Water Adduct Formation Research Articles

Selected Ion Flow Tube – Mass Spectrometry (SIFT-MS) study of the reactions of H3O+, NO+ and O2+ with a range of oxygenated volatile organic carbons (OVOCs)

Selected Ion Flow Tube-Mass Spectrometry (SIFT-MS) uses soft chemical ionisation, typically by H3O+, NO+ and O2+, to analyse trace gases in real time at mixing ratios down to low parts per trillion by volume (pptv) and has recently been demonstrated as an effective method for monitoring volatile organic compounds (VOCs) in the atmosphere. SIFT-MS analysis requires accurate rate coefficient and product ion branching ratio data to allow for accurate mixing ratio calculations without the need for calibration standards. Most rate constant data have been measured using helium as the carrier gas. Here we report rate constants of a number of oxygenated volatile organic compounds (OVOCs) alongside benzene for H3O+, NO+ and O2+ reagent ions in nitrogen carrier gas, using a permeation tube calibration source and a certified gas standard to introduce known concentrations into the SIFT-MS. This includes the first reported literature rate constant for nonanal using SIFT-MS. We found that the rate constants for most compounds measured in nitrogen carrier gas were similar to those measured in helium. However, the NO+ rate constants for ketones measured in nitrogen were 1.2–5 times lower than those measured in helium. We observe higher fragmentation due to changes made to the lens voltages of the instrument in order to tune for higher sensitivity, altering the reagent ion energies. We also show the impact of increasing the flow tube temperature and voltage on the sensitivity and ionisation of benzene, butanone and butanal under both dry and humid conditions. Some of the SIFT-MS compound library entries are data from historic SIFT-MS instruments that lacked a heated flow tube, and therefore suffered from higher water clustering than current commercial SIFT-MS models. We show that a higher flow tube temperature reduces the amount of water adduct formation thereby simplifying compound concentration determination. These results demonstrate the need to ensure that the library data used are acquired under the same conditions as the experiment being performed.

Gas-Phase Chemistry in the GC Orbitrap Mass Spectrometer.

Gas-phase reactions of temporally stored ions play a significant role in trapped ion mass spectrometry. Especially highly labile ion species generated through electron ionization (EI) are prone to undergo gas-phase reactions after relaxation to a low vibrational state. Here, we show that in the C-Trap of the Q Exactive GC Orbitrap mass spectrometer, gaseous water reacts with radical cations of various compound classes. High-resolution accurate mass spectrometry of the resulting ions provides a key to the mechanistic understanding of the chemistry of high energetic species generated during EI. We systematically addressed water adduct formation by use of H2O and D218O in the C-Trap. Mass spectra of halogen cyanides XCN (X=Cl, Br, I) showed the formation of HXCN+ species, indicating hydrogen atomic transfer reactions. Relative ratios of HXCN+/XCN+• increased as the electronegativity of the halide increased. The common internal calibrant perfluorotributylamine forms oxygenated products from water reactive fragment ions. These can be explained by the addition of water to an initial cation followed by elimination of two HF molecules. This addition/elimination chemistry can also explain [M+2]+ and [M+3]+ ions that commonly occur in mass spectra of silylated analytes. High-resolution accurate mass spectra of trimethylsilyl (TMS) derivatives revealed these as [M-CH3•+H2O]+ and [M-CH4+H2O]•+, respectively. This study explains common fragment ions in ion trap mass spectrometry. It also opens up perspectives for the systematic mechanistic and kinetic investigation of high-energy ion reactivity. Graphical Abstract.

Quantitative Phase-Change Thermodynamics and Metastability of Perovskite-Phase Cesium Lead Iodide.

The perovskite phase of cesium lead iodide (α-CsPbI3 or "black" phase) possesses favorable optoelectronic properties for photovoltaic applications. However, the stable phase at room temperature is a nonfunctional "yellow" phase (δ-CsPbI3). Black-phase polycrystalline thin films are synthesized above 330 °C and rapidly quenched to room temperature, retaining their phase in a metastable state. Using differential scanning calorimetry, it is shown herein that the metastable state is maintained in the absence of moisture, up to a temperature of 100 °C, and a reversible phase-change enthalpy of 14.2 (±0.5) kJ/mol is observed. The presence of atmospheric moisture hastens the black-to-yellow conversion kinetics without significantly changing the enthalpy of the transition, indicating a catalytic effect, rather than a change in equilibrium due to water adduct formation. These results delineate the conditions for trapping the desired phase and highlight the significant magnitude of the entropic stabilization of this phase.

