"Inverted" Cyclic(Alkyl)(Amino)Carbene (CAAC) Ruthenium Complex Catalyzed Isomerization Metathesis (ISOMET) of Long Chain Olefins to Propylene at Low Ethylene Pressure.

Isomerization Metathesis (ISOMET) reaction is an emerging tool for "open loop" chemical recycling of polyethylene to propylene. Novel, latent N-Alkyl substituted Cyclic(Alkyl)(Amino)Carbene (CAAC)-ruthenium catalysts (5a-Ru, 3b-Ru - 6c-Ru) are developed rendering "inverted" chemical structure while showing enhanced ISOMET activity in combination with (RuHCl)(CO)(PPh3)3 (RuH) double bond isomerization co-catalyst. Systematic investigations reveal that the steric hindrance of the substituents on nitrogen and carbon atom adjacent to carbene moiety in the CAAC ligand have significantly improved the catalytic activity and robustness. In contrast to the NHC-Ru and CAAC-Ru catalyst systems known so far, these systems show higher isomerization metathesis (ISOMET) activity (TON: 7400) on the model compound 1-octadecene at as low as 3.0 bar optimized pressure, using technical grade (3.0) ethylene. The propylene content formed in the gas phase can reach up to 20% by volume.

Bisphenol A Diglycidyl Ether-Primary Amine Cooligomer-poly(ε-caprolactone) Networks: Synthesis and Characterization.

In this work, the preparation and systematic investigation of cross-linked polyurethane-epoxy (PU-EP) polymer systems are reported. The PU-EP polymers were prepared using a reaction of isocyanate (NCO)-terminated PU-prepolymer with diglycidyl ether of bisphenol A (DGEBA)-amine cooligomer. The oligomerization of DGEBA was carried out by adding furfurylamine (FA) or ethanolamine (EA), resulting in DGEBA-amine cooligomers. For the synthesis of NCO-terminated PU-prepolymer, poly(ε-caprolactone)diol (PCD) (Mn = 2 kg/mol) and 1,6-hexamethylene diisocyanate (HDI) were used. The cross-linking was achieved by adding DGEBA-amine cooligomer to PU-prepolymer, in which the obtained urethane bonds, due to the presence of free hydroxil groups in the activated DGEBA, served as netpoints. During cross-linking, ethanolamine provides an additional free hydroxyl group for the formation of a new urethane bond, while furfurylamine can serve as a thermoreversible coupling element (e.g., Diels-Alder adduct). The PU-EP networks were characterized using attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), differential scanning calorimetry (DSC), dynamical mechanical analysis (DMA) and scanning electron microscopy (SEM). The DMA curves of some PU-EPs (depending on the compositions and the synthetic method) revealed a plateau-like region above the melting temperature (Tm) of PCD, confirming the presence of a cross-linked structure. This property resulted in a shape memory (SM) behavior for these samples, which can be fine-tuned in the presence of furfurylamine through the formation of additional thermoreversible bonds (e.g., Diels-Alder adduct).

Potential Original Drug for Aspergillosis: In Vitro and In Vivo Effects of 1-N,N-Dimethylamino-5-Isocyanonaphthalene (DIMICAN) on Aspergillus fumigatus.

