Effect of copper impurity on the edge emission of ZnTe crystals

The results are given of studies on the edge emission of undoped and copperdoped ZnTe crystals in the temprature range 4.2–300K. The copper impurity has been found to increase the intensity of the principal edge emission band substantially. Analysis of the structure of this emission band indicated that a temprature below 160K the main role is played by the emission from excitons that are most probably bound in Cu_Zn and Li_Zn centers while at higher temperatures it is played by emission during the transition of free electrons to these centers. An appreciable role is played over the entire range of temperatures by emission from free electrons with an energy of 13 MeV. The luminescence quenching energy below 160 K has a value of 7 MeV (the binding energy of a bound exciton) and at higher temperatures it is 78 MeV.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 68–73, August, 1987.     

Stoichiometry-dependent formation of quantum dot-antibody bioconjugates: a complementary atomic force microscopy and agarose gel electrophoresis study

The unique advantages of quantum dot (QD) bioconjugates have motivated their application in biological assays. However, physical characterization of bioconjugated QDs after surface modification has often been overlooked. Here, biotinylated antibodies (biotin-IgG) were attached to commercial streptavidin-conjugated quantum dots (strep-QDs) at different stoichiometric ratios, and these QD bioconjugates were characterized with atomic force microscopy and discontinuous sodium dodecyl sulfate agarose gel electrophoresis (SDS-AGE). The results from these complementary analytical techniques showed that the molar ratio determined the relative sizes, molecular weights and morphologies of the QD bioconjugates. Additionally, the novel discontinuous SDS-AGE analysis confirmed specific binding between biotin-IgG and strep-QDs. Researchers who design QD bioconjugates for cell-based assays should consider stoichiometry-dependent differences in the physical properties of their QD bioconjugates.     

Metal clips induce folding of a short unstructured peptide into an alpha-helix via turn conformations in water. Kinetic versus thermodynamic products

Short peptides corresponding to two to four alpha-helical turns of proteins are not thermodynamically stable helices in water. Unstructured octapeptide Ac-His1-Ala2-Ala3-His4-His5-Glu6-Leu7-His8-NH(2) (1) reacts with two [Pd((15)NH(2)(CH(2))(2)(15)NH(2))(NO(3))(2)] in water to form a kinetically stable intermediate, [[Pden](2)[(1,4)(5,8)-peptide]](2), in which two 19-membered metallocyclic rings stabilize two peptide turns. Slow subsequent folding to a thermodynamically more stable two-turn alpha-helix drives the equilibrium to [[Pden](2)[(1,5)(4,8)-peptide]] (3), featuring two 22-membered rings. This transformation from unstructured peptide via turns to an alpha-helix suggests that metal clips might be useful probes for investigating peptide folding.     

Polymer-protected palladium nanoparticles. Morphologies and catalytic selectivities

Colloidal palladium nanocatalysts prepared by in situ reductions of palladium chloride were immobilized and protected by either of two water-soluble polymers. The particle sizes and size distributions of the palladium colloids were determined by transmission electron microscopy. Their selectivities as catalysts were determined by comparing the extents of hydrogenation of carefully chosen pairs of small-molecule olefins. There was found to be high hydrogenation selectivity with regard to cyclic vs. noncyclic olefins. Selectivity was relatively low, however, among olefins that differed only in size (such as hexene vs. octene), or olefins differing only with regard to the positions of the double bonds (such as 1-octene vs. 3-octene). Selectivity could be improved by careful choice of the immobilizing polymer, and by its use at relatively high concentrations.     

Möbius aromaticity in [12]annulene: cis-trans isomerization via twist-coupled bond shifting

Density functional and coupled cluster calculations show that facile thermal configuration change in [12]annulene occurs via a twist-coupled bond-shifting mechanism. The transition state for this process is highly aromatic with M?bius topology. At the CCSD(T)/cc-pVDZ//BH&HLYP/6-311+G** level, the isomerization of tri-trans-[12]annulene 1a (CTCTCT) to its di-trans isomer 2 (CCCTCT) via such a mechanism has a barrier of 18.0 kcal/mol, in good agreement with earlier experiments. Two other aromatic M?bius bond-shifting transition states were located that result in configuration change for other [12]annulene conformers. This mechanism contrasts sharply with diradical configuration change for acyclic polyenes and with planar bond-shifting mechanisms generally assumed for annulenes. This constitutes evidence that neutral M?bius aromatic annulenes play a role in the dynamic processes of neutral [4n]annulenes.     

