The influence of the surface functionalization of silica particles on their colloidal stability in physiological media is studied and correlated with their uptake in cells. The surface of 55 ± 2 nm diameter silica particles is functionalized by amino acids or amino- or poly(ethylene glycol) (PEG)-terminated alkoxysilanes to adjust the zeta potential from highly negative to positive values in ethanol. A transfer of the particles into water, physiological buffers, and cell culture media reduces the absolute value of the zeta potential and changes the colloidal stability. Particles stabilized by L-arginine, L-lysine, and amino silanes with short alkyl chains are only moderately stable in water and partially in PBS or TRIS buffer, but aggregate in cell culture media. Nonfunctionalized, N-(6-aminohexyl)-3-aminopropyltrimethoxy silane (AHAPS), and PEG-functionalized particles are stable in all media under study. The high colloidal stability of positively charged AHAPS-functionalized particles scales with the ionic strength of the media, indicating a mainly electrostatical stabilization. PEG-functionalized particles show, independently from the ionic strength, no or only minor aggregation due to additional steric stabilization. AHAPS stabilized particles are readily taken up by HeLa cells, likely as the positive zeta potential enhances the association with the negatively charged cell membrane. Positively charged particles stabilized by short alkyl chain aminosilanes adsorb on the cell membrane, but are weakly taken up, since aggregation inhibits their transport. Nonfunctionalized particles are barely taken up and PEG-stabilized particles are not taken up at all into HeLa cells, despite their high colloidal stability. The results indicate that a high colloidal stability of nanoparticles combined with an initial charge-driven adsorption on the cell membrane is essential for efficient cellular uptake.

Quartz crystal microbalance (QCM) is frequently used to investigate adsorption of nanometer-sized objects such as proteins, viruses, or organic as well as inorganic nanoparticles from solution. The interpretation of the data obtained for heterogeneous adsorbate layers is not straightforward in particular if the systems exhibit sizable amounts of dissipation. In this study we investigate the deposition of monodisperse, amine functionalized silica nanoparticles on gold surfaces using QCM with dissipation (QCM-D) to obtain frequency and dissipation changes during adsorption from the liquid phase. These investigations are combined with ex situ scanning electron microscopy (SEM) measurements to study both coverage as well as lateral arrangement of the particles. An ordered layer of particles is found at saturation coverage due to the charged particle surface resulting in a repulsive interaction between the particles. The repulsion ensures a minimal distance between the particles, which leads to a saturation coverage of 15% for particles of 137 nm diameter. The frequency shift is shown to be a linear function of coverage which is a behavior expected for an elastic medium according to the Sauerbrey equation. However, the system shows a strong dependence of the normalized frequency shift on the overtones as well as a large dissipation, which is a clear indication for a system with viscoelastic properties. The analysis of the data show that a reliable determination of the adsorbed mass solely on the basis of QCM-D results is not possible, but additional information as determined by SEM in the present case is required to determine the coverage. From a correlation of the QCM-D results with the structural characterization it is possible to infer that the dissipation is a long ranged phenomenon. A lower boundary of the interaction length could be derived being twice the particle diameter for the particles studied here. In contrast to that the frequency response behaves like local phenomenon.

In light of the importance of nanostructured surfaces for a variety of technological applications, the quest for simple and reliable preparation methods of ordered, nanometer ranged structures is ongoing. Herein, a versatile method to prepare ordered, non-close-packed arrangements of nanoparticles on centimeter sized surfaces by self-assembly is described using monodisperse (118-162 nm Ø), amino-functionalized silica nanoparticles as an exploratory example. It is shown that the arrangement of the particles is governed by the interplay between the electrostatic repulsion between the particles and the interaction between particles and surfaces. The latter is tuned by the properties of the particles such as their surface roughness as well as the chemistry of the linkage. Weak dispersive interactions between amino groups and gold surfaces are compared to a covalent amide linkage of the amino groups with carboxylic acid functionalized self-assembled monolayers. It was shown that the order of the former systems may suffer from capillary forces between particles during the drying process, while the covalently bonded systems do not. In turn, covalently bonded systems can be dried quickly, while the van der Waals bonded systems require a slow drying process to minimize aggregation. These highly ordered structures can be used as templates for the formation of a second, ordered, non-close-packed layer of nanoparticles exemplified for larger polystyrene particles (Ø 368 ± 14 nm), which highlights the prospect of this approach as a simple preparation method for ordered arrays of nanoparticles with tunable properties.

