Magnetization of layered Mn-Ni and Mn-Co thin films

We report magnetization hysteresis loops for compositionally modulated films of Ni-Mn and Co-Mn. The films, prepared by evaporation, have nominal layer thicknesses of 5 to 25 Å and total thickness of 1 μm. Measurements were made on a SQUID magnetometer at 5 and 50 K with a maximum applied field of 10 kOe. The magnetic behavior observed ranges from ferromagnetism to spin-glassiness. Marked field cooling effects were observed for films with nominal layer thicknesses of 6 Å Ni-6 Å Mn, 13 Å Ni-13 Å Mn, 25 Å Ni-25 Å Mn and 5 Å Co-15 Å Mn.     

Biomimetic Cyclization of Enamide-Containing Polyenes as a New Route to Azapolycycles

Enamide 4 was studied for its effectiveness as a polyene precursor in biomimetic cyclizations. While most conventional Lewis acids were poor cyclization promoters, FeCl(3).6H(2)O initiated the conversion of 4 into tricycles 6 and 7 in excellent yield. The two isomeric products result from the cyclization of intermediate aldehyde 5 by either a chair or boat B-ring transition state. These results suggest that enamides may be incorporated into polyene precursors for the construction of larger azapolycycles such as azasteroids.     

Solution and crystallographic studies of branched multivalent ligands that inhibit the receptor-binding of cholera toxin

The structure-based design of multivalent ligands offers an attractive strategy toward high affinity protein inhibitors. The spatial arrangement of the receptor-binding sites of cholera toxin, the causative agent of the severe diarrheal disease cholera and a member of the AB(5) bacterial toxin family, provides the opportunity of designing branched multivalent ligands with 5-fold symmetry. Our modular synthesis enabled the construction of a family of complex ligands with five flexible arms each ending with a bivalent ligand. The largest of these ligands has a molecular weight of 10.6 kDa. These ligands are capable of simultaneously binding to two toxin B pentamer molecules with high affinity, thus blocking the receptor-binding process of cholera toxin. A more than million-fold improvement over the monovalent ligand in inhibitory power was achieved with the best branched decavalent ligand. This is better than the improvement observed earlier for the corresponding nonbranched pentavalent ligand. Dynamic light scattering studies demonstrate the formation of concentration-dependent unique 1:1 and 1:2 ligand/toxin complexes in solution with no sign of nonspecific aggregation. This is in complete agreement with a crystal structure of the branched multivalent ligand/toxin B pentamer complex solved at 1.45 A resolution that shows the specific 1:2 ligand/toxin complex formation in the solid state. These results reiterate the power of the structure-based design of multivalent protein ligands as a general strategy for achieving high affinity and potent inhibition.     

Trace element analysis of maternal scalp hair by external beam proton-induced X-ray emission (PIXE)

We have constructed an external beam proton-induced X-ray emission (PIXE) system for trace element analysis of biological and environmental samples. Optimization of sample preparation and experimental PIXE set up has produced a rapid, accurate, sensitive, and reliable PIXE analysis procedure. The analytical procedure was evaluated using maternal scalp hair from pregnant women 16–19 weeks' gestation. The samples were irradiated with 3.5 MeV protons from the Rutgers Nuclear Physics Department's 8 MV Tandem FN Van de Graaff accelerator. The concentrations of the elements calcium (Ca) to cadmium (Cd) in hair are reported for 50 subjects. The analytical procedure is suitable for non-invasive clinical analysis for evaluation of nutritional states and for environmental exposure to toxic metals.     

Rapid measurements of 235U fission product isotope ratios using an online,high-pressure ion chromatography inductively coupled plasma mass spectrometry protocol with comparison to isotopic depletion models

Journal of Radioanalytical and Nuclear Chemistry - An automated online separation–direct analysis method, RAPID (rapid analysis of post-irradiation debris), has been developed for the...     

Increasing Luminescent Yield By Pulsed Laser Excitation

Luminescence of dyed systems induced by laser irradiation has been studied. Significant increases in luminescence yield have been observed as the laser pulse width decreases. For nanosecond pulses, the weaker emitting systems had the highest percentage of increase. For short pulses, metastable species are not expected to build up and quench the emission.     

Structural, electronic, and chemical properties of multiply iodized aluminum clusters

The electronic structure, stability, and reactivity of iodized aluminum clusters, which have been investigated via reactivity studies, are examined by first-principles gradient corrected density functional calculations. The observed behavior of Al13I(x)- and Al14I(x)- clusters is shown to indicate that for x < or = 8, they consist of compact Al13- and Al14++ cores, respectively, demonstrating that they behave as halogen- or alkaline earth-like superatoms. For x > 8, the Al cores assume a cagelike structure associated with the charging of the cores. The observed mass spectra of the reacted clusters reveal that Al13I(x)- species are more stable for even x while Al14I(x)- exhibit enhanced stability for odd x(x > or = 3). It is shown that these observations are linked to the formation and filling of "active sites," demonstrating a novel chemistry of superatoms.     

Surface tailoring for controlled protein adsorption: effect of topography at the nanometer scale and chemistry

Protein adsorption behavior is at the heart of many of today's research fields including biotechnology and materials science. With understanding of protein-surface interactions, control over the conformation and orientation of immobilized species may ultimately allow tailor-made surfaces to be generated. In this contribution protein-surface interactions have been examined with particular focus on surface curvature with and without surface chemistry effects. Silica spheres with diameters in the range 15-165 nm with both hydrophilic and hydrophobic surface chemistries have been used as model substrates. Two proteins differing in size and shape, bovine serum albumin (BSA) and bovine fibrinogen (Fg), have been used in model studies of protein binding with detailed secondary structure analysis being performed using infrared spectroscopy (IR) on surface-bound proteins. Although trends in binding affinity and saturation values were similar for both proteins, albumin is increasingly less ordered on larger substrates, while fibrinogen, in contrast, loses secondary structure to a greater extent when adsorbing onto particles with high surface curvature. These effects are compounded by surface chemistry, with both proteins becoming more denatured on hydrophobic surfaces. Both surface chemistry and topography play key roles in determining the structure of the bound proteins. A model of the binding characteristics of these two proteins onto surfaces having differing curvature and chemistry is presented. We propose that properties of an adsorbed protein layer may be guided through careful consideration of surface structure, allowing the fabrication of materials/surface coatings with tailored bioactivity.