Steps, ledges and kinks on the surfaces of platinum nanoparticles of different shapes

Platinum nanoparticles with a high percentage of cubic-, tetrahedral- and octahedral-like shapes, respectively, have been synthesized by a shape-controlling technique that we developed recently [Ahmadi et al., Science 272 (June 1996) 1924]. High resolution transmission electron microscopy (HRTEM) is used here to directly image the atomic scale structures of the surfaces of these particles with different shapes. The truncated shapes of these particles are mainly defined by the {100}, {111}, and {110} facets, on which numerous atom-high surface steps, ledges and kinds have been observed. This atomic-scale fine structure of the surfaces of these particles is expected to play a critical role in their catalytic activity and selectivity.     

Optical properties of amorphous films

We have analyzed the optical properties of a-Ge_30-xSb_xS₇₀ chalcogenide glass films (x=0,10,20 and 30 at%); the chalcogenide films were prepared by vacuum thermal evaporation. The optical-absorption data indicate that the absorption mechanism is non-direct transition. We found that the optical band gap, E_opt, decreases from 2.04±0.01 to 1.74±0.01 eV, whereas the refractive index increases with increasing Sb content. Data are analyzed by the Wemple equation, which is based on the single-oscillator model.     

Beating cancer in multiple ways using nanogold

Gold nanoparticles possess a unique combination of properties which allow them to act as highly multifunctional anti-cancer agents (X. H. Huang, P. K. Jain, I. H. El-Sayed and M. A. El-Sayed, Nanomedicine, 2007, 2, 681-693; P. Ghosh, G. Han, M. De, C. K. Kim and V. M. Rotello, Adv. Drug Delivery Rev., 2008, 60, 1307-1315; S. Lal, S. E. Clare and N. J. Halas, Acc. Chem. Res., 2008, 41, 1842-1851; D. A. Giljohann, D. S. Seferos, W. L. Daniel, M. D. Massich, P. C. Patel and C. A. Mirkin, Angew. Chem., Int. Ed., 2010, 49, 3280-3294). Not only can they be used as targeted contrast agents for photothermal cancer therapy, they can serve as scaffolds for increasingly potent cancer drug delivery, as transfection agents for selective gene therapy, and as intrinsic antineoplastic agents. This tutorial review will highlight some of the many forms and recent applications of these gold nanoparticle conjugates by our lab and others, as well as their rational design and physiologic interactions.     

Relaxation mechanisms of the Zeeman sublevels of the phosphorescent triplet state of pyrazine at 1·6K

The observed change in the phosphorescence decay of the spin-aligned triplet state of pyrazine at 1·6K upon application of a magnetic field is examined both experimentally and theoretically. Experimentally, the decay curve is resolved into the three decay components of the three triplet sublevels in the field range of 0–6000 G. Both the decay constants and the fraction of total initial intensity of each decay component are determined for each field strength. Theoretically, the observed change in the decay characteristics is assumed to be solely due to the Zeeman mixing of the zero-field levels in the absence of spin-lattice relaxation processes. This has the effect of distributing the radiative strength of the strongly radiative zero-field level among the other two weakly radiative zero field levels. A simple approximate calculation gives excellent and encouraging agreement with experimental quantities in the range of validity of the approximations made (below 1000 G). A rigorous calculation was then performed using the exact solution of the secular equation resulting from the Hamiltonian including the spin-spin and Zeeman interactions. Due to the difficulty in finding a host of known crystal structure in which pyrazine can dissolve substitutionally and uniquely, the comparison between theory and experiment is made using a polycrystalline sample. A special averaging procedure is used in calculating a theoretical decay curve for each magnetic field strength used. The theoretical decay curve is then decomposed into three components employing the same computer programme used for decomposing the experimental decay curve. The agreement between the observed and the more rigorous calculated decay quantities is excellent up to 2000 G, but observed disagreement appears above 3000 G and increases with field strength. The calculated lifetimes above 3000 G are found to be longer than the observed ones. The difference is due to other relaxation mechanisms at these high fields, for example, in spin-lattice relaxation processes between the Zeeman sublevels of the lowest triplet state.     