Hardy Spaces on the Plane and Double Fourier Transforms

We provide a direct computational proof of the known inclusion where is the product Hardy space defined for example by R. Fefferman and is the classical Hardy space used, for example, by E.M. Stein. We introduce a third space of Hardy type and analyze the interrelations among these spaces. We give simple sufficient conditions for a given function of two variables to be the double Fourier transform of a function in and respectively. In particular, we obtain a broad class of multipliers on and respectively. We also present analogous sufficient conditions in the case of double trigonometric series and, as a by-product, obtain new multipliers on and respectively.     

Shelf-life of99mTc(Sn)-pyrophosphate

The effect of the preparation conditions on the in vitro stability of^99mTc (Sn)-pyrophosphate kit solution has been examined. To extend the shelf-life of the preparation, different methods of protection were tested. Nitrogen purging stabilizes the kit for at least 6 h after labeling when the content of^99mTc-pertechnetate raises to about 5%. However, this method is ineffective in the presence of hydrogen peroxide. The protecting ability of two chemicals was also determined. Gentisic acid gave good results. In the presence of 50 g of gentisic acid per ml of the kit the content of pertechnetate was 1–2% throughout the examined time interval. To eliminate the influence of hydrogen peroxide (6 g per ml of the kit) about 100 g of gentisic acid is needed. N, N-diphenyl-p-phenylenediamine (DPPD) performs some protecting effect only when used in the samples protected by nitrogen purging. However its protecting ability is lower that in the case of gentisic acid.     

Kinetic modelling of the thermal oxidation of polyisoprene elastomers. Part 2: Effect of sulfur vulcanization on mass changes and thickness distribution of oxidation products during thermal oxidation

Thermal oxidation of sulfur vulcanized polyisoprene samples was studied by gravimetry and IR mapping of carbonyl groups (to determine the oxidized layer thickness (TOL)) at temperatures ranging from 60 to 150 °C in air. Oxidation appears noticeably lower than that for the starting non-vulcanized polyisoprene, revealing a stabilizing effect of sulfur-containing species. After a short period where mass loss presumably due to water evaporation predominates, the sample mass increases until a plateau corresponding to 6.3% (at 60 °C) to 0.5% (at 140 °C) mass gain. Practically no weight gain (∼0.1%) was observed at 150 °C. The mass uptake is due to oxygen grafting to the chains. TOL varies from about 4.6 mm (70 °C) to about 1 mm (150 °C).A kinetic model, derived from a mechanistic scheme of radical chain oxidation including stabilizing events due to hydroperoxide reduction by sulfur-containing groups and taking into account the diffusion-reaction coupling, was established and numerically resolved. The model predictions for mass changes and TOL values are in good agreement with experimental data.     

Comparison of Omega and PPP techniques for reactivity calculations in methyl-substituted naphthalenes

The dependence of electron density, superdelocalizability and localization energy on the value of the parameter for the inductive effect of the methyl group in 1,4-dimethyl naphthalene is exactly the same when calculated by the Omega or by the Pople-Pariser-Parr techniques.

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Zusammenfassung Die Abhängigkeit der Elektronendichte, der Superdelokalisierbarkeit und der Lokalisierungsenergie vom Wert des Parameters für den induktiven Effekt der Methylgruppe in 1,4-Dimethylnaphthalin ist genau dieselbe, wenn man diese Größen mit der Omegatechnik oder der PPP-Methode berechnet.

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Résumé La densité électronique, la super délocalisabilité et l'énergie de localisation du 1,4 diméthyl naphtalène dépendent de la même manière de la valeur du paramètre de l'effet inductif du groupe méthyle selon que les calculs sont effectués par la méthode oméga ou par la méthode de Pople-Pariser-Parr.

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This work was done with financial assistance from the National Research Council of Canada. L.-K. H. wishes to acknowledge the award of a Colombo Plan scholarship.