2,2-Azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) assay with an activity equivalent to 1.30 μmol Trolox/g and DPPH (2,2-diphenyl-1-picrylhydrazyl) radicals 1.01 g/L. Positive ion ESI-mass spectrometry for molecular ions at m/z 611 and 633 confirmed rutin as the major compound in the AF. The AF of M. sylvestris presented anti-inflammatory, controlled osteoclastogenic mechanisms and antioxidant abilities in different in vitro and in vivo methods. In addition, we suggest that given its multi-target activity the bioactive fraction may be a good candidate in the therapy of chronic inflammatory diseases.

Content of 4(5)-methylimidazole, caffeine and chlorogenic acid in commercial coffee brands

Content of 4(5)-methylimidazole (4-MeI), caffeine and chlorogenic acid in commercial coffee brands were determined using high-performance liquid chromatography (HPLC) with UV DAD and MS detectors. Positive ion ESI mass spectra of the 4-MeI standard yielded intense signals corresponding to [M+H]+ (83.0604) and [2M+H]+ ions (165.1115). Also, adducts of 4-MeI with acetonitrile from mobile were detected - [M+ACN]+ ions (124.0849). The LOD of 2.5 ng mL-1 and LOQ of 8.4 ng.mL-1 were calculated according to the following formulas: LOD = 3.SD/S, and LOQ = 10.SD/S, where S is the slope of the calibration curve and SD is the standard deviation of the noise. The caffeine content was compared to the results of the standard addition, 1st derivative and liquid-liquid extraction spectrophotometry. 4-MeI was in tens µg g-1 in the Vietnamese coffees while in units µg.g-1 in all Czech and Brazilian coffees (&lt;2.4 µg.g-1 and &lt;4.9 µg.g-1, respectively). The results for caffeine were within the documented range (0.31 - 2.20%) in all coffee samples. The lower content of caffeine and chlorogenic acid was observed in Vietnamese coffees. All the methods used for determination of caffeine in the Czech and Brazilian coffees gave acceptable precision and accuracy. However, there were significant differences in the results in Vietnamese coffees. The caffeine extractability (100 °C, 3 min brewing) almost reached 100% in Czech and Brazilian coffees, while it was less than 90% in Vietnamese coffees. The Czech and Brazilian coffees tend to produce more caffeine in brews than the Vietnamese coffee because of the different composition of blends and the particle size degree.

Further studies on the chemistry of tetramethylthiourea–platinum complexes: Evolution of cis-[PtCl{S[dbnd]C(NMe2)2}(PPh3)2]+ to the dinuclear monothiocarbamato–sulfido complex [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4

Reaction of cis-[PtCl2(PPh3)2] with tetramethylthiourea (tmtu) in methanol under various conditions has been re-investigated. In the absence of base, the simple ligand substitution product [PtCl(tmtu)(PPh3)2]PF6 can be isolated by addition of excess NH4PF6. The complex was characterised by positive-ion ESI mass spectrometry, NMR spectroscopy and an X-ray structure determination. In refluxing methanol with excess Me3N, cis-[PtCl2(PPh3)2] reacts with tmtu to give a yellow solution containing the dinuclear monothiocarbamato complex [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]+; the complex was isolated as BPh4− or PF6− salts. The X-ray structure of [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]BPh4·CHCl3 is described. ESI mass spectrometry has been used to identify various reaction intermediates and by-products in the synthesis of [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]+. [Pt2(μ-S){μ-SC(O)NMe2}(PPh3)4]+ acts as a metalloligand, e.g. towards PhHg+, but a pure product was unable to be isolated. DFT calculations suggest the presence of a Hg⋯OC interaction.