As the recent outbreak of coronavirus disease 2019 (COVID-19) has shown, viral infections are prone to secondary complications like invasive aspergillosis with a high mortality rate, and therefore the development of novel, effective antifungals is of paramount importance. We have previously demonstrated that 1-amino-5-isocyanonaphthalene (ICAN) derivatives are promising original drug candidates against Candida strains (Patent pending), even against fluconazole resistant C. albicans. Consequently, in this study ICANs were tested on Aspergillus fumigatus, an opportunistic pathogen, which is the leading cause of invasive and systematic pulmonary aspergillosis in immunosuppressed, transplanted and cancer- or COVID-19 treated patients. We have tested several N-alkylated ICANs, a well as 1,5-naphthalene-diisocyanide (DIN) with the microdilution method against Aspergillus fumigatus strains. The results revealed that the diisocyanide (DIN) was the most effective with a minimum inhibitory concentration (MIC) value as low as 0.6 µg mL-1 (3.4 µM); however, its practical applicability is limited by its poor water solubility, which needs to be overcome by proper formulation. The other alkylated derivatives also have in vitro and in vivo anti-Aspergillus fumigatus effects. For animal experiments the second most effective derivative 1-N, N-dimethylamino-5-isocyanonaphthalene (DIMICAN, MIC: 7-8 µg mL-1, 36-41 µM) was selected, toxicity tests were made with mice, and then the antifungal effect of DIMICAN was tested in a neutropenic aspergillosis murine model. Compared to amphotericin B (AMB), a well-known antifungal, the antifungal effect of DIMICAN in vivo turned out to be much better (40% vs. 90% survival after eight days), indicating its potential as a clinical drug candidate.

Isocyanide Substitution in Acridine Orange Shifts DNA Damage-Mediated Phototoxicity to Permeabilization of the Lysosomal Membrane in Cancer Cells.

In cancer therapy, immunogenic cell death eliminates tumor cells more efficiently than conventional apoptosis. During photodynamic therapy (PDT), some photosensitizer (PS) targeting lysosomes divert apoptosis to the immunologically more relevant necrosis-like cell death. Acridine orange (AO) is a PS targeting lysosome. We synthesized a new compound, 3-N,N-dimethylamino-6-isocyanoacridine (DM), a modified AO, aiming to target lysosomes better. To compare DM and AO, we studied optical properties, toxicity, cell internalization, and phototoxicity. In addition, light-mediated effects were monitored by the recently developed QUINESIn method on nuclei, and membrane stability, morphology, and function of lysosomes utilizing fluorescent probes by imaging cytometry in single cells. DM proved to be a better lysosomal marker at 405 nm excitation and lysed lysosomes more efficiently. AO injured DNA and histones more extensively than DM. Remarkably, DM's optical properties helped visualize shockwaves of nuclear DNA released from cells during the PDT. The asymmetric polar modification of the AO leads to a new compound, DM, which has increased efficacy in targeting and disrupting lysosomes. Suitable AO modification may boost adaptive immune response making PDT more efficient.

Structural Characterization of Daunomycin-Peptide Conjugates by Various Tandem Mass Spectrometric Techniques.

The use of peptide-drug conjugates has generated wide interest as targeted antitumor therapeutics. The anthracycline antibiotic, daunomycin, is a widely used anticancer agent and it is often conjugated to different tumor homing peptides. However, comprehensive analytical characterization of these conjugates via tandem mass spectrometry (MS/MS) is challenging due to the lability of the O-glycosidic bond and the appearance of MS/MS fragment ions with little structural information. Therefore, we aimed to investigate the optimal fragmentation conditions that suppress the prevalent dissociation of the anthracycline drug and provide good sequence coverage. In this study, we comprehensively compared the performance of common fragmentation techniques, such as higher energy collisional dissociation (HCD), electron transfer dissociation (ETD), electron-transfer higher energy collisional dissociation (EThcD) and matrix-assisted laser desorption/ionization-tandem time-of-flight (MALDI-TOF/TOF) activation methods for the structural identification of synthetic daunomycin-peptide conjugates by high-resolution tandem mass spectrometry. Our results showed that peptide backbone fragmentation was inhibited by applying electron-based dissociation methods to conjugates, most possibly due to the "electron predator" effect of the daunomycin. We found that efficient HCD fragmentation was largely influenced by several factors, such as amino acid sequences, charge states and HCD energy. High energy HCD and MALDI-TOF/TOF combined with collision induced dissociation (CID) mode are the methods of choice to unambiguously assign the sequence, localize different conjugation sites and differentiate conjugate isomers.

Spilanthol Inhibits Inflammatory Transcription Factors and iNOS Expression in Macrophages and Exerts Anti-inflammatory Effects in Dermatitis and Pancreatitis.

