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Brevetoxins are a group of natural neurotoxins characterized by polyether ring systems that are found in the blooms of red tide algae. In a conventional water/organic solvent system, without any other additives, deprotonated molecules of brevetoxins do not appear in high abundance in negative mode electrospray mass spectrometry (ES-MS) due to lack of acidic functional groups; thus, they are not well-suited for collision-induced decomposition (CID) experiments in negative mode electrospray. In this study, several anions were tested for their abilities to form anionic adducts by mixing ammonium salts of these anions with brevetoxin-2 and brevetoxin-3. Under CID, [[M + Cl].sup.-], [[M + Br].sup.-], [[M + OAc].sup.-], [[M + HCOO].sup.-], and [[M + N[O.sub.3]].sup.-] adducts all produced only the respective anions in CID experiments and thus provided no structural information. In contrast, upon CID, both [[M + F].sup.-] and [[M + HC[O.sub.3]].sup.-] precursor adducts gave structurally informative fragment peaks that exhibited similarities to those of [[M - H].sup.-] ions, which indicated that the first step in gas-phase decomposition of these anionic adducts was loss of neutral HF or [H.sub.2]C[O.sub.3] molecules, respectively, leaving deprotonated brevetoxin ([[M - H].sup.-]) to undergo consecutive fragmentations. In comparison to bicarbonate, fluoride formed adducts in higher abundance and provided more fragment peaks, thus more structural information, in MS/MS experiments. It is therefore the anion of choice to study brevetoxins in negative mode electrospray mass spectrometry using the anion attachment approach. The detailed fragmentation mechanisms are discussed, and diagnostic product ions are proposed for the brevetoxin-2 side chain (m/z 95, 133, and 151), the brevetoxin-3 side chain (m/z 97, 135, and 153), and the type-B brevetoxin backbone (m/z 725, 739, 741, and 797). To test the developed methodology, a sample of brevetoxin-2 subjected to in vitro microsomal incubation was analyzed, and a reduction product of the substrate was confirmed to have the structure of brevetoxin-3. 10.1021/ac901341c

The effect of ambient gas on potentials inside the electrospray (ES) capillary was investigated. Potential measurements and differential electrospray emitter potential (DEEP) maps were obtained with the help of a small, movable, disklike platinum wire electrode inserted into the ES capillary. Typical solvents used for electrospray mass spectrometry such as methanol and mixtures of methanol-water and chloroform/methanol have been tested. It was found that oxygen is readily adsorbed from the surrounding ambient gas into the spraying liquid. Following adsorption, it resides in, or near to, the Taylor cone, thereby affecting the electrochemical potential near the ES capillary exit, as well as the character of the inherent electrochemical reactions occurring during the ES process. The potentials measured in an air environment with reactive oxygen present are contrasted against those obtained in an inert nitrogen environment. The kinetics of oxygen admission have been found to be quite fast, i.e., occurring in a matter of seconds, but it takes far longer to purge the system of oxygen by changing the ambient atmosphere to nitrogen. The oxygen effect is present in negative and positive ion modes of ES, but the total ES current is not affected by the change of ambient gas. The magnitude of the oxygen effect owing to ambient air was compared to the effect caused by initially dissolving oxygen in the solution prior to the start of ES; it was found that the presence of oxygen in the ambient gas has a far greater consequence. These results indicate that the presence of reactive gases, such as molecular oxygen, in the region of the ES emitter may have unintended secondary effects on the ES process prior to mass spectrometric analysis.

When targeting a certain class of analytes, such as the phosphorylated lipids in complex biological extracts, interfering species can pose challenges to qualitative and quantitative analyses. Two aspects of lipid analysis were optimized to simplify the isolation and characterization of phosphorylated lipids in biological extracts. A new solid ionic crystal MALDI matrix was synthesized which combined the lipid response enhancing UV-absorber p-nitro-aniline with the protonating agent butyric acid. Mass spectra of the extracts containing phosphorylated lipids were simplified by revealing only protonated molecules [[M + H].sup.+] of the zwitterionic phosphatidylcholine (PC) headgroup-containing lipids, such as lyso-PC, PC, and platelet-activating factor. For the anionic phosphorylated lipids, such as phosphatidylgiycerol, phosphatidic acid, and phosphatidylserine, further spectrum simplification is obtained by the appearance of only the monosodium adducts [[M + Na].sup.+] as the major molecular ions, in preference to the double sodium adducts [[M + 2Na -H].sup.+]. In addition, a new extraction, isolation, and cleanup procedure has been developed to prepare the phosphorylated lipids for MALDI-TOF analysis by the use of immobilized metal ion affinity chromatography media (i.e., ZipTip). The latter procedure was successfully applied to a complex biological tear film lipid layer extract in preparation for MALDI-TOF analysis and phospholipid characterization.