Interactions of ginsenosides with DNA duplexes: A study by electrospray ionization mass spectrometry and UV absorption spectroscopy

Abstract The non-covalent complexes of duplexes DNA and 9 ginsenosides (1 aglycone and 8 glycosides) were investigated using electrospray ionization mass spectrometry (ESI-MS) in the gas phase. The results of relative binding affinities in negative ion mode revealed that several factors impact on the duplex-binding properties of ginsenosides. Glycosylations of 20(S)-protopanaxadiol ginsenosides at the position C-20 and 20(S)-protopanaxatriol classification at the position C-6 enhanced the fraction of bound DNA sharply. A rhamnose moiety shows little lower binding intensities than glucose at the same position. Ginsenosides of 20(S)-protopanaxatriol result in subtle higher binding affinities toward the duplex DNA than 20(S)-protopanaxadiol family. However, glycosylation with two sugar moieties does not show a higher binding affinity than with only one moiety. The collision-induced dissociation experimental data demonstrate the gas-phase stability and fragmentation patterns of the ginsenoside/DNA complexes are related to the glycoside number. Positive ion ESI mass spectra of the complexes were also recorded. The result of ESI-MS suggests that hydrogen bonds are the dominate interaction between ginsenosides and DNA. Similar results were obtained in solution-phase by UV spectroscopy, which exhibit a hyperchromism and blue-shift effect when DNA solution was titrated by individual ginsenoside.

Extending the coordination chemistry of cobalt with the metalloligand [Pt2(μ-S)2(PPh3)4]: Synthesis of the first cobalt(III) derivatives

The coordination chemistry of the metalloligand [Pt2(μ-S)2(PPh3)4] towards cobalt(II) and cobalt(III) centres has been explored using an electrospray ionisation mass spectrometry (ESI MS)-directed methodology. Reaction of [Pt2(μ-S)2(PPh3)4] with CoCl2·6H2O in methanol gave a green-yellow suspension of the known adduct [Pt2(μ-S)2(PPh3)4CoCl2], and the CoBr2 adduct could be similarly prepared. When in situ-generated [Pt2(μ-S)2(PPh3)4CoCl2] is reacted with 8-hydroxyquinoline (HQ) and base, the initial product is the cobalt(II) adduct [Pt2(μ-S)2(PPh3)4CoQ]+, which is then converted in air to the cobalt(III) adduct [Pt2(μ-S)2(PPh3)4CoQ2]+, isolated as its hexafluorophosphate salt. The corresponding picolinate (Pic) derivative [Pt2(μ-S)2(PPh3)4Co(Pic)2]+ was similarly prepared, however reaction of [Pt2(μ-S)2(PPh3)4], CoCl2·6H2O and 8-(tosylamino)quinoline (HTQ) produced only the cobalt(II) adduct [Pt2(μ-S)2(PPh3)4CoTQ]+. Reactions of [Pt2(μ-S)2(PPh3)4], CoCl2·6H2O and dithiocarbamates gave cobalt(III) complexes [Pt2(μ-S)2(PPh3)4Co(S2CNR2)2]+ [R=Et or R2=(CH2)4], and proceeded much more rapidly, consistent with the known ability of the dithiocarbamate ligand to stabilize cobalt in higher oxidation states. A study of the fragmentation of cobalt(III) adducts by positive-ion ESI mass spectrometry indicated that [Pt2(μ-S)2(PPh3)4CoQ2]+ fragments to form the radical cation [Pt2(μ-S)2(PPh3)4]+, which could also be generated by ESI MS analysis of [Pt2(μ-S)2(PPh3)4] in methanol–NaOH solution. In contrast, the corresponding indium(III) derivative [Pt2(μ-S)2(PPh3)4InQ2]+, and the cobalt(III) dithiocarbamate [Pt2(μ-S)2(PPh3)4Co(S2CN(CH2)4)2]+ are much more reluctant to fragment under analogous conditions, and the differences are discussed in terms of cobalt(III) redox chemistry.

