Direct electrochemistry of horseradish peroxidase immobilized in calcium carbonate microsphere doped with phospholipids

Protein electrochemistry affords a direct method to study the biological electron transfer processes. However, supplying a biocompatible environment to maintain the native state of protein is all-important and challengeable. Here, we chose vaterite, one of the crystalline polymorphs of calcium carbonate, with highly porous nature and large specific surface area, which was doped with phospholipids, as the matrix to immobilize horseradish peroxidase (HRP). The integrity of HRP was kept during the simple immobilization procedure. By virtue of this organic/inorganic complex matrix, the direct electrochemistry of HRP was realized, and the activity of HRP for catalyzing reduction of O-2 and H2O2 was preserved.

Use of atomic force microscopy for imaging the initial stage of the nucleation of calcium phosphate in Langmuir-Blodgett films of stearic acid

The nucleation of calcium phosphate on the substrate of steatic acid Langmuir-blodgett film at the initial stage was investigated by atomic force microscopy. Nano-dots, nano-wires and nano-islands were observed in sequence for the first time, reflecting the nucleation of calcium phosphate and the molecular arrangement of carboxylic layer. The nucleation rates perpendicular and parallel to the carboxylic terminal group were estimated from the height and diameter of the calcium phosphate crystals, respectively. And this stage was distinct from the late explosive grown stage, in which the change of the morphology was not obvious. The approaches based on this discovery would lead to the development of new strategies in the controlled synthesis of inorganic nano-phases and the assembly of organized composite and ceramic materials.

Determination of total calcium in plasma by flow injection analysis with tris(2,2 '-bipyridyl)ruthenium(II) electrochemiluminescent detection

We described here a new method for the determination of total calcium in plasma. The method is based on the precipitation of calcium with excess oxalate and the measurement of residual oxalate by flow injection analysis with Ru(bpy)(3)(2+) electrochemiluminescent detection. It has the advantages of extremely stable reagent, user-friendly instrument, high selectivity, good analytical recovery, wide dynamic range, and nice correlation with atomic absorption spectroscopy. The calibration plot for calcium is linear over a concentration range from 0.5 mmol L-1 to 4.8 mmol L-1, which is wider than those obtained by most other methods. The analytical recoveries for plasma calcium are 98.4-101.2% with coefficients of variation (CVs) of 1.96-2.52%. The within-day CVs range from 0.76% to 0.95%, and between-day CVs were from 1.12% to 1.46%. The time for each injection is one minute. Because the proposed method can be readily carried out on increasingly popular instruments for Ru(bpy)(3)(2+) ECL immunoassays and DNA probe assays, Ru(bpy)32+ ECL method is suitable for routine clinical analysis of calcium.

A new blue phosphorescent glass-ceramic: Rare-earth-doped calcium aluminoborate

A new blue phosphorescent glass-ceramic, Eu2+ and Nd3+, co-doped CaO-Al2O3-B2O3, was synthesized. After the irradiation with ultraviolet (UV) light, the glass-ceramic emitted blue long-lasting phosphorescence (LLP) with a spectrum peaking at about 464 nm ascribed to the characteristic 4f(6)5d(1) -> 8S(7/2) transition of Eu2+. This phosphorescence can be seen in the dark 1 h after the irradiation. However, the transparent Eu2+ and Nd3+ co-doped CaO-Al2O3-B2O3 glass did not show the phosphorescence. By the X-ray diffraction diffusion (XRD) data, alpha-CaAl2B2O7 was demonstrated to be the crystallites in the glass-ceramic. We think that alpha-CaAl2B2O7:Eu2+ Nd3+ crystallites produced during the heat treatment of the glass contribute to the LLP of the glass-ceramic.

Copper phthalocyanine organic thin-film transistors with calcium fluoride gate insulator

We report the fabrication of organic thin-film transistors (OTFTs) with copper phthalocyanine (CuPc) as the semiconductor and calcium fluoride (CaF2) as the gate dielectric on the glass substrate. The fabricated transistors show a gate voltage dependent carrier field effect mobility that ranges from 0.001 to 0.5 cm(2) V-1 s(-1). In the devices, the CaF2 dielectric is formed by thermal evaporation; thus OTFTs with a top-gate structure can be fabricated. This provides a convenient way to produce high-performance OTFTs on a large scale and should be useful for the integration of organic displays.

