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Interactions of anions with simple aromatic compounds have received growing attention due to their relevancy in various fields. Yet, the anion-π interactions are generally very weak, for example, there is no favorable anion-π interaction for the halide anion F− on the simplest benzene surface unless the H-atoms are substituted by the highly negatively charged F. In this article, we report a type of particularly strong anion-π interactions by investigating the adsorptions of three halide anions, that is, F−, Cl−, and Br−, on the hydrogenated-graphene flake using the density functional theory. The anion-π interactions on the graphene flake are shown to be unexpectedly strong compared to those on simple aromatic compounds, for example, the F−-adsorption energy is as large as 17.5 kcal/mol on a graphene flake (C84H24) and 23.5 kcal/mol in the periodic boundary condition model calculations on a graphene flake C113 (the supercell containing a F− ion and 113 carbon atoms). The unexpectedly large adsorption energies of the halide anions on the graphene flake are ascribed to the effective donor-acceptor interactions between the halide anions and the graphene flake. These findings on the presence of very strong anion-π interactions between halide ions and the graphene flake, which are disclosed for the first time, are hoped to strengthen scientific understanding of the chemical and physical characteristics of the graphene in an electrolyte solution. These favorable interactions of anions with electron-deficient graphene flakes may be applicable to the design of a new family of neutral anion receptors and detectors. © 2012 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

The effect of both solvent polarity and hydrogen bonding (HB) on the electronic transition energy of Coumarin 102 (C102) has been examined using the time-dependent density functional theory (TDDFT). Solvent effect on both geometry and electronic transition energy is evaluated using the polarizable continuum model (PCM). A linear relation of the absorption maximum of C102 with the solvent polarity function Δ f is found using the TDDFT-PCM method for all solvents except dimethyl sulfoxide. The solvent polarity and the type B HB between the carbonyl oxygen and solvent hydrogen atom make the absorption wavelength redshift, whereas the type A HB between the amino nitrogen atom and solvent hydrogen atom has an opposite effect on the absorption wavelength. The calculated absorption wavelengths of C102 with two type B HB between the carbonyl oxygen and solvent hydrogen atom are in excellent agreement with experimental measurements. The solvatochromism of C102 is analyzed in terms of the Kamlet-Taft equation and the parameters s and a are discussed. © 2010 Wiley Periodicals, Inc. J Comput Chem, 2011. [ABSTRACT FROM AUTHOR]

Abstract: The detection of lead ion is very important both in environment and in biological systems because of its toxicity. A fluoroionophore sensor, N-[4(1-pyrene)-butyroyl]-l-tryptophan (PLT), distinguishing Pb2+ from other 12 metal ions and exhibiting a very high sensitivity (0.15μM) in aqueous solution, has been reported. The present study describes the spectroscopic clarification of the intrinsic differences of the binding model between PLT with Pb2+ and with other ions. The fluorescent property of solid metal carboxylates reflects a character of the metal complex in solution, which results in a facility to solve problems by using solid sample of complex and vibrational spectroscopy. Both FT-infrared and Raman spectroscopy are employed to clarify the binding model between lead ion and its high sensitive and selective fluoroionophore sensor PLT, and essentially to explain why the metal ions other than Pb2+ cannot response to PLT. The IR spectral data clearly show that a bridging bidentate coordination occurs when PLT is coordinated with Cu2+ and Zn2+; while a chelating bidentate coordination between the carboxyl anion and Pb2+ exists in PLT–Pb, which is a new information beyond the NMR results in previous report. Meanwhile, the present study also indicates a characteristic interaction of lead ion and indole ring as well as the hydrogen bonding between amide groups. Furthermore, the quantum chemical calculations at the DFT level confirm the spectral and structural information of PLT–Pb2+ proposed by experiments. Thus, the type of coordination, the interaction of the indole ring with the metal ion, and the hydrogen bonding between amide groups in PLT–Pb are likely responsible for the high selectivity of PLT to the lead(II) ion. [Copyright &y& Elsevier]