A new approach for calculating bond dissociation energies (BDEs) from ES-MS/MS measurements has been developed. The new method features a 'derived effective reaction path length' that has been applied to measure BDEs of alkali metal (L[i.sup.+]) adducts and halide (C[l.sup.-]) adducts of monoacylglycerol, 1,2-diacylglycerol, and 1,3-diacylglycerol lipids. Also studied were lithium-bound dimers of monoacylglycerols, 1,2-diacylglycerols, and 1,3-diacylglycerols. BDEs for the adducts and dimers of the lipids were derived from collision-induced dissociation experiments using a triple quadrupole mass spectrometer with electrospray as the ionization source. Mass spectral data were used to empirically derive a single-exponential growth equation that relates product cross section to collision energy. From these single-exponential equations, a general second-order polynomial was derived using a multivariate growth curve model that enables prediction of BDEs of unknown complexes. Mass spectral results were compared to computer-generated bond dissociation energies using Becke-style three-parameter density functional theory (B3LYP, employing the Lee--Yang--Parr correlation functional), with excellent agreement between experimental and theoretical energy values. The newly developed method is general in nature and can be used for the measurement of metal or halide ionic adduct bond dissociation energies and for the measurement of bond energies of noncovalent interactions such as dimer dissociation energies. The validity of the method has been rigorously established using a triple quadrupole, but it may also be applied to other mass spectrometers that allow user control of the collision cell potential.

Viral infections are propagated by the fusing of the viral membrane with a host cell membrane. Initiation of the fusion process occurs upon perturbation of the membrane of the cell under attack by a subunit of the viral protein known as a fusion peptide. Fusion peptides must insert into the lipid-rich host cell membrane to initiate rupture and merging of the two entities, but much remains unknown about the details of the fusion process. We present detailed electrospray mass spectrometry studies of binding specificities of model fusion peptides P294 and P326 with cell membrane phospholipids, i.e., phosphatidylcholines (PCs, such as 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) and phosphatidylglycerols (PGs, such as 1,2-dimyristoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DMPG)). The fusion peptides clearly bind more strongly to negatively charged DMPG than to zwitterionic DMPC. Detected binding between P294/P326 and PC/ PG in 100% aqueous solution was disrupted by addition of methanol, which is known to weaken hydrophobic interactions; a higher percentage of methanol was needed to destroy a stronger initial binding. Further increases in the methanol volume fraction generally resulted in a reappearance of peptide--lipid binding, with binding strength quotients of 1,2-dilauroyl-sn-giycero-3-phosphocholine (DLPC)/1,2-dilauroyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DLPG)--peptide complexes rising more steeply than those of DMPC/DMPG--peptide complexes. Compared to fusion peptides P294 and P326, a hydrophilic peptide, fibrinopeptide B, showed much weaker affinity for zwitterionic DMPC, but had moderate binding affinity to negatively charged DMPG in 100% aqueous solutions. However, upon progressive addition of methanol, this hydrophilic peptide showed only a minor initial decrease in binding to DMPG before the detected binding eventually increased. These results contrast with those obtained for the hydrophobic peptides, and offer corroborative evidence that hydrophobic interactions play a key role in the mass spectrometrically observed binding between fusion peptides and phospholipids. Because the rate of viral infection has been found to be pH-dependent, the effect of initial solution pH on peptide--lipid binding was also studied. As the pH was lowered, P326--DMPC binding had a steep and immediate weakening, whereas the P294--DMPC binding was slightly strengthened at pH 3.7 and then gradually weakened with a further decrease in pH. Both P326 and P294 exhibited affinities toward unsaturated lipids; (18:1) PC bound slightly more strongly to P294 than (18:3) PC. These experiments offer further evidence of the ability of electrospray mass spectrometry to provide binding information concerning noncovalent interactions that were established principally by the hydrophobic effect in solution.