Spanning [Pt 2(μ-S) 2(PPh 3) 4] metalloligands with 1,4-dimercurated durene

Reaction of the metalloligand [Pt 2(μ-S) 2(PPh 3) 4] with 0.5 mol equivalents of durene-1,4-bis(mercuric acetate) [AcOHgC 6Me 4HgOAc] in methanol gives the polynuclear complex [{Pt 2(μ-S) 2(PPh 3) 4} 2(μ-1,4-C 6Me 4Hg 2)] 2+, isolated as its PF 6 − and BPh 4 − salts. Positive-ion ESI mass spectra indicate that [{Pt 2(μ-S) 2(PPh 3) 4} 2(μ-1,4-C 6Me 4Hg 2)] 2+ undergoes fragmentation by successive loss of PPh 3 ligands, while the ESI mass spectrum of the BPh 4 − salt showed additional ions [Pt 2(μ-S) 2(PPh 3) 4(HgC 6Me 4HgPh)] + and [Pt 2(μ-S) 2(PPh 3) 4HgPh] + as a result of phenyl transfer from BPh 4 − to Hg. A single-crystal X-ray structure determination on [{Pt 2(μ-S) 2(PPh 3) 4} 2(μ-1,4-C 6Me 4Hg 2)](BPh 4) 2 shows that the cation crystallises on a centre of symmetry, with structural features that are comparable to those of the previously characterised complex [Pt 2(μ-S) 2(PPh 3) 4HgPh]BPh 4.

Development of sensitive derivatization method for aldosterone in liquid chromatography–electrospray ionization tandem mass spectrometry of corticosteroids

A highly sensitive quantification method of aldosterone by liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS) was investigated in a positive mode using recently developed picolinyl derivatization. Aldosterone was smoothly and quantitatively converted to the ethyl ether–picolinyl derivative by treatment with HCl–ethanol followed by the esterification with picolinic acid in the presence of 2-methyl-6-nitrobenzoic anhydride and 4-dimethylaminopyridine. The positive ion-ESI mass spectrum of the ethyl ether–picolinyl derivative was characterized by an appearance of protonated molecule ([M+H] +) as a base peak. The ethyl ether–picolinyl derivatization gave a successful result in a separation of aldosterone from corticosterone, dehydrocorticosterone and cortexolone, and also provided an approximately 10-fold higher ESI response in the positive-LC–ESI-MS/MS (selected reaction monitoring; SRM) when compared to that of underivatized molecule (negative mode). The limit of quantification of aldosterone by SRM using ethyl ether–picolinyl derivatization ( m/z 494 → m/ z 448) was 1 pg/0.2 ml serum with accuracy and precision of 92.6% and 5.6%, respectively.

Characterization of Ni(II) complexes of Schiff bases of amino acids and (S)‐N‐(2‐benzoylphenyl)‐1‐benzylpyrrolidine‐2‐carboxamide using ion trap and QqTOF electrospray ionization tandem mass spectrometry

This work demonstrates the application of electrospray ionization mass spectrometry (ESI-MS) using two different mass analyzers, ion trap and hybrid quadrupole time-of-flight (QqTOF) mass analyzer, for the structural characterization of Ni(II) complexes of Schiff bases of (S)-N-(2-benzoylphenyl)-1-benzylpyrrolidine-2-carboxamide with different amino acids. ESI enables the determination of molecular weight on the basis of rather simple positive-ion ESI mass spectra containing only protonated molecules and adducts with sodium or potassium ions. Fragmentation patterns are characterized by tandem mass spectrometric experiments, where both tandem mass analyzers provide complementary information. QqTOF data are used for the determination of elemental composition of individual ions due to mass accuracies always better than 3 ppm with the external calibration, while multistage tandem mass spectra obtained by the ion trap are suitable for studying the fragmentation paths. The novel aspect of our approach is the combination of mass accuracies and relative abundances of all isotopic peaks in isotopic clusters providing more powerful data for the structural characterization of organometallic compounds containing polyisotopic elements. The benefit of relative and absolute mean mass accuracies is demonstrated on the example of studied Ni(II) complexes.