Synthesis and characterization of poly(epsilon-caprolactone)-poly(L-lactide) diblock copolymers with an organic amino calcium catalyst

The quasiliving characteristics of the ringopening polymerization of epsilon-caprolactone (CL) catalyzed by an organic amino calcium were demonstrated. Taking advantage of this feature, we synthesized a series of poly (F-caprolactone) (PCL)-poly(L-lactide) (PLA) cliblock copolymers with the sequential addition of the monomers CL and L-lactide. The block structure was confirmed by H-1-NMR, C-13-NMR, and gel permeation chromatography analysis. The crystalline structure of the copolymers was investigated by differential scanning calorimetry and wide-angle X-ray diffraction analysis. When the molecular weight of the PLA block was high enough, phase separation took place in the block copolymer to form PCL and PLA domains, respectively.

Ring-opening polymerization of epsilon-caprolactone and L-lactide using organic amino calcium catalyst

Poly (6-caprolactone) (PCL) and poly (L-lactide) (PLA) were prepared by ring-opening Polymerization catalyzed by organic amino calcium catalysts (Ca/PO and Ca/EO) which were prepared by reacting calcium ammoniate Ca(NH3)(6) with propylene oxide and ethylene oxide, respectively. The catalysts exhibited high activity and the ring-opening polymerization behaved a quasi-living characteristic. Based on the Fr-IR spectra and the calcium contents of the catalysts, and based on the H-1 NMR end-group analysis of the low molecular weight PCL prepared using catalysts Ca/PO and Ca/EO, it was proposed that the catalysts have the structure of NH2-Ca-O-CH(CH3)(2) and NH2-CaO-CH2CH3 for Ca/PO and Ca/EO, respectively. The ring-opening polymerization of CL and LA follows a coordination-insertion mechanism and the active site is the Ca-O bond.

Synthesis and characterization of PCL/PEG/PCL triblock copolymers by using calcium catalyst

Triblock copolymer PCL-PEG-PCL was prepared by ring-opening polymerization of epsilon-caprolactone (CL) in the presence of poly(ethylene glycol) catalyzed by calcium ammoniate at 60 degreesC in xylene solution. The copolymer composition and triblock structure were confirmed by H-1 NMR and C-13 WR measurements. The differential scanning calorimetry and wide-angle X-ray diffraction analyses revealed the micro-domain structure in the copolymer. The melting temperature T-c and crystallization temperature T-c of the PEG domain were influenced by the relative length of the PCL blocks. This was caused by the strong covalent interconnection between the two domains. Aqueous micelles were prepared from the triblock copolymer. The critical micelle concentration was determined to be 0.4-1.2 mg/l by fluorescence technique using pyrene as probe, depending on the length of PCL blocks, and lower than that of corresponding PCL-PEG diblock copolymers. The H-1 NMR spectrum of the micelles in D2O demonstrated only the -CH2CH2O- signal and thus confirmed. the PCL-core/PEG-shell structure of the micelles.

Synthesis of poly(epsilon-caprolactone)-b-poly(gamma-benzyl-L-glutamic acid) block copolymer using amino organic calcium catalyst

A biodegradable two block copolymer, poly(epsilon-caprolactone)-b- poly(gamma-benzyl-L-glutamic acid) (PCL-PBLG) was synthesized successfully by ring-opening polymerization of N-carboxyanhydride of gamma-benzyl-L-glutamate (BLG-NCA) with aminophenyl-terminated PCL as a macroinitiator. The aminophenethoxyl-terminated PCL was prepared via hydrogenation of a 4-nitrophenethoxyl-teminated PCL, which was novelly obtained from the polymerization of c-caprolactone (CL) initiated by amino calcium 4-nitrobenzoxide. The structures of the block copolymer and its precursors from the initial step of PCL were confirmed and investigated by H-1 NMR, FT-IR, GPC, and FT-ICRMS analyses and DSC measurements.

