Mass spectral characterization of tetracyclines by electrospray ionization,H/D exchange,and multiple stage mass spectrometry

Electrospray ionization (ESI) and collisionally induced dissociation (CID) mass spectra were obtained for five tetracyclines and the corresponding compounds in which the labile hydrogens were replaced by deuterium by either gas phase or liquid phase exchange. The number of labile hydrogens, x, could easily be determined from a comparison of ESI spectra obtained with N2 and with ND3 as the nebulizer gas. CID mass spectra were obtained for [M + H]+ and [M - H]- ions and the exchanged analogs, [M(Dx) + D]+ and [M(Dx) - D]- , and produced by ESI using a Sciex API-III(plus) and a Finnigan LCQ ion trap mass spectrometer. Compositions of product ions and mechanisms of decomposition were determined by comparison of the MS(N) spectra of the un-deuterated and deuterated species. Protonated tetracyclines dissociate initially by loss of H2O (D2O) and NH3 (ND3) if there is a tertiary OH at C-6. The loss of H2O (D2O) is the lower energy process. Tetracyclines without the tertiary OH at C-6 lose only NH3 (ND3) initially. MSN experiments showed easily understandable losses of HDO, HN(CH3)2, CH3 - N=CH2, and CO from fragment ions. The major fragment ions do not come from cleavage reactions of the species protonated at the most basic site. Deprotonated tetracyclines had similar CID spectra, with less fragmentation than those observed for the protonated tetracyclines. The lowest energy decomposition paths for the deprotonated tetracyclines are the competitive loss of NH3 (ND3) or HNCO (DNCO). Product ions appear to be formed by charge remote decompositions of species de-protonated at the C-10 phenol.     

Does electrospray ionization produce gas-phase or liquid-phase structures?

Electrospray ionization of tyrosine from a 3:1 (v:v) CH3OH/H2O solution is found to afford an M - H ion which is a 70:30 mixture of phenoxide and carboxylate ions. This corresponds to the gas-phase equilibrium composition and not the liquid-phase proportions. In contrast, the carboxylate is produced as the dominant ion (approximately 95%) from anhydrous CH3CN and CH3CN/H2O mixtures. The addition of small amounts of CH3OH to the solvent, however, convert the M - H ion back into the gas-phase isomeric ratio. The isomeric structure therefore depends on the solvent system from which an ion is sprayed.     

Capillary electrophoretic determination of phosphate based on the formation of a Keggin-type [PMo12O40]3- complex.

Based on the formation of a Keggin-type [PMo12O40]3- complex, a sensitive capillary electrophoresis (CE) method was developed for the determination of P(V) with direct UV detection at 220 nm. A mixture of alpha- and beta-Keggin-type [PMo12O40]3- complexes was readily formed in a sample solution consisting of a trace amount of P(V), 2.5 mM Mo(VI), 0.050 M p-C6H3(CH3)-2-SO3H (XSA), and 60% v/v CH3CN. When a 0.05 M HCl and 60% v/v CH3CN solution was used as a migration electrolyte, the Keggin complexes exhibited a sharp and well-defined peak in the electropherogram. The peak area was linearly dependent on the P(V) concentration in the range of 5 x 10(-7)-5 x 10(-5) M; a detection limit of 1 x 10(-7) M was achieved. In comparison with indirect UV detection, the direct UV detection is about ten times more sensitive, because the Keggin complexes possess high molar absorptivities. The developed CE method was applied to the determination of P(V) in river water, and the results were in good agreement with those obtained by ion chromatography (IC) and colorimetry (COL) based on the formation of mixed-valence heteropoly blue species.     

Gaseous H5P2O8- ions: a theoretical and experimental study on the hydrolysis and synthesis of diphosphate ion

The structure and reactivity of gaseous H5P2O8- ions obtained from the chemical ionization (CI) of an H4P2O7/H2O mixture and from electrospray ionization (ESI) of CH3CN/H2O/H4P2O7 solutions were investigated by Fourier transform ion cyclotron (FTICR) and triple quadrupole mass spectrometry. Theoretical calculations performed at the B3LYP/6-31+G* level of theory and collisionally activated dissociation (CAD) mass spectrometric results allowed the ionic population obtained in the CI conditions to be structurally characterized as a mixture of gaseous [H3P2O7...H2O]-, [H3PO4...H2PO4]-, and [PO3...H3PO4...H2O]- clusters. The energy profile emerging from theoretical calculations affords insight into the mechanism of diphosphate ion hydrolysis and synthesis.     

