Determination of the bioavailability of biotin conjugated onto shell cross-linked (SCK) nanoparticles

Shell cross-linked nanoparticles (SCKs) presenting surface- and bioavailable biotin functional groups were synthesized via a mixed micelle methodology, whereby co-micellization of chain terminal biotinylated poly(acrylic acid)-b-poly(methyl acrylate) (PAA-b-PMA) and nonbiotinylated PAA-b-PMA were cross-linked in an intramicellar fashion within the shell layer of the mixed micelles, between the carboxylic acid groups of PAA and the amine functionalities of 2,2'-(ethylenedioxy)diethylamine. The hydrodynamic diameters (D(h)) of the micelles and the SCKs with different biotinylated block copolymer contents were determined by dynamic light scattering (DLS), and the dimensions of the SCKs were characterized with tapping-mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The amount of surface-available biotin was tuned by varying the stoichiometric ratio of the biotinylated PAA-b-PMA versus the nonbiotinylated PAA-b-PMA, as demonstrated with solution-state, binding interaction analyses, an avidin/HABA (avidin/4'-hydroxyazobenzene-2-carboxylic acid) competitive binding assay, and fluorescence correlation spectroscopy (FCS). The avidin/HABA assay found the amount of available biotin at the surface of the biotinylated SCK nanoparticles to increase with increasing biotin-terminated block copolymer incorporation, but to be less than 25% of the theoretical value. FCS measurements showed the same trend.     

EFFECTS OF DIETARY VITAMIN E AND SELENIUM ON LIGHT DAMAGE TO THE RAT RETINA*,†

Abstract—In this study we have investigated effects of dietary supplementation or deficiency in α-tocopherol (vitamin E) and selenium on acute light stress to albino rats. Selenium, which is an essential component of the enzyme glutathione peroxidase, and α-tocopherol are thought to be important in preventing in vivo lipid peroxidation. Before light stress, sections of paraffin embedded eyes show an intense yellow autofluorescent pigment localized in the retinal pigment epithelium (RPE) of the deficient rats which is barely visible in tissue sections from the supplemented rats. The fluorescent pigment is thought to be the result of damaging lipid peroxidation reactions. In addition the dcficient rats show increased electroretinogram (ERG) thresholds and decreased ERG-amplitudes compared to the supplemented rats. Acute 12 h light stress did not produce an increase in autofluorescent pigment in the RPE of the supplemented or deficient rats. The supplemented rats. however. showed marked light damage effects as measured by ERG-parameters. Contrary to our expectations, the deficient rats showed a lesser amount of light damage to the ERG than the supplemented rats. Our ERG results to date fail to implicate r-tocopherol levels or glutathione peroxidase activity as major factors in protecting the retina and pigment epithelium from damage after acute light stress.     

Euclidean Green functions for quantum Fainberg-Iofa fields

We give necessary and sufficient conditions for Euclidean Green functions to have analytic continuation to a relativistic field theory with exponential growth in momentum space (= the Fainberg-Iofa fields or the fields with fundamental length).     

Convex interpolating splines of arbitrary degree. III

For given data (x _i, f_i) _i=0 ⁿ (x ₀<x ₁<...<x _n) we consider the possibility of finding a spline functions of arbitrary degreek (k3) with preassigned smoothnessl, where 1l[(k-1)/2]. The splines should be such thats(x _i)=f _i (i=0, 1,...,n) ands is convex or nondecreasing and convex on [x ₀,x _n]. An explicit formula for this function as well as the conditions that guarantee the required properties are established. An algorithm for the determination of the splines and the error bounds is also included.     

N-substitution in the 2-amino- and 2,7-diaminophenoxazin-3-one ring system. Application to the preparation of actinomycin D analogs

A method is described for the direct N²-monoalkylation of the 2-aminophenoxazin-3-one system by treatment with dimethylsulfonium methylide in DMSO-THF, which acts as a base by abstracting a proton from the 2-amino function to form a stabilized anion, which is then alkylated by reaction with an alkyl halide. Selective N⁷-monoalkylation of the 2,7-diaminophenoxazin-3-one system can be accomplished by reaction with aromatic aldehydes in glacial acetic acid to give Schiff bases, which are then reduced with dimethylamine borane. These reactions have been applied to the preparation of N²-benzyl- and 7-benzylaminoactinomycin D.     

