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ABSTRACT: Atmospheric pressure photoionization mass spectrometric (APPI-MS) study on three types of polyisobutylene derivatives is reported. Two of the polyisobutylenes investigated were polyisobutylene with dihydroxy and diolefinic end-groups derived from aromatic moieties [dicumyl chloride, 1,4-bis(2-chloro-2-propyl)benzene], and the third contained no aromatic moieties with a monohydroxy end-group. All three polyisobutylene derivatives (PIBs) had an average molecular weight (M(n)) of approximately 2000 g/mol, with a polydispersity lower than 1.2. In the positive ion APPI mode, protonated PIB molecules were formed, but the molecular weights obtained were considerably lower than those expected, indicating fragmentation of the PIB chains. In the negative APPI mode, using solvents such as tetrahydrofuran and toluene as dopants, no signal was obtained. However, in chlorinated solvents, such as CCl(4), CHCl(3), and CH(2)Cl(2), in the presence of toluene dopant, PIB adducts with chloride ions were formed with relatively high signal intensity. In the case of CH(2)Cl(2), no dopant (toluene) was necessary to generate chlorinated adduct ions, albeit increasing the toluene concentration in the flow increased the PIB signal intensity. The effect of the toluene concentration on PIB signal intensity was studied and models that include (1) photoionization of toluene, (2) formation of chloride ions from the chlorinated solvents by dissociative electron capture, (3) formation of chlorinated adduct ions and charge recombination reactions between the toluene radical cation, (4) chloride ions, and (5) chlorinated adduct ions are proposed based on the experimental results.
Journal of the American Society for Mass Spectrometry 06/2008; 19(5):656-65. · 4.00 Impact Factor
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ABSTRACT: During the high-performance liquid chromatographic (HPLC) analysis of o-phthaldialdehyde (OPA)-derivatized amino acids such as arginine and homoarginine, we observed that the response of the fluorescence detection (FLD) system is decreased when the photodiode array detection (DAD) system (located before the FLD system) was simultaneously switched on. The decrease in the FLD response, i.e., the difference in the FLD peak area (DeltaA) obtained with DAD modes off (A(off)) and on (A(on)) was dependent upon the flow rate, but the relative FLD response decrease (DeltaA/A(off)) was practically independent of the amount of analyte injected. For example, decreasing the flow rate from 1 to 0.5 mL/min resulted in the relative decrease of FLD response from approximately 5% to 11%. It was concluded that DAD caused a photoinduced partial decomposition of the OPA-derivatized amino acids flowing through the cell. The photoinduced dissociation of OPA derivatives was independently supported by using off-line photodiode array spectrometric measurements with long and short irradiation pulses. Based on the experimental results, for description of the variation of FLD responses with the flow rate upon the irradiation by DAD a simple mathematical model is proposed and reported.
Journal of Chromatography 04/2008; 1185(2):301-4. · 4.53 Impact Factor
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ABSTRACT: We tested if asymmetric dimethylarginine (ADMA) contributes to the simultaneous evolution of atherosclerosis and insulin resistance. We investigated the significant predictors of insulin resistance in the context of atherosclerosis, focusing on the role ADMA, symmetric dimethylarginine (SDMA), and l-arginine play in a cohort of young atherosclerotic patients and their age-matched controls. In a case-control study, 60 patients younger than 55 years having at least 30% stenosis of the internal carotid artery and 30 age- and sex-matched controls were recruited at a community-based neurosonologic laboratory. We found a strong positive association between the homeostasis model assessment of beta-cell function and insulin resistance and the ADMA/SDMA ratio that remained statistically significant even after adjusting for all significant and a priori identified determinants (beta = 6.76; 95% confidence interval [CI], 2.13-11.39; P = .005). Interestingly, this relationship was even more pronounced in the atherosclerotic stratum (beta = 8.29; 95% CI, 1.43-15.15; P = .019), whereas, on multiple linear regression, lack of association was seen in subjects free of carotid atherosclerosis (beta = 1.39; 95% CI, -5.46 to 8.26; P = .671). We conclude that ADMA/SDMA ratio is a significant determinant of insulin resistance and may be a better parameter to monitor than ADMA alone. By accounting for the competition at the y+ transporters, ADMA/SDMA ratio could be an indicator of intracellular ADMA level.
