Search

The dispersed iron oxide nanoparticles of ferrofluids in aqueous solution are difficult to characterize due to their protective polymer coatings. We report on the bimodal size distribution of superparamagnetic iron oxide nanoparticles found in the MRI contrast agent Resovist, which is a representative example of commercial nanoparticle-based pharmaceutical formulations. The radii of the majority of the nanoparticles (>99%) range from 4 to 13 nm (less than 1% of the particles display radii up to 21 nm). The maxima of the size distributions are at 5.0 and 9.9 nm. The analysis was performed with in situ characterization of Resovist via online coupling of asymmetrical flow field-flow fractionation (A4F) with small-angle X-ray scattering (SAXS) using a standard copper X-ray tube as a radiation source. The outlet of the A4F was directly coupled to a flow capillary on the SAXS instrument. SAXS curves of nanoparticle fractions were recorded at 1-min time intervals. We recommend using the A4F-SAXS coupling as a routine method for analysis of dispersed nanoparticles with sizes in the range of 1-100 nm. It allows a fast and quantitative comparison of different batches without the need for sample preparation.

We report on the online coupling of asymmetrical flow field-flow fractionation (A4F) with small-angle X-ray scattering (SAXS) for the detection of nanoparticles. The A4F was used to fractionate superparamagnetic maghemite nanoparticles, which were prepared continuously with a micromixer. The outlet of the A4F was directly coupled to a flow capillary of a SAXSess instrument (Kratky type of camera). SAXS curves were recorded in a 1 s time interval. This was possible by using intense synchrotron radiation. The radii of gyration of the nanoparticles, as determined from Guinier plots, increased from 2 to 6 nm with increasing fractionation time of the A4F. A more detailed analysis of the scattering curves revealed that the particles were cylindrical in shape (nanorods), which we attributed to the micromixing preparation technique. The radii of the nanorods increased only slightly from 1.2 to 1.7 nm with increasing fractionation time, while the lengths increased strongly from 7.0 to 30.0 nm. The volume distribution of the nanorods was determined and described by Schnltz--Zimm and log-normal distributions. Nanorod volumes increased from 45 to 263 [nm.sup.3], corresponding to molar masses of 140 x [10.sup.3] to 820 x [10.sup.3] g [mo.sup.- 1]. We propose A4F-SAXS coupling as a new method for analysis of nanoparticles of complex composition in solution. It allows precise online determination of the particle's shape and size distributions. This method can be applied to mixtures of nanoparticles of arbitrary shapes and sizes (1-100 nm). Moreover, the total time needed for fractionation and online SAXS data recording is usually only 20 min.

Self-assembly of Fe(ll) and the ditopic ligand 1,4-bis(2,2':6',2'-terpyridine-4'-yl) benzene results in equilibrium structures in solutions, so-called metallosupramolecular coordination polyelectrolytes (MEPEs). It is exceedingly difficult to characterize such macromolecular assemblies, because of the dynamic nature. Therefore, hardly any structural information is available for this type of material. Here, we show that from dilute solutions, where small aggregates predominate, it is possible to grow nanoscopic crystals at an interface. A near atomic resolution structure of MEPE is obtained by investigating the nanoscopic crystals with electron diffraction in combination with molecular modeling. The analysis reveals a primitive monoclinic unit cell ([P2.sub.1]/c space group, a = 10.4 [Angstrom], b = 10.7 [Angstrom], c = 34.0 [Angstrom] [alpha] = [gamma] = 90[degrees], [beta] = 95[degrees], [rho] = 1.26 g/[cm.sup.3], and Z = 4). The MEPE forms linear rods, which are organized into sheets. Four sheets intersect the unit cell, while adjacent sheets are rotated by 90[degrees] with respect to each other. The pseudooctahedral coordination geometry of the Fe(ll) centers is confirmed by Mossbauer spectroscopy. The combination of diffraction and molecular modeling presented here may be of general utility to address problems in structural materials science. electron diffraction | Mossbauer spectroscopy | molecular modeling | supramolecular chemistry

A complex between poly(ethylene oxide)-block-poly(L-lysine) and a hexa-peri-hexabenzocoronene is examined. It is found that poly(L-lysine) blocks wherein each helix is surrounded by six discotic columns of hexa-peri-hexabenzocoronene forms alpha-helical secondary structure.

A method is described for analyzing the formation of nanoparticles via in situ SAXS and XANES by using synchrotron radiation. A mechanism of nanoparticle formation is described and the coalescence behavior of small nuclei is identified as essential factor in obtaining a narrow size distribution of formed particles.

We studied the magnetic resonance imaging liver contrast agent Resovist by a variety of magnetic measurement techniques, in order to understand the physical mechanism of their high magnetic particle imaging (MPI) performance, with a focus on the size-dependent contributions to the MPI signal. To this end, we used asymmetric flow field-flow fractionation to separate Resovist into a set of fractions with defined hydrodynamic diameters. The individual fractions were magnetically characterized by static magnetization and magnetorelaxometry measurements to obtain the corresponding effective magnetic anisotropy and effective size distribution parameters. In addition, the MPI performance of each fraction was assessed by magnetic particle spectroscopy. We observed an MPI signal gain of about 100% with respect to their iron amount for the best fraction. Relating these finding to the results from magnetic characterization provides more insight into the mechanisms of MPI performance of Resovist. This knowledge may help to improve the design of novel MPI tracers. [ABSTRACT FROM AUTHOR]