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181.
This critical review covers the present state of the art in optical sensing of glucose. Following an introduction into the significance of (continuous) sensing of glucose and a brief look back, we discuss methods based on (a) monitoring the optical properties of intrinsically fluorescent or labeled enzymes, their co-enzymes and co-substrates; (b) the measurement of the products of enzymatic oxidation of glucose by glucose oxidase; (c) the use of synthetic boronic acids; (d) the use of Concanavalin A; and (e) the application of other glucose-binding proteins. We finally present an assessment in terms of the advantages and disadvantages of the various methods (237 references). 相似文献
182.
Szekely O Schilt Y Steiner A Raviv U 《Langmuir : the ACS journal of surfaces and colloids》2011,27(24):14767-14775
We apply a means to probe, stabilize, and control the size of lipid raft-like domains in vitro. In biomembranes the size of lipid rafts is ca. 10-30 nm. In vitro, mixing saturated and unsaturated lipids results in microdomains, which are unstable and coalesce. This inconsistency is puzzling. It has been hypothesized that biological line-active surfactants reduce the line tension between saturated and unsaturated lipids and stabilize small domains in vivo. Using solution X-ray scattering, we studied the structure of binary and ternary lipid mixtures in the presence of calcium ions. Three lipids were used: saturated, unsaturated, and a hybrid (1-saturated-2-unsaturated) lipid that is predominant in the phospholipids of cellular membranes. Only membranes composed of the saturated lipid can adsorb calcium ions, become charged, and therefore considerably swell. The selective calcium affinity was used to show that binary mixtures, containing the saturated lipid, phase separated into large-scale domains. Our data suggests that by introducing the hybrid lipid to a mixture of the saturated and unsaturated lipids, the size of the domains decreased with the concentration of the hybrid lipid, until the three lipids could completely mix. We attribute this behavior to the tendency of the hybrid lipid to act as a line-active cosurfactant that can easily reside at the interface between the saturated and the unsaturated lipids and reduce the line tension between them. These findings are consistent with a recent theory and provide insight into the self-organization of lipid rafts, their stabilization, and size regulation in biomembranes. 相似文献
183.
184.
Improved high-efficiency organic solar cells via incorporation of a conjugated polyelectrolyte interlayer 总被引:1,自引:0,他引:1
Seo JH Gutacker A Sun Y Wu H Huang F Cao Y Scherf U Heeger AJ Bazan GC 《Journal of the American Chemical Society》2011,133(22):8416-8419
The power conversion efficiencies of bulk heterojunction (BHJ) solar cells can be increased from 5 to 6.5% by incorporating an ultrathin conjugated polyelectrolyte (CPE) layer between the active layer and the metal cathode. Poly[N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT) and [6,6]-phenyl C(71) butyric acid methyl ester (PC(71)BM) were chosen for the photoactive layer. CPEs with cationic polythiophenes, in both homopolymer and block copolymer configurations, were used to improve the electronic characteristics. The significant improvement in device performance and the simplicity of fabrication by solution processing suggest a promising and practical pathway for improving polymer solar cells with high efficiencies. 相似文献
185.
Steiner E Bouguet-Bonnet S Blin JL Canet D 《The journal of physical chemistry. A》2011,115(35):9941-9946
Water in mesoporous materials possessing a two-dimensional hexagonal structure has been studied by the variation of its NMR longitudinal relaxation time T(1) as a function of the static magnetic field value, or equivalently of the NMR measurement frequency. This technique, dubbed relaxometry, has been applied from 5 kHz (measurement frequency) up to 400 MHz with various instruments including a variable-field spectrometer operating between 8 and 90 MHz. Moreover, the range 0-5 kHz could be investigated by transverse relaxation, T(2) denoting the corresponding relaxation time, and relaxation in the rotating frame, T(1ρ) denoting the corresponding relaxation time. Measurements of proton relaxation rates (inverse of relaxation times) have been performed with H(2)O and HOD (residual protons of heavy water) at water volumes of 80%, 60%, and 40% relative to the porous volume. Comparison between H(2)O and HOD shows clearly that, above 1 MHz where both sets of data are superposed, relaxation is purely intermolecular and due to paramagnetic relaxation (dipolar interactions of water protons with unpaired electrons of paramagnetic entities). Below 1 MHz, it is possible to subtract the intermolecular contribution (given by HOD data) from H(2)O data so that one is left with intramolecular relaxation which is solely due to water reorientational motions. The analysis of these low-frequency data (in terms of Lorentzian functions) reveals two types of water within the pores: one interacting strongly with the surface and the other corresponding to a second layer. High-frequency data, which arise from paramagnetic relaxation, exhibit again two types of water. Due to their correlation times, one type is assigned to relatively free water within the pores while the other type corresponds to bulk (interparticular) water. Their proportions, given as a function of the volume fraction, are consistent with the above assignments. 相似文献
186.