Simultaneous determination of tetrahydrocortisol, allotetrahydrocortisol and tetrahydrocortisone in human urine by liquid chromatography-electrospray ionization tandem mass spectrometry

Simultaneous quantification method of three major metabolites of cortisone and cortisol, tetrahydrocortisol, allotetrahydrocortisol and tetrahydrocortisone by liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) was investigated in a positive mode using a recently developed picolinyl derivatization. Conversion of each steroid into the corresponding picolinyl derivatives ( 1b, 2b or 3b) was performed by mixed anhydride method using picolinic acids and 2-methyl-6-nitrobenzoic anhydride. Derivatization proceeded smoothly to afford the corresponding 3, 21-dipicolinyl derivatives. Positive ion-ESI mass spectra of the picolinyl derivatives were dominated by an appearance of [M + H] + as base peaks in all cases. The picolinyl derivatives provided 15 to 80-fold higher ESI response in the LC-ESI-MS/MS (selected reaction monitoring: SRM) when compared to those of underivatized molecules in a positive LC-ESI mode. The use of the picolinyl ester, solid-phase extraction, and deuterium labeled internal standards enabled the concentrations of these metabolites in human urine to be determined simultaneously by LC-ESI-MS/MS (SRM) with a small sample volume of less than 1 μl urine.

Determination of antibiotics in aquatic environment by solid-phase extraction followed by liquid chromatography–electrospray ionization mass spectrometry

A robust and sensitive solid-phase extraction followed by liquid chromatography–electrospray ionization mass spectrometric (LC–ESI-MS) method for determination of antibiotics viz., fluoroquinolones, sulfamethoxazole, trimethoprim and cephalosporines in surface waters was developed. The sample recoveries on Oasis HLB cartridges were found to be >80%. Identification was carried out by LC–ESI-MS/MS. The positive ion ESI mass spectra containing the peaks of quasimolecular ions [M+H] + allowed the determination of molecular masses whereas the fragment ions obtained by MS/MS of [M+H] + ions permitted the structural assignment. Quantification was carried out by selective ion monitoring (SIM) using the quasimolecular ions [M+H] + of the parent compounds. The detection and quantification limits were found to be in the range of 0.6–8.1 and 2.0–24.0 μg/L. The surface waters of different lakes and tanks of Hyderabad, India were found to contain a few antibiotics.

Studies on alkaloids binding to GC‐rich human survivin promoter DNA using positive and negative ion electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to investigate the binding of 13 alkaloids to two GC-rich DNA duplexes which are critical sequences in human survivin promoter. Negative ion ESI-MS was first applied to screen the binding of the alkaloids to the duplexes. Six alkaloids (including berberine, jatrorrhizine, palmatine, reserpine, berbamine, and tetrandrine) show complexation with the target DNA sequences. Relative binding affinities were estimated from the negative ion ESI data, and the alkaloids show a binding preference to the duplex with higher GC content. Positive ion ESI mass spectra of the complexes were also recorded and compared with those obtained in negative ion mode. Only the 1 : 1 complex with berbamine was observed with lower abundance in the positive ion mass spectrum while complexes with the other alkaloids were absolutely absent. Collision-induced dissociation (CID) experiments indicate that the complexes with the protoberberine alkaloids (berberine, jatrorrhizine, and palmatine) dissociate via base loss and covalent cleavage. In contrast, product ion spectra of the complexes with the alkaloids reserpine, berbamine, and tetrandrine show the predominant loss of a neutral alkaloid molecule, accompanied by base loss and covalent cleavage to a lesser extent. A comparison of the gas-phase behaviors of complexes with the alkaloids to those with the traditional DNA binders has suggested an intercalative binding mode of these alkaloids to the target DNA duplexes.