The even-electron rule in electrospray mass spectra of pesticides

A study of the fragmentation and ion formation of three major families of pesticides (including herbicides, insecticides, and fungicides) by liquid chromatography/time-of-flight mass spectrometry (LC/TOF-MS) and liquid chromatography/quadrupole time-of-flight mass spectrometry (LC/Q-TOF-MS) was carried out using positive electrospray ionization (ESI) and the results compared with those by gas chromatography (GC)/TOF-MS with electron ionization (EI) in order to test the validity of the even-electron rule in electrospray ionization. First, the majority of the fragmentations by positive ion ESI were even electron (EE) ions (93% of the fragment ions). Secondly, the formation of odd-electron (OE) fragment ions was greater with EI, where the fragment ions were present in a ratio of approximately 1:2 (35% OE ions and 65% EE ions). Thirdly, in-source collision-induced dissociation (CID) fragmentation by LC/TOF-MS and CID fragmentation in the collision cell by LC/Q-TOF-MS/MS resulted in 95% of the fragment ions being identical between the two types of fragmentation. As ESI in the positive ion mode yields an EE precursor ion (normally a protonated molecule), this commonly leads to EE fragment ions by elimination of molecules - a process called the even-electron rule. Neutral radical losses were less common in ESI but were common in the EI spectra of the same compounds. The structures that did lead to OE ions in ESI (exceptions to the even-electron rule approximately 7% of all ESI ions) favored electronegative radical losses in approximately the following order: .SO(2)CH(3), .NO(2), .CH(3), .Cl, .SCH(3), .CH(2)CH, and .OH.     

Infrared multiphoton dissociation spectroscopy study of protonated p-aminobenzoic acid: does electrospray ionization afford the amino- or carboxy-protonated ion?

Infrared multiphoton dissociation spectra of protonated p-aminobenzoic acid generated by electrospray ionization (ESI) from aqueous methanol and acetonitrile solutions were recorded in the gas phase from 2800-4000 cm(-1). The O-protonated ion is more stable than the N-protonated structure in the gas phase, whereas the opposite is true in both solutions. When CH(3)OH/H(2)O was used as the ESI solvent, only the O-protonated ion was observed. In contrast, a 70:30 mixture of the O- and N-protonated species were produced from CH(3)CN/H(2)O. These structural assignments are based on an assortment of experimental data (action spectra, photofragments, photofragmentation kinetics, and H/D exchange) and are fully supported by extensive computations. This work shows that ESI can lead to isomerization and that the ionization site may be varied by changing the solvent from which the substrate is analyzed.     

Direct oxidation of L-cysteine by [FeIII(bpy)2(CN)2]+ and [FeIII(bpy)(CN)4]-

The oxidation of L-cysteine by the outer-sphere oxidants [Fe(bpy)2(CN)2]+ and [Fe(bpy)(CN)4]- in anaerobic aqueous solution is highly susceptible to catalysis by trace amounts of copper ions. This copper catalysis is effectively inhibited with the addition of 1.0 mM dipicolinic acid for the reduction of [Fe(bpy)2(CN)2]+ and is completely suppressed with the addition of 5.0 mM EDTA (pH<9.00), 10.0 mM EDTA (9.010.0) for the reduction of [Fe(bpy)(CN)4]-. 1H NMR and UV-vis spectra show that the products of the direct (uncatalyzed) reactions are the corresponding Fe(II) complexes and, when no radical scavengers are present, L-cystine, both being formed quantitatively. The two reactions display mild kinetic inhibition by Fe(II), and the inhibition can be suppressed by the free radical scavenger PBN (N-tert-butyl-alpha-phenylnitrone). At 25 degrees C and micro=0.1 M and under conditions where inhibition by Fe(II) is insignificant, the general rate law is -d[Fe(III)]/dt=k[cysteine]tot[Fe(III)], with k={k2Ka1[H+]2+k3Ka1Ka2[H+]+k4Ka1Ka2Ka3{/}[H+]3+Ka1[H+]2+Ka1Ka2[H+]+Ka1Ka2Ka3}, where Ka1, Ka2, and Ka3 are the successive acid dissociation constants of HSCH2CH(NH3+)CO2H. For [Fe(bpy)2(CN)2]+, the kinetics over the pH range of 3-7.9 yields k2=3.4+/-0.6 M(-1) s(-1) and k3=(1.18+/-0.02)x10(6) M(-1) s(-1) (k4 is insignificant in the fitting). For [Fe(bpy)(CN)4]- over the pH range of 6.1-11.9, the rate constants are k3=(2.13+/-0.08)x10(3) M(-1) s(-1) and k4=(1.01+/-0.06)x10(4) M(-1) s(-1) (k2 is insignificant in the fitting). All three terms in the rate law are assigned to rate-limiting electron-transfer reactions in which various thiolate forms of cysteine are reactive. Applying Marcus theory, the self-exchange rate constant of the *SCH2CH(NH2)CO2-/-SCH2CH(NH2)CO2- redox couple was obtained from the oxidation of L-cysteine by [Fe(bpy)(CN)4]-, with k11=4x10(5) M(-1) s(-1). The self-exchange rate constant of the *SCH2CH(NH3+)CO2-/-SCH2CH(NH3+)CO2- redox couple was similarly obtained from the rates with both Fe(III) oxidants, a value of 6x10(6) M(-1) s(-1) for k11 being derived. Both self-exchange rate constants are quite large as is to be expected from the minimal rearrangement that follows conversion of a thiolate to a thiyl radical, and the somewhat lower self-exchange rate constant for the dianionic form of cysteine is ascribed to electrostatic repulsion.     