Metabolism 04/2007; 56(3):394-9. · 2.66 Impact Factor
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ABSTRACT: The pathways of the ([M+H](+)) ions generated from electrosprayed solutions of nine 1,3,5-trisubstituted 2-pyrazoline derivatives were studied using energy-variable collision-induced dissociation (CID) and pseudo-MS(3) (in-source CID combined with MS/MS) methods. It was shown that under CID conditions several structurally important product ions such as the 2,4-substituted azete and 1,2-substituted aziridine ions were formed. The compositions of the product ions were unambiguously supported by accurate mass measurement (mass accuracy was within +/- 8 ppm). The fragmentation pathways of 1,3,5-trisubstituted 2-pyrazolines were established by means of pseudo-MS(3). It was found that a substituent at the N-1 position greatly affects the fragmentation pathways of the 2-pyrazoline derivatives. The 1-acetyl- and 1-propionyl-2-pyrazoline derivatives dissociate mainly through formation of a pyrazolium cation, while in the case of 1-phenyl-2-pyrazoline derivatives product ions arising from the consecutive fragmentation of 2,4-substituted azete and 1,2-substituted aziridine ions dominate. Another interesting finding is the formation of a radical cation from the 2,4-substituted azete by loss of a methyl radical. The fragmentation yield as a function of the collision energy for each of the 1,3,5-trisubstituted 2-pyrazolines was determined. Based on the fragmentation yield versus collision energy curves the relative fragmentation stabilities for the 1,3,5-trisubstituted 2-pyrazoline derivatives were also evaluated.
Rapid Communications in Mass Spectrometry 02/2007; 21(11):1799-808. · 2.79 Impact Factor
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ABSTRACT: Asymmetric dimethylarginine (ADMA) has been recently identified as the major endogenous inhibitor of soluble nitric oxide synthase. Its systemic accumulation was observed in conjunction with atherosclerosis and several cardiovascular and metabolic diseases. Here, we propose that ADMA causes insulin resistance by the inhibition of the neuronal isoform of nitric oxide synthase, while the simultaneously observed atherosclerosis is the consequence of endothelial nitric oxide synthase (NOS) inhibition. Our hypothesis rests on animal models in which experimental insulin resistance was induced by intraportal administration of non-selective and selective neuronal nitric oxide synthase inhibitors, N-methyl-L-arginine (L-NMMA) or 7-nitroindazole. In these models, loss of hepatic nitric oxide productions is presumed to hinder a very potent insulin sensitizing mechanism referred to as meal induced sensitization that is anatomically linked to the nitrergic fibers of the anterior hepatic plexus. Cause and effect relationship between ADMA and insulin resistance has been proposed previously by others however the nature of this relationship has not been elucidated in detail. In our hypothesis, we suggest that ADMA by inhibiting both the neuronal and the endothelial forms of NOS, results both in insulin resistance and in accelerated atherosclerosis, therefore ADMA is the molecule responsible for the coexistence of these two conditions. We also suggest animal models and human studies to test our hypothesis, the results of which may offer novel approaches in the prevention of insulin resistance and atherosclerosis.
Medical Hypotheses 02/2005; 65(6):1091-8. · 1.39 Impact Factor
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ABSTRACT: The ring-opening oligomerization reaction of propylene carbonate in the presence of the tert-butylphenol/KHCO3 initiating system was studied by means of Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) and Electrospray Ionization Time of Flight Mass Spectrometry (ESI-TOF MS). According to the MS spectra obtained, different series of peaks were identified. The MS spectra clearly showed that besides the chain-extension reaction yielding oligomers with all propylene oxide units, the formation of oligomers containing carbonate linkages in the chain, and condensation reaction between the latter two also took place. The structure of the oligomers carrying carbonate linkages was determined by the post-source decay (PSD) MALDI-TOF MS/MS method. Based on the MS results, a mechanism for the oligomerization reaction is proposed.
Macromolecular Symposia 09/2004; 215(1):141 - 150.