A novel electrochemical probe has been designed, built, and used to characterize the distribution in solution potential within the metal capillary and Taylor cone of the electrospray (ES) device. The measurement system consists of three electrodes--a counter electrode held at highly negative potential that serves as the cathode, and two anodes consisting of a disk-shaped, mobile, internal (working) electrode, and the internal surface of the surrounding ES capillary (auxiliary electrode, held at ground potential). One-dimensional differential electrospray emitter potential (DEEP) maps detailing solution potential gradients within the electrospray emitter and in the region of the Taylor cone are constructed by measuring the potential at the working electrode vs the ES capillary, as a function of working electrode position along the emitter axis. Results show that the measured potential difference increases as the internal probe travels toward the ES capillary exit, with values rising sharply as the base of the Taylor cone is penetrated. Higher conductivity solutions exhibit potentials of higher magnitude at longer distances away from the counter electrode, but these same solutions show lower potentials near the ES capillary exit. Removal of easily oxidizable species from the solution causes the measured potential difference to have nonzero values at distances further within the capillary, and the values measured at all points are raised. Results are consistent with the characterization of the electrospray system as a controlled-current electrolytic flow cell. Elucidation of the electrochemical details of the electrospray process can lead to mass spectrometric signal enhancement of certain species present in the spraying liquid and also allow the detection of molecules that are usually not observable due to their low ionization efficiencies.

The influence of the diameter of the spray tip employed for nano-electrospray mass spectrometry (nano-ES-MS) upon mass spectral charge state distributions was investigated using angiotensin I ([M.sub.r] = 1296), insulin ([M.sub.r] = 5774), and ubiquitin ([M.sub.r] = 8560) as test analytes. Under a variety of experimental conditions, the charge state distributions of the test peptides and protein consistently shifted toward higher values as the tip orifice diameter decreased. This finding indicates that the use of narrow diameter capillaries can promote the formation of higher charge state ions that are more reactive precursors in tandem mass spectrometry experiments. A detailed comparison of charge state distributions obtained for nanospray capillaries of varying diameters was undertaken while systematically varying experimental parameters such as sample flow rate, analyte concentration, solvent composition, and electrospray current. The general tendency to obtain higher charge states from narrow diameter capillaries was conserved throughout, but tips with smaller orifices were more sensitive to sample flow rate (the average charge state was lowered significantly as flow was raised), whereas tips with bigger orifices were more sensitive to analyte concentration and pH of the solution (as each was lowered, the average charge state increased).

The formation and decomposition (postsource decay, PSD) of anionic adducts in negative ion matrix-assisted laser desorption/ionization (MALDI) time-of-flight mass spectrometry have been studied. Chloride, a small inorganic anion, has been found to form stable anionic adducts with a variety of neutral oligosaccharides that can survive the MALDI process to give readily identifiable signals (with characteristic isotope patterns) allowing subpicomole detection in the best cases. The matrixes that can aid the formation of chloride adducts of oligosaccharides have gas-phase acidities lower than or close to that of HCl (1373 kJ/mol). In PSD experiments, precursor chloride adducts of oligosaccharides yield fragment ions that retain the charge on the sugar molecule rather than solely forming [Cl.sup.-], and these fragments can provide structurally informative product ions. In negative ion MALDI, highly acidic oligosaccharides do not form adducts with chloride anions, but mildly acidic saccharides (e.g., containing a carboxylic acid group) form both deprotonated molecules and chloride adducts, and each may provide structural information concerning the oligosaccharide upon decomposition.