Antibacterial Activity of a Novel Oligosaccharide from Streptomyces californics against Erwinia carotovora subsp. Carotovora

The present study aims to characterize and predict models for antibacterial activity of a novel oligosaccharide from Streptomyces californics against Erwinia carotovora subsp. carotovora using an adaptive neuro-fuzzy inference system and an artificial neural network. The mathematical predication models were used to determine the optimal conditions to produce oligosaccharide and determine the relationship between the factors (pH, temperature, and time). The characteristics of the purified antibacterial agent were determined using ultraviolet spectroscopy (UV/Vis), infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy (¹H- and ¹³C-NMR), and mass spectrometry (MS). The best performances for the model were 39.45 and 35.16 recorded at epoch 1 for E. carotovora Erw₅ and E. carotovora EMCC 1687, respectively. The coefficient (R²) of the training was more than 0.90. The highest antimicrobial production was recorded after 9 days at 25 °C and a pH of 6.2, at which more than 17 mm of the inhibition zone was obtained. The mass spectrum of antimicrobial agent (peak at R.T. = 3.433 of fraction 6) recorded two molecular ion peaks at m/z = 703.70 and m/z = 338.30, corresponding to molecular weights of 703.70 and 338.30 g/mol, respectively. The two molecular ion peaks matched well with the molecular formulas C₂₉H₅₃NO₁₈ and C₁₄H₂₆O₉, respectively, which were obtained from the elemental analysis result. A novel oligosaccharide from Streptomyces californics with potential activity against E. carotovora EMCC 1687 and E. carotovora Erw₅ was successfully isolated, purified, and characterized.     

Recent developments of derivative spectrophotometry and their analytical applications.

Articles about the development of derivative spectrophotometric methods and analytical applications of derivative spectrophotometry (DS) published in the last nine years (since 1994) are reviewed.     

Microstructure dependence of yielding and fracture in Cd-Zn alloys

The coefficient of logarithmic work-hardening, the yield stress and the fracture stress of Cd-2 wt. %Zn alloy of different grain diameters and of Cd-17·4 wt. %Zn alloy decrease with increasing working temperature. Two relaxation temperature regions have been found, the low-temperature region of relaxation (below 483 K) and the high-temperature region (above 483 K). The fracture surface energy for Cd-2 wt. % Zn alloy has been calculated and found to be 1·2 J/m² at the two temperature regions of relaxation. X-ray investigations show that the residual internal strains in the deformed samples increase with increasing working temperature and exhibit a peak value at 483 K.     

Multiphase percolation and Josephson model for high-temperature superconductivity

A four-phase percolation problem is used to simulate the Josephson model for high-temperature superconductivity both as a four-phase and a three-phase system. We implement the method on an IBM PC microcomputer using PASCAL language.     

Hole burning in the optically detected zero-field spectrum using eedor

Using EEDOR, hole burning is demonstrated in the optically detected zero-field spectrum of tetrachlorobenzene in durene at 1.6°K, thus providing evidence that a large contributor to the width in these spectra is inhomogeneous broadening. Using phase sensitive detection in conjuction with EEDOR, a highly resolved optically detected microwave spectrum of a selected narrow distribution of molecules dissolved in a host is recorded. The potential use of this technique in eliminating inhomogeneous broadening from the phosphorescence-microwave double resonance spectrum is indicated.     

On the radical mechanism for photoinduced nucleation of alkane vapors

The addition of 10^?5 — 2 Torr of NO, a radical scavenger, is found to significantly quench the rate of photonucleation of nonane by NO₂ or CH₃I in a diffusion cloud chamber. This confirms a recently proposed radical mechanism for the photoinduced nucleation of these systems. The photonucleation rate of nonane induced by o-tolualdehyde (a system whose mechanism is not known) is similarly quenched by the addition of small amounts of NO, suggesting a radical mechanism. A mechanism for this system, based upon the formation of nonane radicals (resulting from hydrogen abstraction from nonane by the carbonyl molecules in the n,π* singlet or triplet state) followed by further reaction of the radicals to form low vapor pressure species, is discussed. Acetone, a system known to dissociate into radicals, is found to photoinduce nucleation of nonane when excited to the lowest singlet or triplet excited states. This adds further support to the proposed radical mechanism and suggests that acetone dissociates in its lowest singlet as well as its lowest triplet state. A theoretical model is outlined in which the production of large involatile alkanes (dimers and higher polymers) are formed from an initially produced nonane radical. These results are combined with binary nucleation theory in order to calculate the effect of these species on the rate of nucleation. These calculations indicate that low concentrations of these involatile species can indeed induce nucleation. The ability of small, photochemically produced polymers to induce nucleation is also examined and the time dependent space distribution of polymers (e.g., vinyl polymers) generated by chain transfer from a single free radical is derived. The small polymers formed in this process are analogous to the species formed in the photoinduced nucleation of alkane vapors.