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ABSTRACT: Singly positively and negatively charged silver-cluster ions were effectively produced under matrix-assisted laser desorption/ionization (MALDI) conditions up to the aggregation number of n 200, using reductive polar organic matrixes and silver trifluoroacetate (AgTFA). It was found that the matrix greatly influences the resulting cluster ion abundances. The effect of the matrixes with various chemical structures on the cluster formation was systematically investigated. It was also observed that the ion intensities decreased sharply at particular cluster numbers called “magic” numbers, independently of the matrix used, and this is in good agreement with the jellium model theory. The highest observed magic numbers were achieved with HABA [2-(4-hydroxyphenylazo)benzoic acid] and are 139 and 137 for positively and negatively charged cluster ions, respectively. The fragmentations of both singly positively and negatively charged clusters ions were also studied. It was found that even-number clusters lose one silver atom, while clusters with an odd-number emit a single or two silver atoms. The fragmentation behavior of clusters as a function of the cluster size is reported. On the basis of the results a possible mechanism for the cluster ion formation is also presented.
04/2003;
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ABSTRACT: The decarboxylation upon oligomerization of propylene carbonate in the presence of the bisphenol A/KHCO3 initiating system was studied by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Five different series of peaks appeared in the MALDI-TOF MS spectra of the oligomerization mixture. In addition to the chain-extension reaction with the propylene oxide units, the oligomers of all of the propylene oxide units and oligomers containing carbonate end groups condensed. The product of the oligomerization reaction was hydrolyzed under alkaline conditions. It was found that hydrolyzed oligomers do not carry carbonate groups. The results of the MS studies agreed well with those obtained by 1H and 13C NMR spectroscopies and size-exclusion chromatography (SEC). On the basis of the results of the present investigation, a mechanism for the oligomerization is also proposed.
08/2001;
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ABSTRACT: The cooligomerization reactions of the comonomers ethylene carbonate–propylene carbonate, ethylene carbonate–ε-caprolactone and propylene carbonate-ε-caprolactone initiated by the p-tert-butylphenol/KHCO3 system were investigated by means of electrospray ionization mass spectrometry combined with liquid chromatography. Three major cooligomer series were found in each case which were identified such as cooligomers with tert-butylphenol and hydroxyl headgroups. The presence of cyclic cooligomers was also unambigously observed. In addition, cooligomers carrying carbonate linkages were also identified, however, their fraction was very small compared to the cooligomer series without carbonate linkages. Besides the cooligomerization reaction, homooligomerization of ethylene and propylene carbonate was observed, as well as no linear homooligomers of ε-caprolactone were detected. Based on the LC-ESI MS results a mechanism is proposed for the formation of cyclic co-oligomers and the chain degradation of cooligomers containing carbonate linkages.
European Polymer Journal 41(7):1478-1483. · 2.74 Impact Factor
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ABSTRACT: AB, A2B, A1A2B, A2B2 és A3B3 (AB)3 típusú (A=poliizobutilén, B=poli(metil-vinil-éter) ) amfifilikus blokk-kopolimereket állítottunk elő és megvizsgáltuk az architectúra hatását a vizes oldatban lejátszódó micellaképződésre. Fényszórás mérésekből az AB, A2B2, A3B3, és (AB)3 blokk-kopolimerek esetében vizes oldatban vezikulák képződését valószínűsítettük. Megállapítottuk, hogy a csillag alakú blokk-kopolimerekből képződött micellák aggregációs száma és hidrodinamikai sugara a hőmérséklettől független, míg a lineáris AB blokk-kopolimerből képződött micellák esetében jelentős növekedés tapasztalható. Glüköz-, amino-, bisz(imidazolil-1-karboxilát)-, hidroxil-, epoxid-, aldehid- és karboxil-tekelikus polimereket szintetizáltunk. A polimerek szerkezetét NMR és MALDI-TOF MS módszerekkel bizonyítottuk és vizsgáltuk a származékok tömegspektrometiás viselkedését. Megvalósítottuk az nbutil-vinil-éter polimerizációját alán iniciáló rendszerek alkalmazásával is. Biológiailag lebontható politejsav-TDI-poli(etilén-glikol) és politejsav-TDI-poli(propilén-glikol) blokk- és/vagy kopolimereket állítottunk elő. A kopolimerek mechanikai