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In this study, the conformational preferences and photochemistry of acrylic acid (AA, CH2=CHCOOH) monomer isolated in cryogenic argon and krypton matrices were interpreted, based on results of quantum chemical calculations. Natural bond orbital analysis allowed to shed light on the main electronic effects determining the relative stability of the conformers of the molecule in the ground electronic state. The conformational isomerization taking place upon UV-irradiation of the matrix-isolated compound (λ ∼ 243 nm) was explained, based on theoretical complete active space self-consistent field/complete active space with second order perturbation theory (CASSCF/CASPT2) and time-dependent density functional theory (TD-DFT) results, allowing to rationalize the nearly equal populations of the two lowest energy conformers of the molecule observed in the photostationary state. Besides, details of the infrared spectra of the compound were reinterpreted based on the calculated spectra for the two most stable conformers of the molecule. In particular, the assignments for the out-of-plane A″ symmetry vibrations were revised. [ABSTRACT FROM AUTHOR]

Ab initio calculations reveal that radiative lifetime of the lowest excited singlet state of 2-aminopyridine molecule should be around 20 ns, consistent with the molecules of the same type but is about one order of magnitude larger than the claimed experimental fluorescent lifetime in recent years. An S1/S0 conical intersection close to the S1 state has been located, which could be the possible nonradiative channel that is responsible for the fast decay observed in the experiment. [ABSTRACT FROM AUTHOR]

Dewar photoproduct (Dewar PP) is the valence isomer of (6-4) photoproduct ((6-4)PP) in photodamaged DNA. Compared to the extensive studied CPD photoproducts, the underlying repair mechanisms for the (6-4)PP, and especially for the Dewar PP, are not well-established to date. In this paper, the repair mechanism of DNA Dewar photoproduct T(dew)C in (6-4) photolyase was elucidated using hybrid density functional theory. Our results showed that, during the repair process, the T(dew)C has to isomerize to T(6-4)C photolesion first via direct C6′–N3′ bond cleavage facilitated by electron injection. This isomerization mechanism is energetically much more efficient than other possible rearrangement pathways. The calculations provide a theoretical interpretation to recent experimental observations. [ABSTRACT FROM AUTHOR]

We have taken (dA), (dT), and (dA)·(dT) as model systems to study concerted effects of base pairing and stacking on excited-state nature of DNA oligonucleotides using density functional theory (DFT) and time dependent DFT methods. The spectroscopic states are determined to be of a partial → charge-transfer nature in the oligonucleotides. The → charge-transfer transitions produce dark states, which are hidden in the energy region of the steady-state absorption spectra. This is different from the previous assignment that the → charge-transfer transition is responsible for a shoulder at the red side of the first strong absorption band. The → charge-transfer states were predicted to have relatively high energies in the oligonucleotides. The present calculations predict that the → charge-transfer states are not involved in the spectra and excited-state dynamics of the oligonucleotides. In addition, the influence of base pairing and stacking on the nature of the nπ* and ππ* states are discussed in detail. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011 [ABSTRACT FROM AUTHOR]

The photophysics and photochemistry of pyrazine (C4H4N2, D2h) after excitation to the S2 (1 1B2u, 1ππ*) electronic state were studied by using the resonance Raman spectroscopy and complete active space self-consistent field method calculations. The B-band resonance Raman spectra in cyclohexane solvent were obtained at 266.0, 252.7, and 245.9 nm excitation wavelengths to probe the structural dynamics of pyrazine in the S2 (1 1B2u, 1ππ*) state. Three electronic states 1 1B3u, 1 1B1g, and 1 1B2g were found to couple with the S2 (1 1B2u, 1ππ*) state. Two conical intersection (CI) points CI[ S2(B2u)/ S1(B3u)] and CI[ S1/ S0] and one transition state of the isomerization between pyrazine and pyrimidine were predicted to play important roles in the photochemistry of pyrazine. On the basis of the calculations, the mechanism of the photoisomerization reaction between pyrazine and pyrimidine has been proposed. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two sulfides exhibit high adsorption capacities and ultrafast removal of Eu3+. • Selective Eu3+ adsorption against interfering ions in natural water. • Lanthanides recovery from acidic industrial wastewaters is realized. • The adsorption mechanism is ion exchange between Eu3+ and cations. • The soft Lewis basic and flexible layer is beneficial to selective Eu3+ uptake. Efficient and selective capture of lanthanides from radioactive wastewater containing excessive diverse concentrated salts is challenging but urgently demanded for environmental protection and human health. Herein, we present an effective approach for Eu3+ uptake from complex aqueous solutions by using two layered sulfide adsorbents (Me 2 NH 2) 2 (Ga 2 Sb 2 S 7)·H 2 O (FJSM-GAS-1) and (Et 2 NH 2) 2 (Ga 2 Sb 2 S 7)·H 2 O (FJSM-GAS-2). Both adsorbents exhibit ultrafast kinetics (within 2 min) and high absorption capacities for Eu3+ (127.7 and 115.8 mg/g for FJSM-GAS-1 and FJSM-GAS-2 , respectively). The distribution coefficient (K d) can be as high as 6.39 × 105 and 6.00 × 105 mL/g for FJSM-GAS-1 and FJSM-GAS-2 , respectively, exceeding that of reported Eu3+ adsorbents. They still display high selectivity for Eu3+ in presence of excessive competitive cations (e.g., Na+ and K+). Particularly, high K d values remain for Eu3+ removal from Eu3+-contaminated tap, lake and sea water, and lanthanides recovery from acidic industrial wastewater. Absorbed Eu3+ ions can be facilely eluted using a low-cost method. The adsorption mechanism, illuminated via DFT calculations coupled with characterizations of EA, Raman, XPS and EXAFS, is ion exchange between Eu3+ and interlayered cations owing to the strong interactions between Eu3+ and framework S2−. This work confirms that layered sulfides are promising adsorbents for efficient removal of lanthanides/actinides from wastewater for environmental remediation. [ABSTRACT FROM AUTHOR]