Activated macrophages upregulate inducible nitric oxide synthase (iNOS) leading to the profuse production of nitric oxide (NO) and, eventually, tissue damage. Using macrophage NO production as a biochemical marker of inflammation, we tested different parts (flower, leaf, and stem) of the medicinal plant, Spilanthes acmella. We found that extracts prepared from all three parts, especially the flowers, suppressed NO production in RAW macrophages in response to interferon-γ and lipopolysaccharide. Follow up experiments with selected bioactive molecules from the plant (α-amyrin, ß-caryophylline, scopoletin, vanillic acid, trans-ferulic acid, and spilanthol) indicated that the N-alkamide, spilanthol, is responsible for the NO-suppressive effects and provides protection from NO-dependent cell death. Spilanthol reduced the expression of iNOS mRNA and protein and, as a possible underlying mechanism, inhibited the activation of several transcription factors (NFκB, ATF4, FOXO1, IRF1, ETS, and AP1) and sensitized cells to downregulation of Smad (TF array experiments). The iNOS inhibitory effect translated into an anti-inflammatory effect, as demonstrated in a phorbol 12-myristate 13-acetate-induced dermatitis and, to a smaller extent, in cerulein-induced pancreatitis. In summary, we demonstrate that spilanthol inhibits iNOS expression, NO production and suppresses inflammatory TFs. These events likely contribute to the observed anti-inflammatory actions of spilanthol in dermatitis and pancreatitis.

Novel fluorochromes label tonoplast in living plant cells and reveal changes in vacuolar organization after treatment with protein phosphatase inhibitors.

The recently synthesized isocyanonaphtalene derivatives ACAIN and CACAIN are fluorochromes excitable at wavelengths of around 366 nm and bind cysteine-rich proteins with hydrophobic motifs. We show that these compounds preferentially label tonoplasts in living Arabidopsis and tobacco (Nicotiana tabacum SR1) cells. ACAIN-labeled membranes co-localized with the GFP signal in plants expressing GFP-δ-TIP (TIP2;1) (a tonoplast aquaporin) fusion protein. ACAIN preserved the dynamics of vacuolar structures. tip2;1 and triple tip1;1-tip1;2-tip2;1 knockout mutants showed weaker ACAIN signal in tonoplasts. The fluorochrome is also suitable for the labeling and detection of specific (cysteine-rich, hydrophobic) proteins from crude cell protein extracts following SDS-PAGE and TIP mutants show altered labeling patterns; however, it appears that ACAIN labels a large variety of tonoplast proteins. ACAIN/CACAIN could be used for the detection of altered vacuolar organization induced by the heptapeptide natural toxin microcystin-LR (MCY-LR), a potent inhibitor of both type 1 and 2A protein phosphatases and a ROS inducer. As revealed both in plants with GFP-TIP2;1 fusions and in wild-type (Columbia) plants labeled with ACAIN/CACAIN, MCY-LR induces the formation of small vesicles, concomitantly with the absence of the large vegetative vacuoles characteristic for differentiated cells. TEM studies of MCY-LR-treated Arabidopsis cells proved the presence of multimembrane vesicles, with characteristics of lytic vacuoles or autophagosomes. Moreover, MCY-LR is a stronger inducer of small vesicle formation than okadaic acid (which inhibits preferentially PP2A) and tautomycin (which inhibits preferentially PP1). ACAIN and CACAIN emerge as useful novel tools to study plant vacuole biogenesis and programmed cell death.

Biochemical, Histopathological and Molecular Responses in Gills of Leuciscus cephalus Exposed to Metals.

