Renata Bilewicz

Design and assembly of pH-sensitive lipidic cubic phase matrices for drug release.

Bicontinuous lipidic cubic phases (LCPs) exhibit a combination of material properties that make them highly interesting for various biomaterial applications: they are nontoxic, biodegradable, optically transparent, thermodynamically stable in excess water, and can incorporate active molecules of virtually any polarity. Here we present a molecular system comprising host lipid, water, and designed lipidic additive, which form a structured, pH-sensitive lipidic matrix for hydrophilic as well as hydrophobic drug incorporation and release. The model drug doxorubicin (Dox) was loaded into the LCP. Tunable interactions with the lipidic matrix led to the observed pH-dependent drug release from the phase. The rate of Dox release from the cubic phase at pH 7.4 was low but increased significantly at more acidic pH. A small amount of a tailored diacidic lipid (lipid 1) added to the monoolein LCP modified the release rate of the drug. Phase identity and structural parameters of pure and doped mesophases were characterized by small-angle X-ray scattering (SAXS), and release profiles from the matrix were monitored electrochemically. Analysis of the release kinetics revealed that the total amount of drug released from the LCP matrix is linearly dependent on the square root of time, implying that the release mechanism proceeds according to the Higuchi model.

Hybrid biobattery based on arylated carbon nanotubes and laccase.

Single-walled carbon nanotubes (SWCNT) were covalently modified with anthracene and anthraquinone and used for the construction of cathodes for biocatalytic reduction of dioxygen. The nanotubes with aromatic groups casted onto the electrode increased the working surface of the electrode and enabled efficient direct electron transfer (DET) between the enzyme and the electrode. The aryl groups enter the hydrophobic pocket of the T1 center of laccase responsible for exchanging electrons with the substrate. Glassy carbon electrode covered with arylated SWCNT and coated with a layer of neutralized Nafion containing laccase was found to be a very efficient cathode in the hybrid battery. Zn wire covered with a Nafion film served as the anode. The cell parameters were determined: power density was 2 mW/cm(2) and the open circuit potential was 1.5 V.

Cubic phases in biosensing systems

Incorporation of membrane proteins with retained activity in artificial membranes for use in membrane-based sensors has attracted scientists for decades. This review briefly summarises general concepts on relevant cubic phases with and without incorporated proteins and provides some insight into the development of biosensors where bicontinuous cubic phases are used for incorporation of an enzyme. Some new data on impedance characterisation of a supported cubic phase are also shown. An efficient membrane-based electrochemical biosensor requires that the analyte has free access to the immobilised membrane protein and that regeneration of the catalysing enzyme is fast. Long-term stability of the system is also necessary for the biosensor to find applications outside the research laboratory. These basic concepts are discussed in the review along with presentation of those biosensing systems based on cubic phases that are reported in the literature.

Thermoresponsive poly(N-isopropylacrylamide) gel for immobilization of laccase on indium tin oxide electrodes.

We report on the properties of hydrogel matrix for the immobilization of laccase on conductive supports. The poly(N-isopropylacrylamide) gel is attached firmly to the indium-tin oxide (ITO) electrode, following its silanization with dimethylethoxyvinylsilane. The enzyme entrapped in the gel structure remained active longer than in the solution, and its redox and catalytic properties could be investigated by voltammetric methods. The reduction signals of the active sites, T1 and T2, of the Cerrena unicolor laccase were determined to be 0.79 and 0.38 V, respectively. The laccase catalytic activity toward oxygen in poly(N-isopropylacrylamide) was found to depend strongly on temperature. Reversible swelling/shrinking of the matrix was studied at 30 and 35 degrees C. Shrinking of the gel at higher temperature considerably decreased the efficiency of the catalytic reaction, however, interestingly, did not lead to irreversible changes in the enzyme structure. At temperatures below that corresponding to volume phase transition, the catalytic properties of the film were fully restored. High catalytic efficiency of the gel immobilized enzyme made it possible to employ the gel covered electrode for monitoring oxygen in solutions.

Synthesis, x-ray structure and electrochemical properties of a new crown ether with a cis azo unit in the macrocycle

Abstract A chromogenic 13-membered crown ether with a cis azo unit in the macrocycle has been obtained as a side product during the reduction of 1,5-bis (2′-nitrophenoxy)-3-oxapentane. The electrochemical properties of this compound have been studied by the voltammetric method. Its behaviour as an ionophore in ion-selective membrane electrodes has also been investigated. The X-ray structures of the new crown ether 3 and the parent compound 1 have been determined.

13-Membered crown ethers with azo or azoxy unit in the macrocycle - synthesis, membrane electrodes, voltammetry and Langmuir monolayers

Abstract A facile way to obtain substituted azo- and azoxycrown ethers has been developed. Applicability of these crown ethers in sodium-sensitive membrane electrodes has been studied. Voltammetric behavior of the crown ethers bearing azo- and azoxy- subunits in the macrocyclic system has been characterized. Formation of Langmuir-Blodgett monolayers of amphiphilic azocrown ethers on aqueous subphase has been investigated.