The nature of the styrylindolium dye: transformations among its monomer, aggregates and water adducts

The optical properties of styrylindolium dyes are strongly influenced by the external environment. After a detailed investigation by electronic absorption spectroscopy, we found that five states of 2-methoxylstyryl-indolium dye viz. monomer, D-aggregate, H-aggregate, J-aggregate and water adducts can be observed under different conditions. The spectroscopic studies revealed that the conversion rate of the dye among its monomer and the other aggregates is slow due to the steric hindrance of the 3,3-dimethyls. Meanwhile, it could form water adducts by the reaction of the water residue in solvent with the charged electron-deficient CN double bond of the dye. The formation of water adducts is also an important factor that influences the optical properties of the dye because the water addition reaction breaks the dye's π-conjugate. Generally, the dye exists mainly in the monomeric form in freshly prepared solutions. A small portion of the D-aggregate, H-aggregate and J-aggregate can be observed in some cases. In equilibrium solutions, however, significant changes are observed in most solvents with different polarities. The J-aggregate is an unstable state which is irreversibly converted to other species. The monomer converts reversibly among the D-aggregate, H-aggregate and water adducts in the equilibrium state. At the same time, the water adducts are sensitive to the external environment and their content can be modulated by temperature and pH conditions. The dye's prominent optical signal changes arising from pH- and thermal dependence of water addition or the disassociation of the D-aggregate led to potential applications in the field of thermoresponsive probes under given conditions.

Unusual Mass Spectrometric Dissociation Pathway of Protonated Isoquinoline-3-Carboxamides Due to Multiple Reversible Water Adduct Formation in the Gas Phase

The study of the collision-induced dissociation behavior of various substituted isoquinoline-3-carboxamides, which are amongst a group of drug candidates for the treatment of anemic disorders (e.g., FG-2216), allowed for the formulation of the general mechanisms underlying the unusual fragmentation behavior of this class of compounds. Characterization was achieved with high-resolution/high accuracy LTQ-Orbitrap tandem mass spectrometry of the protonated precursor ions. Presented data were substantiated by the synthesis and analysis of proposed gas-phase intermediate structures and stable isotope labeled analogues, as well as by density functional theory calculations. Exemplary, CID of protonated N-[(1-chloro-4-hydroxy-7-isopropoxy-isoquinolin-3-yl)carbonyl]glycine gives rise to the isoquinoline-3-carboxy-methyleneamide product ion which nominally eliminates a fragment of 11 u. This was attributed to the loss of methyleneamine (-29 u) and a concomitant spontaneous and reversible water addition (+18 u) to the resulting acylium ion to yield the protonated isoquinoline-3-carboxylic acid. The same water addition pattern is observed after loss of propylene (-42 u). A further nominal loss of 10 u is explained by the elimination of carbon monoxide (-28 u) followed by another water adduct formation (+18 u) to yield the protonated 1-chloro-3,4,7-trihydroxy-isoquinoline. The source of the multiple gas-phase water addition remained unclear. This atypical fragmentation pattern proved to be highly characteristic for all studied and differentially substituted isoquinoline-3-carboxamides, and offers powerful analytical tools for the establishment of a LC/MS(/MS) based screening procedure for model HIF-stabilizers and their potential metabolites in clinical, forensic and sports drug testing.

Abstract B109: Bioactivated chemotherapeutic agents based on ester-protected hydroxybenzyl phosphates (EHBP) for reversible alkylation of cellular nucleophiles

