Determination of gallium in biological materials by electrothermal atomic absorption spectrometry

In this determination of gallium, the condition of the graphite tubes influences the peak height. Common acids and salts seriously affect the results, but in the presence of EDTA, interferences of nitric and hydrochloric acids are suppressed completely, and interferences of phosphoric acid and some salts are suppressed partly. To compensate for the effects, a standard addition procedure is proposed, and is applied to healthy and tumor.bearing mice. A linear calibration is obtained for 0.12–12 ng Ga in 50-μl aliquots. The method is applied to tissues and body fluids with good recovery and precision.     

Nucleophilic attack of intramolecular hydroxyl groups on electron-rich aromatics using hypervalent iodine(III) oxidation

The hypervalent iodine(III) reagent, phenyliodine bis(trifluoroacetate) (PIFA)-mediated oxidative nucleophilic substitution of electron-rich aromatics involving aromatic cation radical intermediates was utilized in the direct aromatic carbon-oxygen bond formation reaction, and a novel and simple synthetic method for chroman derivatives was developed. As an extension of this methodology, a facile access to spirodienone derivatives was also achieved.     

Real-time monitoring of <Emphasis Type="SmallCaps">L</Emphasis>-glutamate release from mouse brain slices under ischemia with a glass capillary-based enzyme electrode

Real-time monitoring of L-glutamate release from various neuronal regions of mouse hippocampal slices under ischemia (a glucose-free hypoxia condition) is described. A glass capillary microelectrode with a tip size of ∼10 μm containing a very small volume (∼2 μL) of a solution of glutamate oxidase (GluOx) and ascorbate oxidase was used. First, the amperometric response behavior of the electrode at 0 V versus Ag/AgCl was characterized with a standard glutamate solution in terms of continuous measurements, effect of oxygen, viscosity of solution and concentration dependence. The electrode was applied to the real-time monitoring of L-glutamate released from different neuronal regions of acute hippocampal slices submerged in a hypoxia solution. The time-resolved amounts of L-glutamate released at various neuronal regions (CA1, CA3 and DG) of mouse hippocampal slices were quantified and compared with the reported L-glutamate fluxes using difference-image analysis during ischemia.     

Radical addition to oxime ethers for asymmetric synthesis of beta-amino acid derivatives

The diastereoselective alkyl radical addition to chiral oxime ethers was studied with a view to preparing enantiomerically pure alpha,beta-dialkyl-beta-amino acid derivatives. The phase transfer-catalyzed alkylation of Oppolzer's camphorsultam derivative of oxime ether proceeded smoothly to give the alkylated N-(beta-oximino)acyl derivatives. In the presence of BF3.OEt2, radical addition to the oxime ethers proceeded using triethylborane as the radical initiator to give alpha,beta-dialkyl-beta-amino acid derivatives with excellent diastereoselectivity.     

Radiation-induced polymerization of tetraoxane in the solid state. II. Molecular weight distribution

In order to investigate the mechanism of the radiation-induced postpolymerization of tetraoxane in the solid state, the polymer was fractionated, and the fractions were characterized by reduced viscosity. The molecular weight of polymer formed in vacuo decreased drastically after the introduction of oxygen under conditions such that the polymer yield increased. The decrease in the molecular weight in the postpolymerization of tetraoxane is attributed to degradation of the polymer in the presence of oxygen. It is suggested that at least peroxides formed by preirradiation contribute to both the increase in polymer yield and the decrease in molecular weight of the polymer.     

Tandem carbon-carbon bond-forming radical addition-cyclization reaction of oxime ether and hydrazone

The novel tandem radical addition-cyclization of oxime ethers and hydrazones intramolecularly connected with the alpha,beta-unsaturated carbonyl group is described. The radical reaction of oxime ethers 1, 2, and 4 connected with acryloyl and methacryloyl moieties proceeded smoothly to give the heterocycles via a tandem C-C bond-forming process. The tandem reaction of hydrazone 5 took place in the presence of Zn(OTf)(2) as a Lewis acid to give the trans-cyclic product 17 without the formation of the cis-isomer. The diastereoselective radical addition-cyclization reaction of chiral oxime ether 19 was also studied. The tandem reaction of 19 proceeded smoothly even in aqueous media, providing the novel method for asymmetric synthesis of gamma-butyrolactones and beta-amino acid derivatives.     

