A cost-effective computational methodology designed to study astatine (At) chemistry in aqueous solution has been established. It is based on two-component spin-orbit density functional theory calculations and solvation calculations using the conductor-like polarizable continuum model in conjunction with specific astatine cavities. Theoretical calculations are confronted with experimental data measured for complexation reactions between metallic forms of astatine (At(+) and AtO(+)) and inorganic ligands (Cl(-), Br(-) and SCN(-)). For each reaction, both 1:1 and 1:2 complexes are evidenced. The experimental trends regarding the thermodynamic constants (K) can be reproduced qualitatively and quantitatively. The mean signed error on computed Log K values is -0.4, which corresponds to a mean signed error smaller than 1 kcal mol(-1) on free energies of reaction. Theoretical investigations show that the reactivity of cationic species of astatine is highly sensitive to spin-orbit coupling and solvent effects. At the moment, the presented computational methodology appears to be the only tool to gain an insight into astatine chemistry at a molecular level.

Structural information on acetylcholine and its two agonists, nicotine, and muscarine has been obtained from the interpretation of infrared spectra recorded in the gas-phase or in low pH aqueous solutions. Simulated IR spectra have been obtained using explicit water molecules or a polarization continuum model. The conformational space of the very flexible acetylcholine ions is modified by the presence of the solvent. Distances between its pharmacophoric groups cover a lower range in hydrated species than in isolated species. A clear signature of the shift of protonation site in nicotine ions is provided by the striking change of their infrared spectrum induced by hydration. On the contrary, structures of muscarine ions are only slightly influenced by the presence of water.

Single-stranded RNA aptamers have emerged as novel biosensor tools. However, the immobilization procedure of the aptamer onto a surface generally induces a loss of affinity. To understand this molecular process, we conducted a complete simulation study for the Flavin mononucleotide aptamer for which experimental data are available. Several molecular dynamics simulations (MD) of the Flavin in complex with its RNA aptamer were conducted in solution, linked with six thymidines (T6) and, finally, immobilized on an hexanol-thiol-functionalized gold surface. First, we demonstrated that our MD computations were able to reproduce the experimental solution structure and to provide a meaningful estimation of the Flavin free energy of binding. We also demonstrated that the T6 linkage, by itself, does not generate a perturbation of the Flavin recognition process. From the simulation of the complete biosensor system, we observed that the aptamer stays oriented parallel to the surface at a distance around 36 Å avoiding, this way, interaction with the surface. We evidenced a structural reorganization of the Flavin aptamer binding mode related to the loss of affinity and induced by an anisotropic distribution of sodium cationic densities. This means that ionic diffusion is different between the surface and the aptamer than above this last one. We suggest that these findings might be extrapolated to other nucleic acids systems for the future design of biosensors with higher efficiency and selectivity.

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The AtO(+) molecular ion, a potential precursor for the synthesis of radiotherapeutic agents in nuclear medicine, readily reacts in aqueous solution with organic and inorganic compounds, but at first glance, these reactions must be hindered by spin restriction quantum rules. Using relativistic quantum calculations, coupled to implicit solvation models, on the most stable AtO(+)(H2O)6 clusters, we demonstrate that specific interactions with water molecules of the first solvation shell induce a spin change for the AtO(+) ground state, from a spin state of triplet character in the gas phase to a Kramers-restricted closed-shell configuration in solution. This peculiarity allows rationalization of the AtO(+) reactivity with closed-shell species in aqueous solution and may explain the differences in astatine reactivity observed in (211)At production protocols based on "wet" and "dry" processes.

Nanophase segregation of a bi-component thiol self-assembled monolayer is predicted using atomistic molecular dynamics simulations and experimentally confirmed. The simulations suggest the formation of domains rich in acid-terminated chains, on one hand, and of domains rich in amide-functionalized ethylene glycol oligomers, on the other hand. In particular, within the amide-ethylene glycol oligomers region, a key role is played by the formation of inter-chain hydrogen bonds. The predicted phase segregation is experimentally confirmed by the synthesis of 35 and 15 nm gold nanoparticles functionalized with several binary mixtures of ligands. An extensive study by transmission electron microscopy and electron tomography using silica selective heterogeneous nucleation on acid-rich domains to provide electron contrast supports simulations and highlights patchy nanoparticles with a trend towards Janus nano-objects depending on the nature of the ligands and the particle size. These results validate our computational platform as an effective tool to predict nanophase separation in organic mixtures on a surface and drive further exploration of advanced nanoparticle functionalization.

The surface of gold can be modified with alkyl groups through a radical crossover reaction involving alkyliodides or bromides in the presence of a sterically hindered diazonium salt. In this paper, we characterize the Au-C(alkyl) bond by surface-enhanced Raman spectroscopy (SERS); the corresponding peak appears at 387 cm close to the value obtained by theoretical modeling. The Au-C(alkyl) bond energy is also calculated, it reaches -36.9 kcal mol similar to that of an Au-S-alkyl bond but also of an Au-C(aryl) bond. In agreement with the similar energies of Au-C(alkyl) and Au-S-(alkyl), we demonstrate experimentally that these groups can be exchanged on the surface of gold.

There is a global debate and concern about the use of glyphosate (Gly) as an herbicide. New toxicological studies will determine its use in the future under new strict conditions or its replacement by alternative synthetic or natural herbicides. In this context, we designed biomimetic polymer sensing layers for the selective molecular recognition of Gly. Towards this end, complementary surface acoustic wave (SAW) and electrochemical sensors were functionalized with polypyrrole (PPy)-imprinted polymer for the selective detection of Gly. Their corresponding limits of detection were on the order of 1 pM, which are among the lowest values ever reported in literature. The relevant dissociation constants between PPy and Gly were estimated at [Kd1 = (0.7 ± 0.3) pM and Kd2 = (1.6 ± 1.4) µM] and [Kd1 = (2.4 ± 0.9) pM and Kd2 = (0.3 ± 0.1) µM] for electrochemical and gravimetric measurements, respectively. Quantum chemical calculations permitted to estimate the interaction energy between Gly and PPy film: ΔE = −145 kJ/mol. Selectivity and competitivity tests were investigated with the most common pesticides. This work conclusively shows that gravimetric and electrochemical results indicate that both MIP-based sensors are perfectly able to detect and distinguish glyphosate without any ambiguity.