Kinetic selectivity in the N-alkylation of 2-pyridyl porphyrins: a facile approach to the alphaalphabetabeta scaffold

meso-Tetrakis(2-pyridyl)-porphyrin (2-PyP) was tetra-N-alkylated with three different alpha-bromoacetamides to generate a series of water-soluble N-alkylpyridinium porphyrins (1-3). The product mixtures showed a marked preference for the formation of the alphaalphabetabeta atropisomer. With alpha-bromo-N-n-butylacetamide, the corresponding alphaalphabetabeta 2-tetrakis (N-n-butylacetamido)-pyridyl porphyrin (2-TnBuPyP, 3) was obtained in 69% isolated yield in a single step. Prolonged heating lead to equilibration of the rotational isomers for the less bulky alkyl groups, indicating that the observed preference is a kinetic effect. The intermediate products for the N-bornyl case were identified by LC/ESI-MS to deduce an explanation for the observed nonstatistical selectivity.     

Magneto-Coulomb effect in carbon nanotube quantum dots filled with magnetic nanoparticles

Electrical transport measurements of carbon nanotubes filled with magnetic iron nanoparticles are reported. Low-temperature (40 mK) magnetoresistance measurements showed conductance hysteresis with sharp jumps at the switching fields of the nanoparticles. Depending on the gate voltage, positive or negative hysteresis was observed. The results are explained in terms of a magneto-Coulomb effect: The spin flip of the iron island at a nonzero magnetic field causes a shift of the chemical potential induced by the change of Zeeman energy; i.e., an effective charge variation is detected by the nanotube quantum dot.     

Water as a source for oxygen incorporation into acceptor doped SrTiO3 single crystals

The possibility of the incorporation of oxygen and deuteron stemming from the dissociation of water into iron doped strontium titanate single crystals with two different iron concentrations (0.13 and 0.013 at.% Fe) has been investigated. Double labeled water (²H₂¹⁸O) was used for Isotope Exchange Depth Profiling. It acts as an incorporation source of ¹⁸O into Fe-doped SrTiO₃(100) single crystals. Total dissociation of the water takes place in the vicinity of the SrTiO₃ surface and both oxygen and deuteron incorporate into the SrTiO₃. The results of the diffusion profile evaluation confirm that oxygen and deuteron migrate independently in the bulk. Oxygen incorporates into the material at high incorporation rates, practically comparable with the ones resulting from an O₂ atmosphere. The interaction of H₂O with SrTiO₃(100) surfaces was further studied with Metastable Induced Electron Spectroscopy and Ultraviolet Photoelectron Spectroscopy. Neither partial dissociation of water molecules nor any significant formation of surface OD groups was observed.     

Template based growth of nanoscaled films: a brief review

Growth of ultrathin films of metals and inorganic materials using various templates — both solid and liquid has been reviewed. Such nanoscaled films have been found to be effective in fabrication of devices and sensors. Use of crystal nanochannels of some inorganic compounds has been found to induce novel properties to the films grown within them. It is expected the latter approach will lead to the synthesis of materials with hitherto unknown properties.     

A new algorithm for generalized Sylvester‐observer equation and its application to state and velocity estimations in vibrating systems

We propose a new algorithm for block‐wise solution of the generalized Sylvester‐observer equation XA?FXE = GC, where the matrices A, E, and C are given, the matrices X, F, and G need to be computed, and matrix E may be singular. The algorithm is based on an orthogonal decomposition of the triplet (A, E, C) into the observer‐Hessenberg‐triangular form. It is a natural generalization of the widely known observer‐Hessenberg algorithm for the Sylvester‐observer equation: XA?FX = GC, which arises in state estimation of a standard first‐order state‐space control system. An application of the proposed algorithm is made to state and velocity estimations of second‐order control systems modeling a wide variety of vibrating structures. For dense un‐structured data, the proposed algorithm is more efficient than the recently proposed SVD‐based algorithm of the authors. Copyright © 2010 John Wiley & Sons, Ltd.     

