Although multiple methods have been developed to detect metal cations, only a few offer sensitivities below 1 pM, and many require complicated procedures and sophisticated equipment. Here, we describe a class of simple solid-state sensors for the ultrasensitive detection of heavy-metal cations (notably, an unprecedented attomolar limit for the detection of CH(3)Hg(+) in both standardized solutions and environmental samples) through changes in the tunnelling current across films of nanoparticles (NPs) protected with striped monolayers of organic ligands. The sensors are also highly selective because of the ligand-shell organization of the NPs. On binding of metal cations, the electronic structure of the molecular bridges between proximal NPs changes, the tunnelling current increases and highly conductive paths ultimately percolate the entire film. The nanoscale heterogeneity of the structure of the film broadens the range of the cation-binding constants, which leads to wide sensitivity ranges (remarkably, over 18 orders of magnitude in CH(3)Hg(+) concentration).

Selective aggregation and precipitation of like-charged nanoparticles (NPs) covered with carboxylate ligands can be induced by different monovalent cations. The ordering of critical concentrations required for NP precipitation is Cs(+) ≫ K(+) > Li(+) > Na(+) > Rb(+) and does not correlate with the size of hydrated cations M(+), nor can it be predicted by the Hofmeister series. On the other hand, different anions have no effect on the precipitation trends. These observations are rationalized by a theoretical model combining the elements of the DLVO theory with molecular-level calculations. The key component of the model is the cation-specific binding of various metal cations to the carboxylate ligands.

The process of insertion of molecular oxygen and nitrogen into polyhedral oligomeric silsesquioxanes (POSS) has been investigated theoretically. Using ab initio methods, the N2interaction with the POSS has been described with restricted Hartree−Fock (RHF) with a triple-ζ basis set, while systems involving O2 require restricted open shell (ROHF) wave functions, to account for their open-shell ground states. This insertion process is described in terms of the energetic change that the system X2::POSS undergoes when the gas molecule passes from the exterior to the interior of the cage through the largest of its faces. The formation of the cluster occurs through a transition structure that has been characterized for each system. The barrier is a function of the dimension of the face of the POSS and, hence, of the cage dimensions. The results of the calculation are consistent with experimental observations that the O2 molecules pass through a given membrane more easily than N2. Disciplines Chemistry CommentsReprinted (adapted) with permission from

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The first dearomatizing anionic reaction of a phenyl ring promoted by an N-benzyl-N-methylphosphinamide group is described. The intermediate lithium species can be trapped with different electrophiles, affording tetrahydrobenzo[c]-1-aza-2lambda(5)-phospholes with excellent diastereoselectivity. The new process is a simple and very efficient entry to the stereoselective synthesis of functionalized gamma-(N-methylamino)phosphinic acids and esters.