Use of novel picolinoyl derivatization for simultaneous quantification of six corticosteroids by liquid chromatography-electrospray ionization tandem mass spectrometry

Simultaneous quantification method of six corticosteroids, cortisone, cortisol, cortexolone, corticosterone, dehydrocorticosterone and deoxycorticosterone, by LC–electrospray ionization (ESI)-MS in a positive mode using novel picolinoyl derivatization was investigated. Conversion of each corticosteroid into the corresponding picolinoyl derivative was performed by mixed anhydride method using picolinic acids and 2-methyl-6-nitrobenzoic anhydride. Derivatization proceeded smoothly to afford the corresponding 21-monopicolinoyl derivatives. Positive ion-ESI mass spectra of the picolinoyl derivatives were dominated by the appearance of [ M + H] + as base peaks. The picolinoyl derivatives provided 5–10 times higher ESI response in the LC–ESI-MS-selected reaction monitoring (SRM) when compared to those of underivatized molecules in a positive LC–ESI-MS mode. The use of the picolinoyl ester, solid-phase extraction, and deuterium labeled internal standards enabled to determine the concentrations of these corticosteroids in human saliva simultaneously by LC–ESI-MS-SRM.

Effect of Protein Stabilization on Charge State Distribution in Positive- and Negative-Ion Electrospray Ionization Mass Spectra

Changes in protein conformation are thought to alter charge state distributions observed in electrospray ionization mass spectra (ESI-MS) of proteins. In most cases, this has been demonstrated by unfolding proteins through acidification of the solution. This methodology changes the properties of the solvent so that changes in the ESI-MS charge envelopes from conformational changes are difficult to separate from the effects of changing solvent on the ionization process. A novel strategy is presented enabling comparison of ESI mass spectra of a folded and partially unfolded protein of the same amino acid sequence subjected to the same experimental protocols and conditions. The N-terminal domain of the Escherichia coli DnaB protein was cyclized by in vivo formation of an amide bond between its N- and C-termini. The properties of this stabilized protein were compared with its linear counterpart. When the linear form was unfolded by decreasing pH, a charge envelope at lower m/z appeared consistent with the presence of a population of unfolded protein. This was observed in both positive-ion and negative-ion ESI mass spectra. Under the same conditions, this low m/z envelope was not present in the ESI mass spectrum of the stable cyclized form. The effects of changing the desolvation temperature in the ionization source of the Q-TOF mass spectrometer were also investigated. Increasing the desolvation temperature had little effect on positive-ion ESI mass spectra, but in negative-ion spectra, a charge envelope at lower m/z appeared, consistent with an increase in the abundance of unfolded protein molecules.

Rapid separation and identification of phenolic and diterpenoid constituents from Radix Salvia miltiorrhizae by high‐performance liquid chromatography diode‐array detection, electrospray ionization time‐of‐flight mass spectrometry and electrospray ionization quadrupole ion trap mass spectrometry

High-performance liquid chromatography-diode array detection (HPLC-DAD), electrospray ionization time-of-flight mass spectrometry (HPLC-ESI-TOF-MS) and electrospray ionization quadrupole ion trap mass spectrometry (HPLC-ESI-MSn) were used for the isolation, identification and structural analysis of water-soluble phenolic and nonpolar diterpenoid constituents in Dan-shen (Radix Salvia miltiorrhizae) which was prepared by sonication in 70% methanol. Mass spectra were obtained by ESI-TOF-MS and electrospray ionization quadrupole ion trap mass spectrometry (ESI-QIT-MS). A formula database of known constituents in Dan-shen was established and most constituents were rapidly identified by HPLC-DAD/ESI-TOF-MS by matching their accurate molecular masses with the formulae of the compounds in the database. Compounds with the same molecular formula could not be differentiated by TOF-MS; however, QIT-MS could differentiate those compounds and elucidate their structures based on their characteristic fragmentation. HPLC-DAD, HPLC/ESI-TOF-MS and HPLC/ESI-MSn provided complementary information for the identification of the constituents in Dan-shen. Forty constituents were identified in 30 min based on their positive and negative ion ESI mass spectra and liquid chromatographic information. Thus the method described is useful for the rapid analysis of multiple constituents in Dan-shen.

