The electrochemical behavior of 12 non-steroidal anti-inflammatory drugs (NSAIDs) was studied by ... more The electrochemical behavior of 12 non-steroidal anti-inflammatory drugs (NSAIDs) was studied by means of cyclic voltammetry at a glassy carbon electrode. The underlying solvent had a considerable effect to the oxidation potentials of the investigated NSAIDs due to the alteration of their polar intermediates’ solvation. Oxicams were more capable of electrochemical oxidation, and the influence of both specific and non-specific
A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine ... more A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine (Se-CM), which have very close half-wave potential when they are simultaneously analyzed by voltammetric techniques, has been developed and optimized. Thus, selenocystamine remains in the cation exchanger Purolite C 100 H, whereas selenourea is found in the effluent and is determined by square wave cathodic stripping voltammetry using Na(2)CO(3 )as electrolyte. Selenocystamine is then eluted from the cation exchanger using 4 M HCl and analyzed by square wave cathodic stripping voltammetry in the HCl solution. For each voltammetric determination the corresponding parameters were investigated and optimized; the obtained detection limits were 0.3 ng Se mL(-1) for Se-CM and 2 ng Se mL(-1) for Se-U. A flow sheet for the separation of inorganic (Se(IV) and Se(VI)) and organoselenium compounds (Se-U, Se-CM, (CH(3))(2)Se(2), and (CH(3))(2)Se) developed for their electrochemical detection is presented and it was successfully applied to a certified reference material, an environmental soil sample, and a urine sample.
A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine ... more A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine (Se-CM), which have very close half-wave potential when they are simultaneously analyzed by voltammetric techniques, has been developed and optimized. Thus, selenocystamine remains in the cation exchanger Purolite C 100 H, whereas selenourea is found in the effluent and is determined by square wave cathodic stripping voltammetry using Na(2)CO(3 )as electrolyte. Selenocystamine is then eluted from the cation exchanger using 4 M HCl and analyzed by square wave cathodic stripping voltammetry in the HCl solution. For each voltammetric determination the corresponding parameters were investigated and optimized; the obtained detection limits were 0.3 ng Se mL(-1) for Se-CM and 2 ng Se mL(-1) for Se-U. A flow sheet for the separation of inorganic (Se(IV) and Se(VI)) and organoselenium compounds (Se-U, Se-CM, (CH(3))(2)Se(2), and (CH(3))(2)Se) developed for their electrochemical detection is presented and it was successfully applied to a certified reference material, an environmental soil sample, and a urine sample.
The lipophilicity and biomimetic retention profile of three selenium species, methyl-seleninic ac... more The lipophilicity and biomimetic retention profile of three selenium species, methyl-seleninic acid (MSA), Se-Methyl-selenocysteine (MeSeC) and dimethyl-selenourea (DMeSeU), were established. Lipophilicity was measured by the shaking flask method, while for chromatography one reversed-phase (Discovery C-18) column and three biomimetic stationary phases, namely immobilized artificial membrane (IAM), human serum albumin (HSA) and ?1-acid glycoprotein (AGP) were employed, under different mobile phase conditions. These results were combined with previous data obtained under analogous conditions on eight selenium species including selenites (Se(IV)), selenates (Se(VI)), selenomethionine (SeMet), selenocystine (SeCyst), selenocystamine (SeCM), selenourea (SeU), dimethylselenide ((CH3)2Se) and dimethyldiselenide ((CH3)2Se2). The combined data were further used to establish relations between biomimetic retention factors and lipophilicity, the effect of the presence of reduced glutathione (GSH) to retention, as well as to determine the oxidation potential by means of cyclic voltammetry. According to their anode potentials in cyclic voltammetry, only the urea analogues, SeU and, especially, DMeSeU, exhibited considerable antioxidant properties. Moreover IAM retention of Se(IV), Se(VI), SeMet and MeSeC was correlated with Caco-2 apparent permeability coefficient (Papp) available in literature. IAM retention data were further converted to percentage of human oral absorption according to a relevant equation reported in the literature, while from HSA retention results the plasma protein binding was estimated. According to these values, low biopersistence in the human body may be anticipated.
