Amperometric uric acid sensors based on polyelectrolyte multilayer films

Uricase (UOx) and polyelectrolyte were used for preparation of a permselective multilayer film and enzyme multilayer films on a platinum (Pt) electrode, allowing the detection of uric acid amperometrically. The polyelectrolyte multilayer (PEM) film composed of poly(allylamine) (PAA) and poly(vinyl sulfate) (PVS) were prepared via layer-by-layer assembly on the electrode, functioning as H₂O₂-selective film. After deposition of the permselective film (PAA/PVS)₂PAA, UOx and PAA were deposited via layer-by-layer sequential deposition up to 10 UOx layers to prepare amperometric sensors for uric acid. Current response to uric acid was recorded at +0.6 V vs. Ag/AgCl to detect H₂O₂ produced from the enzyme reaction. The response current increased with increasing the number of UOx layers. Even in the presence of ascorbic acid, uric acid can be detected over the concentration range 10⁻⁶-10⁻³ M. The response current and deposited amount of UOx were affected by deposition bath pH and the addition of salt. The deposition of PAA/UOx film prepared in 2 mg ml⁻¹ solution (pH 11) of PAA with NaCl (8 mg ml⁻¹) and 0.1 mg ml⁻¹ solution (pH 8.5) of UOx with borate (100 mM) resulted in an electrode which shows the largest response to uric acid. The response of the sensor to uric acid was decreased by 40% from the original activity after 30 days.     

Emulsion polymerization of styrene by horseradish peroxidase-mediated initiation

A new horseradish peroxidase (HRP)-catalyzed redox initiating system was successfully applied in the emulsion polymerization of styrene, producing stable polymer colloids and nanospheres. The particle size was about 30–50 nm with a diameter distribution (CV) 14–20% obtained by SEM. The molecular weight, was around 10⁵, and was around 10⁶. All the results were well consistent with the control, potassium persulfate (KPS)-initiating polymerization. The obtained experimental results supported a micelle mechanism similar to that of conventional emulsion polymerization of styrene.     

In vivo imaging of brain dopaminergic neurotransmission system in small animals with high-resolution single photon emission computed tomography.

High-resolution single photon emission computed tomography (SPECT) provides a unique capability to image the biodistribution of radiolabeled molecules in small laboratory animals. Thus, we applied the high-resolution SPECT to in vivo imaging of the brain dopaminergic neurotransmission system in common marmosets using two radiolabeled ligands, [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane (beta-CIT) as a dopamine transporter (DAT) ligand and [123I]iodobenzamide (IBZM) as a dopamine D2 receptor (D2R) ligand. Specific images of the striatum, a region with a high density of dopaminergic synapses, were obtained at 240 min and 60 min after injection of [123I]beta-CIT and [123I]IBZM, respectively. Furthermore, a significantly low accumulation of [123I]beta-CIT in the striatum was observed in MPTP-treated animals compared with results for a control group, and a similar accumulation in the control group was observed with the pretreatment of deprenyl in the MPTP-treated animals. However, the striatal accumulation of [123I]IBZM showed no changes among the control, MPTP-treated, and deprenyl-MPTP-treated groups. These SPECT imaging results agreed well with those of DA concentration and motor behavior. Since MPTP destroys nigrostriatal dopamine nerves and produces irreversible neurodegeneration associated with Parkinsonian syndrome, SPECT imaging data in this study demonstrated that deprenyl shows its neuroprotective effect on Parkinsonism by protecting against the destruction of presynaptic dopamine neurons.     

Thermodynamic characterization of binding of DNA with cisplatin in aqueous solution by calorimetry

The behaviour of cis-diamminedichloroplatinum(II) (cisplatin) binding to DNA was studied thermodynamically by calorimetric methods such as flow microcalorimetry and differential scanning calorimetry (DSC). The thermodynamic quantities of binding of cisplatin to DNA were determined from the measurement of the heat of mixing. From the results obtained, it was suggested that the complex formation by the interaction of DNA with cisplatin may be influenced by the entropy term as a dominant factor. UV spectral measurement on solutions having a known concentration of DNA and cisplatin solutions of various concentrations was carried out at room temperature, and the difference of absorption, Δ A ₂₆₀ at wavelength 260 nm between DNA solutions with and without cisplatin was estimated. From the results obtained, a hyperchromic effect in the DNA solution containing cisplatin was found to exist. The appearance of the hyperchromic effect may be considered to originate from the disturbance of the base stacking between adjacent base pairs of DNA by the interaction of DNA with cisplatin. In addition, the thermal stability of the DNA-cisplatin complex was also studied by DSC method. The binding of cisplatin decreases the thermal stability of DNA; the transition temperature and the heat of the helix-coil transition of DNA decrease accompanying the binding of cisplatin. The decrease of the transition temperature is caused by the kinked DNA(helix') accompanying the appearance of the hyperchromic effect by binding cisplatin; also, the decrease of the heat of helix-coil transition may be based on the cooperative action between the heat of helix-coil transition of the kinked DNA(helix') and the heat of dissociation when cisplatin is dissociated from the DNA-cisplatin complex. By taking into consideration these results, the heat of binding of cisplatin to DNA was estimated to be about −106 kJ per mole of cisplatin.     