Attachment of small anions to neutral molecules is an important ionization mechanism in negative ion electrospray mass spectrometry. In this report, the tendency for different anions to remain attached to selected analyte compound classes has been systematically investigated. A rationale for the formation and stability of preferred anionic adducts is proposed in light of thermodynamic considerations. A series of collision-induced dissociation experiments reveals that the gas-phase basicities of the deprotonated analyte molecule ([[M - H].sup.-]) and the anion moiety play important roles in determining the stability of anionic adducts. Adducts of the form [[M - H].sup.-] ... [H.sup.+] ... [[anion].sup.-] manifest increased stability when the two anions have similar gas-phase basicities. Within certain limitations, the difference in [DELTA] G [degrees] values for proton combination with [[M - H].sup.-] and with [[anion].sup.-] can be used as a first-order predictor of adduct stability. In addition, stability increases with the rising gas-phase basicities of the two moieties. The specific interaction between a small inorganic anion (bisulfate) and a neutral analyte molecule ([alpha]-D-glucose) in the form of multiple hydrogen bonding has also been affirmed by computer modeling to contribute to the stability of some anionic adducts. Last, the gas-phase basicity of deprotonated [alpha]-D-glucose (i.e., the gas-phase acidity of [alpha]-D-glucose) is determined by a 'bracketing method' to be in the range of 1373-1407 kJ/mol.

Brevetoxins, the toxic components of 'red tide' algae, all share one of two robust polycyclic ether backbone structures, but they are distinguished by differing side-chain substituents. Electrospray ionization mass spectrometry analyses of brevetoxins have shown that the polyether structure invariably has a very high affinity for sodium cations that results in the production of abundant (M + Na)(super +) ions even when sodium cations are only present as impurities. Because the ionic charge tends to remain localized on the sodium atom and because at least two bonds must be broken in order to produce polycyclic backbone fragmentation, it is extremely difficult to obtain abundant product ions (other than Na(super +)) from (M + Na)(super +) brevetoxin precursor ions in low-energy collision-induced dissociation (CID) MS/MS experiments. This report establishes that acid additives (oxalic acid, trifluoroacetic acid, and particularly hydrochloric acid) in aqueous methanol solutions can promote high yields of protonated brevetoxin molecules (MH(super +) ions) for Btx-1, -2, and -9 brevetoxins. Most importantly, unlike their (M + Na)(super +) counterparts, MH(super +) precursor ions offer readily detectable product ions in CID MS/MS experiments, even under low-energy collisions. This direct structural characterization approach has provided decomposition information from brevetoxins that was previously inaccessible, including the identification of diagnostic product ions for 'type A' brevetoxins (m/z 611) and 'type B' brevetoxins (m/z 779, 473, 179) and characteristic ions for Btx-1 (m/z 221, 139), Btx-2 (m/z 153), and Btx-9 (m/z 157, 85). Precursor ion scans and constant neutral loss scans are proposed to enable screening of individual type A or type B brevetoxins present in naturally occurring mixtures.

Lipid material represents a potential interference for determination of nonpolar compounds (e.g., polycyclic aromatic hydrocarbons) in biological tissue samples. This study reports the development of a selective extraction method using supercritical C[O.sub.2] that allows the GC/MS quantitation of PAHs in the presence of a substantial lipid background. Selective extraction of PAHs relies upon addition of [C.sub.18] adsorbent beads to the initial sample slurry. The dried mixture, including [C.sub.18] adsorbent, is placed in the supercritical fluid extraction (SFE) chamber. During the SFE process, lipids are preferentially retained on the [C.sub.18] beads. This 'SFE plus [C.sub.18]' procedure was developed by first optimizing SFE conditions (100 [degrees] C, 350 bar) for recovery of PAH standards. PAHs containing added model lipid compounds (stearic acid and cholesterol) were then subjected to SFE plus [C.sub.18] treatment followed by GC/MS analysis. Using this approach, a recovery of 94-100% of PAHs was obtained while only 9-17% of the lipid material present was coextracted from the same test sample. The developed method is demonstrated to permit efficient recovery and detection of PAHs spiked into crab tissue, a matrix with a high lipid content.

