Nanocrystalline cellulose-fullerene: Novel conjugates.

The covalent grafting of two amino-fullerene C60 derivatives (C60-LC-NH2 and C60-SC-NH2, LC=long chain and SC=short chain) onto the surface of TEMPO oxidized nanocrystalline cellulose (NCC-COOH) has been reported for the first time. These hybrids (NCC-LC-C60 and NCC-SC-C60) form stable colloidal suspensions at concentrations up to 0.5mg/mL and act as effective photosensitizers for singlet oxygen production as demonstrated by the oxidation of L-methionine-methyl ester to the corresponding sulphoxide. Using the same approach, in a one-pot reaction both a fluorescent target molecule (FITC-LC-NH2) and the C60-LC-NH2 derivative have been successfully attached covalently onto the NCC-COOH surface. These hybrids, which showed no cytotoxicity on MCF-7 human breast cancer cells could be good candidates in photodynamic cancer therapy.

STM investigation of temperature-dependent two-dimensional supramolecular architectures of C60 and amino-tetraphenylporphyrin on Ag(110).

Multicomponent supramolecular self-assemblies of exceptional long-range order and low defectivity are obtained if C(60) and 5-(4-aminophenyl)-10,15,20-triphenylporphyrin (TPP-NH2) are assembled on Ag(110) by sequential evaporation in the submonolayer range of TPP-NH2 and fullerene on the substrate surface and subsequent annealing. A (+/-2 -3, 6 +/- 3) array consisting of supramolecular stripes of a 1:1 C(60)/TPP-NH2 2D adduct develops at 410 K (the low temperature, LT, phase). If the LT phase is annealed at 470 K, then a 3:1 fullerene/TPP-NH2 (+/-3 -5, 5 +/- 5) nanoporous array (the HT phase) forms, with each pore containing a single porphyrin molecule. Phase separation occurs by annealing the HT phase at 520 K. Structural models are proposed and discussed on the basis of the experimental scanning tunneling microscopy results.

Rapid prototyping of multilayer thiolene microfluidic chips by photopolymerization and transfer lamination.

A new fabrication process is described allowing rapid prototyping of multilayer microfluidic chips using commercial thiolene optical adhesives. Thiolene monomer liquid is photopolymerized across transparency masks to obtain partially cured patterns supported on thin polyethylene sheets. The patterns are easily laminated and transferred to a substrate due to the elastomeric nature and adhesiveness of partially cured thiolene. The process characteristics are evaluated by realizing several test structures and fluidic chips. As an example of application, the operation of a microfluidic bead array sensor for pH measurements is then described in some detail.

A highly sensitive method for the analysis of nitrite ions by capillary zone electrophoresis using water-soluble aminophenylporphyrin derivative as chromogenic reagent.

The water soluble 5-p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl) porphyrin, 4, acts as an extremely efficient chromogenic reagent for the detection of very low amounts of nitrites. The amino group of porphyrin 4 reacts smoothly with nitrite in acidic conditions 0.2 M HCl) producing the corresponding diazo-porphyrin derivative which is stable and does not show any appreciable hydrolysis to phenol within 6 h. The reaction is carried out in the presence of 25 mM heptakis-(2,6-di-O-methyl)-beta-cyclodextrin that prevents precipitation of the protonated form of porphyrins 4 or 5 due to the formation of strong inclusion complexes. The capillary zone electrophoresis of the diazoporphyrin and amino-porphyrin mixture shows severe peak tailing. However, symmetrical peaks can be obtained by adding 5 mM beta-cyclodextrin to the background electrolyte (20 mM phosphate buffer, pH 7.0). Calibration curve for nitrite analysis is linear up to 0.25 mM nitrite and the detection limit (at a signal-to-noise ratio of 3) has been estimated to be a 1 microM (50 ppb) of nitrite concentration in aqueous solutions.

