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.     

A water soluble Cu(I)-NHC for CuAAC ligation of unprotected peptides under open air conditions

A reducing agent-free version of CuAAC able to operate under open air conditions is reported. A readily-synthesizable, hydrophilic and highly stable Cu(I)-NHC allows the clean ligations of unprotected peptides comprising sensitive side chains, at millimolar concentrations.     

Ligand designed with pending phenol group

The synthesis of a salicylaldehyde derivative facing an encumbered phenol group on a naphthalene block as a molecular shaft is reported. This molecular unit has been designed to elaborate coordinating ligands holding non-coordinating phenol group for the generation of phenoxyl radical in the close proximity of a metal complex.     

Ring‐opening polymerization of ε‐caprolactone and L‐lactide from silica nanoparticles surface

Coating of silica nanoparticles by biocompatible and biodegradable polymers of ε‐caprolactone and L ‐lactide was performed in situ by ring‐opening polymerization of the cyclic monomers with aluminum, yttrium, and tin alkoxides as catalysts. Hydroxyl groups were introduced on the silica surface by grafting of a prehydrolyzed 3‐glycidoxypropyl trimethoxysilane to initiate a catalytic polymerization in the presence of metal alkoxides. In this manner, free polymer chains were formed to grafted ones, and the graft density was controlled by the nature of the metal and the alcohol‐to‐metal ratio. The grafting reaction was extensively characterized by spectroscopic techniques and quantified. Nanocomposites containing up to 96% of polymer were obtained by this technique. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1976–1984, 2004     

Determination des constantes d'equilibre conditionnelles et des constantes de vitesse des reactions entre le selenium(IV) et cinq orthodiamines aromatiques

The conditional equilibrium and rate constants, at various pH values, of the reaction between selenium(IV) and five aromatic orthodiamines, were determined. A main reaction of second order occurs first between the monoprotonated species of the diamine and the non-dissociated selenious acid. The hydrogen selenite ion and the diprotonated diamine can also react but more slowly. The reaction products are very stable.     

Practical route to relative diffusion coefficients and electronic relaxation rates of paramagnetic metal complexes in solution by model-independent outer-sphere NMRD. Potentiality for MRI contrast agents

The relaxation of electronic spins S of paramagnetic species is studied by the field-dependence of the longitudinal, transverse, and longitudinal in the rotating frame relaxation rates R1, R2, and R1rho of nuclear spins I carried by dissolved probe solutes. The method rests on the model-independent low-frequency dispersions of the outer-sphere (OS) paramagnetic relaxation enhancement (PRE) of these rates due to the three-dimensional relative diffusion of the complex with respect to the probe solute. We propose simple analytical formulas to calculate these enhancements in terms of the relative diffusion coefficient D, the longitudinal electronic relaxation time T1e, and the time integral of the time correlation function of the I-S dipolar magnetic interaction. In the domain of vanishing magnetic field, these parameters can be derived from the low-frequency dispersion of R1 thanks to sensitivity improvements of fast field-cycling nuclear relaxometers. At medium field, we present various approaches to obtain these parameters by combining the rates R1, R2, and R1rho. The method is illustrated by a careful study of the proton PREs of deuterated water HOD, methanol CH3OD, and tert-butyl alcohol (CH3)3COD in heavy water in the presence of a recently reported nonacoordinate Gd(III) complex. The exceptionally slow electronic relaxation of the Gd(III) spin in this complex is confirmed and used to test the accuracy of the method through the self-consistency of the low- and medium-field results. The study of molecular diffusion at a few nanometer scale and of the electronic spin relaxation of other complexed metal ions is discussed.     

Multiscale NMR investigations of two anatomically contrasted genotypes of sorghum under watered conditions and during drought stress

Today, in the presence of global warming, understanding how plants respond to drought stress is essential to meet the challenge of developing new cultivars and new irrigation strategies, consistent with the maintenance of crop productivity. In this context, the study of the relation between plants and water is of central interest for modeling their responses to biotic and abiotic constraints. Paradoxically, there are very few direct and noninvasive methods to quantify and measure the level and the flow of water in plants. The present work aims to develop a noninvasive methodology for living plant based on nuclear magnetic resonance (NMR) at low magnetic field and imaging (MRI) to tackle the issue of water quantity in plants. For this purpose, a portable NMR device measuring the signal level at 8 mT was built. This instrument addresses specific challenges such as miniaturization, accessibility, and overheating in order to maintain the plant intact of time over long period. Time dependence of the water content in sorghum plants is reported under abiotic stress as well as the fraction of transpirable soil water and the photosynthesis activity through the leaves. At high magnetic field (9.4 T), T2 maps were acquired on the same sorghum plants at two time points. The combination of these approaches allows us to identify ecophysiological biomarkers of drought stress. One particular interesting result concerns the spatial distribution of water in two anatomically contrasted sorghum genotypes.