Characteristic Fragmentation Behavior of Steroidal Phosphor‐ amidate Conjugates in Electrospray Ionization Tandem Mass Spectrometry

AbstractNovel steroidal phosphoramidate conjugates of 3′‐azido‐2′,3′‐dideoxythymidine (AZT) and amino acid esters were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry. The MS fragmentation behaviors of the steroidal phosphoramidate conjugates have been investigated in conjunction with tandem mass spectrometry of ESI‐MS/MS. There were three characteristic fragment ions in the positive ion ESI mass spectra, which were the Na adduct ions with loss of steroidal moiety, amino acid ester moiety from pseudo molecular ion (M+Na)+, and the phosphoamino acid methyl ester Na adduct ion by α‐cleavage of the phosphoramidate respectively. The main fragment ions in negative ion ESI mass spectra were the ion (M−HN3)−, the ion (M−AZT−H)−, and the ion (M−steroidal moiety−H)− besides the pseudo molecular ion (M−H)−. The fragmentation patterns did not depend on the attached amino acid ester moiety.

Identification of Mcm2 Phosphorylation Sites by S-phase-regulating Kinases

Minichromosome maintenance 2-7 proteins play a pivotal role in replication of the genome in eukaryotic organisms. Upon entry into S-phase several subunits of the MCM hexameric complex are phosphorylated. It is thought that phosphorylation activates the intrinsic MCM DNA helicase activity, thus allowing formation of active replication forks. Cdc7, Cdk2, and ataxia telangiectasia and Rad3-related kinases regulate S-phase entry and S-phase progression and are known to phosphorylate the Mcm2 subunit. In this work, by in vitro kinase reactions and mass spectrometry analysis of the products, we have mapped phosphorylation sites in the N terminus of Mcm2 by Cdc7, Cdk2, Cdk1, and CK2. We found that Cdc7 phosphorylates Mcm2 in at least three different sites, one of which corresponds to a site also reported to be phosphorylated by ataxia telangiectasia and Rad3-related. Three serine/proline sites were identified for Cdk2 and Cdk1, and a unique site was phosphorylated by CK2. We raised specific anti-phosphopeptide antibodies and found that all the sites identified in vitro are also phosphorylated in cells. Importantly, although all the Cdc7-dependent Mcm2 phosphosites fluctuate during the cell cycle with kinetics similar to Cdc7 kinase activity and Cdc7 protein levels, phosphorylation of Mcm2 in the putative cyclin-dependent kinase (Cdk) consensus sites is constant during the cell cycle. Furthermore, our analysis indicates that the majority of the Mcm2 isoforms phosphorylated by Cdc7 are not stably associated with chromatin. This study forms the basis for understanding how MCM functions are regulated by multiple kinases within the cell cycle and in response to external perturbations.

Mononuclear to Polynuclear Transition Induced by Ligand Coordination: Synthesis, X-ray Structure, and Properties of Mono-, Di-, and Polynuclear Copper(II) Complexes of Pyridyl-Containing Azo Ligands