Gills are major targets for acute metal toxicity in fish, due to their permanent contact with aquatic pollutants. To assess the effects of metals on gills of the Leuciscus cephalus (chub), fish individuals were collected from two sites in the Tur River, Romania, in upstream (site 1) and downstream (site 2) of a metal pollution source. Quantitative and hyperspectral analyses showed that Zn, Sr, and Fe concentrations were significantly higher in gills from site 2 compared with site 1. Malondialdehyde and advanced oxidation protein products levels increased 17 and 28%, respectively, whereas reduced glutathione level diminished significantly in the gills of fish collected from site 2 compared to site 1. The activities of superoxide dismutase, catalase, and glutathione-S-transferase increased significantly at 41, 21, and 28%, respectively. Proliferating cell nuclear antigen (PCNA) protein levels, as well as the amount of DNA damage, were significantly increased for site 2 compared with site 1. The induced oxidative stress generated hyperplasia, hypertrophy, and inflammation in the epithelial cells and apoptosis. Hence, this could suggest that gill cells have tried to counteract the oxidative stress-induced DNA fragmentation by PCNA up-regulation, but the PCNA expression decreased on longer time due to the low level of GSH, resulting in apoptosis.

Gas-Phase Interaction of Anions with Polyisobutylenes: Collision-Induced Dissociation Study and Quantum Chemical Modeling.

The gas-phase interaction of anions including fluoride, chloride, bromide, iodide, ethyl sulfate, chlorate, and nitrate with polyisobutylene (PIB) derivatives was studied using collision-induced dissociation (CID). The gas-phase adducts of anions with PIBs ([PIB + anion](-)) were generated from the electrosprayed solution of PIBs in the presence of the corresponding anions. The so-formed adducts subjected to CID showed a loss of anion at different characteristic collision energies, thus allowing the study of the strength of interaction between the anions and nonpolar PIBs having different end-groups. The values of characteristic collision energies (the energy needed to obtain 50% fragmentation) obtained by CID experiments correlated linearly with the binding enthalpies between the anion and PIB, as determined by density functional theory calculations. In the case of halide ions, the critical energies for dissociation, that is, the binding enthalpies for [PIB + anion](-) adducts, increased in the order of I(-) < Br(-) < Cl(-) < F(-). Furthermore, it was found that the binding enthalpies for the adducts formed with halide ions decreased approximately with the square radius of the halide ion, suggesting that the strength of interaction is mainly determined by the "surface" charge density of the halide ion. In addition, the characteristic collision energy versus the number of isobutylene units revealed a linear dependence.

Electrospray ionization tandem mass spectrometry of the star-shaped propoxylated diethylenetriamine polyols.

The collision-induced dissociation of the protonated five-arm star propoxylated diethylenetriamine polyols was studied under electrospray conditions. Two product ion series were detected because of the cleavage of the C-N bonds in the initiator moiety. No backbone fragmentation of the polyether chains was observed, which allowed to explore the initiation and side-chain propagation process of the oligomers. On the basis of MS/MS spectra, it is probable that the rate of the initiation is larger than that of the chain propagation. The propylene oxide repeat units attach to the five arms with approximately the same probability. Furthermore, it was found that the collision energy necessary to obtain 50% fragmentation (CE50) was linearly dependent on the molecular weight of the polyols.

Histopatological alterations and oxidative stress in liver and kidney of Leuciscus cephalus following exposure to heavy metals in the Tur River, North Western Romania.

Pollution of the aquatic environment by heavy metals is a great concern worldwide. Freshwater fish ingests various metals through gills, skin or diet. Our aim was to investigate the oxidative stress and histopathological injuries induced by Fe, Cu, Zn, Pb, Cd in the liver and kidney of Leuciscus cephalus. Fish samples were collected from two sites in the Tur River, NW Romania, in upstream and downstream of a pollution source. Metals were differently distributed in the liver and kidney of fish. The highest concentrations of Fe, Cu and Pb were found in liver, whereas Zn and Cd concentrations were the highest in kidney in specimens collected from the downstream site. The histopathological changes were associated with metal bioaccumulation, being more severe in kidney than liver. Malondialdehyde (MDA) and advanced oxidation protein products (AOPP) increased significantly in the liver and kidney of fish from downstream site compared to upstream one, whereas reduced glutathione (GSH) decreased. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione-S-transferase (GST) increased significantly in livers, whereas SOD increased in kidney. Our study revealed that liver has a higher capacity and adaptability to counteract ROS compared to kidney. The more pronounced increase of hepatic SOD, CAT and GST activities is related milder structural changes observed in liver compared to kidney, where lesions were not reduced by antioxidant defense system.

