Phosphonate-anchored monolayers for antibody binding to magnetic nanoparticles

Targeted delivery of magnetic iron oxide nanoparticles (IONPs) to a specific tissue can be achieved by conjugation with particular biological ligands on an appropriately functionalized IONP surface. To take best advantage of the unique magnetic properties of IONPs and to maximize their blood half-life, thin, strongly bonded, functionalized coatings are required. The work reported herein demonstrates the successful application of phosphonate-anchored self-assembled monolayers (SAMs) as ultrathin coatings for such particles. It also describes a new chemical approach to the anchoring of antibodies on the surface of SAM-coated IONPs (using nucleophilic aromatic substitution). This anchoring strategy results in stable, nonhydrolyzable, covalent attachment and allows the reactivity of the particles toward antibody binding to be activated in situ, such that prior to the activation the modified surface is stable for long-term storage. While the SAMs do not have the well-packed crystallinity of other such monolayers, their structure was studied using smooth model substrates based on an iron oxide layer on a double-side polished silicon wafer. In this way, atomic force microscopy, ellipsometry, and contact angle goniometry (tools that could not be applied to the nanoparticles' surfaces) could contribute to the determination of their monomolecular thickness and uniformity. Finally, the successful conjugation of IgG antibodies to the SAM-coated IONPs such that the antibodies retain their biological activity is verified by their complexation to a secondary fluorescent antibody.     

Accuracy and robustness of three-way decomposition applied to NMR data

Three-way decomposition is a very versatile analysis tool with applications in a variety of protein NMR fields. It has been used to extract structural data from 3D NOESYs, to determine relaxation rates in large proteins, to identify ligand binding in screening for lead compounds, and to complement non-uniformly recorded (sparse) spectra. All applications so far concerned experimental data sets; it thus remains to address questions of accuracy and robustness of the method using simulated data where the correct answer is known. Systematic tests are presented for relaxation and NOESY data sets. Mixtures of real and synthetic data are used to allow control of various parameters and comparisons with correct reference data, while working with input that is as realistic as possible. The influence of the following parameters is evaluated: signal-to-noise, overlap of signals and the use of a regularization procedure within the algorithm. The main criteria used for the evaluation are accuracy and precision. It is shown that deterioration of accuracy is indicated by internal checks such as decrease of precision. Both with relaxation data and when interpreting NOESY spectra, three-way decomposition exhibits a robust behavior in situations with severe signal overlap and/or poor signal-to-noise, e.g., by avoiding false positives in the NOE shapes of NOESY decompositions. As a complement to this study, three-way decomposition is compared to other methods that achieve the same type of results.     

Phase Recognition in AlN-Ti System by Energy Dispersive Spectroscopy and Electron Backscatter Diffraction

 The combination of energy dispersive spectroscopy (EDS) and electron backscatter diffraction (EBSD) techniques in scanning electron microscope was employed to characterize the reacted interface between Ti matrix and AlN particles. Due to the high localization of EDS and EBSD, representative measurements of chemical composition and reliable determination of the crystal structure were possible for each phase in the reaction zone with complex morphology. The TiN_1−x (cubic, NaCl type), Ti₃AlN (cubic, perovskite type) and Ti-rich Ti₃ Al (hexagonal, Ni₃Sn type) phases were identified in the reaction zone after annealing at 1100 °C. EDS+EBSD combination is an efficient tool for phase analysis at the interface in reactive multicomponent systems. Received August 21, 1999. Revision November 21, 1999.     

Viscoelastic characteristics of filled modified polyethylene melts

The effect of modifying polyethylene with maleic acid on the viscoelastic characteristics of filled melts has been experimentally investigated.Institute of Polymer Mechanics, Academy of Sciences of the Latvian SSR, Riga. Translated from Mekhanika Polimerov, No. 3, pp. 558–560, May–June, 1971.     

Molecular dynamics study of bimetallic Fe–Cu Janus nanoparticles formation by electrical explosion of wires

Bimetallic nanoparticles comprised of two elements which are immiscible in the bulk present a unique combination of physical–chemical properties that strongly depend on the atomic arrangement within the particle. In this study, molecular dynamics (MD) simulations of bimetallic Fe–Cu nanoparticles formation by high-velocity collision of individual metal nanoparticles (IMNPs) were performed. Physically these conditions model fast electrical explosion of two metal wires (Fe and Cu). By varying the size, temperature and velocity of colliding IMNPs, the conditions under which phase-segregated Janus nanoparticles are formed were determined. The model predictions showed good agreement with the experimental results. The present work is a step forward to understanding the formation mechanisms of bimetallic nanoparticles with different chemical configurations.     

Accurate relaxation parameters for large proteins

The practical applicability, performance, and robustness of three-way decomposition (TWD) for the extraction of relaxation parameters are demonstrated for a large protein with 370 residues, the maltose binding protein. An ordinary set of seven relaxation-modulated (15)N HSQC spectra, recorded at another site, is systematically analyzed. For all 341 assigned backbone amide groups, including 21 pairs and one group of three overlapped peaks, T1 decay values were determined. On isolated peaks, TWD extracts T1 values with systematically lower error bounds compared to conventional tools, although for these simple cases the improvements remain limited. However, in the presence of spectral artifacts, the decrease in errors can become significant, demonstrating the higher robustness of TWD. For about half of the peaks in overlapped regions, the decomposition allowed separation of the signals, yielding significantly different T1 values between overlapping signals. For the rest, similarity of the decay times for the two or three overlapping signals could be confirmed within usually low error bounds. The use of TWD thus leads to a significant increase in the number of accessible relaxation probes in large proteins. With a newly implemented graphical user interface, the application of TWD requires merely a peak list, and thus no additional effort compared to conventional approaches is needed.