Nicholaos P. Evmiridis

Effect of the degree and type of the dealumination method on the structural, compositional and acidic characteristics of H-ZSM-5 zeolites

Abstract A series of H-ZSM-5 zeolites with different framework Si/Al ratios were prepared by hydrothermal synthesis and post-synthesis dealumination by various methods, i.e., HCl, steaming, steaming/HCl and ammonium hexafluorosilicate (AHFS). The degree of framework dealumination and the amount/type of the extra-framework phases formed were greatly dependent on the method of dealumination and the severity of the experimental conditions. The hydrothermal treatment of a parent ZSM-5 sample with Si/Al∼27 was very effective and produced significant amounts of Si–Al extra-framework phases, while the reaction with HCl in relatively strongly acidic environments resulted in very low dealumination. Treatment with AHFS was proven to be an appropriate method for preparing moderately dealuminated H-ZSM-5 samples which are free from extra-framework Al. The relative crystallinity and the microporosity of all dealuminated H-ZSM-5 zeolites were retained to a high degree (>80%), even for the severely steamed samples (∼96% dealumination). The morphology of the crystals/particles was not changed significantly; however, each dealumination method had a different effect on the partial breakdown of the crystals and on the formation of extra-framework/amorphous phases with a mesoporous character. The number of acid sites that corresponded to the high-temperature desorption peak of the ammomia-temperature programmed desorption spectra was found to be equivalent to the framework Al (FAl) content of all H-ZSM-5 samples, irrespective of the degree of dealumination and the amount of extra-framework phases. Theses phases had a low capability of adsorbing ammonia compared to the FAl atoms and were the main source of acidity for the severely steamed samples which had almost no FAl.

Monitoring reactive oxygen species in vivo using microdialysis sampling and chemiluminescence detection as an alternative global method for determination of total antioxidant capacity

Abstract A microdialysis sampling system coupled to chemiluminescence (CL) detection was developed to monitor the variation of lucigenin (Luc) CL emission in vivo in real time. The Luc CL emission is linearly correlated to the d-ROM test, thus providing evidence of equivalence to total antioxidant capacity (TAC). Furthermore, the system is simple, low cost, rapid and sensitive enough for real time monitoring of TAC variation in vivo under different physiological and pathological conditions. It is accurate and far more precise than the traditional methods since it overcomes uncontrolled conditions of handling samples. The production capacity of reactive oxygen species (proROS capacity) of individual antioxidant compounds mostly found in biological fluids was investigated using luminol CL emission. The implications of the proROS capacity of antioxidant compounds in biological fluids is further discussed under the perspective of explaining the appearance of certain pathological diseases, and on the basis of establishing a healthy diet for human beings. Further investigation showed that ascorbic acid (AA) plays a protective role in living organisms, so a diet rich in AA is important for health. Furthermore, it was found that lower physiological level of AA or higher physiological level of uric acid (UA) or glucose (GLU) may reduce O 2 into reactive oxygen species (ROS, e.g. H 2 O 2 , O 2 − ) in the presence of Fe(III). This may explain some syndromes in the cases of AA deficiency (e.g. scurvy) and related diseases, e.g. diabetes or gout. From the data obtained, there is a strong indication that the damage or pathological alternation is probably due to the higher level of ROS, which are generated from the reduced oxygen in the presence of pathological level of related reductants.

Dehydrogenation of propane over natural clinoptilolite zeolites

Abstract Clinoptilolite is one of the most commonly used natural zeolites in environmental and industrial applications. In this study, the activity and selectivity of two different clinoptilolite tuffs from Thrace region of Greece were investigated using the model reaction of propane dehydrogenation and were compared to those of synthetic proton and metal-modified ZSM-5 zeolite catalysts. The clinoptilolite bearing tuff from Metaxades (MCH) showed appreciable activity for propane dehydrogenation, similar to that of a steamed Cr-modified ZSM-5 zeolite and considerably higher compared to the second natural clinoptilolite tuff (SF) from the area of Pentalofos and to the H-ZSM-5 zeolite. The total propylene yield for the MCH sample at 540 °C was 8.4%, compared to 3.4% for SF, 5.3% for steamed H-ZSM-5 and 8.3% for steamed Cr-modified ZSM-5. The proton-exchanged forms of both natural zeolites showed improved conversion of propane but resulted in lower propylene selectivity due to subsequent hydrogen transfer, cracking and cyclo-oligomerization reactions induced by the higher number of framework Bronsted acid sites.