Abstract B109 Introduction In cancer treatment, targeting the cellular DNA or its nucleotide precursors has been a viable method for inhibiting the synthesis of new genetic material or causing irreparable damage to the DNA itself. For example, agents such as bleomycins oxidatively degrade DNA, whereas cisplatin forms interstrand cross-links within DNA. Issues of selectivity and delivery remain a major problem in the development of new reactive agents. Typically, covalent reactions are irreversible, suppressing the potency of an agent. Reversible covalent reactions, in contrast, provide a strategy for recovering the reactive potential despite initial interaction with non-targeted constituents. Adding bioactivation to a reversible agent should ensure better selectivity and control for chemotherapy. Quinone methide precursors (QMP) are appropriate for this approach. Reactive and transient QMs and related electrophiles are formed during the metabolic activation of cytotoxic and genotoxic agents and may lead to DNA alkylation. Adducts formed between QMs and deoxyadenosine, deoxyguanosine, deoxycytosine, thymidine have been identified; reversible reaction dominates the initial product profile. We have elected to use dC which forms one reversible adduct to measure the relative reversibility of QM reaction vs bioactivity. We synthesized a series of EHBPs and determined the time-dependent evolution of their dC adduct. Methods QMP: para-series, (agent 1) 4-acetyloxybenzyl diethylphosphate; (agent 2) 3,5-dimethyl-4-acetyloxybenzyl diethylphosphate; meta-series, (agent 3) 3-acetyloxybenzyl diethylphosphate; (agent 4) 2-chloro-3-acetyloxybenzyl diethylphosphate were synthesized, purified, and NMR verified. Adduct analysis: reverse phase-HPLC, unsubstituted and substituted QMPs were incubated ± esterase at 37 °C over 0.5 - 120 h. Results Retention times for dC, internal standard, and all putative QMPs were first determined. Agent 1: Time course hydrolysis by the esterase was essentially complete in 4 hr, resulting in formation of dC and water adducts. The dC adduct formation was maximum at 6 h, thereafter slowly decomposing, with a half-life of approx. 21 h. Time course for formation of the water adduct showed that the product yield remained constant for 6-8 hrs indicating a stable product. These results are consistent with a rate determining hydrolysis of carboxylic ester group by the esterase giving a phenol that in turn rapidly undergoes a 1,6-elimination reaction to a QM. This then reacts with water and dC competitively to produce the identified adducts. Agent 2: Esterase reaction gave similar products to agent 1. However, the half-life for the decomposition of the dC adduct was significantly less (about 10 h) underscoring the effect of the electron releasing groups. Agent 3: Esterase hydrolysis yielded the phenol derivative which underwent so benzylic substitution with water yielding the corresponding benzyl alcohol, dC-N3 adduct did not form. Agent 4: Similar results to Agent 3, but the hydrolysis appeared to be much faster and incomplete. Conclusions dC adduct formation was reversible, electron donating/withdrawing groups significantly affect the rate of adduct formation/decomposition. The meta analog did not form a QM. These results underscore the potential use of EHBPs as chemotherapeutic agents. Citation Information: Cancer Prev Res 2008;1(7 Suppl):B109.

LC–high-resolution multiple stage spectrometric analysis of diuretic compounds: Unusual mass fragmentation pathways

The analysis of diuretic compounds has become of great concern because of their extensive use both in therapy and in illicit treatments (such as masking agents in sport doping and drug abuse). The variety of chemical structures of this class of drugs encouraged the development of new methods and techniques of analysis, especially as regards to acidic compounds. LC/MS has so grown to be the reference technique for this kind of analysis in forensic and anti-doping confirmation purposes. Multiple stage MS permits identification of single drugs with high selectivity, but some unexpected pathways could weaken the entire process. In this work we aim to explain some unusual fragmentation steps using high-resolution MS n . For example, in the case of amiloride an intense product ion in MS 3 analysis generates an apparent loss of 10 Da. Water adduct formation and successive carbon monoxide elimination can explain this uncommon behavior, which was studied using different ion traps. Bendroflumethiazide MS n spectra show instead three successive HF losses, in spite of the presence of a radical site in the parent structure. Homolytic cleavages with radical ion production occur also in the case of protonated positive ion of ethacrynic acid (loss of chlorine radical) showing that such fragmentation behavior is not so rare as generally reported. Different ionization modes were studied and a tentative correlation with acidic-base properties was done. Multiple stage high-resolution mass spectra of positive and negative ions were discussed.

Collision induced dissociation of deprotonated guanine: Fragmentation of pyrimidine ring and water adduct formation

This investigation of collision induced dissociation of deprotonated guanine was conducted by using sequential ion trap tandem mass spectrometry and isotopically labelled guanine analogs to clarify the complex dissociation reactions of pyrimidine ring of deprotonated guanine. The fragmentation patterns confirmed that the gas-phase dissociation processes are initiated from the pyrimidine ring through charge site controlled reactions involving charge redistribution, proton transfer and nucleophilic attack to generate the three primary fragment products by the elimination of ammonia, cyanamide and isocyanic acid. Our findings shed light on the process of pyrimidine ring opening and closure prior to the decomposition of deprotonated guanine and therefore the identity of N1 and exocyclic N 2 is lost in deprotonated guanine as a result of scrambling. Intriguing association products of water addition to fragment ions have been structurally characterized to establish the role of ketene group in the selective gas-phase reaction of water addition and the formation of water adducts. The elimination of CO 2 from negatively charged water adducts provides evidence for the covalent attachment of water to the ketene moiety. The established mechanisms of the dissociation reactions of pyrimidine ring should provide a basis for the structural elucidation of guanine relevant species modified on its active sites. To lend support for our proposals, collision induced dissociation study of 8-phenyl-2′-deoxyguanosine adduct was performed.