Capillary electrophoresis behavior of water-soluble anionic porphyrins in the presence of beta-cyclodextrin and its O-methylated derivatives.

The electrophoretic behavior of water-soluble anionic porphyrins, such as meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP), meso-tetrakis(4-sulfonatophenyl) porphyrin (TSPP) and its zinc(II) and copper(II) complexes (ZnTSPP and CuTSPP, respectively) has been studied by capillary zone electrophoresis using fused-silica capillaries. The selectivity of the separation is strongly dependent on the type and concentration of betacyclodextrin (betaCD) or the O-methylated derivatives added to the background electrolyte. CuTSPP and TSPP can be separated using a pH 2.5 aqueous sodium phosphate buffer in the presence of 1 mM betaCD. Resolution is poorer or absent employing alkylated betaCDs, such as the heptakis (2,6-di-O-methyl)-beta-cyclodextrin or the heptakis(2,3,6-triO-methyl)-beta-cyclodextrin, as additives. On the other hand, separation of TSPP from its copper and zinc complexes has been achieved using a pH 7.0 aqueous sodium phosphate buffer, in the presence of 0.75 mM betaCD and 20% dimethyl sulfoxide (DMSO) as organic modifier. Under such conditions, the calibration curve for quantitative analysis of copper(II) was obtained. A rationale for the observed behavior will be presented and discussed on the basis of binding and protonation equilibria and a simple mathematical model.

Synthesis, characterization, and supramolecular properties of a hydrophilic porphyrin--beta-cyclodextrin conjugate.

Reductive amination of 6-deoxy-6-formyl-beta-cyclodextrin with 5-(p-aminophenyl)-10,15,20-tris(p-sulfonatophenyl)porphyrin in the presence of an excess of sodium cyanoborohydride affords the hydrophilic cyclodextrin-porphyrin conjugate 3 in 23% yield. The structure of 3 was confirmed by NMR spectroscopy and mass spectrometry techniques. Compound 3 showed a marked tendency to dimerize in aqueous conditions via the formation of intermolecular porphyrin-cyclodextrin inclusion complexes and/or through electrostatic interactions. Information on the structure of these aggregates has been obtained by the use of circular dichroism and UV-vis spectroscopy. Aggregation can be avoided by the use of heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin (TM beta CD) that forms a 1:1 inclusion complex with compound 3.

Flavins inhibit human cytomegalovirus UL80 protease via disulfide bond formation.

Among the most potent inhibitors of human cytomegalovirus protease identified by random screening of a chemical library was 1,4-dihydro-7,8-dimethyl 6H-pyrimido[1,2-b]-1,2,4,5-tetrazin-6-one (1) (PTH2). The oxidized form (2), PT, which is present in solutions of PTH2, was shown to be the actual inhibitory species which irreversibly inactivates the protease; recycling of PTH2 by dissolved oxygen results in complete inhibition of the protease at substoichiometric amounts of compound. No evidence for a covalent adduct between the protease and the inhibitor was obtained, and protease activity was restored by incubation of the inactivated enzyme with the reducing agent bismercaptoethyl sulfone, suggesting that disulfide bond formation was responsible for the observed inhibition. The five cysteines of the protease are normally in the reduced state; analysis of tryptic peptides from inhibited protease indicated that disulfide bonds Cys84-Cys87 and Cys138-Cys161 were formed. Using site-directed mutagenesis, the disulfide pair induced between Cys138 and Cys161 disulfide is dependent upon interaction of PT with the protease and does not form spontaneously, unlike that of the Cys84-Cys87 pair which can form in the absence of inhibitor. The inhibitor's redox chemistry is analogous to that of flavin, and, in fact, flavin inhibits the protease by the same mechanism, causing formation of a disulfide bond between Cys138 and Cys161. That the cysteines are dispensable, but can regulate protease activity by formation of a unique disulfide pair, suggests a plausible mechanism for control of proteolysis during the viral life cycle.