Fragmentation mechanisms of protonated benzylamines. Electrospray ionisation-tandem mass spectrometry study and ab initio molecular orbital calculations

Our research into neurotransmitters in a biological fluid presented an opportunity to investigate the fragmentations under low collision energy characterising benzyl-amines protonated under electrospray ionisation (ESI) conditions in a triple quadrupole mass spectrometer. In this work we present the breakdown graphs of protonated 3,4-dihydroxybenzylamine, DHBAH(+), and 3-methoxy, 4-hydroxybenzylamine, HMBAH(+), at various source temperatures and various pressures in the collision cell, the collision energy varying from 0 to 46 eV in the laboratory frame. Both parent ions eliminate first NH(3) at very low collision energy. The fragmentations of [MH - NH(3)](+) occur at high collision energy and are quite different for DHBAH(+) and HMBAH(+): formation of [MH - NH(3) - H(2)O - CO](+) for the former; formation of the radical cation [MH - NH(3) - CH(3)](+.) for the latter. These fragmentations are interpreted by means of ab initio calculations up to the B3LYP/6-311+G(2d,2p) level of theory. The successive losses of H(2)O and CO involve first the rearrangement in two steps of benzylic ions formed by loss of NH(3) into tropylium ions. The transition states associated with this rearrangement are very high in energy (about 400 kJ mol(-1) above MH(+)) explaining (i). the absence of an ion corresponding to [DHBAH - NH(3) - H(2)O](+). The determining steps associated with the losses of H(2)O and with H(2)O + CO are located lower in energy than the transition states associated with the isomerisation of benzylic ions into tropylium ions; explaining (ii). the formation of the radical cation [MH - NH(3) - CH(3)](+.). The homolytic cleavage of CH(3)-O requires less energy than does the rearrangement.     

Atmospheric pressure ionization mass spectrometry of purine and pyrimidine markers of inherited metabolic disorders

Purines and pyrimidines are of interest owing to their significance in processes in living organisms. Mass spectrometry is a promising analytical tool utilized in their analysis. Two atmospheric pressure ionization (API) methods (electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI)) in both negative and positive modes applied to selected purine and pyrimidine metabolites (markers of inherited metabolic disorders) were studied. APCI is less sensitive to alkali metal cations present in a sample and offers higher response than ESI for studied compounds. Both of the techniques afford quasi-molecular ions, but fragmentation also occurs to a certain extent. However, the application of collision-induced dissociation of quasi-molecular ions is essential to confirm a certain metabolite in a sample. Fragmentation of both positive and negative ions was evaluated using multi-stage mass spectrometric experiments. Typical neutral losses correspond to molecules NH(3), H(2)O, HCN, CO, H(2)NCN, HNCO and CO(2). The ion [NCO](-) arises in the negative mode. The cleavage of the glycosidic C-N bond is characteristic for relevant metabolites. Other neutral losses (CH(2)O, C(2)H(4)O(2) and C(3)H(6)O(3)) originate from fragmentation of the glycosidic part of the molecules. In addition to fragmentation, the formation of adducts of some ions with applied solvents (H(2)O, CH(3)OH) was observed. The composition of the solution infused into the ion source affects the appearance of the mass spectra. Tandem mass spectra allow one to distinguish compounds with the same molecular mass (uridine-pseudouridine and adenosine-2'-deoxyguanosine). Flow injection analysis APCI-MS/MS was tested on model samples of human urines corresponding to adenosine deaminase deficiency and xanthine oxidase deficiency. In both cases, the results showed potential diagnostic usefulness.     