The retention behavior of sixty structurally diverse drugs on two immobilized artificial membrane... more The retention behavior of sixty structurally diverse drugs on two immobilized artificial membrane (IAM) columns, IAM.PC.MG and IAM.PC.DD2 types, at two pH values, 7.4 and 5.5, was established. Extrapolated to pure aqueous phase retention factors, logkw(IAM), were determined and the role of acetonitrile as organic modifier was explored, considering the relationships with the slopes, S, of the extrapolation procedure. Good interrelations between retention factors on the two IAM stationary phases were observed, although logkw(IAM.PC.DD2) values are generally higher than logkw(IAM.PC.MG). In order to investigate the underlying retention mechanism, relationships between IAM retention factors and lipophilicity, expressed as logP or logD at pH 7.4 were established. Electrostatic interactions were considered by introducing the positively and negatively charged molecular fractions as additional parameters in the logkw(IAM)/logD relationships. The positive contribution of these fractions supported the involvement of the electrostatic interactions in the retention mechanism. Special attention was given to the retention behavior of zwitterionic compounds and for compounds with special structural characteristics.
ABSTRACT We apply a recently developed time-dependent one-zone leptohadronic model to study the e... more ABSTRACT We apply a recently developed time-dependent one-zone leptohadronic model to study the emission of the blazar Mrk 421. Both processes involving proton-photon interactions, i.e. photopair (Bethe-Heitler) and photopion, have been modeled in great detail using the results of Monte Carlo simulations, like the SOPHIA event generator, in a self-consistent scheme that couples energy losses and secondary injection. We find that TeV gamma-rays can be attributed to synchrotron radiation either from relativistic protons or, alternatively, from secondary leptons produced via photohadronic processes. We also study the variability patterns that each scenario predicts and we find that while the former is more energetically favored, it is the latter that produces, in a more natural way, the usual quadratic behavior between X-rays and TeV gamma-rays. We also use the obtained SEDs to calculate in detail the expected neutron and neutrino fluxes that each model predicts.
The electrochemical behavior of 12 non-steroidal anti-inflammatory drugs (NSAIDs) was studied by ... more The electrochemical behavior of 12 non-steroidal anti-inflammatory drugs (NSAIDs) was studied by means of cyclic voltammetry at a glassy carbon electrode. The underlying solvent had a considerable effect to the oxidation potentials of the investigated NSAIDs due to the alteration of their polar intermediates’ solvation. Oxicams were more capable of electrochemical oxidation, and the influence of both specific and non-specific
A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine ... more A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine (Se-CM), which have very close half-wave potential when they are simultaneously analyzed by voltammetric techniques, has been developed and optimized. Thus, selenocystamine remains in the cation exchanger Purolite C 100 H, whereas selenourea is found in the effluent and is determined by square wave cathodic stripping voltammetry using Na(2)CO(3 )as electrolyte. Selenocystamine is then eluted from the cation exchanger using 4 M HCl and analyzed by square wave cathodic stripping voltammetry in the HCl solution. For each voltammetric determination the corresponding parameters were investigated and optimized; the obtained detection limits were 0.3 ng Se mL(-1) for Se-CM and 2 ng Se mL(-1) for Se-U. A flow sheet for the separation of inorganic (Se(IV) and Se(VI)) and organoselenium compounds (Se-U, Se-CM, (CH(3))(2)Se(2), and (CH(3))(2)Se) developed for their electrochemical detection is presented and it was successfully applied to a certified reference material, an environmental soil sample, and a urine sample.
A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine ... more A simplified procedure based on ion-exchange separation of selenourea (Se-U) and selenocystamine (Se-CM), which have very close half-wave potential when they are simultaneously analyzed by voltammetric techniques, has been developed and optimized. Thus, selenocystamine remains in the cation exchanger Purolite C 100 H, whereas selenourea is found in the effluent and is determined by square wave cathodic stripping voltammetry using Na(2)CO(3 )as electrolyte. Selenocystamine is then eluted from the cation exchanger using 4 M HCl and analyzed by square wave cathodic stripping voltammetry in the HCl solution. For each voltammetric determination the corresponding parameters were investigated and optimized; the obtained detection limits were 0.3 ng Se mL(-1) for Se-CM and 2 ng Se mL(-1) for Se-U. A flow sheet for the separation of inorganic (Se(IV) and Se(VI)) and organoselenium compounds (Se-U, Se-CM, (CH(3))(2)Se(2), and (CH(3))(2)Se) developed for their electrochemical detection is presented and it was successfully applied to a certified reference material, an environmental soil sample, and a urine sample.
