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91.
The development of a highly sensitive amperometric sensor for nitrite using a glassy carbon electrode modified with alternated layers of iron(III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeT4MPyP) and cobalt(II) tetrasulfonated phthalocyanine (CoTSPc) is described. The modified electrode showed an excellent catalytic activity and stability for the nitrite oxidation decreasing the peak potentials about 200 mV toward less positive values and presenting much higher peak currents than those obtained on the bare GC electrode. A linear response range of 0.2-8.6 μmol l−1, with a sensitivity of 0.37 μA l μmol−1 and detection limit of 0.04 μmol l−1 were obtained with this sensor. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was verified to be 1.4% for 10 measurements of 0.2 μmol l−1 nitrite solution. Interference caused by common ions has been investigated in simulated mixtures containing high concentration level of interfering ions and the sensor was found to be tolerant against these ions. The developed sensor was applied for the nitrite determination in water samples and the results were in agreement with those obtained by a comparative method described in the literature. The average recovery for these samples was 100.1 (±0.7)%. 相似文献
92.
Fabris L Antonello S Armelao L Donkers RL Polo F Toniolo C Maran F 《Journal of the American Chemical Society》2006,128(1):326-336
The preparation and properties of a series of gold nanoclusters protected by thiolated peptides based on the alpha-aminoisobutyric acid (Aib) unit are described. The peptides were devised to form 0-3 C=O...H-N intramolecular hydrogen bonds, as required by their 3(10)-helical structure. The monolayer-protected clusters (MPCs) were prepared, using a modified version of the two-phase Brust-Schiffrin preparation, and fully characterized with (1)H NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The MPCs were obtained with core diameters in the range of 1.1-2.3 nm, depending on the reaction conditions. Structured peptides formed smaller clusters. The smallest MPC obtained is in agreement with the average formula Au(38)Pep(18). The results showed that the chemical integrity of the peptide is maintained upon monolayer formation and that the average number of peptide ligands per gold cluster is typically 75-85% the value calculated for alkanethiolate MPCs of similar sizes. The IR and NMR spectra indicated that in the monolayer the peptides are involved in both intra- and interligand C=O...H-N hydrogen bonds. 相似文献
93.
A tapered semiconductor amplifier is injection seeded by a femtosecond optical frequency comb at 780 nm from a mode-locked Ti:sapphire laser. Energy gains of more than 17 dB(12 dB) are obtained for 1 mW(20 mW) of average input power when the input pulses are stretched into the picosecond range. A spectral window of supercontinuum light generated in a photonic fiber has also been amplified. Interferometric measurements show sub-Hertz linewidths for a heterodyne beat between the input and amplified comb components, yielding no detectable phase-noise degradation under amplification. These amplifiers can be used to boost the infrared power in f-to-2f interferometers used to determine the carrier-to-envelope offset frequency, with clear advantages for stabilization of octave-spanning femtosecond lasers and other supercontinuum light sources. 相似文献
94.
The analytical determination of atmospheric pollutants still presents challenges due to the low-level concentrations (frequently in the μg m−3 range) and their variations with sampling site and time. In this work, a capillary membrane diffusion scrubber (CMDS) was scaled down to match with capillary electrophoresis (CE), a quick separation technique that requires nothing more than some nanoliters of sample and, when combined with capacitively coupled contactless conductometric detection (C4D), is particularly favorable for ionic species that do not absorb in the UV-vis region, like the target analytes formaldehyde, formic acid, acetic acid and ammonium. The CMDS was coaxially assembled inside a PTFE tube and fed with acceptor phase (deionized water for species with a high Henry's constant such as formaldehyde and carboxylic acids, or acidic solution for ammonia sampling with equilibrium displacement to the non-volatile ammonium ion) at a low flow rate (8.3 nL s−1), while the sample was aspirated through the annular gap of the concentric tubes at 2.5 mL s−1. A second unit, in all similar to the CMDS, was operated as a capillary membrane diffusion emitter (CMDE), generating a gas flow with know concentrations of ammonia for the evaluation of the CMDS. The fluids of the system were driven with inexpensive aquarium air pumps, and the collected samples were stored in vials cooled by a Peltier element. Complete protocols were developed for the analysis, in air, of NH3, CH3COOH, HCOOH and, with a derivatization setup, CH2O, by associating the CMDS collection with the determination by CE-C4D. The ammonia concentrations obtained by electrophoresis were checked against the reference spectrophotometric method based on Berthelot's reaction. Sensitivity enhancements of this reference method were achieved by using a modified Berthelot reaction, solenoid micro-pumps for liquid propulsion and a long optical path cell based on a liquid core waveguide (LCW). All techniques and methods of this work are in line with the green analytical chemistry trends. 相似文献
95.