tulajdonságait vizsgálatok alapján arra következtettünk, hogy a kopolimerzáció kémiai körülményei és a mechanikai tulajdonságok között szoros kapcsolat van. Az előállított kopolimerekből fóliákat készítettünk és ezek fizikai tulajdonságait a kereskedelemben kapható PVC és LDPE fóliák mechanikai tulajdonságaival hasonlítottuk össze. | AB, A2B, A1A2B, A2B2 and A3B3 (where, A=polyisobutylene, B=poly(methyl vinyl ether)) type block copolymers were synthesized and the effect of their structure on the micelle formation in aqueous media were studied. According to light scattering studies in the case of AB, A2B2, A3B3 and (AB)3 block copolymers the formation of vesicules was confirmed. It was also found that the aggregation number and hydrodynamic radius of the micelles formed from star shaped block copolymers were independent of the temperature, while in the case of micelles formed from linear blocks a significant increase can be observed. Glucose-, amino-, bis(imidazolyl-carboxylate)-, hydroxil-, epoxy-aldehyde-, and carboxyl-telechelic polymers were prepared. The structures of the polymers were confirmed by NMR and MALDI-TOF MS methods. These polymers under mass spectrometric conditions were investigated and phenomena arising in the mass spectrometer were interpreted. The polymerisation of nbutyl-vinyl-ether using the new AlCl3/LiAlH4 initiator systems was also elaborated. The synthesis of biologically degradable poly(lactic acid)-TDI-poly(ethylene glycol) and poly(lactic acid)-TDI-poly(propylene glycol) block and/or copolymers was achieved. A strong connection was found between the chemical conditions of the copolymerization and the observed mechanical properties. The copolymers were converted into foils and their properties were compared to that of the commercially available PVC and LDPE foils.
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ABSTRACT: Részletesen tanulmányoztuk a propilén-karbonát oligomerizációs reakcióját p-tercbutil-fenol/KHCO3 iniciáló rendszer jelenlétében. Biner random kopolimereket állítottunk elő etilén-karbonát, propilén-karbonát és -kaprolacton monomerek felhasználásával. A eredményeink alapján mechanizmust javasoltunk a karbonát-tartalmú láncok degradációjára és a ciklikus kooligomerek kialakulására. Új típusú polikondenzációs reakciót figyelünk meg a 3,6-Di-O-acetil-D-glükál esetében. A képződött poliszacharidok szerkezetét NMR és MALDI TOF módszerekkel derítettük fel. Különböző szegmensméretű poliizobutilén/poli(metil-vinil-éter) diblokk kopolimereket állítottunk elő és ezek szabad térfogatait vizsgáltuk pozitron annihilációs technikával. Megállapítottuk, hogy a monomeregységek beépülése növeli a szabad térfogatokat. Az apoláros poliizobutén és ezek kopolimerjeinek ezüstsók jelenlétében végzett MALDI-TOF MS vizsgálatai során Agn+- és Agn--klaszterek képződését mutattuk ki. Arany és vegyes AgnAum(+,-) klaszterionokat állítottunk elő MALDI körülmények között HAuCl4/AgTFA sókeverék felhasználásával. Megállapítottuk, hogy a HAuCl4/AgTFA arány változtatásával a képződött vegyes klaszter összetétele és eloszlása is kontrollálható. Poliuretán-szénszál kompozitokat állítottunk elő. Megállapítottuk, hogy a kompozit szakítószilárdsága és Young-modolusza a szénszál-tartalommal lineárisan nő. | The oligomerization of propylene carbonate in the presence of p-tert-butyl-phenole/KHCO3 initiator system was studied. Biner random copolymers were synthesized using ethylene carbonate, propylene carbonate and caprolactone monomers. A mechanism was proposed for the degradation of carbonate containing chains and for the formation of cyclic cooligomers. A novel type polycondensation reaction was observed in the case of 3,6-Di-O-acetyl-D-glucal. The structure of the polysaccharides formed was determined by NMR and MALDI TOF MS methods. Polyisobutylene/poly(methyl-vinyl-ether) diblock copolymers of varying block length were prepared and the free volumes of these block copolymers were studied by positron annihilation technique. It was observed that the addition of a new monomer unit increases the free volume. By studying polyisobutylene and its copolymers by MALDI-TOF MS in the presence of silver salts, the formation of Agn+- and Agn--clusters was identified. Gold and mixed AgnAum(+,-) clusters were produced under MALDI conditions from the mixture of HAuCl4/AgTFA/matrix. It was also observed that both the composition and the distribution of the mixed clusters could be controlled by the HAuCl4/AgTFA molar ratio. Polyurethane-carbon fiber composites were prepared. According to our experiments the breaking strength and the Young-modulus of the composite increased linearly with carbon fiber content.