Chemiluminescence (CL) emission generated during oxidation of pyrogallol and its application in analytical chemistry. I. Effect of oxidant compound

An investigation of chemiluminescence (CL)-emission generated by the oxidation of pyrogallol using various inorganic oxidant compounds is reported in this F.I.A.-merging zone application. The oxidant compounds that showed measurable CL-emission were permanganate, periodate, hypochlorite anions, cerium(IV) and hydrogen peroxide. The different oxidant compounds showed CL-emissions at different pH-ranges. The CL-emission was limited by the inner filter effect and this was more intense for oxidants of selective oxidation. Kinetic effects were also found in the case of oxidation by permanganate. Plots of CL-emission against pH give evidence of speciation and or deactivation mechanism effects. The analytical parameters for the determination of the oxidants are given. Sensitivities of 895 600, 19 500, 33 723, 10 680 and 56 703 mV M(-1) were found for the determination of permanganate, cerium(IV), periodate, hypochlorite and hydrogen peroxide, respectively. The calibration curves of the oxidant determination were generally S-shaped; the S-shaped calibration curve of periodate was closer to a straight line relationship while that of hypochlorite was almost a straight line; detection limits in the range of 10(-4) M oxidant concentration were found for nearly all oxidants. The analytical parameters for determination of pyrogallol by the CL-emission generated through oxidation by the different oxidants at optimum conditions were 1.16x10(6) mV M(-1) for permanganate; 0.086x10(6) mV M(-1) for cerium(IV); 0.91x10(6) mV M(-1) for periodate; 0.012x10(6) mV M(-1) for hypochlorite; and 0.25x10(6) mV M(-1) for hydrogen peroxide. The detection limit was 1.0x10(-4) M. The nearly straight-line relationship (initial part of the plot) for CL-emission with oxidant concentration gives an indication that the CL-reaction of pyrogallol oxidation by hypochlorite proceeds through a process that involves energy transfer while the pronounced S-shaped curve produced by permanganate gives the indication that the reaction proceeds through a process that does not involve energy transfer according to the mathematical model of CL-emission that controls the F.I.A.-merging zone technique of the flow apparatus used in this work. The sequence of completeness of the oxidation process by each oxidant was MnO(4)(-)>H(2)O(2)>IO(4)(-)>OCl(-); the stoichiometric quantity of the oxidant per pyrogallol molecule for the rapid part of the overall oxidation by each different oxidant was attempted; this is an index-value of the oxidation state of the fluorescent excited molecule. Finally, the impact of the above findings for further analytical applications is discussed.

Dialysis membrane sampler for on-line flow injection analysis/chemiluminescence-detection of peroxynitrite in biological samples.

Peroxynitrite, as a derivative of nitric oxide, is a potent oxidant. It reacts with several biological molecules, makes cellular and tissue damages, and is related with many diseases; therefore, it is of major concern in current medical research works. In this work, a special perm-selective cellulose acetate membrane sampler is used to implement flow injection analysis (FIA)/chemiluminscence (CL)-detection method for the detection of peroxynitrite with Luminol CL-reagent. Optimum detection conditions were established, and the permeability of peroxynitrite through cellulose acetate (CA) membrane, as well as the interference from matrix constituents were studied. The proposed method has the high sensitivity of the CL-detection and the selectivity of perm-selective membrane sampler. The obtained detection limit of 1x10(-11) M (without dialysis membrane) and 1x10(-10) M (with dialysis membrane), makes it possible to monitor the elusive peroxynitrite in biological samples. The mechanism of luminol CL-emission generated during oxidation by peroxynitrite and the kinetics of peroxynitrite decomposition were also studied using FIA/CL-detection set-up.

Effect of treatment of synthetic zeolite-polymer membranes on their electrochemical-potential response characteristics

SummaryThe performance of synthetic-polymer membrane-electrodes for cation sensing is investigated by obtaining E versus pM graphs and E versus time curves of the same membrane type under different treatments or of membranes constructed by modified procedures. The slopes of E versus pM curves for the salts of monovalent cations show different values for the same membrane type as well as for the different membrane types and are found within the range of 43 to 57 mV per pM. The response time of the membrane is found to be slower when the membranes are plastic phase deficient. Generally, the detection limit is only slightly dependent on the composition of the membrane and the best value is obtained with the polished membranes which is close to the value of pM=5 while for the other membranes the values are within the range of pM 4 to 5. The range of linearity is also slightly dependent on the method of membrane construction and in general is shorter when the membranes are plastic phase deficient. The selectivity coefficients are found to depend significantly on the method of construction of the membrane but in general the selectivity of all the membranes studied in this report is poor. The asymmetry potential is found to be related to an ion exchange process and is developed slowly in 5A-type membranes. However, when the value of asymmetry potential is high, a longer time is needed to reach the final value of e.m.f. in measurements among different concentrations of the same metal ion and much longer is needed where there is switching of measurement from a monovalent cation to a divalent cation.

