Irene Rezzano

Porphyrin thin films coated quartz crystal microbalances prepared by electropolymerization technique

Quartz crystal microbalances (QMB) have been coated by thin films of different metal complexes of protoporphyrin IX dimethyl ester (M-PPIX), deposited by electropolymerization technique. The structure of these films has been characterized by scanning tunnelling microscopy (STM). The sensory behaviour of the obtained QMB have been studied in the presence of four volatile organic compounds (VOC).

Molecular Imprinted Polymers Prepared by Electropolymerization of Ni-(Protoporphyrin IX)

Abstract The features of combining a chemically modified electrode (CME) with an artificial receptor system, prepared by imprinting electropolymerized [Ni (Protoporphyrin IX) dimethyl ester] [Ni-(PPIX)] in the presence of nitrobenzene, were studied. The responses of the modified glassy carbon electrode towards template molecules were analyzed by cycling over the nitrobenzene reduction wave. The specific signal was much higher than the non-specific one which demonstrates the selectivity of such a system. This approach has potential for preparation of selective polymeric films on the surface of different transducers. ∗ Visiting scientist on leave from Institute of Molecular Biology and Genetics, Academy of Sciences of Ukraine, 252143, Kiev, Ukraine. ∗∗ Visiting scientist on leave from Universidad de Buenos Aires, Junin 956, Buenos Aires 1113, Argentina.

Liquid chromatography/electrochemical detection of phenols at a Poly[Ni-(Protoporphyrin IX)] chemically modified electrode

Abstract Poly(Ni-(Protoporphyrin IX)) modified glassy carbon electrodes showed an enhanced response for the oxidation of different phenolic compounds ( p -chlorophenol, p -nitrophenol and phenol). It can also suppress the oxidation of more polar substances such as ascorbic acid and potassium hexacyanoferrate(II). These substantial improvements in the sensitivity and selectivity of liquid chromatography with electrochemical detector (LCEC) for the determination of phenols can be obtained by using electrodes thus coated. The method gives a linear range up to 1.3 μg ml −1 and a detection limit of 13 ng ml −1 for p -nitrophenol. The dynamic behaviour of the detector is evaluated with respect to the solute concentration and flow rate. The surface coating is highly stable under the hydrodynamic conditions prevailing in the flow cell.

Gold nanoparticle‐coated capillaries for protein and peptide analysis on open‐tubular capillary electrochromatography

We report a new method of immobilization of gold nanoparticles (AuNPs) on a fused‐silica capillary through covalent binding. The resulting modified capillary was applied to electrophoretic systems to improve the efficiency of separation and the selectivity of selected solutes. The immobilization of AuNPs on the capillary wall was performed in a very simple and fast way without requiring heating. The surface features of an AuNP‐coated capillary column were determined using the scanning electron microscopy. The chromatographic properties of AuNP‐coated capillaries were investigated through variation of the buffer pH and separation voltage. Effective separations of synthetic peptides mixture were obtained on the AuNP‐coated capillaries. The method shows a remarkable stability since it was reused about 900 times. The capacity factor was duplicated. Therefore, this modification is stable and can be applied to different separation purposes. A complex mixture of tryptic peptide fragments of HSA was analyzed in both the bare‐ and the AuNP‐coated capillaries. Better electrophoretic peptide profile was observed when using the AuNP‐coated capillary.

Comparison of Tyrosinase Biosensor and Colorimetric Method for Polyphenol Analysis in Different Kinds of Teas

Abstract We report the content of polyphenols, expressed as chlorogenic acid equivalents, in a variety of commercially available samples of yerba mate. The 48% of analyzed samples presented a 92 ± 8 mg of extracted chlorogenic acid equivalents per gram of dry base. Composites exhibited a lower extracted amount. Results from samples contained in tea bags are higher, indicating dependence on milling degree. The extracted chlorogenic acid, expressed as mg · g−1, was evaluated by three methods in a unique yerba mate sample: biosensor (89.2 mg · g−1), Folin (90.2 mg · g−1), and high‐performance liquid chromatography (HPLC) analysis (21.0 mg · g−1). Biosensing system validation was performed. Repetitiveness of genuine replicates was consistent with nature of the samples. Discrimination between yerba mate and other plants can be done using principal component analysis (PCA) and the corresponding physical and chemical descriptors. Flavor and taste alterations can be studied by means of analytical methods that involve low‐cost instrumentation. It has been observed that some green tea samples present remarkable differences depending on the specie. Financial support from University of Buenos Aires (UBACyT B059), Argentine National Research Council (CONICET; 641‐PIP98), and ANPCyT (Grant 06‐06600 PICT99) are gratefully acknowledged. Romina R. Carballo also thanks CONICET for a doctoral fellowship. Thanks also to Rafael Ricco (Faculty of Pharmacy and Biochemistry, UBA, Argentina) for helpful assistance. §CONICET permanent staff

Comparison between Three Amperometric Sensors for Phenol Determination in Olive Oil Samples

The analytical performance of two modified electrodes (a tyrosinase biosensor and a glassy carbon electrode (GCE) covered with poly[Ni-(protoporphyrin IX)dimethyl ester]) in comparison with the bare electrode has been evaluated in a flow injection system using standard solutions of oleuropein and olive oil samples. The tyrosinase biosensor appeared to be an appropriate device for the selective determination of phenols, moreover it can be easily incorporated in an on-line system. This method was used to evaluate the stability of the samples.