Determination of traces of purine by cathodic stripping voltammetry at the hanging copper amalgam drop electrode

Abstract In the presence of purine, the copper(II)/copper(Hg) couple splits into copper(II)/copper(I) and copper(I)/copper(Hg) couples, which form two well-separated systems of peaks under voltammetric conditions. The copper(I)/purine complex adsorbs on the electrode surfacer and can be deposited on the electrode surface by electroreduction of copper(II) ions at the HMDE or by electro-oxidation of the hanging copper amalgam drop electrode (HCADE). The deposit can be stripped either cathodically or anodically over the pH range 2–9. The cathodic stripping variant at the HCADE, in solution with pH 2, offers the best results, with linear response for the range 5 × 10 −9 –1.5 × 10 −7 mol dm −3 purine after an accumulation time of 3 min. The detection limit found with the HMDE in the presence of copper(II) ions is higher.

Lyotropic Cubic Phases for Drug Delivery: Diffusion and Sustained Release from the Mesophase Evaluated by Electrochemical Methods.

Lyotropic liquid crystalline systems are excellent carriers for drugs due to their biocompatibility, stability in aqueous environment, and well-defined structure that allow them to host significantly larger amounts of drugs than carriers such as liposomes or gold nanoparticles. Incorporating the drug within the mesophase gel, or the cubosome/hexosome nanoparticles, decreased its toxic effects toward healthy cells, while appropriate mechanisms can stimulate the release of the drug from the carrier when it approaches the cancerous cell environment. Electrochemical methods-chronocoulometry and voltammetry at micro and normal size electrodes-are used for the first time to simultaneously determine the diffusion coefficients and effective concentrations of a toxic anticancer drug, doxorubicin, in the channels of three liquid-crystalline lipidic cubic phases. This approach was instrumental in demonstrating that the drug diffusion and kinetics of release from the mesophases depend on the aqueous channel size, which in turn is related to the identity and structure of the amphiphilic molecules used for the formation of the mesophase. Structural parameters of the cubic phases with the incorporated drug were characterized by small-angle X-ray scattering (SAXS), and molecular dynamics simulations were applied in order to describe the differences in the distribution of doxorubicin in the cubic phase matrix at acidic and neutral pH. The release of the drug from the phase was retarded at physiological pH, while at lower pH, corresponding to the cancer environment, it was accelerated, provided that suitable amphiphilic molecules were employed for the construction of the liquid crystal drug delivery system.

Intermolecular Interactions between Doxorubicin and β-Cyclodextrin 4-Methoxyphenol Conjugates

Newly synthesized derivatives of β-cyclodextrin, mono(6-deoxy-6-(1-1,2,3-triazo-4-yl)-1-propane-3-O-(4-methoxyphenyl))β-cyclodextrin (1) and mono(6-deoxy-6thio(1-propane-3-O-(4-methoxyphenyl))) β-cyclodextrin (2) were designed to be receptors of the anticancer drug doxorubicin, which could potentially decrease the adverse effects of the drug during treatment. In both aqueous and aqueous dimethyl sulfoxide (DMSO) solutions, doxorubicin forms an inclusion complex with the new cyclodextrin derivatives with formation constants of K(s) = 2.3 × 10(4) and K(s) = 3.2 × 10(5) M(-1) for cyclodextrins 1 and 2, respectively. The stabilities of the complexes are 2-3 orders of magnitude greater than those with native β-cyclodextrin, and the flexibility of the linker of the side group of the cyclodextrins contributes to this stability. In a hydrogen-bond-accepting solvent, such as pure DMSO, an association that includes hydrogen bonding and chloride ions is favored over the binding of doxorubicin in the cavity of the cyclodextrin derivative. This contrasts with an aqueous medium in which a strong inclusion complex is formed. Cyclic voltammetry, UV-vis, (1)H NMR, and molecular modeling studies of solutions in DMSO and of solutions in water/DMSO demonstrated that the two different modes of intermolecular interaction between doxorubicin and the cyclodextrin derivative depended on the solvent system being utilized.

Modified electrode surfaces for catalytic reduction of carbon dioxide

Ni(II) complexes with substituted tetraazacyclotetradecanes were incorporated into Nafion films or assembled in monolayers on electrodes in order to obtain electrocatalytic systems for the reduction of carbon dioxide. Reproducible and stable loading of the Nafion films with the complexes has been observed. Systematic increase of N-methyl substitution of the catalytic [Ni(cyclam)]2+ complex leads to a shift of the Ni(II)L/Ni(I)L formal potential to more positive values, however, at the same time to a decrease of the catalytic current of CO2 reduction. Monolayer techniques — the Langmuir–Blodgett and self-assembly methods — were found advantageous for the preparation of electrode surfaces active in the catalytic reduction of CO2 compared to Nafion coatings containing the catalyst. Glassy carbon electrode was suitable for the transfer of Langmuir–Blodgett monolayers. Catalysis was observed only when the electrode was touching the monolayer at the air–water interface or was covered in the dipping mode, hence when the catalyst molecules were oriented with their alkyl chains towards the substrate and macrocyclic head-group towards the solution. Most efficient catalysis was found using electrodes coated by the self-assembly procedure with monolayers of the cyclam complex modified with a pyridine side group. The role of the pyridine moieties was to anchor the catalytic monolayer to the electrode surface.