Periodate oxidation of cyclosophoraoses: a quantitative analysis of the reaction products by ionspray mass spectrometry

The reaction products from the periodate oxidation of cyclosophoraoses, having glucose residues ranging from 17 to 21, were studied by means of ionspray mass spectrometry. Three different samples exhibiting different degrees of oxidation (∼30, ∼65 and ∼85%) were investigated. In order to avoid both insolubility and complex spectra due to water adduct formation, the oxidised cyclosophoraoses were exhaustively reduced in order to convert the aldehydic functions into hydroxyl groups. The individual ions comprising the mass spectral envelope were assigned by taking into account the coexistence of different degrees of oxidation for each cyclosophoraose member. The distribution of variable degrees of oxidation was studied in terms of the statistical Poisson distribution and the experimental data were fitted with the expected theoretical distributions. Detection of unfragmented ions coupled with both high m/z resolution and mathematical modelling allowed the quantitative definition of the distribution of the degree of oxidation for each cyclosophoraose ring size. This information makes possible the use of specific oxidised derivatives as building blocks for complex molecular systems.

Alcohol tracer diffusion, density, NMR and FTIR studies of aqueous ethanol and 2,2,2-trifluoroethanol solutions at 25°C

New measurements have been made of the tracer diffusion coefficients of ethanol and 2,2,2-trifluoroethanol (TFE) in aqueous solution at 25°C across the whole composition range. The limiting values at infinite dilution of these alcohols and the series of primary alcohols from methanol to heptanol, the isomeric propanols and butanols and 2-butoxyethanol are found to vary as the alcohol limiting partial molar volume raised to the power -0.56. The self-diffusion coefficient of water lies on the same curve, suggesting that the rate-determining step for diffusion is the same for these alcohols at infinite dilution as it is for water. 1H, 19F and 13C chemical shift and density measurements have been made and apparent molar volumes obtained from the latter. The composition dependence of the ν2 bending vibration band of water in water–TFE at 1640 cm-1 has been examined. The chemical shift and water IR measurements show that water–TFE behaves like other aqueous halogenoethanol solutions with water and hydroxyl proton shifts moving to higher field with increasing alcohol concentration. The results are consistent with thermodynamic data indicating some degree of microheterogeneity in the TFE-rich region of this system and a strengthening of water–TFE H-bonding on dilution of TFE. This is the opposite of what is observed for water–ethanol. We were unable to find any evidence from the diffusion data for the formation of water adducts to ethanol chains at high ethanol concentration in water–ethanol mixtures as has been suggested in the literature.

Intact noncovalent dimer of estrogen receptor ligand-binding domain can be detected by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESMS) of the estrogen receptor ligand binding domain (ER LBD) in its estradiol-binding form was performed. A dimeric ER LBD was observed, with a greatly reduced capacity for protonation (major charge state for dimer +16 vs. +23 for a monomer). Peak broadening (probably due to heterogeneity resulting from salt and water adduct formation) adversely affected our ability to distinguish between multiple discreet dimeric species and thus prevented us from establishing an accurate average mass for the dimerized domain. A mixture of species with molecular masses between 57,240 Da and 57,900 Da was observed, which would compare to 57,274 Da, 57,546 Da, and 57,818 Da for the calculated masses of the dimer without estradiol, or with one or two bound ligand molecules, respectively. Hence, nonliganded ER LBD dimer appeared to constitute the major species. The presence of low levels of a singly liganded ER LBD dimer cannot be ruled out, but the data argue against the possibility of the ER LBD dimer carrying two molecules of estradiol. Allowing for current limitations in the technology, our data demonstrate that ESMS on a quadrupole mass spectrometer of limited mass range (4000 Da for singly charged ions) has potential utility for studying ligandbinding proteins. In particular, in future it might be possible to compare spectra obtained from agonist- and antagonist-bound receptors and determine from subtle changes in protonation state possible differences in the higher order structure of those noncovalent protein complexes.

