Thermally stable silver nanoparticles formed on a zeolite surface show multiple crystal twinning.

Surface templated and supported silver nanoparticles form on silver-exchanged mineral chabazite upon thermal reduction. The method generates high concentrations of thermostable, uniform silver nanoparticulates that may have applications as catalysts. Properties of such nanoparticles are expected to vary with particle size, composition, metallic character, defect type and density. We establish that these silver nanoparticles are metallic, crystalline and highly twinned. The twinned nature of the particles may influence both their remarkable thermal stability and their enhanced chemical and biological activity.

Reflection coefficients of permeant molecules in human red cell suspensions.

The Staverman reflection coefficient, sigma for several permeant molecules was determined in human red cell suspensions with a Durrum stopped-flow spectrophotometer. This procedure was first used with dog, cat, and beef red cells and with human red cells. The stopped-flow technique used was similar to the rapid-flow method used by those who originally reported sigma measurements in human red cells for molecules which rapidly penetrate the red cell membrane. The sigma values we obtained agreed with those previously reported for most of the slow penetrants, except malonamide, but disagreed with all the sigma values previously reported for the rapid penetrants. We were unable to calculate an "equivalent pore radius" with our sigma data. The advantages of our equipment and our experimental procedure are discussed. Our sigma data suggest that sigma is indirectly proportional to the log of the nonelectrolyte permeability coefficient, omega. Since a similar trend has been previously shown for log omega and molar volume of the permeant molecules, a correlatioo was shown between sigma and molar volume suggesting the membrane acts as a sieve.

Influence of solvent, anion and presence of nitrogen in the ring structure on the mechanism of complexation of alkali metal cations with crown ethers.

The mechanism of complexation of alkali metal cations with macrocyclic ligands such as the simple crown ethers and the role of desolvation vs. ligand rearrangement are discussed. The unique role of water solvent in the rate-determining step of complexations in aqueous solutions is brought into focus. The competitive role of the anion, which becomes of paramount importance in solvents of low permittivity, is reiterated. Monoazo crown ethers are shown to possess isomeric equilibria in methanol solvent. The rate-determining process for the first step of complexation of these macrocycles with Na+ in methanol appears to be the rearrangement of the ligand through inversion to an exo position of the nitrogen lone electron pair. The rate-determining step of the overall complexation is the entrance of the Na+ into the ring with (possibly) concomitant rotation of the lone electron of the nitrogen to an endo configuration.

Oxymyohemerythrin: discriminating between O2 release and autoxidation.

Myohemerythrin (Mhr) is a non-heme iron O2 carrier (with two irons in the active site) that is typically found in the retractor muscle of marine 'peanut' worms. OxyMhr may either release O2, or undergo an autoxidation reaction in which hydrogen peroxide is released and diferric metMhr is produced. The autoxidation reaction can also be promoted by the addition of certain anions to Mhr solutions. This work, using recombinant Themiste zostericola Mhrs, contrasts the results of environmental effects on these reactions. For the O2 release reaction, deltaVdouble dagger(21.5 degrees C) = +28+/-3 cm3 mol(-1), deltaHdouble dagger(1 atm) = +22+/-1 kcal mol(-1), and deltaSdouble dagger(1 atm) = +28+/-4 eu. The autoxidation reaction (pH 8.0, 21.5 degrees C, 1 atm) displays different kinetic parameters: deltaVdouble dagger = -8+/-2 cm3 mol(-1), deltaHdouble dagger = +24.1+/-0.7 kcal mol(-1), and deltaSdouble dagger = +1+/-1 eu. Autoxidation in the presence of sodium azide is orders of magnitude faster than solvolytic autoxidation. The deltaVdouble dagger parameters for azide anation and azide-assisted autoxidation reaction are +15+/-2 and +59+/-2 cm3 mol(-1), respectively, indicating that the rate-limiting steps for the Mhr autoxidation and anation reactions (including O2 uptake) are not associated with ligand binding to the Fe2 center. The L103V and L103N oxyMhr mutants autoxidize approximately 10(3)-10(5) times faster than the wild-type protein, emphasizing the importance of leucine-103, which may function as a protein 'gate' in stabilizing bound dioxygen.