The lipophilicity and biomimetic retention profile of three selenium species, methyl-seleninic ac... more The lipophilicity and biomimetic retention profile of three selenium species, methyl-seleninic acid (MSA), Se-Methyl-selenocysteine (MeSeC) and dimethyl-selenourea (DMeSeU), were established. Lipophilicity was measured by the shaking flask method, while for chromatography one reversed-phase (Discovery C-18) column and three biomimetic stationary phases, namely immobilized artificial membrane (IAM), human serum albumin (HSA) and ?1-acid glycoprotein (AGP) were employed, under different mobile phase conditions. These results were combined with previous data obtained under analogous conditions on eight selenium species including selenites (Se(IV)), selenates (Se(VI)), selenomethionine (SeMet), selenocystine (SeCyst), selenocystamine (SeCM), selenourea (SeU), dimethylselenide ((CH3)2Se) and dimethyldiselenide ((CH3)2Se2). The combined data were further used to establish relations between biomimetic retention factors and lipophilicity, the effect of the presence of reduced glutathione (GSH) to retention, as well as to determine the oxidation potential by means of cyclic voltammetry. According to their anode potentials in cyclic voltammetry, only the urea analogues, SeU and, especially, DMeSeU, exhibited considerable antioxidant properties. Moreover IAM retention of Se(IV), Se(VI), SeMet and MeSeC was correlated with Caco-2 apparent permeability coefficient (Papp) available in literature. IAM retention data were further converted to percentage of human oral absorption according to a relevant equation reported in the literature, while from HSA retention results the plasma protein binding was estimated. According to these values, low biopersistence in the human body may be anticipated.
The retention behavior of sixty structurally diverse drugs on two immobilized artificial membrane... more The retention behavior of sixty structurally diverse drugs on two immobilized artificial membrane (IAM) columns, IAM.PC.MG and IAM.PC.DD2 types, at two pH values, 7.4 and 5.5, was established. Extrapolated to pure aqueous phase retention factors, logkw(IAM), were determined and the role of acetonitrile as organic modifier was explored, considering the relationships with the slopes, S, of the extrapolation procedure. Good interrelations between retention factors on the two IAM stationary phases were observed, although logkw(IAM.PC.DD2) values are generally higher than logkw(IAM.PC.MG). In order to investigate the underlying retention mechanism, relationships between IAM retention factors and lipophilicity, expressed as logP or logD at pH 7.4 were established. Electrostatic interactions were considered by introducing the positively and negatively charged molecular fractions as additional parameters in the logkw(IAM)/logD relationships. The positive contribution of these fractions supported the involvement of the electrostatic interactions in the retention mechanism. Special attention was given to the retention behavior of zwitterionic compounds and for compounds with special structural characteristics.
ABSTRACT We apply a recently developed time-dependent one-zone leptohadronic model to study the e... more ABSTRACT We apply a recently developed time-dependent one-zone leptohadronic model to study the emission of the blazar Mrk 421. Both processes involving proton-photon interactions, i.e. photopair (Bethe-Heitler) and photopion, have been modeled in great detail using the results of Monte Carlo simulations, like the SOPHIA event generator, in a self-consistent scheme that couples energy losses and secondary injection. We find that TeV gamma-rays can be attributed to synchrotron radiation either from relativistic protons or, alternatively, from secondary leptons produced via photohadronic processes. We also study the variability patterns that each scenario predicts and we find that while the former is more energetically favored, it is the latter that produces, in a more natural way, the usual quadratic behavior between X-rays and TeV gamma-rays. We also use the obtained SEDs to calculate in detail the expected neutron and neutrino fluxes that each model predicts.
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