Reaction of singlet oxygen with Ir(I) and Rh(I) thiolato complexes: oxidative addition vs. S-oxidation

Singlet oxygen reacts with Ir(I) and Rh(I) thiolato complexes to form the corresponding Ir(III) and Rh(III) peroxo thiolato complexes which do not undergo intramolecular oxidation of the thiolate moiety.     

Synthesis and characterization of acetylene-terminated aromatic amide resin precursors

A series of 10 acetylene-terminated aromatic amide monomers was synthesized by the triethylamine-promoted reaction of bis[p-(m-chlorocarbonylphenoxy)phenyl] sulfone or bis[p-(m-chlorocarbonylphenoxyl)phenyl]ketone with o- or p-ethynyl- and o- or p-trimethylsilylethynylaniline. Yields were essentially quantitative. Structures were verified by infrared and nuclear magnetic resonance spectroscopy and mass spectral data. Thermal characteristics of the monomers were investigated by means of differential scanning calorimetry and thermogravimetric analysis. The initial glass transition temperatures were generally well below the onset of cure which occurred in the 160–225°C range for the terminal ethynyl monomers and in the 260–295°C range for their trimethylsilylethynyl analogs. Onset of decomposition in air for the resinified terminal ethynyl monomers took place in the 400–485°C range, while resins from the trimethylsilylethynyl monomers underwent breakdown at substantially lower temperatures.     

Ruthenium(0) Catalyzed Isomerization of Allylbenzene. The Detection and Isolation of A Hydrido-η3-Allyl Intermediate

Allylbenzene is isomerized to $\text{cis}$- and $\text{trans}$-β-methylstyrene at 35–60°C in the presence of [(C₆H₅)₃P]₄Ru(π-CH₃CN)·CH₃CN. Two hydrido-η³-1-phenylallyl ruthenium complexes have been detected by proton nmr spectroscopy during the reaction and the predominant one of formula [(C₆H₅)₃P]₂RuH(η³-C₃H₄C₆H₅)(CH₃CN) has been isolated. The structure of this intermediate contains cis phosphines, mutually trans hydrido and acetonitrile ligands and the 1-phenylallyl ligand in a $\text{syn}$-configuration. A similar structure with an $\text{anti}$-configuration of the 1-phenylallyl ligand is suggested for the other detected intermediate. These complexes indicate that this isomerization is initiated by oxidative-addition of ruthenium(0) to an allylic C-H bond with the formation of distinct η³-allyl metal hydride species as has been proposed in a number of metal catalyzed olefin transformations.     

A novel mechanism of proton transfer in protonated peptides

The study presents quantum-chemical calculations on proton transfer in protonated N-acetylglycyl-N1-methylglycinamide (AGA) as a short oligopeptide model. All calculations employ the B3LYP functional and the 6-31++G** basis set. Two different mechanisms of proton transfer are discussed. The rate-determining step of the first mechanism exhibits an energy barrier of about 17.7 kcal mol-1, and it is represented by an isomerization of the proton around the double bond of the carbonyl group. The second mechanism is based on the large conformational flexibility of AGA, where all carbonyl oxygens cooperate. The rate-determining step of this mechanism exhibits an energy barrier of only 8.3 kcal mol-1.     

Synthesis of pisiferol revisited; control of stereochemistry in an intramolecular Diels-Alder reaction

Thermolysis of 4(X=H) gives 6a and 6b(X=H) in a ratio of 1:4 whereas 4 (X=SO₂Ph) gives more of the trans-ring junction product 6a(X=SO₂Ph) suitable for the synthesis of pisiferol [ratio 6a : 6b(X=SO₂Ph) = 1.5:1].