Newly synthesized rhodamine derivatives, L(1) and L(2), are found to bind specifically to Hg(2+) or Cr(3+) in presence of large excess of other competing ions with associated changes in their optical and fluorescence spectral behavior. These spectral changes are significant enough in the visible region of the spectrum and thus, allow the visual detection. For L(1), the detection limit is even lower than the permissible [Cr(3+)] or [Hg(2+)] in drinking water as per standard U.S. EPA norms; while the receptor, L2 could be used as a ratiometric sensor for detection of Cr(3+) and Hg(2+) based on the resonance energy transfer (RET) process involving the donor naphthalimide and the acceptor Cr(3+)/Hg(2+)-bound xanthene fragment. Studies reveal that these two reagents could be used for recognition and sensing of Hg(2+)/Cr(3+). Further, confocal laser microscopic studies confirmed that the reagent L(2) could also be used as an imaging probe for detection of uptake of these ions in A431 cells.

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A systematic computational ab initio study of the conformational dependent proton affinities of methoxymethoxide, tetrahydropyran 2-oxide, methoxymethanol, dimethoxymethane, 1,3-dioxane, and tetrahydropyran has been carried out at the MP2/6-31+G* level of theory. In addition, methoxide, propoxide and methanol, propanol, and dimethyl ether have been computed at the same level as reference systems. Methoxymethoxide and tetrahydropyran 2-oxide exhibit a strong anomeric effect, e.g., the equatorial oxide is a stronger base than the axial one and all are weaker bases than the simple alkoxides. Axial (n π ) protonation is preferred over equatorial (n σ ) by 2-3 kcal/mol. The COCOC acetals are stronger bases (at the acceptor O) then the simple ethers. The structural changes between bond lengths and bond angles for different conformers correlate well with the On π -σ* C-O lone pair delocalization interactions. Thus, the anomeric effect plays an important role in the charged species and in the process of their formation.

Aim: To performe a time-dependent topographical delineation of protein-drug interactions to gain molecular insight into the supremacy of Ortho-7 over HI-6 in reactivating tabun-conjugated mouse acetylcholinesterase (mAChE). Methods: We conducted all-atom steered molecular dynamics simulations of the two protein-drug complexes. Through a host of protein-drug interaction parameters (rupture force profiles, hydrogen bonds, water bridges, hydrophobic interactions), geometrical, and orientation ordering of the drugs, we monitored the enzyme's response during the release of the drugs from its active-site. Results: The results show the preferential binding of the drugs with the enzyme. The pyridinium ring of HI-6 shows excellent complementary binding with the peripheral anionic site, whereas one of two identical pyridinium rings of Ortho-7 has excellent binding compatibility in the enzyme active-site where it can orchestrate the reactivation process. We found that the active pyridinium ring of HI-6 undergoes a complete turn along the active site axis, directed away from the active-site region during the course of the simulation. Conclusion: Due to excellent cooperative binding of Ortho-7, as rendered by several cation-π interactions with the active-site gorge of the enzyme, Ortho-7 may be a more efficient reactivator than HI-6. Our work supports the growing body of evidence that the efficacy of the drugs is due to the differential bindings of the oximes with AChE and can aid to the rational design of oxime drugs.

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