Fragmentation study of noscapine derivatives under electrospray conditions.

RATIONALE: Noscapine is a biologically active molecule with anticancer activity among other things. Therefore, from an analytical point of view, knowledge of the mass spectrometric properties of noscapine and its derivatives is essential. The goal of the present study is to describe the collision-induced dissociation behavior of noscapine and its seven derivatives ionized by protons and lithium and sodium ions. METHODS: Protonated noscapines were produced using electrospray ionization (ESI) mass spectrometry (MS). For the tandem mass spectrometry (MS/MS) experiments nitrogen was used as the collision gas and the collision energies were varied in the range of 1-53 eV (in the laboratory frame). RESULTS: The ESI-MS/MS measurements showed that the MS/MS spectra of the protonated noscapines were more informative than the lithiated and sodiated ones. Based on the MS/MS studies, the main fragmentation channels of the protonated noscapines were found to be the loss of water and the loss of a meconine moiety from the precursor ion; furthermore, methyl transfer was also observed in the MS/MS spectra. CONCLUSIONS: The MS/MS study of the protonated noscapines gives more structural information than that of lithiated and sodiated noscapines. However, the most important fragmentation channel, which leads to the formation of the most intensive product ion in the MS/MS spectra, is independent of the ionization agent.

Estimation of activation energy from the survival yields: fragmentation study of leucine enkephalin and polyethers by tandem mass spectrometry.

A simple collision model for multiple collisions occurring in quadrupole type mass spectrometers was derived and tested with leucine enkaphalin a common mass spectrometric standard with well-characterized properties. Implementation of the collision model and Rice-Ramsperger-Kassel-Marcus (RRKM) algorithm into a spreadsheet software allowed a good fitting of the calculated data to the experimental survival yield (SY) versus collision energy curve. In addition, fitting also ensured to estimate the efficiencies of the kinetic to internal energy conversion for Leucine enkephalin in quadrupole-time-of-flight and triple quadrupole instruments. It was observed that the experimental SY versus collision energy curves for the leucine enkephalin can be described by the Rice-Ramsperger-Kassel (RRK) formalism by reducing the total degrees of freedom (DOF) to about one-fifth. Furthermore, this collision model with the RRK formalism was used to estimate the critical energy (E(o)) of lithiated polyethers, including polyethylene glycol (PEG), polypropylene glycol (PPG), and polytetrahydrofurane (PTHF) with degrees of freedom similar to that of leucine enkephalin. Applying polyethers with similar DOF provided the elimination of the effect of DOF on the unimolecular reaction rate constant. The estimated value of E(o) for PEG showed a relatively good agreement with the value calculated by high-level quantum chemical calculations reported in the literature. Interestingly, it was also found that the E(o) values for the studied polyethers were similar.

A simple method to estimate relative stabilities of polyethers cationized by alkali metal ions.

Dissociation of doubly cationized polyethers, namely [P + 2X](2+) into [P + X](+) and X(+), where P = polyethylene glycol (PEG), polypropylene glycol (PPG) and polytetrahydrofuran (PTHF) and X = Na, K and Cs, was studied by means of energy-dependent collision-induced dissociation tandem mass spectrometry. It was observed that the collision voltage necessary to obtain 50% fragmentation (CV(50)) determined for the doubly cationized polyethers of higher degree of polymerization varied linearly with the number of degrees of freedom (DOF) values. This observation allowed us to correlate these slopes with the corresponding relative gas-phase dissociation energies for binding of alkali ions to polyethers. The relative dissociation energies determined from the corresponding slopes were found to decrease in the order Na(+) > K(+) > Cs(+) for each polyether studied, and an order PPG ≈ PEG > PTHF can be established for each alkali metal ion.

Size effect on fragmentation in tandem mass spectrometry.