Mobile phase variations in thermospray liquid chromatography-mass spectrometry of pesticides

The effect of four different mobile phase compositions with reversed-phase methanol-water (50:50) + 0.05 M ammonium acetate, methanol-water (50:50) + 0.05 M ammonium formate, acetonitrile-water (50:50) + 0.05 M ammonium acetate and acetonitrile-water (50:50) + 0.05 M ammonium formate were compared in filament-on thermospray liquid chromatography-mass spectrometry for the determination of carbamate and chlorotriazine pesticides. In the positive-ion mode, [M + H]+ and [M + NH4]+ were generally the base peaks for the chlorotriazines and the carbamates, respectively. Depending on the mobile phase used, other adduct ions obtained corresponded to [M + CH3CN + H]+, [M + CH3OH + NH4]+, [M + CH3COONH4 + NH4 - 2H2O]+, [M + CH3CN + NH4]+, [M + CH3COONH4 + H - H2O]+ and the dimer [2M + H]+. In the negative-ion mode, [M - H]- and adducts with the ionizing additive [M + CH3COO]- or [M + HCOO]- were obtained. Other ions for the carbamates carbaryl and oxamyl corresponded to [M - CONHCH3 + CH3COOH]- and [M - CON(CH3)2 + HCOO]-, respectively. The variation of mobile phase composition provides additional structural information in thermospray liquid chromatography-mass spectrometry with no appreciable loss of sensitivity. Applications are reported for the determination of carbamate and chlorotriazine pesticides at the ng/g level in spiked and real soil samples, respectively.     

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 microg/L. The surface waters of different lakes and tanks of Hyderabad, India were found to contain a few antibiotics.     

Analytical application of acetate anion in negative electrospray ionization mass spectrometry for the analysis of triterpenoid saponins--ginsenosides

Ginsenosides containing different numbers of glycosyl groups can be easily differentiated based on the formation of characteristic ginsenoside-acetate adduct anions and deprotonated ginsenosides generated by electrospray ionization (ESI) of methanolic solutions of ginsenosides (M) and ammonium acetate (NH4OAc). Ginsenosides containing two glycosyl groups gave a characteristic mass spectral pattern consisting of [M+2OAc]2-, [M-H+OAc]2- and [M-2H]2- ions with m/z values differing by 30 Th, while this mass spectral pattern was not observed for ginsenosides containing one glycosyl group. Formation of [M+2OAc]2- was influenced by the chain length of glycosyl groups and was used to differentiate the ginsenosides containing different combinations of monosaccharide and disaccharide units in the glycosyl groups. Under identical collisional activation conditions, [M+OAc]-, [M-H+OAc]2- and [M+2OAc]2- underwent proton abstractions predominantly to generate [M-H]-, [M-2H]2- and [M-H+OAc]2- ions, respectively. The ion intensity ratios, I[M-H](-/I) [M+OAc]-, I[M-2H](2-/I) [M-H+2OAc]2- and I[M-H+OAc](2-/I) [M+OAc]2-, being sensitive to the structural differences of ginsenosides, could differentiate the isomeric ginsenosides, including (i) Rf, F11 and Rg1, (ii) Rd and Re, and (iii) Rb2 and Rc. Additionally, NH4OAc was found to enhance the sensitivity of detection of ginsenosides in the form of [M-H]- down to the femtomole level.     

