Sándor Kéki

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.

Fast microwave-mediated bulk polycondensation of D,L-lactic acid

The polycondensation of D,L-lactic acid upon microwave irradiation was studied. The results of polycondensation by means of microwave were compared to those obtained from conventional heating of lactic acid at 100°C, and it was found that the reaction proceeds with much higher rate upon microwave irradiation. The oligomer mixtures formed were investigated by means of matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS). The molecular mass of the poly(lactic acid) formed under microwave irradiation was found to increase with irradiation time, and the formation of cyclic oligomers after 20 min of reaction time was also revealed.

Photoinduced Smart, Self-Healing Polymer Sealant for Photovoltaics

Polyisobutylene (PIB)-based polymer networks potentially useful as smart coatings for photovoltaic devices have been developed. Low molecular weight coumarin functional triarm star PIB was synthesized via a single step SN2 reaction of bromoallyl functional triarm star PIB with 4-methylumbelliferone or umbelliferone in the presence of sodium hydride. Quantitative end functionality was confirmed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. UVA (λmax = 365 nm) induced reversible photodimerization of the coumarin moieties resulted in cross-linked elastomeric films exhibiting self-healing behavior. The extent of photodimerization/photoscission was monitored by UV-vis spectroscopy. The low oxygen (1.9 × 10(-16) mol m m(-2) s(-1) Pa(-1)) and moisture (46 × 10(-16) mol m m(-2) s(-1) Pa(-1)) permeability of the cross-linked polymer films suggest excellent barrier properties of the cross-linked polymer films. The self-healing process was studied by atomic force microscopy (AFM). For this, mechanical cuts were introduced in the cross-linked PIB films through micromachining with an AFM tip and the rate of healing induced by UV, sunlight, or both was followed by taking AFM images of the film at different time intervals during the repair process.

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.

Identification of silymarin constituents: An improved HPLC-MS method

A high-performance liquid chromatographic/tandem mass spectrometric method was developed for the determination of the major bioactive flavonolignans in silymarin, a herbal remedy extracted from the milk thistle Silybum marianum. In this study, eight active components of silymarin with the same elemental composition, including silychristins A and B, silydianin, silybin A and B, isosilybin A and B and an unknown compound were completely separated. Furthermore, three additional components were detected and partly separated; presumably two silybin stereoisomers and one isosilybin stereoisomer. The collision-induced dissociation (CID) MS/MS spectra of these silymarin constituents were studied: the spectral similarity values of the component pairs were determined, and simple criteria were found for distinguishing the components.

Increased production of asymmetric dimethylarginine (ADMA) in ankylosing spondylitis: Association with other clinical and laboratory parameters

OBJECTIVE Asymmetric dimethylarginine (ADMA) has been associated with atherosclerosis, vascular diseases and, recently, also with arthritis including rheumatoid arthritis (RA) and ankylosing spondylitis (AS). METHODS Serum ADMA, arginine and symmetric dimethylarginine (SDMA) levels were assessed by liquid chromatography in 61 AS and 26 osteoarthritis (OA) patients with no known cardiovascular disease. RESULTS Serum ADMA levels were significantly increased in AS compared to OA patients (0.95 ± 0.17 μM versus 0.70 ± 0.25 μM; p < 0.001). There were no differences in serum arginine and SDMA levels. Serum ADMA levels also positively correlated with age (R = 0.258; p = 0.043), body mass index (R = 0.368; p = 0.003), erythrocyte sedimentation rate (R = 0.329; p = 0.009) and ADMA levels negative correlated with chest expansion (R = -0.251; p = 0.04). No correlations were found between ADMA levels and disease duration, pain intensity, BASDAI, BASFI, BASMI, quality of life, CRP, HLA-B27 positivity, endothelial dysfunction or carotid atherosclerosis. CONCLUSION ADMA may serve as a marker of systemic inflammation and may reflect functional immobility in AS. Further studies are needed to assess the possible role of ADMA in AS and AS-related vascular disease.