The reaction of isophthaloylbis( N, N-diethylthiourea), HL, with UO(CHCOO)·2HO and NEt as a supporting base gives a tetranuclear, anionic complex of the composition [{UO(L)}(OAc)], in which the uranyl ions are S, O-chelate bonded. Each two of them are additionally linked by an acetato ligand. Similar reactions of various uranyl starting materials (uranyl acetate, uranyl nitrate, (NBu)[UOCl]) with corresponding pyridine-centered ligands (pyridine-2,6-dicarbonylbis( N, N-dialkylthioureas), HL) yield mononuclear, neutral compounds, in which the thiourea derivatives are coordinated as S, N, N, N, S-five-dentate chelators. The equatorial coordination spheres of the formed hexagonal bipyramidal complexes [UO(L)(solv)] are completed by solvent ligands (HO, MeOH, or DMF). Attempted reactions without a supporting base result in decomposition of the organic ligands and the formation of hexanuclear uranyl complexes with pyridine-2,6-dicarboxylato ligands, while the use of an excess of base results in condensation and the formation of dinuclear [{UO(L)(μ-OMe)}] complexes. A stable complex of the composition [UO(L)] results from reactions of common uranyl starting materials with 2,2'-bipyridine-6,6'-dicarbonylbis( N, N-diethylthiourea) (HL). The equatorial coordination sphere of the neutral, hexagonal bipyramidal complex is occupied by an SNS donor atom set, which is provided by the hexadentate organic ligand. While the uranium complexes with {L} and {L} are labile and rapidly decompose in acidic solutions, [UO(L)] is stable over a wide pH range, and the ligand readily extracts uranyl ions from aqueous solutions into organic solvents.

Reactions of (NBu4)­[MOCl4] complexes (M = Tc or Re) with an excess of hexafluoroacetylacetone (Hhfac) give products with a composition of (NBu4)­[MOCl3(hfac)] as bright yellow (Tc) or red (Re) solids. The products are stable as solids but rapidly decompose in solution. A number of related phenylimidorhenium­(V) complexes were synthesized starting from [Re­(NPhF)­Cl3(PPh3)2], where (NPhF)2– is a para-fluorinated phenylimido ligand. Products with compositions of [Re­(NPhF)­Cl2(PPh3)­(acac)], [Re­(NPhF)­Cl2(PPh3)­(hfac)], [Re­(NPhF)­Cl2(PPh3)­(tfac)], [Re­(NPhF)­Cl2(PPh3)­(naphtfac)], and [Re­(NPhF)­Cl2(PPh3)­(tbutfac)] (Hacac = acetylacetone, Htfac = trifluoroacetylacetone, Hnaphtfac = naphthoyltrifluoroacetylmethane, and Htbutfac = tert-butyro­yl­trifluoroacetylmethane) were isolated from reactions of the quite soluble [Re­(NPhF)­Cl3(PPh3)2] with the corresponding β-diketones and studied spectroscopically and by X-ray diffraction. The β-diketonates are coordinated in a meridional arrangement with the phenylimide. The formation of two isomers was detected for nonsymmetric β-diketones with a preference for the “equatorial” position for the more bulky substituents. Products with more than one chelating ligand were not obtained. The technetium complexes [Tc­(NPhX)­Cl3(PPh3)2] (X = p-F or p-CF3) were prepared from reactions of pertechnetate, PPh3, HCl, and substituted arylacetylhydrazines and isolated as green solids. They are sufficiently stable as solid but rapidly decompose in moist solvents upon hydrolysis of the Tc–N bonds. From reactions of [Tc­(NPh)­Cl3(PPh3)2] or [Tc­(NPhF)­Cl3(PPh3)2] in dry solvents, the complexes [Tc­(NPh)­Cl2(PPh3)­(hfac)] and [Tc­(NPhF)­Cl2(PPh3)­(hfac)] were prepared and isolated in crystalline form. An X-ray diffraction study shows that fluorination of the para position of the phenylimido ligand results in a slight lengthening of all bonds in the coordination sphere of technetium.