Reduction of Au(III) by a ß-cyclodextrin polymer in acid medium. A stated unattainable reaction.

Gold nanoparticles (AuNPs) can be prepared from the reduction of Au(III) with cyclodextrins acting as both, reducing and capping agent. It has been stated that a basic medium (pH=9-12) is a mandatory condition to achieve such reduction. We demonstrated, for the first time, the reduction of Au(III) by a crosslinked ß-cyclodextrin-epichlorohydrin polymer (ßCDP) in acid medium (pH ∼3). The coordination of Au(III) to the ßCD in ßCDP polymer required a ßCD:[AuCl4]- ratio of 4:1. The same ratio was necessary to achieve a 50% of the reduction of Au(III) to Au0 within the first 24h of reaction. During this initial time, the reaction showed a concentration-dependent reduction rate while for longer times the reduction rate was diffusion-dependent. An overall mechanism to explain this dependency has been proposed. The 13C NMR spectrum identified the oxidation of the COH groups to carboxylic ones by recording a signal at 175.6ppm. Gold nanoparticles cores (AuNPs) with a diameter of 34.2±7.7nm, determined by Transmission Electron Microscopy (TEM), was prepared by refluxing HAuCl4 in an aqueous solution of ßCDP. The AuNPs core was capped by dimers of the ßCDP polymer as determined by Dynamic Light Scattering measurements.

Conformational Changes of Enzymes and Aptamers Immobilized on Electrodes.

Conformation constitutes a vital property of biomolecules, especially in the cases of enzymes and aptamers, and is essential in defining their molecular recognition ability. When biomolecules are immobilized on electrode surfaces, it is very important to have a control on all the possible conformational changes that may occur, either upon the recognition of their targets or by undesired alterations. Both enzymes and aptamers immobilized on electrodes are susceptible to conformational changes as a response to the nature of the charge of the surface and of the surrounding environment (pH, temperature, ionic strength, etc.). The main goal of this review is to analyze how the conformational changes of enzymes and aptamers immobilized on electrode surfaces have been treated in reports on biosensors and biofuel cells. This topic was selected due to insufficient information found on the actual conformational changes involved in the function of these bioelectrochemical devices despite its importance.

Vertical self-assembly of modified multiwalled carbon nanotubes on gold surfaces induced by chitosan and Tween.

Multiwalled carbon nanotubes modified with 2-aminoethanethiol (MWNT-AET) were vertically self-assembled on gold electrodes with the assistance of chitosan and Tween. According to AFM and cyclic voltammetric determinations the best results were achieved using chitosan.

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).

Gold nanoparticles enhancing dismutation of superoxide radical by its bis(dithiocarbamato)copper(II) shell.

In the past few years three topics in nanoscience have received great attention: catalytic activity of gold nanoparticles (AuNPs), their electron transfer properties, and magnetism. Although these properties could have much in common no report on their synergism has been published. Here we present 10-nm gold nanoparticles conveniently capped with a mixed self-assembled monolayer containing bis(dithiocarbamato)copper(II) complexes, which dismutate superoxide radical with extremely high efficiency (IC(50) = 0.074 µM). This behavior is interpreted as the result of an electron transfer (ET) process between AuNP core and the analyte when associated to copper(II). The ET process involving a charged AuNP core was detected by EPR and UV-vis spectroscopy.

A copper(II) thiosemicarbazone complex built on gold for the immobilization of lipase and laccase.

A self-assembled monolayer (SAM) of imidazole-2-carbaldehyde thiosemicarbazone (H(2)ImTSC) on gold was formed and characterized by ATR-FTIR, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and X-ray Photoelectron Spectroscopy (XPS). The self-assembly of the ligand through its thioenolate group was confirmed by ToF-SIMS and the presence of XPS peaks at 161.9 (S(2p1/2)) and 163.1eV (S(2p3/2)). The two nitrogen donor atoms of self-assembled HImTSC were able to coordinate (kappa(2)-N,N) copper(II) when set to interact with a CuCl(2) solution upon a second deprotonation of the ligand. This way, two types of modified gold sheets for the immobilization of lipase and laccase were obtained: (a) SAM of the ligand on gold (Au-HImTSC), and (b) SAM of HImTSC with a second monolayer of copper(II) (Au-ImTSC-Cu(II)). The highest immobilization of enzyme was achieved for laccase on Au-ImTSC-Cu(II) according to XPS and enzymatic activity determinations. Copper(II) played a an important recognition role through coordination to the enzyme and/or electrostatic interactions. Nevertheless, the positively charged surface of Au-ImTSC-Cu(II) affected the activity of laccase.