Binding of DNA purine sites to dirhodium compounds probed by mass spectrometry

The adducts formed between the antitumor active compounds [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2), Rh(2)(O(2)CCH(3))(4), and Rh(2)(O(2)CCF(3))(4) with DNA oligonucleotides have been assessed by matrix-assisted laser desorption ionization (MALDI) and nanoelectrospray (nanoESI) coupled to time-of-flight mass spectrometry (TOF MS). A series of MALDI studies performed on dipurine (AA, AG, GA, and GG)-containing single-stranded oligonucleotides of different lengths (tetra- to dodecamers) led to the establishment of the relative reactivity cis-[Pt(NH(3))(2)(OH(2))(2)](2+) (activated cisplatin) approximately Rh(2)(O(2)CCF(3))(4) > cis-[Pt(NH(3))(2)Cl(2)] (cisplatin) > [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2) > Rh(2)(O(2)CCH(3))(4) approximately Pt(C(6)H(6)O(4))(NH(3))(2) (carboplatin). The relative reactivity of the complexes is associated with the lability of the leaving groups. The general trend is that an increase in the length of the oligonucleotide leads to enhanced reactivity for Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2) and Rh(2)(O(2)CCH(3))(4) (except for the case of [Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](2+), which reacts faster with the GG octamers than with the dodecamers), whereas the reactivity of Rh(2)(O(2)CCF(3))(4) is independent of the oligonucleotide length. When monitored by ESI, the dodecamers containing GG react faster than the respectiveAA oligonucleotides in reactions with Rh(2)(O(2)CCF(3))(4) and Rh(2)(O(2)CCH(3))(2)(CH(3)CN)(6)](BF(4))(2), whereas AA oligonucleotides react faster with Rh(2)(O(2)CCH(3))(4). The mixed (AG, GA) purine sequences exhibit comparable rates of reactivity with the homopurine (AA, GG) dodecamers in reactions with Rh(2)(O(2)CCH(3))(4). The observation of initial dirhodium-DNA adducts with weak axial (ax) interactions, followed by rearrangement to more stable equatorial (eq) adducts, was achieved by electrospray ionization; the Rh-Rh bond as well as coordinated acetate or acetonitrile ligands remain intact in these dirhodium-DNA adducts. MALDI in-source decay (ISD), collision-induced dissociation (CID) MS-MS, and enzymatic digestion studies followed by MALDI and ESI MS reveal that, in the dirhodium compounds studied, the purine sites of the DNA oligonucleotides interact with the dirhodium core. Ultimately, both MALDI and ESI MS proved to be complementary, valuable tools for probing the identity and stability of dinuclear metal-DNA adducts.     

Differentiation of isomeric 2-aryldimethyltetrahydro-5-quinolinones by electron ionization and electrospray ionization mass spectrometry

A series of isomeric 2-aryl-6,6-dimethyltetrahydro-5-quinolinones (set I) and 2-aryl-7,7-dimethyltetrahydro-5-quinolinones (set II) were studied under positive ion electron ionization (EI) and electrospray ionization (ESI) techniques. Under EI conditions, the molecular ions were found to be less stable in set I isomers, and they resulted in abundant fragment ions, i.e., [M-CH(3)](+), [M-CO](+.), [M-HCO](+), [M-(CH(3),CO)](+), and [M-(CH(3),CH(2)O)](+), when compared with set II isomers. In addition, the set I isomers showed specific fragment ions corresponding to [M-OH](+) and [M-OCH(3)](+). The retro-Diels-Alder (RDA) product ion was always higher in set II isomers. The ESI mass spectra produced [M + H](+) ions, and their decomposition showed favorable loss of CH(3) radical, CH(4) and C(2)H(6) molecules in set I isomers. The set II isomers, however, showed predominant RDA product ions, and specific loss of H(2)O. The selectivity in EI and ESI was attributed to the instability of set I isomers by the presence of a gem-dimethyl group at the α-position, and it was supported by the data from model compounds without a gem-dimethyl group. Density functional theory (DFT) calculations successfully corroborated the fragmentation pathways for diagnostic ions. This study revealed the effect of a gem-dimethyl group located at the α-position to the carbonyl having aromatic/unsaturated carbon on the other side of the carbonyl group.     

