Roberto Cao

Amperometric biosensor for xanthine with supramolecular architecture

Xanthine oxidase modified with 1-adamantanyl residues was supramolecularly immobilized on Au electrodes coated with Au nanoparticles coated with a perthiolated beta-cyclodextrin polymer; the analytical response of the electrode toward xanthine was evaluated.

Thermal stabilization of trypsin by enzymic modification with β-cyclodextrin derivatives

Streptoverticillum sp. transglutaminase was used as catalyst for the attachment of several β‐cyclodextrin derivatives to the glutamine residues in bovine pancreatic trypsin. The modifying agents used were mono‐6‐ethylenediamino‐6‐deoxy‐β‐cyclodextrin, mono‐6‐propylenediamino‐6‐deoxy‐β‐cyclodextrin, mono‐6‐butylenediamino‐6‐deoxy‐β‐cyclodextrin and mono‐6‐hexylenediamino‐6‐deoxy‐β‐cyclodextrin. The transformed trypsin preparations contained about 3 mol of oligosaccharides/mol of protein. The specific esterolytic activity of trypsin was increased by about 4–21% after conjugation. The Km values for cyclodextrin–trypsin complexes represented about 58–87% of that corresponding to the native enzyme. The optimum temperature for esterolytic activity of trypsin was increased by about 5–10 °C after enzymic modification with the cyclodextrin derivatives. The thermostability was increased by 16 °C for the modified trypsin. Thermal inactivation at different temperatures ranging from 45 to 60 °C was markedly increased for the oligosaccharide–trypsin complexes. This modification also protected the enzyme against autolysis at alkaline pH.

Chitosan and silver nanoparticles as pudding with raisins with antimicrobial properties

Chitosan nanoparticles (CS-NP) containing small silver nanoparticles are reported (Ag@CS-NP). CS-NP was synthesized using tripolyphosphate (TPP) as a polyanionic template. TPP also served to electrostatically attract Ag(+) inside CS-NP, where it was reduced by the terminal glucosamine units of the biopolymer. This procedure is environmental friendly, inexpensive, and permits the synthesis of very small AgNP (0.93-1.7 nm), with only a discrete dependence from the amount of silver nitrate used (5-200mg). The obtained hybrid nanocomposites Ag@CS-NP were characterized by DLS, HRTEM, and HAADF-STEM presenting a mean hydrodynamic diameter of 78 nm. The antimicrobial activity of Ag@CS-NP against Candida glabrata, Sacharomyces cerevisiae, Escherichia coli, Klebsiella pneumoniae, Salmonella, Staphylococcus aureus, and Bacillus cereus corresponded to MIC values lower than for AgNO(3).

Hydrogen peroxide biosensor with a supramolecular layer-by-layer design.

A new sensor design is reported for the construction of an amperometric enzyme biosensor toward H (2)O(2). It was based in the supramolecular immobilization of alternating layers of horseradish peroxidase (either modified with 1-adamantane or beta-cyclodextrin-branched carboxymethylcellulose residues) on Au electrodes coated with polythiolated beta-cyclodextrin polymer. The analytical response of the electrodes, using 1 mM hydroquinone as an electrochemical mediator, increases when the number of enzyme layers increases. The biosensor having three enzyme layers showed a sensitivity of 720 microA/M cm (2) and a detection limit of 2 microM and retained 96% of its initial activity after 30 days of storage. The host-guest supramolecular nature of the immobilization method was confirmed by cyclic voltammetry.

EPR characterization of a series of mono- and bis-thiosemicarbazone copper(II) complexes

Abstract EPR studies at room and low temperatures of cooper(II) complexes of acetaldehyde thiosemicarbazone (AlTSC), pyruvic acid thiosemicarbazone (PTSC) and ribose bis-thiosemicarbazone (RibTSC) have been undertaken. Computer simulation of the EPR spectra has revealed differences in the magnetic parameters of the compound. Two species with different metal-ligand ratios were found to be present in PTSC. The higher degree of tetrahedral distortion displayed by the two mono-thiosemicarbazones with respect to RibTSC suggests that monothiosemicarbazone copper(II) complexes may be more effective superoxide dismutase-like mimics than bis-thiosemicarbazone complexes are.