Stelling A Salzer R Kirsch M Sobottka SB Geiger K Koch E Schackert G Steiner G 《Analytical and bioanalytical chemistry》2011,400(9):2745-2753
Established methods for characterization of tissue and diagnostics, for example histochemistry, magnetic resonance imaging
(MRI), X-ray tomography, or positron emission tomography (PET), are mostly not suitable for intra-operative use. However,
there is a clear need for an intra-operative diagnostics especially to identify the borderline between normal and tumor tissue.
Currently, vibrational spectroscopy techniques (both Raman and infrared) complement the standard methods for tissue diagnostics.
Vibrational spectroscopy has the potential for intra-operative use, because it can provide a biochemically based profile of
tissue in real time and without requiring additional contrast agents, which may perturb the tissue under investigation. In
addition, no electric potential needs to be applied, and the measurements are not affected by electromagnetic fields. Currently,
promising approaches include Raman fiber techniques and nonlinear Raman spectroscopy. Infrared spectroscopy is also being
used to examine freshly resected tissue ex vivo in the operating theater. The immense volume of information contained in Raman
and infrared spectra requires multivariate analysis to extract relevant information to distinguish different types of tissue.
The promise and limitations of vibrational spectroscopy methods as intra-operative tools are surveyed in this review. 相似文献
187.
Well-defined nanoparticles composed of a tetraphenylmethane-based microporous polymer network with an average particle diameter of 30-60 nm were fabricated by a miniemulsion polymerization technique. Strong green emission was observed and efficient excitation energy transfer from nanoparticles to surface-bound dye molecules was explored. 相似文献
188.
Differential scanning calorimetry study of the solidification sequence of austenitic stainless steel
Darja Steiner Petrovič Grega Klančnik Miran Pirnat Jožef Medved 《Journal of Thermal Analysis and Calorimetry》2011,105(1):251-257
The solidification sequence of austenitic stainless steels can be predicted with thermodynamic calculations. Another way is
to use models where the value of the Creq./Nieq. ratio determines the relationship between the solidification mode and the composition factor. In this study the solidification
of AISI 304LN stainless steel at different cooling rates was studied using differential scanning calorimetry (DSC). The samples
were linearly heated above the liquidus temperature to 1550 °C at heating rates of 5, 10, and 25 K/min. The solidification
(cooling) scans from 1550 °C involved the same selected ramps. After the DSC measurements the samples were metallographically
analyzed to reveal the variations in the solidification microstructures. The microhardness of the solidified samples was also
measured. It was found that the cooling rate critically influenced the solidification. The solidification behavior, which
depends on the cooling rate, determines the evolution of the microstructure. At the slowest cooling rates a relief-cell morphology
was observed, and at the fastest cooling rate the formation of dendrites was evident. With an increasing cooling rate the
liquidus temperature decreased and the reaction enthalpy increased. 相似文献
189.
190.
Tatiana Y. Karogodina Igor G. Dranov Dr. Svetlana V. Sergeeva Dr. Dmitry V. Stass Prof. Dr. Ulrich E. Steiner 《Chemphyschem》2011,12(9):1714-1728
Oxidation of dihydrorhodamine 123 (DHR) to rhodamine 123 (RH) by oxoperoxonitrite (ONOO?), formed through recombination of NO and O2.? radicals resulting from thermal decomposition of 3‐morpholinosydnonimine (SIN‐1) in buffered aerated aqueous solution at pH 7.6, represents a kinetic model system of the reactivity of NO and O2.? in biochemical systems. A magnetic‐field effect (MFE) on the yield of RH detected in this system is explored in the full range of fields between 0 and 18 T. It is found to increase in a nearly linear fashion up to a value of 5.5±1.6 % at 18 T and 23 °C (3.1±0.7 % at 40 °C). A theoretical framework to analyze the MFE in terms of the magnetic‐field‐enhanced recombination rate constant krec of NO and O2.? due to magnetic mixing of T0 and S spin states of the radical pair by the Δg mechanism is developed, including estimation of magnetic properties (g tensor and spin relaxation times) of NO and O2.? in aqueous solution, and calculation of the MFE on krec using the theoretical formalism of Gorelik at al. The factor with which the MFE on krec is translated to the MFE on the yield of ONOO? and RH is derived for various kinetic scenarios representing possible sink channels for NO and O2.?. With reasonable assumptions for the values of some unknown kinetic parameters, the theoretical predictions account well for the observed MFE. 相似文献