Protonation-induced paramagnetism. Structures and stabilities of six- and seven-coordinate complexes of Os(II) in singlet and triplet states: a density functional study

Li, Yeh, and Taube in 1993 (J. Am. Chem. Soc. 1993, 115, 10384) synthesized a number of complexes which can be formally regarded as protonated Os(II) species. Some of these were paramagnetic, in contrast to the diamagnetism of the closed shell 5d(6) Os(II) ions. This intriguing phenomenon is investigated theoretically using density functional theory. The geometries, stabilities, and electronic structures of a series of six- and seven-coordinate osmium complexes were studied in gas phase and aqueous solution using the B3P86 functional, in conjunction with the isodensity-polarized continuum model of solvation. The general formula for these complexes is [Os(NH(3))(4)H(L(1)(x)())(m)()(L(2)(y)())(n)()](()(x)()(+)(y)()(+3)+), where L(1) and L(2) = H(2)O, NH(3), CH(3)OH, CH(3)CN, Cl(-), and CN(-), which could be regarded as protonated Os(II) species or hydrides of Os(IV), although according to this work the osmium-hydrogen interaction is best described as a covalent Os(III)-H bond, in which the hydrogen is near-neutral. The ground states are generally found to be singlets, with low-lying triplet excited states. Solvation tends to favor the singlet states by as much as approximately 18 kcal mol(-)(1) in the 3+ ions, an effect which is proportional to the corresponding difference in molecular volumes. To have realistic estimates of the importance of spin-orbit coupling in these systems, the spin-orbit energy corrections were computed for triplet [Os(NH(3))(4)](2+), [Os(NH(3))(4)H](3+), and [Os(NH(3))(4)H(H(2)O)](3+), along with gas-phase Os and its ions as well as [Os(H(2)O)(6)](3+). The seven-coordinate triplet-state complex [Os(NH(3))(5)H(CH(3)OH)](3+), which had been successfully isolated by Li, Yeh, and Taube, is predicted to be a stable six-coordinate complex which strongly binds to a methanol molecule in the second coordination shell. The calculations further suggest that the singlet-triplet splitting would be very small, a few kilocalories per mole at most. The geometries and the electronic structures of the complexes are interpreted and rationalized in terms of Pauling's hybridization model in conjunction with conventional ligand field theory that effectively precludes the existence of true seven-coordinate triplet-state complexes of the above formula.     

ESI／MS of N-（O, O-Diisopropyl） Phosphoryl Aromatic Amino Acids and their Stability Investigation Using HPLC／UV／ESI／MS

The full scan ESI/MS and ESI/MS^2 of N-(O, O-diisopropyl) phosphoryl aromatic amino acids (DIPPAAAs), N-(O, O-diisopropyl) phosphoryl phenylalanine, N-(O, O-diisopropyl)phosphoryl tryptophan and N-(O, O-diisopropyl) phosphoryl tyrosine, were obtained. The specific ions for them were found. Their stability in the LC mobile phase was investigated using developed HPLC/UV/ESI/MS and the results demonstrated that the DIPPAAAs were stable in the mobile phase (5 mmol/L NH4Ac-MeCN (80:20,v/v, pH7.5) within 48 h.     

Disproportionation of O-methylhydroxylamine catalyzed by aquapentacyanoferrate(II)

The aquapentacyanoferrate(II) ion, [Fe(II)(CN)(5)H(2)O](3-), catalyzes the disproportionation reaction of O-methylhydroxylamine, NH(2)OCH(3), with stoichiometry 3NH(2)OCH(3) → NH(3) + N(2) + 3CH(3)OH. Kinetic and spectroscopic evidence support an initial N coordination of NH(2)OCH(3) to [Fe(II)(CN)(5)H(2)O](3-) followed by a homolytic scission leading to radicals [Fe(II)(CN)(5)(?)NH(2)](3-) (a precursor of Fe(III) centers and bound NH(3)) and free methoxyl, CH(3)O(?), thus establishing a radical path leading to N-methoxyamino ((?)NHOCH(3)) and 1,2-dimethoxyhydrazine, (NHOCH(3))(2). The latter species is moderately stable and proposed to be the precursor of N(2) and most of the generated CH(3)OH. Intermediate [Fe(III)(CN)(5)L](2-) complexes (L = NH(3), H(2)O) form dinuclear cyano-bridged mixed-valent species, affording a catalytic substitution of the L ligands promoted by [Fe(II)(CN)(5)L](3-). Free or bound NH(2)OCH(3) may act as reductants of [Fe(III)(CN)(5)L](2-), thus regenerating active sites. At increasing concentrations of NH(2)OCH(3) a coordinated diazene species emerges, [Fe(II)(CN)(5)N(2)H(2)](3-), which is consumed by the oxidizing CH(3)O(?), giving N(2) and CH(3)OH. Another side reaction forms [Fe(II)(CN)(5)N(O)CH(3)](3-), an intermediate containing the nitrosomethane ligand, which is further oxidized to the nitroprusside ion, [Fe(II)(CN)(5)NO](2-). The latter is a final oxidation product with a significant conversion of the initial [Fe(II)(CN)(5)H(2)O](3-) complex. The side reaction partially blocks the Fe(II)-aqua active site, though complete inhibition is not achieved because the radical path evolves faster than the formation rates of the Fe(II)-NO(+) bonds.     