Interaction of nitric oxide with gold nanoparticles capped with a ruthenium(II) complex.

Gold nanoparticles capped with a cis-(4-aminothiophenol)bis(bipyridyl)(chloro)ruthenium(II) complex that are able to coordinate nitric oxide, become fluorescent and then liberate it by photolabilization when irradiated at 430 nm is reported.

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.

Complexes of 2-acetyl-gamma-butyrolactone and 2-furancarbaldehyde thiosemicarbazones: antibacterial and antifungal activity.

Cobalt, nickel, copper and zinc coordination compounds of two thiosemicarbazones with general composition ML(2) (L: monodeprotonated ligand corresponding to 2-acetyl-gamma-butyrolactone thiosemicarbazone, HL(1), and 2-furancarbaldehyde thiosemicarbazone, HL(2)) and also complexes with general composition MCl(2)(HL(2)) were synthesized (except [NiCl(2)(HL(2))] and [Co(L(2))(2)]). The interaction of CuCl(2) with HL(2) gave [CuCl(HL(2))], a copper(I) complex. The ligands and metal complexes were characterized by IR, (1)H and (13)C NMR spectroscopy, and magnetic susceptibility measurements. The crystal structure of [Ni(L(2))(2)]x 2dmso was determined and a trans-square planar coordination of the two kappa(2)-N,S chelate rings forming polymeric strips through H-bonds with dmso was observed. Actually, in all the reported complexes both ligands behaved as kappa(2)-N,S chelates, except in the case of [Co(L(1))(2)] in which HL(1) is tridentate kappa(3)-N,S,O. The antimicrobial properties of all compounds were studied using a wide spectrum of bacterial and fungal strains. The copper complexes of HL(2) were the most active against all strains, including dermatophytes and phytopathogenic fungi. Most of the studied compounds, especially [Cu(L(1))(2)], presented good activity against Haemophilus influenzae, a very harmful bacterium to humans.

Nitric oxide binding and photodelivery based on ruthenium(II) complexes of 4-arylazo-3,5-dimethylpyrazole.

Two fluorescent ligands, 3,5-dimethyl-4-(6'-sulfonylammonium-1'-azonaphthyl)pyrazole (dmpzn, 1) and 3,5-dimethyl-4-(4'-N,N'-dimethylaminoazophenyl)pyrazole (dmpza, 2) were obtained by condensation of ketoenolic derivatives with hydrazine. 1 and 2 formed the novel dinuclear complexes [(H(2)O)(3)ClRu(micro-L)(2)RuCl(H(2)O)(3)] (3 or 4) and [(H(2)O)(NO)Cl(2)Ru(micro-L)(2)RuCl(2)(NO)(H(2)O)] (6 or 7) (where L 1 = 2 or , respectively) which were characterized by IR, NMR and elemental analysis. The nitrosyl complexes were prepared by bubbling purified nitric oxide through methanol solutions of the corresponding ruthenium(II) chloroderivative or by reaction of the appropriate ligands with Ru(NO)Cl(3). Complexes 3 and 4 were found to bind NO, resulting in an increase in fluorescence. Ligand 1 also formed the mononuclear nitrosyl complex [Ru(NO)(bpy)(2)(dmpzn)]Cl(2) (8) which released NO in water at physiological pH and in the solid state as revealed by fluorescence and IR measurements, respectively.

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.

Building layer-by-layer a bis(dithiocarbamato)copper(II) complex on Au[111] surfaces.