The ability to observe abundant gas-phase metal cluster ions in electrospray ionization mass spectrometry (ESI-MS) is highly dependent on experimental conditions. Alkali halides (MX) and other alkali metal salts were used to investigate the formation of cluster ions in ESI-MS. All compounds were found to give cluster ions of the form [([M.sub.n - 1][X.sub.n]).sup.+] and [([M.sub.n][X.sub.n -]).sup.-], with only two alkali salts yielding doubly charged cluster ions. In homologous alkali halide series, the relative abundances of cluster ions increased with increasing size of either the cation (positive ion mode) or the anion (negative ion mode). Calculations using an electrostatic model show that the gas-phase stability of cluster ions is greater for smaller cations or anions when a fixed counterion is employed. This stability calculation goes in a direction just opposite to the trend in cluster ion abundances observed in ESI-MS. Studies of equimolar mixtures consisting of two alkali halides reveal two distinct trends. When the equimolar mixture was composed of differing ions that participate in the droplet charge excess with the same counterion, the less solvated ions were found to form more abundant cluster ions. When the ions participating in the charge excess were fixed, the preferred counterion in observed clusters was the one that is more solvated in solution and forms more stable clusters in the gas phase. These observations can be rationalized by an extended form of the charged residue model where the weakly solvated ions that are part of the charge excess are preferentially enriched in offspring droplets during uneven fission. By contrast, transfer of a particular counterion located in the bulk of the droplets to the offspring droplets is not disfavored when this counterion is strongly solvated.

A three-electrode electrochemical cell coupled to an electrospray (ES) mass spectrometer has been developed and employed for on-line linear sweep voltammetry-ES mass spectrometry and electrochemical reaction studies. Generated in this type of electrochemistry/mass spectrometry (EC/MS) experiment are ion abundance vs potential profiles that provide molecular weight and structural information pertaining to intermediates and products of anodic oxidation of diphenyl sulfide, anodic pyridation of 9,10-diphenylanthracene, and reduction of nitrobenzene. Anodic oxidation of diphenyl sulfide in methylene chloride media at the platinum electrode yielded diphenyl surfoxide and pseudodimer sulfonium ion along with products of further oxidation. The obtained ion abundance vs potential profiles offer additional evidence to corroborate previously proposed reaction mechanisms for pseudodimer sulfonium ion generation from diphenyl sulfide, as well as pyridine addition to DPA radical cation also in methylene chloride at the platinum electrode. From the latter experiment, a newly found reaction product, [[DPA(py) - H].sup.+], is reported. Despite the inherent tendency of ES devices to induce oxidation processes in the positive ion mode, intermediates and products of nitrobenzene reduction in nonaqueous and organic/water media were detected in both negative and positive ES modes.

A newly invented probe accessory for fast electrochemistry/electrospray mass spectrometry (EC/ESMS) is presented and evaluated. The device features a low-volume, three-electrode electrochemical cell which has been designed with a minimum distance between the working electrode and the 'Taylor cone' inherent to the electrospray process. This configuration limits the time between electrochemical generation of ions and mass spectrometric analysis to an absolute minimum. A fused-silica layer insulates the microcylinder working electrode from the sample solution until immediately prior to the electrospray region, postponing electrode processes until the last moment. The same fused-silica layer insulates the working electrode from the surrounding auxiliary electrode, a stainless steel capillary that also serves as the electrospray capillary. The performance and capabilities of the novel electrochemistry/electrospray mass spectrometry system have been evaluated using polycyclic aromatic hydrocarbons (PAHs) as test analytes. In the positive ion EC/ESMS mode, oxidized forms (one-electron removal) of PAHs are produced in high yield. The ability to analyze reaction products appearing subsequent to the initial oxidation is also demonstrated.

The effect of analyte concentrations upon charge state distributions in electrospray ionization mass spectrometry (ESMS) was investigated using four compounds which showed doubly charged and singly charged positive ions (gramicidin S, 4,4[prime]-bipiperidine), multiply charged negative ions (Trypan Blue), or doubly charged and singly charged negative ions (eosin Y) in ES mass spectra. For each of the above compounds, the charge associated with analyte molecules was calculated to increase in solution with increasing concentration, yet the analyte charge state distributions in ES mass spectra were observed to monotonically shift toward lower values. In order to rationalize these observations, we introduce the ratio N/[N.sub.o], the ratio of the number of excess charges on all droplets produced by electrospray (N) to the total number of analyte molecules in all droplets ([N.sub.o]). For each compound, the N/[N.sub.o] value decreases with increasing analyte concentration. The lower N/[N.sub.o] value is proposed to be an underlying factor critical to explaining the desorption of a higher proportion of gas-phase ions of lower charge state at elevated analyte concentrations. We propose that the lower N/[N.sub.o] value is indicative of a decreased efficiency of analyte charging and an increased level of ion pairing of charged analyte molecules with available counterions. Furthermore, in comparing N/[N.sub.o] values and observed analyte charge state distributions as functions of increasing analyte concentration, the decreasing N/[N.sub.o] ratio predicts a much greater extent of shifting of analyte charge states toward lower values than was observed. This implies that the actual degree of ion pairing in droplets was considerably alleviated as compared to that indicated by the calculated N/[N.sub.o] values. This finding conforms to a description of the ES process wherein uneven fission of droplets occurs at the Rayleigh limit, thereby generating offspring droplets of higher charge to mass ratio, hence an augmented N/[N.sub.o] value.