High-performance liquid chromatography-electrospray ionization-mass spectrometric determination of emedastine difumarate in human plasma and its pharmacokinetics

A selective and sensitive method employing high-performance liquid chromatography (HPLC)-electrospray ionization (ESI)-mass spectrometry is developed and validated for the determination of emedastine difumarate in human plasma. With naphazoline hydrochloride as the internal standard, emedastine difumarate is extracted from plasma with ethyl acetate. The organic layer is evaporated, and the residue is redissolved in the mobile phase. An aliquot of 10 microL is chromatographically analyzed on a prepacked Phenomenex Luna 5u CN 100A (150 x 2.0-mm i.d.) column, using a mobile phase comprised of methanol-water (20 mM CH(3)COONH(4), pH 4.0) (80:20, v/v). Standard curves are linear (r(2) = 0.9990) over the concentration range of 0.05-30 ng/mL and had good accuracy and precision. The within- and between-batch precisions did not exceed 15% for the relative standard deviation. The lower limit of detection is 0.01 ng/mL. The validated HPLC-ESI-MS method is successfully used to study emedastine difumarate pharmacokinetics in 12 healthy volunteers.     

Development of FIA equipped with a chemiluminescence detector using a mixed reagent of luminol and 1,10-phenanthroline.

We developed an FIA system equipped with a chemiluminescence detector using a mixed chemiluminescence reagent of luminol and 1,10-phenanthroline for the detection of metal ions and metal complexes. The carrier, mixed chemiluminescence reagent comprising luminol, 1,10-phenanthroline, and cethyltrimethylammonium bromide, and H2O2 solutions were fed by corresponding pumps at a definite flow rate. Sample solutions dissolving hematin, [Co(NH3)4(H2O)2]2(SO4)3, CuSO4, NiCl2, K3[Fe(CN)6], and K4[Fe(CN)6] were analyzed as models by the means of the present FIA system. Solutions of hematin, [Co(NH3)4(H2O)2]2(SO4)3, CuSO4, and NiCl2 were detected as positive peaks, as usual. The order of the catalytic activity of these samples for the present chemiluminescence reaction using the mixed chemiluminescence reagent was [Co(NH3)4(H2O)2]2(SO4)3 > hematin > CuSO4 > NiCl2. On the other hand, sample solutions of K3[Fe(CN)6] and K4[Fe(CN)6] were detected as negative peaks and were determined over the ranges of 1 x 10(-8) - 1 x 10(-6) M with a detection limit of 1 x 10(-8) M and 2 x 10(-8) - 4 x 10(-6) M with a detection limit of 2 x 10(-8) M, respectively. Their negative peaks were observed reproducibly with a relative standard deviation of 2 - 5%.     

New structural features of unsupported chains of metal ions in luminescent [(NH3)4Pt][Au(CN)2]2 x 1.5(H2O) and related salts

Luminescent [(NH(3))(4)Pt][Au(CN)(2)](2).1.5(H(2)O), which forms from aqueous solutions of [(NH(3))(4)Pt]Cl(2) and K[Au(CN)(2)], crystallizes with extended chains of the two ions with multiple close Pt...Au (3.2804(4) and 3.2794(4) A) and Au...Au (3.2902(5), 3.3312(5), and 3.1902(4) A) contacts. Nonluminescent [(NH(3))(4)Pt][Ag(CN)(2)](2).1.4(H(2)O) is isostructural with [(NH(3))(4)Pt][Au(CN)(2)](2).1.5(H(2)O). Treatment of [(NH(3))(6)Ni]Cl(2) with K[Au(CN)(2)] forms [(NH(3))(2)Ni][Au(CN)(2)](2) in which the [Au(CN)(2)](-) ions function as nitrile ligands toward nickel, which assumes a six-coordinate structure with trans NH(3) ligands. The [Au(CN)(2)](-) ions self-associate into linear columns with close Au...Au contacts of 3.0830(5) A, and pairs of gold ions in these chains make additional but longer (3.4246(5) A) contacts with other gold ions.