Early Appearance of Aflatoxin in Developing Corn Kernels After Inoculation withAspergillus flavus

regimes were defined in thermal units Thompson, D. L., Payne, G. A., Lillehoj, E. B., and Zuber, M. S. 1983. Early appearance of (Table 1), which were calculated as f[(day aflatoxin in developing corn kernels after inoculation with Aspergillus flavus. Plant Disease temp. X 9 hr) + (night temp. X 67:1321-1322. 15 hr)]/241 -10 C. For each replicate, half of the plants were moved morning Developing kernels of corn (Zea mays L.) of the cultivar Gaspe X W103 were inoculated with and evening between the two rooms to Aspergillusfilavus Link ex Fr., grown in four postinoculation regimes, harvested at weekly intervals achieve the four temperature regimes. from 2 to 37 days after inoculation, and assayed for aflatoxin B 1. Aflatoxin B 1 levels averaged 238 One room was set to a day/ night ppb 2 days after inoculation and 2,482 ppb for all other dates. Aflatoxin levels were near maximum 9 days after inoculation and accumulations were minimal after that time. There was no evidence of temperature of 26/ 22 C and the other at a temperature effect in the range of 13.5-21.5 C thermal units per day. 34/30 C with day/ night times of 9/15 hr and uninterrupted night to give a short day length effect. Aflatoxin contamination of preharvest MATERIALS AND METHODS Ears were harvested in the shuck, dried corn (Zea mays L.) continues to be a This study was conducted in controlled- for 1 wk at 60 C, bulked, and shelled for serious problem in the southeastern environment rooms at the Southeastern each cultivar-replicate treatment. Kernels United States (13). Infection of develop- Plant Environment Laboratories, Raleigh, were ground, blended, and assayed for ing kernels by Aspergillus.flavus Link ex NC. Lighting and other environmental aflatoxin by the Official First Action Fr. and subsequent production of aspects of the rooms have been de- Method of AOAC, Sections 26.049aflatoxin is influenced by many factors. scribed (3). 26.051, and 26.075 (1). Quantities of Temperature is one factor that appears to Plants of the corn cultivar Gaspe X aflatoxin B 1 were determined on influence aflatoxin production in grain. W103 were grown singly in 20.3-cm activated thin-layerchromatographic The warmer temperatures of the plastic pots (4,000 ml) in a substrate of (TLC) plates coated with 0.5 mm of Southeast have been implicated as a one-third gravel and two-thirds Peat-lite. Absorbosil- 1. Plates were developed with major reason for higher levels of Before inoculation, plants were grown at water:acetone:chloroform ( 1.5:12:88, aflatoxin in the Southeast than in the the day/night temperature regime of v/v/v) in unequilibrated tanks and Midwest (13). In support of this 26/22 C with an interrupted night to fluorescent zones were measured densitohypothesis, Thompson et al (12) found a provide long day length. Plants were metrically (2). Aflatoxin B, was congeneral trend toward increased toxin with irrigated twice each day with a modified firmed in representative positive samples increased temperature over a range of half-strength Hoagland's solution (3). A by formation of water adduct (I). 9.5-17.5 thermal units per day and treatment unit consisted of five plants. Aflatoxin B 1 values were transformed suggested that temperatures higher than Each of two replicates was grown at a to logarithms for analyses of variance those used may give higher toxin levels, different time.

Some Correlations Between Chelate Extraction Distribution Ratios, Bond Types, and Solvent Physical Properties

Abstract Correlations between extraction distribution ratios, bond types, and common solvent physical properties were determined for 19 extraction systems. Different types of bonding are involved in the water adduct formation on different types of chelates.

Water Adduct Formation in Extracted Chelates

Abstract Water adducts of 1,10-phenanthroline, 4,7-diphenyl-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, tris(4,7-diphenyl-1,10-phenanthroline) Fe(II) perchlorate, tris(4,7-diphenyl-1,10-phenanthroline) Ru(II) chloride, tris(1,10-phenanthroline) Fe(II) perchlorate, and bis(2,9-dimethyl-1,10-phenanthroline) Cu(I) perchlorate had 5.1 ± 0.9, 0 ± 1.3, 6.8 ± 0.6, 5.6 ± 1.5, 4.8 ± 0.7, 6.3 ± 0.6, and 6.5 ± 1.0 molecules of H2O, respectively, associated with them when they were extracted into nitromethane. All deviations are at the 95% C.I.