Here we report on the synthesis, physical and chemical properties, and stability of Pd nanoparticles encapsulated within poly(amidoamine) (PAMAM) dendrimers. Specifically, amine- and hydroxyl-terminated PAMAM dendrimers ranging in generation from 4 to 8 were studied. Under appropriate conditions, addition of K2PdCl4 results in covalent attachment of the PdCl3 - hydrolysis product of this complex to tertiary amines within the dendrimers. Reduction with NaBH4 results in conversion of dendrimer-encapsulated PdCl3 - to nearly size monodisperse, encapsulated, zerovalent Pd nanoparticles. Details regarding the Pd species present in solution and within the dendrimer prior to reduction are reported, as is the maximum Pd2+ loading of the dendrimers. Dendrimer-encapsulated Pd nanoparticles undergo oxidation in air, but this process is slowed significantly when coordinating ions are removed from solution. In the absence of O2, dendrimer-encapsulated Pd nanoparticles are stable indefinitely. The oxidation product is not PdO, but rather Pd ions coordinated to the dendrimer interior. Dendrimer generation does not affect the rate of Pd oxidation. The dendrimer itself undergoes irreversible oxidation in the presence of O2. Finally, the oxidation of dendrimer-encapsulated Pd nanoparticles is reversible. Specifically, H2 gas can be used to re-reduce partially oxidized Pd nanoparticles without changing their average size.

This review discusses recent advances in the science and technology of Coulter counting. The Coulter counting principle has been used to determine the size, concentration, and in favorable cases the surface charge, of nanometer-scale colloidal particles, viruses, DNA and other polymers, and metal ions. A resurgence of interest in the field of COulter counting is occurring because of the advent of new technologies that permit fabrication of membranes containing single, robust, and chemically well-defined channels having smaller and more uniform sizes than could be prepared in the past. These channels are prepared from biological materials, such as self-assembling membrane proteins, and from synthetic materials such as polymers, carbon nanotubes, and silicon-based inorganic materials. In addition to particle characterization, there have been a few recent examples of using Coulter counters to study chemical processes, such as the dehybridization of DNA.

This Account reports on the properties and applications of carbon nanotube-based Coulter counters (CNCCs). CNCCs provide a means for determining the diameter and electrophoretic mobility (or electrokinetic surface charge) of individual nanoparticles dispersed in aqueous solutions, as well as the nanoparticle concentration. Such measurements do not require CNCC calibration or sample labeling. Because CNCCs measure the characteristics of individual particles, they provide the true average and polydispersity distribution of nanoparticle properties. CNCCs can differentiate between individual nanoparticles based on their surface charge and size, and CNCCs can be used to determine the apparent surface pK(a) of polymeric nanoparticles. Nanoparticle characterization by CNCC, electron microscopy, conductometric titration, and light scattering are compared.

Early detection of the beginning stage of cardiovascular disease (CVD) is an approach to prevention because the process is reversible at this stage. Consequently, several methods for screening for CVD have been introduced in recent years incorporating different analytical methods for characterizing the population of blood-borne lipoprotein subclasses. The gold standard method for lipoprotein subclassification is based on lipoprotein density measured by sedimentation equilibrium using the ultracentrifuge. However, this method has not been adopted for clinical studies because of difficulties in achieving the precision required for distinguishing individuals with and without CVD particularly when statistical classification methods are used. The objective of this study was to identify and improve the major factors that influence the precision of measurement of lipoprotein density profile by sedimentation equilibrium analysis and labeling with a fluorescent probe. The study has two phases, each contributing to precision. The first phase focuses on the ultracentrifugation-related variables, and the second phase addresses those factors involved in converting the fluorescent lipoprotein density profile to a digital format compatible with statistical analysis. The overall improvement in precision was on the order of a factor of 5, sufficient to be effectively applied to ongoing classification studies relating to CVD risk assessment.

The purpose of this study is to determine whether the nature of the post-translational modifications of the major apolipoproteins of HDL is different for density-distinct subclasses. These subclasses were separated by ultracentrifugation using a novel density-forming solute to yield a high-resolution separation. The serum of two subjects, a control with a normolipidemic profile and a subject with diagnosed cardiovascular disease, was studied. Aliquots of three HDL subclasses were analyzed by MALDI and considerable differences were seen when comparing density-distinct subclasses and also when comparing the two subjects. A detailed analysis of the post-translational modification pattern of apoA-1 shows evidence of considerable protease activity, particularly in the more dense fractions. We conclude that part of the heterogeneity of the population of HDL particles is due to densitydependent protease activity.