Superoxide Dismutase Mimetic Activity of the Metal (II) Complexes of a Dithiocarbamate Derivative of β-Cyclodextrin1

Abstract The synthesis of a new β-cyclodextrin derivative containing a dithiocarbamate group (3) by condensation of mono-2-methylamino-2-deoxy-β-CD (2) with CS2 in the presence of NEt3 is reported. SOD-mimetic activity was found for the Mn(II) and Cu(II) complexes of 2 and 3 (IC50 = 0.76-7.4 μ). To study the influence of the cyclodextrin residue on the catalytic activity of these complexes, a comparison was made with diethylamine and diethyldithiocarbamate complexes. Complexes of 2 and 3 resulted in 1.3 to 11 fold higher activities. An explanation for this observation, in terms of a possible cooperation of the cyclodextrin residue with the catalytic center of the complex, is given.

Novel enzyme biosensor for hydrogen peroxide via supramolecular associations.

A polythiolated-beta-cyclodextrin polymer was synthesized and used as a coating material for gold electrodes. The functionalized electrodes were employed for immobilizing adamantane-modified horseradish peroxidase via supramolecular associations. The enzyme-containing electrode was used as an amperometric biosensor device with 1mM hydroquinone as electrochemical mediator. The biosensor exhibited a fast amperometric response (10s), a good linear response toward H(2)O(2) concentrations between 28 microM and 5.5 mM, and a low detection limit of 7 microM. The biosensor showed a sensitivity of 109 microA/Mcm(2) and retained 98% of its initial electrocatalytic activity after 40 days of storage at 4 degrees C in 50mM sodium phosphate buffer pH 7.0. The host-guest supramolecular nature of the immobilization method was confirmed by cyclic voltammetry.

Stabilization of trypsin by chemical modification with β-cyclodextrin monoaldehyde

The monoaldehyde derivative of β-cyclodextrin was attached to trypsin via reductive alkylation with NaBH4. The thermostability was enhanced from 49.5 °C to 60 °C for modified trypsin. The activation free energy of thermal inactivation at 50 °C was increased by 3.2 kJ mol−1. The conjugated enzyme retained 100% of its initial activity after 3 h incubation at pH 9.

Interpretation of the sod-like activity of a series of copper(II) complexes with thiosemicarbazones

Abstract In the present paper we report the SOD-like activity of a series of copper(II) complexes with acetaldehyde, acetophenone, 2-oxo-glutaric acid, methyl-furfural, piruvic acid, salicylaldehyde, 2-acetylpyridine thiosemicarbazones and ribose bis(thiosemicarbazone). The complexes were studied by EPR spectroscopy. A linear correlation between f=g‖/A‖ and the SOD-like activity was observed. The higher f values correspond to copper(II) complexes with enhanced tetrahedral distortion.

Interactions of nitric oxide with copper(II) dithiocarbamates in aqueous solution.

This is the first report on the formation of air-stable copper nitrosyl complexes. The interaction of nitric oxide, NO, with Cu(DTC)(2).3H(2)O (DTC: dithiocarbamate) and was studied in aqueous solution at pH 7.4 and 293 K. The stability constants were determined from UV-Vis data, using LETAGROP program. The high values obtained, log beta(1)=9.743(5) and log beta(2)=15.44(2) for Cu(ProDTC)(2)-NO, (ProDTC=L-prolinedithiocarbamate) and log beta(1)=8.723(5) and log beta(2)=11.45(2) for Cu(MorDTC)(2)-NO system, (MorDTC=morpholyldithiocarbamate), indicate the formation of two stable nitrosyl complexes, Cu(DTC)(2)NO and Cu(DTC)(2)(NO)(2). Coordinated NO is neither affected by the presence of air nor when the solution is purged with Ar. Cu(MorDTC)(2)NO.3H(2)O was isolated in the solid state and its nuNO (IR) band at 1682 cm(-1), but affected by temperature variations over 333 K.