Fivefold Coordination of a CuII-Aqua Ion: A Supramolecular Sandwich Consisting of Two Crown Ether Molecules and a Trigonal-Bipyramidal [Cu(H2O)5]2+ Complex

Lead (II) ion detection in surface water with pM sensitivity using aza-crown-ether-modified silver nanoparticles via dynamic light scattering

In this paper, we reported ultrasensitive lead ion detection in environmental water with pM sensitivity using aza-crown-ether-modified silver nanoparticles (ACE-Ag NPs) through dynamic light scattering (DLS). The colorimetric method based on ACE-Ag NPs is not capable of detecting Pb2+ ions over other metal ions (Fe3+, Co2+, Cu2+, Hg2+, Cd2+, Ag+, Li+, Na+, K+ and Cs+) with high sensitivity. But DLS has improved the selectivity and sensitivity of the Pb2+ detection system (50-fold or more) over colorimetric method, and its detection limit is 0.25 pM (1.03 ppt). The Pb2+ DLS assay can be applied to detect Pb2+ in the environmental water, such as in Yangtze and East Lake water samples with a detection limit of 0.20 and 0.22 pM, which is much lower than the maximum contamination level of 4.8×10(-8) M for lead in surface water defined by the national environmental quality standards of China (GB 3838-2002). Also, this method has a good performance in the determination of Pb2+ in drinking water, which is much lower than the maximum contamination level (MCL) of 72 nM for lead as defined by the US Environmental Protection Agency (EPA).

Exploring the Hydration of Pb2+: Ab Initio Studies and First-Principles Molecular Dynamics

Even though lead is a well-known toxicant widely scattered throughout the world since antiquity, its chemistry is poorly documented at the molecular level. Here we investigate the hydration of the Pb(2+) ion by means of first-principles molecular dynamics (Car-Parrinello molecular dynamics, CPMD). We found that the hydrated cation is heptacoordinated in a dynamically holodirected arrangement roughly corresponding to a fluxional distorted pentagonal bipyramid. The time-averaged Pb-O bond length is especially large and amounts to 2.70 A with an associated root-mean-square deviation of 0.26 A. This results from a dynamic exchange between short (<2.6 A), intermediate (2.6-3.0 A) and long (>3.0 A) Pb-O bonds. The latter very long Pb-O distance implies that the determination of the coordination number n(c) from experimental work may not necessarily yield values directly comparable to the theoretical value of n(c)=7, since not all experimental techniques would recognize such a long distance as a bond to the metal cation. Pronounced disorders are evidenced in the second shell, characteristic of a chaotropic cation, and exchanges between the first and second shells cannot be excluded on a timescale of a few tens of picoseconds.