The collision energy or collision voltage necessary to obtain 50% fragmentation (characteristic collision energy/voltage, CCE or CCV) has been systematically determined for different types of molecules [poly(ethylene glycols) (PEG), poly(tetrahydrofuran) (PTHF), and peptides] over a wide mass (degrees of freedom) range. In the case of lithium-cationized PEGs a clear linear correlation (R(2) > 0.996) has been found between CCE and precursor ion mass on various instrument types up to 4.5 kDa. A similar linear correlation was observed between CCV and the mass-to-charge ratio. For singly and multiply charged polymers studied under a variety of experimental conditions and on several instruments, all data were plotted together and showed correlation coefficient R(2) = 0.991. A prerequisite to observe such a good linear correlation is that the energy and entropy of activation in a class of polymers is likely to remain constant. When compounds of different structure are compared, the CCV will depend not only on the molecular mass but the activation energy and entropy as well. This finding has both theoretical and practical importance. From a theoretical point of view it suggests fast energy randomization up to at least 4.5 kDa so that statistical rate theories are applicable in this range. These results also suggest an easy method for instrument tuning for high-throughput structural characterization through tandem MS: after a standard compound is measured, the optimum excitation voltage is in a simple proportion with the mass of any structurally similar analyte at constant experimental conditions.

[Role of iron metabolism-regulator hepcidin in perinatal iron homeostasis]. / A vasháztartást szabályzó hepcidin kimutatása és szerepe a perinatalis vasháztartásban.

Hepcidin is a recently recognized defensin-like peptide, which is considered to be the central regulator of iron metabolism. Hepcidin decreases the expression of iron transporting molecules. Hepcidin reduces gastrointestinal iron absorption, iron release from the macrophages, and hence it decreases serum iron levels. Clarification of hepcidin role in iron homeostasis could provide an explanation to anemia of inflammation and chronic diseases. At start of our work there was no commercially available method for measuring urine hepcidin levels. The aim of our study was to develop an easily achievable, reliable quantification method for the determination of urine hepcidin levels in human, in addition to examine a possible association of hepcidin with neonatal iron homeostasis. According to the sequence of native, human hepcidin we have synthesized peptide derivatives from which 1-7 peptide derivatives might be suitable representatives of the 25-amino-acid form of hepcidin in immune adsorption method. We presented a novel laser-desorption mass spectrometry based semi-quantitative, reproducible method for measuring hepcidin concentration in human urine first using the synthesized peptide derivative acetyl-1-25 peptide as hepcidin related internal standard. We described an easy and quickly achievable solid-phase extraction method which is suitable for purification of urine and concentration of hepcidin. In our study we have first measured serum prohepcidin and urine hepcidin in healthy human newborns. Serum prohepcidin levels showed no significant changes, however, urine hepcidin levels increased significantly during the first postnatal days. Serum prohepcidin and urine hepcidin levels showed no significant association in healthy human newborns. Associations have been demonstrated between cord blood prohepcidin values and mean corpuscular hemoglobin concentration as well as between urine hepcidin levels and serum iron and total iron binding capacity values. We have demonstrated that neonates with detectable non-protein-bound iron levels in cord blood were presented with lower prohepcidin concentrations. In summary, our results suggest a possible link between hepcidin and early iron adaptation of newborn's, however, further investigations should be done to elucidate this issue.

Ligand size distribution of phenanthroline-functionalized polyethylene glycol-iron(II) complexes determined by electrospray ionization mass spectrometry and computer simulation.