VUV-UV excited luminescent properties of calcium borophosphate doped with rare earth ions

The VUV-UV spectra of rare earth ions activated calcium borophosphate, CaBPO5:RE (RE = Ce3+, sm(3+), Eu2+, Eu3+, Tb3+ and Dy3+) were determined. The bands at about 155 nm in the VUV excitation spectra are attributed to the host lattice absorptions. The bands at 166 and 190 nm for the sample CaBPO5:Sm have been considered as related to the f-d transition and the charge transfer band (CTB) of Sm3+ ions, and the band at 169 nm for the sample CaBPO5:Dy is assumed to be connected with the f-d transition of the Dy3+ ions in CaBPO5. The partial reduction of Eu3+ CaBPO5:Eu prepared by high temperature solid state reaction in air is confirmed by the VUV-UV spectra.

VUV excited luminescence of europium activated calcium borophosphate prepared in air

XAFS (EXAFS and XANES) at Eu-L-3 edge were used to determine the local structure and the valences of europium in CaBPO5:Eu prepared in air. The results of EXAFS showed that the doped europium atoms were nine-coordinated by oxygen atoms and the distances of bond Eu-O were 2.39 Angstrom in the host lattice. XANES at Eu-L-3 edge exhibited that Eu2+ and Eu3+ coexisted in the matrix. The luminescent spectrum of the material excited by VUV at 147 nm presented a similar spectrum with that excited by f-f transition of Eu2+ at 396 nm and f-d transition of Eu2+ at 312 nm. The broad emission band due to both 4f(6)5d - 4f(7) transition of EU2+ and f - f transition of Eu3+ could be observed in emission spectra, which indicated that the trivalent europium ions were reduced in air in the matrix at high temperature by the defects [V-Cn]" formed by aliovalent substitution between Ca2+ and Eu3+ ions. The UV excitation spectrum showed the typical f-f transition of Eu3+ and f-d transition of Eu2+. The bands with the maxima at about 113 and 158 nm in VUV excitation spectrum were assigned to originate from the absorption of the host lattice.

Species of rare earth (III), calcium (II) and zinc (II) in the presence of L-histidine and L-typtophane

Rare earth(III)-histidine (His)- tryptophane (Trp). Ca(II)-His-Trp and Zn(II)-His-Trp systems were studied by potentiometric titration and computer simulation under physiological conditions. The species of the systems and their stability constants were determined. The distributions of species of rare earth(III), Ca(II) and Zn(II) were discussed.

Sol-gel deposition of calcium silicate red-emitting luminescent films doped with Eu3+

Eu3+-activated calcium silicate (CaO-SiO2:Eu3+) luminescent films were prepared by the sol-gel method. The structural evolution of the film was studied by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM), and the luminescence properties of the phosphor films were investigated as a function of heat treatment temperature. The XRD study indicates that a kilchoanite phase forms in the film sintered at 800 degreesC, which is different from that in gel powder treated under the same conditions. The SEM results show that the film thickness decreases and the particles in the film become smaller with increasing heat treatment temperature. The CaO-SiO2:Eu film shows the characteristic emission of Eu3+ under UV excitation, with the Eu3+ D-5(0)-->F-7(2) band (616 nm) being the most prominent. A large difference in the Eu3+ lifetime is observed between the film samples treated at 500 and 700 degreesC (or above). Concentration quenching occurs when the Eu3+ doping concentration is above 6 mol% of Ca2+ in the film.

Species of rare earth(III) and calcium(II) in the presence of L-aspartic acid and L-arginine

Rare earth (III)-Asp-Arg and Ca(II)-Asp-Arg systems were studied by potentiometric titration under physiological conditon. The species of each system were determined. The distribution of Tb (III) and Ca(II) species was discussed, as well as in the quaternary system of Tb(III)-Ca(II)-Asp-Arg.