Characterization of the Intermediate in and Identification of the Repair Mechanism of (6‐4) Photolesions by Photolyases

Quantum mechanics/molecular mechanics calculations are employed to assign previously recorded experimental spectroscopic signatures of the intermediates occurring during the photo‐induced repair of (6‐4) photolesions by photolyases to specific molecular structures. Based on this close comparison of experiment and theory it is demonstrated that the acting repair mechanism involves proton transfer from the protonated His365 to the N3′ nitrogen of the lesion, which proceeds simultaneously with intramolecular OH transfer along an oxetane‐like transition state.     

Theoretical Study of the Interactions between Isolated DNA Bases and Various Groups IA and IIA Metal Ions by Ab Initio Calculations

Interactions of the DNA bases adenine (A), guanine (G), cytosine (C), and thymine (T) with various metal ions (M) of groups IA and IIA of the periodic table of the elements were studied at the HF, MP2, and DFT levels of theory. The structures and thermodynamic stabilities of these species were studied at the gas phase. The calculations uphold that there exist two active sites in G and one in A, C, and T. The calculations also show that the O² atom in T is a more active site for metal ion bindings than that in C. The stability energies for G … M complexes are larger than those for A … M complexes and the stability energies for T … M complexes are larger than those for C … M complexes. As z/r ratio for the metal ion increases, the interaction energy for the complex increases systematically. Thermodynamic quantities such as ΔH, ΔG, ΔS, and ln K were determined for each complexation reaction, [Base+M ⁿ⁺ →(Base … M) ⁿ⁺]. A, G, and C complexation reactions except for C … Rb⁺ are exothermic. The situation is quite different for T complexation reactions and all except for T … Be²⁺ and T … Mg²⁺ are endothermic.     

Automated Technique for Identifying Experimental Vibrational–Rotational Molecular Spectra Based on Variational Calculations

We describe a technique for automated identification of experimental vibrational–rotational molecular spectra, which is based on variational calculations. The proposed technique is used to analyze the experimental spectra of triatomic molecules H₂O and HDO. This technique significantly accelerates processing and analysis of experimental data and drastically improves accuracy and quality of the results obtained. The possibility of applying this technique for analyzing spectra of other polyatomic molecules is discussed.     

Water vapour line assignments in the 9250-26 000 cm frequency range

Line parameters for water vapour in natural abundance have recently been determined for the 9250-13 000 cm⁻¹ region [M.-F. Mérienne, A. Jenouvrier, C. Hermans, A.C. Vandaele, M. Carleer, C. Clerbaux, P.-F. Coheur, R. Colin, S. Fally, M. Bach, J. Quant. Spectrosc. Radiat. Transfer 82 (2003) 99] and the 13 000-26 000 cm⁻¹ region [P.-F. Coheur, S. Fally, M. Carleer, C. Clerbaux, R. Colin, A. Jenouvrier, M.-F. Mérienne, C. Hermans, A.C. Vandaele, J. Quant. Spectrosc. Radiat. Transfer 74 (2002) 493] using a high-resolution Fourier-transform spectrometer with a long-path absorption cell. These spectra are analysed using several techniques including variational line lists and assignments made. In total, over 15 000 lines were assigned to transitions involving more than 150 exited vibrational states of H₂¹⁶O. Twelve new vibrational band origins are determined and estimates for a further 16 are presented.     

A self-dual variational approach to stochastic partial differential equations

Unlike many of their deterministic counterparts, stochastic partial differential equations are not amenable to the methods of calculus of variations à la Euler–Lagrange. In this paper, we show how self-dual variational calculus leads to variational solutions of various stochastic partial differential equations driven by monotone vector fields. We construct solutions as minima of suitable non-negative and self-dual energy functionals on Itô spaces of stochastic processes. We show how a stochastic version of Bolza's duality leads to solutions for equations with additive noise. We then use a Hamiltonian formulation to construct solutions for non-linear equations with non-additive noise such as the stochastic Navier–Stokes equations in dimension two.     

HPLC technique for quantitation of Chimassorb 944, and its evaluation in analysis of real and standard samples of polyolefins

A high performance liquid chromatography (HPLC) method is presented for the determination of Chimassorb 944 in polymeric matrix. A reversed phase column octadecyl silane (ODS) is used as a stationary phase. As a mobile phase, a mixture of THF:methanol:triethanol amine (90:10:1.5) (v:v:w) is used. The HPLC system was equipped with an UV detector and the absorbance of the analyte was recorded at 240 nm. In the case of polymers, 0.5 g of them along with 100 mg Irganox 1010 (for preventing oxidation of Chimassorb 944) were dissolved in boiling xylene, and then extracted with sulfuric acid 1 M four times. The extract was neutralized with sodium hydroxide solution and the analyte was re-extracted into carbon tetrachloride and then injected to the HPLC system. This method is an accurate and relatively fast technique for determination of Chimassorb 944 in polymers.     

The Importance of Ligand-Induced Backdonation in the Stabilization of Square Planar d10 Nickel π-Complexes

The electronic nature of Ni π-complexes is underexplored even though these complexes have been widely postulated as intermediates in organometallic chemistry. Herein, the geometric and electronic structure of a series of nickel π-complexes, Ni(dtbpe)(X) (dtbpe=1,2-bis(di-tert-butyl)phosphinoethane; X=alkene or carbonyl containing π-ligands), is probed using a combination of ³¹P NMR, Ni K-edge XAS, Ni K_β XES, and DFT calculations. These complexes are best described as square planar d¹⁰ complexes with π-backbonding acting as the dominant contributor to M−L bonding to the π-ligand. The degree of backbonding correlates with ²J_PP from NMR and the energy of the Ni 1s→4p_z pre-edge in the Ni K-edge XAS data, and is determined by the energy of the π*_ip ligand acceptor orbital. Thus, unactivated olefinic ligands tend to be poor π-acids whereas ketones, aldehydes, and esters allow for greater backbonding. However, backbonding is still significant even in cases in which metal contributions are minor. In such cases, backbonding is dominated by charge donation from the diphosphine, which allows for strong backdonation, although the metal centre retains a formal d¹⁰ electronic configuration. This ligand-induced backbonding can be formally described as a 3-centre-4-electron (3c-4e) interaction, in which the nickel centre mediates charge transfer from the phosphine σ-donors to the π*_ip ligand acceptor orbital. The implications of this bonding motif are described with respect to both structure and reactivity.