The complex formation in solution, and the gas-phase dissociation of a phenanthrolineterminated poly(ethylene glycol) with Fe(2+) ions were investigated. The size distribution of poly(ethylene glycol)-α-monomethyl-ω-5-[1,10]phenanthroline (mPEG_phen) was determined by electrospray ionization mass spectrometry (ESI-MS). Based on the measured ligand size distribution of mPEG_phen by ESI-MS, the 1:3 complex formation (Fe(2+)/mPEG_Phen) was computer-simulated as a pure random assembly process. The simulated distribution fits excellently to that of the complex Fe(mPEG_phen) 3 (2+) determined from the ESI-MS intensities. In addition, the collision-induced dissociation (CID) of the Fe(mPEG_phen) 3 (2+) complex was also studied by tandem mass spectrometry (ESI-MS/MS) and by computer simulation, as well. The ESI-MS/MS intensity distribution of the Fe(mPEG_phen) 2 (2+) formed from Fe(mPEG_phen) 3 (2+) by the loss of an mPEG_phen ligand under CID conditions fits quite well to the calculated one.

Self-assembly study of polydisperse ethylene oxide-based nonionic surfactants.

The self-assembly behavior of polyethoxylate-based multicomponent nonionic surfactants was studied. Using the dynamic light scattering method, thermodynamical parameters such as the critical micelle concentration (cmc) and hydrophile-lipophile balance (HLB), as well as the micelle size and micelle size distribution, were determined. The number average molecular weight and number average HLB of the samples were determined by MALDI-TOF-MS and 1H NMR techniques, and the data were evaluated. A connection was found between the HLB and the ln(cmc) value of the samples which can be described by a simple equation. Using this equation and plotting ln(cmc) versus the average number of ethylene oxide units, lines were obtained at different temperatures, and their slope allowed the calculation of the contribution of a single ethylene oxide unit to the Gibbs free energy of micellization.

Description of response and charge-state distribution of poly(ether glycol)s in electrospray.

The responses and charge-state distributions of poly(ethylene glycol) (PEG) and poly(propylene glycol) (PPG) (Mn = 400-1000 g/mol) at constant electrolyte concentrations (NaCl, 10(-3) mol/L) in electrospray were studied as a function of the analyte concentration in the concentration range of 10(-2) to 10(-7) mol/L. Single charging occurred in the case of PEG and PPG with Mn = 400 g/mol. It was observed that the response changed nearly linearly with the concentration of the polymer in the low concentration region but above a certain concentration the response leveled off. Saturation of the response at higher concentrations of PEG and PPG of Mn = 1000 g/mol, where double and triple charging occurred, was also observed. Based on the equilibrium partitioning theory a model was developed to account for the response curves and charge-state distributions of singly, doubly and triply charged adduct ions generated from solutions of PEG and PPG. The experimental and the theoretical response curves and charge-state distributions calculated with the model are in fairly good agreement.

A simple method for estimating activation energies using the fragmentation yield: collision-induced dissociation of iron(II)-phenanthroline complexes in an electrospray ionization mass spectrometer.

The gas-phase stabilities of Fe(Phi)3(2+) complexes, where Phi represents the 1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 3,4,7,8-tetramethyl-1,10-phenanthroline, and 4,7-diphenyl-1,10-phenanthroline ligands were investigated by collision-induced dissociation (CID) in the capillary-first skimmer region upon changing the voltage difference between the capillary and the skimmer. The loss of only one ligand from the Fe(Phi)3(2+) complexes was observed with each of the phenanthroline ligands studied. An increase in the voltage difference between the capillary and the skimmer resulted in a higher fragmentation yield as calculated from the intensity of the precursor and the fragment ion. The fragmentation yield versus capillary-skimmer voltage difference plots were evaluated by means of the Arrhenius and the Rice-Ramsperger-Kassel (RRK) model by fitting the model parameters to the experimental data. Both models yielded practically the same results. In addition, if the internal energy gained through the capillary-skimmer region is estimated correctly, the approximate value of the critical energy (activation energy) for fragmentation can be extracted from the fragmentation yield versus capillary-skimmer voltage difference plots. It was found that the gas-phase stabilities of the Fe(Phi)3(2+) complexes are nearly identical except for the more stable Fe(II)-4,7-diphenyl-1,10-phenanthroline complex. The critical energy for fragmentation was estimated to be approximately 1.2 and 0.9 eV for the Fe(II)- 4,7-diphenyl-1,10-phenanthroline, and the other complexes, respectively.