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.

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.

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.

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.

A surgical approach to the problem of severe lateral instability at the ankle.

A unified approach to ligamentous instability of the lateral side of the ankle was investigated in 100 ankles of 81 patients (age range, ten to 59 years). The approach consisted of augmentation of the collateral ligament system by means of the anterior portion of the peroneus brevis passed forward through the fibula and secured to the talocalcaneal interosseous ligament. In addition, torn ligaments were repaired or tightened in some cases. One hundred seven operations were performed between 1977 and 1983. Ninety-seven ankles were restored to clinical stability; 83 ankles were essentially asymptomatic. All three ankles that did not ultimately stabilize were in adolescent girls with chronic instability, one of whom was treated by three procedures. Of the remaining five repeat procedures, four had been adolescent girls initially treated for chronic ankle instability.

Staged femoral lengthening.

Lengthening of short femurs, including those with actual or anticipated shortening of several inches, has been carried out using serial lengthenings. Up to 5 individual lengthenings, each of approximately one inch, have been performed on involved femurs. In cases where shortening was due to epiphyseal injury, e.g. osteomyelitis of the distal femur, good results have been achieved. Congenital shortening has not been completely corrected because of subluxation of the hip during lengthening. The principle complication has been fracture through the plate and graft. Usually this fracture could be used as the indication for additional lengthening, thus minimizing the problem. It is believed that this approach offers advantages in terms of decreased total cost in time and money, making it suitable for private patients. An additional advantage is the lack of disastrous complications. Technical problems have been numerous, however. The procedure should not be undertaken casually or for minor leg length inequality.

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.

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.

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.

Comparison of the effects of steroid, aspirin and sodium salicylate on articular cartilage.

Rabbit knee joints were compressed to produce cartilage degeneration in control and test animals who received intramuscular injections of prednisolone and aspirin or sodium salicylate by gavage. After three weeks of compression, animals were sacrificed and articular cartilage was analyzed grossly and histologically. Gross and histological specimens from salicylate treated animals showed less while the steroid treated rabbits showed more degenerative change. These data suggest that salicylate inhibits cartilage destruction while steroids enhance it.