On-line high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESMS) has been successfully applied to the separation and identification of brevetoxins associated with 'red tide' algae. Brevetoxins are toxic polyethers produced by the marine dinoflagellate Gymnodinium breve. They are responsible for fish kills, and they pose certain health risks to humans. The LC-MS method employs reversed-phase microbore HPLC on a [C.sub.18] column with a mobile phase consisting of 85:15 methanol/water, a flow rate of 8 [[micro]Liter]/min, and a postcolumn split ratio of 3:1 (UV absorbance detector/mass spectrometer). A brevetoxin culture sample was found to contain at least six components, including two well-separated peaks corresponding to the brevetoxins PbTx-2 and PbTx-1, as well as several unknown compounds, including one with a molecular mass of 899 Da (possibly an isomer of PbTx-9). The brevetoxin molecules exhibited a high tendency to bind to alkali cations in positive ion ESMS. For standard PbTx-9, PbTx-2, and PbTx-1 brevetoxins analyzed on our LC-MS system, the detection limits (employing mass spectrometer scans of 100 m/z units) were determined to be less than 600 fmol, 1 pmol, and 50 fmol, respectively (S/N = 3); the total analysis time was about 35 min.

The variability of ESMS charge state distributions was investigated for a number of analytes when the ionic strength of their solutions was altered over a wide range. Solution ionic strength was adjusted by adding varying amounts of electrolytes (N[H.sub.4]OAc, CsCl, or [(n-[C.sub.4][H.sub.9]).sub.4]N+Cl-) to protein solutions of myoglobin and lysozyme. Measured solution pH values were found to be nearly constant over the entire range of CsCl and [(n-[C.sub.4][H.sub.9]).sub.4]N+Cl- addition, and a slight increase in pH was observed upon N[H.sub.4]OAc addition. Analyte peak intensities in positive ion ESMS reproducibly decreased as the solution ionic strength increased. However, analyte charge state distributions remained quite constant despite 4 orders of magnitude variation in electrolyte concentration. In negative ion ESMS of phenolphthalein diphosphate (free acid form) and eosin Y, analyte charge state distributions also exhibited only minor variations while signal intensity decreased dramatically with increasing solution ionic strength upon addition of CsCl. These observations in positive and negative ion ESMS provide evidence that 'spectator' electrolytes present in solution have no significant effect upon the degree of multiple charging. The factors which determine the distribution of multiply charged analyte ions in the gas phase are thus independent of certain others which influence the efficiency of production of gas-phase analyte ions. In the context of theoretical descriptions of the electrospray process, the rate constants for desorption of multiply charged ions into the gas phase described in ion evaporation theory are likely to be invariant with spectator electrolyte concentration. Alternatively, the presence of added ion pairs in the ultimate droplet produced according to single ion in a droplet theory does not alter the level of charge attachment/charge separation of analyte molecules.