Experimental evidence of an x-ray laser.

A three-stage neodymium:glass laser has been used to produce collimated x-radiation from an aqueous copper(II) sulfate gel. The 1.06-mum Q-switch pulse from the neodymium laser was focused by a cylindrical lens to a horizontal line traversing a microscope slide sandwich that contained a thin film of gel. The emission from the gel was detected as a 0.2-mm spot on shielded, standard x-ray photographic film at distances that varied from 30 to 110 cm from the sandwich. Spot size did not increase with distance, suggesting coherence of the x-rays.

Reflection coefficients of permeant nonelectrolytes for dog and beef red cell membranes.

The reflection coefficient, sigma, for several small permeant nonelectrolytes was determined for dog and beef red blood cell membranes. Our sigma values were considerably higher than those previously reported for dog cells; e.g., out sigma urea was 87% higher than the sigma urea of Rich, Sha'afi, Barton and Solomon (J. Gen. Physiol. 50: 2391, 1967). Our sigma values for urea were only slightly greater in beef cells than previously reported by Farmer and Macey (Biochim. Biophys. Acta 290: 290, 1972). We found that a trend exists when (1 - sigma) is plotted against the log of the permeability coefficient, omega. This observation is also consistent with our previously reported sigma data for human red cell membranes (Owen & Eyring, J. Gen. Physiol. 66: 241, 1972). This trend suggests that small hydrophilic molecules interact highly with cell membrane water. The exceptions to this trend were lipophilic molecules, indicating they do not interact with water while penetrating the red cell membrane.

Kinetics of sodium dodecyl sulfate solubilization of Mycoplasma laidlawii plasma membranes.

The kinetics of sodium dodecyl sulfate solubilization of aqueous suspensions of Mycoplasma laidlawii membranes have been investigated by light scattering in a stopped-flow apparatus. There was evidence of direct interaction between the membranes and sodium dodecyl sulfate micelles above the critical micelle concentration, although of lower order kinetically than with monomeric dodecyl sulfate anions below the critical micelle concentration. The activation energy remained the same in either case, about 10 kcal/mol. Static light-scattering studies at higher resolution showed that the solubilized membranes are in the form of small aggregates.

Angular dependent ESCA and infrared studies of segmented polyurethanes.

The understanding of surface bonding and composition of complex polymer mixtures used for biomedical implant materials can be accomplished by a combination of techniques. In this study, vibrational spectroscopic probes of bulk and surface bonding and composition are combined with measurements with angular dependent X-Ray Photoelectron Spectroscopy (XPS or ESCA). These data provide a detailed description in the surface composition of Biomer and Avcothane, commercially available biomedical grade polymers and model systems polydimethylsiloxane (DMS) and Avcomat, all of which have been cast as smooth films from solution. Impurities are observed segregated in the near surface region sampled by ESCA which are not observed in the surface infrared results. Both Attenuated Total Reflectance (ATR) and Photoacoustic (PA) sampling are utilized, ATR to provide a depth profile and demonstrate the higher surface sensitivity of PA sampling. The combined results describe the depth of segregation of DMS blocks in Avcothane, the presence of DMS within the topmost 20 A in Biomer, and similar impurities in the model polymers. These results point out the need for multitechnique approach and the control of sample preparation and morphology in understanding complex polymer surfaces.

Piezoelectric detection of photoacoustic signals.

Piezoelectric detection of photoacoustic signals offers a number of advantages over the better known microphonic technique for condensed phase samples. Experimental techniques are greatly simplified by taking advantage of the acoustic impedance match offered by solid state detectors with solid or liquid samples. Such piezoelectric detectors prove suitable for ac steady state measurements as well as impulse-transient response detectors. Several example spectra of Nd(III) are presented with emphasis on the effects of the fluorescence-lifetime in Nd:glass laser material.