A Pulsed EPR and DFT Investigation of the Stabilization of Coordinated Phenoxyl Radicals in a Series of Cobalt Schiff-Base Complexes

We recently demonstrated how the aerobic addition of acetic acid to N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexane-diamino Co^II, [Co(1)], leads to the formation of an unusual coordinated Co^III-phenoxyl radical. In this work, some of the structural aspects associated with the Schiff-base-derived ligand (1) that are crucial for the acid-mediated formation of the phenoxyl radical are investigated. For comparison with [Co(1)], we therefore studied the influence of acetic acid on two complexes: (1) the N,N′-bis(3,5-di-tert-butylsalicylidene)-1,2-ethane-diamino Co^II complex, [Co(2)], that lacks the cyclohexyl group of [Co(1)], and (2) the N′-disalicylidene-ethylenediamine Co^II salen complex, [Co(3)], that lacks both the tertiary butyl groups and the cyclohexyl groups. It is shown that the cyclohexyl group of [Co(1)] is not involved in the formation or stabilization of the phenoxyl radical, whereas the tertiary butyl groups of [Co(1)] play a crucial role. In addition, the characteristics of the phenoxyl radical, formed after aerobic addition of acetic acid to [Co(2)], are analyzed in detail by pulsed electron paramagnetic resonance, in combination with isotopic labeling. The experimental data are compared to density functional theory computations and to previous data on the acid-mediated phenoxyl radical of [Co(1)].     

Regulation of nestin expression by thrombin and cell density in cultures of bone mesenchymal stem cells and radial glial cells

Background  

Bone marrow stromal cells and radial glia are two stem cell types with neural phenotypic plasticity. Bone marrow mesenchymal stem cells can differentiate into osteocytes, chondrocytes and adipocytes, but can also differentiate into non-mesenchymal cell, i.e. neural cells in appropriate in vivo and in vitro experimental conditions. Likewise, radial glial cells are the progenitors of many neurons in the developing cortex, but can also generate astrocytes. Both cell types express nestin, an intermediate filament protein which is the hallmark of neural precursors.     

A Micellar Mitotane Formulation with High Drug‐Loading and Solubility: Physico‐Chemical Characterization and Cytotoxicity Studies in 2D and 3D In Vitro Tumor Models

Adrenocortical carcinoma (ACC) is a rare tumor and prognosis is overall poor but heterogeneous. Mitotane (MT) has been used for treatment of ACC for decades, either alone or in combination with cytotoxic chemotherapy. Even at doses up to 6 g per day, more than half of the patients do not achieve targeted plasma concentration (14–20 mg L^?1) even after many months of treatment due to low water solubility, bioavailability, and unfavorable pharmacokinetic profile. Here a novel MT nanoformulation with very high MT concentrations in physiological aqueous media is reported. The MT‐loaded nanoformulations are characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and powder X‐ray diffraction which confirms the amorphous nature of the drug. The polymer itself does not show any cytotoxicity in adrenal and liver cell lines. By using the ACC model cell line NCI‐H295 both in monolayers and tumor cell spheroids, micellar MT is demonstrated to exhibit comparable efficacy to its ethanol solution. It is postulated that this formulation will be suitable for i.v. application and rapid attainment of therapeutic plasma concentrations. In conclusion, the micellar formulation is considered a promising tool to alleviate major drawbacks of current MT treatment while retaining bioactivity toward ACC in vitro.     

Packet loss characteristics for <Emphasis Type="Italic">M</Emphasis>/<Emphasis Type="Italic">G</Emphasis>/1/<Emphasis Type="Italic">N</Emphasis> queueing systems

In this contribution we investigate higher-order loss characteristics for M/G/1/N queueing systems. We focus on the lengths of the loss and non-loss periods as well as on the number of arrivals during these periods. For the analysis, we extend the Markovian state of the queueing system with the time and number of admitted arrivals since the instant where the last loss occurred. By combining transform and matrix techniques, expressions for the various moments of these loss characteristics are found. The approach also yields expressions for the loss probability and the conditional loss probability. Some numerical examples then illustrate our results.     

Approximations of spectra of Schrödinger operators with complex potentials on ℝd

We study spectral approximations of Schrödinger operators T = ?Δ+Q with complex potentials on Ω = ?^d, or exterior domains Ω??^d, by domain truncation. Our weak assumptions cover wide classes of potentials Q for which T has discrete spectrum, of approximating domains Ω_n, and of boundary conditions on ?Ω_n such as mixed Dirichlet/Robin type. In particular, Re Q need not be bounded from below and Q may be singular. We prove generalized norm resolvent convergence and spectral exactness, i.e. approximation of all eigenvalues of T by those of the truncated operators T_n without spectral pollution. Moreover, we estimate the eigenvalue convergence rate and prove convergence of pseudospectra. Numerical computations for several examples, such as complex harmonic and cubic oscillators for d = 1,2,3, illustrate our results.     