On the re-assessment of the optimum conditions for the determination of platinum, palladium and rhodium in environmental samples by electrothermal atomic absorption spectrometry and microwave digestion

The experimental conditions for the determination of platinum, palladium and rhodium by graphite furnace atomic absorption spectrometry (GFAAS) are re-assessed. A certified material (BCR-723) was used as a working sample and analyzed using various extraction and atomization procedures in order to find the optimal experimental conditions that enable the quantitative and reproducible detection of platinum, palladium and rhodium in environmental matrices. Evidently, literature observations regarding the atomization conditions were proven fairly adequate. However, the provision of the optimum extraction conditions revealed several parameters that lie behind the reported uncertainties. The appropriate combination between extraction conditions and atomization programs afforded a considerable improvement in the recoveries and analytical features of platinum, palladium and rhodium determination with GFAAS. Cross-examination of the analytical data with various CRMs (certified reference materials) was used to validate the robustness of the method in heterogeneous matrices bearing different element levels. Under the optimum experimental conditions the method permits the determination at concentrations as low as (LOD(3S/N)) 1.9 ng g(-1), 0.45 ng g(-1) and 0.6 ng g(-1) for Pt, Pd and Rh, respectively affording recoveries in the range of 93-101%. The method was successfully applied to the assessment of Pt, Pd and Rh accumulation in real road dust and soil samples in Greece.

Betulinic acid-mediated inhibitory effect on hepatitis B virus by suppression of manganese superoxide dismutase expression

The betulinic acid (BetA) purified from Pulsatilla chinensis (PC) has been found to have selective inhibitory effects on hepatitis B virus (HBV). In hepatocytes from HBV‐transgenic mice, we showed that BetA substantially inhibited HBV replication by downregulation of manganese superoxide dismutase (SOD2) expression, with subsequent reactive oxygen species generation and mitochondrial dysfunction. Also, the HBV X protein (HBx) is suppressed and translocated into the mitochondria followed by cytochrome c release. Further investigation revealed that SOD2 expression was suppressed by BetA‐induced cAMP‐response element‐binding protein dephosphorylation at Ser133, which subsequently prevented SOD2 transcription through the cAMP‐response element‐binding protein‐binding motif on the SOD2 promoter. SOD2 overexpression abolished the inhibitory effect of BetA on HBV replication, whereas SOD2 knockdown mimicked this effect, indicating that BetA‐mediated HBV clearance was due to modulation of the mitochondrial redox balance. This observation was further confirmed in HBV‐transgenic mice, where both BetA and PC crude extracts suppressed SOD2 expression, with enhanced reactive oxygen species generation in liver tissues followed by substantial HBV clearance. We conclude that BetA from PC could be a good candidate for anti‐HBV drug development.

Periodate oxidation and its contribution to instrumental methods of micro-analysis--a review.

A comprehensive review that summarizes the periodate oxidation contribution to the development of selective instrumental methods of micro-analysis in the fields of electrochemistry, spectrophotometry, luminometry, chromatography, as well as studies on successful fabrication of sensors or labeling techniques are given in this review.

Determination of glucose and fructose in mixtures by a kinetic method with chemiluminescence detection

A kinetic method of analysis is described, based on oxidation by periodate for the determination of glucose and fructose in sample solutions. The method combines flow injection and chemiluminescence (CL) detection. The detection is based on the CL signal generated during oxidation of pyrogallol by periodate. The method is selective for the determination of vic-diols and polyols; the method is designed to determine hexose contents as low as 200 μg. However, the method can be tailored for even lower amounts (10 times less). When the total hexose concentration is known, the individual fructose and glucose content can be determined from the rate constant that best-fits the kinetic data; the relative standard deviation of three independent kinetic experiments with the same ratio of concentrations was found to be within 2% and the standard error of the rate constant from the fitting treatment was found to be less than 10% in all samples of different concentration ratios between glucose and fructose. The method can be automated and controlled by computer software. Data points from two kinetic experiments with different sample quantities in the reaction mixture are required for the determination of the total hexose content and the individual fractions of glucose and fructose.