Photo-controllable tristability of a dithiolato-bipyridine-Pt(II) complex molecule containing two azobenzene moieties

A new platinum complex with both an azo-bound dithiolato ligand and an azobenzene-bound bipyridine ligand exhibits tristability reversibly controllable using different energy lights.     

Efficient sequential segment coupling using N-alkylcysteine-assisted thioesterification for glycopeptide dendrimer synthesis

A highly pure MUC1-derived glycopeptide dendrimer of 22 kDa was prepared by a sequential segment coupling, achieved by an N-alkylcysteine (NAC)-assisted thioesterification. The glycopeptide having C-terminal NAC was prepared by the Fmoc method and converted to the thioester by 3-mercaptopropionic acid treatment. The thioester was condensed with a lysine trimer carrying NAC to afford tetramer, which was then converted to the thioester. Two tetramers were condensed with ethylenediamine to give the octameric glycopeptide dendrimer.     

Interfacial and aggregation properties of the binary mixture of decanoyl-N-methyl-glucamide and hexadecyltriphenylphosphonium bromide

The interfacial and aggregation behavior of the nonionic surfactant decanoyl-N-methyl-glucamide (Mega-10) with the cationic surfactant hexadecyltriphenylphosphonium bromide (HTPB) have been studied using interfacial tension measurements and fluorescence techniques. From interfacial tension measurements, the critical micellar concentrations (cmc) and various interfacial thermodynamic parameters have been evaluated. The experimental results were analyzed in the context of the pseudophase separation model, the regular solution theory, and the Maeda’s approach. These approaches allowed us to determine the interaction parameter and composition in the mixed state. By using the static quenching method, the mean micellar aggregation numbers of pure and mixed micelles of HTPB+Mega-10 were obtained. It was found that that the aggregation number decreases with increasing mole fraction of HTPB. This behavior is attributed to the presence of the bulky head group of HTPB, which creates steric head group incompatibility and/or electrostatic repulsion. The micropolarity of the micelle was monitored with pyrene fluorescence intensity ratio. It was observed that the increasing participation of HTPB induces the formation of micelles with a hydrated structure. The polarization of the fluorescent probe Rhodamine B was monitored in micellar medium and found to increase with the increase of ionic content. This behavior suggests the formation of mixed micelles with a more ordered or rigid structure.     

Solubilization of endocrine disruptors in micellar media

The interaction of endocrine disruptor chemicals (EDCs) such as nonylphenol (NP) and β-estradiol with cationic micelle of hexadecyltrimethylammonium ion (HTA⁺) and a monolayer of HTA⁺ ion adsorbed at the electrode surface has been investigated in the presence of hydrophilic modified (2-hydroxypropyl)-β-cyclodextrin. NP, which has a similar structure to HTA⁺, decreased the critical micelle concentration (cmc) of hexadecyltrimethylammonium bromide more effectively. At the low HTA⁺ concentration, HTA⁺ inhibited the adsorption of I₂. However, as the HTA⁺ concentration increased, a monolayer of HTA⁺ was formed at the electrode surface and caused the adsorption of iodine molecule (I₂). In the presence of micelle, the I₂ was dissolved in the micelle. Both EDCs caused the formation of HTA⁺ monolayer even at the HTA⁺ concentration below the cmc.     

Arraying heterotypic single cells on photoactivatable cell-culturing substrates

This article describes a photochemical method for the site-selective assembly of heterotypic cells on a glass substrate modified with a silane coupling agent having a caged functional group. Silane coupling agents having a carboxyl (COOH), amino (NH 2), hydroxyl (OH), or thiol (SH) group protected by a photocleavable 2-nitrobenzyl group were synthesized to modify the surfaces of glass coverslips. The caged substrates were first coated by the adsorption of a blocking agent, bovine serum albumin (BSA), to make the entire surface non-cell-adhesive and then irradiated at 365 nm under a standard fluorescence microscope. The photocleavage reaction on the surface was followed by contact angle measurements and X-ray photoelectron spectroscopy. When COS7, NIH3T3, and HEK293 cells were seeded onto these substrates in a serum-free medium, the cells adhered selectively and efficiently to the irradiated regions on the caged NH 2 substrate, whereas the other caged COOH, SH, and OH substrates were nonphotoactivatable for cell adhesion. Qualitative and quantitative analysis of BSA adsorbed to the uncaged substrates revealed that this highly efficient photoactivation on the caged NH 2 substrate arose because of the following reasons: (i) upon photoactivation, BSA adsorbed in advance on the 2-nitrobenzyl groups was readsorbed onto the uncaged functional groups and (ii) BSA readsorbed onto the NH 2 groups became unable to passivate the surface against cell adhesion whereas BSA on the other groups still had normal passivating activity. It was also demonstrated that heterotypic single COS7, NIH3T3, and HEK293 cells were positioned at any desired arrangement on the caged NH 2 substrate by repeating the UV irradiation at optimized array spot sizes and cell seeding in optimized cell concentrations. The present method will be particularly useful in studying the dynamic processes of cell-cell interactions at a single-cell level.     

Selective electrochemical sensing of acidic organic molecules via a novel guest-to-host proton transfer reaction

Ferrocene-containing amidopyridine receptors bind carboxylic acids and the amino acid phenylalanine in acetonitrile via a novel proton transfer process that enables guests to be electrochemically sensed by positive shifts in the ferrocene-centred redox potentials.