Modular Redesign of a Cationic Lytic Peptide To Promote the Endosomal Escape of Biomacromolecules

Endocytosis is an important route for the intracellular delivery of biomacromolecules, wherein their inefficient endosomal escape into the cytosol remains a major barrier. Based on the understanding that endosomal membranes are negatively charged, we focused on the potential of cationic lytic peptides for developing endosomolysis agents to release such entrapped molecules. As such, a venom peptide, Mastoparan X, was employed and redesigned to serve as a delivery tool. Appending a tri‐glutamate unit to the N‐terminus attenuates the cytotoxicity of Mastoparan X by about 40 fold, while introduction of a Ni^II‐dipicolylamine complex enhances cellular uptake of the peptide by about 17 fold. Using the optimized peptide, various fluorescently labeled macromolecules were successfully delivered to the cytosol, enabling live‐cell imaging of acetylated histones.     

How dominant is the most efficient pathway through the potential energy landscape of a slowly diffusing disordered system?

It has been suggested that the most-efficient pathway taken by a slowly diffusing many-body system is its geodesic path through the parts of the potential energy landscape lying below a prescribed value of the potential energy. From this perspective, slow diffusion occurs just because these optimal paths become particularly long and convoluted. We test this idea here by applying it to diffusion in two kinds of well-studied low-dimensional percolation problems: the 2d overlapping Lorentz model, and square and simple-cubic bond-dilute lattices. Although the most efficient path should be at its most dominant with the high-dimensional landscapes associated with many-body problems, it is useful to examine simpler, low-dimensional, constant-potential-energy problems such as these ones, both because the simpler models lend themselves to more accurate geodesic-path-finding approaches, and because they offer a significant contrast to many of the models used in the traditional energy-landscape literature. Neither the continuum nor the lattice percolation examples are adequately described by our geodesic-path formalism in the weakly disordered (relatively-fast-diffusion) limit, but in both cases the formalism successfully predicts the existence of the percolation transition and (to a certain extent) the slow diffusion characteristic of near-percolation behavior. The numerical results for these models are not nearly accurate enough near their transitions to describe critical exponents, but the models do showcase the qualitative validity of the geodesic perspective in that they allow us to see explicitly how tortuous and sparse the optimal pathways become as the diffusion constants begin to vanish.     

Combinational sensitization of Leishmania with uroporphyrin and aluminum phthalocyanine synergistically enhances their photodynamic inactivation in vitro and in vivo

Leishmania were previously shown to undergo photolysis when their transgenic mutants were induced endogenously to accumulate cytoplasmic uroporphyrin or when loaded exogenously with aluminum phthalocyanine chloride. A combinational use of both is reported here, which renders Leishmania far more susceptible to photolysis. Fluorescence microscopy of cells loaded with the two photosensitizers localized them to different subcellular sites. Pre-exposure of Leishmania to both synergistically sensitized them for photolysis as extracellular promastigotes and intracellular amastigotes in infected macrophages in vitro when illuminated at specific wavelengths to excite the respective photosensitizers for production of reactive oxygen species. Both Leishmania stages lost their viability completely when doubly photosensitized optimally and illuminated at low intensity, the host cells being left unscathed. Inoculation of mice with photoinactivated Leishmania produced no lesions, which invariably developed in the control groups during a period of observations for 8 weeks. Pretreatment of Leishmania with both photosensitizers rendered these cells susceptible to clearance from the ear dermis by white light illumination. The results suggest that double photosensitization for synergistic activity enhances the efficacy and safety of photodynamic therapy in general and for Leishmania in particular.     

Simple and selective determination of arsenite and arsenate by electrospray ionization mass spectrometry

Arsenic pollution of public water supplies has been reported in various regions of the world. Recently, some cancer patients are treated with arsenite (As^III); most Japanese people consume seafoods containing large amounts of negligibly toxic arsenic compounds. Some of these arsenic species are metabolized, but some remain intact. For the determination of toxic As^III, a simple, rapid and sensitive method has been developed using electrospray ionization mass spectrometry (ESI-MS). As^III was reacted with a chelating agent, pyrrolidinedithiocarbamate (PDC, C₄H₈NCSS^-) and tripyrrolidinedithiocarbamate-arsine, As(PDC)₃, extracted with methyl isobutyl ketone (MIBK). A 1 μL aliquot of MIBK layer was directly injected into ESI-MS instrument without chromatographic separation, and was detected within 1 min. Arsenate (As^V) was reduced to As^III with thiosulfate, and then the total inorganic As was quantified as As^III. This method was validated for the analysis of urine samples. The limit of detection of As was 0.22 μg L⁻¹ using 10 μL of sample solution, and it is far below the permissible limit of As in drinking water, 10 μg L⁻¹, recommended by the WHO. Results were obtained in < 10 min with a linear calibration range of 1-100 μg L⁻¹. Several organic arsenic compounds in urine did not interfere with As^III detection, and the inorganic As in the reference materials SRM 2670a and 1643e were quantified after the reduction of As^V to As^III.