Short-term changes in carbon isotope composition of soluble carbohydrates and starch: from canopy leaves to the root system

Changes in the 13C discrimination of current leaf photosynthesis might have profound impacts on root respiratory substrates. Therefore, the aim of this study was (1) to refine a method for the isolation of root and leaf starch and soluble sugars (neutral fraction) for stable carbon isotope analysis and (2) to assess the short-term temporal variability of the C isotope composition (delta13C) of starch and of the neutral fraction of beech roots and leaves at different canopy heights. An existing method for isolating starch for stable C isotope analysis based on enzymatic hydrolysis was modified to account for the low starch content of the samples. This was achieved by removing the enzyme (alpha-amylase) by ultrafiltration after the hydrolysis, resulting in very low carbon blanks. The neutral fraction was separated from organic acids and cations by ion-exchange chromatography. An anion-exchange resin in the [HCO3]--form was chosen that ensured high precision of C blanks. Beech leaves at 5, 10 and 20 m above the forest floor as well as roots were sampled six times during a day/night cycle in July 2003. Delta13C values of bulk material, starch and the neutral fraction increased from the lower to the higher canopy with mean differences between 5 and 20 m of 3.8, 3.4 and 2.7 per thousand for the delta13C values of starch, neutral fraction and bulk foliage, respectively. The delta13C value of foliar starch increased from the morning to the afternoon and decreased during the night, but diurnal differences (up to 3.1 per thousand) were only statistically significant for leaves sampled at 5 and 10 m height. In roots, no diurnal variation in the delta13C of starch was observed during the short time frame of one day and the delta13C of the neutral fraction did not differ between samples taken at 16:30 and 22:00. Calculated delta13C values of starch, which was mobilised during the night, were more positive than the total starch (all sampling times pooled) in leaves. Furthermore, the delta13C values of mobilised starch were approximately 5 per thousand more positive than that of the mobilised neutral fraction. Hence, the delta13C of potential sources for export from canopy leaves to roots varied considerably in their C isotope composition.     

Nanoscale zinc antimonides: synthesis and phase stability

Highly crystalline single-phase nanoparticles of the important thermoelectric materials Zn4Sb3 and ZnSb were prepared from solvochemically activated powders of elemental zinc and elemental antimony. Low-temperature reactions with reaction temperatures of 275-300 degrees C were applied using an excess of elemental zinc. The nanoscale thermoelectrics obtained were characterized by X-ray powder diffraction, transmission electron microscopy, and thermal analysis. nc-Zn4Sb3 showed particle sizes of 50-70 nm, whereas particle sizes of 15-20 nm were observed for nc-ZnSb. Calorimetric investigations showed an increased heat capacity, Cp, for nc-Zn4Sb3 with respect to the bulk material which could be reduced to the bulk value by annealing nc-Zn4Sb3 at 190 degrees C. Interestingly, nc-Zn4Sb3 showed exothermic decomposition into zinc-poorer ZnSn at 196 degrees C in an open system, indicating that Zn4Sb3 is metastable in nanocrystalline form at room temperature.     

Aggregation behaviors of gemini nucleotide at the air-water interface and in solutions induced by adenine-uracil interaction

Cationic gemini surfactants having nucleotides as counterions (called nucleo-gemini hereafter) were synthesized and their aggregation behavior at air-water surfaces as well as in bulk solutions were studied. Fluid solutions of these nucleo-gemini surfactants show transitions to hydrogels upon addition of complementary nucleoside bases or other nucleo-gemini surfactants having complementary bases as counterions. The FTIR-ATR measurements show that the carboxylate groups of uridine form hydrogen bonds with the amine groups of adenosine. The aggregation behavior was also confirmed at the air-water interface by Brewster angle microscopy as well as surface pressure measurements; the monolayer of a gemini nucleotide was observed to undergo a transition to multilayers when nucleosides with complementary bases were added into the subphase. Isotherm curves of surface pressure monitored in parallel show a decrease in molecular area upon addition of such nucleosides.     

New Homoleptic Rare‐Earth Metal Complexes Comprising the Unsymmetrically Substituted Amidinate Ligand [MeC(NEt)(NtBu)]–

New homoleptic complexes of selected rare‐earth elements containing the unsymmetrically substituted amidinate ligand [MeC(NEt)(NtBu)]^– [= (L)^–] were synthesized and fully characterized. Treatment of in situ‐prepared Li(L) ( 1 ) with anhydrous lanthanide(III) chlorides, LnCl₃ (Ln = Sc, La, Ce, Ho), afforded three different types of amidinate complexes depending on the ionic radius of the central metal atom. The large La³⁺ formed the octa‐coordinate DME solvate La(L)₃(DME) ( 2 ). Using Ce³⁺, the octa‐coordinate “ate” complex Li(THF)[Ce(L)₄] ( 3 ) was formed. Depending on the crystallization conditions, compound 3 could be crystallized in two modifications differing in the coordination environment around Li. In the case of the smaller Sc³⁺ and Ho³⁺ ions, six‐coordinate homoleptic Sc(L)₃ ( 4 ) and Ho(L)₃ ( 5 ) were isolated. The title compounds were fully characterized by spectroscopic and analytical methods as well as single‐crystal X‐ray diffraction. With Ln = La and Ce, several by‐products incorporating lithium, chlorine and/or oxygen were also isolated and structurally characterized.     

Conversion of N-arylglycolohydroxamic acids to 1,2,3-oxathiazolidin-4-one 2,2-dioxides

N-Arylglycolohydroxamic acids 1A are converted by in situ prepared 2,2′-dipyridyl sulfite to 1,2,3-oxathiazolidin-4-one 2,2-dioxides 5 , the formation of which can be rationalized via a radical pair mechanism. The alkylating potential of the heterocyclic system 5 is demonstrated by the alkaline ethanolysis giving rise to the open chained 2-ethoxypropionanilide 6 .