Surface functionalization of silica nanoparticles supports colloidal stability in physiological media and facilitates internalization in cells

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.     

Nitrosyltechnetium(I) Complexes with 2‐(Diphenylphosphanyl)aniline

[Tc^I(NO)Cl(H₂L1)₂]⁺ cations (H₂L1 = 2‐(diphenylphosphanyl)aniline) are formed during reactions of H₂L1 with (NBu₄)[Tc(NO)Cl₄(MeOH)] or (NH₄)TcO₄/HCl/NH₂OH mixtures. Different isomers were isolated depending on the counterions and solvents used. The technetium(I) complexes cis‐NO,Cl,trans‐P,P‐[Tc^I(NO)Cl(H₂L1)₂]Cl, trans‐NO,Cl,cis‐P,P‐[Tc^I(NO)Cl(H₂L1)₂]₂(TcCl₆), and trans‐NO,Cl,trans‐P,P‐[Tc^I(NO)Cl(H₂L1)₂](PF₆) were isolated in crystalline form and studied by spectroscopic methods and X‐ray crystallography. DFT calculations show that there are only minor energy differences between the three isomers and the formation of the individual compounds is most probably strongly influenced by interactions with solvents and counterions.     

Detecting functional magnetic resonance imaging activation in white matter: Interhemispheric transfer across the corpus callosum

Background  

It is generally believed that activation in functional magnetic resonance imaging (fMRI) is restricted to gray matter. Despite this, a number of studies have reported white matter activation, particularly when the corpus callosum is targeted using interhemispheric transfer tasks. These findings suggest that fMRI signals may not be neatly confined to gray matter tissue. In the current experiment, 4 T fMRI was employed to evaluate whether it is possible to detect white matter activation. We used an interhemispheric transfer task modelled after neurological studies of callosal disconnection. It was hypothesized that white matter activation could be detected using fMRI.