Reactions of two hydrated cupric salts (CuCl(2).2H(2)O and Cu(ClO(4))(2).6H(2)O) with three azopyridyl ligands, viz. 2-[(arylamino)phenylazo]pyridine [aryl = phenyl (HL(1a)), p-tolyl (HL(1b)), and 2-thiomethyl phenyl (HL(1c))], 2-[2-(pyridylamino)phenylazo]pyridine (HL(2)), and 2-[3-(pyridylamino)phenylazo]pyridine (HL(3)), afford the mononuclear [CuClL(1)] (1), dinuclear [Cu(2)X(2)L(2)(2)](n)()(+) (X = Cl, H(2)O, ClO(4); n = 0, 1; 2, 3), and polynuclear [CuClL(3)](n)() (4) complexes, respectively, in high yields. Representative X-ray structures of these complexes 1-4 are reported. X-ray structure analysis of 4 reveals an infinite 1D zigzag chain that adopts a saw-tooth-like structure. Variable-temperature cryomagnetic measurements (2-300 K) on the complexes 2-4 have revealed weak magnetic interactions between the copper centers with J values -1.04, 9.88, and -1.31 cm(-1), respectively. Positive ion ESI mass spectra of the soluble complexes 1-3 are studied which provide the evidence for the integrity of the complexes also in solution. Visible range spectra of the complexes 1-3 in solution consist of intense and broad transitions in the range 700-600 nm. The solid-state spectrum of the insoluble copper complex 4, on the other hand, shows a structured band near 700 nm. The intensities of the transitions of the dinuclear complexes are much higher than those of the corresponding mononuclear copper complexes. Redox properties of the present copper complexes are reported. Notably, the dinuclear complex, 3, displays two successive redox processes: Cu(II)Cu(II) right harpoon over left harpoon Cu(II)Cu(I) right harpoon over left harpoon Cu(I)Cu(I). It catalyzes aerial oxidation of L-ascorbic acid. The catalytic cycle is most effective up to H(2)A/3 (H(2)A = L-ascorbic acid) molar ratio of 20:1.

Electrospray ionization and tandem mass spectrometry characterization of novel heterotrimetallic Ru(η 5-C 5H 5)(dppf)SnX 3 complexes and their heterobimetallic Ru(η 5-C 5H 5)(dppf)X precursors

Electrospray ionization and tandem mass spectrometry were used to characterize some novel heterotrimetallic complexes Ru(η 5-C 5H 5)(dppf)SnX 3 ( 1) (dppf = diphenylphosphine ferrocene; X = Cl, Br) and their heterobimetallic precursors Ru(η 5-C 5H 5)(dppf)X ( 2) (X = Cl, Br, I, N 3). The positive-ion ESI mass spectra of 1 and 2 in acetonitrile solution showed the predominant presence of the [Ru(η 5-C 5H 5)(dppf)] + cation ( 3) of m/ z 721. In the positive-ion ESI mass spectrum of the complex Ru(η 5-C 5H 5)(dppf)N 3 ( 2d), another prominent cation of m/ z 735, i.e. [Ru(η 5-C 5H 5)(dppf)N] + ( 4), was also observed. Its formation was proposed to occur via the oxidation of the ruthenium atom (Ru II → Ru III) followed by the loss of N 2. The positive-ion ESI tandem mass spectra of ions 3 and 4 showed mainly fragments formed by neutral losses of C 5H 5, C 6H 5 and P(C 6H 5) 2. Finally, cation 3 was proposed to be the catalytic active species in the single-step conversion of methanol to acetic acid.

Carbohydrate Recognition in Cross-Linked Sugar-Templated Poly(acrylates)

A low reloading capacity is a serious weakness for any recognition material. To raise the overall amount of saccharides bound by templated poly(acrylates) with immobilized copper(II) complexes, I enlarged the number of attractive binding forces inside the matrix by polymerizing cross-linking monomers with various amounts of free hydroxyl groups. The material preparation was conducted in the presence of either aqueous methanol or alkaline water as porogenic solvent. All rebinding experiments were carried out in water at physiological pH. Positive ion ESI mass spectrometry shows only weak copper(II)−saccharide interactions under sugar rebinding conditions. The formation of multiple hydrogen bondings between the polymer backbone and the sugar template are demonstrated to be advantageous for the overall material capacity. Increasing the flexibility of the polymer backbone in a templated polar matrix enhances the overall material capacity for disaccharides (∼80 μmol of sugar per gram polymer) and diminishes the material selectivity only slightly. The polymer selectivity for discrimination of α- and β-glycosidic bonds in the disaccharides maltose and lactose is higher in a polar than in a nonpolar matrix. The polymer preference for the smaller, less polar monosaccharide glucose decreases along with an increasing matrix polarity in favor of the larger, more polar disaccharide lactose.