A bis(dithiocarbamato)copper(II) complex (CuDTC2) was built on Au{111} surfaces (sheets and electrode beads) using different building blocks in a layer-by-layer (LbL) procedure. The process was followed by AFM and cyclic voltammetry. Initially 4-piperidinemethanethiol, which was synthesized here for the first time, was self-assembled on a gold surface and a highly organized array was obtained. The resulting monolayer was treated with CS2 and NH3 to transform the NH groups of piperidine into dithiocarbamate groups (DTC) with the formation of an amphiphilic ligand (DTCpipS) with thiolate and DTC terminal anionic groups. Two reductive desorption peaks were observed in the cyclic voltammogram of self-assembled DTCpipS, a more intense peak at -0.87 V (thiolate group) and a broader, less intense peak at -0.68 V, corresponding to the desorption of the DTC group bound to the gold surface after the ligand made a approximately 180 degrees flip on the surface. Copper(II) and the morpholyldithiocarbamate anion were associated with self-assembled DTCpipS in order to complete the formation of the CuDTC2 complex on the gold surface. In the voltammogram of the LbL self-assembled CuDTC2 complex the reductive desorption peak at -0.68 V disappeared and one single peak was observed at -0.85 V. This corresponds to the reorientation of all of the DTCpipS dianions in order to coordinate to copper(II) through the DTC groups, leaving the self-assembly only through the thiolate groups. The complete formation of the LbL self-assembled CuDTC2 complex was confirmed by XPS and ToF SIMS, with a detected fragment corresponding to the whole complex.

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.

Bienzymatic supramolecular complex of catalase modified with cyclodextrin-branched carboxymethylcellulose and superoxide dismutase: stability and anti-inflammatory properties.

A bienzymatic supramolecular assembly of CAT and SOD is reported. CAT was chemically glycosilated with CD branched CMC and then associated with SOD modified with 1-adamantane carboxylic acid. SOD was remarkably resistant to inactivation by H(2)O(2) and its anti-inflammatory activity was 4.5-fold increased after supramolecular association with the modified CAT form. [structure: see text]

Supramolecular-mediated immobilization of L-phenylalanine dehydrogenase on cyclodextrin-coated Au electrodes for biosensor applications.

A supramolecular approach was used for adsorbing a monolayer of adamantane-modified phenylalanine dehydrogenase on beta-cyclodextrin-coated Au electrodes. The enzyme electrode (poised at +200 mV vs. Ag/AgCl) showed a linear amperometric response up to 3 mM L-phenylalanine (L-Phe) with a lower detection limit of 15 microM. The reversible nature of this immobilization approach was confirmed.

Improved pharmacological properties for superoxide dismutase modified with beta-cyclodextrin-carboxymethylcellulose polymer.

Superoxide dismutase was glycosidated with cyclodextrin-branched carboxymethylcellulose. The modified enzyme contained 1.4 mol polymer per mol protein and retained 87% of the initial activity. The anti-inflammatory activity of superoxide dismutase was 2.2-times increased after conjugation and its plasma half-life time was prolonged from 4.8 min to 7.2 h.

Improved anti-inflammatory properties for naproxen with cyclodextrin-grafted polysaccharides.

Mannan and carboxymethylcellulose, previously activated by periodate oxidation, were grafted with mono-6-butylenediamino-6-deoxy-beta-cyclodextrin derivatives by reductive alkylation in the presence of sodium borohydride. The formation of supramolecular complexes between these polymers and Naproxen was confirmed by fluorescence spectroscopy. The solubility of the drug was 3.8-4.6 fold increased in the presence of the cyclodextrin-grafted polysaccharides. The in vivo anti-inflammatory property of Naproxen was 1.7 times higher after supramolecular association with beta-cyclodextrin-branched mannan.

Cyclodextrin-grafted polysaccharides as supramolecular carrier systems for naproxen.

Dextran, mannan and carboxymethylcellulose, previously activated by periodate oxidation, were grafted with beta-cyclodextrin moieties by reductive alkylation in the presence of sodium borohydride. These polymers were used as supramolecular carriers for naproxen, improving the "in vivo" anti-inflammatory properties of this drug.

Chemical glycosidation of trypsin with O-carboxymethyl-poly-beta-cyclodextrin: catalytic and stability properties.

The polysaccharide O-carboxymethyl-poly-beta-cyclodextrin was synthesized (molecular mass 13,000 Da, 40% carboxy groups) and attached to the surface of bovine pancreatic trypsin. The resulting neoglycoenzyme retained high proteolytic and esterolytic activity and contained approx. 1.0 mol of polymer/mol of enzyme. The optimum temperature for trypsin activity was increased by 10 degrees C after this transformation. Thermostability of the polymer-enzyme complex was increased by about 14 degrees C over 10 min incubation. The conjugate was also more resistant to thermal inactivation at different temperatures, ranging from 45 to 60 degrees C, demonstrating the influence of supramolecular and polymer-protein electrostatic interactions on trypsin thermostabilization. Additionally, the conjugate was 36-fold more resistant to the action of the anionic surfactant SDS. This modification also protected the enzyme from autolysis at alkaline pH.