Study of peptide–ligand interactions in open‐tubular capillary columns covalently modified with porphyrins

The inner surface of fused silica capillaries has been covalently modified with different porphyrins (deuteroporphyrin, complexes of deuteroporphyrin with metal ions Fe(III), Cu(II), Zn(II), Ni(II), and Cu(II)–meso–tetra (carboxyphenyl) porphyrin) and it was applied for the separation of biologically active peptides by open‐tubular capillary electrochromatography. Separations were performed in a mobile phase composed of 25 mM potassium phosphate, pH 4.0, 5% v/v ACN and 10 mM hydroquinone. Changes in the effective electrophoretic mobility of peptides were studied concerning porphyrin central metal atom, attachment geometry, and the presence of coordinating or aromatic amino acid residues in the peptide sequence. The results showed that differences in metal core on the porphyrin and the spatial conformation of attached porphyrin result in changes in the analyte interaction with the stationary phase.

Linear Scan Stripping Voltammetry at Glassy-Carbon Based Thin Mercury Film Electrodes for Determination of Trace Aluminium in Dialysis Fluids.

Abstract Linear scan cathodic stripping voltammetry at glassy-carbon based thin mercury film electrodes is a simple and inexpensive alternative for determining trace Al(III) in dialysis fluids. The efficiency of a variety of ligands (SVRS, Cupferron and Blue Black Eriochrome R) was evaluated comparing their voltamperometric response by application of a linear scan mode, after preconcentration into the mercury film electrode as Al(III) complexes. The best results were obtained when Cupferron was used as ligand, since its stripping current compares favourably in terms of sensitivity and resolution. The sharply defined cathodic peak at -1.3 V, corresponding to the reduction of the interfacial accumulated complex, could be used for quantitation. The response is linear up to 50 μg/l; correlation coefficient, 0.995. The relative standard deviation (at 20 μg/l level) is 3.5%, a detection limit of 0.5μg/l was estimated from the signal to noise characteristics of the response for 5 μg/l, which compares favourably ...

Amperometric Detection of Peroxides Using Peroxidase and Porphyrin Biomimetic Modified Electrodes

Biosensors designed with crosslinked redox hydrogel and horseradish peroxidase have been evaluated in aqueous and nonaqueous media. Electrodes made of a single layer of active material were prepared with Os(byp)2ClPyCH2NHPoly(allylamine) polymer, (PAA-Os), attached to the enzyme by PEG-400 bifunctional reagent with the Os sites acting as electron wires. The electrodes proved to be stable in the presence of organic solvent considering the time evolution of the redox charge and the catalytic current. However, a reasonable decrease in the enzyme response is apparent while increasing solvent content in solution for detection of hydrogen and lauroyl peroxide. As an alternative biomimetic strategy, electrodes were modified with consecutive layers of PAA-Os and electropolymerized Fe-protoporphyrin IX. The electrochemical detection of peroxides was also possible with this system, proving that the poly[Fe-protoporphyrin IX]/Osmium complex system can mimic the peroxidase activity towards hydrogen and organic peroxides. The replacement of Fe-protoporphyrin by Ni-protoporphyrin IX and PAA-Os by PAA in different experiments demonstrates that the mechanism for peroxide reduction involves both Os and Fe-protoporphyrin IX sites. The enzymatic electrodes were applied to benzoyl peroxide quantitation in a pharmaceutical product. The method validation demonstrates that a simple and rapid FIA detection can be applied.

Specific α-bridge cleavage by heme oxygenase of [α-14C]deuterohemin IX, [α-14C]hematohemin IX and 2,4-diacetyl[α-14C]deuterohemin IX

Abstract The enzymatic oxidations of [α-14C]hematohemin IX and 2,4-diacetyl[α-14C]-deuterohemin IX were carried out by using a microsomal heme oxygenase system from rat liver in combination with the biliverdin reductase from the same origin. In every case the bilirubins formed were devoid of radioactivity, indicating the α-selective oxidation of the three hemins. Hematohemin IX was oxidized at the highest rate, followed by deuterohemin IX and 2,4-diacetyldeuterohemin. When the three hemins were preincubated with microsomal heme oxygenase in the absence of NADPH, and the latter was added after the preincubation period, it was found that the enzymatic oxidation of the hemins was inhibited. Therefore, for the maximal rate of oxidation both hemin and NADPH must be present simultaneously. In the presence of hemin IX (the natural substrate), the enzymatic oxidation of the synthetic hemins was inhibited. The oxidation of 2,4-diacetyldeuterohemin IX was the most inhibited, while the oxidation of hematohemin IX was affected to a much lesser degree. These results are in agreement with the higher affinity (Km=150 μM) of hematohemin IX for the enzyme, as compared to 2,4-diacetyldeuterohemin IX (Km=660 μM) and deuterohemin IX (ifKm=330 μM)