Metallocenes, substituted metallocenes, and organometallic salts containing metal-carbon bonds have been investigated by electrospray mass spectrometry (ESMS). Organometallic salts yielded stable cations in high abundances; metallocenes appeared in the oxidized form (i.e., as bis(cyclopentadienyl) metal cations, Cp2M+). Identifications were confirmed by inspection of the natural isotope distribution patterns. ESMS response vs concentration (log-log) plots showed a linear range between 10 to the -9 and 10 to the -5 M for both Cp2Fe and (Cp2Fe)+(PF6)-. For solutions of equivalent concentration, however, the salt form always yielded a higher abundance of Cp2Fe+. Neutral metallocenes are ionized by an electrochemical oxidation (electron-removal) mechanism at or near the electrospray (ES) capillary (needle). Increasing electrospray appearance potentials for Cp2M+ (M = metal) formation correlated with increasing half-wave potentials for oxidation (E(sub 1/2)(ox)) and increasing ionization energies (IE) in the series: decamethylferrocene, 1,1 prime-dimethylferrocene, ferrocene, formylferrocene, carboxylferrocene, acetylferrocene, 1,1 prime-diacetylferrocene, osmocene, and ruthenocene. For osmocene (relatively high E(sub 1/2)-(ox) and IE), ESMS conditions were established whereby protonation was competitive with oxidation, thus creating two pathways of ion formation. In methylene chloride solvent, chloride ion was incorporated into the inner sphere of certain metallocenes subjected to ESMS, forming Cp2RuCl+ and Cp2-OsCl+ complexes via nucleophilic addition. These latter Ru-(IV) and OS(IV) species also formed analogous gas-phase complexes with trifluoroacetate ion and hydroxide ion. Results have been rationalized on the basis of ion stability considerations.

Surface-induced dissociation (SID) has been used to produce daughter ion spectra of small protonated peptides generated by fast atom bombardment (FAB). The relative abundances of daughter ions depends critically upon the energy of the ion/surface collision. A wide array of decomposition processes may be observed using E(sub LAB) collision energies in the range 10-20 eV. At approximately 13-eV collision energy, the variety of decomposition processes is maximized for the small peptides studied; hence, maximum structural information may be deduced. Collisionally-activated dissociations (CAD) using argon gas and the identical protonated peptides could not produce as large an array of daughter ions in a constant condition experiment. An apparent contradiction is thereby posed because SID is known to produce a narrow distribution of ion internal energies relative to CAD. This apparent contradiction is resolved by considering the rather large kinetic energy spread of ions leaving the FAB source. For the SID process, this large initial kinetic energy distribution is converted into a significantly wider spread in center-of-mass collision energy, leading to a broader variety of decomposition processes (high and low energy) compared to CAD.

The influence of the diameter of the spray tip employed for nano-electrospray mass spectrometry (nano-ES-MS) upon mass spectral charge state distributions was investigated using angiotensin I (M[SUBr] = 1296), insulin (M[SUBr] = 5774), and ubiquitin (M[SUBr] = 8560) as test analytes. Under a variety of experimental conditions, the charge state distributions of the test peptides and protein consistently shifted toward higher values as the tip orifice diameter decreased. This finding indicates that the use of narrow diameter capillaries can promote the formation of higher charge state ions that are more reactive precursors in tandem mass spectrometry experiments. A detailed comparison of charge state distributions obtained for nanospray capillaries of varying diameters was undertaken while systematically varying experimental parameters such as sample flow rate, analyte concentration, solvent composition, and electrospray current. The general tendency to obtain higher charge states from narrow diameter capillaries was conserved throughout, but tips with smaller orifices were more sensitive to sample flow rate (the average charge state was lowered significantly as flow was raised), whereas tips with bigger orifices were more sensitive to analyte concentration and pH of the solution (as each was lowered, the average charge state increased). [ABSTRACT FROM AUTHOR]

Examines the stabilization of anionic adducts in negative ion electrospray mass spectrometry. Indication of gas phase basicity; Mechanisms of ion formation; Stability of chloride and bromide adducts.

Focuses on the use of electrospray ionization tandem mass spectrometry (MS/MS) for the structural elucidation of protonated brevetoxins in red tide algae. Brevetoxin precursor ions observed in low-energy collision induced disassociation MS/MS experiments; Decomposition information from brevetoxins; Ability of precursor ions to screen individual brevetoxins.

Reports on the formation and decomposition of anionic adducts in negative ion matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Formation of stable anionic adducts with a variety of neutral oligosaccharides by chloride; Gas-phase acidities of the matrixes that can aid the formation of chloride adducts of oligosaccharides.