A straightforward procedure for the preparation of nucleoside analogue 1 and its regioisomer 2 containing a dihydro-1,4-dithiin as sugar moiety has been accomplished in four steps by our readily available heterocyclic system 5. Nucleobase insertion was carried out by direct addition of N4-acetylcytosine to sulfoxide derivatives via Pummerer-type glycosidation reaction. 相似文献
96.
Kraus T Verpoorte E Linder V Franks W Hierlemann A Heer F Hafizovic S Fujii T de Rooij NF Koster S 《Lab on a chip》2006,6(2):218-229
We present a 3-D microfluidic device designed for localized drug delivery to cellular networks. The device features a flow cell comprising a main channel for nutrient delivery as well as multiple channels for drug delivery. This device is one key component of a larger, fully integrated system now under development, based upon a microelectrode array (MEA) with on-chip CMOS circuitry for recording and stimulation of electrogenic cells (e.g. neurons, cardiomyocytes). As a critical system unit, the microfluidics must be carefully designed and characterized to ensure that candidate drugs are delivered to specific regions of the culture at known concentrations. Furthermore, microfluidic design and functionality is dictated by the size, geometry, and material/electrical characteristics of the CMOS MEA. Therefore, this paper reports on the design considerations and fabrication of the flow cell, including theoretical and experimental analysis of the mass transfer properties of the nutrient and drug flows, which are in good agreement with one another. To demonstrate proof of concept, the flow cell was mounted on a dummy CMOS chip, which had been plated with HL-1 cardiomyocytes. A test chemical compound was delivered to the cell culture in a spatially resolved manner. Envisioned applications of this stand-alone system include simultaneous toxicological testing of multiple compounds and chemical stimulation of natural neural networks for neuroscience investigations. 相似文献
97.
Cristian Micheletti Flavio Seno Amos Maritan Jayanth R. Banavar 《Annals of Combinatorics》1999,3(2-4):431-450
Fundamental challenges in molecular biology can be addressed by using simple models on a lattice, where statistical mechanics and combinatoric techniques can be employed. The basic premise is that it is sensible to test any proposed method on the simplest of models in order to assess their validity before launching a full-scale attack on realistic problems. In this paper we follow this strategy and we present different efficient schemes to perform protein design and to extract effective amino acid interaction potentials.This work was supported in part by INFM, INFN sez. di Trieste, NASA and NATO. 相似文献
98.
99.
100.
The crystal structure of bis(4-nitropyrazol-1-yl)methane has been determined by X-ray diffraction. The nitro groups form angles of 16.45(6) and 11.83(7)°, respectively, with the pyrazole ring to which they are attached. The internal and external angles of the pyrazole rings follow a set of empirical rules: (1) N(1)-N(2)-C(3) is smaller than N(2)-N(1)-C(5); (2) N(2)-C(3)-C(4) is larger than N(1)-N(2)-C(3) and at least one chosen between C(3)-C(4)-C(5) and C(4)-C(5)-N(1); (3) C3-C4-C5 is not the largest internal angle; (4) R1-N1-N2 is smaller than R1-N1-C5; (5) N2-C3-R3 is smaller than R3-C3-C4, or R5-C5-N1 is smaller than C4-C5-R5; (6) C3-C4-R4 and R4-C4-C5 are nearly the same. Provided that the angle considered is not part of another ring, the first five rules are valid for all the pyrazoles investigated up to now, while violation of the last rule is good evidence for steric hindrance or marked asymmetry of the 3- and 5-substituents. 相似文献