Genetic algorithm-tuned entropy-based fuzzy C-means algorithm for obtaining distinct and compact clusters

A modified approach had been developed in this study by combining two well-known algorithms of clustering, namely fuzzy c-means algorithm and entropy-based algorithm. Fuzzy c-means algorithm is one of the most popular algorithms for fuzzy clustering. It could yield compact clusters but might not be able to generate distinct clusters. On the other hand, entropy-based algorithm could obtain distinct clusters, which might not be compact. However, the clusters need to be both distinct as well as compact. The present paper proposes a modified approach of clustering by combining the above two algorithms. A genetic algorithm was utilized for tuning of all three clustering algorithms separately. The proposed approach was found to yield both distinct as well as compact clusters on two data sets.     

Simulation of generation-collection experiments with homogeneous kinetics: application to electrochemical investigation of superoxide radical anion generation by osteoclasts on bone

We report simulations of electrochemical generation-collection experiments in which the generator is a small disc producing a specified time-dependent flux of the analyte and the collector is a large planar electrode which collects the analyte at the mass transport-controlled rate. This geometry corresponds to many experiments in bioelectrochemistry where a relatively large sensor is used to detect the products of a cell's metabolism at low concentration. In particular, our simulations are motivated by attempts to understand our results on the detection of the superoxide radical anion burst generated by osteoclasts (bone-resorbing cells) in response to various stimuli. Superoxide is present at low levels and disproportionates in aqueous media; however, the homogeneous kinetics are included in our simulations and the results show that it is possible to estimate the magnitude of the flux of superoxide produced by the cells and to accurately determine the time-dependence of the flux in response to stimuli such as injection of parathyroid hormone, vitamin D(3) and pertussis toxin. In all these cases, the superoxide anion flux was successfully modeled as uniform across the cell surface with time-dependence of the form j(0)e(-k(d)t) + j(∞). j(∞) is the sustained flux of superoxide and the first-order rate constant k(d) and the magnitude j(0) describe the transient component of the flux. The simulations indicate that for cell-electrode gaps D approximately < √(D/k(d)), where D is the diffusion coefficient, the value of k(d) can be accurately extracted from the time-dependence of the collector current without detailed knowledge of parameters which are hard to measure during the experiment, e.g., the cell radius a and cell-electrode separation d. In the case of parathyroid hormone, the first-order rate constant describing the decay of the transient component was k(d) = 1.8 ± 0.8 × 10(-1) s(-1), but much slower decays were observed in response to pertussis toxin (k(d) = 1.5 ± 0.5 × 10(-2) s(-1)) and vitamin D(3) (k(d) = 1.1 ± 0.5 × 10(-3) s(-1)).     

Ultrafast dynamics of epicocconone, a second generation fluorescent protein stain

Femtosecond upconversion experiment has been carried out for epicocconone and its butylamine adduct in acetonitrile and tert-butanol. An ultrafast component is found to dominate the decay of fluorescence of epicocconone in acetonitrile solution. Upon reacting with butylamine, a model for the epicocconone-protein adduct, this ultrafast component remains almost unaffected but an additional rise time occurs, indicating the formation of a highly emissive species from the locally excited state. This phenomenon is central to the extraordinary applications of epicocconone in biotechnology. The magnitude of the rise time of the butylamine adduct is similar to that of the longer component of the decay of epicocconone in acetonitrile, suggesting that the dynamics of epicocconone and its butylamine adduct are similar. The ultrafast component is slowed upon increasing the viscosity of the solvent. This results in a marked increase in quantum yield and suggests that it corresponds to rapid bond isomerization, leading to a nonradiative decay. Surprisingly, in water/sucrose mixtures, the ultrafast component remains unaffected but there is still an increase in quantum yield, suggesting that there are at least two nonradiative pathways, one involving bond isomerization and another involving proton transfer. The correct interpretation of these data will allow the design of second generation protein stains based on the epicocconone scaffold with increased quantum yields and photostability.