The transition from spark to arc discharge and its implications with respect to nanoparticle production

Indium (III) phthalocyanine (InPc) was encapsulated into nanoparticles of PEGylated poly(d,l-lactide-co-glycolide) (PLGA-PEG) to improve the photobiological activity of the photosensitizer. The efficacy of nanoparticles loaded with InPc and their cellular uptake was investigated with MCF-7 breast tumor cells, and compared with the free InPc. The influence of photosensitizer (PS) concentration (1.8–7.5 μmol/L), incubation time (1–2 h), and laser power (10–100 mW) were studied on the photodynamic effect caused by the encapsulated and the free InPc. Nanoparticles with a size distribution ranging from 61 to 243 nm and with InPc entrapment efficiency of 72 ± 6 % were used in the experiments. Only the photodynamic effect of encapsulated InPc was dependent on PS concentration and laser power. The InPc-loaded nanoparticles were more efficient in reducing MCF-7 cell viability than the free PS. For a light dose of 7.5 J/cm² and laser power of 100 mW, the effectiveness of encapsulated InPc to reduce the viability was 34 ± 3 % while for free InPc was 60 ± 7 %. Confocal microscopy showed that InPc-loaded nanoparticles, as well as free InPc, were found throughout the cytosol. However, the nanoparticle aggregates and the aggregates of free PS were found in the cell periphery and outside of the cell. The nanoparticles aggregates were generated due to the particles concentration used in the experiment because of the small loading of the InPc while the low solubility of InPc caused the formation of aggregates of free PS in the culture medium. The participation of singlet oxygen in the photocytotoxic effect of InPc-loaded nanoparticles was corroborated by electron paramagnetic resonance experiments, and the encapsulation of photosensitizers reduced the photobleaching of InPc.     

Isotope exchange in reactions between D2O and size-selected ionic water clusters containing pyridine, H+ (pyridine)m(H2O)n

Pyridine containing water clusters, H(+)(pyridine)(m)(H(2)O)(n), have been studied both experimentally by a quadrupole time-of-flight mass spectrometer and by quantum chemical calculations. In the experiments, H(+)(pyridine)(m)(H(2)O)(n) with m = 1-4 and n = 0-80 are observed. For the cluster distributions observed, there are no magic numbers, neither in the abundance spectra, nor in the evaporation spectra from size selected clusters. Experiments with size-selected clusters H(+)(pyridine)(m)(H(2)O)(n), with m = 0-3, reacting with D(2)O at a center-of-mass energy of 0.1 eV were also performed. The cross-sections for H/D isotope exchange depend mainly on the number of water molecules in the cluster and not on the number of pyridine molecules. Clusters having only one pyridine molecule undergo D(2)O/H(2)O ligand exchange, while H(+)(pyridine)(m)(H(2)O)(n), with m = 2, 3, exhibit significant H/D scrambling. These results are rationalized by quantum chemical calculations (B3LYP and MP2) for H(+)(pyridine)(1)(H(2)O)(n) and H(+)(pyridine)(2)(H(2)O)(n), with n = 1-6. In clusters containing one pyridine, the water molecules form an interconnected network of hydrogen bonds associated with the pyridinium ion via a single hydrogen bond. For clusters containing two pyridines, the two pyridine molecules are completely separated by the water molecules, with each pyridine being positioned diametrically opposite within the cluster. In agreement with experimental observations, these calculations suggest a "see-saw mechanism" for pendular proton transfer between the two pyridines in H(+)(pyridine)(2)(H(2)O)(n) clusters.     

Approximation of Parametric Derivatives by the Empirical Interpolation Method

We introduce a general a priori convergence result for the approximation of parametric derivatives of parametrized functions. We consider the best approximations to parametric derivatives in a sequence of approximation spaces generated by a general approximation scheme, and we show that these approximations are convergent provided that the best approximation to the function itself is convergent. We also provide estimates for the convergence rates. We present numerical results with spaces generated by a particular approximation scheme—the Empirical Interpolation Method—to confirm the validity of the general theory.     

Kurtosis and compressibility near the chiral phase transition

The properties of net quark number fluctuations in the vicinity of the QCD chiral phase transition are discussed in terms of an effective chiral model in the mean-field approximation. We focus on the ratio of the fourth- to second-order cumulants (kurtosis) and the compressibility of the system and discuss their dependence on the pion mass. It is shown that near the chiral phase transition, both observables are sensitive to the value of mπ$m_{\pi }$. For physical mπ$m_{\pi }$, the kurtosis exhibits a peak whereas the inverse compressibility shows a dip at the pseudocritical temperature. These structures disappear for large mπ$m_{\pi }$. Our results, obtained in an effective model with two flavors, are qualitatively consistent with recent results of 2+1$2+1$ flavor lattice gauge theory. We also discuss the high- and low-temperature properties of these observables and the role of the coupling of the quark degrees of freedom to the Polyakov loop.     

The quark condensate in relativistic nucleus-nucleus collisions

We compute the modification of the quark condensate <ˉq q> in relativistic nucleus-nucleus collisions and estimate the 4-volume, where the quark condensate is small (<ˉqq>/<ˉqq>⁰≤ 0.1–0.3) using hadron phase-space distributions obtained with the quark-gluon string model. As a function of the beam energy the 4-volume rises sharply at a beam energy E^lab/A ≃ (2–5) GeV, remains roughly constant up to beam energies ≃ 20 GeV and rises at higher energies. At low energies the reduction of the condensate is mainly due to baryons, while at higher energies the rise of the 4-volume is due to the abundant mesons produced. Based on our results we expect that moderate beam energies on the order of 10 GeV per nucleon are favourable for studying the restoration of chiral symmetry in a baryon-rich environment in nucleus-nucleus collisions. Received: 4 December 1997 / Revised version: 31 July 1998     

Immobilized 2-(4-hydrazinocarbonylphenyl)-4,5-diphenylimidazole as solid phase luminophore in peroxyoxalate chemiluminescence

A new luminophore for application in peroxyoxalate chemiluminescence is presented. An analogue of the well-known chemiluminescence compound lophine, i.e. 2-(4-hydrazinocarbonylphenyl)-4,5-diphenylimidazole (HCPI), has been covalently immobilized to controlled pore glass and a porous methacrylate resin. By using this reagent in a solid phase detection reactor, sensitive determinations of hydrogen peroxide have been demonstrated. In homogeneous solution HCPI emits poorly as a result of 1,1-oxalyldiimidazole excitation, but when immobilized its efficiency is almost comparable to highly efficient luminophores such as 3-aminofluoranthene. Linearity extends in the single stream flow system over several orders of magnitude with both materials. The limit of detection was 1 nmol/l (10 fmole injected), when using the porous methacrylate support.