Optimum conditions for the synthesis of linear polylactic acid-based urethanes

The reactions of polylactic acid (PLA) oligomers and isocyanates (4,4′-diphenylmethane diisocyanate and toluene diisocyanate) are reported. The effects of the reaction conditions, that is, the reaction time, reaction temperature, molar ratios, isocyanates, and catalyst, on the number-average molecular weight (Mn ) are demonstrated. The optimum reaction conditions are determined by the synthesis of relatively high Mn PLA-based linear polyurethanes. The structure of the polymer samples was investigated with dynamic light scattering, 1H NMR, IR, and matrix-assisted laser-desorption ionization time-of-flight mass spectroscopy (MALDI-TOF MS).

Diazo Transfer−Click Reaction Route to New, Lipophilic Teicoplanin and Ristocetin Aglycon Derivatives with High Antibacterial and Anti-influenza Virus Activity: An Aggregation and Receptor Binding Study

Semisynthetic, lipophilic ristocetin and teicoplanin derivatives were prepared starting from ristocetin aglycon and teicoplanin psi-aglycon (N-acetyl-D-glucosaminyl aglycoteicoplanin). The terminal amino functions of the aglycons were converted into azido form by triflic azide. Copper catalyzed 1,3-dipolar cycloaddition reaction with lipophilic alkynes resulted in the title compounds. Two of the teicoplanin derivatives showed very good MIC and MBC values against various Gram-positive bacteria, including vanA enterococci. The aggregation and interaction of a n-decyl derivative with bacterial cell wall components was studied. One of the lipophilic ristocetin derivatives displayed favorable anti-influenza virus activity.

Energy-dependent collision-induced dissociation of lithiated polytetrahydrofuran: Effect of the size on the fragmentation properties

The fragmentation properties of singly and doubly lithiated polytetrahydrofuran (PTHF) were studied using energy-dependent collision-induced dissociation. The product ion spectrum of [PTHF + Li]+ showed the formation of three different series corresponding to product ions with hydroxyl, aldehyde and vinyl end-groups. Interestingly, besides these series, two additional, non-lithiated product ions C4H9O+ and C4H7+ were identified in the MS/MS spectra. The MS/MS of the doubly lithiated PTHF ([PTHF + 2Li]2+) with a number of repeat units ranging from 8 to 27 showed the formation of product ions similar to those of the singly lithiated series, however, doubly lithiated product ions and product ions formed by the loss of one Li+-ion from the precursor ion also appeared with significant abundances. Analysis of the breakdown curves for the singly and doubly charged PTHF indicated that the series A ions are formed most probably together with the series B ions, while members of the series C ions appeared at significantly higher collision energies. The fragmentation properties of [PTHF + Li]+ and [PTHF + 2Li]2+ were also interpreted using the survival yield method. It was found that the collision energy/voltage necessary to obtain 50% fragmentation (CV50) was dependent linearly on the number of the repeat units, i.e., on the size, or the number of degrees of freedom (DOF).

Serum asymmetric dimethylarginine negatively correlates with intima-media thickness in early-onset atherosclerosis.

Background: Asymmetric dimethylarginine (ADMA) assumes a significant role in atherosclerosis by inhibiting the endothelial nitric oxide synthase (eNOS). Moreover, ADMA inhibits the inducible NOS (iNOS), the isoform that triggers atherosclerosis via peroxynitrite formation. Therefore, we investigated whether ADMA is a risk or protective factor in the atherosclerotic process. Intima-media thickness (IMT) of the common carotid artery, a surrogate for vascular diseases, was chosen as the outcome variable of interest. Methods: Sixty patients younger than 55 years having at least 30% stenosis of the internal carotid artery and 30 age- and gender-matched controls were recruited at a community-based neurosonological laboratory. We investigated relatively young patients to circumvent the confounding effect age has in the development of atherosclerosis. Results: The IMT showed a negative correlation with ADMA upon analysis of the pooled data (Spearman correlation coefficient –0.300, p = 0.0041) and the atherosclerotic stratum (Spearman correlation coefficient –0.323, p = 0.012). A multiple linear regression model containing all determinant factors of IMT previously identified by simple regression was used to further quantify the relationship between IMT and ADMA. The negative association between IMT and ADMA remained statistically significant (β: –0.510, CI: –0.894, –0.127; p = 0.010), furthermore it was even stronger in the atherosclerotic stratum (β: –0.67, CI: –1.16, –0.18; p = 0.008). Conclusions: A minimal increase in ADMA concentration may be protective by inhibiting iNOS but not eNOS in states where iNOS is induced, e.g. inflammation accompanying atherosclerosis.