Viral infections are propagated by the fusing of the viral membrane with a host cell membrane. Initiation of the fusion process occurs upon perturbation of the membrane of the cell under attack by a subunit of the viral protein known as a fusion peptide. Fusion peptides must insert into the lipid-rich host cell membrane to initiate rupture and merging of the two entities, but much remains unknown about the details of the fusion process. We present detailed electrospray mass spectrometry studies of binding specificities of model fusion peptides P294 and P326 with cell membrane phospholipids, i.e., phosphalidylcholines (PCs, such as 1 ,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)) and phosphatidylglycerols (PGs, such as 1,2-dimyristoyl-sn-glycero-3-Ephospho-rac -(1-glycerol)] (DMPG)). The fusion peptides clearly bind more strongly to negatively charged DMPG than to zwitterionic DMPC. Detected binding between P294/P326 and PC/PG in 100% aqueous solution was disrupted by addition of methanol, which is known to weaken hydrophobic interactions; a higher percentage of methanol was needed to destroy a stronger initial binding. Further increases in the methanol volume fraction generally resulted in a reappearance of peptide-lipid binding, with binding strength quotients of 1,2-dilauroyl-sn-glycero-3-phospho-choline (DLPC)/1,2-dilauroyl-sn-glycero-3-[phospho-rac- (1-glycerol)] (DLPG)-peptide complexes rising more steeply than those of DMPC/DMPG-peptide complexes. Compared to fusion peptides P294 and P326, a hydrophilic peptide, fibrinopeptide B, showed much weaker affinity for zwitterionic DMPC, but had moderate binding affinity to negatively charged DMPG in 100% aqueous solutions. However, upon progressive addition of methanol, this hydrophilic peptide showed only a minor initial decrease in binding to DMPG before the detected binding eventually increased. These results contrast with those obtained for the hydrophobic peptides, and offer corroborative evidence that hydrophobic interactions play a key role in the mass spectrometrically observed binding between fusion peptides and phospholipids. Because the rate of viral infection has been found to be p11-dependent, the effect of initial solution pH on peptide-lipid binding was also studied. As the pH was lowered, P326-DMPC binding had a steep and immediate weakening, whereas the P294-DMPC binding was slightly strengthened at pH 3.7 and then gradually weakened with a further decrease in pH. Both P326 and P294 exhibited affinities toward unsaturated lipids; (18:1)PC bound slightly more strongly to P294 than (18:3)PC. These experiments offer further evidence of the ability of electrospray mass spectrometry to provide binding information concerning noncovalent interactions that were established principally by the hydrophobic effect in solution. [ABSTRACT FROM AUTHOR]

A charge detector has been constructed and mounted inside the vacuum housing of a commercial mass spectrometer (Micromass-Waters Quattro I, Waters Corp., Manchester, UK). The in-house built single-pass charge detector is composed of a designed, complete electronics system that includes a low-noise charge amplifier. Communication to the data acquisition system was enabled, and analog and digital filters were devised, followed by their tuning and programming. Data treatment scripts for data analysis and plotting were automated, and the assembled system was calibrated and tested. The instrument has an acquisition speed of ∼200 detection events/s, and it permits detection down to ∼510 charges (= three times RMS noise) for a single measured particle. The charge detector was employed to determine the oligomer distribution of a megadalton polymer, polyethylene glycol (PEG). The PEG size distribution exhibits a maximum at ∼ m / z 5910 with the oligomeric population mass distribution peaking near 4.45 MDa. In studies of methanol droplet dynamics, "charge vs time-of-flight" plots enabled clear visualization of the zone near the Rayleigh limit to droplet charging. The highest population of methanol droplets near the Rayleigh limit carried 5000-7000 charges. This corresponds to droplet weights of 10-20 GDa, with the high-end tail extending above 70 GDa. This visualization of the most highly charged droplets (that bear numbers of charges near those defined by the Rayleigh equation) was exploited as a calibration aid for our charge detector, which lacks a means of precisely defining ion energy. A maximum m / z error of -12.3% was calculated for the method, i.e., less than the potential error in assigning the true level of charging of the most highly charged droplets relative to the Rayleigh limit. With these limitations in mind, the introduced method will provide a new means for aiding the calibration of m / z values in charge detectors.